Piezoresistive composite via additive manufacturing and composite filament associated therewith

Abstract

To provide an additive manufacturing process utilizing a composite and a continuous filament thereof capable of forming printed parts exhibiting piezoresistive behavior.SOLUTION: A composite filament suitable for additive manufacturing may comprise a continuous polymer phase of a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with one another, and electrically conductive particles distributed in the continuous polymer phase, such as microparticles, nanoparticles, or any combination thereof. The first thermoplastic polymer is dissolvable or degradable and the second thermoplastic polymer is insoluble or non-degradable under a specified condition. Removal of the first thermoplastic polymer from a printed part may introduce porosity thereto, thereby inducing or enhancing piezoresistivity within the printed part. An aqueous mixture comprising the electrically conductive particles and the first and second thermoplastic polymers may have water removed therefrom, and a resulting composite residue may be extruded to form the composite filament.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates generally to additive manufacturing, and more specifically to additive manufacturing processes utilizing composites and continuous filaments thereof capable of forming printed parts exhibiting piezoresistive behavior. [Background technology]

[0002] Additive manufacturing, also known as three-dimensional (3-D) printing, is a rapidly growing technology field. While additive manufacturing has traditionally been used for rapid prototyping activities, the technique is increasingly being used to produce commercial and industrial parts with numerous complex shapes. Additive manufacturing processes typically work by building an object layer by layer, for example, by 1) the deposition of a stream of molten printing material derived from a continuous filament, or 2) the sintering of powdered particulates of the printing material using a laser. The layer-by-layer deposition is usually performed under computer control to deposit the printing material in precise locations based on a digital three-dimensional "blueprint" of the part to be manufactured, with consolidation of the printing material occurring as the material is deposited to form the printed part. The printing material that forms the body of the printed part may be referred to herein as the "build material."

[0003] Additive manufacturing processes that use a stream of molten printing material to form a part typically utilize a thermoplastic polymer filament as the source of the molten printing material. Such additive manufacturing processes are sometimes referred to as "fused deposition modeling (FDM®)" processes or "fused filament fabrication (FFF)" processes. The latter term will be used herein. Additive manufacturing processes that use thermoplastic pellets as the source of the printing material are also known.

[0004] Additive manufacturing processes that use powder particles of a printing material often employ direct heating at selected locations in the particle bed after deposition of the printing material to promote coalescence of the powder particles into a consolidated part. Techniques suitable for promoting the consolidation of powder particles to form a consolidated part include, for example, powder bed fusion (PBF), selective laser sintering (SLS), electron beam melting (EBM), binder jetting, and multi-jet fusion (MJF).

[0005] A wide range of printed parts with various geometries can be fabricated using both types of additive manufacturing processes. In many cases, the build materials used in both types of additive manufacturing processes may be largely structural in nature and not inherently functional build materials. Also, it may be difficult to introduce functional features into printed parts after their deposition. Functional features of potential interest in printed parts include, but are not limited to, electrical conductivity, piezoelectric behavior, piezoresistive behavior, phase change behavior, color change behavior, etc.

[0006] Piezoresistive materials undergo a change in resistance with applied mechanical strain. For example, pressure sensors based on piezoresistive materials are used in many applications, including automotive, medical, industrial, consumer, and architectural devices. Currently, there is a lack of printing materials capable of exhibiting significant conductivity after printing, limiting options for producing printed parts with a sufficient degree of piezoresistive behavior. While some printing materials (polymers) exist that are somewhat conductive, they have not yet been demonstrated to produce printed parts with piezoresistive behavior. Filaments containing carbon-based additives are one example of currently available printing materials that can exhibit conductivity, but their conductivity is typically low (less than 1 S / cm), and the piezoresistive behavior that can potentially be obtained from them can be correspondingly limited. Porous networks, such as foams, can increase piezoresistive behavior, but such porosity is difficult to reliably incorporate into printed parts using currently available printing materials. Summary of the Invention

[0007] The present disclosure provides a composite filament comprising: a continuous polymer phase comprising a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with each other, wherein the first thermoplastic polymer is soluble or degradable under specified conditions and the second thermoplastic polymer is insoluble or non-degradable under specified conditions; and a plurality of conductive particles distributed in the continuous polymer phase, wherein the plurality of conductive particles comprises microparticles, nanoparticles, or any combination thereof.

[0008] The present disclosure also provides a composite or composite pellet comprising: a continuous polymer phase comprising a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with each other, wherein the first thermoplastic polymer is soluble or degradable under specified conditions and the second thermoplastic polymer is insoluble or non-degradable under specified conditions; and a plurality of conductive particles distributed in the continuous polymer phase, the plurality of conductive particles comprising microparticles, nanoparticles, or any combination thereof.

[0009] The present disclosure also provides a printed part comprising: a continuously printed polymer matrix comprising a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with each other, wherein the first thermoplastic polymer is soluble or degradable under specified conditions and the second thermoplastic polymer is insoluble or non-degradable under specified conditions; and a plurality of conductive particles distributed in the continuously printed polymer matrix, the plurality of conductive particles comprising microparticles, nanoparticles, or any combination thereof.

[0010] The present disclosure also provides a piezoresistive printed component that includes a printed polymer matrix having porosity defined therein and including a plurality of conductive particles distributed in a thermoplastic polymer.

[0011] The present disclosure still further provides a method for forming a composite filament containing conductive particles, the method including: combining a plurality of conductive particles and a water-soluble first thermoplastic polymer with an aqueous dispersion of a water-insoluble second thermoplastic polymer to provide a combined aqueous mixture; removing water from the combined aqueous mixture to provide a composite residue comprising at least a portion of the conductive particles distributed in a continuous polymer phase comprising the first thermoplastic polymer and the second thermoplastic polymer, wherein the first thermoplastic polymer and the second thermoplastic polymer are immiscible with each other in the continuous polymer phase; and extruding the composite residue into a composite filament comprising the conductive particles distributed in the continuous polymer phase.

[0012] The present disclosure also provides a method of printing that includes providing a composite filament of the present disclosure and depositing the composite filament layer-by-layer above its softening temperature to form a printed part. [Brief explanation of the drawings]

[0013] The following figures are included to illustrate certain aspects of the present disclosure and should not be considered as exclusive embodiments. The disclosed subject matter is capable of considerable modification, alteration, combination, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

[0014] [Figure 1] FIG. 1 shows a schematic diagram of an exemplary fused filament fabrication process for producing a part using a build material and a removable support material. [Figure 2] 1 illustrates a diagram of an exemplary part having an overhang. [Figure 3] 1 shows a schematic diagram of an exemplary part defined as a porous network in a continuous polymer matrix. [Figure 4] 1 shows a plot of resistance as a function of weight applied to the composite films of Examples 1-5. [Figure 5A] 1 shows a photograph of the composite filament of Example 6. [Figure 5B] 1 shows a photograph of the composite filament of Example 7. [Figure 6] 10 shows a plot of resistance as a function of weight applied to the composite filament of Example 8. [Figure 7A] 1 shows SEM images of a silver microflake / TPU composite film (Example 1) at two different magnifications. [Figure 7B] 1 shows SEM images of a silver microflake / TPU composite film (Example 1) at two different magnifications. [Figure 8A] 1 shows cross-sectional SEM images of a silver microflake / TPU composite filament (Example 6) at two different magnifications. [Figure 8B] 1 shows cross-sectional SEM images of a silver microflake / TPU composite filament (Example 6) at two different magnifications. [Figure 9A] 1A and 1B show cross-sectional SEM images (before and after PVA removal) of the composite filaments of Examples 7 and 8, respectively, at two different magnifications. [Figure 9B]1A and 1B show cross-sectional SEM images (before and after PVA removal) of the composite filaments of Examples 7 and 8, respectively, at two different magnifications. [Figure 9C] 1A and 1B show cross-sectional SEM images (before and after PVA removal) of the composite filaments of Examples 7 and 8, respectively, at two different magnifications. [Figure 9D] 1A and 1B show cross-sectional SEM images (before and after PVA removal) of the composite filaments of Examples 7 and 8, respectively, at two different magnifications. [Figure 10] 13 shows a plot of resistance versus applied pressure for a printed part with porosity introduced therein. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present disclosure relates generally to additive manufacturing, and more specifically to additive manufacturing processes utilizing composites and continuous filaments thereof capable of forming printed parts exhibiting piezoresistive behavior. More specifically, the present disclosure provides composite filaments suitable for fused filament fabrication additive manufacturing processes that are capable of forming printed parts with piezoresistive properties after further processing. Composites in pellet form may also be formed by utilizing the blending process disclosed herein.

[0016] As discussed above, additive manufacturing processes such as fused filament fabrication are powerful tools for generating printed parts with a wide range of complex shapes. In many cases, the polymers used to perform fused filament fabrication are largely structural in nature and do not solely impart functional properties to the printed part. There are limited examples of polymer filaments compatible with fused filament fabrication that exhibit even moderate electrical conductivity, and the resulting piezoresistive behavior may be weak and of insufficient magnitude for various intended applications.

[0017] In response to the aforementioned shortcomings, the present disclosure provides polymer composites and composite filaments obtained therefrom that are suitable for additive manufacturing (e.g., fused filament fabrication) and capable of forming printed parts with significant piezoresistivity after processing to introduce porosity, as further discussed herein. Composite filaments suitable for fused filament fabrication can have diameters appropriate for the drive unit for a particular printing system, such as about 1.0 mm to about 10.0 mm (common filament diameters include 1.75 mm and 2.85 mm). The composite filaments can also be spoolable in lengths, such as at least about 1 foot, or at least about 5 feet, or at least about 10 feet, or at least about 25 feet, or at least about 50 feet, or at least about 100 feet, or at least about 250 feet, or at least about 500 feet, or at least about 1000 feet. Other characteristics that may determine whether a composite filament is suitable for fused filament fabrication include the temperature required for extrusion of the filament, which should not be unnecessarily high. Suitable filaments for fused filament fabrication may minimize printing problems such as weeping from the print nozzle or clogging of the print nozzle. Suitable composite filaments may also, for example, easily separate from the print bed or alternatively exhibit strong adhesion to the permanent substrate, forming printed parts that have sufficient mechanical strength once printed and exhibit good interlayer adhesion once printed.

[0018] Composites of the present disclosure may include conductive particles distributed in a continuous polymer phase comprising a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with each other, where one of the thermoplastic polymers is soluble or degradable and can be removed from the other thermoplastic polymer under specified conditions, thereby introducing porosity into the composite, or a filament or printed part formed therefrom, in a controlled manner. The term "continuous polymer phase" refers to the bulk phase in which the conductive particles are dispersed. The continuous polymer phase may contain the first thermoplastic and the second thermoplastic distributed co-continuously or non-co-continuously with each other. In a co-continuous distribution of the first thermoplastic and the second thermoplastic polymer, the first thermoplastic and the second thermoplastic polymer may exist as separate, continuous polymer matrices intermingled with each other. The first thermoplastic and the second thermoplastic polymer may, in some cases, define an interpenetrating network of the two thermoplastic polymers, where there is connectivity between at least a majority of the first thermoplastic polymer and at least a majority of the second thermoplastic polymer throughout the continuous polymer phase. In contrast, in a non-cocontinuous distribution of a first thermoplastic polymer and a second thermoplastic polymer, isolated pockets of one of the thermoplastic polymers may exist in a continuous matrix of the other. Thus, in a cocontinuous distribution, any cross-section of the polymer composite contains at least a portion of both the first thermoplastic polymer and the second thermoplastic polymer. Composites containing separate cocontinuous or non-cocontinuous regions are also within the scope of the present disclosure. Because the thermoplastic polymers are immiscible with each other (including physical blends of the first and second thermoplastic polymers), the introduction of controlled porosity or channels into the printed part can be imparted by removing one of the polymers. Very fine porosity features, much smaller than those achievable by direct printing, can be realized. In a non-limiting example, one of the thermoplastic polymers is a water-soluble polymer and the other thermoplastic polymer is a water-insoluble polymer.In other cases, one of the thermoplastic polymers is soluble in an organic solvent, while the other thermoplastic polymer is not soluble in the same organic solvent (but may be soluble in a different organic solvent). In still other cases, one of the thermoplastic polymers may be decomposed into by-products that separate from the composite, and the conditions promoting the decomposition do not affect the other thermoplastic polymer. Decomposition by melting, which removes one of the thermoplastic polymers from the other, is also within the scope of the present disclosure. By varying the ratio of the soluble / decomposable thermoplastic polymer to the other thermoplastic polymer in the composite, the extent of porosity may be adjusted to the desired extent, which also affects the piezoresistivity that can be achieved. Advantageously, the conductive particles may remain well distributed in the composite filament after its formation.

[0019] It should also be understood that the first thermoplastic polymer and the second thermoplastic polymer do not necessarily comprise a single polymer of each type. Thus, depending on the specific needs of the application, the first thermoplastic polymer may comprise one or more thermoplastic polymers, such as two thermoplastic polymers that are soluble or degradable under specified conditions, and the second thermoplastic polymer may comprise one or more thermoplastic polymers, such as two thermoplastic polymers that are non-soluble or non-degradable under specified conditions.

[0020] Surprisingly and advantageously, the conductive particles may remain substantially associated with or located in the thermoplastic polymer, which remains undissolved or undegraded, thus minimizing losses incurred when the soluble or degradable polymer is removed (e.g., by exposure to an appropriate solvent or other conditions that may favor the removal of one of the thermoplastic polymers over the other). Thus, a porous network of conductive particles distributed in the remaining thermoplastic polymer (e.g., the insoluble or non-degradable thermoplastic polymer) may be achieved after printing and further processing. The conductive particles may be uniformly distributed in the remaining thermoplastic polymer that defines the porous network.

[0021] Advantageously, composites capable of forming printed parts with piezoresistive behavior can be formulated using a room-temperature aqueous process using water-soluble polymers. Polyvinyl alcohol (PVA), polyethylene glycol (PEG, also known as polyethylene oxide), or any combination thereof, may be suspended in an aqueous phase and combined with conductive particles in the aqueous phase containing a second thermoplastic polymer with which the water-soluble polymer is immiscible. After removing the water from the combined aqueous phase, the two thermoplastic polymers may form a continuous polymer phase, in which the two thermoplastic polymers remain immiscible with each other and the conductive particles are distributed throughout the continuous polymer phase while being substantially located in the second thermoplastic polymer (i.e., the water-insoluble polymer). In one example, the continuous polymer network and the conductive particles therein may be obtained as a cast film before being processed into a continuous filament. As discussed above, after removing the water from the combined aqueous phase, the conductive particles, although distributed throughout the continuous polymer phase, are surprisingly predominantly located within the water-insoluble polymer. Thus, once formed into a printed part, the water-soluble polymer can be removed to impart a porous polymer network without releasing significant amounts of conductive particles. The composite residue obtained from the composite film (e.g., obtained after drying and chopping / pulverization) can be converted into a continuous filament by extrusion. Subsequent removal of the water-soluble polymer can produce a porous polymer network of the remaining thermoplastic polymer and distributed conductive particles, either before or after printing. Thus, the continuous filament (composite filament) or the resulting printed part can have porosity defined therein by removal of the water-soluble polymer. In either case, the porous polymer network can be capable of exhibiting piezoresistive behavior.

[0022] While composite filaments can be particularly advantageous when formed in accordance with the disclosure herein, it should be understood that composite residues (e.g., fragments) resulting from film casting, breaking, and optional further processing can also be useful in similar printing processes or as precursors to composite filaments suitable for fused filament fabrication. The composite residues resulting from intermediate composite films can be utilized directly or extruded under conditions effective to provide larger fiber forms than composite filaments. The larger fiber forms can then be cut, pulverized, or the like to provide composite pellets that also contain conductive particles distributed in a continuous polymer phase comprising a mixture of immiscible thermoplastic polymers. Similar to composite filaments, composite pellets or similar non-filamentary composite materials can then be processed into printed parts with piezoresistive properties under suitable additive manufacturing conditions. Porosity may be introduced into printed parts to induce or enhance piezoresistive behavior.

[0023] Before discussing various aspects of the present disclosure in more detail, a brief discussion of additive manufacturing processes, specifically, fused filament fabrication processes, will first be provided so that the features of the present disclosure may be better understood. FIG. 1 shows a schematic diagram of an exemplary fused filament fabrication process for producing a part using a build material and a removable support material. As shown in FIG. 1, a print head 100 includes a first extruder 102a and a second extruder 102b, each configured to receive a filament-like printing material. The first extruder 102a is configured to receive a first filament 104a from a first payout reel 106a and provide a melt stream 108a of the first printing material, and the second extruder 102b is configured to receive a second filament 104b from a second payout reel 106b and provide a melt stream 108b of the second printing material. Both melt streams are initially deposited on a print bed (not shown in FIG. 1) to facilitate the layer-by-layer growth of a supported part 120. The first printing material (build material) supplied by the first extruder 102a may include a composite filament of the present disclosure (e.g., a continuous filament containing conductive particles distributed in a continuous polymer phase including mutually immiscible thermoplastic polymers) used to fabricate the part 110, and the second printing material (removable support material) supplied by the second extruder 102b may be a dissolvable or degradable polymer used to fabricate the removable support 112 below the overhang 114. The overhang 114 is not in direct contact with the print bed or the underlying print layer formed from the build material. Because the overhang 114 cannot be deposited in free space, the removable support 112 serves as a temporary structure for depositing the part 110 thereon. In the part configuration shown in FIG. 1 , the removable support 112 is interposed between the overhang 114 and the print bed; however, it should be understood that in alternatively configured parts, the removable support 114 may be interposed between two or more portions of the part 110. FIG. 2, for example, shows an exemplary part 200 in which a removable support 202 is interposed between an overhang defined between the part 200 and a print bed 204, and a removable support 206 is interposed between two portions of the part 200.

[0024] 1 , once printing of part 110 and removable support 112 is complete, support part 120 may be subjected to support removal conditions 125 (such as, for example, dissolution or disintegration conditions) that result in removal of removable support 112, leaving part 110 with overhang 114 unsupported thereon. Support removal conditions 125 may include contacting support part 120 with a solvent in which removable support 112 is soluble or degradable and part 110 is not. Support removal conditions 125 may also promote the decomposition or dissolution of one of the thermoplastic polymers in the continuous polymer phase, thereby leaving conductive particles dispersed in the remaining thermoplastic polymer defined as a porous network.

[0025] 3 shows a schematic diagram of an exemplary component 300 defined as a porous network formed from a continuous polymer matrix 302. When the continuous polymer matrix 302 contains conductive particles in a suitable distribution, enhanced piezoresistive behavior can be observed.

[0026] While the additive manufacturing process shown in FIG. 1 could, in principle, be modified to introduce porosity into a printed part (such as exemplary part 300 in FIG. 3 ) for the purpose of inducing or increasing piezoresistive behavior within the printed part, doing so can be problematic in various aspects. Introducing microporous features using coextruded build material and a removable support material can be difficult, and coextrusion in this manner can significantly increase the time required to complete the printing process. Printing parts with porosity defined therein as a regular array (such as present in part 300 in FIG. 3 ) can also be achieved using a single print head depositing a suitable build material, but the resolution of the printing process may similarly limit the pores or channels to an excessively large size, and the printing process can significantly increase complexity.

[0027] It should be understood that when a printed part having an overhang is formed using the composite filament of the present disclosure, a removable support similar to removable support 114 of FIG. 1 may be introduced to facilitate the fabrication of the printed part, if desired. The dissolvable or degradable material (sacrificial material) defining the removable support may include the same or a different dissolvable or degradable thermoplastic polymer that comprises a portion of the as-printed polymer matrix defining the part. Furthermore, the dissolvable or degradable polymer in the as-printed polymer matrix defining the part may be removed to define porosity in the printed part under the same or different conditions used to eliminate the removable support and define the overhang. Defining the porosity in the printed part and eliminating the removable support may occur in any order, including substantially simultaneously defining the porosity and eliminating the removable support.

[0028] Thus, composite filaments of the present disclosure may be suitable for use in fused filament fabrication and may include a continuous polymer phase including a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with each other, and a plurality of conductive particles distributed in the continuous polymer phase, which may include microparticles, nanoparticles, or any combination thereof. The first thermoplastic polymer may be soluble or degradable under specified conditions, and the second thermoplastic polymer may be insoluble or non-degradable under specified conditions. Examples of soluble or degradable thermoplastic polymers, insoluble or non-degradable thermoplastic polymers, and conductive particles are provided below.

[0029] The continuous polymer phase or the conductive particles may constitute a majority or minority component of the composite filaments disclosed herein. In various embodiments, the conductive particles may be present in the continuous polymer phase at a particle:polymer weight ratio ranging from about 10:90 to about 95:5, or any subrange therebetween, based on the total composite weight in which both thermoplastic polymers are present. These weight percentages correspond to particle volume percentages ranging from about 1.2% to about 68% by volume. The foregoing volume percentages are again based on the total composite volume before removal of one of the thermoplastic polymers, and are shown in Table 1 as 10.49 g / cm for Ag particles. 3 Estimate the particle density of the conductive particles. Other types of conductive particles may be present in similar volume percentage ranges. In more specific examples, the weight ratio of conductive particles to the continuous polymer phase in the composite filament may range from about 20:80 (3 vol.% Ag particles) to about 80:20 (62 vol.% Ag particles), or from about 30:70 (5 vol.% Ag particles) to about 70:30 (21 vol.% Ag particles), or from about 40:60 (7 vol.% Ag particles) to about 60:40 (15 vol.% Ag particles), based on the total composite weight with both thermoplastic polymers present. After removing one of the thermoplastic polymers, the volume percentage range of the conductive particles may range from about 2 vol.% to about 80 vol.%. The maximum loading of conductive particles may be selected so that the composite filament maintains structural integrity as a continuous filament and remains printable by fused filament fabrication. Additionally, the loading of conductive particles can be selected so that the printed part has desired mechanical properties and / or a desired degree of piezoresistiveness after removal of one of the thermoplastic polymers. The conductive particles can be distributed within the continuous polymer phase in a manner such that the conductive particles remain substantially dispersed individually, both in the composite filament or the resulting printed part. The distribution of the conductive particles in the continuous polymer phase can be substantially uniform in the portion of the continuous polymer phase in which the conductive particles are present (e.g., a substantially uniform distribution of conductive particles within a non-degradable or non-dissolving thermoplastic polymer).

[0030] The ratio of the first thermoplastic polymer to the second thermoplastic polymer may likewise vary over a wide range. In a non-limiting example, the ratio of the first thermoplastic polymer to the second thermoplastic polymer may range from about 1:99 to about 99:1 by weight. In more specific examples, the ratio of the first thermoplastic polymer to the second thermoplastic polymer may be in the range of about 10:90 to about 90:10, or about 20:80 to about 80:20, or about 30:70 to about 70:30, or about 40:60 to about 60:40, or about 10:90 to about 20:80, or about 20:80 to about 30:70, or about 30:70 to about 40:60, or about 40:60 to about 50:50, or about 50:50 to about 60:40, or about 60:40 to about 70:30, or about 70:30 to about 80:20, or about 80:20 to about 90:10. The ratio of the first thermoplastic polymer to the second thermoplastic polymer can be selected to achieve a desired degree of flexibility after the printed part is formed and the first thermoplastic polymer is removed, or to adjust the degree of porosity formed in the printed part. Similarly, this ratio can be adjusted to facilitate the formation of and / or printing with a composite filament before removing one of the thermoplastic polymers. Based on the degree of porosity formed, the piezoresistive behavior can be varied accordingly. The piezoresistive behavior can be observed by a decrease in resistance when a higher mechanical load (weight) is carried by the continuous polymer phase or the printed part formed therefrom. An increase or appearance of piezoresistive properties can be observed after removing at least a portion of the first thermoplastic polymer from the printed part.

[0031] After removing at least a portion of the first thermoplastic polymer from the printed part, the printed part may have a degree of porosity proportional to the amount of first thermoplastic polymer that has been removed. In non-limiting embodiments, the printed part may have a porosity ranging from about 5% to about 80%, or from about 10% to about 50%, or from about 30% to about 70%, based on the amount of removed mass relative to the total mass of the printed part before removal of the first thermoplastic polymer. The pore size or channel size of the interconnected pores may depend on the degree of dispersion of the first thermoplastic polymer in the continuous polymer phase as well as the amount of first thermoplastic polymer that has been removed.

[0032] Once the first thermoplastic polymer has been at least partially removed from the printed part, the conductive particles may be present in the printed polymer matrix with the second thermoplastic polymer (the remaining thermoplastic polymer) in a particle:polymer mass ratio of about 20:80 to about 97:3 based on the total mass of the part after removing the first thermoplastic polymer, which corresponds to a particle:polymer volume percentage ranging from about 2% to about 80% by volume.

[0033] Conductive particles suitable for use in any embodiment of the present disclosure may have an average particle size in the micrometer or nanometer size range, or a combination of micrometer and nanometer-sized conductive particles may be used. In more specific examples, suitable conductive particles may have a diameter of about 25 microns or less, or about 10 microns or less, e.g., about 1 micron to about 10 microns, or about 2 microns to about 8 microns. Smaller conductive particles, e.g., having an average particle size of about 100 nm or less, or about 500 nm or less, e.g., about 10 nm to about 100 nm, or about 20 nm to about 80 nm, or about 100 nm to about 500 nm, may also be utilized in the present disclosure, either alone or in combination with larger conductive particles in the micrometer size range. The average particle size in the present disclosure is defined as D 50 D represents a value, which refers to the diameter at which 50% of the sample (by volume unless otherwise specified) is composed of particles with a diameter less than that diameter.50 may also be referred to as "average particle size." Measurement of such average particle size may be made by analysis of optical images, including via SEM analysis, or by using the on-board software of a Malvern MASTERSIZER 3000 Aero S instrument, which uses light scattering techniques for particle size measurement.

[0034] Conductive particles suitable for use in the present disclosure may include metals, carbonaceous conductors, or any combination thereof. Metals that can comprise conductive particles include, but are not limited to, highly conductive metals such as silver, copper, aluminum, and gold. Exemplary forms of conductive particles comprising metals may include, for example, nanoparticles, nanoflakes, nanowires, nanorods, microflakes, and the like, such as silver nanoparticles, silver nanoflakes, silver microflakes, silver nanowires, silver nanorods, aluminum microflakes, aluminum nanowires, copper microflakes, copper nanoparticles, copper nanowires, gold nanoparticles, and the like, or any combination thereof. Carbonaceous conductors that can be used alone or in combination with one or more conductive particles comprising metals may include, but are not limited to, carbon black, carbon fiber, graphene, carbon nanotubes, and the like, or any combination thereof.

[0035] Once processed into a composite filament and / or formed into a printed part, the conductive particles may be substantially individually distributed throughout the continuous polymer phase. In various embodiments, at least a majority of the conductive particles may be located in the second thermoplastic polymer in the continuous polymer phase or otherwise associated with the second thermoplastic polymer. The degree of localization or association between the conductive particles and the second thermoplastic polymer may be determined based on the amount of conductive particles lost upon dissolution or decomposition of the first thermoplastic polymer when establishing porosity as disclosed herein. In a non-limiting example, at least about 80%, at least about 85%, at least about 90%, or at least about 95% of the conductive particles originally blended with the continuous polymer phase may remain associated with the second thermoplastic polymer after the first thermoplastic polymer is removed.

[0036] In some examples, the first thermoplastic polymer may be water-soluble, and the second thermoplastic polymer may be water-insoluble. Examples of water-soluble thermoplastic polymers suitable for use in the present disclosure may include, for example, polyvinyl alcohol, polyethylene glycol, any copolymers thereof, or any combination thereof. Some or other examples of suitable first thermoplastic polymers may include, but are not limited to, polyvinylpyrrolidone, polyoxazoline (e.g., poly(2-ethyl-2-oxazoline)), cellulose esters, polylactic acid, polylactate, polycaprolactone, any copolymers thereof, or any combination thereof. Solubility or decomposability in aqueous acid solutions is also included within the scope of solubility in the present disclosure. Polylactic acid can be effectively decomposed by contact with aqueous acid. Polylactic acid can also be effectively used as a construction material (i.e., as the second thermoplastic polymer) in the present disclosure. When polylactic acid is used as the second thermoplastic polymer, the specified conditions for dissolving or decomposing the first thermoplastic polymer can be selected so as not to decompose the polylactic acid (i.e., non-acidic conditions). Similar considerations apply to polyesters such as polycaprolactone, which may also be degradable under aqueous acid conditions, but may be suitable for use as the second thermoplastic polymer if the first thermoplastic polymer is removed under conditions that do not promote its degradation.

[0037] A wide range of thermoplastic polymers may be utilized as the second thermoplastic polymer in the present disclosure. Any thermoplastic polymer may constitute a suitable second thermoplastic polymer, provided that the second thermoplastic polymer is insoluble and / or non-degradable under the specified conditions under which the first thermoplastic polymer is soluble or degradable. The second thermoplastic polymer may also be selected based on printing feasibility and the physical properties of the resulting printed part after removal of the first thermoplastic polymer. Suitable thermoplastic polymers that can be used as the second thermoplastic polymer may exhibit a softening temperature or melting point sufficient to facilitate deposition (printing) at temperatures ranging from about 50°C to about 400°C, or from about 70°C to about 275°C, or from about 100°C to about 200°C, or from about 175°C to about 250°C. The melting point may be determined using ASTM E794-06(2018) with a 10°C heating and cooling rate, and the softening temperature may be determined using ASTM D6090-17.

[0038] Illustrative examples of thermoplastic polymers that can be used as the second thermoplastic polymer in the present disclosure include, for example, polyamide, polycaprolactone, polylactic acid, poly(styrene-isoprene-styrene) (SIS), poly(styrene-ethylene-butylene-styrene) (SEBS), poly(styrene-butylene-styrene) (SBS), high-impact polystyrene (HIPS), polystyrene, thermoplastic polyurethanes (thermoplastic Polyurethane, TPU), poly(acrylonitrile-butadiene-styrene) (ABS), polymethyl methacrylate, poly(vinylpyrrolidine-vinyl acetate), polyester, polycarbonate, polyethersulfone, polyoxymethylene, polyetheretherketone, polyetherimide, polyethylene, polyethylene oxide, polyphenylene sulfide, polypropylene, polystyrene, polyvinyl chloride, poly(tetrafluoroethylene), poly(vinylidene fluoride), poly(vinylidene fluoride-hexafluoropropylene), polyvinylpyrrolidone-co-polyvinyl acetate (PVP-co-PVA), any copolymers thereof, and any combinations thereof. Although some of the aforementioned second thermoplastic polymers are water soluble, they may still be utilized as the second (insoluble and / or non-degradable) thermoplastic polymer when the first (soluble and / or degradable polymer) is removed under non-aqueous conditions (e.g., by dissolution with an organic solvent).

[0039] In some embodiments, the second thermoplastic polymer that remains associated with the conductive particles after removing the first thermoplastic polymer may itself be a conductive polymer. Further enhanced piezoresistive behavior can be achieved by distributing conductive particles within a conductive polymer that defines a porous network. Suitable conductive polymers may include, but are not limited to, polyacetylene, polyaniline, polypyrrole, polythiophene (including poly-(3,4-ethylenedioxythiophene, PEDOT), polyphenylene and other polyarylenes, polyphenylene vinylene, and the like. Such conductive polymers may also be blended with non-conductive thermoplastic polymers.

[0040] Preferably, the polymer composites and composite filaments of the present disclosure may be substantially free of thermosetting polymers, including UV curable resins and similar resins capable of forming thermosetting polymers.

[0041] In a non-limiting example, a composite of the present disclosure can be obtained under aqueous processing conditions to provide conductive particles distributed in a continuous polymer matrix comprising a first thermoplastic polymer and a second thermoplastic polymer. In some embodiments, the composite can be obtained in the form of a film before being subsequently processed into a composite filament. After obtaining the composite, the composite can be processed (e.g., by extrusion) into a composite filament suitable for fused filament fabrication, processed into larger composite fibers or filaments, converted into pellets, and / or used directly in the form of a chopped or pulverized composite film (e.g., composite pieces). Suitable extrusion conditions can be performed above the melting or softening temperature of the continuous polymer matrix, for example, using a single-screw or twin-screw extruder.

[0042] In some embodiments, the conductive particles may be combined with an aqueous dispersion of a second thermoplastic polymer. A first thermoplastic polymer (e.g., a water-soluble polymer) may then be added to the aqueous dispersion. The water is evaporated to form a composite film, which may then be extruded into filaments.

[0043] In other embodiments, the conductive particles may be combined with an aqueous dispersion of a second thermoplastic polymer. The water may then be evaporated, and a first thermoplastic polymer (e.g., a water-soluble polymer) may be combined with the residue, which may then be blended together to form a composite. Subsequent extrusion may then provide a composite filament.

[0044] Thus, in some embodiments, a method for forming a composite according to the disclosure herein may include combining a plurality of conductive particles and a first thermoplastic polymer that is water-soluble (or alternatively, degradable under specified conditions) with an aqueous dispersion of a second thermoplastic polymer that is water-insoluble (or alternatively, non-degradable under specified conditions in which the first thermoplastic polymer is soluble or degradable) to provide a combined aqueous mixture; and removing water from the combined aqueous mixture to provide a composite residue comprising at least a portion of the conductive particles distributed in a continuous polymer phase comprising the first thermoplastic polymer and the second thermoplastic polymer, wherein the first thermoplastic polymer and the second thermoplastic polymer may remain immiscible with each other in the continuous polymer phase.

[0045] In an alternative procedure, the first thermoplastic polymer may be at least partially replaced with soluble or degradable particles that can undergo separation or removal from the second thermoplastic polymer under specified conditions. The liquid that is removed under specified conditions may similarly at least partially replace the first thermoplastic polymer, provided that the blend of liquid, second thermoplastic polymer, and conductive particles retains the ability to be processed into continuous filaments according to the present disclosure. The soluble or degradable particles or liquid may undergo degradation or removal under conditions similar to those used to promote the degradation or removal of the first thermoplastic polymer. In a non-limiting example, the soluble or degradable particles or liquid may be water-soluble, and the second thermoplastic polymer may be water-insoluble under specified conditions.

[0046] In yet another embodiment, a gas-forming substance may be utilized to introduce porosity into a continuous polymer matrix comprising a second thermoplastic polymer. Specifically, a first thermoplastic polymer may be at least partially replaced with a gas-forming substance (e.g., microspheres containing a gas or a material that decomposes into a gas under specified conditions) and combined with a second thermoplastic polymer. The formation of gas within the second thermoplastic polymer, when processed under suitable conditions, may result in the formation of cells and the definition of porosity therein.

[0047] The composite residue may be utilized directly in the form of shreds or a pulverized film (e.g., when the combined aqueous mixture is cast as a composite film and water is evaporated therefrom). In further embodiments, the composite residue may be extruded into composite filaments suitable for fused filament fabrication, or into larger diameter composite fibers having conductive particles distributed in a continuous polymer phase. If desired, the larger composite fibers may be chopped or similarly processed into composite pellets having conductive particles similarly distributed in a continuous polymer phase. In some embodiments, the composite film, after evaporating water therefrom, may be broken into a plurality of composite pieces (e.g., by chopping or pulverization), and the composite pieces may be extruded to form composite filaments.

[0048] Optionally, a composite or composite filament obtained as described above may be processed to remove at least a portion of the first thermoplastic polymer therefrom, thereby defining porosity in the continuous polymer phase. Such composite filaments may include a second thermoplastic polymer defined as a porous polymer network having conductive particles distributed therein. Further optionally, once porosity has been defined in the foregoing manner, the pores or channels within the porous polymer network may be refilled with one or more additives, such as additional conductive particles, thermally conductive particles, reinforcing fibers, colorants, stabilizers, plasticizers, etc., to further modify the composite properties. Such additives may be introduced into a liquid solution or dispersion, which is then evaporated upon refilling.

[0049] Once the composite filament is formed according to the disclosure herein, it may be deposited layer by layer above its softening temperature to form a printed part having a specified shape. After printing, the printed part may include a continuous polymer matrix including a first thermoplastic polymer and a second thermoplastic polymer that remain immiscible with each other, and a plurality of conductive particles distributed in the continuously printed polymer matrix.

[0050] At least a majority of the conductive particles may be substantially located in or associated with the second thermoplastic polymer, such that the first thermoplastic polymer is removed from the printed part by dissolution or decomposition (e.g., by water solubility) without removing a significant fraction of the conductive particles. After removing the first thermoplastic polymer from the continuously printed polymer matrix, a printed part having porosity defined therein may be obtained. Specifically, such a printed part may include a printed polymer matrix that exhibits piezoresistivity, has porosity defined therein, and includes a plurality of conductive particles distributed in a thermoplastic polymer (e.g., the second thermoplastic polymer remaining after dissolution or decomposition of the first thermoplastic polymer). Suitable types of printed parts having piezoresistivity behavior are not considered to be particularly limited in this disclosure.

[0051] Optionally, the resulting porosity in the printed part may be refilled with one or more additional additives. Such refilling may be performed in a manner similar to that described above with respect to refilling of porous composite filaments.

[0052] Embodiments disclosed herein include the following.

[0053] A. Composite filaments that may be suitable for additive manufacturing. The composite filaments include a continuous polymer phase including a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with each other, where the first thermoplastic polymer is soluble or degradable under specified conditions and the second thermoplastic polymer is insoluble or non-degradable under specified conditions, and a plurality of conductive particles distributed in the continuous polymer phase, where the plurality of conductive particles include microparticles, nanoparticles, or any combination thereof.

[0054] A1. Composite. The composite includes a continuous polymer phase including a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with each other, where the first thermoplastic polymer is soluble or degradable under specified conditions and the second thermoplastic polymer is insoluble or non-degradable under specified conditions, and a plurality of conductive particles distributed in the continuous polymer phase, where the plurality of conductive particles include microparticles, nanoparticles, or any combination thereof. Optionally, the first thermoplastic polymer and the second thermoplastic polymer may have a co-continuous distribution in the continuous polymer phase.

[0055] A2. Composite Pellets. The composite pellets include a continuous polymer phase including a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with each other, where the first thermoplastic polymer is soluble or degradable under specified conditions and the second thermoplastic polymer is insoluble or non-degradable under specified conditions, and a plurality of conductive particles distributed in the continuous polymer phase, where the plurality of conductive particles include microparticles, nanoparticles, or any combination thereof. Optionally, the first thermoplastic polymer and the second thermoplastic polymer may have a co-continuous distribution in the continuous polymer phase.

[0056] B. Printed part comprising immiscible polymers. The printed part comprises a continuously printed polymer matrix comprising a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with each other, where the first thermoplastic polymer is soluble or degradable under specified conditions and the second thermoplastic polymer is insoluble or non-degradable under specified conditions, and a plurality of conductive particles distributed in the continuously printed polymer matrix, the plurality of conductive particles comprising microparticles, nanoparticles, or any combination thereof. Optionally, the first thermoplastic polymer and the second thermoplastic polymer may have a co-continuous distribution in the continuously printed polymer matrix.

[0057] C. Piezoresistive Printed Part: The printed part includes a printed polymer matrix having porosity defined therein and including a plurality of conductive particles distributed in a thermoplastic polymer.

[0058] D. A method for forming a composite filament. The method includes combining a plurality of conductive particles and a water-soluble first thermoplastic polymer with an aqueous dispersion of a water-insoluble second thermoplastic polymer to provide a combined aqueous mixture, removing water from the combined aqueous mixture to provide a composite residue comprising at least a portion of the conductive particles distributed in a continuous polymer phase comprising the first thermoplastic polymer and the second thermoplastic polymer, wherein the first thermoplastic polymer and the second thermoplastic polymer are immiscible with each other in the continuous polymer phase, and extruding the composite residue into a composite filament comprising the conductive particles distributed in the continuous polymer phase. Optionally, the first thermoplastic polymer and the second thermoplastic polymer may have a co-continuous distribution in the continuous polymer phase.

[0059] E. Printing Method. The method includes providing a composite filament of A and depositing the composite filament layer-by-layer above its softening temperature to form a printed part.

[0060] Each of embodiments A through E may have one or more of the following additional elements in any combination.

[0061] Element 1: The first thermoplastic polymer is water-soluble and the second thermoplastic polymer is water-insoluble.

[0062] Element 2: At least a majority of the conductive particles are located in the second thermoplastic polymer in a continuous polymer phase or in a continuously printed polymer matrix.

[0063] Element 2A: The first thermoplastic polymer and the second thermoplastic polymer have a co-continuous distribution.

[0064] Element 3: The first thermoplastic polymer comprises polyvinyl alcohol, polyethylene glycol, or any combination thereof.

[0065] Element 4: The conductive particles are present in the continuous polymer phase in a particle:polymer weight ratio ranging from about 10:90 to about 95:5 based on the total composite weight.

[0066] Element 5: The ratio of the first thermoplastic polymer to the second thermoplastic polymer ranges from about 30:70 to about 70:30 by weight.

[0067] Element 6: The conductive particles have an average particle size of about 10 microns or less.

[0068] Element 7: At least a portion of the conductive particles have an average particle size of about 100 nm or less.

[0069] Element 8: The conductive particles include a metal, a carbonaceous conductor, or any combination thereof.

[0070] Element 9: The conductive particles are present in the printed polymer matrix at about 2% to about 20% by volume, based on the total volume of the printed polymer matrix.

[0071] Element 10: Removing water from the combined aqueous mixture includes casting the combined aqueous mixture as a composite film and allowing the water to evaporate.

[0072] Element 11: The method further includes breaking the composite film into a plurality of composite pieces after evaporating water from the composite film, and extruding the composite pieces to form composite filaments.

[0073] Element 12: The method further includes removing at least a portion of the first thermoplastic polymer from the printed part to introduce porosity into the printed part.

[0074] As a non-limiting example, exemplary combinations applicable to A through E include, but are not limited to, 1 and 2 or 2A; 1 and 3; 1 and 4; 1 and 5; 1 and 6; 1 and 7; 1 and 8; 2 or 2A and 3; 2-4; 2A, 3, and 4; 2 or 2A, 3, and 5; 2 or 2A, 3, and 6; 2 or 2A, 3, and 7; 2 or 2A, 3, and 8; 3 and 4; 3 and 5; 3 and 6; 3 and 7; 3 and 8; 4 and 5; 4 and 6; 4 and 7; 4 and 8; 5 and 6; 5 and 7; 5 and 8; 6 or 7, and 8; any of 1 through 8, and 9; any of 1 through 9, and 10; any of 1 through 10, and 11; 10 and 11; and any of 1 through 11, and 12.

[0075] To facilitate a better understanding of the present disclosure, the following examples of preferred or representative embodiments are given, which should in no way be read as limiting or defining the scope of the invention. [Example]

[0076] Formation of Composite Films. The following general procedure was utilized to prepare composite films that could be further processed into composite filaments. Silver microflakes were combined with an aqueous polymer dispersion, and the aqueous polymer dispersion was combined with a solution of a water-soluble polymer. The resulting combined aqueous mixture was cast as a film and the water was allowed to evaporate. The resulting composite residue was analyzed, optionally ground, and extruded into composite filaments.

[0077] Silver microflakes (approximately 2-4 μm) were purchased from Inframat Advanced Materials, LLC. Thermoplastic polyurethane (TPU) emulsion (Alberdingk U 615) was purchased from Alberdingk Boley Inc. Polyvinyl alcohol (PVA, SELVOL™ E 203S, a low-viscosity partially hydrolyzed polyvinyl alcohol) was purchased from Sekisui Specialty Chemicals. Poly(ethylene glycol) (PEG) with an average molecular weight (Mn) of 35,000 was purchased from Sigma-Aldrich, Inc.

[0078] Example 1: Basic piezoresistive formulation without water-soluble polymer. One gram of silver microflakes was combined with 1.25 g of TPU emulsion, and the resulting mixture was rolled on a movil rod roller for 4 hours to thoroughly mix. A film was cast by pouring the mixture into a tray. Water from the mixture was evaporated under ambient conditions in a fume hood, under vacuum overnight, or in a 60°C oven for 2 hours. After drying, the weight ratio of silver microflakes to TPU was 2:1.

[0079] Example 2: Piezoresistive formulation with PVA. Example 1 was repeated except that 1.0 g of a 25 wt % solution of PVA was combined with the mixture of silver microflakes and TPU. After drying, the mass ratio of silver microflakes to TPU to PVA was 4:2:1.

[0080] At scale, processing was performed by mixing 180 g of silver microflakes with 225 g of Alberdink U 615 TPU emulsion (90 g TPU solids) and rolling the mixture on a mobile rod roller for 4 hours. The rolled mixture was poured onto a tray, and films were cast by removing water under ambient conditions, under vacuum, or in an oven at 60°C for 2 hours. The dried material was crushed into small pieces and further dried overnight under vacuum at 40°C. 90 g of additional dried material (equivalent to 60 g of silver microflakes and 30 g of TPU) was combined with 15 g of PVA and compounded in a Haake mixer at 180°C. Filaments were successfully extruded from the material produced under scale-up conditions.

[0081] Example 3: Sonicated film of Example 2. The dried film of Example 2 was sonicated in water for 3 hours to remove the PVA. Sonication was performed using a Branson 1510 ultrasonic bath.

[0082] Example 4: Piezoresistive formulation with PEG. Example 1 was repeated except that 0.25 g of a 40 wt % solution of PEG was combined with the mixture of silver microflakes and TPU. After drying, the mass ratio of silver microflakes to TPU to PEG was 4:2:1.

[0083] The scale-up synthesis of Example 2 was performed, except that PEG was used instead of PVA. After compounding, the resulting mixture had a mass ratio of silver microflakes to TPU to PEG of 4:2:1. Filaments were successfully extruded from the material produced under scale-up conditions.

[0084] Example 5: Sonicated film of Example 4. The dried film of Example 4 was sonicated for 3 hours to remove the PVA. Sonication was carried out using a Branson 1510 ultrasonic bath.

[0085] SEM characterization of the composite film. After drying, some easily removable silver microflakes remained on the surface of the film, but the majority of the silver microflakes remained dispersed in the continuous polymer phase. The addition of PVA or PEG had little effect on dispersion stability.

[0086] The product from Example 1 was analyzed by scanning electron microscopy (SEM). Cross-sectional SEM images showed good distribution of silver microflakes in the composite matrix. The SEM images are shown in Figures 7A and 7B and are discussed below with reference to composite filaments prepared therefrom.

[0087] Ash Analysis of Composite Films The silver content of the films of Examples 1-5 was determined by ash analysis and is summarized in Table 1 below. [Table 1] The discrepancy between the silver content for the films of Examples 1, 2, and 4 is believed to arise from water retention in the composite film. The film of Example 1 was not dried under vacuum before analysis, which may explain its higher-than-expected water content, even though this film did not contain a water-soluble polymer. After removing the water-soluble polymer from the films of Examples 2 and 4, the experimental silver content was very close to that predicted by theory (samples of Examples 3 and 5). The close correlation with theory indicates that the PVA and PEG were effectively removed by sonication, and that little silver dispersed in the water-soluble phase (PVA or PEG) of the two immiscible polymers.

[0088] Flexibility of Composite Films. The composite films of Examples 1-5 were qualitatively evaluated for their flexibility and brittleness by manually bending the films. The composite film of Example 1 cracked immediately after bending. The composite film of Example 2 was very brittle, but after removing the PVA (Example 3), the film was much more flexible and could be folded in half without cracking or breaking. Comparing Examples 4 and 5, the composite film was significantly more flexible after removing the PEG (Example 5). The PEG system (Example 4) was not as stiff as the PVA system (Example 2).

[0089] Electrical Properties of Composite Films. The piezoresistive performance of the composite films of Examples 1-5 was evaluated by measuring the change in resistance as the applied pressure was varied. Composite films for piezoresistivity measurements were prepared by drying in a 60°C oven for 2 hours to obtain a film thickness of 0.8 mm. Resistance was measured using a multimeter connected to the composite. Resistance was measured with five different weights applied to the composite film: 72 g, 122 g, 272 g, 572 g, and 1072 g. An aluminum plaque (72 g) was placed on the film as the top electrode to better distribute the force applied to the composite and provide a consistent contact area. Additional weights were added to the aluminum plaque to reach the specified total weight. Figure 4 shows a plot of resistance as a function of the weight applied to the films of Examples 1-5. All composite films showed a decrease in resistance with increasing applied weight (load). The composite film lacking PVA or PEG (Example 1) tended to exhibit lower initial resistance than the other films, especially in the low applied pressure range. At the lowest applied pressure, the composite film containing PVA (Example 2) had a statistically significant 14.3% higher resistance than the comparative film containing PEG (Example 4). After removal of PVA or PEG, the resistance values ​​were very close to each other (Examples 3 and 5), but were still much higher than the resistance of TPU alone (Example 1) at the lowest applied pressure. The composite films with PVA / PEG exhibited higher initial resistance values ​​than those without and showed greater sensitivity at lower pressure ranges (i.e., lower weights). As pressure increased, the resistance values ​​became indistinguishable from each other.

[0090] Composite Filaments. The composite films prepared as described above were further processed into composite filaments using a Filabot EX6 filament extruder. The extruder consisted of an extruder, an air channel, and a filament take-up. The extruder had four heating zones: i) a feed port nozzle, ii) a rear zone, iii) a middle zone, and iv) a front zone. The extruder was modified with a digital voltage readout to control the extrusion screw motor speed and, therefore, the extrusion rate. The feed channel nozzle could be replaced with a nozzle of a different diameter. The air channel could be adjusted for airflow. The air channel position could be adjusted relative to the distance from the exit nozzle or by raising the air channel on a jack. In this experiment, the height of the air channel was kept constant. The air channel distance from the exit nozzle was also varied to maintain a constant filament diameter. Table 2 summarizes the filament extrusion conditions used to prepare the composite filaments of Examples 6 and 7 (see below). Filament diameter was measured using an in-line thickness gauge. [Table 2]

[0091] Example 6: Piezoresistive filaments lacking water-soluble polymer. The composite film of Example 1 was prepared at 100 times the previous scale, ground into small pieces, and dried under vacuum for 2 hours. The ground material was then extruded into the filaments specified in Table 2. Figure 5A shows a photograph of the composite filament of Example 6.

[0092] Example 7: Piezoresistive filament containing PVA. The composite film of Example 2 was prepared at 100 times the previous scale, ground into small pieces, and dried under vacuum for 2 hours. The ground material was then extruded into filaments as specified in Table 2. Figure 5B shows a photograph of the composite filament of Example 7. The as-produced composite filament had a mass of 2.63 g / cm as measured by gas pycnometry using a Micromeritics ACCYPYC 1330 instrument. 3 The average density was 1.025g.

[0093] Example 8: Sonicated Piezoresistive Filament of Example 7. The composite filament of Example 7 was sonicated in water for 3 hours, immersed in water for 24 hours, and then dried in a vacuum oven to remove the PVA. Sonication was performed using a Branson 1510 ultrasonic bath. The sonicated composite filament had a mass fraction of 2.97 g / cm as measured by gas pycnometry. 3 The increase in density as measured by gas pycnometry is consistent with at least partial removal of PVA from the composite filaments and the formation of porosity in the composite filaments.

[0094] Flexibility of the composite filaments. The composite filaments of Examples 6 and 7 were both very brittle and could easily break when bent. After ultrasonic treatment and PVA removal (Example 8), the composite filaments were significantly more flexible and less brittle, with a rougher surface and less gloss.

[0095] Electrical Properties of Composite Filaments. The electrical properties of 5 cm sections of the composite filaments were measured using a multimeter connected to each end of the filament. The composite filaments of Examples 6 and 7 both exhibited infinite resistance. In contrast, the composite filament of Example 8 exhibited a resistance of several hundred MΩ after removal of the PVA. Further ultrasonic treatment and immersion in water for two days resulted in a further reduction in resistance to 4 MΩ.

[0096] After removing the PVA from the filament, the resistance change over various weight loads was studied. Resistance was measured at five different weights applied to the composite film: 72 g, 122 g, 272 g, 572 g, and 1072 g. To perform these measurements, one contact of a multimeter was connected to the end of the composite filament, and the second contact of the multimeter was connected to the conductive film disposed on the filament. Figure 6 shows a plot of resistance as a function of weight applied to the composite filament of Example 8. As shown, the resistance decreased from 12.2 MΩ to 2.4 MΩ as the applied weight increased. Therefore, a piezoresistive composite can be obtained from the composite filament after removing the PVA.

[0097] SEM Characterization of Composite Filaments. Figures 7A and 7B show SEM images of the silver microflake / TPU composite film (Example 1) at two different magnifications. As shown, the silver microflakes were mostly uniformly dispersed in the polymer matrix, with some regions of non-uniform dispersion and porosity present. The porosity of the film may explain its piezoresistive behavior.

[0098] Figures 8A and 8B show cross-sectional SEM images of a silver microflake / TPU composite filament (Example 6) at two different magnifications. Compared to the corresponding film (Figures 7A and 7B), the silver microflakes were more uniformly dispersed and more densely packed in the filament. In contrast to the porous film, porosity was not evident in the filament. The lack of porosity and dense silver microflake packing may explain the lack of conductivity.

[0099] Figures 9A and 9B, and Figures 9C and 9D show cross-sectional SEM images at two magnifications of the composite filaments of Examples 7 and 8 (before and after PVA removal), respectively. The composite filament of Example 7 exhibited uniform silver microflake distribution and dense packing, indicating that the addition of PVA did not destroy the particle dispersion. Porosity was evident in the composite filament of Example 8, which may explain its conductive and piezoresistive effects.

[0100] Printing of Composite Filament. The composite filament of Example 7 was printed as single-layer and multi-layer 2 cm x 2 cm square coupons using a Hyrel HYDRA 16A 3D printer with an HT2-250 extruder print head. The thickness of each printed layer was approximately 200 microns. A five-layer coupon was selected as an exemplary sample for further evaluation, described below. Extrusion was performed at 170°C with an extrusion rate of 10 mm / s onto a glass plate held at 45°C.

[0101] The as-printed coupons were non-conductive. After sonicating the as-printed coupons to remove the PVA, the resulting porous coupons were conductive both on their surface and across their cross-sectional thickness. Resistance was then measured across the cross-sectional thickness using applied weights of 10, 50, 100, 200, 500, and 1000 g. Figure 10 shows a plot of resistance versus applied pressure. As shown, resistance gradually decreased with increasing pressure.

[0102] All documents described herein are incorporated by reference for purposes of all jurisdictions where such practice is permitted, including any priority documents and / or testing procedures to the extent not inconsistent with this text. While forms of the disclosure have been illustrated and described, as is evident from the foregoing general description and specific embodiments, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, the disclosure is not intended to be limited thereby. For example, the compositions described herein may not include any component or composition not expressly listed or disclosed herein. Any method may lack any step not listed or disclosed herein. Similarly, the term "comprising" is considered synonymous with the term "including." Whenever a method, composition, element, or group of elements is preceded by the transitional phrase "comprising," it is understood that the inventors also contemplate the same composition or group of elements with the transitional phrase "consisting essentially of," "consisting of," "selected from the group consisting of," or "is" preceding the composition, element, or list of elements, and vice versa.

[0103] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and the like used in this specification and the related claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and appended claims are approximations that may vary depending upon the desired properties sought to be obtained by embodiments of the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0104] Whenever a numerical range with a lower and upper limit is disclosed, any number within that range and any included range is specifically disclosed. Specifically, all ranges of values ​​disclosed herein (in the form "from about a to about b," or, equivalently, "from approximately a to b," or, equivalently, "from approximately a to b") should be understood to describe all numbers and ranges encompassed within the broader range of values. Also, terms in the claims have their plain and ordinary meaning unless expressly and unambiguously defined otherwise by the patentee. Furthermore, when used in the claims, the indefinite articles "a" or "an" are defined herein to mean one or more than one of the element they introduce.

[0105] One or more exemplary embodiments are presented herein. For clarity, not all features of a physical implementation are described or illustrated in this application. It is understood that in developing a physical embodiment of the present disclosure, numerous implementation-specific decisions must be made to achieve the developer's goals, which may vary from implementation to implementation and from time to time, such as compliance with system-related, business-related, government-related, and other constraints. While the developer's efforts may be time-consuming, such efforts would nevertheless be routine for one of ordinary skill in the art having the benefit of this disclosure.

[0106] Thus, the present disclosure is well adapted to achieve the ends and advantages mentioned, as well as those inherent therein. The specific embodiments disclosed above are illustrative only, as the disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design shown herein, other than as set forth in the following claims. It is therefore apparent that the specific exemplary embodiments disclosed above may be altered, combined, or modified, and all such variations are considered within the scope and spirit of the present disclosure. The illustratively disclosed embodiments preferably may be practiced in the absence of any element not specifically disclosed herein and / or any optional element disclosed herein.

Claims

1. It is a composite filament, A continuous polymer phase comprising a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with respect to each other, The first thermoplastic polymer is soluble or degradable under specified conditions, the second thermoplastic polymer is insoluble or non-degradable under the specified conditions, and The first thermoplastic polymer and the second thermoplastic polymer are co-continuously distributed in the continuous polymer phase and define a mutual penetration network, The continuous polymer phase comprises a plurality of conductive particles, including microparticles, nanoparticles, or any combination thereof, A composite filament having a diameter of approximately 1.0 mm to approximately 10.0 mm and a spoolable length of at least approximately 1 foot.

2. The composite filament according to claim 1, wherein the first thermoplastic polymer is water-soluble and the second thermoplastic polymer is water-insoluble.

3. The composite filament according to claim 2, wherein at least the majority of the conductive particles are located in the second thermoplastic polymer in the continuous polymer phase.

4. The composite filament according to claim 2, wherein the first thermoplastic polymer comprises polyvinyl alcohol, polyethylene glycol, or any combination thereof.

5. The composite filament according to claim 1, wherein the conductive particles are present in the continuous polymer phase in a particle:polymer weight ratio in the range of about 10:90 to about 95:5 based on the total composite mass.

6. The composite filament according to claim 1, wherein the conductive particles have an average particle size of about 10 microns or less.

7. The composite filament according to claim 1, wherein the conductive particles include a metal, a carbonaceous conductor, or any combination thereof.

8. A method, To provide the composite filament described in claim 1, A method comprising depositing the composite filament layer by layer above its softening temperature to form a printed component.

9. The method according to claim 8, wherein the first thermoplastic polymer is water-soluble and the second thermoplastic polymer is water-insoluble.

10. The method according to claim 9, further comprising removing at least a portion of the first thermoplastic polymer from the printed component to introduce porosity to the printed component.

11. The method according to claim 9, wherein at least the majority of the conductive particles are located in the second thermoplastic polymer in the continuous polymer phase.

12. Printed parts, A continuously printed polymer matrix comprising a first thermoplastic polymer and a second thermoplastic polymer that are immiscible with respect to each other, The first thermoplastic polymer is soluble or degradable under specified conditions, the second thermoplastic polymer is insoluble or non-degradable under the specified conditions, and The first thermoplastic polymer and the second thermoplastic polymer are co-continuously distributed in the continuously printed polymer matrix and define an interpenetration network, A printed component comprising a plurality of conductive particles distributed in the continuously printed polymer matrix, the plurality of conductive particles including microparticles, nanoparticles, or any combination thereof.

13. The printed component according to claim 12, wherein the first thermoplastic polymer is water-soluble and the second thermoplastic polymer is water-insoluble.

14. The printed component according to claim 13, wherein at least the majority of the conductive particles are located in the second thermoplastic polymer in the continuously printed polymer matrix.

15. The printed component according to claim 13, wherein the first thermoplastic polymer comprises polyvinyl alcohol, polyethylene glycol, or any combination thereof.

16. It is a method, To provide an aqueous mixture by combining a plurality of conductive particles and a first water-soluble thermoplastic polymer with an aqueous dispersion of a second water-insoluble thermoplastic polymer. To provide a composite residue comprising at least a portion of the conductive particles distributed in a continuous polymer phase containing the first thermoplastic polymer and the second thermoplastic polymer, wherein the first thermoplastic polymer and the second thermoplastic polymer are immiscible with each other in the continuous polymer phase, by removing water from the combined aqueous mixture. Here, the first thermoplastic polymer and the second thermoplastic polymer are co-continuously distributed in the composite residue and define a mutual penetration network. The process includes extruding the composite residue onto a composite filament containing the conductive particles distributed in the continuous polymer phase, A method wherein the composite filament has a diameter of about 1.0 mm to about 10.0 mm and a spoolable length of at least about 1 foot.

17. The method according to claim 16, wherein the first thermoplastic polymer comprises polyvinyl alcohol, polyethylene glycol, or any combination thereof.

18. The method according to claim 16, wherein removing water from the combined aqueous mixture comprises casting the combined aqueous mixture as a composite film and evaporating the water.

19. The method according to claim 18, further comprising: evaporating the water from the composite film, then breaking the composite film into a plurality of composite pieces, and extruding the composite pieces to form the composite filament.

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