Preparation And Performance Of PLA/PBF Food Packaging Composites With High Barrier And High Toughness

With the increasingly serious energy and environmental problems,polylactic acid(PLA)has been widely used due to its good biocompatibility and biodegradability.However,the disadvantages of poor toughness,low crystallization rate and low melt strength seriously restrict the further industrial development of PLA.In recent years,the modification of PLA has received extensive attention,but most of them can only ameliorate one of disadvantages and can not make all the shortcomings of polylactic acid be improved in a balanced manner.It always takes a cost of losing part of the advantages of polylactic acid to improve the certain aspect of performance.In this work,the biodegradable furan-based polyester PBF was added into PLA by melt blending to obtain the composites realizing the balance of rigidity and toughness.Next,the compatibilizer was added to improve the mechanical properties and melt strength of the system.In order to broaden the application of PLA in antibacterial food packaging,nano-zinc oxide was introduced into the system to prepare composite films.The composite films,with excellent mechanical properties and high crystallinity,possess good antibacterial propert and gas barrier performance.Moreover,it exhibits a robust preservation performance for broccoli.It is expected to become a biodegradable food packaging plastic with low cost,simple preparation and good performance.The main work is summarized as follows:(1)Preparation and performance of PLA/PBF composites.PLA/PBF composites were prepared by melt blending method,and composites PBF5,PBF10,PBF20 and PBF30 were obtained.Blending PBF with PLA can significantly improve the tensile toughness and crystallinity of PLA,while the tensile strength of the composite material decreases less,so that the rigidity and toughness of the materials can reach a balance.Among them,PBF20 has the best mechanical properties.The tensile strength is 71.8 MPa,the elongation at break is 121.1%,and the Young's modulus is 1385.9 MPa,exceeding that of both PLA and PBF.The section morphology of the composites present the typical"sea-island structure",resulting in a limited improvement in the impact toughness of the system.In addition,compared with PLA,the crystallinity of the composites have greater increase,but the melt strength is not improved.(2)Preparation and performance of PLA/PBF/POE-g-GMA composites.The phase separation behavior of PLA/PBF composites was ameliorated by introducing the compatibilizer POE-g-GMA(glycidyl methacrylate grafted polyolefin elastomer).PLA/PBF/POE-g-GMA composites were prepared through the dynamic vulcanization process.A small amount of DCP was added during the blending process to initiate low crosslinking of the system.Moderate crosslinking improves the mechanical properties of the system without affecting its processing performance.Compared with PLA/PBF composites,the phase separation behavior of obtained PLA/PBF/POE-g-GMA composites has been greatly ameliorated,so the tensile toughness and impact toughness have been significantly improved.PBF20/GPOE(GPOE is the abbreviation of POE-g-GMA)has the best mechanical properties,with a tensile strength of 71.2 MPa,an elongation at break of 261.0%,and an impact strength of 9.0 k J/m~2.Meanwhile,the cross-linked structure produced in the dynamic vulcanization process improves the heat resistance and thermal stability of the system,and the thermal deformation temperature and thermal decomposition temperature are increased by about 60?and 40?,respectively.The complex viscosity and storage modulus of the composites are two orders of magnitude higher,and the melt strength is greatly improved.(3)Preparation and performance of PLA/PBF/POE-g-GMA/Zn O composites.Firstly,silane coupling agent HDTMS was used to ameliorate the agglomeration and hydrophilicity of nano-zinc oxide(Zn O)and improve its dispersibility in the polymer.After that,the modified nano-zinc oxide was added to the composites by the master batch method,and the PLA/PBF/POE-g-GMA/Zn O composites were prepared.Although the mechanical properties of the composites are slightly reduced after adding zinc oxide compared to the composites PLA/PBF/POE-g-GMA,but there is still a big improvement compared with PLA.Meanwhile,the crystallinity of the composites increase with the increase of the content of nanoparticles,and the melt strength in the low frequency region is significantly enhanced compared with PLA.(4)The application of PLA/PBF/POE-g-GMA/Zn O composites to food packaging.The prepared PLA/PBF/POE-g-GMA/Zn O composites were pressed into films with a thickness of tens of microns.The addition of modified nano-zinc oxide not only significantly improves the crystallinity and gas barrier properties of the composite films,but also endows it good antibacterial properties.When the addition amount of modified nano-zinc oxide is 1.5 wt%,the composite film has an effect on Escherichia coli,Staphylococcus aureus and Bacillus subtilis.The antibacterial rates reached at 99.2%,100%and 99.9%,respectively.At the same time,nano zinc oxide also brings a good anti-UV shielding performance.When the addition amount is 2wt%,the UV shielding can basically reach 100%.After adding zinc oxide,the crystallinity and the gas barrier performance are improved.The above properties make PLA/PBF/GPOE/Zn O composite films have a good preservation effect when packaging fresh-cut broccoli samples,having better sensory quality evaluation,lower quality loss rate,and smaller changes in relative conductivity and chlorophyll content.