The effects of extrusion parameters and blend composition on the mechanical, rheological and thermal properties of LDPE/PS/PMMA ternary polymer blends

Abstract

Polymer blending is one of the popular methods for producing tailor-made materials by combining the properties of individual polymers. Binary polymer blends have quite commonly been used over the past few decades. Recently, researchers have shifted their focus towards ternary polymer blends and this study aims to investigate a ternary polymer blend system consisting of low-density polyethylene (LDPE), polystyrene (PS) and polymethyl methacrylate (PMMA). The LDPE/PS/PMMA blend was processed by melt blending using a twin-screw extruder. The effects of the extrusion process parameters (i.e., screw speed and barrel set temperatures) and the blend composition on the mechanical, rheological and thermal properties of the polymer blend and the degree of crystallinity of the LDPE matrix were studied. Three different screw speeds (i.e., 50 rpm, 100 rpm and 150 rpm), two different barrel set temperatures (i.e., 200 °C and 220 °C), and two different component mass ratios (i.e., 70/10/20 and 70/20/10) were studied. The results showed that the tensile properties of the LDPE/PS/PMMA blend were significantly influenced by its microstructure. Yield strength and Young's modulus decreased at first and then increased with increasing screw speed. The blend processed at a barrel set temperature of 220 °C was found to have better tensile properties than the blend processed at 200 °C. Furthermore, the blend with a PS content of 10 wt% possessed better tensile properties than the blend with a PS content of 20 wt%. Regardless of the blend compositions and the process settings, the LDPE/PS/PMMA blends reported better mechanical properties than those of pure LDPE with a Young's Modulus of 240 MPa and a yield stress of 10.47 MPa. The rheology of the blend was also significantly affected by the process parameters and the blend composition. However, different process parameters and mass ratios did not indicate a significant influence on the melting temperature (around 109.5 °C) and the degradation initiation temperature (around 252.3 °C) of the LDPE/PS/PMMA blend, but both the melting temperature and the degradation initiation temperature of the ternary blend were found to be slightly lower than those of pure LDPE. The degree of crystallinity of the LDPE matrix was also affected by both the screw speed and the barrel set temperature. The results revealed that, better mechanical properties can be achieved by blending PS and PMMA with LDPE without significantly affecting the thermal properties compared to those of pure LDPE.