Effect of nanometer PTFE on space charge characteristics and DC dielectric properties of low density polyethylene
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摘要: 为研究驻极体材料纳米聚四氟乙烯(PTFE)对低密度聚乙烯(LDPE)空间电荷特性及直流介电性能的影响，选用纳米PTFE粉末与LDPE共混，制备得到不同填料质量分数(0.1wt%、0.3wt%、0.5wt%)的纳米PTFE/LDPE复合材料。SEM图像表明，粒径为20 nm左右的PTFE粒子在LDPE基体中分散性良好，结晶尺寸减小。FTIR表明，掺杂纳米PTFE粒子不会改变LDPE原有的化学结构。DSC结果表明，纳米PTFE粒子作为异相成核剂促进了材料的异相成核，提高了复合材料的结晶度。利用电声脉冲法(PEA)测试了室温下纳米复合材料的空间电荷分布，并测试了纳米复合材料的电导电流特性及直流击穿特性，结果表明，较低掺杂含量的纳米复合材料能明显抑制材料内部的空间电荷积聚，并且提高了复合材料空间电荷注入的阈值场强和材料的耐电强度。热刺激电流(TSC)结果表明掺杂含量较少时，纳米复合材料的陷阱能级最深，并随着掺杂含量的增加，纳米复合材料的陷阱能级逐渐变浅，浅陷阱密度逐渐增大。最后利用Materials Studio软件仿真分析F原子对LDPE陷阱能级的影响，表明F原子较强的电负性是影响纳米PTFE/LDPE复合材料陷阱能级的重要因素。Abstract: In order to study the effect of nano polytetrafluoroethylene (PTFE), a electret material, on the space charge characteristics and DC dielectric properties of low density polyethylene (LDPE), nano PTFE powder and LDPE were blended to prepare nano PTFE/LDPE composites with different filler mass fractions (0.1wt%, 0.3wt%, 0.5wt%). The images of SEM show that PTFE particles with a particle size of about 20 nm are well dispersed in LDPE matrix. The crystal size decreases. FTIR shows that doping nano PTFE particles does not alter the original chemical structure of LDPE. DSC shows that the use of nano PTFE particles as heterogeneous nucleating agents promotes heterogeneous nucleation of the material and improves the crystallinity of the composite material. The space charge distribution of nanocomposites at room temperature was measured using the electroacoustic pulse method (PEA), and the conductivity current characteristics and DC breakdown characteristics of nanocomposites were tested. The results showe that nanocomposites with lower doping content can significantly inhibit the accumulation of space charges inside the material, and improve the threshold field strength of space charge injection and the electrical resistance of the material. The thermal stimulation current (TSC) results indicate that when the doping content is low, the trap energy level of the nanocomposite material is the deepest, and as the doping content increases, the trap energy level of the nanocomposite material gradually becomes shallower, and the shallow trap density gradually increases. Finally, the materials studio software is used to simulate and analyze the influence of F atom on the trap energy level of LDPE, indicating that the strong electronegativity of F atom is an important factor affecting the trap energy level of nano PTFE/LDPE composites.
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Key words:
- PTFE /
- nanocomposites /
- LDPE /
- space charge /
- conduction current /
- DC breakdown
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图 1 LDPE及PTFE/LDPE纳米复合材料的红外图谱
Figure 1. Infrared spectra of LDPE and PTFE/LDPE nanocomposites
图 2 LDPE及PTFE/LDPE纳米复合材料的结晶形态
Figure 2. Crystal morphologies of LDPE and PTFE/LDPE nanocomposites
图 3 LDPE及其纳米PTFE/LDPE复合材料的DSC曲线
Figure 3. DSC curves of LDPE and PTFE/LDPE nanocomposites
图 4 加压极化时LDPE及其纳米复合材料的空间电荷分布
Figure 4. Space charge distribution of LDPE and its nanocomposites under pressure polarization
图 5 短路去极化时LDPE及其纳米复合材料空间电荷分布
Figure 5. Space charge distribution of LDPE and its nanocomposites during short-circuit depolarization
图 6 LDPE及其纳米复合材料短路时空间电荷平均体密度
Figure 6. Average bulk density of space charge during short circuit of LDPE and its nanocomposites
图 8 LDPE及其纳米复合材料的电导特性
Figure 8. Conductivity characteristics of LDPE and its nanocomposites
图 9 LDPE及其纳米复合材料直流击穿场强Weibull分布图
Figure 9. Weibull distribution of DC breakdown field strength of LDPE and its nanocomposites
图 10 LDPE及其纳米复合材料TSC温度谱(a)与陷阱能级分布(b)
Figure 10. TSC temperature spectra (a) and trap energy level distribution (b) of LDPE and its nanocomposite materials
图 11 LDPE及不同数目F原子取代H原子的电子态密度
Figure 11. Density of electronic states of LDPE and different numbers of F atoms replacing H atoms
图 12 LDPE及其纳米复合材料的离子跳跃电导拟合曲线(a)与跳跃距离(b)
Figure 12. Fitting curves of ion jump conductivity (a) and jump distance (b) of LDPE and its nanocomposite materials
表 1 低密度聚乙烯(LDPE)及纳米聚四氟乙烯(PTFE)/LDPE复合材料组成
Table 1. Components of low density polyethylene (LDPE) and nano polytetrafluoroethylene (PTFE)/LDPE composite materials
Materials LDPE/g nano-PTFE/g 1010/g LDPE 39.88 0 0.12 0.1wt%PTFE/LDPE 39.84 0.04 0.12 0.3wt%PTFE/LDPE 39.76 0.12 0.12 0.5wt%PTFE/LDPE 39.68 0.20 0.12 Note: 1010—Antioxygen 1010. 
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表 2 LDPE及其复合材料的DSC数据
Table 2. DSC data of LDPE and its nanocomposites
Sample Tc/℃ Tm/℃ Wc/% LDPE 95.15 110.66 35.75 0.1wt%PTFE/LDPE 96.06 112.54 37.07 0.3wt%PTFE/LDPE 94.87 111.25 36.64 0.5wt%PTFE/LDPE 95.96 110.05 36.13 Notes：$ T\mathrm{_c} $, $ T\mathrm{_m} $—Melting and crystallization peak temperatures of the material, respectively; $ W_{\mathrm{c}} $—Crystallinity of the material.
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表 3 各试样的电导斜率和过度阈值场强
Table 3. Conductivity slope and transition threshold field strength of each sample
Sample $ j $ $ E $/(kV·mm–1) $ j_{{\Omega}} $ $ {j}_{{\mathrm{t}}} $ $ {j}_{{\mathrm{c}}} $ $ {E}_{\Omega {\text{-}}{\mathrm{t}}} $ $ {E}_{{\mathrm{t}}{\text{-}}{\mathrm{c}}} $ LDPE 2.13 7.01 2.68 9.8 24.9 0.1wt%PTFE/LDPE 0.71 3.94 — 12.5 — 0.3wt%PTFE/LDPE 0.95 3.66 — 10.3 — 0.5wt%PTFE/LDPE 1.11 3.51 — 9.1 — Notes：$ j $, E—Slope and electric field strength; $ {j}_{\Omega } $ , $ {j}_{{\mathrm{t}}} $, $ {j}_{{\mathrm{c}}} $—Slope of the conductivity current; $ {E}_{\Omega {\text{-}}{\mathrm{t}}} $, $ E_{\mathrm{t}\text{-}\mathrm{c}} $—Threshold electric field of transition.
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表 4 各试样的特征击穿场强E0和形状参数β
Table 4. Characteristic breakdown field strength E0 and shape parameters β of each sample
Sample $ {E}_{0} $/(kV·mm–1) $ \beta $ LDPE 370.2 13.17 0.1wt%PTFE/LDPE 440.3 13.87 0.3wt%PTFE/LDPE 410.0 10.03 0.5wt%PTFE/LDPE 395.6 12.14
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