| With the crisis of environment pollution and petroleum resources shortage loominglarger and larger, the research and development of non-petroleum based degradable polymerare imperative. Holding lots of advantages which synthetic fibers can hardly compare, Sisalfiber can be used to reinforce PLA (polylactide) to prepare biodegradable composites whichnot only reduce the cost of PLA, improve their overall performance and price-performanceratio, and further expand the range of industrial application, but also imply the practicalmeaning to solve the above issues and achieve sustainable development.According to principle of lactide coordination ring-opening polymerization, stannousoctanoate (Oct2Sn) was used to activate hydroxyl groups onto sisal fiber surface, and thentrigger L-lactide coordination ring-opening polymerization in the thesis. Consequentially,polylactide molecular chain was grafted onto sisal fiber surface in order to improve theinterface properties between sisal fiber and matrix. The impact of surface modificationmethods on properties of sisal fiber was comparatively studied. What’s more, Unmodifiedand modified sisal fiber reinforced PLA composites were prepared by melt blending followedcompression molding. The impact of fiber contents, modification methods and annealingtreatment on the overall performance of composites was investigated. And the burialdegradation behavior of composites in real soil environment was revealed. The experimentalresults show that:The pectin, lignin and other impurities of sisal fiber were removed by alkali treatment.Meanwhile, the bound water content and diameter of sisal fiber were reduced. The content offree hydroxyl groups, length-diameter ratio and thermal stability under N2environment ofsisal fiber were enhanced. As evidenced by TGA, FT-IR and electron microscopy analysisresults, polylactide molecular chains were grafted onto sisal fiber surface by L-lactidegraft-copolymerization modification. Furthermore, cellulose microfibrils of sisal fiber werescattered completely from each other and fiber diameter was reduced dramatically.Owing to the effective and great improvement of the interfacial properties between sisalfiber and matrix PLA by lactide graft copolymerization modification, the strength andmodulus of LAgSF/PLA were enhanced significantly. The maximum value of its tensile strength, flexural strength, tensile modulus and flexural modulus were79.01MPa,107.28MPa,3486.06MPa and5974.62MPa, respectively, which compared with neat PLA were enhancedby22.88%,24.82%,97.02%and102.44%, respectively. Unfortunately, the elongation atbreak and toughness of composites weren’t improved yet. Besides, the crystallinity andcrystal perfection of composites both were improved by annealing treatment. So did thestrength and modulus. The most remarkable promotion effect was played by LAgSF amongthe unmodified and modified sisal fibers, which may be also attributed to the greatimprovement of the mechanical properties of LAgSF/PLA composite.With the increase of the degradation time, the degradation rate of PLA was relativelyslow in real soil burial degradation experiment. However, the degradation rate of compositeswas speeded up due to the addition of sisal fiber. And the higher fiber content was, the fasterthe degradation rate of composites became. It’s witnessed that the sisal fibers of compositessurface occurred degradation firstly. And then the PLA matrix around sisal fibers washydrolyzed rapidly due to the strong hydrophilicity of sisal fiber. Moreover, compositessurface became white and rugged gradually. The glass transition, cold crystallization and melttemperature of composites all decreased though the crystallinity increased during degradation.In addition, the degradation rate of composites in20cm depth burial degradation was fasterthan that of10cm. The degradation rate of composites was slowed down by annealingtreatment, and the higher the crystallinity was, the slower the degradation rate was. |
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