Structure development in thermoset recyclate-filled polypropylene composites

Polypropylene containing comminuted fiber reinforced thermoset recyclate ha s been shown to exhibit enhanced mechanical properties relative to particul ate-filled materials. Optimum mechanical performance in these recyclate-fil led materials is achieved in compositions made from rubber-modified polypro pylene containing maleic anhydride-modified PP in conjunction with silane c oupling agent. Although matrix crosslinking was found to enhance properties in both filled and unfilled systems, composite properties are dominated by the development of strong interfacial bonding between polypropylene and re cyclate reinforcement. A mechanism for the formation of interfacial bonding is proposed involving reaction between maleic anhydride functionalized PP, formation of trisilanol groups and their subsequent condensation with hydr oxyl groups on the recyclate surfaces, together with molecular entanglement and co-crystallization of the grafted and ungrafted polypropylene molecule s. Furthermore, in the absence of treatment there is evidence that the elas tomer particles encapsulate the filler particles. However, this effect is s trongly hindered when functionalized-PP is added, either in isolation or in combination with the silane co-treatment. The crystalline nucleation of PP by thermoset recyclate and treatment is also considered. The treatment sys tem investigated was found to promote interfacial bonding to both the polye ster (DMC) and woven glass-reinforced phenolic recyclates investigated, sug gesting it may be suitable for treating mixed composite scrap.