Abstract

Absorption and desorption isotherms for water vapour in full chrome leather at 5, 20 and 35°C are given. They agree satisfactorily with those previously found by the author and by Kanagy, but uptakes are higher than obtained by most other investigators, probably because they allowed insufficient time for complete equilibrium. The moisture content at 65% r.h. is far higher than usually assumed in leather analysis. At high humidities, regains exceed 70%. Although the outline of the hysteresis cycle was measured by slow approach to equilibrium (years), this period was only necessary because of slow diffusion of moisture through air; the equilibrium values obtained by rapid equilibration in a vacuum are little different. At humidities up to about 60%, the shape of the ascending humidity isotherm is different if the specimens are heated to 100°C beforehand. The descending branch is little changed. The usual hysteresis cycle defines an area which is crossed by isotherms descending from points on the rising boundary curve, or ascending from points on the descending boundary curve. A number of these isotherms are shown. Data are given for absorption and desorption at 20°C, 65% r.h. of leathers with different chrome contents. The width of the hysteresis cycle under these conditions increases with chrome content, probably because crosslinking by chromium reduces swelling during absorption, and reduces shrinking during desorption.