Mechanical and morphological properties of PP/NR/LLDPE ternary blend - effect of HVA-2

Improvements in impact strength of polypropylene can be sought by melt blending with rubbers. In this study, blends of PP, natural rubber and linear low density polyethylene (PP/NR/LLDPE) were prepared in a laboratory scale extruder. The rubber content in the ternary blend was at 10 and 20% with LLDPE content fixed at 25% of the overall plastics content. After mixing and pelletising, the samples were injection moulded and tested for mechanical properties. The study showed that the mechanical properties were modified significantly with the addition of HVA-2. The incorporation of HVA-2 into the ternary blend improved the elongation at break, but no significant change was observed in the yield strength values. At both testing temperatures of 0 and 27 degreesC, the impact properties of 64/20/16 PP/NRILLDPE ternary blends improve significantly as HVA-2 increases from 0 to 7.5%. However, the 72/10/18 PP/NR/LLDPE shows an optimum value at 0.5% HVA-2 concentration. SEM study shows that the number of holes due to the extraction of NR particles reduced significantly upon the addition of HVA-2. This observation indicates that the HVA-2 has crosslinked the rubber phases. The crosslinking of the rubber particles will increase the cohesive strength of natural rubber allowing it to undergo greater deformation before cohesive failure. It is also notable that the crosslinking can prevent the elastomer domain from re-aggregation and breakdown at shear stresses prevailing during the molding process and maintains mechanical properties effectively. In this study, the HVA-2 was also shown to be an effective compatibilizer by reducing the interfacial tension and improving adhesion between immiscible polymers, thus increasing the compatibility of the blend. (C) 2002 Elsevier Science Ltd. All rights reserved.