REACTIVE EXTRUSION OF POLYPROPYLENE POLYETHYLENE BLENDS - KINETIC-MODEL DEVELOPMENT/

A mathematical model for the changes in molecular weight distribution that occur when free-radical initiator is added to a blend of linear l ow-density polyethylene and polypropylene during extrusion was develop ed. Experimental verification employed a size-exclusion chromatograph equipped with both differential refractive index detection and a solve nt-evaporation interface to enable infrared detection. The model combi nes two previously published models (a polypropylene degradation model and a polyethylene modification model) using a single parameter: an i nitiator partition coefficient. All of these models were shown to prov ide excellent fits to new reactive extrusion data. However, with one o f the initiators used, the polyethylene modification model required va lues of initiator efficiency greater than unity. This result was also recently observed in another study and may be due to localized variati ons in peroxide concentration or to an inadequacy in the reactions spe cified for polyethylene with this initiator.