| Résumé : |
Woolled sheepskins showing partial hair-slip were extensively studied. This defect is detected in the "crust" state. Shearlings are first fully dechromed, subsequently de-woolled and chrome tanned. The influence of either a partial or complete beamhouse operation on the finished layer is examined.
On the grain layer, these leathers show modifications of the collagen, which show up in the form of irreversibly dried areas, different degrees of overheating (bare areas), residual epidermal layer and cementing materials (e.g. mucoids and mucopolysaccharides), as a consequence of not having had a proper liming and bating treatment.
By means of the scanning electron microscope (SEM) coupled to an X-ray dispersive energy analyser (EDAX) it is possible to explore, first, the morphology of the grain layer and, secondly, the surface distribution of the inorganic elements, such as : sodium, potassium, calcium, chlorine, sulphur and chromium, especially the two latter elements. A quantitative analysis can carried out, in order to compare faulty and undamaged areas, by means of this advanced technique which makes it possible. :
a) to determine how the chrome is distributed on the surface,
b) to make a detailed "mapping" of the areas studied and to visualise them through photography, where both maximum and minimum accumulation of surface chrome can be observed,
c) to detect and diagnose similar defects in much smaller areas, to be found in leathers intended for processing into "nappa" (processing without either wool or hair) and in "wet-blue" imported leathers.
Once the nature of the defect becomes known and, provided that no irreversible alterations in the collagen protein have taken place, it will be possible to optimise processing in order either to eliminate or to reduce such a defect to negligible levels. In this manner, the quality of the end-product will be improved substantially. |
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A study of the grain layer using a scanning electron microscope (SEM) fitted with an energy dispersive X-ray analyser : Part 1 in JOURNAL OF THE SOCIETY OF LEATHER TECHNOLOGISTS & CHEMISTS (JSLTC), Vol. 73 (Année 1989)
