Patent Application
20230191364
The present subject matter generally relates to functional carbon materials, namely a sulfonated and carbonized carbon material, and a method of making the same.
Porous carbon has been used across many applications such as water purification, CO2 capture, supercapacitors and battery technologies. Generally, increasing the specific surface area and pore volume of porous carbons make them more effective in their applications. For instance, increased pore volume and surface area allows for CO2 to interact with more sites within a porous carbon matrix, resulting in greater amounts of CO2 being captured by the carbon sorbents, and more efficiently scrubbing commercial production process streams. Highly porous carbon with large pore volumes has been synthesized through a variety of techniques with varied starting materials. These processes typically involve costly processing steps or starting materials that are expensive, making these materials difficult to produce at a commercially-relevant scale. Additionally, methods of enhancing the pore characteristics, such as activation, typically involve harsh chemicals and additional processing steps.
Current methods for synthesizing porous carbon materials for CO2 capture often involve complex or specialized starting materials, such as metal-organic frameworks or activation procedures that can involve many steps and harsh chemicals like potassium hydroxide (KOH). While it has been shown previously that sulfonating polymers, such as polyethylene, through exposure to sulfuric acid can allow these materials to be converted to carbons, such carbon materials are only produced with a two-step sulfonation treatment.
Moreover, carbon materials are important and commonly used across a variety of high-performance industries, including the automobile, additive manufacturing (e.g., 3D printing), and aerospace industries. Their ability to provide durability while being lightweight makes carbon composites potential alternatives to heavier metal counterparts. Currently, carbon fibers are mostly made from relatively expensive precursors (polyacrylonitrile) and require multiple energy-intensive steps for fabrication, hindering the ability to produce low-cost carbon fibers.
According to some aspects of the present disclosure, a structure comprising one or more carbonized materials having a shape based on a polymer based template structure and formed of a chemical compound having the structure shown in
According to some aspects of the present disclosure, a structure comprising one or more carbonized materials each formed of a chemical compound having the structure shown in
According to some aspects of the present disclosure, a method of manufacturing carbonized materials comprising the steps of preparing a precursor material, sulfonating the precursor material at a temperature of about 140° C. to about 160° C. to form a sulfonated material for about 2 hours to about 12 hours, and carbonizing the precursor material at a temperature of about 600° C. to about 800° C. to form a carbonized material.
These and other features, aspects, and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.
A full and enabling disclosure of the present disclosure, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.
Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present disclosure.
Reference will now be made in detail to present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. Like or similar designations in the drawings and description have been used to refer to like or similar parts of the invention.
As used herein, the terms “first,” “second,” and “third” may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. The terms “coupled,” “fixed,” “attached to,” and the like refer to both direct coupling, fixing, or attaching, as well as indirect coupling, fixing, or attaching through one or more intermediate components or features, unless otherwise specified herein.
The singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.
Approximating language, as used herein throughout the specification and claims, is applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately,” “generally,” and “substantially,” is not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value, or the precision of the methods or apparatus for constructing or manufacturing the components and/or systems. For example, the approximating language may refer to being within a ten percent margin.
Moreover, the technology of the present application will be described with relation to exemplary embodiments. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Additionally, unless specifically identified otherwise, all embodiments described herein should be considered exemplary.
Here and throughout the specification and claims, range limitations are combined and interchanged, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. For example, all ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other.
As used herein, the term “and/or,” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition or assembly is described as containing components A, B, and/or C, the composition or assembly can contain A alone; B alone; C alone; A and B in combination; A and C in combination; B and C in combination; or A, B, and C in combination.
The generation of porous carbon materials can be crucial in a wide range of applications, including batteries, pollutant removal from water sources, catalyst support and CO2 capture from commercial processes. Disclosed herein are carbon materials formed using a polypropylene surgical mask as a template and applying a combination of crosslinking and carbonization steps to result in porous carbon fibers. Also disclosed herein are carbon materials, specifically ordered mesoporous carbon materials (OMCs) having an average pore size greater than about 10 nm, and a method of forming the same using nanostructured thermoplastic elastomers (TPEs) as precursors. Also disclosed herein are carbon materials formed from 3D printed polypropylene-based structures, including 3D printed structures formed of polypropylene-based filament containing additives (e.g., carbon fiber fillers).
Each method involves using an initial structure formed of precursor material(s) as a template to fabricate resulting, multi-functional carbon materials. The precursor material may be any material having a polyolefin backbone, including but not limited to homopolymers, blended materials, and copolymers. For example, the precursor material(s) may be any one or more of the following: polypropylene (PP), PE, or thermoplastic elastomers (e.g., nanostructured thermoplastic elastomer containing crosslinked polyolefins, polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS), polystyrene-block-polyisoprene-block-polystyrene (SIS), and polystyrene-block-polybutadiene-block-polystyrene (SBS), etc.). The precursor material(s) may include fiber filler or may be free of fiber filler. The initial material or template structure is one of a 3D printed structure, a fiber, a porous scaffold, an injection molded structure, an extruded structure, or a compression molded structure. In various examples, the initial material may be a structured plastic waste, such as polypropylene-based surgical masks or N95 masks. In other examples, the initial material may be a nanostructured thermoplastic elastomer, or structured plastics prepared using fused deposition modeling (FDM) and having a complex 3D shape, such as a gyroid-shape object. In some instances, the printed precursor material may be printed from polypropylene-carbon nanofiber filaments. Using FDM printed shapes allows production of nearly zero-shrinkage, lightweight carbon structures having highly tailorable geometry.
Efficient transformation of polyolefins precursors, such as the precursor materials discussed above, into carbonaceous products, such as the porous carbons disclosed herein, requires thermally stabilizing the polyolefin chains through crosslinking prior to carbonization. Accordingly, each of the methods disclosed herein includes a combination of sulfonation, cross-linking, and carbonization steps to fabricate resulting, multi-functional carbon materials.
In a first method for generating porous carbons having surface areas of about 500 m2/g to about 2500 m2/g and pore volumes of about 5 cm3/g to about 45 cm3/g, the initial structure used is a structured plastic wastes (e.g. nonwoven polypropylene mats) including fibers exhibiting controlled pore sizes and formed of a precursor material such as, for example, polypropylene. This method utilizes stabilization via cross-linking combined with carbonization to convert a coating applied to the precursor materials of the initial structure into porous carbon materials. Specifically, a commercially-available phenolic resin coating, resol, is applied to the initial structure to coat the fibers by submerging the initial structure into a precursor-containing solution, such as a resol-ethanol solution for about 2 minutes. The solvent is then allowed to evaporate from the initial structure, leaving a resol-coated initial structure. The resol-coated initial structure is then cross-linked at about 100° C. to about 150° C. for about 2 hours to about 24 hours and is subsequently carbonized by heating the resol-coated initial structure to a carbonization temperature of about 800° C. at a rate of about 5° C./min. The carbonization temperature is maintained at about 800° C. for about 2 hours.
Using structured plastic waste as the initial structure allows the structured plastic waste to act as a template and, when crosslinked and carbonized, the polymers that make up the fibers of the structured plastic waste undergo pyrolysis. As shown in
The increased surface area and pore volume of the hollow fibril materials may make the resulting hollow fibril materials more efficient in various applications. For instance, increased pore volume and surface area may allow for CO2 to interact with more sites within a porous carbon matrix, resulting in greater amounts of CO2 being captured by the fibril materials, and more efficiently scrubbing commercial production process streams. In addition to exhibiting a higher surface area and a higher pore volume as compared to known porous carbons, the resulting porous carbon fibers are produced for a similar cost. Moreover, both the simplicity of the processes and highly affordable starting materials allow the resulting porous carbon fibers to be produced by these methods in amounts that can easily be scaled to larger processes.
In a second method, porous carbons are produced through selective sulfonation and thermal stabilization of matrix species in the precursor materials of the initial structure and degradation of uncrosslinked parts of the polymer domains within the material. The crosslinking mechanism of precursor material is initiated through a sulfonation step which is followed by olefination and subsequent addition/rearrangement. Polyolefin based chains can then crosslink, followed by ring closure and degradation of functional groups at elevated temperatures. This process is shown in
The initial structure is generally prepared based on the specific precursor materials included. For example, the initial structure may be thermally stabilized (e.g., through thermal annealing) to prevent deconstruction of the defined structures of the initial structure. The initial structures may further be resized or reshaped (e.g., through trimming), printed, or otherwise prepared.
After the initial structure is prepared, the precursor materials of the prepared initial structure may be crosslinked. Crosslinking the precursor materials may include using a nonvolatile solvent (e.g., concentrated sulfuric acid) to selectively crosslink chemical species of the precursor material, allowing for specific constituents to degrade upon carbonization and the generation of pores.
In some examples, crosslinking may be achieved in conjunction with sulfonation of the prepared initial structure. The prepared initial structure may be submerged in a neat sulfuric acid solution at an elevated sulfonation temperature for one or more extended periods of time and at atmospheric pressures. It is contemplated that other solutions may be used for sulfonation, including fuming acid and diluted sulfuric acid, without departing from the scope of the present disclosure. The elevated sulfonation temperature ranges from about 100° C. to about 200° C. For example, the elevated sulfonation temperature may be about 140° C., about 150° C., about 155° C., about 160° C., about 165° C., about 170° C., about 175° C., about 180° C., about 185° C., about 190° C., about 195° C., about 200° C. or any value or range of values therebetween. The period of time for which the initial structure may be submerged may be about 2 hours, about 6 hours, or about 12 hours. However, it is contemplated that the sulfonation time may range from about 15 minutes to about 72 hours without departing from the scope of the present disclosure. This submersion in the neat sulfuric acid sulfonates the initial structure. After or during sulfonation, the initial structure is stabilized through crosslinking. For example, where the initial structure is a PP-based mask, the sulfonation effectively crosslinks the polypropylene fibers prior to carbonization.
In other examples, the prepared initial structure may be sulfonated at an elevated sulfonation temperature for one or more extended periods of time and at atmospheric pressures. The sulfonated initial structure may then be de-sulfonated. De-sulfonation may include heating in the initial structure to a predetermined de-sulfonation temperature for a period of time. For example, the initial structure may be heated to about 120° C. for about one hour. De-sulfonation eliminates sulfur, oxygen, and hydrogen to yield unsaturated polyolefin, providing the reaction sites for effectively crosslinking the matrix. In various examples, the crosslinked and/or sulfonated structure may be rinsed with water prior to carbonization.
To briefly describe the thermal stabilization mechanism, the initial sulfonation reaction of polypropylene proceeds by reacting with the secondary/tertiary carbons along the polymer backbone, followed by the homolytic dissociations of sulfonyl groups, which results in unsaturated bonds within the polymer chain. These double bonds from sulfonation continue to react through a secondary addition, rearrangement, and dissociation, leading to formation of radical species that directly couple with other reactive groups from surrounding polymer chains, effectively producing crosslinked network structures. These crosslinked polymers can then be converted to carbons upon pyrolysis, potentially stripping away functional groups upon exposure to elevated temperatures in inert atmospheres.
In various examples, the sulfonation-crosslinking step may also impart additional functionality into the carbon fibers, such as inherent incorporation of sulfur heteroatoms into the carbon framework. Sulfur doping of the carbonized materials can enhance the functionality of associated carbon-based materials in many applications, including energy storage, catalysis, and CO2 adsorption.
The crosslinked and/or sulfonated structure (e.g., a sulfonated polyolefin) is then converted to carbonaceous materials (e.g., porous carbons) using carbonization processes, including without limitation, pyrolysis under N2. In various examples, the crosslinked and/or sulfonated structure is carbonized by heating the sulfonated structure from an initial temperature to a carbonization temperature at a predetermined rate. The initial temperature may be about 25° C., and the carbonization temperature may be any temperature or temperature range of about 800° C. to about 1400° C. The predetermined rate may have a range of about 1° C./min to about 10° C./min. For example, the predetermined rate may be 5° C./min. In some examples, various rates may be used to reach one or more temperatures during carbonization (e.g., heating the crosslinked and/or sulfonated structure to a first temperature at a first rate and then heating the crosslinked and/or sulfonated structure from the first temperature to a second temperature at a second rate). The carbonization temperature may then be maintained for a predetermined holding time. For example, the carbonization temperature may be maintained for about 2 hours. In general, increasing the carbonization temperatures can enhance the degree of graphitization, which improves the electrical and thermal conductivities, as discussed in more detail elsewhere herein.
Throughout this process, the initial fibril structures of the masks can be completely retained, resulting in a carbon fiber mat with mechanical flexibility. In fact, the resulting carbon fibers exhibit retention of the shape of the initial structure, increased flexibility and durability, and a greater than 50% carbon yield from the initial structure. During the carbonization process, gaseous products are released through the decomposition of the fiber, which may induce porosity, as well as enhanced surface areas. For example, the carbonized fiber or other materials may have a pore structure having an average surface area greater than about 200 m2/g and an average pore volume less than about 1 cm3/g. In some examples, the average surface area may be about 250 m2/g to about 700 m2/g.
In a third method, at least portions of the second method may be applied to form porous carbons, specifically ordered mesoporous carbons (OMCs), using nanostructured TPEs as precursor materials. For example, due to the immiscibility between different segments, SEBS can self-assemble into nanostructures, including spheres, cylinders, and/or gyroids, that can serve as the starting precursor materials. Then the aggregated PS domains can efficiently serve as physical crosslinkers to enhance the TPE's mechanical properties. Additionally, these block copolymers (BCPs) have higher molecular weights and domain spacing ranging from about 20 nm to about 50 nm, which are larger than typical sizes of surfactant micelles.
The initial structure is generally prepared based on the specific precursor materials included. In various examples, the initial structure may be thermally stabilized (e.g., through thermal annealing) to prevent deconstruction of the defined structures of the initial structure. Where the precursor materials are thermoplastic elastomers, such as SEBS powders, being used to form ordered mesoporous carbons (OMCs), the powders may be treated using thermal annealing at about 160° C. for about 12 hours to obtain long-range ordering of the nanostructures. As previously noted, in various examples, the initial structures may further be resized or reshaped (e.g., through trimming), printed, or otherwise prepared.
After the initial structure is prepared, the precursor materials of the prepared initial structure may be crosslinked. Crosslinking the precursor materials may include using a non-volatile solvent (e.g., concentrated sulfuric acid) to selectively crosslink chemical species of the precursor material, allowing for specific constituents to degrade upon carbonization and the generation of pores. Where the precursor material is a SEBS precursor material, polymer crosslinking may be performed through submerging the SEBS precursor material (e.g., SEBS powders or polystyrene-block-polybutadiene-block-polystyrene (SBS) pellets) in concentrated sulfuric acid for extended periods of time at elevated temperatures.
In some examples, crosslinking may be achieved in conjunction with sulfonation of the prepared initial structure. The prepared initial structure may be submerged in a neat sulfuric acid solution at an elevated sulfonation temperature for one or more extended periods of time and at atmospheric pressures. It is contemplated that other solutions may be used for sulfonation, including fuming acid and diluted sulfuric acid, without departing from the scope of the present disclosure. The elevated sulfonation temperature ranges from about 140° C. to about 200° C. For example, the elevated sulfonation temperature may be about 140° C., about 150° C., about 155° C., about 160° C., about 165° C., about 170° C., about 175° C., about 180° C., about 185° C., about 190° C., about 195° C., about 200° C. or any value or range of values therebetween. The period of time for which the initial structure may be submerged may be about 4 hours, about 6 hours, or about 12 hours. However, it is contemplated that the sulfonation time may range from about 10 minutes to about 72 hours without departing from the scope of the present disclosure. This submersion in the neat sulfuric acid sulfonates the initial structure.
After or during sulfonation, the initial structure is stabilized through crosslinking. For example, the crosslinking reaction may be configured to proceed through multiple mechanisms that occur in tandem throughout the sulfonation process. Initially, sulfonic acid groups are introduced to the polymer backbone, which is followed by elimination to form double bonds. These double bonds react through further additions and dissociations, consequently forming radical species that crosslink the polymer chains through intermolecular radical-radical coupling. The step of using sulfonation-enabled crosslinking to crosslink the initial structure can enable successful conversion to carbon upon exposure to high temperatures (>800° C.) in an inert atmosphere, resulting in a high carbon yield of PP and PE (i.e., up to about 70% wt), as discussed elsewhere herein.
Where the initial structure is formed of a TPE precursor material such as SEBS, the sulfuric acid used creates distinct reactions for PS and PEB blocks, as shown in
In various examples, the sulfonation-crosslinking step may also impart additional functionality into the precursor materials, such as inherent incorporation of sulfur heteroatoms into the carbon framework. Sulfur doping of the carbonized materials can enhance the functionality of associated carbon-based materials in many applications, including energy storage, catalysis, and CO2 adsorption. Additionally, large-pore mesoporous materials having a range of pore characteristics can be fabricated using this method, as discussed in more detail in Examples #-#. The pore textures and doping content can be altered by varying the processing conditions and precursor identity.
The sulfonated initial structure may then be de-sulfonated. De-sulfonation may include heating in the initial structure to a predetermined de-sulfonation temperature for a period of time. For example, the initial structure may be heated to about 120° C. for about one hour. De-sulfonation eliminates sulfur, oxygen, and hydrogen to yield unsaturated polyolefin, providing the reaction sites for effectively crosslinking the matrix. In various examples, the crosslinked and/or sulfonated structure may be rinsed with water prior to carbonization.
The crosslinked and/or sulfonated structure may be calcinated under an inert atmosphere to selective decompose the PS minority phase to produce mesoporous polymers. The crosslinked and/or sulfonated structure may be heated at a predetermined rate to a calcination temperature for a predetermined amount of time. For example, the crosslinked and/or sulfonated structure may be heated to a temperature of about 400° C. for about 3 hours at a ramp rate of about 10° C./min. In other examples, the crosslinked and/or sulfonated structure may be heated to a temperature of about 600° C.
The crosslinked and/or sulfonated structure (e.g., a sulfonated polyolefin) may be converted to carbonaceous materials (e.g., porous carbons) using carbonization processes, including without limitation, pyrolysis under N2. It is also contemplated that the crosslinked and/or sulfonated structure may be calcinated as described above before being converted to carbonaceous materials using carbonation processes. The crosslinked and/or sulfonated structure is carbonized by heating the sulfonated structure from an initial temperature to a carbonization temperature at a predetermined rate for a predetermined time. The carbonization temperature may be any temperature or temperature range of about 600° C. to about 1400° C. For example, the carbonization temperature may be about 600° C., about 800° C., about 1000° C., about 1200° C., or about 1400° C. The predetermined rate may have a range of about 1° C./min to about 10° C./min. For example, the predetermined rate may be about 5° C./min or about 10° C./min.
In some examples, various rates may be used to reach one or more temperatures during carbonization (e.g., heating the crosslinked and/or sulfonated structure to a first temperature at a first rate and then heating the crosslinked and/or sulfonated structure from the first temperature to a second temperature at a second rate).The carbonization temperature may then be maintained for a predetermined holding time. For example, the crosslinked and/or sulfonated structure may be heated to a temperature of about 600° C. at a rate of about 1° C./min and then subsequently heated from 600° C. to a second temperature at a ramp rate of about 5° C./min. The second temperature may be, for example, about 800° C., about 1000° C., or about 1200° C. The second temperature may be maintained for a predetermined time such as for about 3 hours or about 4 hours.
The production of OMCs through the third method described herein (e.g., sulfonation induced crosslinking and subsequent carbonization) is simple and scalable and can be extended to a broad selection of SEBS-based precursors. This enables the production of OMCs with multitudes of different pore characteristics. For instance, altering molecular weight of the constituents of the TPEs can produce OMCs with a broad range of pore sizes using the same processing methods. SEBS-derived OMCs to exhibit average pore sizes ranging from 4.7 nm to 16.1 nm, while the surface areas and degree or ordering of the SEBS-OMCs are reduced in comparison to other materials templated by surfactant-based molecules. Specifically, the resulting products have a higher molecular weight than traditional templates which provides enhanced mobility during the evaporation induced self-assembly process to establish well-ordered nanostructures. The increased pore size may enable use of the OMCs.
In a fourth method, by combining sulfonation-enabled crosslinking chemistry with a subsequent carbonization step, FDM-printed materials (such as, for example but not limited to, parts printed or otherwise formed using polyethylene, polypropylene, a combination thereof, and/or polypropylene-based filament, containing carbon fiber fillers) can be successfully converted to carbon materials, while retaining dimensional stability.
The initial structure is generally prepared based on the specific precursor materials included. For example, the initial structure may be thermally stabilized (e.g., through thermal annealing) to prevent deconstruction of the defined structures of the initial structure, may be resized or reshaped (e.g., through trimming), printed, or otherwise prepared. Where the initial structure is prepared using 3D printed structured polypropylene materials as the precursor materials, the initial structure may be printed a 3D printer. The mass of the initial printed structure may be taken after the structure is prepared. In various examples, the PP materials may include carbon fiber filler or other additives (e.g., the materials may be polypropylene-carbon nanofibers). The precursor materials may also be prepared before the initial structure is formed. For example, the precursor materials may be recycled PP filament prepared from plastic waste, such as disposable cups.
After the initial printed structure is prepared, the precursor materials of the prepared initial structure may be crosslinked. Crosslinking the precursor materials may include using a nonvolatile solvent (e.g., concentrated sulfuric acid) to selectively crosslink chemical species of the precursor material, allowing for specific constituents to degrade upon carbonization and the generation of pores. For example, polymer crosslinking may be performed through submerging the printed structure in concentrated sulfuric acid for extended periods of time at elevated temperatures.
In some examples, crosslinking may be achieved in conjunction with sulfonation of the prepared initial structure. The prepared initial structure may be submerged in a neat sulfuric acid solution at an elevated sulfonation temperature for one or more extended periods of time and at atmospheric pressures. The printed structure remains wholly submerged during the entirety of the sulfonation reaction. It is contemplated that other solutions may be used for sulfonation, including fuming acid and diluted sulfuric acid, without departing from the scope of the present disclosure. The elevated sulfonation temperature ranges from about 130° C. to about 170° C. For example, the elevated sulfonation temperature may be about 130° C., about 135° C., about 140° C. , about 145° C., about 150° C., about 155° C., about 160° C., about 165° C., about 170° C. or any value or range of values therebetween. The period of time for which the initial structure may be submerged may be about 48 hours. However, it is contemplated that the sulfonation time may range from about 15 minutes to about 72 hours without departing from the scope of the present disclosure. This submersion in the neat sulfuric acid sulfonates the initial structure.
After or during sulfonation, the initial structure is stabilized through crosslinking. For example, the crosslinking reaction may be configured to proceed through multiple mechanisms that occur in tandem throughout the sulfonation process. Initially, at elevated temperatures sulfuric acid reacts with the PP backbone of the precursor materials, followed by the homolytic dissociations of sulfonyl groups, leading to the formation unsaturated bonds within the polymer chains. Subsequently, alkene groups from sulfonation may continue to react through one or more different mechanisms (e.g., secondary addition, dissociation, and rearrangement), resulting in the formation of radical species that can form crosslinked network structures through intermolecular couplings. This may also lead to some chain scissions of the PP during the sulfonation process. The step of using sulfonation-enabled crosslinking to crosslink the initial structure can enable successful conversion to carbon upon exposure to high temperatures (>800° C.) in an inert atmosphere, resulting in a carbon structure having substantially the same shape as the printed initial structure, as discussed elsewhere herein.
Where the initial structure is a 3D printed structure, the sulfonation process is also configured to create micro-size cracks within the structure. These cracks may have an average crack-to-crack distance of about 100 μm to about 200 μm or any value or range of values therebetween. The cracking of the initial structure allows for diffusion of the sulfuric acid which provides a mechanism for full crosslinking of the structure.
In various examples, the sulfonation-crosslinking step may also impart additional functionality into the sulfonated and/or crosslinked structure, such as inherent incorporation of sulfur heteroatoms into the carbon framework. Sulfur doping of the carbonized materials can enhance the functionality of associated carbon-based materials in many applications, including energy storage, catalysis, and CO2 adsorption.
The sulfonated and/or crosslinked structure may then be de-sulfonated. De-sulfonation may include heating in the initial structure to a predetermined de-sulfonation temperature for a period of time. For example, the initial structure may be heated to about 120° C. for about one hour. De-sulfonation eliminates sulfur, oxygen, and hydrogen to yield unsaturated polyolefin, providing the reaction sites for effectively crosslinking the matrix. In various examples, the crosslinked and/or sulfonated structure may be rinsed with water prior to carbonization.
The crosslinked and/or sulfonated structure (e.g., a sulfonated polyolefin) may be converted to carbonaceous materials (e.g., porous carbons) using carbonization processes, including without limitation, pyrolysis under N2. It is also contemplated that the crosslinked and/or sulfonated structure may be calcinated as described above before being converted to carbonaceous materials using carbonation processes. The crosslinked and/or sulfonated structure is carbonized by heating the sulfonated structure from an initial temperature to a carbonization temperature at a predetermined rate for a predetermined time. The carbonization temperature may be any temperature or temperature range of about 600° C. to about 1400° C. For example, the carbonization temperature may be about 600° C., about 800° C., about 1000° C., about 1200° C., or about 1400° C. The predetermined rate may have a range of about 1° C./min to about 10° C./min. For example, the predetermined rate may be about 5° C./min or about 10° C./min.
In some examples, various rates may be used to reach one or more temperatures during carbonization (e.g., heating the crosslinked and/or sulfonated structure to a first temperature at a first rate and then heating the crosslinked and/or sulfonated structure from the first temperature to a second temperature at a second rate).The carbonization temperature may then be maintained for a predetermined holding time. For example, the crosslinked and/or sulfonated structure may be heated to a temperature of about 600° C. at a rate of about 1° C./min and then subsequently heated from 600° C. to a second temperature at a ramp rate of about 5° C./min. The second temperature may be, for example, about 800° C., about 1000° C., or about 1200° C. The second temperature may be maintained for a predetermined time such as for about 3 hours or about 4 hours.
The production of carbon structures through the fourth method described herein (e.g., sulfonation induced crosslinking and subsequent carbonization of a printed structure) is simple and scalable and be used to generate complex, large-scale carbon structures. The fourth method allows PP-to-carbon conversion in thick PP-based structures with controlled dimensional shrinkage. This also produces carbons that may be used as heating elements and allows conversion of plastic waste. Due to the open design space and ease of customizability afforded by FDM, the fourth method has the capacity to create complex structures that can be transformed into carbons, directly enabling the ability of on-demand carbon manufacturing with customized macroscopic structures.
As described in more detail in Examples 1-37, a suite of characterization techniques has been employed to confirm the microstructures and properties of these resulting carbon structures. Furthermore, these microstructures and properties enable potential use of the carbon structures in several practical applications, including 3D-printing, oil sorbents, nanofillers for imparting electrical conductivity and Joule heating behaviors of composites, water purification, and energy storage. It will be understood that these steps may be applied to any initial structure formed of the precursor materials without departing from the scope of the present disclosure.
In this Example 1, the initial structure was a structured plastic waste, namely common surgical masks formed of nonwoven polypropylene mats. Samples 1.1-1.3 (“S1.1”, “S1.2”, and “S1.3”, respectively) were taken of the mask. Each Sample was submerged into a precursor-containing solution, a resol-ethanol solution, for about 2 minutes. S1.1 was submerged in a solution containing about 2% resol, S1.2 was submerged in a solution containing about 4% resol, and S1.3 was submerged in a solution containing about 8% resol. The solvent was then allowed to evaporate from the Samples, leaving a resol-coated initial structure. The resol-coated initial structure of each Sample was then cross-linked at about 150° C. for about 2 hours. Each Sample was subsequently carbonized by heating the resol-coated initial structure to a carbonization temperature of about 800 ° C. at a rate of about 5° C./min. The carbonization temperature was maintained at about 800° C. for about 2 hours.
The N2 adsorption-desorption behavior of the carbonized materials of each Sample was characterized using gas physisorption measurements, which can determine pore volume, pore size distribution, and surface area of the carbon samples. Results of the testing are shown in Table 1 below and can be seen in
As shown by the data from preliminary nitrogen adsorption experiments illustrated in Table 1 and
In this Example 2, the initial structure was a structured plastic waste, namely common surgical masks formed of a porous mat of polymer fibers (e.g., melt-blow polypropylene fibers). Each polymer fiber had well-defined fibril microstructures with an average fiber diameter of about 10 nm. These microstructures are shown in
The initial structure was submerged in a neat sulfuric acid solution at a temperature of about 155° C. for various extended periods of time and at atmospheric pressures. This submersion in the neat sulfuric acid sulfonated the polymer fibers, which were then stabilized through crosslinking. The sulfonated polymer fibers were rinsed with water and carbonized by heating the sulfonated polymer fibers from 25° C. to 800° C. at a rate of 5° C./min. The temperature was maintained at about 800° C. for about 2 hours. In other examples, the sulfonated polymer fibers were carbonized by heating to 1000° C. for 2 hours.
The retention of the initial fibril structures of the polymer fibers of the initial structure after sulfonation is shown by comparison of the SEM images included in
In addition to the increased flexibility and durability, the production of the carbon materials using this method resulted in minimal mass loss. Table 2 sets forth the results of the testing, which are shown in
Under optimization, sulfonation for about 6 hours lead to about 65% mass retention after carbonization. Accordingly, about 2 grams of the polymer fibers produced about 1.2 grams to about 1.4 grams of the resulting carbon fibers. Generally, increasing the amount of exposure results in higher degrees of carbonization of the polypropylene fibers. At sufficiently long exposure times (about 10 hours), the structures and their performance deteriorated. However, as illustrated by
In this Example 3, the initial structure selected was PP-based surgical masks. During the step of preparing the initial structure step, the surgical masks were cut to remove the elastic bands and metal nosepiece. The resulting fabric was separated into three constituent layers, including two layers of non-woven fabrics and a melt-spun mat layer. In this Example, only outer layers were used to form 5 samples of the initial structure (each sample consisting of a section cut to have an average size of about 8 cm by about 5 cm).
To sulfonate the samples of the initial structure, these about 1 gram in total of the mask-formed initial structures were transferred into glass containers containing about 25 ml of concentrated sulfuric acid (98 wt %). In this step, a glass slide was placed on top of the mask-formed initial structures to keep the initial structures completely submerged in the sulfuric acid throughout the reactions. The glass containers were then placed in a muffle furnace and heated to about 155° C. During heating, a temperature ramp of about 1° C./min was used. Heating occurred for various amounts of time.
Upon sulfonation, the samples of the initial structure were removed from the muffle furnace and cooled down to room temperature. To wash the samples, sulfuric acid was first removed from the glass containers. Subsequently, the samples were carefully placed in a quartz funnel, where each sample was washed at least three times with deionized water in order to completely remove the residue acid. The neuralization was confirmed by pH papers. The samples were then dried by placing on a glass petri dish in a vacuum oven for overnight.
A PerkinElmer Frontier Attenuated Total Reflection (ATR) Fourier-transform infrared (FTIR) spectrometer was used to record the changes in chemical compositions of the sulfonated samples as a function of time. The scan range was 4000 cm−1-600 cm−1 with 32 scans and a resolution of 4 cm−1. The progress of the sulfonation reaction was monitored by tracking mass gain as a function of sulfonation time, as well as through FTIR spectroscopy. Results of these monitoring methods are illustrated in
As shown in
In this Example 4, the samples from Example 3 were analyzed to determine the morphological changes of the fiber structure after various sulfonation time periods using a Zeiss Ultra 60 field emission scanning electron microscope (SEM). Specifically, the fiber structures of the initial samples of Example 3 and the sulfonated samples of Example 3 (including samples sulfonated for about 2 hours and for about 12 hours) were further investigated using SEM. During these measurements, energy dispersive X-ray spectroscopy (EDS) was coupled for determining the content of different elements within the materials after sulfonation. Additionally, fiber diameters were determined and recorded using ImageJ image analysis software. X-ray photoelectron spectroscopy (XPS) experiments were performed using a Thermo-Fisher ESCALAB Xi+ spectrometer equipped with a monochromatic Al X-ray source (1486.6 eV) and a MAGCIS Ar+/Arn+ gas cluster ion sputter (GCIS) gun. Measurements were performed using the standard magnetic lens mode and charge compensation. The base pressure in the analysis chamber during spectral acquisition was at 3×10-7 mBar. Spectra were collected at a takeoff angle of 90° from the plane of the surface. The pass energy of the analyzer was set at 150 eV for survey scans with an energy resolution of 1.0 eV; total acquisition time was 220 s. Binding energies were calibrated with respect to C1 s at 284.8 eV.
As shown in
It was also found that extending the reaction time to about 12 hours did not alter the fiber diameters, and yet can result in slight distortion and curving of the fibers, as shown in
In this Example 5, carbonization of the sulfonated and thermally stabilized samples from Example 4 was performed using an MTI Corporation OTF-1200X tube furnace under an N2 atmosphere. The samples were heated at a rate of about 1° C./min until reaching a temperature of about 600° C. The samples were then heated at a rate of about 5° C./min until reaching a carbonization temperature of about 800° C. or higher. The carbonization temperature was maintained for a holding time of about 3 hours.
Samples from Example 4 were evaluated to determine carbon yield after two distinct crosslinking times (about 2 hours of sulfonation and about 12 hours of sulfonation). Carbon yield was determined using Thermogravimetric analysis (TGA) conducted using a Discovery Series TGA 550 (TA Instruments) to determine the mass loss of polymer precursors as a function of pyrolysis temperature. Sulfonated samples, approximately 10-20 mg in mass, along with a control sample of un-sulfonated PP were pyrolyzed under a N2 environment, replicating the carbonization procedure used in the tube furnace.
All organic components of the control sample were completely degraded with 0% mass retention after exposure to about 800° C. under N2. As shown in
Additionally, the samples undergoing only 2 hours of sulfonation exhibited hollow structure carbon fibers (see
Specifically, the fiber structures of the initial samples of Example 3 and the sulfonated samples of Example 3 (including samples sulfonated for about 2 hours and for about 12 hours) were further investigated using SEM. During these measurements, energy dispersive X-ray spectroscopy (EDX) was coupled for determining the content of different elements within the materials after sulfonation. Additionally, fiber diameters were determined and recorded using ImageJ image analysis software. X-ray photoelectron spectroscopy (XPS) experiments were performed using a Thermo-Fisher ESCALAB Xi+ spectrometer equipped with a monochromatic Al X-ray source (1486.6 eV) and a MAGCIS Ar+/Arn+ gas cluster ion sputter (GCIS) gun. Measurements were performed using the standard magnetic lens mode and charge compensation. The base pressure in the analysis chamber during spectral acquisition was at 3×10-7 mBar. Spectra were collected at a takeoff angle of 90° from the plane of the surface. The pass energy of the analyzer was set at 150 eV for survey scans with an energy resolution of 1.0 eV; total acquisition time was 220 s. Binding energies were calibrated with respect to C is at 284.8 eV.
Furthermore, Raman spectroscopy was employed to characterize the degree of graphitization of the resulting carbon fibers. In general, carbon materials with higher degrees of graphitization can exhibit better electrical and thermal conductivity through facilitating the electron transport along the in-plane direction as opposed to the amorphous carbon counterparts. Results of the spectroscopy are shown in
The N2 adsorption-desorption behavior of the mask-derived carbon fiber was characterized using gas physisorption measurements, which can determine pore volume, pore size distribution, and surface area of the carbon samples. Specifically, pore size distribution of samples was estimated from the adsorption isotherm using the Barrett, Joyner and Halenda (BJH) model, whereas the surface area was determined from the typical Brunauer Emmett and Teller (BET) analysis.
The sulfonated fibers prior to the carbonization possess no micropores. As shown in
To further demonstrate the use of derived carbon fibers in practical applications, experiments using the samples from Example 5 were performed to determine Joule heating. The ability of a material to reach elevated temperatures upon the application of low voltages through Joule heating provides great potential in several applications, including thermotherapy, crude oil recovery, and thermochromics. Joule heating is a result of electrons colliding with atoms within a conductor, and which generates heat in regions where current transmits. Equation 1 simplistically depicts the Joule heating of a current density j in an electrical field E in a material of electrical conductivity . . . σ.
Q=j·E=·E2 Equation 1
This relationship demonstrates that the thermal energy produced from Joule heating is directly dictated by the conductivity of the material where enhanced conductivity results in increased output of energy in to form of Joule heating. In Joule heating experiments, carbonized mask fibers were subjected to different voltages, then allowed to be equilibrated. Specifically, the Joule heating capabilities of the carbonized mask fibers were determined by connecting the fibers
This relationship demonstrates that the thermal energy produced from Joule heating is directly dictated by the conductivity of the material where enhanced conductivity results in increased output of energy in to form of Joule heating. In Joule heating experiments, carbonized mask fibers were subjected to different voltages, then allowed to be equilibrated. Specifically, the Joule heating capabilities of the carbonized mask fibers were determined by connecting the fibers to a DC power supply using a glass slide as a support. The voltage was increased in increments of 1 V and the temperature was measured using a thermal camera (from HTI) until the equilibrium state was reached. This relationship demonstrates that the thermal energy produced from Joule heating is directly dictated by the conductivity of the material where enhanced conductivity results in increased output of energy in to form of Joule heating. In Joule heating experiments, carbonized mask fibers were subjected to different voltages, then allowed to be equilibrated. Specifically, the Joule heating capabilities of the carbonized mask fibers were determined by connecting the fibers to a DC power supply using a glass slide as a support. The voltage was increased in increments of 1 V and the temperature was measured using a thermal camera (from HTI) until the equilibrium state was reached.
As shown in
To further highlight the applications of the resulting carbon fibers from Example 5, water contact angle measurements were recorded and analyzed using a goniometer and Contact Angle software from Ossila. The carbonized mask fibers from Example 5 exhibit high water contact angles (
Oil adsorption studies were performed by submerging carbonized mask fibers into 20 mL various organic solvents for at least 5 minutes, and recording the mass adsorbed immediately after removing from the solvent. The carbon mask fibers exhibited varied adsorption capacities for different organic solvents, with a maximum amount of up to 14 grams of mineral oil per gram of carbon fiber. The difference in the uptake capacity against different solvents is primarily associated with the surface energy of carbon surfaces and the interactions between the surface functional groups and solvent molecules.
The hydrophobicity of carbon materials enables their use for oil adsorption. The favorable interactions between organic solvents and hydrophobic carbon drives the adsorption of oils to the carbon surface. Additionally, this performance is highly cyclable, where the sorbate can be efficiently removed, and the carbon fibers can be reused in further adsorption. This advantageous property was confirmed in
In this Example 8, samples of Example 6 were further tested through activation of the resulting carbon fiber product. The activation process was performed by physically grinding the previously produced carbon fiber product with potassium hydroxide (KOH) at a 1:2 mass ratio. After activation at 700° C. with a ramp rate of 1° C./min for 1 h, the product was washed with DI water, centrifuged, and then dried. This process was repeated 6 times. The carbonized masks were activated through reacting with KOH to enhance the porosity of the carbon fibers and increase surface area.
From the N2 isotherm in
To gauge the performance of the activated mask in water remediation applications, dye adsorption studies were performed with a water-soluble dye, basic blue 17. The adsorption capacities as a function of time in 3 different dye concentrations were investigated, which were 0.07 mg/mL, 0.15 mg/mL, and 0.30 mg/mL. The activated mask fibers had adsorption capacities of roughly 0.033 mg/mg, 0.09 mg/mg, and 0.19 mg/mg for the 0.07 mg/mL, 0.15mg/mL, and 0.30 mg/mL solutions, respectively. Results for the 0.15 mg/mL solution are shown in
The dye adsorption kinetics were fit to a pseudo first order model using Equation 2 where qe is the amount of dye adsorbed at equilibrium, qt is the amount of dye adsorbed at equilibrium, is the amount of dye adsorbed at time is the amount of dye adsorbed at time t, and k1 is the first order equilibrium rate constant
At 0.15 mg/mL and 0.30 mg/mL, the rate constant of the dye adsorption by the activated fibers (0.649 hAt 0.15 mg/mL and 0.30 mg/mL, the rate constant of the dye adsorption by the activated fibers (0.649 hAt 0.15 mg/mL and 0.30 mg/mL, the rate constant of the dye adsorption by the activated fibers (0.649 h−1 and 0.213 h−1, respectively) was significantly higher than the adsorption by the standard commercially available PAC (0.076 h−1 and 0.075 h−1, respectively).
In this Example 9, the initial structure selected was PP-based surgical masks. During the step of preparing the initial structure step, the surgical masks were cut to remove the elastic bands and metal nosepiece. The resulting fabric was separated into three constituent layers, including two layers of non-woven fabrics and a melt-spun mat layer. In this Example 10, only outer layers were used to samples of the initial structure with each sample weighing about 0.3 grams.
To sulfonate the samples of the initial structure, the samples were transferred into glass containers containing about 30 ml of concentrated sulfuric acid (98 wt %). In this step, a glass slide was placed on top of the mask-formed initial structures to keep the initial structures completely submerged in the sulfuric acid throughout the reactions. The glass containers were then placed in a muffle furnace and heated to about 145° C.
Upon sulfonation, the samples of the initial structure were removed from the muffle furnace and cooled down to room temperature. To wash the samples, sulfuric acid was first removed from the glass containers. Subsequently, the samples were washed at least three times with deionized water in order to completely remove the residue acid. The samples were then placed in a vacuum oven overnight to dry to ensure any residual water was removed.
A PerkinElmer Frontier Attenuated Total Reflection (ATR) Fourier-transform infrared (FTIR) spectrometer was used to record the changes in chemical compositions of the sulfonated samples as a function of time. The scan range was 4000 cm−1-600cm−1 with 32 scans and a resolution of 4 cm−1. The progress of the sulfonation reaction was monitored through FTIR spectroscopy. Results of this monitoring are illustrated in
As shown in
In addition to FTIR spectroscopy, the change in the chemical composition of crosslinked PP fibers as a function of reaction time was investigated through XPS.
In this Example 10, after the sulfonation crosslinking reaction, the samples of Example 9 were washed and subsequently carbonized under N2 atmosphere at about 800° C. The crosslinking reaction enabled carbon yields up to about 45% as shown in
Nitrogen sorption isotherms at 77 K were used to determine the pore characteristics of the carbonized fibers as a function of sulfonation time and are depicted in
After carbonization, the heteroatom content of the carbon fibers was determined through XPS.
The heteroatom content of the materials is further elucidated in the high resolution XPS scans in
In this Example 11, carbonized samples from Example 10 were tested using a Micromeritics Tristar II instrument to determine CO2 and N2 sorption performance at ambient temperature. Due to the largely similar pore characteristics of the samples of Example 10, the effect of the increased presence of sulfur groups can be observed in the CO2 adsorption isotherms in
In this Example 12, the initial structure was formed of bulk SEBS with 27 vol % styrene content (amorphous polymer, Mn: 121,000 g/mol, a 1.07). Preparation of the initial structure included annealing the initial structure at a temperature of about 170° C. to about 180° C. for about 12 hours. The initial structure was sulfonated in sulfuric acid at 85° C. for 2 h. Subsequently, a de-sulfonation step was conducted by heating the initial structure at 120° C. for about 1 hour. The sulfonated initial structure was carbonized by heating the sulfonated structure from about 25° C. to a carbonization temperature of about 800° C. at a rate of about 5° C./min. The carbonization temperature of about 800° C. was maintained for about 2 hours. This process resulted in OMCs with average pores sizes of about 22 nm and an average surface area of about 513 m2/g.
As shown in
As shown in
In Examples, 13-19, samples were formed of materials having the properties shown in Table 4 below.
Each of SEBS118, SEBS89, SEBS130, and SEBS100 may be referred to herein as a “SEBS materials”. The SEBS materials used in this study are amorphous, providing an important mechanism for facilitating the crosslinking reaction and enabling significantly shorter reaction times for bulk sample crosslinking.
In this Example 13, the initial structure was formed of SEBS118 precursor material. The initial structure was annealed under a nitrogen atmosphere at a temperature of about 160° C. for about 12 hours to establish long-range ordering in the structure's nanostructures. Samples of about 0.300 grams of the respective annealed SEBS material was then submerged in about 3 grams of concentrated sulfuric acid solution at a temperature of about 150° C. for varying amounts of time. Other samples of the annealed initial structure formed of SEBS118 precursor material were sulfonated by submerging about 0.300 grams of the annealed SEBS118 material in about 3 grams of concentrated sulfuric acid solution at a temperature of either about 85° C. or about 125° C. for varying amounts of time. Measurements were taken for reaction times of about 0.25 hour, about 0.5 hour, about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 6 hours, and about 8 hours. This submersion in the neat sulfuric acid crosslinked the olefinic block (PEB) of the structure of the SEBS118 precursor material. After the sulfonation was complete, the contents of the reaction vessel were passed through a glass fritted funnel, and the polymer was removed. The sulfonated material was washed with 200 mL of deionized water at least three times to completely remove the residual acid and other reaction by-products. The washed material was then dried under vacuum.
The reaction progress was monitored using measurements for mass gain and gel fraction of the sulfonated and cross-linked product. Mass gain throughout sulfonation was monitored by massing the starting material prior to sulfonation and comparing to the final mass after washing and drying. As shown in
To measure the gel fraction of the sulfonated material, the material was washed in hot toluene at a temperature of about 85° C. for about 12 hours to remove any uncrosslinked fractions and the mass was compared before and after. As shown in
The samples sulfonated at the temperatures of about 85° C. and about 125° C. exhibited slower kinetics than the samples sulfonated at 150° C. The lower temperature samples also demonstrated lower plateau values of mass gain and gel fraction. As shown in
In this Example 14, the changes in chemical composition of the sulfonated polymers of Example 13 during the sulfonation reaction were further illustrated using the Fourier transform infrared (FTIR) spectra shown in
For samples sulfonated at a temperature of about 150° C., rapid PS functionalization was observed as evidenced by a prominent vibration associated with the disubstituted aromatic rings of the PS block at 1006 cm−1. At shorter reaction times (e.g., about 0.25 hour, about 0.5 hour, and about 1 hour), this vibration was dominant, while the alkyl stretching vibrations associated with the PEB block at 2851 cm−1 and 2920 cm−1 only diminished slightly. This result indicates that the primary reaction occurring at short timescales (within the first hour) is the sulfonation of PS segments.
However, as also shown in
For samples sulfonated at temperatures of about 85° C. and about 125° C., the FTIR spectra indicated a reduced presence of the characteristic bands (sulfonic acids: 1033 cm−1 and 1006 cm−1 , alkenes: 1615 cm−1) associated with the crosslinking reaction, in addition to the retention of the alkyl stretching vibrations (2851 cm−1 and 2920 cm−1 ), as shown in
In this Example 15, titration experiments were performed on samples of the sulfonated SEBS118 materials sulfonated at a temperature of about 150° C. of Example 13. The titration experiments were conducted to determine the amount of sulfonic acid groups on the polymer backbone as a function of crosslinking time (i.e., the degree of sulfonation). This was accomplished by introducing samples of about 200 mg of the sulfonated SEBS118 in about 0.1 M sodium chloride (NaCl) solutions for about 48 hours to exchange the protons of the sulfonic acid with sodium ions. The solution in which each sample was soaked was then titrated using a 0.026 M NaOH solution until a pH of 7 to determine the concentration of acid present within the solution and thus the amount of sulfonic acid that was present in the polymer after reaction.
Where VNaOH is the volume of NaOH required to neutralize the solution, MNaOH is the molarity of the NaOH solution, mSEBS is the mass of sulfonated polymer that was added to the NaCl solution, M(w,SEBS) is the molecular weight of the polymer (118,000 g/mol), and N is the number of repeat units (about 2640). Ultimately, this calculation provides the percentage of repeat units that contain sulfonic acid groups after the sulfonation reaction.
As shown in
In this Example 16, the effects of the sulfonation reaction on the nanostructure of the SEBS118 material of Example 13 sulfonated at a temperature of about 150° C. were determined using small angle x-ray scattering (SAXS). As shown in
As shown in
Additionally, as shown in
Referring again to
In this Example 17, thermogravimetric analysis (TGA) experiments were conducted on samples of the SEBS118 materials of Example 13 using a Discovery Series TGA 550 from TA instruments. Samples were heated in N2 atmosphere at ramp rates of 10° C./min. Samples included neat SEBS118 and SEBS118 materials after sulfonation for 4 hours at a temperature of about 150° C. Samples of sulfonated PS were also tested.
In this Example 18, sulfonated samples of SEBS118 materials were calcinated after washing. The washed structures were heated in a tube furnace under a N2 atmosphere at about 400° C. for about 3 hours with a ramp rate of about 10° C./min to form calcinated SEBS118 samples. Samples of the sulfonated and/or crosslinked SEBS118 materials were also carbonized by pyrolyzing the materials in a tube furnace by first heating to about 600° C. with a ramp rate of about 1° C./min followed by increasing the temperature to either a) about 800° C., b) about 1000° C., or c) about 1200° C. at a ramp rate of about 5° C./min.
As shown in
SAXS patterns were generated of the calcinated SEBS118 materials as well as the carbonized SEBS118 materials. As shown in
Nitrogen adsorption and desorption isotherms were recorded at 77 K through the use of a Tristar II 3020 (Micromeritics). As shown in
In this Example 19, samples of the SEBS118 materials sulfonated for about 1 hour, about 2 hours, and about 3 hours were carbonized at a temperature of about 800° C. under N2 atmosphere. These results indicate that sulfonation times are still sufficient for producing relatively well-ordered porous carbon materials and confirm the presence of ordered mesopore structures.
As shown in
As shown in
Scanning electron microscopy images (SEM) were recorded on a Zeiss Ultra 60 field-emission SEM with an accelerating voltage of 17 kV and samples were carbon sputtered coated prior to imaging. Pore size analysis of SEM images was conducted using ImageJ software. X-ray photoelectron spectroscopy experiments were carried out using an ESCALAB Xi+ spectrometer (Thermo Fisher) equipped with a monochromatic Al X-ray source (1486.6 eV) and a MAGCIS Ar+/Arn+ gas cluster ion sputter gun. All spectra were recorded with a takeoff angle of 90° with respect to the surface, and the base pressure during spectral acquisition was 3×10-7 mbar. High resolution scans were fit using Avantage software from Thermo Fisher. Values determined using the SEM images are found in Table 5 below.
Specifically, Table 5 includes values for domain spacings, pore textures and sulfur content of SEBS derived mesoporous materials determined through SAXS, nitrogen adsorption/desorption isotherms and XPS, respectively. Samples are named using the following naming convention which consists of two parts X-Y, where X represents the identity of the polymer precursor and Y represents the calcination/carbonization temperature. SEBS118-OMS is an exception and represents ordered mesoporous silica produced using SEBS118-800 as a template.
These XPS results of the calcinated mesoporous polymer, and the SEBS118-derived OMCs carbonized up to 1200° C., indicate the presence of sulfur doping in the mesoporous products. Specifically, the mesoporous polymer and SEBS118-OMC carbonized at 800° C. exhibited sulfur contents of about 1.8 at % and about 1.5 at %, respectively. Increasing carbonization temperature to about 1000° C. and about 1200° C. decreased the sulfur content to about 0.9 at % and about 0.7 at % as the heteroatoms are eliminated from the framework at elevated temperatures.
Raman spectroscopy experiments were conducted using a 328i spectrometer (Andor Kymera) with 600 I/mm gratings centered around 532 nm. The system was equipped with an Andor Newton camera, and the laser was operated at 532 nm with a power of ˜20 mW. As shown in
In this Example 20, to show that the third method described above can be used with various TPEs to produce OMCs with different pore sizes, additional samples were sulfonated, crosslinked and carbonized. These samples each has an initial structure formed of one of SEBS89 precursor materials, SEBS100 precursor materials, and SEBS130 precursor materials. The initial structures were annealed under a nitrogen atmosphere at a temperature of about 160° C. for about 12 hours to establish long-range ordering in the structure's nanostructures. Each sample of the respective annealed SEBS material (about 0.300 grams each) was then submerged in about 3 grams of concentrated sulfuric acid solution at a temperature of about 150° C. for varying amounts of time. Measurements were taken for reaction times of about 0.25 hour, about 0.5 hour, about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 6 hours, and about 8 hours. After the sulfonation was complete, the contents of each reaction vessel were passed through a glass fritted funnel, and the resulting polymer was removed. Each sample of sulfonated material was then washed with 200 mL of deionized water at least three times to completely remove the residual acid and other reaction by-products. The washed materials were then dried under vacuum.
The changes in chemical composition of the sulfonated polymers during the sulfonation reaction were illustrated using the FTIR spectra shown in
The sulfonate and/or crosslinked samples were then carbonized by pyrolyzing the materials in a tube furnace by first heating to about 600° C. with a ramp rate of about 1° C./min followed by increasing the temperature to about 800° C. at a ramp rate of about 5° C./min. This carbonization formed the samples into samples of OMCs derived from their respective precursors (e.g., SEBS100-derivce OMCs).
SAXS profiles were generated of the carbonized samples, with results shown in
A summary of the resulting properties shown in
These results show that controlling the molecular weight of the precursor provides the ability to manipulate the pore texture of the final porous product. For instance, the domain spacing of the OMC. prepared using SEBS89, is reduced to about 24.2 nm as compared to the SEBS118-derived counterpart of Example 19 (33.9 nm). This is also confirmed through the nitrogen adsorption/desorption isotherm in
These results further demonstrate the versatility of this process through successful extension to a SEBS precursor (SEBS100) which is grafted with maleic anhydride (2 wt %). The samples of SEBS100 were successfully crosslinked, as determined through FTIR spectroscopy shown in
In this Example 21, samples of initial structures were polystyrene-block-polybutadiene-block-polystyrene (SBS) pellets having an average diameter of about 8 nm to about 20 nm and having a molecular weight of about 118,000 g/mol, Ð of about 1.59, and ϕPS≈0.20. Samples of the pellets were placed in a reaction vessel containing about 3 g of sulfuric acid, which was then heated at either a temperature of about 100° C. or about 150° C. for varying amounts of time. Following sulfonation, the crosslinked samples were removed and washed with DI water three times to remove byproducts and residual acid. Subsequently, the samples were then dried overnight at 125° C. The progress of the sulfonation reaction was monitored through recording mass gain, gel fraction, and the evolution of functional groups in the polymer through FTIR spectroscopy, the results of which are provided in
The extent of crosslinking was investigated by gel fraction testing where samples were vigorously stirred in toluene for 60 min, and sample mass before and after extraction was compared. As shown in
These results are further supported through FTIR spectra provided in
Small angle x-ray scattering (SAXS) measurements were taken of neat samples of the SBS pellets and of the samples sulfonated at a temperature of about 100° C. As shown in
In this Example 22, samples of the sulfonated materials of Example 20 were carbonized by heating the samples under a N2 atmosphere at a rate of 1° C./min to 600° C. and thereafter 5° C./min to 800° C. using a tube furnace.
Thermal degradation profile of sulfonated SBS was further characterized by thermogravimetric analysis (TGA) under a nitrogen environment to 800° C. at a rate of 20° C./min. The TGA was used to study the decomposition of the SBS precursors and their carbon yield. The TGA results shown in
In this Example 23, the structure of the SBS-derived OMCs after carbonization of the materials used to form the samples examined in Example 22 were studied through a suite of characterization measurements. Nitrogen physisorption experiments were employed to investigate the surface area, porosity and PSD of the SBS-derived OMCs at varied reaction temperatures. The liquid nitrogen physisorption isotherms of OMC samples (at 77 K) were characterized on a Micromeritics Tristar II 3020. As shown in
Surface areas were found through Brunauer-Emmett-Teller (BET) analysis. BET surface areas of SBS100 and SBS150 were found to be about 176 m2/g and about 373 m2/g, respectively. As shown in
An ESCALAB Xi+spectrometer (Thermo Fisher) equipped with a monochromatic A1 X-ray source (1486.6 eV) and a MAGCIS Ar+/Arn+ gas cluster ion sputter gun was used for X-ray photoelectron spectroscopy (XPS) characterization. A base pressure in the analysis chamber of 3×10−7 mbar and a takeoff angle of 90° from the surface was set for spectral acquisition. As shown in
In this Example 24, the initial structure was a 3D-printed structure formed from PP-CF precursor materials. The CF content of the initial structure was about 15 wt %. The initial structure was printed into a gyroid-shaped following the recommended procedure from the manufacturer (0.4 mm print head, 0.2 mm layer height, bed temp 80° C., nozzle temp 225° C.). The initial structure was soaked in concentrated sulfuric acid (98%) at about 155° C. for about 6 hours. During sulfonation, a cracked, sulfur-doped carbon framework was created including cracking that occurs during sulfonation to assets in the diffusion of the sulfuric acid. After sulfonation was completed, the sulfonated initial structure was removed from the acid and washed with water. The sulfonated structure was then carbonized by heating the sulfonated structure to a temperature of about 800° C. at a heating ramp of 1° C./min.
To confirm the mass retention, FTIR spectroscopy was performed on the resulting carbonized structure. As shown in
The ability to easily produce complex shapes may have applications such as heat sink, where large surface area is required for heat dissipation. Current heat sink technology has an over $10 billion USD market, but is largely limited to material selection (aluminum), and shape (only block-type shape can be produced). Our fabricated material will be well-suited for such application due to following advantages, 1) high thermal conductivity of our graphitic carbons; 2) large surface area from our unique printed structure; 3) significantly reduced materials and energy cost compared to metal fabrication; 4) no post-manufacturing waste being generated; 5) lightweight nature of our materials.
In this Example 25, 3D printed initial structures were generated using an Ultimaker S5 FDM 3D printer. Commodity PP was used as starting materials, which can be directly converted to structured carbon. Each initial structure sample was formed of a gyroid cube with 1.65 cm in dimension, a wall thickness of about 0.6 mm, and a 20% infill density. The initial structure samples were printed using a nozzle temperature of 220° C., a bed temperature of 80° C. with Magigoo PP bed adhesive. A printing speed of 40 mm/s and a 20% fan speed were used during printing. The mass of printed structures, as well as parts after crosslinking, gel fraction test, and carbonization was obtained using a balance.
The initial printed structure samples were transferred to glass containers and submerged in 150 mL of concentrated sulfuric acid. The printed structures were completely submerged in sulfuric acid throughout the reaction. The containers were placed into a muffle furnace and heated to either 130° C., 150° C., or 170° C. at a ramp rate of about 1° C./min for crosslinking reactions to occur. The sulfonation process was held under isothermal conditions for a controlled amount of time. Upon sulfonation, the initial printed structure samples were removed from the muffle furnace and passively cooled to room temperature. The initial printed structure samples were then removed from the glass containers and rinsed by deionized water at least three times to completely remove the residual acid and other reaction by-products. The neutralization of acid wastes was confirmed using pH papers. Each of the initial printed structure samples was then rinsed with acetone to facilitate drying and placed in a vacuum oven for overnight.
These results indicated that the sulfonation temperature not only directly dictates the kinetics of PP crosslinking, but also influence the ability of a part to retain its printed geometry.
The sulfonation kinetics of PP can be elucidated by understanding their mass uptake as a function of time and reaction temperature, as shown in
An attenuated total reflection Fourier transform infrared (FTIR) spectrometer was used to monitor changes in the chemical composition of sulfonated printed structure samples as a function of time. The scan range was 4000 cm−1-600 cm−1 with 32 scans and a resolution of 4 cm−1.
Differential scanning calorimetry (DSC) was performed using a Discovery 250 (TA Instruments). A heat-cool-heat cycle was employed with an initial heating cycle from 20° C. to 220° C. at a rate of 10° C./min to erase thermal history. Samples were cooled to 20° C. at a rate of 5° C./min and then heated back to 220° C. at a rate of 10° C./min. Data analysis was performed using Trios software and results are shown in
A gel fraction test was performed by soaking crosslinked printed structure samples in hot xylene at 120° C. for about 24 hours and comparing the mass before and after extraction for determining the content of insoluble fractions. Additionally, as shown in
A Zeiss Ultra 60 field-emission scanning electron microscope (SEM) was also used to understand morphological changes in the printed structure samples after sulfonation for various amounts of time and after the carbonization process, with an accelerating voltage of 10 kV. In our 3D printed parts, PP with approximately 0.6 mm wall thicknesses of each layer were employed and a full degree of crosslinking was obtained within about 48 hours. This phenomenon cannot be simply explained by sluggish diffusion of sulfuric acid within polyolefin matrix, which would take much longer time for achieving complete penetration (more than several days). A close examination of the morphology of these gyroid parts after crosslinking for various times using SEM revealed that micro-size cracks are generated through the reaction process. These cracks provided an important mechanism for significantly facilitated diffusion and crosslinking kinetics, through which the acid can penetrate into these cracking-channels within printed parts for furthering the reaction. These cracks were observed to develop over time and their initiations have a strong dependence on reaction temperature. Since the reaction of PP is from outside in, the chemical changes on the outer layers of the printed parts directly alter their thermal expansivity and hydrophobicity.
Using SEM, we found that the crosslinking was completely penetrated through thick, printed PP parts after crosslinking at 150° C. for about 48 hours, confirmed by solid PP structures after rigorous solvent extraction using hot xylene. The averaged crack-to-crack distances for samples were slightly reduced to 108 μm at 150° C. For samples that were crosslinked at 170° C., significant disruption to the layered microstructure was observed and the averaged crack-to-crack distance increased to 208 μm. Additionally, at 170° C. the formation of pores within the printed structure was observed. These voids were resulted from the release of gaseous byproducts from the sulfonation reaction developing within the softened polymer structure, causing framework expansion and disruption to the overall structure. For PP samples crosslinked at 150° C., approximately 4% of dimensional expansion was observed in the printing directions after about 48 hours.
In this example 26, carbonization of the sulfonated printed structure samples of Example 26 was performed using a tube furnace under a N2 atmosphere at a rate of about 1° C./min to 600° C. and thereafter at a rate of about 5° C./min to 800° C. Various samples were heated to a higher carbonization temperature of 1400° C. to be used to confirm the geometry stability and mass yield of carbon products.
Carbon yield was calculated for each of the samples having various sulfonation conditions, as shown in
Raman spectroscopy was performed using a Andor Kymera 328i spectrometer (with 600 l/mm gratings centered on 532 nm) equipped with Andor Newton camera. The laser was operated at 532 nm, with ˜20 mW power. As shown in
Since our method inherently incorporates sulfur groups into the carbon framework, XPS was used to assess the heteroatom content present in the final carbon structures, as shown in
SEM was used to elucidate the impact of carbonization conditions on the microstructures of PP-derived carbons. Nitrogen physisorption experiments were conducted using a Tristar II 3020 surface area and pore size analyzer (Micromeritics). The sorption measurements using N2 at 77 K confirmed that only very limited pores (within the range of p/p0 from 0.01 to 0.05) were generated, as shown in
In this Example 28, dimensional shrinkage between the initial prints and the final carbon structures was assessed through the measurement of critical dimensions (including length, width, and height) of as printed and carbonized samples. A variety of gyroids were prepared with a unit dimension between about 1 cm and about 4 cm. Each of these sample gyroids were sulfonated at 150° C. for about 48 hours and carbonized at 800° C.
In this Example 29, cubic gyroid structures with 2 cm in dimension, and a range of packing densities from 20% to 100%, were prepared. A control PP sample was also prepared by compression molding (2 mm in thickness). A first set of samples and the control sample were sulfonated at 150° C. for about 48 hours and carbonized at 800° C. The control sample was unable to be sufficiently crosslinked and resulted in structural collapse after carbonization. A second set of samples were sulfonated at 150° C. for about 72 hours and carbonized at 800° C.
The dimensional shrinkage and carbon yield were systematically assessed using the same approach set forth in Example 28. As shown in
Upon increasing the sulfonation time to about 72 hours, the yield achieved with these specimens was found to increase up to 55% with an 80% infill density and 50% with a 100% infill density. The degree of shrinkage in these densely packed parts was found to reduce overall with increasing in-fill density. Furthermore, in the 3D printed parts, inherent void channels were still observed even with 100% in-fill density). These channels can play an important role for encouraging sulfuric acid diffusion for PP crosslinking.
In this Example 30, a variety of carbon products (as well as printed PP parts as starting materials) with relatively complex shapes (including hexagonal structures, wing-shape, pyramid, and The Thinker) were printed using PP starting materials as shown in
In this Example 31, the mechanical properties of carbon structures from Example 28 were systematically investigated using compressive testing methods, to elucidate how the mechanical property anisotropy inherent to the FDM process impacts the final properties of carbon structures. Compressive mechanical testing was performed in accordance with a modified ASTM D695 standard using an MTS Insight test frame with a 5k N load cell and compression grips. A strain rate of 1 mm/min was used. Mechanical property data was analyzed using Igor Pro 8 to identify compressive yield strength by the point of zero slope in the stress strain curve and compressive modulus through the initial slope of the linear elastic regime. As shown in
In this Example 32, model heating elements having a W-shape were sulfonated at a temperature of 150° C. for about 48 hours and then carbonized at a temperature of 800° C. were prepared and attached to a power source. The Joule heating capabilities of the carbonized elements were determined by connecting the carbonized elements to a DC power supply (from Dr. Meter) using a ceramic block as a support. The voltage was increased in increments of 1 V, and the temperature was measured using a thermal camera (from HTI) and/or a thermocouple until the equilibrium state was reached. The temperature of a heating element was tracked as a function of time for two defined power settings as shown in
As shown in
The relationship between power supplied and the temperature of the element was further demonstrated by incrementally increasing the power. As shown in
In this Example 33, recycled 3D filament was prepared by washing and drying PP from used disposal cups, which were granulated and subsequently extruded using a Filabot EX2 filament extruder with Filabot Puller at a barrel temperature of 225° C. and a screw speed of 15 rpm. The recycled filament was sulfonated at a temperature of 150° C. for about 48 hours and then carbonized at a temperature of 800° C. The specimens prepared from recycled PP filament exhibited an average carbon yield of ˜57 wt % and consistent shrinkage with that of commercially available, virgin PP filaments. The values of commercially available, virgin PP filaments are shown below in Table 8.
This demonstrates that the process of the fourth method used in this Example 33 has potential as a plastic upcycling approach, creating value to post-consumer waste for addressing the challenges of massive PP waste.
In this Example 34, sample initial structures were formed of a polypropylene-based filament, containing 15 wt % chopped carbon fiber fillers (PP-CF), was printed using the fused deposition modeling (FDM) method. The initial structures were each a model gyroid-shape sample (˜16 mm in all dimensions). Each initial structure was fully submerged in concentrated sulfuric acid within beakers. They were then transferred to a muffle furnace and the temperature was increased by 2° C./min until the sulfonation temperature of about 150° C. was reached. For crosslinking of PP-CF, isothermal conditions were maintained for a controlled time. Specimens were then removed from the glass containers and washed three times with DI water to completely remove residual acid and other reaction by-products. The neutralization of acid waste was confirmed using pH paper. Samples were then rinsed with acetone to accelerate drying and placed under vacuum in a vacuum oven overnight.
Sulfonation and crosslinking of the initial structures resulted in cracks generating after about 2 hour of reaction time, which is earlier than when PP counterparts with the absence of fillers demonstrated cracks under an identical crosslinking condition (i.e. 150° C.). The directionality of these microcracks in PP-CF systems can be attributed to the anisotropically enhanced mechanical properties in printed parts due to the presence of CFs, which were aligned by the extrusion shear force involved during the FDM process along with the printing direction.
Completely dried sulfonated samples were placed in an tube furnace tube furnace under an inert nitrogen environment for carbonization. A ramp rate of 1° C./min was used from ambient temperature up to 600° C. after which a 5° C./min rate was used until 800° C. was reached. Once the carbonization temperature was reached the procedure was finished and the furnace was allowed to cool naturally to ambient temperature, which took about 4 hours (from 800° C. to 25° C.). .
Upon pyrolysis, at least 67 wt % carbon yield, compared with the initial printed parts, was achieved for samples crosslinked for about 12 hours and longer, as shown in
In this Example 35, a series of cube shaped PP-CF parts were prepared, with sizes ranging from 2 to 5 cm and an in-fill density of 50%. Each cube was crosslinked at 150° C. for 24 hours and carbonized at 800° C. to quantitatively assess the shrinkage degree upon polymer-to-carbon conversion.
Carbon morphology at a nanoscale was found to be rough and porous as confirmed by SEM and nitrogen phisiosorption BET (see
Additionally, carbon parts produced through this method exhibit substantially enhanced mechanical performance (
In this Example 36, a variety of initial structures were printed using PP-CF precursor material, including a rhombic dodecahedral lattice, a golden eagle, a motorcycle helmet, and a koi. All parts successfully preserved their printed geometry with a consistent shrinkage of less than 5% across all directions and a carbon yield of more than 65 wt %, as shown in Table 9 below. These results further confirm that the described method is broadly applicable to various sample sizes and geometries.
In this Example 37, to further investigate the generalizability of using fiber fillers to enhance structure retention upon PP to carbon conversion, a series of FDM PP filaments were prepared containing different CF loading from 0 to 10 wt %. These filaments were printed into identical specimens and their shrinkage behaviors were examined. The results of shrinkage measurements are shown in
Joule heating performance was also assessed to further demonstrate the application of 3D printed carbons from PP-CF filaments. The results are shown in
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
This application claims priority to U.S. application Ser. No. 17/848,342 to Zhe Qiang et al. filed on Jun. 23, 2022, which claims priority to U.S. Provisional Application No. 63/214,145 to Zhe Qiang et al. filed on Jun. 23, 2021, and to U.S. Provisional Application No. 63/311,804 to Zhe Qiang et al. filed on Feb. 18, 2022. The contents of these applications are incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63311804 | Feb 2022 | US | |
| 63214145 | Jun 2021 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17848342 | Jun 2022 | US |
| Child | 18112446 | US |
