Integration of recycled denim waste cotton fibre and jute fibre in thermoplastic bio composite applications

High-stiffness and high-strength natural fibres are commonly utilized in thermoplastic matrices to manufacture biobased thermoplastic composites. Low-end applications such as construction and furniture industries do not require a high load-bearing capacity, thus favoring cost-effective, moderately strong, sustainable natural materials and quickly manufacture thermoplastic composites. Recycled biobased cotton fibres collected from the denim industry can effectively penetrate this composite industry due to their cost-effectiveness and desirable physical and mechanical properties. However, retaining structural integrity and enhancing the reinforcing efficiency of recycled yarns in composites pose challenges. Addressing these issues, we propose a new method of extracting recycled cotton from denim waste fabric and transforming it into dry preform with minimal damage to the structural integrity of cotton fibres. Jute fibres have been introduced alongside recycled denim fibers within a polypropylene matrix to optimize the hybrid reinforcing efficacy of the composites. The effect of denim fibre length on composite quasi-static tensile and flexural test results showed that a yarn length of 20 mm yielded the highest tensile strength (⁓27.83 MPa), tensile modulus (⁓ 1.76 GPa), flexural strength (⁓62.35 MPa), and flexural modulus (⁓1.17 GPa). Composites comprising recycled denim yarn and jute fibre improved the tensile modulus to approximately ⁓2.1 GPa and the impact strength to approximately ⁓66.1 kJ/m², following the hybrid rule of mixture, while jute fiber serves to increase the stiffness and toughness of the composites. This work demonstrates that recycled denim cotton fibre and strong jute fibre can be successfully integrated into thermoplastic composites to achieve tailored mechanical properties.