Cloused cycle of production of ulltrafine polytetrafluoroethylene and new areas of use of fluoropolymer manufacture waste

The features of processes of ultrafine polytetrafluoroethylene manufacture of waste technological polytetrafluoroethylene by hydrothermal method and thermal degradation with an exhaustive fluorination in the presence of cobalt trifluoride were studied. Compositions and properties of gaseous and solid products of pyrolysis and recycling in ultrafine polytetrafluoroethylene manufacture were determined. Methods of use of ultrafine polytetrafluoroethylene, gaseous products, and spent catalyst were developed. On the basis of the experiments a closed scheme of producing ultrafine polytetrafluoroethylene was proposed in view of its application with recycling of accompanying gas fraction, and separating manufacture waste with recycling of cobalt trifluoride catalyst and using the resulting cobalt difluoride for producing composite coatings and lubricants.     

Thermal Decomposition of Polytetrafluoroethylene Oxide

The thermal degradation of polytetrafluoroethylene oxide has been examined by the isothermal and thermogravimetric methods in the temperature range 450 to 650°C. The main components of the volatile gas are trifluoro-acetyl fluoride, carbonyl fluoride, and tetrafluoroethylene. The thermogravimetric decompositions of polytetrafluoroethylene oxide and of polytetrafluoroethylene have been compared.     

Radiation-Enhanced Thermal Depolymerization of Polytetrafluoroethylene

The initial stage of thermal and radiation-enhanced thermal depolymerization over the temperature range of 310–460°C in vacuum was studied for polytetrafluoroethylene specimens with different thicknesses. Conditions for the occurrence of depolymerization in the kinetic and diffusion regions were determined. The specific features of depolymerization kinetics for low-molecular-mass polytetrafluoroethylene specimens obtained by preliminary irradiation of virgin samples at room temperature were revealed. A possible role of depolymerization in radiation crosslinking of polytetrafluoroethylene irradiated above the crystallite melting point was considered.     

A new antifriction and sealing material based on radiation-modified polytetrafluoroethylene

The current situation with research into the effect of ionizing radiation exposure on the structure and properties of polytetrafluoroethylene was analyzed. New methods of radiation-induced modification, that improve the performance characteristics of polytetrafluoroethylene, were discussed. The results of research into properties of polytetrafluoroethylene irradiated at temperatures exceeding the melting point of its crystalline phase in media with different compositions were presented. It is shown that, under certain irradiation conditions, an extremely strong increase (up to 10 000-fold) in the wear resistance of polytetrafluoroethylene can be achieved, with the creepage decreased up to 100-fold. A conclusion was made that high-temperature radiation-induced modification can yield new modifications of the polymer, in which the advantages offered by untreated polytetrafluoroethylene are combined with high mechanical and triboengineering characteristics.     

Polytetrafluoroethylene‐jacketed stirrer modified with graphene oxide and polydopamine for the efficient extraction of polycyclic aromatic hydrocarbons

Steel stirrers jacketed with polytetrafluoroethylene can be regarded as an ideal substrate for stirrer bar sorptive extraction. However, it is still a great challenge to immobilize graphene onto a polytetrafluoroethylene stirrer due to the high chemical resistance of the surface of a polytetrafluoroethylene stirrer. We describe here a method to modify the surface of polytetrafluoroethylene stirrers with graphene. In this work, graphene was used as the sorbent due to its excellent adsorption capability for aromatic compounds, such as polycyclic aromatic compounds. Graphene was successfully immobilized onto polytetrafluoroethylene‐stirrer by a bio‐inspired polydopamine functionalization method. The graphene‐modified polytetrafluoroethylene‐stirrer shows good stability and tolerance to stirring, ultrasonication, strong acidic and basic solutions, and to organic solvents. The multilayer coating was characterized by scanning electronic microscopy and Fourier transform infrared spectroscopy. After the optimization of some experimental conditions, the graphene‐modified polytetrafluoroethylene stirrer was used for the stirrer bar sorptive extraction of polycyclic aromatic hydrocarbons, in which the binding between the polycyclic aromatic hydrocarbons and the graphene layer was mainly based on π–π stacking and hydrophobic interactions. The graphene‐modified polytetrafluoroethylene‐stirrer‐based stirrer bar sorptive extraction and high‐performance liquid chromatography method was developed for the determination of polycyclic aromatic hydrocarbons with great extraction efficiency, with enrichment factors from 18 to 62. The method has low limits of detection of 1–5 pg/mL, wide linear range (5–100 and 10–200 pg/mL), good linearity (R ≥ 0.9957) and good reproducibility (RSD ≤ 6.45%). The proposed method has been applied to determine polycyclic aromatic hydrocarbons in real dust samples. Good recoveries were obtained, ranging from 88.53 to 109.43%.     

Formation of oxide layers modified with polytetrafluoroethylene or graphite on aluminum and titanium alloys by plasma electrolytic oxidation

For one-stage formation of coatings containing polytetrafluoroethylene or graphite, it was proposed to use Na₂SiO₃ + NaOH aqueous electrolyte containing siloxane-acrylate emulsion and dispersed powders of polytetrafluoroethylene or graphite. The phase and elemental composition and surface morphology of the formed coatings were determined. It was shown that the introduction of polytetrafluoroethylene markedly increases the hydrophobic and wear-resistant properties of coatings.     

Change in the porosity of polytetrafluoroethylene during radiation modification above the melting temperature

The X-ray degree of crystallinity, ??, and the density, ??, of suspension-polymerized polytetrafluoroethylene after its irradiation above the melting temperature of the crystalline phase are studied. A comparison of dose dependences of ?? and ?? makes it possible to infer that pores occur in the initial polytetrafluoroethylene and that porosity substantially decreases during irradiation. The time of pore contraction in polytetrafluoroethylene after its radiation modification above the meting temperature is estimated with respect to the order of the magnitude. This estimate is based on the consideration of viscous flow under the action of surface-tension forces.     

Fabrication of polytetrafluoroethylene- and graphite-containing oxide layers on aluminum and titanium and their structure

Stable aqueous electrolyte emulsions with negatively charged micelles containing dispersed particles of polytetrafluoroethylene (PTFE) or graphite are obtained using siloxane-acrylate emulsion as an emulsifier. The oxide coatings formed in such electrolytes contain carbon, polytetrafluoroethylene, or graphite. The coatings with PTFE particles are similar to monolithic polytetrafluoroethylene with respect to its hydrophobic characteristics. According to X-ray photoelectron spectroscopy data, the surface of the formed coatings predominantly contains aliphatic carbon (C-C and C-H bonds) and some fraction of oxidized (or, in the case of PTFE-containing electrolytes, fluorinated) carbon.     

Electron-beam charging of polytetrafluoroethylene

The charging of polytetrafluoroethylene films by irradiation with fast electrons having an energy insufficient for the complete penetration through the entire thickness of the polymer was theoretically analyzed. The calculation results take into account the distribution of both the dose rate and the bulk electron thermalization rate over the film thickness in the approximation of prescribed radiation-induced conductivity of polytetrafluoroethylene. The influence of the parameters of radiation-induced conductivity on the charging behavior and on the time dependence of the transient current detected with the use of the split Faraday cup was examined. It was found that the observed transient current inversion is adequately explained with allowance for the specifics of radiation-induced conductivity in polytetrafluoroethylene.     

Magnetic composites based on ultrafine polytetrafluoroethylene and cobalt containing nanoparticles

Composite materials based on ultrafine polytetrafluoroethylene and cobalt-containing nanoparticles were synthesized by the method of high-speed thermal decomposition of cobalt formate in a pseudoboiling layer of grains of ultrafine polytetrafluoroethylene. It has been found that ultrafine polytetrafluoroethylene is a composite material that consists of a core of polytetrafluoroethylene and a membrane of fluoroalkanes. In the formation of cobalt nanoparticles, interaction between them and the shell of ultrafine polytetrafluoroethylene-fluoroalkanes takes place. The result of the interaction is the formation of cobalt fluoride, which makes a significant contribution to the magnetic properties of composite materials. At room temperature, ferromagnetic behavior is characteristic for materials; the coercive force at 300 K is 700 Oe, while at 77 K it reaches 900 Oe.     

Polytetrafluoroethylene physisorption‐assisted emulsification microextraction as a cleanup and preconcentration step in the gas chromatography determination of aliphatic hydrocarbons in marine sediment samples

For the first time, the application of polytetrafluoroethylene powder as an extractant phase collector or holder in liquid‐phase microextraction has been developed. For this purpose, the analytical performances of two different ways of applying polytetrafluoroethylene powder in microextraction methods including polytetrafluoroethylene physisorption‐assisted emulsification microextraction and dispersive liquid‐phase microextraction via polytetrafluoroethylene extractant phase holders have been compared for analysis of aliphatic hydrocarbons in aqueous phases. Under the same conditions, the former showed better extraction efficiencies over the latter and as a result, it was applied as preconcentration and cleanup step in the analysis of aliphatic hydrocarbons in sediment samples followed by gas chromatography analysis. The linearity of the polytetrafluoroethylene physisorption‐assisted emulsification microextraction method was obtained over a range of 3.7 and 2000 ng/g (R ² > 0.993). The relative standard deviations were less than 6.5% (n = 3). The limits of detection and quantification obtained by this method were 1.1–9.0 and 3.7–30 ng/g, respectively, indicating that satisfactory results were achieved by the procedure.     

Composite tribological materials based on molybdenum disulfide nanoparticles and polytetrafluoroethylene microgranules

Tribological materials based on molybdenum disulfide nanoparticles localized on the surface of ultradispersed polytetrafluoroethylene were prepared. The composition and properties of the new composite materials were studied. Introduction of ultradispersed additives based on polytetrafluoroethylene with MoS₂ and on polytetrafluoroethylene and nanodiamonds prepared by detonation synthesis (taken as reference samples) decreases the viscosity of MS-20 aviation oil. The dependence of the friction coefficient on the Sommerfeld number for the composites obtained was examined. Introduction of additives leads to a decrease in the friction coefficient with increasing linear sliding velocity, in contrast to the initial oil for which the trend is opposite. The dependence of the friction coefficient on the concentration of additives in the initial oil was demonstrated. Modification of polytetrafluoroethylene microgranules with 3 wt % MoS₂ nanoparticles allows the amount of additive to the oil to be considerably reduced.     

Modification of polypropylene fibrous materials with ultradispersed polytetrafluoroethylene

The effects of narrowly and widely dispersed fractions of ultradispersed polytetrafluoroethylene on the structures of melt-spun polypropylene fibrous materials and the ultimate tensile half-cycle characteristics of polypropylene filaments and nonwoven materials have been studied via X-ray diffraction analysis, optical microscopy, and differential scanning calorimetry. It has been shown that the addition of 1–2% ultradispersed polytetrafluoroethylene, which exists as an individual phase in polypropylene, allows a significant increase in the relative tensile stress of the filament and its elastic modulus.     

Determination of molar mass distribution of poly(tetrafluoroethylene)

High-temperature static and dynamic laser light scattering characterization of polytetrafluoroethylene in perfluorotetracosane has been accomplished after solving the following experimental difficulties: (1) constructing a high-temperature laser light scattering spectrometer which can be operated at a temperature as high as 340 °C, (2) developing a new all-glass apparatus for dissolving and filtering, (3) measuring the refractive index increment of polytetrafluoroethylene in perfluorotetracosane at 325 °C, and (4) establishing a scaling relation between the molecular weight (M) and the translational diffusion coefficient at both infinite dilution and the zero scattering angle from only two broadly distributed polytetrafluoroethylene samples so that we can convert the translational diffusion coefficient distribution to the molecular weight distribution. This paper presents a summary of our published results of the characterization of poly(tetrafluoroethylene), which emphasizes the experimental details of high-temperature laser light scattering and the principle of the transformation from a translational diffusion coefficient distribution to a molecular weight distribution.     

Effect of the degree of radiation-induced cross-linking of polytetrafluoroethylene on its wear resistance

The effect of the dose of the γ-irradiation at temperature exceeding the melting point of the crystalline phase on the degree of radiation-induced cross-linking of polytetrafluoroethylene was examined, with the relative content of CF₃ groups and wear rate under conditions of dry sliding friction over steel chosen as characteristic parameters. The wear rate of radiation-cross-linked polytetrafluoroethylene decreases exponentially with an increase in the content of CF₃ groups and can be evaluated with sufficient accuracy from the IR data.     

Wear-Resistant composite coatings with increased chemical resistance,produced by electrodeposition on a cathode

The formation and properties of coatings produced by electrodeposition on a cathode on the basis of an amine-containing oligomeric film-forming?ent modified with highly dispersed polytetrafluoroethylene, polyphenylene sulfide, and fluorine rubber were studied. A procedure is suggested for introduction of powdered polyphenylene sulfide into a formulation for cathodic electrodeposition. It was found that polyphenylene sulfide and polytetrafluoroethylene form a separate phase in a coating; during electrodeposition on a cathode, fluorine rubber SKF-264B enters into a chemical interaction with the amine-containing oligomeric film-forming agent; a scheme of this interaction is suggested. A formulation was created with a triple modification of the amine-containing oligomeric film-forming agent with polytetrafluoroethylene, polyphenylene sulfide, and fluorine rubber. This formulation forms a wear-resistant coating with increased chemical and corrosion resistance.     

Formation of composite membranes containing hydrophobic polymer layers by electron-beam sputter deposition

The chemical structure and the contact and morphological properties of composite membranes prepared by electron-beam sputter deposition of a polytetrafluoroethylene layer on the surface of track-etched polypropylene membrane have been studied. It has been found that the application of such layers results in bilayer composite membranes with both the layers having hydrophobic properties. It has been shown that an increase in the thickness of the deposited polytetrafluoroethylene layer leads to development of its roughness, resulting in the formation of a polymer with superhydrophobic properties on the surface of the initial membrane.     

Epoxy Coatings with Low Surface Energy from Powdered Compounds Modified with Finely Dispersed Polytetrafluoroethylene Particles

Highly hydrophobic epoxy coatings with the surface energy as low as 14.5 mJ m^–2 and contact angles with water of 120°–150° were prepared from powdered compounds modified with less than 2 wt % finely dispersed polytetrafluoroethylene particles by dry mixing. As shown by scanning electron microscopy, EDX microanalysis, and atomic-force microscopy, the film formation at 180°С and formation of a polymer network matrix are accompanied by predominant migration of polytetrafluoroethylene particles to the air/coating interface, leading to gradient distribution of fluorine across the film and significant enrichment of the coating surface with fluorine. By varying the polytetrafluoroethylene content, it is possible to obtain hydrophobic coatings with satisfactory physicomechanical properties, smooth or rough surface, including micrometric and nanometric roughness, and different surface energy.     

Characteristics of porous polytetrafluoroethylene films prepared from powder suspensions in alcohol

With the aim of developing the fabricating technology of porous polytetrafluoroethylene films by the method similar to that applied in the papermaking industry, the behavior of suspensions of polytetrafluoroethylene powders in isopropanol has been studied. Correlations of sedimentation rates and mean sizes of powder particles with the structure of porous films have been established. The linear relationship between the sizes of pores and the mean sizes of powder particles has been found. It has been shown that the relative width of the pore-size distribution is virtually independent of powder particle sizes.     

Properties of fractions of ultradisperse polytetrafluoroethylene soluble in supercritical carbon dioxide

The morphology and structure of FORUM ultradisperse polytetrafluoroethylene fractions obtained via separation of the initial sample with supercritical carbon dioxide are studied by means of scanning and transmission electron microscopy, thermogravimetric and X-ray structural analysis, and IR and NMR spectroscopy. The lowest molecular mass fractions of the ultradisperse polytetrafluoroethylene are involved in the dissolution process, while an increase in production parameters (pressure and temperature) entails gradual involvement of higher molecular mass oligomers in this process. On the basis of the experimental data, the chain length of oligomers soluble in supercritical carbon dioxide is estimated.