PLA/Lignin-g-polyester生物基复合材料的制备及聚酯链段结构对性能的影响研究

Preparation of Biorenewable PLA/Lignin-g-polyester Composites and the Effects of Lignin-g-polyester Structures on Composite Properties

利用木质素开环δ-戊内酯(DVL)与L-丙交酯(L-LA)制备木质素表面接枝PDVL与PLLA链段,通过改变制备方法,制备lignin-g-PDVL-ran-PLLA、lignin-g-PDVL-b-PLLA 2种序列结构不同的木质素接枝聚合物(lignin-g-polyester).进而将lignin-g-polyester与PLA溶液复合后,采用溶液挥发成膜法制备一系列不同比例、不同序列链段的聚乳酸/木质素接枝聚合物复合材料(PLA/lignin-g-polyester).通过傅里叶红外光谱(FTIR)、核磁共振氢谱(1H-NMR)确定其结构;示差扫描量热仪(DSC)、场发射电子扫描显微镜(FE-SEM)等检测复合材料的热学性能及其内部形貌. FE-SEM的结果表明lignin-g-polyester在基材中以粒子形式均匀分散,与PLA基材相容性提高. DSC结果表明lignin-g-polyester能促进PLA的结晶;且无规的lignin-g-PDVL-ran-PLLA比具有规整嵌段结构的lignin-g-PDVL-b-PLLA更有利于促进PLA的结晶行为;同时Lignin-g-polyester改善了PLA复合材料的力学性能,且含有lignin-g-PDVL-b-PLLA比lignin-g-PDVL-ran-PLLA更能提高聚合材料的强度与韧性.复合材料拉伸过程所形成的空穴与褶皱是复合材料韧性提高的关键成因.此外,所制的PLA/lignin-g-polyester复合材料具有较优的紫外屏蔽性能.

Lignin a commonly used modifier for bio-based PLA materials due to its good biodegradability,structural stability, and the nature of biomacromolecule. However, the poor compatibility between neat lignin and PLA matrix compromises greatly its further application. To this end, lignin-g-polyester with two different molecular structures, i.e. lignin-g-PDVL-ran-PLLA and lignin-g-PDVL-b-PLLA, were specially designed for compatibility improvement and successfully synthesized via ring-opening polymerization with δ-valerolactone (DVL) and L-lactone (L-LA). PDVL as a soft component could reduce the brittleness of PLA with its long polymer chains while L-LA would enhance the compatibility between lignin nanofillers and PLA matrix due to the structural similarity with PLA. Lignin-g-polyester fillers with various segment structures were prepared by tuning the monomer ratio, and a series of PLA/lignin-g-polyester composites with different filler contents were further fabricated via the solution casting method. Structures of lignin-g-polyester were characterized by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H-NMR), while the uniform dispersion of lignin-g-polyester fillers in PLA composites was verified by field emission scanning electron microscopy (FESEM). Differential scanning calorimetry (DSC) was utilized to study the thermal properties and crystallization behaviors of as-fabricated composites, which indicated a boosted crystallization with improved crystallinity with the addition of nanofillers. Furthermore, lignin-g-PDVL-ran-PLLA outperformed lignin-g-PDVL-b-PLLA in terms of the facilitation effect. Mechanical testing showed that PLA/lignin-g-polyester composites possessed better mechanical properties than neat PLA did, which could result from the multiple effects induced by holes and wrinkles that formed between lignin-g-polyester nanofillers and PLA matrix during the stretching process. In contrast to DSC results, the mechanical properties of PLA/lignin-g-PDVL-b-PLLA composites were much better than those of PLA/lignin-g-PDVL-ran-PLLA composites. In addition, the UV-Vis transmission spectroscopy suggested that lignin-g-polyester could endow the composites with an excellent UV-shielding property.