Microstructures And Properties Of Hydroxypropyl Methylcellulose Based Photophobic Films

When food and medicines are directly exposed to light,they may undergo many negative changes,such as oxidation of lightsensitive moieties(carotenoids and vitamins,etc.),variations of color,disappearance of aroma,and formation of off-flavors.Using light-shielding packaging for food and medicines can eliminate the effect.It has been found that a new type of light-shielding edible film can be prepared by adding salt to hydroxypropyl methylcellulose(HPMC)film.In this paper,the effects of salt types and hydroxypropyl methylcellulose types on the multiscale structure,mechanical properties and photophobic properties of HPMC/salt film were studied.The results showed that the formation mechanism of the white color of HPMC film after the addition of salt was mainly due to the apperance of the microporous structure inside the film.Then,lipid-soluble tea polyphenols(LTP)was added to HPMC/salt system to prepare photophobic antioxidant control-release film since microporous materials are always considered to have control-release property.Moreover,the porous structure which can directly affect the control-release of LTP to endow film with different sustained antioxidant properties could be ajusted by changing the salt content.The main findings are as follows:(1)Monosodium phosphate(MP),sodium citrate(SC),sodium lactate(SL)and magnesium citrate(MC)can be blended with hydroxypropyl methylcellulose(HPMC)to make photophobic(white)films at lower drying temperatures.’Small angle X-ray scattering(SAXS),wide angle X-ray diffraction(XRD),scanning electronmicroscopy(SEM),whiteness determination,dynamic mechanical analysis(DMA)and texture analysis were adopted to study the variation of microstructures and properties.These four kinds of HPMC/salt films showed decreased crystallinity and increased compactness and smoothness of the self-similar structures in larger scale ranges.HPMC/MP,HPMC/SC and HPMC/SL film showed coarser and porous morphologies,lower mechanical parameters and higher whiteness than pure HPMC film.HPMC/MC film showed smoother morphologies,higher tensile strength,elongation andwhiteness than pure HPMC film.Porous structures and more compact self-similar structures might contribute to the photophobic property of these films,and relatively smooth morphology might dominate the increasing mechanical parameters of HPMC/MC film.(2)Photophobic(white)films were prepared by mixing hydroxypropyl methylcellulose(HPMC)of different molecular weights with sodium citrate(SC).SAXS,XRD,SEM,DMA,whiteness determination and texture analysis were used to investigate the effect of HPMC molecular weight on the aggregation structures and properties of HPMC film.The crystalline integrity decreased with the increased molecular weight of HPMC for these HPMC/SC films.Similar crystallinity was observed for 6HPMC/SC and 15HPMC/SC,which was larger than that of 50HPMC/SC.All the three HPMC/SC film showed surface fractal structure with similar Ds.With the increasing molecular weight of HPMC,the HPMC/SC film showed honeycomb structureswith smaller holes and more compact porous structure,Tg first increased and then decreased a little,the tensile strength and elongation increased with the increasing HPMC molecular weight.50HPMC/SC films with the smallest pores showed the largest whiteness.(3)Hydroxypropyl methylcellulose(HPMC)/sodium citrate(SC)/lipid tea polyphenol(LTP)photophobic films with different pore sizes frommicron scale to nanometer scalewere prepared by regulating the SC content(1-7%).The microstructures,physical and sustained antioxidant properties of these films were studied by using wide angel X-ray diffraction,small angle X-ray scattering(SAXS),scanning electron microscope,whiteness meter,ultraviolet spectrophotometer,texture analyzer and peroxide value test.Composite films with higher SC content showed larger pore size and whiteness.With the increasing SC content,crystallinity first increased then decreased.The addition of SC decreased the Ds(surface fractal dimension)value,smoothness of the cross-section structure,tensile strength,elongation and modulus of composite films.HPMC/SC/LTP microporous films possessed controlrelease property in oil system,reflected by the lowest peroxide value of peanut oil enclosed in film with 3%SC during three weeks,meaning this film showed the best sustained antioxidant property.