Abstract
In this study, PVDF/PTFE composite membranes were prepared by adding a PTFE nanoemulsion to a PVDF solution and casting it through the conventional non-solvent-induced phase separation method. The objective was to explore the effectiveness of using a simple and economical method to modify PVDF membranes with PTFE to enhance their anticorrosion performance, especially under highly acidic or alkaline conditions. PTFE nanoparticles (of around 200 nm in size) in nanoemulsion form were blended with PVDF at a mass ratio of PTFE:PVDF in the range of 0–0.3:1. The obtained membranes were examined to determine the effect of the added PTFE nanoparticles on the structure of the modified PVDF membranes as well as on their mechanical strength and surface characteristics. The membranes were then immersed in various concentrations of acidic or alkaline solutions for varied durations ranging from a few days up to as long as 180 days (6 months). The impacts of by the corrosive solutions on the tensile strength, surface roughness, and water flux of the membranes with different exposure times were quantified. The results showed that although a certain extent of change may occur with extended immersion times, greatly enhanced anticorrosion performance was obtained with the prepared PVDF/PTFE membranes compared with the unmodified PVDF membrane. For example, after being immersed in 5 mol-H+··L−1 H2SO4, HCl, and HNO3 solutions for 6 months, the tensile strength at breaking point remained at up to 69.70, 74.07, and 71.38%, respectively, of the initial strength for the PVDF/PTFE (M30) membrane. This was in contrast to values of only 55.77, 70.43, and 61.78% for the unmodified PVDF membrane (M0). Although the water flux and surface roughness showed a change trends to the tensile strength, the PVDF/PTFE (M30) membrane had much higher stability than the PVDF (M0) membrane. In a continuous filtration experiment containing H2SO4 at 0.01 mol-H+·L−1 for 336 h (14 days), the PVDF/PTFE membrane showed a maximum flux change of less than 30%. This was in comparison with a change of up to 50% for the PVDF membrane. However, the PVDF/PTFE membranes did not seem to have a greatly enhanced anticorrosion performance in the alkaline solution environment tested.
Highlights
Many industries, including electroplating, semiconductor fabrication, acid mining, pharmaceutical manufacturing, and phosphorus acid production industries, often produce highly corrosive wastewater during their processes
The higher porosity of the membranes with PTFE nanoparticles was probably caused by two factors: (1) The liquid in the PTFE nanoemulsion, which was added with the PTFE nanoparticles into the polyvinylidene fluoride (PVDF)/PTFE composite, and may have behaved as a porogen and increased the pore voids, contributing to a greater porosity in the obtained composite membrane; and (2) the compatibility between PVDF and PTFE nanoparticles was lower in PVDF/PTFE composite membranes (i.e., M10–M30), which may have led to a greater amount of liquid being retained in the membrane structure, leading to the final membrane having greater porosity than the PVDF in the solo PVDF
PVDF/PTFE composite membranes with enhanced anticorrosion performance were obtained by a simple method involving the blending of PTFE nanoparticles with PVDF polymer and the fabrication of membranes through the common non-solvent-induced phase separation process
Summary
Many industries, including electroplating, semiconductor fabrication, acid mining, pharmaceutical manufacturing, and phosphorus acid production industries, often produce highly corrosive wastewater during their processes. This includes concentrated acidic or alkaline effluents that must be treated or purified to specific standards before discharge or reuse [1]. The interest in membrane technology for application in the treatment of highly corrosive industrial effluents, for the recovery of acids and metal components and the reuse of treated effluents to attain a zero discharge status, has increased considerably over the years [8,9]. Most of the conventional or available membranes in the market are not tolerated that well, and the membranes have often been limited to a pH application range of 2–12 or even narrower
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