Preparation And Properties Of PLA/PBAT/PPC Biodegradable Blending Controlled-release Antioxidant And Antibacterial Active Films

Microbial spoilage and oxidative deterioration have always been a significant threat to food safety and consumer health.The rise of antioxidant and antibacterial active packaging has provided an effective method to extend the shelf life of food.With the increasingly serious environmental pollution problems caused by traditional packaging,new type of active packaging based on biodegradable materials is becoming the development direction of future packaging.Under the premise of ensuring the basic properties meet requirements,designing a safe and efficient active controlled-release system and effectively combining the system with the biodegradable packaging matrix is the focus and key of current research.In this work,an antioxidant and antibacterial responsive controlled-release activity system was prepared,and the formulation of biodegradable packaging matrix materials were designed and studied.Finally the activity system was added to the biodegradable packaging matrix to prepare a new type of biodegradable antioxidant and antibacterial active film.The results showed as follows:(1)Synthesis and characterization of p H responsive controlled-release tea polyphenols/mesoporous zinc oxide nano-complex with Antioxidant and antibacterial activity.Two kinds of mesoporous zinc oxide nanoparticles N-Zn O and C-Zn O were first prepared by hydrothermal method.Polyoxyethylene polyoxypropylene ether block copolymer(Poloxamer 188)and sucrose were used as double-templates,and zinc nitrate and zinc acetate as zinc source respectively.Then the N-Zn O with better properties were selected as a nano-carrier.Tea polyphenols(TP)were loaded on the carrier to prepared antioxidant and antibacterial controlled-release activity nano-complex T-Zn O.Finally,the properties of the mesoporous nano-zinc oxide carrier and the nano-complex were studied.The results showed as follows:Both N-Zn O and C-Zn O,have hexagonal wurtzite structure.The structure of N-Zn O prepared with zinc nitrate as zinc source is superior to C-Zn O with zinc acetate as zinc source.The specific surface area of N-Zn O was 80.614 m~2/g,while the average pore size was 7.426nm,and the pore volume was 0.424 cm~3/g.The TP loading content of T-Zn O can reach 74.46%-76.28%,while T-Zn O has excellent free radical scavenging ability and obvious bacteriostatic effect.The p H-responsive controlled-release effect of T-Zn O is obvious,and weakly acidic conditions can promote the release of tea polyphenols from the complex,which shows a certain application potential in active controlled-release packaging.(2)Preparation and characterization of PLA/PBAT/PPC biodegradable blending films.Using melt blending method,three biodegradable materials,poly(lactic acid)(PLA),poly(butylene adipate-co-terephthalate)(PBAT)and Poly(propylene carbonate)(PPC)were blended in different proportions to prepare modified blending films,and the optimal proportion of the ternary blending modification films was studied.The results showed as follows:All the blending films at different proportions are partially compatible systems,and the compatibility and homogeneity of the systems are gradually improved with the decrease of PBAT components and the increase of PPC components.In terms of barrier properties,the oxygen barrier and water vapor barrier properties of the blending films increase with the increasing of PPC content.Blending has little effect on the melting point of the polymer,but the melting onset temperatures show to varying degrees of decline compared with pure PLA.All the blended films have ultraviolet shielding ability,and the barrier property to oxygen and water vapor as well as the light transmission property increases with the PPC content.When the proportion of PLA/PBAT/PPC is 40/10/50,the blending film has the best comprehensive mechanical properties,which can be used as active films matrix.(3)Preparation and characterization of Controlled-release antioxidant and antibacterial active films based on biodegradable blending polymers.The blending films with PLA/PBAT/PPC proportions of 40/10/50 was selected as the base material,and different concentrations of TP,N-Zn O and T-Zn O were introduced to prepare a series of biodegradable active films.The structure and properties of the active films were studied.The results showed as follows:The introduction of TP and T-Zn O can reduce the size of the dispersed phase of the active films matrix.T-Zn O shows a better ability of improving the homogeneity and compatibility of the different phases in films matrix,and reduces the melt onset temperature significantly,which means an effective improvement of hot processability.TP and T-Zn O are mainly combined with the matrix polymer molecules by hydrogen bonding,and can improve the mechanical properties of the films.ZT1(1%T-Zn O addition)has the comprehensive modification effect,with tensile strength and elongation at break were increased by 20.94%and 233.51%,respectively.The introduction of TP and T-Zn O can also improve the barrier properties of the films to varying degrees.Among them,3%TP and 3%T-Zn O addition have the best improvement in oxygen barrier properties,and the oxygen transmission coefficients decrease by 23.85%and 18.46%,respectively.The water vapor transmission rate decreased in different degrees.Through the DPPH free radical scavenging test,it is found that both T2(2%TP addition)and ZT2(2%T-Zn O addition)films have significant free radical scavenging effects,while ZT2 film has time delay effect,and a higher final scavenging percentage.Compared to the active nano-complex,the controlled-release behavior of tea polyphenols by the active films is altered,with the p H condition of the maximum release shifts to the neutral direction in the prophase.The release amount reach the maximum at p H=7,which is higher than that at p H=5.5,while the release of tea polyphenols is still inhibited under condition of p H=4.4.In the metaphase and anaphase of the release process,the release of tea polyphenols in weak alkaline conditions at p H=8.5 surpass that in p H=7.4 conditions due to stronger hydrolysis of the films matrix in alkaline conditions.The active films shows better inhibition against S.aureus than against Escherichia coli,and overall,the ZT2 films with the addition of active ligands T-Zn O have a better antibacterial effect compared to the T2 films with the addition of pure tea polyphenols.