基于双连续相的乙烯—醋酸乙烯共聚物/聚已内酯共混物多孔材料的制备

【作者】 张洁；

【导师】 吴德峰；

【作者基本信息】 扬州大学 ， 材料学， 2010， 硕士

【摘要】 两种或多种聚合物的混合是实现彼此性能互补从而获得新型聚合物材料的重要途径之一。不过大部分聚合物之间是热力学不相容的,对应的共混体系大多呈两相结构。与分散-连续的相形态相比,具有双连续相形态的聚合物共混物由于其特殊的相互贯穿的亚微观/宏观网络的织态结构,因此能够较好地实现基体组分间性能的互补,并能够进一步拓展其应用领域。通过选择性蚀刻去除双连续共混物中某一组分,以此获得聚合物基多孔材料就是其应用领域的拓展途径之一。不过要控制多孔材料的孔径以满足不同领域的需求(如药物控制释放、组织工程支架等),就要明确影响聚合物不相容共混体系双连续相形态形成及演化的因素。因此本论文采用了两种不相容的具有生物相容性的高分子材料乙烯-醋酸乙烯共聚物(EVA)和聚己内酯(PCL),首先通过熔融共混的方法制备了一系列不同组分比和粘度比的EVA/PCL共混物,然后利用形态表征和流变学的方法剖析了共混材料的相行为,通过建立不相容相形态与材料粘弹行为之间的联系,明确了影响共混体系双连续形态的控制因素。在此基础上,通过研究共混物的相形态和加工条件之间的关系,最终实现了双连续形态可控的目标,并进一步通过选择性蚀刻得到了具有不同孔径大小的EVA多孔材料。(1)扫描电子显微镜(SEM)测试的结果表明,EVA/PCL共混物为典型的热力学不相容共混体系。EVA和PCL的组成比显著影响共混体系的相形态,随组分比的变化,共混物表现出分散-连续的形态和双连续的形态;流变学测试的结果表明,由于EVA和PCL具有较大的粘度差异(粘度比为0.02),且EVA具有较高的弹性效应和松弛时间,因此共混体系双连续组成范围较宽(PCL的浓度为40-60 wt%之间);而单纯基于粘度比和弹性比的粘弹模型都不能很好地预测该体系的相反转浓度;(2)基体组分的本体性质强烈影响双连续相形态的形成。随着体系两组分粘度比的降低,共混物形成双连续结构的组成范围越来越大,且形成的双连续形态结构越清晰。此外,较低的界面张力值有利于体系双连续结构的形成:EVA与PCL间界面张力越小,共混体系形成双连续结构的分散相浓度越偏向于低浓度,且形成的双连续结构范围越来越宽;(3)共混工艺同样显著影响双连续相形态的演化。剪切作用会使双连续相畴减小,这是因为EVA具有较大的粘度和弹性,对共混体系毛细管数的贡献远超剪切下PCL相的破碎趋势,因此两相只会发生高度的变形而不会破碎。此外,等温退火过程中共混物的双连续相畴会粗化,而凝聚速率则随着退火温度的升高而增加;在非等温退火过程中,相畴的凝聚速率同样随退火温度的升高而增加,共混体系粘度随温度升高而下降是影响凝聚效应的决定性因素;(4)传统的溶液浇铸-粒子滤沥法制备得到的EVA和PCL多孔材料孔径分布不均匀,开孔结构和闭孔结构共存,且孔间联通性较差。而基于双连续相共混物制得的多孔材料的连贯度和孔隙率都有明显提高。通过控制加工和退火条件来控制双连续形态,能够有目的地设计并控制EVA多孔材料的结构和形态,从而得到具有一系列特征孔径(1.5-120μm)的孔材料。更多还原

【Abstract】 Blending two or more polymers together to achieve property complement is one of the important routes to obtain new polymer materials. However, many blends present two-phase structure due to the thermodynamic incompatibility between the component polymers. Compared with that of the blends with‘sea-island’morphology, the co-continuous blends usually show better performance and potential applications in more fields because of their special sub-microcosmic/macroscopical network structure. The fabrication of porous materials by selective etching one of the component in the co-continuous blends is one of the further applications of such blend material. To obtain different pore sizes to meet different requirements such as drug controlled release and tissue engineering scaffold. it is necessary to deeply explore how the co-continuous phase morphology form and evolve during melt mixing.Therefore, two biocompatible polymers, ethylene-vinyl acetate copolymer (EVA) and poly(ε-caprolactone) (PCL) were used in this work to prepare EVA/PCL blends with various component ratio and viscosity ratio by blending. Then the phase behavior of the blends was analyzed by morphological and rheological approaches, and the dominant factors determining formation and evolution of the co-continuous phase morphology were studied by relating the immiscible morphology to the viscoelastic behavior of the blends. Through establishing the relationship between co-continuous phase morphology and processing conditions, the porous materials with various pore sizes based on EVA were fabricated successfully by selective solvent etching.(1) The Scanning Electron Microscopy (SEM) results showed that the EVA/PCL blends were thermodynamically immiscible. The component ratio affected the phase morphology of the blends significantly. The blends showed dispersed-continuous and co-continuous morphology at different component ratios. The results of rheological tests showed that the blends had a wide co-continuous region (PCL concentrations of 40~60 wt%) due to high viscosity ratio between PCL and EVA, and to higher elasticity and longer relaxation time of EVA. The models merely based on viscosity or elasticity can hence not be well used to describe the phase inversion point of the blends.(2) The bulk properties of component polymers strongly influenced the formation of co-continuous structure. The co-continuous morphology became clearer and the composition range increased as viscosity ratio reduced. In addition, the low interfacial tension between two components favored the formation of co-continuous morphology. The lower the interfacial tension was, the lower co-continuous phase concentration was, and the wider co-continuous composition range.(3) The processing conditions also affected the evolution of co-continuous phase morphology significantly. The shear flow reduced the co-continuous phase domain because the contribution of EVA to the capillary numbers highly exceeded the breakup tendency of PCL in shear flow, and as a result, the two phases were highly deformed but not break up. Moreover, in the isothermal annealing process, the co-continuous phase domain increased and the coalescence rate growed as temperature increased; in the nonisothermal annealing process, the co-continuous phase domain also increased with increasing annealing temperature. The coalescence effect is dominated by the decrease of viscosity of the blend systems.(4) The porous materials based on EVA or PCL prepared by the traditional solution casting-particle filter method showed poor porous morphology: wide pore size distribution, co-existance of the open-cell and the closed-cell structure and low pore connectedness. However,for those porous materials based on co-continuous blends, the pore connectedness and porosity were improved evidently. The pore size (1.5-120μm) could be controlled by designing and controling the processing and annealing conditions of the co-continuous blends.更多还原