Efficient Synthesis And Applications Of Functional Hemicelluloses

Preraration of novel and functional biomaterials and biopolymers from biomass hasattracted extensive attention because of the depletion of non-renewable petroleum-basedresources. Exploitation of biopolymers and biomaterials deriving from renewable resources isan important approach to address environmental and resource problems in the world today.Hemicelluloses, comprising the non-cellulose cell-wall polysaccharides of agricultural andforest plants, are considered to be inexhaustible and renewable resources for the productionof functional biopolymers and biomaterials. However, hemicelluloses have not beeneffectively exploited, and the utilization of hemicelluloses is one of the most important andchallenging research areas in agricultural and forest biomass conversion.For the purpose of efficiently conversing agricultural and forest biomass to value addedproducts and promoting the higher value applications of hemicelluloses, the current workfocused on hemicelluloses separation, functional derivatization, and biomaterial preparation,as well as the physico-chemical properties and application potentials of the derivatives andbiomaterials from hemicelluloses. This work not only offers efficient and new methods forpreparing novel and important hemicelluloses-based biopolymers and biomaterials forpapermaking, water treatment, medicine, and food industry, but also facilitates the practicalapplications of hemicelluloses and the high-value conversion of agricultural and forestbiomass.1. Distribution, isolation and physico-chemical characterizations of hemicellulosicfractions from bamboo Dendrocalamus membranaceus Munro (DmM) and wheat straw(Triticum aestivum L). The anatomical and ultrastructure structure of DmM and wheat strawwas studied by using scanning electron microscope (SEM), transmission electron microscope(TEM), and laser scanning microscope (CLSM). The hemicelluloses distribution in the cellwalls of DmM and wheat straw was studied by using monoclonal antibody andcellular immunolabelling. The results showed that the secondary wall of DmM was composedof8-10layers, and the concentration of xylan-rich hemicelluloses in cell wall was:S3>S2>CML. However, in the case of wheat straw the secondary wall all most occupied thewhole cell wall, and the concentration of xylan-rich hemicelluloses in cell wall was:CML>S3>S2. Hemicelluloses were isolated from the delignified DmM by a sequentialtreatment combining organic and organic alkaline base extraction. It was found that the yieldsof the fractions from H1to H6were2.42,0.42,13.82,3.14,2.53and1.24%of the initialamount of dewaxed DmM, respectively, which accounted for94.1%of the originalhemicelluloses.13C-NMR and HSQC indicated that the alkali-soluble hemicellulosic fractions are mainly composed of the (1→4)-linked β-D-xylopyranosyl backbone with4-O-methyl-α-D-glucuronic acid and α-L-arabinofuranosyl residues attached to O-2and O-3of the xylose, respectively. Moreover, it revealed that the average molecular weight ofhemicellulosic fraction extracted with DMSO and0.5M KOH is lower than those of the twohemicellulosic fractions extracted with2M KOH and3M KOH. The DMSO and0.5MKOH-soluble hemicelluloses have higher polydispersity indexes, indicating a widermolecular weight distribution. The rheology and atomic force microscope (AFM) testsconfirmed the difference in morphology of hemicelluloses molar chains.2. New strategies for the chemical modification of hemicelluloses and preparation ofnovel hemicelluloses esters. Hemicellulose succinate and maleate were homogeneouslyprepared in ionic liquid1-butyl-3-methylimidazolium chloride ([BMIM]Cl). Hemicellulosesuccinate with a substitute degree (DS) of high up to1.80could be produced at a muchshorter time scale in [BMIM]Cl without any catalysts, which is probably due to the excellentdissolving capacity and catalytic effect of ionic liquid, while hemicellulose maleates with DSof0.095⁰.75could be prepared in [BMIM]Cl by using LiOH as catalyst.Octenylsuccinylated hemicelluloses and dodecenylsuccinylated hemicelluloses wereprepared in DMSO by using triethylamine as catalyst. These derivatives exhibitedself-assembly behavior and emulsifying ability, and could form stable polymeric micelleswith diameter of70¹50nm. Three hydrophobic hemicelluloses with long-chain esters(laurate, cetylate and stearic acid esters) were also successfully synthesized by couplingreaction, and which can be used as thermoplastic materials.3. Microwave-induced synthesis of ionic hemicellulosic derivatives and theirphysicochemical properties. Microwave irradiation was first introduced into efficientsynthesis of ionic hemicellulosic derivatives with high DS: carboxymethyl hemicelluloses,quaternized hemicelluloses, amphoteric hemicelluloses, and carbamoylethyl carboxyethylatedhemicelluloses. It was found that microwave irradiation could significantly promote thechemical reaction efficiency and accelerate the carboxymethylation of hemicelluloses withsodium monochloroacetate. Therefore, carboxymethyl hemicelluloses, quaternizedhemicelluloses, amphoteric hemicelluloses, and carbamoylethyl carboxyethylatedhemicelluloses with high DS could be could be obtained in much shorter time scales ascompared to conventional heating method.Results from rheological analysis suggested that functional groups in derivatives showedsignificant influence on theirrheological behaviors. These four hemicellulosic derivativesaqueous solutions exhibited shear-thinning behavior in the range of testing shear rates, and carboxymethyl hemicelluloses and quaternized hemicelluloses showed lower viscosity andmodulus in comparison with the native hemicelluloses due to the decreasing entanglementsbetween hemicelluloses chains as a result from electrostatic repulsion betweencarboxylmethyl groups and quaternized groups. However, amphoteric hemicelluloses andcarbamoylethyl carboxyethylated hemicelluloses showed higher viscosity and modulus ascomparedto the native hemicelluloses due to the opposite charges attraction. Quaternizedhemicelluloses could absorb pDNA effectively. Quaternized hemicelluloses with cholesterolshowed more effective transfection for293T cells. Amphoteric hemicelluloses andcarbamoylethyl carboxyethylated hemicelluloses could improve the physical properties ofhand sheets of BKP and OCC pulp.4. Preparation of externally enhanced and internally plasticized hemicelluloses-basedfilms and their structure-activity relationships. Cellulose nanofibres (CNF) werefirst introduced into hemicelluloses to produce nanocomposite films with significantlyenhanced mechanical properties.5wt%CNF could produce nanocomposite films with30%and80%increments in tensile stress and tensile strain due to the high aspect ratio and stronginteractions between CNF and the hemicelluloses matrix. SEM and AFM images showed thatthe surface of the hemicelluloses film and the nanocomposite films were primarily composedof nodules that had a diameter of10⁷0nm. The hemicelluloses film was semicrystalline,which was indicated by the distinct peak at around2θ=18°.The pendent long carbon chains (2-OSA half ester groups) acted as internal plasticizerby interfering with the association of hydroxyls and disturbing the regular arrangement ofhemicelluloses chains in film-forming process due to the steric hindrance of2-OSA half estergroups. For this reason, the internally plasticized films have amorphousstructure and betterfilm-forming performance than the externally plasticized film. The hydrophobic alkenylchains also can yield low moisture-sensitive films that can be used in moisture-richconditions. Furthermore, internal plasticization is a more effective method in improving themechanical properties of hemicelluloses films.5. Novel smart hemicelluloses-based hydrogels: preparation, structure, properties andapplications. Novel multi-stimulus-response hydrogels based on hemicelluloses wereprepared by free radical graft copolymerization of acrylic acid and hemicelluloses by usingMBA as crosslinker and APS/TMEDA as redox initiator system. Higher MBA/XH or AA/XHratio resulted in denser crosslinking network, and thus decreased swelling ratio. The ionichydrogels prepared were sensitive to pH, ionic strength and composition of the medium, andorganic solvents. In addition, the hydrogels showed reversible on-off switching behavior in acidic-basic solutions or water-ethanol or acetone solutions. Metal ion binding to XH-g-AAhydrogel is an ion exchange mechanism. The expansion of the polymeric network and porousstructure in the initial adsorption stage favor the diffusion and adsorption of metal ions fromthe exterior to interior of the hydrogel. The maximum adsorption capacities of Pd2+, Cd2+, andZn²⁺were high up to859,495, and274mg/g, respectively. The hydrogel also exhibitedhighly efficient regeneration and metal ion recovery efficiency.A novel thermosensitive semi-IPN hydrogel based on hemicelluloses were prepared byfree radical graft copolymerization (UV radiation) of NIPAAm and glycidyl methacrylatederivatized hemicelluloses by using CMH as semi-IPN molecular chains. The hydrogelexhibited thermosensitive properties, and did not show inhibition for cell growth and skinirritation, and thus can be used as a safe, non-toxic and biodegradable biomaterial in targetingdrug release.6. New polysaccharide conjugates with matching performance and its application indrug release. New hemicellulosic derivatives containing terminal alkynes were synthesizedthrough nucleophilic substitution reaction. Sharpless-Huisgen reaction with copper as acatalyst was first used to synthesize a new macromolecule based on propargyl-hemicellulosesand6-azide-β-cyclodextrin in water or DMSO, and the macromolecule was further preparedinto carrier material or scaffold with20⁴00μm pore size. Due to the presence of β-CD, thecarrier material or scaffold could be used as a matrix for ketoprofen loading and controlledrelease. The MTT assay and skin irritation tests showed that there was no obviouscytotoxicity and allergy ofhemi-g-β-CD carrier materials, and thus can be used as a safe andnon-toxic biomaterial in targeting drug release or cell culture.7. Synthesis of novel polymeric amphiphiles by conjugating cholesterol tocarboxymethyl hemicelluloses (CCMH) and their self-assembling behaviors andnanoparticles. The mean diameter of CCMH nanoparticles was in the range of8¹10nm. Thecritical aggregation concentration (CAC) values of the CCMH were low (0.0024-0.017mg/mL), and decreased with an increase in the DS of cholesterol. CCMH nanoparticles weresensitive to the pH of the release media as well as the drug loading contents. The blankCCMH nanoparticles did not show any toxicity to A549cells. The cellular uptake ofDOX-loaded CCMH nanoparticles was better than that of free DOX, and DOX-loadedCCMH nanoparticles showed better release properties, which can be used as a new carrier forantitumor drugs delivery.