Study On Technology And Process Mechanism Of Precise Degumming Of Flax Roving With Bacillus Subtilis HR5

Flax fiber is known as the"queen of natural fibers".The flax is made into roving through retting,carding and other processes,and the roving made into spinning after degumming.Among them,degumming of flax roving directly determines the quality of spun yarn.Chemical method is widely used in flax roving degumming industry,which has bottleneck problems such as large fiber damage,high cost and large pollution.Therefore,it is imperative to establish a green and environmentally friendly biological degumming technology and realize green processing of flax fiber,which is in line with the requirements of the national green development strategy.Flax fibers are short fibers,the fibers are connected by gum,which cannot be completely removed,and the lack of uniform standards for the degree of gum removal,resulting in the degumming process cannot be accurately controlled,making it difficult to obtain a stable degree of degumming of flax roving fibers.Therefore,this study was carried out to develop a standard for the biological degumming of flax roving,the screening of degumming microorganisms and the development of degumming technology,as well as the analysis of the mechanism of the biological degumming process,to build a biological precision degumming technology system for flax roving and to guide the application of biological degumming of flax roving.The main research results are as follows:1.The biological degumming standards for flax roving are defined to enable precise control of the degumming process.The study measured the gum composition of flax roving after multiple batches of degumming in industrial production,combined with the grey system to establish a model of gum content and yarn strength,based on which a standard for biological degumming of flax roving was proposed:the degumming rate of flax roving should be controlled at45%～51%,the pectin and hemicellulose content after degumming should be controlled at0.59%～0.81%,11.83%～12.61%,and the content of wax,water soluble matter and lignin should be maintained at 0.38%～0.54%,1.61%～2.16%,1.24%～1.52%;based on degumming standards,the weak points（dislocations）in flax fibers can be effectively controlled to prevent them from being damaged during degumming and affecting fiber strength.2.A strain with good degumming performance of flax roving was obtained by screening.Through genome analysis and degumming process optimization,the application potential of this strain in degumming of flax roving was evaluated.The degumming effect of the screened microorganisms was evaluated by using the agar medium containing only chopped flax roving,and the Bacillus subtilis HR5 with the best effect was obtained,which can rapidly degrade the gum without damaging the fibers.The strain HR5 has a genome size of 4.19 Mb and 24 genes for enzymes related to degumming,including 5 genes for mannanase,9 genes for xylanase,7 genes for pectinase and 3 genes for cellulase;the strain contains a variety of antibacterial synthetic gene clusters and has ability to resist miscellaneous bacteria.The optimum degumming conditions of flax roving with strain HR5 were established through process optimization:degumming temperature 37℃,liquor ratio 1:60,oxygen deliver coefficient 99.5 h^-1,the inoculum amount was 5%,and the degumming cycle was 24 h.Under the optimum degumming conditions,it hardly secretes cellulase and does not cause damage to the roving fiber,and the activities of mannanase and xylanase are high,the activity of pectinase is moderate,and the degumming rate of roving is 35.1%.The strain has good degumming performance and has application potential.The degumming effect can be further strengthened by innovating the entire biological degumming technology system.3.The biological precision degumming technology system for flax roving based on pretreatment and synergy was created.In this study,a high-pressure moist-heat compound sodium citrate pretreatment technology was established,which improved fiber dispersibility,promoted the pre-removal of gum,eliminated the interference of bacteria,promoted the rapid growth and enzyme production of inoculated microorganisms,and significantly increased the degumming rate to 45.5%,and the degumming cycle could be shortened to 20 h.The biological degumming technology was researched on the pilot scale,combined with the established degumming standards,the flax roving was pretreated with sodium citrate,adjusted for roving winding elasticity and controlled by the microbial degumming process,and supplemented with oxygen bleaching treatment to build an in-situ biodegumming technology system.The results of the pilot test showed that the degumming rate of roving was 45.2%,and the contents of wax,water soluble matter,pectin,hemicellulose,and lignin were 0.45%,1.83%,0.66%,11.85%and 1.35%,which met the preset biological degumming standard.Compared with chemical degumming,the degumming process does not need to use acid,and the amount of alkali is reduced by 91%.To realize the high-value utilization of degumming waste liquid and reduce the cost of wastewater treatment,the composition of biological degumming waste liquid was analyzed by nuclear magnetic¹H-NMR.It was found that the degumming liquid could be used for production of oil by Mortierella alpine.After the degumming waste liquid was used,COD and BOD₅concentrations dropped significantly4.The mechanism of the degumming process of flax roving by Bacillus subtilis HR5 was revealed.Transcriptome analysis was performed on the degumming process of Bacillus subtilis HR5,the flax roving were pretreated with sodium citrate and then degummed.The citric acid cycle,glycolysis pathway and pentose phosphate pathway of the strain were enhanced,indicating that the pretreatment with sodium citrate which could strengthen the above pathways,promoted the rapid growth of Bacillus subtilis HR5,and then improved the degumming effect.In the early stage of degumming,the expression of hemicellulase genes were high,and mannanase and xylanase played a major role.With the degradation of hemicellulose,pectinase began to play a role.During the degumming process,hemicellulase’s sequence of secretion and expression were earlier than that of pectinase.The strain HR5 has a complete metabolic pathway for gum monosaccharides such as mannose,xylose and galactose,which are degraded to monosaccharides and converted into glucose-6-phosphate,glyceraldehyde-3-phosphate and pyruvate in the bacterium to participate in the glycolytic pathway and provide energy for the growth of the strain.In addition,the microscopic observation of the distribution of the strains and the morphology of the gum showed that the strains had a movement tendency,which could tend to adsorb to the gum,secrete degumming enzymes to degrade the gum,and separate from the fibers with the gum removal without damaging the dislocation area.Bacillus subtilis HR5adsorbs gum and secretes degumming enzyme,which promotes gum degradation,disperses fibers,and completes degumming of flax roving.This study establishes a system for the biological and precise degumming of flax roving,reveals the mechanism of action of the microbial degumming process,and the flax yarn produced by the biological degumming technology meets the requirements of national first-class products and significantly reduces the amount of acid and alkali chemicals,providing theoretical and technical support for the industrial application of biological degumming technology for flax roving.