Superhydrophobic and Oleophilic Open-Cell Foams from Fibrillar Blends of Polypropylene and Polytetrafluoroethylene

Abstract

Effective removal of oils from water is of global significance for environmental protection. In this study, we investigate the hydrophobicity and oleophilicity of open-cell polymer foams prepared in a continuous and scalable extrusion process. The material used to prepare the open-cell foams is a fibrillar blend of polypropylene (PP) and polytetrafluoroethylene (PTFE). Scanning electron microscopy (SEM) images of the morphology of the PP/PTFE fibrillar blend reveal that the PTFE has a fibrillar morphology in the PP matrix. SEM micrograph of the extruded foam shows the formation of an interconnected open-cell structure. Using nitrogen pycnometry, the open-cell content is estimated to be 97.7%. A typical bulk density of the open-cell foam is measured to be about 0.07 g cm(-3) corresponding to a void fraction of 92%. Thus, a large three-dimensional space is made available for oil storage. A drop of water on the cross-section of the extruded open-cell foam forms a contact angle of 160° suggesting that the open-cell foam exhibits superhydrophobicity. The open-cell foam can selectively absorb various petroleum products, such as octane, gasoline, diesel, kerosene, light crude oil, and heavy crude oil from water and the uptake capacities range from about 5 to 24 g g(-1). The uptake kinetics can be enhanced by exposing the open-cell foam to high intensity ultrasound which increases the surface porosity of the thin, impervious, foam "skin" layer. The reusability of the foam can be improved by using a matrix polymer which demonstrates superior elastic properties and prevents the foams from undergoing a large permanent deformation upon compression to "squeeze out" the oil. For example, when the PP homopolymer matrix is replaced with a PP random copolymer, the permanent deformation for 10 compressive cycles is reduced from about 30% to 10%. To the best of our knowledge, these PP-based open-cell foams outperform PP-based absorbents conventionally used for oil-spill cleanup applications such as nonwoven PP fibers or melt-blown PP pads.

Tuning viscoelastic and crystallization properties of polypropylene containing in-situ generated high aspect ratio polyethylene terephthalate fibrils

“…To observe the morphology of the PET domains in the PP/PET blends (T processing ¼ 255 C), a solvent-vapour etching technique is used [16]. The sample is exposed to xylene vapours for 45 min at 60 C. This type of treatment preferentially etches the PP matrix which is soluble in xylene, which exposes the PET domains and increases the contrast using a Scanning Electron Microscope (SEM, JEOL 6060).…”

Facile fabrication of robust superhydrophobic porous materials and their application in oil/water separation

“…Impressive examples such as the Torrey Canyon and the Bohai Bay spill accidents, not only induced serious environment pollution, but also threatened the ecological system. [5][6][7][8][9][10][11][12][13][14] Up to now, various superhydrophobic porous materials have been prepared via various chemical and physical strategies. 4 Porous materials, including fabrics, membranes, meshes and sponges, with superhydrophobicity have believed to be promising in oil/water separation.…”

Heat transfer in microcellular polystyrene/multi-walled carbon nanotube nanocomposite foams

“…As a result, decreasing the cell size to below 10 lm is the only choice for decreasing the gas conductivity. Adding nucleating agents to enhance heterogeneous bubble nucleation is commonly known to increase the cell density and to reduce the cell size [31][32][33]. MWCNTs with a high aspect ratio are good candidates to initiate heterogeneous bubble nucleation.…”