The effect of orientation on the mechanical properties of metallocene polyethylene

A comprehensive study has been made on the effect of orientation on the mechanical properties of a metallocene linear low-density polyethylene (m-LLDPE) and a metallocene very low-density polyethylene (m-VLDPE). Tensile and simple shear behaviours were studied for this new class of polyethydenes at different angles to the original draw direction. For this purpose large dumbbell shaped samples were extended at room temperature and then cut at different angles to the direction of orientation. The effects of draw ratio on the yield stress and elastic modulus were also investigated. While unoriented m-LLDPE showed a shoulder followed by a distinct maximum after which a neck was formed. m-VLDPE extended uniformly without any neck formation in the tensile experiments. The number of methydene units incorporated within the lamellae thickness were calculated using rubber elasticity theory and also measured by wide angle X-ray diffractometry. These comparisons showed that there was good agreement between the results.