Synthesis And Modification Of Polyurethane-acrylate Composite Emulsions

Presently, with the rapid development of industry, people pay more attention to environmental pollution and the more stringent environmental legislations have been worldwide made to reduce the emission of volatile organic compounds (VOC) into air. Environment-friendly materials have played an important role in many researches and applications. On this occasion, waterborne coatings were born and have been the best way to reduce VOC.Waterborne polyurethanes (WPUs) are an important class of materials widely used in many applications. As a type of environment-friendly materials, WPUs exhibit some performances at almost the same level as conventional solvent-borne polyurethanes, such as excellent adhesion and high abrasion resistance. However, as for hardness, water and weather resistance, WPUs are usually inferior to solvent-based counterparts, and hence cannot fulfill the requirement of wood paint.One of the approaches to develop aqueous system with superior performance is to produce hybrid emulsion with a multi-phase structure in each emulsion particle. Acrylic resins show excellent properties in terms of hardness, weatherability, chemical resistance and gloss, however, they show poor perfomance as regards toughness, abrasion resistance, cold resistance and adhesion properties, which are peculiar to polyurethane resins. In this dissertation, polyurethane-acrylate (PUA) composite emulsions which possess the morphology of core-shell of polyurethane/polyacrylate were prepared by the 'in situ' copolymerization of methyl methacrylate (MMA) and butyl acrylate (BA) in the presence of caster oil-based polyurethane dispersions as seeded emulsion, which were obtained by converting polyurethane prepolymer previously synthesized in high-boiling solvent and containing vinyl monomer added into during the course of prepolymer neutralization in order to reduce the viscosity of the system, into aqueous emulsions. The process has no need of desolventizing, so productive cost is reduced and pollution is abated as well.The effects of the type of initiator, dosage of initiator and emulsifier, hydrophilic group content and polymerization technique on polymerization process and PUA emulsion were studied. The effects of core/shell ratio, 'rigid/soft' monomer ratio and the dosage of castor...