新型氧化羟丙基醋酸酯淀粉的制备及其膜性能测定

【目的】探究新型氧化羟丙基醋酸酯淀粉的制备及膜成型最佳工艺条件，测定膜的性能，为研发淀粉胶囊提供参考依据。【方法】选用木薯淀粉改性的氧化羟丙基淀粉和醋酸酐为原料，通过改变氧化羟丙基淀粉与醋酸酐的比例（10∶1.5、10∶2.0和10∶4.0），制备新型氧化羟丙基醋酸酯淀粉。以氧化羟丙基醋酸酯淀粉为原料，甘油和山梨醇混合物为增塑剂，结冷胶为增强剂，用流延法制备成薄膜。通过红外吸收光谱法、X-射线、扫描电镜法、黏度测定仪和热重等对酯化淀粉进行物相鉴定，同时测定膜的抗拉强度、吸水性、疏水性和外观形态等性能。【结果】制备3种新型氧化羟丙基醋酸酯淀粉，取代度分别为0.100、0.142和0.152，并对其进行结构表征，红外吸收光谱分析结果显示，氧化羟丙基淀粉与醋酸酐发生酯化反应，取代度低，淀粉的空间结构更疏松。黏度分析结果显示氧化羟丙基淀粉的黏度最高，3种酯化后的淀粉黏度均较氧化羟丙基淀粉黏度低，取代度越高的淀黏度反而越小。电镜扫描分析结果显示，酯化反应仅发生在淀粉颗粒表面，并未对淀粉颗粒的内部结构造成破坏，且随着酯化量的减少，淀粉的空间结构越疏松。热重曲线分析结果显示，随着温度的升高，氧化羟丙基淀粉和酯化淀粉的质量变化有所不同。综上所述，氧化羟丙基淀粉的羟基被羰基取代，形成新型羟丙基淀粉醋酸酯淀粉并对其进行铺膜，测定并比较膜的性能从而筛选出性能最好的酯化淀粉膜，即氧化羟丙基淀粉与醋酸酐比例为10∶4.0时，淀粉膜的性能最佳，此时断裂伸长率为20.3%，吸水率为17.5%，最大接触角为88.6°。【结论】氧化羟丙基淀粉与醋酸酐比例为10∶4.0时，所得氧化羟丙基醋酸酯淀粉膜性能最佳（机械强度、吸水性和疏水性等均有所改善），有望用于淀粉胶囊的制备。

Preparation of new oxidized hydroxypropyl acetate starch and determination of its film performance

【Objective】 The purpose of this study was to explore the preparation of new oxidized hydroxypropyl acetate starch and the best process conditions for starch membrane preparation, measuring the determination of membrane properties, which would provide reference for the development of starch capsules.【Method】 The oxidized hydroxypropyl acetate starch been prepared from oxidized hydroxypropyl starch derived from cassava starch and acetic anhydride. The ratios of acetic anhydride and starch(10∶1.5, 10∶2.0, 10∶4.0) were selected. Then thin film could be prepared by tape casting method, oxidized hydroxypropyl acetate starch as raw material, glycerol and sorbitol as plasticizer, gellan gum as strengthening agent were selected as influencing factors. The phase identification of the oxidized hydroxypropyl acetate could be carried out by infrared absorption spectrometry(FT-IR), X-ray diffraction, scanning electron microscope method(SEM), viscometer, thermogravimetric analysis, etc. The tensile strength, moisture absorption, hydrophilicityand appearance and morphology of the membrane were measured simultaneously.【Result】 Three new oxidized hydroxypropyl acetate starches were prepared and characterized, the degrees of substitution were 0.100, 0.142 and 0.152 respectively. FT-IR analysis showed that the oxidized hydroxypropyl starch was esterified with acetic anhydride, the degree of substitution was low, and the space structure of starch was looser. The viscosity analysis showed that the viscosity of oxyhydroxypropyl starch was the highest, and the viscosity of three kinds of starch after esterification was lower than oxyhydroxypropyl starch, while the viscosity of starch with higher degree of substitution was smaller. SEM analysis showed thatthe esterification reaction only took place on the surface of starch granules and did not destroy the internal structure of starch granules and the spatial structure of starch was looser with the reduce of esterification amount. Thermogravimetric curve analysis showed that the quality of oxyhydroxypropyl starch and esterified starch changed differently with the increase of temperature. The result indicated that hydroxyl of the oxidized hydroxypropyl starch has been replaced by carboxyl, three new hydroxypropyl starch acetate starch been prepared. By determiningand comparing the performances of thin films, the following conclusion could be drawn: the performance of starch film was the best when the proportion of acetic anhydride and starch was 10∶4.0. Under this condition, the thin film could reach the following result: elongation at break 20.3%, maximum water absorption 17.5%, and contact angle 88.6°.【Conclusion】 The oxidized hydroxypropyl acetate starch film are the best(the mechanical strength, absorbance and hydrophobicity are all improved) and it is expected to be used in the preparation of capsules when the ratio of acetic anhydride to oxidized hydroxypropyl starch is 10∶4.0.