The effect of composition and processing conditions on the structure development in injection molded dynamically vulcanized PP/EPDM blends

The effect of composition and processing conditions on the spatial structur al variation in dynamically vulcanized injection molded poly(propylene)/eth ylene-propylene-diene rubber (PP/EPDM) was investigated using matrixing mic robeam X-ray system and transmission optical microscopy techniques. The str ucture gradient in the thickness direction in these samples is composed of very thick, highly oriented, skin regions followed by core regions of lower preferential chain orientation. In these samples, the shear-crystallized l ayers are observed to be much thicker than the comparably processed pure PP The nucleation densities in the PP phase were too high to allow for observ ation of individual crystallites in most of the regions except near the ver y core, where sparsely distributed PP crystallites, that appear bright unde r cross polars, were observed. The wide-angle X-ray scattering (WAXS) patte rns taken at different distances from the skin indicate that chain axes are mostly oriented in the flow direction, and distinct bimodal c-axis and a* axis oriented dual population of orientation is observed in the PP phase, c -axis orientation factors, f(c), start at intermediate values at the skin a nd increase steadily and after showing a maximum roughly in the middle of t he shear crystallized region, decrease towards the core, and in most cases never achieve a state of isotropy. In the blends that contain very small po lypropylene fractions (ca similar to 15%), unusually high orientation level s were observed. This was attributed to the "shear amplification" phenomena that dominates the thin PP regions between the rubber particles and causes significant orientation levels in the thin layers of PP coating, the rubbe r particles with the relative motion of the particles in the shear flow fie ld.