The morphological evolution and mechanical properties of polypropylene/SiO2/POE ternary composites under different processing conditions

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Abstract
As the phase morphology of polypropylene composites is highly sensitive to processing conditions and considerably determines the final properties, fabricating composites with controllable phase morphology and macroscopic properties remains an ongoing task. In this study, to achieve an optimal balance between stiffness and toughness in composites, SiO2 and POE (polyolefin elastomer) were selected as modifiers, and the effects of mixing time, rotational speed, and mixing sequence of PP/SiO2/POE (70/15/15) composites on phase morphology and material performance were systematically investigated. From the perspective of mixing time, samples prepared within 6-8 minutes exhibited a higher number of uniformly distributed core-shell structure, resulting in excellent mechanical properties. When the rotational speed was set at 60 rpm, the optimal performance was achieved. Considering the mixing sequence, the one-step method provided favorable core-shell morphology and desirable mechanical performance,. Under the aforementioned conditions, a polypropylene composite with an excellent balance of stiffness (1245 MPa) and toughness (57.19 kJ/m2) was successfully fabricated. Notably, SEM and the spreading coefficient theory analysis revealed that SiO2 and POE tend to form a core-shell structure within the composite. However, the stability of this structure varies with processing conditions. Mechanical testing further confirmed that the presence of the SiO2/POE core-shell structure contributes to a balanced stiffness-toughness, while variations of the structure lead to corresponding changes in the macroscopic properties of composites. The relationship between phase morphology and performance was further elucidated through DMA and DSC analyses. Morphological examination of impact-fractured surfaces indicated that in highly tough composites containing core-shell structures, energy dissipation primarily occurs through shear yielding and plastic deformation, revealing the underlying toughening mechanism.

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