Effect of isotactic polypropylene on crystal structure and morphology of β-modified random copolymerized polypropylene

It is difficult for the direct addition of β-nucleating agents to obtain high contents of β-crystals because of the effect of the random copolymer structure of random copolymerized polypropylene (PPR). In this study, the β-crystallinity of PPR was improved by introducing a small amount of isotactic polypropylene (iPP) into β-modified PPR. After optimizing the conditions, the degree of crystallinity increased to 56.5%, while the relative content of β-crystal was as high as 92.4% and its β-crystallinity increased by 61.5%. Its crystallization growth process showed that iPP first forms β-nuclei and further induced PPR to produce β-crystals. Due to the high content of β crystal, toughness had been greatly improved. The impact test was carried out at − 15, 0, and 23 °C, the impact strength of pure PPR was 2.3, 3.8, and 22.8 kJ/m², respectively. After adding 20 wt% iPP in β-modified PPR, the impact strength increased to 3.3, 7.7 kJ/m², and 45.9 kJ. In addition, its elongation at break reached 574.4%, which is four times of the elongation at pure PPR. The self-rigid and high-content β-crystals of iPP molecular chains have synergistic effect, which makes the tensile strength of the composite system almost unchanged. This study provides a method to regulate the structure and molecular chain activity of PPR crystal, which lays the foundation for the improvement of PPR performance.