Weak interfaces can impede crack propagation in rigid natural materials containing small amounts of organic compounds. Inspired from this, we start from the core-shell structured isotactic propylene (iPP)/polypropylene random copolymers (PPR) homocomposites and construct serval kinds of interfaces to study the toughening mechanisms by applying the crystallization epitaxies of PPR on iPP. Through molecular chain diffusion and crystallization epitaxy, derived models from microscopic core-shell structured crystals in the homocomposites to macroscopic layer-by-layer assemblies with different interfaces are established to magnify the role that each layer plays during crack initiation and propagation. As a result, the ductile β-PP interface can decrease crack tip strength so that a further step of crack initiation is triggered in the composite laminates with a fold of fracture energy consumption compared to the laminates with weak or rigid interfaces. At last, we come back to the core-shell structured homocomposites and toughen them with an improve in impact toughness from ∼10.8 to ∼18.2 kJ/m by manipulating the content of ductile interfaces. This work provides a novel research routine and a new toughening mechanism toward the toughening of PP and can be extended to study the fracture mechanisms of other toughening systems with core-shell structures.

中文翻译：

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高韧性聚丙烯无规共聚物α/β核壳结构的增韧机理

弱界面会阻碍含有少量有机化合物的刚性天然材料中的裂纹扩展。受此启发，我们从核壳结构的等规丙烯（iPP）/聚丙烯无规共聚物（PPR）均质复合材料出发，构建多种界面，应用PPR在iPP上的结晶外延来研究增韧机理。通过分子链扩散和结晶外延，建立了从均质复合材料中的微观核壳结构晶体到具有不同界面的宏观层层组装的衍生模型，以放大各层在裂纹萌生和扩展过程中所起的作用。因此，延性β-PP界面可以降低裂纹尖端强度，从而在复合材料层合板中触发进一步的裂纹萌生步骤，与具有弱或刚性界面的层合板相比，其断裂能量消耗成倍增加。最后，我们回到核壳结构均质复合材料，并通过控制延性界面的含量将其增韧，将冲击韧性从~10.8 kJ/m提高到~18.2 kJ/m。这项工作为PP增韧提供了新颖的研究思路和新的增韧机制，并可推广到其他核壳结构增韧体系的断裂机制研究。