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(1-butene) (UHMW-PB1) melt-grown crystal (MGC) films were drawn using the PIN drawing technique. Although the UHMW-PB1 MGC films had poor ductility in the crystalline state, they were ultradrawable in the molten state above the static melting temperature (Tm). 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 μm 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 °C, reaching a maximum at 200 °C, and decreased at higher temperatures. A DRmax of 170 was achieved at 200 °C under optimum conditions. The efficiency of the drawing, based on the Herman crystalline orientation function (fc) and tensile properties versus DR, was lower for films drawn at higher temperatures. The highest fc of 0.996, tensile modulus of 14 GPa, and strength of 900 MPa were obtained by ultradrawing with DR = 50 at 155 °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.