Polymers 2023 , 15 , 1393
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Figure 4. The effect of plasma treatment on ( a ) the surface roughness of fibres and ( b ) the interfacial interaction between the fibre and matrix [126]. Combining chemical treatments with physical plasma treatments was studied on flax fibres by Gieparda et al. [127] to understand the synergistic effects. The authors used silanisation and plasma treatment both individually and in combination. The results revealed an increased thermal stability with a significant impact on fibre diameter and specific surface area. Erwin et al. [128] studied liquid plasma treatment on coir fibre with microwave plasma in the liquid. The mediums were water and sodium bicarbonate (NaHCO 3 ) solution. The interfacial shear strength of the coir fibre–epoxy matrix increased after liquid plasma treatment with both water and sodium bicarbonate because of chemical adhesion which facilitated mechanical interlocking. 3.2.2. Steam Explosion Steam explosion is another physical modification technique for natural fibres. This in- volves heating the fibres at a high temperature and pressure, causing mechanical disruption of the cellular material that undergoes fibrillation. The selection of steaming temperature and exposure time is very important to achieve optimal fibre properties. Han et al. [129] studied the effects of steam treatment on wheat straw under different pressures and times. They reported that the treatment enhanced the dimensional stability with the removal of lignin, ash and extracts. 4. Production Technology Natural fibre-reinforced hybrid composites are now extensively applied to deal with technological problems [130–132]. Table 3 lists composites made of natural fibres that have widespread applications in areas where the cost of reinforcements limits the utilisation of conventional, lightweight, reinforced plastic materials [133–135]. Cabedo et al. [136] compared almond shell, rice husk and seagrass as fillers in PHB/fibre composites prepared by the melt-blending process. They studied the influence of fibre type and fibre content on morphology, thermal, mechanical and barrier properties, compostability and processability. They concluded that all three fibres were suitable for the development of fully compostable biocomposites for packaging applications. Rawi et al. [75] studied the effects of compres- sion moulding parameters on the mechanical properties of bamboo fabric, poly (lactic acid) (PLA) composites for packaging applications. They reported that the composites with the highest compression pressure of 1.01 MPa at 3 min exhibited a superior tensile strength of 80.71 MPa and flexural properties of 124 MPa. They [137] also compared polypropylene (PP) and bamboo fabric PLA composites to investigate the use of environmentally friendly
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