Morphology Of Polytetrafluoroethylene Research Articles

The effect of α-irradiation from enriched uranium on the leaching properties of PTFE

Abstract In the uranium enrichment plants of the South African Nuclear Energy Corporation SOC Ltd (Necsa), sintered polytetrafluoroethylene (PTFE) filters were used to remove gas entrained solid particles, in order to prevent blocking of the isotope separating elements. When these plants were decommissioned and dismantled, the filters which mostly contained solid uranium fluoride and uranium oxyfluoride compounds and compressor ring dust, were broken into pieces, put into metal drums, and stored. This waste contains enriched uranium and can't be disposed of at the current disposal site (Vaalputs), which only accepts low and intermediate level waste. Initial attempts, directly after removal from the enrichment plants, to decontaminate these filters using various aqueous solutions, were unsuccessful probably because of the known non-wettability of PTFE surfaces. However, recent attempts to leach the absorbed enriched uranium were successful. This resulted in a study to determine the effect of mainly α-irradiation from the enriched uranium on the morphology of PTFE. A Monte Carlo N-Particle transport code (MCNP), a general purpose radiation transport code modelling the interaction of radiation with materials that simulate nuclear processes, was used to determine the rate of PTFE radiolysis. The results confirmed that the dose rate received from mainly the α-particles (97%) during the storage period had caused significant structural damage to the PTFE depending on the enrichment grade and the amount of uranium on the filters. To confirm the modelling data, analytical techniques, including micro X-ray tomography, thermogravimetric analysis and X-ray diffraction were used to study the morphology changes in the PTFE structure of the research samples. Experimental results indicated that the crystallinity increased while the molecular weight of the PTFE decreased. This could be attributed to the radiation induced degradation of the PTFE by the absorbed enriched uranium.

Radiation Degradation of Polytetrafluoroethylene-Lead Composites

Composites of polytetrafluoroethylene (PTFE) with Pb (0-15 wt.%) were fabricated and irradiated up to 50 kGy in a 60Co-gamma chamber to evaluate the effect of Pb in improving the radiation tolerance of PTFE. Thermal and mechanical properties were measured for the irradiated and un-irradiated PTFE samples and its composites. The number average molecular weight of PTFE was estimated at different doses from the enthalpy of crystallization values obtained by Differential Scanning Calorimetry. Reduction in the percentage increase in the enthalpy of crystallization and melting of PTFE-15% Pb composite, during irradiation indicated the stabilizing effect of lead on PTFE. Surface morphology of PTFE and its composites revealed that the formation of micro-cracks and blisters in PTFE, owing to radiation damage was controlled by lead. Elongation at break values and SEM images of the irradiated composites indicated that 15% Pb offered better stability to PTFE than 10% Pb.

Studies on Wear Properties of Polystyrene in the Presence of Fibrillated Network of Polytetrafluoroethylene

Polystyrene (PS) is an important commodity plastic; however, it is not known as a suitable material for tribological applications. It has a relatively high friction coefficient in contact with metallic surfaces and high abrasion loss factor. Polytetrafluoroethylene (PTFE) is a known friction modifier, has a low friction coefficient, and is extensively used to reduce the friction coefficient and wear rate (with engineering plastics to improve tribological properties). It is known for fluoroelastomers and engineering plastics that fine particles of PTFE have the greatest effect on improving the specified properties. Here, oriented, fibrillated network morphology of PTFE in PS matrix was prepared. The wear studies show a large reduction in both the friction coefficient (45% reduction) and the wear rate (2% incorporation of PTFE leads to a 49% reduction). But the friction coefficients do not show any significant change on increasing PTFE. A similar observation was made for the wear rate. Scanning electron microscope (SEM) images of the worn surfaces show a crack tip bridging mechanism, and it was observed that with the increase in PTFE content, the extent of crack tip bridging increases. This extensive improvement may be attributed to the unique morphology of the blend system.

Morphology of polytetrafluoroethylene before and after irradiation

Supramolecular structure and morphology of as-polymerized, sintered, and gamma-irradiated suspension PTFE were studied with scanning electron microscopy. Irradiation was performed both below and above melting point of crystal phase. Fibrillar supramolecular structure of as-polymerized PTFE is preserved after its sintering. In contrast to as-polymerized PTFE, in the sintered polymer some segments of fibrils form lamellae of thickness 100–300 nm and length up to several microns, with fibrils arranged perpendicularly to a lamella. Irradiation below the melting point (20 and 200 °C) does not change quantitatively PTFE morphology. In both cases and also in the case of pristine PTFE, dense and loose (porous) regions are present in its morphology. Dense regions are packages of irregular shape and consist of densely packaged fibrils. Loose regions consist of individual ribbons and fibrillar lamellae. Irradiation at 200 °C increases greatly the width of lamellae. PTFE structure rearrranges drastically under irradiation above the melting point. New morphology units, spherulites of size about 50 μm, are formed, the spherulites consisting of radially extending fibrils, and porosity decreases substantially. Formation of spherulites is ascribed to radiation-induced chain scission and decrease in molecular mass and viscosity of polymer.

The Morphology of Polytetrafluoroethylene (PTFE) Thin Films Formed by Pulsed-Laser Deposition

ABSTRACTThin films of polytetrafluoroethylene have been formed by the pulsed-laser deposition technique. The structure of the films was found to be dependent upon the substrate temperature during deposition. At substrate temperatures from room temperature to 200°C the films were determined, by transmission electron microscopy and X-ray diffraction techniques, to be amorphous. Films formed at higher substrate temperatures were found to contain both amorphous and crystalline components. The data for the crystalline component is consistent with it being highly ordered with the long helical molecular chains aligned parallel to the film-substrate interface plane. The maximum amount of crystalline material occurred when the substrate temperature was close to the melting temperature of the polymer.

Effect of cyclic loading on the morphology of polytetrafluoroethylene

Effect of cyclic loading on the morphology of polytetrafluoroethylene