Study On Modification Of Hemicellulose In Papermaking Waste Liquor And Its Biological Activity

In recent years,with the rapid development of biomass refining,people have paid more and more attention to the comprehensive utilization and development of plant fiber raw materials and papermaking waste,which can not only replace the gradually reduced fossil-based materials,but also improve the disadvantage of low efficiency and high pollution of traditional utilization methods.In this paper,APMP(Alkaline Peroxide Mechanical Pulping)pulping waste liquor,which is the most noticeable in the paper industry,is used as a raw material to separate and purify hemicellulose,and modify it according to its structural characteristics so that it can be reused.At the same time,it can also improve the efficiency of papermaking enterprises,which is in line with the green development concept of modern ecological industry.There are scores of free reactive hydroxyl groups on the side chains of hemicellulose,which are similar in nature to low-molecular-weight alcohols.They react with acids to form esters and react with alkylating agents to form ethers,and it can be cross-linked and modified to prepare hemicellulose-based materials.In this paper,the hemicellulose extracted from the waste liquor of papermaking is used as the raw material.At a temperature of 75?,the molar ratio of NaOH/ClCH2COOH is 1:2;the reaction is performed for 2 h,and the final synthesis of carboxymethyl hemicellulose with a degree of substitution(DS)of 1.47.And using FT-IR,1H-NMR and 2D HSQC technology to characterize hemicellulose and carboxymethyl hemicellulose,and finally determine the xylose unit C-2 and C-3 position of the hydroxyl group has been successfully replaced.At the same time,the molecular weight and thermal stability of carboxymethyl hemicellulose were characterized by gel chromatography(GPC)and thermal weight loss analyzer(TGA),and finally the molecular weight and thermal stability of the modified product were increased.There are unsubstituted active hydroxyl groups on carboxymethyl hemicellulose,which can be esterified with acid.Using the above carboxymethyl hemicellulose(DS=1.47)as the raw material,in a homogeneous medium N,N-dimethylacetamide/lithium chloride system,p-hydroxybenzoic acid was added,and esterification reaction occurred to generate carboxymethyl hemicellulose p-hydroxybenzoate.Response surface methodology was used to optimize the esterification process.The optimal process conditions were obtained using Design Expert software:the reaction temperature was 79.08?,the reaction time was 4.98 h,and the amount of p-hydroxybenzoic acid(mol/mol)was 2.14.Under these conditions,the degree of substitution in the esterification reaction was 0.232.Biological activity research on HC,CMHC and P-CMHC,the results show that HC modified CMHC and P-CMHC have a strong free radical scavenging rate,up to 100%,that is,strong antioxidant.At the same time,CMHC and P-CMHC are both more hygroscopic and moisturizing than HC,and have strong hydrophilicity and water retention;in terms of antibacterial properties,both CMHC and P-CMHC have obvious antibacterial activity against Bacillus subtilis and Salmonella,and P-CMHC is stronger.The MTT method was used to determine the cytotoxicity,and according to the cytotoxic grading relationship,the final cell proliferation rates of CMHC and P-CMHC were both greater than 100%,which belonged to grade 0 and had no cytotoxicity.Finally,hemicellulose extracted from APMP pulping waste liquor is used as a raw material,and N,N-methylenebisacrylamide(MBA)is used as a cross-linking agent,and monomer acrylic acid(AA)is converted by free radical polymerization graft copolymerization.Acrylamide(AM)was grafted onto the molecular chain of hemicellulose and cross-linked modified to prepare hemicellulose-based hydrogel.According to the experimental determination,the hydrogel is sensitive to temperature/pH,and the sensitivity mechanism is analyzed.In addition,this study explored the water retention properties of hydrogels,and the results showed that the prepared hydrogels had very good water retention,the water retention rate at pH 6(water)was 79.46%(144 h).These properties indicate that hemicellulose-based hydrogel materials can be used in the fields of industry and agriculture or biomedicine in the future.