SI24472A - Fluoro-polymer nanocomposites with tailored friction properties - Google Patents

Abstract

The invention describes three - dimensional and thin - layer forms of fluoro - polymeric nanocomposites with adapted friction properties that contain nanomaterials based on inorganic nanotubes as additives for reducing friction. The term nanotechnology nanomaterials means nanomaterials appearing in cylindrical geometry or derived from cylindrical geometry using mechanical or chemical methods. More specifically, this invention describes a process for regulating the frictional properties of PVDF-based PVDF-based nanowires based on MoS2 as an inorganic reducing agent. Friction of nanomaterials based on PVDF / MoS2 nanotubes is significantly lower compared to PVDF coating without the mentioned additives.

Description

Fluoro-polymers nanocomposites with adapted friction properties

The invention discloses fluoro-polymer nanocomposites with customized friction properties in three-dimensional and thin-layer morphology containing inorganic nanomaterials as friction reducing additives. More specifically, the invention discloses polyvinylidene fluoride (PVDF) polymers containing MoS ₂ based nanomaterials and a method for adjusting the sliding properties of PVDF based polymers.

FIELD OF THE INVENTION

The present invention relates generally to the field of polymer nanocomposites and more specifically to methods of adapting the physical properties of thermoplastic high-performance fluoro-polymers, in particular the friction properties of polyvinylidene fluoride-based polymers, using MoS _2- based nanotubes.

BACKGROUND OF THE INVENTION

Polyvinylidene fluoride (PVDF) is a highly inert thermoplastic fluoro-polymer with high thermal stability up to 175 ° C. It is useful for many applications that depend on its individual crystallization phase, such as pipelines, power line insulators, composite electrode binder materials for lithium-ion batteries, biomedical membranes, components for the pharmaceutical and food processing industries, such as piezoelectric and pyroelectric material, etc. PVDF is found in five crystalline forms (α, β, γ, δ, ε), and in three of these (β, γ, δ), the strongly pole structure is oriented in such a way that the PVDF is piezoelectric (A. Lovinger, Macromolecules 1982; 15, 40-44). PVDF has a relatively high PVDF - PVDF coefficient of friction in the range 0.250.45, which limits its use in self-lubricating coatings or in coatings subjected to heavy friction or in use as protective coatings. Inorganic solid lubricant molybdenum disulfide (MoS ₂ ) is a well-known lubricant that has been used extensively for decades. Its effective lubricating properties originate from the easy inter-sliding of the MoS ₂ layers along the basal (001) planes and the surface inertia of the basal (001) planes of MoS ₂ . MoS _2, in the usual form of flat sheets, which can be synthesized or exploited by a natural mineral, is often used as a dry lubricant or as an additive to oils or greases. Unfortunately, the solid edges of crystalline scales are prone to oxidation, which reduces the lubrication efficiency, especially in humid environments. Thin sheets with a high active surface and a relatively low number of unsaturated edges at the edges are therefore desirable. The standard use of MoS ₂ plates as an adjunct to friction reduction and recent discoveries of new MoS ₂ morphologies have made it possible to prepare new PVDF-based nanocomposite films containing MoS ₂ nanotubes or layered MoS ₂ nanotubes for self-lubricating and protective coatings.

Curved, self-terminated MoS ₂ forms, such as nanotubes and fullerene-like particles with nanobubule morphology (Margulis L, Salitra G, Tenne R, Talianker M: Nested fullerene-like structures.Nature 1993, 365: 113-114) . These designs have been extensively researched regarding their particular suitability for the next generation of lubricants. Under mechanical loading, these nanoparticles slowly deform and stratify into nanosheets, which are transferred to the substrate (third-body effect)) and provide effective lubrication until completely stratified (Chhowalla M, Amaratunga GAJ: Ultra low friction and wear MoS ₂ nanoparticle thin films. Nature 2000, .407: .164-167).

Different morphologies and combinations of MoS ₂ nanotubes and nano bulbs synthesized from M ₆ C _y H _z , 8.2 <y + z <10, where M is a transition metal (Mo, W, Ta, Nb), C is chalcogen (S, Se, Te), H is halogen (I), have been disclosed in US 8,007,756 B2.

Spontaneous partial delamination of MoS ₂ nanotube walls in synthesized material (Remškar M, Viršek M, Mrzel A: The MoS ₂ nanotube hybrids. Appl Phys Lett 2009,95: 133122-1-133122-3) and thin MoS ₂ nanotube walls (M. Remskar, A. Mrzel, M. Virsek, M. Godec, M. Krause, A. Kolitsch, A. Singh and A. Seabaugh, Nanoscale Res. Lett. 6, 26 (2011) allow low energy consumption during process run-in friction.

Leaching of MoS ₂ nanotubes can be achieved by chemical means through the intercalation of highly reactive molecules such as butyl lithium (Visic et al., Nanoscale Research Letters 2011, 6: 593) or mechanically during the sliding process.

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PVDF / M0S2 composites were described in: a) US 5,024,882, where MoS ₂ was added to PVDF in powder form <40 pm for use in slide bearing composites. The process of making the material was described; b) US 2011/0045309 Al, where MoS ₂ without designation was used as a dry lubricant or in combination with PVDF to adjust the coefficient of friction of the metal workpiece, c) US 5,976,190, where MoS _{2 was} without designation, incorporated into the intermediate layer between the clamping tube and the tube made of light metal, which both form an orthopedic clamping connection, d) US 6.106.936, where MoS _{2 is} described only as a metal compound with a layered structure used as a component of lubricant for sliding bearings, e) US 6,528,143 BI, wherein MoS _2, without designation, is a component of a metal-based plastic coating; f) US20130071623 Al, wherein MoS _{2 is} without formulation, a solid lubricant dispersed within the polymer.

In all PVDF / MoS ₂ composites listed above, standard macro or micro-scale MoS ₂ tiles were used.

PVDF / MoS ₂ composites, where MoS _{2 has} been described as nanotubes, are described in: g) US 20080248201 and US20080249221 A1, where PVDF is indicated indirectly as one of the polyvinylidene halides, and MoS ₂ as a possible nanofiller among a wide variety of materials for h) US20060233692 Al, which describes a method by which a substrate of a metallic mixture can be directly coated with nanotubes, including the MoS ₂ nanotubes, and then applied to the polymer coating. PVDF is described as a polymeric binder for carbon nanotubes.

PVDF / MoS ₂ nanocomposites, where MoS _{2 is} in cylindrical nanotubes or layered MoS ₂ nanotubes, and blended into PVDF before coating, and would have been tested for lubrication properties, have not yet been described.

Friction testing using polyalphaolefin oil (PAO), to which MoS ₂ nanotubes were added, showed significantly reduced friction and improved wear properties under conditions of boundary lubrication at steel contact. The coefficient of friction of the session decreased by more than 2 times, while the wear was reduced by as much as 5 to 9 times (M. Kalin, J. Kogovšek, M. Remškar, Wear 280/281, 36 • · (2012), doi : 10.1016 / j.wear.2012.01.011). The improvement over the base oil was greater for rough surfaces where the friction coefficient decreased by up to 65%, compared to a reduction of about 40% on smooth steel surfaces under boundary lubrication conditions. Friction was largely independent of surface roughness (J. Kogovšek, M. Remškar, A. Mrzel, M.Kalin, Tribology International 61 (2013) 40-47).

Interference with MoS ₂ nanotubes in isotactic polypropylene (iPP) reduced the friction coefficient by 15% and wear by more than 50% (M. Naffakh, M. Remskar, et al., J. Mater.Chem. 22, 17002-17010 (2012 )). It is the only polymer composite based on MoS ₂ nanotubes reported to date.

SUMMARY OF THE INVENTION

The invention describes three-dimensional and thin-film forms of fluoro-polymer nanocomposites with customized friction properties containing inorganic nanotube-based nanomaterials as friction-reducing additives. The term nanotubes-based nanomaterials means nanomaterials that appear in cylindrical geometry or are derived from cylindrical geometry by mechanical or chemical methods. More specifically, the present invention describes a method for regulating the friction properties of PVDF-based polymers with MoS _2- based nanotubes as an inorganic friction-reducing additive. The friction of PVDF / MoS ₂ based nanomaterials is significantly lower compared to PVDF coating without the aforementioned additives.

DETAILED DESCRIPTION OF THE INVENTION

It is an object of the present invention to provide three-dimensional and thin-film forms of fluoropolymer nanocomposites with customized friction properties containing nanomaterials based on inorganic nanotubes as friction-reducing additives.

According to the invention, the problem is solved by a method for adjusting the coefficient of friction of PVDF and polymers based on PVDF, by incorporating MoS ₂ .

By the process of the invention, MoS ₂ nano-based materials are added to PVDF as a solution in a suitable solvent or PVDF as melt, and further homogenized by mechanical stirring.

Fluorine polymer nanocomposites with custom friction properties of the invention contain fluorothermoplastic polymeric material, MoS ₂ nanotubes based on low friction additives, and additives such as agglomeration or sedimentation inhibitors. The fluorothermoplastic material may be a polymer or copolymer based on polyvinylidene fluoride, the fluorothermoplastic material being a homogeneous polymeric mixture containing from 99 - 5% of polymers or copolymers based on polyvinylidene fluoride. The proportion of nano-based MoS ₂ nanotubes is in the range of 0.1 wt. % to 50 wt. % by weight of fluorothermoplastic polymeric material, and MoS ₂ nanotubes in MoS ₂ nanotubes may be partially stratified or fully stratified.

Nanocomposite thin films can be prepared by various techniques used for polymer-nanoparticle mixtures in liquid or plasticized state. Two of these are: a) pouring the solution onto a suitable substrate and drawing the film with a scalpel; b) application of the coating to a suitable rotating base. The films were dried under different heating regimes with or without the use of a controlled composition atmosphere.

Using the described application methods, PVDF / MoS ₂ was prepared on the basis of nanotubes in the form of films and coatings with a thickness between 10 pm and 500 pm. The controlled crystal structure and morphology of nanocomposites can be prepared using various auxiliary additives as inhibitors of agglomeration and sedimentation of nanomaterials based on MoS ₂ nanotubes and by varying the deposition and drying conditions.

We tested the physical and chemical properties of the nanocomposites thus prepared, in particular their crystal structure, surface morphology, the distribution of MoS ₂ -based nanomaterials within PVDF-based polymers, and the thickness of the nanocomposite films.

The properties of the nanocomposite coatings thus prepared were tested in flat-on-flat and ball-on-disc configurations. The friction on nanotubes-based PVDF / M0S2 nanocomposites was significantly reduced compared to PVDF coatings without M0S2-based nanotubes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the X-ray spectrum for PVDF / M0S2 films with 0 wt. % (mark - 0), 1 wt. % (mark - 1), and 2 wt. % (label - 2) M0S2 nanotubes. Slope peaks corresponding to M0S2 are indicated by *. Other peaks correspond to PVDF.

FIG. 2 is an optical image taken in screening mode and shows a homogeneous distribution of M0S2 nanotubes within a PVDF film containing 0.5% by weight of MoS ₂ nanotubes.

FIG. 3 is a line electron microscopic image of the top surface of a PVDF / M0S2 nanotube film containing 2% by weight of M0S2 nanotubes and showing a porous structure.

FIG. 4 is a line electron microscopic image of the lower surface (on contact with the glass substrate) of a PVDF / M0S2 nanotube film containing 1% by weight of M0S2 nanotubes.

FIG. 5 shows the results of friction testing in flat-to-plane geometry on PVDF / M0S2 nanocomposite films with (a) 0 wt.%, (B) 1 wt.%, And (c) 2 wt. % of MoS ₂ nanotubes, and with AISI 316 polished stainless steel as contact material.

FIG. 6 shows the results of friction testing in ball-on-disk geometry on PVDF / M0S2 nanocomposite films with (a) 0 wt. %, (b) 2 wt. %, and (c) 16.7 wt. % of M0S2 nanotubes, and with AISI 316 stainless steel ball.

The following examples are set forth to illustrate the invention but are not limited thereto.

EXAMPLE 1:

PVDF was added to dimethylformamide (DMF) in 20 wt. % and dissolved for 24 hours at low mixing and heating rates up to 50 degrees C. The homogeneous PVDF / DMF solution was stirred with a magnetic stirrer for 15 minutes before nanotubes were added. MoS ₂ nanotubes in 0.5 wt.%, 1 wt.% And 2 wt.% By weight of PVDF were added to the PVDF / DMF solution and mixed with a magnetic stirrer for an additional 30 minutes. The dispersion thus produced was sonicated for 30 minutes in an ultrasonic bath at 40 kHz and 200 W. Homogeneous dispersion of the nanotubes in the polymer solution was obtained.

The dispersion was poured onto a glass plate and a 300 pm film scalpel film was drawn using a film applicator (Erichsen). The films were dried at 22 ° C and 50% relative humidity for 24 hours. After drying, the films were removed from the glass plate. The surface of the film exposed to air during drying was referred to as the upper surface. The surface of the film formed on the film / glass interface was designated as the lower surface.

X-ray diffraction (XRD) was performed at room temperature with a D4 Endeavor diffractometer (Bruker AXS) using a quartz monochromato Cu Cu radiation source (λ = 0.1541 nm) and a Sol - X energy dispersion detector. ° to 73 ° with a step size of 0.04 ° and 4 with a signal capture time. The crystal structure of the PVDF / MoS ₂ nanotube film characterized by X-ray diffraction is presented in FIGURE 1 and confirms the presence of MoS ₂ in the film. Peaks belonging to MoS ₂ are marked with an asterisk (*). The other peaks correspond to the γ-phase of PVDF. The peak at 16.8 ° corresponds to the doubled cell γ - phase PVDF.

Homogeneous distribution of MoS ₂ nanotubes in PVDF containing 0.5 wt. % of MoS ₂ nanotubes is shown on an optical microscope image taken in reflective mode in FIGURE2.

The morphology of PVDF / M0S2 nanocomposites was studied using a FE-SEM scanning electron microscope, Supra 35 VP, Carl Zeiss. The upper surface of the PVDF / M0S2 nanotube films was porous and composed of beads as shown in FIG. MoS ₂ nanotubes are not visible because they are covered with PVDF. The lower surface of the PVDF / M0S2 nanotube film shows MoS ₂ nanotubes covered with a thinner PVDF layer than the upper surface. The MoS ₂ nanotubes on the lower surface became visible when higher accelerating voltages were applied in a row electronic scan, as shown in FIG. 4.

The thicknesses of PVDF and PVDF / MoS ₂ films and surface roughness were exchanged with a Profilometer (Form Talysurf Series, Taylor - Hobson Ltd), with a resolution of x -, 25 pm, y -1 pm, and z - 3 nm. Pure PVDF films were 18.7 pm ± 1 pm thick. PVDF / MoS ₂ films containing 1 wt. % MoS ₂ nanotubes _; were 22.3 pm ± 1 pm thick. PVDF / MoS ₂ films containing 2 wt. % of MoS _2> nanotubes were 30 pm ± 1 pm thick.

The upper surface of the pure PVDF film and the PVDF / MoS ₂ nanotube films were attached to the tribometer support with carbon adhesive tape. The lower surface of the PVDF and PVDF / MoS ₂ nanotube films was in contact with the polished AISI 316 stainless steel. These experiments were performed using a CF-800XS tribometer (RDM Test Equipment). The load on the friction carrier was 223g. The calculated contact pressure was 83 kPa. The sliding of films from PVDF and PVDF / MoS ₂ nanotubes along AISI 316 stainless steel was in reciprocal mode. Friction was measured only in the forward direction. The relative speed was 300 mm / min. Each path was 300 mm long. Friction was measured under normal ambient conditions: relative humidity in the range of 43-52% and in the temperature range: 20-25 ⁰ C. The friction tests were performed in a flat-to-plane geometry for PVDF / MoS ₂ nanocomposite films with 0% , 1 Tues. % and 2 wt. % of MoS ₂ nanotubes. The results are presented in FIG. The presence of MoS ₂ nanotubes in PVDF films eliminated the emergence of escape-related peaks characteristic of pure PVDF films. The presence of MoS ₂ nanotubes reduced the coefficient of friction. After 40 m of sliding distance, the contact friction coefficient of pure PVDF / AISI 316 was 0.42; for contact PVDF / 1 Tues. % of MoS ₂ / AISI 316 nanotubes was 0.31 and for PVDF / 2 contact wt. % of MoS ₂ / AISI 316 nanotubes was 0.11. 1 Tues. % of MoS ₂ nanotubes in PVDF is

reduced friction by more than 20% relative to pure PVDF. 2 Tues. % of MoS ₂ nanotubes in PVDF reduced friction by more than 70%.

The results of friction testing in the flat-to-plane geometry presented graphically in FIG. 5 show that the MoS ₂ nanotubes added to PVDF, as described in the invention, greatly reduce the friction at the PVDF / MoS ₂ nanotube contact - AISI316.

EXAMPLE 2

PVDF was added to dimethylformamide (DMF) in 20 wt. % and dissolved for 24 hours with gentle mechanical stirring. Subsequently, a homogeneous PVDF / DMF solution was stirred with a magnetic stirrer for 15 minutes. Then we added MoS ₂ nanotubes in 2 wt. % and 16.7 wt. % by weight of PVDF, into PVDF / DMF solution and stirred with a magnetic stirrer for an additional 15 minutes. The dispersion thus produced was sonicated lh 45 'in an ultrasonic bath at 40 kHz and 200 W.

PVDF coatings and PVDF / MoS _2> nanotube coatings were prepared by dropping the solution directly onto AISI 316 disks polished to an arithmetic mean roughness of Ra 2 micrometer. The coatings were dried at 22 ° C and at 50% relative humidity until a constant mass was reached.

The pure PVDF coatings thus made on AISI 316 disks were 50 pm thick. PVDF / MoS ₂ coatings containing 2 wt. % of MoS ₂ nanotubes on AISI 316 discs were 50 pm thick. PVDF / MoS ₂ coatings containing 16.7 wt. % MoS ₂ nanotubes _; were 60 pm thick.

Friction testing was performed using a standard 6 mm diameter ball bearing made of AISI 316 stainless steel that formed contact with the surface of PVDF coatings and PVDF / MoS ₂ nanotubes. The arithmetic mean surface roughness of the Ra ball was 200 nm, the load on it was 1 N, the radius of the circle was 5.2 mm, the contact pressure was 0.2 MPa and the velocity of the ball relative to the disk was 1 cm / s.

The results of friction testing in ball-on-disk geometry, presented graphically in FIG. 6, show that PVDF-added MoS ₂ nanotubes, as described in the invention, reduce the friction on contact between PVDF / MoS ₂ nanotubes and AISI 316. PVDF coating / MoS ₂ nanotubes with 2 wt. % of MoS ₂ nanotubes showed reduced friction by 7% relative to the pure PVDF coating. PVDF / MoS ₂ nanotube coating with 16.7 wt. % of MoS ₂ nanotubes showed 73% reduced friction with respect to the clear PVDF coating on the first 12 m of slip. After 12 m of slip, the coefficient of friction gradually increased to 0.43 and slowly approached 0.47 at 77 m of slip.

The results of the friction tests obtained in the ball-on-disk geometry showed that the PVDF-added MoS ₂ nanotubes, as described in the invention, greatly reduce the friction on contact between the PVDF / MoS ₂ nanotube composite and AISI 316.

Claims (11)

PATENT APPLICATIONS 1. Fluoro-polymer nanocomposites with modified friction properties for adjusting the friction coefficient of polyvinylidene fluoride (PVDF) containing fluorothermoplastic polymeric material, MoS ₂ nanotubes as a low friction additive, and additives such as agglomeration inhibitors or sedimentation inhibitors. 2. Fluoro-polymer nanocomposites according to claim 1, wherein the fluorothermoplastic material is a polyvinylidene fluoride (PVDF) based polymer. 3. Fluoro-polymer nanocomposites according to claim 1, wherein the fluorothermoplastic material is a polyvinylidene fluoride based copolymer. The fluoro-polymer nanocomposites according to claim 1, wherein the fluorothermoplastic material is a homogeneous polymer mixture containing 99 -5% of polymers or copolymers based on polyvinylidene fluoride. 5. Fluoro-polymer nanocomposites according to claim 3, wherein the polyvinylidene fluoride-based copolymer is dissolved in dimethylformamide (DMF). 6. Fluoro-polymer nanocomposites according to claim 1, wherein the MoS ₂ nanotubes are partially stratified in the MoS ₂ nanotubes based on nanotubes. 7. Fluoro-polymer nanocomposites according to claim 6, wherein the MoS ₂ nanotubes in the MoS ₂ nanotubes are completely layered. The fluoro-polymer nanocomposites of claim 1, wherein the proportion of nano-based MoS ₂ nanotubes is in the range of 0.1 wt. % to 50 wt. % based on the proportion of fluorothermoplastic polymer material. Films, coatings and three-dimensional nanocomposites made from fluoro-polymer nanocomposites according to claim 1. Films, coatings and three-dimensional nanocomposites according to claim 9, prepared by pouring a solution, by processing coatings on rotating substrates or made of melt. Films and coatings according to claim 9 for use in reducing friction.