UNIPLANAR DEFORMATION OF ISOTACTIC POLYPROPYLENE .2. PHASE-STRUCTURE

The phase structures of uniplanar-drawn isotactic polypropylene (iPP) have been investigated. Three phases (alpha-crystal, smectic and amorphous) are found to coexist in the uniaxially compressed samples. From thermal analyses and density measurements, the fractions and densities of these phases have been evaluated. At a compression draw temperature of 50-degrees-C < T(s) (the upper smectic phase stability limit), the amount of alpha-crystal decreased significantly and the smectic phase increased on developing a compression ratio up to approximately 10. The transition energy for smectic to crystal phase was found to be approximately 5.5 cal g-1. At a draw temperature > T(s) decrystallization without smectic phase stability proceeded during the deformation. No draw-induced crystallization was observed. At all deformation temperatures, the density of the phase increased in the initial stage of deformation reaching a limit on further draw.