Production of controlled‐rheology polypropylene resins by peroxide promoted degradation during extrusion

Abstract Results of experimental and modeling studies of the peroxide promoted degradation of polypropylene (PP) are presented. Experiments were carried out, in glass ampoules and in a plasticating extruder. The initiator, 2.5‐dimethyl‐2,5‐bis(tert‐butylperoxy)hexane was used as a radical generator. The extruder used had a 38 mm diameter and 24:1 L/D single‐screw. In these experiments, the effect of peroxide concentration and screw speed on the molecular weight distribution (MWD) of the polypropylene resin was studied. Samples collected from the experimental runs were analyzed for melt flow index (MFI), flow curve, extrudate swell, and MWD. The measured data are presented and correlations among various parameters are considered. Generally, it can be concluded that controlled‐rheology (CR) resins with lower molecular weight, narrower MWD, and reduced viscosity and elasticity, can be produced, A kinetic model for the peroxide Initiated degradation of PP is proposed. Simulations based on this model are compared with experimental data for the production of CR resins. The experimental data were obtained from three sources: (i) industry, (ii) literature, and (iii) present experimental work. The comparison was done in terms of average molecular weights of the resin. Agreement between model predictions and experimental results is quite satisfactory suggesting that this model should find use in commercial practice.