RU2467034C1 - Accumulative antifriction and sealing material based on polytetrafluoroethylene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to nanocomposite material based on polytetrafluoroethylene. The nanocomposite structural material contains ultrafine diamond-containing filler. The filler used is ultrafine detonation nanodiamonds, with the following ratio of components: ultrafine detonation nanodiamonds 1.0-5.0%; polytetrafluoroethylene - the balance up to 100%. The material is subjected to radiation modification.

EFFECT: obtaining articles for general industrial use as antifriction and lining-sealing material.

3 cl, 1 tbl, 1 dwg, 12 ex

Description

The invention relates to the field of production of polymeric materials with improved performance characteristics, namely to radiation-modified polymer composite materials of antifriction and sealing purposes based on polytetrafluoroethylene (PTFE) containing a functional filler. Ultrafine detonation nanodiamonds (UDD) were used as a functional filler. The invention allows to obtain products intended for general industrial use as anti-friction and gasket-sealing material.

PTFE is a material that combines good anti-friction, thermal, anti-adhesive and anti-corrosion properties. The disadvantages of PTFE are the high intensity of wear during dry friction on steel and high creep under load, which allows its use only at low loads, while a complex of high requirements for physical and mechanical characteristics, creep and wear resistance is imposed on structural materials of tribological and sealing purposes .

To increase wear resistance and reduce creep, various organic and inorganic additives are usually introduced into PTFE to withstand its sintering temperature.

RF patent No. 2064943, IPC C08J 5/14 describes a material obtained on the basis of PTFE and diamond powder of natural origin with a grain size of 20-80 microns with a content of 20-60 wt.%. The material is obtained by cold pressing at a pressure of 30-50 MPa, followed by sintering at 370 ± 5 ° C. The roughness of the treated surface is 0.42-0.45 microns with a tool wear of 14-15 mg and a heating temperature of 40-45 ° C.

RF patent No. 2177963, IPC C08J 5/16, C08L 27/16, C08K 9/00 describes a polymer tribological composition intended for use in friction units of machinery and equipment. The composition includes: PTFE and 0.1-1.0 wt.% Natural diamond powder activated in an AGO-2 planetary mill for 5 minutes. The invention improves the wear resistance and elasticity of the composite material and improve its strength characteristics.

RF patent No. 2269550 (IPC C08L 27/18) describes a composition comprising PTFE and a carbon-containing filler, which further comprises a nanodispersed modifier selected from the group consisting of sodium titanate or ultrafine ceramic Sialon, or a carbon-containing product of detonation synthesis, and additionally contains fluorine-containing oligomer. An increase in strength and a decrease in defectiveness, a decrease in the coefficient of friction during operation without lubrication are shown.

RF patent No. 2216553, IPC C08J 5/16, C08L 27/18, describes an antifriction polymer material made from a composition containing PTFE and a carbon-containing additive, and fullerene soot powder is used as a carbon-containing additive 1-10% by weight of the composition. It has been shown that the addition of fullerene soot improves the antifriction and antiwear properties of PTFE.

RF patent No. 21114874, IPC C08J 5/16, C08L 27/18, C08K 3/04, C09K 3/10 - prototype, describes a polymer composition for sealing purposes containing PTFE and a filler, characterized in that it contains 0.1- as a filler 1.5 wt.% Ultrafine diamond-containing powder obtained by detonation synthesis from organic raw materials (TU 84-415-115-87), containing up to 92-95 wt.% Of the main powder. It is shown that the material has a good set of physicomechanical characteristics, high wear resistance and increased load capacity, which are due to the high structural activity of the filler with respect to PTFE.

An analysis of these sources shows that the fillers can modify PTFE in the direction of improving the operational characteristics of the material based on it. At the same time, it should be noted that the possibilities of this method of improving properties are practically exhausted. Varying the amount and type of fillers does not allow to achieve a more significant increase in physical and mechanical properties and wear resistance. So, the limit values of the relative linear wear during friction without lubrication of the best PTFE-based compositions reached to date are (1-10) μm / km.

The authors of the proposed technical solution suggested that the efficiency of the introduction of fillers can be repeatedly enhanced by the thermo-radiation modification of PTFE when it is treated with penetrating gamma rays in the temperature range above the melting point in a selected gas medium.

In RF patent No. 21211228, IPC C08J 3/28, C08F 2/46, PTFE products were irradiated with gamma rays at an elevated temperature in the melt in an inert medium. In this case, irradiation is carried out to an absorbed dose of 5-35 Mrad with a decrease in the product temperature during irradiation by 0.8-1 deg / Mrad, maintaining the product temperature below the melting temperature of PTFE, but above its crystallization temperature.

RF patent No. 2414488, IPC C08J 7/18, C09K 11/06 describes a radiation-chemical method for producing luminescent PTFE, which consists in the fact that a block or film product of PTFE is subjected to gamma rays with an average energy of 1.25 MeV at a temperature above the melting temperature crystalline phase, in the presence of water vapor with a pressure of 10 ^-2 -1 mm RT.article and absorbed dose rates of 1-5 Gy / s to an absorbed dose of 200 kGy. The data presented showed a qualitative change in the structure of the material and, as a consequence, its physicochemical properties.

The technical task of the present invention is to develop a composite polymer material of antifriction and sealing purposes based on PTFE with high wear resistance and low creep.

This problem is solved by modifying PTFE during processing by introducing nano-sized fillers of an organic nature and directed radiation-chemical modification of the obtained nanocomposite. Ultrafine detonation nanodiamonds were used as nanoscale fillers.

The essence of the solution described is the radiation modification of the PTFE / UDD nanocomposite with gamma radiation with an average quantum energy of 1.25 MeV absorbed dose of not more than 20 Mrad at a temperature above the melting point of the crystalline phase of PTFE in an inert gas medium.

A significant effect of reducing creep and increasing wear resistance is observed during the radiation treatment of PTFE containing 1.0-5.0 weight percent UDD, polytetrafluoroethylene - the rest is up to 100%.

The composite preparation process is carried out by

machining the polymer powder, dispersing the nanofiller, dosing the components in the required proportions and mixing them in a high-speed mill, followed by pressing the nanocomposites blanks on hydraulic presses in unheated steel molds, followed by high-temperature sintering.

Nanocomposites based on PTFE and UDD, modified under the stated conditions (with an absorbed dose of not more than 20 Mrad), have increased stress values at 10% strain (up to 50%), reduced total compressive strain (up to 60%), and significantly improved elastic properties and reduced creep (the proportion of reversible deformation in the total deformation increases 4 times), an abnormally high wear resistance (up to 5000 times higher compared to unirradiated nanocomposites) (Table 1). Radiation modification does not lead to a noticeable change in the friction coefficient of nanocomposites (Table 1).

When the filler content is less than 1%, these effects are markedly reduced. At a filler concentration of 5%, the wear rate at a modification dose of 20 Mrad is higher than at 2.5% (Table 1). Thus, we can conclude that the optimal composition of radiation modifications of the developed nanocomposites is in the range of 1-5%. The decrease and increase in the content of the filler for the specified interval leads to a deterioration of physical, mechanical and tribological characteristics.

It is quite obvious that such significant changes in these (and a number of other) properties suggest the corresponding structural changes in radiation-modified PTFE-UDD compositions compared to the initial unirradiated analogues.

The structural changes in the radiation modifications of PTFE-UDD-based nanocomposites were studied by scanning electron microscopy (SEM).

The surface morphology of the chips of the initial and radiation-modified composite PTFE + 2.5% UDD is presented in figure 1. The cleaved surface of the initial composite is loose, heterogeneous, caverns are observed, as well as pores of micro- and nanometer scale (Fig. 1a). The filler is distributed randomly, poorly moistened with polymer (figb). The crystalline regions have a lamellar structure.

Radiation exposure causes significant changes in the morphology of the composite. The surface becomes dense, cavities and pores are tightened (figv). Spherulites are formed, consisting of radially spaced fibrils, ranging in size from 30 to 70 microns (figv, g). The centers of spherulites are hybrid regions consisting of polymer chains firmly bound to UDD particles.

The general picture of the processes occurring during radiation modification is a sequence of molecular and supramolecular changes. Molecular mechanisms (radiation-induced destruction of polymer chains) lead to a general decrease in the viscosity of the polymer medium, which in turn creates the possibility of subsequent crystallization near pores and nanodiamonds acting as nuclei of spherulites. In this case, the adhesion of the filler with the polymer matrix increases substantially and, in general, the packing density of structural elements increases and the porosity decreases.

The invention is illustrated by the following examples.

Example 1

1.00 g (1.00% wt.) Of the UDD was subjected to dispersion on an MP / 0.5 planetary mill designed for fine and ultrafine, dry or wet grinding of powders for 30 min.

99.00 g (99.00% wt.) Of high molecular weight polytetrafluoroethylene (PTFE) powder was subjected to mechanical dispersion in a high speed mill for 5 minutes.

A dry mixture of dispersed PTFE and UDD was processed in a high-speed mill for 6-10 minutes until the mixture was homogenized. Billets were obtained by pressing on hydraulic presses of various forces in steel unheated molds, followed by heat treatment (sintering) at a temperature of 380 ° C.

Example 2

Analogously to example 1, the processes of dispersion, homogenization, pressing / extrusion are carried out. The amount of UDD is 2.50 g (2.50% wt.).

Example 3

Analogously to example 1, the amount of UDD is 5.00 g (5.00% wt.).

Examples 4-12 are similar to examples 1-3 using radiation exposure. The sintered preforms from the PTFE + UDD nanocomposite are placed in a heat chamber filled with an inert gas and heated to a temperature of 327-329 ° C, which allows the crystalline phase of the polymer to melt (for unirradiated PTFE, the crystallite has a melting point of _Tm = 327 ° C). Then the material is irradiated at a gamma radiation source with gamma-ray energy 1.25 MeV to a predetermined absorbed dose (Table 1). After the cessation of irradiation, the samples were cooled to room temperature.

Table 1 The test results of the physical and mechanical properties and wear of the initial and irradiated nanocomposites based on PTFE and UDD No.
ra Sample mark P ¹⁾ , MPa ε _Σ ,% ²⁾ ε _arr / ε _Σ ²⁾ k I, μm / km ³⁾ one PTFE + 1% UDD (non-irradiated) eighteen 27 0.09 0.16 1350 2 PTFE + 2.5% UDD (non-irradiated) 17 27 0.09 0.14 850 3 PTFE + 5% UDD (non-irradiated) eighteen 24 0.13 0.12 600 four PTFE + 1% UDD (irradiated, 5 Mrad) twenty 17 0.21 0.17 120 5 PTFE + 2.5% UDD (irradiated, 5 Mrad) 22 fifteen 0.22 0.19 65 6 PTFE + 5% UDD (irradiated, 5 Mrad) 21 17 0.21 0.18 62 7 PTFE + 1% UDD (irradiated, 10 Mrad) 22 16 0.25 0.15 0.5 8 PTFE + 2.5% UDD (irradiated, 10 Mrad) 22 13 0.26 0.14 1.5 9 PTFE + 5% UDD (irradiated, 10 Mrad) 21 fifteen 0.25 0.18 9.5 10 PTFE + 1% UDD (irradiated, 20 Mrad) 25 eleven 0.34 0.16 0.2 eleven PTFE + 2.5% UDD (irradiated, 20 Mrad) 24 10 0.35 0.14 0.3 12 PTFE + 5% UDD (irradiated, 20 Mrad) 25 eleven 0.33 0.17 1.0 Note: ¹⁾ The elastic modulus (E _о ) and stress (P) at 10% deformation under compression are determined for samples with a diameter of 10 mm and a height of 15 mm, ²⁾ ε _Σ and ε _arr are the values of the total and reversible deformation at 5 loading cycles ( 5 MPa / min, P _max = 25 MPa) under compression, ³⁾ Friction coefficient (k) and wear rate (I) at P = 5 MPa, V = 1 m / s (roughness and hardness of the counterbody, respectively, Ra = 0.15, HRc 40).

Figure 1 - SEM image of the cleaved surface of the initial (a, b) and radiation-modified (c, d) nanocomposite based on PTFE and UDD (2.5%). On figv and 1d. arrows indicate spherulites and radially oriented fibrils, which are part of spherulites, respectively.

Claims (3)

1. Nanocomposite structural material based on polytetrafluoroethylene containing ultrafine diamond-containing filler, characterized in that ultrafine detonation nanodiamonds are used as filler in the following ratio of components,%:
ultrafine detonation nanodiamonds 1.0-5.0 polytetrafluoroethylene the rest is up to 100,
subjected to radiation modification. 2. The material according to claim 1, characterized in that the radiation modification is carried out by gamma radiation with an average quantum energy of 1.25 MeV, an absorbed dose of not more than 20 Mrad at a temperature above the melting point of the crystalline phase of polytetrafluoroethylene in an inert medium. 3. The material according to claim 1 or 2, characterized by the formation of spherulites, consisting of radially oriented fibrils, and reduced, compared with unirradiated material, porosity.

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