Integration of recycled thermoplastics and agricultural waste in natural fiber-reinforced composite filaments for 3D printing: An overview

Abstract

As a result of the growing amount of plastic waste and agricultural waste, finding suitable and sustainable feedstocks for AM has motivated the use of natural fiber reinforced recycled thermoplastic composites (NFRRPCs) for AM manufacture using FDM techniques. Such recycled thermoplastic with agricultural waste fibers have been reviewed critically by investigating material selection, fiber treatments, filament fabrications, printability, mechanical and thermal performance and engineering applications. According to the literature, surface treatments and compatibilizers are suitable to enhance the adhesion of the fiber-matrix, mechanical properties, thermal stability and consistency of the filament. But too much fiber loading can lead to higher melt viscosity, higher agglomeration, porosity and nozzle clogging, which is then detrimental to the inter-layer adhesion and the challenges associated with printed-part performance. The analysis further includes emerging approaches, such as hybrid fibers, nano-reinforcement, bio-based compatibilizers as well as manufacturing approaches based on artificial intelligence, machine learning, and digital twin. What makes this review novel is the suggestion of an integrated conceptual framework of recycled polymer quality, fiber treatment, composite compounding, filament fabrication, printability, interlayer adhesion, and final mechanical performance. This structure provides a clearer perspective on the processing-structure-property relationships of NFRRPC filaments and outlines the strengths and needs for research addressing the broader integration of the filaments with circular economy principles, combined with reliability, scalability, and commercialization efforts.