Investigation On Refinement Of Hemp Fibers And High-count Hemp/Cotton Blended Spinning Technology

Hemp fiber is one of the most important raw materials as textile fibers.Because it contains phenolic compounds such as tetrahydrocannabinol which can be used for the production of drugs,hemp fibers were included in the international drug control list.Consequently,the cultivation of hemp was strictly controlled and the development of hemp fiber had fallen to the bottom.With the cultivation of low-toxic or non-toxic hemp,hemp which had a glorious history in China and the world,had returned back and caught people's attention.Under the background of green environmental protection,circular economy and sustainable development,the structural performance,processing technology and comprehensive utilization of hemp fiber have been extensively studied and laid the theoretical foundation for the development of industrial technology.Although the research on hemp fiber has never ceased over years and some breakthroughs have been made in the relationship between chemical composition,morphological structure,and performance.However,for the reason of short fiber length and high lignin content of the single hemp fiber,how can meet the spinning requirements and ensure the demands of high-count final hemp products in the textile industry has become an issue.The research on the highly efficient and environmentally-friendly degumming process has always been a technical problem that cannot be solved.In addition,due to the short and poor cohesion of the hemp fibers in the spinning process which can lead to extra drop of fiber and low quality of yarn,limit the use of hemp fibers in high-quality textile products and applications.On the one hand,the problem of hemp is fundamentally due to the stability of its own performance.As one kind of natural fiber,hemp fiber comes from nature,and different growth environments,harvesting time,or sampling sections will make a big difference in its performance.The lignin content,which is an important index for evaluating the degumming effect of hemp fiber,is currently used the measurement method for the quantitative analysis method of ramie chemical composition?GB/T5889-1986??hereinafter abbreviated as:86th standard?.The discrepancies of the results are extremely large,which poses a significant obstacle to the evaluation of the quality of the technical hemp fibers.Therefore,this paper first proposes some improvement in the lignin determination method which based on the existing method,and studies the differences among hemp raw materials,which lays a foundation for the subsequent selection of degumming processing of raw materials;secondly,in order to improve the degumming efficiency,physical and mechanical properties of degummed hemp fibers without the extra damage on the cellulose in hemp,through different degumming process and the adjustment of the parameters during the process,the degumming effects of different pretreatment methods,laccase treatment,the use of scouring agent and2,2,6,6-Tetramethyl-1-piperidinyloxy?TEMPO?-laccase system on hemp raw hemp were discussed,respectively.On the other hand,the current research based on hemp spinning is mostly limited to the blending of different raw materials into yarns.As a natural fiber with various special functions?such as antibacterial,deodorant,anti-ultraviolet,etc.?,the products of hemp fibers should be high-grade.Focusing on the spinning process,the high-count hemp yarns is a problem that must be solved.This article studies how to reduce the control of hemp falling during the process of spinning,and discusses the after-spinning processes,especially the settings of roving twist coefficient which affected the final quality of the hemp/cotton blended yarn.The main conclusions obtained are as follows:Based on the theory that the ultrasonic treatment could lose the lignin physical structure in hemp fibers.The ultrasound-assisted sulphuric acid method was used as a method for the determination of lignin content.The effects of ultrasonic treatment time,concentration of concentrated sulphuric acid and hydrolysis time on the determination of lignin content were studied.The best process parameters of ultrasound-assisted sulphuric acid method was as follows:the ultrasonic treatment time is 15 min;the concentration of concentrated sulphuric acid is 72%;and the hydrolysis time is 12 h.Then,the same hemp fibers were treated with ultrasound-assisted sulphuric acid method and the 86th method for the determination of lignin content.The stability was also analyzed.The standard deviation and relative standard deviation were reduced from 4.06%and 29.53%to 0.15%and 0.25%,respectively,indicating that the ultrasound-assisted sulphuric acid method were more stable and reliable.Secondly,the chemical composition and structure,crystal structure,cross-sectional morphology and physical properties of raw hemp fiber were tested and analyzed on the raw hemp fiber according to the different harvesting time and sampling sections on hemp stems origin from the same cultivating area.With the increase of fiber maturity,the content of lignin in the raw hemp fiber increased significantly,especially the hemp fiber in the top and middle sections.The increment of lignin was particularly obvious,and the difference between the contents was up to 3.02%;meanwhile,the content of water soluble substance decreased with the increase of the fiber maturity,and the difference of the water content between the early and the late hemp fibers in the bottom of hemp stem was 3.93%.But the difference of other non-cellulosic substances was relatively smaller.The differences between the chemical components were also confirmed by the further tests of infrared spectroscopy and X-ray diffraction.The inhomogeneity of the raw hemp fibers had a significant effect on the subsequent refinement process and had been confirmed by the test of the physical properties of degummed hemp fibers.When the same degumming process was used on different raw hemp fibers,the test results showed that the length and fineness of the treated fiber samples varied greatly:after degumming,the early fibers obtained from the top section had the shortest technical fiber length?11.36 dtex?and the finest fineness?42 mm?.And,the longest technical fiber was the early hemp fiber obtained from the middle section?67 mm?;the strongest fiber was the early hemp fiber obtained from the bottom section?21.55 dtex?.For the refinement of raw hemp fibers,this paper discussed several aspects including the choice of pretreatment method,scouring agent,the degumming effect of laccase and TEMPO oxidation treatment.Firstly,three pretreatment methods:pre-alkaline treatment,pre-oxygen treatment,and pre-ultrasonic treatment,were explored,and their optimal process parameters were obtained respectively.Then,the optimal parameters of pretreatment method were compared with each other to obtain the optimal pretreatment method.The pretreatment which had the best degumming effect was pre-alkaline treatment and the best parameters were obtained.?where:the sodium hydroxide concentration is 5 g/L,the temperature is 70°C.,the bath ratio is 1:25,and the treatment time is 120 min?.With this pre-alkaline treatment,the colloid removal rate could reach 26.3%,and the hemicellulose component removal effect was significantly improved compared with two other pretreatments.Based on the determination of the pretreatment method,the effects of various factors?laccase concentration,time,and liquor ratio?on the lignin removal of raw hemp fibers with the two-bath alkaline-laccase degumming process were further discussed.And a numerical regression of the final lignin content with three factors was obtained?y=-0.128₁-0.335₂-11.893₃+24.53₃²+15.123,where:y was the lignin content,x₁ was the laccase concentration,x₂ was treatment time,and x₃ is the liquor ratio?.This regression could predict the lignin content of the alkaline-laccase degumming process and achieve the aim of controlled degumming process.Subsequent verification tests also demonstrated the feasibility of this regression equation.At the same time,the results of infrared spectroscopy and scanning electron microscopy showed that the pre-alkaline-laccase system had good effects on the removal of non-cellulosic material,especially the lignin component.The content of lignin of the degummed hemp fibers was 11.06%.In view that the residual non-cellulosic material in the degummed fiber which obtained from the pre-alkaline-laccase treatment was still too large to meet the requirements for subsequent spinning process,so subsequent alkali scouring treatment was required.The process of the alkaline process had been excessively explored by researchers for many years.This paper mainly studied on the addition auxiliaries?chelators,reducing agents and surfactants?in the alkaline scouring process.Under the laboratory conditions,take the weight loss rate of fiber as the main evaluation criteria,it found that sodium pyrophosphate as a chelating agent and sodium sulfite as reducing agent can enhance the effect of alkali scouring process.For the selection of surfactants,complex synergistic effects among sodium lauryl sulfate?K12?,laureth polyoxyethylene ether?AEO-9?,tea seed powder?TSP?and sodium carboxymethyl cellulose?CMC?were discussed through orthogonal test analysis.Based on the analysis of the polarity,variance and the rotation sum of squares of the lignin residue content of the degummed hemp fibers,the optimal compounding ratio was obtained combined with the results of the weight loss rate of the degummed hemp fibers?50.78%K12,7.81%AEO-9,15.63%TSP,25.78%CMC?.In order to reduce the consuming amount of sodium hydroxide in the refinement process,the high selective TEMPO oxidation system could be used as a refinement method for the removal of non-cellulosic material in hemp fibers with the control of the reaction degree.Firstly,TEMPO-laccase alkaline system was used as a pretreatment method,followed by alkali scouring treatment to explore the feasibility of this system in the refinement of hemp fibers.And the role of sodium hypochlorite was also discussed.It was found that TEMPO-laccase alkaline pretreatment system could effectively remove the non-cellulosic substances from the raw hemp fibers.And when the amount of sodium hypochlorite was 16%,the effect of the gum removal was most obvious:the residue gum rate was only 9.12%,and the lignin content was 4.58%.The removal of lignin and other non-cellulosic materials is mainly caused by the oxidation of the primary C6 hydroxyl groups on the carboxyl groups.The chemical structure,crystalline structure and nuclear magnetic resonance spectroscopy can confirm the occurrence of this oxidation reaction from the qualitative point of view.The change of the functional group further clarified from the quantitative point of view the fundamental reason why TEMPO mediated oxidation can remove non-cellulosic substances.The strength of the degummed hemp fiber after the TEMPO-laccase alkali treatment system obtained with 16%sodium hypochlorite was 3.24 cN/dtex,and the breaking elongation was 3.49%.On the basis of ensuring the effective removal of the non-cellulosic material,the mechanical performance can also meet the requirements of the following spinning process.Although the properties of the degummed hemp fibers obtained by the TEMPO-laccase alkaline system were acceptable.But the treatment process was slightly cumbersome which consisted of three steps,so the two-step TEMPO-laccase acid system combined with alkali scouringcwas preliminarily explored.It had been found that this system can further reduce the lignin content and residue ratio of the degummed hemp while simplifying the refinement process.The final degummed hemp technical fiber had excellent physical and mechanical properties with a length of 53 mm,a fineness of 4.68 dtex and a strength of 6.69 cN/dtex.The processibility of hemp/cotton blended yarns which was also studied in this article.And the study was mainly focused on the problems of the greater loss of hemp fibers during the hemp/cotton blended yarns spinning process,and the low count and low quality of the final yarn product.Through the selection of raw materials,the equipment modification,the adjustment of process parameters,the selection of process routes and their combining usage,the optimal spinning process was explored.Firstly,through the comparison of the quality of degummed hemp fibers,it was determined that the proper material of hemp fibers for the blended hemp/cotton yarn was obtained from the TEMPO-laccase acid system.The degummed fibers had relatively desirable physical and mechanical properties,which was also confirmed by the spinning test.Secondly,with regard to the improvement of pre-spinning equipment and adjustment of process parameters,the loss of hemp fiber in the improved combed comb program was reduced by 16.7%compared to the original cotton spinning process,and the production rate was also increased from 65%.to 81.7%.However,the quality of the blended yarn obtained after the improvement of pre-spinning process was reduced compared to that before the improvement,which was reflected in the decrease of the twist,the increase in the number of spun yarns,details,and the number of neps,the decrease in the yarn strength,and the increase in the strength variation etc.In order to improve this reduction in the quality of the finished blended yarn,based on the improvement of the low-loss processing technology,the processing of the high-count hemp/cotton blended yarn was explored.The test result was to adopt two drawing process and compact-siro spinning process.According to the different blended yarns counts,reasonable twist coefficient and appropriate reduction of the feeding amount of roving can improve the quality of blended yarn.In the experiments of the twist coefficient of the roving,the 9.8 tex?60^S?,8.4 tex?70^S?,and 7.4 tex?80^S?hemp/cotton blended yarns were spun and tested.Firstly,the trial spinning was performed.Subsequently,pilot spinning was performed by fine-tuning the problems that occurred during the trial spinning process.Through this two-step spinning process,the optimal twist coefficient of the 9.8 tex hemp/cotton blended yarn was 94;the best twist coefficient of the 8.4 tex hemp/cotton blended yarn was 102;the 7.4 tex hemp/cotton blended yarn was The optimal twist coefficient is 96.The quality of the three blended yarns had been significantly improved.