[article]
| Titre : |
The role of the finish in affecting leather comfort |
| Type de document : |
texte imprimé |
| Auteurs : |
Mortimer Greif, Auteur |
| Année de publication : |
1970 |
| Article en page(s) : |
p. 117-126 |
| Note générale : |
Bibliogr. |
| Langues : |
Anglais (eng) |
| Catégories : |
Absorption
Adsorption
Coefficient de diffusionUn coefficient de diffusion est une grandeur caractéristique du phénomène de diffusion de la matière. Le coefficient de diffusion mesure le rapport entre le flux molaire dû à la diffusion moléculaire, et le gradient de concentration de l'espèce chimique considérée (ou, plus généralement, de la variable d'effort entraînant cette diffusion), comme formulé par la loi de Fick.
Confort
Croûte (cuir)On entend par "cuir en croûte" des cuirs ayant subi les opérations jusqu'au tannage, à l'exclusion de toute opération de corroyage ou de finissage, mais qui, par opposition aux wet-blue ont été séchés.
Cuirs et peaux -- Finition
Perméation
Polymères
|
| Index. décimale : |
675 Technologie du cuir et de la fourrure |
| Résumé : |
Leather is a unique material, possessing unusual strength and suppleness. It is able to mould itself to the shape of the foot and is capable of expanding and contracting along with the foot as the temperature and humidity vary. It can absorb relatively large quantities of water without being characterised as wet or damp. Leather provides a level of comfort which has proven extremely difficult to duplicate.
For the most part, the aforementioned properties are independent of the finish or the finishing process. However, in the recent literature, data have been obtained which correlates comfort with water vapour permeability of a shoe upper material. It is this property which the finish affects directly.
Crust leather is an extremely permeable material, able to transmit both liquid water and water vapour. The finish is expected to confer a degree of "waterproofness" to the leather; it must help keep liquid water from permeating from outside. At the same time, the finish must be of such a nature to permit the passage of water vapour from within. In effect, the finish must act like a screen possessing a mesh size small enough to prohiba the passage of clusters of water molecules, liquid water, yet large enough to permit transfer of single molecules, water vapour.
Permeation of water or any molecular species can result in a number of ways. If the medium through which the transport occurs contains a microporous structure or cracks of finite size, permeation can occur by means of convection or capillary flow. This type of flow is not particularly temperature sensitive and the rate of flow is constant for most gases. However if the transport medium is continuous and free of cracks or imperfections, then the rate of transport is very selective and is dependent upon the mobility and the solubility of the permeating substance in the medium in question. This latter process is called thermally acti¬vated diffusion and it is this subject which will be treated in this paper.
Crust leather is a highly porous material which allows permeation through a convective or capillary flow mechanism. When finish is applied to the grain layer, it is not likely that the grain layer is completely sealed because a significant volume fraction of the finishing material is volatile. Thus, assuming the leather to be saturated with finishing materials, voids would reappear after the carrier solvent evaporated. The pore volume and the pore size would be reduced but in all likelihood they would still be large enough to permit the transmission of water vapour and possibly liquid water. However, if at some point in the finishing process, a continuous film forms on the surface of the leather, an effective barrier to liquid water is obtained. This continuous film will restrict the passage of water vapour as well.
It is conceivable that during the finishing process, a continuum of leather fibres and finish ingredients could form. This continuum would then possess similar restrictive properties to the flow of liquid water and the vapour. The important feature is this : if a continuous coating forms either within or on the surface of the leather, liquid water will not permeate. Water vapour could only pass by virtue of a thermally activated diffusion process. |
| Note de contenu : |
- Permeation
- Mathematics of diffusion
- Experimental
- Mechanism of the permeation process
- The diffusion coefficient
- Sorption of polymers
- Polymer data
- Finished leather
- Table 1 : Sorption and transmission properties of some common polymers |
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in JOURNAL OF THE SOCIETY OF LEATHER TRADES' CHEMISTS > Vol. 54, N° 3 (03/1970) . - p. 117-126
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