Polymer impregnation and its effect on the rupture properties of leather
This study investigated the modification of leather rupture properties following impregnation with polyurethane. It was hypothesised that a better polymer - leather interaction would increase strength. Surface properties of leather fibres were altered (using a hydrophobic agent based on a phosphate ester) to more closely match those of the polymer. This resulted in a more even distribution of polymer on the leather fibrils. Application of the hydrophobic agent alone was investigated and optimum offers of the treatments determined. An untreated sample and one impregnated without surface treatment were included as controls. Trouser tear testing was used to assess rupture resistance as well as a stratigraphic tear test which was used to evaluate any changes in peeling properties. An approximately linear relationship between peeling strength and sample split depth was observed which indicated that the grain - corium junction is a gradually changing interface. The surface modification of fibres led to increases in tear strength. Applying polymer to leather with surface modified fibres resulted in further increases in tear strength. Investigation of single fibres determined that no treatments influenced the fibre strength. There was, however, a decrease in the interfacial bond strength between fibre and polymer when surface modification was used. This was related to an increased fibre pull out length for treated samples. Leathers of 11% hydrophobing agent and 10% polyurethane gave the best combination of tear strength and softness. It was concluded that polymer impregnation of hydrophobic leather resulted in a bonded fibre structure. When stress is applied to such leather, fibres debond from the network and disentangle from the fibre structure. Work must be done to overcome surface friction between fibre and polymer. However, there is a balance between (a) interfacial bond strength and friction, and (b) fibre strength. This balance can be manipulated to obtain optimum overall strengthening
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