Effect of Leather Finishing on Water Vapour Transmission. Part I. Water Vapour Transfer through Pigment Finished Leather

Abstract

In this paper the influence of soft leather coating thickness on moisture transmission behaviour is presented. It is shown that water vapour permeability decreases and sorption increases according to exponential law as coating thickness increases. The increase of water vapour sorption can be attributed to the decrease of top layer porosity, interaction of water molecules with leather collagen and acrylic polymer. The higher water amount in the leather permits the lower water vapour permeability. As water molecules amount becomes higher than that can bind to polymers, the clustering of water occurs. In the leather some cluster formation is observed only at high water vapour activity. In acrylic coating tendency to clustering is distinct. It is found that cluster size depends on the polymer nature and relative humidity.
Water vapour sorption behaviour may be classified as non-Fickian – “two-stage” sorption and it is characteristic for various coating thickness of leather. Changes in the leather surface topography in humid conditions depend on the coating thickness also: water accumulation increases thin-coated surface unevenness, while in the case of thick-coated surface unevenness decreases due to the expansion of the overall volume of coating and smoothing of embossed grain.