Effect of Leather Finishing Technology on Water Vapour Transmission. Part II. Water Vapour Transfer through Microporous Film Laminated Leather
Keywords:laminated leather, coating film, penetrant, water vapour permeability, absorption, adhesion loss.
The water vapour transfer through microporous film laminated leather has been investigated. Water vapour transmission is a multi-stage process, consisting of penetrant absorption, solubility, desorption and diffusion. Adhesively bonded microporous film does not worsen moisture transfer properties of the laminated leather. Notwithstanding water vapour permeability decreases and absorption increases due to the nonporous adhesive layer. In laminated leather and its layers water vapour absorption may be classified as non-Fickian: sigmoidal – for microporous film and two-stage – for all leather samples.
Water vapour accumulation at the leather/adhesive layer interface causes the adhesion loss of coating polyurethane film and changes in the failure mode. Water vapour induced film delamination begins at the weakened sites of the interface (i.e. small cavities, voids, and topographical irregularities of leather, etc.). Under driving gradient the local accumulation of interfacial water expands and multi-layers of water molecules build up. The splitting of the interfacial water layers begins the loss of adhesion. At long penetrant activity at both sides the film delamination propagation and blister formation in the laminated leather may occur.
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