Polymer impregnation and its effect on the rupture properties of leather

This research concerns an investigation into the impregnation of leather wi th a polyurethane emulsion as a means of strengthening the grain layer and the grain - cerium junction. Since three quarters of the leather produced i s used for the manufacture of shoes, a possible application of this researc h could be the development of direct sticking of shoe uppers to soles witho ut the need for the current abrasion process. It was hypothesized that modification of the leather - fiber surface proper ties to more closely match the polyurethane impregnant would result in an i ncrease in leather strength. It was determined experimentally that the poly mer was hydrophobic and so the leather was treated with a waterproofing age nt to result in surfaces that were more alike. The peel test used in this research involved splitting the leather at vario us depths through the cross section. This enabled the strength of the leath er to be determined at any point within the grain or cerium. This provided information concerning areas of strength or weakness within the leather str ucture and an increase in the peeling strength of the leather treated with the waterproofing agent and polymer was observed. Investigation of single fibers determined that none of the treatments influ enced the fiber strength. There was, however, a decrease in the interfacial bond strength between fiber and polymer when surface modification was used . This was related to an increased fiber pull out length for treated sample s. It was concluded that polymer impregnation of hydrophobic leather resulted in a bonded fiber structure. When stress is applied to such leather, fibers debond from the network and disentangle from the fiber structure. Work mus t be done to overcome surface friction between fiber and polymer and this i ncreases the peeling strength observed.