Thermal and X-Ray Structural Studies of Structural Changes in the Active Layer of Polytetrafluoroethylene Ultrafiltration Membranes

Autor: Yu. M. Golovin, O. A. Abonosimov, A. Yu. Selivanov, D. A. Rodionov, S. I. Lazarev
Rok vydání: 2021
Předmět:
Zdroj: Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques. 15:947-953
ISSN: 1819-7094
1027-4510
DOI: 10.1134/s1027451021050086
Popis: An analytical review on the study of structural changes in membranes is presented. Ultrafiltration films of polytetrafluoroethylene membranes in the temperature range from 30 to 500°С are investigated by thermogravimetry. An analysis of the thermal data is carried out, which indicates that in the temperature range from 100 to 215°C, the first stage of destruction occurs, where the value of the lost mass for the air-dry sample is 33%, and for the water-saturated sample, the mass loss is 10%, which is 3 times less than the first sample. For the working sample, a slow process of mass change is observed in a wide temperature range from 100 to 410°C, which with total weight loss is about 9%. The second stage of destruction occurs in the temperature range from 410 to 500°C with a loss of mass for an air-dry sample of 61 and 85% for a water-saturated sample, and the working sample loses 86% of its mass. The data on X-ray crystallography (X-ray crystallography) allow us to conclude that the effect of water and transmembrane pressure leads to a significant change in the morphology of polymer molecules at the supramolecular level. If for an air-dry sample of a polytetrafluoroethylene ultrafiltration membrane, a diffuse nature of the reflection with a maximum at 2θ = 12° is observed, then for a water-saturated sample an intense diffraction peak appears at 2θ = 17° against the background of an amorphous halo. For the working sample, the reflection has a compact structure with a sharp asymmetric peak at 2θ = 13.8°. Complementary methods of TG (thermogravimetry), DSC (differential scanning calorimetry), X-ray diffraction analysis (XRD), and gravimetry have established that conformational changes in molecules in the polytetrafluoroethylene-membrane matrix occur as a result of the detachment of side monomers or oligomers and their sublimation from the film volume under the influence of transmembrane pressure and the interaction of water molecules.
Databáze: OpenAIRE
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