Polymer, Vol.48, No.1, 363-370, 2007
Ultradrawing above the static melting temperature of ultra-high molecular weight isotactic poly(1-butene) having low ductility in the crystalline state
Ultra-high molecular weight isotactic poly(l-butene) (UHMW-PBI) melt-grown crystal (MGC) films were drawn using the PIN drawing technique. Although the UHMW-PBI MGC films had poor ductility in the crystalline state, they were ultradrawable in the molten state above the static melting temperature (T-m). The drawability of the MGC films was strongly influenced by the draw temperature, the sample thickness, and the contact time between the metal heater and sample, and it increased with decreasing sample thickness. The maximum draw ratio (DRmax) was nearly constant when the sample thickness was less than 100 mu m at a given draw temperature. The contact time between the metal heater and sample needed to draw continuously in the molten state was at least 0.1 s. The ductility increased rapidly above 130 degrees C, reaching a maximum at 200 degrees C. and decreased at higher temperatures. A DRmax of 170 was achieved at 200 degrees C under optimum conditions. The efficiency of the drawing, based on the Herman crystalline orientation function (f(c)) and tensile properties versus DR, was lower for films drawn at higher temperatures. The highest f(c) of 0.996, tensile modulus of 14 GPa, and strength of 900 MPa were obtained by ultradrawing with DR = 50 at 155 degrees C. This modulus corresponded to 58% of the X-ray crystal modulus (24 GPa), whereas the modulus of PB1 films drawn in the crystalline state corresponded to only 12-13% (3 GPa) of the theoretical crystal modulus. (c) 2006 Elsevier Ltd. All rights reserved.