Modification of polymer blends by irradiation

Modification of polymers, especially of polyolefin-elastomer blends (e.g. ethylene/propylene/diene terpolymer, ethylene/propylene copolymer, ethylene/vinyl acetate copolymer, etc.), by irradiation with a beam of fast electrons is discussed. Irradiation of polymer blends usually results in enhanced interactions between the constituents, caused among other things, by grafting induced at the polymer interphase. As a result, mechanical properties are affected to an extent depending on the proportion and type of constituent polymers, stabilizer content, and radiation dose. Breaking strength (sigma), relative elongation at break (epsilon) and melt flow rate (MFR) were examined for a triblock styrene/butadiene/styrene (SBS) copolymer; polypropylene (PP), and a PP-SBS blend (50:50 by wt.). In PP, the content of the crystal phase was determined (Table 1). Irradiation was found to make SBS crosslink, as a result, sigma rose by 25% and epsilon remained unaffected. PP was found to become degraded upon irradiation (MFR rose as much as 16 times), whereby sigma and epsilon decreased considerably. In pure PP, the content of the crystal phase was found to increase. The variations of sigma and epsilon in the irradiated PP-SBS blend follow a tendency similar to that in the SBS copolymer examined. This fact suggests the SBS copolymer to have a decisive effect on the macroscopic properties of the PP-SBS blend.