Preparation and properties of nano SiO₂ modified cellulose acetate aqueous polymer emulsion for leather finishing

Poor water solubility of cellulose acetate is a key factor limiting its application in leather finishing field. Herein, a self-emulsifying aqueous emulsion was synthesized by using cellulose diacetate (CDA) as the substrate, dimethylolbutyric acid (DMBA) as the hydrophilic agent, and hexamethylene diisocyanate (HDI) as the bridging agent. Because the flexible carbon chain of HDI has the advantages of easy bending and deformation, the problem of large steric hindrance and low reactivity of -OH during water-based CDA can be solved by using the method of converting reactive functional groups and transferring reactive sites. At the same time, the flexible molecule 1,4-butanediol (BDO) and propylene glycol polyether (N210) are used as chain extenders to increase the molecular stretch and curl ability by adjusting the ratio of molecular soft and hard segments, and improve emulsion stability and coating flexibility. And through the reaction of -NH₂ and -NCO on the surface of nano SiO₂ modified by KH550, the nano SiO₂ is evenly distributed in the CDA water-based polymer to improve the comprehensive performance of the emulsion coating. Thus the nano-SiO₂ modified cellulose acetate water-based polymer emulsion (SiO₂/WCDA) is obtained for leather finishing. The emulsion particles show an oil-in-water (O/W) core–shell structure, and the average particle size and dispersion coefficient (PDI) of the particles are 88.79 nm and 0.150, respectively. The surface of the coating film is compact, flat, and hydrophobic, with the contact angle is 104.3 °. In addition, the coating film has good adhesion, water resistance, heat resistance, yellowing resistance, chemical resistance, flexibility and mechanical properties.