[article]
| Titre : |
Some investigations into methods of unhairing - I. Lime-sulphide processing |
| Type de document : |
texte imprimé |
| Auteurs : |
R. S. Andrews, Auteur ; Mary Dempsey, Auteur |
| Année de publication : |
1966 |
| Article en page(s) : |
p. 218-245 |
| Note générale : |
Bibliogr. |
| Langues : |
Anglais (eng) |
| Catégories : |
Chaux Sulfurée
Cuirs et peaux de moutons
Epilage
Hydroxyde de sodiumL'hydroxyde de sodium, appelé également soude caustique7, est un corps chimique composé minéral de formule chimique NaOH, qui est à température ambiante un solide ionique. Fusible vers 318 °C, il se présente généralement sous forme de pastilles, de paillettes ou de billes blanches ou d'aspect translucide, corrosives et très hygroscopiques. Il est très soluble dans l'eau et légèrement soluble dans l'éthanol.
La solution d'hydroxyde de sodium, souvent appelée soude, est une solution aqueuse transparente. Concentrée, elle est corrosive et souvent appelée lessive de soude.
Les propriétés chimiques de l'hydroxyde de sodium sont surtout liées à l'ion hydroxyde HO- qui est une base forte. En outre, l'hydroxyde de sodium réagit avec le dioxyde de carbone (CO2) de l'air et se carbonate.
La solubilité de la soude caustique dans l'eau augmente avec la température, à pression constante ou ambiante.
Sulfure de sodium
|
| Index. décimale : |
675 Technologie du cuir et de la fourrure |
| Résumé : |
Experimental lime-sulphide treatment has been assessed from the fibre structure of the pickled pelt (after fixing it in formalin + salt) compared with that from "normal" processing : soaking, liming, deliming, bating and pickling, or soaking, painting, liming, deliming, bating and pickling. Ease of unhairing and removal of epidermis have also been considered. The investigation included experiments on the influence of temperature, composition of the lime liquor, alkaline baths subsequent to painting, duration of piling in paint and composition of tir ; paint.
Unhairing and epidermis removal are shown to be two different process.cs under the conditions of lime-sulphide treatment, in which unhairing is only removal of hair shaft leaving the root and a short length of shaft within the grain layer. The paint, penetrating from the flesh, appeared to have passed the root, both bulb and club types, as well as newly initiated hair papillae, and begun attack on the hair at the level of the sebaceous gland. Breakdown of the hair shaft can extend both inwards towards the root and outwards along the free hair shaft: the hair cuticle was more resistant than the internai structure. Readily visible damage to the free hair shaft was caused by high amount of water in the paint or high amount of sulphide in the presence of high amount of water.
The "normal" paint used in the experiment was approximately 0-8 g Na2S + 5 g lime + 7 g water to 100 g pelt, and at the end of piling for 24 hours belly unhaired readily but butt did not. With this paint, increased time in pile did not improve the degree of unhairing, nor did raised temperature which did however, improve the removal of epidermis. Liming after painting completed unhairing and removal of epidermis, but it seems possible that caustic soda after painting might have an adverse effect on unhairing if this has not at least begun at the end of piling. Caustic soda in the paint did not improve unhairing, but where the hair was loose the removal of epidermis was seen to be easier than in its absence.
Painting opened up fibre bundles but did not open up the weave pattern, in contrast to liming or to painting followed by liming, after which fuller fibre bundles and less compactly interweaving pattern occurred. Increasing sodium sulphide in the paint increased splitting up and, especially when the pelt was piled at raised temperature, led to separation and a damaged appearance of the fibre structure. Caustic soda in a lime-sulphide paint, increased the fullness of the fibre bundles. Raised temperature had a marked effect in opening up the structure, particularly of the belly, which, at room temperature, usually appeared little opened up.
Immersion and movement in lime liquor containing a low concentration of sodium sulphide satisfactorily unhaired the pelt, and, especially at raised temperature, opened up the fibre structure. |
| Note de contenu : |
- Materials and methods
- Alkaline treatment subsequent to painting : Unhairing
- Experiments on flesh side painting : Duration of piling in paint - Composition of the Paint - Microscopical observations
- Composition of the lime liquor : Unhairing and Epidermis Removal - Fibre structure
- Table 1 : Experimental treatments and scores for hair removal
- Table 2 : Flesh-painting experiments
- Table 3 : Scores for hair removal after piling in paint
- Table 4 : Composition of the paint : Amount of sodium sulphide or caustic soda scores for unhairing and removal of epidermis
- Table 5 : Hair and epidermis : Scores
- Table 6 and 7 : Hair and epidermis removal |
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in JOURNAL OF THE SOCIETY OF LEATHER TRADES' CHEMISTS > Vol. 50, N° 6 (06/1966) . - p. 218-245
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Some investigations into methods of unhairing - I. Lime-sulphide processing in JOURNAL OF THE SOCIETY OF LEATHER TRADES' CHEMISTS, Vol. 50, N° 6 (06/1966)
