Preparation And Properties Of Carboxymethyl Starch With High Degree Of Substitution Andhigh Viscosity

Carboxymethyl starches(CMS) with medium andhigh degree of substitution(DS) were prepared from corn starch respectively. And compound modifications of cross-linking and esterification were carried out by epoxy chloropropane andglutaric anhydride(GA), respectively, to improve the viscosity of CMS. The results showed that these two kinds of compound modifications improved the viscosity of starch. Specific research contents and results were showed as follows:CMS of medium DS was prepared by sodiumhydroxide solution. Effects of starch concentration, dosage of chloroacetic acid and sodiumhydroxide, sodiumhydroxide concentration, temperature and time of etherification on DS were studied by single factor experiment, which showed the better process conditions were as follow: starch concentration was 30%; 70 g chloroacetic acid; dosage of sodiumhydroxide was 2(molar ratio of alkali and acid); mass fraction of sodiumhydroxide solution was 55%; 50℃ was adopted to etherify starch for 5h. Under this condition, the DS of CMS was 0.7471. The paste viscosity of CMS with DS from 0.1028 to 0.7471 first increased and then decreased. And the maximum viscosity of CMS was 3210 mPa.s when the DS was 0.2466.CMS ofhigh DS was prepared by solid sodiumhydroxide which was added by two times. The influence of various factors,such as adding sequence of acid and alkali, solvent, solvent concentration, starch concentration, dosage of chloroacetic acid and sodiumhydroxide, temperature and time of alkalization, sodiumhydroxide for alkalization, temperature and time of etherification, sodium carbonate used to replace sodiumhydroxide for etherification, on DS were discussed respectively. Comparison of effects on DS of different types of starches, etherifying agents and sodiumhydroxide states were also studied. According to the results of single factor experiment, starch concentration, sodiumhydroxide and chloroacetic acid dosage, and etherification temperature were selected as factors and then designed orthogonal experiment. The results showed that the optimal process was follow: starch concentration was 25%, 115 g chloroacetic acid, dosage of sodiumhydroxide was 2(molar ratio of alkali and acid), etherification temperature was 40℃. Under this condition, the DS of CMS was 1.2104.Study on the physicochemical properties ofhigh DS of CMS. There were absorption peaks of –COO- in the FTIR spectrogram of CMS. It was showed by SEM of CMS that there was expansion and obvious cracks, a big bursthole in the centre of particles, and surface became very rough. XRD patterns showed that the crystalline structure of CMS was destroyed and the crystallinity decreased. When DS was from 0.6575 to 1.2043, the paste viscosity of CMS decreased, the transparency and freeze-thaw stability were much better than native corn starch, and thehigher DS, the better the transmittance and freeze-thaw stability. When DS was 1.2043, the paste transparency of CMS was 38 times that of native starch, and almost no water was analyzed after 6 repeated freeze-thaw cycles, but the viscosity was 970 mPa.s.Compound modification of cross-linking was carried out by epoxy chloropropane to improve the paste viscosity of CMS. When DS was from 0.3727 to 1.1753, the paste viscosity of carboxymethyl cross-linked starch after cross-linked by epoxy chloropropane was 4.28~6.96 times that of single modified CMS. When DS was 0.3727, the effect of cross-linking improved paste viscosity was the most obvious, from the original 2300 mPa.s to 16000 mPa.s, which was 6.96 times that of the CMS. It is proved that the paste viscosity of CMS can begreatly improved by cross-linking.Compound modification of esterification was carried out byglutaric anhydride to improve the paste viscosity of CMS. There was a new absorption peaks at 1564.50 cm-1 in the FTIR spectrogram of CMS with DS being 0.1174, which proved thatglutaric anhydride(GA) was successfullygrafted on starch molecules after esterified by 8%gA. When DS was from 0.3727 to 1.1753, the paste viscosity of carboxymethylglutaric anhydride starch was higher than that of single modified CMS. Especially, When DS was 0.3262, the paste viscosity incresed from the original 2200 mPa.s to 7520 mPa.s, which was 3.42 times that of the CMS. Comparation with the transparency of CMS and carboxymethylglutaric acid starch showed that there was an obvious effect on the paste transparency of CMS after esterification, when the DS of carboxymethyl was low.