Structure of Polytetrafluoroethylene Modified by the Combined Action of γ-Radiation and High Temperatures

Abstract

By means of X-ray computed microtomography (XCMT), the existence of a developed porous structure with an average pore diameter of ~3.5 μm and pore content of ~1.1 vol.% has been revealed in unirradiated polytetrafluoroethylene (PTFE). It has been found that the combined action of gamma radiation (absorbed dose per PTFE of ~170 kGy) and high temperatures (327–350 °C) leads to the disappearance of the porous structure and the formation of several large pores with sizes from 30 to 50 μm in the bulk of thermal-radiation modified PTFE (TRM-PTFE). It has been established by X-ray diffraction (XRD) analysis that the thermal-radiation modification of PTFE leads to an increase in the interplanar spacings, the degree of crystallinity and the volume of the unit cell, as well as to a decrease in the size of crystals and the X-ray density of the crystalline phase in comparison with the initial polymer. It is assumed that the previously-established effect of improving the deformation-strength and tribological properties of the TRM-PTFE can be due not only to the radiation cross-linking of polymer chains but also to the disappearance of the pore system and to the ordering of the crystalline phase of PTFE

Radiation Shielding Tests of Crosslinked Polystyrene-b-Polyethyleneglycol Block Copolymers Blended with Nanostructured Selenium Dioxide and Boron Nitride Particles

“…It should also be noted that when the gamma radiation energy increases, the RPE rates decrease, meaning that these decreases in the RPE rates confirm that all of our results are compatible with the other attenuation parameters (i.e., , , HVL, TVL, MFP) computed and experimentally detected. These conclusions obtained are consistent with the results of the research composites developed for gamma-ray shielding with various nanostructured additives, including polymers [ 11 , 12 , 30 , 31 , 32 , 33 ]. As a result, the current alterations in nanoparticle proportions are quite efficacious for diminishing the influence of gamma radiation.…”

“…Doyan et al worked on the polymeric film materials of polyvinyl alcohol (PVA), trichloroethylene (TCE), and cresol red (CR) dye to expose the gamma beams for eventual implementation in radiation dosimetry; their results indicate that enhancement of the radiation rate altered the hue of the polymeric film, from purple (pH > 8.8) with no radiation (0 kGy) to yellow (nearly pellucid) (2.8 < pH < 7.2) at the uppermost rate (12 kGy); in other words, these results demonstrated a useful dose range of 0–12 kGy for the investigated polymeric film samples [ 31 ]. Smolyanskii et al worked on the construction of polytetrafluoroethylene developed via the combination of gamma irradiation and high temperatures, and concluded that these conditions (327–350 °C) lead to the evanescence of the poriferous texture and the creation of a few large pores [ 32 ]; furthermore, they indicated that it is important to carry out new research on the continuity of changes in the structure and irradiation–chemical operations, depending on the irradiation temperature. A. Abu Saleem et al focused on the shielding properties of epoxy + carbon- and glass-fiber composites doped with lead nanoparticles [ 33 ]; their conclusions indicate that the values rise as lead nanoparticle rates increase up to a specific proportion (~15 wt%), after which the enhancement in the values becomes negligible.…”

Thermoradiationally Modified Polytetrafluoroethylene as a Basis for Membrane Fabrication: Resistance to Hydrogen Penetration, the Effect of Ion Treatment on the Chemical Structure and Surface Morphology, Evaluation of the Track Radius

“…In addition, the detected effect of a significant deterioration of the hydrogen permeability of TRM-PTFE films may be associated with the elimination of the micropore system as a result of the combined action of γ-irradiation and high temperatures [ 23 ].…”

“…The irradiation temperature varied from 323 to 350 °C, nitrogen was used as the external medium, irradiation was carried out at a dose of 50 kGy at a dose rate of ~3 Gy/s. Corrections for the difference between the electron densities of the Fricke dosimeter and PTFE were taken into account during the radiation treatment (the absorbed dose conversion factor for PTFE was 0.87 [ 23 ]).…”

“…After a certain material thickness t, which is called the thickness of the charged particle equilibrium, the radiation energy absorption decreases [ 24 , 25 ]. The PTFE plate thickness required to achieve maximum energy absorption is t = 2.5 mm [ 23 ]. The electron density can be calculated using the formula: where n is the electron density, m −3 ; p is the density of PTFE (2.15 kg/m 3 for the initial PTFE [ 2 , 3 ]); N A = 6.023 × 10 23 mol −1 is the Avogadro constant, M is the molar mass, kg/mol, Z i is the atomic number, and Σ i Z i is the total number electrons per molecule.…”