As one of the fastest-growing additive manufacturing (AM) technologies, fused deposition modelling (FDM) shows great potential in printing natural fibre-reinforced composites (NFRC). However, several challenges, such as low mechanical properties and difficulty in printing, need to be overcome. Therefore, the effort to improve the NFRC for use in AM has been accelerating in recent years. This review attempts to summarise the current approaches of using NFRC as a feeder for AM. The effects of fibre treatments, composite preparation methods and addition of compatibilizer agents were analysed and discussed. Additionally, current methods of producing feeders from NFRCs were reviewed and discussed. Mechanical property of printed part was also dependent on the printing parameters, and thus the effects of printing temperature, layer height, infill and raster angle were discussed, and the best parameters reported by other researchers were identified. Following that, an overview of the mechanical properties of these composites as reported by various researchers was provided. Next, the use of optimisation techniques for NFRCs was discussed and analysed. Lastly, the review provided a critical discussion on the overall topic, identified all research gaps present in the use of NFRC for AM processes, and to overcome future challenges.

WPCs are being used in a large number of applications in the automotive, construction, electronic, and aerospace industries. There are an increasing number of research studies and developments in WPC technology involving rice husk as fillers. This study investigated the effects of different compositions of rice husk (RH) filler on the mechanical and morphological properties of recycled HDPE (rHDPE) composite. The composites were prepared with five different loading contents of RH fibers (0, 10, 20, 30, and 40 wt%) using the twin screw extrusion method. Maleic acid polyethylene (MAPE) was added as a coupling agent. Results showed that tensile and flexural properties improved with increasing RH loading. However, the impact strength of the composites decreased as the RH loading increased. SEM micrographs revealed good interfacial bonding between the fiber and polymer matrix.

In this study, a biodegradable, cheap and durable recycled high-density polyethylene (rHDPE) polymer reinforced with rice husk (RH) fibre was fabricated into a foam structure through several processes, including extrusion, internal mixing and hot pressing. The effect of filler loading on the properties of the foam and the influence of RH surface treatments on the filler–matrix adhesion and mechanical properties of the composite foam were investigated. The morphological examination shows that 50 wt.% filler content resulted in an effective dispersion of cells with the smallest cell size (58.3 µm) and the highest density (7.62 × 1011 sel/cm³). This small cell size benefits the mechanical properties. Results indicate that the tensile strength and the Young’s modulus of the alkali-treated RH/rHDPE composite foam are the highest amongst the treatments (10.83 MPa and 858 MPa, respectively), followed by UV/O₃, which has shown considerable increments compared with the untreated composite. The flexural and impact tests also show the increment in strength for the composite foam after chemical treatment. Although the UV/O₃ surface treatment has minor influence on the mechanical enhancement of the composite foam, this method may be a reliable surface treatment of the fibre-reinforced composite.

The use of rice husks (RH) to reinforce polymers in biocomposites are increasing tremendously. However, the incompatibility between the hydrophilic RH fibers and the hydrophobic thermoplastic matrices leads to unsatisfactory biocomposites. Surface modification of the fiber surface was carried out to improve the adhesion between fiber and matrix. In this study, the effect of surface modification of RH via alkali, acid and ultraviolet-ozonolysis (UV/O₃) treatments on the properties of composites recycled high density polyethylene (rHDPE) composites was investigated. The untreated and treated RH were characterized by Fourier Transform Infrared (FTIR) and Scanning Electron Microscope (SEM). The composites containing 30 wt% of RH (treated and untreated) were then prepared via extrusion and followed by compression molding. As compared to untreated RH, all surface treated RH exhibited rougher surface and showed improved adhesion with rHDPE matrix. Tensile strength of UV/O₃-treated RH composites showed an optimum result at 18.37 MPa which improved about 5% in comparison to the composites filled with untreated RH. UV/O₃ treatment promotes shorter processing time and lesser raw material waste during treatment process where this is beneficial for commercialization in the future developments of wood plastic composites (WPCs). Therefore, UV/O₃ treatment can be served as an alternative new method to modify RH surface in order to improve the adhesion between hydrophilic RH fibre and hydrophobic rHDPE polymer matrix.

Carbon nanotubes (CNTs) have a huge potential as conductive fillers in conductive polymer composites (CPCs), particularly for bipolar plate applications. These composites are prepared using singlefiller and multifiller reinforced multiwalled carbon nanotubes (MWCNTs) that have undergone a chemical functionalization process. The electrical conductivity and mechanical properties of these composites are determined and compared between the different functionalization processes. The results show that UV/O₃‐treated functionalization is capable of introducing carboxylic functional groups on CNTs. Acid‐treated CNT composites give low electrical conductivity, compared with UV/O₃‐treated and As‐produced CNTs. The in‐ and through‐plane electrical conductivities and flexural strength of multifiller EP/G/MWCNTs (As‐produced and UV/O₃‐treated) achieved the US Department of Energy targets. Acid‐treated CNT composites affect the electrical conductivity and mechanical properties of the nanocomposites. These data indicate that the nanocomposites developed in this work may be alternative attributers of bipolar plate requirements.

The hydrophilic nature of rice husks (RH) is incompatible with hydrophobic polymer matrix and has a tendency to form aggregates Therefore, surface modification plays a major role in order to improve and develop natural fiber reinforced polymer composites with better mechanical properties. In this study, modification of RH surfaces by alkali, acid and ultraviolet-ozonolysis (UV/O₃) treatment were carried out. The untreated and treated RH was characterised by FTIR, TGA and SEM. The composites of treated and untreated RH containing 30 wt% of RH fibers were then prepared by extrusion and comparative study is being done. Flexural strength of untreated RH, alkali-treated RH, acid-treated RH and UV/O₃-treated RH composites are 27.97, 31.25, 30.22 and 30.87 MPa respectively. All surface treated RH composites was found to improve its adhesion with polymer matrix. Flexural strength of composites filled with UV/O₃-treated RH shows similar results compared to alkali treatment. Therefore, UV/O₃ treatment can be used as an alternative method to modify RH surface in order to improve the adhesion between hydrophilic RH fibre and hydrophobic rHDPE polymer matrix.