To investigate the effect of low molecular weight species on the physical properties of ultra-drawn gel films, three different grades of polyethylene with molecular weight of 800, 30,000 and 300,000 were incorporated into ultra-high molecular weight polyethylene (mol.wt. 3,000,000).
Dried gel films with various contents of low molecular weight species in ultra-high molecular weight polyethylene were prepared by the cast film method from the 2 wt% of polyethylene solution in decalin. They were drawn at the various temperature condition up to draw ratio of 150 by using universal testing machine with temperature chamber and various physical properties of these ultra-drawn gel films were observed; tensile strength and modulus by Instron, melting temperature by DSC, density and crystallinity by density gradient column, film surface structure by SEM, degree of orientation by wide angle X-ray diffractometer.
It is observed that with increasing contents of low molecular weight species in the blends the drawability of dried gel films is improved at the first up to the certain amount of low molecular weight species depending on their molecular weight. Above this content, however, the drawability rapidly decreased. It is confirmed that the drawability of dried gel films is increased with increasing drawing temperature under the temperature conditions up to 120℃.
It is also observed that the most important factor for the mechanical properties such as tensile strength and modulus is the draw ratio ; The tensile strength and modulus appear to increase linearly with the draw ratio independent of the combination of materials used. The highest mechanical properties obtained in this experiment are tensile strength of 2.3 GPa and Young's modulus of 110 GPa, which are 10 times and 80 times greater than those from ultra-drawn melt films respectively.
On the other hand properties such as the melting temperature, the density and crystallinity and the orientation angle are levelled off above the draw ratio of 20. It seems that those properties set up if the surface tissue of gel films is changed from interconnected lamellar to fibrillar structure.
From the results of this experiment, it is concluded that the low molecular weight species improve the drawability of dried gel films and act an important role in the enhancement of the mechanical properties with easy processability.
