Effect of HDPE on mechanical and physical properties of LLDPE/LDPE blown films

Abstract

The effect of HDPE on mechanical and physical properties of LLDPE/LDPE blown films were studied. Two types of LLDPE, produced by using Ziegler-Natta (zn-LLDPE) and metallocene catalytic systems (m-LLDPE); two grades of HDPE with different melt flow indices; 0.04 g/10min (HDPE1) and 0.7 g/10min (HDPE2), were used. In the first part, blown films were prepared at various compositions at a fixed LDPE content of 15% by weight, while HDPE content was varied from 5 to 30% by weight. The mechanical properties of the blown films were measured: i.e., stiffness (Young’s modulus), tensile strength, elongation at break, tear resistance, impact resistance and puncture resistance. Various physical properties were also characterized: i.e., haze, gloss, amount of gel particles, initial seal temperature and mass throughput. Furthermore, their thermal property was investigated. These included the non-isothermal melt-crystallization and melting behavior. The results obtained indicated that increasing HDPE content caused an increase in the crystallinity of blown films which caused the Young’s modulus in increase, while the clarity decreased. The blown films containing 15% HDPE by weight exhibited the most suitable mechanical and physical properties of blown films. The blown films containing HDPE1 had inferior mechanical properties with rough surface. Almost all blown films containing m-LLDPE showed better mechanical properties but more haze than the ones containing zn-LLDPE. In the second part, HDPE2 was kept constant at 15% by weight, while the LDPE content was varied (i.e., 5, 15 and 25% by weight). It was found that the mechanical properties of blown films decreased but better physical properties, especially lower haze and initial seal temperature. The blown films containing m-LLDPE exhibited better mechanical properties, while the blown films containing zn-LLDPE exhibited better physical properties.