Enhancing the mechanical and thermal properties of waterborne polyurethane composites with thermoset epoxy resin microspheres
Epoxy resin, amine curing agent (IPDA) and polytetramethylene ether glycol (PTG2000) were used to prepare a new type of highly cross-linked and uniform thermoset epoxy resin microspheres (Ems) through reaction-induced phase separation. Its structure, particle size and thermal properties were characterized. The results showed that the epoxy resin microsphere was an active microsphere containing hydroxyl and amino groups on the surface, with certain monodispersity and a high glass transition temperature (Tg) (178.33 °C). Ems were further successfully used to prepare waterborne polyurethane/epoxy resin microsphere (WPU/Ems) composite films by in situ polymerization. When the composite film contained 4 wt% Ems, the tensile strength increased by 2.5-fold and the elongation-at-break hardly changed compared with pure WPU. Also, the thermal stability of the composite films was significantly improved with the addition of Ems. Fourier transform infrared spectroscopy and scanning electron microscopy results proved that WPU was grafted onto Ems with specific association. Ems were well dispersed in the WPU matrix and acted as chemical cross-linkers. Ems and WPU formed strong interfacial interaction through covalent grafting, which significantly improved the mechanical properties and thermal stability of the prepared composites.