Dynamic mechanical properties of poly(propylene) blends with poly [ethylene-co-(methyl acrylate)]

Blends of poly(propylene) (PP) were prepared with poly [ethylene-co-(methyl acrylate)] (EMA) having 9.0 and 21.5% methyl acrylate comonomer. A similar series of blends were compatibilized by using maleic anhydride grafted PP. The morphology and mechanical properties of the blends were investigated using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) in tensile mode. The DMA method and conditions were optimized for polymer film specimens and are discussed in the experimental section. The DSC results showed separate melting that is indicative of phase-separated blends, analogous to other PP-polyethylene blends but with the added polarity of methyl acrylate pendant side groups that may be beneficial for chemical resistance. Heterogeneous nucleation of PP was decreased in the blends because of migration of nuclei into the more polar EMA phase. The crystallinity and peak-melting temperature did not vary significantly, although the width of the melting endotherm increased in the blends indicating a change had occurred to the crystals. DMA analysis showed the crystal-crystal slip transition T-alpha* and glass transition (T-g) for PP as well as a T-g of the EMA copolymer occurring chronologically toward lower temperatures. The storage modulus of PP and the blends was generally greater with annealing at 150degreesC compared with isothermal crystallization at 130degreesC. The storage modulus of the blends for isothermally crystallized PP increased with 5% EMA, then decreased for higher amounts of EMA. Annealing caused a decrease with increasing copolymer content. The extent of the trend was greater for the compatibilized blends. The T-g of the blends varied over a small range, although this change was less for the compatibilized blends.