Analysis of Structural Transformations and Water State in a Microfiltration Polyamide Membrane
摘要
The paper presents the results of studies of structural transformations and the state of water in samples of MMK-045 nonworking, water-saturated, and working membranes using the methods of IR spectroscopy NTR and X-ray phase analysis. Three types of hydrogen bonds have been identified: (‒CO…H2O…CO–) (III) type ~30 kJ/mol, H2O…HN (II) type ~16 kJ/mol, and (I) type ~9 kJ/mol. Sorption water in a water-saturated sample, reducing the energy of intermolecular (NH…O=C) bonds, changes the configuration of PA6 macromolecules without changing the trans-conformers. At the same time, FTIR spectrum of the working membrane sample (absence of absorption band at 1478 cm–1) shows breaking of H‑bonds, accompanying changes in the configurations of molecules with increasing gauche conformers. Manifestation of a complex absorption band at ~1723 and 1737 cm–1, attributed to terminal carboxyl groups (COOH), indicates the destruction of PA6 macromolecules. Disappearance of the absorption band at ~3089 cm–1 for the first time experimentally confirms the connection between the Fermi resonance phenomenon in polymer molecules and the destruction of PA6 macromolecules to elementary structural units. X-ray studies indicate structural changes mainly at the supramolecular level in MMK-045 membrane samples. In a water-saturated sample, the density of molecules in the amorphous phase increases (2θ = 26.4°), and in the working one it decreases (2θ = 20.9°). The total crystallinity in the working membrane sample relative to the nonworking one decreased from 36 to 33%, not as a result of recrystallization, but rather as a result of a reduction in crystallites of α-phases, and increased in crystalline formations of γ-phases with imperfect crystalline structure.