High-performance polypropylene film prepared from reactor powders having different characteristics

Ultra-high molecular weight isotactic polypropylene (UHMW-iPP) reactor powders have been successfully ultra drawn below melting temperature (Tm) by a combination of calendar rolling and tensile drawing techniques. Two UHMW-iPP reactor powders having different MWs were synthesized by using the same Ziegler-Natta catalyst system at 70 °C in hexane. The resultant tensile properties increased with increasing draw ratio, due to orientation-crystallization during tensile draw, which was indicated by DSC and WAXD measurements. The film drawn under optimum conditions exhibited the maximum tensile modulus of ∼25 GPa, independent of sample MW, corresponding to 70% of the ultimate modulus of iPP crystal. However, the higher maximum tensile strength of ∼1.0 GPa was achieved for the reactor powder having the higher MW, which is three times as high as those of commercial high-strength iPP tapes. Such a fact that high performances have been achieved by processing from reactor powder state below Tm implies that crystallization with less entanglement occurs during polymerization. When drawability and resultant properties were compared among different iPP reactor powders prepared under different conditions, it was clarified that they were predominantly affected by not only MW but also by the reactor powder morphology, especially surface smoothness.