The α-, β-, and γ-polymorphs of polypropylene–polyethylene random copolymer modified by two kinds of β-nucleating agent

The α-, β-, and γ-polymorphs of polypropylene random copolymer with two kinds of β-nucleating agent (TMB-5 and WBG-2) have been studied via wide-angle X-ray diffraction and differential scanning calorimetry. It was found that the addition of 0.5 wt% β-nucleating agent (β-NA) hardly induces appreciable β-modification content, until β-NA content is up to 1 wt%. It seems that low amount of β-NA is not enough to counterbalance the nucleation ability and high content of defects (stereo- and regioerrors) of co-PP, and only α- and γ-modifications are obtained in the samples. Moreover, the relative amount of γ-crystal depends on the crystallization temperature. Although TMB-5 has better heterogeneous nucleation effect than WBG-2, the ability to form stable β-polymorph of WBG-2 is stronger than that of TMB-5. Since large amount of β-nucleation sites overcome the defects of co-PP molecular chain and curb the formation of γ-crystal, competitive growth of α- and β-polymorphs ultimately leads to the coexistence of α- and β-modification.