The curing of UF resins studied by low-resolution1H-NMR

Abstract

A series of UF resins and one MUF resin were studied by low-resolution 1 H-NMR. The mobility of the resin during curing could be followed by measuring the spin-spin relaxation time (T 2 ) with curing time. The relative curing behavior was similar to that found by traditional gel time measurements. In addition, extra features in the T 2 plots with curing time showed at what point the bulk of the condensation reactions took place. The speed of cure was also related to the chemical groups in the liquid resin, and it was found that the linear methylol groups were mainly responsible for the curing speed of the resins. By studying the curing with different hardener levels and glue concentrations it was found that a UF resin is more sensitive to the glue mix concentration than an MUF resin. A cured resin was also studied after curing to investigate postcuring effects. Water seemed to play the biggest role in the postcure, with substantial amounts present immediately after cure, which decreased with curing time and aging. For the low mol ratio resins studied here further curing reactions did not seem to play a major role in the post curing phenomenon.