ALCA_December_2016_LR

THE 

OF THE AMERICAN 

LEATHER CHEMISTS ASSOCIATION 

December 2016 Vol. CXI, No. 12 JALCA 111(12), 427-462, 2016 

Contents 

113th Annual 

Convention 

to be held at the 

Pinehurst Resort 

Village of Pinehurst, NC 

June 13-16, 2017 

For more information go to 

www.leatherchemists.org/ 

annual_meeting.asp 

Synthesis and Application of a New Phosphate Ester Based on 

Nonionic Amphiphilic Polyurethane as Leather Fatliquoring Agent............. 427 

by Hanping Li, Yong Jin, Baozhu Fan, Rui Qi and Xinfeng Cheng 

Minimization of Chromium Discharge in Leather Processing by 

using Methanesulfonic Acid: A Cleaner Pickling-masking-chrome 

Tanning System..................................................................................................... 435 

by Chunxiao Zhang, Fuming Xia, Biyu Peng, Qing Shi, 

Dominic Cheung and Yongbin Ye 

Development of Chrome-free Tanning in Supercritical CO 2 

Fluid 

using Zr-Al-Ti Complex....................................................................................... 447 

by Xinhua Liu, Feng Li, Qin Huang, Wiehua Dan and Nianhua Dan 

Studies on the use of Bi-functional Enzyme for Leather Making............... 455 

by G. Jayakumar, M. Sathish, R. Aravindhan and J. Raghava Rao 

Lifelines................................................................................................................... 461 

ALCA and Industry News 

Call for Papers – 113th Annual Convention, June 13-16, 2017................... 462 

ISSN: 0002-9726 

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Mr. Robert F. White, Journal Editor, 1314 50th Street, Suite 103, Lubbock, TX 79412, USA. 

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JOURNAL OF THE 

AMERICAN LEATHER CHEMISTS ASSOCIATION 

Proceedings, Reports, Notices, and News 

of the 

AMERICAN LEATHER CHEMISTS ASSOCIATION 

OFFICERS 

David Peters, President 

DLP Advisors 

8206 Santa Rosa Court 

Sarasota, FL 34243 

Mike Bley, Vice-President 

Eagle Ottawa – Lear 

2930 Auburn Road 

Rochester Hills, MI 48309 

Shawn Brown 

Quaker Color 

201 S. Hellertown 

Quakertown, PA 18951 

Joseph Hoelfer 

The Dow Chemical Company 

400 Arcola Rd. 

Collegeville, PA 19426 

COUNCIL 

Jeffrey D. Miller 

GST AutoLeather, Inc. 

31601 Industrial Road 

Livonia, MI 48150 

Andreas W. Rhein 

Tyson Foods, Inc. 

800 Stevens Port Drive 

Dakota Dunes, SD 57049 

Beat Schelling 

Wickett & Craig of America 

120 Cooper Rd. 

Curwensville, PA 16833 

Katie Thudium 

Eagle Ottawa – Lear 



Dr. Meral Birbir 

Department of Biology 

Marmara University 

Istanbul, Turkey 

Chris Black 

Consultant 

St. Joseph, Missouri 

Dr. Eleanor M. Brown 

Eastern Regional 

Research Center 

U.S. Department of Agriculture 

Wyndmoor, Pennsylvania 

Kadir Donmez 

Leather Research Laboratory 

University of Cincinnati 

Cincinnati, Ohio 

Dr. Anton Ela’mma 

Retired 

Perkiomenville, Pennsylvania 

Elton Hurlow 

Buckman International 

Memphis, Tennessee 

Prasad V. Inaganti 

Wickett and Craig of America 

Curwensville, Pennsylvania 

Steve Lange 

Leather Research Laboratory 

University of Cincinnati 

Cincinnati, Ohio 

Xue-Pin Liao 

National Engineering Laboratories 

Sichuan University 

Chengdu, China 

Dr. Cheng-Kung Liu 





EDITORIAL BOARD 

John Moore 

Retired 

Petaluma, California 

Dr. Edwin H. Nungesser 

Dow Chemical Company 

Spring House, Pennsylvania 

Dr. J. Raghava Rao 

Central Leather 

Research Institute 

Chennai, India 

Andreas W. Rhein 

Tyson Foods, Inc. 

Dakota Dunes, South Dakota 

Dr. Bi Shi 

National Key Laboratories 

Sichuan University 

Chengdu, China 

George Stockman 

Retired 

Clemson, SC 

Maryann M. Taylor 





Dr. Palanisamy 

Thanikaivelan 

Central Leather 

Research Institute 

Chennai, India. 

Brandon Yoemans 

S. B. Foot Tanning Co. 

Red Wing, Minnesota 

PAST PRESIDENTS 

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Williams, T. F. Oberlander, A. H. Winheim, R. M. Koppenhoefer, H. G. Turley, E. S. Flinn, E. B. Thorstensen, M. Maeser, R. G. Henrich, R. Stubbings, D. Meo, Jr., R. 

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COPYRIGHT 2016. THE AMERICAN LEATHER CHEMISTS ASSOCIATION

427 

Synthesis and Application of a New Phosphate 

Ester Based on Nonionic Amphiphilic Polyurethane 

as Leather Fatliquoring Agent 

by 

Hanping Li, A,B Yong Jin, A,B * Baozhu Fan, C,D Rui Qi C,D and Xinfeng Cheng C,D 

A 

Key Laboratory of Leather Chemistry and Engineering, Ministry of Education, 

Sichuan University, Chengdu 610065, China 

B 

National Engineering Laboratory for Clean Technology of Leather Manufacture, 

Sichuan University, Chengdu 610065, China 

C 

Chengdu Institute of Organic Chemistry, Chinese Academy of Science, Center of Polymer Science and Technology, 

Chengdu 610041, China 

D 

University of Chinese Academy of Sciences, 

Beijing 100049, China 

Abstract 

A new polyurethane phosphate ester (PUP-2) was successfully 

synthesized based on a nonionic amphiphilic polyurethane 

(PU-2). The structures and properties of PU-2 and PUP-2 were 

characterized by FTIR and surface tensiometer. The fatliquoring 

experiments were carried out in three different groups (treated with 

PUP-2 alone, with the complex of hexadecyl phosphate ester (SLP) 

and PUP-2, or with the complex of SLP, PUP-2 and other 

commercialized fatliquoring agents, respectively). The physical and 

organoleptic properties of the resultant leathers were investigated 

and SEM was carried out in the study of fiber splitting. The leathers 

treated in the three different fatliquoring experiments all did not 

have fatty spew defect. Furthermore, the resultant leathers treated 

with PUP-2 alone or with the complex of SLP and PUP-2 had the 

advantage of resistance to yellowing. This new phosphate ester 

meets the requirements for the leathers with a good performance in 

resistance to yellowing and avoiding fatty spew defect. 

Introduction 

Currently a wide variety of fatliquoring agents are being used in 

leather manufacturing. 1-3 Phosphorylated fatliquoring agents are 

widely used due to the advantages of low toxicity, low stimulation 

and good biodegradability. 4, 5 Most of the phosphate esters used 

at present are natural phosphate esters or synthetic phosphate 

esters which are usually synthesized based on modified natural 

oils or high-carbon alcohols. 6, 7 

However, the natural phospholipids have some disadvantages 

such as easy to mildew, dull color and low emulsion stability. 8,9 In 

addition, the synthetic phosphate esters based on modified 

natural oils can be oxidized due to the carbon-carbon double 

bonds of natural oils, 10 thus resulting in the poor performance of 

leathers and limiting their applications. What’s more, although 

the high-carbon alcohol phosphate esters can improve the oil 

feeling, waxy feeling and waterproofness of leathers, they usually 

result in fatty spew formation on the leather surface when the 

temperature is low, which can be attributed to their low 

emulsification, poor permeability and high freezing point. Thus, 

it was really necessary for the leather industry to develop a new 

phosphate ester with higher emulsification, richer permeability, 

lower freezing point and no carbon-carbon double bonds to be 

substituted for the traditional ones. 

In this paper, a new polyurethane phosphate ester (PUP-2) was 

prepared, which consists of the soft molecular chains. And 

carbon-carbon double bonds are not involved here, too. 

Moreover, the nonionic amphiphilic structural features can 

improve the permeability and stability of the resultant 

fatliquoring emulsions. The above advantages of the 

polyurethane phosphate ester are in accord with the growing 

demand for the leathers with the good properties of resistance to 

yellowing and avoiding fatty spew defect. 

*Corresponding author e-mail: jinyong@scu.edu.cn 

Manuscript received March 25, 2016, accepted for publication June 14, 2016. 

JALCA, VOL. 111, 2016

Phosphate Ester as Fatliquoring Agent 428 

Experimental 

Materials 

Isophorone diisocyanate (IPDI), polyethylene glycol monomethyl 

ether (MPEG, Mn=750 g/mol) and polyoxypropylene ether 

(PPG, Mn=2000 g/mol), AR grade, were purchased from 

Shanghai Chemical Reagents Corporation, China. Dibutyltin 

dilaurate (DBTDL), phosphorus pentoxide (P 2 

O 5 

) and 

hexadecanol, AR grade, were purchased from Ke Long Chemical 

Corporation, China. SWA, FG-B, FL-71, NL-20, HN01, A18, JM, 

JMK, OF, FS-90, melamine, dicyandiamide, dispersing tannin, 

chestnut and protein filler, purchased from Dowell Technology 

Co., Ltd., were used as industrial grade. Wattle extract, industrial 

grade, was purchased from UNITY Corporation, Argentina. PF 

aldehyde, industrial grade, was purchased from Zschimmer & 

Schwarz Chemicals. Basic chromium sulphate, industrial grade, 

was purchased from Ming Feng Chemical Corporation, China. 

Wet blue bovine hides were purchased from Da Fan Jiu Leather 

Corporation, China. Other chemicals were of analytical grade 

and used as received. All of them were used without further 

purification. 

Synthesis of Hexadecyl Phosphate Ester (SLP), 

PU-2 and PUP-2 

A certain amount of hexadecanol was plunged into a 100 ml 

three-necked flask equipped with a stirrer and a thermometer at 

50°C. Under the high-speed stirring, a quantitative amount of 

P 2 

O 5 

with a mole ratio of ROH: P 2 

O 5 

=3: 1 which was divided into 

four same parts was added with an internal of 10 min. After all 

of P 2 

O 5 

was added and dispersed completely, the system was 

heated up to 85°C and maintained for 5 h. Then, a small amount 

of water with a mole ratio of P 2 

O 5: 

H 2 

O=1: 1 was added at 30°C. 

After 1.5 h, the product of SLP was obtained. 

The calculated amount of MPEG and DBTDL (a mole ratio of 

MPEG: DBTDI=1: 0.002) were placed in a four-necked flask 

equipped with a thermometer and a mechanical stirrer. While 

stirring heated to 60°C, the calculated amount of IPDI with a 

mole ratio of MPEG: IPDI=1: 1 was added dropwise into the 

flask. The reaction was carried out at 60°C for 4 h. PPG-2000 

with a mole ratio of MPEG: PPG-2000=1: 1 was then added and 

allowed to react for another 2 h at 80°C. The nonionic 

amphiphilic diblock polyurethane (PU-2) was obtained. 

A certain amount of PU-2 was plunged into a 100 ml threenecked 

flask equipped with a stirrer and a thermometer at 50°C. 

A quantitative amount of P 2 

O 5 

with a mole ratio of PU-2: P 2 

O 5 

=1: 

2 which was divided into four same parts was added with an 

internal of 10 min. After all of the P 2 

O 5 

was added and dispersed 

completely, the system was heated up to 85°C and maintained 

for 5 h. After the reaction, mixture was cooled to 30°C, 

a calculated amount of water was added with a certain 

Scheme 1. Synthesis of PU-2 and PUP-2. 

mole ratio (H 2 

O: P 2 

O 5 

=2: 1) by stirring. After 1.5 h, the polyurethane 

phosphate ester (PUP-2) was prepared. The preparation of PU-2 and 

PUP-2 is shown schematically in Scheme 1. 

Application on Leathers 

The wet blue bovine hid was cut into two pieces (200mm x 

150mm), which had the symmetry along the spine to make sure 

the same fiber woven status. One was treated with fatliquoring 

agents and the other one was not as a comparison. The retanning 

and fatliquoring process of leathers is shown in Table I, and the 

three ways of fatliquoring were carried out as follows: 

Experiment 1- Treated with PUP-2 alone, its weight was 2%, 4%, 

8% or 12% of wet blue bovine hide’s weight respectively. 

Experiment 2- Treated with the complex of SLP and PUP-2, and 

the total weight of them was 8% of wet blue bovine hide’s weight. 

There were four weight ratios between SLP and PUP-2, SLP: 

PUP-2=1:9, SLP: PUP-2=2:8, SLP: PUP-2=3:7 or SLP: PUP-2=4:6, 

respectively. 

Experiment 3- Treated with the complex of SLP, PUP-2 and other 

commercialized fatliquoring agents. The weight of SLP and 

PUP-2 was 2% of wet blue bovine hide’s weight, and the 

commercialized fatliquoring agents accounted for the remaining 

6% (2.5%JM, 1.5%JMK,1.5%FS-90 and 0.5%OF, respectively). 

Description of the Experimental Tests 

FTIR Characterization 

The FTIR spectrum was recorded with a Thermo Fisher Nicolet 

6700 spectrophotometer in KBr pellets. The range of 400-4000 

cm -1 was scanned and the result was recorded. 


429 Phosphate Ester as Fatliquoring Agent 

Surface Tension Measurement 

The surface tension was determined by a BZY-1 automatic 

tensiometer, which was configured with a platinum plate and a 

sample cell. The platinum plate was rinsed with ethanol and 

deionized water several times and then flamed with an alcohol 

lamp to get rid of the contaminants before and after every test. 

After calibrating the tensiometer, a quantitative of the product 

solution, which was stabilized for at least 24h, was measured 

three times at 25°C, and the final surface tension value of the 

product was determined by an average of the three values. 

Physical and Organoleptic Properties Test 

The final leathers were sampled and conditioned according to 

the standard method. 11 With a tensile machine AI-7000S 

(GOTECH TESTING MACHINES INC, Taiwan), the physical 

properties, such as tensile strength, tear strength and elongation 

12, 13 

were tested with the standard methods. 

The softness, grain tightness and lubricating sense of the treated 

resultant leathers were assessed as the organoleptic properties 

with hand and visual examinations by three different qualified 

leather technologists and reported as an average value. They 

were visually examined and measurements were given on a scale 

of 0-10 points for each functional property, where higher points 

indicate better properties exhibited. 

Fatty Spew Test 

The leathers which were treated with PUP-2 alone (8%, w/w), the 

complex of SLP and PUP-2 (SLP: PUP-2=3: 7, 8%, w/w), or the 

complex of SLP, PUP-2 (SLP: PUP-2=3: 7, 2%, w/w) and other 

commercialized fatliquoring agents (6%, w/w) were respectively 

placed at a temperature of -37°C for a week. 

Resistance to Yellowing 

Testing: The resistance to yellowing of leathers was tested with a 

Q-LAB QUV resistant to climate testing equipment (GOTECH 

TESTING MACHINES INC, Taiwan). The test was conducted 

according to ISO 105-B02 standard method 2: 50°C, 65%RH, 

Xenon arc test lamp, 7 IR filter and 42 W/m 2 . 14 

Table I 

Retanning and fatliquoring process. 

Process Amount Product Time Temperature pH 

200% Water 

Wash 

0.05-0.2% Formic acid 

0.20% SWA 

40 min 

0.10% FG-B Check pH (4.0) 

Drain & Wash 

100% Water 

0.50% FL-71 10 min 

2% NL-20 30 min 40°C 

Check pH (4.5) 

2% Wattle extract 40 min 

Retanning 

0.2-0.4% Formic acid 20 min Check pH (3.8) 

3% Chrome 

30min 

4% ANO1 

2% PF aldehyde 60 min 

0.50% Sodium formate 20 min 

0.35-0.6% Sodium bicarbonate 30 min Check pH (4.1) 

Table I continued on following page. 



Table I continued. 

Drain & Wash & Pile over night 

150% Water 

2% NL-20 

1% Sodium formate 

20 min 

0.50% Sodium bicarbonate 60 min Check pH (5.2) 

80% Water 

40°C 

3% A18 20 min 

1.50% Melamine 

Filling 

1.50% Dicyandiamide 

0.50% Dispersing tannin 

40 min 

1.50% Wattle extract 

1.50% Chestnut 

1% JM 

1% JMK 

60 min 

30 min 

40°C 

100% Water 65°C 

0.40% Formic acid 20 min 

45°C 

0.1-0.4% Formic acid 40 min Check pH (4.1) 

Drain & Wash 

Fatliquoring 

100% Water 

2% Protein filler 20 min 

x% Fatliquor agent 40 min 

0.25% Formic acid 30 min 

55°C 

0.25% Formic acid 30 min Check pH (3.8-4.0) 

Drain & Wash 

Hook to dry, Stake 

Evaluation: An X-RiteColor Premier 8200 spherical 

spectrophotometer (X-Rite, USA) was used to measure the 

coloring of leather samples. Spectral reflectance values were 

measured between 400-700 nm range with 20nm intervals, and 

16 readings were obtained for each sample. The reflectance 

readings were converted to CIE L*a*b* values with related 

formulas, and color differences were calculated by CIELAB 1967 

color difference formula listed in Eq.1. 15 

ΔE= [(L-L 0 

) 2 + (a-a 0 

) 2 + (b-b 0 

) 2 ] 1/2 (1) 



The CIELAB 1976 color difference formula calculates the linear 

distance between the coordinates of the sample and target color, 

and this difference is shown by ΔE. 

Scanning Electron Microscopic Analysis (SEM) 

A JSM-5900LV scanning electron microscope (Shimadzu, Japan) 

was used for the analysis. The micrographs for the cross section 

were obtained by operating the SEM at low vacuum with an 

accelerating voltage of 20kV at the same magnification level. 

Results and Discussion 

Characterization of Synthetic Chemicals 

FTIR of SLP, PU-2 and PUP-2 

As shown in Figure 1, the common structures of PU-2 and 

PUP-2 were evidenced by the common peaks at 3444-3480 cm -1 , 

2867-2869 cm -1 , 1720-1639 cm -1 and 1108-1105 cm -1 related to 

different common groups (N-H, C-H, C=O, and C-O-C, 

respectively). The characteristic peaks of phosphate ester at 1151- 

1295 cm -1 and 1015-1028 cm -1 ascribed to P=O and P-O-C were 

observed for PUP-2 and SLP. The results indicated that SLP, 

PU-2 and PUP-2 were all synthesized successfully. 

Surface Tension of PUP-2 and PU-2 

From the results of surface tension shown in Figure 2, it was very 

clear that the surface tension was lower in PUP-2 solution than 

in PU-2 solution at every same concentration. Meanwhile, the 

CMC of the PUP-2 was much lower than that of PU-2 according 

to the CMC data (4.12 ×10 -6 mol/L for PUP-2 and 1.01×10 -5 mol/L 

for PU-2). The results indicated that PUP-2 was more effective in 

reducing surface tension, which suggested that PUP-2 might play 

a good role in fatliquoring process. A possible explanation was 

that hydrophobic groups in PUP-2 were closer between each 

other because of the phosphorylation. 16 

Characterization of Resultant Leathers 

Physical and Organoleptic Properties of Leathers 

The resultant leathers were treated with different amounts of 

PUP-2 alone (Experiment 1), with the complex of SLP and PUP-2 

in different weight ratios (Experiment 2), or with the complex of 

SLP, PUP-2 and other commercialized fatliquoring agents 

(Experiment 3), and their physical and organoleptic properties 

were tested. As seen from Figure 3, Figure 4 and Table II, the 

leathers treated with three different kinds of PUP-2 based 

fatliquoring agents showed a clearly improvement in physical 

(tensile strength, elongation and tear strength) and organoleptic 

properties (softness, lubricating sense and grain tightness) 

compared with non-fatliqured leathers, especially when PUP-2 

alone (8%, w/w) or the complex of SLP and PUP-2 (SLP: PUP- 

2=3:7, 8%, w/w) was applied. 

SEM Analysis 

SEM studies of the grain pattern of leathers are given in Figure 

5, at a magnification of ×1000. As compared with the A, the fiber 

splitting of B, C, and D were comparatively better in SEM. The 

fatliquoring agents based on PUP-2 penetrated deeply resulting 

in better fiber splitting and softness due to its nonionic 

amphiphilic structure and soft molecular chains. 

Fatty Spew Test 

Fatty spew formation was not observed on the surface of three 

kinds of leathers which were treated with PUP-2 alone, the 

complex of SLP and PUP-2, or the complex of SLP, PUP-2 and 

other commercialized fatliquoring agents. It can be attributed to 

the soft C-O-C bonds of PUP-2 with a low freezing point and the 

nonionic amphiphilic structure resulting in better dispersion and 

deeper penetration of fatliquoring agents as reported by Nashy. 17 

Figure 1. FT-IR spectra of SLP, PU-2 and PUP-2. 

Figure 2. Surface tension at different concentrations of PU-2 and PUP-2. 



Resistance to Yellowing 

Reflectance measurements were carried out for all combination 

leathers. The ‘L’, ‘a’ and ‘b’ values used as the parameters to 

assess color are given in Table III. ‘L’ represents whiteness, which 

on a scale of 0-100; and 100 means pure white. ‘a’ represents red 

and green axis, where ‘a’ >0 means red and ‘a’ 0 means yellow 

and ‘b’


a little decrease in white and a little increase in green. However, 

the increase of ‘b’ value from I, II and III was 2-4, which meant 

an increase in yellow tones when exposed to light. As a result, the 

increase of ‘ΔE’ value from I, II and III was 3-5. As seen from the 

Table III, the changes of ‘b’ and ‘ΔE’ mainly happened between 

0-6 hours. Compared with II and III, I, which was the nonfatliquored 

leathers, also had a 2-4 change on ‘b’ and 3-5 on ‘ΔE’, 

which meant that the change of ‘b’ and ‘ΔE’ of II and III was not 

attributed to SLP or PUP-2. However, the natural phospholipids, 

which usually contain the unsaturated acids, are prone to 

oxidation 18-21 and the oxidation reaction always leads to the 

performance of yellowing. 22-24 In summary, the leathers treated 

with PUP-2 alone (8%, w/w) or the complex (SLP: PUP-2=3:7, 8%, 

w/w) all showed a good performance in resistance to yellowing. 

It can be attributed to no unsaturated carbon-carbon double 

bonds, which were easily oxidized. 25 

Figure 4. Physical properties of leathers treated with the complex 

of SLP and PUP-2 in different weight ratios, or with the complex of 

SLP, PUP-2 (SLP: PUP-2=3:7, 2%, w/w) and other commercialized 

fatliquoring agents (6%, w/w). (The Y axis is a normalized scale for all 

three measured values.) 

Figure 5. SEM images of the cross section of leathers. (A) Nonfatliqured 

leathers, 1000× (B) Leathers treated with PUP-2 alone 

(8%, w/w), 1000×. (C) Leathers treated with the complex of SLP and PUP- 

2 (SLP: PUP-2=3:7, 8%, w/w), 1000×. (D) Leathers treated the complex 

of SLP, PUP-2 (SLP: PUP-2=3:7, 2%, w/w) and other commercialized 

fatliquoring agents (6%, w/w), 1000×. 

Table III 

Yellowing resistance of resultant leathers. 

Time (h) I II III 

L a b ΔE L a b ΔE L a b ΔE 

0 77.54 -0.52 9.56 76.94 -1.62 10.31 77.74 -2.18 10.41 

6 76.28 -0.93 12.91 3.52 76.63 -1.84 13.38 3.09 77.26 -2.33 13.24 2.95 

12 75.34 -1.04 13.40 4.46 76.29 -2.24 13.64 3.45 76.85 -2.71 13.39 3.13 

24 75.20 -1.39 13.64 4.78 76.04 -2.92 13.95 3.97 76.70 -3.24 13.89 3.78 

Δ6 -1.26 -0.41 3.26 -0.31 -0.22 3.07 -0.84 -0.15 2.83 

Δ12 -2.20 -0.52 3.84 -0.65 -0.62 3.33 -0.89 -0.35 2.98 

Δ24 -2.34 -0.87 4.08 -0.90 -1.30 3.64 -1.04 -1.06 3.48 

I: Non-fatliquored leathers (the comparison of the leather treated with 8% PUP-2). 

II: Leathers treated with PUP-2 alone (8%, w/w). 

III: Leathers treated with the complex of SLP and PUP-2 (SLP: PUP-2=3:7, 8%, w/w). 



Conclusions 

A new phosphorylated ester (PUP-2) was successfully 

synthesized, which was effective in reducing surface tension and 

had a good performance in improving physical and organoleptic 

properties of resultant leathers. The fatty spew formation was 

not observed on the surface of three kinds of leathers treated 

with PUP-2 based fatliquoring agents. Meanwhile, since all basic 

raw materials of PUP-2 do not contain carbon-carbon double 

bonds, the leathers treated with PUP-2 alone (8%, w/w) or the 

complex of SLP and PUP-2 (SLP: PUP-2=3:7, 8%, w/w) had a 

good resistance to yellowing. Therefore, PUP-2 completely meets 

the requirements of resistance to yellowing and avoiding fatty 

spew defect for leathers. 

Acknowledgements 

This work was financially supported by the National High-tech 

Research and Development Projects (863) (2013AA06A306), 

National Natural Science Foundation of China (21474065) and 

Sichuan Province Leaders in Academic and Technical Training 

Project Funding (2015/100-5). 

References 

1. Wang, X. C., Feng, J. Y and An, H. R.; Phosphate modified 

lanolin fatliquors produced by a sustained-release method. 

JSLTC 88, 228-230, 2004. 

2. Ornes, C.L.; Studies of fatliquoring: II. The influence of type 

of oil, degree of sulfation, and neutralization level of fatty 

acids on some physical properties of shoe upper leather. 

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435 

Minimization of Chromium Discharge in Leather 

Processing by using Methanesulfonic Acid: 

A Cleaner Pickling-masking-Chrome Tanning System 

by 

Chunxiao Zhang, 1 Fuming Xia, 1 Biyu Peng, 1,2 * Qing Shi, 3 Dominic Cheung 3 and Yongbin Ye 4 

1 

National Engineering Laboratory for Clean Technology of Leather Manufacture, 

Sichuan University, Chengdu 610065, P. R. China 

2 

Key Lab. of Leather Chemistry and Engineering of Ministry of Education, Sichuan University, 

Chengdu, Sichuan 610065, P. R. China 

3 

BASF Advanced Chemicals Co., Ltd., 

Pudong, Shanghai, 200137, P. R. China 

4 

Zhejiang Tongtianxing Group J.S.Co., Ltd., 

Quzhou, Zhejiang, 324022, P.R. China 

Abstract 

Chrome tanning is the most important and widely used tanning 

method in leather manufacture hitherto. However, chromium 

discharge may be a serious environmental concerned pollutant 

in leather processing, which originates from both chrome 

tanning and post-tanning operations. In order to minimize the 

emissions of chromium from the whole leather processing, a 

novel leather processing method integrating high chromium 

exhaustion and low chromium leaching-out based on the 

application of methanesulfonic acid (MSA) was designed and 

optimized. The results indicated that, being superior to the 

conventional processes, the chrome tanning and retanning 

processes with MSA were conducted at a high beginning pH 

(5.0) smoothly and the total chromium utilization ratio was 

increased to 95.8% from 81.0% in the novel processes. 

Accordingly, the total Cr dosage was decreased by 26.7% around, 

the residual Cr concentrations in each chrome-containing 

wastewater was decreased by 44%-85%, varying with the 

operations, and the total Cr discharge generated in the whole 

leather processing was reduced by 83.8% around, from 2.737 kg/t 

salted-wet hide to 0.443kg/t salted-wet hide before next chrome 

precipitation treatment. The area yields, mechanical properties 

and organoleptic properties of the leather from the new method 

were comparable with that from conventional processes. 

Introduction 

Chrome tanning is the technology of using a chrome tanning 

agent, basic chromium sulfate (BCS), to convert the pelts to 

leathers. Conventionally, in order to achieve good penetration of 

chromium into pelts, a “pickling-masking-tanning” process is 

adopted. The pelts are acidified to pH 2.5-3.2 with formic acid 

and sulfuric acid in slat solution before tanning, named pickling, 

to lower the reactivity of the carboxyl groups of collagen, and 

chromium complexions are also modified by added ligands, 

typically carboxylates, to reduce the affinities of them towards 

collagen, named masking. 1,2 The relative affinities of ligands to 

chrome ions from potential masking agents are listed as follows: 

hydroxide > oxalate > citrate > lactate > malonate > maleate > 

phthalate >glycolate> tartrate > succinate >adipate> acetate > 

carboxyl of collagen >formate> sulfite > sulfate > chloride > 

nitrate > chlorate. 1 According to the above list, the affinity of 

formate to chromium ion is a little weaker than that of the 

carboxyl of collagen, so it is chosen as the dominant masking 

agent. However, only 60%-80% of the offering chrome is 

effectively utilized in the conventional chrome tanning process. 

As a result, the chrome concentration in spent float is in a range 

of 1,000-3,000mg/L, 3 causing a significant disposal problem. 

Therefore, cleaner chrome tanning processing, i.e., maximizing 

the chrome uptake and minimizing the residual amount of 

chrome in floats, is a matter of great concern to all tanners. 

*Corresponding author e-mail: pengbiyu@scu.edu.cn; Tel.+86-28-85401208. 

Manuscript received March 23, 2016, accepted for publication June 30, 2016. 


Methanesulfonic Acid for Cleaner Tanning System 436 

The low chrome utilization ratio in the conventional chrome 

tanning process can be probably attributed to that the lower 

affinity of the masked chromium complex ions with carboxyls of 

collagen side chain. The adding of organic acids in pickling and 

carboxylates during tanning introduces relatively large 

quantities of carboxylates into the tanning float, which may 

produce rather strong masking effects to chromium ions, 

resulting from the strong coordinating ability of carboxylates 

with chromium ion. Hence, the possibility of carboxyls of 

collagen entering into the inner spheres of chromium complex 

ions to substituted existing organic ligands is decreased 

accordingly. The uptake ratio of chrome is kept a rather low 

level. Many researches on optimizing masking agents have been 

done. Carboxylates with different molecular structure, including 

aliphatic and aromatic dicarboxylates, 4,5 low molecular weight 

polyacrylates, 6 and so on, were chosen as masking agents. 

Though these kinds of masking agents can increase the 

chromium exhaustion to a certain degree, it is difficult to achieve 

the chromium utilization ratio beyond 85%, and the leather is 

often negatively affected by the irrelevant application of the 

additives. Therefore, it may be deduced that the current picklingmasking-tanning 

system is not beneficial to high-exhaustion of 

chrome. 

Theoretically, taking every effort to promote the reaction activity 

between chrome and collagen can improve the tanning 

effectiveness. For example, resulting from the increase of both 

the dissociation degree of carboxyl of collagen side chain and the 

hydrolyzation degree of chromium ion at a high pH, it is 

beneficial to the uptake of chromium by collagen when the bated 

pelts are directly chrome tanned or after preprocessed with 

syntans at a high beginning pH over 6.0, 7-9 called non-pickling 

chrome tanning. However, the excessive fast combination of 

chromium on pelt surface will cause difficult penetration of 

chromium and bad hand feeling of leather when tanning at the 

high initial pH. Hence, to find a new kind of acid with weaker 

affinity to chromium than formic acid to establish a novel 

pickling-masking-chrome tanning system, which can well 

balance the competing process rates of Cr penetration and 

reaction with collagen when chrome tanning is conducted at a 

reasonably highly initial pH value, will be a possible approach to 

achieve high-exhaustion of chrome and minimize chrome 

discharge in chrome tanning. 

Methanesulfonic acid (MSA) is a kind of organic strong acid. For 

there is an electron donor, methyl, connecting directly with 

sulfur atom, its pKa value (-0.6) is higher than sulfuric acid 

(pKa=-3.0), and much lower than formic acid (pKa=3.68) and 

acetic acid (pKa=4.76) 10 , thus the acidity of MSA is weaker than 

common inorganic acids, and stronger than most of organic 

acids. MSA has been used in electroplate industry to substitute 

sulfuric acid as it is considered as a “green acid” due to its 

environmental advantages: far less corrosive and easily 

biodegradable. 11 Though the structure and geometric parameters 

of the Cr (III) complex ions of sulfate and methanesulfonate are 

rather similar, forming Cr (III) complexes is more easily in 

methanesulfonate solution than sulfate solution, 12 and Cr (III) 

complex ions in methanesulfonate are more stable. 13-15 Therefore, 

the coordination ability of methanesulfonate toward Cr(III) is 

stronger than sulfate. It can be deduced that pickling with MSA 

has the potential to well balance the contradiction of the highexhaustion 

and penetration of chromium during chrome 

tanning, theoretically. 

According to the above analysis, a novel pickling-maskingchrome 

tanning system based on the application of MSA was 

designed to achieve the high-exhaustion of chrome. The process 

parameters were optimized, such as initial tanning pH value, 

dosage of chrome, and the leather quality was evaluated. The 

chrome discharge in the whole leather processes was also traced. 

Experimentals 

Materials and Instruments 

Salted-wet cattle hides from Sichuan, China, were purchased 

from a local tannery (Chengdu Xinshi Leather Industry Co., 

Ltd.). Methanesulfonic acid (MSA, 70%) was offered by 

BASF-AE. Chromium (III) sulfate hydrate (Cr 2 

(SO 4 

) 3·6H 2 

O, CP) 

was purchased from Aladdin Co.. Chromosal B (a chromium 

tanning agent with 33% of basicity and 26% of Cr 2 

O 3 

content) 

was purchased from LANXESS Inc. The following applied 

leather chemicals, including syntans, fatliquors, polymers, filling 

agents, etc. were industrial grade and from Sichuan Dowell 

Science & Technology Co., Ltd. The other chemicals were 

analytic grade. 

Ultraviolet and Visible Spectrophotometer (TU-1810PC, Beijing 

Purkinje General Instrument Co., LTD, China), Stainless 

Experimental Drum (GSD400-4, Wuxi Xinda Light Industry 

Machinery Co., Ltd. China), Inductively Coupled Plasma 

Emission Spectrometer (AES-ICP, 2100DV, Perkin Elmer Inc. 

America), Precision Slice Machine (C520L, Camog (a) Inc., 

Italy), Desktop Scanning Electron Microscope (Phenom Pro, 

Phenom World Inc., Netherland). 

Evaluation of the Masking Effect of MSA to Chromium Ion 

The appropriate chromium(III) sulfate hydrate (11.6g) was 

dissolved in deionized water (250.00ml) to get a solution with Cr 

concentration of was 0.2mol/L. Samples (20.00ml) were removed 

and mixed with MSA at different ratios. As a control, the molar 

ratio of formic acid to chromium was 1:1. The solutions were 

then aged by standing at room temperature (20-22°C) for 

3 hours. A solution of NaHCO 3 

(5%, w/w) was added slowly with 

magnetic stirring for 30min to adjust the pH to 4.0. The total 

volumes were diluted to 100.00ml respectively. Have been aged 


437 Methanesulfonic Acid for Cleaner Tanning System 

for 12 hours at 40°C, the ultraviolet-visible spectrum analysis 

was conducted at the wave lengths from 700nm to 350nm at 

0.5nm interval respectively. 

Substituting Sulfuric Acid and/or Formic Acid with 

MSA in Pickling 

Salted-wet cattle hides were conducted soaking, fleshing, liming, 

splitting, deliming and bating procedures as normal processes. 

A whole grain-layer limed cattle hide with thickness of 3.0 mm 

after splitting was divided into pieces adjacently and 

symmetrically, and they were distributed to different tanning 

groups for evaluating and comparing tanning effects. The bated 

pelts were put into drums and soaked in 50% of water at 23°C 

(based on the weight of limed hides, the same below) and pickled 

to pH 2.9 around with a certain amount of MSA, the mixtures of 

formic acid and MSA, or sulfuric acid and MSA, respectively, in 

the presence of 6.0% (w/v) of NaCl. After pickling overnight, 

6.0% Chromosal B together with 1.0% of sodium formate was 

added into each drum. When chrome completely penetrated into 

hide inner-layer after running for about 180min at 23°C, the pH 

was basified to around 4.0 with NaHCO 3 

solution carefully. Then 

a certain amount of hot water (60°C) was added to make the total 

water offer be total 200% of limed hide weight. After running for 

another 120 min at 40°C, the drums were stayed overnight. The 

next day, the pH of tanning liquors was adjusted to 4.0±0.1 once 

more. The Cr contents in spent tanning liquors were determined. 

Optimization of Processing Parameters of MSA Pickling- 

Chrome Tanning 

The adjacent and symmetrical bated pelts were prepared and 

pickled to different pH with varying amounts of MSA. After 

pickling overnight, chrome tanning was carried out with a 

varying offer amount of Chromosal B, with or without using 

sodium formate. All other operations were the same as above. As 

a control, two groups of pelts were pickled as per the conventional 

method (formic acid 0.5% and sulfuric acid 1.0-1.2%) and were 

tanned with 6.5% of Chromosal B alone or the combinations of 

5.0% of Chromosal B and 0.5% of sodium formate respectively. 

The Cr contents in spent tanning liquors were determined. Cr 

distribution, shrinkage temperature values (Ts) and the 

appearances of the chrome-tanned leather were determined and 

compared. 

Tracing Chrome Discharge in Whole Leather Wet-end 

Processing Based on MSA Pickling-chrome Tanning 

Bated pelts were divided into two groups. Among them, a whole 

piece of grain-layer limed cattle hide was cut into two half sides 

along with the backbone line, symmetrically, and they were 

distributed to different tanning groups for evaluating and 

comparing tanning effects. As shown in Table I, the two groups 

of pelts were chrome tanned with a conventional picklingchrome 

tanning process (No. i) and MSA pickling-chrome 

tanning process (No. ii), respectively. After stacked and aged for 

7 days, the tanned leathers were carried out sammying, shaving 

(thickness 1.1-1.2 mm), and wetting as the normal operations. 

Then the shaved tanned leathers were put in drums and 

conducted with a normal (No. i) and a modified (No. ii) chrome 

retanning processes correspondingly. Then the chrome retanned 

leathers were neutralized, retanned with syntans, dyed and 

fatliquored as the normal procedures for shoe upper leather, and 

was also used to substitute formic acid to fix syntans, dyestuff 

and fatliquors in No. ii process. The chromium concentrations 

in chromium-containing wastewaters were analyzed and the 

main leather properties were also measured. 

Determination of Chromium Concentration in Spent 

Tanning Liquors 

The spent tanning liquors were filtered with 100 mesh filter 

cloth and digested with the mixture of hydrochloric acid and 

nitric acid at 120°C for 120min. The digestion solutions were 

appropriately diluted and their chromium concentrations were 

measured with AES-ICP. The chromium concentrations of spent 

tanning liquors were calculated. 

Determination of Chromium Content and Distribution 

in Leather 

The chrome-tanned leather samples of each tanning group were 

taken out in the adjacent and symmetrical parts of the same 

hide, and washed thoroughly to remove uncombined chromium 

salt. Then the samples were freeze-dried at -55°C and 20pa 

vacuum for 24hours. The dried leathers were averagely split into 

three layers using Precision Slice Machine. A certain quantity of 

the dried leather sample was completely digested with the 

mixture of nitric acid and chloride acid at 120°C for 120min. 

The digestion solutions were appropriately diluted and their 

chromium concentrations were measured with AES-ICP. The 

chromium content in each layer of the leather was calculated. 

Scanning Electron Microscopy (SEM) Analysis 

The samples of the dried crust leathers of each tanning group 

were viewed microscopically using Desktop Phenom Pro 

Desktop Scanning Electron Microscope. Then the pattern of 

both the grain on the surfaces and the collagen fibril on the 

section were evaluated. 

Test of Physical and Mechanical Properties of Crust Leather 

Dried crust leather samples of each tanning group were taken 

out in the adjacent and symmetrical parts of the same hide for 

testing physical and mechanical properties. The dichloromethane 

extracts were evaluated as per ISO 4048-2008. Samples were 

conditioned as per IUP method (IUP 2, 2000). Physical 

properties such as tensile strength, elongation at break, tear 

strength and bursting strength were examined as per the 

standard procedures (IUP 6, 2000; IUP 8, 2000; IUP 9, 1996). 



Table I 

Leather making processes for shoe upper leather. 

Operations Chemicals Dosages (%) Parameters Comments 

Bating 

Pickling Water 50 23°C 

NaCl 6.0 10 min 

No. i HCOOH 0.5 30 min 

H 2 

SO 4 

1.1 180 min 

No. ii MSA 0.9 180 min 

Overnight No. i pH 2.96; No. ii pH 4.86 

Cr- tanning 

No. i Chromosal B 6.5 

HCOONa 0.5 180 min Cr penetrate evenly 

No. ii Chromosal B 4.5 180 min Cr penetrate evenly 

Basifying NaHCO 3 

X 180 min 30 min interval 

Overnight 

Water (60°C) 150 120 min Stable at 40°C 

Draining Cr sewage 200% 

Stacking 

7 days 

Sammying Cr sewage 20% 

Shaving 

Thickness 1.1-1.2 mm 

Wetting Water (40°C) 200 

Nonionic wetting agent 0.3 

Nonionic degreasing agent 0.1 

NaHCO 3 

0.3 120 min pH 4.5 


Cr-retanning Water (40°C) 200 

No. i HCOOH 0.5 120 min pH 3.5 around 

Chromosal B 3.5 

HCOONa 0.5 

Table I continued on following page. 



Table I continued. 

NaHCO 3 

X 120 min pH 4.2 around 

No. ii Chromosal B 3.5 

MSA-Na 0.5 90 min 

NaHCO 3 

X 120 min pH 4.2 around 

Overnight 


Neutralizing Water 150 40°C 

Neutralizing Syntans 1.5 30min 

NaHCO 3 

1.0 90min pH 5.1 


Organic retanning/ 

Filling 

Water 150 40°C 

Synthetic Fatliquor 2.0 30min 

Polyacrylate Retanning Agents 9.0 60min 

Polysulfone Syntan 4.0 

All the chemicals were diluted 

with 3 times hot water 

Polynaphthalene Sulphonate 2.0 

Melamine Resin 3.0 

Protein Filling 3.0 

Vegetable Tannin 3.0 90min 

No. i HCOOH 0.5 

No. ii MSA 0.5 30min pH4.5 around 


Washing Water 200 10min Cr sewage 200% 

Fatliquoring/ 

Dyeing 

Water 150 55°C 

+ Dyestuffs 3.0 30min 

+ Mixture of Fatliquors 10.0 

All chemicals were diluted 

with 3 times hot water 

No. i HCOOH 1.5 90min pH3.6 around 

No. ii MSA 1.8 90min pH3.6 around 


Vacuum Drying, Hanging Drying, Stacking as conventional methods 



Results and Discussions 

The Masking Effect of Methanesulfonic Acid (MSA) on 

Chromium Ions 

UV-Vis is the most common technique for characterizing Cr(III) 

species. The positions of the two peaks are changeable depending 

on ligands associated to chromium ion, and the slight variations 

in the wavelengths are attributed to the fact that Cr(III) reacted 

with different ligands. 16 In order to evaluate the masking effect 

of MSA towards chromium ions, UV-Vis spectral studies of 

chromium sulfate solutions with different ratios of MSA at pH 

4.0 were conducted, and the results are showed in Figure 1 and 

Table II. 

Two fairly strong absorptions of [Cr(H 2 

O) 6 

] 3+ complex are known 

in the visible and near-ultraviolet region from 700nm to 350nm. 

These peaks correspond to two transitions from ground states to 

the excited states: 4 A 2g 

→ 4 T 2g 

and 4 A 2g 

→ 4 T 1g 

. 17 The spectrum is the 

characteristic of [Cr(H 2 

O) 6 

] 3+ complex in which Cr(III) ion is 

octahedral, and the water molecules in this complex could be 

replaced by various ligands present in the solution, resulting the 

color change of the solution from green to blue. 15 The results in 

Figure 1 and Table II indicate that the two peaks are slightly 

shifted to the blue region by 0.5nm to 1.5nm, varying with the 

concentrations of MSA, meaning that one or more water 

molecules in the inner sphere of Cr(III) complex are replaced 

with MSA, forming the MSA-complexes of Cr(III). Therefore, 

the affinity of MSA to Cr(III) is stronger than that of sulfuric 

acid. But the peaks in formic acid solution are obviously shifted 

by 3.5nm and 7.0nm respectively, indicating the formation of the 

stronger formic acid-complexes of Cr(III), for the affinity of 

carboxyl is much stronger than that of methanesulfonate to 

Cr(III). Therefore, the masking effect of MSA on chromium ions 

is between sulfate and formate. 

The Influence of Pickling with MSA on Chrome Tanning 

In order to pre-search the possibility of establishing a new 

pickling-chrome tanning system, MSA was used to completely 

or partially substitute sulfuric acid and/or formic acid in pickling 

process, and the influences of pickling methods on chrome 

tanning effects were examined firstly. The results are shown in 

Table III. 

The results in Table III show that MSA pickling can increase 

chromium uptake to a certain degree, comparing with 

conventional pickling. The improving effect of replacing sulfuric 

acid with MSA on chromium exhaustion, i.e. combining MSA 

and formic acid in pickling (No.2), isn’t as evident as substituting 

formic acid (No.3). The chromium uptake arrives at 79% when 

pickling with MSA alone. The reason may be ascribed to the 

strong masking effect of formate toward Cr(III) ions as the 

results above (Figure 1 and Table II). Although there is no adding 

of formic acid in pickling method No.3 and No.4, the added 1.0% 

of sodium formate in tanning processing still produces enough 

masking effect toward Cr(III), which significantly negatively 

influences the complex ability of masked chromium ions with 

collagen carboxyls. In order to illustrate the impact of masking 

effect on chromium uptake, only MSA was used in pickling 

without adding formic acid and formate (No.5), and the result 

shows that the chromium uptake is remarkably raised to 

Figure 1. UV-Vis spectrum of chromium (III) ion in different 

concentrations of ligands. 

Table II 

Measured wavelength of the two peaks in the UV-Vis spectrum of 

chromium solutions with different concentrations of ligands. 

Ratio of masking agent to 

chromium (mol/mol) 

MSA 

HCOOH 

0:1 0.5:1 1:1 2:1 3:1 1:1 

λ max,1 423.0 422.5 422.5 422.0 421.5 419.5 

λ max,2 583.5 583.0 583.0 583.0 583.0 576.5 



86%, whilst the residual chromium concentration is decreased to 

335mg/L. The results indicate that the excessively strong 

masking effect toward chromium ion from an overdose of 

formate is not beneficial to the combination of chrome by 

collagen, and MSA pickling exhibits good effect on improving 

the high exhaustion of chrome in the case of no addition of any 

other masking agents. 

Optimizing of Parameters of MSA Pickling-chrome 

Tanning Process 

According to the above results (Table III), the application of 

MSA can promote the absorption of chromium, hence, aiming at 

minimizing chromium discharge to a maximum degree, the 

main control parameters of MSA pickling-chrome tanning 

process, including pickling pH, masking agent and chrome 

offers, were further investigated. The results in Table IV show 

that, though the Cr offer is raised by about 30% in method No.6, 

from 0.89% to 1.16%, comparing with method No.7, the Cr 

uptake ratio is increased to 80% from 75% of method No.7, in 

which (No.7) 0.5% of sodium formate is added together with 

chrome powder. This further illustrates that the strong masking 

effects from formate to Cr(III) ion negatively influence the 

combination of chrome by collagen. The only difference between 

methods No.8 and No.6 is the kind of used acid in pickling, but 

the Cr uptake ratio in methods No.8 is much higher, which 

further indicates that MSA pickling can promote chrome 

exhaustion. This advantage can be mainly ascribed to the 

moderate masking effects of MSA towards Cr(III) ion. In order 

to minimize chromium discharge to a maximum degree, the 

initial tanning pH is raised to 5.0, and the offer is reduced to 

0.81% (method No.9) in consideration of the much enough Cr 

content in the leather from MSA process with a regular Cr offer 

(method No.8). As expected, the Cr exhaustion is further 

enhanced to 95%, and the shrinkage temperature (Ts) reaches to 

107°C, which can satisfy the requirement of chrome tanning 

standard accordingly, the residual Cr concentration in 

wastewater is further reduced to 115mg/L from 372mg/L. 

However, combining formic acid even at a rather low level of 

0.15% in method No.10 makes more Cr resided in wastewater 

than in method No.9. This indicates the negative effects of 

formate on chromium absorption over again. 

Figure 2. Cr contents and distributions of chrome tanned leathers with 

different pickling methods. 

Table III 

Influence of pickling with different acids on chrome uptake. 

Pickling methods 

No.1 

FA a +SA b 

No.2 

MSA+FA 

No.3 

MSA+SA 

No.4 

MSA-I 

No.5 

MSA-II 

Acid dosage (%) 

FA a 0.6, 

+SA b 0.9 

MSA 2.2, 

+FA 1.2 

MSA 1.5, 

+SA 0.5 

MSA 3.1 MSA 3.1 

Pickling pH 2.9±0.1 2.9±0.1 2.9±0.1 2.9±0.1 2.9±0.1 

Tanning end pH 4.1±0.1 4.1±0.1 4.1±0.1 4.1±0.1 4.1±0.1 

Cr offer (%) 1.07 1.07 1.07 1.07 1.07 

Sodium formate offer c (%) 1.00 1.00 1.00 1.00 0 

Cr in waste bath (mg/L) 1074±10 1040±10 914±8 799±8 335±5 

Cr uptake ratio (%) 72 73 77 79 86 

a 

FA-formic acid; b SA-sulfuric acid; c Sodium formate was added together with chrome powder. 



As mentioned before, there is a worry about Cr penetration into 

the inner layer of pelts when chrome tanning conducted at a high 

initial pH and with a low offer of Cr, hence, the chromium 

contents and distributions in chrome-tanned leathers from the 

above methods in Table IV were further investigated. The results 

are illustrated in Figure 2. 

Figure 2 indicates that the Cr content of chrome-tanned leather 

is consistent with the corresponding calculated value according 

to the data in Table IV. The addition of sodium formate in 

conventional process can improve the uniformity of Cr 

distribution in leather, but the combined Cr amount is decreased 

obviously, comparing method No.6 and No.7. In the MSA 

pickling process, being attributed to the moderate masking 

effect of MSA towards Cr(III) ions, there is no negative influence 

on the penetration and distribution of chromium in the leather. 

Chrome tanning at a high initial pH of about 5.0 with MSA, the 

penetration of chromium is not hindered, and the “excessive 

surface tanning effect” is not observed, and the addition of other 

masking agents is not necessary. Hence, raising initial tanning 

pH and appropriate reduction Cr offer in MSA pickling-tanning 

process is a practicable approach to further decrease chromium 

discharge. 

Tracing Chrome Discharge in Whole Leather 

Wet-end Processing 

The efficiency of the novel pickling-chrome tanning method 

with MSA was further evaluated on improving chrome tanning 

and leather quality in comparison with the conventional process. 

Because chrome in wet-blue leather will also leach out at varying 

levels in the following post-tanning operations, including 

wetting, neutralizing, organic retanning/filling and dyeing/ 

fatliquoring, the emission of chromium was also traced in whole 

leather wet-end processing. 18 

In the novel process, the pelts was pickled with MSA to a 

relatively high pH value of about 4.9 and tanned with a reduced 

Cr offer and without adding any other masking agent, and then 

Figure 3. The effectiveness of the novel process on improving Cr distribution. 

Table IV 

Influence of pickling pH and Cr offering in MSA pickling on chrome tanning. 

Pickling methods 

Conventional 

MSA 

No.6 No.7 No.8 No.9 No.10 

Acid dosage (%) 

FA a 0.50 

+SA b 1.10 

FA 0.50 

+SA 1.00 

MSA 3.00 MSA 1.00 

FA 0.15 

+MSA 0.70 

Pickling pH 2.9±0.1 2.9±0.1 2.9±0.1 5.0±0.1 5.0±0.1 

Basification pH 4.1±0.1 4.1±0.1 4.1±0.1 4.1±0.1 4.1±0.1 

Chromosal B (Cr) offer (%) 6.5 (1.16) 5.0 (0.89) 6.5 (1.16) 4.5 (0.81) 4.0 (0.72) 

Sodium formate offer c (%) 0 0.50 0 0 0 

Cr in waste water (mg·L -1 ) 864±8 802±8 372±4 155±3 224±3 

Cr uptake ratio (%) 80 75 91 95 91 

Shrinkage temperature (°C) 120±2 112±1 118±2 107±2 107±1 

a 

FA-formic acid; b SA-sulfuric acid; c Sodium formate was added together with chrome powder 



retanned with 0.63% of Cr offer and 0.5% of sodium 

methanesulfonate to substitute sodium formate at pH 4.5. The 

tanning effects are shown in Table V and Figure 3. 

The results show that the novel chrome tanning process is going 

well at a high beginning pH of 4.9. As shown in Table V, the Cr 

absorption ratio in the novel process is increased to 94% from 

75% in the conventional process, and the residual Cr in spent 

tanning float is reduced to 166.6mg/L from 1076.6mg/L (see 

Table VI), correspondingly, which are consistent with the results 

of No.9 method in Table IV. On basis of the novel picklingchrome 

tanning, the next chrome retanning operation was a 

little modified, i.e., wet-blue leather was conducted retanned 

with methanesulfonate as the masking agent at initial pH 4.5 

around. Further, the chrome uptake rate is increased to 96% 

from 76% in the conventional retanning process. All in all, both 

the novel tanning and retanning process with MSA exhibit 

obvious effectiveness on increasing chrome exhaustion. 

As shown in Figure 3, though the total Cr offer was reduced by 

30% (from 1.16% to 0.81%) in the novel MSA pickling-tanning 

process, the average Cr content of the chrome tanned leather is 

only a little lower than that from the conventional tanning 

process, and there is no obvious difference in the average Cr 

contents and Ts of the retanned leather between the two 

processes. This can be ascribed to the high exhaustion of chrome 

in the novel processes. Therefore, the total Cr offer can be 

obviously decreased. The Cr distribution in the vertical section 

of the leather retanned with novel process is more uniform than 

that in the leather from conventional retanning process, and the 

Cr content in the grain layer is not remarkable higher than in the 

middle layer. This once again proves that chromium penetrating 

into the inner layer is not hindered when tanning at the high 

beginning pH in the novel process. The area yield of leather is 

also not diminished (see Table V); hence no excessive tanning 

effectiveness has happened in the novel process. 

As mentioned before, besides the high-concentration chromecontaining 

effluents from tanning, sammying and chrome 

retanning, all the spent liquors from following post-tanning 

operations contain chrome resulting from the releasing of 

chrome from leather. All the chrome-containing effluents 

should be treated to decrease the Cr concentration to lower than 

1.5mg/L before discharged into sewage system in China, 

according to the strict statutory limits. Hence, the chrome 

discharge in whole leather wet-end processing was traced. 

Generally, a certain amount of formic acid is added to lower pH 

to promote the combination and fixation of anionic chemicals, 

such as anionic syntans, dyestuffs and fatliquors, in the posttanning 

processes. MSA was also used to substitute formic acid 

in the post-tanning processes of wet-blue leather from the novel 

pickling-chrome tanning and retanning methods, and the Cr 

concentrations of the spent liquors from main wet-end processes 

are shown in Table VI. 

Table V 

Effects of MSA pickling to a high pH on chrome tanning and retanning. 

Operations 

Pickling 

methods 

Acid dosage 

(%) 

Pickling pH 

Cr offer 

(%) 

Ts (°C) 

Cr uptake 

rate (%) 

Yield of leather a 

(sq.ft/kg) 

Cr-tanning 

Conventional 

FA 0.5; 

SA 1.1; 

Na-FA b 0.5 

2.9±0.1 1.16 118±2 75 3.10 

MSA MSA 0.9 4.9±0.1 0.81 107±2 94 3.10 

Cr- retanning 

Conventional 

FA 0.5; 

Na-FA b 0.5 

3.5±0.1 0.63 124±2 76 7.54 

MSA Na-MSA c 0.5 4.5±0.1 0.63 121±2 96 7.52 

a 

yield of leather in Cr tanning=areas of wet-blue (sq.ft)/weight of limed hide (kg); 

yield of leather in Cr retanning=areas of final leather (sq.ft)/ weight of shaved leather (kg). 

b 

Na-FA: sodium formate; added together with chrome powders. 

c 

Na-MSA: sodium methanesulfonate; added together with chrome powders. 



It can be seen that the chromium concentration of each 

wastewater is decreased by 46.1%-84.5%, the total chromium 

discharge amount is reduced by 83.8%, and the total Cr 

utilization ratio is increased to 95.8% from 81.0% in the novel 

technology of integrating application of MSA in picklingchrome 

tanning and post-tanning processes, comparing with 

the corresponding one from the conventional processes. Not 

only does the novel leather making process using MSA increase 

chromium exhaustion during chrome tanning and retanning, 

but also decrease chromium leaching out in post-tanning 

operations effectively, hence, the total Cr discharge is minimized. 

Operations 

Table VI 

Tracing Cr discharge in whole 

leather wet-end processing a 

No. i a 

Conventional 

(mg·L -1 ) 

No. ii a 

Novel 

(mg·L -1 ) 

Decrease 

rate (%) 

chrome tanning 1076±10 167±2 84.5 

Samming 465±3 107±3 77.0 

Wetting 16±2 7±1 58.9 

Chrome retanning 541±6 88±2 83.7 

Neutralizing 18±2 7±2 62.7 

Washing 9±2 5.0±1 43.8 

Moreover, considering that the residual Cr concentration was 

very low in the spent tanning liquor, it can be recycled directly in 

pickling process after simply filtrated. It is expected that the 

main problems of recycling the conventional spent chrome 

tanning liquor, such as dark color and rough grain of chrome 

tanned leather, from the high-concentration residual chromium 

will be overcome. Also, the chrome-containing sludge generated 

from alkali-precipitation of low concentration chromecontaining 

wastewater from post-tanning processes will be 

dramatically decreased. The further research is ongoing. 

Comparison of Leather Properties 

One of the main factors affecting the acceptability of a novel 

leather making method by tanners is whether it can improve or 

at least keep the original properties of the final leather. Hence 

the main properties of the leathers from the adjacent and 

symmetrical parts of a same hide respectively conducted the 

processing procedures of No. i and No. ii in Table I were 

evaluated by scanning electron microscope, and the results are 

shown in Figure 4. 

As mentioned before, excessive binding and depositing of 

chrome on the surface of leather resulting in wrinkled grain is a 

potential risk for tanning at a high initial pH. The electron 

micrographs illustrate that the grain pattern is a little smoother 

of the leather from MSA processing than conventional 

processing, and there is no any deposition of chromium on 

surface and inside the hair pores, hence, the excessive tanning 

effect in leather surface does not happen. The fiber bundles are 

well separated and their diameters are finer, and there is less 

Organic retanning/ 

Filling 

29±2 12±1 57.3 

Washing 15±2 8±1 46.1 

Dyeing/Fatliquoring 41±2 15±2 64.2 

The input and output of the Cr in whole process 

(kg/t salted-wet hide) b 

Total Cr offer 14.411 10.561 26.7 

Total Cr discharge 2.737 0.443 83.8 

Total Cr utilization 

ratio (%) 

81.0 95.8 - 

a 

The process parameter of No. i and No. ii seen Table I; 

b 

1.0t salted-wet hide was changed into 1.1t limed hide 

and 0.262t shaved grain chrome-tanned leather, and the 

samming water amount is 200 kg/t. 

Figure 4. SEM images of the grain pattern (×300) and vertical sections 

(×1000, ×5000) of the crust leather. 



densely blocky adhesion between fibers of the leather from MSA 

processing than the other one, which can be attributed to that 

the inner layer is well tanned, and the chemical used in posttanning 

processing are well absorbed and penetrate into the 

inner layer. 

Actually, it is found that the absorptions of anionic chemicals, 

especially dyestuffs and fatliquors, were obvious improved in the 

novel processing through observing the color depths and the 

turbidities of spent floats. The content of fatliquor in leather is 

higher and the distribution is more even as illustrated in 

Figure 5. The higher fatliquor content in middle layer may result 

from higher content of chrome (see Figure 4).Hence, the leather 

is softer and with better physical-mechanical performances, as 

shown in Table VII. 

The Pilot-scale Experiment Results 

In order to verify the acceptability of the novel pickling-chrome 

tanning method with MSA, the pilot-scale experiments were 

conducted in Tongtianxing Leather Co., which is the biggest 

furniture leather plant in China. Bating pelts of Ireland cowhides 

were taken out from the tannery production line of furniture 

leather, and conducted pickling with 1.0% MSA to pH of 4.5, and 

then tanning with 0.85% of Cr offer based on the weight of limed 

pelts of 2.5-2.8mm thickness. Satisfactorily, the same results with 

laboratory experiments were obtained. The twice repeated results 

indicated that the residual Cr concentration in the spent tanning 

liquor was 270mg/L. As the control, it was 2608mg/L from the 

tannery tanning float, tanning with 1.16% Cr offer as per 

conventional methods. The Cr content in leather was 3.15%, a little 

lower than the control, 3.31%, and the shrinkage temperature 

reached to 95°C, in the case of Cr offer decreased by 26.7%. 

The wet-blue leathers were post-tanned and finished as per the 

tannery’s furniture leather procedures. The resultant leathers 

passed through the examination of the quality inspectors from 

the tannery. Skilled tanners commented that, in the aspects of 

organoleptic properties comparing with the tannery products, 

the leather was more stretching, the fullness and softness were 

better, and the grain pattern of the final leather was more 

uniform. In their opinions, pickling-tanning method with MSA 

is interesting and commercially acceptable. 

Conclusion 

The novel pickling-masking-chrome tanning system with MSA 

can remarkably increase the chromium exhaustion without 

impairing Cr penetration in both chrome tanning and retanning, 

resulting from the suitable and moderate masking effect of the 

MSA ligand towards Cr(III) ion. Accordingly, the total chrome 

offer can be reduced by about 26.7%, and the total Cr utilization 

ratio can be increased to 95.8% from 81.0% around, resulting in 

the total chromium emission in the whole leather processing is 

reduced by 83.8%, comparing with the conventional process. 

The area yield, physical and organoleptic properties of the 

leather are comparable with those from conventional processes. 

Acknowledgment 

Figure 5. Fatliquor content in the final leather (dichloromethane extracts). 

Samples 

Table VII 

Physical properties of crust leathers. 

Tensile 

strength 

(N/mm 2 ) 

Tear strength 

(N/mm) 

Elongation 

at break (%) 

Conventional 7.5±1.2 25.6±5.7 45.7±4.7 

MSA 7.9±0. 9 32.0±3.4 56.7±3.2 

This work was financially supported by BASF Advanced 

Chemical Co., Ltd. and the National Key Technology R&D 

Programs of the Ministry of Science and Technology 

(2014BAE02B01). Tongtianxing Leather Co., China provided the 

required conditions for pilot-scale experiments. 

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B.; A novel formaldehyde-free synthetic chrome tanning 

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9. Suresh, V., Kanthimathi, M., Thanikaivelan, P., Raghava, 

J.R. and Unni, B.N.; An improved product-process for 

cleaner chrome tanning in leather processing. J. Clean. 

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acids in liquid sulfur dioxide. J. Phys. Chem. 63, 2061-2062, 

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J.; Environmental benefits of methanesulfonic acid: 

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Study of Cr(III)/Cr(II) system in methanesulfonate and 

sulfate solutions: temperature dependences. J. Electroanal. 

Chem. 689, 269-275, 2013. 

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5666-5672, 2009. 

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and mechanism of chromium electrodeposition from 

methanesulfonate solutions of Cr(III) Salts. Surf. Eng. Appl. 

Ekect. 50, 384-389, 2014. 

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447 

Development of Chrome-free Tanning in 

Supercritical CO 2 

Fluid using Zr-Al-Ti Complex 

by 

Xinhua Liu, 1,2 Feng Li, 1,2 Qin Huang, 1,2 Weihua Dan, 1,2 * and Nianhua Dan 1,2 * 

1 

Key Laboratory of Leather Chemistry and Engineering of Ministry of Education, Sichuan University, 

Chengdu, 610065, P.R. China 

2 

National Engineering Laboratory for Clean Technology of Leather Manufacture, Sichuan University, 

Chengdu, 610065, P.R. China 

Abstract 

In the current study, a green technology for the leather tanning 

process was developed, based on Zr-Al-Ti complex as a tanning 

agent in supercritical CO 2 

fluid (SCF-CO 2 

). The operating 

parameters in the tanning process, including dosage of the 

tanning agent, reaction time, tanning temperature and tanning 

pressure, were optimized using the orthogonal testing method. 

The physicochemical properties, morphological features, 

organoleptic properties, hydrothermal stability and microscopic 

fibrous construction of the Zr-Al-Ti tanned leather were also 

evaluated. The results showed that the optimum process 

conditions were: a tanning agent dosage of 40% of the bated pelt 

weight, a tanning time of 1.5h, a final temperature of 40°C and a 

reaction pressure of 8.5 MPa. The shrinkage temperature, tear 

strength, tensile strength and elongation at break of Zr-Al-Ti 

tanned leather in water media and in SCF-CO 2 

exhibited no 

statistically significant differences. However, SEM and 

histological observations revealed that the fiber bundles of 

leather tanned using the Zr-Al-Ti complex tanning agent in 

SCF-CO 2 

seemed to disperse more unevenly compared to those 

in water media, as well as conventional chrome tanned leather. 

Moreover, the degree of “opening up” of the fiber bundles and 

the visible interspace among them in the Zr-Al-Ti tanned leather 

in SCF-CO 2 

seemed to be much larger. Based on these results, we 

infer that the chrome-free tanning process in SCF-CO 2 

may 

endow similar leather characteristics compared to Zr-Al-Ti 

tanned leather in a water medium, which could effectively 

reduce the discharge of waste water compared to a conventional 

chrome tanning process, thus contributing to the development 

of a greener, or cleaner, technology for the leather tanning 

process. 

Introduction 

In recent years, concerns over environmental issues have led to 

many greener, or cleaner, approaches to leather tanning 

processes in the leather industry. 1-4 At present, chrome(III) is 

still recognized as endowing leather with unmatchable 

hydrothermal stability and excellent organoleptic properties; 

hence, its use as a tanning agent is widespread in the industry. 5 

Nevertheless, chrome tanning has some negative attributes, 

including: the possibility that uncombined residues of trivalent 

chromium in leather may be transformed into hexavalent 

chromium in some extreme conditions due to the insufficient 

penetration and combination of the chrome tanning agent; 6 such 

agents could give rise to concerns about water treatment issues 

related to BOD and COD; in some countries, chromium 

resources may be limited and even restricted to certain purposes 

only. 7,8 Therefore, the development of an eco-friendly chromefree 

tanning agent is of key importance for leather tanning. 

9, 10 

The Zr-Al-Ti complex tanning agent, abbreviated DMT-II, is a 

novel chrome-free tanning agent, which has been prepared by 

our group based on the interactions of metal molecules through 

coordination bonds. 11, 12 According to our previous study, 11 the 

combination of the three metal ions in solution results in the 

regeneration of a more complex multi-heteronuclear composite, 

which may be conducive to the tanning process. Moreover, it has 

been confirmed that DMT-II can endow leather with appropriate 

hydrothermal stability and superior organoleptic properties, 

comparable to chrome tanning agents. 12 

*Corresponding authors’ e-mail: lamehorse-8@163.com (N. Dan), danweihua_scu@126.com (W. Dan); 

Tel.: +86 28 85408988; fax: +86 28 85408988. 

Manuscript received October 29, 2015, accepted for publication May 10, 2016. 


Chrome-free Tanning in Supercritical CO 2 

448 

Reduction or elimination of sewage discharge at the source 

might solve certain contaminant concerns in the leather 

manufacturing industry. 13 Supercritical CO 2 

fluid (SCF-CO 2 

) has 

been utilized extensively in many areas, such as printing, dyeing, 

and cleaning. 14-16 In recent years, the technology of leather 

manufacturing based on SCF-CO 2 

has also been explored, with 

its core principle being the use of SCF-CO 2 

instead of water as a 

medium in the different parts of the leather manufacturing 

process. 17,18 It has been reported that the penetration, distribution 

uniformity and combination of the chemical reagents used in 

each working procedure seem to be promoted significantly 

under SCF-CO 2 

, 19, 20 as the fluid can effectively control reactivity 

and reaction selectivity owing to its high compatibility, high 

dispersion, and low viscosity. 21 Therefore, the chemical reagents 

used in the process exhibit relatively high levels of utilization. 

Moreover, as CO 2 

can provide an inert chemical microenvironment, 

these reagents may be much more easily recycled 

in SCF-CO 2 

. 

In the present study, SCF-CO 2 

was used instead of water as a 

medium in the chrome-free Zr-Al-Ti tanning process. The 

process conditions, including dosage of the tanning agent, 

reaction time, tanning temperature and pressure of the reaction 

caldron were optimized using the orthogonal testing method. In 

addition, the physicochemical properties, morphological 

features, organoleptic properties, hydrothermal stability, 

chemical components, and microscopic fibrous construction of 

the Zr-Al-Ti tanned leather were further studied. Our aim is to 

explore the feasibility of an anhydrous or micro water tanning 

method using supercritical CO 2 

fluid as the medium and 

Zr-Al-Ti complexes as a chrome-free tanning agent, with a view 

to the sustainable development of cleaner leather 

manufacturing process and effluent. 

modifications. 11 A brief description of the preparation process is 

as follows: first, zirconium sulphate, aluminum sulphate, 

titanium sulphate and citric acid, in a ratio of 5:4:1:2 (w/w), were 

dissolved in 1 L of water under continuous magnetic stirring. 

Then, the mixture was heated and maintained at a constant 

temperature of 90° C for 30 minutes. Finally, the solution was 

dried using spray drying (GPL5, Sichuan Wang Chang Drying 

Equipment Co. Ltd.) to obtain the DMT-II. 

Leather Tanning Process 

The tanning process was carried out using bated cow pelts with 

a pH of 7.0–7.5. The bated cow pelts were soaked in the Zr-Al-Ti 

complex tanning solutions with different concentrations (based 

on the pelt weight) for 12 h and then drained for 30 min. 

Subsequently, the flesh side of the pelts was further soaked in a 

sodium bicarbonate solution with a stock concentration of 30 

mg/ml. Finally, the pretreated pelts were placed in the 

supercritical CO 2 

fluid reaction unit to undergo the tanning 

reaction. The detailed operating conditions for the tanning 

process are shown in Table I according to the design principles 

Figure 1. Schematic of the SCF-CO 2 

reaction unit. 

Experimental Procedures 

Materials 

The bated cattle pelts used in the tanning process were selfprepared 

according to the method describe in our previous 

report. 12 The chemicals used for the synthesis of DMT-II and for 

tanning the leather were of analytical grade and purchased from 

Chengdu Kelong Reagent Chemical Factory, P. R. China. In 

addition, the supercritical CO 2 

fluid equipment, with operating 

temperatures between −20 and 300° C , was designed in-house. 

Figure 1 shows a schematic of the SCF-CO 2 

reaction unit. The 

maximum operating pressure and effective working volume of 

the equipment were 20 MPa and 1000 mL, respectively. 

Preparation of Zr-Al-Ti Complex Tanning Agent 

The Zr-Al-Ti complex tanning agent (DMT-II) was self-prepared 

according to the method detailed in a previous study, with slight 

Level 

Table I 

The factors and levels of orthogonal tests 

for the Zr-Al-Ti complex tanning process. 

Tanning 

time /h 

Factors 

Tanning 

temperature 

/°C 

Tanning 

pressure / 

MPa 

DMT-II 

offer /% a 

1 2 45 9.5 24 

2 1.5 40 8.5 32 

3 1 35 7.5 40 

a 

The DMT-II tanning solution was used in the tanning 

process and its dosage was based on the limed pelt after 

weight gain to 1.2 times. 


449 Chrome-free Tanning in Supercritical CO 2 

of the orthogonal test method. Simultaneously, samples of 

chrome-free tanned leather and chrome tanned leather, both 

using water as the medium, were also prepared as a control, 

based on the methods from our previous report. 12 

Shrinkage Temperature Analysis 

The shrinkage temperature of the leather specimens from each 

tanning group was measured using a MSW-YD4 shrinkage 

meter from the Yangguang Research Institute of the Shanxi 

University of Science Technology, according to the Chinese 

Industrial Standard QB/T 2713-2005. 

ICP Analysis 

The leather specimens from each tanning group were split into 

three layers (grain layer, middle layer, and flesh layer) with the 

same thickness, using a precise splitting machine. Each layer of 

the leather specimens was placed in a drying oven for over 4 

hours, following which a certain number of the dried samples 

were digested and further analyzed using an inductively coupled 

plasma (ICP) spectrometer (Optima 2100DV, Germany). The 

homogeneous degree of DMT-II in the leather specimens was 

calculated using the following formula (1). 

where A 2 

represents the metal ion content of the middle layer, 

and A 1 

and A 3 

are the metal ion contents of the grain layer and 

flesh layer, respectively. 

Microstructure Characteristics 

Scanning Electron Microscope Observation 

The leather specimens from each tanning group were sampled in 

official sampling position. The samples were lyophilized in a 

vacuum chamber (0.05 bar) for 48 hours and their cross sections 

were observed microscopically using a scanning electron 

microscope (SEM, Hitachi S3000N, Hitachi, Ltd., Japan). 12 All 

the specimens were coated with aurum and imaged at an 

accelerating voltage of 5 kV. 

Histological Observation 

The leather specimens from each tanning group were sampled 

adjacently and symmetrically from the same hide, and fixed in a 

10% formaldehyde solution for more than 24 hours. The crossand 

longitudinal- sections of the specimens were prepared using 

a CM1950 freezing microtome (Leica, Germany) to a thickness 

of 12 µm, and adhered to glass slides. Morphologic observation 

was performed using the Van Giesen staining method with 

picric acid and fuchsin acid. Finally, an E400 optical microscope 

(Nikon, Japan) was used to carry out a histological examination 

of the stained samples. 12 

(1) 

Physical-mechanical Properties and Organoleptic Assessment 

The dried crust leather samples from each tanning group were 

tested using an AI-7000S Versatile Material Experiment Machine 

(Gotech High Technology Co. Ltd., Taiwan, China) according to 

the standard procedures for testing physical and mechanical 

properties. Physical properties such as tensile strength, 

elongation at break, and tear strength were examined as per the 

standard procedures IUP 6 (2000), IUP 8 (2000), and IUP 9 

(1996). 22 Further, the specimens from each tanning group were 

assessed by hand for softness, grain tightness, grain smoothness, 

strength, and fullness, through the visual examination of 

experienced tanners, who have worked in the leathermanufacturing 

industry for more than ten years. 

Chemical Composition Analysis 

The leather specimens from each tanning group were subjected 

to chemical composition analysis to determine the moisture, 

sulfate ash, and fat content, according to the methods laid out by 

the Chinese Industrial Standard QB/T 2706-2722 (2005). 


Orthogonal Experiment Analysis 

Table II shows the results of orthogonal experiments determined 

by the shrinkage temperature, Ts. The influence of the tanning 

conditions on the shrinkage temperature of the leather specimens 

from each tanning group are directly reflected by the R values. As 

shown in Table II and Figure 2, the tanning conditions for the 

shrinkage temperature of the leather specimens, ranked in order 

from the most to the least influential, are: (DMT-II offer) > 

(tanning time) > (tanning temperature) > (tanning pressure). 

Figure 2 shows the effects of each tanning operating condition on 

the shrinkage temperature of the leather specimens. The Ts values 

increased dramatically for DMT-II dosages of less than 32%. As 

the DMT-II offer was increased, the Ts tended towards a steady 

value; however, operating under these conditions would be more 

costly. Generally, with an increasing concentration of DMT-II, the 

coordination probability between carboxyl groups in collagen 

fibrils and DMT-II would increase, 12 thus increasing the combined 

amount of DMT-II and further improving the shrinkage 

temperature. Furthermore, our previous study indicated that the 

reaction between collagen fibrils and DMT-II reaches chemical 

equilibrium when the DMT-II offer reaches 40%. 12 In addition, 

when the tanning process starts within 1 h, the penetration of the 

tanning agent could promptly penetrate into the leather. By 

prolonging the rotation time to 1.5 h, the combination of the 

tanning agent with the carboxyl of the collagen chains approaches 

an equilibrium point. Furthermore, increasing the tanning 

temperature accelerates the hydrolysis and polycomplexation of 

the DMT-II molecules, 12 resulting in bigger molecular dimensions; 

this may promote the permeation of DMT-II into the pelts and 



450 

further the combination of the metal complex with the collagen. 

However, when the tanning temperature is set too high, DMT-II 

molecules might become too large and react with the collagen too 

early, leading to the case hardening of leather, 23 which would 

negatively affect the permeation of DMT-II molecules. In 

summary, taking into account the cost and tanning results, the 

optimum operating conditions of the Zr-Al-Ti tanning process in 

SCF-CO 2 

were determined to be: a tanning agent dosage of 40% of 

the bated pelt weight, a tanning time of 1.5 h, a final temperature 

of 40°C, and a reaction pressure of 8.5 MPa. 

Shrinkage Temperature Analysis 

The shrinkage temperature determines the thermostability of 

leather. Table III shows the shrinkage temperatures of the leather 

specimens from each tanning group. The shrinkage temperature 

of the Zr-Al-Ti tanned leather in SCF-CO 2 

increased by around 

24 °C compared to the bated cattle skin, which indicates that the 

hydrothermal stability of leather may be efficiently improved by 

the tanning agent. 24 Note that the shrinkage temperature of the 

Zr-Al-Ti tanned leather in SCF-CO 2 

was somewhat lower than 

that in the water fluid. This may be because the pelts could not 

achieve sufficient mechanical interaction in the SCF-CO 2 reaction 

unit compared to the conventional drum. On the other hand, 

though the combination of the DMT-II in the tanned leather 

under SCF-CO 2 

was higher, as confirmed by the ICP analysis, 

the effective combination with collagen fibrils (i.e. the multipoint 

attachment) was insufficient. 17 Additionally, as is well known, 

hydrolysis and polymerization of metal tanning agents usually 

occur in an aqueous medium; thus, the aforementioned reaction 

of the Zr-Al-Ti tanning agent would be inhibited to some extent 

in SCF-CO 2 

, leading to a lower shrinkage temperature. 

Therefore, the tanning process taking place in an almost 

anhydrous environment may be very beneficial for saving 

tanning water and reducing tanned effluent discharge. At the 

same time, unlike for the conventional chrome tanning process, 

there was no need to introduce any additional sodium 

bicarbonate to increase alkalinity in the tanning process 

occurring in the SCF-CO 2 

reactor. Meanwhile, 1.5 h of tanning 

time, which was significantly lower than that of the Zr-Al-Ti 

tanned leather in water fluid, was quite enough in the SCF-CO 2 

. 

This would undoubtedly substantially save on energy 

consumption and labor costs. 

Table II 

Results of orthogonal experiments. 

Tanning time /h 

Tanning 

temperature / ° C 

Pressure /MPa Dosage /% Ts / °C 

1 2 45 9.5 24 82.0 

2 2 40 8.5 32 87.5 

3 2 35 7.5 40 83.3 

4 1.5 40 9.5 40 85.7 

5 1.5 35 8.5 24 84.8 

6 1.5 45 7.5 32 86.7 

7 1 35 9.5 32 83.6 

8 1 45 8.5 40 84.3 

9 1 40 7.5 24 82.8 

K 1 

84.3 83.7 84.3 83.2 

Ts 

K 2 

85.7 85.5 85.3 85.9 

K 3 

83.6 84.3 83.9 84.4 

R 2.1 1.8 1.4 2.7 

Significance 

DMT-II offer > Tanning time > Tanning temperature > Tanning Pressure 



ICP Analysis 

Table IV shows the ICP results for the Zr-Al-Ti tanned leathers 

in the SCF-CO 2 

and water fluids. The DMT-II contents of each 

layer of the tanned leather in SCF-CO 2 

were higher compared to 

those in water, which indicates that the penetration and 

combination of the DMT-II is promoted under SCF-CO 2 

. 

Moreover, the DMT-II in the tanned leather exhibited a 

significantly higher homogeneous degree in the SCF-CO 2 

compared to the water. 

Physical-mechanical Properties Analysis 

Table V shows the results of the physical-mechanical property 

analysis for the Zr-Al-Ti tanned leathers in the SCF-CO 2 

and 

water fluids, and the conventional chrome tanned leather. The 

tear strengths, tensile strengths and elongation at break of the 

three samples were not very different, and ensures that all three 

fulfilled the fundamental requirements for the mechanical 

strength of leathers. 12 However, it is still noteworthy that the 


exhibited a slightly lower 

tensile strength than the other two specimens, while possessing 

the highest elongation at break. 

The organoleptic properties of the three different leathers were 

also evaluated. All of the professional, skilled tanners consulted 

in this study believed that there were no visible differences 

among these leathers in respect to the strength, fullness and 

hand feeling; some differences were noted in respect to the 

softness, grain tightness and grain smoothness. More 

specifically, the softness and grain smoothness of the Zr-Al-Ti 

tanned leather in SCF-CO 2 

was superior to that in water, while its 

grain tightness exhibited a slight inferiority. 

Chemical Composition Analysis 

The chemical compositions of the leather specimens from each 

tanning group were studied using the methods outlined in the 

Chinese Industrial Standard QB/T 2706-2722 (2005), as shown 

in Table VI. According to the proximate composition results, the 

moisture content of the Zr-Al-Ti tanned leather in SCF-CO 2 

was 

slightly higher compared with that in the water. Generally, the 

moisture content of leather or fur should be between 12–18%, as 

the density, thickness, area, and tensile strength of the leather 

vary greatly with the moisture content. Leathers with lower 

moisture content appear much harder and crisper, whereas those 

with higher moisture content tend to be much easier to deform 

and mildew. A higher content of sulfated ash was found in the 


compared to that in the 

water, which might suggest that the amount of infiltration and 

combination of DMT-II was significantly higher due to more 

loosely weaved collagen fibrils. Meanwhile, the Zr-Al-Ti tanned 

leather in SCF-CO 2 

exhibited lower dichloromethane extract 

Figure 2. The effect of each tanning operating condition on the shrinkage temperature of the leather specimens. 



452 

content, as the SCF-CO 2 

was able to extract a small amount of 

grease from the bated pelts. As is well known, the 

dichloromethane extract content of leather is closely associated 

with its water resistance performance, extensibility and 

breathability. The lower dichloromethane extract content may be 

beneficial for the breathability of the leather, especially when 

used as shoe upper leather. In addition, the Zr-Al-Ti tanned 

leather in SCF-CO 2 

was found to have a significantly higher 

protein content than that in water fluid, which indicates that the 

tanning process in supercritical CO 2 

fluid does not excessively 

damage the basic framework of collagen fibrils in leather. 

Overall, the chemical compositions of the two leathers were 

similar but still showed some differences, which may be closely 

related to their specific leather properties. 

Microstructure Characteristics 

SEM Analysis 

The scanning electron micrographs of the leather specimens 

from each tanning group, presented in Figure 3, show that the 

degree of “opening up” of the fiber bundles in the Zr-Al-Ti 

tanned leathers in both media were higher compared to the 

bated pelts. Moreover, no apparent dense blocky crystals of 

DMT-II were observed between the collagen fibers, which 

indicates that all the inner layers were well tanned. 21 The fiber 

bundles of these two leathers were weaved very tightly and the 

fibrous clearance was relatively close. As a result, the 

tanning effects achieved by DMT-II were clearly apparent 

compared to the bated pelts, which implies that the DMT-II 

tanning process was conducted successfully in the SCF-CO 2 

. 

Specimens 

Table III 

Shrinkage temperatures of the leather 

specimens from each tanning group. 

Table IV 

ICP results for the leather specimens 

from each tanning group. 

Ts / ° C 

Bated cattle pelts 63.7 ± 2.1 


87.4 ± 2.6 

Zr-Al-Ti tanned leather in water fluid 94.6 ± 3.5 

conventional chrome leather 105.1 ± 5.3 

Table V 

The mechanical properties of each leather specimen. 

Specimens 

Tear strength/ 

(N/mm) 

Tensile 

strength/MPa 

Elongation at 

break /% 

Zr-Al-Ti 

tanned 

leather in 

SCF-CO 2 

Zr-Al-Ti 

tanned 

leather in 

water fluid 

Chrome 

tanned 

leather 

45.7 ± 3.5 44.8 ± 2.8 46.4 ± 1.3 

10.6 ± 0.6 13.7 ± 1.6 12.3 ± 1.1 

95.2 ± 3.7 75.3 ± 6.0 78.9 ± 5.5 

Table VI 

Chemical compositions of each leather. 

Specimens 

Layer 

classification 

DMT-II 

content / 

(mg/g) 

homogeneous 

degree of 

DMT-II 

Specimens 

Zr-Al-Ti 

tanned 

leather in 

SCF-CO 2 

Zr-Al-Ti 

tanned 

leather in 

water fluid 

Chrome 

tanned 

leather 

Zr-Al-Ti 

tanned 

leather in 

water fluid 

Grain layer 36.32 

Middle layer 32.86 

Flesh layer 36.89 

Zr-Al-Ti Grain layer 37.65 

SCF-CO 2 Flesh layer 37.12 

tanned 

leather in 

Middle layer 35.13 

89.77% 

93.97% 

Moisture /% 15.91 ± 2.52 14.98 ± 2.31 13.13 ± 1.98 

Sulfated ash /% 17.95 ± 1.28 16.70 ± 2.13 6.93 ± 1.65 

Dichloromethane 

extracts /% 

0.78 ± 0.02 1.05 ± 0.05 2.31 ± 0.59 

Protein /% 48.66 ± 3.12 36.50 ± 2.91 38.79 ± 2.61 



Histological Analysis 

Histological examination mainly showed the intact total framework 

of the cross and longitudinal sections of the three different 

specimens, as shown in Figures 4 and 5. The degree of “opening up” 

of the fiber bundles and the visible interspace among them seemed 

to be much larger in the SCF-CO 2 

specimen compared to the one in 

water, which may be beneficial for the infiltration and combination 

of DMT-II, since most of the penetration time is determined by the 

efficiency of DMT-II assimilating into the collagen fibrils. 25 In this 

case, the CO 2 

can directly infiltrate the grain and reticular layers of 

crust leathers, which should have a positive impact on the 

penetration of the DMT-II. In addition, the fibrils of the Zr-Al-Ti 


seemed to be more loosely weaved, 

which corresponds with the results of the physical-mechanical 

property and organoleptic assessment analyses. Based on these 

results, it may be inferred that the gaps between the collagen fiber 

bundles would be increased in the SCF-CO 2 

due to its function of 

“decentralizing fibers.” 

Figure 3. Scanning Electron Microscope cross sections of crust leathers: 

(1) Bated cattle skin (×200); (2) Zr-Al-Ti tanned leather in SCF-CO 2 

(×200); (3) Zr-Al-Ti tanned leather in water fluid (×200). 

Conclusions 

A green technology for a leather tanning process in supercritical 

CO 2 

fluid media (SCF-CO 2 

) was developed and evaluated based 

on Zr-Al-Ti complex as tanning agent. The operating conditions 

of the tanning process were optimized using the orthogonal test 

method, with the following conditions found to be optimal: a 

tanning agent dosage of 40% of the bated pelt weight, a tanning 

time of 1.5 h, a final temperature of 40° C and a reaction pressure 

of 8.5 MPa. The shrinkage temperature of the Zr-Al-Ti tanned 

leather in water media and in the SCF-CO 2 

exhibited no 

statistically significant differences. ICP analysis confirmed that 

the distribution uniformity and combination of the Zr-Al-Ti 


was better compared to the 

conventional Zr-Al-Ti tanned leather in water fluid. The slightly 

lower tensile strength and higher elongation at break of the 


were due to its more loosely 

woven fibrils. Meanwhile, histological observations showed that 

the degree of “opening up” of fiber bundles, and the visible 

interspace among them in the Zr-Al-Ti tanned leather in 

SCF-CO 2 

seemed to be much larger compared to that in the 

water fluid. SEM analysis confirmed that all the inner layers 

were well tanned. As a whole, the fundamental properties and 

microscopic fibrous construction of the Zr-Al-Ti tanned leather 

in SCF-CO 2 

exhibited no remarkable differences compared to 

the conventional Zr-Al-Ti tanned leather in water. However, this 

chrome-free process could help with waste water treatment by 

eliminating the chromium discharge at the source, thus 

contributing to the development of sustainable leather 

manufacturing processes. 

Figure 5. Histological observation of the cross sections of crust leathers 

j. Bated cattle skin (×40), m. Bated cattle skin (×100); 

k. Zr-Al-Ti tanned leather in SCF-CO 2 

(×40), n. Zr-Al-Ti tanned leather 

in SCF-CO 2 

(×100); 

i. Zr-Al-Ti tanned leather in water fluid (×40), o. Zr-Al-Ti tanned 

leather in water fluid (×100). 

Figure 4. Histological observation of the longitudinal sections of 

crust leathers. 

a. Bated cattle skin (×40), d. Bated cattle skin (×100), g. Bated cattle 

skin (×200); 

b. Zr-Al-Ti tanned leather in SCF-CO 2 

(×40), e. Zr-Al-Ti tanned leather 

in SCF-CO 2 

(×100), h. Zr-Al-Ti tanned leather in SCF-CO 2 

(×200); 

c. Zr-Al-Ti tanned leather in water fluid (×40), f. Zr-Al-Ti tanned leather 

in water fluid (×100), i. Zr-Al-Ti tanned leather in water fluid (×200). 



454 

Acknowledgement 

This work is supported by the National Natural Science 

Foundation of China (contract grant numbers 51473001 and 

21276164). 

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455 

Studies on the use of Bi-functional Enzyme for Leather Making 

by 

G. C. Jayakumar, 1 M. Sathish, 1 R Aravindhan 2 * and J. Raghava Rao 1 * 

1 

Chemical Laboratory 

2 

Leather Process Technology Division 

Central Leather Research Institute, Council of Scientific & Industrial Research 

Adyar, Chennai, India 

Abstract 

Preparation of skin or hide for tanning involves several unit 

processes/operations. This results in the generation of significant 

quantity of solid and liquid wastes, which is of major concern for 

the leather fraternity. However, several alternate technologies are 

available to address this issue. One of the well explored systems 

is application of enzymes in conventional leather processing. In 

the present research, application of bi-functional enzymefibrozyme 

(mixture of protease and amylase) for leather 

processing was studied. The present study relies upon the 

characteristic evaluation methods to ascertain the efficiency of 

enzymes in unhairing and fiber opening. Initially, various 

concentrations of enzymes were applied to cow hides by drum 

method. In this approach, 3.5% of fibrozyme is optimized for 

efficient removal of hair and proteoglycans. This is based on the 

organoleptic evaluation of enzyme treated pelts. The efficiency of 

enzyme was primarily evaluated through staining technique. 

Moreover, physical strength parameters were measured to assess 

the impact on fibers due to enzyme treatment. Morphological 

evaluation was carried out to confirm that there is no coalescent 

or distortion of fibers after enzyme treatment. Hydrothermal 

stability of experimental wet blue leather was found to be 108ºC, 

which confirms better exhaustion and fixation of chromium. The 

study provides an avenue for integrated enzymatic dehairing and 

fiber opening using a single formulation of protease and amylase. 

Introduction 

Development of cleaner technologies for leather manufacture is one 

of the emerging fields of research to attain the eco-labelling. 1 It is a 

real challenge to attain paradigm shift in adopting modern 

technologies in traditional sector like leather. 2 There are several unit 

processes and operations involved to clean the matrix. Pretanning 

is carried out primarily to prepare the skins/hides for tanning. In 

conventional leather making, liming and reliming steps are very 

imperative as it is prerequisite to remove hair, flesh and to open up 

the fiber bundles for the diffusion of chemicals. Lime-sulfide 

process is extensively used in terms of hair removal due to its high 

efficiency. However, generation of pollution due to this process 

cause serious health hazard to the workers as well as the 

environment. Sulfide assisted process also leads to the degradation 

of hairs, which results in high COD in the effluent. Several alternate 

technologies have been designed to reduce the pollution load. 

Application of enzymes in leather processing is one such option, 

which aids in the reduction of the pollution load, increase the 

efficiency of the process thereby reducing the duration. 2-3 Protease, 

amylase and lipase are the three major enzymes that are widely used 

in bio-processing methods. Conventional reliming process takes a 

minimum of one day to few days depending on the type of end 

product. However, enzyme assisted fiber opening considerably 

reduce the duration and effectively scissors the proteoglycans. 4-5 

Amylase helps in the fiber opening and effective removal of the 

adipose tissue from the skin/hide. 

In the present study, a technical evaluation method has been 

formulated in order to evaluate the efficacy of the enzymes in 

leather processing. Staining technique is employed to understand 

the role of protease and amylase in leather making. Proteaseamylase 

mixture is treated with cow hides at various 

concentrations and their organoleptic properties have been 

evaluated and the offer of enzyme is optimized. The present 

study provides a new dimensional approach in analytical 

methods to assess the leather properties. 

Experimental 

Materials 

Wet salted cow hides were used as raw materials during this 

study. All chemicals used for leather processing were of 

commercial grade while the chemicals used for the analysis of 

spent liquors were of analytical grade. Fibrozyme (formulated 

protease and amylase product having protease activity - 100 U/g, 

amylase activity - 1000 U/g) was supplied by Southern Petro 

Chemicals Industries Corporation (United Alacrity), Chennai. 

Bovine Serum Albumin (BSA), Mucin, Folin ciocelatu reagent, 

Periodic acid was procured from Sigma-Aldrich, India and other 

analytical chemicals were procured from SD Fine Chem Ltd., India. 

*Authors for correspondence e-mail: (J. Raghava Rao) clrichem@mailcity.com; (R Aravindhan) aravindhanr78@gmail.com; 

Tel: + 91 44 2441 1630; Fax: + 91 44 2491 1589 

Manuscript received March 3, 2016, accepted for publication May 27, 2016. 


Bi-functional Enzyme 456 

Quantification on the Release of Protein, 

Proteoglycan Processes 

Five wet salted cow hides were taken and cut in to sides. The left 

halves were processed for enzymatic unhairing and fiber opening 

process as given in Table I and the right halves were used as 

control, where, lime sulphide method was employed for dehairing 

and conventional reliming using lime was carried out for fiber 

opening. The pH of the float was adjusted using sodium carbonate 

to 8.5-9.0 before addition of enzyme for effective unhairing 

treatment. The spent liquor collected after the unhairing and fiber 

opening from both control and experimental processes were 

filtered through Whattman filter paper (cellulose filters, 0.25 psi 

wet burst, thickness-180 μm, pore size-11 μm). The filtered 

samples were then estimated for the release of protein and 

proteoglycan. 6 Proteins are estimated as described by Bradford 

method, 7 where a standard graph was prepared using BSA and the 

amount of protein present in the sample sourced from the control 

and experimental processes was estimated. 

For the estimation of proteoglycans, Schiff’s assay method was 

carried out, 8 where the periodate oxidizable glycoconjucates can 

be estimated. Standard graph was prepared using mucin as 

working standard and the amount of proteoglycan present in the 

samples were estimated. 

Staining Techniques 

Haematoxylin and Eosin (H&E) staining is a routinely used 

technique in histopathology laboratories as it provides the 

pathologist/researcher a very detailed view of the tissue. H&E 

staining is considered to be a critical assay to study the tissue 

samples. This technique was carried out for staining the relimed 

pelt (control) and fibrozyme treated pelt, to understand the 

changes brought about in the fibers. From each sample the color 

images were acquired with a light microscope and digital camera 

running under image analysis program. 9 

Chrome Tanning 

The enzyme treated pelts were washed thoroughly and pickled. The 

deliming and bating processes were eliminated for the enzyme 

based process as the pH of the enzyme treated pelts was around 8±1. 

In addition, no lime was also used during the fiber opening process. 

The pickled pelts were subsequently processed for conventional 

chrome tanning using 8% BCS as given in Table II. The spent liquor 

was collected to analyze the exhaustion of chromium, which is an 

indirect measure of fiber opening in the hide matrix. The control 

pelts were conventionally processed in to chrome tanned leather by 

carrying out deliming, bating and pickling. 

Determination of Shrinkage Temperature 

The shrinkage temperature, which is a measure of hydrothermal 

stability of leather, is determined using a Theis shrinkage tester. 10 

A 2 cm 2 samples from control and experimental leathers was cut 

and clamped between the jaws of the clamp, and was immersed 

in a solution of water: glycerol mixture (3:1). The temperature of 

the solution was gradually increased and the solution was kept 

under stirring using a mechanical stirrer. The temperature at 

which the leather shrinks was noted and determined as the 

shrinkage temperature. 

Post Tanning Process 

Control and experimental leathers were shaved to a uniform 

thickness of 1.1±0.1 mm and converted in to an upper crust leather 

Table I 

Process recipe for fibrozyme enzyme application. 

Process Chemicals % Time (h) Remarks 

Soaking I Water 300 

Water 300 

Soaking II 

Sodium carbonate 0.4 

2 

Adjust the pH of soak liquor 

to 9-9.5 and left overnight 

Biocide 0.1 

Enzyme treatment Water 30 

Fibrozyme 2.5-4 

6 

Adjust the bath pH to 9-9.5. 

No. of cycles – 6 (10’ run and 50’ 

stop and left overnight) 

Washing Wetting agent 0.2 10 Dry drumming 

Washing Water 100 

Wetting agent 0.2 

10 


457 Bi-functional Enzyme 

by following the post tanning recipe provided in Table III. After 

post tanning operations, the leathers were piled overnight. Next 

day, the leathers were set, hooked to dry, staked and buffed. 

Evaluation of Physical and Organoleptic 

Properties of Leathers 

The samples for physical testing were obtained as per IULTCS 

methods. 11 The samples were conditioned at 80°F and 65% R.H. 

for 48 h. 12 Physical properties such as tensile strength, %elongation, 

tear strength and grain crack strength were determined as per 

standard procedures. 13,14 Each value reported is an average of four 

measurements. The crust leathers were further assessed for 

softness, grain smoothness, fullness and general appearance by 

tactile evaluation. Three experienced tanners rated the leathers on 

a scale of 0-10 points for each functional property. 

Scanning Electron Microscopic (SEM) Analysis 

of Processed Leathers 

Samples from control and experimental pelts and from the 

respective crust leathers were cut from the official sampling 

position. 11 Samples were first washed in water. Subsequently, the 

samples were dehydrated gradually using acetone and methanol as 

per standard procedures. 15 A Quanta 200 series scanning electron 

microscope was used for the analysis. The micrographs for the grain 

surface and cross section were obtained by operating the SEM at an 

accelerating voltage of 5 KV with different magnification levels. 


Optimization of Enzyme Application 

The amount of enzyme used for the experiment has been 

calculated based on the enzyme activity. Drum based deharing 

Table II 

Process recipe for chrome tanning process. 

and fiber opening has been employed during the study. After 

ensuring thorough soaking, 2.5-4% of enzyme (w/w based on 

soaked weight) has been used for the experiment. The enzyme 

treatment has been carried out for 12 h with 10 min of 

intermittent running. The visual and organopleptic assessment 

of the dehaired and fiber opened pelts have been carried out and 

the results are depicted in Figure 1. The observations have been 

compared with that of the control pelts processed employing 

conventional liming and reliming processes. It could be observed 

from the figure that at concentrations less than 3.5%, complete 

hair removal has not been achieved. Hence a minimum of 3.5% 

of enzyme is required to achieve complete unhairing. During the 

process, no objectionable odor has been observed. Moreover, the 

fiber opening and grain smoothness have been observed to be 

better at higher concentration and has been observed to be better 

than that of the control pelts. Hence, based on assessment rating, 

3.5% of fibrozyme is being optimized for further studies. 

Proteoglycan Release After Enzyme Treatment 

Opening up of fiber bundles is a crucial step in leather making. 

Ever since, the quote “Leathers are made in lime yard” always 

signifies the importance of opening up of fiber bundles to 

fibrillar level in order to enhance the uptake of chemicals added 

during tanning and post tanning processes. Conventional 

reliming process depends on the plumpness brought about due 

to the difference in concentration gradient inside and outside the 

pelts. However, in the case of enzyme assisted process, release of 

proteoglycans is considered to be the indirect measurement of 

fiber opening. As, in the latter case, no visual changes can be 

observed except for a clean pelt after removal of short hairs. The 

amount of proteins and proteoglycans released during the 

control and experimental trials are provided in Table IV. It could 

be observed that a significant quantity of protein and 

proteoglycans have been released from the skin, which is an 

Chemicals % Offer Time Remarks 

Pickle liquor 50 

Chrome 

tanning agent 

8 2-3 h 

Check pH 

2.8-3.0 

Check 

penetration 

Water 50 30 min 

Sodium 

formate 

1 15 min 

Sodium 

bicarbonate 

1-1.5 

4x15 min 

+ 1 h 

Check pH 

3.8-4.0 

Water 50 

Drain/washed 

Aged for 48 h 

Figure 1. Assessment rating of fibrozyme treated and control pelts 



Table III 

Post-tanning recipe for the manufacture 

of upper leather from wet blue. 

Process/chemicals % 

Washing 

Duration 

(min) 

Remarks 

Water 100 10 Drained 

Neutralization 

Water 150 

Sodium formate 1.0 10 

Sodium bicarbonate 1.0 3x15+45 

Washing 

pH – 5.0 - 5.2, 

Drained. 

Water 200 15 Drained 

Retanning, Dyeing and Fat liquoring 

Water 100 

Grain tightening 

acrylic syntan 

Semi-synthetic 

fatliquor 

4.0 30 

3.0 45 

Acid dye 3.0 30 

Synthetic fatliquor 4.0 

Phenol –naphthalene 

based syntan 

5.0 

Mixed in hot 

water 

indication that the enzyme has cleaved proteoglycans and aided 

in opening up of the fiber bundles. This is in accordance with 

the visual assessment made in the earlier section. 

Histological Examination of the Control and 

Experimental Pelts 

The pelts obtained after fiber opening by employing both 

conventional reliming and fibrozyme treatment have been 

subjected to histological examination by adopting Hematoxylin 

and Eosin (H&E) staining technique. By employing this 

technique, a clear picture about the opening up of the fiber 

bundles could be obtained. The H&E stained images of raw cow 

hide, conventionally relimed and enzyme treated cow pelts are 

shown in Figure 2 (a-c). Collagen fibers being acidophilic, reacts 

with the eosin dye and are stained pink. From the figure a wellorganized 

collagen fiber could be seen in all three raw materials. 

Apart from this, it is also clearly observed that the level of 

separation/opening of the fibers varied distinctly with respect to 

the type of sample. Stained image of raw hide (2a) showed 

compact fiber orientation as compared to relimed (2b) and 

enzyme treated pelt (2c). Moreover, the splitting of fibers in case 

of the enzyme treated pelt was better, which is evident from the 

higher distance between the collagen fibers. 

Stratigraphic Distribution of Chromium 

in Wet Blue Leathers 

The layer wise distribution of chrome content in both control 

and experimental wet blue leathers was assessed to estimate the 

chrome penetration and distribution, which would in turn 

provide a substantiate evidence on the level of opening up of the 

fibers. Chrome content in grain, middle and flesh layer has been 

determined to be 3.59, 3.51 and 3.64% Cr 2 

O 3 

, respectively and the 

average chrome content in the leather has been found to be 3.62% 

Cr 2 

O 3 

. The uniform distribution of chrome content in the leather 

Melamine syntan 6.0 60 

Semi-synthetic 

fatliquor 

4.0 30 

Wattle 4.0 30 

Formic acid 1.5 4x10+20 

Washing 100 15 

The dye 

exhaustion 

was checked. 

Drained. 

Drained. Crust 

leathers were set 

twice, hooked to 

dry, conditioned, 

and staked. 

Figure 2. Photomicrographs of H&E stained raw (A), relimed (B) and 

fibrozyme (C) treated cow hides 


459 Bi-functional Enzyme 

confirms the through-through penetration. This is possible only 

when the uniform and efficient opening up of the fiber bundles 

have been achieved. Also, the chrome exhaustion has been found 

to be 75% with the shrinkage temperature of 108ºC. 

Visual Assessment of Wet Blue Leathers 

The wet blue leathers obtained from control and experimental trials 

were visually assessed by experienced tanners. Various parameters 

such as color of the wet blue, chrome patches, grain smoothness and 

general appearances have been used for assessing the wet blue 

leathers. The results are provided in Table V. It could be observed 

from the table that the rating of the experimental wet blue is in the 

range of 8-9, which indicates that the fibrozyme based deharing and 

fiber opening has not deteriorated the quality of the final leather. 

Specifically, no grain damage has been observed in the case of 

enzyme treated (Experiment) wet blue leathers. The general 

assessment also indicates that the enzyme processed leathers are on 

par to that of conventionally chrome tanned leathers. 

Physical Characteristics of Crust Leather 

The strength characteristics like tensile, tear and grain crack 

strength of the crust leathers processed from control and 

experimental wet blue leathers have been analyzed. The tensile, 

tear and the grain crack strength of the experimental upper 

Table IV 

Release of protein and proteoglycans in the spent liquor. 

Process 

Protein 

(mg/g of raw wt) 

Proteoglycans 

(mg/g of raw wt) 

Enzyme Liquor 26.8±0.5 4.7±0.3 

Wash liquor 

(10 min) I 

Wash liquor 

(10 min) II 

9.2±0.3 1.8±0.2 

3.2±0.4 1.1±0.3 

leather have been determined to be 270 Kg/cm 2 , 50 Kg/cm, 43 Kg 

with distension of 9.28 mm, respectively. Similarly values of 265 

Kg/cm 2 , 40 Kg/cm, 32 Kg with distension of 9.00 mm, 

respectively has been obtained for control leathers. Hence, it 

could be inferred that the fibrozyme treatment has not affected 

the final leather quality, rather proper opening up of the fiber 

bundles has aided in obtaining higher strength characteristics. 

Organoleptic Properties of Crust Leathers 

The control and experimental crust leathers have been assessed 

by experienced tanners for their organoleptic properties. 

Table VI 

Organoleptic property of cow upper leather. 

Parameters Control Experimental 

Softness 8±1 8±1 

Roundness 8±1 9±0.5 

Fullness 7±1 8±1 

Grain tightness 8±1 8±1 

Color uniformity 7±0.5 7±1 

Strength 8±0.5 8±1 

Grain smoothness 7±1 8±1 

General appearance 7±1 7±2 

*rating on a scale of 1–10 with 10 being the best 

Table V 

Visual assessment data of the wet blue leather. 

Parameter Control Experimental 

Color of the wet blue 8±1 8±1 

Chrome patches Nil Nil 

Grain smoothness 8±0.5 9±0.5 

General appearances 8±0.5 8±0.5 

*rating on a scale of 1–10 with 10 being the best 

Figure 3. Scanning Electron Microscopy images of curst leathers of 

cow hide: a) Grain and b) Cross-section of fibrozyme treated leathers 

c) Grain and d) Cross-section of control leathers 



The leathers have been assessed for various organoleptic 

properties such as softness, roundness, fullness, grain tightness, 

color uniformity, strength, grain smoothness and general 

appearance. The results are provided in Table VI. It could be 

observed from the table that the experimental leathers are on par 

with that of the control leathers in terms of grain tightness, grain 

smoothness, roundness, dye affinity and strength. In addition, it 

was also observed that there were no grain damage and the 

experimental leathers are softer than the control leathers. 

Scanning Electron Microscopy Evaluation 

Scanning electron microscopic (SEM) images of the control and 

experimental pelts are provided in Figure 3 (a-d). Figure 3a and c 

shows the grain pattern of the control and experimental pelts, 

respectively. It could be observed that the grain layer of both the pelts 

is devoid of any hair. Also, the grain is found to be smooth and does 

not show any damage. Fig. 3b and d shows the cross sectional view of 

the control and experimental pelts, respectively. It could be observed 

from the figure that the fiber bundles have better opened up structure. 

Hence, it could be inferred that the fibrozyme could be effectively used 

for both dehairing and fiber opening of cow hides in a single step. 

Conclusions 

In the present study, a single step enzymatic dehairing and fiber 

opening of cow hides has been established. Offer of enzyme has been 

optimized to 3.5% (w/w) based on the soaked weight of the cow 

hides. From the hand evaluation properties, the enzyme treated pelts 

have shown clean and complete removal of hairs and the skin is 

devoid of any scud or short hairs. The stratigraphic distributions of 

chromium in control and experimental wet blue leathers have been 

found to be uniform throughout the cross section of the leather. An 

average chrome content of 3.62% and shrinkage temperature of 

108ºC has been obtained for the experimental leathers. The visual 

and organoleptic assessment of the experimental leathers has been 

rated high by the experienced tanners. The physical strength met the 

upper leather norms. The morphological evaluation of experimental 

pelts through SEM also substantiates that there is no coalescence and 

distortion of fibers due to enzyme treatment. The H&E staining 

technique also confirmed the complete opening up of the fiber 

bundles in the experimental leathers. Thus this single step 

methodology could be successfully implemented in tanneries. This 

method not only saves time but also completely eliminates the use of 

lime and sulphide in leather processing. 

Acknowledgement 

Financial support from CSIR, New Delhi under 12 th plan project 

“S&T Revolution in Leather with a Green Touch” (STRAIT - 

CSC 0201) is greatly acknowledged. CSIR-CLRI Communication 

No. A/2016/CHL/CSC0201/1202. 

References 

1. Saurabh, S., Richi, V. M., Rekha, K., Jasmine, I., Rajendra, 

K.S.; Enzyme mediated beam house operations of leather 

industry: a needed step towards greener technology. Journal 

J. Clean. Prod. 54, 315-322, 2013 

2. Ramasami, T., Prasad, B.G.S.; Environmental Aspects of 

Leather Processing, Proc LEXPO XV (ILTA, Calcutta) 43- 

71, 1991. 

3. Venba, R., Kanth, S., Chandrababu, N.; Novel approach 

towards high exhaust chromium tanning - Part I: Role of 

Enzymes in the Tanning Process. JALCA 103, 401-411, 2008 

4. Dettmer, A., Schacker Dos Anjos, P., Gutterres, M.; Enzymes 

in the Leather Industry, a special review paper. JALCA. 108 

Number: 4 Page: 146-158 Year: 2013 

5. Andrioli, E., Gutterres, M.; Associated use of enzymes and 

hydrogen peroxide for cowhide hair removal. JALCA. 109, 

41-48, 2014 

6. Saravanan, P., Shiny Renitha, T., Gowthaman, M.K., 

Kamini, N.R.; Understanding the chemical free enzyme 

based cleaner unhairing process in leather manufacturing. 

J. Clean. Prod. 79, 258-264, 2014. 

7. Bradford, M.M.; A rapid and sensitive for the quantitation 

of microgram quantities of protein utilizing the principle of 

protein-dye binding. Anal. Biochem.72, 248-254, 1976. 

8. Madhan, B., Rao, J.R., Nair, B.U.; Studies on the removal 

of interfibrillary materials Part-I: removal of protein, 

proteoglycan, glycosoaminoglycans from conventional pretanning 

process. JALCA 105, 2010. 

9. Jayakumar G.C., Sivaraman, G., Saravanan, P., Mohan, 

R., Rao, J.R.; Cohesive system for enzymatic unhairing 

and fiber opening: an architecture towards eco-benign 

pretanning operation. J. Clean. Prod. 83, 428-436, 2014. 

10. Fathima, N. N., Rao J. R., Nair, B.; Augmentation of garment 

sheepskin type properties in goatskins: Role of chromiumsilica 

tanning agent. JSLTC 87, 227-232, 2003. 

11. IUP 2, Sampling, JSLTC 84, 303, 2000. 

12. IUP 6, Measurement of tensile strength and percentage 

elongation, JSLTC 84, 317-321, 2000. 

13. IUP 8, Measurement of tear load-double edge tear, JSLTC 

84, 327-329, 2000. 

14. SLP 9 (IUP 9), Measurement of Distension and Strength of 

Grain by the Ball Burst test, Official methods of analysis, 

The Society of Leather Technologists and Chemists, 

Northampton, 1996. 

15. Usharani, N., Jayakumar, G.C., Rao, J.R., Chandrasekaran, 

B., Nair, B.U.; A microscopic evaluation of collagen-bilirubin 

interactions: in vitro surface phenomenon. Microsc. 253, 

109-18, 2014 


461 

Lifelines 

Hanping Li, a postgraduate, is working at Key Laboratory of 

Leather Chemistry and Engineering of Ministry of Education, 

Sichuan University, China, and mainly engaging in the research 

of green leather chemicals and environment friendly functional 

materials. 

Yong Jin, professor, is currently working as a scientist and teacher 

at the National Engineering Laboratory for Clean Technology of 

Leather Manufacture, Sichuan University, China. He obtained his 

PhD degree at the Chengdu Institute of Organic Chemistry, 

Chinese Academy of Science, China, in 2003. His main research 

areas include green leather chemicals and cleaner leather making 

technology, environment friendly functional materials. 

Baozhu Fan, a postgraduate, is working at the Chengdu Institute 

of Organic Chemistry, Chinese Academy of Science, China, and 

specializing in the research of surfactant materials. 

Rui Qi, a doctor, is working at the Chengdu Institute of Organic 

Chemistry, Chinese Academy of Science, China, and mainly 

engaging in the research of polymer self-assembly and 

environment friendly functional materials. 

Xinfeng Cheng, a doctor, is working at the Chengdu Institute of 

Organic Chemistry, Chinese Academy of Science, China, and 

mainly engaging in the research of intelligent polymer and 

environment friendly functional materials. 

Chunxiao Zhang, PhD candidate from Sichuan University, 

majoring in leather chemistry and engineering. Focusing on the 

cleaner production of leather making, the researching fields 

contain salt-free pickling, high exhaustion chrome tanning, 

ammonia-free deliming and the application of enzyme in tanyard. 

Fuming Xia is a postgraduate student in Sichuan University and 

studying in the Key Lab of Leather Chemistry and Engineering 

of Ministry of Education in Sichuan University. Focuses on 

researching the technologies of salt-free pickling and high 

chrome exhaustion tanning. 

Biyu Peng, see JALCA 110, 2015 

Qing Shi, graduated from Donghua University China, 2002, 

with focus on engineering of dyeing and finishing. 2005/10— 

2015/7 worked BASF for textile auxiliary finishing technical 

support, 2015/7 until now, worked in BASF for new development 

of surfactant and polymer. 

Dominic Cheung, graduated from Hong Kong Polytechnic 

University in 1987 and major in textile chemistry. Worked in 

Ciba for textile dyes and chemicals areas, covering various 

functions from lab to technical marketing and later worked for 

Huntsman in setting up R&D center for textile chemicals in 

Guangzhou. Right now, serves the Care Chemicals Division on 

industry marketing for textile & leather in BASF. 

Ye Yongbin, Bachelor, graduated from Sichuan University. 

Working in Zhejiang Tongtianxing Group J. S. Co., Ltd. In 

charge of the new product research and development. 

Xinhua Liu. as a doctoral student in the Key Laboratory of 

Leather Chemistry and Engineering of Ministry of Education in 

Sichuan University, he is focusing on the extraction and 

modification of collagen for versatile applications. 

Feng Li. as a master in the Key Laboratory of Leather Chemistry 

and Engineering of Ministry of Education in Sichuan University, 

his research focuses on the preparation and evaluation of 

chrome-free tanning agents and their applications. 

Qin Huang. as a master in the Key Laboratory of Leather 

Chemistry and Engineering of Ministry of Education in Sichuan 

University, his research focuses on the preparation and 

evaluation of chrome-free tanning agents and their applications. 

Weihua Dan, as a professor in the Key Laboratory of Leather 


University, his research focuses on the development of ecological 

leather and fur, and the preparation and evaluation of collagenbased 

biomaterials. 

Nianhua Dan, as a lecturer in the Key Laboratory of Leather 


University, his research focuses on the development of ecological 

leather and fur, and the synthesis and modification of leather 

chemicals. 

Gladstone C. Jayakumar, see JALCA 106, 68, 2011 

M. Sathish, see JALCA 110, 379, 2015 

R. Aravindhan, see JALCA 106, 208, 2011 

J. Raghava Rao, see JALCA 93, 156, 1998 


462 

Call For Papers 

for the 113th Annual Convention of the 

American Leather Chemists Association 

Pinehurst Resort, Village of Pinehurst, NC 

June 13-16, 2017 

If you have recently completed or will shortly be completing research studies relevant to hide 

preservation, hide and leather defects, leather manufacturing technology, new product 

development, tannery equipment development, leather properties and specifications, tannery 

environmental management, or other related subjects, you are encouraged to present the 

results of this research at the next annual convention of the Association to be held at the 

Pinehurst Resort Village of Pinehurst, NC, June 13-16, 2017. 

Abstracts are due by April 1, 2017. 

Full Presentations are due by June 1, 2017. 

They are to be submitted by e-mail to the ALCA Vice-President and Chair of the 

Technical Program: 

Mike Bley 

Eagle Ottawa - Lear 



E-mail: mbley@lear.com 

In accordance with the 

Association Bylaws, 

all presentations are 

considered for 

publication by 

The Journal of the 

American Leather 

Chemists Association. 

The Abstract should begin with the title in capital letters, followed by the authors’ names. An 

asterisk should denote the name of the speaker, and contact information should be provided 

that includes an e-mail address. The abstract should be no longer than 300 English words, 

and in the Microsoft Word format. 

Full Presentations at the convention will be limited to 25 minutes. In accordance with the 

Association Bylaws, all presentations are considered for publication by The Journal of the 

American Leather Chemists Association. They are not to be published elsewhere, other than 

in abstract form, without permission of the Journal Editor. For further paper preparation 

guidelines please refer to the JALCA Publication Policy on our website: leatherchemists.org. 

Full Presentations are to be submitted by e-mail to the JALCA editor: 

Robert F. White 

Journal Editor 

The American Leather Chemists Association 

E-mail: jalcaeditor@prodigy.net 

Mobile Phone (616) 540-2469 


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