PREPARATION OF HIGH MODULUS POLYPROPYLENE SHEET BY THE ROLLER-DRAWING METHOD

A polypropylene sheet was drawn through a pair of heated rollers and mechanical properties, molecular orientation and microstructure of the roller-drawn sheet were investigated. With increasing draw ratio, Young's modulus, dynamic storage modulus, and tensile strength increased and the intensity of tan delta peak in the beta -dispersion region decreased. The degree of orientation of crystal c-axis increased with draw ratio and reached a constant value above draw ratios of 7-9, while the degree of orientation of amorphous molecular chains increased with increasing draw ratio even in the high draw ratio range. There is a good correlation between the degree of orientation and the dynamic storage modulus measured below beta -dispersion temperature. The increase of the fraction of tie molecules and crystalline bridges, however, plays an important role in the improvement of the modulus above the beta -dispersion temperature.