Preparation of foam material via co-sintering of NaCl and PTFE for oil/water separation

Bulk polytetrafluoroethylene (PTFE) foam is a great potential oil-water separation material, owing to the high hydrophobicity and lipophilicity property. However, the technique of fabricating PTFE foam with low cost, controllable porosity and high mechanical strength remains an urgent requirement due to its high chemical inertness induced limitation. A kind of bulk PTFE foam material is prepared by cold pressing co-sintering method, employing sodium chloride (NaCl) as pore forming agent. SEM measurements reveal that the size and distribution of pore structure are mainly determined by the particle size and content of NaCl, because the migration and diffusion behaviors of PTFE particles suffer from more inhibition induced by increased NaCl particles during sintering. The PTFE foam with uniformly distributed pore structures can be obtained from composite mixed with 70 wt% NaCl and 30 wt% PTFE, with a low thermal conductivity as low as 0.069 W/(m K). With the decrease of PTFE content in raw composite, the density and mechanical properties of PTFE foam gradually declines. However, the tensile strength remains as low as 0.2 MPa, with an elongation rate of 21%, which guarantees the required mechanical strength avoiding being broken when use as a bulk oil absorption material. Remarkably, the PTFE foam shows a strong hydrophobicity, with a mean water contact angle of 137 degrees, and with a mean surface roughness of 4.41 mu m. It exhibits separation efficiency larger than 99% in 30 cycles, with separation flux larger than 4000 L/m2/h within 15 cycles, indicating excellent recyclability and stability. The PTFE foam sample also shows desirable continuous separation performance for oil/water mixture. The proposed bulk PTFE foam with low manufacturing cost and stable chemical and mechanical properties will provide data and theoretical support for the material applied in oil/water separation and thermal-protective coating.