交联聚丙烯压电驻极体的压电性能及振动能量采集研究

以电子束辐照交联聚丙烯(IXPP)泡沫薄板为原材料, 首先利用热压工艺对微观结构进行改性, 然后采用电晕充电方法对样品实施极化处理, 使之具有压电效应, 成为压电驻极体. 通过准静态和动态压电系数d₃₃、复电容谱, 以及等温衰减的测量, 研究了IXPP压电驻极体膜的机电耦合性能; 同时考察了基于IXPP压电驻极体膜的振动能量采集器在{3-3}模式下对环境振动能的俘获. 结果表明, IXPP压电驻极体的准静态压电系数d₃₃可高达620 pC/N; 厚度方向的杨氏模量和品质因数(FOM, d₃₃·g₃₃)分别是0.7 MPa和11.2 GPa^-1; 在50, 70和90℃下进行等温老化, 经过24 h后, IXPP压电驻极体膜的准静态压电系数d₃₃分别降低到初始值的54%, 43%和29%; 采用面积为3.14 cm²的IXPP压电驻极体膜为换能元件, 当振子质量为25.6 g, 振动频率为820 Hz时, 振动能量采集器在匹配负载附近可以输出高达65 μW/g²的功率.

Piezoelectric property of cross-linked polypropylene piezoelectret and its application in vibration energy harvester

Piezoelectrets, also known as ferroelectrets, are space-charge electrets based polymer foams with strong piezoelectric effect. The piezoelectric effect in piezoelectrets originates from the regularly arranged dipolar space charges in the polymer matrix, achieved by properly charging the specific foam structure. The large figure of merit (FOM, d₃₃·g₃₃) in piezoelectrets implies that such kinds of materials are promising candidates in energy harvesters. In this article, the electron-irradiated cross-linked polypropylene (IXPP) foam sheets are rendered piezoelectric (i.e. to become piezoelectrets) by modification of the microstructure using hot-pressing process and polarization using corona charging at room temperature. The electromechanical properties of the fabricated IXPP piezoelectrets are investigated by measurements of quasi- and dynamic piezoelectric d₃₃ coefficients, dielectric resonance spectrum, and isothermal decay at elevated temperatures. The energy harvesting from vibrations by using the IXPP piezoelectret films, at various vibration frequencies, load resistances, and seismic masses, are also studied. Results indicate that the quasi-static piezoelectric d₃₃ coefficients of IXPP films up to 620 pC/N can be achieved. The variation of quasi-static piezoelectric d₃₃ coefficient is dependent on the applied pressures, from 0.1 to 1.3 kPa, while it shows good linearity at larger pressures from 1.3 to 15 kPa. The typical values of Young's modulus in the thickness direction and the figure of merit (FOM) are 0.7 MPa and 11.2 GPa^-1, respectively. The d₃₃ coefficients will drop to 54%, 43%, 29% of the initial values after annealing the samples for 24 h at 50, 70, 90℃, respectively. At an exciting frequency of 820 Hz, the normalized output power of 65 μW/g² is obtained from an IXPP film with an area of 3.14 cm² and a seismic mass of 25.6 g around the optimum load resistance. Such thin, light and flexible IXPP piezoelectret films may be applied in vibration energy harvesters for powering low-power electronic devices.