A study of mechanical properties and processability of blown films using b-LLDPE and LDPE blends.

摘要

Butene based linear low density polyethylene (b-LLDPE) is a locally made polymer that has superior mechanical properties, but lower processability compared to low density polyethylene (LDPE). In the present study, the aim is to blend the two polymers at different blend ratios to enhance the processability of b-LLDPE. Effects of draw ratio (DR) and blow ratio (BR) on the mechanical properties of b-LLDPE and LDPE films were investigated. Different mechanical tests, such as tensile, impact and tear resistance were studied. Crystallinity and orientation tests of the produced films were carried out for characterization purposes. It was found that a draw ratio of 21 and a blow ratio of 1.6 are optimum selections.;Using the abovementioned draw and blow ratios, the effect of blending on the mechanical properties and processability was investigated. Blend ratios of 5, 10, 15, 20 and 50% of LDPE were used. Having a blend ratio of up to 20% of LDPE with b-LLDPE brought a great achievement. Blending with LDPE reduces the torque needed to turn the motor, which lowers the energy consumption and lowers the cost of the process, in turn. From the mechanical tests results, many mechanical properties improved dramatically. Adding up to 20% of LDPE enhanced the yield strength in machine direction except for the 5% LDPE. The tensile strength in MD increased up to 15% LDPE. In both directions, the ductility profiles are similar. There was an enhancement in ductility at blend ratios of 5 and 10 %. At 15 and 20% of LDPE the ductility was almost unaltered. There was an enhancement of about 45% at blend ratios of 15 and 20% in the toughness of the films in machine direction. In the transverse direction, the toughness increased by 50% when adding only 10% of LDPE. The impact properties were affected greatly with the addition of LDPE. With the addition of only 5% of LDPE, the failure energy and the energy to peak force were increased by almost 25%. Adding 10% of LDPE, showed deterioration in the failure energy but the energy to peak force was enhanced. The effect of blend ratio on the Elmendorf tear resistance was carried out. If 5 or 10% of LDPE is added, the enhancement of TD tear resistance will be around 90%. At 15 and 20% of LDPE the enhancement was amazingly 115 and 100%, respectively.;In general, the study of blend effect on mechanical properties showed improvement up to 20% LDPE. Furthermore, the torque requirement was reduced with the increase of blend ratio.