Effect of Crystallization Conditions on Space Charge Characteristics of $\beta$ -pp

The impact strength of PP at low temperature can be improved obviously by adding $\boldsymbol{\beta}$ nucleating agent into PP. However, the $\boldsymbol{\beta}$ crystal form is not a stable crystal form, and the content and morphology of the $\boldsymbol{\beta}$ crystal are affected by the crystallization conditions. In this paper, the rare earth $\boldsymbol{\beta}$ nucleating agent WBG was selected as the modifier of polypropylene. The effect of crystallization cooling rate and annealing treatment on $\boldsymbol{\beta}$ -crystal content and space charge characteristics of polypropylene was studied. The results show that the $\boldsymbol{\beta}$ nucleating agent WBG can induce the formation of $\boldsymbol{\beta}$ crystal form in PP. Compared with the rapidly cooled crystalline sample, the slower crystallization rate and annealing treatment increase the relative content of $\boldsymbol{\beta}$ crystal and increase the size of $\boldsymbol{\beta}$ crystal, but the distribution uniformity is worse. The introduction of the nucleating agent promotes the crystallization process of the $\boldsymbol{\beta}$ crystal in the PP, thereby effectively reducing the structural defects in the crystal region, thereby reducing the amount of space charge. However, after slow cooling crystallization and annealing treatment, the amount of space charge in $\boldsymbol{\beta}$ -PP increases, and the uniformity of distribution of $\boldsymbol{\beta}$ crystals is deteriorated by heat treatment, which may be the reason for the decrease of space charge suppress ability.