Reaction injection molding process of polyurethane-unsaturated polyester blends

Abstract

An engineering analysis on the reaction injection molding process of polyurethane-unsaturated polyester IPNs was carried out through model simulations and actual experiments. The polyurethane network was prepared by reacting 4,4``-diphenyl methane diisocyanate(MDI), poly (propylene glycol) (PPG) and trimethylol propane(TMP) using cobalt naphthenate as a catalyst, and the unsaturated polyester resin composed of phthalic anhydride, propylene glycol and fumaric acid was crosslinked with styrene in the presence of methyl ethyl ketone peroxide and cobalt naphthenate. For the computer simulation model, the reaction kinetics and the viscosity model were established. Results in the reaction kinetics of IPN formation showed that there are complicated interactions between the two reactions in spite of the different reaction mechanisms. It was revealed that MDI had a significant catalytic effect on the unsaturated polyester reaction. A small amount of MDI raised the rate of unsaturated polyester reaction by accelerating the initiator decomposition. Therefore the reaction rate of unsaturated polyester increased in the polyurethane/unsaturated polyester mixed system. However, the final conversion of unsaturated polyester reaction decreased in the mixed system by the cage effect of the polyurethane network which restricted the diffusion of the styrene monomer. On the other hand, the polyurethane reaction rate in the mixed system was not altered significantly. For the rheological model, the viscosity changes during the reaction course were described as a function of temperature and conversion. The viscous activation energy for the polyurethane reaction mixture showed a constant value, while that for the unsaturated polyester system revealed linear dependence on conversion. To simulate the RIM process, balance equations calculating the temperature and conversion change in a disc type mold were established. These equations were solved numerically by a explicit finite difference...