Waste nylon fibre hardeners for improved UF wood adhesives water resistance

Abstract

Improved water resistance of hardened UF resins for plywood was achieved by addition of up to 20% on UF resin solids of the hydrochloride salt of hydrolysed waste nylon fibre obtained from ladies stockings. The nylon salt is added in powder form directly to the glue mix of the UF resin for ease of handling, and also functions as the only hardener of the resin. The salt remains as a finely devided powder in suspension in the glue mix at ambient temperature ensuring a long pot-life. Its rapid dissolution as the temperature of the glue line increases during hot pressing also ensures rapid availability of both the acid functions for hardening and of the nylon short oligomers for reaction with the UF resin. The short length oligomers of nylon still present in the salt coreact during hot pressing with the UF resin forming in the majority an unitary hardened, solid network. The amidic groups present in the body of the chains of the short nylon oligomers are shown to react with the methylol groups of the UF resin and thus the nylon is bound in the hardened network by a series of methylene linkages between the majority of its secondary amide groups to the urea. The determining parameter as regards performance results is the set of conditions used to hydrolyse the nylon fibre and to prepare the salt. The waterproofing obtained approaches, but is lower than, that of melamine-urea-formaldehyde adhesives of low melamine content.