Mechanism of Low‐Temperature Brittle–Ductile Transition of Polypropylene/Low‐Density Polyethylene Blend Foam under Compressive Stress Caused by Cell Stretching

To enhance the low‐temperature toughness of polypropylene/low density polyethylene (PP/LDPE) blend, which is a crucial blend for polyolefin material with wide applications in frigid regions, the PP/LDPE blend foam with stretched cells is fabricated via a facile injection foaming together with open‐mold stretching process. During the open‐mold stretching, the relatively miscible PP and LDPE chains are debonded, and then the stretched and oriented cells structure with lots of tiny interphase cavities between the PP and LDPE phases and the fine lamellae are formed in the foam system. Such interphase cavities provide an adequate movement space for the frozen PP and LDPE chains and lamellae, and effectively relaxed and transferred stress, which greatly promote the uniform compressive behavior accompanied by the completely compacted cells at −25 °C. Moreover, the compressive fracture surface changes from relatively flat and smooth for the stretched PP foam to obvious yield folds and deformation for the stretched blend foam, and the compressive strain of stretched PP/LDPE blend foam is highly enhanced by a roughly 31%, 53%, and 44% increase than that of PP, PP/LDPE, and stretched PP foam samples, respectively, achieving the low‐temperature brittle–ductile transition for PP.