Hydrophobic Modification of Starch by Alkali-Catalyzed Addition of 1,2-Epoxyalkanes
| Main Authors: | , , |
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| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0038-9056 |
| Online Access: | http://www.viks.sk/chk/star_11_01_555_559.doc |
| Abstract: | Summaries. An efficient method of preparing hydrophobic a-hydroxy starch ethers using aqueous alkaline conditions is described. -Hydroxy starch ethers were synthesized by addition of 1,2-epoxyalkanes to an aqueous alkaline starch gel in the presence of sodium sul-fate as a co-catalyst. The reaction, carried out in a stirred autoclave at 140 °C and 3.9 bar, was optimized with respect to the concentrations of sodium hydroxide and 1,2-epoxyalkane. Optimum yields and molar substitutions (MS) were obtained at molar ratios of sodium hydroxide to anhydroglucose unit (AGU) of 0.5 to 1.0. The amount of molar substitution could be controlled by 1,2-epoxyalkane concentration. Thus, a series of a-hydroxyoctyl starch ethers with MS from 0.7 to 2.4 were synthesized in yields up to 90% by using these conditions. Starches with different amylose contents were also converted to the corresponding ethers using a threefold excess of 1,2-epoxyoctane and an equimolar ratio sodium hydroxide : AGU. The reaction is hardly effected by the origin of the starch and its amylose content. The influence of the 1,2-epoxyalkane chain length was investigated by performing the conversion with a series of terminal epoxyalkanes from 1,2-epoxyhexane to 1,2-epoxydodecane. The results indicated that the hydrophobic character of the starch ethers increased by increasing the molar substitution and alkyl chain length. All products were insoluble in water, but soluble in mixtures of methanol and methylene chloride. Furthermore the starch ethers can be converted into shaped articles by extrusion technology without the addition of plasticizers. Conclusions. A series of -hydroxyalkyl starch ethers (C6 to C12) was prepared by a two-phase reaction of an aqueous alkaline starch gel with 1,2-epoxyalkanes at 140 °C and 3.9 bar in the presence of sodium sulfate as a co-catalyst. Thus, starch ethers with various MS values were obtained in high yields by optimization of the reaction parameters such as the sodium hydroxide concentration. It was possible to adjust the molar substitution using the 1,2-epoxyalkane concentration and, in this way, to influence specifically the hydrophobic character of the products. Furthermore, the hydrophobic character of the starch ethers depends on the chain length of the 1,2-epoxyalka-ne used. In view of thermoplastic processing, the material properties have been investigated at the Fraunhofer Institute for Process Engineering and Packaging (Freising, Germany). |
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| ISSN: | ISSN 0038-9056 |
