| Under the background of “double carbon” target,the development direction of the textile industry pays more attention to green and low carbon.The chemical fiber production process has high energy consumption and carbon emissions,and it is difficult to degrade naturally and recycle.Relatively speaking,the development and utilization of biomass fiber are more in line with the development requirements of low-carbon ecology.Hemp is an excellent textile biomass raw material.Its fiber has excellent moisture absorption,moisture release,air permeability,and antibacterial properties.The development of hemp fiber and textiles helps to meet the global demand for natural fibers and ecological textiles.However,the current traditional alkali boiling degumming process for the preparation of hemp fiber has problems such as long process flow,large water consumption and energy consumption,and large pollution of degumming wastewater,which seriously restricts the development and utilization of hemp fiber.Therefore,it is urgent to develop a clean and efficient hemp degumming method.Organic solvents can effectively dissolve the lignin and hydrolyze part of hemicellulose to achieve efficient separation of biomass components.More importantly,organic solvent degumming waste liquid can realize the recycling of organic solvents,reducing the consumption of chemicals in the degumming process and the pollution of wastewater after degumming.Therefore,the use of organic solvent degumming is a degumming method that is more in line with the future development direction.Because of the complexity of the structural components of hemp and the problems existing in the traditional alkali boiling degumming process,the two-step degumming process of organic acid combined with organic alkali was used to prepare hemp fiber,and the effect of organic solvent treatment on the degumming effect of hemp was studied.The structural changes of lignin in the two-step process were further studied,and the mechanism of organic solvent promoting delignification was analyzed.The results are as follows :(1)The effect of organic acid pretreatment on the efficiency of two-step hemp degumming.Effects of different organic acids(formic acid,acetic acid,lactic acid,and glycolic acid)pretreatment on the chemical composition of hemp bast.Subsequently,the effect of the two-step process of organic acid-alkali boiling(NA)on the degumming efficiency of hemp was explored,and compared with the hemp fiber prepared by the traditional alkali boiling process.Finally,the reuse performance of glycolic acid waste liquid was studied.The results showed that glycolic acid(GA)pretreatment showed the best lignin hemicellulose removal effect(removal rates were 27.26 % and 45.12 %,respectively),and glycolic acid still maintained a high hemicellulose removal rate(23.66%)after direct reuse three times.The two-step degumming process of GA20 + 0.5NA can remove 70.22 % of lignin and 84.83 % of hemicellulose.Glycolic acid pretreatment can effectively promote the removal of lignin and hemicellulose by subsequent alkali boiling,and obtain hemp fiber with good dispersibility(11.11 dtex).(2)The effect of organic alkali treatment on the efficiency of two-step hemp degumming.In order to further improve the degumming efficiency and reduce the production of degumming waste liquid,the organic alkali which can effectively dissolve lignin was selected as the alkali treatment reagent in the two-step process,and then the effect of organic alkali treatment on the degumming efficiency of two-step hemp was studied in detail.Firstly,the effects of two organic alkalies(ethanolamine and triethylamine)treatments on the chemical composition of hemp phloem were compared.The ethanolamine(ETA)treatment showed higher delignification ability,with a lignin removal rate of 85.95% and hemicellulose removal rate of 41.84 %.Subsequently,the effects of ethanolamine treatment temperature and time on the efficiency of hemp degumming were studied.Through single-factor experiments,the optimal treatment conditions of the glycolic acid-ethanolamine two-step process were determined: GA100°C 10 % 1 h + ETA 110°C 2 h.At this time,the hemicellulose removal rate was50.18% and the lignin removal rate was 88.46%.Compared with the traditional alkali cooking degumming process,the two-step process of glycolic acid-ethanolamine avoids the use of sodium hydroxide and various alkaline additives,shortens the process time,and prepares hemp fiber with fineness of 10.09 dtex and breaking strength of 3.16 c N/dtex.Finally,the effect of the reuse of ethanolamine wastewater on the degumming effect of hemp was studied.The results showed that ethanolamine had high lignin solubility in the process of reuse,and the lignin removal rate of ethanolamine wastewater could still reach79.80% after four times reuse.(3)Study on the separation mechanism of lignin in two-step degumming process.Lignin was extracted from raw bast fiber,glycolic acid treated fiber,sodium hydroxide treated fiber and ethanolamine treated waste liquid respectively.By studying the structural changes of lignin under different treatment systems,the synergistic mechanism of organic acid pretreatment on lignin removal and the solubilization mechanism of lignin in ethanolamine treatment were analyzed.The results showed that hemp lignin was GSH grass lignin.Glycolic acid pretreatment mainly acts on the β-β bond of lignin,while the β-O-4 bond is relatively retained,and the repolymerization of lignin is effectively inhibited,which is beneficial to the removal of lignin during alkali cooking.In the treatment of ethanolamine,lignin underwent amination reaction,which increased the solubility of lignin,and ethanolamine showed high delignification ability. |
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