Polypropylene-Elastomer (TPO) Nanocomposites

PP/PP-g-MA/MMT/elastomer thermoplastic olefin (TPO) nanocomposites were prepared in a twin-screw extruder at fixed 30 wt% elastomer and 0-7 wt% MMT content. The ratio of maleated polypropylene, PP-g-MA and organoclay was maintained at 1. Elastomer particle size and shape in the presence of MMT were evaluated for three different molecular weight grades of polypropylene (PP) (H= high, M= medium and L= low) and five different ethylene-co-octene elastomers (EOR) with different melt flow index (MFI) and octene contents. The MMT particles are located exclusively in the PP phase in the PP/PP-g-MA/MMT/EOR nanocomposites as seen from TEM images. TPO nanocomposites with toughness ranging from 450 J/m to 800 J/m (super toughness) are obtained based on the molecular weight of the PP, elastomer type and MMT content. Elastomers having a melt flow index (MFI) in the range of 0.5-1.0 showed significant improvement in the impact strength of L-PP while most H-PP blends gave ‘super-tough’ materials without MMT and maintain this toughness in the presence of MMT. For the similar elastomer particle sizes in nanocomposites, the impact strength varies as H-PP> M-PP> L-PP. The ductile-brittle (D-B) transition temperature decreases with increased molecular weight of the PP and the addition of MMT. Elastomers having a melt flow index (MFI) in the range of 0.5-1.0 showed a significant decrease in the D-B transition temperature for both L-PP and H-PP nanocomposites.