Bioscience Evidence 2024, Vol.14, No.6, 293-303 http://bioscipublisher.com/index.php/be 296 4 Processing Techniques and Treatment of Hemp Fibers 4.1 Fiber extraction methods: traditional retting vs. modern techniques Fiber extraction from hemp involves several methods, each with its own advantages and limitations. Traditional retting methods, such as dew retting and water retting, have been widely used. Dew retting, which relies on natural environmental conditions, is a common practice in regions with favorable climates, such as Northwest France and the Netherlands. This method can be effective but is highly dependent on weather conditions, which can lead to variability in fiber quality (Placet et al., 2017; Réquilé et al., 2021). Water retting, on the other hand, involves submerging hemp stalks in water to facilitate microbial activity that breaks down pectins, allowing fibers to be separated. While effective, water retting generates significant wastewater and can be time-consuming (Sadrmanesh and Chen, 2018). Modern techniques aim to address these limitations. Enzymatic retting, for instance, uses specific enzymes to break down pectins more efficiently and with less environmental impact. Steam explosion and mechanical decortication are other modern methods that have been explored. Steam explosion involves treating hemp stalks with high-pressure steam, which disrupts the plant structure and facilitates fiber separation. Mechanical decortication uses mechanical means to separate fibers from the woody core, offering a faster and more environmentally friendly alternative to traditional retting (Sadrmanesh and Chen, 2018; Zimniewska, 2022) (Figure 2). 4.2 Chemical and enzymatic treatments for enhanced properties Chemical and enzymatic treatments are employed to enhance the properties of hemp fibers, making them more suitable for textile applications. One innovative approach involves the use of combined microwave energy (MWE) and deep eutectic solvents (DES) for degumming hemp fibers. This method effectively removes lignin, pectin, oil, and wax, resulting in fibers with higher cellulose content and improved thermal stability. The treated fibers also exhibit a higher ultraviolet protection factor (UPF) compared to traditional alkali-treated fibers (Ahmed et al., 2022). Enzymatic treatments, such as those using pectinases and other specific enzymes, can selectively degrade pectins and hemicelluloses, improving fiber fineness and flexibility. These treatments are often combined with mechanical processes to achieve optimal results. For example, bio-degumming, which uses biological agents to remove non-cellulosic components, has been shown to enhance the quality of hemp fibers for high-performance applications (Musio et al., 2018; Placet et al., 2018). Figure 2 Schematic value chains of hemp fibre extraction for textile purposes (Adopted from Zimniewska, 2022) Image caption: (A) (green line)—traditional order of processes including straw retting, (B) (orange line)—with use of decortication of straw excluding retting with use of degumming, (C) (orange-brown line)—decortication of raw non-retted straw for technical use of the fibres, (D) (green-grey line)—with use of decortication following retting aimed at preparation of fibre for cottonisation or woolenisation (own elaboration) (Adopted from Zimniewska, 2022)
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