冷却方式对MMT/LDPE介电性能的影响

Effects of Cooling Methods on Dielectric Properties of MMT/LDPE

采用熔融插层法制备了蒙脱土/低密度聚乙烯（MMT/LDPE）纳米复合材料,探讨空气自然冷却、空气快速冷却、水冷却和油冷却四种制备工艺对复合材料介电性能的影响。利用XRD、FTIR、AFM、PLM、DSC和TSC等分别对复合材料和纳米MMT粒子的微观形态、复合材料的电导、击穿、介电频谱和空间电荷特性进行表征。结果表明,经表面修饰的纳米MMT粒子在基体聚合物中已经剥离并均匀分散;不同冷却方式对复合材料的结晶度有一定的影响,其中油冷却试样结晶速率最高,结晶尺寸最小;纳米MMT的加入使复合材料内部陷阱密度和深度均有所增加,且试样的介电性能有不同程度的改善。油冷却试样抑制空间电荷的作用比较明显,在20和40 k V/mm的场强下,试样中正电荷的峰值与空气自然冷却试样相比分别下降了63.57%和51.39%;且油冷却试样的电导率最小,击穿场强值最大;在1~105 Hz的测试频率范围内,与空气自然冷却试样相比,其他三种试样的介电常数和介质损耗角正切值都有不同程度的降低。

The melting intercalation method was used to prepare montmorillonite/low density polyethylene （MMT/LDPE） nano-composites. Through natural air cooling, rapid air cooling, water cooling, and oil cooling methods, the effects of different preparation processes on the dielectric properties of the composites were studied. The MMT/LDPE composite materials were characterized by XRD, FTIR, AFM, PLM, DSC, and TSC test. All experimental results show that the surface modified nano-MMT particles have been exfoliated and uniformly disperse in polyethylene. Different cooling processes have influence on the crystallinity of the composites. The oil cooling sample has higher crystallization rate and smaller crystal size. The density and depth of trap in the composites with nano-MMT are increased, which effectively improves dielectric properties of the polymer. Space charge in the composites by oil cooling process is evidently inhibited under 20 kV/mm and 40 kV/mm field strength. The peak value of positive charge is decreased by 63.57% and 51.39% as compared with that of natural air cooling. The oil cooling sample shows the smallest conductivity, and the largest breakdown strength. In the frequency range of 1-10^5 Hz, the dielectric constant and dielectric loss angle tangent of other threetypes of rapid air cooling, water cooling and oil cooling samples decrease at different degrees in contrast to natural air cooling sample.