Development of a novel polyvinyl acetate type emulsion curing agent for urea formaldehyde resin

Abstract

High formaldehyde emission and poor water resistance are two main disadvantages of urea formaldehyde (UF) resin. For that reason, a novel polyvinyl acetate (PVAc) type emulsion curing agent was developed in this paper. PVAc type emulsions, including PVAc, the co-polymer of PVAc and N-hydroxymethyl acrylamide (PVAc–NMA), and the ternary co-polymer of PVAc, NMA, and urea (PVAc–NMA–urea), were the main components. Water, aluminum chloride, ammonium dihydrogen phosphate, polypropylene glycol, silicone oil, and urea were the other components. Under heating, aluminum chloride and ammonium dihydrogen phosphate often underwent thermal decomposition and hydrolysis in solution, produce free acid to cure UF resin, so the curing agent could enhance the curing rate, and then shorten the curing time. In this curing agent, ammonium dihydrogen phosphate and urea worked as formaldehyde removers and reacted with free formaldehyde in UF resin, thus the formaldehyde emission exuded from the plywood could be effectively limited and reduced. The bonding strength of plywood was not improved very much, especially the dry bonding strength, but the wet bonding strength was little enhanced for the active hydroxymethyl group contained in PVAc–NMA and PVAc–NMA–urea underwent a self-cross-linking reaction to improve the bonding strength and adhesion force to the bonded substrate. More importantly, the results from the industrial production experiments were shown to be very good.