PP/LLDPE/EPDM Blends: Effect of the Elastomer Viscosity on Impact Properties

Abstract

Blending is an attractive method of creating materials with better performance than separate components. Such blends have already reached a massive application in the case of thermoplastics like polyethylene (PE) and polypropylene (PP), although their complex structure frequently hinders the prediction of the structure-properties relationship. Isotactic PP poor impact strength at room and low temperatures is well known. Blends of PP with elastomers as impact modifier have been studied extensively during the last decade. Some results on improvement of the rubber dispersability and blend stiffness by the addition of high density polyethylene (HDPE) have been reported. However, the effect of the third component is still a matter of discussion. In this chapter, PP/LLDPE/EPDM blends are prepared and focus is on the effect of the content and viscosity of the elastomer on the morphology of the disperse phase. Particle size distribution is obtained by transmission electron microscopy (TEM) and image analysis techniques. Izod Impact Strength (IS) properties were also determined at room and low temperature on press molded specimens. The morphology of the ternary blends studied, exhibits an increasing degree of LLDPE/EPDM interpenetration with the LLDPE content. The addition of LLDPE in both low and high viscosity elastomer improves its dispersability, affecting mainly the larger particles of the distribution. For a given composition, ternary blends with L-EPDM show higher impact strength. At low temperature, the dispersive effect of LLDPE is less significant on the impact properties.