Structure And Function Of Lignin Grafted Polylactic Acid

Poly(lactic acid)(PLA)is one of the most important biodegradable polymers in environmentally friendly materials with good biodegradability and biocompatibility.However,the disadvantages of PLA such as slow crystallization rate,poor thermal stability and poor UV-shield property limit its application.Generally preparing blends,copolymers or using fillers can improve PLA's property.Physical blending is a simple and practical method to improve the performance of polylactic acid,so the choice of modifier is particularly important.Lignin is the second most abundant natural macromolecule in nature,which has thermal stability,antibacterial activity and UV-shield property,but it is difficult to play the modification effect because of its poor dispersion degree as modifier in polyester matrix.By synthesizing lignin grafted poly(lactic acid),the dispersion of lignin can be improved in poly(lactic acid).If the grafted polymer is dextral poly(lactic acid)(PDLA),it is possible to introduce stereocomplex to further improve its crystallization properties.In this work,we mainly use alkylated lignin to graft dextral polylactic acid,and then use it as modifier to blend with levopolylactic acid.The thermal,crystallization and degradation properties of the modifier and its blends were studied to clarify the relationship between structure and properties.The main work is as follows:1.To improve the dispersion of lignin in the poly(lactic acid)matrix,a series of lignin grafted dextran poly(lactic acid)(LGPDn)with controlled molecular weight were synthesized by 1-bromododecane modified lignin as initiator through ring-opening polymerization.2.The solubility,UV-shield property,thermal stability,crystallization and degradation properties of grafted polymers with different molecular weights were studied.It is found that the grafted polymer not only improves the solubility of lignin,but also has better crystallization and degradation properties than star copolymer.3.A series of the different proportion of LGPDn/PLLA were prepared by solution casting.The effect of grafted polymer on PLLA's crystallization properties and morphology was studied.PLLA blending with grafted polymers promoted the formation and growth of stereocomplex and inhibited homocrystal formation.