At present, environmental sustainability is a big concern due to the limited resources and the adverse impacts of petroleum-based materials. Green composites (GCs) attracted intensive research interest for the last few decades from academicians, scientists, researchers, and practitioners both from the ecological and economic point of view and are presently being considered as one of the most promising research domains. Composites produced from renewable and/or natural resources thanks to their biodegradability and sustainability properties are envisaged as the next-generation materials to meet the growing demand worldwide. GCs are intensively investigated due to their multifunctional properties and utilization in a wide variety of fields including automobile, marine, aerospace, structural and infrastructural applications, packaging, electronics industry, sports, and biomedical applications. They also show potentials to replace the expensive as well as non-degradable petroleum-based composites. After the shelf life, it can be disposed of easily without harming the environment. The processing techniques, properties, and applications of green composites are comprehensively assessed in this review article. The feasibility of the naturally available fiber and polymers for green composites are also discussed highlighting the existing challenges with possible suggestions. It was intended to present a full overview of biodegradable polymer composites reinforced with natural fiber, as well as the necessary future directions for the concerned researchers.

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The conversion of poly (hexamethylene adipamide) or polyamide 66 precursor fiber to carbon fibers was accomplished through thermal stabilization and carbonization processes. Thermal stabilization was conducted of cupric chloride (CuCl2)–ethanol-impregnated polyamide 66 (PA66) fibers in the air. To determine the influence of heating rate on the fiber structure and properties of the resultant carbon fibers, carbonization experiments were performed at selected temperatures of 500, 700, 900, and 1100°C using 2.5 and 5 °C/min heating rates with no dwelling. The results conclusively revealed that the volume density and tensile properties of the PA66 fiber were higher at 2.5 °C/min heating rate. After fixing the heating rate as 2.5°C/min, further carbonization experiments were conducted at temperatures from 500 to 1100°C, using increments of 100°C with no dwelling time. Linear density, volume density, fiber diameter, carbon yield, elemental composition, tensile, and electrical properties exhibited a strong dependence on the carbonization temperature. After taking into account the effects of structural defects (i.e., microvoids), tensile strength, and tensile modulus of the carbon fibers increased to 794 MPa and 92.4 GPa, respectively, when carbonized at 1100°C. X-ray diffraction analysis of the carbon fibers further revealed the existence of a greatly disordered (i.e., amorphous) structure, which developed during the carbonization process. FT-IR analysis confirmed the formation of highly aromatic carbon clusters at temperatures of 500°C and higher. The outcomes of electrical conductivity in this study confirm that the PA66 precursor was converted into a semi-conducting state once it was carbonized.