Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/20—Compounding polymers with additives, e.g. colouring
  • C08J3/205—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase
  • C08J3/21—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase the polymer being premixed with a liquid phase
  • C08J3/212—Compounding polymers with additives, e.g. colouring in the presence of a continuous liquid phase the polymer being premixed with a liquid phase and solid additives
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K7/00—Use of ingredients characterised by shape
  • C08K7/22—Expanded, porous or hollow particles
  • C08K7/24—Expanded, porous or hollow particles inorganic
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/20—Conductive material dispersed in non-conductive organic material
  • H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
  • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
  • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08J2327/16—Homopolymers or copolymers of vinylidene fluoride
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/70—Nanostructure
  • Y10S977/734—Fullerenes, i.e. graphene-based structures, such as nanohorns, nanococoons, nanoscrolls or fullerene-like structures, e.g. WS2 or MoS2 chalcogenide nanotubes, planar C3N4, etc.
  • Y10S977/742—Carbon nanotubes, CNTs
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S977/00—Nanotechnology
  • Y10S977/70—Nanostructure
  • Y10S977/788—Of specified organic or carbon-based composition

Definitions

• the invention relates generally to electrically conductive polyvinylidene fluoride composites containing carbon nanotubes, and the methods for preparing them.
• Plastics are synthetic polymers which have a wide range of properties that make them useful for a variety of applications ranging from packaging and building/construction to transportation; consumer and institutional products; furniture and furnishings; adhesives, inks and coatings and others. In general, plastics are valued for their toughness, durability, ease of fabrication into complex shapes and their electrical insulation qualities.
• PVDF polyvinylidene fluoride
• -BbC ⁇ CFa- polyvinylidene fluoride
• PVDF polyvinylidene fluoride
• This structure which contains alternating -CH 2 - and -CF 2 - groups along the polymer backbone, gives the PVDF material polarity that contributes to its unusual chemical and insulation properties.
• PVDF is a semicrystalline engineered thermoplastic whose benefits include chemical and thermal stability along with melt processibility and selective solubility. PVDF offers low permeability to gases and liquids, low flame and smoke characteristics, abrasion resistance, weathering resistance, as well as resistance to creep and other beneficial characteristics.
• PVDF is a common item of commerce and has a wide variety of applications (e.g., cable jacketing, insulation for wires and in chemical tanks and other equipments).
• PVDF also form co-polymers with other polymer and monomer families, most commonly with the co-monomers hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), and tetrafluoroethylene (TFE), as well as terpolymers and olefins.
• HFP hexafluoropropylene
• CTFE chlorotrifluoroethylene
• TFE tetrafluoroethylene
• the properties of the copolymers is strongly dependent on the type and fraction of the co-monomers as well as the method of polymerization. For example, HFP makes a homogenous copolymer with PVDF.
• the PVDF copolymer phase segregates if the other monomer is not fluorinated.
• electrically conductive plastics Recently, demand and applications for electrically conductive plastics have grown. In these uses, one seeks to exploit the unique properties of plastics, often as an alternative to metals. For example, electrically conductive polymeric materials are desirable for many applications including the dissipation of electrostatic charge from electrical parts, electrostatic spray painting and the shielding of electrical components to prevent transmission of electromagnetic waves.
• Conductivity i.e., the ability of material to conduct or transmit heat or electricity
• bulk resistivity i.e., volume resistivity
• Bulk resistivity which is the inverse of conductivity, is defined as the electrical resistance per unit length of a substance with uniform cross section as measured in ohm-cm.
• ESD electrostatic discharge
• the next level of resistivity which ranges from approximately 10 4 ohm/cm and lower, protects components contained within such plastic against electromagnetic interference ("EMI") as well as prevents the emission of interfering radiation, and is referred to as the EMI shielding level of conductivity.
• EMI electromagnetic interference
• the primary method of increasing the electrical conductivity of plastics have been to fill them with conductive additives such as metallic powders, metallic fibers, ionic conductive polymers, intrinsically conductive polymeric powder, e.g., polypyrrole, carbon fibers or carbon black.
• metallic fiber and powder enhanced plastics have poor corrosion resistance and insufficient mechanical strength. Further, their density makes high weight loadings necessary. Thus, their use is frequently impractical.
• carbon black has become the additive of choice for many applications.
• the use of carbon black also has a number of significant drawbacks.
• the quantities of carbon black needed to achieve electrical conductivity in the polymer or plastic are relatively high, i.e. 10- 60%.
• These relatively high loadings lead to degradation in the mechanical properties of the polymers.
• low temperature impact resistance i.e., a measure of toughness
• Barrier properties also suffer. Sloughing of carbon from the surface of the materials is often experienced. This is particularly undesirable in many electronic applications.
• outgassing during heating may be observed. This adversely affects the surface finish.
• high loadings of carbon black may render the surface of conductive plastic parts unsuitable for automotive use.
• Carbon fibrils have been used in place of carbon black in a number of polymer applications.
• Carbon fibrils referred to alternatively as nanotubes, whiskers, buckytubes, etc., are vermicular carbon deposits having diameters less than 1.0 ⁇ and usually less than 0.2 ⁇ . They exist in a variety of forms and have been prepared through the catalytic decomposition of various carbon-containing gases at metal surfaces. Such fibers provide significant surface area when incorporated into a structure because of their size and shape. They can be made with high purity and uniformity.
• the polymers used by Nahass in the Examples of the '502 patent for preparing conductive, high toughness polymeric compositions include polyamide, polycarbonate, acrylonitrile-butadiene-styrene, poly (phenylene ether), and thermoplastic urethane resins and blends.
• nanotube-containing polymer composites of the art are useful and have valuable strength and conductivity properties, many new uses for such composites require that very high strength and low conductivity be achieved with low nanotube loading in the polymer. Accordingly, the art has sought new composite compositions which achieve these ends.
• composites containing polyvinylidene fluoride polymer or copolymer and carbon nanotubes have extraordinary electrical conductivity.
• Composites with less than 1% by weight of carbon nanotubes have been found to have a bulk resistivity many times lower than the bulk resistivity of other polymer composites having similar nanotube loading.
• Composites with as little as 13% by weight carbon nanotubes have a bulk resistivity similar to that of pure carbon nanotube mats.
• Composites containing polyvinylidene fluoride polymer or copolymer and carbon nanotubes may be prepared by dissolving the polymer in a solvent to form a polymer solution and then adding the carbon nanotubes into the solution.
• the solution is mixed using a sonicator or a Waring blender.
• a precipitating component is added to precipitate out a composite comprising the polymer and the nanotubes.
• the composite is isolated by filtering the solution and drying the composite.
• Composites containing polyvinylidene fluoride polymer or copolymer and carbon nanotubes may also be prepared by adding carbon nanotubes to a polymer emulsion and then mixing the emulsion with a Waring Blender. The water/solvent is then removed by evaporation to obtain the composite comprising the polymer and the nanotubes.
• Fig. 1 is a graph plotting composite resistivity as a function of nanotube loading in a PVDF/HFP composite.
• Fig. 2 is a graph plotting composite resistivity as a function of graphite concentration for PVDF composites with 13% nanotube loading.
• Fig. 3 is a logarithmic graph plotting resistivity as a function of nanotube weight fraction for various polymer composites.
• Fig. 4 is a graph plotting composite conductivity as a function of nanotube loading in various polymer composites.
• PVDF-Nanotube Composites It has now been discovered that composites containing PVDF polymer or copolymer and carbon nanotubes have electrical conductivities much higher than other polymer/carbon nanotube composites known in the art.
• PVDF composite refers broadly to any composite containing PVDF or a copolymer of vinylidene fluoride and another monomer, and carbon nanotubes. Unlike other polymer composites, PVDF composites with bulk resistivities as low as pure carbon nanotubes can be formed.
• percent nanotube loading % nanotube loading
• PVDF composites results in far higher conductivities than similar loadings in other polymer composites.
• a PVDF composite with 5% nanotube loading has a bulk resistivity of .42 ohm-cm while a poly(paraphenylene sulfide) composite with 5%> nanotube loading has a bulk resistivity of 3.12 ohm-cm.
• PVDF composites containing carbon nanotubes in an amount as little as 1%> or less by weight have an exceptionally low bulk resistivity compared to the pure PVDF polymer or copolymer, and have exceptionally low resistivity compared to other polymer composites at similar nanotube loadings.
• Nanotube loading may be widely varied.
• PVDF composites may be made with nanotube loadings of broadly from .01-30%) desirably from 0.5-20% and preferably from 1-15%. It has been found that PVDF composites have much lower bulk resistivities compared to other polymer composites at any given nanotube loading.
• PVDF composites with as little as about 13% nanotube loading has a bulk resistivity comparable to a pure nanotube mat, i.e., between .02 ohm-cm to .08 ohm-cm.
• PVDF composites with about 13%> to 20% nanotube loading all have bulk resistivity values within the range of the resistivity values of a pure nanotube mat.
• PVDF composites can be formed with bulk resistivity of less than about 10 ohm-cm or less than about 1 ohm-cm. The bulk resistivity of PVDF composite may be adjusted by varying the nanotube loading to meet the level of conductivity required for its intended application.
• nanotube loading in PVDF was set by the limit of percolation and will depend on various factors such as the method of composite formation, the materials used, etc. For example, Table 1 shows that the lower limit of nanotube loading under the conditions in Example 1 is well under 1%, but apparently above 0.2%.
• the monomers which may be used with vinylidene fluoride monomer to fonn PVDF copolymers for the composites of the invention include hexafluoropropylene, polystyrene, polypropylene, CTFE, TFE, terpolymers or olefins.
• the copolymers may be produced broadly from a de minims amount of a monomer other than vinylidene fluoride to as much as 90%> by weight of such monomer.
• Desirably copolymers of the invention contain from 1%> to 70%> by weight of such other monomer and preferably from 10% to 50%> by weight thereof.
• the PVDF composites of the invention also include mixtures of PVDF and other polymers, including those wherein the PVDF and other polymers are miscible or immiscible with one another.
• the PVDF composites of the invention also include mixtures of PVDF and copolymers formed from vinylidene fluoride and another monomer, as described above, and mixtures of these mixtures with other polymers.
• Carbon Nanotubes A variety of different carbon nanotubes may be combined with PVDF or
• the nanotubes used in the invention have a diameter less than 0.1 and preferably less than 0.05 micron.
• United States Patent No. 4,663,230 to Tennent hereby incorporated by reference, describes carbon fibrils that are free of a continuous thermal carbon overcoat and have multiple ordered graphitic outer layers that are substantially parallel to the fibril axis.
• United States Patent No. 5,171,560 to Temient et al hereby incorporated by reference, describes carbon nanotubes free of thermal overcoat and having graphitic layers substantially parallel to the fibril axes such that the projection of said layers on said fibril axes extends for a distance of at least two fibril diameters.
• these Tennent fibrils may be characterized as having their c-axes, the axes which are perpendicular to the tangents of the curved layers of graphite, substantially perpendicular to their cylindrical axes. They generally have diameters no greater than 0.1 ⁇ and length to diameter ratios of at least 5. Desirably they are substantially free of a continuous thermal carbon overcoat, i.e., pyrolytically deposited carbon resulting from thermal cracking of the gas feed used to prepare them. These fibrils are useful in the present invention.
• Tennent inventions provided access to smaller diameter fibrils having an ordered outer region of catalytically grown multiple, substantially continuous layers of ordered carbon atoms having an outside diameter between about 3.5 to 70 nm, and a distinct inner core region, each of the layers and the core being disposed substantially concentrically about the cylindrical axis of the fibrils, said fibrils being substantially free of pyrolytically deposited thermal carbon. Fibrillar carbons of less perfect structure, but also without a pyrolytic carbon outer layer have also been grown.
• the "unbonded" precursor nanotubes may be in the form of discrete nanotubes, aggregates of nanotubes, or both. Nanotubes aggregate in several stages or degrees. Catalytically grown nanotubes produced according to U.S.S.N. 08/856,657, filed May 15, 1997, hereby incorporated by reference, are formed in aggregates substantially all of which will pass through a 700 micron sieve. About 50% > by weight of the aggregates pass through a 300 micron sieve. The size of as-made aggregates can, of course, be reduced by various means, but such disaggregation becomes increasingly difficult as the aggregates get smaller.
• Nanotubes may also be prepared as aggregates having various morphologies (as determined by scanning electron microscopy) in which they are randomly entangled with each other to form entangled balls of nanotubes resembling bird nests ("BN"); or as aggregates consisting of bundles of straight to slightly bent or kinked carbon nanotubes having substantially the same relative orientation, and having the appearance of combed yarn ("CY") e.g., the longitudinal axis of each nanotube (despite individual bends or kinks) extends in the same direction as that of the surrounding nanotubes in the bundles; or, as aggregates consisting of straight to slightly bent or kinked nanotubes which are loosely entangled with each other to form an "open net” (“ON”) structure.
• CY combed yarn
• the morphology of the aggregate is controlled by the choice of catalyst support.
• Spherical supports grow nanotubes in all directions leading to the formation of bird nest aggregates.
• Combed yarn and open nest aggregates are prepared using supports having one or more readily cleavable planar surfaces, e.g., an iron or iron- containing metal catalyst particle deposited on a support material having one or more readily cleavable surfaces and a surface area of at least 1 square meters per gram.
• fibrils of different microscopic and macroscopic morphologies useful in the present invention include the multiwalled fibrils disclosed in U.S. Patent Nos. 5,550,200, 5,578,543, 5,589,152, 5,650,370, 5,691,054, 5,707,916, 5,726,116, and 5,877,110 each of which are incorporated by reference. Single walled fibrils may also be used in the composites of the invention.
• Single walled fibrils and methods for making them are described in U.S. Patent No. 6,221,330 and WO 00/26138, both of which are hereby incorporated by reference.
• Single walled fibrils have characteristics similar to or better than the multi-walled fibrils described above, except that they only have a single graphitic outer layer, the layer being substantially parallel to the fibril axis.
• PVDF composites containing carbon nanotubes with different grades, sizes, morphologies, or types have different bulk resistivity at a given fibril loading.
• CC combed candy
• BN bird nest
• CC nanotubes which are aggregated in parallel bundles, are easier to disperse in the polymer than BN nanotubes, resulting in a more even distribution of fibrils in the composite and hence, lower bulk resistivity.
• PVDF composites formed from PVDF polymer or copolymers and carbon nanotubes make it possible to use conductive plastic, with all its property and fabrication advantages, in place of metals or pure graphite in a number of applications.
• PVDF composites of the invention may be used in applications where exceptional electrical conductivity is important. Examples of such uses include current collectors for high power electrochemical capacitors and batteries. Current commercial materials used for these purposes have bulk resistivities of approximately 1 ohm-cm. Other applications include conducting gaskets or EMF shield coatings. In these applications, a difference of, for example, .04 ohm-cm in bulk resistivity will have a very significant impact on product perforaiance. Still further uses include bipolar plates for PEM fuel cells as well as bifunctional (binder and conductivity enhancers) additives to a lithium battery cathode.
• These bipolar plates are formed by preparing a PVDF composite as disclosed herein and then extruding a PVDF composite sheet with a thickness of, for example, 2 mm.
• a single screw extruder may be used for the sheet extrusion.
• Flow channels may be engraved between two hot plates, one with a mirror pattern of the front plate channel and the other with a mirror pattern of the back plate channel.
• the channels may run parallel to each other from one corner to another, with each channel separated from the other by 0.5 mm.
• the channels may have a width and depth of 0.5 mm.
• PVDF composites may be prepared by a solution method in which PVDF polymer or copolymer is dissolved in a solvent such as acetone to form a solution.
• a solvent such as acetone
• Other soluble solvents such as tetrahydrofuran, methyl ethyl ketone, dimethyl formamide, dimethyl acetamide, tetramethyl urea, dimethyl sulfoxide, trimethyl phosphate, 2-pyrrolidone, butyrolacetone, isophorone, and carbitor acetate may be used.
• Nanotubes are dispersed in the solvent by applying energy to the polymer- nanotube mixture.
• the energy source can be a mechanical homogenizer, ultrasonic sonif ⁇ er, high speed mixer, Waring blender, or any other mixing means known in the art.
• a precipitating component such as water is added to precipitate or quench the solid composite containing the polymer and the nanotubes.
• the precipitating component may be any medium which is miscible with the solvent, but in which the PVDF polymer or copolymer mixture is insoluble.
• the solvent may optionally be removed by filtration or evaporation and dried to isolate the PVDF composite.
• the composite may be isolated by drying or evaporating steps such as heat drying, vacuum drying, freeze-drying, etc. known in the art.
• PVDF composites may also be prepared by a melt compounding process in which the PVDF polymer or copolymer is mixed with nanotubes in the mixing head of a mixer such as a Brabender mixture at high temperatures (i.e., over 200°C) to melt and compound the PVDF polymer or copolymer into the carbon nanotubes to form the composite.
• a mixer such as a Brabender mixture at high temperatures (i.e., over 200°C) to melt and compound the PVDF polymer or copolymer into the carbon nanotubes to form the composite.
• PVDF composites prepared using the solvent solution method have significantly lower bulk resistivity and thus were better electrical conductors, than PVDF composites made using traditional melt compounding methods.
• solvent solution method allows for better intermixing of the PVDF with the carbon nanotubes in the PVDF composites, thus resulting in lower bulk resistivity. It has also been found that at low nanotube loadings, using sonicators or ultrasonic sonifiers resulted in PVDF composites having lower bulk resistivities than PVDF composites made using mechanical mixing means such as Waring blenders.
• PVDF composites may be prepared using PVDF emulsions.
• carbon nanotubes are directly mixed with or dispersed in PVDF emulsions (or PVDF latex, or any dispersions of PVDF in water) by applying an energy source such as a mechanical homogenizer, ultrasonic sonif ⁇ er, high speed mixer, Waring blender, or any other mixing means known in the art.
• the water (or liquid) in the mixture is then removed, for example, by evaporation or any drying means known in the art to recover the PVDF composite.
• PVDF polymer Kynar 761
• Hyperion CC carbon nanotubes were added and dispersed into the polymer solution for two to five minutes using a high shear blender (i.e., Waring blender). Water was added to the dispersion to precipitate out the polymer with the nanotubes. The material was filtered and the filtrate was dried in a vacuum oven at 100°C to remove acetone and water, leaving behind the dry nanotube/PVDF composite. Multiple sheets of the composite with thickness of 0.003-0.01 inches were made using a compression molder. Bulk resistivity of the thin sheet samples was measured using a four probe method. Tensile strength was also measured. Multiple batches with different amounts of carbon nanotubes were tested. The results are reported in Table 1 below:
• Example I show that a PVDF composite with less than 1% nanotube loading had a significantly lower bulk resistivity than a pure PVDF polymer.
• the bulk resistivity of the composites dropped significantly as the nanotube loading increased to approximately 3%o.
• the bulk resistivity of the PVDF composite was below 1 ohm-cm.
• the bulk resistivity approached .08 ohm-cm, which is comparable to that of a pure CC nanotube mat.
• the PVDF composite had bulk resistivities within the ranges of those of pure CC nanotube mats.
• EXAMPLE II Using the procedure of Example I and Kynar 761 PVDF, a comparison was made of the resistivity of composites prepared with Hyperion CC nanotubes and with Hyperion BN nanotubes, respectively. The results are reported in Table 2 below:
• Example II confirm that at low nanotube loadings, PVDF/CC nanotube composites have significantly lower bulk resistivity than PVDF/BN nanotube composites.
• Example III Example I was repeated, except that an ultrasound sonicator or a homogenizer was used instead of a Waring blender to disperse the nanotubes in the polymer solution. The results are reported below in Table 3 :
• PVDF composites with low carbon nanotube loadings made with a sonicator generally had lower bulk resistivities than composites which were made with a Waring blender.
• PVDF composites made with a homogenizer had similar bulk resistivity values to those made with a Waring blender.
• Example I was repeated, except that the nanotubes were heat treated under hydrogen, argon, or air before they were dispersed into the polymer solution.
• Heat treatment of the nanotubes was carried out by heating the nanotubes under a flowing gas at the following conditions: hydrogen - 600°C for 30 minutes; argon - 1000°C for 30 minutes.
• Air oxidation was carried out by heating the nanotubes in an oven in air at 450°C for 2 hours. The results are reported below in Table 4:
• PVDF composites formed from air oxidized nanotubes showed significantly poorer conductivity (i.e., higher bulk resistivity) but higher tensile strength (at 5-20% fibril loading) compared to composites formed from nontreated nanotubes.
• PVDF/HFP copolymer Polyvinylidene fluoride-hexafluoropropylene copolymer was obtained from Solvay Advanced Polymers (21508) and the procedure of Example I was repeated with the PVDF/HFP copolymer instead of the pure PVDF Kynar 761 polymer. The results are reproduced in Table 5: Table 5
• the PVDF/HFP copolymer has lower crystallinity than PVDF polymer.
• the results of Example V showed that as little as 0.6% nanotube loading resulted in a bulk resistivity as low as 30 ohm-cm.
• the bulk resistivity of the PVDF/HFP composite continued to drop as the nanotube loading was increased to approximately 13%.
• the -19- bulk resistivity dropped below 1 ohm-cm at 3.1% nanotube loading and the lowest reported bulk resistivity observed was 0.072 ohm-cm at 13.3% nanotube loading, which is within the range of bulk resistivity for a pure CC nanotube mat.
• no improvement in bulk resistivity was observed for PVDF/HFP composites with more than 13.3% nanotube loading.
• PVDF/HFP composites with nanotube loadings up to approximately 3% appeared to have lower bulk resistivities than those of PVDF composites with the same nanotube loadings.
• the conductivity of a PVDF composite may be improved by using a PVDF/HFP copolymer, or a lower grade PVDF with less crystallinity, instead of a pure PVDF polymer.
• the tensile strength of this PVDF/HFP composite is lower and thus the selection of the copolymer composite or the polymer composite will depend on the properties required in the final application.
• the bulk resistivity of the PVDF composite is lower than that of the PVDF/HFP composite at higher nanotube loading (i.e., -20% or greater). It was further observed that PVDF/HFP composites with over 16% nanotube loading had rough surfaces and holes, and were difficult to mold since they broke easily.
• EXAMPLE VI A different grade of PVDF/HFP copolymer (Kynar 2801) was obtained from Elf Atochem and the procedure of Example I was repeated. Kynar 2801 is also known as Kynar-Flex. The results are reproduced in Table 6:
• the Kynar 2801 copolymer composite exhibited lower bulk resistivity above 13%) nanotube loading. At 20% nanotube loading, the Kynar 2801 composite had bulk resistivity values of about .05 ohm-cm, which is within the range of a pure CC nanotube mat.
• PVDF composites were prepared by melt compounding PVDF (Kynar 761) and Hyperion CC nanotubes and/or graphite (Lonza KS-75) in the mixing head of a Brabender mixer at 100 RPM for approximately five minutes at the temperature specified. Each of the mixtures were prepared by sequential addition of the compounds in the following order: PVDF, nanotubes, then graphite, unless the mixtures were premixed as indicated by an asterisk (*).
• flat sheets were prepared by pressing small pieces of the composite between thin, chromed plates at approximately 240°C with the thin plates being cooled to room temperature in one to two minutes. Resistivity was measured with a linear four probe head. The results are reported below in Table 7:
• PVDF-Sol PVDF/nanotube composite made from solution
• PVDF-Melt PVDF/nanotube composite made by melt compounding
• PPS poly(paraphenylene sulfide)/nanotube compound made by melt compounding
• EVA poly(co-ethylene-vinyl acetate)/nanotube compound made by melt compounding
• PS polystyrene/nanotube compound made by melt compounding
• PE polyethylene/nanotube compound made by melt compounding
• the nanotube weight fraction was calculated by dividing the nanotube weight by the composite weight.
• the nanotube volume fraction was calculated by dividing the volume of the nanotubes by the volume of the composite. These volumes were calculated by dividing each of the nanotube and polymer weights by their respective densities (the volume of the composite is the sum of the nanotube and polymer volumes).
• Example VIII showed that the resistivities of the PVDF and PVDF/HFP composites are orders of magnitude lower than the resistivities of even the best conductive polymers at any given nanotube loading level.
• the PVDF and PVDF/HFP composites had bulk resistivity values ranging from .42 to .55 ohm-cm, while the bulk resistivity of the PPS composite was 3.12 ohm-cm.
• the PVDF and PVDF/HFP composites had bulk resistivity values between .04-.09 ohm-cm, which is within the range of a pure CC nanotube mat.
• No other polymer composite at 20% nanotube loading or at any higher nanotube loading level had a bulk resistivity value within the range of that of a pure CC nanotube mat.
• Fig. 3 sets forth a logarithmic plot of nanotube weight vs. resistivity. A line is drawn which unequivocally distinguishes the resistivity of the PVDF composites from all other polymer composites, illustrating clearly that PVDF composites are superior to other polymer composites in electrical conductivity.
• Fig. 4 sets forth a plot of nanotube weight vs. conductivity. As Fig. 4 confirms, PVDF composites have clearly superior conductivity than other polymer composites known in the art. Additionally, Fig. 4 further shows that, unlike other polymer composites known in the art, conductivity for PVDF composites increase exponentially as the nanotube loading is increased to approximately 20%. PVDF composites also obtained the conductivity of a pure CC nanotube mat (i.e., 12.5- 50/ohm-cm). Composites made from other polymers were unable to reach the conductivity range of a pure CC nanotube mat, even as the nanotube loading was increased beyond 30%>.
• EXAMPLE IX Multilayered structure comprising a first layer of a PVDF composite, a second layer of a thermoplastic or thermoplastic blend/composite, and an optional third adhesive layer between the first and second layers.
• the second layer can be a nylon-6 (6,6, 11, or 12), a nylon-clay composite known for excellent barrier and high heat distortion properties, or a nylon blend.
• the adhesive layer can be a PVDF-nylon blend with relatively lower viscosity.
• This layered structure can be fabricated in a sheet form, or into a container of any shape and size, or into a tubing/pipe.
• the inner layer for the container and tubing forms is preferably a PVDF composite layer.
• the PVDF polymer is known for its resistance to heat and hydrocarbons
• the nylon material in particular, nylon-clay composite is known for its high heat distortion temperature, excellent barrier properties and good mechanical properties, containers and tubing formed from this multilayered structure can be used for safe storage and transport wide-range of hydrocarbons.
• a multilayered tubing may be prepared using the following materials: PVDF composite of Kynar 761 and 13%o loading nanotube, clay-nylon-6 composite and a PVDF (Kynar 741)-Nylon-6(30%>) blend.
• the preparation of a three-layer tubing was carried out in a coextrusion system equipped with three extruders.
• the inner diameter of the tubing and thickness of each layer are: inner diameter: 20 mm; thickness of inner PVDF composite layer: 0.6 mm; thickness of adhesive PVDF-nylon blend layer: 0.2 mm; thickness of outer clay-nylon composite layer: 1 mm.
• EXAMPLE X A PVDF emulsion, Kynar 720, was obtained from Elf Atochem. Hyperion CC carbon nanotubes were added and dispersed into the Kynar 720 emulsion using a high shear blender (i.e., Waring blender). The water/liquid present in this mixture was removed by evaporation and thin specimens of the PVDF composite with dimensions of approximately 0.5' x 3" x. 0.01' were prepared by hot press. The resistivities were measured and reported below:
• Example X confirai The results of Example X confirai that PVDF composites with low bulk resistivity may be prepared using PVDF emulsions. At 20%> nanotube loading, the PVDF composite prepared using this method had a bulk resistivity within the range of a pure CC nantube mat.

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