Recent developments within the topic of biomaterials has taken hold of researchers due to the mounting concern of current environmental pollution as well as scarcity resources. Amongst all compatible biomaterials, polycaprolactone (PCL) is deemed to be a great potential biomaterial, especially to the tissue engineering sector, due to its advantages, including its biocompatibility and low bioactivity exhibition. The commercialization of PCL is deemed as infant technology despite of all its advantages. This contributed to the disadvantages of PCL, including expensive, toxic, and complex. Therefore, the shift towards the utilization of PCL as an alternative biomaterial in the development of biocomposites has been exponentially increased in recent years. PCL-based biocomposites are unique and versatile technology equipped with several importance features. In addition, the understanding on the properties of PCL and its blend is vital as it is influenced by the application of biocomposites. The superior characteristics of PCL-based green and hybrid biocomposites has expanded their applications, such as in the biomedical field, as well as in tissue engineering and medical implants. Thus, this review is aimed to critically discuss the characteristics of PCL-based biocomposites, which cover each mechanical and thermal properties and their importance towards several applications. The emergence of nanomaterials as reinforcement agent in PCL-based biocomposites was also a tackled issue within this review. On the whole, recent developments of PCL as a potential biomaterial in recent applications is reviewed.

Natural fibre as a reinforcing agent has been widely used in many industries in this era. However, the reinforcing agent devotes a better strength when embedded with a polymer matrix. Nevertheless, the characteristic of natural fibre and polymer matrix are in contrast, as natural fibre is hydrophilic, while polymer is hydrophobic in nature. Natural fibre is highly hydrophilic due to the presence of a hydroxyl group (-OH), while polymer matrix has an inherent hydrophobic characteristic which repels water. This issue has been fixed by modifying the natural fibre’s surface using a chemical treatment combining an alkaline treatment and a silane coupling agent. This modifying process of natural fibre might reduce the attraction of water and moisture content and increase natural fibre surface roughness, which improves the interfacial bonding between these two phases. In this paper, the effect of alkaline and silane treatment has been proven by performing the mechanical test, Scanning Electron Micrograph (SEM), and Fourier Transform Infrared spectrometry (FTIR) to observe the surface structure. The chemical compositions and thermal properties of the composites have been obtained by performing Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) tests. 1.0% silane treatment displayed better strength performance as compared to other composites, which was proven by performing Scanning Electron Micrograph (SEM). The assumption is that by enduring chemical treatment, kenaf fibre composites could develop high performance in industry applications.

Fused Deposition Modelling (FDM) gets the most attention in development and manufacturing industries. The demand for FDM in industries increases gradually over time and attracts many researchers to enhance the quality of the FDM’s fillers. The most popular filler reinforcements in use are synthetic or carbon fibre. However, these fibres are harmful to the environment. To overcome the issue and replace the current fibres and achieve the bio-composites filler, researchers suggested using natural fibre to replace the synthetic and carbon fibres as the reinforcement, which is also combined with bio-polymer matrix such as thermoplastics as the polymer matrix in FDM’s industries. Many experiments and tests are conducted to prove the capability of the natural fibre as the main material in composite industries. FDM is a world-wide technology that aims to be environmentally friendly, thus, this paper focuses on biodegradable fillers for FDM.

The thermal and rheological properties of bio-composite filament materials are crucial characteristics in the development of a bio-composite Fused Deposition Modeling (FDM) filament since the printing mechanism of FDM strongly depends on the heating and extrusion process. The effect of chemical treatment on the thermal and rheological properties was investigated to develop composite filaments for FDM using natural fibres such as sugar palm fibre (SPF). SPF underwent alkaline and silane treatment processes before being reinforced with PLA for improving adhesion and removing impurities. Thermogravimetric Analysis (TGA), Differential Scanning Calorimetric (DSC), and Melt Flow Index (MFI) analyses were conducted to identify the differences in thermal properties. Meanwhile, a rheological test was conducted to investigate the shear stress and its viscosity. The TGA test shows that the SPF/PLA composite treated with NaOH and silane showed good thermal stability at 789.5 °C with 0.4% final residue. The DSC results indicate that the melting temperature of all samples is slightly the same at 155 °C (in the range of 1 °C), showing that the treatment does not interfere with the melting temperature of the SPF/PLA composite. Thus, the untreated SPF/PLA composite showed the highest degradation temperature, which was 383.2 °C. The SPF/PLA composite treated with NaOH and silane demonstrated the highest melt flow index of 17.6 g/min. In conclusion, these findings offer a reference point for determining the filament extrusion and printability of SPF/PLA composite filaments.

This study investigated the optimum NaOH concentration treatment for rubber crumbs that improves adhesion between the polymer matrix and rubber filler in rubber polyester composites. The composite was prepared by mixing rubber crumbs from waste rubber gloves with unsaturated polyester matrix. Rubber crumbs were cryogenically ground from waste gloves and treated with 1%, 4%, 7%, and 10% NaOH (by volume). Treatment with 7% and 10% NaOH provides better wettability and hydrophilicity for rubber as it decreases the surface contact angle by approximately 27%. Higher concentration of NaOH intensively etched the rubber and made the surface rougher with more microcracks, providing a larger surface area for greater polyester coverage and holding the rubber firmly. It also induced more functional groups that increased the rubber surface energy and removed the hydrophobic layer on the rubber. These factors strengthened the interfacial rubber–polyester adhesion, as shown by the SEM micrograph of the tensile fracture which the rubber crumbs adhere well to the polyester matrix. The FTIR analysis of rubber treated with higher NaOH concentration showed a higher peak intensity, which demonstrated more polar groups were generated on the rubber surface. More polar groups created further connections to the polar groups in the polyester matrix, thereby enhancing adhesion between the rubber filler and the matrix.

Due to the increasing awareness on environmental impact and the needs towards sustainability, weight reduction of the vehicles is one of the most promising solutions to improve fuel efficiency towards achieving the reduction in carbon dioxide emissions. Fibre metal laminate is one of the lightweight material that inherits advantages of metal and fibre reinforced composite. Therefore, the drive of this study is to determine the effect of water absorption on tensile properties, thickness swelling and forming analysis of the natural fibre metal laminate. Fabrication of natural fibre metal laminate consists of two layers of kenaf woven fabric in polypropylene matrix and aluminium 5052-O as the skin. The results show that the natural fibre metal laminate absorbs 0.67% water and has 0.91% thickness swelling. The water content has minimal effect on the tensile properties of the natural fibre metal laminate. While for the forming analysis, the natural fibre metal laminate has higher formability compared to an aluminium sheet and has a higher potential to be formed into complex shape.