Synthesis Of Phosphate Starch Under Outfield Intensifying

Phosphate starch is one kind of starch derivative produced from esterification of starch and phosphate. As a kind of multifunctional additive, it can be widely used in paper-making, textile, food industry and has great practical value and market prospect. Because starch is a morphologically complex polymer substance, consisting of loose amorphous regions that are interspersed with highly regular crystalline regions, it is difficult for chemical reagent to contact with inner molecular, which results in low starch activity in reaction, low reaction efficiency and products with low degree substitution (DS). Therefore, there is great interest in methods to modify the structure in the crystalline region, or decrease the size of crystalline regions. It is also significant to widening application of starch phosphate. In this thesis, the effects of outfield intensifying (ultrasonic wave, microwave and mechanical activation) on structure and properties of cassava and maize starch and its application in preparation of phosphate starch were investigated.Firstly, ultrasonic wave and microwave pretreated starch was used to synthesize phosphate starch by semi-dry process, and mechanical activated starch was used to synthesize phosphate starch by dry process, respectively. The effects of ultrasonic, microwave and activation time and power, the value of pH, reaction temperature and time, the amounts of phosphates and urea on degree of substitution(DS) and reaction efficiency(RE) were discussed. The results indicated that ultrasonic wave, microwave and mechanical activation considerably enhanced the chemical reactivity of starch, and then promoted the DS and RE of the cassava and maize starch phosphate. At the optimum condition, the DS of the phosphate starch were increased by 22.8% comparing with that of the products without pretreatment.Secondly, the ultrasonic wave, microwave and mechanical activation effects on physicochemical properties of cassava and maize starch were investigated by analyzing the variation of rheological characteristics and transparency. The results indicated that apparent viscosity, thixotropy and shear-thinning nature of the starch pastes decreased; starch pretreated by outfield intensifying had pseudoplastic characteristics according with the power law. In addition, transparency increased because of the effect of ultrasonic and microwave to some extent, but longtime ultrasonic and microwave treatment would result in decrease of transparency. The transparency increased with increasing of mechanical activation time.Finally, the ultrasonic wave, microwave and mechanical activation effects on functional groups, crystal structure, granular morphology and thermal property of cassava and maize starch and their phosphate were investigated respectively by using Fourier transform infrared spectroscopy, X-ray diffractometry, scanning electron microscopy and analysis of starch-iodine compound absorption spectrum. Structure analysis suggested that ultrasonic wave, microwave and mechanical activation wouldn't destroy functional groups of starch, but damaged crystal structure; crystallmity decreased; reaction activity was improved; there were dents on starch granules surface and chains ruptured; phosphate groups were added in glucose units of starch but it can't be manifested in the FTIR spectra. There were a certain of dents and splits on phosphate starch granules surface. Esterification of starch not only occurred in the amorphous region of starch granule, but also damaged its crystalline region.