| In this study, based on the hydrophilicity of carboxymethyl group and steric hindrance and hydrophobicity of alkyl group, a series of composite-modified starch with different ratios of hydrophilic group to hydrophobic group were synthesized by introducing alkyl group in to carboxymethyl starch, the stability and solution properties of carboxymethyl starch were improved. The synthetic conditions of esterification and properties of aqueous solutions of composite-modified starch were studied in detail. Acetylated carboxymethyl starch, which has the similar aqueous solution properties with sodium alginate, was prepared by changing the molar ratio of carboxymethyl group to acetyl group. It provided the law of viscosity of the aqueous solutions and extended the application of starch and carboxymethyl starch.Firstly, carboxymethyl starch (CMS), a cold-water-soluble starch derivative was prepared via etherification between starch and chloroacetic acid. Secondly, the alkyl group esterified carboxymethyl starch was prepared by the esterification of CMS. The maximum degree of the reaction efficiency (RE) of ACMS and BCMS was80%and73.1%. respectively using anhydride as esterification reagent in water. The maximum degree of reaction efficiency (RE) of HCMS and OCMS was84%and75.6%, respectively using fatty acid chlorides in DMSO. The chemical structure of alkylated CMS was characterized by IR and the thermal stability was analyzed by TG.The aqueous solution properties of the series of hydrophilic/hydrophobic composite-modified starch, such as the thickening properties, salt-tolerance, temperature sensitivity and relative hysteresis area and its influence factors, such as temperature, shear rate, degree of substitution of alkyl group was discussed in detail and the regularity of the solution properties of alkyl was summarized. The increase of viscosity of the acetylated CMS mainly depends on the stretching of the molecular starch chain because of the steric hindrance of acetyl group. The thickening effect of the aqueous solution of butyl group, hexyl group and octyl group is relying on the hydrophobic interaction in the formation of the network structure. The viscosity of the octylated CMS reaches35800mPa.s when the DSoctyl is0.41.The weak hydrophobic aggregation can not improve the shear-resistance and relative hysteresis area. Therefore, the shear-resistance and relative hysteresis area were getting worse with the increase of the chain length of alkyl group. But the temperature sensitivity of CMS was improved as the chain length of alkyl group increased. The Eα value was decreased from2.082kJ/mol to0.077kJ/mol. Improving the rigidity of the molecular chain and reducing the network structure of the hydrophobic contribution to the viscosity of the solution are benefit for improving the salt-tolerance and shear-resistance of the aqueous solution.Acetylated CMS (DScm=0.76. DSacetyl=0.30) with good salt-tolerance, shear-resistance and similar viscosity value with sodium alginate was chosen and the influences of the aqueous solution were studied. The aqueous solution properties of ACMS. such as shear-resistance, salt-tolerance, temperature sensitivity and viscosity stability were compared with that of sodium alginate. The results indicated that the shear-resistance, salt-tolerance, temperature sensitivity and viscosity stability of ACMS with optimal molar ratio of carboxymethyl grou to acetyl group is similar with that of sodium alginate. It may replace sodium alginate in some areas of the food, textile and other applications. |
PDF Full Text Request