Interplay between crystallization behaviors and extensional deformation of isotactic polypropylene and its blend with poly(ethylene-co-octene)

Comparison investigation of the interaction between crystallization behaviors and extensional deformation of both isotactic polypropylene (iPP) and its blend with poly(ethylene-co-octene) (iPP/PEOc) was carried out in this study. The samples of iPP and the iPP/PEOc (80/20, wt.%) blend were prepared by changing the cooling rate during nonisothermal crystallization. Tensile testing showed that with the decrease of cooling rate, the progressive destruction of ductility of the two samples was resulted from the more perfect crystallites formed in the cooling process. The influence of cooling rate on the tensile properties is more prominent for pure iPP than for the iPP/PEOc blend. The crystalline structure was proven to be partially destroyed under the extensional deformation, and such crystalline structure destruction was in close association with the deformation of the specimens. The oriented noncrystalline molecular chains could easily be reorganized into more perfect crystals in postheating runs. The original crystalline structure has been found, to some extent, to determine the extensional deformation and the final crystallization behavior.