SYNOPSIS
A method based on the use of 13C NMR relative peak intensity ratios for different characteristic chemical groups, known or supposed to contribute to urea-formaldehyde ( UF ) resin strength and formaldehyde emission is presented. The method relates results obtained by 13C NMR analysis of liquid UF resins with their strength, formaldehyde emission, and percent crystallinity in the resin-hardened state. Correlation of different peak ratios with experimental results allows the proposal of equations relating the sum of a number of different 13C NMR peak ratios with the three mentioned physical properties of the same resins in their hardened state. Resin strength and percent crystallinity appear to be loosely, inversely related. The equations presented appear to have some applied value in predicting physical properties of hardened industrial-type UF resins from a single 13C NMR spectrum of the original liquid resins, as well as to render easier comparison between difficult UF resin formulations. This approach has allowed identification of which chemical groups really contribute to the physical properties of the hardened resin, and to what extent.