Effect of heated p-t-octylphenol formaldehyde resole on the vulcanization of natural rubber

Thermal reactions of p-t-octylphenol formaldehyde resole, SP-1045, at 160 degrees C were investigated using infrared (IR) spectroscopy and gel permeation chromatography (GPC). The formation of o-methylene quinone intermediate and the dissociation of dimethylene ether-linkage in SP-1045 were found. Characteristic peak intensities in IR absorbance spectra of the o-methylene quinone intermediate increased while those of dimethylene ether-linkage in SP-1045 decreased linearly as heating time of SP-1045 was increased. Notable change of molecular weight distribution of the resole was not observed within 1.5 hours in GPC. Trimer content increased continuously with the increase of heating time while dimer content began to increase after heating SP-1045 for 6 hours. The vulcanizing behavior of natural rubber (NR) compounds containing heated SP-1045 was studied using a rheometer. It was observed that the scorch time of the NR compounds were not affected by the thermal reactions of SP-1045. However, torque increase (delta-torque) in rheographs of the NR compounds decreased as the heating time of SP-1045 was increased.