Study On Efficient Separation Of Ramie "Three-Component" And Improvement Of Fiber Properties

As one of the perennial herbaceous plant,ramie fiber is a kind of hemp fibers with excellent quality.The degummed ramie fibers are slender and strong with white appearance and silky luster.Meanwhile,ramie fiber exhibits the advantages of good air permeability,fast dilution and heat dissipation,anti-mold and has been recognized as the"king of natural fibers".However,raw ramie contains large amount of gummy contents(20%?30%),and the biggest problem before spinning is how to fully remove the gummy con tents on the surface of ramie to obtain ramie fibers with excellent properties.At present,the commonly used degumming methods are traditional alkali degumming and biological degumming.However,the disadvantages of high pollution and difficult treatment of degumming wastewater have become the key bottlenecks and challenges restricting the sustainable development of traditional alkali degumming.Comparatively,the environmental pollution of biological degumming is re latively small,but the bacteria and enzymes used in degumming treatment are easily inactivated,which made the degumming effect unstable.Nowadays,most enterprises are trying to optimize the traditional degumming process by exploring the combination of d ifferent degumming methods,but the equipment of combined degumming method is complex and high cost,the degumming process was also long and complicated.Therefore,it is essential to find a new degumming system to simplify the degumming process while ensuring the quality of ramie fibers,so as to realize the efficient and rapid preparation of ramie fibers.Based on this,the thesis explored the possibility of one-step ramie degumming enabled by the green and environment friendly deep eutectic solvent(DES).The basic research contents are summarized as bellow:(1)The synthesized choline chloride/urea(CU),choline chloride/imidazole(CI),ethylamine hydrochloride/ethylene glycol(EE)eutectic solvent were used for ramie one-step degumming,the optimal conditions were:160?of the temperature,2h of degumming time,1:20 of solid-liquid ratio.The residual gum content of fiber reached to the minimum(3%?5%)under the optimal conditions,and the yield was over 70%,which was higher than that of the traditional alkali(TAL)method.SEM test indicated that DES could effectively remove the adhesive gummy materials of ramie fibers.FTIR analysis indicated that the chemical structure of cellulose was not changed after DES treatment,and the strength of characteristic peaks related to non-cellulosic components such as hemicellulose and lignin decreased significantly after DES tretment.XRD analysis showed that compared with raw ramie fiber,the crystallinity index(Cr I)of DES degummed fibers increased by 8.52%(CU),11.68%(CI)and 13.26%(EE),respectively.¹³C-NMR spectra showed that DES could effectively remove hemicellulose and lignin,and EE had the strongest ability to remove lignin among the three kinds of DESs,the second was CU,and the last was EE.Chemical composition analysis showed that compared with the TAL method,DES was more efficient for removing lignin,and the lignin content was much lower than that of TAL method.Raman mappin g test further verified that DES had a strong lignin removal ability.The mechanical test showed that the CU degummed fibers had the highest tenacity,which was very close to that of the TAL treated fibers.The CI degummed fibers showed the highest break elongation,but the EE degummed fibers showed a low breaking tenacity and elongation,which was not suitable for ramie degumming process.The degree of polymerization(DP)of the DES degummed fibers was lower than that of the TAL treated fibers,which may be due to the partial depolymerization of cellulose during the DES degumming process.(2)On the basis of separating ramie fibers,the lignin rich materials(LRMS)and hemicellulose rich materials(HRMS)in the waste solution of the CU degumming solution were separated by“Water precipitation and alcohol precipitation method”,which preliminarily realized the comprehensive utilization of resources.FTIR and UV tests showed that LRMS had a relatively complete lignin structure,and HRMS had an obvious polysaccharide structure.But there is also a small amount of lignin existed in HRMS.The content of acid insoluble lignin in HRMS and LRMS was about 90%and 10%,respectively.The type and content of monosaccharides in HRMS were confirmed by GC analysis,and results indicated that HRMS were composed of six kinds monosaccharides including rhamnose,arabinose and xylose,etc.The content of glucose accounted for more than 34%,while the content of other gyrogroups was less than 10%.(3)Cellulose protective reagent anthraquinone(AQ)was added to the choline chloride/urea DES to improve the mechanical properties of degummed fiber.The experiments showed that compared with fiber degummed without AQ,Cr I,DP value,breaking strength,elongation and rupture of fiber degummed with 0.2 g/L AQ increased by 5.89%,3.31%,20.12%,10.59%and 66.67%,respectively,and the content of cellulose decreased by 1.42%.FTIR analysis showed that AQ could protect carbohydrates and promote the degradation of lignin,the strength of characteristic peak of hemicellulose was increased and the characteristic peak of lignin was decreased.XRD analysis showed that the Cr I of degummed ramie fiber reached to the maximum when the AQ concentration was 0.2g/L.TG analysis revealed that the addition of AQ was benefit for improving thermal properties of ramie fiber,and the maximum thermal decomposition temperature of fiber degummed with AQ was 351?,which was higher than that of raw ramie(331?)as well as fiber degummed without AQ(337?).AQ mainly plays a role in the heat preservation stage(60?120min),in which the fiber yield,residual gum content and mechanical properties increased obviously compared with fiber degummed without AQ.