Poly(hydroxyamide) as support for thin-film composite membranes for water treatment

Preparation of a porous support for a thin-film composite (TFC) membrane was achieved based on a highly aromatic poly(hydroxyamide) (PHA) formed from 5-hydroxyisophthalic acid and 4,4′-(hexafluoroisopropylidene)dianiline. PHA synthesis was confirmed by Fourier transform infrared and proton nuclear magnetic resonance (¹H NMR) spectroscopies. PHA was soluble in N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), and tetrahydrofuran (THF) with Mw 6.1 × 10⁴ Da. Moreover, PHA showed good thermal stability up to 390 °C. Parameters for an appropriated PHA porous structure support membrane by the phase-inversion method were determined. Porous PHA support offers higher thermal stability and better adhesion between support amide thin skin layer than the ones used actually. Water permeation flux was 543 L m⁻² h⁻¹ for PHA porous support, whereas thin-film composite membrane PHA-TFC formed presented a decrease in water permeation flux (2.5 L m⁻² h⁻¹) and a salt rejection capacity of 29% which situates it as a nanofiltration membrane.