The Preparation And Properties Of Dialdehyde Cross-linked Guar Gum

In order to improve the property of guar gum and enlarge its application field, guar gum was modified by the cross-linking and dialdehyde oxidation. The preparation of dialdehyde cross-linked guar gum was investigated by using phosphorous oxychloride as a cross-linking agent, sodium periodate as an oxidizing agent, sodiumhydroxide as a catalyst and ethanol as a solvent in this research. The cross-linking degree was determined by the sedimentation volume, and the aldehyde content was measured by the acid-base titration method. The effect of the reaction temperature, reaction time, pH, amount of phosphorous oxychloride and sodium periodate on the sedimentation volume of cross-linked guar gum and the dialdehyde content of dialdehydecross-linked guar gum was investigated. 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 dialdehyde oxidation. The structure and thermal properties of guar gum, cross-linked guar gum and dialdehyde cross-linked guar gum were characterized by FT-IR, TGA and DSC, respectively. At the same time, the particle morphology of guar gum, cross-linked guar gum and dialdehyde cross-linked guar gum were observed by a polarizing microscope.For the cross-linking modification, the best conditions were as follows:reaction time75min, reaction temperature33℃, amount of phosphorous oxychloride1.2%, pH11.5. The impact order of four process conditions on the sedimentation volume from primary to secondary was the amount of phosphorous oxychloride, reaction time, reaction temperature and pH. For dialdehyde modification, the best conditions were as follows: reaction temperature40℃, reaction time3.Oh, pH4.0, amount of ethanol74.5%. The impact order of four process conditions on the sedimentation volume from primary to secondary was the amount of ethanol, reaction time, pH and reaction temperature.The content of phosphorus had an inversely proportional relationship to sedimentation volume, so the cross-linking degree was able to be determined by the sedimentation volume. In the FT-IR of dialdehyde cross-linked guar gum, the aldehyde group was proved by the characteristic absorption peak of C=O group. After guar gum was cross-linked, its thermal stability, retrogation, alkali resistance, acid resistance, viscosity stability and freeze-thaw stability were all improved. For dialdehyde guar gum and dialdehyde cross-linked guar gum, their retrogation, freeze-thaw stability and viscosity stability were improved except alkali and acid resistance. The DSC curve of guar gum, cross-linked guar gum, dialdehyde guar gum and dialdehyde cross-linked guar gum showed the endothermic peak at a span of20～200℃. The Maltese cross was not observed on the particle surface of guar gum, which was different from starch granules. The shape of cross-linked guar gum and guar gum particles presented thready. The shape of dialdehyde guar gum and dialdehyde cross-linked guar gum particles was massive. The structure of dialdehyde cross-linked guar gum was destroyed severely from the observation.