METHOD OF MANUFACTURING CARBON FIBER AND CARBON FIBER MANUFACTURED THEREBY

Abstract

A method of manufacturing carbon fiber includes (a) preparing a solution by mixing a raw material containing at least one chlorine group in the side chain of a repeat unit with a solvent, (b) forming a fibrous material by spinning the solution, (c) forming a ladder-like chemical ring structure in the fibrous material by hydrothermally treating the fibrous material with a hydrochloric acid solution at a predetermined temperature for a predetermined time, and (d) carbonizing the result of step (c).

Claims

1. A method of manufacturing carbon fiber, comprising: (a) preparing a solution by mixing a raw material containing at least one chlorine group in a side chain of a repeat unit with a solvent; (b) forming a fibrous material by spinning the solution; (c) forming a ladder-like chemical ring structure in the fibrous material by hydrothermally treating the fibrous material with a hydrochloric acid solution at a predetermined temperature for a predetermined time; and (d) carbonizing a result of step (c).

2. The method of claim 1, wherein the raw material comprises any one selected from the group consisting of polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), copolymers of vinyl chloride with other monomers, and combinations thereof.

3. The method of claim 1, wherein the raw material has a concentration of 1 wt % to 25 wt %.

4. The method of claim 1, wherein spinning the solution is performed so that a spinning material is discharged into a medium.

5. The method of claim 1, wherein spinning the solution is performed so that a temperature of the solution is 35 C. to 45 C.

6. The method of claim 1, wherein spinning the solution is performed at a discharge rate of 0.5 ml/h to 8 ml/h.

7. The method of claim 1, wherein hydrothermally treating the fibrous material is performed at a hydrochloric acid concentration of 0.1 wt % to 40 wt % in a closed container.

8. The method of claim 1, wherein hydrothermally treating the fibrous material is performed at a temperature of 200 C. to 300 C.

9. The method of claim 1, wherein hydrothermally treating the fibrous material is performed for 20 hours or more.

10. The method of claim 1, wherein carbonizing the result is performed at a temperature of 800 C. to 2,000 C. in an inert gas atmosphere.

11. The method of claim 10, wherein carbonizing the result is performed to reach the temperature at a heating rate of 5.5 C./min or less.

12. The method of claim 10, wherein carbonizing the result is performed by maintaining the temperature for 0.5 to 3 hours.

13. A carbon fiber obtained by carbonizing a fibrous material having a ladder-like chemical structure, wherein the fibrous material is prepared by spinning of a raw material containing at least one chlorine group in a side chain of a repeat unit and hydrothermal treatment with a hydrochloric acid solution.

14. The carbon fiber of claim 13, having a longitudinal tensile strength of 600 MPa to 1,500 MPa.

15. The carbon fiber of claim 13, having a thickness of 20 m to 70 m.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0012] The above and other features of the present disclosure will now be described in detail referring to certain exemplary embodiments thereof illustrated in the accompanying drawings, which are given hereinbelow by way of illustration only, and thus are not limitative of the present disclosure, and wherein:

[0013] FIG. 1 schematically shows an example of a spinning process in manufacture of carbon fiber according to an aspect of the present disclosure.

[0014] FIG. 2A is a scanning electron microscope (SEM) image of the cross-section of PVC fiber formed in Example 1.

[0015] FIG. 2B is an SEM image of the cross-section of PVC fiber formed in Reference Example 1;

[0016] FIG. 2C is an SEM image of the cross-section of PVC fiber formed in Reference Example 2;

[0017] FIG. 3A is a graph showing results of thermogravimetric analysis of carbon weight depending on the temperature during carbonization of hydrothermally treated PVC fiber in each of Comparative Example 1 (C1) and Reference Examples 3 to 7 (R3 to R7);

[0018] FIG. 3B is a graph showing the carbon yield of manufactured carbon fiber depending on changes in hydrothermal treatment (stabilization) temperature in Comparative Example 1 and Reference Examples 3 to 7;

[0019] FIG. 4 is a graph showing the transmittance depending on the wavenumber as results of FT-IR analysis of the hydrothermally treated fiber in each of Comparative Example 1 (C1) and Reference Examples 3 to 7 (R3 to R7);

[0020] FIG. 5A is a graph showing the transmittance depending on the wavenumber as results of FT-IR analysis of the hydrothermally treated fiber in each of Example 1 (E1) and Reference Example 6 (R6);

[0021] FIG. 5B is a graph showing results of thermogravimetric analysis of carbon weight depending on changes in temperature during carbonization of the hydrothermally treated PVC fiber in each of Comparative Example 1 (C1), Example 1 (E1), and Reference Example 6 (R6);

[0022] FIG. 6A is an SEM image of the cross-section of carbon fiber manufactured in Reference Example 6;

[0023] FIG. 6B is a further enlarged image of the carbon fiber manufactured in Reference Example 6;

[0024] FIG. 7A is an SEM image of the cross-section of carbon fiber manufactured in Example 1;

[0025] FIG. 7B is a further enlarged image of the cross-section of carbon fiber manufactured in Example 1;

[0026] FIGS. 8A and 8B are SEM images of the cross-section of carbon fiber manufactured in Reference Example 6; and

[0027] FIG. 9 is a flowchart schematically showing a process of manufacturing carbon fiber according to an aspect of the present disclosure.

DETAILED DESCRIPTION

[0028] The above and other objects, features and advantages of the present disclosure will be more clearly understood from the following preferred embodiments taken in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments disclosed herein, and may be modified into different forms. These embodiments are provided to thoroughly explain the disclosure and to sufficiently transfer the spirit of the present disclosure to those skilled in the art.

[0029] Throughout the drawings, the same reference numerals will refer to the same or like elements. For the sake of clarity of the present disclosure, the dimensions of structures are depicted as being larger than the actual sizes thereof. It will be understood that, although terms such as first, second, etc. may be used herein to describe various elements, these elements are not to be limited by these terms. These terms are only used to distinguish one element from another element. For instance, a first element discussed below could be termed a second element without departing from the scope of the present disclosure. Similarly, the second element could also be termed a first element. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0030] It will be further understood that the terms comprise, include, have, etc., when used in this specification, specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. Also, it will be understood that when an element such as a layer, film, area, or sheet is referred to as being on another element, it may be directly on the other element, or intervening elements may be present therebetween. Similarly, when an element such as a layer, film, area, or sheet is referred to as being under another element, it may be directly under the other element, or intervening elements may be present therebetween.

[0031] Unless otherwise specified, all numbers, values, and/or representations that express the amounts of components, reaction conditions, polymer compositions, and mixtures used herein are to be taken as approximations including various uncertainties affecting measurement that inherently occur in obtaining these values, among others, and thus should be understood to be modified by the term about in all cases. Furthermore, when a numerical range is disclosed in this specification, the range is continuous, and includes all values from the minimum value of said range to the maximum value thereof, unless otherwise indicated. Moreover, when such a range pertains to integer values, all integers including the minimum value to the maximum value are included, unless otherwise indicated.

Method of Manufacturing Carbon Fiber

[0032] Referring to FIGS. 1 and 9, a method of manufacturing carbon fiber according to an aspect of the present disclosure includes: [0033] (a) preparing a solution by mixing a raw material containing at least one chlorine group in the side chain of a repeat unit with a solvent (S10); [0034] (b) forming a fibrous material by spinning the solution (S20); [0035] (c) forming a ladder-like chemical structure in the fibrous material by hydrothermally treating the fibrous material with a hydrochloric acid solution at a predetermined temperature for a predetermined time (S30); and [0036] (d) carbonizing the result of step (c) (S40);

[0037] The raw material in step (a) (S10) may be a material containing a carbon main chain and at least one chlorine group in the side chain, and may be a polymer, an oligomer, or a low-molecular-weight material.

[0038] The weight average molecular weight (Mw) of the raw material in step (a) (S10) is not particularly limited, but may be, for example, 2,000 g/mol to 500,000 g/mol.

[0039] The raw material in step (a) (S10) may include any one selected from the group consisting of polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), copolymers of vinyl chloride and with other monomers, and combinations thereof, and may include, for example, polyvinyl chloride.

[0040] When the raw material in step (a) (S10) is a copolymer of vinyl chloride and another monomer, the other monomer may include an ethylenically unsaturated compound. Examples of the copolymer may include vinyl chloride (chloroethylene)-ethylene copolymer, chloroethylene-dichloroethylene copolymer, and the like.

[0041] The concentration of the raw material of the solution in step (a) (S10) may be 1 wt % to 25 wt %. Here, a fibrous material may be stably formed by subsequent spinning of the solution having the above concentration.

[0042] The solvent of the solution in step (a) (S10) may be used without limitation so long as it is able to effectively dissolve the raw material, and may include acetone, N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAc), nitrobenzene, cyclohexane, chloroform, methyl isobutyl ketone, etc., and may include, for example, dimethylacetamide (DMAc).

[0043] The spinning in step (b) (S20) may be performed so that a spinning material is discharged into a medium as shown in FIG. 1, and may be conducted by wet spinning. The medium may include a material in which the raw material is insoluble or poorly soluble, may correspond to a so-called coagulation bath, and may include, for example, water.

[0044] The spinning in step (b) (S20) may be performed so that the temperature of the solution is 35 C. to 45 C. If the temperature of the solution is less than 35 C., the cross-section of the formed fibrous material may be flat rather than round, and it may be difficult to evenly distribute tensile stress throughout the fiber, deteriorating mechanical strength of carbon fiber that is subsequently manufactured. On the other hand, if the temperature of the solution exceeds 45 C., a fibrous material having high porosity may be formed due to fast exchange between the medium and the solution, the density of carbon fiber that is subsequently manufactured may be lowered, and the properties thereof may deteriorate.

[0045] The spinning in step (b) (S20) may be performed at a discharge rate of 0.5 ml/h to 8 ml/h. When spinning is performed at this discharge rate, a fibrous material may be stably formed.

[0046] The spun fibrous material in step (b) (S20) may be continuously wound by a winder such as a roller, etc., and may be wound to have a predetermined spinning draw ratio. The spinning draw ratio may correspond to the (linear speed when winding the fibrous material)/(discharge linear speed when forming the fibrous material), and the draw ratio may be 1.2-6.

[0047] The spinning in step (b) (S20) may be performed using a wet spinning machine with a spinneret diameter of 50 m to 200 m.

[0048] The hydrothermal treatment in step (c) (S30) is a stabilization process to minimize decomposition of the fibrous material formed in step (b) (S20) during subsequent carbonization and to obtain high carbon yield.

[0049] The hydrothermal treatment in step (c) (S30) may be performed with an aqueous hydrochloric acid solution having a hydrochloric acid concentration of 0.1 wt % to 40 wt % in a closed container. For example, the concentration of the aqueous hydrochloric acid solution may be 25 wt % to 40 wt %. When hydrochloric acid having the above concentration is further included during hydrothermal treatment, a stable ladder-like ring structure may be formed while accelerating the separation of chlorine group from the fibrous material.

[0050] The hydrothermal treatment in step (c) (S30) may be performed with an aqueous solution, and may be conducted at a predetermined pressure, for example, a pressure ranging from the vapor pressure of the aqueous solution to 30 bar.

[0051] The hydrothermal treatment in step (c) (S30) may be performed at a temperature of 200 C. to 300 C. If the temperature is less than 200 C., the fibrous material may not be sufficiently stabilized, whereas if the temperature exceeds 300 C., thermal decomposition of the fibrous material may occur.

[0052] The hydrothermal treatment in step (c) (S30) may be performed for 20 hours or more, preferably for 24 to 48 hours. If the hydrothermal treatment time is less than 20 hours, formation of the ladder-like chemical ring structure may not be complete, and thermal decomposition may occur rapidly in the subsequent carbonization process, which may lower yield, resulting in carbon fiber having high porosity. On the other hand, if the hydrothermal treatment time exceeds 48 hours, an improvement in yield may be insignificant and energy may be wasted.

[0053] The hydrothermal treatment in step (c) (S30) may be performed to reach the above temperature at a heating rate of 5 C./min to 12 C./min.

[0054] When the hydrothermal treatment in step (c) (S30) is performed in this way, a ladder-like chemical ring structure may be formed in the fibrous material, and an OCO structure, CO bond, CC bond, OH group (hydroxyl group), etc. may be included and detected. The ladder-like ring structure may include consecutive ring structures linked by sharing carbon-carbon bonds, and may contain substantially no nitrogen or may contain nitrogen below the detection limit. The ladder-like structure may include a structure in which each 4-12 membered ring shares a specific atom-atom (e.g., carbon-carbon) bond with an adjacent 4-12 membered ring and is continuously connected linearly or curvedly. The ladder-like structure may include fused polycyclic ring structure, and each ring except the end ring may be connected to 2 to 3 rings. The ladder-like ring structure may, for example, include a structure similar to the oxidation and cyclization steps during carbonization of linear low-density polyethylene (LLDPE), and may further include an OCO structure.

[0055] The carbonization in step (d) (S40) may be performed at a temperature of 800 C. to 2,000 C. in an inert gas atmosphere. Carbonization may proceed stably in the above temperature range and the desired yield may be obtained. The inert gas may include helium, argon, neon, etc.

[0056] The carbonization in step (d) (S40) may be performed to reach the above temperature at a heating rate of 5.5 C./min or less, for example, at a heating rate of 0.5 C./min to 5 C./min. If the heating rate exceeds 5.5 C./min, the hydrothermally treated fibrous material may undergo thermal decomposition rapidly, and a large number of pores may be formed, which may deteriorate the properties of the manufactured carbon fiber.

[0057] The carbonization in step (d) (S40) may be performed by maintaining the above temperature for 0.5 to 3 hours.

[0058] Carbon fiber manufactured in steps (a) to (d) (S10 to S40) may have high crystallinity, low porosity, and good mechanical properties, and manufacturing costs may be significantly reduced.

[0059] The yield of carbon fiber manufactured by the above method may be 50 wt % or more, 60 wt % or more, or 65 wt % or more, and 90 wt % or less. The yield may be calculated as (carbon weight of manufactured carbon fiber/carbon weight of raw material)*100%.

Carbon Fiber

[0060] Carbon fiber according to another aspect of the present disclosure may be obtained by carbonizing a fibrous material having a ladder-like chemical structure, in which the fibrous material may be prepared by spinning of a raw material containing at least one chlorine group in the side chain of a repeat unit and hydrothermal treatment with a hydrochloric acid solution.

[0061] The fibrous material having the ladder-type chemical structure, raw material, spinning, and hydrothermal treatment are substantially the same as described above, and thus a redundant description thereof will be omitted.

[0062] The carbon fiber may have longitudinal tensile strength of 600 MPa to 1,500 MPa.

[0063] The carbon fiber may have a thickness (maximum length of the fiber cross-section perpendicular to the longitudinal direction) of 20 m to 70 m.

[0064] The carbon fiber may have a density of 1.02 g/cm.sup.3 to 1.25 g/cm.sup.3.

[0065] Since the carbon fiber is not derived from polyacrylonitrile (PAN), it may contain substantially no nitrogen or may contain nitrogen below the detection limit.

[0066] A better understanding of the present disclosure may be obtained through the following examples and comparative examples. However, these examples are not to be construed as limiting the technical spirit of the present disclosure.

Example 1

[0067] (a) A spinning solution having a concentration of 17 wt % was prepared by mixing polyvinyl chloride (PVC) with dimethylacetamide (DMAc).

[0068] (b) The spinning solution was spun into a coagulation bath containing water using a wet spinning machine, and the fibrous material was wound by a roller. Here, the temperature of the spinning solution was 40 C., the spinneret diameter was 160 m, the discharge rate was 2 ml/h, and the draw ratio was 5.

[0069] (c) The fibrous material was placed in a hydrothermal treatment machine and hydrothermally treated with a 37 wt % aqueous hydrochloric acid solution under conditions of a temperature of 250 C., a heating rate of 10 C./min, a pressure equal to or greater than vapor pressure of the aqueous solution, and a total of 24 hours, forming a ladder-like chemical ring structure in the fibrous material.

[0070] (d) Carbon fiber was manufactured by carbonizing the hydrothermally treated fibrous material in an argon gas atmosphere under conditions of a heating rate of 5 C./min, a temperature of 900 C., and a temperature maintenance time of 1 hour.

Comparative Example 1

[0071] Carbon fiber was manufactured under the same conditions as in Example 1, with the exception that the hydrothermal treatment in step (c) was omitted and the carbonization in step (d) was performed on the result of step (b).

Reference Example 1

[0072] Carbon fiber was manufactured under the same conditions as in Example 1, with the exception that the temperature of the spinning solution in step (b) was changed to 30 C.

Reference Example 2

[0073] Carbon fiber was manufactured under the same conditions as in Example 1, with the exception that the temperature of the spinning solution in step (b) was changed to 50 C.

Reference Example 3

[0074] Carbon fiber was manufactured under the same conditions as in Example 1, with the exception that the temperature in step (c) was changed to 100 C. and the treatment time was changed to 12 hours.

Reference Example 4

[0075] Carbon fiber was manufactured under the same conditions as in Example 1, with the exception that the temperature in step (c) was changed to 150 C. and the treatment time was changed to 12 hours.

Reference Example 5

[0076] Carbon fiber was manufactured under the same conditions as in Example 1, with the exception that the temperature in step (c) was changed to 200 C. and the treatment time was changed to 12 hours.

Reference Example 6

[0077] Carbon fiber was manufactured under the same conditions as in Example 1, with the exception that the temperature in step (c) was changed to 250 C. and the treatment time was changed to 12 hours.

Reference Example 7

[0078] Carbon fiber was manufactured under the same conditions as in Example 1, with the exception that the temperature in step (c) was changed to 300 C. and the treatment time was changed to 12 hours.

Reference Example 8

[0079] Carbon fiber was manufactured under the same conditions as in Example 1, with the exception that the heating rate in step (d) was changed to 7.5 C./min.

[0080] The conditions of Example, Reference Examples, and Comparative Example are briefly shown in Table 1 below.

TABLE-US-00001 TABLE 1 (b) (c) Hydro- (c) Hydro- Temperature thermal thermal (d) Heating of spinning treatment treatment rate during Classification solution temperature time carbonization Example 1 40 C. 250 C. 24 hours 5 C./min (E1) Comparative 40 C. 5 C./min Example 1 (C1) Reference 30 C. 250 C. 24 hours 5 C./min Example 1 (R1) Reference 50 C. 250 C. 24 hours 5 C./min Example 2 (R2) Reference 40 C. 100 C. 12 hours 5 C./min Example 3 (R3) Reference 40 C. 150 C. 12 hours 5 C./min Example 4 (R4) Reference 40 C. 200 C. 12 hours 5 C./min Example 5 (R5) Reference 40 C. 250 C. 12 hours 5 C./min Example 6 (R6) Reference 40 C. 300 C. 12 hours 5 C./min Example 7 (R7) Reference 40 C. 250 C. 24 hours 7.5 C./min Example 8

Test Example 1Analysis of Shape and Properties of Carbon Fiber Depending on Temperature of Spinning Solution

[0081] The properties of the carbon fiber manufactured according to each of Example 1 and Reference Examples 1 and 2, and each PVC fiber spun in step (b) were measured using a universal testing machine, and the cross-section of the spun PVC fiber was observed using an SEM. The results thereof are shown in FIGS. 2A to 2C and Table 2 below.

TABLE-US-00002 TABLE 2 Tensile strength of Density of Tensile strength of Classification PVC fiber PVC fiber carbon fiber Example 1 85.2 MPa 1.31 g/cm.sup.3 865.1 MPa Reference 80.1 MPa 1.21 g/cm.sup.3 250.9 MPa Example 1 Reference 30.9 MPa 1.08 g/cm.sup.3 50.8 MPa Example 2

[0082] Referring thereto, in Reference Example 1 (FIG. 2B), in which the temperature of the spinning solution was less than 35 C., the cross-section of the PVC fiber was flat, and tensile strength of the final carbon fiber was reduced. Also, in Reference Example 2 (FIG. 2C), in which the temperature of the spinning solution exceeded 45 C., the properties of the carbon fiber were deteriorated owing to high internal porosity of the fiber due to fast exchange between the medium and the solvent. In Example 1 (FIG. 2A), it was confirmed that PVC fiber was formed in a stable shape.

Test Example 2Analysis of Carbon Fiber Yield Depending on Hydrothermal Treatment Temperature and Time, and Chemical Structure and Cross-Section of Hydrothermally Treated PVC Fiber

[0083] The carbon weight of carbon fiber depending on changes in the temperature according to Example 1, Comparative Example 1, and Reference Examples 3 to 7 (E1, C1, R3 to R7) was measured by thermogravimetric analysis (TGA). The results thereof are shown in the top of FIG. 3 and the bottom of FIG. 5, and the calculated carbon yield is shown in Table 3 below and the bottom of FIG. 3. Also, the transmittance spectrum results depending on the specific wavenumber of the carbon fiber manufactured in each example by Fourier transform infrared spectroscopy (FT-IR) are shown in FIG. 4 and the top of FIG. 5. Also, the cross-section of the carbon fiber manufactured in each of Reference Example 6 and Example 1 was observed using an SEM, and the results thereof are shown in FIGS. 6A and 6B and 7A and 7B.

TABLE-US-00003 TABLE 3 Classification Carbon yield (wt %) Comparative Example 1 3.7 Reference Example 3 5.9 Reference Example 4 15.1 Reference Example 5 49.4 Reference Example 6 58.0 Reference Example 7 51.0 Example 1 67.3 Carbon yield: (carbon weight of carbon fiber/carbon weight of raw material)*100%

[0084] Referring to Table 3 and FIGS. 3 and 4, the highest carbon yield was exhibited at a hydrothermal treatment temperature of 250 C., and the peak of the cyclized CH related wavenumber and the peak of the CO related wavenumber were formed, indicating cyclization. Thermal decomposition occurred at a hydrothermal treatment temperature of 300 C., and the peak of the cyclized CH related wavenumber and the peak of the CO related wavenumber were not clearly formed at 100 C. and 150 C.

[0085] Also, referring to the top of FIG. 5, in Example 1 (E1), in which the hydrothermal treatment time was 24 hours, the transmittance peaks of the OCO related wavenumber and OH related wavenumber were more clearly formed compared to Reference Example 6 (R6) in which the hydrothermal treatment time was 12 hours. Referring to the bottom of FIG. 5, Example 1 exhibited high carbon weight in the carbonized fiber.

[0086] Also, referring to FIGS. 6A and 6B, for the carbon fiber of Reference Example 6, in which the hydrothermal treatment time was 12 hours, a ladder-like chemical ring structure was not complete in the PVC fiber before carbonization, and thus microscale pores were generated during carbonization, and referring to FIGS. 7A and 7B, in Example 1, uniform chemical reaction occurred inside and outside the fiber, minimizing the formation of pores in the carbon fiber.

Test Example 3Analysis of Properties and Cross-Section of Carbon Fiber Depending on Heating Rate During Carbonization

[0087] The properties of the carbon fiber manufactured in each of Example 1 and Reference Example 8 were measured using a universal testing machine, and the cross-sections thereof were observed using an SEM. The results thereof are shown in FIGS. 7A and 7B and 8 and Table 4 below.

TABLE-US-00004 TABLE 4 Tensile strength of Density of Classification carbon fiber carbon fiber Example 1 865.1 MPa 1.15 g/cm.sup.3 Reference Example 8 632.8 MPa 1.27 g/cm.sup.3

[0088] Referring thereto, in Example 1, in which carbonization was performed at a relatively low heating rate, manufacture of carbon fiber having a structurally uniform shape was confirmed, and in Reference Example 8, thermal decomposition occurred rapidly, forming a large number of pores in the fiber and deteriorating the properties of the fiber.

[0089] As is apparent from the above description, a method of manufacturing carbon fiber according to the present disclosure is capable of manufacturing carbon fiber at high yield from a raw material containing a chlorine group in the side chain, such as PVC, etc., among compounds having a carbon skeleton, which are inexpensive compared to conventional PAN.

[0090] In addition, carbon fiber manufactured according to the present disclosure can exhibit high crystallinity, low porosity, and good mechanical properties.

[0091] The effects of the present disclosure are not limited to the foregoing. It should be understood that the effects of the present disclosure include all effects that can be inferred from the description of the present disclosure.

[0092] Although specific embodiments of the present disclosure have been described, those skilled in the art will appreciate that the present disclosure may be embodied in other specific forms without changing the technical spirit or essential features thereof. Thus, the embodiments described above should be understood to be non-limiting and illustrative in every way.