Improvement of the mechanical properties of an HDPE/PS blend by compatibilization and incorporation of CaCO3

Generally, recycled polymer blends exhibit solid dispersion-like morphology with poor mechanical properties. The aim of this work was to enhance the mechanical properties of a HDPE/PS (75/25) blend, in particular the stiffness and the impact strength. In order to improve the stiffness, CaCO3 filler was incorporated. It was shown that PS and CaCO3 were separately dispersed with poor adhesion to the HDPE matrix. The incorporation of CaCO3 significantly enhanced the stiffness but lowers the impact resistance. Elastomer copolymers were incorporated in order to compensate for the embrittlement caused by the CaCO3 filler. Depending on their chemical structure, either grafted with a reactive function or ungrafted, the elastomers acted differently at the interfaces of the HDPE/PS/CaCO3 system. SEBS acts exclusively at the HDPE-PS interface whereas SEBSgMA acts at both the HDPE-PS and the HDPE-CaCO3 interface. The SEBSgMA elastomer lowered the stiffening effect caused by CaCO3 and provided an insufficient increase in impact properties. One the other hand, SEBS, which concentrates its action at the HDPE-PS interface, retained much of the stiffening effect of CaCO3 and provided a greater improvement in impact properties than SEBSgMA. In the recycled HDPE/PS (75/25) blend, the incorporation of 20 vol% CaCO3 and 4 vol% SEBS led to an increase in both impact strength (from 39 to 70 kJ/m(2)) and in stiffness (from 1335 to 1560 MPa). So, encouraging results were obtained, enabling us to predict a promising future for this approach to the recycling of commingled plastics.