Patent Application
20250171312
The present application relates to low-cost carbon nano-onions and method for their production.
Carbon materials have been crucial in human civilization's evolution and laid the foundation for numerous technological and social advancements. Coal, graphite, and activated carbon are examples of traditional carbon compounds extensively used in various industries, from water treatment to energy production. Graphene, fullerene, carbon nanotubes (CNTs), and graphdiyne are examples of novel carbon allotropes that have recently appeared and attracted substantial attention because of their distinctive architectures and extraordinary capabilities. These carbon allotropes have been widely explored in energy storage, biosensing, biology, biomedicine, photovoltaics, catalysts, environment, etc. (Wang et al., “Biomass-Derived Carbon Materials: Controllable Preparation and Versatile Applications,” Small 17(40): e2008079 (2021)).
A form of carbon nanomaterial known as a carbon nano onion (CNO) comprises several concentric carbon shells that resemble fullerenes (C60) (Zeiger et al., “Review: Carbon onions for electrochemical energy storage,” J. Mater. Chem. A 4(9):3172-3196 (2016)). CNO refers to their structure; layered like an onion, CNOs are composed of closely spaced graphitic layers with quasi-spherical and polyhedral shapes, with each shell enclosing the one before it (Zeiger et al., “Review: Carbon Onions for Electrochemical Energy Storage,” J. Mater. Chem. A 4(9):3172-3196 (2016)). Depending on the synthesis process and environmental factors, they typically range in size from 2 to 200 nm (Dhand et al., “A Comprehensive Review on the Prospects of Multi-functional Carbon Nano Onions as an Effective, High-performance Energy Storage Material,” Carbon N. Y. 175:534-575 (2021)). Because of their zero dimensional nanostructure, high surface area, electric conductivity, low cytotoxicity, remarkable optoelectrical properties, CNOs have many potential applications, such as supercapacitors (Liu et al., “Hierarchical Porous Carbon Based on the Self-templating Structure of Rice Husk for High-performance Supercapacitors,” RSC Adv. 5(25):19294-19300 (2015)), electronics, biosensing (Mohapatra et al., “Enzymatic and Non-enzymatic Electrochemical Glucose Sensor Based on Carbon Nano-onions,” Appl. Surf Sci. 442:332-341 (2018)), photovoltaics, catalysis (Zhang et al., “Synthesis of Hollow Carbon Nano-onions and Their Use for Electrochemical Hydrogen Storage,” Carbon N. Y. 50(10):3513-3521 (2012)), drug delivery (Miriyala et al., “Synthesis of Carbon Onion and Its Application as a Porous Carrier For Amorphous Drug Delivery,” Crystals 10(4):281 (2020); Majumder et al., “Functionalized Carbon Nano Onion as a Novel Drug Delivery System for Brain Targeting,” J. Drug Deliv. Sci. Technol. 63(3):102414 (2021); Bartkowski and Giordani, “Carbon Nano-onions as Potential Nanocarriers for Drug Delivery,” Dalt. Trans. 50(7):2300-2309 (2021)), biomedical diagnostics (Xin et al., “Fabrication of Ultra-bright Carbon Nano-onions Via a One-step Microwave Pyrolysis of Fish Scale Waste in Seconds,” Green Chem. 24:3969 (2022)), and lubricant additives (Luo et al., “One-step Gas-liquid Detonation Synthesis of Carbon Nano-onions and Their Tribological Performance as Lubricant Additives,” Diam. Relat. Mater. 97:107448 (2019)).
Iijima published the first study on CNOs in 1980, describing how they were produced as a byproduct of carbon nanotube manufacturing (S. I. Li, “Direct Observation of the Tetrahedral Bonding in Graphitized Carbon Black By High Resolution Electron Microscopy,” J. Cryst. Growth 50:675-683 (1980)). Ugarte initially revealed the presence of the onion-structure, quasi-spherical, hollowed cage with concentric graphene layers in 1992 after exposing carbon soot to a powerful electron beam under harsh conditions (D. Ugarte, “Curling and Closure of Graphitic Networks Under Electron-beam Irradiation,” Nature 359(6397):707-709 (1992)). Since then, scientists have experimented with numerous methods to create CNOs, including high-temperature annealing of nano diamonds (Kuznetsov et al., “Onion-like Carbon From Ultra-disperse Diamond,” Chem. Phys. Lett. 222: 343-348 (1994)), arc discharge underwater (Sano et al., “Properties of Carbon Onions Produced by an Arc Discharge in Water,” J. Appl. Phys. 92(5):2783-2788 (2002)), chemical vapor deposition (CVD) (Chen et al., “New Method of Carbon Onion Growth by Radio-frequency Plasma-enhanced Chemical Vapor Deposition,” Chem. Phys. Lett. 336(3-4):201-204 (2001)), high-energy ball milling (Huang et al., “Highly Curved Carbon Nanostructures Produced by Ball-milling,” Chem. Phys. Lett. 303(1-2):130-134 (1999)), laser ablation (Dorobantu et al., “Pulse Laser Ablation System for Carbon Nano-onions Fabrication,” Surf Eng. Appl. Electrochem. 50(5):390-394 (2014); Calabro et al., “Liquid-phase Laser Ablation Synthesis of Graphene Quantum Dots From Carbon Nano-onions: Comparison With Chemical Oxidation,” J. Colloid Interface Sci. 527:132-140 (2018)), flame synthesis or pyrolysis (Mongwe et al., “Synthesis of Chain-like Carbon Nano-onions by a Flame Assisted Pyrolysis Technique Using Different Collecting Plates,” Diam. Relat. Mater. 90:135-143 (2018)), ion implantation (Cabioc'h et al., “Fourier Transform Infra-red Characterization of Carbon Onions Produced by Carbon-ion Implantation,” Chem. Phys. Lett. 285(3-4):216-220 (1998)), etc.
Kuzenetsov et al. successfully demonstrated the annealing of nanodiamonds (NDs) under vacuum and high temperatures ranging from 1500 to 2000° C., which is also the most common method to produce CNOs (Kuznetsov et al., “Onion-like Carbon From Ultra-disperse Diamond,” Chem. Phys. Lett. 222: 343-348 (1994)). Sano et al. developed an approach for producing CNOs by arc discharge when two electrodes made of graphite are submerged in water (Sano et al., “Properties of Carbon Onions Produced by an Arc Discharge in Water,” J. Appl. Phys. 92(5):2783-2788 (2002)). Another common approach for synthesizing CNO was CVD of hydrocarbon gases (methane, acetylene, and ethylene) in the presence of metal catalysts (such as nickel, iron, and cobalt) using high pressures and temperatures (Du et al., “A Facile Approach for Synthesis and In Situ Modification of Onion-like Carbon With Molybdenum Carbide,” Phys. Status Solidi Appl. Mater. Sci. 208(4):878-881 (2011); Chatterjee et al., “Nitrogen-rich Carbon Nano-onions for Oxygen Reduction Reaction,” Carbon N. Y. 130:645-651 (2018)). Alternatively, CNO was synthesized by ball-milling graphite powder mixed with an aluminum catalyst (Estrada-Guel et al., “Synthesis of Nano Carbon Onions by a Mechanical-Chemical Route,” Microsc. Microanal. 17(S2):1552-1553 (2011)), or liquid-phase laser ablation of toluene with silicon (Yang et al., “Luminescent Hollow Carbon Shells and Fullerene-like Carbon Spheres Produced by Laser Ablation With Toluene,” J. Mater. Chem. 21(12):4432-4436 (2011)). Recently, Jin et al. fabricated porous CNOs from rice husk via a multi-step process involving nickel catalyst and nitric acid (Jin et al., “Synthesis of Porous Carbon Nano-onions Derived From Rice Husk for High-performance Supercapacitors,” Appl. Surf Sci. 488:593-599 (2019)). A recent study also reported CNOs from fish scales using microwave pyrolysis (Xin et al., “Fabrication of Ultra-bright Carbon Nano-onions Via a One-step Microwave Pyrolysis of Fish Scale Waste in Seconds,” Green Chem. 24:3969 pp. 1-2 (2022)).
While CNO can be produced using several different approaches, the current synthesis of CNOs is hindered by high precursor costs and the synthesis methods often requiring costly catalysts, harsh chemicals, solvents, non-atmospheric pressures, and high energy. The scalability of the production is also constrained by these factors, making it challenging to synthesize CNOs in large quantities (Xin et al., “Fabrication of Ultra-bright Carbon Nano-onions Via a One-step Microwave Pyrolysis of Fish Scale Waste in Seconds,” Green Chem. 24:3969 (2022)). According to literature, the costs of CNOs (>$1M/ton) are several orders higher compared to other carbon materials including carbon nanotubes ($100,000/ton) and graphene nano platelets ($70,000/ton) (Liu et al., “Carbon Nano-Onions Made Directly from CO2 by Molten Electrolysis for Greenhouse Gas Mitigation,” Adv. Sustain. Syst. 3(10):1900056 (2019)). For enabling wide applications of CNOs, a novel synthesis must be developed to significantly reduce the costs of CNOs.
The present application is directed to overcoming these and other deficiencies in the art.
One aspect of the present application relates to a carbon nano-onion comprising a structure comprising a plurality of substantially concentric carbon shells. The substantially concentric carbon shells have a spherical, quasi-spherical, and/or polyhedral configuration or combinations thereof, wherein said substantially concentric carbon shells have surfaces functionalized with oxygen-containing functional groups.
Another aspect of the present application relates to a composite material comprising the carbon non-onion disclosed herein and a polymer mixed with said carbon nano-onion.
Another aspect of the present application relates to a method of preparing an oxygen-functionalized carbon nano-onion. The method comprises providing a fixed carbon-containing source and treating the fixed carbon-containing source by joule heating under conditions effective to transform the fixed carbon-containing source into an oxygen-functionalized carbon nano-onion comprising a plurality of substantially concentric carbon shells, where said substantially concentric carbon shells have a spherical, quasi-spherical, and/or polyhedral configuration or combinations thereof.
Another aspect of the present application relates to a method of preparing a composite material. The method comprises providing the carbon nano-onion disclosed herein, blending a polymer with the carbon nano-onion to form a mixture, and forming a composite material from the mixture.
Carbon nano-onion (CNO) is a special class of carbon nanomaterials with impressive characteristics. It has been widely used in electronics, photovoltaics, energy storage, biosensing, biomedicine, and catalysts. Conventional CNO fabrication often demands costly petrochemical-based precursors, catalysts, harsh chemicals, hazardous solvent, and vacuum pressure. Due to its extremely high costs, CNO applications are limited. Herein, the joule-heating based synthesis of low-cost CNOs produced using biomass residues, such as lignin and biochar is reported. This method does not require solvent, chemicals, catalysts, or specific gas environment and can produce oxygen functionalized CNOs within short synthesis times. The CNOs produced using three different feedstocks had similar electric conductivity, similar particle sizes and crystalline structures. Their oxygen functional groups can be tuned by controlling the synthesis conditions, also showing high dispersity in various organic solvents. When the CNOs were used as additives in polylactic acid, 0.5% mass loading could increase tensile strength and modulus by 43.6% and 128.4%, respectively. When applied as additives in polymer, CNOs based on different precursors resulted in similar tensile properties in PLA, which was agnostic to the precursor origin of CNOs. Overall, this work shows a promising pathway to valorize biomass residues in an environmentally friendly, market-feasible approach.
The present application discloses a super facile and green route for synthesizing biobased low-cost CNOs using electricity alone. This non-catalytic, solvent and chemical-free approach can produce oxygen-functionalized CNOs with tunable properties from biomass residue byproducts, such as lignin and biochar. Lignin is the second most abundant biopolymer on earth, abundantly available from pulping or cellulosic biorefineries as byproducts, which the estimation of 225 million tons available by 2030. The majority of lignin is currently burned for heat and power (Ekielski and Mishra, “Lignin for Bioeconomy: The Present and Future Role of Technical Lignin,” Int. J. Mol. Sci. 22(1):1-24 (2021), which is hereby incorporated by reference in its entirety), whereas lignin valorization remains the major hurdle for emerging biorefineries. Biochar is also an abundantly available low-cost material, easily produced by biomass pyrolysis. While various biochar applications are explored, it is generally considered for soil amendments with estimated costs of $200-400/tons. Thus, making low-cost CNOs from lignin or biochar for advanced applications will greatly benefit renewable industries.
The present application discloses the production of CNOs using lignins and biochar based on a joule heating method. The biobased CNOs were characterized to show their tunable structures and properties. The CNOs were further used as an additive in polylactic acid (PLA) to produce property-advanced biopolymer nearly agnostic to the CNO precursors. PLA is the most commonly used biobased and biodegradable polymer. However, its high cost, relatively low mechanical performance, low thermal tolerance, and poor gas barrier properties relative to petroleum-based plastics hinder its market applications (Dehnou et al., “A Review: Studying the Effect of Graphene Nanoparticles on Mechanical, Physical and Thermal Properties of Polylactic Acid Polymer,” RSC Adv., 13(6):3976-4006 (2023), which is hereby incorporated by reference in its entirety). The results described herein show that CNO-engineered PLA nanocarbon composites can overcome the abovementioned weaknesses, positioning PLA for broader and advanced applications.
One aspect of the present application relates to a carbon nano-onion comprising a structure comprising a plurality of substantially concentric carbon shells. The substantially concentric carbon shells have a spherical, quasi-spherical, and/or polyhedral configuration or combinations thereof, wherein said substantially concentric carbon shells have surfaces functionalized with oxygen-containing functional groups.
In some embodiments, the substantially concentric carbon shells can have surfaces functionalized with any heteroatom-containing functional groups and/or metals. Functionalization of the surfaces can be modified according to the use intended for the carbon nano-onions.
In some embodiments, the substantially concentric carbon shells have surfaces functionalized with oxygen-containing functional groups and nitrogen-containing functional groups. In some embodiments, the substantially concentric carbon shells have surfaces functionalized with oxygen-containing functional groups and sulfur-containing functional groups.
In some embodiments, the carbon nano-onion, or the carbon nano-onion structure of the present disclosure is prepared by joule heat treatment of a fixed carbon-containing source. Joule heating (also referred to as resistive, resistance, or Ohmic heating) is a process in which thermal energy is produced by passing current though an electrical conductor. An embodiment of a joule heating reactor of the present disclosure is illustrated in
The carbon nano-onion of the present disclosure can be prepared by joule heat treatment of any fixed carbon-containing source. In some embodiments, the fixed carbon-containing source is biomass.
The term “biomass,” as used herein, refers to renewable organic material that comes from plants and animals. In some embodiments of the carbon nano-onion, the biomass is lignin, biochar, any fixed carbon-containing biomass, or mixtures thereof. Suitable types of lignin include, without limitation, Hardwood Kraft Lignin (HKL), Softwood Kraft Lignin (SKL), Oragnosolv Hardwood Lignin, Oragnosolv Softwood Lignin, Herbaceous biomass-derived lignin, Acetosolv Lignin, Milled Wood Lignin (MWL), steam-explosion lignin, plasma-extraction lignin, chemically modified lignins, or combinations thereof.
The structure of the carbon nano-onions of the present disclosure can have concentric carbon shells, meaning the shells share a common center and larger shells surround smaller shells. When two or more shapes are perfectly concentric, the centers of the objects align exactly, and they share the same axis. In some embodiments, the structure of the carbon nano-onion of the present disclosure comprises substantially concentric shells, where the centers of the shells might be slightly offset, but the deviation is small enough that for the purposes of the design and function of the carbon nano-onion, the shells can be treated as if they are concentric. In some embodiments, exact alignment is not critical and slight deviations are expected. In some embodiments of the carbon nano-onion, each of the plurality of substantially concentric carbon shells are spaced about 0.3 nm to about 0.4 nm, or any amount or range therein, from its adjacent carbon shell. For example, in some embodiments each of the plurality of substantially concentric carbon shells are spaced about 0.31 nm to about 0.32 nm, about 0.31 nm to about 0.33 nm, 0.31 nm to about 0.34 nm, about 0.31 nm to about 0.35 nm, 0.31 nm to about 0.36 nm, about 0.31 nm to about 0.37 nm, about 0.31 nm to about 0.38 nm, about 0.31 nm to about 0.39 nm, about 0.33 nm to about 0.34 nm, about 0.33 nm to about 0.35 nm, 0.33 nm to about 0.36 nm, about 0.33 nm to about 0.37 nm, about 0.33 nm to about 0.38 nm, about 0.33 nm to about 0.39 nm, about 0.33 nm to about 0.4 nm, about 0.35 nm to about 0.36 nm, about 0.35 nm to about 0.37 nm, about 0.35 nm to about 0.38 nm, about 0.35 nm to about 0.39 nm, about 0.35 nm to about 0.4 nm, about 0.37 nm to about 0.38 nm, about 0.37 nm to about 0.39 nm, about 0.37 nm to about 0.4 nm, or about 0.39 nm to about 0.4 nm from its adjacent carbon shell. In some embodiments, the plurality of substantially concentric carbon shells are in the form of spherical graphitic layers. In some embodiments, the plurality of substantially concentric carbon shells are in the form of quasi-spherical graphitic layers. In some embodiments, the plurality of substantially concentric carbon shells are in the form of polyhedral graphitic layers. In some embodiments, the plurality of substantially concentric carbon shells comprise sp2 hybridized carbons.
In some embodiments, the structure of the carbon nano-onion comprises a stack in a turbostratic form. The term “turbostratic,” as used herein, refers to a class of carbon having structural ordering in between that of amorphous carbon and that of crystalline graphite. Unlike in a pristine graphite structure, the carbon atoms in turbostratic carbon are not arranged in a regular, well-defined crystal lattice. Rather, the orientation of the carbon layers is more asymmetrical.
In some embodiments of the carbon nano-onion, the oxygen-containing functional groups comprise ethers, esters, carboxylic acids, ketones, aldehydes, or combinations thereof.
Another aspect of the present application relates to a composite material comprising the carbon non-onion disclosed herein and a polymer mixed with said carbon nano-onion.
In some embodiments, the polymer is a thermoplastic polymer. In some embodiments, the thermoplastic polymer comprises a plastic, polylactic acid, polyamide 6 (PA6), polyhydroxyalkanoates (PHAs), polyesters, polyethylene (PE), polypropylene (PP), polystyrene, polyvinyl chloride, or combinations thereof. Other thermoplastic polymers are known and can be used in the composite materials described herein.
In some embodiments, the polymer is a thermoset polymer. In some embodiments, the thermoset polymer comprises an epoxy resin, Triglycidyl p-amino-phenol, diglycidyl ester of hexahydrophthalic acid, epoxycresol novolak, epoxyphenol novolak, or combinations thereof. In some embodiments, the thermoset polymer comprises epoxy resin, and the epoxy resin is a bisphenol-A based epoxy. Other thermoset polymers are known and can be used in the composite materials described herein.
In some embodiments, the composite material further comprises a synthetic and/or natural fiber. An example of a suitable synthetic fiber is, without limitation, fiberglass. Suitable natural fibers include, without limitation, wood, agricultural plant fibers, or combinations thereof. In some embodiments, the wood is Red Oak.
In some embodiments, the composite material further comprises a curing agent. In some embodiments, the curing agent is a low viscosity curing agent 2120 Epoxy Hardener.
In some embodiments, the composite material contains 0.001 wt % to 10 wt % of the carbon nano-onion structure, or any amount or range therein. For example, in some embodiments the composite contains 0.001 wt % to 0.01 wt %, 0.001 wt % to 0.1 wt %, 0.001 wt % to 0.5 wt %, 0.001 wt % to 1 wt %, 0.001 wt % to 2 wt %, 0.001 wt % to 3 wt %, 0.001 wt % to 4 wt %, 0.001 wt % to 5 wt %, 0.001 wt % to 6 wt %, 0.001 wt % to 7 wt %, 0.001 wt % to 8 wt %, 0.001 wt % to 9 wt %, 0.001 wt % to 10 wt %, 0.01 wt % to 0.1 wt %, 0.01 wt % to 0.5 wt %, 0.01 wt % to 1 wt %, 0.01 wt % to 2 wt %, 0.01 wt % to 3 wt %, 0.01 wt % to 4 wt %, 0.01 wt % to 5 wt %, 0.01 wt % to 6 wt %, 0.01 wt % to 7 wt %, 0.01 wt % to 8 wt %, 0.01 wt % to 9 wt %, 0.01 wt % to 10 wt %, 0.1 wt % to 0.5 wt %, 0.1 wt % to 1 wt %, 0.1 wt % to 2 wt %, 0.1 wt % to 3 wt %, 0.1 wt % to 4 wt %, 0.1 wt % to 5 wt %, 0.1 wt % to 6 wt %, 0.1 wt % to 7 wt %, 0.1 wt % to 8 wt %, 0.1 wt % to 9 wt %, 0.1 wt % to 10 wt %, 0.5 wt % to 1 wt %, 0.5 wt % to 2 wt %, 0.5 wt % to 3 wt %, 0.5 wt % to 4 wt %, 0.5 wt % to 5 wt %, 0.5 wt % to 6 wt %, 0.5 wt % to 7 wt %, 0.5 wt % to 8 wt %, 0.5 wt % to 9 wt %, 0.5 wt % to 10 wt %, 1 wt % to 2 wt %, 1 wt % to 3 wt %, 1 wt % to 4 wt %, 1 wt % to 5 wt %, 1 wt % to 6 wt %, 1 wt % to 7 wt %, 1 wt % to 8 wt %, 1 wt % to 9 wt %, 1 wt % to 10 wt %, 2 wt % to 3 wt %, 2 wt % to 4 wt %, 2 wt % to 5 wt %, 2 wt % to 6 wt %, 2 wt % to 7 wt %, 2 wt % to 8 wt %, 2 wt % to 9 wt %, 2 wt % to 10 wt %, 3 wt % to 4 wt %, 3 wt % to 5 wt %, 3 wt % to 6 wt %, 3 wt % to 7 wt %, 3 wt % to 8 wt %, 3 wt % to 9 wt %, 3 wt % to 10 wt %, 4 wt % to 5 wt %, 4 wt % to 6 wt %, 4 wt % to 7 wt %, 4 wt % to 8 wt %, 4 wt % to 9 wt %, 4 wt % to 10 wt %, 5 wt % to 6 wt %, 5 wt % to 7 wt %, 5 wt % to 8 wt %, 5 wt % to 9 wt %, 5 wt % to 10 wt %, 6 wt % to 7 wt %, 6 wt % to 8 wt %, 6 wt % to 9 wt %, 6 wt % to 10 wt %, 7 wt % to 8 wt %, 7 wt % to 9 wt %, 7 wt % to 10 wt %, 8 wt % to 9 wt %, 8 wt % to 10 wt %, or 9 wt % to 10 wt % of the carbon nano-onion structure.
The carbon nano-onions described herein have the ability to improve the properties of polymers when the polymers are combined with the carbon nano-onions to form the composite materials described herein.
In some embodiments, the composite material has a higher tensile strength than that of the polymer without the carbon nano-onion structure. As used herein, “tensile strength” is defined as the maximum stress, measured as force per unit, that a material can bear before breaking when it is stretched or pulled.
In some embodiments, the composite material has a higher tensile modulus than that of the polymer without the carbon nano-onion structure. As used herein, “tensile modulus” refers to a mechanical property that measures a material's stiffness when subjected to tension or compression and is defined as the ratio of stress (force per unit area) to its strain (displacement or deformation) in the linear elasticity deformation region.
In some embodiments, the composite material has a higher flexural strength than that of the polymer without the carbon nano-onion structure. As used herein, “flexural strength,” also referred to as “bending strength,” is defined as a material's maximum stress before it yields to bending.
In some embodiments, the composite material has a higher flexural modulus than that of the polymer without the carbon nano-onion structure. As used herein, “flexural modulus,” also referred to as “bending modulus,” is the tendency for a material to resist bending, and is defined as the ratio of stress to strain in flexural deformation.
In some embodiments, the composite material has a higher impact strength than that of the polymer without the carbon nano-onion structure. As used herein, “impact strength” is defined as measure of a material's ability to resist cracking, fracturing, tearing, or damage under sudden application of force, and is expressed in terms of the amount of energy absorbed before fracture. The near-instantaneous implementation of load causes the material to absorb the energy, and when the amount of energy exceeds that which the material can accommodate, the material will experience fracture, cracking, tearing, or damage.
Polymers are permeable to gases and vapors to different extents. In some embodiments, the composite material has lower oxygen transmission and water vapor transmission than that of the polymer without the carbon nano-onion structure. As used herein, the oxygen transmission rate is defined as the rate at which oxygen gas permeates through a material over a given time. Water vapor transmission is the measure of the passage of water vapor through a material over a given time.
In some embodiments, the composite material has a higher thermal stability than that of the polymer without the carbon nano-onion structure. As used herein, “thermal stability,” is defined as the ability of a material to resist the action of heat energy by maintaining its mechanical properties, such as strength, toughness, or elasticity at a given temperature.
Another aspect of the present disclosure relates to a method of preparing an oxygen-functionalized carbon nano-onion. The method comprises providing a fixed carbon-containing source and treating the fixed carbon-containing source by joule heating under conditions effective to transform the fixed carbon-containing source into an oxygen-functionalized carbon nano-onion comprising a structure comprising a plurality of substantially concentric carbon shells, where the substantially concentric carbon shells have a spherical, quasi-spherical, and/or polyhedral configuration or combinations thereof.
In some embodiments of the method, the fixed carbon-containing source comprises biomass. In some embodiments the biomass is lignin, biochar, any fixed carbon-containing biomass, or mixtures thereof. Suitable types of lignin include, without limitation, Hardwood Kraft Lignin (HKL), Softwood Kraft Lignin (SKL), Oragnosolv Hardwood Lignin, Oragnosolv Softwood Lignin, herbaceous biomass-derived lignin, Acetosolv Lignin, Milled Wood Lignin, steam-explosion lignin, plasma-extraction lignin, chemically modified lignins, or combinations thereof. In some embodiments, when the biomass comprises lignin, the method further comprises subjecting the lignin to a carbonization process prior to said treating. In some embodiments, where the biomass comprises biochar, the method further comprises subjecting the biomass to pyrolysis to produce the biochar used in said treating.
In some embodiments of the method, said providing the fixed carbon-containing source comprises mixing the fixed carbon-containing source sample with 1 wt % to 10 wt % electrically conductive materials, or any amount or range therein, to form a mixture of fixed carbon-containing source and conductive materials, and subjecting the mixture of fixed carbon-containing source and conductive materials to grinding. For example, in some embodiments, the fixed carbon-containing source sample is mixed with 1 wt % to 2 wt %, 1 wt % to 3 wt %, 1 wt % to 4 wt %, 1 wt % to 5 wt %, 1 wt % to 6 wt %, 1 wt % to 7 wt %, 1 wt % to 8 wt %, 1 wt % to 9 wt %, 1 wt % to 10 wt %, 2 wt % to 3 wt %, 2 wt % to 4 wt %, 2 wt % to 5 wt %, 2 wt % to 6 wt %, 2 wt % to 7 wt %, 2 wt % to 8 wt %, 2 wt % to 9 wt %, 2 wt % to 10 wt %, 3 wt % to 4 wt %, 3 wt % to 5 wt %, 3 wt % to 6 wt %, 3 wt % to 7 wt %, 3 wt % to 8 wt %, 3 wt % to 9 wt %, 3 wt % to 10 wt %, 4 wt % to 5 wt %, 4 wt % to 6 wt %, 4 wt % to 7 wt %, 4 wt % to 8 wt %, 4 wt % to 9 wt %, 4 wt % to 10 wt %, 5 wt % to 6 wt %, 5 wt % to 7 wt %, 5 wt % to 8 wt %, 5 wt % to 9 wt %, 5 wt % to 10 wt %, 6 wt % to 7 wt %, 6 wt % to 8 wt %, 6 wt % to 9 wt %, 6 wt % to 10 wt %, 7 wt % to 8 wt %, 7 wt % to 9 wt %, 7 wt % to 10 wt %, 8 wt % to 9 wt %, 8 wt % to 10 wt %, or 9 wt % to 10 wt % conductive materials. In some embodiments, the conductive materials are carbon black, acetylene black, metal powder, carbon nano-onions, or combinations thereof.
In some embodiments of the method, the joule heating is carried out for 2 min to 10 min, or any amount or range therein. For example in some embodiments, the joule heating is carried out for 2 min to 3 min, 2 min to 4 min, 2 min to 5 min, 2 min to 6 min, 2 min to 7 min, 2 min to 8 min, 2 min to 9 min, 2 min to 10 min, 3 min to 4 min, 3 min to 5 min, 3 min to 6 min, 3 min to 7 min, 3 min to 8 min, 3 min to 9 min, 3 min to 10 min, 4 min to 5 min, 4 min to 6 min, 4 min to 7 min, 4 min to 8 min, 4 min to 9 min, 4 min to 10 min, 5 min to 6 min, 5 min to 7 min, 5 min to 8 min, 5 min to 9 min, 5 min to 10 min, 6 min to 7 min, 6 min to 8 min, 6 min to 9 min, 6 min to 10 min, 7 min to 8 min, 7 min to 9 min, 7 min to 10 min, 8 min to 9 min, 8 min to 10 min, or 9 min to 10 min.
In some embodiments of the method, the joule heating is carried out with DC electric source.
In some embodiments of the method, the joule heating is carried out with AC electric source.
In some embodiments of the method, the joule heating is carried out at a maximum voltage of 5 V to 10 kV, or any amount or range therein. For example, in some embodiments the joule heating is carried out at a maximum voltage of 5 to 100 V, 5 to 200 V, 5 to 300 V, 5 to 400 V, 5 to 500 V, 5 to 600 V, 5 to 700 V, 5 to 800 V, 5 to 900 V, 5 to 1000 V, 5 V to 5 kV, 50 to 100 V, 50 to 200 V, 50 to 300 V, 50 to 400 V, 50 to 500 V, 50 to 600 V, 50 to 700 V, 50 to 800 V, 50 to 900 V, 50 to 1000 V, 50 V to 5 kV, 50 V to 10 kV, 100 to 200 V, 100 to 300 V, 100 to 400 V, 100 to 500 V, 100 to 600 V, 100 to 700 V, 100 to 800 V, 100 to 900 V, 100 to 1000 V, 100 V to 5 kV, 100 V to 10 kV, 150 to 200 V, 150 to 300 V, 150 to 400 V, 150 to 500 V, 150 to 600 V, 150 to 700 V, 150 to 800 V, 150 to 900 V, 150 to 1000 V, 150 V to 5 kV, 150 V to 10 kV, 200 to 300 V, 200 to 400 V, 200 to 500 V, 200 to 600 V, 200 to 700 V, 200 to 800 V, 200 to 900 V, 200 to 1000 V, 200 V to 5 kV, 200 V to 10 kV, 250 to 300 V, 250 to 400 V, 250 to 500 V, 250 to 600 V, 250 to 700 V, 250 to 800 V, 250 to 900 V, 250 to 1000 V, 250 V to 5 kV, 250 V to 10 kV, 300 to 400 V, 300 to 500 V, 300 to 600 V, 300 to 700 V, 300 to 800 V, 300 to 900 V, 300 to 1000 V, 300 V to 5 kV, 300 V to 10 kV, 350 to 400 V, 350 to 500 V, 350 to 600 V, 350 to 700 V, 350 to 800 V, 350 to 900 V, 350 to 1000 V, 350 V to 5 kV, 350 V to 10 kV, 400 to 500 V, 400 to 600 V, 400 to 700 V, 400 to 800 V, 400 to 900 V, 400 to 1000 V, 400 V to 5 kV, 400 V to 10 kV, 450 to 500 V, 450 to 600 V, 450 to 700 V, 450 to 800 V, 450 to 900 V, 450 to 1000 V, 450 V to 5 kV, 450 V to 10 kV, 500 to 600 V, 500 to 700 V, 500 to 800 V, 500 to 900 V, 500 to 1000 V, 500 V to 5 kV, 500 V to 10 kV, 550 to 600 V, 550 to 700 V, 550 to 800 V, 550 to 900 V, 550 to 1000 V, 550 V to 5 V, 550 V to 10 kV, 600 to 700 V, 600 to 800 V, 600 to 900 V, 600 to 1000 V, 600 V to 5 kV, 600 V to 10 kV, 650 to 700 V, 650 to 800 V, 650 to 900 V, 650 to 1000 V, 650 V to 5 kV 650 V to 10 kV 700 to 800 V, 700 to 900 V, 700 to 1000 V, 700 V to 5 kV, 700 V to 10 kV, 750 to 800 V, 750 to 900 V, 750 to 1000 V, 750 V to 5 kV, 750 V to 10 kV, 800 to 900 V, 800 to 1000 V, 800 V to 5 kV, 800 V to 10 kV, 850 to 900 V, 850 to 1000 V, 850 V to 5 kV, 850 V to 10 kV, 900 to 1000 V, 900 V to 5 kV, 900 V to 10 kV, 950 to 1000 V, 950 V to 5 kV, 950 V to 10 kV, 1000 V to 5 kV, 1000 V to 10 kV, or 5 kV to 10 kV. The maximum voltage can be more or less depending on the scale in which the method is carried out.
In some embodiments of the method, the joule heating is carried out at a maximum current of 0.1 to 1000 A, or any amount or range therein. For example, in some embodiments the joule heating is carried out a maximum current of 0.1 to 10 A, 0.1 to 20 A, 0.1 to 30 A, 0.1 to 40 A, 0.1 to 50 A, 0.1 to 60 A, 0.1 to 70 A, 0.1 to 80 A, 0.1 to 90 A, 0.1 to 100 A, 0.1 to 500 A, 0.1 to 1000 A, 0.5 to 10 A, 0.5 to 20 A, 0.5 to 30 A, 0.5 to 40 A, 0.5 to 50 A, 0.5 to 60 A, 0.5 to 70 A, 0.5 to 80 A, 0.5 to 90 A, 0.5 to 100 A, 0.5 to 500 A, 0.5 to 1000 A, 1 to 10 A, 1 to 20 A, 1 to 30 A, 1 to 40 A, 1 to 50 A, 1 to 60 A, 1 to 70 A, 1 to 80 A, 1 to 90 A, 1 to 100 A, 1 to 500 A, 1 to 1000 A, 10 to 20 A, 10 to 30 A, 10 to 40 A, 10 to 50 A, 10 to 60 A, 10 to 70 A, 10 to 80 A, 10 to 90 A, 10 to 100 A, 10 to 500 A, 10 to 1000 A, 15 to 20 A, 15 to 30 A, 15 to 40 A, 15 to 50 A, 15 to 60 A, 15 to 70 A, 15 to 80 A, 15 to 90 A, 15 to 100 A, 15 to 500 A, 15 to 1000 A, 20 to 30 A, 20 to 40 A, 20 to 50 A, 20 to 60 A, 20 to 70 A, 20 to 80 A, 20 to 90 A, 20 to 100 A, 20 to 500 A, 20 to 1000 A, 25 to 30 A, 25 to 40 A, 25 to 50 A, 25 to 60 A, 25 to 70 A, 25 to 80 A, 25 to 90 A, 25 to 100 A, 25 to 500 A, 25 to 1000 A, 30 to 40 A, 30 to 50 A, 30 to 60 A, 30 to 70 A, 30 to 80 A, 30 to 90 A, 30 to 100 A, 30 to 500 A, 30 to 1000 A, 35 to 40 A, 35 to 50 A, 35 to 60 A, 35 to 70 A, 35 to 80 A, 35 to 90 A, 35 to 100 A, 35 to 500 A, 35 to 1000 A, 40 to 50 A, 40 to 60 A, 40 to 70 A, 40 to 80 A, 40 to 90 A, 40 to 100 A, 40 to 500 A, 40 to 1000 A, 45 to 60 A, 45 to 70 A, 45 to 80 A, 45 to 90 A, 45 to 100 A, 45 to 500 A, 45 to 1000 A, 50 to 60 A, 50 to 70 A, 50 to 80 A, 50 to 90 A, 50 to 100 A, 50 to 500 A, 50 to 1000 A, 55 to 60 A, 55 to 70 A, 55 to 80 A, 55 to 90 A, 55 to 100 A, 55 to 500 A, 55 to 1000 A, 60 to 70 A, 60 to 80 A, 60 to 90 A, 60 to 100 A, 60 to 500 A, 60 to 1000 A, 65 to 70 A, 65 to 80 A, 65 to 90 A, 65 to 100 A, 65 to 500 A, 65 to 1000 A, 70 to 80 A, 70 to 90 A, 70 to 100 A, 70 to 500 A, 70 to 1000 A, 75 to 80 A, 75 to 90 A, 75 to 100 A, 75 to 500 A, 75 to 1000 A, 80 to 90 A, 80 to 100 A, 80 to 500 A, 80 to 1000 A, 85 to 90 A, 85 to 100 A, 85 to 500 A, 85 to 1000 A, 90 to 100 A, 90 to 500 A, 90 to 1000 A, 100 to 500 A, 100 to 1000 A, 200 to 500 A, 200 to 1000 A, 300 to 500 A, 300 to 1000 A, 400 to 500 A, 400 to 1000 A, 500 to 1000 A, 600 to 1000 A, 700 to 1000 A, 800 to 1000 A, or 900 to 1000 A.
Another aspect of the present application relates to a method of preparing a composite material. This method involves providing the carbon nano-onion disclosed herein, blending a polymer with the carbon nano-onion to form a mixture, and forming a composite material from the mixture. In some embodiments of the method, polylactic acid (PLA) is fabricated with carbon nano-onion additives by dispersing the carbon nano-onions in 100 mL dichloromethane (DCM), stirring with a magnetic stir bar, and then subsequently adding PLA to the carbon nano-onion and DCM mixture.
In carrying out the method of preparing a composite material, the resulting composite material can have the various characteristics described herein, including those described above.
In some embodiments of the method, said providing is carried out by dispersing the carbon nano-onion in a solvent and said forming comprises removing the solvent from the mixture. Suitable solvents include, without limitation, DI water, acetone, methanol, ethanol, 2-propanol, tetrahydrofuran (THF), N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dichloromethane (DCM), dimethyl sulfoxide (DMSO), pyridine, diethyl ether, toluene, chloroform, 1-butanol, cyclohexane, hexene, 1, 4-dioxine, ethylene glycol, or ethylene glycol monomethyl ether.
In some embodiments, the method is carried out in a heated extruder. An extruder is a motor-driven screw inside a tube or barrel. Various raw materials can be fed into the extruder, while a hot fluid can be circulated through a hollow jacket around the outside of the barrel in order to melt the material inside the barrel.
In some embodiments of the method, said forming is carried out by injection molding. Injection molding is a manufacturing process for producing parts by injecting molten material into a mold. Material, such as thermoplastic or thermosetting polymers, is fed into a heated barrel, mixed, and injected into a mold cavity, where it cools and hardens to the configuration of the cavity.
In some embodiments, said forming is carried out in a hot press. Hot pressing is a manufacturing process that involves the application of heat and pressure to a material to create a dense and uniform product. Material is placed in a mold and then heated to high temperature while applying pressure, which causes the material to soften and flow, filling the mold to create a dense and uniform product.
In some embodiments, said forming is carried out by a film casting process. Film casting is a process for producing thin films that involves dissolving a polymer in a volatile solvent which is subsequently evaporated.
In some embodiments of the method, the polymer is a thermoplastic polymer. In some embodiments the thermoplastic polymer comprises plastics, polylactic acid, polyamide 6 (PA6), polyhydroxyalkanoates (PHAs), polyesters, polyethylene (PE), polypropylene (PP), polystyrene, polyvinyl chloride, or combinations thereof. Other thermoplastic polymers are known and can be used.
In some embodiments of the method, the polymer is a thermoset polymer. In some embodiments, the thermoset polymer comprises an epoxy resin, Triglycidyl p-amino-phenol, diglycidyl ester of hexahydrophthalic acid, epoxycresol novolak, epoxyphenol novolak, and combinations thereof. In some embodiments, the thermoset polymer comprises epoxy resin, and the epoxy resin is a bisphenol-A based epoxy. Other thermoset polymers are known and can be used.
In some embodiments, the method further comprises blending a natural fiber or a synthetic fiber with the polymer and the carbon nano-onion. An example of a suitable synthetic fiber is, without limitation, fiberglass. Suitable natural fibers include, without limitation, wood, agricultural plant fibers, or combinations thereof. In some embodiments, the wood is Red Oak.
In some embodiments, when the polymer is a thermoset polymer, the forming step can further comprise adding a curing agent. In some embodiments, the curing agent is a low viscosity curing agent 2120 Epoxy Hardener. In some embodiments, said forming step can further comprise coating a glass fiber with the mixture.
The above disclosure is general. A more specific description is provided below in the following examples. The examples are described solely for the purpose of illustration and are not intended to limit the scope of the present application. Changes in the form and substitution of equivalents are contemplated as circumstances suggest or render expedient. Although specific terms have been employed herein, such terms are intended in a descriptive sense and not for the purposes of limitation.
The following examples are provided to illustrate embodiments of the present application but are by no means intended to limit scope.
Organosolv lignin (OL) and Kraft lignin (KL) are provided by industrial sources. Biochar (BC) was a co-product during fast pyrolysis of pinewood at 500° C., produced in the Biocentury Research Farm of Iowa State University. Carbon black was purchased from Chemical Store, Inc. PLA (Ingeo 2500HP) was purchased from NatureWorks. Graphene nanoplatelets (GNPs) (2-10 nm thickness) was procured from ACS Materials, LLC. OL and KL were washed in deionized water at 90° C. for 4 hrs under continuous stirring at 300 rpm. The washed OL and KL were dried overnight in a vacuum oven and stored. All solvents were procured from Fisher Chemicals.
Before joule heating, lignins were degassed by heating under an inert environment from room temperature to 500° C. at 10° C./min and 500° C. to 700° C. at 8° C./min. The carbonized lignins were milled for 3 min. During the joule heating process, about 0.8 g of pre-carbonized lignin mixed with 5% carbon black were tightly packed inside a quartz-tube reactor and in contact with copper electrodes covered with copper wool at the two ends. The same amount of milled biochar was mixed with 8% carbon black when biochar is the precursor. Carbon black was added to improve the electric conductivity of the starting materials. In the reactor, the electrodes were connected to a Hanmatek HM 305 adjustable DC power supply unit with a maximum voltage and current set at 32 V and 4 A. A schematic illustration of a possible reactor setup is given in
Fabrication of Polylactic Acid (PLA) with CNO Additives
A solution mixing followed by an injection molding method was used to prepare PLA composites with CNO additives. CNOs were first dispersed into 100 mL of dichloromethane (DCM) and stirred using a magnetic stir bar for 1.5 hrs. PLA was subsequently added to the CNO and DCM mixture and stirred for an additional 2.5 hrs. The mixture was then dried in a vacuum oven to remove the solvent. The dried PLA-CNO was processed using Haake Minijet injection molder (Thermo Scientific). A schematic illustration of a possible fabrication process is given in
HRTEM analysis was conducted using a JEOL 2100 scanning TEM (Japan Electron Optics Laboratories) with a Gatan OneView 4K camera (Gatan, Inc.) and an operating voltage of 200 kV. Samples were prepared by drop casting of 10 μL ethanol with CNOs in a 200 mesh copper grid. Image J software was used to analyze the TEM images. The average interlayer spacing (d002) and nanoparticles diameter were calculated from the corresponding output of the image processing.
XRD was performed using Siemens D500 diffractometer with Cu Kα radiation (λ=1.5432 Å). The step time was 2 s and a Bragg angle range was 100-50°.
The interlayer spacing d002(nm) was evaluated based on the (002) peak position from Bragg's law:
where λ is the wavelength (nm), θ is the Bragg angle for the corresponding (002) peak.
Crystallite thickness (Lc) and crystallite lateral size (La) were determined using (002) and (100) peaks using Scherrer's formula:
where B and θ associated with the full width at half maxima (FWHM) and the Bragg angle, respectively; K=0.89 and 1.84 for (002) and (100) peaks, respectively. Gaussian peak fitting was used to determine (0 0 2) and (1 0 0) peak locations.
Aromaticity (fa) evaluated by deconvoluting 2θ from 15 to 30° over two pseudo-Voigt peaks at roughly 20° for γ peak and around 26° for (002) for peak applying the following formula:
where A002 and Aγ are the peak areas for (002) and γ peaks, respectively.
Raman spectroscopy was performed using DXR Raman Microscope (Thermo Fisher, Waltham, MA) and a 532 nm laser with a power of 5 mW to determine the degree of graphitization. A 50× lens was used for local Raman spectra. The spectra were deconvoluted into four peaks (D, G, D+D″, and 2D) by Gaussian peak fitting. The band intensities, including the intensity ratio (ID/IG) and area ratio i.e. peak integrated area ratio (AD/AG) of the D to G peak, were calculated. I2D/IG ratio was also calculated from the intensity of 2D and G peaks to determine the graphitic layers.
Surface functional groups were identified using XPS (Kratos Amicus X-ray Photoelectron Spectrometer). All survey and elemental scans were performed using 1 eV and 0.1 eV steps, respectively, with a pass energy of 150 eV. The C1 peak level spectra at 284.6 eV was used to correct the change in the binding energy brought on by the sample's surface charge-up.
Dispersion of CNOs was performed in the following 20 solvents: DI water, acetone, methanol, ethanol, 2-propanol, tetrahydrofuran (THF), N, N-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dichloromethane (DCM), dimethyl sulfoxide (DMSO), pyridine, diethyl ether, toluene, chloroform, 1-butanol, cclohexane, hexene, 1, 4-dioxine, ethylene glycol, and ethylene glycol monomethyl ether. Two milligrams of the sample was dispersed into a 20 mL solvent and sonicated for an hour. The sonicated solution was centrifuged at 1000 rpm for an additional hour.
FTIR was performed using a Thermo Scientific Nicolet iS10 equipped with a Smart iTR accessory in a range of 500-4000 cm−1 and scanned 64 times with 4 cm−1 resolution.
Thermal analyses were determined by using a TGA-DSC STARe system, Metler Toledo. Thermal stability of CNO was evaluated by heating 30 mg of CNO from room temperature to 900° C. at 10° C./min using either nitrogen or air with a flow rate of 100 mL/min. Ash content in CNO was determined by performing proximate analysis using the following procedure: heating about 30 mg of CNO using 100 mL/min nitrogen from room temperature to 120° C. at 10° C./min and keeping for 5 mins, from 120° C. to 900° C. at 10° C./min and holding at the final temperature for 30 min, and finally introducing air at 900° C. to combust the residues. The experiments were duplicated to report average results. For thermal stability analysis of PLA composite, about 30 mg of PLA composite containing CNO (PLA-CNO) were heated from room temperature to 700° C. at 10° C./min in the presence of nitrogen.
Electric conductivity of CNOs can be measured based on the following equations.
where R is the electrical resistance (Ω), U is the stabilized voltage (V), and I is the stabilized electrical current (A) during the joule heating.
where ρ is the electrical resistivity (Ω·m), L is the length of the sample between the two electrodes, A is the inner cross-sectional area of the reactor.
where σ is the electrical conductivity (S/m).
An Instron 5944 tensile tester was used to test the tensile properties of PLA-CNOs at 10 mm/min according to the ASTM D638 method. The 3-point bending test was conducted in the Instron 5944 tensile tester using the ASTM D7264 method. A Tinius Olsen Impact tester was used to perform the impact strength. ASTM D256 specifications were used to create notches in the impact bar. At least five specimens were tested for each test.
The scanning electron microscope (SEM, Quanta-FEG 250, FEI) was used to observe the morphology of polymer or polymer composites at their tensile bar fracture surfaces.
The thermal behavior of PLA/CNO composite was determined by differential scanning calorimetry (DSC, Q2000, TA instruments) under nitrogen atmosphere. Approximately 10 mg of composite sample was used for the measurement under the following protocol: firstly, the sample was heated from 25° C. to 220° C. at 20° C./min and kept at 220° C. for 5 min to eliminate thermal history. Secondly, the sample was cooled down to −50° C. to detect the cold crystallization temperature (Tcc). Finally, the samples were heated again to 220° C. at 20° C./min to determine the melting temperature (Tm).
ASTM D3985 standards were used to determine the oxygen transmission rate (OTR) in an oxygen permeation testing analyzer (MOCON's OX-TRAN model 2/21) under a carrier gas mixture of 98% nitrogen, 2% hydrogen, and a test gas of 99.9% oxygen. A water vapor transmission (WVTR) test was performed in a Permatran-W (MOCON) under a nitrogen carrier gas and water vapor as the test gas. Test specimens (0.5 mm thickness and 25 mm dia.) were prepared using injection molding with a cylinder temperature of 240° C. and mold temperature of 90° C. The oxygen transmission and water vapor transmission were collected every 30 min and stopped once the steady state condition of oxygen and water vapor concentration was reached.
Raman spectra of the OL-CNOs are given in
The I2D/IG ratios of OL-CNO plotted in
While the above results confirm the formation of graphitic CNO, their functional groups were investigated using XPS. Conventionally synthesized CNO often do not have surface functional groups, causing chemical incompatibility issues in their applications (Zeiger et al., “Review: Carbon Onions for Electrochemical Energy Storage,” J. Mater. Chem. A, 4:3172-3196 (2016); Chen et al., “New Method of Carbon Onion Growth by Radio-Frequency Plasma-Enhanced Chemical Vapor Deposition,” Chemical Physics Letters, 336:201-204 (2001); Dorobantu et al., “Pulse Laser Ablation System for Carbon Nano-Onions Fabrication,” Surface Engineering and Applied Electrochemistry, 50:390-394 (2014); Mongwe et al, “Synthesis of Chain-Like Carbon Nano-Onions by a Flame Assisted Pyrolysis Technique Using Different Collecting Plates,” Diamond and Related Materials, 90:135-143 (2018); Bagge-Hansen et al., “Detonation Synthesis of Carbon Nano-Onions via Liquid Carbon Condensation,” Nat Commun, 10:3819 (2019); Liu et al., “Carbon Nano-Onions Made Directly from CO2 by Molten Electrolysis for Greenhouse Gas Mitigation,” Adv. Sustainable Syst., 3(10):1900056 (2019); Roddatis et al., “Transformation of Diamond Nanoparticles into Carbon Onions under Electron Irradiation,” Phys. Chem. Chem. Phys., 4:1964-1967 (2002); Rettenbacher et al., “Preparation and Functionalization of Multilayer Fullerenes (Carbon Nano-Onions),” Chemistry—A European Journal, 12:376-387 (2006); Du et al., “Onion-Like Fullerenes Synthesis from Coal,” Fuel, 86: 294-298 (2007); Garcia-Martin et al., “Method to Obtain Carbon Nano-Onions by Pyrolisys of Propane,” Open Physics, 11(11):1548-1558 (2013); which are hereby incorporated by reference in their entirety).
The above results show that the biobased CNOs have moderately crystallized multiple-shelled carbon structures with functionalized surfaces. Such structures are impossible to obtain with high-temperature thermal annealing of CND since the resulting CNO are highly crystallized without surface functional groups. Conventionally prepared pristine CNO often have poor dispersibility in solvents due to the lack of surface functionalities, which limits their applications (Dhand et al., “A Comprehensive Review on the Prospects of Multi-functional Carbon Nano Onions as an Effective, High-Performance Energy Storage Material,” Carbon N. Y., 175:534-575 (2021), which is hereby incorporated by reference in its entirety). Accordingly, CNOs were chemically modified in previous studies to improve solvent solubilities (Pdrez-Ojeda et al., “Carbon Nano-onions: Potassium Intercalation and Reductive Covalent Functionalization,” J. Am. Chem. Soc., 143(45):18997-19007 (2021); Molina-Ontoria et al., “Preparation and Characterization of Soluble Carbon Nano-onions by Covalent Functionalization, Employing a Na—K alloy,” Chem. Commun., 49(24):2406-2408 (2013); which are hereby incorporated by reference in their entirety). In comparison, CNO synthesized in this work using the joule heating process had tunable oxygen-functional groups, which were expected to improve solvent dispersibility. To confirm, OL-CNO (i.e., OL-6 min) was dispersed in 20 common solvents (17 polar and 3 hydrocarbon solvents) and the dispersion solutions were monitored for up to 2 weeks. As shown in
The CNO was synthesized using the joule heating method in this work, indicating electrically conductive materials are formed. The electrical conductivity of CNO was measured during their synthesis based on the process voltage and current conditions. Neither carbonized lignins nor as-received biochar is electrically conductive. Although adding small amounts of carbon black could allow a weak current between two electrodes to initiate the joule heating, the electrical resistance of the precursors was still very high. As the joule heating heats the materials, carbonization reactions transform amorphous carbons of lignins or BC into ordered graphene carbons. The improved carbon structures of the treated samples, in turn, increased the electrical conductivity of the newly formed structures. This changing electrical property of the materials is evident in
Various carbon materials, such as single or multiwall CNT, graphene, graphite, graphene oxide (GO), carbon fibers (CF), or their hybrids, have been used in polymers for improving mechanical, thermal, or gas/vapor barrier properties. However, CNO application for polymer property enhancers has yet to be explored. In this work, CNOs were explored as inexpensive additives for property-enhanced polymer using PLA as the polymer matrix.
Other mechanical properties of PLA composite containing OL-6 min were also measured, and the results are summarized in Table 4 to compare with the properties of neat PLA. In addition to improving tensile properties, 0.5% OL-6 min could increase PLA's flexural strength by 9.4%, flexural modulus by 20%, and impact strength by 60.4%. The mechanical property results of PLA composite containing 0.5% GNP were also included in the same table to evaluate the reinforcing effect of CNO compared to GNP. GNP is a nanocarbon of single or multilayer graphite plane (Liu et al., “Carbon Nano-Onions Made Directly from CO2 by Molten Electrolysis for Greenhouse Gas Mitigation,” Adv. Sustain. Syst., 3(10):1900056 (2019), which is hereby incorporated by reference in its entirety). It is a commercial additive or filler used to improve the mechanical and other properties of polymers. Our results show that with the same mass loading of 0.5%, CNO outperformed GNP in increasing the tensile strength and modulus of PLA. It also shows that adding GNP reduces the flexural modulus of PLA and has nearly no effect on its impact strength. In comparison, adding CNO could simultaneously improve the tensile, flexural and impact properties of PLA. The results suggest that the biobased CNO is a higher-performing additive than GNP.
Reinforcement effects of CNT, GNP, or CF are well known since their unidirectional sp2 carbon structures can effectively transfer mechanical load applied to the polymers (Papageorgiou et al., “Mechanisms of Mechanical Reinforcement by Graphene and Carbon Nanotubes in Polymer Nanocomposites,” Nanoscale, 12:2228-2267 (2020); Yao et al., “Recent Advances in Carbon-Fiber-Reinforced Thermoplastic Composites: A Review,” Composites Part B: Engineering, 142:241-250 (2018); which are hereby incorporated by reference in their entirety). Since the quasi-sphere CNO structures have zero dimension, CNOs were previously not considered in polymer reinforcement (Vindhyasarumi et al., “A Comprehensive Review on Recent Progress in Carbon Nano-Onion Based Polymer Nanocomposites,” European Polymer Journal, 194:112143 (2023), which is hereby incorporated by reference in its entirety). The unexpected and impressive high performance of CNOs as a reinforcing additive observed in this work could be attributed to the excellent comparability of the oxygen-functionalized CNOs in PLA. The rich oxygen functional groups in CNO can improve chemical compatibility with the polyester polymer to promote uniform dispersion of the nanoparticles in the polymer matrix. Agglomerated nanoparticles were nearly not noticeable in the SEM image of the fracture surface of the PLA-CNO tensile bar (
The effect of CNO additives on thermal properties of PLA was also evaluated.
Table 6 shows the oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) of neat PLA and PLA-CNOs. Both OTR and WVTR of PLA decreased dramatically by introducing CNOs. The PLA with 0.5% OL-6 min reduced OTR by 67.4% and WVTR by 48.4% compared to neat PLA. The permeation and diffusion of gas and vapor molecules through the polymer's amorphous phase determine the oxygen and water-vapor barrier properties for semi-crystalline polymers like PLA (Valapa et al., “Effect of Graphene Content on the Properties of Poly(lactic acid) Nanocomposites,” RSC Adv., 5(36):28410-28423 (2015), which is hereby incorporated by reference in its entirety). The addition of impermeable materials in PLA restricts gases or vapors infiltration by forming a tangled channel and the tangled pathway forces the light molecular compounds to swing around, improving the barrier properties (Yang et al., “Poly(lactic acid)/lignin Films with Enhanced Toughness and Anti-oxidation Performance for Active Food Packaging,” Int. J. Biol. Macromol., 144:102-110 (2020), which is hereby incorporated by reference in its entirety). The well-distributed nanoparticles of CNO in the polymer matrix and the outstanding chemical compatibility of CNO and PLA could have played key roles in developing the tangled pathways which hinder gas transportation through the PLA film. The CNO-to-PLA interfacial interaction is significantly enhanced by the rich oxygen functional groups on the CNO surface, which can also positively impact the barrier characteristics. These findings unequivocally demonstrate the potential of biobased CNO in PLA for packaging applications, which can shield food products from oxidation by limiting the absorption of oxygen molecules and limiting water vapor transmission from the surroundings.
As shown above, using a small quantity of CNOs as additives could significantly improve PLA's mechanical, thermal, and gas barrier properties altogether. Table 7 lists previously reported PLA composites reinforced by other carbon materials for comparison. Reinforced PLA composites have been extensively investigated as PLA is the most important biodegradable polymer. For example, Batakliev et al. added 6% of multi-wall CNT (MWCNT) to PLA to increase the tensile strength by 20% and tensile modulus by approximately 17% (Batakliev et al., “Effects of Graphene Nanoplatelets and Multiwall Carbon Nanotubes on the Structure and Mechanical Properties of Poly(lactic Acid) Composites: A Comparative Study,” Appl. Sci., 9(3):469 (2019), which is hereby incorporated by reference in its entirety). Gavali et al. added 15% CF to increase the tensile strength by 32%, flexural strength by 22%, and Tg by 3% (Gavali et al., “Mechanical and Thermo-mechanical Properties of Carbon fiber Reinforced Thermoplastic Composite Fabricated Using Fused Deposition Modeling Method,” Mater. Today Proc., 22:1786-1795 (2019), which is hereby incorporated by reference in its entirety). Their work achieved a 53% increase in impact strength by adding 20% CF. Gao et al. added 5% GNP to PLA to increase the tensile strength and tensile modulus by 41.3% and 23.7% (Gao et al., “Influence of Filler Size on the Properties of Poly(lactic Acid) (PLA)/Graphene Nanoplatelet (GNP) Nanocomposite,” Eur. Polym. J., 86:117-131 (2017), which is hereby incorporated by reference in its entirety). In another work by Park et al., 1% alkylated GO was added to increase the tensile strength and tensile modulus by 37.8% and 68.2%, respectively, and Tg by 3.3° C. (Park et al., “Melt Rheology and Mechanical Characteristics of Poly(Lactic acid)/Alkylated Graphene Oxide Nanocomposites,” Polymers (Basel)., 12(10):1-16 (2020), which is hereby incorporated by reference in its entirety). Kim and Jeong added 1% exfoliated graphite to increase the tensile strength of PLA by 9.3%, the tensile modulus by approximately 17%, and Td by 12° C. (Kim and Jeong, “Polylactide/exfoliated Graphite Nanocomposites with Enhanced Thermal Stability, Mechanical Modulus, and Electrical Conductivity,” J. Polym. Sci. Part B Polym. Phys., 48(8):850-858 (2010), which is hereby incorporated by reference in its entirety. Pinto et al. incorporated 0.4% GO or GNP into PLA film by solvent casting, increasing the tensile strength by 15% and tensile modulus by 85% (Pinto et al., “Effect of Incorporation of Graphene Oxide and Graphene Nanoplatelets on Mechanical and Gas Permeability Properties of Poly(lactic Acid) Films,” Polym. Int., 62(1):33-40 (2013), which is hereby incorporated by reference in its entirety). The Tg and Tm increased by 4.4 and 1.5° C. for 0.4% GO and 6.3 and 0.5° C. for 0.4% GNP. In their study, OTR decreased by 67.3% for 0.4% GO and 68.1% for 0.4% GNP. Kim et al. synthesized a GOCNT hybrid via exfoliation mixing in solvent and subsequently prepared PLA nanocomposites with GOCNT (Kim et al., “Exploration of Hybrid Nanocarbon Composite with Polylactic Acid for Packaging Applications,” Int. J. Biol. Macromol., 144:135-142 (2020), which is hereby incorporated by reference in its entirety). They reported that 0.4% GOCNT increased tensile strength by 75%, tensile modulus by 130%, and decreased OTR by 67%. However, Tg and Tm decreased by 1° C. and 0.2° C. by adding GOCNT. The comparison with the previous studies shows that the oxygen-functionalized CNOs synthesized as disclosed herein are far superior to other carbon additives or fillers to significantly improve the mechanical (tensile, bending, and impact) performance, thermal tolerance, and (oxygen and water vapor) barrier properties of PLA altogether using a very small quantity.
The presented joule heating method for producing CNOs is simple, fast, and has high product yields. The yield for CNOs produced by joule heating is around 95% for OL-CNO, around 93% for KL-CNO, both per the pre-carbonized lignin, and 90% for BC-CNO per as-received biochar. The presented joule heating method for synthesizing CNOs can be scaled easily by simply enlarging the reactor size and adjusting the voltage and current limits of the power electric source. The energy required for producing BC-CNOs was 15.6 MJ/kg for 6 min treatment. It has been reported that the energy consumption for producing carbon materials was 100,000 MJ/kg for carbon nanotubes (Arvidsson et al., “Prospective Life Cycle Assessment of Graphene Production by Ultrasonication and Chemical Reduction,” Environ. Sci. Technol. 48(8):4529-4536 (2014), which is hereby incorporated by reference in its entirety), 44 MJ/kg for carbon black, 100-900 MJ/kg for carbon fiber (Khayyam et al., “Improving Energy Efficiency of Carbon Fi Ber Manufacturing Through Waste Heat Recovery: A Circular Economy Approach With Machine Learning,” Energy 225:120113 (2021), which is hereby incorporated by reference in its entirety). The recent low-energy syntheses of GNP by others reported the energy consumption of 7.2-14.4 MJ/kg (Luong et al., “Gram-scale Bottom-up Flash Graphene Synthesis,” Nature 577(7792) (2019); Osazuwa and Kontopoulou, “Graphene Nanoplatelets Derived From Thermomechanical Exfoliation of Graphite,” 1:1-6, (2019); which are hereby incorporated by reference in their entirety). Other than the low energy consumption, the solvent, chemical, catalyst-free process presented herein also uses cheap precursors, which can significantly reduce the production costs of CNOs. Considering biomass residues have low material costs and the joule heating process requires electricity only, the costs of the biobased CNOs are expected to be very low. Using biochar as the precursor of CNOs is especially attractive. In biomass pyrolysis, the process energy is used to convert biomass into bio-oil as the primary product. The carbon-condensed biochar obtained as a byproduct can be directly used in the joule heating reactor for producing CNOs.
Although CNOs have versatile applications, their widespread uses are hindered by their extremely high costs attributed to the petroleum-based precursors and the costly synthesis method. In this work, a simple joule heating method was developed to obtain low-cost biobased CNOs with tunable oxygen functional groups from lignins and biochar in high yields (95%), without catalyst, solvents, or harsh chemicals. Benefiting from their turbostratic graphene structures rich in surface functional groups, the CNOs showed high electrical conductivity and excellent solvent dispersion. When added to the polymer matrix, as low as 0.1-0.5 wt % of CNOs significantly increased mechanical, thermal, and gas barrier properties of PLA, suggesting the CNO-engineered PLA nanocomposites are useful in many advanced polymer applications. The energy consumption of synthesizing CNOs by the joule heating method was low, which demonstrates that biobased CNOs could be produced at significantly lower costs than conventional CNOs. This work shows a promising pathway to valorize biomass residues for producing highly attractive nanocarbon materials.
Polylactic Acid (PLA) Ingeo 2500HP was purchased from NatureWorks LLC (Minnetonka, Minnesota). Red Oak (RO) chips were milled with a planetary ball mill and then sieved into particles with a mesh size <70 m. Biobased carbon nano-onions (CNO) were synthesized in house from a softwood organosolv lignin based on the joule heating method described in Example 1.
PLA-RO-CNO composite was fabricated using two-step processes, including twin screw extrusion and injection molding. Prior to the extrusion process, PLA, RO, and CNO were vacuum-dried overnight to remove any form of moisture. Before mixing with PLA, RO and CNO were premixed by grinding their mixture in a mortar and pestle for 30 mins. The PLA, RO, and CNO mixture was subjected to a twin-screw extrusion process at 220° C. and 180 rpm. The mixture was compounded for 5 min to prepare a homogeneous blend. A similar extrusion process was applied for neat PLA, PLA-CNO, and PLA and RO mixture. The extruded samples were processed in an injection molder at 220° C. to prepare composites.
The addition of CNO was found to significantly improve the tensile strength (
Incorporating CNO in addition to RO further improved the tensile modulus of composites. The tensile modulus of PLA-10RO-0.5CNO, PLA-20RO-0.5CNO, and PLA-30RO-0.5CNO were 7.2, 7.4, and 8.2 GPa, respectively, corresponding to 26.3, 19.4, and 13.9% increases compared to the corresponding PLA-RO composites. It also showed that the tensile modulus increases with the CNO loading.
Adding CNO to neat PLA slightly reduced the elongation-at-break from 3 to 2.8. However, PLA-RO-CNO composites showed higher elongation at break than PLA-RO composites. This increase suggests CNO may act as a compatibilizer or interface modifier to promote stronger interaction among the PLA, RO, and CNO. The oxygen-functional groups in the CNO may have facilitated a strong hydrogen bonding of the CNO with PLA and RO.
Compared to PAL-CNO, there were significant decreases in void size and RO fiber pullout in PLA-RO-CNO composites. Fiber breakage rather than fiber pullout was observed, suggesting the presence of CNO enhanced the interface bonding of RO and the PLA matrix to improve stress transfer. The interface adhesion was improved, probably due to the uniform dispersion of the functionalized CNO that could promote durable covalent or non-covalent bonding with both PLA and RO. For instance, hydrogen bonds in the oxygen-functionalized CNO, and the ether and ester groups present in the PLA and RO can interact to form an improved interface between the hydrophobic PLA matrix and hydrophilic RO fiber. According to the XPS result reported in applicant's previous work, CNO contains a unique type of hydrophobic π-π* domain in the basal plane and hydrophilic carboxyl groups on the surface of the CNO. Consequently, CNO demonstrates an amphiphilic nature and thus serves as a compatibilizer for immiscible mixtures or composites of hydrophilic fillers and hydrophobic polymers.
On the other hand, it was also found that PLA-RO-CNO composites produce more char residues than neat PLA or PLA-RO composites. This finding suggests a strong interaction between CNO and RO in the polymer matrix promotes char-forming carbonization reactions. The increased char formation may correspond to improved fire retardancy of a material, as char can serve as a physical barrier to restrict oxygen penetration and formation of combustible elements, thereby limiting the tendency of the material for combustion. While further studies are needed, CNO could potentially be used as a biobased safe fire retardant.
In this work, a bisphenol-A based epoxy from Fiberglast, USA (Epoxy 2000), a low viscosity curing agent 2120 Epoxy Hardener (Fibreglast, USA) and E-glass fiber (Style 7781 E-glass, Fiberglast, USA) were employed. Carbon nano onion (CNO) was used as synthesized using Joule heating as described in Example 1.
In this work, two approaches were employed to prepare composites. In the first approach, epoxy resin was modified with the CNO. As shown in
In the second approach, a solution of 0.1 mg/ml CNO in acetone was prepared by ultrasonicating the solution for 1.5 hours (
As a control case, unmodified epoxy and GF were used to prepare a composite.
For tensile testing, the composite was cut into a dimension of 80×20 mm with a thickness of 2 mm. The tensile test was performed in an Instron 3369 tensile tester equipped with a 50 kN load cell and tests were performed according to ASTM D3039 standard.
Tensile properties of the composites with different CNO mass loadings fabricated using the first approach was compared in
The tensile properties of the composite prepared using the second approach are also compared in
Although preferred embodiments have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the claims which follow.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 63/603,725, filed Nov. 29, 2023, which is hereby incorporated by reference in its entirety.
This invention was made with government support under OISE1826978 awarded by National Science Foundation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63603725 | Nov 2023 | US |
