Application Of Organic Solvent Fractionated Industrial Alkali Lignin In Lignin/PBAT Composite Films

In this thesis,typical industrial lignin was fractionated by organic solvents and the structure of the lignin fractions was characterized.The obtained lignin fractions were blended with the degradable plastic polyadipate/butylene terephthalate(PBAT)to prepare lignin/PBAT composite films,and systematically studied the properties of the composite films obtained.In this thesis,the biodegradable plastic PBAT was used as the matrix.Typical industrial lignin was fractionated with organic solvents and the chemical structures of the lignin fractions were also characterized and systematically studied.The prepared lignin/PBAT composite films and their performance were also been discussed.Three industrial alkaline lignin(SL,HL,and GL)samples were dissolved and fractionated using acetone to obtain corresponding acetone-soluble lignin components(SSL,SHL,and SGL)with low molecular weight and acetone-insoluble components(ISL,IHL,and IGL)with high molecular weight,respectively.The results showed that the method of acetone fractionation could obtain low molecular weight lignin components and improve the heterogeneity of industrial lignin without changing the basic chemical structure of lignin.The main linkages in SL and HL are?-?,and in GL are?-O-4.After acetone fractionation,the carbohydrates in SL were mainly concentrated in the insoluble fractions,which resulted in a higher purity of the acetone-soluble components.The quantitative ³¹P-NMR spectra and TGA results showed that the aliphatic hydroxyl content and the residual carbon rate of the lignin fractions raised with the increase of the molecular weight.The composite films were manufactured by blending the acetone-soluble lignin with PBAT,and the influences of the different chemical structures of lignin on the properties of the composite films were discussed.In general,composite films prepared by acetone-soluble lignin exhibited better tensile properties.When the addition of acetone-soluble lignin was up to 40 wt.%,the performance of the composite films comprising softwood lignin was better than that of films composed of hardwood lignin and gramineous lignin.Importantly,the tensile strength and elongation at break of PBAT/acetone-soluble softwood lignin(40 wt.%)composite film reached 14.71 MPa and161.79%,respectively,and the lignin component had better melting compatibility with PBAT matrix.Thermal degradation tests showed that the addition of lignin would reduce the thermal stability of the composite films.The thermal stability of the films prepared by gramineous lignin was lower than that of films with the addition of hardwood or softwood lignins.The hydrophilicity and hydrophobicity tests of the composite films showed that the PBAT/softwood lignin films were hydrophilic,while the PBAT/hardwood and gramineous lignin films were hydrophobic.In order to further study the effects of fractionated softwood lignin on the properties of PBAT/lignin composite films,three solvents of ethyl acetate,methanol,and acetone were used to sequentially fractionate softwood lignin.Four lignin fractions were obtained and named as ESL,MSL,ASL,and RSL,respectively.The results showed that as the ability of the organic solvent to dissolve lignin gradually increased,the molecular weight of the corresponding fractionated lignin regularly increased.Compared with the original SL,the fractionated lignin had lower polydispersity,and the heterogeneity was significantly improved.The main linkages of all lignin components were?-?,and there was a small amount of?-O-4 ether linkage with the molecular weight increases.The thermal analysis results showed that the thermal stability and T_g value of lignin components increased with the molecular weight rising,and ESL showed higher thermal stability than other lignin fractions.A series of composite films were fabricated by blending PBAT and different lignin fractions obtained with sequential solvent fractionation from SL.The results of tensile properties showed that the mechanical properties of the composite films prepared by the ethyl acetate-soluble lignin significantly improved.Especially,when the addition of ESL was 30 wt.%,the tensile strength and elongation at break of the PBAT/ESL film increased to 21.77 MPa and 403.52%from 10.86 MPa and 62.03%of the PBAT/SL film.However,the impacts of the MSL and ASL on the mechanical properties of PBAT/lignin films were equivalent to SL,which proved that the lignin with low molecular weight and polydispersity was more conducive to be applied towards PBAT composite film fabrication.When the addition of ESL was raised to 40 wt.%,the PBAT/ESL film had better tensile properties(24.09 MPa and 466.59%).Furthermore,when adding MAH-g-PBAT plasticizer,the composite film still showed good tensile properties(25.48MPa and 476.14%)at 50 wt.%lignin(ESL)content.The thermal analysis results showed that the addition of lignin would reduce the thermal stability of the composite films.The hydrophilicity and hydrophobicity tests of the composite films showed that with the ESL addition increasing(from 30 wt.%to 50 wt.%),the hydrophilicity and hydrophobicity of the films changed significantly,and the contact angle distinctly decreased from 105.13°to 78.25°.