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.

Melt blowing: General equation development and experimental verification

“…This activation energy is closely bracketed by AE values from Tadmor and Gogos' data ( 1 979) for commercial polypropylene: Exxon PP CD460 has AE = 1 I .4 kcal/mol, while Union Carbide PP E612 has AE = 9.3 kcal/ mol. For the viscoelastic model, the assumed value of the elastic modulus G was 28 kPa; this G value is based on data taken by Tzoganakis et al (1988) for polypropylene with M,/M,, = 4.49…”

Evolution of the peroxide‐induced degradation of polypropylene along a twin‐screw extruder: Experimental data and theoretical predictions

“…[7][8][9][10] Later, these models were coupled to descriptions of flow in processing equipment. For example, Tzoganakis and coworkers 9,10 and Pabedinskas et al 11 combined kinetic models of the peroxideinduced PP degradation reaction with flow in singlescrew extruders. Kim and White 12 and, more recently, Berzin et al 13 predicted MW changes along twin-screw extruders.…”

Mixing analysis of reactive polymer flow in conveying elements of a co-rotating twin screw extruder

“…In this process, a peroxide free rad- 3,4 ical initiator is added to a stream of molten PP in an extruder, and at the high temperature conditions of the system the peroxide molecules thermally decompose into free radicals which initiate a random scission of the polymer chains. Longer chains have a higher probability of being attacked by the peroxide radicals, and so a general decrease of the molecular weight of the polymer and a narrowing of the molecular weight distribution (MWD) result.…”

“…The specific reaction rates in equation (2) follow from the kinetic model of Tzoganakis et al: 3,4 dI…”