Formation of bicontinuous, hydrophobic nylon 12 membranes via cold-solvent-induced phase separation for membrane distillation application

摘要

Skinless nylon 12 microporous membranes were prepared via a cold-solvent-induced phase-separation process from a binary nylon 12-formic acid system. Through the incorporation of an aging step, polymer nucleation in the dope was enhanced, and the formed membranes exhibited a special particulate structure composed of interlocked sticklike or sheaflike crystallites, which coexisted with continuous microporosity. The crystallite size was affected by the polymer concentration in the dope and the aging time; for example, aging alone allowed for the reduction of the particle diameter from about 20 mu m to about 1 mu m. Because the membranes were skinless and hydrophobic (contact angles approximate to 105 degrees), they were potentially appropriate for desalination via membrane distillation (MDi). For the case of desalting 3.5% NaCl(aq) by means of direct-contact MDi, very high rejection ratios (similar to 99.6%) were achieved for all membranes under the operation conditions (temperature of the hot stream = 50 degrees C, temperature of the cold stream = 20 degrees C, and circulation rate = 0.7 L/min), whereas the highest permeation flux obtainable was 5.15 L/m(2) h. The membranes were strong, with tensile strengths ranging from 4.7 to 6.3 N/mm(2). Finally, we discovered a shift from alpha to gamma structure as the dope polymer increased, whereas the crystallinity was about 27% in all cases. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47036.