Effects Of Different Types Of Plasticizers On The Structure And Properties Of Hydroxypropyl Methylcellulose/Sodium Dihydrogen Phosphate Light-proof Film

Light-proof packaging can reduce the negative effects of light on photodegradation,discoloration and odor of photosensitive components in food.Hydroxypropyl methylcellulose(HPMC)-based film is a good substitute for petroleum based packaging due to its renewable,degradable,excellent mechanical properties and excellent water vapor resistance.The always used HPMC/TiO2 light-proof film can initiate photocatalytic oxidation reaction and has relative lower mechanical properties;The existing HPMC/calcium salt light-proof film needed to be formed at higher drying temperature,which can cause higher cost and lower ductility to the film.A new type of hydroxypropyl methylcellulose light-proof filrn-HPMC/NaH2PO4 film was prepared in this paper,which can overcome the photocatalytic oxidation reaction of HPMC/TiO2 film and the defect of higher drying temperature dependence of HPMC/calcium salt film;Furthermore,different plasticizers were used to improve the ductility of this HPMC/NaH2PO4 film.The main research results were as follows:(1)By adding NaH2PO4 to HPMC,a new type of HPMC/NaH2PO4 light-proof film can be prepared by drying it at room temperature using a simple casting method.HPMC/NaH2PO4 film appeared to be white and the formation of white color was independent of drying temperature.The whiteness of the film increases with the increase of NaH2PO4 content,and begins to decrease when it reaches 15%.The interaction between NaH2PO4 and HPMC may occur between H2PO4-1 and CH3.After adding NaH2PO4,the hole structure in the film makes the film white and gives the film light-proof property.The surface fractal structure of HPMC/NaH2PO4 film is denser and smoother than that of pure HPMC film.These denser and smoother fractal structures may also cause the film to whiten.The elongation decreases with the increase of NaH2PO4 content;when NaH2PO4 does not exceed 10%,the tensile strength and modulus of HPMC/NaH2PO4 film does not decrease significantly;when NaH2PO4 reaches 15%,the tensile strength and modulus decreases significantly.NaH2PO4 makes pores appear inside the HPMC film and reduces the cross-sectional smoothness of the film.These morphological structures may dominate the reduction in elongation of the film.(2)PEG with different molecular weight were used to improve the ductility of HPMC/NaH2PO4 film,and the effects of them on the structure,light-proof properties and mechanical properties of the film were studied.After adding PEG with different molecular weights,the stretching vibration of the characteristic functional groups H-O-H and hydroxyl functional groups in the film changes.PEG800 and PEG2000 reduce the crystallinity of the film,while PEG 1500 and PEG4000 increase the crystallinity of the film.The film containing PEG has a larger fractal dimension than the pure HPMC/NaH2PO4 film.When the molecular weight of PEG is 4000,6000 and 8000,the film has the lowest density and smoothness.The cross-sectional shape of the film containing PEG800,PEG1500 and PEG2000 is smooth,and the cross-section of the system is smoother after adding PEG6000 and PEG8000.The Tg of the film basically decreases as the molecular weight of PEG decreases.After adding different molecular weight PEG to plasticize,the film's light-proof performance remains unchanged or slightly increases.The elongation increases with the increase of the molecular weight of PEG.PEG6000 and PEG8000 have no significant difference in improving the ductility of the film,and are very good.(3)Ionic liquid[EMIM]Ac was used to improve the ductility of HPMC/NaH2PO4 film,and the effects of different content of[EMIM]Ac on the structure,light-proof properties and mechanical properties of the film were studied.The crystallinity of the film added with[EMIM]Ac increases,and the crystallinity of the film containing 8%[EMIM]Ac is the highest.All films have self-similar structures and all exhibit surface fractals.The compactness and smoothness of the fractal structure of the film containing 8%[EMIM]Ac are reduced All films have a porous morphological structure.The pore size of the film containing[EMIM]Ac is smaller than that of the unplasticized film,and the number of pores increases.The addition of[EMIM]Ac leads to a decrease in Tg,and the degree of decrease becomes larger as the content of[EMIM]Ac increases.The water content of the film containing 8%[EMIM]Ac is significantly increased.The whiteness of HPMC/NaH2PO4 film decreases with the increase of[EMIM]Ac content,but it still has good light-proof performance.Except for the HPMC/NaH2PO4 film with 8%[EMIM]Ac,the tensile strength of the HPMC/NaH2PO4 film decreased slightly.The tensile strength and modulus of the remaining doses of HPMC/NaH2PO4 film did not change significantly.The elongation of the film increases with the increase of[EMIM]Ac dosage.It shows that the ionic liquid[EMIM]Ac can improve the ductility of the HPMC/NaH2PO4 film,which is mainly related to the reduction of the pore size of the film,the reduction of the glass transition temperature and the increase of the moisture content of[EMIM]Ac.(4)Different types of ionic liquids were used to improve the ductility of HPMC/NaH2PO4 films,and their effects on film structure,light-proof performance and mechanical properties were studied.The degree to which the ionic liquid increases the crystallinity of the film is:[BMIM]BF4>[BMIM]C1?[EMIM]Ac.The film with[BMIM]BF4 has the smallest number of holes and the smallest hole size.The degree of Tg reduction of the film added with different ionic liquids is[BMIM]C1>[BMIM]BF4>[EMIM]Ac.After adding ionic liquid,the moisture content of the film increased,and the moisture content of the film containing[BMIM]C1 increased the most.The whiteness of HPMC/NaH2PO4 films with[EMIM]Ac and[BMIM]Cl decreased slightly,but the whiteness of HPMC/NaH2PO4 films with[BMIM]BF4 did not change significantly.After the addition of ionic liquid,the tensile strength and modulus of HPMC/NaH2PO4 film were not significantly changed compared with the original film,while the elongation increased significantly,the degree of increase was[BMIM]BF4>[BMIM]C1?[EMIM]Ac.It shows that different ionic liquids can improve the ductility of HPMC/NaH2PO4·film,and[BMIM]BF4 improves the ductility of HPMC/NaH2PO4 system the most.The improvement effect of[BMIM]BF4 is better than[BMIM]C1 mainly because its plasticized HPMC/NaH2PO4 film has less pore structure and smaller pore size.