Low-porosity, functionalized carbon micropowder

Abstract

The present invention comprises novel, low-porosity, functionalized carbon micropowder derived from natural sugars and a method for producing said carbon micropowder.

Description

Detailed Description of the Invention

[0001] 〔Field of the Invention〕 The present invention includes a novel, low-porosity, functionalized carbon micro-powder derived from natural sugars, and a method for producing said carbon micro-powder.

[0002] 〔Background of the Invention〕 Graphite, carbon black, as well as activated carbon micro-powders and activated carbon nano-powders are useful in a wide range of applications including battery and ultracapacitor electrodes, and are also useful as functional fillers in polymers to provide enhanced mechanical properties, thermal stability, barrier properties, electrical conductivity and thermal conductivity. However, as functional fillers in polymers, all of these carbon powders have structural characteristics that result in significant performance trade-offs or limitations in many of the most desirable performance characteristics.

[0003] For example, graphite having a planar structure based on a graphene infrastructure [References 1-2] can be utilized as high aspect ratio platelets that exhibit a very high modulus as well as high electrical and thermal conductivities. However, the planar structure of graphite, which consists of stacked slip planes of graphene, generally results in aggregation and poor dispersion of graphite powder in a polymer matrix, leading to structural defects and compromised mechanical properties due to irregular and relatively unstable polymer-graphite interfaces. In applications where mechanical properties, such as thermal conductivity, are not as critical, graphite powder cannot increase thermal conductivity without simultaneously increasing electrical conductivity, which is undesirable for many thermal interface applications in electronics where the thermal interface material needs to be electrically insulating.

[0004] Carbon black micro-powders and carbon black nano-powders [References 3-5] most commonly consist of spherical primary particles rather than planar platelets like graphite. Spherical particles are inherently less efficient as functional fillers compared to high aspect ratio particles such as platelets or needles, and these spherical particles also tend to aggregate into complex clusters, limiting their dispersion in the polymer matrix and resulting in irregular and unstable interfaces and defects that compromise mechanical properties. Carbon black powders also suffer from the limitation of not allowing a unique improvement in thermal conductivity relative to electrical conductivity.

[0005] Activated carbon powder is typically derived from a cellulose starting material [Reference 6] and generally consists of highly porous particles that can have a wide range of shapes and pore sizes. These materials are classified as macroporous (pores with diameters greater than 50 nm), mesoporous (pores in the range of 2 nm to 50 nm in diameter), and microporous (pores with diameters less than 2 nm) according to the pore size range. Activated carbon powder has a high surface area and high void volume, and as a result, activated carbon powder is very useful in filtration and adsorption applications. However, due to the poor structural integrity, very irregular shape, and poor interfacial compatibility with polymers of activated carbon powder, it is generally not useful as a functional filler in polymers.

[0006] In contrast to graphite, which has a 2-D layered planar structure and is mainly crystalline, carbon black and activated carbon have a complex 3-D structure and are mainly amorphous. Until recently, the bonding of carbon atoms and the detailed structure of these materials were not well understood. However, it is now well established that the curvature, porosity, and 3-D structure of these materials result from the presence of some 5- and 7-membered aromatic rings, in contrast to the 6-membered aromatic rings present in graphite [References 7 - 11]. They are structurally related to fullerenes, which have closed spherical and elliptical structures, because 5- and 6-membered rings alternate.

[0007] 〔Summary of the Invention〕 The present invention includes novel, low-porosity, functionalized carbon micropowders derived from natural sugars, and methods for producing said carbon micropowders.

[0008] Thus, in some embodiments, the present invention provides oxygen-functionalized carbon micropowders characterized by having one or more of the following properties: a) a carbon content of 65% to 95% and an oxygen content of 35% to 5% by weight; b) 500 m 2Specific surface area (BET method) of less than / g; c) percent crystallinity of 5% to 75% (XRD method); d) the particles have a platelet morphology with an aspect ratio greater than 5:1; e) the particles have significant curvature so as not to be planar; and f) the particles have a smooth and pore-free appearance at a magnification of 1,000 times by SEM. In some preferred embodiments, the powder has two or more of characteristics a) to f). In some preferred embodiments, the powder has three or more of characteristics a) to f). In some preferred embodiments, the powder has four or more of characteristics a) to f). In some preferred embodiments, the powder has five or more of characteristics a) to f). In some preferred embodiments, the powder has characteristics a) to f).

[0009] In some preferred embodiments, the present invention provides an oxygen-functionalized carbon micropowder produced by dehydrating a naturally occurring sugar by a method comprising the following steps: a) mixing the sugar with a concentrated strong acid to effect partial dehydration of mainly the carbonaceous material; b) rinsing the carbonaceous material with water to remove the acid; c) drying the material to remove free water; and d) grinding or milling the carbonaceous material to obtain a micropowder. In other preferred embodiments, the present invention provides a method for producing an oxygen-functionalized carbon micropowder, comprising steps a) to d).

[0010] In some preferred embodiments, the sugar is a naturally occurring hexose. In some preferred embodiments, the hexose is selected from the group consisting of fructose, glucose, and galactose. In some preferred embodiments, the sugar is a naturally occurring disaccharide. In some preferred embodiments, the disaccharide is selected from the group consisting of sucrose and lactose. In some preferred embodiments, the concentrated acid is selected from the group consisting of concentrated sulfuric acid and concentrated phosphoric acid. In some preferred embodiments, the sugar is a crystalline sugar. In some preferred embodiments, the sugar crystals have a minimum dimension greater than 100 microns. In some preferred embodiments, the method includes an additional step of heating the micro powder to a temperature above 100° C. to reduce the oxygen content. In some preferred embodiments, the carbon micro powder has an oxygen content of 5% to 35%. In some preferred embodiments, the carbon micro powder has a percent crystallinity (XRD method) of 5% to 75% and / or optionally has one, two, three, four, or five of the characteristics (a) to (e) listed above.

[0011] In some preferred embodiments, the present invention provides a polymer composite comprising one or more of the above-described carbon micro powders and a thermosetting polymer or a thermoplastic polymer. In some preferred embodiments, the composite comprises 1% to 60% carbon micro powder. In some preferred embodiments, the thermosetting resin is an epoxy resin, an unsaturated polyester resin, a polyurethane resin, a cyanoacrylate resin or a silicone resin. In some preferred embodiments, the thermosetting polymer is initially a liquid resin, and the carbon micro powder is dispersed in the liquid resin before the resin is cured (solidified). In some preferred embodiments, the thermoplastic polymer is polyethylene, polypropylene, poly(vinyl chloride), poly(ethylene terephthalate) polycarbonate, polystyrene, polyamide, poly(methyl methacrylate) or polyacrylonitrile. In some preferred embodiments, the bulk thermal conductivity of the composite is greater than 0.27 W / m-K, and the electrical resistivity of the composite is greater than 1.0E10 Ohm-cm.

[0012] [Brief Description of the Drawings] Figure 1 shows a scanning electron microscope (SEM) image of a carbon micro powder prepared from the dehydration of crystalline fructose.

[0013] Figure 2 is a graph of the thermogravimetric analysis of a carbon micro powder prepared from the dehydration of crystalline fructose.

[0014] Figure 3 shows a bar graph comparing the bulk thermal conductivities of epoxy resin composites containing carbon micro powders at various stages derived from crystalline fructose, the micro powders having different heat treatment histories.

[0015] Figure 4 is a plot showing the storage modulus (E'), loss modulus (E'') and tanδ as a function of temperature for an epoxy resin control sample.

[0016] Figure 5 is a plot showing the storage modulus (E’), loss modulus (E’’), and tanδ as a function of temperature for a 20% carbon / epoxy resin composite sample.

[0017] Figure 6 is a plot showing the storage modulus (E’), loss modulus (E’’), and tanδ as a function of temperature for a 40% carbon / epoxy resin composite sample.

[0018] Figure 7 shows photographs of a 30% carbon / poly(vinyl chloride) (PVC) composite sample prepared from carbon micro powder derived from crystalline fructose. The sample in the mold of the cavity after 3 hours of evaporation time and the sample taken out of the mold after 24 hours are shown.

[0019] [Detailed Description of the Invention] A limitation shared by all known types of carbon powders discussed above is that the hydrophobic nature of the carbon powder results in poor interfacial bonding with many polymers (e.g., epoxy resins, unsaturated polyester resins, polyamides, polyesters, poly(vinyl chloride), etc.), resulting in a relatively high-energy and unstable interface between the carbon particles and the polymer. In order to form highly stable composites using these more polar polymers and achieve optimal performance characteristics, it is desirable to have carbon particles that are functionalized to some extent on their outer surfaces with polar oxygen-containing functional groups. One method that has been used to introduce oxygen functionalization to graphite is to treat graphite with a strong oxidizing agent (thereby converting the graphite to graphite oxide), followed by partial reduction to achieve the desired degree of oxygen functionalization [References 15 - 17]. However, such treatments are complex, costly, and generally result in a significant loss of the most desirable performance characteristics (e.g., strength, modulus, electrical conductivity, thermal conductivity) compared to graphite. Many other methods have been disclosed for functionalizing the surface of carbon powders, but those methods generally suffer from the limitations of complexity, high cost, and / or loss of performance characteristics.

[0020] The present invention includes novel, low-porosity, functionalized carbon micropowders derived from natural sugars, and a method for manufacturing said carbon micropowders. Since these carbon powders are derived from sugars based on natural renewable plants, they have unique environmental sustainability advantages over carbon black powders and synthetic graphite derived from non-renewable resources. There are relatively few published examples of well-characterized carbon powder materials derived from natural sugars, and unlike the carbon powders of the present invention, the reported examples are highly porous materials more closely related to known activated carbon powders derived from cellulose-based starting materials [References 12 - 14]. In a related but clearly different result reported by Whitener [Reference 15], an amorphous carbon film was produced by dehydrating glucose with concentrated sulfuric acid to obtain a carbonaceous suspension that forms a carbon film of nanoscale thickness on the surface of water when dripped into water.

[0021] The carbon micropowders of the present invention exhibit a unique combination of structural and performance characteristics not shown by known carbon powders. The carbon micropowders of the present invention exhibit a significant degree of crystallinity, hardness, and structural integrity with very low porosity. The particles are non-flat platelets with a low degree of random curvature that suppresses the aggregation or "stacking" of platelets that occur as flat platelets such as graphite. The degree of oxygen functionalization can be easily controlled by simply heating the powder in the temperature range of about 100 °C to 600 °C, thereby varying the oxygen content to less than about 35 wt% to 5 wt%, thereby allowing the surface polarity of the powder to be adjusted to the polarity of the host polymer for the optimal stability and performance characteristics of the resulting composite.

[0022] The powder of the present invention is derived from natural sugars by a simple one-step dehydration reaction, followed by rinsing, filtering, and drying steps, thereby enabling the powder to be produced inexpensively on a large scale. Preferred starting materials are common crystalline hexose sugars including fructose, glucose, galactose, and crystalline disaccharides, namely sucrose and lactose. The present invention discloses novel carbon micro powders, methods for producing them, and examples of useful applications of these materials, particularly as functional fillers for thermosetting and thermoplastic polymers to enhance thermal stability, thermal conductivity, and mechanical properties.

[0023] Crystalline hexose sugars and disaccharides useful as starting materials for the present invention exist in their crystalline state as cyclic hemiacetals or cyclic hemiketals, 5-membered ring structures (furanose) or 6-membered ring structures (pyranose). When these crystalline sugars are treated with concentrated acid, they rapidly dehydrate, and since the vapor escapes as a carbon solid formed during the dehydration reaction, a black, mainly carbonaceous material with a macrostructure like layered ash, containing very large pores and voids in the range of millimeters to centimeters in size, is formed. The resulting carbon material is easily crushed into flakey solids, which are repeatedly rinsed with distilled water, filtered to remove the acid, and then washed with an organic solvent (e.g., acetone) to remove soluble organic impurities. After air drying, the resulting carbon material is crushed into coarse powder and then ground into fine powder. Grinding can be effectively carried out using a mortar and pestle on a small scale or various types of mills (e.g., ball mill, hammer mill, etc.) on a large scale. The resulting carbon micro powder is then screened using a micro screen sieve to isolate the desired particle size range for specific applications (e.g., <50 microns, 50 - 150 microns, etc.).

[0024] Mainly amorphous, highly porous or complex, irregular in shape and generally 500m 2In contrast to known activated carbon powders or carbon black powders having a surface area greater than / g, the primary particles of the carbon powders of the present invention have a smooth and non-porous surface, a consistent platelet morphology, a low but significant degree of random curvature, and a surface area (BET method) of less than 500 m 2 / g.

[0025] The micropowders provided by the present invention are useful as functional fillers in thermosetting and thermoplastic polymers for producing polymer composites with high-performance characteristics. The micropowders provided by the present invention can be easily dispersed in a wide range of polymers, and the particle size and degree of oxygen functionalization can be varied over a wide range to provide various specific mechanical, electrical, thermal, and other performance characteristics that exceed the performance characteristics exhibited by the polymer without the filler. For example, the micropowders of the present invention containing about 30% oxygen functionalization can be easily dispersed in epoxy resins at a filling level of 5 wt% to 60 wt%, and after curing, show a significant increase in the elastic modulus at room temperature and excellent maintenance of the elastic modulus at high temperatures. Consistent with the improvement in the maintenance of the elastic modulus at high temperatures, the epoxy resin composites of the present invention exhibit a significantly higher glass transition temperature compared to the corresponding cured epoxy resins without carbon micropowders. The increase in the glass transition temperature indicates that the good bonding interaction between the polymer chains and the carbon particles results in a very stable interface.

[0026] Other important performance characteristics of thermosetting and thermoplastic polymers that can be improved using the carbon micropowders of the present invention include, but are not limited to, tensile strength, compressive strength, dimensional stability, and flame retardancy.

[0027] The technique is not limited to the resins used to manufacture the polymer-micro carbon powder composite material. In some embodiments, the polymer is a thermoplastic polymer, a thermosetting polymer, and / or an elastomeric polymer. In some embodiments, the polymer is a liquid thermosetting polymer. In some embodiments, the polymer is an unsaturated polyester polymer. In some embodiments, the polymer is an epoxy polymer. In some embodiments, the polymer is a vinyl ester polymer. In some embodiments, the polymer is a thermosetting polyurethane polymer. In some embodiments, the polymer is an alkyl cyanoacrylate polymer. In some embodiments, the polymer is a propylene polymer. In some embodiments, the polymer is an ester polymer, an amide polymer, a styrene polymer, a vinyl polymer (e.g., a vinyl chloride polymer), an imide polymer, a dimethyl siloxane polymer, an olefin polymer, a carbonate polymer, a nitrile rubber polymer, a styrene-co-acrylic acid polymer, a urethane polymer, a silicone polymer, an ethylene-co-vinyl acetate polymer, a methyl methacrylate polymer, a butyl rubber polymer, an acrylic rubber polymer, an N-vinyl pyrrolidone polymer, an ethylene oxide polymer, an ethylene-propylene-diene monomer polymer, a styrene butadiene rubber polymer, an ethylene-co-octene polymer, a halobutyl rubber polymer, a silylated sulfonated ether ketone polymer, a benzimidazole polymer, a fluorinated benzimidazole polymer, a sulfonated styrene ethylene butylene styrene polymer, a hydroxylated monomer polymer, a hyperbranched monomer polymer, a sulfonated ether ketone polymer, a sulfonated benzimidazole copolymer polymer, a phosphoric acid doped benzimidazole polymer, a sulfonated aryl-enthioether-sulfone polymer, a sulfonated benzimidazole polymer, a phenylene-vinylene polymer, a thiopene polymer, a fluorene polymer, an aniline polymer, a pyrrole polymer, an amidoamine dendrimer polymer, an acrylamide polymer, a vinyl ester polymer, an unsaturated ester polymer, or a styrene butadiene polymer.Furthermore, the technology is found to be used with monomers such as amino acids, sugars, and nucleotides (deoxynucleotides and ribonucleotides).

[0028] Accordingly, in some embodiments, the technology produces polymers that include carbon micro powder in a thermoplastic polymer, a thermosetting polymer, and / or an elastomeric polymer. Further, in some embodiments, the polymer that includes carbon micro powder is an unsaturated polyester polymer. In some embodiments, the polymer that includes carbon micro powder is an epoxy polymer. In some embodiments, the polymer that includes carbon micro powder is polypropylene. In some embodiments, the polymer that includes carbon micro powder is polyester, polyamide, polystyrene, polyvinyl (e.g., polyvinyl chloride), polyimide, polydimethylsiloxane, polyolefin, polycarbonate, nitrile rubber, poly(styrene-co-acrylic acid), polyurethane, silicone, poly(ethylene-co-vinyl acetate), poly(methyl methacrylate), butyl rubber, acrylic rubber, poly(N-vinylpyrrolidone), poly(ethylene oxide), ethylene-propylene-diene monomer rubber, natural rubber, styrene butadiene rubber, poly(ethylene-co-octene), halobutyl rubber, silylated-sulfonated poly(ether ketone), poly(benzimidazole), fluorinated poly(benzimidazole), sulfonated polystyrene ethylene butylene polystyrene, hydroxylated polymer, highly branched polymer, crosslinked sulfonated poly(ether ketone), sulfonated polybenzimidazole, phosphoric acid doped polybenzimidazole, sulfonated polyaryl-enthioether-sulfone, sulfonated polybenzimidazole, poly(phenylene-vinylene), polythiophene, polyfluorene, polyaniline, polypyrrole, polyamidoamine dendrimer, polyacrylamide, vinyl ester, unsaturated polyester or polystyrene butadiene. Furthermore, the technology is found to be used with biomolecules such as proteins, DNA, RNA, lipids, sugars, and crystalline cellulose.

[0029] The epoxy resin composite containing the carbon micro powder of the present invention having a high oxygen content (e.g., 30%) as described above shows almost no improvement in either electrical conductivity or thermal conductivity compared to an epoxy resin without a filler; however, a similar epoxy resin composite containing the carbon micro powder of the present invention having a lower oxygen content (e.g., <25%) shows an improved thermal conductivity along with a negligible improvement in electrical conductivity. This result is surprising and, in contrast to known carbon micro powders and nano powders that generally show a strong correlation between electrical conductivity and thermal conductivity, prevents a significant improvement in one property without a simultaneous improvement in the other property. Therefore, known carbon powder fillers are generally not useful as thermal conductive materials for electronic device applications that require high thermal conductivity but very low electrical conductivity, while the low oxygen content carbon powder of the present invention is useful for these applications.

[0030] The carbon powder of the present invention having a significantly low oxygen content (e.g., <25%) is produced by thermal activation of a powder having a higher oxygen content. For example, when a powder having a high oxygen content is heated briefly (for about 15 minutes in air) at 500 °C, a powder having an oxygen content of less than 25% is obtained. Longer heating under an inert atmosphere supplies a powder having an oxygen content in the range of 25% to less than 5%.

[0031] Although not bound by theory, the surface functionalization of the powders of the present invention results in favorable interfacial interactions with relatively polar polymers such as epoxy resins or polyamide resins, with associated increases in elastic modulus, thermal stability, and Tg. However, when the oxygen functionalization is too high (e.g., >25%), the oxygen groups reduce the structural order and crystallinity of the carbon structure (see the XRD analysis results of the following examples), suppress the movement of vibrational phonons, and as a result, the thermal conductivity appears to be very low compared to, for example, non-functionalized graphite. Amorphous carbon powders can be highly electrically conductive in polymer composites at very low loadings compared to crystalline graphite powders, and such differences in crystallization are known to correlate with thermal conductivity but not necessarily with electrical conductivity. Thus, when the oxygen content on the surface of the carbon powders of the present invention is reduced sufficiently (e.g., <25%) to allow for more efficient movement of vibrational phonons, a disproportionately high ratio of thermal conductivity to electrical conductivity is observed (compared to known carbon powders).

[0032] Studies on the electrical and thermal conductivities of partially reduced graphite oxides [References 15 - 17] provide evidence that these properties are strongly affected by the oxygen content and can be "tuned" to some extent by changing the oxygen content; however, the required oxidation and reduction reactions are much more complex and costly than the simple dehydration reactions used in the present invention, and it has not been demonstrated that a large increase in the thermal conductivity of graphite oxide can be achieved without a corresponding increase in electrical conductivity.

[0033] 〔Examples〕 (Preparation of Functionalized Carbon Materials from Crystalline Fructose) To crystalline fructose (30.107 g, 0.167 mol), concentrated sulfuric acid (38.0 mL, 0.699 mol) in a 150 mL beaker was added. The mixture was stirred with a glass stirring rod for about 90 seconds, as a result, most of the crystalline sugar dissolved with a strong exothermic reaction, the color rapidly darkened, first becoming amber, then brown to black, and subsequently, a highly porous carbon pillar that swelled sufficiently beyond the upper end of the beaker was rapidly formed. The product was cooled at room temperature for 5 minutes, and then it was transferred to a 600 mL beaker containing 300 mL of deionized water. The product was pulverized and dispersed in water using a glass stirring rod, and it was dispersed as a suspended solid in water. This suspension was suction filtered through a Buchner funnel using Whatman #1 qualitative filter paper. The filtered solid was resuspended in 300 mL of deionized water and suction filtered three or more times, and as a result, a clear and colorless water filtrate was obtained by the fourth washing. Next, the solid was suspended twice in 200 mL of acetone and suction filtered to remove organic impurities. Then, the solid was transferred to a 600 mL beaker and dried in air overnight. The yield of the product after air-drying overnight at room temperature was 22.310 grams.

[0034] (Grinding and Sieving of Functionalized Carbon Materials for Producing Carbon Micro-Powders) The product obtained as above was ground using a mortar and pestle and sieved using a standard 45 micron (325 mesh) polyamide sieve to separate and isolate a powder fraction having a particle size distribution with a maximum diameter of less than 45 microns.

[0035] (Scanning Electron Microscopy of Carbon Micro-Powders Derived from Crystalline Fructose) Scanning electron microscope (SEM) images were obtained using a Zeiss LEO 1550VP scanning electron microscope. Figure 1 shows SEM images of one of the carbon micro-materials of the present invention derived from the dehydration of crystalline fructose using concentrated sulfuric acid at four different magnifications. After pulverizing into fine micro-powders, the particle size range shown in the images was isolated by sieving through a standard polyamide sieve of 45 microns (325 mesh). The particles exhibit a smooth and non-porous surface and a platelet morphology with a maximum diameter of less than 50 microns (consistent with the isolation procedure) and a low degree of random curvature. The thickness of the platelets varies considerably, but generally is one to two orders of magnitude smaller than the width dimension (i.e., 0.5 microns to 5 microns), so the aspect ratio of the particles is in the range of 10 to 100. There is no evidence of particle stacking or aggregation apparent in the images.

[0036] (Elemental analysis of carbon micro-powder derived from crystalline fructose) A sample of carbon micro-powder derived from crystalline fructose was dried in an oven at 150 °C (open air atmosphere) until a constant weight was achieved. The total weight loss was 28.4%. Elemental analysis of the sample gave the following results: carbon: 67.11%, hydrogen: 2.69%, oxygen: 28.99%, sulfur: 0.082% (Thermogravimetric analysis (TGA) of carbon micro-powder prepared from crystalline fructose) TGA analysis was performed under a nitrogen atmosphere using a TA Instruments Q500 thermosensor. The sample was air-dried at room temperature and pulverized into micro-powders before running the TGA. The TGA of the produced sample is the graph shown in Figure 2, from which it is shown that the total weight loss from room temperature to 500 °C is 40%. Since the weight loss (presumably the loss of free water) outside the inflection point at about 77 °C continues quite continuously in the remaining temperature range, the progress of a dehydration reaction by a desorption reaction involving hydroxyl (alcohol) functional groups is suggested.

[0037] (Elemental analysis of carbon micro powder derived from crystalline fructose and activated by heating to 500 °C) As described above for the elemental analysis sample, a sample of carbon micro powder derived from crystalline fructose dried at 150 °C was activated by heating in a heating furnace (open air atmosphere) from 25 °C to 500 °C at a heating rate of 34 °C / min. When the temperature reached 500 °C (14 minutes), the sample was immediately removed from the heating furnace and cooled to room temperature. The sample showed a weight loss of 31.7%. Elemental analysis of the sample (Galbraith Laboratories, Knoxville, TN) gave the following results: carbon: 73.65%, hydrogen: 2.68%, oxygen: 22.69%.

[0038] (Specific surface area analysis (BET method) of carbon micro powder derived from crystalline fructose and heat-activated at 500 °C) A sample of carbon micro powder derived from crystalline fructose was dried in a dryer (open air atmosphere) at 150 °C until a constant weight was achieved. The coarse powder was then ball milled at 330 rpm for 2.0 hours (dry, 1 cm diameter ceramic balls) to obtain a fine micro powder with a maximum particle size of approximately 50 μm. The micro powder was activated by heating to 500 °C twice at a heating rate of 34 °C per minute. Each time the sample reached 500 °C, heating was stopped and the sample was immediately cooled to room temperature. The total weight loss was 37.7%. Specific surface area analysis of the sample (BET method, Particle Technology Labs, Downers Grove, IL) showed a surface area of 325.08 m 2 / g.

[0039] (X-ray powder diffraction (XRD) analysis of carbon micro powder derived from crystalline fructose with respect to commercially available graphite) XRD analysis was performed using a Bruker D8 Discover XRD instrument. Two carbon micro powders of the present invention, prepared as described above for elemental analysis samples, were analyzed to determine their percent crystallinity. One of the samples was dried to a constant weight at 150 °C without further heat treatment, while the other sample was further activated by heating to 500 °C. The XRD analysis showed percent crystallinities of 9.2% and 27.7% for the two samples, respectively. This result indicates that the crystallinity increases significantly as the oxygen content decreases with heat treatment. For comparison, XRD analysis was performed on a commercially available graphite powder sample. As expected, the graphite was highly crystalline (95.4%).

[0040] (Preparation of 20% Carbon / Epoxy Resin Composite Test Samples Using Carbon Micro Powders Derived from Crystalline Fructose) The carbon micro powder (1.298 g, <45 microns) prepared from crystalline fructose as described above was dispersed in 4.422 g of an epoxy resin (bisphenol A resin) using an IKA T 25 overhead stator-rotor disperser with an S25N-8G (8 mm diameter) micro mixing head operating at 25,000 rpm for a mixing time of 10 minutes. The mixture was degassed under vacuum until foaming subsided and the surface of the dispersion appeared smooth and bubble-free. A diethylenetriamine curing agent (1.0 g) was added, and the mixture was gently stirred with a spatula for 5 minutes, then poured into a cavity mold to prepare test specimens for dynamic mechanical analysis. The test specimens were cured at room temperature for 2 days and then heat-cured at 150 °C for 1.0 hour.

[0041] (Measurement of Electrical Conductivity of Carbon / Epoxy Resin Composite Samples Containing 20% and 40% of Carbon Micro Powders Derived from Crystalline Fructose and Heat-Activated at 500 °C) Measurements of the resistivity (reciprocal of the conductivity) of 20% and 40% carbon / epoxy resin test samples prepared from carbon micro powder derived from crystalline fructose and activated at 500 °C were carried out. The measurements were performed using a Static Solutions Ohm-Stat RT-1000 apparatus. The 20% and 40% carbon-loaded composite samples showed resistivities of 1.23E13 ohm-cm and 9.81E12 ohm-cm, respectively, indicating very low electrical conductivity (i.e., high insulation).

[0042] (Measurement of the thermal conductivity of carbon / epoxy resin composite samples containing carbon micro powder derived from crystalline fructose) Thermal conductivity measurements were performed by ThermTest Inc. (Fredericton, NB, Canada) using a ThermTest TPS 2500 S Analyzer. Figure 3 shows a bar graph comparing the bulk thermal conductivities of epoxy resin composites containing carbon micro powder at various stages derived from crystalline fructose. The upper graph shows data for carbon micro powder dried to a constant weight at 150 °C without further thermal activation, while the lower graph shows data for carbon micro powder dried to a constant weight at 150 °C and then further activated by heating to 500 °C. Carbon micro powder dried at 150 °C without further heating activation showed a statistically significant but very small improvement in bulk thermal conductivity compared to the carbon-free epoxy resin control (e.g., +0.0035 W / m-K, a 1.3% increase relative to the epoxy resin control, 20% loading). In contrast, carbon micro powder further heat-activated by heating to 500 °C showed a much larger improvement in bulk thermal conductivity compared to the epoxy resin control (e.g., +0.0162 W / m-K, a 6.0% increase relative to the epoxy resin control, 20% loading).

[0043] (Dynamic mechanical analysis (DMA) of 20% and 40% carbon / epoxy resin samples) The 20% and 40% carbon / epoxy resin samples, along with an epoxy resin control sample, were analyzed by DMA using a TA Instruments RSA III Dynamic Mechanical Analyzer. The analysis was performed on specimens having dimensions of approximately 25 mm × 10 mm × 2 mm in three-point bending mode as a temperature ramp study at a heating rate of 5 °C / min and a frequency of 1 Hz. Figures 4, 5, and 6 show plots of the DMA results for the epoxy resin control, 20%, and 40% carbon / epoxy resin samples, respectively. Each plot shows the storage modulus (E’), loss modulus (E’’), and tanδ as a function of temperature.

[0044] Figure 4 is a plot of the epoxy resin control sample, showing an initial storage modulus of 2.9 GPa at 30 °C, which gradually decreases with increasing temperature to 1.0 GPa at 78 °C and then decreases rapidly as the temperature continues to rise. The glass transition temperature (Tg) can be estimated as the temperature at which the rate of change of E’ (i.e., the second derivative) reaches a maximum, or the temperature at which E’’ reaches a maximum value, or the temperature at which tanδ reaches a maximum value, from each of the three parameters E’, E’’, or tanδ. The estimated values of E’ and E’’ both indicate that the Tg of the epoxy resin control is approximately 80 °C, while the maximum value of tanδ indicates that the Tg is approximately 87 °C (note: it is typical for the estimated value from tanδ to be higher).

[0045] Figure 5 is a plot of the 20% carbon / epoxy resin composite sample, showing an initial storage modulus of 3.9 GPa at 30 °C (i.e., a 35% increase relative to the epoxy resin control), which gradually decreases with increasing temperature to 1.0 GPa at 93 °C (i.e., 15 degrees higher than the corresponding temperature of the epoxy resin control) and then decreases rapidly as the temperature continues to rise. The Tg estimated from E’ or E’’ is approximately 95 °C (i.e., 15 degrees higher than the epoxy resin control), while the Tg estimated from tanδ is approximately 102 °C (the Tg is also 15 degrees higher than the epoxy resin control).

[0046] Figure 6 is a plot of the 40% carbon / epoxy resin composite sample, showing an initial storage modulus at 30 °C of 3.7 GPa (i.e., a 28% increase relative to the epoxy resin control), which gradually decreases with increasing temperature to 1.0 GPa at 100 °C (i.e., 22 degrees higher than the corresponding temperature of the epoxy resin control), and then rapidly decreases as the temperature continues to rise. The Tg estimated from E’ or E’’ is about 100 °C (i.e., 20 degrees higher than the epoxy resin control), while the Tg estimated from tanδ is about 105 °C (18 degrees higher than the epoxy resin control).

[0047] (Elemental analysis of carbon micro powder derived from crystalline fructose and activated by heating to 500 °C in nitrogen atmosphere) A sample of carbon micro powder derived from crystalline fructose, dried to a constant weight at 150 °C (open air atmosphere as described above), was activated by heating in a nitrogen atmosphere furnace from 25 °C to 500 °C at a heating rate of about 30 °C / min. When the temperature reached 500 °C (15 minutes), the temperature was held at 500 °C for an additional 10 minutes, and then slowly cooled back to room temperature under a nitrogen atmosphere. The sample showed a weight loss of 13.4%. Elemental analysis of the sample (Galbraith Laboratories, Knoxville, TN) gave the following results: carbon: 75.57%, hydrogen: 2.42%, oxygen: 19.66%.

[0048] (Elemental analysis of carbon micro powder derived from crystalline fructose and activated by heating to 600 °C in nitrogen atmosphere) A sample of carbon micro powder derived from crystalline fructose, dried to a constant weight at 150 °C (in an open air atmosphere as described above), was activated by heating in a nitrogen atmosphere furnace at a heating rate of about 25 °C / min from 25 °C to 600 °C. When the temperature reached 600 °C (for 15 minutes), the temperature was held at 600 °C for an additional 10 minutes and then slowly cooled back to room temperature under a nitrogen atmosphere. The sample showed a weight loss of 33.9%. Elemental analysis of the sample (Galbraith Laboratories, Knoxville, TN) gave the following results: carbon: 86.62%, hydrogen: 2.55%, oxygen: 8.81%.

[0049] (Measurement of Thermal Conductivity of Carbon Micro Powder Derived from Crystalline Fructose) Thermal conductivity measurements were performed by ThermTest Inc. (Fredericton, NB, Canada) using a ThermTest TPS 2500 S analyzer. Bulk thermal conductivity was measured for two carbon micro powders with different heat treatment histories. The first measurement was performed on carbon micro powder dried to a constant weight at 150 °C in open air and without further thermal activation. On the other hand, the second measurement was performed on carbon micro powder dried to a constant weight at 150 °C in open air and then further activated by heating to 600 °C under a nitrogen atmosphere as described above. The carbon micro powder dried at 150 °C and without further thermal activation showed a bulk thermal conductivity of 0.1014 W / m-K (average of 5 measurements, standard deviation = 0.0002 W / m-K). The carbon micro powder dried at 150 °C and heated to 600 °C under a nitrogen atmosphere for further activation showed a bulk thermal conductivity of 0.1119 W / m-K (average of 5 measurements, standard deviation = 0.0002), which was a 10% increase compared to the sample not activated at 600 °C.

[0050] (Preparation of 30% Carbon / Poly(vinyl chloride) (PVC) Composite Samples Using Carbon Micro Powder Derived from Crystalline Fructose) As described above, carbon micro powder (1.532 g) prepared from crystalline fructose was dry mixed with PVC powder (3.527 g, Aldrich Lot# 13328 TDV) in a mixed glass vial and stirred with a spatula until uniformly mixed. By adding THF solvent (15 mL, laboratory reagent grade) while stirring, a viscous but flowable suspension was obtained as a result. The mixed glass vial was cooled in an ice bath, and the suspension was mixed using an IKA T 25 overhead stator-rotor disperser having an S25N-8G (8 mm diameter) micromixing head. The mixing RPM was gradually increased to 25,000 over 5 minutes, and then the mixing was continued at 25,000 RPM for an additional 5 minutes. The resulting suspension was poured into a cavity mold and left at room temperature in open air to evaporate THF. After 3 hours, the sample was dried until it could be touched and removed from the mold. They had the consistency of soft vinyl. After 24 hours, the sample had a hard but flexible consistency and continued to harden as the residual THF evaporated. Figure 7 shows a photograph of the sample in the cavity mold after 3 hours and a photograph of the sample removed from the mold after 24 hours.

[0051] [References] [Reference 1] “Graphite” Wikipedia [Reference 2] Jui, G.; Wilhelm, H.; L’Heureux, J. L.; “High Purity Graphite Powders for High Performance”, Technical Bulletin, Timcal Graphite and Carbon, Timcal Ltd. [Reference 3] “Carbon Black”, Wikipedia [Reference 4] “Carbon Additives for Polymer Compounds”, Technical Bulletin, Timcal Graphite and Carbon, Timcal Ltd. [Literature 5] "Carbon Powders for Lithium Ion Battery Systems" Technical Bulletin, TImcal Graphite and Carbon, Timcal Ltd. [Literature 6] Manocha, S. M.; "Porous Carbons", Sadhana: Academy Proceedings in Engineering and Sciences, 28, 335, 2003 [Literature 7] Harris, P. J. F.; "New Perspectives on the Structure of Graphitic Carbons", Critical Reviews in Solid State and Materials Sciences, 30, 255, 2005 [Literature 8] Harris, P. J. F.; "Imaging the Atomic Structure of Activated Carbon", J. Phys.: Condens. Matter, 20, 362201, 2008 [Literature 9] Smith, M. A.; Foley, H. C.; Lobo, R. F.; "A Simple Model Describes the PDF of a Non-graphatizing Carbon", Carbon, 42, 241, 2004 [Literature 10] Li, Y.; Inam; F.; Kumar, A.; Thorp, M. F.; Drabold, D. A.; "Pentagonal Puckering in a Sheet of Amorphous Graphene", Phys. Status Solidi B, 9, 2082, 2011 [Literature 11] Marriott, A. S.; Hunt, A. J.; Bergstrom, E.; Wilson, K.; Budarin, W. L.; Thomas-Oates, J.; Clark, J. H.; Frydson, R.; “Investigating the Structure of Biomass-derived Non-graphatizing Mesoporous Carbons by Electron Energy Loss Spectroscopy in the Transmission Electron Micrcoscope and X-ray Photoelectron Spectroscopy”, Carbon, 67, 514, 2014 [Literature 12] Yu, J.; Yoon, S. B.; Chai, G. S.; “Ordered Uniform Porous Carbon by Carbonization of Sugars”, Carbon, 39, 1421, 2001 [Literature 13] Harmas, M; Thomberg, T.; Romann, T.; Janes, A.; Lust, E.; “Carbon for Energy Storage Derived from Granulated White Sugar by Hydrothermal Carbonization and Subsequent Zinc Chloride Activation”, J. Electrochem. Soc., 164, A1866, 2017 [Literature 14] Fechler, N.; Wohlgemuth, S.; Jaker, P.; Antonietti, M.; “Salt and Sugar: Direct Synthesis of High Surface Area Carbon Materials at Low Temperatures via Hydrothermal Carbonization of Glucose under Hypersaline Conditions”, J. Mater. Chem. A, 1, 9418, 2013 [Literature 15] Whitener, K; “Rapid Synthesis of Thin Amorphous Carbon Films by Sugar Dehydration and Dispersion”, AIMS Material Science, 3(4), 1309, 2016 [Literature 16] Morimoto, N.; Kubo, T.; Nishina, Y.; “Tailoring the Oxygen Content of Graphite and Reduced Graphene Oxide for Specific Applications”, Scientific Reports, 6, 21715, 2016 [Literature 17] Zhou, T.; Liu, F.; Suganuma, K.; Nagao, S.; “Use of Graphene Oxide in Achieving High Overall Thermal Properties of Polymer for Printed Electronics”, RSC Adv., 6, 20621, 2016 [Literature 18] Park, W.; Hu, J.; Jauregui, L. A.; Ruan, X.; Chen, Y. P.; Electrical and Thermal Conductivities of Reduced Graphene Oxide / Polystyrene Composites" [Document 19] Liao, K.; Aoyama, S.; Abdala, A. A.; Macosko, C.; “Does Graphene Change Tg of Nanocomposites?”, Macromolecules, 47, 8311, 2014 All publications and patents mentioned in the above specification are hereby incorporated by reference in their entirety for all purposes. Various modifications and variations of the described compositions, methods, and uses of the technology will be apparent to those skilled in the art without departing from the scope and spirit of the described technology. Although the technology has been described in relation to specific exemplary embodiments, it should be understood that the claimed invention should not be unduly limited to such specific embodiments. Indeed, various modifications of the described forms for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims. Figure 7 shows a photograph of the sample after 24 hours.

Brief Description of the Drawings

[0052]

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Claims

1. An oxygen-functionalized carbon micro powder comprising carbon particles and having the following characteristics a), c), d), e), and f): a) A carbon content of 65% to 95% and an oxygen content of 35% to 5% by weight; c) A percent crystallinity of 5% to 75% (XRD method); d) The particles have a platelet morphology with an aspect ratio greater than 5:1; e) The particles have a significant curvature such that they are not planar; and f) The particles have a smooth and pore-free appearance at a magnification of 1,000 times by SEM.

2. The oxygen-functionalized carbon micro powder according to claim 1, wherein the powder further has the following characteristic b): b) Specific surface area (BET method) of less than 500 m² / g. ２ / g.

3. A polymer composite comprising one or more of the carbon micro powders according to claim 1 or 2 and a thermosetting polymer or a thermoplastic polymer.

4. The polymer composite according to claim 3, wherein the composite comprises 1% to 60% of the carbon micro powder.

5. The polymer composite according to claim 3, wherein the thermosetting polymer or the thermoplastic polymer is an epoxy resin, an unsaturated polyester resin, a polyurethane resin, a cyanoacrylate resin, or a silicone resin.

6. The polymer composite according to claim 3, wherein the thermosetting polymer is initially a liquid resin, and the carbon micro powder is dispersed in the liquid resin before the resin is cured (solidified).

7. The polymer composite according to claim 3, wherein the thermoplastic polymer is polyethylene, polypropylene, poly(vinyl chloride), poly(ethylene terephthalate), polycarbonate, polystyrene, polyamide, poly(methyl methacrylate), or polyacrylonitrile.

8. The polymer composite according to claim 3, wherein the bulk thermal conductivity of the composite is greater than 0.27 W / m-K and the electrical resistivity of the composite is greater than 1.0E10 ohm-cm.

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