Study On Functional Materials Based On Konjac Glucomannan

In this work, six kinds of functional materials based on konjac glucomannan(KGM),a type of natural polsyaccharides with abundant raw materials,good biocompatibility andbiodegradability, were prepared via several methods such as etherification, graftcopolymerization, esterification, photochemical reduction, as well as blending. Moreover,the structures，related properties and applications of the obtained materials were alsosystematically studied. This research could take full advantage of the abundant konjacresources in the Wuling area, broaden the research range for KGM and further improve theextra value of the products.These results are as follows:(1) A quaternary ammonium derivative of KGM was prepared by a dry process fromKGM and2,3-epoxypropyl trimethylammonium chloride (EPTMAC).We determined theoptimization of the experimental conditions by studying on the effects of water amount,alkaline catalyst amount, reaction temperature and reaction time on the degree ofsubstitution(DS), which the DS is0.42under the optimal condition. The synthesizedproducts were then characterized using several instrumental techniques such as Fouriertransform infrared spectroscopy (FTIR), scanning electron micrography (SEM), andthermgravimetric analyzer(TGA) to confirm that the cationic moiety has been insertedonto the KGM backbone. In addition, the flocculation characteristics of the cationicderivative of KGM have been evaluated in a1.0%kaolin suspension withspectrophotometry via investigating of the influence of flocculants amount, pH, saltconcentration, temperature, and setting time on the flocculation. Flocculatioan efficiencycan reach95%under certain condition. The results showed that the synthesized cationicKGM could be potentially used as a high-performance flocculating agent.(2) A new KGM-based superabsorbent polymer, KGM-g-poly(acrylic acid-co-acrylamide), was prepared by the free radical grafting solution polymerization of acrylicacid(AA) and acrylamide(AM) mononers onto KGM in the presence of N,N’-methylenebisacrylamide as a crosslinker with K2S2O8as an initiator. The effects ofreaction parameters, including the amount of crosslinking agent and initiator, the weightratio of both (AA+AM) to KGM and AM to (AA+AM), neutralization degree of AA, bathtemperature, and reaction time, on the water absorbency of the superabsorbent wereinvestigated. FTIR, SEM and TGA were used to characterize the structures of the grafted copolymer, respectively. The maximum water absorbency of the optimized product was650g/g for distilled water. Both the water retention of the products under a fixedtemperature and the salt resistance of the products were also discussed. Furthermore, thewater retention of the grafted copolymer in soils was studied. The effect of the copolymeron the aggregate distribution of soils was also evaluated. The results showed that thegrafted copolymer could be used as a good water retaining agent in soils.(3)A novel polyampholyte hydrogel, KGM-g-poly(acrylic acid-co-trimethylallylammonium chloride), was prepared by the free-radical grafting solution polymerization ofacrylic acid(AA) and trimethylallyl ammonium chloride(TMAAC) monomers onto KGMin the presence of N,N ’-methylenebisacrylamide as a crosslinker with K2S2O8as aninitiator. The structures of the graft copolymers were confirmed with FTIR, SEM andTGA, respectively. The influneces of reaction variables, including the amount ofcrosslinking agent and initiator, the weight ratio of both (AA+TMAAC) to KGM and AAto (AA+TMAAC), neutralization degree of AA, bath temperature, as well as reaction time,on the water absorbency of the superabsorbent polymer were investigated. The maximumwater absorbency of the optimized product was550g/g for distilled water. Moreover, theeffects of the pH value of the solution on the water absorbency of the copolymers werestudied. The results showed there was a maximum value of water absorbency at the acidicconditions and at the alkaline conditions, respectively. The water absorbency at theisoelectric point was relatively low. These results suggested that KGM-g-(PAA–co-PTMAAC) hydrogels showed unique pH dependent swelling properties in contrast ofthose of conventional poly (acrylic acid) based hydrogels. In addition, the influence of theconcentration of aquous NaCl slution on the water absorbency of the hydrogels was alsoinvestigaged under three different pHs.(4) KGM nitrate (KGMN) with high degree of substitution (DS) was preparatedusing KGM as subtstrate, concentrated H2SO4as catalyst, and fuming HNO3as modifier.The effects of the preparation conditions on the DS of KGMN were investigated, whichthe DS of the product was2.63under the optimal synthesizing condition. FTIR spectrashowed that-NO2groups had been successfully introduced into KGM molecules. SEMimages indicated that the morphology of KGMN became loose, which might be related tothe enhanced hydrophobicity as the introduction of-NO2. TGA tests showed the thermalstability of KGMN decreased compared with that of KGM, and moreover, the higher theDS, the lower thermal stability. In addition, KGMN showed thermal properties of instantaneous explosion and combustion. The preliminary results indicated that KGMNcould be used as a new environment-friendly energetic material.(5) KGM/silver nanoparticles composites have been preparated directly in the dilutehydrosol of KGM using photochemical reduction of Ag+. The KGM/Ag composites havebeen characterized by means of FTIR, transmission electron microscopy(TEM), TGA anddifferential scanning calorimetry(DSC).The results of FTIR showed that the wavenumbersand the strength of some characteristic peaks of KGM treated by silver nanoparticles werechanged obviously, which the characteristic peaks of the O-H stretching and the C-O-(H)stretching became wider with increasing the concentrations of reactants, and thecharacteristic peaks of the O-H stretching and the C-O-(H) stretching shifted to highwavenumbers with increasing the time of photochemical reduction.The images of TEMindicated that Ag nanoparticles were finely dispered inside the KGM films with differentshapes, such as sphere-like(average diameters of10-30nm) and star-like(edge lengths ofabout20nm),respectively.These suggested that the morphology and the agglomeratedstate of Ag nanoparticles in the composites changed with the condititonos of thepreparation.The KGM/Ag nanocomosites had remarkably different thremal properties andmechanical properties compared with those of KGM. The mechanism interaction betweenthe polysaccharides and the silver nanoparticles has been generally discussed.(6) Titanium dioxide (TiO2) nanoparticles were dispersed into KGM matrix to getnanocomposites through the blending method. The nanocomposites were characterized byFTIR, TEM, and TGA.The results indicated that the characteristic peaks of FTIR of KGMhad obviously been changed by the introduction of nano-TiO2and the thermostability ofKGM/TiO2nanocomposites was better than that of the KGM film.Most nano-TiO2particles were finely dispersed in the KGM/TiO2nanocomposites, as shown in the TEMimages. The mechanical performance of nanocomposites was improved. Moreover, theantibacterial tests indicated that the nanocomposites had excellent antibacterialperformance.