Degradation of crosslinked resins in water and electrolyte solutions

In addition to chemical processes such as the hydrolysis of ester groups, there are physical processes contributing to the hygrothermal degradation of crosslinked polyester resins. This paper discusses the interaction between physical and chemical processes and reports short and long term observations on the degradation of several resins of various compositions during immersion in aqueous liquids. Initial swelling is accompanied by weight changes which are the result of (i) absorption of water (ii) leaching of non-bound substances and (iii) leaching of hydrolysis products. Leached substances are identified qualitatively by n.m.r. spectroscopy and, in some cases, semi-quantitatively by gas-liquid chromatography (g.l.c.). Osmotic disc cracks greatly accelerate the hydrolysis process and appear to be caused mainly by the presence of residual or added glycol in the resins. (These cracks were almost entirely absent from a vinyl ester resin). Scanning and high resolution transmission electron micrographs demonstrate the nature and extent of surface physical damage by water.