Evaluation of Biofiller Effects on Virgin and Post Consumed HIPS: Thermal and Mechanical Characterisation

Plastics continue to dominate industrial production, yet their accumulation as waste and the reliance on mineral-based fillers raise serious sustainability and environmental concerns. This thesis addresses these issues by examining the use of bio-calcium carbonate fillers obtained from food waste (ESF-A1, ESF-A2, ESF-B3) in virgin (HIPS-V) and post-consumer (HIPS-PC) high-impact polystyrene systems. For reference, conventional CaCO₃ was included in the formulations. The blends were prepared through twin-screw extrusion followed by injection molding, and the resulting composites were systematically evaluated by FTIR, TGA, DSC, melt flow index measurements, tensile testing, and Charpy impact analysis. The results demonstrate that although the biofillers had different surface characteristics, which influenced their hydrophobicity and thermal response, they all preserved their carbonate structure. Both mineral and bio-based fillers improved stability, according to thermal analysis, whereas biofillers left fewer residues, highlighting their environmental advantage. According to the mechanical characterisation, the addition of filler generally increased stiffness while decreasing ductility and tensile strength; ESF-B3 showed the most balanced outcome across all matrices. Melt flow tests indicated that biofillers maintained processability better than mineral CaCO₃, and although impact strength decreased in all systems, ESF-B3 again displayed relatively superior performance. Taken together, ESF-B3 exhibited the most significant potential as a sustainable alternative filler, integrating technical functionality with environmental benefits. These findings support the comprehensive incorporation of waste derived bio-calcium carbonate into polystyrene-based composites as a step towards more circular and resource efficient material alternatives.