Rheological and thermal behaviour of vinyl ester resin

The rheological behaviour of synthesized vinyl ester resin (VER) based on epoxy novolaks containing methyl, ethyl and butyl acrylates as reactive diluent (40% w/w) was studied using a Haake Rotovisco RV 20 viscometer. The zero-shear viscosity of VER containing acrylates decreases linearly with temperature and increases with the size of the alkyl substituent in the acrylate. The average values of activation energy for flow at constant shear stress (25–100 Pa) were 11.79, 13.29 and 14.75 kcal/mol for VER containing methyl, ethyl and butyl acrylates, respectively. The activation energy at constant shear rate decreases with increase in the shear rate (50–400 sec −1). The curing and decomposition behaviour of the resin containing acrylates as reactive diluent (40% w/w) and benzoyl peroxide (2 phr) as initiator were studied by DSC and TGA. The activation energy for the curing reaction calculated by the Ozawa method, was found to be minimum whereas the thermal stability and the activation energy for the decomposition reaction calculated by the Coats and Redfern method were found to be maximum, for the resin with ethyl acrylate as reactive diluent.