The Rheological Properties And Miscibility Of Hydroxypropyl Methylcellulose/Hydroxypropyl Starch System

Food package,as an important part of food commodities,is used to protect the food from tampering or contamination effects of external environmental conditionals in the circulation,extending food shelf-life or storage period.Edible films and coatings,as a new packaging materials for food with safty,edibility and even some nutritional value,have strong potentials to be applied in areas such as food packaging,food preservation,fast food and pharmaceutical capsules,has become a research hotspot in food packaging.Hydroxypropyl methylcellulose(HPMC)is one of the most widely used edible film materials with food and pharmaceutical application.HPMC films are strong,flexible,fully transparent,oleophobic.However,HPMC is thermal-gel,which lead to poor processing performance at low temperature and high production energy consumption.Moreover,its greater price limits its broader application,even when used for higher value medical purpose such as capsules.Hydroxypropyl starch(HPS)is another materials widely applied to food and pharmaceutical fields.In contrast,HPS,as cooling-gel with lower price and abundant sources,is one of the most promising materials to reduce the costs and improve processibility and barrier properties of HPMC.By blending HPMC with HPS,the HPMC/HPS thermal/cooling-gel bi-phasic systems were builded.The effects of blend ratio,solution concentration and shearing on the rheological properties of HPMC/HPS system were studied using rheometer,and the interaction mechanism of HPMC and HPS in solution and the consistency of blend system were discussion,the relationship between rheological properties and structure were established.The results shows that the blend system have a critical concentration at 8%,lower than this concentration,HPMC and HPS exist mainly as individual chains or phase region,over the critical concentration,the individual chains and phase region start to contact each other,and formed a microgel structure with gel center of HPS and HPMC chains intertwined or associated with each other in the crowed space,making the blend solution behave as polymer melt.The rheological property of blend system confirms with the log-additivity rule at a great degree,implying a good compatible of this system.It also presents positive-negative deviations from the mixture rule,suggesting the blend system exists a continuous-discrete type of morphology and change of continuous phase occurred at blend ratio of 4:6.HPMC/HPS composite films were prepared by casting,the consistency and phase separation were explored with SEM,DMA and TGA,the mechanical properties and Oxygen permeability of composite films were also tested.The results indicated the blend system was immiscible but compatible to a certain degree,since there was no observable boundary between the two phases in SEM and most of the composite films showed only one peak in the DMA and DTG curves.The increased HPS content could significant improve the oxygen barrier property of HPMC films.The was a cross point of mechanical properties for the films with different blending ratios under different relative humility conditions,which provide information to obtain optimized mechanical properties for desired applications.A simpler dying technique with iodine,which allows the different phases to be distinguished under a conventional optical microscope,has been developed for the study of morphology and phase transition of HPMC/HPS blends.The mechanical and transparency properties were also tested in this work.Then,the relationship between morphologies,phase transition,transparency and mechanical properties were established.The blending system is immiscible and there is a phase transition point depending on blending ratio and solution concentration.However,there were many interphasic regions occur in the blend system,indicating a good compatible between HPMC and HPS.It was found that the lower transparency point of the blend and phase transition region of HPMC from continuous phase to separated phase corresponded with the decrease of tensile modulus.The modulus and elongation were also decreased with increased solution concentration,likely due to the change in morphologies where HPMC gradually changed from a continuous phase to a separated phase.The effect of HPS chemical structural change on the rheological properties of HPMC/HPS blend system were investigated using rheometer.The consistency and phase transition along with temperature change were further explored by combing rheology and iodine dying technique.The relationship between morphologies,phase transition,rheological properties and gel properties were established.The viscosity,shear-thinning of HPMC/HPS blend solution at low temperature were decreased with increased hydroxypropyl substitution degree.Hydroxypropylation of starch also narrowed the linear viscoelastic region,lower the phase transition temperature,improve the solid-like behavior at low temperature and fluid-like behavior at high temperature of the blend system.HPMC and HPS could form continuous phases at low and high temperatures,respectively.However,as separated phase,HPS at low temperature,and HPMC at high temperature,play a dominant role in controlling the viscoelastic properties of the blends.The tan δ peaked at about 45 °C,corresponding with the rapid change in viscosity of the blends at about 45 °C,meaning a change of the continuous phase in the matrix,which confirmed with the two continuous phases observed in morphological result at 45 °C.Synchrotron SAXS was applied to study the effects of HPS chemical structural change on the crystalline structure and microstructure of HPMC/HPS composite films.The mechanical property,oxygen permeability and thermal stability were also investigated in this work.The SAXS results shows both the hydropropylation of HPS and blending process significantly decreased the recrystallization of starch,and lead to a much more loosen amorphous structure.The mechanical properties,oxygen permeability and thermal stability,closely related with the crystalline and amorphous structure of the composite films,were the comprehensive results of both HPS chemical structure change affects and the consistency of the two components affects.