Abstract: Based on the evaluation of the chemical structures of three kinds of urea-formaldehyde(UF) resin with low formaldehyde emission by ¹³C NMR, the technique of ¹³C CP/MAS NMR was applied to study the chemical structure of UF resins. Results indicated that the curing procedure of three kinds of UF resin with low formaldehyde emission was diverse in different curing system, the structure of cured resin was different as well. Without hardener, the cross-linkage degree of UF resin was lower, the content of methylol of cured UF resin was the higher and formaldehyde emission was increased. The hardener accelerated the curing reaction. the content of methylol was decreased. In three kinds of curing system, the content of methylol was the highest for UF-3; it was the lowest of 0.0582 for UF-2 with ammonium chloride as curing agent; for UF-1, it was the lowest without hardener and composite curing system of 0.0784 and 0.0713 respectively. The curing reaction of different kinds of UF resin was different in different curing system, the structure of cured resin, mechanical properties and formaldehyde emission were different too.

Key words: ¹³C CP/MAS NMR, urea-formaldehyde resin, chemical structure, formaldehyde emission