Transformation of the Supermolecular Structure of Surface Layers in Composite Polysulfone and Polyethersulfone Ultrafiltation Membranes

Results are presented from studying active and drainage layers of composite ultrafiltration polysulfone and polyethersulfone membranes via thermogravimetry (TG), differential scanning calometry (DSC), and X-ray diffraction analysis in the air-dried state and after exposure to transmembrane pressure and permeate diffusion. It is found that thermal effects of polymer layers are observed on the TG and DSC curves of the composite membrane samples. The thermal properties of Lavsan (PET) are apparent in the temperature range of 32 to 240°C; those of polysulfones, from 240 to 450°C. Deconvolution of endothermic peaks shows that the peak at Tgt = 64.1°C correlates with glass transition temperature; the peak at Tm = 188.4°C, with the melting of PET crystallites according to the empirical rule of two thirds: Tgt ≈ 2/3Tm. Degradation of both PET and polysulfone macromolecules starts at T = 450°С. It is shown that transmembrane pressure and the diffusion of water alter the chemical composition of Lavsan in ~50% of its mass as a result of hydrolysis. X‑ray diffraction measurements of the active membrane layer at 2θ ≈ 17.5° confirms the amorphous structure of polysulfones. The shift of the diffraction angle toward large angles 2θ ≈ 19.24° for PS indicates an increase in the packing density of macromolecules in amorphous formations of the working sample. It is concluded that the density of packing falls for polyethersulfone at 2θ ≈ 17.34°.