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, CaCO 3 filler was incorporated. It was shown that PS and CaCO 3 were separately dispersed with poor adhesion to the HDPE matrix. The incorporation of CaCO 3 significantly enhanced the stiffness but lowers the impact resistance. Elastomer copolymers were incorporated in order to compensate for the embrittlement caused by the CaCO 3 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/CaCO 3 system. SEBS acts exclusively at the HDPE‐PS interface whereas SEBSgMA acts at both the HDPE‐PS and the HDPE‐CaCO 3 interface. The SEBSgMA elastomer lowered the stiffening effect caused by CaCO 3 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 CaCO 3 and provided a greater improvement in impact properties than SEBSgMA. In the recycled HDPE/PS (75/25) blend, the incorporation of 20 vol% CaCO 3 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.