Crystalline structure of polypropylene in blends with thermoplastic elastomers after electron beam irradiation

Isotactic polypropylene (PP) was blended in extruder with 0-50% addition of styrene-ethylene/butylene-styrene (SEBS) and styrene-butadiene-styrene (SBS) block copolymers. Granulated blends were irradiated with electron beam (60 kGy) and 1 week later processed with injection molding machine. Properties of samples molded from irradiated and non-irradiated granulates were investigated using DSC, WAXS, MFR, SEM and mechanical and solubility tests. It was found that the SEBS based systems are more resistant to irradiation in comparison to similar blends with SBS copolymer. Such behavior can be explained by the presence of double bonds in elastic SBS block. Irradiation of PP-SBS blends leads to considerable structure changes of crystalline and amorphous PP phases and elastic SBS phase. It indicates creation of new (inter)phase consisting of products of grafting and cross-linking reactions. Irradiated PP-SBS blends show significant improvement of impact strength at low temperatures. (C) 2005 Elsevier Ltd. All rights reserved.