超临界二氧化碳辅助下反应挤出发泡一体化制备改性聚丙烯与含氟高分子复合薄层多孔材料及其压电特性研究

Piezoelectric materials are widely used in high-tech devices and potential energy harvesting applications due to their ability to inter-convert mechanical and electrical energy. Piezoelectric materials based on cellular polymers have received intensive attentions due to their advantages such as lightweight, low-cost, flexibility, and easy of shaping. However, there is still a lack of polymeric piezoelectric materials with high piezoelectric activity, excellent stability, and good mechanical properties. This project intends to: prepare composite of fluoropolymer and fluoro-contained polypropylene with long chain structure (LCBPP); use supercritical foaming process and utilize the difference between the solubility of supercritical carbon dioxide (scCO2) in modified PP and fluoropolymer to obtain the closed cellular polymers with “sea-island" structure, in which PP acts as the continuous phase and the cells enclosed by fluoropolymer form the dispersed phase; convert the cellular polymers into porous piezoelectric material through corona charging. The obtained material will be integrated PP and fluoropolymer piezoelectric materials to their respective advantages, such as excellent piezoelectric activity, thermal stability and mechanical properties, and overcome the intrinsic defects of piezoelectric materials based on porous fluoropolymer with open cell structure,such as the poor charge stability. This research will be focused on: how to prepare PP-fluoropolymer composite and control its morphology and properties using supercritical reactive extrusion process; how to obtain the cellular polymer with the desired morphology and manipulate the shape, size and density of the closed cells using supercritical foaming process; study on the crucial factors affecting properties of the designed piezoelectric materials.

压电材料可实现机械能与电能的相互转换，广泛应用于高科技器件与能量捕获领域。孔洞型聚合物压电材料具有重量轻、成本低、柔性好、易成型的优点，近年来倍受关注。本项目拟制备含氟改性长支链聚丙烯（LCBPP）-含氟高分子复合材料，并利用超临界二氧化碳（scCO2）在改性PP和含氟高分子中溶胀特性的差异，通过超临界发泡形成PP为连续相、含氟高分子富集于孔洞内壁的“海岛”结构闭孔发泡材料，再经电晕充电制成孔洞型压电材料。该材料将兼具含氟高分子压电材料的高压电活性、热稳定性及PP压电材料的优良力学性能。主要研究内容包括，利用scCO2辅助下的反应挤出制备LCBPP-含氟高分子复合材料及其相形态和性能的调控；通过后续超临界发泡过程获得设想结构的发泡材料并控制其泡孔形态、尺寸及密度；揭示影响所得压电材料性能的关键因素。

孔洞型聚丙烯压电材料在众多的压电材料中性能突出且成本低廉。但传统的无机颗粒致孔剂挤出制备的孔洞型聚丙烯需要二次膨化才具有较高的压电系数，且电荷稳定性较差，压电系数会随着负载压力增大或者温度的升高而下降。研究表明，引入氟元素可以有效提高聚丙烯的电荷稳定性，但现有的氟化技术主要是在聚丙烯孔洞膜表面进行氟气氟化改性，该改性工艺既不环保又无法对大量孔内壁界面进行改性。超临界二氧化碳发泡技术是一种绿色环保且无杂质引入的发泡方式，本项目采用超临界二氧化碳间歇发泡和挤出发泡法制备孔洞型聚丙烯压电薄膜，探索了发泡工艺对于泡孔结构和压电性能的影响以及泡孔结构和压电特性之间的关系。并将挤出发泡和取向拉伸耦合一体化制备具有较好的压电特性的孔洞型聚丙烯薄膜。其中在间歇发泡方面提出了不等温发泡新策略，极大提高等规线性聚丙烯（iPP）的可发泡性和泡孔可塑性，拓宽了iPP的应用领域和压电薄膜原料的选择范围。除此以外，本项目对超临界二氧化碳辅助下含氟接枝改性聚丙烯进行深入探索，然后用间歇法，对于含氟接枝改性和含氟高分子掺混改性不同聚丙烯体系的受限发泡工艺进行研究。探讨含氟接枝改性聚丙烯体系可发泡性以及发泡体泡孔结构和压电特性的影响，探索不同含氟高分子掺混量和掺混方式对于含氟改性后的聚丙烯体系可发泡性、泡孔结构和压电特性的影响。为一步法制备孔洞型聚丙烯压电薄膜材料以及改性提高其压电特性提供理论指导。

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