Microcellular injection molded outstanding oleophilic and sound-insulating PP/PTFE nanocomposite foam

Lightweight and open-cell thermoplastic foams have proven superior to common counterparts in terms of functional performances, such as oil absorption, sound and thermal insulation, contributing to energy saving, environmental protection, and sustainable development of the economy and society. Herein, a novel strategy was employed to prepare lightweight, oleophilic, and sound-insulating polypropylene (PP)/polytetrafluoroethylene (PTFE) composite foams by combining the microcellular injection molding (MIM) and in-situ fibrillation technologies. Thanks to the pronouncedly promoted crystallization and melt strength of the PP matrix by the nano-fibrillar PTFE fibrils obtained by the in-situ fibrillation process, the foaming ability of PP in the MIM process was effectively improved, reaching an expansion ratio of up to 20.2 and a cell population density of 108 cells/cm3. Notably, the nano-scale structures on cell walls together with thin cell-wall thickness of the PP/PTFE foam, significantly increased the open-cell content to 98.3%. The high porosities and large expansion ratios, assisted by the capillary penetration action caused by the uniquely elongated cells, effectively increased the oil absorption capacity up to 22.5 g/g with a high recovery of 97.4%, particularly for raw crude oil. Moreover, a high porosity and low airflow resistivity dramatically improved the sound insulation by reducing impedance and enhancing viscous dissipation, presenting as a sound absorption coefficient of higher than 0.5, and a transmission loss of up to 50 dB. Hence, the flexible, scalable and cost-effective MIM technology shows a promising future in the manufacture of multifunctional microcellular polymer products.