Analysis of the hydrolysates from cured and uncured urea-formaldehyde (UF) resins with two F/U mole ratios

摘要

Uncured and cured urea-formaldehyde (UFcured) resins prepared with formaldehyde/urea (F/U) mole ratios of 1.0 and 1.2 and at the catalyst levels of 1, 2 and 3% NH4Cl were hydrolyzed for 5, 15 and 30 min and the degradation products were evaluated using gel permeation chromatography, Fourier-transform infrared (FTIR) and liquid carbon-13 nuclear magnetic resonance (C-13-NMR) spectroscopies. The molar masses of the degradation products, their functional groups and structures were determined. An extended hydrolysis time and higher catalyst levels resulted in compounds with higher molar masses. Similar functional groups and distribution of chemical species were found by both FTIR and C-13-NMR spectroscopies in the hydrolysates of UFcured, indicating water hydrolysis of hydroxymethyl groups and then methylene linkages. Methylene linkages and mono- and tri-hydroxymethyl ureas were mainly responsible for the liberation of formaldehyde from UFcured during hydrolysis. The indicated compounds are believed to contribute to the long-term release of formaldehyde from the resins. This is the first systematic report on the composition of UFcured wed hydrolysates.