Synthesis Of Modified Lignin Filler And Properties Of Polymer Composites

Lignin is the most abundant aromatic organic polymer compound in nature,and as a by-product of wood hydrolysis and papermaking,the industrial yield is very large.Using lignin to develop polymer filler has good theoretical research and practical application value.However,the high heterogeneity of lignin and its poor dispersibility and compatibility in polymer matrix seriously restrict the development and application of lignin composites.Based on the above problems,this paper adopts the grading methods for lignin,and the structure of the different relative uniformity of lignin to affect the structure and properties of polymer composites,and introduce on lignin molecules and polymer segments,effectively improve the lignin composite materials’microstructure uniformity is poor,macro performance instability"problem.The specific work carried out in this paper is as follows:In this study,alkali lignin was used as raw material,and multiple uniform lignin grades were obtained by means of ethanol gradient classification method with relatively uniform performance and dissolution,and lignin was prepared by grafting poly（methyl methacrylate）（L-g-PMMA）to modify poly methyl methacrylate（PMMA）.The influence of graft copolymer fillers prepared by different grades on the thermodynamic properties of PMMA was investigated.The nano-hydrogels prepared by different grades of lignin nanoparticles and polyvinyl alcohol（PVA）were analyzed,and the effects of different sizes of lignin nanoparticles on the mechanical properties of hydrogels were investigated.The pyrolysis mechanism of PLLA/LG-PDLA was studied.Specific research results are as follows:A series of lignin grades with relatively uniform properties were obtained by ethanol-temperature gradient classification method.Then,a series of modified lignin-based fillers（L-g-PMMA）were synthesized by introducing poly methyl methacrylate into lignin through atomic transfer radical polymerization.Finally,the composite was prepared from polymethyl methacrylate.The strength and toughness of the composite（PMMA/L-g-PMMA）can be adjusted by the type and proportion of S/G units and the ratio of flexible/rigid bonds in the lignin macromolecule.Lignin nanoparticles（LNPs）of different sizes were prepared by solvent transfer method using a series of lignin grades with relatively uniform properties,and were added into polyvinyl alcohol matrix as filler.GPC,³¹P-NMR,2D-HSQC-NMR,TEM,rheological and tensile tests revealed that LNPs with different structural sizes had significant differences in mechanical properties of PVA hydrogels.The toughness and strength of PVA were increased by 6.33%and 289.9%,respectively,by LNPs₇₀.LG-g-PDLA was synthesized,and blended with L-poly（lactic acid）to prepare PLLA/LG-g-PDLA.The degradation mechanism of LG-g-PDLA/LG-PDLA was studied by NMR and gel permeation chromatography.The results show that the pyrolysis products of PLLA/LG-PDLA contain a large amount of L-La and a small amount of D-and meso-Lactide at 240°C.NMR and liquid chromatography data analysis showed that the pyrolysis mechanism of PLLA/LG-g-PDLA was mainly gradual depolymerization accompanied by a small amount of random depolymerization.The yield of lactide under different pyrolysis conditions has guiding significance for optimizing the recovery of PLA.