Resarch On Synthesis And Performance Of The Ultrasonic Modified ST/PU Composite Materials

In this paper, the ultrasonic method is utilized to modify natural taro starch, in order to expand the application range of natural taro starch. Polyurethane material has good mechanical properties and biocompatibility, but it can almost not be degraded. In this study, the ultrasound modified starch is mixed with polyurethane and the degradation properties of polyurethane material can be improved by means of degradation properties of the ultrasonic modified starch. Thus, composite materials are prepared with good degradation properties, mechanical properties and biocompatibility. This will has the certain research significance in the development of tissue engineering scaffold material and drug carrier material.In the experiment, modified starch is prepared by using the probe type ultrasonic instrument. The preparation conditions of ultrasonic modified starch are optimized and the ultrasonic properties of modified starch are measured. When the ultrasonic processing time is 10min and the mass fraction of starch aqueous solution is 20%, ultrasonic modified starch with good solubility can be obtained. During the process of ultrasonic, the control temperature is lower than 50℃, avoiding the occurrence of gelatinization phenomena. The density of ultrasonic modified starch grain is 841.5kg/m3, lower than the density of natural taro starch grain. The light transmittance of ultrasonic modified starch is 28.13%, lower than the light transmittance of natural taro starch. The retrogradation test of ultrasonic modified starch shows that it has good retrogradation property. The ultrasonic modified starch particles are observed by using scanning electron microscope. It found that after ultrasonic treatment, the basic shape of starch granules is not changed and many rectangular pits appear on the external surface of starch granule, making the total external surface of starch granule surface increase. X-ray diffraction analysis of crystal structure of starch granules showed that after ultrasonic processing the crystalline region of starch particles is not change, but changes occur on the non-crystalline region of starch particles.In the experiment, the polyurethane (PU) aqueous solution is prepared through the prepolymerization reaction, chain extension reaction, neutralization reaction and dispersion method. The effect of the R value (n(NCO)/n(OH)), molecular weight of polyethylene glycol (PEG), neutralization degree and dosage of acetone and the influence of solid content on preparation of the PU synthetic aqueous solution has been studied. Results show that when the R value is not lower than 3, neutralization degree is 80%～100%, the dosage of acetone is 80% and the solid content is 35%～38%, PU aqueous solution with good stability can be obtained. As the PEG molecular weight ranges from 200 to 800, milk white transparent PU aqueous solution with good stability is prepared. The prepared PU aqueous solution has good stability to alkali, storage stability, centrifugal stability, as well as high and low temperature stability.Ultrasonic modified ST/PU composite membrane is prepared, and influence factors of the preparation of ultrasonic modified ST/PU composite membrane are studied through single factor variable method. Results show that when the R value is 3, PEG molecular weight is 200, neutralization degree is 100%, solid content is 38%, ultrasonic modified ST content is 7% and the membrane drying method is natural dry membrane drying method, the prepared ultrasonic modified ST/PU composite membrane has good film-forming property. As the increase of ultrasonic modified ST content, swelling property of composite membrane will increase. Infrared spectrum analysis shows that the ultrasonic modified ST and PU are mainly connected by hydrogen bonds.The ultrasonic modified ST/PU composite microspheres are prepared by phase separation method. The findings show that as the R value is 3, PEG molecular weight is 200, solid content is 38%, modified ST content is 6% and CaCl2 solution concentration is 8%, the sphere of composite microspheres is good, without trailing phenomenon. Before and after the drying of ultrasonic modified ST/PU composite microspheres, average particle size are 3.14mm and 2.12mm, respectively. Before and after drying, composite particle size distributions are both normal distribution. Compared with PU microspheres, the microspheres breakage rate of ultrasonic modified ST is lower and its mechanical strength is better.The microscopic analysis of ultrasonic modified ST/PU composite microsphere surface and profile indicates that the ultrasonic modified ST/PU composite microspheres ball is roundness. It has smooth surface and a lot of dense radial hole in internal composite microspheres, which is beneficial to medicine carrying and drug release. In the modification of composite microspheres, the moisture content of composite microspheres increases with the rising of modified ST content. Swelling properties of the composite microspheres and degradation performance increase with the rising of the modified ST content.The drug-loading ultrasound modified ST/PU composite microspheres is prepared and composite microspheres drug-polymer interactions presents a leveled off after the first increase trend, as drug concentration increases. When drug concentration increases, coating rate firstly increases and then decreases. The vitro release studies of composite microspheres show that, with the extension of time, the accumulative release rate of the drug will gradually increase, and with the increase of the content of ultrasonic modified ST, the drug release rate is accelerated. Hence, the drug release rate can be regulated by adjusting the ultrasonic ST content.