Application Of Carboxymethyl Hemicellulose In Strengthening Paper And Fluorescence Composite Film

In recent years,biomass resources have attracted great attention in many fields including biology,medicine,food,and chemicals due to their abundance,pollution-free,and renewability.Hemicellulose is the second largest content of biomass polysaccharide compounds.However,less research about hemicellulose has been studied compared with cellulose ascribed to its complex structure,especially in high value-added applications.This kind of polysaccharide compound contains lots of functional groups,and thus presents high reactivity,leading to applications such as food packaging,wastewater treatment,paper reinforcement,and drug sustained release.Although hemicelluloses have demonstrated promising application as paper strengthening agents,the influences of different hemicellulosic fractions on the mechanical properties of papers are not clear,which hinder the utilization of hemicelluloses.In addition,hemicellulose can be regarded as an ideal carbon source for the preparation of biomass fluorescence carbon dots through hydrothermal methods because of its abundant carbon,oxygen and hydrogen elements.The synthesis of fluorescence carbon quantum dots?CDs?from renewable biomass is very attractive due to its sustainable and cost-efficient features,and can be applied in fields of biosensor and nano-enhancement.The research contents are as follows:1.Four hemicellulosic fractions(HC_pH5.5,HC_15%,HC_30%,and HC_75%)were extracted from corncob by alkali-ethanol fractional precipitation method.The effects of the physicochemical structure of the four hemicelluloses on the carboxymethyl modification and the strengthening on the secondary fiber were studied.The results indicated that the hemicellulosic fraction HC_15%obtained from 15%ethanol was difficult to be modified due to abundant branched structure and esterification reactions,while HC_75%obtained from 75%ethanol with less branched structure was more easily to be chemically modified.Furthermore,the carboxymethylated hemicellulosic fraction CHC_30%with few branches and the highest molecular weight had a significant effect on improving paper strength.When the content CHC_30%is only 1%,the tensile index,burst index,and tensile energy absorption index of the paper sheet are increased by 27.8%,29.5%and 40.6%,respectively.2.We proposed a facile,universal,and highly effective synthesis method to prepare fluorescent CDs from hemicellulose by hydrothermal treatment and oxygen-alkali decomposition.Compared with the current methods for synthesizing CDs from biomass,our approach offers ultrahigh yield?42.5%based on the weight of biomass and 99.0%based on the weight of HTC?that is much higher than those obtained from other methods.Furthermore,the photoluminescence?PL?quantum yield?QY?is high up to 16.6%.The physiochemical properties of the as-prepared CDs can be tuned by reaction temperature.The fluorescence of CDs can be effectively quenched by Cu²⁺,which enables the application of CDs as fluorescent Cu²⁺nano-probe with a detection limit of 85 nmol L^-1.The ease of operation,mild fabricating condition,and low cost enable our methods a great potential in the large-scale synthesis and application of CDs from biomass.3.Green and biodegradable films with excellent UV-shielding performance were prepared through solution mixing method by using industrial hemicellulose as raw material,and polyvinyl alcohol and CDs as additives.The effects of different contents of fluorescence CDs on the UV-shielding and mechanical properties of the composite film were investigated.The results indicated that CDs were uniformly dispersed in the composite film and formed a stable chemical bond with the hemicelluloses by chemical reaction.The addition of CDs effectively improved the mechanical properties of the hemicellulose/polyvinyl alcohol composite film,where the tensile strength and the elastic modulus increased by 114.3%and 90.7%when 1.92%CDs was added,respectively.There was no significant change in elongation at break.In addition,CDs maintain fluorescence characteristics?typical excitation and emission spectra?in the composite films,resulting in effective absorption of ultraviolet light and conversion into blue-green light.The effect became obvious with the increase of CDs content.In addition,the composite film had good transparency.These results indicate that the composite film shows great potential in UV-shielding application of agriculture and food.