【作者】 孙强英；

【导师】 黄莉茜；

【作者基本信息】 东华大学 ， 纺织材料与纺织品设计， 2009， 硕士

【摘要】 聚乳酸(PLA)是一种以可再生生物资源为原料的热塑性聚酯,具有良好的生物降解性、生物相容性、较强的机械性质和易加工性。聚乳酸材料的开发和应用,不但可以解决环境污染问题,更重要的意义在于为以石油资源为基础的塑料工业开辟了取之不尽的原料资源。然而,聚乳酸也存在不少缺陷,如性脆、抗冲击性能差、热稳定性差、成本较高等,这些缺点限制了PLA的应用范围,因而需要对聚乳酸进行改性,使其达到更广泛的应用。为了改善PLA的性能,尤其是冲击韧性,本论文拟采用弹性体聚乙烯-乙酸乙烯酯(EVA)与PLA共混,以提高PLA韧性。但弹性体增韧往往造成材料模量及热稳定性的下降,而层状粘土/聚合物基纳米复合材料具有提高聚合物模量和热稳定性的特点,所以本论文拟采用弹性体EVA及层状硅酸盐蒙脱土(MMT)与PLA进行共混,通过不同的共混工艺,共同改性PLA,希望综合聚合物/弹性体材料和聚合物/蒙脱土纳米复合材料的优点,在提高材料韧性的同时减少模量和热稳定性的下降,并分析EVA与蒙脱土的协同增韧机理。首先,为了增加PLA与EVA的相容性,采用两种不同的增容剂乙烯-乙酸乙烯酯接枝马来酸酐(EVA-MAH)和乙烯—丙烯酸酯—甲基丙烯酸缩水甘油酯(E-MA-GMA)与PLA、EVA进行熔融共混,共混物微观结构及力学性能的分析结果表明,E-MA-GMA的增容作用更有效,因而选用E-MA-GMA作为PLA/EVA共混物的增容剂。对PLA/EVA/GMA共混物的力学性能研究发现,当增容剂含量恒定时,随着EVA含量的增加,共混物的拉伸强度和弹性模量逐渐下降,但断裂伸长率和断裂功明显增加;当EVA组分含量恒定时,随着增容剂含量增加,力学性能先增加后下降,过量的增容剂对提高共混物力学性能不利,PLA/EVA/GMA的最佳配比为70/30/5。对PLA、PLA/EVA(70/30)、PLA/EVA/GMA(70/30/5)共混物的冲击性能、动态力学性能及热稳定性进行了研究,结果发现:(1)共混物的冲击强度因增容剂E-MA-GMA的加入而显著提高,弹性体EVA和增容剂E-MA-GMA的加入使断裂方式由脆性向韧性转变;(2)增容剂的加入使得共混物的两个玻璃化温度相互靠近,两相相容性增加;(3)EVA的加入降低了共混物的热稳定性,但增容剂的加入又使共混物热稳定性提高。在PLA/EVA共混物研究的基础上,通过不同共混工艺制备了PLA/EVA/MMT复合材料。首先采用熔融共混的方法制备了不同MMT含量的PLA/(EVA/MMT)/GMA共混体系,其中MMT含量分别为1.5%,3%,6%。共混物力学性能及微观形态的研究结果表明,随蒙脱土含量的增加,PLA/(EVA/MMT)/GMA共混物的拉伸强度、断裂伸长率及断裂功均逐渐减小,且分散相的分散性下降,因而选用MMT含量为1.5%作为制备PLA/EVA/MMT共混物的配比。然后采用不同的共混工艺制得的PLA/EVA/MMT共混物,力学性能研究结果发现,不同的共混工艺对试样的拉伸强度几乎无影响,断裂伸长率和弹性模量略有不同。其中,PLA/(EVA/MMT/GMA)/GMA试样的力学性能最好,断裂功最大。对比研究了纯PLA、PLA/EVA/GMA(70/30/5)及PLA/(EVA/MMT/GMA)/GMA共混物,结果发现PLA/EVA/GMA共混物的断裂伸长率和缺口冲击强度较纯PLA有较大的提高,但弹性模量明显下降,添加蒙脱土后,共混物的缺口冲击强度进一步提高,且弹性模量较PLA/EVA/GMA(70/30/5)共混物提高了6.13%。SEM和DMA的分析结果表明,蒙脱土的加入提高了分散相与基体的相容性,使分散相粒径进一步减小。从而使共混物的冲击韧性进一步提高。更多还原

【Abstract】 Poly(lactic acid)(PLA)is a thermoplastic polymer that can be derived from renewable natural resources.It has a number of interesting properties including biodegrability,biocompatibility,good mechanical properties and processability.For these reasons,the use of PLA can be a solution to environmental pollution。Moreover,it supplies sufficient sources for plastic materials conventionally petroleum-based.However, PLA is now not widely used because of its brittleness,thermal instability and high cost.To expand the fields of its application,PLA needs to be modified.Aiming at improving the properties of PLA,especially the impact toughness,this article selected Poly(ethylene-co-vinyl acetate)(EVA)as toughening agent to blend with PLA.The elastomers always made the modulus and thermal stability of blends decline,while Polymer/layered silicates nancomposites have the advantage of improving modulus and thermal stability of blends.So this article selected both EVA and montmorillonite(MMT)to blend with PLA.The advantages of Polymer/elastomers composite and Polymer/layered silicates nano--composite were combined to prepare PLA/EVA/MMT composites by melt blending,and the toughening mechanism of EVA and MMT was also studied.At first,in order to improve the compatibility of PLA and EVA,two different compatilizers,EVA-MAH and E-MA-GMA,were used to melt blending with PLA and EVA.The analysis of morphology and mechanical properties of blends indicated that E-MA-GMA is more effective,so it was selected as the compatilizer for PLA/EVA blends. Mechanical properties of PLA/EVA/GMA blends were investigated and the results showed that when the content of E-MA-GMA remained the same,the strength and modulus of blends decreased gradually with the increase in EVA content,but the elongation at break and the area under the stress-strain curve increased evidently.When the content of EVA remained the same,the mechanical properties of blends could not always be improved by the increasing of E-MA-GMA,and excessive amount of E-MA-GMA even impaired the mechanical properties.So the optimal ratio for PLA/EVA/GMA blend was 70/30/5.Then the impact toughness, dynamic mechanical property and thermal stability of PLA,PLA/EVA (70/30)and PLA/EVA/GMA(70/30/5)blends were investigated,and the results indicated that:(1)the addition of E-MA-GMA increased the impact strength of blends and the fracture varied from brittle to ductile with the addition of EVA and E-MA-GMA;(2)the addition of E-MA-GMA made the T_g of both PLA and EVA shift towards each other;(3)the thermal stability of blends was lowered by EVA,but it could be improved by the addition of E-MA-GMA.Based on the studies of PLA/EVA blends,PLA/EVA/MMT composites were produced through various blending technologies.At first,three PLA/(EVA/MMT)/GMA blends with different content of MMT were produced by melt mixing,in which the content of MMT was 1.5%,3% and 6%respectively.The mechanical properties and phase morphology of the blends were investigated,and the results showed that the strength,the elongation at break and the area under the stress-strain curve decreased with the increasing of MMT,and the size of EVA dispersed in the PLA matrix became bigger,so the optimal content of MMT is 1.5%.Therefore, in the following studies,the content of MMT in the PLA/EVA/MMT blends was 1.5%.The studies of PLA/EVA/MMT blends produced by different blending technologies indicated that blending technologies made no difference in strength,but the elongation at break and modulus of blends changed due to different blending technologies,and the PLA/(EVA/MMT/GMA)/GMA blend had the best mechanical properties. The mechanical properties of PLA,PLA/EVA/GMA(70/30/5)and PLA/(EVA/MMT/GMA)/GMA blends were compared,and the results showed that the elongation at break and impact strength were improved by the addition of EVA and E-MA-GMA,but the modulus decreased evidently;the addition of MMT further improved the impact strength of the blend,meanwhile,the modulus increased by 6.13%compared to that of PLA/EVA/GMA blend.The results of SEM and DMA indicated that MMT could increase the dispersion of EVA,making the EVA particles smaller,and this could further improve the impact toughness of the blend.更多还原