Study On Isolation, Carboxymethylation Of Hemicellulose From Bamboo And Properties Of Its Composite Film

In recent years,the exploitation and utilization of lignocellulosic biomass resources has become a global research hotspot.The preparation of biodegradable biomass-based composite membranes based on hemicellulose has received extensive attention.However,due to the low molecular mass of hemicellulose itself,the membrane material prepared based on hemicellulose generally displays poor film formation,strength and flexibility,so it is necessary to improve the application performance of hemicelluloses via additive application or surface modification strategy.Based on this,this study focused on the isolation,carboxymethylation modification of hemicellulose from bamboo,and its composite film properties.The current study mainly investigated the influence of the degree of substitution（DS）on the properties of carboxymethyl hemicellulose and its composite film,which might provide theoretical basis and technical support for the high-value application of hemicellulose.The effects of reaction conditions on hemicellulose yield and monosaccharide content were investigated based on univariate experimental method.With the increase of KOH content,H₂O₂ content,liquid-solid ratio,reaction time and reaction temperature,the hemicellulose yield exhibited a trend from rise to decline.The optimal reaction conditions were determined as follows:a liquid-solid ratio of 20:1（KOH content of3.0wt%,H₂O₂ content of 1.8wt%）,a reaction temperature of 60℃,and a reaction time of6 h.Based on the above conditions,the yield of hemicellulose reached 18.00%and the total sugar content touched 72.32%.The isolate hemicellulose was characterized by SEM,FT-IR and TG methods.SEM images indicated that the hemicellulose from bamboo isolated by alkaline hydrogen peroxide method exhibited an irregular flocculent structure with a rough surface.FT-IR results revealed that the C-O stretching vibration peak andβ-（1,4）glycosidic bond characteristic absorption peaks of xylan appeared at 1018 cm^-1and 898 cm^-1,indicating that the main chain of hemicellulose was formed byβ-（1,4）glycosidic bonds between xylose units.TG analysis displayed that the hemicellulose pyrolysis could be divided into three stages,with the main pyrolysis range from 200 to300°C and the maximum weight loss at 257°C.Carboxymethylation modification of hemicellulose was carried out with ultrasound assistance.The effects of reaction conditions on the DS of hemicellulose were investigated,and SEM,FT-IR,GPC,TG,Zeta potential,and other methods were used to characterize the carboxymethyl hemicellulose with different DS.The experimental results demonstrated that with the increase of Na OH concentration,Cl CH₂COOH concentration,alkali treatment time,etherification time and etherification temperature,the DS of carboxymethyl hemicellulose showed a trend of rising first and then decreasing.The increased alkali treatment temperature was found to lead to the decreased DS of carboxymethyl hemicellulose.The optimal conditions for carboxymethylation modification of hemicellulose were illustrated as follows:Na OH concentration of 1.2mol/L,Cl CH₂COOH concentration of 0.6 mol/L,alkali treatment time of 40 min,etherification time of 150 min,alkali treatment temperature of 30℃,and etherification temperature of 70℃.Based on the optimal conditions,the DS of the carboxymethyl hemicellulose could attain 0.59.SEM images exhibited that compared with unmodified hemicellulose,carboxymethyl hemicellulose was more densely cross-linked and the lamellar structure was more pronounced.FT-IR results revealed that the C=O and C-O-C stretching vibration peak signals of carboxymethyl hemicellulose at 1611 cm^-1 and1315 cm^-1 were significantly enhanced,indicating that the modified carboxymethyl functional groups were successfully grafted onto hemicellulose.In addition,the thermal stability,solubility and electronegativity of carboxymethyl hemicellulose were significantly improved with the increase of DS.The carboxymethyl hemicellulose/sorbitol/gallic acid composite films were prepared via solution casting method.The microstructure,chemical structure,mechanical properties,air permeability,antibacterial properties,light transmittance,and preservation performance of the composite films were evaluated.The experimental results showed that the DS of carboxymethyl hemicellulose had an important influence on the relevant properties of composite films.The film-forming property and mechanical properties of the composite films improved with the increase in the DS of carboxymethyl hemicellulose,as well as the air barrier properties and light transmission were also significantly improved.In comparison to the hemicellulose composite film,the elongation at break of the composite film with carboxymethyl hemicellulose（DS=0.33）was increased by154.91%;the air permeability of the composite film with carboxymethyl hemicellulose（DS=0.59）was decreased by 48.31%and the light transmission at 800 nm was increased from 60.36%to 85.42%.The results of antibacterial experiments illustrated that with the increase DS of carboxymethyl hemicellulose resulted in the improved antibacterial effect of the composite films.Compared with the hemicellulose composite film,the zone of inhibition of the carboxymethyl hemicellulose（DS=0.59）composite film against Staphylococcus aureus increased from 24 mm to 27 mm.The results of preservation experiments of the composite film displayed that the increased DS of carboxymethyl hemicellulose led to the enhanced preservation impacts of the composite films on blueberries,thus facilitating the reduced weight loss rates of blueberries.After 9 days of storage,the weight loss of blueberries in the blank group was 20.34%,while the weight loss of blueberries in the coated group attained 15.36%（DS=0.59）.