Curing of urea-formaldehyde adhesives with collagen type hydrolysates under acid condition

Abstract

Condensation of dimethylol urea and its mixtures with urea or hydrolysate of chrome-tanned leather waste (mass fraction in mixture 0.05) in the presence of a variable quantity of phthalic acid, as acid curing agent (within mass fraction limits 0.01-0.1), was studied through TG technique. During condensation of sole dimethylol urea or of its mixture with urea, oxy-methylene as well as methylene cross-links are produced at a ratio of approx. 1:1, presence of leather waste hydrolysate reduces this ratio to approx. 1:2 in favour of more stable methylene bridges. Higher concentrations of phthalic acid (above mass fraction 0.05) lead to formation of a new TG mass decrement wave in the 150-180°C temperature interval, which probably relates to transition of more unstable oxy-methylene bridges to more stable methylene bridges, with splitting-off of formaldehyde. Oxy-methylene bridges may be regarded as a potential source of formaldehyde emissions by cured urea-formaldehyde adhesive films. Hydrolysate of chrome-tanned leather waste and a suitable concentration of acid curing agent distinctly reduce formaldehyde emission from cured urea-formaldehyde adhesive films.