Preparation Of Cotton Stalk Bark Fibers And Their Feasibility As Textile Fibers

Cotton stalks are available in abundant but have limited applications. In 2015-2016, global fiber production has reached 5.4 million tons. About 26 million tons of cotton stalks are produced due to cotton cultivation. Currently, most of these cotton stalks are still burned in the field. Bark of cotton stalks accounts for 27 % total mass of cotton stalks. Extraction of lignocellulosic fibers from bark of cotton stalks will not only improve the supply of textile materials but also alleviate the environmental pollution from straw burning. Some researchers have extracted cotton stalk bark fibers(CSBF) using alkali under atmospheric pressure. However, few reports are now available on the industrial application of CSBF in textiles, mainly due to their coarse fineness(51 dtex) and/or high lignin content(>11.8 %). In this study, three methods were studied to extract CSBF, including successive treatments of steam explosion, alkali and hydrogen peroxide, bacteria and enzyme treatments, as well as bacterial pretreatment and alkali treatment under high temperatures in succession. The CSBF were then blended with cotton and processed into cotton/CSBF blended yarns and their knitted fabrics. The spinning properties of CSBF, the handle and dyeing properties of cotton/CSBF blended fabrics were analyzed.CSBF could be extracted using combined treatments of steam explosion, alkali and hydrogen peroxide in succession. Steam pressure of 2 MPa and holding time of 120 S were considered appropriate for fiber extraction. CSBF after steam-explosion treatment had a relatively coarse fineness of 49.3 dtex, high hemicellulose content of 15.7%, lignin content of 24.3% and breaking strength of 2.7 cN/dtex. Subsequent alkali treatment reduced lignin content to 13.3% and fiber fineness to 28.3 dtex. The last peroxide treatment reduced lignin content to 11.8%, fiber fineness to 26.8 dtex and resulted in CSBF with tensile properties similar to cotton.Fiber bundles could be seperated from bark of cotton stalks using combined treatments of bacteria and enzyme in succession, but it was difficult to obtain CSBF with good fineness. Strains that could secret pectinolytic enzymes were employed to remove the gum inside bark of cotton stalks. Subsequent treatments of complex enzymes could reduce the hemicellulose content to 5.8% and lignin content to 8.2%, but the fibers remained a coarse fineness of 55.0 dtex. Synergistic effect was found between different enzymes in the degumming process. The experimental result of compound enzymes was significantly better than that of single enzyme.CSBF with both good fineness and low lignin content could be extracted using combined treatments of bacteria and alkali under high temperatures in succession. Fiber bundles after bacterial pretreatment had a lignin content of 15.3 % and hemicellulose content of 12.6 %. After being treated by 4 % alkali at 130? for 5 h, such bundles were changed into fibers with fineness of 24.0 dtex, length of 50.8 mm and lignin content of 3 %. The fibers had a slightly low breaking strength of 2.0 cN/dtex, Young's modulus of 56.2 cN/dtex and crystalline structure of type I. Lignin components inside CSBF could be removed more efficiently under high temperatures, resulting in finer and softer fibers.CSBF could be blended with cotton, processed into cotton/CSBF blended yarns and corresponding knitted fabrics. Cotton/CSBF blended yarns had breaking strength lower than that of pure cotton yarns with same cotton counts and twist factors. The critical twist factor of blended yarns was always higher than that of pure cotton yarns with the same counts.The maximum ratio of CSBF available in their cotton blended yarns could reach 30 % whereas corresponding ratio of jute was only 10 %. Cotton/CSBF blended yarns with blending ratio of 90/10 had unevenness 25.9 % lower and tenacity 61.6 % higher than that of cotton/jute blended yarns with the same blending ratio. Cotton/CSBF blended fabrics had bursting strength higher, and are softer and smoother than the fabrics of cotton/jute blends. When the proportion of CSBF in their cotton blended yarns increased from 10 % to 30 %, CV % of yarn unevenness raised by 69.9 %, hairiness index increased by 78.6 %, and breaking strength and elongation decreased by 20.6 % and 6.5 %, respectively. Correspondingly, the bursting strength of the blended fabrics decreased by 27 % and the faibrics turned to be stiffer and coarser.Dye sorption of Reactive Red 120 on CSBF was 15.7 % higher than that on cotton, which should be attributed to less negative Zeta potential and lower crystallinity % of CSBF compared to cotton. Dyeing 1 ton of CSBF with a dye sorption of 30 g/Kg required 38.5 Kg of Reactive Red 120, which was 27 % lower than that needed in the dyeing of cotton. Dyed fabrics of cotton/CSBF blends had higher K/S but lower L~* compared to pure cotton fabrics. Moreover, dyed fabrics of cotton/CSBF blends had the same laundering and light colorfastness, but slightly lower staining and wet crocking colorfastness than pure cotton fabrics.Overall, CSBF in our study can be used as a good alternative to traditional bast fibers for highly valuable textile applications. The results in our study will not only alleviate the environmental pressure but also improve the sustainable development of fiber industry.