Characterisation and cure phenomena of phenolformaldehyde resins

Different phenolformaldehyde novolak resins were characterised by various methods. Gel permeation chromatography (GPC) was used to show the different molecular weight distributions among the different resins, as well as to give a quantitative analysis of the lower molecular weight species of the resin. Infra-red spectrophotometry along with GPC were used to show that the different molecular species of the resins were predominantly hydrogen bonded via the phenolic hydroxyl group. Thermal analysis methods, infra-red spectroscopy and x-ray diffraction techniques were utilised to elucidate certain characteristics of the different resins. Differential thermal analysis, Shawbury curometry and infra-red spectroscopy were used to study the factors affecting the cure of phenolformaldehyde resins. By various methods it was shown that the phenol content had marked effects on the cure properties of the resins, affecting not only the cure rate and the cure temperature but also the extent of cure. Further investigations into the reaction of phenol with hexamine indicated that the initiation of cross-linking by hexamine decomposition was not solely a heat dependent process. By varying the water content of phenolic resins it was shown that the water content affects both the cure of the resins and the formation of low molecular weight intermediates. Various methods of heat treating resin:hexamine mixtures indicated that under certain conditions components of a molecular weight intermediate between phenol and dihydroxydiphenylmethane could be produced. Finally a selection of commercially available moulding powders was obtained and the resin constituents characterised by the methods used previously for pure resin samples. From these results an attempt was made to predict the cure properties of the different moulding powders and to show how differences in the moulding powder compositions affects the moulding behaviour of these compounds.