Simultaneous durability and strength enhancement of β-polypropylene through montmorillonite and melt-soluble β-nucleating agent addition

β-polypropylene (β-PP) demonstrating both increased toughness and strength was prepared by simultaneously adding montmorillonite (MMT) and a melt-soluble β-nucleating agent (β-NA). The MMT functioned as a “micro-stirrer” to promote the dissolution of β-NAs in the β-PP melt due to an increased shear rate around the existing particles. A subsequent recrystallization on cooling triggered a transition from dot-like to fibrous β-NAs, and leaf-like β-crystals were obtained via epitaxial crystallization on the fibrous β-NAs formed in situ. Accordingly, the strength and toughness of β-PP were enhanced simultaneously, suggesting that MMT improved the toughness of the β-PP. For example, when the MMT fraction was 2%, the β-PP/MMT composite exhibited an increase of 90% in elongation at break and 60% in impact strength in comparison to pure β-PP. This study provides a valuable guide to achieving an outstanding combination of strength and toughness in PP composites by tailoring the morphology of β-NAs, which is also applicable to other β-PP composites.