Fiber reinforced elastomeric stator

Abstract

Embodiments disclosed herein relate to a composition useful for forming a stator or a portion thereof. The composition may include: a curable elastomer; a fiber or fibrous compound; a fiber dispersion compound; and optionally carbon black.

Claims

1. A positive displacement drilling motor comprising: a rotor deployed in a stator, the rotor configured to rotate eccentrically in the stator when drilling fluid passes through the motor; wherein the stator comprises an elastomeric stator liner deployed in a stator tube, the elastomeric stator liner comprising: a curable elastomer; from about 1.25 to about 1.75 phr aramid fibers; from about 0.5 to about 15 phr amorphous silicon dioxide having a surface area in a range from about 10 m.sup.2/g to about 30 m.sup.2/g; and from about 10 to about 100 phr carbon black; wherein phr is defined as parts per hundred parts of the curable elastomer, and wherein the aramid fibers are dispersed through the curable elastomer.

2. The drilling motor of claim 1, wherein the elastomeric stator liner comprises from about 1.5 to about 1.75 phr aramid fibers.

3. The drilling motor of claim 1, wherein the amorphous silicon dioxide is spherical.

4. The drilling motor of claim 1, wherein the amorphous silicon dioxide has an average particle size in a range from about 30 nm to about 300 nm.

5. The drilling motor of claim 1, wherein the curable elastomer comprises at least one of nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), fluoroelastomer (FKM), fluoro ethylene/propylene rubbers (FEPM), and perfluoroelastomers (FFKM).

6. The drilling motor of claim 1, wherein the curable elastomer comprises at least one of NBR or HNBR and has a Mooney Viscosity (ML(1+4) at 121 C.) in a range from about 20 to about 120.

7. The drilling motor of claim 1, wherein the elastomeric stator liner further comprises one or more curatives and/or activators, each in an amount ranging from about 1 to about 50 phr.

8. A positive displacement drilling motor comprising: a rotor deployed in a stator, the rotor configured to rotate eccentrically in the stator when drilling fluid passes through the motor; wherein the stator comprises an elastomeric stator liner deployed in a stator tube, the elastomeric stator liner comprising: a curable elastomer; from about 0.5 to about 1.8 phr fibrous material; from about 0.5 to about 36 phr silicon dioxide; and from about 10 to about 100 phr carbon black; wherein phr is defined as parts per hundred parts of the curable elastomer, and wherein the silicon dioxide has a surface area in a range from about 10 m.sup.2/g to about 30 m.sup.2/g.

9. The drilling motor of claim 8, wherein the silicon dioxide has an average particle size in a range from about 30 nm to about 300 nm.

10. The drilling motor of claim 8, wherein the silicon dioxide is an amorphous silicon dioxide.

11. The drilling motor of claim 8, wherein the elastomeric stator liner comprises from about 0.5 to about 15 phr of the silicon dioxide.

12. The drilling motor of claim 8, wherein the fibrous material comprises an aramid fiber.

13. The drilling motor of claim 8, wherein the fibrous material of the elastomeric stator liner comprises an aramid fiber in an amount of from about 1 to about 1.8 phr.

14. The drilling motor of claim 8, wherein the curable elastomer comprises at least one of nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), fluoroelastomer (FKM), fluoro ethylene/propylene rubbers (FEPM), or perfluoroelastomers (FFKM).

15. The drilling motor of claim 14, wherein the curable elastomer comprises at least one of NBR or HNBR and has a Mooney Viscosity (ML(1+4) at 121 C.) in a range from about 20 to about 120.

16. A drilling assembly comprising: the positive displacement drilling motor of claim 1; a motor output shaft directly or indirectly connected to the rotor; and a drill bit directly or indirectly connected to the motor output shaft.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a cross-sectional view of a rotor useful in mud motors according to embodiments disclosed herein.

(2) FIG. 2 shows a cross-sectional view of a stator according to embodiments disclosed herein.

(3) FIG. 3 shows a cross-sectional view of an assembled positive displacement motor according to embodiments disclosed herein.

(4) FIG. 4 shows a cross-sectional view of an assembled positive displacement motor according to embodiments disclosed herein, having an even-wall stator liner.

(5) FIGS. 5-8 compare the physical properties of stators according to embodiments herein to stators without fiber.

DETAILED DESCRIPTION

(6) In one aspect, embodiments disclosed herein relate generally to stators used with positive displacement drilling motors. More specifically, embodiments disclosed herein relate to a fiber reinforced stator, and compositions for forming the fiber reinforced stator, wherein the fiber is easily incorporated and well dispersed throughout the elastomeric matrix.

(7) Referring to FIG. 1, a typical rotor 10 includes at least one lobe 12 (wherein, for example, channels 14 are formed between lobes 12), a major diameter 8, and a minor diameter 6. The rotor 10 may be formed of metal or any other suitable material. The rotor 10 may also be coated to withstand harsh drilling environments experienced downhole.

(8) Referring to FIG. 2, a stator 20 according to embodiments herein comprises at least two lobes 22, a major diameter 7, and a minor diameter 5. Rotor 10 (FIG. 1) typically includes n lobes, and the corresponding stator 20 used in combination with the rotor 10 generally includes either n+1 or n1 lobes. Referring to FIG. 3, the stator 20 generally includes a cylindrical external tube 24 and a liner 26. The liner 26 is typically injected or extruded into the cylindrical external tube 24 around a mold (not shown) that has been placed therein. The liner 26 is then cured for a selected time at a selected temperature (or temperatures) before the mold (not shown) is removed. A thickness 28 of the liner 26 is generally controlled by changing the dimensions of the mold (not shown). A curing pressure, temperature, and time may be selected using means know in the art so as to completely cure the elastomer. After completion of the curing process, the stator will be returned to normal atmospheric conditions. Final machining may be required to complete the stator (e.g., ends of the liner may need to be trimmed, ends of the stator may be threaded, etc.).

(9) As illustrated in FIG. 2, liner 26 has a non-uniform thickness. In other embodiments, even-wall stators may be formed using fiber reinforced compositions disclosed herein, such as illustrated in FIG. 4. Positive displacement motor (PDM) 30 comprises a stator 32 and a rotor 34. The stator 32 comprises an external tube 38 that may be formed from, for example, steel or another material suitable for downhole use in a drilling environment. The stator also comprises a liner 36. The external tube 38 comprises a shaped inner surface 44 that comprises at least two lobes 46 formed thereon. The lobes 46 are helically formed along a selected length of the external tube 38 so that the lobes 46 define a helical pattern along the selected length. The helical form of the inner surface 44 generally corresponds to a desired shape for stator lobes. The liner 36 typically comprises at least two lobes 40, and a thickness 42 of the liner 36 may be either uniform or non-uniform throughout a cross-section thereof, and formed by injection molding, extrusion molding or other means followed by curing and finishing, as noted above. The lobes 40 (and the liner 36) are helically formed along a selected length of the external tube 38 such that the liner 36 conforms to the helically shaped inner surface 44 so that the at least two lobes 46 formed on the shaped inner surface 44 correspond to the lobes 40 formed in the liner 36. The external tube 38, including the inner surface 44, may be helically shaped by any means known in the art including machining, hydroforming, extrusion, and the like.

(10) Stator liners according to embodiments disclosed herein may be formed from a fiber reinforced elastomeric or polymeric material. In other embodiments, stator liners may include a composite structure, such as an elastomeric layer and one or more fiber reinforced layers intermediate the external tube (housing) and the elastomeric outer layer. The intermediate fiber reinforced layer(s) may provide additional stiffness and/or wear resistance of the liner.

(11) Stator liners, portions of stator liners, or reinforcing layers thereof, may be formed from a composition including: a. a curable or cross-linkable elastomeric or polymeric material, such as various elastomers, polymers, and other synthetic or natural materials known in the art; b. a fiber or fibrous material; c. a fiber dispersion compound; and d. carbon black.
The compositions used to form stator liners or portions thereof may also include plascticizers, curatives (i.e., curing or crosslinking agents), activators, processing aids, and waxes.

(12) The curable elastomeric materials may include, for example, G.R.S., NEOPRENE, butyl and nitrile rubbers, fluorinated or perfluoro elastomers or rubbers, and soft PVC, among other polymers. In some embodiments, the elastomeric compound may include one or more of NBR, HNBR, FEPM, FKM, and FFKM.

(13) In some embodiments, the elastomeric material may include a copolymerization product of 1,3-butadiene and acrylonitrile having a Mooney Viscosity ML(1+4) at 121 C. in the range from about 20 to about 120. The acrylonitrile content may be in the ranges from about 19 wt. % to about 49 wt. %, and the hydrogenation may be full or partial, leaving a residual double bond content from less than 1% to about 18%.

(14) In other embodiments, the elastomeric material may be a copolymer of vinylidene fluoride and hexafluoropropylene having a Mooney Viscosity ML(1+10) at 100 C. in the range from about 10 to about 160. In some embodiments, the fluorine content of the elastomeric material may be in the range from about 60 to about 70%.

(15) Elastomeric materials may also be a copolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene, with or without a cure site monomer, having a Mooney Viscosity ML(1+4) at 121 C. in the range from about 25 to about 65.

(16) In other embodiments, the elastomeric material may be a copolymer of tetrafluoroethylene and propylene, with or without a cure site monomer, having a Mooney Viscosity ML(1+4) at 100 C. in the range from about 35 to about 160. In some embodiments, the fluorine content of the elastomeric material may be in the range from about 55 to about 65%.

(17) The aforementioned polymers may be used alone or in combination with one or more additional polymers or grades of a similar polymer at a ratio in the range from about 20:80 to about 80:20.

(18) The fiber or fibrous material may include at least one of carbon fibers, boron fibers, ceramic fibers, glass fibers, thermoplastic fibers, natural fiber, metallic fibers, synthetic fibers, and carbon nanotubes. For example, in some embodiments the fibers may include fibers made from E-glass, polyethylene PEI, PVDC, PTFE, PVDF, PVF, EFP, PEEK, PPS, and PEI. In some embodiments, the fiber or fibrous material may include aramid fibers, such as those sold under the mark KEVLAR (a mark of E.I. DuPont de Nemours of Wilmington, Del.).

(19) Aramid fibers useful in some embodiments herein may have an average diameter in the range from about 0.5 to about 25 microns in some embodiments; from about 1 micron to about 20 microns in other embodiments; and from about 5 microns to about 15 microns, such as about 12 microns, in yet other embodiments. The fibers may have a length in the range from about 1 mm to about 50 mm in some embodiments; from about 5 mm to about 40 mm in other embodiments; and from about 10 mm to about 30 mm, such as about 20 mm, in yet other embodiments. Aramid fibers may have an aspect ratio (length to diameter) in the range from about 1:1 to about 300:1 in some embodiments, and from about 1:1 to about 200:1 in other embodiments. The aramid fibers may have a tensile strength of over 500,000 psi and be able to withstand temperatures of up to about 400 C.

(20) In some embodiments, fiber reinforced stator liners, or the layers/portions of a stator liner that are fiber reinforced, may include up to about 2 wt % fiber, such as in the range from about 0.5 to about 1.8 phr, based on the total amount of elastomeric compound, in some embodiments, from about 1 to about 1.8 phr in other embodiments, and from about 1.25 to about 1.75 phr in yet other embodiments. In other embodiments, the fiber may be present in an amount from a lower limit of about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, or 1.6 phr to an upper limit of about 1.2, 1.3, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, or 1.8 phr, where any lower limit may be combined with any upper limit.

(21) While it has been proposed to add significantly greater quantities of fiber, such as 10 phr or greater, it has been found that incorporation of fibers in quantities less than about 1.8 phr, such as from about 1.5 to about 1.75 phr, may provide an optimal balance of significant improvements in physical properties, as well as excellent improvements in stator torque output capacity and stator endurance at high torque levels, with minimal negative impact on the compound resilience, elasticity, dispersity, and processability. It is theorized that greater quantities of fiber may result in discontinuities or imperfections in the elastomer matrix, possibly due to inefficient dispersion of the fiber at higher concentrations, which may result in little or no improvement in stator performance.

(22) Fiber dispersion compounds are defined herein as compounds that facilitate the incorporation of the fiber with the elastomeric material, and may include solid dispersion compounds, liquid dispersion compounds, or combinations thereof. One example of a solid fiber dispersion compound useful in embodiments disclosed herein may include amorphous silicon dioxide. In some embodiments, amorphous silicon dioxide having an average particle size in the range from about 0.03 microns to about 0.3 microns (30 nm to 300 nm) and a surface area in the range from about 10 to about 30 m.sup.2/g, such as about 20 m.sup.2/g, may be used as a fiber dispersion compound. It is theorized that the relatively spherical amorphous silicon dioxide particles may provide a bearing effect and a viscosity-lowering effect on the resulting admixture of the fibers with the elastomeric material, allowing for improved processablity of the elastomeric mixture and improved dispersion of fibers throughout the resulting elastomeric matrix upon cure. Other solid fiber dispersion compounds, such as nano or micron sized spherical structures that may provide similar viscosity-reducing and bearing effects may also be used, and may include various natural and synthetic clays (alumina silicates, silica aluminates, etc.), magnesium silicates, coal dust, and/or silicon dioxide powder. Liquid dispersion compounds that may be useful in embodiments herein may include liquid polymers, waxes, and various processing aids or plasticizers.

(23) In some embodiments, incorporation of the fiber into the curable composition mixture may be facilitated by use of a predispersion of fiber in a fiber dispersion compound. For example, a mixture of 5 wt. % to about 70 wt. % fiber in 95 wt. % to about 30 wt. % fiber dispersion compound may be admixed with an elastomeric material prior to injection or extrusion molding of the curable composition in a mold. In some embodiments, the fiber dispersion compound may be used in an amount ranging from about 0.5 to about 36 phr, such as from about 0.5 to about 15 phr in other embodiments. In other embodiments, the fiber dispersion compound may be present in an amount from a lower limit of about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or 2.0 phr to an upper limit of about 1.25, 1.5, 1.75, 2.0, 2.5, or 5 phr, where any lower limit may be combined with any upper limit.

(24) In some embodiments, curable compositions useful for forming a stator liner or a portion/layer thereof may be formed by admixing: a. a curable or cross-linkable elastomeric or polymeric material, such as various elastomers, polymers, and other synthetic or natural materials known in the art; b. a fiber or fibrous material in an amount ranging from about 0.5 to about 1.8 phr (based on the total amount of component a) predispersed in a fiber dispersion compound (c); c. the fiber dispersion compound in an amount ranging from about 0.5 to about 36 phr; d. optionally, carbon black in an amount ranging from about 10 to about 100 phr; e. optionally, one or more curatives and/or activators, each in an amount ranging from about 1 to about 50 phr.

(25) In other embodiments, curable compositions useful for forming a stator liner or a portion/layer thereof may be formed by admixing: a. a curable or cross-linkable elastomeric or polymeric material, such as various elastomers, polymers, and other synthetic or natural materials known in the art; b. an aramid fiber in an amount ranging from about 1 to about 1.8 phr (based on the total amount of component a) predispersed in amorphous silicon dioxide as fiber dispersion compound (c); c. amorphous silicon dioxide (fiber dispersion compound) in an amount ranging from about 1 to about 12 phr; d. carbon black in an amount ranging from about 10 to about 100 phr; e. optionally, one or more curatives and/or activators, each in an amount ranging from about 1 to about 50 phr.

(26) The above described curable compositions may be formed using a screw mixer, a BANBURY mixer, a single or multiple screw extruder, or other mixing devices as known in the art for intimately mixing a polymeric or elastomeric resin material with one or more additive compounds. The mixing process may further provide heat, melting the polymeric or elastomeric resin material during the mixing process, and the resulting fluid mixture may then be extruded, injected, or otherwise disposed between a stator tube (housing) and a mold that has been placed therein. The liner material may then be cured and the stator finished (trimming, threading, etc.), as described above.

(27) It has been found that the curable compositions according to various embodiments herein are processable using injection molding equipment (used in about 90% of the current stator manufacturing processes). Further, it has been found that the unique combination of fiber, fiber dispersion compounds, and carbon black allows for uniform fiber dispersion and pronounced property improvements to be achieved. A uniform fiber density is advantageous because it helps achieve, for example, uniform wear resistance throughout the thickness of the liner. A uniform fiber density is particular desirable proximate the lobes because the lobes experience the highest mechanical and thermal stresses. Additional support and wear resistance proximate the lobes help increase the longevity of the liner. Note that, in some embodiments, the liner thickness is at a maximum proximate the lobes, and a uniform fiber density supports and helps stiffen these regions so as to reduce deformation of the lobes caused by, for example, fluid pressure and contact with the rotor. Such results were heretofore unattainable with random fiber placement/orientation methods, as much higher fiber loadings were required to compensate for the agglomeration and non-uniformity of the fiber displacement, negatively impacting elongation properties, tear strength, compression set, and other dynamic properties affecting stator life and sealing performance. Additionally, the high fiber loadings typical of prior methods result in a compound viscosity spike and drastic changes to compound cure characteristics, making such mixtures unsuitable for some manufacturing processes, including injection molding processes. Embodiments of curable compounds disclosed herein overcome these deficiencies, resulting in an improved stator and a simplified manufacturing process.

(28) As noted above, curable compositions disclosed herein may provide for improved processability using injection molding tooling. For example, NBR and other elastomeric compounds having a Mooney Viscosity ML(1+4) at 121 C. in the range from about 25 to about 40, and in some embodiments up to about 50, may be preferred when forming the stator via injection molding equipment typically used to produce stators having a length in the range from about 10 to about 25 feet (from about 3 to about 7.5 meters). Compositions useful with extrusion molding may include elastomeric compounds having a Mooney Viscosity ML(1+4) 100 C. in the range from about 25 to about 65, and in some embodiments up to about 80. Compositions useful with compression molding may include elastomeric compounds having a Mooney Viscosity ML(1+4) 100 C. in the range from about 25 to about 90, and in some embodiments up to about 120. Compositions useful with transfer molding may include elastomeric compounds having a Mooney Viscosity ML(1+4) 100 C. in the range from about 20 to about 45.

(29) The above described stators may be used in a mud motor or drilling assembly used for the drilling of a wellbore through a subterranean formation. A lower end of the rotor may be coupled either directly or indirectly to, for example, a drill bit. In this manner, the PDM provides a drive mechanism for a drill bit independent of any rotational motion of a drill string generated proximate the surface of the well by, for example, rotation of a rotary table on a drilling rig. Accordingly, PDMs are especially useful in drilling directional wells where a drill bit is connected to a lower end of a bottom hole assembly (BHA). The BHA may include, for example, a PDM, a transmission assembly, a bent housing assembly, a bearing section, and the drill bit. The rotor may transmit torque to the drill bit via a drive shaft or a series of drive shafts that are operatively coupled to the rotor and to the drill bit. In operation, a drilling fluid is passed through the mud motor assembly, eccentrically rotating the rotor as the drilling fluid passes through the progressive cavity motor. The motor output shaft transmits the eccentric rotor motion (and torque) to the concentrically rotating drill bit to drill the formation.

EXAMPLES

(30) TABLE-US-00001 TABLE 1 Formula 1 Formula 3 (comparative) Formula 2 (comparative) Polymer 100 100 100 Carbon Black 90 90 75 Plasticizer 20 20 20 40% Fiber predispersion 0 4 15 Curatives 5.5 5.5 5.5 Activators 11 11 11 Total 226.5 230.5 226.5

(31) TABLE-US-00002 TABLE 2 Formula 1 Formula 2 Formula 3 ASTM D412-06 Tensile (psi) 2100 1900 1300 Elongation (%) 300 250 70 Mod at 25% 200 800 800 ASTM D624-00 260 230 230 Tear Die C Tstrength (lbf/in) Tstrength (lbf/in) after 72 hr 200 220 water immersion at 300 F. ASTM D395 (22 hrs at 35 37 65 250 F.) Compression Set % ASTM D429 90 degree 90 120 Adhesion Peel (lbf/in) Adhesion Peel (lbf/in) after 15 30 72 hr water immersion at 300 F. RPA (30 mins at 300 F.) ML 0.29 0.29 MH 15 15

(32) Table 1 is a side-by-side formulation comparison, on the basis of adding the fibers into the same formulation with equal total phrs, Formula 1 (comparative example, typical of commercially available stators) has no fibers, Formula 3 (comparative example) has about 6 phr aramid fiber (predispersed in amorphous silicon dioxide); and Formula 2 (according to embodiments herein), includes about 1.6 to 1.7 phr aramid fibers (predispersed in amorphous silicon dioxide). Table 2 compares the physical properties of the resulting materials upon cure. The stiffness improvement, over the comparative example without fibers, in 25% modulus is around 400% while other properties show minimal change, such as elongation, compression set, and ML. This is due to excellent uniformity of fiber dispersion obtained by the current method and the optimal fiber phrs so that fiber achieves a synergistic interaction with the carbon black at a very low loading of 1.7 phr to boost the modulus. The disadvantage of high fiber loading is apparent in formula 3 that the compound has a dramatic loss of elongation and compression set values goes up significantly. On the other hand, the low loading of fiber thereby renders minimal impact to other properties. Further, the fiber is high in surface area and high in aspect, which increases the interaction between fiber/CB and polymer matrix, giving rise to an enhanced high temperature performance and high bond strength between the rubber and adhesive.

(33) FIGS. 5 through 8 graphically compare the physical properties of the composition of Formula 1 (comparative) to that of Formula 2. As noted above and illustrated in FIG. 5, the 25% modulus for the cured composition based on Formula 2 is significantly greater than that for Formula 1 (greater than 800 psi vs. less than 200 psi). FIGS. 6 and 7 illustrate the differences in peel strength and tear strength, both prior to and subsequent to immersion in water at 300 F. for 72 hours, simulating downhole operating conditions. With regard to peel strength, Formula 2 showed improvements both before and after immersion. Tear strength for Formula 2 was less than that for Formula 1 before immersion, but under simulated downhole conditions showed marked improvement as compared to Formula 1.

(34) FIG. 8 compares stator performance for stators formed from Formula 1 (NBR reg) and Formula 2 (NBR Fiber). The performance test was performed on a 6.25 inch long section of a stator having an external diameter of inch using a simulated drilling fluid. The stators were formed using the same mold and tested under the same test procedure. The pressure drop of the test stator was set to 300 psi per stage after the warm-up and initial tests and the motor output (rpm and torque) were measured over time. The test was stopped upon failure of the stator. The rpm of the stators was roughly equivalent, which is expected based upon the differential pressure per stage. The initial torque output for the stator with fiber (Formula 2) was greater and decreased at a slower rate over time. Endurance of the stator based on Formula 2 was significantly greater, as shown on the graph. Further, filtering of the stator effluent drilling fluid during testing showed significantly less chunking and flaking of polymeric material from the stator of Formula 2 as compared to the stator of Formula 1.

(35) As described above, embodiments disclosed herein provide for a novel method for uniformly dispersing fibers in an elastomeric matrix. In addition to the above noted advantages with respect to uniform fiber density, improved processability in the manufacture of stators, embodiments disclosed herein may also provide for mud motors having improved durability and/or power generation. For example, the fibers may serve to strengthen and stiffen the elastomer of the stator so that it is better able to withstand a certain amount of degradation in properties without failure or chunking and can operate with less interference with the rotor without leakage.

(36) In addition to stator manufacture, compositions disclosed herein may also be useful for manufacturing fiber reinforced seals and other fiber reinforced oilfield equipment. For example, the benefits realized by use of a fiber predispersion, such as a mixture of aramid fibers in amorphous silicon dioxide, may improve the manufacturing process and/or resulting properties of seals and other fiber reinforced oilfield equipment. The effective dispersion and synergistic effects realized with the fiber and fiber dispersion compound in combination with carbon black may also benefit various fiber reinforced oilfield equipment. Accordingly, seals, stator liners, and other oilfield products or portions or reinforcing layers thereof, may be formed from according to embodiments disclosed herein using a composition including: a. a curable or cross-linkable elastomeric or polymeric material, such as various elastomers, polymers, and other synthetic or natural materials known in the art; b. a fiber or fibrous material; c. a fiber dispersion compound; and d. optionally carbon black.
The compositions used to form seals and other oilfield product or portions/layers thereof may also include plascticizers, curatives (i.e., curing or crosslinking agents), activators, processing aids, and waxes.

(37) While the disclosure includes a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the present disclosure. Accordingly, the scope should be limited only by the attached claims.