| The h-LLDPE is well known for its superior mechanical properties but at the same time is very difficult to process. On the other hand LDPE is much better in processing but has lower mechanical properties. Thus a blend of h-LLDPE/LDPE is an option which could improve processability and at the same time provide better mechanical properties. Of the two, h-LLDPE and LDPE, h-LLDPE is difficult to process and thus in this research, the processability and the mechanical characteristics of h- LLDPE/LDPE blends are studied. The processability window and polymer degradation studies for h-LLDPE were established for different die temperatures (210, 230, 250 and 270°C), and it was found that the optimum die temperature was 230°C. Also, effects of draw ratio (DR) and blow ratio (BR) on the mechanical properties of the blown films were studied. Mechanical tests such as tensile and Elmendorf tear test were conducted in both MD (machine) and TD (transverse) directions. Also, impact tests were carried out. Different mechanical tests of blown film samples at different DRs of 7, 21, 36, 49, 64 and 86 were accomplished. The DR 21 which resulted in higher impact resistance to failure of films was selected as the optimum DR. Other blown films of h-LLDPE were produced at different BRs of 1.12, 1.4 and 1.78 and mechanically tested. The study showed that the optimum BR should be in the range of 1.4 to 1.78; therefore an average value of 1.6 was selected. Consequently with the selected values of die temperature (230°C ), draw ratio (21), and blow ratio (1.6) the effect of blending h-LLDPE with LDPE was studied.;Pure h-LLDPE, LDPE and their blends (5%, 10%, 15%, 20% and 50%) were processed, and the effect of blending was studied using thermal, birefringence and mechanical techniques. The crystallinity for different blends was determined using DSC instrument. The cyrstallinity values were found to be in the range of 40% close to that of pure h-LLDPE and were not affected by the blend ratio. The birefringence of the blends has been studied using an optical microscope and an index of orientation has been reported. There is an increase in MD orientation when the blend ratio increases (-3x10-3 to 5x10 -3) from 0 to 50%, and then the birefringence decreases. Mechanical tests such as tensile, impact and elmendorf tear test were also conducted on the blended films. With addition of up to 20% LDPE, many mechanical properties of the blend showed improvement. There was a 20% enhancement in MD yield strength by small addition of LDPE without any decrease in the MD ductility. The MD toughness also displayed an increment of around 43% in its properties with this small addition of LDPE. The enhancement in TD tensile strength was more than 75% with very low blend ratio of 10% LDPE. The TD ductility slightly improved in comparison to pure h-LLDPE. TD toughness showed a small increase up to a blend ratio of 50%. A 20% improvement was observed in the impact peak force with very small addition of LDPE. In case of impact failure energy there was some decrease with respect to the blend ratio. The tear resistance also showed some kind of deterioration in the MD direction, but there was a large improvement for tear resistance in the TD direction. The TD tear resistance improved by almost 100% by addition of LDPE for the low blend percentages up to 20%.;In general, the study of blend effect of h-LLDPE/LDPE on mechanical properties of blown films showed improvement up to 20% blends. In addition the torque requirement for the film process was reduced with the increase of blend ratio, except at 5% blend ratio. |
