Patent Application
20220136138
The present invention relates generally to the field of nano-ribbons. In particular, the present invention relates to a nano-ribbon produced from a multilayer filament.
Strong, light, and inexpensive materials are often sought after for their unique properties. For example, such materials have a high surface area and a low weight-to-strength ratio useful in light-weighting transportation, filtration, insulation, and apparel. In particular, nano-fibers (<500 nm diameter) have unique characteristics compared to micro-fibers, such as higher surface area and extremely high porosity in non-woven fabrics. Their applications range from uses in batteries as porous membrane separators to biomedical applications as cellular scaffolds to high surface area filters. Current nano-fiber fabrication methods include electrospinning, centrifugal spinning, and melt-blowing. Although there are many benefits of nano-fibers, a key barrier in the wide-scale adoption of the material is their significantly higher cost compared to microfibrous meltblown media, which are produced an order of magnitude faster.
One of the challenges to electrospun and meltblown nano-fibers is that they have very little orientation and are thus typically weaker than a drawn/oriented fiber from traditional fiber processing. The strongest fully oriented filament microfibers currently found in the industry are spun and drawn from the extruder (for example, at about 7000 m/min) and are typically also post-drawn to further increase the orientation. These fibers are used in applications such as ropes, tent fabrics, boating sails, architectural textiles, and other industrial textiles that require high tensile strength.
Currently, electrospinning and melt blowing processes do not easily allow for nano-fibers to be length oriented to the degree of melt spun filament fibers, nor can yarns and subsequently knitted/woven textiles be easily produced from the fibers made by these methods.
In one embodiment, the present invention is a process for converting a multilayer filament to a plurality of nano-ribbons. The process includes co-extruding a first layer and a second layer to form the multilayer filament, and separating the multilayer filaments to form a plurality of nano-ribbons having substantially flat cross-sections.
In another embodiment, the present invention is a nano-ribbon yarn including ribbons having a thickness of between about 10 nanometers and about 10 microns, wherein the ribbons have a substantially flat cross-section.
While the above-identified drawings and figures set forth embodiments of the invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this invention. The figures may not be drawn to scale.
The present invention is a nano-ribbon and a method of producing the nano-ribbon. In one embodiment, the nano-ribbons are highly oriented and have increased tensile strength and can be produced as bundles of ribbons or fibers (i.e., yarns), that can be woven or knitted into various textiles. Due to their increased tensile strength, the nano-ribbons can be used in a vast range of applications in addition to nonwovens. The layer thicknesses are also controllable with a narrow distribution. In addition, the resulting nano-ribbons can also be chopped and formed into a nonwoven fabric. The resulting nano-ribbons can provide a thin, yet warm material. Without being bound by theory, it is believed that the nano-ribbons provide warmth due to their inducement of the Knudsen Effect. Once pore sizes approach the size of the mean free path of air (73 nm), air molecules collide with the matrix (nanofibers) more often, losing energy with each collision, making heat transfer slower, and resulting in much better insulation. Thus, less material is needed to provide a greater deal of warmth.
The alternating polymer or resin layers, or polymer or resin pairs 14 and 16, may include, but are not limited to: polyethylene terephthalate (PET) and polypropylene (PP), nylon 6 or 6,6 and PP, thermoplastic polyurethane (TPU) and PP, styrenic block copolymers (e.g, styrene-ethylene/butylene-styrene (SEBS)) and PP, transparent polymer (TPX) such as polymethylpentene (PMP) and PET, TPX and PP, PP and PE, PP and polybutylene terephthalate (PBT), polylactic acid (PLA) and PP, polybutylene succinate (PBS) and PP, PLA and dimer acid based (DAB) polyamide, polyhydroxyalkanoates (PHA) and PP, PHA and DAB polyamide, polyhydroxybutyrate (PHB) and PP, PHB and DAB polyamide, and hydrophobic/hydrophilic versions of the same polymer. Two particularly suitable polymer or resin pairs are PET and PP, and PLA and PP. If needed, in one embodiment, additives can be added to the base polymers that cause the alternating polymers to further reduce the chemical affinity to each other.
Each of the multilayer filaments 10 must include at least two layers. However, the multilayer filaments 10 can include any number of layers without departing from the intended scope of the present invention. In one embodiment, the multilayer filaments include up to about 1000 layers. In one embodiment, each of the layers of the multilayer filaments has a thickness of between about 1 and about 500 nm, particularly between about 50 and about 250 nm, and more particularly between about 50 and about 150 nm.
Once extruded, the multilayer filaments 10 may optionally be cooled in a water bath 30. The multilayer filaments 10 can also be length oriented to be drawn thinner. Orientation simply means that the long chains of polymers are oriented lengthwise in the same direction and can also impart higher crystallinity in the polymer. This improves the overall tensile strength of the material along the length because any force applied along the length is supported by the carbon backbone of the polymer, rather than the intertwining and entangling of the polymers chains.
In one embodiment, the multilayer filaments 10 are stretched to a maximum of fifteen times their original length. In one embodiment, the multilayered filaments are length oriented at a ratio of about 15:1, particularly about 10:1, and more particularly about 6:1. The multilayer filaments can be length oriented by any method known to those of skill in the art. In one embodiment, orientation is achieved using a draw stand 32 which heats and stretches the continuous filament fibers across a series of godet rollers and winds them into a cone. This process also decreases the thickness of the multilayer filaments, and therefore the individual layers. Generally, the higher the feed rate of the resin, the thicker the resulting layers. If desired, the speeds can be adjusted in line to produce a first region having a specified degree of orientation, and a second region having a different degree of orientation. In one embodiment, the multilayer filaments are length oriented at a temperature of between about 60° C. and about 290° C., and particularly at about 100° C. Temperature is typically set at or above the glass transition temperature (Tg) of the polymers to make the material malleable enough to be stretched (i.e., length oriented). The faster the multilayer filaments are being oriented, the higher the temperature can be increased in order to have sufficient heat transfer. For example, 290° C. is higher than the melt temperature (Tm) of PET, but if running at 1000 m/min, the PET is not in contact with the rollers long enough to melt. In one embodiment, the multilayer filaments are being length oriented at a maximum speed of 100 m/min heated to 100° C. Once length oriented, the multilayer filaments 10 may pass through a pneumatic texturizer 34 and wound onto a bobbin 36.
The layers of the multilayer filaments 10 need to be physically separated, or delaminated, from each other to form single nano-ribbons. Because the alternating layers 14 and 16 of the multilayer film 10 are immiscible with each other and have very little chemical affinity for each other, the layers can be easily separated from each other. The incompatible layers allow for the materials to be coextruded together but to also easily come apart from each other once solidified and agitated. Upon delamination, there is a clear single layer separation for most layers, which are the continuous filament nano-ribbons. The multilayer filaments 10 are separated without the use of any sacrificial polymers that are dissolved away. In one embodiment, the multilayer filaments are separated by mechanical or chemical methods. An example of a suitable method for chemically separating the layers includes, but is not limited to, treating with a polar solvent.
Examples of suitable methods of mechanical separation include, but are not limited to: compressed air (i.e., pneumatic texturizer), high pressure water (hydroentanglement), sonication, and ultrasonication. It should be noted that it is the velocity and/or the kinetic energy of the fluid (gas, air, liquid, water, etc.) and not necessarily the set pressure on the separation device that causes the separation to occur. It should be noted that it may be preferred to delaminate the layers in a separate process and not in-line with the fiber making.
The nano-ribbons 12 produced by separating the multilayered filaments 10 have one or more layers. In the majority of the volume, each layer within the multilayer filament 10 is separated into single sheets comprising one resin. In other embodiments, particularly at extremely small scales <500 nm, Van der Waals forces can become strong enough that some layers may remain together in groups of two or more. The nano-ribbons 12 can be designed to be composed of more than one layer, such as three layers, where the outermost layers are composed of polymers or resins that will separate from each other, but not from the innermost layers. These multilayer nano-ribbons can be designed to be functionally layered to perform other functions, such as having shape memory properties, wicking, charged filtration, or many others where a function can be derived using more than one layered resin and may or may not have different additives in each layer.
The individual nano-ribbons 12 are a thin, flexible material having a much longer length than width, with sufficient strength and length, and/or fiber-fiber friction when bundled in a yarn, to be used in a textile. Each of the nano-ribbon layers have a continuous or cut length. The nano-ribbon width is dependent on the width of the multilayered filament, which can be as wide as about 200 μm. The thickness of the resulting nano-ribbons produced using the method of the present invention can be between about 1 and about 1000 nm, particularly between about 1 nm and about 500 nm, and more particularly between about 50 nm and about 150 nm. The layer thickness of the resulting nano-ribbons is determined by a number of factors including, but not limited to: the number of extruded layers, the total filament thickness, the density of the polymers or resins used, and the length orientation. Generally, the denser the resin, the thinner the resulting layers.
In one embodiment, the nano-ribbons have a thickness of between about 1 and about 500 nm and a width of between about 1 and about 200 μm.
The resulting nano-ribbons produced using the above method are highly fibrous with a look and feel similar to yarn and have high tensile strength and high surface area. The high tensile strength of the nano-ribbons is due to the length orientation step of the process of the present invention. In one embodiment, the nano-ribbons have a tensile strength of about between about 150 and about 480 MPa, particularly between about 360 and about 390 MPa, and more particularly between about 440 and about 480 MPa. In practice, because the nano-ribbons produced by the method of the present invention have a high surface area, they can stick easily to metal and other surfaces due to Van der Waals forces and static electricity. Thus, in one embodiment, a lubricant, such as a silicone lubricant, can be coated onto the nano-ribbons for smoother processing.
In one embodiment, the nano-ribbons can be designed to have a first region 38 with a first thickness and a second region 40 with a second, different thickness.
In one embodiment, the nano-ribbons have a porous structure, as shown in
The nano-ribbons produced by the method of the present invention can be formed into a yarn, which can then be formed into a textile, or a thin flexible sheet of material with sufficient strength and tear resistance (even when wet) to be used for clothing, interior fabrics, and other functional, protective or aesthetic applications. As used herein, “yarn” is defined as a thin material having a much longer length than width and is formed from many fibers to provide sufficient mechanical strength and flexibility to be converted to a textile (e.g., knit, woven, crochet etc.). Knitted, woven, crocheted, carpeted, and stitched textiles are made by looping and intertwining yarns together into sheets. The nano-ribbons can be used in any number of fields. For example, they can be used as thermal insulation, as a filtration medium, as a highly absorptive material, as a dusting and cleaning material, or as a scaffold for growing cells of plant, animal, human, bacteria.
It is important to note, in one embodiment, when the multilayered filament is mechanically separated with compressed air, the material is not blown apart into disparate pieces that need to be recombined to form a yarn. Rather, since the layers are continuous along the length of the multilayer filament, each layer could be described as a continuous filament nanofiber, they are just adhered and stacked together in a larger filament (the multilayer filament). The mechanical agitation causes the layers to become individually separate exposing their surface area, but are still intertwined together. Therefore, a single filament can become as many as 1000 nanofilaments. The separated nano-ribbons are still held together in a strand that is soft to the touch and yarn-like instead. It is also important to note that to those skilled in the art, one could also chop the strand of yarn into staple nano-ribbons and convert it to a calendared nonwoven web. Staple fibers are defined as short fibers typically 3 inches or less in length.
Because the method of producing the nano-ribbon is a high throughput manufacturing process, is solvent free, and does not need to use a sacrificial polymer to separate nanofibers from bulk, it is an economical method for producing ultrafine nano-ribbons or nano-fibers (<100 nm), particularly compared to electrospinning, melt blowing, and islands in the sea, which are inhibited by at least one of the above.
The present invention is more particularly described in the following examples that are intended as illustrations only, since numerous modifications and variations within the scope of the present invention will be apparent to those skilled in the art. Unless otherwise noted, all parts, percentages, and ratios reported in the following examples are on a weight basis.
A multilayer stack having 500 alternating layers of PET and PP was extruded using a 250 layer feedblock, one multiplier, and a fiber faceplate having 2 rows of 16 holes. The PET grade used was 7352 supplied by Eastman Chemical Company (Kingsport, Tenn.), and the PP grade was 1024 supplied by Exxon Mobil Corporation (Irving, Tex.). Two extruders were used, a first extruder for the PET layers, a second for the PP layers. The first extruder was set to 279° C. with a first necktube set to 279° C., the second extruder was set to 279° C. with a second necktube set to 279° C. The necktubes connected and directed the resin from the extruders to the feedblock and die. The feedblock and die were set at 279° C. The first extruder was a single screw with a barrel diameter of 32 mm and was operated at 50 rotations per minute (rpm), the second extruder was a single screw with a barrel width of 32 mm and was operated at 16.5 rpm. The multilayer filaments were passed through a chilled water bath and further directed to a level winder, Model 96B supplied by Leesona (Burlington, N.C.) and collected on a cone. The take up winder was set to 30, 43, and 49 m/min. The final multilayer filaments contained 375-398 layers. One embodiment containing a 398 layer stack was 841 μm by 300 μm and continuous in length. The individual layers were each measured to be 2.11 μm in thickness prior to any post-drawing.
The multilayer filaments were then length oriented on a draw stand supplied by Retech Aktiengesellschaft (Meisterschwanden, Switzerland) with 10 cm wide godet rolls heated to 90° C. The fastest roll was set to 4× the speed of the slowest roll. The resulting multilayer filaments had cross-sections that were 332 μm by 115 μm and continuous in length. The individual layer thicknesses were measured to be ˜830 nm.
In another embodiment having fibers containing 376 layers, the layer stack was 500 μm by 160 μm and continuous in length. The individual layers were measured to be about 1.32 μm prior to post drawing. The same fibers were then length oriented with the roll speed ratio at 4:1 at 90° C. The resulting fibers were then 226 μm by 92 μm and continuous in length. The resulting individual layers were measured to be about 600 nm thick.
The length oriented multilayer filaments were then passed through a compressed air Heiberlein SLIDEJET DT15-2 (Wattwill Switzerland) nozzle with compressed air set at 30 psi and 10 m/min. The exposure to high velocity air caused the layers to separate, and the resulting material was a continuous fibrous string or nano-ribbon yarn. When compressed air was set above 80 psi, the material would often break.
In another embodiment, the multilayer filaments were separated through ultrasonication, which both separated and further fibrillated the nano-ribbons along their length.
The samples were observed under scanning electron microscopy (SEM) and using a Phenom ProX (Thermo Fisher Scientific, Waltham, Mass.). Based on individual observations, there is clearly a range of single layer nanofibers, as well as sets of 2-3 layers that remained adhered together, contributing to the distribution.
To determine mechanical properties, the multilayered filaments were prepared according to ASTM test method D2256-10(2015) with a 25.4 mm gauge length (separation distance between the grips). The samples were tested on the MTS RF100 load frame supplied by Instron (Norwood, Mass.) at 60 mm/min. Tensile testing results were calculated from 3 samples, and broke at an average load of 3.07 N, and had an average break tenacity of 167 Nm/g. The Youngs Modulus was calculated to be 217 MPa.
A multilayer stack having 250 alternating layers of PLA and PP was extruded using a 250 layer feedblock, and a fiber faceplate having 1 row of 31 holes. The PLA grade used was 4032 supplied by NatureWorks LLC (Minnetonka, Minn.) and the PP grade was 1024 supplied by Exxon Mobil Corporation (Irving, Tex.). Two extruders were used, a first extruder for the PLA layers, a second for the PP layers. The first extruder was set to 226° C. with a first necktube set to 226° C., the second extruder was set to 226° C. with a second necktube set to 226° C. The necktubes connected and directed the resin from the extruders to the feedblock and die. The feedblock and die was set at 226° C. The first extruder was a single screw with a barrel diameter of 32 mm and was operated at 50 rotations per minute (rpm), the second extruder was a single screw with a barrel diameter of 32 mm and was operated at 38 rpm. The multilayer filaments were passed through a chilled water bath and further directed to a level winder Model 96B supplied by Leesona (Burlington, N.C.) and collected on a cone. The take up winder was set to 60 m/min. The final multilayer filaments contained 244 layers. One embodiment containing a 244 layer stack was 527 μm by 244 μm, and continuous in length. The individual layers were each measured to be 2.15 μm in thickness prior to any post-drawing.
The multilayer filaments were then length oriented on a draw stand supplied by Retech Aktiengesellschaft (Meisterschwanden, Switzerland) with 10 cm wide godet rolls heated to 90° C. and a 6:1 speed ratio. The resulting multilayer filaments had cross-sections that were 193 μm by 91 μm and continuous in length. The individual layer thicknesses were measured to be ˜790 nm.
The length oriented multilayer filaments were then passed through a compressed air Heiberlein SLIDEJET DT15-2 (Wattwill Switzerland) nozzle with compressed air set at 30 psi and 10 m/min. The exposure to high velocity air caused the layers to separate and the resulting material was a continuous fibrous string or nanoribbon yarn.
The samples were observed under scanning electron microscopy (SEM) and using a Phenom ProX (Thermo Fisher Scientific, Waltham, Mass.). This sample was completely separated into single layers with only a few observable layers still stacked together.
To determine mechanical properties, the multilayered filaments were prepared according to ASTM test method D2256-10(2015) with a 25.4 mm gauge length (separation distance between the grips). The samples were tested on the MTS RF100 load frame supplied by Instron (Norwood, Mass.) at 60 mm/min. Tensile testing results were calculated from 3 samples, and broke at an average load of 5.4 N, and had an average break tenacity of 279 Nm/g. The Youngs Modulus was calculated to be 363 MPa.
The nano-ribbon yarn was then coated in a water based Lurol ASM lubricant or spin finish supplied by Goulston Technologies (Monroe, NC) to improve processability during knitting. A single strand of the nano-ribbon yarn was then knitted on a SWG041N2 15-gauge knitting machine supplied by Shima Seiki USA (Monroe Twp, N.J.), set with a stitch value of 33. No supporting yarn was used to reinforce the nano-ribbon yarn during knitting.
A multilayer stack having 500 alternating layers of PLA and PP was extruded using a 500 layer feedblock and a fiber faceplate having 1 row of 8 holes. The PLA grade used was 4060D supplied by NatureWorks LLC (Minnetonka, Minn.) and the PP grade was 1024 supplied by Exxon Mobil Corporation (Irving, Tex.). Two extruders were used, a first extruder for the PLA layers, a second for the PP layers. The first extruder was set to 232° C. with a first endcap set to 224° C., the second extruder was set to 232° C. with a first endcap set to 224° C. The extruders were connected directly to the feedblock, and no necktubes were used. The first extruder was a single screw with a barrel diameter of 8 mm and was operated at 265 rotations per minute (rpm), the second extruder was a single screw with a barrel diameter of 8 mm and was operated at 234 rpm. The multilayer filaments were passed through a chilled water bath and further directed to a draw stand supplied by Retech Aktiengesellschaft (Meisterschwanden, Switzerland) with 10 cm wide godet rolls heated to 90° C. and collected on a cone. The take up roller was set to 70 m/min.
The multilayer filaments were then length oriented on the same draw stand at 90° C. and a 6:1 speed ratio.
The length oriented multilayer filaments were then passed through a compressed air Heiberlein SLIDEJET DT15-2 (Wattwill Switzerland) nozzle with compressed air set at 30 psi and 10 m/min. The exposure to high velocity air caused the layers to separate, and the resulting material was a continuous fibrous string or nanoribbon yarn.
To determine mechanical properties, the multilayered filaments were prepared according to ASTM test method D2256-10(2015) with a 25.4 mm gauge length (separation distance between the grips). The samples were tested on the MTS RF100 load frame supplied by Instron (Norwood, Mass.) at 60 mm/min. Tensile testing results were calculated from 3 samples, and broke at an average load of 12.4 N, and had an average break tenacity of 356 Nm/g. The Youngs Modulus was calculated to be 463 MPa.
Although specific embodiments of this invention have been shown and described herein, it is understood that these embodiments are merely illustrative of the many possible specific arrangements that can be devised in application of the principles of the invention. Numerous and varied other arrangements can be devised in accordance with these principles by those of ordinary skill in the art without departing from the spirit and scope of the invention. Thus, the scope of the present invention should not be limited to the structures described in this application, but only by the structures described by the language of the claims and the equivalents of those structures.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2020/051687 | 2/27/2020 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62812030 | Feb 2019 | US |
