具有压电性和热释电性的PVDF纤维的研究

【作者】 任萍；

【导师】 张华；

【作者基本信息】 天津工业大学 ， 材料学， 2004， 硕士

【摘要】 压电和热释电材料是指由于静压力的变化，或温度的改变产生相应感应电荷的变化的材料。压电材料的主要功能是能够将机械能与电能相互转化。目前研究的压电材料大多是膜或块状压电材料，如聚偏氟乙烯压电膜或压电陶瓷块。对于纤维状柔性压电材料的研究几乎未见报道，而压电纤维作为一种特殊的压电材料形式应用越来越广泛。聚偏氟乙烯(PVDF)作为一种压电材料，具有很强的压电效应和热释电效应，也是目前在压电高分子材料中研究的较为系统、应用最广泛的高聚物。与目前常用的无机物压电材料相比(如石英、压电陶瓷类)它还有声阻抗小、频率响应宽、介电常数小、耐冲击性强、便于加工成任意形状等优点。 本论文主要研究了利用熔融法纺制PVDF纤维，并对纤维进行了极化，目的是探索提高PVDF可纺性的途径，确定最佳原料型号和工艺参数，制备出以PVDF为基本原料的纤维，将纤维进行极化，探索极化条件对PVDF纤维微观结构的影响。 本论文采用聚偏氟乙烯为主要原料，利用熔融纺丝法对PVDF进行纺丝研究，并添加了另一种压电高聚物尼龙11(PA11)共混纺丝，并对其共混纤维性能进行了研究。PVDF是半结晶性高聚物，分子链呈线型而且有一定的柔顺性，其成纤性在理论上是可行的，但因温度对其剪切速率的影响不大，所以温度的改变并不能提高它的可纺性。PVDF可纺性较差，而PA11是一种良好的成纤高聚物。二者均为较好的压电材料，从PVDF／PA11共混纤维的可纺性和压电性两方面讨论，50wt／50wt的PVDF／PA11纤维性能最好。由于PVDF的压电性与晶体结构有关，于是利用红外光谱、差热分析、广角X光衍射和扫描电镜等测试手段对纯PVDF纤维以及PVDF／PA11共混纤维的结构性能及晶型转变进行了深入的研究。发现PVDF熔纺纤维与普通的PVDF原生膜不同，PVDF原生膜只含有α相，而PVDF熔纺纤维中既含有α相结晶又含有β相结晶，这是由于在纺丝过程中喷丝头拉伸和卷绕过程中的拉伸造成的。拉伸有利于PVDF纤维的α相结晶向β相结晶转变，且拉伸倍数越高β相含量越高；较低温度区域内(＞100℃)，温度提高有利于α相结晶向β相转变，较高温度区域内(＞100℃)，温度提高对α相向β相转变作用不大。共混纤维拉伸比率的提高，有利于PVDF中β相的生成，且β相的含量随拉伸倍数的提高而增加。但拉伸对共混纤维中PA11的晶型转变影响较小而淬火却有利于PA11的晶型转变，但对其中的PVDF晶型转变影响不大。 本课题还进行了PVDF纤维与膜的极化研究，自行设计了极化装置，并对极化前后纤维利用静电测量、红外光谱和扫描电镜等方法进行对比研究，揭示了PVDF在电场作用下微观结构的变化情况。发现PVDF纤维在电场作用下微观结构变化较大，极化后微晶取向发生较大变化，极化以后微晶变化为沿电场方向取向的厚片状，熔融态的PVDF在电场作用下凝固时变化更明显，与不加电场直接凝固的PVDF膜相比，在电场作用下几乎所有的分子链都沿电场方向取向所以出现有序的片晶结构，而且结构致密。从红外吸收光谱来看极化后的吸收率比极化前减少。更多还原

【Abstract】 Piezoelectricity is a phenomenon when a mechanical stress is applied to some piezoelectric material; electrical charges appear between its two opposite sides. Conversely, if an electrical field is applied to this material, it will generate mechanical strain. Also, for material showing Pyroelectric properties, electric charges will appear under the effect of temperature. According to these proprieties, a piezoelectric element is an electromechanical transducer (energy converter). At present, most of the piezoelectric material is film or ceramic cylinder. The soft piezoelectric fiber is not reported. As a piezoelectric polymer, PVDF (polyvinylindine fluoride) has many advantages, many due to its mechanical properties, such as flexibility, high mechanical resistance, and dimensional stability. PVDF is a piezoelectric polymer, which was studied systematically and was applied extensively.The research studies how to melt-spin PVDF fibers and polarize the fibers. It is an object to choose the PVDF material, probe melt-spinning technology parameters; and improve the spinning ability of PVDF. Then the fiber was polarized and the effect of poling parameters on microstructure was studied.The research prepared PVDF fibers using melt spinning. PVDF is semi-crystalline polymer, and its molecule chain is linear and soft. Manufacturing fibers is feasible theoretically, however it is hard in reality and increasing the temperature cannot improve the spinning ability of PVDF. PA 11 is suitable for manufacturing fibers; so two-polymer blend fibers were prepared. According to piezoelectricity and spinning property, we found the optimal proportion of two composites, and 50wt/50wt PVDF/PA11 fibers were suitable. Because of the crystalline leading to the piezoelectricity of PVDF, PVDF fiber and PVDF/PA11 fiber’s structures and crystalline were investigated and analyzed by means of Wide angle X-ray Diffraction, Differential Scanning Calorimetry, Fourier Transmittance Infra-red Spectroscopy and Scanning Electron Microscopy, etc. It was shown that there are two kinds of crystalline- a phase and B phase in PVDF fiber. The a phase can change to B phase by stretching. In the range of low temperature the higher content of B crystalline was achieved during the higher drawing ratio and the higherdrawing temperature. In the blend fiber, stretching benefit to phase transiting of PVDF, but not PA11, and quenching benefit to phase transiting of PA 11, but not PVDF.After designing poling equipments, fibers were polarized. The microstructure changes of the fibers were studied by means of DSC, FTIR and SEM. The results show that: the fiber was polarized in dimethyl silicone fluid, and the microstructure changed. The microcrystalline was same to the direction of electric field. The microcrystalline orientation of the film that was obtained by Melting PVDF congealing in the effect of electric field changed along electric field obviously. Comparing with the film congealing without electric field their crystalline plate become thick. FTIR absorbance of the polarized fiber decreases than that of the fiber before polarized.更多还原