STUDIES ON THE RELATIONSHIP BETWEEN ORIENTATION MECHANISM AND MECHANICAL PROPERTIES OF ORIENTED POLYPROPYLENE. (8) INTERPRETATION OF ORIENTATION BEHAVIOR OF POLYPROPYLENE CRYSTALS DURING UNIAXIAL STRETCHING OF BULK POLYMER IN TERMS OF SPHERULITE DEFORMATION MECHANISM

The orientation behavior of crystallites during uniaxial stretching and its recovery behavior during heat-treatment without tension for highly isotactic as well as lowly isotactic polypropylenes, are interpreted in terms of a spherutlite deformation mechanism modified from that proposed by Sasaguri, Yamada and Stein.Four deformation parameters characterizing the spherulite deformation mechanism, i. e., fraction of the folded-chain type crystal within crystal lamella at undeformed state, easiness of crystal transition from folded-chain type to fringed-micellar type and that from fringed-miceller type to folded-chain type, and easiness of lamella detwisting, showed reasonable changes with degree of tacticity of the polymer, conditions of annealing and stretching of the bulk polymers.The prefered orientation recovery of crystal c-and b-axis than a′-axis during heat-treatment of stretched bulk polymer without tension, may be interepreted in terms of almost reversible deformation recovery of the spherulite and that of lamella detwisting, but irreversible crystal transitions between fringed-micellar tye and folded-chain type.