Cationisation of Glycerol Plasticised Wheat Starch under Microhydric Molten Conditions
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0038-9056 |
| Online Access: | http://www.viks.sk/chk/star_7_03_297_303.doc |
| Abstract: | SUMARRIES. Cationisation of glycerol plasticised wheat starch was performed in a molten mixture under the action of thermo-mechanical energy using two reagents:3-chloro-2-hydroxy-propyltrimethylammonium chloride and 2-epoxypropyltrimethylammonium chloride. The reaction was catalysed with sodium hydroxide under microhydric conditions. The results showed that under these conditions the reaction proceeds rapidly and reaches completion within a few minutes. The reaction efficiencies were higher for lower degrees of substitution (DS). The epoxide showed a higher reactivity than the chloro derivative. Both destructurisation of starch granules and increased sodium hydroxide concentration enhanced the reaction, but an increase in plasticiser concentration had a negative effect. Measurements of intrinsic viscosity showed a decrease of the average molecular weight of the product, which was attributed to the thermo-mechanical melting process. An increase in water affinity with DS was seen in the water sorption properties of the chemically modified starch. CONCLUSION. In this study it was shown that starch cationisation can be performed on starch plasticised with glycerol under mi-crohydric conditions in a molten medium. The chemical modification can reach high degrees of conversion in a short period of time. The influence of various parameters such as reagents concentrations, addition order, plasticis-er amount, temperature and starch granule destructurisa-tion were examined. Reactivity depends on the reagent, the epoxide being much more advantageous. The reaction efficiency was measured for both reagents. It was found that the transformation of the hydrochloride (I) into the epoxide (II) in-situ is the rate determining step. The excellent chemoselectivity of this reaction should be emphasised. Despite the presence of a relatively large amount of the polyhydroxylated plasticiser glycerol, excellent REs were obtained, particularly with reagent (II) (94%), which showed no interference of the plasticiser with the reaction. Although the process of melting under thermo-mechanical energy clearly led to a reduction of molecular size as shown by intrinsic viscosity, chemical modification did not appear to cause any further depolymerisation. The chemical modification of starch strongly increased its water sorption properties. |
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| ISSN: | ISSN 0038-9056 |
