Printable mixed-filler epoxy composites

Abstract

To provide a material for three-dimensional printing having excellent mechanical characteristics.SOLUTION: A composition 10 of a substance contains at least 10 wt.% of epoxy functionalized secondary-dimensional shape particles 14, 0.1 to 5 wt.% of a carbon nanotube, an epoxy resin, and a curing agent. A method for producing a composition of a substance includes: mixing the epoxy resin, the carbon nanotube, and a solvent, and producing a material; drying the material; mixing the material with the curing agent, and producing the composition of the substance. A method for printing the composition of the substance includes: producing the composition of the substance by combining epoxy functionalized graphene, the carbon nanotube, the epoxy-based resin, and the curing agent; extrusion-printing the composition of the substance in a desired pattern; and curing the pattern.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to three-dimensional printable composites, and more particularly to 3D printable composites comprising high loadings of functionalized particles. [Background technology]

[0002] New three-dimensional (3D) particle-filled epoxy polymer composites, such as thermosets, have advantages over established thermoplastic polymer composites. They have improved mechanical properties, such as strength and modulus. These composites form robust structures with high crosslink density after curing, resulting in exceptional mechanical properties. Polymer composites used in aerospace, energy, and automotive applications must have excellent mechanical properties.

[0003] Achieving significantly better mechanical properties requires high filler particle loadings, such as more than 10% by weight of the total composite. However, particle agglomeration and poor particle dispersion in the epoxy matrix make it very difficult to achieve higher particle loadings. Due to these issues, high particle loadings result in poor mechanical properties. Specifically, achieving increased modulus while maintaining high strength is a major challenge. Such formulations cannot be used for 3D printing.

[0004] The main challenge in using these composite formulations for extrusion 3D printing is meeting the key rheological requirements: low viscosity under shear during extrusion, and a rapid increase in viscosity and elasticity after extrusion, which are necessary to maintain the 3D printed shape after extrusion. Highly dispersed particles do not form strong networks in the resin and do not exhibit suitable viscosities for 3D printing, even at high particle concentrations, making it difficult to meet the rheological requirements. Some approaches add rheological modifiers, such as clay particles, to adjust the rheology of the composite. This results in inferior mechanical properties of the composite, such as reduced toughness and strength.

[0005] Current approaches disclose a range of epoxy composites incorporating two-dimensional graphene and carbon nanotube (CNT)-reinforced particles that are unsuitable for extrusion 3D printing due to at least one of several issues. These issues include low graphene particle loadings, typically less than 2 wt%, which have low viscosity and do not exhibit shear-thinning behavior along with the elasticity required for 3D printing. Other composites have high particle loadings of graphene and CNT, but poor dispersion leads to inhomogeneity in filler distribution and poor printability. For epoxy formulations with A+B systems that incorporate amine curing agents, they cure rapidly at room temperature, resulting in clogging of extrusion printing tubes and nozzles. Summary of the Invention

[0006] According to embodiments illustrated herein, there is provided a composition of matter comprising at least 10 wt. % epoxy-functionalized two-dimensionally shaped particles, in the range of 0.1-5 wt. % carbon nanotubes, an epoxy resin, and a curing agent.

[0007] According to aspects illustrated herein, there is provided a method of making a composition of matter that includes mixing an epoxy resin, carbon nanotubes, and a solvent to form a material, drying the material, and mixing the material with a hardener to form the composition of matter.

[0008] According to aspects illustrated herein, there is provided a method of printing a composition of matter that includes: forming a composition of matter by combining epoxy-functionalized graphene, carbon nanotubes, an epoxy-based resin, and a curing agent; extrusion printing the composition of matter into a desired pattern; and curing the pattern. [Brief explanation of the drawings]

[0009] [Figure 1] 1 shows a graphical representation of one embodiment of a composition of matter.

[0010] [Figure 2] 1 shows a flow chart of one embodiment of a method for producing a composition of matter.

[0011] [Figure 3] 1 shows a graph of viscosity versus shear rate for different compositions of matter.

[0012] [Figure 4] 1 shows a graph of a vibration stress sweep at a fixed vibration frequency.

[0013] [Figure 5] A graph of the raw stress-strain data is shown.

[0014] [Figure 6] 1 shows a bar graph of toughness results.

[0015] [Figure 7] 1 shows a bar graph of tensile strength data. DETAILED DESCRIPTION OF THE INVENTION

[0016] Embodiments herein involve epoxy composite formulations incorporating high loadings, greater than 10 wt%, of functionalized 2D-shaped particles such as graphene, clay, and small amounts of carbon nanotubes that can be directly 3D printed through extrusion printing. The cured structures of these formulations exhibited superior mechanical properties when compared to those made with the base resin alone or with epoxy resin and 2D particles.

[0017] Palo Alto Research Center (PARC) has conducted extensive research into increasing particle loading in composites. These approaches address the issue of using functionalized filler particles, which have superior dispersibility when compared to traditional non-functionalized particle formulations. Functionalized filler particle composites have resulted in cured structures with over 300% higher modulus while maintaining tensile strength.

[0018] FIG. 1 shows a graphical representation of a composition of matter 10. In the representation of FIG. 1, the background represents an epoxy matrix 12 containing functionalized 2D particles 14, such as graphene, clay, fumed silica, etc. "Functionalized" particles include particles that have functional groups attached to them that can form bonds with other particles. In some of PARC's work, these functional groups formed particle networks that linked other particles. Examples of these include U.S. Pat. Nos. 10,882,972 and 10,138,317, which are incorporated by reference in their entireties. The particles herein are "epoxy-functionalized," meaning that they have epoxy groups.

[0019] Compositions of matter of embodiments include carbon nanotubes (CNTs). As further discussed, the CNTs can be single-walled nanotubes (SWNTs), multi-walled nanotubes, or functionalized nanotubes, which can have, by way of example, at least one carboxyl (COOH) group or epoxy group. Other functional groups can also be added. Nanotubes with carboxyl functional groups can also be referred to as carboxylated nanotubes, and those with epoxy groups can be referred to as epoxy-functionalized nanotubes. The term "carbon nanotubes" includes any variation of CNTs, including those listed above as examples.

[0020] 2 shows a flow chart of an embodiment of a method for producing a composition of matter. At 20, epoxy-functionalized particles, an epoxy-based resin, CNTs, and a solvent are mixed together in a solution to disperse the functionalized particles and CNTs. At 22, the solution undergoes drying to remove the solvent and obtain an epoxy resin containing the functionalized particles and CNTs. This is then mixed with a curing agent at 24. A "printing" process, such as extrusion printing or other 3D printing process, then uses the resulting material to form a structure or pattern, which is then cured.

[0021] In the following examples, specific compounds and percentages are used experimentally. No limitations to specific percentages of such specific compounds are intended or should be inferred. For example, the epoxy-functionalized particles used consist of epoxy-reacted fluorographene, but other types of epoxy-functionalized particles may be used. Similarly, the following weight percentages of epoxy-functionalized particles are 15 weight percent, but can range anywhere from 5 weight percent to 20 weight percent in increments of 0.5 weight percent, and the weight percentage of CNTs is 1 weight percent, but can range anywhere from 0.1 weight percent to 5 weight percent in increments of 0.1 weight percent. [Example]

[0022] In a first example, a 20-g ink sample was obtained by mixing 3 g (15 wt %) of epoxy-reacted fluorographene (ERFG) particles with 15.8 g of epoxy-based resin (in this case, Epon 826 from Hexion Epoxy Systems, Inc.) in a high-performance ball mill equipped with 3 mm spherical grinding media. This resulted in well-dispersed ERFG particles in the resin, which were recovered from the mixer using acetone solvent and left overnight at 80 °C in air to partially remove the acetone. Next, we added 0.2 g (1 wt %) of SWCNTs (in this example, SWCNTs manufactured by Nanoamor (Nanostructured and Amorphous Materials, Inc.)) to 2 ml of acetone solvent and mixed at 500 rpm in a centrifugal planetary mixer. The CNT-acetone dispersion was added to the ERFG-epoxy mixture and mixed using the grinding media in the planetary mixer. The resulting ERFG-CNT-epoxy-acetone mixture was dried overnight at 60 °C in an oven maintained at house vacuum (approximately 23 psig) to completely remove the acetone. A latent curing agent (approximately 5 wt%) in the form of 1-ethyl-3-methylimidazolium dicyanamide, an ionic liquid available from Sigma-Aldrich, was added to the mixture and mixed again. [Example]

[0023] Similar formulations were prepared by replacing the CNTs with COOH-functionalized SWNTs.

[0024] Comparative "base" formulations containing only ERFG particles, meaning epoxy-functionalized 2D particles without any particle filler, without added CNTs, were also prepared to measure and compare their rheological and mechanical properties.

[0025] The rheological properties of the formulations were measured to evaluate their printability. Steady shear viscosity measurements allow for estimation of the change in viscosity as a function of shear rate. The viscosities of all formulations exhibit shear-thinning behavior, as shown in Figure 2, where viscosity decreases with increasing shear rate. However, the viscosity of the formulations increases by almost two orders of magnitude at the lowest shear rate after the addition of 1 wt% CNT or 1 wt% CNT-COOH. As the shear rate increases, the viscosity decreases, reaching a near-plateau value at shear rates above 100 s−1, and then increases again as the shear rate decreases. Having an optimally high viscosity at the lowest shear rate is a key requirement for printable inks, as it provides better control compared to extrusion printing. The rapid increase in viscosity as the shear rate decreases is a key indicator of elastic recovery in the formulation. This is a desirable rheological characteristic for inks usable for extrusion printing. However, the viscosity needs to be optimized to allow smooth printing without clogging the printer nozzles, yet be of sufficiently high viscosity that it flows only when force is applied.

[0026] Figure 3 shows the viscosity-shear rate profiles of different formulations. Viscosity measurements are first recorded with increasing shear; after reaching a set maximum shear value, the shear rate is decreased and the viscosity is recorded. As used herein, the term "formulation" refers to different formulation embodiments. The term "sample" refers to the same version of each formulation. In Figure 2, plot 30 shows data for 15 wt% ERFG, 5 wt% ionic liquid (IL), increasing shear, and plot 32 shows data for 15 wt% ERFG, 5 wt% ionic liquid (IL), decreasing shear. Plots 34 and 36 show data for increasing and decreasing shear versions of the formulation containing 1 wt% SWNTs, respectively. Plots 38 and 40 show data for increasing and decreasing shear formulations, respectively, in which the SWNTs are carboxylated. As can be seen in Figure 2, the base formulation does not demonstrate the desired viscosity versus shear profile, while the formulations containing SWNT or SWNT-COOH demonstrate the desired profile.

[0027] At least two samples of each formulation were tested in Figures 4-7. Figure 4 shows oscillatory stress sweeps of the formulations performed at a fixed frequency (0.1 Hz) and demonstrates a significant increase in ink elasticity with the addition of 1 wt% CNT or 1 wt% CNT-COOH. Plot 50 shows the elastic contribution, and 52 shows the viscous contribution data for the base formulation. Plot 54 shows the elastic contribution, and 56 shows the viscous contribution data for the formulation with 1 wt% CNT. Plot 58 shows the elastic contribution, and 60 shows the viscous contribution data for the formulation with carboxylated CNT.

[0028] The elastic contribution (G') is smaller than the viscous contribution (G'') for all values ​​of oscillatory stress for formulations without CNTs. This indicates lower elasticity in these formulations, which may lead to collapse of the structure after extrusion printing. However, the storage modulus (G') increases by almost two orders of magnitude with the addition of CNTs and CNT-COOH fillers, becoming higher than the loss modulus (G'') at low oscillatory stresses. The increased elasticity allows the structure to retain its shape without collapse after extrusion printing.

[0029] Figures 5-7 show results from four samples of the base formulation as plots 70, 72, 74, and 76 in Figure 5; two samples of the CNT-containing formulation as plots 80 and 82 in Figure 5; and three samples of the carboxylated CNT formulation as plots 84, 86, and 88 in Figure 5. The samples consisted of "dogbone" shaped cured structures formed from an open molding procedure followed by thermal curing. Figure 5 shows the raw stress-strain data. This data indicates that the CNT-reinforced formulations have significantly increased toughness, while the modulus remains relatively unaffected.

[0030] Figure 6 shows the toughness values ​​for each sample. The data show increased toughness for both the CNT and CNT-COOH composites. In particular, the CNT composite has an approximately 80% increase in toughness when compared to the cured sample of the base formulation. The carboxylated CNT composite shows an approximately 50% increase in toughness.

[0031] Figure 7 shows the tensile strength data. Inks containing CNTs, whether carboxylated or not, show an average increase in strength of approximately 10% compared to the base formulation. In addition, these inks exhibited desirable flow characteristics during printing, and printed structures retained their shape until cured.

[0032] In this way, the desired properties of the printable composites used in their manufacture can be increased: experiments have shown that these composites have more desirable shear, stress-strain profiles, and increased toughness and tensile strength compared to formulations containing the same ingredients but without the addition of CNTs.

[0033] All features disclosed in this specification, including the claims, abstract, and drawings, and all steps in any method or process disclosed, may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification, including the claims, abstract, and drawings, may be replaced by an alternative feature serving the same, equivalent, or similar purpose, unless otherwise specified.

[0034] It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements may thereafter occur to those skilled in the art, which are also intended to be encompassed by the present embodiments. Another aspect of the present invention may be as follows. [1] A composition of matter comprising at least 10% by weight of epoxy-functionalized two-dimensionally shaped particles, 0.1 to 5% by weight of carbon nanotubes, an epoxy resin, and a curing agent. [2] The composition of matter of [1], wherein the two-dimensionally shaped particles comprise one or more of functionalized graphene, clay, and alumina platelets. [3] The composition of matter of [1], wherein the carbon nanotubes are bare. [4] The composition of matter of [1], wherein the carbon nanotubes are functionalized. [5] The composition of matter of [4], wherein the carbon nanotubes are functionalized with either at least one carboxyl group or at least one epoxy group. [6] The composition of matter described in [1], wherein the composition of matter has a viscosity of at least 1000 Pascal-seconds at zero shear. [7] The composition of matter described in [1], wherein the composition of matter has a viscosity of at least 10 Pascal-seconds at a shear rate of 100 / sec. [8] The composition of matter described in [1], wherein the carbon nanotubes include single-walled carbon nanotubes. [9] The composition of matter of [1], wherein the epoxy-functionalized two-dimensionally shaped particles comprise epoxy-reacted fluorographene particles.

[10] The composition of matter of [1], wherein the curing agent comprises an ionic liquid.

[11] The composition of matter of [1], wherein the curing agent comprises 1-ethyl-3-methylimidazolium dicyanamide.

[12] The composition of matter of [1], wherein the composition of matter has improved toughness compared to a composition of matter that does not contain carbon nanotubes.

[13] The composition of matter of

[12] , wherein the composition of matter has an improved toughness of at least 50 percent.

[14] The composition of matter of [1], wherein the composition of matter has improved tensile strength compared to a composition of matter that does not contain carbon nanotubes.

[15] The composition of matter of

[14] , wherein the composition of matter has an improved tensile strength of at least 10%.

[16] A method for producing a composition of matter, comprising: mixing an epoxy resin, carbon nanotubes, and a solvent to form a material; drying the material; mixing said material with a curing agent to form said composition of matter.

[17] The method of

[16] , wherein mixing the epoxy-functionalized graphene with carbon nanotubes comprises mixing the epoxy-functionalized graphene with one of single-walled carbon nanotubes, multi-walled carbon nanotubes, carboxylated nanotubes, or epoxy-functionalized carbon nanotubes.

[18] A method for printing a composition of matter, comprising: forming the composition of matter by combining epoxy-functionalized graphene, carbon nanotubes, an epoxy-based resin, and a curing agent; extrusion printing said composition of matter in a desired pattern; and curing the pattern.

[19] The method according to

[18] , wherein the curing agent is a thermal curing agent.

Claims

1. A composition for three-dimensional printing comprising epoxy-reacted fluorographene particles in the range of 5 to 20 weight percent, carbon nanotubes in the range of 0.1 to 5 weight percent, an epoxy resin, and a curing agent.

2. A three-dimensional printing composition as described in claim 1, wherein the composition comprises one or more of functionalized graphene, clay, and fumed silica.

3. The three-dimensional printing composition of claim 1 , wherein the carbon nanotubes are either bare or functionalized.

4. The three-dimensional printing composition of claim 3 , wherein the carbon nanotubes are functionalized with either at least one carboxyl group or at least one epoxy group.

5. 10. The three-dimensional printing composition of claim 1, wherein the composition has a viscosity of at least 1000 Pascal-seconds at zero shear.

6. 10. The three-dimensional printing composition of claim 1, wherein the composition has a viscosity of at least 10 Pascal-seconds at a shear rate of 100 Pa / sec.

7. The three-dimensional printing composition of claim 1 , wherein the carbon nanotubes comprise single-walled carbon nanotubes.

8. The three-dimensional printing composition of claim 1 , wherein the curing agent comprises an ionic liquid.

9. The three-dimensional printing composition of claim 1 , wherein the curing agent comprises 1-ethyl-3-methylimidazolium dicyanamide.

10. 10. The three-dimensional printing composition of claim 1, wherein the composition has at least a 50 percent improved toughness compared to a composition without carbon nanotubes.

11. 10. The three-dimensional printing composition of claim 1, wherein the composition has at least a 10 percent improved tensile strength compared to a composition without carbon nanotubes.

Images