The Isolation And Characterization Of Hemicellulose From Flax And Switchgrass

Flax is an important textile raw material with a variety of excellent properties,and its cell wall structure is complex,usually requiring the removal of a part of the cellulose companion organism(gum)to extract the spintable fiber.There is currently little basic study on the amount of residual gum in flax fiber,hence scientific theory or consensus have not been established.It has been suggested that the lignin is harmful to the characteristics of fiber and must be entirely eliminated.For now,there is no clear conclusion about the relationship between the physicochemical properties and fiber properties of pectin and hemicellulose polysaccharides.As a result,the most critical work of hemicellulose reuse has been systematically studying the content,structure,and correlation with the properties of hemicellulose fibers and their extraction methods in order to seek comprehensive utilization of cellulosic materials,which is of great importance for basic theory research related to hemicellulose.This research takes hemicellulose polysaccharide as the research object.First,we reviewed the structure of hemicellulose,the separation method and its application,the research of flax development and utilization,and chemical composition,the profile of switchgrass and its processing and utilization.Second,the influence of hemicellulose polysaccharide components on fiber characteristics and changes in the chemical composition of hemicellulose in flax after scouring and bleaching were investigated in depth.The degradation mechanism and difficulty of degradation of hemicellulose polysaccharides in the scouring and bleaching process were also explored through the deconstruction of hemicellulose polysaccharides in flax fiber.Then,from the standpoint of structural study and exploitation of hemicellulose polysaccharides,borate alkaline and cellulolytic enzyme-assisted methods were used to isolate hemicellulose polysaccharides with various compositions,structures,and properties from switchgrass,and the characteristics of their products,as well as their effects on the composition and structure of cellulose residues after extraction,were investigated.Hemicellulose is the most essential component of flax gum since it is a composite polymer made up of several polysaccharides.In terms of the residual components in flax fibers after degumming,the previous studies have focused on the levels of lignin,hemicellulose,pectin,water solubles,and wax.After analyzing the cellulose polymerization degree(DP),crystallinity(Cr I),hemicellulose polysaccharides composition and ratio,and lignin content after treatment,the effect of scouring and bleaching methods on the chemical composition of flax fiber was studied in this paper.The Cl-AO,EAO,and AO were all heterogeneously hydrolyzed in terms of hemicellulose component content,but AA was less impacted by polysaccharide types.The mechanical and apparent properties of flax fibers were characterized after scouring and bleaching to study the correlation between the content and proportion of hemicellulose polysaccharides(xylan-XYL,galactoglucomannan-GGM,and glucomannan-GM)and the properties of flax fibers.The linear regression relationship between the chemical components of flax fibers,especially the content of hemicellulose polysaccharides,and their physicochemical properties was analysed by Origin.The presence of XYL and GGM hemicellulose components in flax samples was negatively correlated with mechanical properties of flax fibers,whereas the content of GM in hemicellulose of flax samples was positively correlated with mechanical properties of flax fibers.This suggests that the presence of XYL and GGM hemicellulose components may have a negative effect on the strength and elongation properties of flax fibers.The morphology of flax fiber and the XYL/GM ratio had a significant relationship.The trend is backed up by a strong link between the XYL/GM ratio and fiber morphological features,with the greater the XYL/GM ratio,the longer and finer the fibers are.Nonetheless,flax fibers with a low XYL/GM ratio have better tensile strength,length,and fineness.To better understand the influence of chemical composition on the mechanical and morphological qualities of flax fibers,the changes in the chemical structure of flax fiber during different scouring and bleaching methods were explored in detail in this work.To analyze the changes in hemicellulose fractions during the scouring and bleaching process from the molecular point,the three polysaccharides of flax hemicellulose were isolated and obtained after exploring the effects of extraction time and the number of extractions of the concentrated alkali-soluble boric acid complexation separation and grading method.Following that,chromatography and nuclear magnetism technology were used to deconstruct the distinct polysaccharides of flax fiber hemicellulose.This research focuses on the extraction,separation,and characterization of flax hemicellulose,as well as the use of instrumental analysis to characterize the structure of flax hemicellulose polysaccharide and provide a theoretical foundation for studying the influence of hemicellulose on fiber properties.With intense alkali dissolving and boric acid complexation,the hemicellulose polysaccharides were isolated progressively from flax roving.The yield of XYL,GM,and GGM separated by Ba(OH)₂ aqueous solution was 16.7%,23.4%,and 47.7%,respectively,of total hemicellulose.The yield of hemicellulose was 87.6%.The structure of the flax hemicellulose component XYL was established by NMR spectra to be L-arabinose-glucuronic acid-D-xylan.The backbone of the GGM is repeated(1?4)-?-D-Map and 4-?-D-Glcp(2.05:1),with the side chain(1?3)-?-D-Man and?-D-Glc.When compared to GGM,there was no branched galactose,indicating that they are not the same polysaccharides from different fractions.Glucuronate groups in XYL are highly reactive with scouring and bleaching chemicals.XYL>GGM>GM is the order of removal.For a more efficient and convenient extraction of XYL,this study focused on the XYL-rich switchgrass.NaOH/boric acid system(NaOH/H₃BO₃)applied to the hemicellulose extraction of XYL was investigated to understand if applying boric acid shifts the product's yields and components.The effects of boric acid on the structure of the switchgrass residues and the extracted hemicellulose were also investigated.The hemicellulose extracted with borate alkaline had a larger amount of xylan(63.79%)than the solution without boric acid,according to the chemical composition of the extracted hemicellulose.Furthermore,hemicellulose extracted with borate alkaline had a larger molecular weight(M_w=51.2 k Da)and a lower degree of polydispersity than hemicellulose extracted with alkaline(1.3).The galactose concentration of borate alkaline extracted hemicellulose is significantly higher than that of conventional alkaline extracted hemicellulose.Additionally,compared to alkaline extraction,the presence of borate had a protective impact on hemicellulose extraction in terms of chain scission or fracture,resulting in a larger amount of uronic acids.Chemical approaches for hemicelluloses isolation had some drawbacks,such as structural change and pollution of the environment.Cellulolytic enzyme-assisted xylan extraction was utilized to investigate the prospect of a non-polluting hemicellulose extraction process with reduced structural damage and a high branching degree,in order to better define hemicellulose structures for successful usage.In this study,a novel cellulolytic enzyme-aided hemicellulose(CEH)isolation method was developed for the separation of hemicellulose with a natural branching structure.In detail,the holocellulose was firstly prepared by the removal of lignin using peroxyacetic acid(PAA)method.The CEH was separated from the cellulose residue by enzymatic hydrolysis of the cellulose and the alcoholic precipitation reaction of hemicellulose polysaccharides after the holocellulose was hydrolyzed in a buffer containing cellulase.The yield of CEH increased significantly as the cellulase dosage was raised.Structural characteristics of CEH were investigated and compared with hemicelluloses isolated by conventional alkaline extracted hemicellulose(AEH)and DMSO extracted hemicellulose(DMSOH)methods.Gel permeation chromatography(GPC)analysis indicated that the CEH had a weight-average molecular weight of 44 k Da,which was comparable with AEH(43 k Da)but higher than DMSOH(37 k Da).The chemical composition analysis revealed that the CEH retained a higher proportion of glucuronic acid compared to the AEH and DMSOH.The CEH showed a highly branched hemicellulose structure,which retained methoxyl groups,O-Acetyl groups,and 4-O-methyl-glucuronic acid attached to the xylan backbone.In conclusion,CEH is a new method that can minimize the hydrolysis of hemicellulose,which could be used to evaluate the initial structure of hemicellulose to determine its industrial applications.