Abstract
A preoriented isotactic polypropylene film, which was prepared by drawing and annealing (Ta=157°C), was highly redrawn at an angle of α (α=0, 30, 45, 60 and 90°) to the preoriented direction at Trd (Trd=110 and 157.5°C). For the film B (Trd=110°C), the original structure, though slightly remained, was almost transformed into a new structure with two types of crystal orientation and the amorphous orientation function fam showed such high value as 0.568-0.633. For the film C (Trd=157.5°C), the WAXD patterns showed no reflections based on the original structure, but indicate a high degree of crystal orientation. On the other hand, the value of fam is considerably lower than that for the film B and it is considered that the strained amorphous chains formed by the redrawing, may relax during the redrawing at a higher temperature. Both films, B and C showed a dependence of Tm on heating rate, say, an effect generally known as superheating. The superheating effect may be attributed to the strained amorphous chains (tie chains) and to the crystallite size for the films B and C, respectively. Dynamic moduli of the films B and C (α=45°) were 9 and 6GPa, respectively.
