Computer simulation of the reaction injection molding process of polyurethane-unsaturated polyester blends

Abstract

A computer simulation model was developed to analyze the reaction injection molding (RIM) process of a binary system of polyurethane and unsaturated polyester. The polyurethane was made from 4,4``-diphenyl methane diisocyanate(MDI), poly (propylene glycol) (PPG) and trimethylol propane(TMP) with dibutyltin dilaurate (T-12) 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. The reaction kinetics and the viscosity functions of each component polymers were obtained through experiments and the balance equations of chemical species, momentum and energy in cylindrical coordinates were established for a disc type mold. Withe the aid of a computer, these equations were solved simultaneously to calculate the temperature, conversion and viscosity profiles during filling and curing at various molding conditions. The increase of the initiator concentrations, feed temperature and circulating fluid temperature shortened the reaction time and raised the maximum temperature. when a mold made of low thermal conductivity material was used, the difference between the wall and the center could be decreased. As the thickness of the mold cavity was increased the reaction time and maximum temperature were all increased. And the effect of the fill time was very small. Finally, an attempt of the moldability analysis was made with the criteria of cycle time and maximum temperature. The main results are summarized as follows. The higher the circulating fluid temperature, the smaller the effects of the initiator concentrations and feed temperature became. And the most important parameter was the circulating fluid temperature.