Hydroxypropyl methylcellulose (HPMC) film has excellent performance, but because HPMC is a thermal gel, the viscosity at low temperature is too low, which is not conducive to coating (or dipping) and drying at lower temperature to prepare edible film, resulting in poor processing performance; in addition, its high cost limits its application. Hydroxypropyl starch (HPS) is a low-cost cold gel, its addition can increase the viscosity of HPMC at low temperature, improve the processing performance of HPMC, and reduce the production cost, further, the same hydrophilicity , glucose units and hydroxypropyl groups all contribute to improve the compatibility of these two polymers. Therefore, a hot-cold gel blend system was prepared by blending HPS and HPMC, and the effect of temperature on the gel structure of the HPMC/HPS hot-cold gel blend system was systematically studied by using rheometer and small angle X-ray scattering techniques. , combined with the influence of heat treatment conditions on the microstructure and properties of the membrane system, and then constructed the relationship between the gel structure of the blend system-membrane structure-membrane properties under the heat treatment conditions.
The results show that at high temperature, the gel with higher HPMC content has higher modulus and more significant solid-like behavior, the self-similar structure of gel scatterers is denser, and the size of gel aggregates is larger; at low temperature, the HPS content Higher gel samples have higher modulus, more prominent solid-like behavior, and denser self-similar structure of gel scatterers. For the samples with the same blending ratio, the modulus and solid-like behavior significance and self-similar structure density of the gels dominated by HPMC at high temperature are higher than those dominated by HPS at low temperature. The drying temperature can affect the gel structure of the system before drying, and then affect the crystalline structure and amorphous structure of the film, and finally have an important impact on the mechanical properties of the film, resulting in the tensile strength and modulus of the film dried at high temperature. Higher than dry at low temperature. The cooling rate has no obvious effect on the crystalline structure of the system, but has an effect on the density of the microdomain self-similar body of the film. In this system, the density of the self-similar structure of the film may affect the mechanical properties of the film. Performance has a major impact.
Based on the preparation of the blended membrane, the study found that the use of iodine solution to selectively dye the HPMC/HPS blended membrane established a new method for clearly observing the phase distribution and phase transition of the blended system under a microscope. method, which has methodological guiding significance for the study of phase distribution of starch-based blend systems. Using this new research method, combined with infrared spectroscopy, scanning electron microscopy and extensometer, the phase transition, compatibility and mechanical properties of the system were analyzed and studied, and the compatibility, phase transition and film appearance were constructed. relationship between performance. The microscope observation results show that the system undergoes phase transition when the HPS ratio is 50%, and the interphase mixing phenomenon exists in the film, indicating that the system has a certain degree of compatibility; infrared, thermogravimetric analysis and SEM results further verify the blending. The system has a certain degree of compatibility. The modulus of the blended film changes when the HPS content is 50%. When the HPS content is greater than 50%, the contact angle of the blended sample deviates from the straight line connecting the contact angles of the pure samples, and when it is less than 50%, it deviates negatively from this straight line. , which are mainly caused by phase transitions.
Post time: Apr-25-2024