Perfluoroalkoxy (PFA)-α-Alumina Composites: Effect of Environment on Tribological Performance

Sidebottom, Mark A.; Atkinson, Cooper; Campbell, Kasey L.; Babuska, Tomas F.; Junk, Christopher P.; Burch, Heidi E.; Krick, Brandon A.

doi:10.1007/s11249-019-1257-5

Cited by 14 publications

(7 citation statements)

References 32 publications

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“…The shoulders present in the 1725−1685 cm −1 range and at 1449 cm −1 are characteristic of perfluorinated carboxylate salt formation, which were not present in the unworn sample. These new peaks have been observed by multiple groups in recent years and strongly correlate with tribochemical species that only accumulate in ultralow wear samples [13], [20], [21], [32], [36], [37]. The shoulder of the self-mated sample is more pronounced than that of the on-steel sample, and the additional carboxylic salt accumulation could explain the lower steady-state wear rates of the self-mated sample.…”

Section: Ptfe/peek Compositesmentioning

confidence: 55%

“…Thus, it is less likely to form the inherently wear-resistant alumina-rich tribofilms previously observed with PTFEalumina on steel. 13,18,32 If the alpha-alumina remained in its microscale state, it could become a source of abrasion and wear of developed tribofilms.…”

Section: Ptfe-aluminamentioning

confidence: 99%

“…13 Fluoropolymers with lower molecular weights will have higher crystallinity, which was observed by Sidebottom et al using differential scanning calorimetry analysis of perfluoroalkoxy polymer wear debris compared to the bulk material, indicating that sliding induces chain scission and chain shortening. 32 Shear-induced polymer chain scission of PTFE C−C bonds and reactions with the sliding countersample and environment can generate carboxylic acid end groups which are observable through IR spectroscopy. 16,18,20,21 These chemical species are only present after sliding, indicating that there are chemical differences between the bulk polymer and the tribofilms (i.e., polymer transfer film on the countersample and running film on the wear surface of the polymer).…”

Section: Introductionmentioning

confidence: 99%

“…Running films have also been shown to have higher hardness and elastic moduli than the bulk polymer . These tribochemical changes and more robust mechanical properties of tribofilms contribute to the improved wear properties in PTFE composites. ,,,− ,− …”

Section: Introductionmentioning

confidence: 99%

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Ultralow Wear Self-Mated PTFE Composites

et al. 2022

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Remarkably low wear rates were observed in PTFE–PEEK and polytetrafluoroethylene (PTFE)-alpha-alumina composites when evaluated in a “self-mated” configuration, where a polymer pin is slid against a polymer countersample of the same composition. Each composite was tested in a controlled humidity environment on a linearly reciprocating tribometer on two different countersamples: a polymer countersample (self-mated) and a stainless steel countersample for comparison. For all the self-mated PTFE–PEEK composites [polyether ether ketone (PEEK) wt % 10, 20, 30, 40, and 50], the average friction coefficient was reduced, and the steady-state and total specific wear rates were improved when compared to testing against stainless steel. Self-mated PTFE–PEEK (wt % 10–40) achieved ultralow wear rates on the order of 10–9 mm3/Nm and friction coefficients of 0.08–0.14. When compared with samples slid against stainless steel, IR spectroscopy of the sliding surface showed that the self-mated PTFE–PEEK composites accumulate more PEEK at the sliding interface and more expression of a tribochemical carboxylate species, which have been linked with ultralow wear PTFE materials. The PTFE composites slid on steel rely on the formation of transfer films for ultralow wear performance. This is achieved by unidirectional increasing surface energy gradients from the polymer pin to the steel substrate, which dominate the transport and wear of PTFE composites slid on steel. However, the self-mated ultralow wear PTFE-based composites rely only on the formation and stability of tribofilms that consist of tribochemically altered PTFE with new carboxylate end groups as well as accumulated filler (i.e., PEEK or alumina). These films have self-regulating, minimal differences in surface energy. The close match of these low-energy surfaces contributes to low friction and ultralow wear. The self-mated PEEK-filled PTFE outperforms the alumina-filled PTFE primarily because of the ease at which PEEK accumulates at the surface. Additionally, the reinforcement and anchoring of the surface is better for a polymer blend than a particle-reinforced composite.

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Section: Ptfe/peek Compositesmentioning

confidence: 55%

Section: Ptfe-aluminamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ultralow Wear Self-Mated PTFE Composites

et al. 2022

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“…[22][23][24] Xing et al prepared carbon nanotube (CNT)/PFA polymer films by a dispersion-sintering process and investigated the morphology, resistivity, electrothermal properties, and thermal diffusivity of the composite films and found that the addition of CNTs effectively enhanced the thermal performance and heat transfer ability of the nanocomposite films. [25] Teflon ® PFA samples with different weight fractions of α-alumina were prepared by Sidebottom et al [26] The frictional properties of the PFA-α-alumina composites were found to be very similar to those of the unfilled PFA and the composites. Zhang et al prepared graphene-PFA nanocomposites using ultrasonic dispersion and hot compression molding processes, which found that the addition of graphene to the PFA matrix could effectively improve the thermal conductivity of the composites, with a maximum thermal conductivity of 5.017 W/(m K), meeting the needs of many industrial applications.…”

mentioning

confidence: 99%

Low concentration of inorganic fullerene tungsten sulfide nanofiller to achieve cost‐effective and significant enhancement on thermal and dynamic mechanical properties of perfluoroalkoxy nanocomposites

et al. 2021

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Special insulated wires beyond the conventional pure perfluoroalkoxy (PFA) polymers need to be developed to meet the increasing thermal management and mechanical performance requirements. Advanced PFA nanocomposites enhanced by inorganic fullerene tungsten sulfide (IF-WS 2 ) nanoparticles have been fabricated by melt blending and hot press processes. Benchmarked against the PFA, the presence of IF-WS 2 nanoparticles in the composites resulted in a maximum tensile strength of 21.35 MPa and a maximum elongation at break of 275%, which are 66% and 149% higher than those of pure PFA, respectively. The nanocomposites with 0.5 wt% IF-WS 2 achieved a 17.5% increase in storage modulus, 26.8 C increase in the onset melt temperature, while 1 wt% IF-WS 2 increased the glass transition temperature (T g ) by 3.4 C and the crystallinity (χ c ) by up to 34.4%. And when the additional amount of IF-WS 2 nanomaterials is 0.25%, the best combination of performance is obtained.

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Physical and Chemical Evolution of PTFE-α-Al2O3 Composites Versus 304 SS Tribofilms During Dry Sliding

Haque,

Junk,

Sidebottom

2024

Tribol Lett

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Polytetrafluoroethylene (PTFE) is renowned for its remarkably low friction coefficient (µ ~ 0.1) yet exhibits notably high wear rates (K ~ 104) in dry sliding applications. To mitigate this, various metallic and non-metallic fillers have been explored, consistently demonstrating a reduction in wear rates of unfilled PTFE between 10 and 104 times. Among these fillers, α-Al2O3 is one of the most extensively studied materials. 5 wt% of α-Al2O3 filler into PTFE yields a composite material, PTFE- α-Al2O3, characterized by a wear rate a staggering 104 times lower than unfilled PTFE. This reduction in wear has been attributed to the formation of tribofilms on the PTFE composite and metal counterbody material. These tribofilms emerge due to the interaction between broken fluropolymer chains and environmental water and oxygen. This interaction results in the creation of carboxylate salt groups, which subsequently react with metal/metal oxide particles (both from the counterbody and the metal filler) to form tribofilms. Despite numerous studies scrutinizing the chemical composition of the tribofilms pre- and post-test, the chemical development of these films has remained largely unexplored. In this study, the authors utilize attenuated total reflection infrared spectroscopy (ATR-IR), transmission infrared (IR) spectroscopy, optical microscopy, and stylus profilometry to observe tribofilm development. A thorough topographical and chemical description of the tribofilm is provided via these techniques. The ratio of carboxylate salt groups directly corresponds with improved wear performance and these changes are very local to the worn polymer surface. This discovery contributes to a deeper understanding of the tribological behavior of PTFE-α-Al2O3 composites. Graphical Abstract

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Perfluoroalkoxy (PFA)-α-Alumina Composites: Effect of Environment on Tribological Performance

Cited by 14 publications

References 32 publications

Ultralow Wear Self-Mated PTFE Composites

Ultralow Wear Self-Mated PTFE Composites

Low concentration of inorganic fullerene tungsten sulfide nanofiller to achieve cost‐effective and significant enhancement on thermal and dynamic mechanical properties of perfluoroalkoxy nanocomposites

Physical and Chemical Evolution of PTFE-α-Al2O3 Composites Versus 304 SS Tribofilms During Dry Sliding

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