Research On The Relation Between Microstructure And Properties Of Hydroxypropylmethyl Cellulose/ Hydroxypropyl Starch Blends

HPMC film has high performance. However, HPMC is hot gel, which makes it is hard to form even edible films through dipping(or coating) and drying at lower temperature. Another factors which interfere its application is its higher price. HPS, recognized as a cheap cool gel, which can overcome the shortcomings of HPMC. What’s more, both of these two materials have glucose unit and hydroxypropyl oxygen groups, which is good at improving their miscibility. Thus, HPS was blended with HPMC. Rheometer and SAXS were used to study the influence of temperature on the solid-like behavior, modulus and structure of HPMC/HPS blending gel. Meanwhile, the film structure and properties at different drying temperatures and cooling rates were studied, then, the relationship among gel structure, film tructure and film properties were established. The results demonstated that at higher temperature, samples containing higher HPMC ratio showed higher modulus, more obvious solid-like behavior, more compact self-similar structure and much larger gel aggregates; at lower temperature, samples containing higher HPS ratio showed higher modulus, more obvious solid behavior, more compact self-similar structure. For samples with the same HPS ratio, the modulus, solid-like behavior, self-similar structures of HPMC dominating gel at higher temperature were larger than that of HPS dominating gel at lower temperature. Drying temperature can affect the crystalline and amorphous structure of the films by impacting the gel structure. Eventually, the different crystalline and amorphous structure can result in different mechanical properties, the films dried at higher temperature showed higher tensile strength and modulus. Cooling rate do not have much influence on the crystalline degree of the films, but affect the self-similar structure of the films, the compactness of which may make a big difference in determing the mechanical properties.Based on the preparation of blending films, a simple technique through identifying the HPS in the blend under a normal optical microscope through dying HPS with iodine was established. This method offers an easy and clear way to study the phase distribution of the starch-based system. By adopting this observing method and combing with SEM, FTIR, Extensograph, et al., the phase transition, miscibility and mechanical properties of this system were studied thoroughly, and the relationship between phase transition, miscibility and film properties was eatablished. Research on OM showed that phase transition occured when HPS ratio was 50% and interphase mixing was observed which proved that this system showed compatibility to some extent. FTIR and SEM further proved the compatibility of this system. Contact angel showed a sharp change at HPS ratio of 50% and modulus showed a turning point at this blending ratio, which were due to phase transition to a large extent.In this work, the influences of plasticizers on the multilevel structure, mechanical properties and transparency were studied. And the acting mechanisms of plasticizers on the mechanical properties were established. All the plasticizers increased the crystalline degree, among which, glycerol had the most obvious effect, followed by PEG, then propylene glycol. The influences of plasticizers on the structure of microcell depended on the type of the plasticizer. PEG decreased the compactness of the self-similar structure, propylene glycol increased the compactness of the self-similar structure of all samples except for pure HPMC. Glycerol plasticized samples did not possess self-similar structure, but showed lamellar structure of 15.7nm. The order of the extent of the influence of plasticizers on decreasing Tg was PEG>glycerol>propylene glycol, indicating that PEG showed the most obvious effect to loose the amorphous region, followed by glycerol, then propylene glycol. PEG could improve the mechanical properties of the blends most obviously, followed by glycerol, then propylene glycol. Thus, we could conclude that the influence of plasticizers on the mechanical properties depended to a large extent on the influence of their loosing effect of the amorphous region. The order of extent of the influence of plasticizers on increasing the transparency was glycerol>PEG>propylene glycol.In this work, the influences of citric acid on the microstructure and property were studied, and the action mechanisms of citric acid on mechanical properties were infered. For pure samples, after crosslinked, the Tg increased. For blending samples, a new Tg was observed between the Tg of pure samples, indicating the crosslinking of HPMC and HPS chains. After crosslinked, the crystalline degree of samples increased, the compatibility decreased, thermo-stability was improved, the hydrophilic property decreased. After crosslinked, the tensile strength and modulus increased, the elongation of sample 50:50 decreased, while elongation of 100:0 increased. It was guessed that there were maybe four factors which impacted the mechanical properties of the crosslinked samples: crosslinking effect, the degradation effect of citric acid, the lower extent of compatability and the higher crystalline degree.