The Effect Of Lignin On Properties Of PLA/PPC Composite Packaging Film

Polylactic acid(PLA)and polypropyl carbonate(PPC)are biodegradable polymers that can be used in green packaging.Lignin is also a biorenewable resource,which can be used to improve the performance of degradable high-performance composite packaging film by its molecular modification,morphology and particle size control.In this paper,PLA/PPC/lignin composite packaging films were prepared by blow molding and tape casting,and the effect of lignin on the properties of PLA/PPC composite packaging films was discussed.PLA/PPC composite packaging films were prepared by blow molding process with PLA and PPC as main raw materials,ADR-4368 as chain extender and ATBC as plasticizer.The results showed that when the dosage ratio of PLA/PPC/ADR/ATBC was 60:40:0.8:8,the composite packaging film had good mechanical properties.The tensile strength was 21.73MPa,the elongation at break increased to 377.17%,and the elastic modulus decreased to1184.33 MPa.PLA/PPC/AL composite packaging films were prepared by blow molding process with PLA/PPC/ADR/ATBC(60:40:0.8:8)blend as the substrate and alkaline lignin(AL)as the filler.SEM images showed that the compatibility between AL and PLA/PPC was not ideal;moreover,when 0.5%AL was added,the elongation at break was sharply reduced by 41.3%compared with pure PLA/PPC film.The barrier performance test results showed that when the AL content was 1%,the oxygen barrier performance of PLA/PPC/AL composite packaging film was 11.8%higher than that of PLA/PPC film,but its water vapor permeability showed an overall upward trend.In order to improve the compatibility of AL in PLA/PPC matrix,AL was modified by tert-butyldimethylchlorosilane(TBDMSCl),and the modified lignin(SAL)was melt-blended with PLA/PPC composite to blown films.FTIR and ~1H NMR analysis showed that the methylsilyl chain was successfully grafted onto the hydroxyl group on the alkali lignin surface.SEM images showed that the compatibility between SAL and PLA/PPC was significantly improved.DSC test showed that the addition of SAL improved the crystallization ability of PLA.The test results of mechanical and barrier properties showed that compared with PLA/PPC film,when the SAL content was 1.5%,the mechanical strength and oxygen barrier properties of PLA/PPC/SAL composite packaging film were the best,with the tensile strength increased by 6.9%and the oxygen barrier property increased by33.7%.The water vapor permeability of the composite packaging film reached the lowest value when the SAL content was 1%,which was 13.1%lower than that of PLA/PPC film.In order to further improve the dispersion of AL in PLA/PPC matrix,lignin nanoparticles(LNPs)were prepared by acid precipitation method and then modified by methyl silanization.The modified lignin nanoparticles(SLNPs)and PLA/PPC composites were cast into films.The results showed that compared with PLA/PPC cast film,the elongation at break of PLA/PPC/SLNP2 composite packaging film increased by 106.5%when the SLNPs content was 2%.The tensile strength increased by 14.6%,the oxygen barrier increased by 55.7%,the water vapor permeability decreased by 12.3%,and the UV resistance increased by 93.3%.