The effect of fast electron irradiation on the properties and structure of isotactic polypropylene (iPT)-thermoplastic elastomer blends

After having been irradiated with fast electrons (30 kGy), isotactic polypropylene (iPP) and iPP - butadiene/styrene block copolymer (SBS) blends showed an increased fluidity at 190 degrees C. The degradation thus evidenced proceeded with no participation of cross-linking (the irradiated polymers were completely soluble in boiling xylene). Structurally, the blends were found to be heterogeneous as shown by DMTA and confirmed by SEM measurements. Two glass transitions were observed: one at -79 degrees C corresponding to the T-g of the polybutadiene block and another at 32 degrees C corresponding to the T-g of the iPP amorphous phase. The fast electron beam resulted in an increased crystalline phase proportion (as determined by the WAXS method) in the iPP, iPP-SBS and iPP-SBS(10%) blends. In the ordered domains of the irradiated iPP and iPP-SBS(10%) the resulting transformations were related in nature, viz., in the (040), (130) and (111) planes the crystallites were larger as compared with those in original iPP; in the iPP-SBS(50%), the crystallites were reduced in the (400) and (130) planes and increased in size in the (111) planes. irradiation resulted in increased tensile strength and considerably reduced (50-fold) elongation at break [except for iPP-SBS(50%)].