Abstract

This paper experimentally tests the waterproof and oil-proof properties of natural cow and sheep leather and their polyurethane coating. Based on experimental phenomena and contact angle data, a microcosmic analysis of the waterproof and oil-proof properties of leather is conducted in conjunction with SEM images of different leather surfaces. The study found that: natural cow leather exhibits better oil resistance than natural sheep leather, while natural sheep leather has better waterproofing than natural cow leather. After coating with waterborne polyurethane (WPU) for 1, 2, and 3 layers, both cow and sheep leather are not penetrated by water or oil droplets. The static contact angle of water on the surfaces of cow and sheep leather varied with the number of WPU coats but is always greater than that of oil. For cow leather the order of water contact angles is 3 layers > 0 layers > 1 layer > 2 layers; for oil contact angles it is 0 layers > 3 layers > 2 layers > 1 layer. For sheep leather the water contact angle order is 0 layers > 1 layer > 3 layers > 2 layers; for oil contact angles it is 0 layers > 1 layer > 2 layers > 3 layers. The microstructural formation of the leather surface, arrangement of collagen fibres, and internal fat content significantly impact the waterproof and oil-proof properties of the leather, leading to differences in water and oil contact angles among cow and sheep leather with varying WPU coating layers.