FOAM PELLETS

BACKGROUND Field of Invention

[0001] The present invention relates generally to polymeric powders and more specifically to high-fineness thermoplastic powders.

Description of Related Art

[0002] Polymeric powders have a wide range of uses. A polymeric powder can, for instance, be used to produce a fiber-reinforced composite. To illustrate, the polymeric powder can be introduced to a fibrous material — whether the powder is dry or wet, such as in a slurry — and subsequently melted to form a matrix of the powder’s polymeric material within which fibers of the fibrous material are dispersed. And polymeric powders can be used to form other components. Particles of a polymeric powder can, for example, be sintered or melted to one another at desired locations (e.g., using selective laser sintering or selective laser melting) to form a component. As another example, a polymeric powder can be molded (e.g., during compression molding) to form a component.

[0003] Depending on its intended use, a polymeric powder’s effectiveness can increase as its particles become smaller. To illustrate using the fiber-reinforced composite discussed above, smaller particles may better reach interstices between the fibers than larger particles, leading to more uniform distribution of the polymeric material — and less voids — throughout the composite once the powder is melted. Smaller particles can also be combined with larger particles to provide a mixture with improved particle packing.

[0004] Producing high-fineness polymeric powders is, however, difficult at best.

Typically, to produce a polymeric powder, a polymeric material (e.g., in the form of pellets) is milled. But as the particles become smaller, the energy required to further reduce their sizes increases. And at a certain point, that energy may cause the particles’ polymeric material to melt, preventing further size-reduction. In some processes, this problem is alleviated to some extent by cryogenically-cooling the polymeric material prior to milling.

But such cryogenic cooling is not only expensive, it may not be enough to permit the production of suitably fine polymeric powders. SUMMARY

[0005] Some of the present methods, at least by milling foam pellets to produce it, can provide for a high-fineness polymeric powder, such as one having a Dv50 value of less than or equal to 30 micrometers, wherein Dv50 is defined as the median equivalent spherical diameter of a volume-based distribution of equivalent spherical diameters determined by laser diffraction according to ISO 13320:2009. Without limiting the invention, it is believed that foam pellets may be reduced to such a fine powder because their cell walls, which ultimately form the powder, have thicknesses (e.g., on the order of 10 pm or smaller) that are comparable to or smaller than the desired particle size and/or that their cellular structure may be more friable than a solid structure. In some methods, these benefits can be enhanced by cryogenically-cooling the foam pellets prior to milling them.

[0006] The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically; two items that are “coupled” may be unitary with each other. The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. The term “substantially” is defined as largely but not necessarily wholly what is specified (and includes what is specified; e.g., substantially 90 degrees includes 90 degrees and substantially parallel includes parallel), as understood by a person of ordinary skill in the art. In any disclosed embodiment, the terms “substantially” and “approximately” may be substituted with “within [a percentage] of’ what is specified, where the percentage includes 0.1, 1, 5, and 10 percent.

[0007] The phrase “and/or” means “and” or “or.” To illustrate, A, B, and/or C includes:

A alone, B alone, C alone, a combination of A and B, a combination of A and C, a combination of B and C, or a combination of A, B, and C. In other words, “and/or” operates as an inclusive “or.”

[0008] Further, a device or system that is configured in a certain way is configured in at least that way, but it can also be configured in other ways than those specifically described. [0009] The terms “comprise” (and any form of comprise, such as “comprises” and “comprising”), “have” (and any form of have, such as “has” and “having”), “include” (and any form of include, such as “includes” and “including”), and “contain” (and any form of contain, such as “contains” and “containing”) are open-ended linking verbs. As a result, an apparatus that “comprises,” “has,” “includes,” or “contains” one or more elements possesses those one or more elements, but is not limited to possessing only those one or more elements. Likewise, a method that “comprises,” “has,” “includes,” or “contains” one or more steps possesses those one or more steps, but is not limited to possessing only those one or more steps.

[0010] Any embodiment of any of the apparatuses, systems, and methods can consist of or consist essentially of - rather than comprise/have/include/contain - any of the described steps, elements, and/or features. Thus, in any of the claims, the term “consisting of’ or “consisting essentially of’ can be substituted for any of the open-ended linking verbs recited above, in order to change the scope of a given claim from what it would otherwise be using the open-ended linking verb.

[0011] The feature or features of one embodiment may be applied to other embodiments, even though not described or illustrated, unless expressly prohibited by this disclosure or the nature of the embodiments.

[0012] Some details associated with the embodiments are described above and others are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The following drawings illustrate by way of example and not limitation. For the sake of brevity and clarity, every feature of a given structure is not always labeled in every figure in which that structure appears. Identical reference numbers do not necessarily indicate an identical structure. Rather, the same reference number may be used to indicate a similar feature or a feature with similar functionality, as may non-identical reference numbers.

[0014] FIG. 1 is a flow chart showing some of the present methods for producing a powder comprising a thermoplastic material at least by milling foam pellets comprising the thermoplastic material.

[0015] FIG. 2 is a schematic view of a system including a mill, the system being usable in at least some of the methods of FIG. 1.

[0016] FIGs. 3A and 3B are schematic views of foam pellets, each of which is usable in at least some of the methods of FIG. 1.

[0017] FIG. 4 is a flow chart showing some of the present methods for producing foam pellets, such methods and pellets being usable in at least some of the methods of FIG. 1. [0018] FIG. 5 A is a schematic view of a system including an extruder for extruding a composition comprising a thermoplastic material and a blowing agent into a liquid-containing chamber to produce foam (or pre-foam) pellets. [0019] FIG. 5B is a schematic view of a system including a pressure chamber for impregnating non-foam pellets with a blowing agent to produce foam (or non-foam, expandable) pellets.

[0020] FIG. 5C is a schematic view of a system including a chamber for polymerizing a precursor of a thermoplastic material in the presence of a blowing agent to produce foam (or non-foam, expandable) pellets. Each of FIGs. 5A-5C’s systems is usable in at least some of the methods of FIG. 4.

[0021] FIGs. 6A and 6B are optical microscopy images of a comparative thermoplastic powder that was produced by milling non-foam pellets.

[0022] FIGs. 6C-6E are scanning electron microscopy images of FIGs. 6A and 6B’s comparative thermoplastic powder.

[0023] FIG. 7A is an optical microscopy image of a sample one of the present thermoplastic powders that was produced by milling foam pellets.

[0024] FIGs. 7B-7E are scanning electron microscopy images of FIG. 7A’s sample thermoplastic powder.

DETAILED DESCRIPTION

[0025] Referring now to FIG. 1, shown are some of the present methods for producing a thermoplastic powder. While FIG. 2’s system and FIGs. 5A-5C’s systems are referenced to illustrate some of FIG. l’s steps, such systems are not limiting on those steps, which can each be performed using any suitable system. The present methods include a step 10 of milling foam pellets, each comprising a thermoplastic material, to produce a powder comprising the thermoplastic material.

[0026] Referring additionally to FIG 2 to illustrate, foam pellets 18, each comprising a thermoplastic material, can be introduced into a mill 22 that size-reduces the foam pellets into a powder 24 comprising the thermoplastic material. In this illustration, mill 22 comprises a mechanical mill, which can include one or more movable elements that contact the foam pellets to size-reduce them. Non-limiting examples of such a mechanical mill include a grinder (to be clear, “milling” includes grinding), a hammer mill, a ball mill, and a rod mill. While the present methods enable the use of a mechanical mill (e.g., 22) to produce high fineness powders, in some methods, non-mechanical mills (e.g., jet mills) are used. In FIG.

2, only one mill 22 is depicted; however, the present methods can be performed using two or more mills, which can, for example, be used in series. To illustrate, the foam pellets can be introduced into a first one of the mills to produce a powder-precursor (e.g., having larger particles than the powder), and the powder-precursor can be introduced into a second one of the mills to produce the powder.

[0027] In some methods, when the foam pellets (e.g., 18) are introduced into the mill (e.g., 22, and, if there are two or more mills, the first one of the mills), each of a majority of the foam pellets is discrete. As used herein, “each of a majority of’ a group of structures refers to 51%, 55%, 60%, 65%, 70%, 75%, 80%, 90%, 95%, or more of the structures in that group. To illustrate, each of a majority of the foam pellets may not be bonded to any other of the foam pellets, whether by sintering, melting, adhesive, a coating, or the like. In such methods and others, each of a majority of the pieces of foam entering the mill may be no larger than one of the foam pellets. Size-reducing such discrete foam pellets may require less energy and produce finer powders than size-reducing larger pieces of foam.

[0028] In some methods, each of a majority of the foam pellets (e.g., 18) introduced into the mill (e.g., 22) comprises the same material. For example, each of a majority of the foam pellets can comprise a majority (e.g., 51%, 55%, 60%, 65%, 70%, 75%, 80%, 90%, 95%, or more), by weight and/or volume, of a same thermoplastic material. For further example, and using polypropylene by way of illustration, which may be replaced in this example with any of the thermoplastic materials discussed below, each of a majority of the foam pellets may be recognized by a person of ordinary skill in the art as a polypropylene foam pellet. In some methods, each of a majority of the foam pellets can consist of the same composition. Correspondingly, powders produced using such foam pellets can include — or consist of — particles, each of a majority of which comprises a majority (e.g., 51%, 55%, 60%, 65%, 70%, 75%, 80%, 90%, 95%, or more), by weight and/or volume, of a same thermoplastic material and/or consists of the same composition. While the present methods permit production of high-fineness powders using foam pellets (e.g., 18) that comprise the same material as discussed above, in some methods, foam pellets of differing materials can be used (e.g., polycarbonate foam pellets and polyetherketone foam pellets).

[0029] The foam pellets (e.g., 18) can comprise any suitable thermoplastic material, including, for example, polystyrene, polyethylene, polypropylene, polycarbonate, polyvinyl chloride, polyamide, polyetherketone, liquid crystal polymer, ethylene vinyl alcohol copolymer, acrylonitrile vinyl alcohol copolymer, acrylonitrile butadiene styrene copolymer, and/or polyurethane. In some embodiments, the thermoplastic material comprises polystyrene, polyethylene, polypropylene, polycarbonate, polyvinyl chloride, polyetherketone, liquid crystal polymer, ethylene vinyl alcohol copolymer, acrylonitrile vinyl alcohol copolymer, acrylonitrile butadiene styrene copolymer, and/or polyurethane. In some embodiments, the thermoplastic material comprises polystyrene, polyethylene, polypropylene, polycarbonate, polyvinyl chloride, polyetherketone, liquid crystal polymer, ethylene vinyl alcohol, acrylonitrile vinyl alcohol copolymer, and/or acrylonitrile butadiene styrene copolymer. In some embodiments, the thermoplastic material excludes polyurethane. The present methods can permit production of high-fineness powders from foam pellets comprising thermoplastic materials that may otherwise be relatively difficult (e.g., due to their glass transition temperatures or other characteristics) to powderize, such as polypropylene, polycarbonate, polyvinyl chloride, polyamide, and/or the like. The present methods need not, and in some embodiments do not, use foam pellets comprising thermoplastic materials that may be relatively easy to powderize, such as polyurethane.

[0030] FIG. 3 A depicts an exemplary foam pellet 18a. As shown, foam pellet 18a includes cells 26 (shown in black) bounded by walls 30 (shown in white). Walls 30 can, but need not, completely bound each of a majority of cells 26; for example, foam pellet 18a can be open-cell or closed-cell. In foam pellet 18a, walls 30 are thin. To illustrate, a majority of walls 30 can each have a thickness that is on the order of 10 pm (e.g., less than or equal to any one of, or between any two of, 1, 2, 4, 6, 8, 10, 15, and 20 pm). Such thin walls may readily break apart during milling of foam pellet 18a, facilitating production of a high fineness powder from the same, which may be further facilitated by those walls having thicknesses that are comparable to or smaller than the desired powder particle size. Provided by way of illustration, the density of foam pellet 18a can be, for example, less than or equal to any one of, or between any two of, 0.05, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, and 1.00 grams per cubic centimeter.

[0031] Foam pellet 18a is spherical. However, foam pellets (e.g., 18) usable in the present methods can have any suitable shapes. For example, FIG. 3B depicts a foam pellet 18b that, though otherwise similar to foam pellet 18a, is cylindrical. Suitable foam pellets can have one or more of these and/or one or more other (e.g., prismatic and irregular) shapes, and such foam pellets can — but need not — have the same shape as one another. In some methods, regardless of their shapes, each of a majority of the foam pellets (e.g., 18) has a maximum transverse dimension (e.g., 34, illustrated in FIGs. 3A and 3B) that is less than or equal to any one of, or between any two of: 1.00, 0.75, 0.50, and 0.25 centimeters (cm). As used herein, “pellets” encompasses granules and beads. [0032] A polymeric powder (e.g., 24) produced using the present methods can include particles having a variety of sizes. And those particle sizes can be adjusted by, for example, using one or more filters, sieves, screens, and/or the like that inhibit particles larger a selected size from passing through them. To illustrate, such filter(s), sieve(s), and/or screen(s) can be positioned to restrict exit of such over-sized particles from mill 22 and/or, along with a conveyor (e.g., a screw, pneumatic, or the like the conveyor), to redirect such over-sized particles back into the mill if they have exited it.

[0033] Being produced by milling foam pellets (e.g., 18), the present powders (e.g., 24) can have particle sizes that are very fine. For instance, the thermoplastic powder can be characterized by a volume-based distribution of equivalent spherical diameters determined by laser diffraction according to ISO 13320:2009, and the distribution exhibits a Dv50 value of less than or equal to 30 micrometers, wherein Dv50 is defined as the median equivalent spherical diameter of the distribution (in other words, 50 percent of the distribution has an equivalent spherical diameter less than or equal to 30 micrometers). In some embodiments, the Dv50 value is 5 to 30 micrometers, or 10 to 30 micrometers, or 5 to 25 micrometers, or 10 to 25 micrometers. In some embodiments, the distribution exhibits a Dv97 value of less than or equal to 100 micrometers, or less than or equal to 75 micrometers; wherein Dv97 is defined as the equivalent spherical diameter corresponding to 97 percent of the cumulative undersize distribution (in other words, 97 percent of the distribution has an equivalent spherical diameter less than or equal to 100 micrometers). Within this limit, the D97 value can be 25 to 100 micrometers, or 25 to 85 micrometers, or 25 to 70 micrometers, or 30 to 100 micrometers, or 30 to 85 micrometers, or 30 to 70 micrometers.

[0034] Returning to FIG. 1, some of the present methods include a step 38 of cryogenically-cooling the foam pellets (e.g., 18) prior to milling them. This cooling can be achieved by, for example, exposing the foam pellets to a cryogenic fluid, such as, for example, liquid nitrogen. To illustrate, FIG. 2’s system includes an enclosure 42 that contains a cryogenic fluid (e.g., supplied from a tank 46). Prior to being introduced into mill 22, foam pellets 18 are directed through enclosure 42 and thereby immersed in the cryogenic fluid. In this example, transport of foam pellets 18 through enclosure 42 is achieved through use of a screw conveyor 50. While not required in the present methods to achieve high fineness powders, such cryogenic cooling can increase the friability of foam pellets, enhancing the above-described benefits of using the same. [0035] Some of the present methods include a step 54 of producing the foam pellets (e.g., 18). While the foam pellets can be produced in any suitable fashion, FIG. 4 shows several options for doing so. For example, in some of the present methods, the foam pellets are produced at least by extruding a composition comprising the thermoplastic material and a blowing agent (step 58). To illustrate, as shown in FIG. 5A, thermoplastic material 62 (e.g., in the form of non-foam pellets) and a blowing agent 66 can be introduced into an extruder 70 within which the blowing agent can be dispersed throughout the thermoplastic material. The thermoplastic material/blowing agent composition can then exit extruder 70 — before or after being cut into pellets by a blade 78 — into a liquid-containing chamber 74. In chamber 74, the pellets can be cooled. Depending on the pressure and temperature within chamber 74, the cooled pellets may be foam pellets (e.g., expanded pellets) or non-foam, expandable pellets. If the pellets are non-foam, expandable pellets, they can subsequently be heated to convert them to foam pellets.

[0036] For further example, in some of the present methods, the foam pellets can be produced at least by impregnating the thermoplastic material with a blowing agent by exposing the thermoplastic material to heat and pressure in the presence of the blowing agent (step 82). Referring to FIG. 5B by way of illustration, thermoplastic material 62 (e.g., in the form of non-foam pellets) and blowing agent 66 can be introduced into a pressure chamber 86 (e.g., an autoclave). The pressure and temperature within pressure chamber 86 can be increased such that thermoplastic material 62 is impregnated (e.g., saturated) with blowing agent 66. The blowing-agent-impregnated thermoplastic material can then be exposed to reduced pressure and/or increased temperature to produce foam pellets.

[0037] For yet further example, in some of the present methods, the foam pellets can be produced at least by polymerizing a precursor of the thermoplastic material in a solution including a blowing agent (step 90). To illustrate with reference to FIG. 5C, a precursor 94 of the thermoplastic material (e.g., one or more monomers and/or one or more oligomers) can be polymerized in a solution 98 including blowing agent 66 to produce pellets comprising the thermoplastic material and the blowing agent. To facilitate such polymerization, the solution can be agitated by an agitator 102. Pellets produced in this manner can be subsequently heated to produce foam pellets.

[0038] Any suitable blowing agent can be used in the present methods, including, for example, a hydrocarbon, carbon dioxide, a nitrogen-containing material (e.g., azodicarbonamide, 4,4’-oxybis(benzenesulfonylhydrazide), and p-toluenesulfonyihydrazide), and/or sodium bicarbonate.

[0039] Some of the present methods for producing a thermoplastic powder comprise: milling foam pellets with a mill, each of the foam pellets comprising a thermoplastic material, to produce a powder comprising the thermoplastic material, wherein the thermoplastic powder comprises particles characterized by a volume-based distribution of equivalent spherical diameters determined by laser diffraction according to ISO 13320:2009, and the distribution exhibits a Dv50 value of less than or equal to 30 micrometers, wherein Dv50 is defined as the median equivalent spherical diameter. In some methods, the powder has a Dv97 value of less than or equal to 100 micrometers, wherein Dv97 is defined as the equivalent spherical diameter corresponding to 97 percent of the cumulative undersize distribution.

[0040] In some methods, when the foam pellets are introduced into the mill, each of a majority of the foam pellets is not bonded to any other of the foam pellets. In some methods, when the foam pellets are introduced into the mill, each of a majority of the foam pellets comprises a majority, by weight, of a same thermoplastic material.

[0041] In some methods, the thermoplastic material comprises polystyrene, polyethylene, polypropylene, polycarbonate, polyvinyl chloride, polyamide, polyetherketone, liquid crystal polymer, ethylene vinyl alcohol copolymer, acrylonitrile vinyl alcohol copolymer, acrylonitrile butadiene styrene copolymer, and/or polyurethane. In some embodiments, the thermoplastic material comprises polystyrene, polyethylene, polypropylene, polycarbonate, polyvinyl chloride, polyetherketone, liquid crystal polymer, ethylene vinyl alcohol copolymer, acrylonitrile vinyl alcohol copolymer, acrylonitrile butadiene styrene copolymer, and/or polyurethane. In some embodiments, the thermoplastic material comprises polystyrene, polyethylene, polypropylene, polycarbonate, polyvinyl chloride, polyetherketone, liquid crystal polymer, ethylene vinyl alcohol, acrylonitrile vinyl alcohol copolymer, and/or acrylonitrile butadiene styrene copolymer. In some embodiments, the thermoplastic material excludes polyurethane.

[0042] Some methods comprise, prior to milling the foam pellets, cooling the foam pellets at least by exposing the foam pellets to a cryogenic fluid. In some methods, exposing the foam pellets to the cryogenic fluid comprises immersing the foam pellets in the cryogenic fluid. In some methods, the cryogenic fluid comprises liquid nitrogen. [0043] Some methods comprise producing the foam pellets at least by extruding a composition comprising the thermoplastic material and a blowing agent. Some methods comprise producing the foam pellets at least by impregnating the thermoplastic material with a blowing agent by exposing the thermoplastic material to heat and pressure in the presence of the blowing agent. Some methods comprise producing the foam pellets at least by polymerizing a precursor of the thermoplastic material in a solution including a blowing agent. In some methods, the blowing agent comprises a hydrocarbon, carbon dioxide, a nitrogen-containing material (e.g., azodicarbonamide, 4,4’- oxybis(benzenesulfonylhydrazide), and p>-ta\ uenesulfony !hydrazide), and/or sodium bicarbonate.

[0044] Some of the present thermoplastic powders comprise: particles, each of a majority of which comprise a majority, by weight, of a same thermoplastic material; wherein the particles are characterized by a volume-based distribution of equivalent spherical diameters determined by laser diffraction according to ISO 13320:2009, and the distribution exhibits a Dv50 value of less than or equal to 30 micrometers, wherein Dv50 is defined as the median equivalent spherical diameter. In some embodiments of the thermoplastic powder, the powder does not comprise polyurethane. In some embodiments of the thermoplastic powder, the distribution exhibits a Dv97 value of less than or equal to 100 micrometers, wherein Dv97 is defined as the equivalent spherical diameter corresponding to 97 percent of the cumulative undersize distribution.

[0045] The invention includes at least the following aspects.

[0046] Aspect 1 : A method for producing a thermoplastic powder, the method comprising: cooling foam pellets at least by exposing the foam pellets to a cryogenic fluid, wherein each of the foam pellets comprises a thermoplastic material selected from the group consisting of polystyrene, polyethylene, polypropylene, polycarbonate, polyvinyl chloride, polyetherketone, liquid crystal polymer, ethylene vinyl alcohol copolymer, acrylonitrile vinyl alcohol copolymer, acrylonitrile butadiene styrene copolymer, polyurethane, and combinations thereof; milling the cooled foam pellets with a mill to produce a thermoplastic powder comprising the thermoplastic material; wherein the thermoplastic powder comprising particles characterized by a volume-based distribution of equivalent spherical diameters determined by laser diffraction according to ISO 13320:2009, and the distribution exhibits a Dv50 value of less than or equal to 30 micrometers, wherein Dv50 is defined as the median equivalent spherical diameter. [0047] Aspect 2: The method of aspect 1, wherein, when the foam pellets are introduced into the mill, each of a majority of the foam pellets is not bonded to any other of the foam pellets.

[0048] Aspect 3: The method of Aspect 1 or 2, wherein, when the foam pellets are introduced into the mill, each of a majority of the foam pellets comprises a majority, by weight, of a same thermoplastic material.

[0049] Aspect 4: The method of any one of Aspects 1-3, wherein the foam pellets do not comprise polyurethane.

[0050] Aspect 5: The method of any one of Aspects 1-4, wherein the distribution exhibits a Dv97 value of less than or equal to 100 micrometers, wherein Dv97 is defined as the equivalent spherical diameter corresponding to 97 percent of the cumulative undersize distribution.

[0051] Aspect 6: The method of any one of Aspects 1-5, wherein exposing the foam pellets to the cryogenic fluid comprises immersing the foam pellets in the cryogenic fluid. [0052] Aspect 7: The method of any one of aspects 1-6, wherein the cryogenic fluid comprises liquid nitrogen.

[0053] Aspect 8: The method of any one of Aspects 1-7, comprising producing the foam pellets at least by polymerizing a precursor of the thermoplastic material in a solution including a blowing agent.

[0054] Aspect 9: The method of any one of Aspects 1-7, comprising producing the foam pellets at least by impregnating the thermoplastic material with a blowing agent by exposing the thermoplastic material to heat and pressure in the presence of the blowing agent.

[0055] Aspect 10: The method of any one of Aspects 1-9, comprising producing the foam pellets at least by extruding a composition comprising the thermoplastic material and a blowing agent.

[0056] Aspect 11: The method of any one of Aspects 8-10, wherein the blowing agent comprises a hydrocarbon, carbon dioxide, a nitrogen-containing material, and/or sodium bicarbonate.

[0057] Aspect 12: A thermoplastic powder prepared according to the method of Aspect 1 and comprising: particles, each of a majority of which comprise a majority, by weight, of a same thermoplastic material; wherein the particles are characterized by a volume-based distribution of equivalent spherical diameters determined by laser diffraction according to ISO 13320:2009, and the distribution exhibits a Dv50 value of less than or equal to 30 micrometers, wherein Dv50 is defined as the median equivalent spherical diameter.

[0058] Aspect 13: The thermoplastic powder of Aspect 12, wherein the powder does not comprise polyurethane.

[0059] Aspect 14: The thermoplastic powder of Aspect 12 or 13, wherein the distribution exhibits a Dv97 value of less than or equal to 100 micrometers, wherein Dv97 is defined as the equivalent spherical diameter corresponding to 97 percent of the cumulative undersize distribution.

EXAMPLES

[0060] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters that can be changed or modified to yield essentially the same results.

[0061] Two thermoplastic powders were prepared: a comparative one produced by milling non-foam pellets and a sample one produced by milling foam pellets. Images of the two powders were obtained using both optical microscopy (FIGs. 6A and 6B for the comparative powder, and FIG. 7A for the sample powder) and scanning electron microscopy (FIGs. 6C-6E for the comparative powder, and FIGs. 7B-7E for the sample powder). Prior to its imaging, each of the powders was dispersed onto a carbon tape. For the optical microscopy, a KEYENCE instrument was used. And for the scanning electron microscopy, a JEOL 7800 F was used, with an acceleration voltage of 5 kilovolts and magnifications of 80x (for both powders, FIGs. 6C-6E and FIGs. 7B and 1C), 3000x (for the sample powder, FIG. 7D.), and 5000x (for the sample powder, FIG. 7E).

[0062] As best seen in the scanning electron microscopy images, the comparative powder’s particles were relatively large, typically ranging in particle size from 200 pm to 500 pm (FIGs. 6C-6E). In contrast, the sample powder’s particles were much smaller, having particle sizes of between 20 pm and 100 pm, with many having sizes on the smaller end of that range (FIGs. 7B-7E). That the sample powder had particles that were significantly smaller than those of the comparative powder is readily apparent at least by comparing FIGs. 6C-6E of the comparative powder to FIGs. 7B and 7C of the sample powder; this same field of view imaged on the order of a hundred of the sample powder’ s particles but only a few of the comparative powder’s particles.

[0063] The above specification and examples provide a complete description of the structure and use of illustrative embodiments. Although certain embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. As such, the various illustrative embodiments of the methods and systems are not intended to be limited to the particular forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than the one shown may include some or all of the features of the depicted embodiment. For example, elements may be omitted or combined as a unitary structure, and/or connections may be substituted. Further, where appropriate, aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples having comparable or different properties and/or functions, and addressing the same or different problems.

Similarly, it will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments.

[0064] The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s) “means for” or “step for,” respectively.