Compatibilization of polymer blends using peroxide-induced reactive extrusion
Variable quantities of functionalized peroxides bearing carboxylic acid groups were reacted with polypropylene in a twin screw extruder. Systematic variations in the molecular structure of the peroxides were found to significantly affect the grafting efficiency of the carboxylic acid group onto the polypropylene backbone, as well as affect the polymer degradation process. This behavior was attributed to the relative reactivities of the different free radicals generated by thermal decomposition of the peroxides. The peroxides which yielded reactive methyl radicals were more efficient at producing polymeric radicals, relative to the peroxides which generated less reactive ethyl radicals. Increased grafting efficiency and polypropylene degradation were attributed to this increase in the quantity of polymeric radicals. In addition, the peroxides which yielded radicals bearing double bonds were found to have a higher grafting efficiency. This behavior was attributed to an increased reactivity of the alkenyl radicals, relative to the alkyl radicals, and to the potential for the polymeric radicals to add across the double bond to create the graft. The functionalized polypropylene (f-PP) was investigated as a compatibilizing additive for PP/PA-6,6 (80/20) blends. Differential scanning calorimetry showed an 80$\sp\circ$C decrease in the PA-6,6 crystallization temperature with incorporation of the f-PP into the blend. A near linear increase in the impact strength of the blends was observed with f-PP incorporations up to 30% of the PP phase. Moreover, blends containing 30% f-PP demonstrated impact properties approaching that of pure PA-6,6. A novel telechelic polymeric peroxide (peroxy-PCl) based on a polycaprolactone (PCl) backbone has been used in an attempt to compatibilize blends of dissimilar polymers (PE/PS) via copolymer formation by controlled hydrogen abstraction and grafting. Each blend composition was compounded with both counter rotating and corotating twin-screw extruders to compare extrusion parameters on the overall compatibilization process. Regardless of the extruder type, only slight decreases in the phase dimensions of the blends were observed with peroxy-PCl additions. As compared to the blends processed on the counter rotating extruder, the blends compounded on the corotating extruder demonstrated a significant enhancement in tensile properties with peroxy-PCl addition. Evaluation of the peroxy polymer with each of the component polymers revealed extensive side reactions (e.g., cross-linking and degradation) initiated by the decomposition products of the peroxide groups. A copolymer with a block-graft architecture was synthesized using peroxy-PCl as an initiator for styrene polymerization. This copolymer was evaluated as a third component compatibilizer in polar/nonpolar (PBT/PS) polymer blends. The compatibilizing efficiency of this copolymer was compared to other PS-PCl copolymers with different architectures (e.g., block architecture and graft architecture). The copolymer containing the block-graft architecture was the most effective at reducing the minor phase dimensions while enhancing the overall impact strength of the blend.