Synthesis and Characterization of Cross-linked Carboxymethyl Potato Starch Ether Gels

摘要

Hydrogels were synthesized by cross-linking of potato starch (PS) with dichloroacetic acid (DCA) in the presence of monochloroacetic acid (MCA) to form etherified carboxy-methyl starch (CMS) gels, to be used for ultrasonic medical examinations. By ether-ification cross-linked CMS-hydrogels can be produced, that are stable in contrast to the in the long-term unstable esterified gels, that were presented in the last paper. The rheological benchmarks for the CMS-hydrogels were set in comparison with synthetic ultrasonic gels. Gels with potato starch contents in the reaction batch ranging from 12.5% to 20% showed the best compliance with the benchmark parameters. The DS values of these CMS-hydrogels vary from 0.42 to 0.49, increasing with decreasing amount of starch in the reaction mixture. The free swelling capacities (FSC) vary between 77 g/g for the 12.5% PS-gel and 34 g/g for 20% PS-gel, the turbidities of the samples being in the range from 14.5 NTU (Nephelometric Turbidity Units) (12.5% PS) up to20.5 NTU (20% PS). The variation of the PS fraction in the reaction mixture showed that with an increased amount of PS in the reaction batch the number of cross-links of the CMS-gels increases, too. At a higher number of cross-links the swelling capacity is reduced and the concentration needed to form stable hydrogels is greatly increased. Thus a hydrogel of a polymer concentration of 5 mass-% from a 12.5% PS batch was produced, that showed the best accordance with the rheological benchmark parameterssuch as gelatinization time, visco-elastic and pseudoplastic properties and long-term stability. The ultrasonic pictures taken with this CMS-gel were not different from those taken with the synthetic gels. This hydrogel was then subjected to long-term-stability measurements performed over one year and to rheological temperature cycle tests. The tests showed that the long-term stability of the gels is sufficient for their use as ultrasonic gel.