Fire retardancy of an aqueous, intumescent, and translucent wood varnish based on guanylurea phosphate and melamine-urea-formaldehyde resin

Abstract Various concentrations of guanylurea phosphate (GUP) were incorporated into an aqueous melamine-urea-formaldehyde (MUF) resin to synthesize a fire-retardant, translucent, and intumescent varnish. The effects of the GUP on the curing, light transmittance, and thermal stability of the resulting varnish, and combustion behavior of the varnish-coated plywood were determined by viscosimetry, Fourier-transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV–vis) spectroscopy, thermogravimetry (TG), and cone calorimetry, respectively. The results show that GUP decelerated the curing rate; the resulting varnish film was translucent and UV-absorbing. The calorimetry demonstrated that GUP did not change the thermal stability but significantly facilitated charcoal formation of the varnish. The presence of the GUP resulted in an increased intumescent thickness of the varnish and substantially suppressed and delayed the mass loss, smoke production, and heat release of the coated plywood. At 12% GUP concentration the resulting varnish film exhibited an optimal combination of translucency and fire retardancy. These findings demonstrate that the GUP can be incorporated into aqueous MUF resin for the synthesis of a clear intumescent varnish capable of fire retardancy.