24. Chitin Fibers

Several attempts were made in the 1920s and the 1930s to dissolve chitin using ionic salts and produce fibers. For instance, chitin was dissolved in lithium thiocyanate and made into fibers. Instead of using native chitin, chitin xanthates were made by steeping chitin in 28–50 % NaOH solutions at room temperature for 2 h. Later the chitin was exposed to carbon disulfide to obtain the chitin xanthate. Fibers obtained were drawn to 250 % using hot glycerin. Dry strength of the fibers ranged from 1 to 1.2 g per denier, and the breaking elongation was 30 %. Using similar methods, other researchers had reported obtaining fibers with strength ranging from 0.9 to 1.5 g per denier with fineness being 3.08–18 deniers. Attempts were also made to combine chitosan xanthates with cellulose xanthates and produce fibers with better quality than chitin and viscose rayon fibers [97Agb]. However, fibers obtained using these approaches were considerably weak when wet and practically not useful. Some attempts had been made to cross-link the fibers with formaldehyde to improve wet stability, but the elongation and modulus had to be sacrificed [77Nog]. Some of the approaches used to obtain chitin fibers and the properties of the fibers obtained are listed in Table 24.1. Although good tensile strength was obtained using both the halogenated and amide–lithium chloride systems, the wet strengths were only about 0.2–0.5 g/denier, and the fibers were therefore not practically useful. Tokura et al. developed chitin fibers by suspending chitin in 99 % acetic acid to form a gel and later by dispersing the gel in dichloroacetic acid and isopropyl alcohol [79Tok]. Fibers obtained had fineness ranging from 2 to 25 denier, dry strength was between 0.7 and 1.6 g per denier, and elongation ranged from 2.7 to 3.4 %. However, the wet strength of the fibers was only between 0.1 and 0.3 g per denier.