Preparation And Aging Performance Of Lignin Alkyl Ester/Polylactic Acid Composite Films

Lignin is one of the major macromolecular components of wood and other plant resources and has excellent UV absorption properties.Lignin can be used to co-modify degradable polym er materials to give them new or improved properties.Polylactic acid,which has the characteris tics of good biodegradability,biocompatibility and environmental friendliness,limits its applica tion range due to the shortcomings of poor flexibility.In this study,esterified enzymatically hyd rolyzed lignin was blended with polylactic acid(PLA)to prepare a lignin alkyl ester/polylactic acid composite film(LEs/PLA),and its tensile properties,thermal properties and ultraviolet shi elding properties were characterized,and the toughening mechanism and aging performance of LEs/PLA composite film were studied.The main contents and results of this study are as follow s:(1)Using enzymatic hydrolyzed lignin as raw materials,three fatty acid acid chlorides,ca prylyyl chloride,dodecyl chloride and stearoyl chloride,were used as modifiers to synthesize li gnin octyl ester(LE8),lignin dodecyl ester(LE12),and lignin octadecyl ester(LE18)at 100°C/4 h.LEs/PLA composite film was prepared by blending LEs with PLA(x indicates the mass pr oportion of LEs,x=1,2.5,5,10,15%).The esterified modified lignin has better compatibility w ith PLA,and the elongation at break of LEs/PLA composite film is significantly improved,amo ng which 10% LE12/PLA has the best toughness,and the elongation at break is as high as 205.1%,which is 24.7 times that of pure PLA(8.3%).(2)Physical aging is the continuous evolution of the thermodynamic properties of polymer materials over time during use at room temperature,resulting in significant changes in the phys ical properties of the materials,so the changes in the tensile properties of LEs/PLA composite f ilms during physical aging were investigated.Through 84 days of physical aging,the elongatio n at break of the LEs/PLA composite film decreased,but the elongation at break of the composi te film with 10 wt%LE18 was still 30.7% after 84 days of physical aging,which was 6.3 times t hat of pure PLA(4.8%).When the cold crystallization temperature of LEs/PLA composite film decreased,the crystallinity increased slightly,and when the amount of LEs added was greater th an 5 wt%,the crystallinity of LEs/PLA composite film hardly changed significantly,indicating that the three-dimensional network structure and hydrophobic alkane chain of LEs promoted th e micro-Brownian motion of PLA molecular chain.With the extension of aging time,the tensile strength of LEs/PLA composite film increased significantly.Adjusting the appropriate amount of LEs is conducive to improving the durability of the composite film.(3)The performance changes of LEs/PLA composite films during UV aging were investig ated by UV accelerated aging method to compare the effects of different fillers on the UV durab ility of PLA-based composite films.After UV aging,the tensile strength of PLA and LEs/PLA f irst increased and then decreased,and the elongation at break continued to decrease,but the cha nge of elongation at break of LEs/PLA composite films in the first 200 h UV aging was small,a nd the elongation at break of 10% LE12/PLA and 10% LE12/PLA composite films was still hig her than 30%;its crystallinity showed a trend of first increasing and then gradually decreasing.The crystallinity tends to increase first and then decrease gradually.The differences in the abov e properties indicate that the addition of LEs has a delaying effect on the UV degradation of PL A-based composite films,and the higher the addition of LEs,the more significant the delaying effect.In this study,LEs/PLA composite films with high elongation at break and UV shielding ab ility were prepared by solvent casting method.The physical aging and UV aging of LEs/PLA c omposite films were investigated,and it was found that by regulating the additional amount of LEs and the length of the grafted saturated alkane chains,the LEs/PLA composite films exhibit ed delayed effects in aging,which expanded the application scope of PLA and lignin and provid ed a research idea and experimental basis.