Silane functionalized ethylene/diene copolymer modifiers in composites of heterophasic polypropylene and microsilica

SUMMARY Ethylene/1,7-octadiene copolymer was polymerised with metallocene catalyst and hydrosilylated to form silane functionalised polyethylenes (PE-co-SiX, X=Cl, OEt, Ph). The functionalised species were tested as modifi ers in composites of rubber toughened polypropylene (heterophasic PP, hPP) and microsilica fi ller (µSi). A metallocene-based functionalised PE (PE-co-SiF) produced earlier in our laboratory and three commercial grades of functionalised polyolefi ns (one PE- and two PP-based) were used as reference modifi ers. Major differences were seen in the toughness of the composites both above and below the glass transition temperature (Tg) of PP. In addition to increasing the stiffness, the microsilica fi ller enhanced the toughness of the heterophasic polypropylene by over 200% at ambient temperature. Below the T g of PP (at -20 °C), the infl uence of μSi was the opposite and the impact strength of the hPP/μSi composite was below that of unfi lled hPP. With the addition of just 2 wt% of functionalised polyethylene, the poor cold toughness of hPP/μSi composite was improved by nearly 100%. With the same addition, the toughness of the composites at ambient temperature was improved by 50 to 100% compared with the unfi lled hPP. This behaviour was explained by signifi cant changes in the fracture mechanism. Addition of functionalised PE increased the concentration of microsilica in the rubbery phase, allowing the crack to enter that phase. The rubbery phase was also able to absorb a large amount of impact energy below the glass transition temperature of PP.