Study On Lignin-graft-poly(d-lactide)/Poly(l-lactide) Composite Films

Lignin,as one of renewable functional polymer,has great applicational prospect in polymer modification,but its pratical application has been limited due to the undesirable miscibility deriving from the large amount of aromatic structures and hydroxyl groups.Fortunatly,chemical modification is a powerful strategy to improve lignin miscibility and expand its application fields.Grafting copolymerization is an effective way to modify its structure and enchance the properties of lignin.In this work,alkali Lignin-graft-polylactic acid copolymers(LG-g-PDLA,LG-g-PDLLA,and LG-g-PLLA)were synthesized to blend with PLLA matrix for improving its original properties.The effects of three different lignin copolymers on PLLA matrix were studied in detail.And the degradation behavior,depolymerizing products and possible degradation mechanism of the stereocomplexed PLLA/LG-g-PDLA were analysised as well In addition,natural active product loaded composite films trans-RSV/PLLA/LG-g-PDLA were developed.And the main research results are presented as following.LG-g-PDLA,LG-g-PDLLA,and LG-g-PLLA have been synthesized via ring-opening polymerization of D-,DL-,and L-lactic acid.Then composite films of poly(L-lactic acid)/lignin-graft-polylactic acid(PLLA/LG-g-PDLA,/LG-g-PDLLA,and/LG-g-PLLA)complex films were prepared.The results showed that,compared with LG-g-PDLA and LG-g-PLLA,a small amount of LG-g-PDLA addition could improve the crystallization rate,reduce the glass transition temperature and cold crystallization temperature of PLLA due to the stereocomplex crystallites.The thermal stability,tensile strength and strain of the stereocomplex films were also enhanced.Moreover,the PLLA/LG-g-PDLA films presented good ultraviolet resistance and excellent biocompatibilityPreviously,lignin-graft-poly(D-lactic acid)(LG-g-PDLA)was reported with a UV blocking capability,good compatibility and accelerating the crystallization in PLLA system.With the deepening of this research,we noted an unexpected effect of this copolymer on the thermal degradation and L-lactide recovery of PLLA.Herein,to clarify the effects of LG-g-PDLA in PLLA pyrolysis,PLLA/LG-g-PDLA blend film were prepared.The pyrolysis products,thermal degradation kinetics and mechanism of the blend film were studied in detail with thermogravimetric analysis(TGA)and pyrolysis-gas chromatograph/mass spectra(Py-GC/MS).During the pyrolysis,the LG-g-PDLA fragments with free-radicals could condense with the carboxyl ends of PLLA.PLLA could effectively unzipping depolymerize to avoid racemization and produced more the optically pure L-lactide.This is the first report of lignin-based filler with multifunction;besides adding the properties and enhancing the performances of PLLA application,the PLLA/LG-g-PDLA blend system also presented a good example of completely green materials for feedstock recycling.A new drug-loaded film for blending poly(L-lactide)(PLLA)with lignin-based functional filler,which enhanced stability and sustained release of trans-resveratrol(trans-RSV).In addition,trans-RSV loaded PLLA/lignin films showed good antioxidant and anticancer effects.Incorporation of the optimized amount of lignin-based filler to PLLA matrix was key to achieve these desired functions.Benifiting from the stereocomplex formation(PLLA and PDLA side chains),similar polyphenolic structures between lignin and trans-RSV,and UV chromophoric groups of lignin,trans-RSV loaded PLLA/lignin-graft-PDLA films(R/P/LGPD)have good performances on mechanical property,uniformity distribution of drug,and light barrier property.The release behaviors of trans-RSV could be controlled by variation of LG-g-PDLA content.This system therefore offers great potential for the delivery of poor water soluble and light stability drugs.