Study On Process Optimization Of Choline Chloride-urea For Ramie Degumming And Recyling Of Solvents

Ramie is an important perennial herb,from which ramie fibers are obtained by removing surrounding gums.Ramie fibers have many advantages,like long length,high strength,good luster,etc.,which are known as the “queen of natural fibers”.In terms of chemical composition,raw ramie is consisted of cellulose and gums.It is necessary to remove gums through the degumming process to extract ramie fibers with excellent mechanical properties for subsequent spinning processes.Nowadays,the most widely used degumming methods are chemical methods.Although the degumming effect is stable and mechanical properties of degummed fibers are high,there are many challenges should be addressed,such as long process,high energy consumption and irreparable environmental problem.Therefore,it is meaningful for society and ecology to develop a high-efficiency,low-cost,and pollutionfree degumming process.The emerging deep eutectic solvents have many outstanding characteristics such as easy availability,low melting point,recyclability,and recovery.They are generally divided into four types,namely type ? to type ?,where the components of type III deep eutectic solvents are usually non-toxic,degradable,and green organics.Currently,type III deep eutectic solvents have been applied in the field of wood biomass pretreatment,and more explorations are needed for related studies.A deep eutectic solvent composed of choline chloride and urea was chosen to extract ramie cellulose fibers in this study(the whole degumming technique can be completed in one-step boiling process).For purpose of minimizing the cost and realizing sustainable development of degumming process,the feasibility of recyclability of degumming solution is explored.Meanwhile,lignin and polysaccharides could be extracted from the degumming solution,realizing value-added utilization of additional products.More details of the research are summarized as follows.Choline chloride-urea,choline chloride-ethylene glycol,choline chloride-glycerol and choline chloride-lactic acid were used for screening effective degumming solvent.Choline chloride-urea was determined to be the best solvent among the four by comparing the weight loss rate,appearance,and mechanical properties of prepared fibers,which was proved to be suitable for ramie degumming.The single-factor control method was carried out to explore the influences of three parameters(molar ratio,temperature,and time)on the degumming effect.The degumming effect is evaluated through tenacity,breaking elongation,and density of the degummed fibers.The results indicated that the appropriate molar ratio of solvent are1:1.5,1:2,1:2.5 and the optimal range of degumming temperature and degumming time is from 150 to 170°C and from90 to 120 min,respectively.For optimizing the degumming process,the orthogonal experiments were carried out.And the degummed fibers were characterized by different analysis.The results revealed that the mechanical properties of ramie fibers were relatively good when the molar ratio is 1:2,the temperature and time are 170? and 90 min respectively.The mechanical properties of ramie fibers treated by the choline chloride-urea deep eutectic solvent were basically the same as those by traditional alkaline method.Compared with raw ramie,the cellulose content,the crystallinity,and the pyrolysis temperature of the fibers obtained from choline chloride-urea deep eutectic solvent were all greatly increased.It could be seen from the FESEM images that the surface of the fibers degummed by choline chloride-urea deep eutectic solvent was relatively smooth and free of impurities.It can be observed through the NMR spectrum that the cellulose structure of degummed fibers is almost unchanged.The possibility of cyclic degumming of the degumming solution was explored.The recycling times of degumming solution were determined by the DP,the mechanical properties,residual gum,and yield of fibers.In conclusion,it can be proved that the choline chloride-urea deep eutectic solvent possesses the ability of repeated degumming(degumming solution could be recycled at least 4 times),and the cost is greatly reduced,which brings the possibility to realize the widely used of the choline chloride-urea degumming process.