Studies On Preparation And Properties Of Benzyl-modified Starch And Starch Derivatives

Hydrophobic modified products of starch and its derivatives have good physical and chemical properties. They show wide application prospects in various areas. In this thesis, benzyl group was selected as the hydrophobic group. And preparation and properties of benzyl starch and its derivatives were studied.Benzyl starch with high degree of substitution(DS) was prepared by reaction of starch with benzyl chloride which was used as hydrophobic reagent in the mixed solvent containing isopropanol and water. The effects of some reaction factors on DS, such as amount of isopropanol in the solvent, dosage of alkali, reaction time, reaction temperature, and type and dosage of catalyst were investigated. Besides, the possible catalyzing process was discussed. A new UV-spectrometric method for determination of DS of benzyl in benzyl starch was developed. This new method is rapid, simple, and accurate, with more operational possibilities and satisfactory results.On the basis of syntheses of benzyl starch and hydroxyethyl starch, benzyl hydroxyethyl starch with different DS of benzyl and hydroxyethyl parts was prepared by reaction of starch with both benzylchloride and chlorohydrin. The effects of reaction method, catalyst, dosage of benzyl chlorid and chlorohydrin on DS of benzyl and hydroxyethyl groups were studied. With the help of catalyst, DS of benzyl groups of the derivative is above 0.09, and molar degree of substitution of hydroxyethyl groups is 0.80-1.01 using one-step method.Benzyl carboxymethyl starch was prepared in isopropanol with some water, using self-made benzyl starch with different DS of benzyl group as raw material. DS of carboxymethyl part was affected by DS of benzyl group in benzyl starch, dosage of chloroactic acid, content of water in solvent, reaction time and temperature, as well as dosage of alkali. The optimal reaction conditions are obtained and they are 60℃, 6 hours in isopropanol with 3% water, and the ratio of NaOH to benzyl chloride of 2.0.Surface tensions of the solutions of benzyl starch, benzyl hydroxyethyl starch and benzyl carboxymethyl starch were examined, and they were 53.0 mN·m~-1, 48.7 mN·m~-1 and 42.0 mN·m~-1 respectively. These results are mainly affected by DS of benzyl group. Benzyl starch with DS of benzyl part of 0.025-0.105 has good water-solubility at 80℃. And it is also concluded by study on viscosity of benzyl carboxymethylstarch that benzyl group increases the viscosity of the starch derivative with low DS of carboxymethyl and makes it less affected by salt.