【作者】 李兆乾；

【导师】 周晓东； 裴重华；

【作者基本信息】 华东理工大学 ， 先进材料与制备技术， 2010， 博士

【摘要】 植物纤维／聚乳酸(PLA)复合材料由于其能够完全降解、来源于可再生资源等优势逐渐引起研究者的关注。但其不足也很明显,植物纤维和聚乳酸亲和性差,造成复合材料的界面性能较差,植物纤维的增强效果得不到充分的发挥。本文从合成两种新型的可用于植物纤维／PLA复合材料的大分子偶联剂出发,对天然纤维的表面改性、天然纤维／PLA复合材料的动／静态力学性能、复合材料的稳定性及降解性等进行了较为系统的研究,主要获得了以下几个方面的研究成果：(1)设计合成了两种新型大分子偶联剂：γ-甲基丙烯酰氧基丙基三甲氧基硅烷(MPS)接枝聚乳酸(MPS-g-PLA); PLA与甲基丙烯酸缩水甘油酯(GMA)共聚物PLA-co-PGMA。红外光谱与核磁共振结果表明：PLA分子骨架接枝了MPS支链；GMA与PLA先形成大分子单体,而后合成出嵌段共聚物。两种偶联剂优化的合成条件分别为：MPS-g-PLA反应温度为110℃,反应时间5 h,投料质量比为5：1,引发剂用量1wt.%; PLA-co-PGMA反应温度70℃,AIBN用量为2wt.%, PLA-GMA:GMA摩尔比为1：25,反应时间5 h。PLA及共聚物的水解研究表明：MPS-g-PLA和PLA-co-PGMA均可降解；降解速率均慢于聚乳酸,尤其是PLA-co-PGMA。(2)采用大分子偶联剂对两种天然纤维(细菌纤维素和剑麻纤维)进行了表面改性。接触角测试表明：MPS-g-PLA改性使细菌纤维素的表面能大幅降低,主要降低其极性力部分；PLA-co-PGMA改性,同样主要降低纤维表面能的极性力部分。大分子偶联剂处理同样可以提高剑麻纤维的疏水性。扫描电子显微镜分析表明：大分子偶联剂处理使剑麻纤维表面变得更为粗糙。通过界面热力学计算得知：两种偶联剂处理均降低了纤维与聚乳酸树脂的界面张力,这有助于提高纤维在树脂中的分散与浸润,改善纤维与基体的相容性。表面处理使纤维与树脂的界面剪切强度提高35%以上。(3)剑麻纤维的加入提高了PLA树脂的模量。偶联剂表面改性可进一步提高PLA的强度和模量。当剑麻纤维含量为30 wt.%时,MPS-g-PLA表面处理的复合材料的拉伸强度、冲击强度、弯曲强度和模量比纯PLA分别提高了4.8%、25.3%、3.5%和82.7%；PLA-co-PGMA表面处理,则相应的提高了6.2%、29.4%、7.8%和79.3%。增塑剂PEG提高了PLA断裂伸长率,降低了其强度和模量。加入30%剑麻纤维,复合材料拉伸强度提高了21.81%,但降低了其断裂伸长率和冲击强度。偶联剂处理纤维将增塑PLA的拉伸强度、弯曲强度和模量均进一步提高,而冲击强度进一步降低。这表明应力通过界面很好的从基体传递到纤维。30wt.%剑麻纤维／聚乳酸复合材料的储能模量比纯PLA可提高1倍。MPS-g-PLA表而处理纤维复合材料储能模量比未处理纤维复合材料轻微降低；而PLA-co-PGMA表面处理则与未处理纤维复合材料相当。剑麻纤维的加入降低了PLA的损耗因子,但纤维改性与否对复合材料损耗因子影响较小。材料断面形貌分析表明：大分子偶联剂处理使纤维与树脂结合紧密,相容性提高。(4)PLA及其剑麻纤维复合材料在30℃、相对湿度80%的条件下,稳定性研究表明：PLA及其复合材料的吸湿率随时间的延长逐渐增加,而后在30天内基本达到吸湿平衡；剑麻纤维的加入提高了材料的吸湿性。纯PLA在30天内拉伸强度有所提高；而纤维复合材料拉伸性能下降,经合成偶联剂表面改性处理纤维后可以明显减缓这种力学性能的降低,提高复合材料的稳定性。偶联剂处理可以使纤维与基体界面产生良好的界面粘结,这有效改善了复合材料的稳定性。在高温高湿土埋环境下PLA及其剑麻纤维复合材料都具有很好的降解性能。与未经大分子偶联剂处理的纤维复合材料相比,经处理的纤维复合材料降解速率较慢。(5)采用纳米纤维增强PLA制备了透明的细菌纤维素／聚乳酸纳米复合材料,通过马来酸酐对细菌纤维素表面改性,使细菌纤维素和PLA之间形成有效的结合,改善了两相的界面相容性,从而提高了复合材料力学性能。课题研究的天然纤维／聚乳酸复合材料是一种绿色复合材料。通过改善纤维与树脂界面提高其综合性能,有望扩大其应用领域,这对解决当前环境问题,实现可持续发展有着重要的意义。更多还原

【Abstract】 Nature fiber/polylctide (PLA) composites are gaining considerable attention due to their fully degradation and deriving entirely from renewable resources. However, there are some limitations. The most important restraint is the poor interfacial compatibility between the hydrophilic fiber and the hydrophobic polylactide matrix, which limits the performance of the final composite.In this work, the study was carried out systematically such as the synthesis of macromolecular coupling agents, surface treatment of nature fibers, static and dynamic mechanical properties of nature fiber/PLA composite, stability and biodegradibility of the composites. And the main results in this work are summed as follows:(1) Two types of coupling agent,γ-Methacryloxypropyltrimethoxysilane-graft-PLA (MPS-g-PLA) and polylactide-glycidyl methacrylate copolymer (PLA-co-PGMA), were successfully designed and synthesized. Their structure was characterized by Fourier transform infrared spectroscopy (FTIR) and Hydrogen nuclear magnetic resonance (’H-NMR). Furthermore, their synthetic procedure was optimized:in the case of MPS-g-PLA, reacting for 5 h under 110℃with the mass ratio 5:1, amounts of initiator 1wt.%; for PLA-co-PGMA, reacting for 5 h under 70℃with the molar ratio of monomers 5:1, amounts of initiator 2wt.%. Hydrolytic degradation of PLA and its copolymers showed that the degradation rates of the copolymers slightly differ from neat PLA, especially PLA-co-PGMA.(2) Macromolecular coupling agents were employed for surface modification of bacterial cellulose (BC) and sisal fiber (SF). Contact angle measurements showed that the surface energy of BC after modification was decreased due to the reduction in its polar component. Concentration of MPS-g-PLA and pH influenced surface properties of BC. Surface modification can also improve the surface hydrophobicity of SF. Scanning electron microscopy (SEM) photographs showed surface modification made SF surface rough. Interfacial thermodynamic properties were studied and the results suggested that the surface modification decreased interfacial tension of BC/PLA and were more efficient in improving the interfacial shear strength.(3) The addition of SF enhanced modulus of PLA. After fiber treatment with MPS-g-PLA. the tensile strength of PLA composite with 30% fiber can be increased by 4.8%; with an impact strength by 25.3%; a flexural strength by 3.5%, and a flexural modulus by 82.7%; while fiber treatment with PLA-co-PGMA, the tensile strength of PLA composite can be increased by 6.2%; with a impact strength by 29.4%; a flexural strength by 7.8%, and a flexural modulus by 79.3%. Plasticizer was used to decrease the processing temperature and enhance impact strength of composites; which make efficiency of surface modification obvious. At 30 wt% SF loading, tensile strength improved by 21.81%, while strain at break and impact strength dropped compared to neat plasticized PLA. Surface modification of SF had further increased tensile strength of composites and decreased its impact strength, which suggests effective stress transfer between fiber and matrix. The DMA storage modulus increased with the addition of SF. Compared to unmodified fiber, the interfacial binding strength of composites with PLA-co-PGMA and MPS-g-PLA was higher. SEM micrographs of the fracture surface of Notched Izod impact specimen indicated that the adhesion between fiber and matrix could be improved by the addition of coupling agents.(4) Stability of PLA and its composites was estimated under damp condition. The results revealed that conditioning to equilibrium at 80% relative humidity and 30℃took about 30 d and resulted in decrease of tensile strength of composites. However, surface modification of SF had a remarkable effect on the stability of SF/PLA composites and relieved decline of their tensile strength by keeping interphase damage to a minimum level. Biodegradability of PLA and its composites was evaluated by the soil-burial test. Both fiber and matrix phases of the PLA composites were biodegradable; they have a relatively high biodegradability and the presence of SF affected the weight loss. Biodegradability was restrained for treated SF composites, as the interfacial adhesion is improved due to the surface modification of the fiber.(5) Transparent nanocomposite consisting of two biocompatible materials, bacterial cellulose (BC) and PLA was prepared. Maleic anhydride was first grafted onto BC nanofibers, which made BC nanofibers well disperse into PLA matrix and the interfacial adhesion between BC and PLA was improved.Natural fiber/PLA composite is a green composite. Improvement of physico mechanical properties of the composites will expand in application field. It is of great significance for solving the current environment issues and achieving sustainable development.更多还原