Natural fiber reinforced thermoplastic matrix composites have been increasingly used in semistructural applications in automotive applications because of their good specific strength and modulus, low carbon footprint and recyclability. This research work studies the effects of material treatment(s) on the mechanical behaviors of hemp fiber reinforced polypropylene (PP) composites. The material treatment(s) are realized by chemically treating the hemp fiber with different concentration NaOH and/or adding maleic anhydride grafted polypropylene (MAPP) to the PP matrix. The purpose of the material treatment(s) is to enhance the bonding between the hemp fibers and the polypropylene matrix which otherwise has low surface energy and limited bonding. The mechanical behaviors are investigated with different combinations of material treatment(s) such as 5 wt% MAPP, 5% NaOH treated hemp fiber, 10% NaOH treated hemp fiber, and 5% NaOH+5 wt% MAPP. 15 wt% and 30 wt% hemp fiber loadings are used in the composites with these material treatments. It is found that the material treatment(s) result(s) in composites with better mechanical properties compared to the composites without any treatment(s). The composites with 5 wt% MAPP addition show the best mechanical properties.

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Long fibre-reinforced thermoplastic or long fibre thermoplastic (LFT) composites possess superior specific modulus and strength, excellent impact resistance, and other advantages such as ease of processability, recyclability, and excellent corrosion resistance. These advantages make LFT composites one of the most advanced lightweight engineering materials and enable their increasing use in various applications. This review paper summarises the research and development work that has been conducted on LFT composites since their initial development. Different aspects of LFTs, such as process development, fibre orientation distribution (FOD), fibre length distribution (FLD), and their effects on the mechanical properties of LFT composites are described. The characterisation of the FOD and FLD in the LFT composites using advanced imaging technology such as highresolution 3D micro-CT scanning technique is summarised. Research and development of LFT hybridisation and LFT additives are also discussed. Finally, conclusions are made and the future outlook of LFT composites is given.