Synthesis And Properties Of Carboxylmethyl Hydroxypropyl Guar Gum

Guar gum is of a unique molecular structure, it is one of the well water-soluble compounds of natural polymers known. It has been widely used in the food, oil, drilling, pharmaceutical, paper, printing and architectural coatings. Because its short comings restrict its development, such as the high content of insoluble residue, lowly dissolving and swelling, and the instable viscosity, it needs to be modified into carboxylmethyl hydroxypropyl guar gum(CMHPG).In the processes of synthesis, acetone was used as medium to replace ethanol (or isopropanol); sodium methoxide was used as catalyst to replace sodium hydroxide. Investigate effect of process conditions on properties of products. Preferred processes are obtained. The results show that the preferred synthesis conditions are that the mass ratio of propylene oxide to guar gum is 0.2:1, and that of chloroacetic acid to guar gum is 0.4:1, the reaction lasts 160 minutes. If acetone and sodium methylate are used as medium and catalyst respectively, the mass ratio of catalyst to guar gum is 0.3:1, and reaction temperature is 45-50℃; if ethanol (or isopropanol) and sodium hydroxide are used as medium and catalyst respectively, the mass ratio of catalyst to guar gum is 0.3:1, and reaction temperature is 65-70℃. The substitution degree of carboxymethyl is 0.48 and that of hydroxypropyl is 0.37, and viscosity of product solution (0.5%) is 1030mPa?s using acetone and sodium methylate as medium and catalyst respectively. The substitution degree of carboxymethyl is 0.43 and that of hydroxypropyl is 0.36, and viscosity of product solution (0.5%) is 1120mPa?s using ethanol and sodium hydroxide as medium and catalyst respectively. The substitution degree of carboxymethyl is 0.46 and that of hydroxypropyl is 0.38, and viscosity of product solution (0.5%) is 1070mPa?s using isopropanol and sodium hydroxide as medium and catalyst respectively. Detect the transmittance on solution of CMHPG. Investigate effect of pH and NaCl on viscosity of solution of CMHPG. The results show that transmittance on solution of CMHPG increases with the increase of substitution degree. The substitution degree of carboxymethyl is 0.48, and the substitution degree of hydroxypropyl is 0.37, the transmittance on solution (0.5%) of CMHPG is 72.62%. When the pH is less than 8, the viscosity of solution of CMHPG increases rapidly with increase of pH; when the pH is more than 8, the viscosity of solution of CMHPG decreases gradually. With the increase of the concentration of NaCl, the viscosity of solution of CMHPG increases slowly. IR is used to characterize the structure of CMHPG.