基于PTFE平板膜负泊松比效应评价膜结构的新方法建立与可靠性研究

Aiming at the problem that the single membrane structure is difficult to accurately reflect the separation performance of the membrane material, a new method for evaluating the membrane structure from the viewpoint of the negative Poisson ratio was put forward on the basis of the study about preparation of PTFE sheet membrane via "extrusion-calendering-biaxial stretching-heat setting method" and the reliability was verified. Firstly, the microstructural evolution of membrane materials was studied, and the influence of molecular weight, extrusion, calendering and biaxial stretching process parameters on the negative Poisson's ratio and membrane structures were clarified. Secondly, a new method of membrane structure evaluation is established on the basis of exploring the essential relationship between the negative Poisson's ratio and the membrane structures from the microscopic morphology. Finally, the reliability of the new method is verified by the microbial challenge, and its application in the field of negative Poisson polymer microporous membrane is explored. The development of this project not only can broaden the control idea of PTFE membrane structures, but also provide a new evaluation method for the structures of other polymer microporous membranes with negative Poisson ratio and promote the development of polymer bulk material.

针对目前单一膜结构难以准确反映膜材料分离性能的问题，以聚四氟乙烯（PTFE）平板膜为研究对象，在采用“挤出-压延-双向拉伸-热定型法”制备PTFE平板膜的研究基础上，提出从膜材料负泊松比效应角度评价膜结构的新方法，并对其可靠性予以验证。首先，研究膜材料的微观形态演变行为，明确PTFE分散树脂分子量、挤出、压延及双向拉伸工艺参数等对负泊松比效应、膜结构的影响规律。其次，从微观形态出发探清负泊松比效应与膜结构之间的本质关系，并建立膜结构评价新方法。最后，通过微生物挑战验证新方法的可靠性，探索其在负泊松比聚合物微孔膜领域中的应用局限性。本项目的开展，不仅能拓宽PTFE膜结构调控思路，而且为其它负泊松比聚合物微孔膜的结构提供一种全新的评价方法，促进制膜用聚合物本体材料的发展。

针对目前单一膜结构难以准确反映膜材料分离性能的问题，以聚四氟乙烯（PTFE）平板膜为研究对象，在采用“挤出-压延-双向拉伸-热定型法”制备PTFE平板膜的研究基础上，提出从膜材料负泊松比效应角度评价膜结构的新方法，并对其可靠性予以验证。项目研究了双向拉伸法过程中PTFE微孔膜内部微观形态演变过程、负泊松比现象及膜结构变化。结果表明：当PTFE分散树脂分子量提高，晶型转变形成的伸直链片晶尺寸大，拉伸过程中不易断裂，因此PTFE微孔膜的孔径较小；当提出过程中剪切力提高，PTFE微孔膜内部节点减少、纤维增加，引起PTFE微孔膜孔径下降；双向拉伸过程中，随着纵向拉伸比增加，PTFE原纤在应力作用下伸长，原纤节点构成的孔隙尺寸增加，导致微孔膜孔径增加，然而，横向拉伸过程中，纵向拉伸形成的节点发生劈裂并旋转，原纤发生倾斜，构成各向同性三维网状结构，微孔膜厚度增加，呈现负泊松比特性。结合微孔膜形态结构演变过程、膜结构及负泊松比现象，项目提出了膜结构评价新方法。当PTFE微孔膜负泊松比值最大时，其过滤效率和过滤阻力最优。本项目的开展，不仅能拓宽PTFE膜结构调控思路，而且为其它负泊松比聚合物微孔膜的结构提供一种全新的评价方法，促进制膜用聚合物本体材料的发展。