Pure PTFE Research Articles

Thermal Analysis of the Poly(Siloxane)–Poly(Tetrafluoroethylene) Coating System

Thermal properties of poly(siloxane)–poly(tetrafluoroethylene) (SIL–PTFE) system were investigated, using Perkin Elmer DSC-7 differential scanning calorimeter and TGA-7 thermogravimetric analyzer. For SIL–PTFE compositions, one glass transition temperature Tg has been found, in accordance with the reciprocal rule up to about 40 mass% of PTFE. However, for higher PTFE contents, Tg values about –118 to –112°C were observed that can be ascribed to motions of cross-linked SIL structures. Endo- and exothermic transitions, found in the range from 70 to 290°C, not observed for pure SIL and PTFE components, are considered as specific ones for the SIL–PTFE semi-IPN structures.

Rapid isoelectric focusing of proteins in hydrolytically stable capillaries

Three new types of capillary coatings for capillary isoelectric focusing that avoid siloxane chemistry, resulting in hydrolytically stable coatings, are described and tested: phenyl—silica, acrylamide-reacted vinyl—silica, and pure PTFE. Capillaries of these three types were compared using standard proteins and a biological mixture of proteins similar to what might be encountered in actual use. Of these, the acrylamide-coated capillary produced the highest-quality results. In contrast to capillaries prepared using siloxane reactions, the capillaries described herein exhibited greatly enhanced stability at high pH.

ESCA study on tribochemical characteristics of filled PTFE

ESCA analyses were performed on the frictional tracks on metal blocks covered with the transfer films of PTFE-based composites containing zinc, copper, and lead powders. Results show that the tribochemical reactions between PTFE and an aluminum or an iron counterface as well as between PTFE and zinc filler were found to occur under experimental conditions. Compounds of iron or aluminum fluoride were detected at the interface between the transfer film and the steel or aluminum substrate when PTFE composite pins rub against a steel or an aluminum counterface. This means that a chemical reaction between them has occurred. But the formation of a chemical bond between the transfer film of the composite and the substrate is not the real reason why metallic fillers reduce the wear of the PTFE, because the chemical reaction can also be detected when a pure PTFE pin rubs against a steel or an aluminum disk under these test conditions. The consumption of fluorine in PTFE at the interface between the films and the substrate is much more serious than that on the surface of the transfer films. It was found that the chemical reaction of the PTFE to the steel or aluminum substrate is by means of the fluorinc atom and not the carbon atom in the PTFE.

SF/sub 6/ decomposition under power arcs. I. Physical aspects

For pt.I see ibid., vol.26, no.6, p.1163-76, Dec. 1991. In order to define the origin and the production rate of the CF/sub 4/ formed under the effect of arcing in circuit breakers containing SF/sub 6/ as a gaseous insulator, a series of measurements was taken in two Alsthom circuit breakers in which the gaseous insulator (SF/sub 6/, N/sub 2/), the material from which the nozzle is made (PTFE+CaF/sub 2/, pure PTFE, RPS Ryton R4) and the electrode metal (Cu/W alloy, copper) were changed. Moreover, with the aim of refining the results concerning the influence of the chemical composition of the insulator used to make the nozzle, several insulators (Megelite, PPS Ryton R4, Kel'F, Teflon, polypropylene and nylon) were exposed to sparking in an SF/sub 6/ atmosphere. >

SF/sub 6/ decomposition under power arcs. II. Chemical aspects

For pt.I see ibid., vol.26, no.6, p.1163-76, Dec. 1991. In order to define the origin and the production rate of the CF/sub 4/ formed under the effect of arcing in circuit breakers containing SF/sub 6/ as a gaseous insulator, a series of measurements was taken in two Alsthom circuit breakers in which the gaseous insulator (SF/sub 6/, N/sub 2/), the material from which the nozzle is made (PTFE+CaF/sub 2/, pure PTFE, RPS Ryton R4) and the electrode metal (Cu/W alloy, copper) were changed. Moreover, with the aim of refining the results concerning the influence of the chemical composition of the insulator used to make the nozzle, several insulators (Megelite, PPS Ryton R4, Kel'F, Teflon, polypropylene and nylon) were exposed to sparking in an SF/sub 6/ atmosphere.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modifiers and processing aids

Micropowder of poly(tetrafluoroethylene) (PTFE) can be used in base oils to improve the tribological properties significantly, if oil molecules are covalently linked to primary PTFE particles in the dispersion. Enhanced properties are not only determined by the amount of PTFE micropowder added to the oil but as well by the surface charge, radical concentration, and the size and distribution of PTFE particles in the oil phase.The chemical compatibilization (=cc) between PTFE micropowder and ester oil by the use of two types of PTFE micropowder, which differ in radical concentration and the amount of functional groups is shown. The concentration of PTFE micropowder in the dispersions was varied from 5 to 20 wt%. Both the pure PTFE micropowder and the oil-PTFE-cc dispersions were characterized by ESR and FTIR spectroscopy as well as by zeta potential measurements. Rheological and tribological tests were performed on the ester oil and the oil-PTFE-cc dispersions. Qualitative differences are discussed in terms of particle interactions, dispersion stability, chemical compatibilization efficiency and the amount of functional groups.A correlation between flow properties and surface charge of the PTFE particles within the dispersions was obtained. The influence on tribological properties is discussed as well.

Dynamic tests on PTFE sliding layers under earthquake conditions

The first part of a programme to assess the characteristics of PTFE sliding bearings during earthquake motions is described. Tests were performed on pure PTFE elements sliding on stainless steel. Representative normal loads were applied together with a sliding action, giving a maximum acceleration of 0.2 g and a maximum velocity of 38 cm/sec, i.e. motions equivalent to a moderate to severe earthquake.&#x0D; At 0°C friction was found to have maximum coefficients which fell from 17 to 13% as the normal pressure was increased from 15 to 25 MN/m2. At 20°C corresponding values were reduced to 15 and 10%. Maximum friction generally occurred in the first cycle of loading after which values fell. After 5 cycles the range was typically 9 to 5%.&#x0D; Tests on lubricated PTFE layers showed coefficients of friction less than 2% under the above test conditions; the maintenance of this low value over the years would depend on the effective retention of the grease.&#x0D; It is possible that, by careful design of bearings for higher pressures, and utilizing filled PTFE materials, lower overall friction values for the dry condition may be achieved.

On the sliding friction of a light alloy on pure or charged PTFE at rapidly variable speeds (0 to 100 km/h). (in French) : P. Nadal et al., Compt. Rend., 258 (1964) 3182–3184

On the sliding friction of a light alloy on pure or charged PTFE at rapidly variable speeds (0 to 100 km/h). (in French) : P. Nadal et al., Compt. Rend., 258 (1964) 3182–3184

The role of filler geometrical shape in wear and friction of filled PTFE

Under reciprocating conditions a study has been made of the wear and friction properties of pure and Al 2O 3-filled PTFE mated to stainless steel. Spherical and irregular particles of comparable size (approximately 7 μ) were used as the fillers. It was found that the abrasive damage due to Al 2O 3 was greatly reduced by using spherical particles. Particle shape also had an effect on the coefficient of friction, μ, being the same as pure PTFE for spherical but greater for irregular filled material. Both optical and electron microscopic observations of the mating surfaces were used to interpret the role of filler particle shape.