Tribological properties of PTFE‐filled thermoplastic polyimide at high load,velocity, and temperature

The effect of 20 wt% polytetrafluoroethylene (PTFE) fillers on the friction and wear properties of thermoplastic polyimides (TP) are investigated, under dry sliding in line contact against steel under 50 to 200 N, 0.3 to 1.2 m/s, and 60 to 260°C. Besides the lubricating mechanisms of PTFE based on mechanical shear, the thermal and tribophysical interactions in the sliding interface are considered in this research by using thermoanalytical measurements, Raman spectroscopy, and calculating the maximum polymer sliding temperature T*. The effect of hydrolysis of the TP bulk material, causing high friction at 100 to 140°C, is covered by PTFE. A transition at pv‐values 2.2 MPa m/s (T* = 120°C) is due to thermally controlled sliding of PTFE, while a transition at pv‐values 3.2 MPa m/s (T* = 180°C) remains controlled by degradation of the TP bulk material into monomer fractions. The reduced coefficient of friction in the presence of PTFE leads to smaller degradation and orientation of the molecular back‐bone and side‐chains within the TP structure. The formation of a homogeneously mixed transfer film is only observed at 180 to 260°C. The PTFE forms a fibrillar structure during wear at high sliding velocities, while they wear as separate particles at high normal loads. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers     

Tribological behaviors of carbon series additions reinforced CF/PTFE composites at high speed

The tribological, mechanical, and thermal properties of carbon series additions reinforced CF/PTFE composites at high speed were investigated. In this work, carbon fiber (CF) filled polytetrafluoroethylene (PTFE) composites, which have excellent tribological properties under normal sliding speed (1.4 m/s), were filled with some carbon materials [graphene (GE), carbon nanotubes (CNTs) and graphite (Gr)] respectively to investigate the tribological properties of CF/PTFE composites at high sliding speed (2.1 and 2.5 m/s). The results reveal that the carbon series additions can improve the friction and anti‐wear performances of CF/PTFE, and GE is the most effective filler. The wear rate of 0.8 wt % GE/CF/PTFE was decreased by 50 ? 55%, 55 ? 60%, 40 ? 45% at 1.4, 2.1, and 2.5 m/s compared with CF/PTFE. SEM study shows GE could be helpful to form smooth and continuous transfer film on the surface of counterparts. Meanwhile, GE can improve its tensile strength and elastic modulus obviously. Thin layer structure of GE could enhance the thermal conductivity, which can be helpful to dissipate heat of CF/PTFE composites wear surface. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43236.     

Structure and mechanical properties of isotactic polypropylene and iPP/talc blends functionalized by electron beam irradiation

The structure and mechanical properties of isotactic polypropylene (iPP) functionalized by electron beam irradiation are investigated by differential scanning calorimetry, wide‐angle X‐ray diffraction, thermogravimetry, thermomechanical analysis, melt index and mechanical measurements. The experimental results show that the degree of crystallinity, the thermal degradation temperature and the dimensional stability increase with dose in the range 0–5 kGy. At 5 kGy, the initial and final degradation temperatures of the irradiated iPP are raised by 66 °C and 124 °C, respectively. The melt index increases with increasing dose. The mechanical measurements show that the stiffness of iPP is greatly enhanced by electron beam irradiation. A small dose of irradiation (0.75 kGy) can increase the Young's modulus to 1284 MPa compared with 1112 MPa for unirradiated iPP. Adding 10 % by weight of irradiated iPP powder into iPP/talc (70/20 % by weight) blends, changes the processing parameters significantly and makes the Young's modulus rise substantially. At a dose of 40 kGy the Young's modulus of iPP/talc blend jumps to 3611 MPa against the original 2201 MPa. © 2000 Society of Chemical Industry     

Durable polytetrafluoroethylene composites in harsh environments: Tribology and corrosion investigation

The tribological properties and mass loss of polytetrafluoroethylene (PTFE) composites filled with carbon fiber (CF) or potassium titanate whisker (PTW) after the immersion in 30% sulfuric acid solution for 5 or 15 days were studied under different temperatures (25, 50, and 75°C). Results show that PTW/PTFE composites exhibit better anticorrosive and antiwear properties than those of CF/PTFE composites. Acid immersion has no obvious effect on the wear rate of the PTW/PTFE composite. The wear rate of CF/PTFE immersed for 15 days is thrice as much that of untreated composites and 3.6 times as much that of PTW/PTFE composites. Results also indicate that the wear rate of PTFE composites increases with the increasing corrosive mass loss rate and is more dependent on the corrosive mass loss rate rather than the friction coefficient. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effect of interfacial coating and testing conditions on the flexural performance of carbon woven fibre-reinforced polyamide laminates

ABSTRACT

This study addresses the effects of testing temperature and speed on carbon woven fibre-reinforced polyamide 6 composites (CF/PA6) with or without polyurethane dispersion (PUD) surface treatment. Dynamic mechanical analysis (DMA) was employed to check visco-elastic properties of CF/PA6 laminates. CF/PA6 laminates with and without surface treatment are tested and evaluated by three-point bending tests. Five testing temperatures (30°C, 60°C, 90°C, 120°C, 150°C) and three testing speeds (0.1, 1, 10?mm?min^?1) were chosen to investigate the time-temperature behaviour of CF/PA6 laminates. Results showed that PUD surface-treated CF/PA6 laminates exhibited better performance on mechanical properties but lower viscosity at various testing conditions owing to enhanced interfacial bonding capability.     

Tribological performance of filled PTFE‐based friction material for ultrasonic motor under different temperature and vacuum degrees

In this work, a glass fiber reinforced polytetrafluoroethylene (PTFE)‐based friction material with good properties for ultrasonic motor was fabricated. The effects of temperature and vacuum degree on the tribological behavior of the PTFE‐based friction material were investigated; the evolutions of friction‐wear modes and mechanisms were also discussed as function of temperature and vacuum degree. The results show that the delamination and fatigue wear are predominant under the effects of repeated shearing and dynamic contact under atmospheric environment. While wear mechanisms change from adhesive to abrasive and fatigue wear as it is cooled from 30 to ?60 °C at vacuum environment. Under high vacuum, adhesive wear was prone to taking place at room temperature for high frictional heat which increased the wear rate and extended the running‐in period. Experiment shows that the highest no‐load speed, output power, and holding torque of ultrasonic motor at room temperature under atmospheric environment are 220 rpm, 9.9 W, and 1.21 N m, respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45358.     

Radiation–chemical modification of PTFE in the presence of graphite

PTFE with a 15% addition of graphite was subjected to irradiation using an electron beam of 10 MeV energy with absorbed doses of 26, 52, 78, 104, and 156 kGy. The effect of electron‐beam irradiation on the mechanical, sclerometic, and tribological properties, the crystallinity degree, and the morphology of the polymer surface was examined. It was found that the modification through irradiation entailed a gradual increase in the degree of crystallinity, which had a direct influence on the mechanical properties. An increase in the hardness, Young's modulus, and compressive strength of the polymer irradiated with an electron beam was also demonstrated. The electron‐beam irradiation reduced the value of components of the work‐of‐indentation, showing the growing resistance to deformation. An analysis of the scratch test parameters showed a reduced depth of penetration of the indenter into the material, proportionally to the irradiation value, at relatively constant values of the scratch depth after scratching load removal. A stereometric analysis of the scratch traces on the material allowed to determine coefficients of the wear micromechanism, β, and resistance to wear, W_β. It was found that after irradiation (especially with a dose of 4 × 26 kGy), a significant quantity of the material showed traces of ploughing, which meant a positive effect on the wear mechanism. The value of the wear resistance coefficient W_β for PTFE subjected to the absorbed irradiation dose increased intensively, which portended a significant reduction of the tribological wear compared to the nonirradiated material. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42348.     

Coating of polytetrafluoroethylene/polyacrylate: Core-shelled structure and tribological behaviors

In order to improve the tribological properties of polytetrafluoroethylene (PTFE), the core-shelled PTFE/polyacrylate nanoparticles were prepared by seed emulsion polymerization and its tribological behaviors were investigated. The core–shell structure was determined by a Fourier transform infrared spectrometer and transmission electron microscopy. The results of thermoanalysis showed that polyacrylate had lost more weight than PTFE/polyacrylate composite above 300 °C, which indicated an improvement in the thermal stability. Moreover, the friction and wear results indicated that friction coefficient of PTFE/polyacrylate coating keeps at a relatively lower level, which is between that of PTFE and polyacrylate, and the wear volume is the smallest, so that an excellent performance of low friction and wear resistance was demonstrated. Besides, the tribological properties of the core-shelled coating are maintained to be stable under high load or high speed. Therefore, the core-shelled nanoparticles would be potential to polymer coating as high-performance solid lubricants. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47774.     

Effect of Disinfection on Adhesion of Reline Polymers

Cylinders (3.5 × 5.0 mm) of the reline resins Kooliner (K), New Truliner (N), Tokuso Rebase Fast (T), and Ufi Gel Hard (U) were bonded to cylinders (20 × 20 mm) of the denture base resin Lucitone 550 (L), and samples were divided into two controls and four test groups (n = 8). Shear tests (0.5 mm/min) were performed after polymerization or immersion in water (37°C) for 7 days (controls); two or seven cycles of disinfection by immersion in sodium perborate (50°C/10 min) or microwave irradiation (650 W/6 min). Statistical analyses (α = 0.05) revealed that two cycles of microwave and chemical disinfection increased the mean bond strengths of materials T (9.08 to 12.93 MPa) and L (18.89 to 23.02 MPa). For resin L, seven cycles of chemical (15.72 MPa) and microwave (17.82 MPa) disinfection decreased the shear bond strength compared with the respective control (21.74 MPa). Resins U (13.12 MPa), K (8.44 MPa), and N (7.98 MPa) remained unaffected.     

Gas holdup in a two-phase vertical tubular reactor at high pressure

Gas holdup in a tubular reactor was measured at pressures from 5 to 14 MPa at 300°C using a differential pressure cell. The effects on gas holdup of gas density, liquid superficial velocity and gas superficial velocity were studied using vacuum tower bottoms from a Venezuelan feedstock with 95.1 wt% +524°C material. Hydrogen was used at superficial gas velocities from 0.7 to 2.0 cm/s. The feed density at 15°C (0.1 MPa), 300°C (5.57 MPa) and 400°C (13.9 MPa) was measured and showed a linear decrease with temperature. Increased gas density at a constant temperature of 300°C increased the gas holdup at all superficial gas velocities. An increase in the liquid flow rate from about 0.04 to 0.1 cm/s did not affect the gas holdup.     

Effect of processing parameters on morphology and tensile properties of PP/EPDM/organoclay nanocomposites fabricated by friction stir processing

Nanocomposites-based on polypropylene (PP), ethylene-propylene diene monomer (EPDM) and Cloisite 15A have wide applications in automotive and aerospace industries and medical apparatus due to their excellent mechanical, thermal and chemical properties. In this study, a nanocomposite of PP/EPDM/nanoclay containing PP (77 wt%), EPDM (20 wt%) and nanoclay (3 wt%) was fabricated by friction stir processing (FSP) method. X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry and tensile testing were performed to determine the morphology and tensile properties of this nanocomposite. The Box-Behnken design was applied to investigate the effect of the process parameters such as tool rotational speed, traverse speed and shoulder temperature on the tensile properties of the nanocomposite. The results showed that the tensile strength increased from 15.8 to 18.2 MPa with increasing the tool rotational speed and shoulder temperature while the elongation-at-break dropped from 46 to 22 %. A maximum tensile strength of 17.6 MPa and a minimum elongation-at-break of 26 % were obtained at the traverse speed of 40 mm/min when the rotational speed and shoulder temperature were at the central levels themselves. The prediction models showed that when the tool rotational speed, traverse speed and shoulder temperature were set, in the given order, as 1200 rpm, 45.65 mm/min and 113.65 °C, a simultaneous maximization of tensile strength of 16.03 MPa and elongation-at-break of 46.41 % was obtained.     

Preparation of presintered zirconia blocks for dental restorations through colloidal dispersion and cold isostatic pressing

This work proposes an effective method for dispersion of zirconia suspension for dental block preparation and optimizes the cold isostatic pressing (CIP) pressure to improve the densification of slip-casted zirconia blocks. Two batches of 44 wt% zirconia suspension were prepared using distilled water in a pH 2 medium containing 0.5 wt% polyethyleneimine as dispersant. The first batch was sonicated for different durations (from 5 min to 30 min), and the second batch was dispersed through ball milling at rotational speeds of 200, 300, and 400 rpm for 60, 90, and 120 min. All suspensions were subjected to sedimentation test and particle size measurement. Results revealed that the optimum ultrasonication duration was 10 min, which yielded the smallest particle size of 133 nm. Ball milling at 300 rpm for 120 min achieved the maximum dispersion of particles, with an average size of 75 nm. Under the optimum conditions of ultrasonication duration, ball milling duration, and ball milling speed, the particle size decreased to 48 nm, which is close to the primary particle size. These dispersion techniques and parameters were selected for preparing a suspension to be consolidated into blocks through slip casting and were enhanced through CIP at pressure ranging from 100 MPa to 300 MPa. CIP compaction at 250 MPa significantly increased the shrinkage percentage of green zirconia blocks, with pore radius decreased to 18 nm. The density of zirconia pressed at 250 MPa and presintered at a low temperature of 950 °C was 59% of the theoretical density and was higher than that of commercial presintered blocks. Thus, CIP should be conducted under a compaction pressure of 250 MPa to produce dense and homogeneous zirconia blocks.     

Effect of processing conditions on intrinsic viscosity of extruded cornstarch

Unmodified cornstarch from dent corn was used in this study to determine the effect of twin-screw extrusion conditions on the intrinsic viscosity of this polysaccharide and water. The study focused on the intrinsic viscosity of the cornstarch as a function of the key variables. Primary variables examined were temperature (75, 100, and 125°C), starch concentration or consistency (35, 50, and 65%), and screw speed (100, 200, and 300 rpm) during the extrusion processing. The most favorable conditions examined were the extrusion of the cornstarch at 35% consistency, 100°C, and 200 rpm. Two-thirds of the original intrinsic viscosity of the unmodified starch was retained upon extrusion at 35% consistency at all temperatures and the screw speeds (200 and 300 rpm) examined. Also, similar values were observed at 50% consistency for 75°C at 100 and 200 rpm and for 100°C at all three screw speeds. © 1996 John Wiley & Sons, Inc.     

Low stress creep response of PTFE sealants applied to PEM fuel cells

Viscoelastic properties of polytetrafluoroethylene (PTFE) play a crucial role in forecasting its long-term behavior in engineering applications. An attempt is made to explore the viscoelastic properties of PTFE sealants that are utilized in polymer electrolyte membrane fuel cell (PEMFC). It is to be noted that PTFE sealants are vulnerable to creep under constant loading at elevated temperatures. Moreover, the creep of sealants will lead to leakage of reactants from the cell, which affects the performance of PEMFC. PTFE is an excellent choice as a sealant material in low-temperature polymer electrolyte membrane fuel cell (LT-PEMFC), which operates in the temperature range of 60–80°C. PTFE can be prominently used as sealants in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC), as it possesses no significant change in its physical properties within the temperature range of −150 to 300°C along with the working conditions of HT-PEMFC. In LT-PEMFC, the sealants will typically be subjected to low stresses in the range of 1–5 MPa. In this article, the creep response of PTFE sealant material is extensively studied at various temperatures of 25 (room temperature), 35, 45, 55, and 65°C and at three stress levels of 2, 3, and 4 MPa. The time–temperature superposition principle is utilized to develop master curve at a reference temperature of 25°C, to forecast long-term creep characteristics of PTFE sealants. Moreover, the master curve for creep compliance is developed for 4.5 h.     

Influence of PTFE as a solid lubricant on the mechanical,electrical, and tribological properties of CF-reinforced PC composites

The objective of this research was to study the effects of polytetrafluoroethylene (PTFE) as a solid lubricant on the mechanical, electrical, and tribological properties of carbon fiber (CF)-reinforced polycarbonate (PC) composites. Samples were prepared by means of single-screw extrusion and injection molding processes. The mechanical tests included tensile, flexural, and failing weight impact tests, while the electrical tests consisted of surface and volume resistivity tests. The tribological testing was conducted under dry sliding conditions using pin-on-disk configuration. The results showed that the addition of CF managed to significantly reduce the electrical resistivity as the CF loading approached 10–15 wt%. The addition of PTFE managed to reduce the resistivity of the composite, that is, from 4.51 to 0.53 × 10 (Ωcm). The incorporation of 15 wt%. CF resulted with an increase of 45% in tensile strength and 51.5% in flexural strength, while the addition of PTFE had a negative impact on both properties. It was shown that PTFE was able to reduce the friction coefficient, μ and wear rate, K up to 0.257 and 6.35 × 10⁶ (mm³/Nm), respectively, which can be attributed to the excellent abilities of PTFE to form transfer film. The composite consisting of 15 wt% CF and 10 wt%. PTFE showed highest improvement in term of electrical resistivity, and is deemed the most suitable composition for this study. Scanning electron microscopy was also carried out to further elucidate the fracture and wear mechanism of the PC/CF/PTFE composites.     

Heat resistance of radiation crosslinked poly(ε-caprolactone)

Polycaprolactone (PCL) was gamma-irradiated at different phases such as solid state at 30 to 55°C, molten state, and supercooled state, under vacuum or air atmosphere, to elucidate its crosslinking behavior. Irradiation in the molten state (80°C) gave higher gel content compared to room temperature. The resulting gel, however, contains many voids due to the gas evolved during irradiation. Conversely, irradiation of PCL in the supercooled state led to the highest gel content among the three irradiation conditions and it was free of voids. Based on these findings, to evaluate heat resistibility of crosslinked PCL prepared by irradiation in supercooled state, the crosslinked PCL was hot pressed at 200°C to form a film. Unirradiated PCL melted at 60°C. The film prepared from 160 kGy irradiated PCL (crosslinked sample) under an applied load of 0.667 MPa, at a temperature of 110°C did not break even after 3 h. At a temperature of 120°C, the film has a tensile strength of 3 MPa. Furthermore, the film extended by hot pressing is transparent and has high heat shrinkability. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 581–588, 1998     

Radiation grafting of vinyl monomers onto poly(tetrafluoroethylene) powder produced by γ irradiation and properties of grafted poly(tetrafluoroethylene) filled low density polyethylene

Scrap poly(tetrafluoroethylene) (PTFE) was γ irradiated under an ambient atmosphere in order to produce extensive chain scission and oxidative degradation. After irradiation the PTFE was ground into a fine powder (2°‐PTFE) and grafted with styrene (St), vinyl acetate (VAc), and 4‐vinylpyridine (4‐VP) by using the direct irradiation technique. The grafted PTFE were then blended with low density polyethylene (LDPE). The study covered the characterization of irradiated PTFE and grafted 2°‐PTFE powder with various methods. Mechanical grinding was found to reduce trapped radicals formed during the irradiation process faster than the annealing process. Grafting on 2°‐PTFE was followed by gravimetric analysis, TGA, and the change in the particle size of the samples. Although we reached almost 20% grafting by weight in the St and 4‐VP monomers, VAc grafting was found to be maximum at around 8% by weight at the maximum absorbed dose. The addition of VAc grafted 2°‐PTFE into LDPE produced better final mechanical properties with a fine dispersion. However, as may be expected, the incorporation of the other two 2°‐PTFEs into LDPE showed low film quality and poor mechanical properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 816–826, 2001     

Solid state extrusion of polytetrafluoroethylene fibers

Polytetrafluoroethylene (PTFE) was solid state extruded to fiber form at temperatures between 250 and 300°C and at pressures between 7000 and 15,000 psi. The PTFE fibers had a diameter of 0.0502 inches and the reduction ratio for extrusion was 55.8. The fibers were tested for mechanical strength, and examined with a scanning electron microscope, which revealed a fibrous structure at high magnifications. The melting point of the fibers was 342°C by differential scanning calorimetry. The tensile properties were enhanced with an increase in processing temperature and pressure, the highest properties resulting from an extrusion temperature of 300°C and pressures greater than 10,000 psi. A tensile strength of 5500 psi and a secant modulus of 250,000 psi were obtained.     

C/C–SiC composites derived from single-source poly(silylene–acetylene) precursors

Carbon-fiber-reinforced carbon–silicon carbide (C/C–SiC) composites were prepared by impregnating carbon fibers with ethynylphenyl-terminated poly(silylene–acetylene) (EPTSA) as a single-source precursor with subsequent hot pressing and pyrolysis. The structural evolution, crystallization behavior, and graphitization of bulk C–SiC ceramics, as well as their mechanical properties and ablation behavior, were investigated. The EPTSA precursor starts to transform into inorganic SiC ceramic materials at 800°C, which is characterized by an amorphous structure with weight loss, shrinkage, and densification between 800 and 1000°C. The formation of SiC crystals inhibited the growth of the graphitic structure between 1000 and 1200°C. As the temperature was raised, both graphite and SiC crystals continued to grow, and the crystalline forms became more complete. The carbon-fiber cloth (T300CF)-reinforced C–SiC composite (T300CF/C–SiC) prepared using polymer infiltration and pyrolysis (PIP) exhibited excellent mechanical properties. After five PIP cycles, the flexural strength, flexural modulus, and interlaminar shear strength of the T300CF/C–SiC composite reached 169 MPa, 32.5 GPa, and 9.38 MPa, respectively. In addition, the chopped-carbon-fiber-reinforced C–SiC composite fabricated using the PIP process demonstrated good oxyacetylene-torch ablation properties.     

Study on Tribological Properties of Polytetrafluoroethylene Drawn Uniaxially at Different Temperature

Summary: Wear behavior correlations with morphology have been established from polytetrafluoroethylene (PTFE) drawn at 200, 327, and 375 °C with draw ratio about 4. The friction coefficient and wear rate for PTFE drawn at 327 °C are lower and the wear rate is lower than that of undrawn PTFE by about 30%. The structures of samples were characterized by scanning electron microscope (SEM), DSC, and wide angle X‐ray diffraction (WAXD). Results indicate that the debris morphologies of samples are different. The differences in the tribological behavior of undrawn and drawn samples were attributed to the improvement of the degree of the crystalline, fibrillation, and orderliness by drawing, especially, for PTFE drawn at 327 °C. The orderliness of molecular arrangement along the drawn direction is also higher for PTFE drawn at 327 °C than those of PTFE drawn at 200 and 375 °C, respectively. Therefore, the intensity of covalent bond along drawn direction is higher. The shear resistance and the deformability of the material are greatly improved and the size of the wear breakage unit decreases, which results in a good tribological property for PTFE drawn at 327 °C.

SEM morphology of fractured surface perpendicular to the draw direction for PTFE drawn at 327 °C.