Mechanical and Thermal Properties of Polypropylene (PP)/ Waste Cellulose (WC) Composite for Industrial Applications

Abstract This study investigated the mechanical and thermal properties of recycled polypropylene (rPP) composites reinforced with waste cardboard cellulose (WC) and modified with aluminum hydroxide Al(OH) 3 and potassium alum (KAl(SO₄)₂·12H₂O) additives. The composites were fabricated using a twin-screw extruder and characterized before and after UV exposure .Waste cellulose was dispersed as a homogeneous suspension rather than a solution, as cellulose is insoluble in water. Results showed that tensile strength increased by 15–30% with cellulose addition (10–30 wt.%), while elastic modulus improved by 20–40% depending on filler content and additive type. Composites containing Al(OH)₃ exhibited higher tensile performance compared to alum-modified ones. Impact strength showed a moderate enhancement with cellulose addition but slightly decreased with inorganic additives. DSC analysis revealed an increase in melting temperature (Tm) by 2–5°C and crystallinity (Xc) by 5–10% for cellulose-reinforced composites. Although no conventional compatibilizer such as maleic anhydride-grafted polypropylene (MAPP) was employed, the observed mechanical improvement is attributed to physical interlocking, hydrogen bonding interactions, and the stabilizing effect of inorganic additives .Alum-modified composites exhibited enhanced thermal stability, while cellulose-containing composites retained 85–90% of their initial mechanical properties after UV exposure, compared to 70–75% for neat rPP .