Synthesis And Properties Of Oxidized Cross-linking Guar Gum

Guar gum is an eco-friendly galactomannan with unique properties. Practical applications of guar gum are restricted probably because of its shortcomings, so chemical modification as cross-linking and oxidation on guar gum are available to broaden its application.The aim of this study was to investigate the technology parameters of preparing cross-linking oxidized guar gum based on guar gum as a raw material, dimethyldichlorosilane as a cross-linker, hydrogen peroxide as an oxidant and ethanol as a solvent. The cross-linking degree was determined by the sedimentation volume, and the carboxyl content was measured by the acid-base titration method. The effects of the reaction temperature, reaction time, amount of ethanol, pH and amount of dimethyldichlorosilane on the sedimentation volume of cross-linking guar gum were studied. The effects of the reaction temperature, reaction time, amount of ethanol, pH, amount of copper sulfate and amount of hydrogen peroxide on the carboxyl content of oxidized cross-linking guar gum were studied. On the basis of one-factor-at-a-time design the response surface methodology was used to optimize the above parameters of the cross-linking and oxidation. After optimizing the parameters of cross-linking guar gum through the Box-Behnken method, the best conditions for cross-linking modification were as follows: amount of dimethyldichlorosilane 2.5%, reaction time 1.5h, reaction temperature 15.6, amount of ethanol 84% and pH 10.4, the sedimentation volume of cross-linking guar gum was 0.85 m L. The impact order of five phosphorous on the sedimentation volume from primary to secondary was the amount of ethanol pH reaction time reaction temperature and amount of dimethyldichlorosilane. For oxidation modification the best conditions were as reaction temperature 60.2, reaction time 3.6h, amount of hydrogen peroxide 18.0%, amount of ethanol solution 70 %, pH 8.3, the carboxyl content of oxidized cross-linking guar gum was 0.810%. The results of response surface method indicated that the most significant factor on carboxyl content was the amount of reaction time followed by the reaction temperature, amount of ethanol, amount of hydrogen peroxide and pH.The chemical structural and textural characteristics of the guar gum, cross-linking guar gum and oxidized cross-linking guar gum were determined by Fourier transform infrared spectra, TGA DSC and XRD, respectively. The IR spectroscopy of oxidized cross-linking guar gum was different from the IR spectroscopy of guar gum at wave number 898 cm-1, which belonged to the stretching vibration of –SiCH3. It proved that the-SiCH3 groups were obtained from the cross-linking. The adsorption peaks at wave number 898 cm-1 and 1718 cm-1 in IR spectrum of oxidized cross-linking guar gum proved that the dimethylsilane groups and carboxyl groups were successfully introduced into guar gum molecules by the cross-linking and oxidation. The intensity of –OH groups of guar gum was distinctly greater than the intensity of –OH groups of oxidized cross-linking guar gum, it proved that the numbers of the –OH groups of the oxidized cross-linking guar gum were reduced by the cross-linking and oxidation. After guar gum was cross-linked and oxidized, its thermal stability, retrogation, hot and cold viscosity stability were all improved, but its swelling power and freeze-thaw stability decreased.The decolorization application of oxidized cross-linking guar gum on dye wastewater was studied using the decolorization rate as the analysis index and the reactive brilliant blue X-BR, direct violet 9 and acid bright blue P-BL solution as the simulated dye wastewater. The effects of amount of oxidized guar gum, decolorization time, decolorization temperature and pH were investigated. The results showed that the decolorization rate was 96.6% 77.4%70.4% in the order of reactive brilliant blue X-BR, direct violet 9 and acid bright blue P-BL. The experimental research showed that this product was good at decolorization and will be favorable for the application prospect in the dye wastewater treatment.