Nanoscale grain refinement is a mature and powerful tool to enhance the mechanical and physical properties of metals and alloys. However, similar cases are rarely reported in the widely used semicrystalline polymers. Herein, we demonstrate a feasible strategy to fabricate the ultrafine-grained isotactic polypropylene (iPP) by rapid quenching of stretched melt. The grain refinement happens to regularly arranged nano-lamellae in both thickness and lateral directions, leading to an order of magnitude improvement in the number density of lamellae compared to normal melt crystallization. We have shown that such grain refinement greatly enhances the tensile toughness of iPP material without sacrificing the modulus and strength. Rope-like fracture morphology is observed in the toughened samples after the mechanical tests. It is indicated that the refined crystalline grains with low structural stability probably favor the formation of fibrils. This work provides a generalized approach to mechanically toughen the semicrystalline polymers by grain refinement on the nano-lamellar scale.

纳米级晶粒细化是增强金属和合金的机械和物理性能的成熟而强大的工具。然而，在广泛使用的半结晶聚合物中很少报道类似的情况。在这里，我们演示了一种可行的策略，可以通过快速淬火拉伸熔体来制造超细颗粒的全同立构聚丙烯（iPP）。晶粒细化恰好在厚度和横向两个方向上规则地排列了纳米薄片，与正常的熔体结晶相比，导致了薄片数量密度的提高。我们已经表明，这种晶粒细化在不牺牲模量和强度的情况下大大提高了iPP材料的拉伸韧性。机械测试后，在增韧的样品中观察到了绳状的断裂形态。结果表明，具有低结构稳定性的细晶粒可能有利于原纤维的形成。这项工作提供了一种通用的方法，可以通过纳米层级的晶粒细化来机械增韧半结晶聚合物。