超支化聚酯改性纳米SiO_2/环氧树脂的介电特性

Effect of Hyperbranched Polyester Grafting Nanosilica on Dielectric Properties of Epoxy Resin

为改善纳米SiO_2与环氧树脂(EP)的界面性能及复合材料的介电参数,通过超支化聚酯协同偶联剂处理对纳米SiO_(2.)进行表面接枝,制备不同配比的纳米SiO_2/EP复合材料,研究不同改性方式及SiO_2含量下复合材料的介电特性。X射线光电子能谱及傅里叶红外光谱分析表明,端羧基超支化聚酯经100℃、40 min共混反应可成功接枝至纳米SiO_2表面;材料断面扫描电镜分析表明,质量分数为10%掺杂时,经超支化表面接枝改性的纳米SiO_2在EP溶液中不易团聚;热刺激去极化电流测试表明,纳米复合材料内部出现0.86～1.15 eV深陷阱;质量分数为7%掺杂比例下,复合材料的交流击穿电场强度比单纯偶联剂改性方式提高了19%;质量分数为5%掺杂比例下,工频下材料的介质损耗因数和介电常数分别下降至0.58%和4.38;研究结果表明超支化聚酯处理可在纳米SiO_2表面引入超支化基团。长链自由基的引入可抑制纳米SiO_2团聚,增强无机粒子与环氧基团的结合强度,并在纳米SiO_2/EP界面区域引入深陷阱,进而显著改善复合材料的介电特性。

To improve the interfacial properties of nanosilica/epoxy resin and the insulating behavior of composite materials, hyperbranched polyester and silane coupling agent were used to modify the surfaces of nanosilica in this study. Nanosilica/epoxy resin composites with different filling ratios were prepared, their dielectric properties under different modification methods were investigated. XPS and FTIR spectra show that the hyperbranched polyester can be grafted to nanosilica surface by 40 min of blending reaction under 100℃. SEM observation suggests that within 10% filling quality ratio, nanosilica particles treated by hyperbranched polyester are not prone to agglomerate in epoxy resin. TSDC measurement indicates that 0.86~1.15 eV deep traps are present in the modified nanocomposites.Moreover, the AC breakdown strength of the epoxy resin composites filled with polyester-treated nanosilica is 19% higher than that of the silane-treated composites at a filling quality ratio of 7%. The dielectric loss factor and relative permittivity of composites are also decreased to 0.58% and 4.38 at 5% filling quality ratio. The results mentioned above show that active carboxyl groups can be implanted to nanosilica surfaces by the hyperbranched polyester treatment. Terminal carboxyl radicals with long chains effectively inhibit the agglomeration of nanosilica and enhance the bonding strength between inorganic particles and epoxy matrix. As a result, trap energy of epoxy resin composites is increased, and the insulating behaviors of the epoxy resin composites are obviously improved.