Bioscience Evidence 2024, Vol.14, No.6, 293-303 http://bioscipublisher.com/index.php/be 294 2 Hemp Fiber Composition and Structure 2.1 Chemical composition: cellulose, hemicellulose, lignin, and pectin Hemp fibers are primarily composed of cellulose, hemicellulose, lignin, and pectin. The cellulose content in hemp fibers is a critical factor influencing their mechanical properties and suitability for textile applications. Studies have shown that the cellulose content in hemp fibers can vary significantly, with values ranging from 64.2% to 70.5% (Zommere et al., 2013). This high cellulose content contributes to the strength and durability of the fibers. Hemicellulose content in hemp fibers ranges from 16.99% to 23.79%, while lignin content varies between 5.68% and 7.96%. Pectin, although present in smaller quantities (1.37% to 1.64%), plays a crucial role in the fiber's structural integrity and interaction with other components. Chemical treatments, such as alkali treatment, can significantly alter the chemical composition of hemp fibers. For instance, selective chemical treatments have been shown to increase the α-cellulose content from 75% to 94% by removing non-cellulosic components like pectin and hemicellulose (Wang et al., 2007). This purification process enhances the fiber's crystallinity and mechanical properties, making them more suitable for high-performance textile applications. 2.2 Microstructure: fiber morphology and crystalline structure The microstructure of hemp fibers is characterized by a unique morphology and crystalline structure. Microscopy studies have revealed that hemp fibers possess an interconnected web-like structure, with nanofibers forming bundles of cellulose fibers with widths ranging between 30 and 100 nm and lengths of several micrometers (Wang et al., 2007). This intricate morphology contributes to the fiber's mechanical strength and flexibility. The crystalline structure of hemp cellulose is typically semicrystalline, as evidenced by wide-angle X-ray diffraction (XRD) patterns (Bonatti et al., 2004). The relative crystallinity of hemp fibers can be significantly enhanced through chemical and mechanical treatments. For example, the crystallinity of untreated hemp fibers, initially at 57%, can be increased to 71% after such treatments (Wang et al., 2007). This increase in crystallinity is associated with improved mechanical properties and thermal stability. 2.3 Comparative analysis with other natural fibers (e.g., cotton, flax) When compared to other natural fibers such as cotton and flax, hemp fibers exhibit several distinct advantages and similarities. Both flax and hemp fibers have similar biological, physical, chemical, and mechanical properties, influenced by factors such as cultivation conditions and initial treatment methods (Zommere et al., 2013). The cellulose content in flax fibers ranges from 64.57% to 75.38%, which is comparable to that of hemp fibers. However, the hemicellulose and lignin contents in flax fibers are slightly different, with hemicellulose ranging from 12.97% to 26.07% and lignin from 4.78% to 7.44%. In terms of mechanical properties, the high cellulose content and degree of polymerization in both hemp and flax fibers contribute to their strength and durability. However, the presence of non-structural components like pectin and the microfibril angle can influence the overall performance of the fibers (Marrot et al., 2013). For instance, hemp fibers have been shown to have a significant amorphous matrix polymer rate, which can affect their mechanical properties compared to flax. 3 Physicochemical Properties of Hemp Fibers 3.1 Mechanical properties: tensile strength, elasticity, and rigidity Hemp fibers exhibit notable mechanical properties, making them suitable for various applications, including reinforcement in composite materials. The tensile strength and elasticity of hemp fibers are influenced by environmental conditions, particularly moisture. Studies have shown that water sorption significantly affects the tensile stiffness and strength of hemp fibers, with a remarkable increase in fiber stiffness of up to 250% under cyclic loading conditions (Placet et al., 2012). Additionally, the mechanical properties of hemp fiber composites can be enhanced through treatments such as alkali treatment, which improves tensile strength and impact resistance (Frącz et al., 2021). However, moisture absorption can lead to a reduction in mechanical properties, as observed in water-immersed hemp fiber composites (Dhakal et al., 2007; 2018).
RkJQdWJsaXNoZXIy MjQ4ODYzMg==