AbstractThe influence of the filler content and surface modification of Elateriospermum tapos seed shell (ETSS)-filled recycled polypropylene (rPP) on the tensile, thermal, and morphological properties was investigated. Maleic acid (MA) was used for the chemical modification of ETSS. It was found that increasing the ETSS content decreased the tensile strength and elongation at break of composites. However, the modulus of elasticity increased with the addition of ETSS. The thermal properties of composites were examined using thermal analysis (TGA) and differential scanning calorimetry (DSC). The addition of ETSS indicated better thermal stability of rPP/ETSS composites. The degree of crystallinity (Xc) of the composites decreased with increasing ETSS content. The tensile strength and modulus of elasticity of modified composites was higher than unmodified composites. Surface modification with maleic acid increased the thermal stability and crystallinity of the modified rPP/ETSS composites. Scanning electron microscopy showed that the filler-matrix interaction improved with the modification of ETSS with maleic acid.