Sustainable recycling of polypropylene (PP) waste: Development and optimization of rice husk reinforced PP composite

The growing emphasis on sustainability has driven research toward the recycling of polypropylene (PP) waste reinforced with natural fillers. This study investigates the development of rice husk–reinforced recycled polypropylene (RH-PP) composites for assistive applications using a cost-effective and scalable injection molding process. Nine composite formulations were developed by varying RH content (10–30 wt%) and particle sizes (125–500 µm), and their mechanical, thermal, chemical, and morphological properties were characterized. The optimal composite formulation (80 wt% PP, 20 wt% RH, 125 µm) exhibited enhanced performance with compressive strength of 57.3 MPa, bending strength of 45.3 MPa, tensile strength of 49.2 MPa, and impact energy of 4.2 KJ/mm 2 . Thermogravimetric analysis (TGA) showed a maximum degradation temperature of 407.6°C, while differential scanning calorimetry (DSC) revealed crystallinity values ranging from 38.8% to 40.7%. Scanning electron microscopy (SEM) confirmed improved interfacial adhesion and uniform filler dispersion. The integration of Grey Relational Analysis (GRA) enabled multi-response optimization, identifying the most influential parameters. The findings demonstrate that RH-PP composites offer a sustainable and mechanically robust alternative to virgin PP for use in orthotic and prosthetic applications.