| Edible filmshave became a new type of green packaging materials due to its advantages includingsafety, edible and biodegradable.Hydroxypropyl methyl cellulose(HPMC) has a ability of good film forming, good mechanical properties, which has been widely used in food and medicine field. Currently, it has became the mature substitute for gelatin capsules.However,since HPMCis a kind of thermal gel, its application was limited by its high gel temperature, poor oxygen isolation performance after film-forming and higher costsfor many applications.Hydroxypropyl starch(HPS) has similar structure with hydroxypropyl methyl cellulose(HPMC), and it is a kind of cold gel.In theory, it is a good way to reduce the gel temperature of HPMC through blending with HPS.Oxygen resistance ability may also be improvedsince HPS has good oxygen barrier property.This paper investigatedthe HPMC/HPS blend film, in particularfocused on the influerence of different storage conditionson the microstructures and properties of the blends.HPMC/HPS composite film is a kind of hydrophilic polysaccharide edible film, any changes of humidity or temperature in storage environmentcould affect its properties significantly.In order to obtain relatively good mechanical performance of composite film for storage valuation, this paperinvestigated the effect of storage on the composite film under different preparation conditions firstly through the single factor experiment which set the film-forming solution concentration, film forming temperature and plasticizer content as single factors, the tensile strength and elongation at break astest indicators.By using the response surface method, this chaptergained the optimized preparation conditions, in which film-forming solution concentration was10%, film-forming temperature was70℃ and the plasticizer content was20%.This thesismainly focused on studying the effect of different humidity(33%, 57%, 75%), temperature(4℃, 27℃,45℃, 60℃) and storage time onthe microstructures and properties of blend films.The results showed that the tensile strength of blend film decreased with the increasing of relative humidity, while increased the elongation at break.Both permeabilityand light transparencywere alsodecreased.The analysis of FTIR spectra of blend filmshowed that the higher humidity, the stronger of formation of hydrogen bonding interaction between material and moisture, which resulted in astronger affect on the properties of the blend material.XRD spectra showedthat the increasing of humidity couldchange the crystalline structureof blend material.The DSC curve proved that the increased of humidity could make the enthalpy of membrane increased. SEM could observe clearly swelling effect of film that happenedat high moisture conditions.The effect of environment temperature on the properties of blend material was also significant. The temperature increased the tensile strength of the blend films, in particular for the sample containing higher HPS content,such as the blend 7-3.Higher temperature(60℃)exacerbated water lossing, which resulted in lost the package performance.The WVTR of filmdropped first then increased slightly with increasing temperature. The oxygen resistance and light transparency bothdecreased. The DMA results showed that the glass transition temperature of blend material was increased with increasing storage temperature, resulting in increasing the stiffnessof the material. XRD also proved that temperature increased the crystallinity of blend material.With increasing storage time, the tensile strength of blend material was increased, permeability and light transparency were slightly decreased, which corresponding to the aging of the blend material.XRD spectra showed that HPMC could inhibit the recrystallization of starch components, which resulted inkeeping the crystal structure of the blend material stablein the longer storage. A phase separation could be observed by SEM. |
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