Polymer modification is intended to introduce certain chemical changes that result in preferred properties of the modified material. In a reactive extrusion(REX) process, the synthesis or modification of a polymeric material takes place simultaneously with its processing and shaping into a finished plastic product.
In this study, the effects of processing conditions were investigated through experiments and simulations in PE-g-PS reactive extrusion process. Mixture of styrene and initiator was added to the PE melt and consequently graft copolymerization occurred in an extruder.
Reaction kinetic was investigated through reactions in a mixer. Viscosity as a function of temperature, shear rate and composition was also found by using a mixer as a torque rheometer.
In the simulation study, the screw characteristic curves were used to find the pressure profile and the degree of fill along the screw axis. There exists partially filled state that is caused by starved feeding. Mean residence time of each element was calculated from flow rate, degree of fill and free volume between screw and barrel. Temperature profile was found by using energy equation, which contains heat of polymerization and viscous dissipation also. Conversion and degree of grafting was calculated from the reaction kinetic, residence time and temperature profile.
Comparison between simulation with experiment was done. As screw speed increased, residence time was slightly decreased. Conversion and degree of grafting were increased as increasing screw speed because of large viscous heating. Mean residence time is not much affected by varying temperature. Conversion and degree of grafting are increased as temperature increased, but in experiment, conversion and degree of grafting were not increased any more above 190℃ because of too fast initiator decomposition. As feed rate increased, mean residence time is decreased. Conversion is decreased because of short residence time. conversion and degree of grafting were lower than simulated results at high flow rate due to poor mixing and heat transfer.
