Study On UV Shielding Performance Of Surface Coating And Copolymerization Modified Pet Film

Polyethylene terephthalate(PET)film has good mechanical properties and excellent light transmittance,which is usually used in the field of visible food and drug packaging.However,due to its poor ultraviolet(UV)shielding property,the effective ingredients in food and drugs will deteriorate,shorten the quality guarantee period of products,and even pose a threat to human health,which seriously limits its wide application.For the modification of PET film materials,coating modification and copolymerization modification are two main methods.Coating modification can give new properties to PET film on the basis of maintaining the original properties of PET film;copolymerization modification can control the molecular structure of PET,fundamentally change the material properties and give new properties to PET film.Therefore,in this paper,on the basis of ensuring the original excellent performance of PET film,the method of coating modification and copolymerization modification was used to improve the UV shielding performance of PET polyester film,and finally realize preparation of fully shielding UV film,improving the competitiveness of PET film materials.Zinc oxide quantum dots(ZnO QDs)are widely used in the preparation of transparent UV absorbing materials because of their small size and excellent UV absorption properties.Using polyvinyl alcohol(PVA)as resin matrix and ZnO QDs as UV absorber,a coating with UV shielding property was constructed on the surface of PET film to improve the UV shielding property of PET film.ZnO QDs was synthesized by sol-gel method.In order to reduce its UV photocatalytic effect and enhance the service life of the coating,a layer of silica was coated on the surface of ZnO QDs to form ZnO QDs@SiO₂ nanoparticles.Rhodamine B degradation experiments showed that the SiO₂ encapsulated on the surface of ZnO QDs significantly reduced the photocatalytic activity of ZnO QDs.The coating showed excellent UV shielding performance on PET film.The transmittance of ultraviolet-visible(UV-Vis)spectrum is only 5%in the UV region(<355 nm),and it still showed high transmittance(87%)in the visible region.Even when exposed to30 W UV lamp for 100 h,the UV-Vis transmission spectrum did not change significantly,showing good UV durability.However,the degradation of the coating will occur after longer UV irradiation,which will reduce the performance of the coating.In addition,the ZnO QDs@SiO₂/PVA coating has the same ink absorption property as the commercial SiO₂/PVA ink absorption coating.Therefore,the as prepared ZnO QDs@SiO₂/PVA coating can form an ink-jet printing coating with high light transmittance and high UV shielding property on PET film.Then,a new UV shielding coating was formed on PET film with trans-cinnamate epoxidized soybean oil(TESO)as resin matrix and sericite as UV shielding agent to solve photocatalytic degradation defect of ZnO QDs@SiO₂/PVA coating and its problem of poor adhesion on PET film.TESO was prepared by the reaction of epoxidized soybean oil and trans-cinnamic acid.TESO was cured by[2+2]cycloaddition reaction under ultraviolet light.In order to further compare the effects of[2+2]cycloaddition reaction and free radical reaction on the properties of the coating materials,the acrylic epoxidized soybean oil resin(AESO)cured by free radical reaction was synthesized from acrylic acid and epoxidized soybean oil.The results showed that TESO had better adhesion,bending resistance and UV shielding properties than AESO on PET film.On this basis,nano sericite was added to improve the hardness and UV barrier of the coating.This coating on PET film showed excellent UV shielding performance and had the function of protecting film,which solved the existing problem of ZnO QDs@SiO₂/PVA coating on PET film.The above coating modification method was difficult to achieve high band UV shielding,even if ZnO nanoparticles with excellent UV absorption properties were added.By means of copolymerization modification,?-truxillate(TA)with multi phenyl ring structure was used to replace part of terephthalic acid to copolymerize with ethylene glycol.A new poly(ethylene?-truxillate-co-ethylene terephthalate)(PETT)material was synthesized.The effects of TA on the chemical structure,thermal properties,crystallization behavior,mechanical properties and UV shielding properties of PETT were studied.Thermal analysis showed that a small amount of TA can significantly reduce the crystallinity and melting temperature of PETT,but did not affect its thermal stability.Only adding 10 wt%TA,PETT can shield most of the UV(<400 nm),which makes up for the defect that the original PET cannot shield the UV-A band(320–400 nm).In terms of mechanical properties,the yield stress of PET increased significantly from 29.8 MPa to 40.2 MPa of PETT(10 wt%TA).A small amount of TA can provide excellent UV shielding and mechanical properties for PET.Finally,TESO/sericite coating on PETT(10 wt%TA)film showed 100%UV shielding performance and had the function of protecting the film.However,the light transmittance of the film in the visible light region has a cert ain drop.Therefore,the film coating material designed and prepared in this paper realizes the preparation of full UV shielding PET packaging materials,and has a potential application prospect.