Synthesis of Carboxymethyl Starch
| Hlavní autori: | , , |
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| Médium: | Článok |
| Jazyk: | angličtina slovenčina |
| ISSN: | ISSN 0038-9056 |
| On-line prístup: | http://www.viks.sk/chk/star_00_413_419.doc |
| Abstrakt: | Summaries. Carboxymethyl starch (CMS) was obtained under heterogeneous conditions as a product of the reaction of starch and monochloroacetic acid (MCA) in the presence of sodium hydroxide. The influence of the composition of the reaction mixture, the reaction time and temperature and the type of starch being carboxymethylated on the degree of substitution, DS. and limiting viscosity number, [], was studied. The reaction temperature influenced the DS values, the highest values of the DS being obtained when the carboxymethylation was performed at 58 9 C. Increase of the molar ratio of NaOH to an-hydroglycose units leads to an increase in DS, but only to certain extent. The values of the DS and [] of CMS increased almost linearly with increasing MCA amount in the reaction mixture. The reaction mixture changes caused by adding water to ethanoi influenced the DS values of the obtained CMS samples, the maximum DS value being obtained for CMS sample synthesized in ethanol with 25% (v/v) water. Conclusions. Carboxymethyl starch was obtained under heterogeneous conditions as a product of the reaction of starch and monochloroacetic acid, MCA. in the presence of sodium hydroxide. In the present work, carboxymethylation was performed in an ethanol/water mixture and the influence of solvent composition, concentration of NaOH and MCA, temperature and duration of reaction and the type of starch being carboxymethylated on the degree of substitution, DS, and limiting viscosity number, [], was studied. Three types of starch were carboxymethylated: native starch, starch enriched with amylose and oxidized starch. The increase of reaction temperature increased the DS values for the samples obtained by carboxymethylation of all starch types, the values of [] for samples obtained by carboxymethyiation of native starch (CMNS) and starch enriched with amylose (CMSA) decreased abruptly at a reaction temperature of 58 °C, while for the samples obtained by carboxymethylation of oxidized starch (CMOS) values of [] increased with the reaction temperature. An abrupt decrease in [] might indicate some conformation-al change of CMNS and CMSA macromolecules or their degradation, but no evidence for this is still available. Increase of the molar ratio of NaOH to anhydroglycose units leads to a DS increase, but only to a certain extent, the values of the DS and [] of CMS incrased almost linearly with increasing MCA amount in the reaction mixture. The reaction mixture changes caused by adding water to ethanol influenced the DS values of the obtained CMS samples, the maximum DS value being obtained for CMS sample synthesized in ethanol with 25% (v/v) of water. The starch type and its previous history have practically no influence on the DS values when carboxymethylation is carried out in water as the reaction medium while the opposite is true for carboxymethylation in ethanol as the reaction medium. |
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| ISSN: | ISSN 0038-9056 |
