辅助电场对低密度聚乙烯微观结构演变与直流电气特性的影响

Influence of assisted electric field on the microstructure evolution and direct current electrical properties of low-density polyethylene

低密度聚乙烯(low-density polyethylene,LDPE)是电缆绝缘的基础材料.辅助电场可以调控聚合物的微观结构,但是其目前在电气绝缘领域的应用却鲜有报道.分别在LDPE试样成型过程中的熔融、冷却结晶及全阶段(即熔融及冷却结晶全阶段)施加辅助电场,制备了基于电场辅助的LDPE试样.探究了在不同阶段施加辅助电场对LDPE的微观结构演变、直流击穿特性、电导特性、空间电荷特性和陷阱特性的影响规律.结果表明,与未处理的LDPE相比,在熔融阶段、冷却阶段和全阶段施加辅助电场的LDPE具有更多更小的球晶,在全阶段施加辅助电场的LDPE的球晶数量最多,尺寸最小.同时,辅助电场能够明显提升LDPE的直流电气特性.其中,全阶段施加辅助电场的LDPE与未处理LDPE相比,击穿场强提升了35.8%,电导率降低了72.0%,平均空间电荷密度降低了20.2%.本研究为电气绝缘聚合物的微观结构调控和直流电气特性提升提供了新的思路.

Low-density polyethylene(LDPE)is the basic material of the high-voltage direct current(DC)power cable insulation.The assisted electric field is a common way to regulate the microstructure of polymers,but its application in the field of electrical insulating polymers is rarely reported.In order to study the influence of the assisted electric field on the microstructure evolution and DC electrical properties of LDPE,the LDPEs without and with being treated with assisted electric field are prepared in the melting stage,cooling stage,and the whole stage(i.e.the melting stage and cooling stage),respectively.The influence of the assisted electric field applied in the different stages on the microstructure evolution of LDPE is characterized by the scanning electron microscopy(SEM)and differential scanning calorimetry(DSC).The DC electrical properties of the untreated LDPE and the treated LDPE are investigated via measuring their breakdown strengths,conductivities,space charges and surface potential decays.The results show that,compared with the untreated LDPE,the LDPE treated with the assisted electric field in the whole stage has the smallest spherulite size and the largest spherulite number,followed by the LDPE treated in the cooling stage and the melting stage.The assisted electric field applied in different stages can significantly improve the DC electrical properties of LDPE.Compared with the untreated LDPE,the LDPE treated in the melting stage,the cooling stage and the whole stage increases the breakdown strength but greatly reduces the conductivity and space charge accumulation.The DC electrical properties of LDPE treated with the assisted electric field in the whole-stage are the best.Compared with untreated LDPE,the LDOE treated in whole stage increases the breakdown field strength by 35.8%,reduces the conductivity by 72.0%,and the space charge accumulation by 20.2%.More and smaller spherulites lead to the formation of more interface paths and introduce more deep-traps,which contributes to improving the DC electrical characteristics of the electric field assisted LDPE.This work provides a new idea for improving the DC electrical properties of polymers.