Recycled Sisal Fiber-Reinforced Polypropylene Derived from Industrial Waste Stream

This paper presents the development and comprehensive characterization of recycled polypropylene (rPP) composites reinforced with recovered sisal fibers sourced from secondary agricultural waste streams. The rPP matrix was obtained from post-industrial waste generated during the manufacturing of household appliances at Hisense GORENJE company (Slovenia). To enhance the interfacial compatibility between the hydrophobic polymer matrix and the lignocellulosic reinforcement, maleic anhydride-grafted polypropylene (MAPP) was incorporated at a constant concentration of 3 wt.% as a compatibilizing agent. Composite formulations containing 10, 20, and 30 wt.% of sisal fibers were systematically investigated through mechanical testing (tensile strength, tensile modulus, and impact resistance), morphological analysis (SEM), spectroscopic characterization (FTIR), and thermal analyses (TGA–DTA and DSC). FTIR analysis suggested the interactions between the functional groups of MAPP and the lignocellulosic fibers; however, no distinct absorption band attributable to ester carbonyl formation was detected. SEM observations revealed improved fiber–matrix adhesion in the compatibilized systems, supporting the effectiveness of MAPP in promoting the interfacial bonding. The addition of sisal fibers significantly enhanced the mechanical performance of the rPP, with increases of up to 45% in tensile modulus and 92% in tensile strength at 30 wt.% fiber loading. Nevertheless, the composite containing 20 wt.% sisal fibers exhibited the most favorable balance between stiffness, strength and impact resistance. Overall, the results demonstrate the strong potential of rPP/sisal composites as lightweight, sustainable materials, enabling the dual valorization of industrial and agricultural waste streams and supporting circular-economy-oriented applications in the white-goods sector.