Antiwear and lubrication properties of polyurethane/polytetrafluoroethylene‐bonded coating

Polytetrafluoroethylene (PTFE) particles were irradiated with ⁶⁰Co γ‐ray to improve their dispersing capacity in polyurethane (PU), which was used as a binder of a PTFE‐based bonded solid lubricating coating. The PU/PTFE‐bonded solid lubricating coating was prepared on a steel block by spraying and curing at room ambient, and the tribological properties of the PU/PTFE coatings were evaluated on a ring‐on‐block tester at a speed of 1.25–2.5 m/s and a load of 314–785 N. The wear life of bonded coatings on PTFE volume concentrations, curing humidities and times, coating thickness, and sliding conditions was also investigated. It was found that a 60‐μm thickness coating, which has a 40% PTFE volume concentration, cured at 75% relative humidity for 4 days, has a longer wear life of 844 m/μm at 314 N and 1.25 m/s. The PTFE/PU coating was wear‐resistant when the load × speed value was less than 687 Nm/s^?1; at same time, the wear life for a thinner coating is sensitive to sliding condition variations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3454–3459, 2002     

The Tribological Properties of Oxidation-Treated Carbon Fiber-Reinforced PTFE Composite under Oil-Lubricated Conditions

The effect of air-oxidation and ozone surface treatment of carbon fibers (CF) on tribological properties of CF reinforced Polytetrafluoroethylene (PTFE) composites under oil-lubricated condition was investigated. Experimental results revealed that ozone treated CF reinforced PTFE (CF/PTFE) composite had the lowest friction coefficient and wear. X-ray photoelectron spectroscopy (XPS) study of carbon fiber surface showed that the increase in the amount of oxygen-containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with PTFE matrix.     

Temperature effect on mechanical strength and frictional properties of polytetrafluoroethylene-based core-shell nanocomposites

Polytetrafluoroethylene (PTFE) has shown an outstanding lubricity as a solid lubricant, but its application is limited due to its low-mechanical strength and high-wear rate. In this study, core-shell nanoparticles were synthesized using PTFE as the core and polymethylmethacrylate (PMMA) as the shell. The formed core-shell nanocomposites by leveraging the core-shell nanoparticles as basic structural units exhibit remarkable enhancement on uniformity, tensile strength, and wear resistance, compared to mechanically mixed composites with the same composition. Our experiments demonstrated the following results: (1) Owing to the excellent uniformity, the maximum tensile strength of core-shell nanocomposites was 62 MPa, three times higher than that of mechanically mixed composites. (2) The composite matrix formed by PMMA shell had better reinforcement and protection effect on inner PTFE phase, resulting in a reduced wear rate of 0.3 × 10⁻⁵ mm³/(N m), one order of magnitude lower than that of mechanically mixed composites. (3) The friction coefficient and interfacial mechanical properties of the core-shell nanocomposites at different temperatures have been systematically studied to get insights into lubrication mechanisms. It is proved that the temperature can decrease the modulus and increase the interfacial adhesion as well as the loss tangent of the core-shell nanocomposites, thus affecting the lubrication properties in multiple ways.     

An investigation of the friction and wear behaviors of polyphenylene sulfide filled with solid lubricants

Composites of polyphenylene sulfide (PPS) filled with solid lubricant particles of graphite (C), molybdenum disulfide (MoS₂), and polytetrafluoroethylene (PTFE) were prepared by compression molding. The size of the solid lubricant particles was 3‐;5 µm. The friction and wear behaviors of the composites were examined with a pinon‐disk test rig. The worn composite pin surfaces and the transfer films formed on the counterface were analyzed with scanning electron microscopy. An X‐ray photo‐electron spectroscope (XPS) was used to characterize the chemical states of the elements in the transfer film. It has been found that graphite and PTFE as the fillers increase the wear resistance of PPS considerably, while MoS₂ as the filler decreases the wear resistance of PPS greatly. The fillers promote the decomposition of PPS and generate compounds, which accounts for the changes in the wear resistance of the composites.     

Study on the tribological characteristics of solid lubricants embedded tin‐bronze bearings

The friction and wear characteristics of graphite, MoS₂, and PTFE embedded tin‐bronze bearings were studied using a pin‐on‐disc tester. The results indicated that solid lubricants decreased and stabilized the friction coefficient, and decreased the wear rate by two to three orders of magnitude. When the content of solid lubricants, PTFE mixed with graphite, was 20–40%, the performance of the solid lubricants embedded bearing (SLEB) was the best. Wear scar was analyzed by means of X‐ray diffraction (XRD), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). The results show that the transfer films of solid lubricants reduce adhesion between the SLEBs and the mating material, and the wear mechanism of SLEBs changes to fatigue and adhesive wear. The main reason for fatigue wear is microcracks expanding at Pb points in SLEBs. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2394–2399, 2001     

Adhesion aspects of poly(p-xylylene) to SiO2 surfaces using γ-methacryloxypropyltrimethoxysilane as an adhesion promoter

The use of organo-silanes as coupling agents offers the potential to create novel structures using materials that would otherwise suffer from poor adhesion. γ-methacryloxypropyltrimethoxysilane (γ-MAPTS) layers were deposited on hydroxylated SiO₂ surfaces using both vapor and solution deposition techniques. The films were characterized using variable angle spectroscopic ellipsometry, infrared spectroscopy, contact-angle measurements and X-ray photoelectron spectroscopy. Film thickness was relatively constant at ～6 Å for solution deposition times from 2 min to 2 h at 60° C. Water contact angle increased from 0° to 45° after silane deposition from solution. Room temperature vapor-deposited γ-MAPTS films showed similar thicknesses to those of solution deposited films but a markedly lower contact angle of 10°. Parylene N was chemical vapor deposited on the γ-MAPTS films and its adhesion was tested using the Scotch^® Tape test. The γ-MAPTS improved adhesion of parylene N to the hydroxylated surface, with the adhesion for the vapor deposited silane films exhibiting a temperature and time dependence.     

Low-pressure plasma surface modification of polyurethane films with chitosan and collagen biomolecules

Polyurethane (PU) was synthesized using castor oil and a trade grade of hexamethylene diisocyanate, and then PU films were prepared for wound dressing applications. The PU films were then plasma treated with the low-pressure nitrogen plasma to functionalize with peroxide and hydroperoxide groups in order to attach with acrylic acid monomers. Therefore, the polyacrylic acid polymer branches were formed on the film surfaces. Carboxylic acid groups were activated by N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide hydrochloride/N-hydroxysuccinimide and bonded with chitosan and collagen biomolecules. Untreated, nitrogen plasma treated, polyacrylic acid grafted, and finally chitosan and collagen-immobilized PU films were characterized by several tests. The tests included the attenuated total reflectance Fourier transform infrared spectroscopy, static contact angle, atomic force microscopy, scanning electron microscopy, fibroblast L929 cell culture, and antibacterial activity assay to evaluate their in vitro cytocompatibility. The results confirmed that chitosan and collagen were immobilized successfully on the PU surfaces. The chitosan-immobilized PU and collagen-immobilized PU improved the adhesion and proliferation of fibroblast cells compared to untreated PU films. The chitosan-modified PU films exhibit the best antibacterial properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47567.     

Adhesion to Sodium Naphthalenide Treated Fluoropolymers. Part III. Mechanism of Adhesion

Adhesion of fluoropolymers to copper and to other polymers is examined using a range of fluoropolymer types (PTFE, PFA, extruded, skived and cast films), surface modification techniques such as sodium naphthalenide (Na/naphth), acid stripping and lamination to produce surfaces of controlled roughness, and three tests of adhesion (90 degree peel tests, torsional shear tests and stripping of transmission electron microscopy (TEM) replicas). A combination of chemical and physical modification is required to produce good adhesion, with the relative importance of each dependent upon the specific adhesion test used. For relatively smooth-surfaced films, Na/naphth appears to function by increasing both the chemical functionality and the mechanical integrity of a surface layer. Untreated PTFE and PFA show interfacial failure and negligible adhesion. Smooth-surfaced PTFE with superficial surface modification, e.g. after lamination to shiny copper foil or after acid stripping of defluorinated material, often fails by fibrillation of the fluoropolymer surface. For short sodium etch times, adhesion is improved and the failure mode is interfacial. For long etch times, there is a mixed mode of failure. Fibrillation in smooth-surfaced PFA systems was not observed. Adequate adhesive strength in these systems could only be achieved by an increase in the surface roughness. The best adhesion could be achieved by surface roughening, followed by Na/naphth treatment. For such PTFE surfaces plated with copper, peel and shear tests showed a mixed mode of failure, with copper and fluoropolymer found on both failure surfaces by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDS). Extensive fibrillation occurred at the locus of failure. Provided chemical modification is adequate to allow wetting, the roughness of the surface dominates the properties of the adhesive bond. Prolonged Na/naphth treatment (e.g. one hour) causes a reduction in peel strengths.     

Lamination of polytetrafluoroethylene films via surface thermal graft copolymerization with ionic and zwitterionic monomers

Surface thermal graft copolymerization with concurrent lamination was carried out between two argon plasma‐pretreated polytetrafluoroethylene (PTFE) films in the presence of aqueous zwitterionic solutions of N,N‐dimethyl‐N‐methacrylamidopropyl‐N‐(3‐sulfopropyl)ammonium betain (DMASAB), N,N‐dimethyl(methacryloylethyl)ammonium propansulfonate (DMAPS), and 1‐(3‐sulfopropyl)‐2‐vinylpyridinium betaine (SVPB), as well as an aqueous ionic solution of potassium‐2‐sulfopropylacrylate (SPA) and potassium‐2‐sulfopropyl methacrylate (SPM), under atmospheric conditions and in the complete absence of an added initiator and system degassing. The lap shear adhesion strength between the PTFE films from simultaneous grafting and lamination depended on the argon plasma pretreatment time of PTFE films, the thermal lamination temperature, the concentration of the monomer solution, and the ionic nature of the grafted chains. Lap shear adhesion strength greater than 120 N/cm² and exceeding the yield strength of the PTFE substrate used could be readily obtained in most PTFE/zwitterion/PTFE assemblies after simultaneous thermal graft copolymerization and lamination. The chemical compositions of the graft‐copolymerized surfaces were studied by X‐ray photoelectron spectroscopy (XPS). © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 816–824, 1999     

Toughening of polylactide via in situ formation of polyurethane crosslinked elastomer during reactive blending

Polylactide (PLA)/polyurethane (PU) composites were prepared by reactive blending method with in situ formation of PU particles via the reaction between polyester polyol (PPG) and toluene‐2,4‐diisocyanate (TDI). The interfacial compatibility and adhesion between the PLA and PU phases were greatly improved by the reaction of the terminal hydroxyl groups of PLA and N?C?O groups of TDI forming graft copolymer, as confirmed by FTIR spectroscopy. The elongation at break and notch impact strength of PLA/PU composites increased considerably with increasing PU content, and the tensile strength of PLA/PU composites decreased slightly compared with that of pure PLA. Upon addition of 12 wt % PU, the elongation at break and notch impact strength increased to 175.17% and 10.96 kJ/m², respectively, about 27 times and 5.4 times greater than the corresponding values for the pure PLA. The tensile strength decreased only slightly to 48.65 MPa. The excellent interfacial adhesion, the dispersed PU elastomeric particles acting as stress concentration areas, and the triggering of large matrix shear yield as well as many fibrils by internal cavitation were the main mechanical toughening mechanisms. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44383.     

Interface enhancement between polytetrafluoroethylene and glass fibers modified with a titanate coupler

The use of glass fibers (GFs), molybdenum disulfide (MoS₂), and talc was evaluated to reinforce polytetrafluoroethylene (PTFE) for potential applications in automobile shock absorber pistons. The orthogonal experiment results show that the optimal GF/MoS₂/talc/PTFE weight ratio was 2:3:3:92 for the PTFE composite; this ratio resulted in better mechanical properties, hardness, low linear expansion, and wear rate. Chemical coupling and high‐temperature activation treatment on the surface of GF greatly enhanced the interfacial adhesion between the PTFE matrix and GF, as revealed by atomic force microscopy analysis. This resulted in reductions in the wear rate and linear expansion coefficient by two orders of magnitude compared with that of PTFE. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44668.     

Improving hydrophobicity of polyurethane by PTFE incorporation

A simple and facile method was established of incorporating polytetrafluoroethylene (PTFE) on to polyurethane (PU) to improve hydrophobicity of PU by incorporating low levels of fluorine at a molecular level. Nanocomposites were made by preparing PU in the presence of PTFE using seeded miniemulsion polymerization method. The resulting PTFE/PU nanocomposites were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectrometry, differential scanning calorimetric, and thermo gravimetric analysis (TGA). FTIR and TEM indicated changes observed in their structure, size and morphology. The water contact angle of PTFE/PU nanocomposite films increased with increasing amount of PTFE and more on blending with silica nanoparticles but a slight decrease in thermal stabilities of SiO₂/PTFE/PU nanocomposites were noticed. The hydrophobicity imparted by PTFE to PU surface was found to be at its best for 1 : 2 PTFE/PU latex film. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42779.     

Improved adhesion of poly(tetrafluoroethylene) by NH3-plasma treatment

—Surface modification of poly(tetrafluor oethylene) (PTFE) by NH₃-plasma treatment was investigated by means of contact angle measurement, XPS, and ATR FT/IR spectroscopy. The modified surfaces were adhesively bonded to nitril rubber. The NH₃-plasma irradiation made PTFE surfaces hydrophilic. The contact angle of water on the modified PTFE surface was 16 deg, and the surface energy was 62-63 mJ/m². The NH₃-plasma irradiation improved adhesion between PTFE and nitril rubber using a phenol-type adhesive. The peel strength of the joints reached 8.1 × 10³ N/m. Carbonyl and amido groups were created on PTFE surfaces by the NH₃-plasma irradiation. The mechanism of the improvement of adhesion by the NH₃-plasma irradiation is discussed.     

Synthesis and characterization of polyurethane–chitosan interpenetrating polymer networks

A polyurethane–chitosan (PU–CH) coating was synthesized from castor-oil-based PU prepolymer and highly deacetylated and depolymerized chitosan. The films cast with the coating were used for the characterization. X-ray photoelectron spectroscopy, a surface-sensitive technique, indicated the chemical bonding between the chitosan and PU prepolymer as well as the enrichment of chitosan on the surface of the film PU–CH. Electron spin resonance (ESR) spectroscopy using the nitroxyl radical 4-hydroxy-2,2,6,6-tetramethyl piperidine-1-oxyl (4-hydroxy-TEMPO) as a reporter group was used to study the chain mobility in the film PU–CH. It was observed that T_50G of the probe and the first glass transition temperature (T_g1) of the film PU–CH were 10 and 18°C higher than those in the PU film, respectively, and the activation energy (27.0 kJ mol⁻¹) of tumbling for the probe covalently bonded with PU–CH was 12.8 kJ mol⁻¹ higher than that of the probe with the film PU. It suggests that the molecular motion in the PU–CH was restricted by grafted and crosslinked interpenetrating polymer networks (IPNs). The results of the differential thermal analysis and thermogravimetric analysis proved that the thermostability of the film PU–CH was significantly higher than that of the film PU, and the T_g1 value is in good agreement with that calculated from ESR. It could be concluded that the IPNs resulted from the chitosan grafting and crosslinking with PU exist in the film PU–CH. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1321–1329, 1998     

Properties and interfacial bonding of regenerated cellulose films coated with polyurethane–chitosan IPN coating

Water-resistant films were prepared by coating a castor oil-based polyurethane–chitosan (PU–CH), in which grafted interpenetrating polymer networks (IPNs) were produced, on a regenerated cellulose (RC) film. The tensile strengths of the coated films cured at 90°C for 5 min reached 853 kg cm⁻² (dry state) and 503 kg cm⁻² (wet state) and were obviously higher than those of the films of uncoated and coated with PU coating. Moreover, the coated films have excellent water resistivity, low vapor permeability, and good size stability, and their optical transmittance is even better than that of the RC film in the range of 400–800 nm. The interfacial structure of the coated films was investigated by using spectroscopy infrared, ultraviolet spectroscopy, transmission electron microscopy, and electron probe microanalysis. It was shown that the strong interfacial bonding with chemical and hydrogen bonds between the RC film and the coating exists. The PU prepolymer in the IPN coating penetrated through the interface into the RC film and partly crosslinked with the cellulose, forming a semi-IPNs. The chitosan in the PU–CH coating plays an important role not only in accelerating the cure of the coating but also in improving the mechanical properties and biodegradability of the coated film. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1313–1319, 1998     

Surface modification of polytetrafluoroethylene by Ar+ irradiation for improved adhesion to other materials

A surface of thin square polytetrafluoroethylene (PTFE) samples (1 × 1 × 0.2 cm³) was irradiated with Ar⁺ at 1 keV with varying ion dose from 5 × 10¹⁴ to 1 × 10¹⁷ ions/cm² with and without an oxygen environment. The irradiated surface of the samples was examined by scanning electron microscopy (SEM) for surface textural changes and x-ray photoelectron spectrometry (XPS) for changes in chemical structure. A wettability test was conducted on the irradiated surface of PTFE samples by water droplets. A Scotch ™ tape adhesion test, after a thin film of Cu or Al was evaporated on the irradiated surface, and a tensile test after irradiated samples were glued to sample holders by an adhesive glue (Crystal Bond) was also run. The SEM micrographs showed increasing roughness with fiber forest-like texture with increasing ion dose. The Ar⁺ with an O₂ environment produced finer and denser fiber forest-like texture than that without O₂. The high-resolution XPS spectra showed decreased intensity of the F1s peak and formation of the O1s peak when irradiated with the O₂ environment. The increase of the O1s peak may be attributed to the reaction of oxygen atoms and the free radicals created by Ar⁺ bombardment. The wettability of water droplets on the irradiated surfaces was found to be inversely proportional to the surface roughness. Adhesion tests were conducted on 2000 Å thick Al or Cu film. Full detachment of the metal films was observed when PTFE samples were not modified. Partial detachment of the Al film occurred when PTFE was irradiated without the O₂ environment, regardless of ion dose. No detachment of the film occurred when PTFE was irradiated with the O₂ environment with the ion dose exceeding 1 × 10¹⁶ ions/cm². Partial detachment of Cu film was observed with or without the O₂ environment when the ion dose was 5 × 10¹⁴ ions/cm². No detachment occurred with or without the O₂ environment when the ion dose was 1 × 10¹⁵ ions/cm² or greater. The tensile test showed that adhesion of an adhesive cement (Crystal Bond) to the irradiated PTFE samples increased significantly with increasing ion dose up to 1 × 10¹⁶ ions/cm². Possible mechanisms for the improved adhesion are given. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1913–1921, 1997     

Properties and interfacial bonding for regenerated cellulose–polyurethane/amylose acetate sipn composite films

Composite films were obtained by placing a polyurethane/amylose acetate semi‐interpenetrating polymer network (SIPN) coating onto the surfaces of regenerated cellulose (RC) film. The properties of the composite film, such as tensile strength, 79.9 MPa (in dry state), 49.5 MPa (in wet state), water resistance (R), 0.62, dimensional stability (S_c), 3.0%, and water vapor permeability (P), 5.96 × 10⁻⁵ Kgm⁻²h⁻¹, are better than those of the uncoated RC film or RC film with PU coating. The interfacial strength was characterized with infrared spectroscopy (IR), ultraviolet spectroscopy (UV), transmission electron microscopy (TEM), and electron probe microanalysis (EPMA). The results showed the existence of covalent and hydrogen bonds between the SIPN coat layer and the RC layer. It was also found that the PU prepolymer in the coating layer penetrated into the cellulose bulk, and reacted with the cellulose molecules, which formed another SIPN.     

The Mechanical and Tribological Properties of Anodic Oxidation Treatment Carbon Fiber-Filled PU Composite

The interfacial adhesion of the carbon fiber (CF) reinforced polyurethane (PU) composite was improved by the means of anodic oxidation treatment. The mechanical and reciprocating sliding wear properties were studied and results showed that the anodic oxidation treatment have definitely improved the mechanical strength. And the wear and the friction coefficient of PU decreased with the addition of CF. The friction coefficients of anodic oxidation treated CF/PU composites are lower than those of PU and CF/PU composite. The interfacial adhesion between the CF and PU dominated the main wear mechanisms.     

Improving adhesion between thin chromium film and polyimide substrate by Ar+ irradiation

Ar⁺ irradiation and annealing at an elevated temperature are used to improve the adhesion of deposited Cr thin films by vacuum evaporation onto polyimide (PI) substrates. The Ar⁺ ions of 50 and 200 keV and various Ar⁺ doses ranging from 1 × 10¹³ to 2 × 10¹⁶ ions/cm² are chosen for the experiments, after many preliminary trials. The surface analyses are conducted employing Rutherford Backscattering Spectroscopy (RBS), Fourier transform infrared spectrometry (FTIR), X-ray photoelectron spectroscopy (XPS), and Scanning electron microscopy (SEM). Ar⁺ irradiation produces an interfacial layer of about 100 Å (10 nm) thick in which Cr particles and PI molecules are physically mixed and chemically bonded. The chemical bonds of Cr? O and a trace of Cr?C are observed by XPS and FTIR. Impact-wear tests are also conducted in order to determine the effects of the Ar⁺ irradiation on the wear property of a Cr/PI system. A significant increase in the property is observed and the increase appears to be a function of the degree of adhesion of the Cr film to the PI substrate.     

An atomistic study of the abrasive wear and failure of graphene sheets when used as a solid lubricant and a comparison to diamond-like-carbon coatings

The failure mechanisms of graphene under nanoscale sliding conditions are examined using atomistic simulations to evaluate its use as a solid lubricant and to simultaneously answer principal questions regarding wear of lamellar films comprised of atomically-thin sheets. To determine the failure behavior of graphene and the impact of adhesion on wear and failure, an asperity is slid over a substrate-supported graphene film with various adhesion strengths. For a purely-repulsive asperity, the graphene never delaminates and lower substrate-membrane adhesion appears to reduce the overall damage to the graphene layer and permits the recovery of more of the load-bearing capability of the graphene post-tearing. When tri-layer graphene is benchmarked with a 2 nm repulsive asperity against an 86% sp³ content diamond-like-carbon (DLC) coating of the same thickness (1.0 nm), the graphene supports up to 8.5 times the normal load of DLC during indentation, and up to twice the normal load of DLC during sliding even after failure of one or more layers. The preliminary results indicate that graphene has promise as a solid lubricant with thickness on the order of nanometers due to its atomically-thin configuration and high load carrying capacity.