Study On The Preparation And Application Of PP/PVA/PP Active Packaging Film Based On Multilayer Controlled Release Technology

With the improvement of food quality and safety requirements,many new packaging technologies have been developed.Active packaging film is one of the most promising packaging technologies.The increasing environmental problems caused by non-degradable plastic packaging materials make biodegradable packaging materials become a hot topic.Poly-(vinyl alcohol)(PVA)is a polyhydroxy and biocompatible synthetic polymer.It exhibits excellent properties of film forming,emulsifying,adhesive,transparency,oxygen barrier and biodegradability.However,the PVA chain contains many hydroxyl groups and is sensitive to water molecule.The barrier properties of films will decrease sharply with increasing of relative humidity.This restricts its application in many fields and is also a major obstacle to expand the application of polyvinyl alcohol film in packaging.In this paper,the hydrophobic modification of PVA films was combined with the development of functional packaging films with antimicrobial and antioxidant activities.Firstly,PVA films were modified by boric acid and nano-montmorillonite(MMT)in order to obtain PVA films with optimized comprehensive properties.The effect of MMT on the structural,mechanical,barrier,water resistance,thermal stability and morphology properties of cross-linked PVA/BA film was investigated.Secondly,the active PVA films with antibacterial and antioxidant activities were prepared by incorporating tea polyphenols(TP)into the films.The effect of TP on the structural,physicochemical,mechanical,antioxidant and antimicrobial properties of PVA film was investigated.Thirdly,the hydrophobic film polypropylene(PP)was used as the inner layer material,and the PP/PVA/PP active packaging multilayer films were prepared by dry lamination.Meanwhile,the permeability of the inner film was controlled by the micropore designing in the inner layer film to achieve the purpose of controlled release active substance.The effect of micropore size on the structural,physicochemical,mechanical,antioxidant and antimicrobial properties of PP/PVA/PP film was studied.Then the release behaviors of TP from monolayer PVA films and PP/PVA/PP multilayer films into different food simulant were studied by migration experiments.The effect of micropore size on the release properties of TP was analyzed and the release behavior of TP from films was characterized by the kinetic model.The release rule of TP from monolayer PVA film and PP/PVA/PP multilayer films to different food mimics was revealed based on these results.Finally,the different films were applied to the trichiurus haumela packaging and the effects of different films on the quality change of trichiurus haumela during cold storage were studied.The main results were as follows:1.Boric acid and MMT were combined to modify the PVA films and the formula of film with good comprehensive properties was obtained.(1)The results showed that the interaction among PVA,boric acid and MMT were occurred through chemical cross-linking and hydrogen bonding.The MMT was well dispersed in the PVA/BA matrix as a whole and it was predominantly exfoliated.There were also partial intercalated structures of MMT layers in the films,which increased with increasing MMT content.(2)The properties of the films changed as the MMT content varied.The films incorporated with MMT became a little darker and tendency toward yellowness,the opacity increased,the water resistance and thermal stability were improved with the increasing amount of MMT.As the MMT content increased from 0% to 3%,the tensile strength increased,while the oxygen permeability and water vapour permeability reduced.However,these properties deteriorated slightly due to partially aggregations of MMT in the PVA film structure with increasing MMT content from 5% to 7%.(3)The PVA film incorporated with 5% boric acid and 3% MMT showed the best comprehensive properties among these films.It indicated that adding appropriate amount of MMT to cross-linked PVA/BA film could further improve the properties and enlarged potential applications of PVA based films for packaging application.2.The effect of TP on the properties of PVA films was studied on the basis of modified PVA film.(1)The MMT layers were well dispersed and mainly exfoliated in the PVA matrix.And partial disordered intercalated structures were also observed in the film.MMT dispersion status in the structure of the films was not changed for TP incorporation.(2)FTIR spectra indicated that interactions between TP and PVA were involved in the films.The properties of the films changed as the TP content varied.The results showed that for the incorporation of TP into the films,the opacity increased,the color became a little darker and tendency toward greenness and yellowness,the tensile strength increased significantly but elongation at break decreased and the hydrophobic property was improved with increasing TP.As the content of TP in the films increased,the WVTR and OTR decreased,which indicated the gas barrier property of the films was improved.TP was dispersed uniformly in the films and no aggregation was observed.The antioxidant activity of the films was significantly improved for TP incorporation and raised with the increasing TP content.It was also demonstrated that the active films incorporated with TP could inhibit bacterial growth.The antimicrobial capacity of the films incorporated with TP against E.coli and S.aureus increased as the TP content in the films increased.This study revealed that PVA/MMT nanocomposite films incorporated with TP showed good potentiality used as active packaging films or coating material to develop active packaging material.3.The PP/PVA/PP active multilayer films were prepared and the effect of micropore size on the properties of the films was studied.(1)The cross-section morphology of the four PP/PVA/PP active multilayer films were similar.The adhesion between the layers of the films was tightly.There was no effect on the cross-section morphology of interface layer PVA films for dry lamination process.The micropores in the inner layer of the multilayer films were approximately circular and the rings with similar wrinkle were observed at the edge of micropores.This was mainly due to the instantaneous high temperature for the laser punching during the preparation of PP microporous films.(2)With the increase of the micropore size in the inner layer of the PP/PVA/PP active multilayer films,the color of the composite film was almost unchanged,the opacity increased,the tensile strength and elongation at break decreased slightly,and the water resistance increased significantly,the gas barrier(water vapour and oxygen)properties decreased slightly.(3)The films exhibited antioxidant and antimicrobial activity through the DPPH free radical scavenging and inhibition rate experiments,which increased with increasing of micropore size.It was ascribed to the difference of release rate of TP from films,which also proved that the micropores in the inner layer of the multilayer film showed controlled release property.4.The release rule of TP into different food simulants in monolayer PVA active films and PP/PVA/PP multilayer films was revealed.(1)Comparing with the release properties of different monolayer PVA films in the same food stimulant,the equilibrium concentration of TP in the food stimulant increased with increasing of TP content in the films,but the release percentage of TP reduced.Comparing with the release properties of the same monolayer PVA films in the different food stimulant,the release percentage of TP when reaching equilibrium state was as follow from high to low: 50% ethanol > 10% ethanol > water > 3% acetic acid > 95% ethanol.(2)Comparing with the release properties of different PP/PVA/PP multilayer films in the same food stimulant,the release rate of TP from films into food stimulant increased with the increasing of the micropore size.The time taken for the four multilayer films to achieve release equilibrium in different food simulants was as follow from slow to fast: PP/PVA/PP-1?PP/PVA/PP-2?PP/PVA/PP-3?PP/PVA/PP-4.The results showed that the release rate of TP from films into food stimulant in the film can be controlled by micropore size.(3)For monolayer PVA films,the Fick+first-order kinetic model could simulate the release behavior of TP into food simulates well.It was also indicated that the release of TP was the result of random diffusion and relaxation of the film structure.In comparison,the fitting accuracy of the kinetic model for the release of TP from the film into 95% ethanol was slightly lower.In addition,the diffusion coefficient(D)decreased slightly with the increase of TP content in the film,indicating that there was a certain effect of the content of TP in the film on the release rate of TP.(4)For the PP/PVA/PP multilayer films,the Fick kinetic model could simulate the release behavior of TP into food simulates well.In comparison,the fitting accuracy of the kinetic model for the release of TP from the film into 95% ethanol was slightly lower,which was similar with the result of monolayer PVA films.In addition,the diffusion coefficient(D)increased with the increase of the pore size of the inner layer of the multilayer film,indicating that the release rate of the release of TP into food stimulants from films increased with the increase of the pore size.It was proved that the release of active substances can be controlled by adjusting the pore size of the inner layer of the multilayer film.(5)Either PVA monolayer films or PP/PVA/PP multilayer films,there were differences between the release properties of the same PVA films in the different food stimulants.The diffusion coefficient(D)of the same film in 50% ethanol was higher than that of other food stimulants,which showed that 50% ethanol was more likely to promote the release of TP.The difference of release of TP into different food stimulants from films is worthy of further study from the interaction between the film and food stimulants.5.The effect of monolayer PVA active films and PP/PVA/PP multilayer films packaging on the quality change of trichiurus haumela during refrigerated storage were studied.(1)The TVC,TVB-N,K value and sensory changes of trichiurus haumela showed good correlation.The results showed that the monolayer PVA active films and PP/PVA/PP multilayer films incorporated with TP can effectively inhibit growth of microorganisms and lipid oxidation of the fish,delay the degradation of fish protein,maintain its unique flavor and prolong its shelf life.And the preservation effect for the trichiurus haumela increased with increasing content of TP.(2)For the trichiurus haumela packed with the films that had same content of TP but with different release rate of TP,there were difference between preservation effect for the trichiurus haumela.It showed that there was some relationship between the release rate of TP and the quality change of trichiurus haumela,which still need to be further studied in future.