Ultrahigh-cell-density polypropylene (PP) foam was prepared by supercritical carbon dioxide (scCO₂) foaming in the presence of porous polytetrafluoroethylene (PTFE) micropowder. The voids of PTFE microparticles were filled with supercritical CO₂, causing them to split into multiple granules due to the force of its expansion during the pressure release, resulting in the formation of a large number of nucleation sites. The cell density of this foam reached 10¹⁰–10¹¹ cells/cm³, which was 2–5 orders of magnitude higher than pristine PP foam. We proposed that the nanoscale granules resulting from the splitting of PTFE microparticles, and the growth of nucleated small cells that generated the local strain field variation in the multiple-phase system, were responsible for the considerably increased nucleation number of PP foaming. Additionally, the tensile strength and sound absorption property of PP/PTFE foam were largely enhanced and the preparation of ultrahigh-cell-density PP/PTFE foam was easily controlled over a wider foaming temperature window.

中文翻译：

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在聚丙烯的超临界二氧化碳发泡中添加PTFE超细粉的优点：超高孔密度，高拉伸强度和良好的隔音性能

在多孔聚四氟乙烯（PTFE）微粉存在下，通过超临界二氧化碳（scCO ₂）发泡制备超高孔密度聚丙烯（PP）泡沫。PTFE微粒的空隙中充满了超临界CO ₂，由于其在压力释放过程中的膨胀力而分裂成多个颗粒，导致形成大量成核点。该泡沫的孔密度达到10 ¹⁰ –10 ^11孔/ cm ³，比原始PP泡沫塑料高2-5个数量级。我们提出，由PTFE微粒分裂产生的纳米级颗粒，以及在多相系统中产生局部应变场变化的有核小孔的生长，是导致PP发泡成核数显着增加的原因。此外，PP / PTFE泡沫的拉伸强度和吸声性能大大提高，超高孔密度PP / PTFE泡沫的制备易于在较宽的发泡温度范围内进行控制。