Ultradrawing of ultrahigh molecular weight polyethylene reactor powders prepared by highly active catalyst system

Drawability of ultrahigh molecular weight polyethylene (UHMW-PE) reactor po wders, prepared by using a highly active Ziegler type catalyst, has been st udied as functions of catalyst activity, polymerization temperature, monome r pressure and sample molecular weight. Compacted powder films of UHMW-PE, prepared in a 1000-fold range of polymerization rates, were drawn by a two- stage technique; i.e. the initial solid-state coextrusion at 110 degreesC f ollowed by tensile drawing at 135 degreesC, some 5 degreesC below the melti ng point. It was found that an appropriate range of molecular weights (M-v = 1.6- 3.0 X 10(6)) existed for achieving a high draw. The UHMW-PE prepared even at a high polymerization rate of 43,600 (g of PE)/(mmol of transition metal,h) could be drawn to draw ratios (DR) over 50, producing tapes with tensile modulus and strength over 100 acid 1.0 GPa, respectively. This leve l of catalyst activity is sufficient fur the modern industrial production o f UHMW-PE. The reduction of polymerization rate, by lowering monomer pressu re and polymerization temperature, produced UHMW-PE with improved ductility . Furthermore, at the same polymerization rate, the ductility of reactor po wder was improved more significantly by lowering the former parameter than the latter, reflecting the characteristic effect of each of these polymeriz ation variables on the morphology formation during polymerization. Thus, th e reactor powders prepared at 40-60 degreesC and monomer pressure of 1 atm could be drawn to DR's of 100-125. Such highly drawn products exhibited ten sile moduli and strength up to 144 and 1.6 GPa, respectively. (C) 2001 Publ ished by Elsevier Science Ltd.