Bio-inspired lightweight polypropylene foams with tunable hierarchical tubular porous structure and its application for oil-water separation

Abstract

Inspired by nature, the biomimetic polypropylene (PP) foams with tunable hollow tubular structure, hierarchical porous structure and rough inner surface characteristics were designed and massively fabricated (with a speed exceed 0.5 m/s) via environment-friendly supercritical carbon dioxide (scCO2) continuous extrusion foaming. Additionally, the inner diameter of the as-prepared biomimetic tubular PP foams can be easily adjusted from extreme low (∼0.4 mm) to very high (∼20.0 mm) size through a fixed 2.0 mm circle extruder die by carefully controlling the radially distributed temperature and melt viscoelasticity. Furthermore, we also theoretically analyzed the reasons of the formation of such biomimetic hierarchical tubular structure during foaming and drew up the corresponding schematic diagram. More interestingly, thanks to the above biomimetic structure, the as-prepared PP foam strips exhibited both superior absorption and filtration ability during the oil-water separation, in which the deionized water could be filtered quickly through the foam strips while the oil was absorbed in seconds. Besides, the relationship between pore size and hydrophobicity of polymer foams was theoretically analyzed by the Young-Laplace equation. More importantly, we believe that the design principles and processing strategies reported here can also be applied to other materials and it has great potential application in the environmental sewage treatment.