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 The result indicated that hydroxyl of the oxidized hydroxypropyl starch has been replaced by carboxyl, three new hydroxypropyl starch acetate starch been prepared.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.