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The purpose of this study is to investigate the natural Luffa vine (LV) fiber to be effectively used as cellulose fiber reinforcing material for lightweight and decay-resistance composite materials. The physical, chemical, thermal, and morphological properties of the LV fibers, together with their microstructure are investigated. The test results conclude that the LV density, microscopic characteristics, and mechanical properties show that this crop is a lightweight (200–550 kg/m3) natural fiber with a porous structure and a high specific modulus (1.18–2.04 MPa∙ m3/kg). The chemical, X-ray diffraction and the Fourier transform infrared spectroscopy analyses indicate that the LV has a high lignin content (25.18%) and a relatively high relative crystallinity (37.18%) of cellulose, and it contains saponins, which increase its erosion resistance and hardness. The thermogravimetric analysis reveals that the fibers can stand up to 315.4 °C. Moreover, due to their kinetic activation energy of 63.9 kJ/mol, they can be used as reinforcement materials in thermoplastic green composites with a working temperature below 300°. • Luffa vine (LV) have a multi-level porous structure and a high specific modulus. • The presence of saponins help LV develop corrosion-resistant composites. • The LV lignin is mostly guajacyl lignin and only a small amount of syringyl lignin. • The LV thermal properties meet to a working temperature of composites below 300 °C. [ABSTRACT FROM AUTHOR]

• Luffa vine (LV) is a low-density natural plant fiber with a porous structure. • The secondary wall of LV fiber cell contains two layers with spiral thickening. • Sclerenchyma cell of LV exhibits excellent micromechanical properties. • The microscopic characteristics endow LV with good processability. • The pit pairs on cell walls provide good permeability to LV fibers. The exploration of luffa vine (LV) in the polymer composites field can contribute to the development of lightweight composites and expand their use in new wide scale applications. In this study, the physical and chemical properties and the microstructure of the LV fibers were investigated by various techniques. The results of LV density and microscopic characteristics indicated that this crop is a lightweight (with density mainly concentrated in 0.30–0.45 g cm−3) natural fiber with a porous structure (the ratio of wall to lumen: 0.2–0.3). Transmission electron microscopy and nanoindentation analyses showed that the secondary wall of the LV sclerenchyma cell is made up of two layers with spiral thickening and exhibiting a high nanoindentation modulus (7.8–10.4 GPa) and a high nanoindentation hardness (0.40–0.58 GPa). The chemical composition and X-ray diffraction analysis indicated that the LV has high lignin content (20–25%) and a relatively high relative crystallinity index of cellulose, which are conducive to increase the hardness of the LV fiber. Moreover, microscopic characteristics analysis also revealed that the LV fiber cells have a relatively high aspect ratio (30.3), there are pit pairs on the LV fiber cell walls, and the core fiber cells of the LV have relatively high flexibility coefficient (0.8), which are beneficial to increase the processability of composite materials with the LV fibers as reinforcement. [ABSTRACT FROM AUTHOR]