Physical modification of polytetrafluoroethylene flat membrane by a simple heat setting process and membrane wetting remission in SGMD for desalination

• PTFE flat membrane with low surface free energy was prepared by a heat setting process.
• Anti-fouling property is enhanced and the membrane wetting time is decreased.
• The PTFE flat membrane shows excellent performance in SGMD.

In order to remit the membrane wetting in membrane distillation (MD), polytetrafluoroethylene (PTFE) flat membrane with low surface free energy and high water contact angle (WCA) was prepared by a simple heat setting process. Membrane morphology evolution, such as breakage of fibrils and fusion of PTFE resin, and its influence on membrane characters including pore size, porosity and roughness were discussed. The effect of the heat setting process on the membrane wetting was evaluated by the membrane wetting time (MWT) in a static absorption experiment (SAE) and sweep gas membrane distillation (SGMD). The results show that the crystallinity decreases with increasing the heat setting temperature and time, which leads to low surface free energy and therefore low adsorbing capacity of penetrating agent and the long wetting time in the static absorption experiment and SGMD. In addition, pore size increases firstly and then decreases due to the breakage of fibrils and fusion of PTFE resin, respectively, which further affects the permeate flux. Therefore, we propose that the anti-fouling property and separation performance of PTFE flat membrane in SGMD can be well handled and hope that such a PTFE flat membrane would be potentially useful in seawater desalination.