Effect of sPP Content on Electrical Tree Growth Characteristics in iPP/sPP Blend Cable Insulation

Polypropylene (PP) is considered to be a recyclable alternative to XLPE for cable insulation by virtue of its higher melting point and higher electrical resistivity. This work focuses on the effect of syndiotactic PP (sPP) content on the AC electrical tree growth characteristics in isotactic PP (iPP)/sPP blend insulation. The growth rate of electrical tree in PP blends decreased with the increase of sPP content from 0 to 15 wt%. When sPP content continues to increase, the crystallinity and deep trap density of the blend decline, resulting in the increasing initial probability and growth rate of electrical tree. The PP blend with 15 wt% sPP shows an excellent resistance to electrical tree, which is attributed to the higher crystallinity. The higher crystallinity results in a higher deep trap density in sPP/iPP blends. The increased deep trap density is conducive to reduce the mean free path of charges and confine impact ionization, resulting in the lower growth speed of electrical tree.