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Title:
PROCESS FOR AND POLYMER COMPOSITES OF FLOWABLE POLYMERS WITH SHORT FIBERS AND/OR EXFOLIATED NANOCLAYS
Document Type and Number:
WIPO Patent Application WO/2007/053640
Kind Code:
A3
Abstract:
A process for fabricating a polymer composite of one or more flowable polymers with short fiber inclusions or nanoclay inclusions. The short man-made polymeric fibers or the nanoclay, along with a thermoplastic or elastomeric polymer matrix, are charged into a mixer. The mixer is operated for more than about 400 rotations at a shear rate of at least about 2000 radians/second.

Inventors:
FAULKNER ROGER W (US)
FELTON COLIN (US)
Application Number:
PCT/US2006/042545
Publication Date:
December 21, 2007
Filing Date:
November 01, 2006
Export Citation:
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Assignee:
US UNLTD INC (US)
FAULKNER ROGER W (US)
FELTON COLIN (US)
International Classes:
C08K9/04; B82B1/00
Foreign References:
US20040059037A12004-03-25
US6828371B22004-12-07
US20050143508A12005-06-30
US6709146B12004-03-23
Attorney, Agent or Firm:
DINGMAN, Brian, M., Esq et al. (O'CONNELL DEMALLIE & LOUGEE, LLP,1700 West Park Driv, Westborough MA, US)
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Claims:

CLAIMS

I . A process for fabricating a polymer composite of one or more flowable polymers with short fiber inclusions, comprising: charging into a mixer both short man-made polymeric fibers and a polymer matrix comprising at least one of a thermoplastic material and an elastomeric material; and operating the mixer for at least about 400 rotations at a shear rate of at least about 2000 radians/second. 2. The process of claim 1, in which the man-made polymeric fibers are crystalline polyamides with diameters less than about 20 microns.

3. The process of claim 1 , in which the man-made polymeric fibers comprise crystalline fluoropolymers with diameters less than about 20 microns.

4. The process of claim 1, in which the man-made polymeric fibers comprise crystalline polyester fibers with diameters less than about 20 microns.

5. The process of claim 1, in which the man-made fibers comprise polyaramids or t polyimides with diameters less than about 20 microns.

6. The process of claim 5, comprising para-polyaramid fibers in the form of a pulp.

7. The process of claim 1, in which the man-made fibers comprise carbon nanotubes. 8. The process of claim 1 , in which the matrix comprises one or more thermoplastic polyolefins.

9. The process of claim 1 , in which the matrix comprises one or more thermoplastic polyamides.

10. The process of claim 1, in which the matrix comprises one or more thermoplastic fluoropolymers.

I 1. The process of claim 1 , in which the matrix comprises one or more engineering thermoplastics.

12. The process of claim 11, in which the matrix comprises polyphenylene sulfide.

13. The process of claim 1, in which the mixer is a thermokinetic mixer. 14. The process of claim 13, in which the matrix comprises a thermoplastic.

15. The process of claim 13, in which the matrix comprises an elastomer.

16. The process of claim 1, in which the polymeric fibers do not melt, degrade or dissolve during the mixing.

17. The process of claim 1, further comprising adding water into the mixer before it is operated or during mixing.

18. A polymer composite made by the process of claim 1.

19. A process for fabricating a polymer composite of one or more flowable polymers with dispersed nanoclay, comprising: charging into a mixer both nanoclay and a polymer matrix comprising at least one of a thermoplastic material and an elastomeric material; and operating the mixer for at least about 400 rotations at a shear rate of at least about 2000 radians/second. 20. The process of claim 19, in which the mixer is operated at a shear rate of at least about 4000 radians/second.

21. The process of claim 19 in which the nanoclay comprises an ion-exchanged clay.

22. The process of claim 21 in which the clay comprises onium-exchanged montmorillonite clay. 23. The process of claim 19, further comprising adding water into the mixer before it is operated or during mixing. 24. A polymer composite made by the process of claim 19.

Description:

Process for and Polymer Composites of Flowable Polymers with Short Fibers and/or

Exfoliated Nanoclays

CROSS-REFERENCE TO RELATED APPLICATIONS This invention is based upon and claims the benefit of priority from U.S.

Provisional Application Serial No. 60/731 ,960 filed on November 1, 2005, and U.S. Provisional Application Serial No. 60/822,661, filed on August 17, 2006. The entire contents of both such provisional applications are incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to polymers with certain inclusions, and methods of making such polymers.

BACKGROUND OF THE INVENTION Short fiber reinforcements are common in both elastomeric and thermoplastic compounds. The vast majority of short fiber reinforcements used in plastics are inorganic materials such as glass fiber, slag wool, carbon fibers, mineral fibers (examples: asbestos, wollastonite, sepiolite, attapulgite), synthetic ceramic whiskers (e.g., BN or SiC), carbon nanotubes, or metal wires for example. Natural lignocellulosic fiber reinforcejnents (wood fiber, and the bast fibers from hemp, sisal, jute, cotton, flax, and kenaf are prominent examples) are also used to a significant and growing extent as thermoplastics reinforcements (these are only applicable in thermoplastics that can be processed below about 220° C). Usage of man-made polymeric short fibers as thermoplastic reinforcements is by comparison a very small part of the market, partially because of difficulties with processing.

Mixtures of elastomers with short polymeric fibers are well known in the prior art. Both meltable (e.g., nylon and polyester) and non-meltable polymeric fibers such as lignocellulosic fibers and polyaramids are used as elastomer reinforcements. Polyaramid fibers in various forms have long been used to stiffen elastomers, especially since the negative health effects of asbestos fiber became known. Polyaramids include both para- polyaramid liquid crystal fibers, which can be readily fibrillated to pulp, and various non- liquid crystalline meta-polyaramid fibers that do not readily fibrillate. Among these fibers, para-polyaramid fibers like Kevlar™ from Dupont orTwaron™ from Twaron

fibers, para-polyaramid fibers like Kevlar™ from Dupont or Twaron™ from Twaron Products, either as chopped fibers or pulp, produce particularly desirable properties in reinforced elastomers, such as increased tensile strength, tensile elongation, modulus, hardness, abrasion resistance, and tear strength, provided that they are well dispersed. The uniformity of the dispersion also impacts fatigue resistance. It has previously been impossible to obtain a well-dispersed mixture of polyaramid pulp in an elastomer by conventional polymer mixing methods using neat pulp as a feed. It has also proved particularly difficult to disperse short polymer fibers of any kind when the fiber diameter is less than about 20 microns. Polyaramid pulp masterbatches are available commercially from Dupont

Advanced Elastomer Systems (hereafter "Dupont") in which the Kevlar™ brand polyaramid is well dispersed in an elastomer such as natural rubber (NR), nitrile- butadiene copolymer rubber (NBR), or polychloroprene rubber (CR). In these three cases, fairly dilute slurry of polyaramid pulp is first disaggregated via aqueous grinding with a high-speed disperser such as for example a Cowles blade mixer or a pulp beater. When well dispersed, the polyaramid pulp thickens the water, acting as a thixotrope. After preparing the well-dispersed aqueous polyaramid pulp mixture, latex of the given polymer (NR, CR, or NBR latex) is added and the fiber/latex mixture is coagulated in a controlled manner, which coats each polyaramid fiber with polymer. The coagulated mixture is then dried and extruded to yield the final product form in which the polyaramid pulp is very well dispersed in the polymer phase. One example of this process (applied to FKM fiuoroelastomer latex) can be found in US patent 5,194,484. This same type of process can be applied to any polymer that is manufactured as latex. This is an expensive process however, in terms of capital cost, and is not well suited to production of a wide variety of different polymer/polyaramid dispersions in the same equipment, due to the difficulty of changing from one material to the next.

Polyaramid pulp masterbatches are also available commercially from Rhein Chemie (a Division of Bayer) (hereafter "Rhein Chemie") in which Twaron™ brand polyaramid is well dispersed in a wide variety of elastomers, including polymers such as HNBR and EPDM that are difficult or impossible to prepare by the latex blending approach described above, which is believed to be used by Dupont in preparing most of their Kevlar™/elastomer dispersions.

Polyaramid pulp masterbatches can also be formed from solutions of elastomer in

solvent. This has been applied commercially in the past to formation of polyaramid pulp mixtures with polychloroprene (CR) and fluoroelastomers (FKM) dissolved in MEK in particular. This method is especially relevant for elastomers (such as EPDM, πR, and HNBR) that are manufactured in solution. In either the solvent method or the latex method, the polyaramid pulp is first dispersed either in a compatible solvent or in a pre-formed polymer solution at low concentration, using similar methods to what is used in water in the latex-based method of US patent 5,194,484; then, this can be mixed with either particulate elastomer or an elastomer solution (if the elastomer was not already dissolved in the solvent when the polyaramid pulp dispersion was formed), and then the solvent is removed to yield the final dispersion.

Another way to achieve improved polyaramid pulp dispersions in polymers is to modify the polyaramid pulp to make it more dispersible. One means to do this is via fluorination, as practiced by Inhance Products Division of Fluoroseal LTD, of Houston, Texas. When Kevlar™ pulp is fluorinated, the surface energy of the polyaramid surface is increased, which leads to easier dispersability. Reactive chemical groups (OH groups for example) are also produced on the fiber surface during fluorination, which can be used to couple the fluorinated polyaramid to the polymer matrix via covalent chemical bonds. The fiber ends are also morphologically changed, in that a fraying occurs which also contributes to dispersability. Fluorinated polyaramid pulp is commercially available as Inhance KF™ fibers from Inhance/Fluoro-Seal, Ltd., Houston, TX, though at a relatively high price (roughly double that of unmodified polyaramid pulp) that inhibits all but the highest value applications.

Polyaramid short fibers are also used in thermoplastics. Polyaramid pulp is not used to any significant extent, because it has not proved possible to disperse it into a thermoplastic matrix. Chopped polyaramid fibers are used in plastics primarily in plastic bushings where they contribute low friction and wear resistance. Theoretically, polyaramid pulp could be highly reinforcing in plastics if it could be well dispersed, and if it was wetted by the thermoplastic.

Repeated internal mixer (Banbury or Shaw Intermix for example) or extruder mixing cycles, or long mixing time on a two roll rubber mill ("rubber milling") can eventually yield a well-dispersed polyaramid cut fiber/polymer masterbatch, but this is expensive, and greatly reduces throughput compared to typical polymer mixing cycles. So even with short-cut fibers, which can be dispersed by conventional means, there is a

need for a more efficient method for dispersing these fibers in flowable polymers (especially cut fibers with diameter less than about 20 microns).

Carbon nanotubes have very special properties in polymer composites, including superior reinforcement, and large effects on electrical conductivity. Unlike conductive carbon black, carbon nanotubes are strong enough to survive the shear stresses imposed by typical polymer mixing and processing operations, so the electrical conductivity imparted by carbon nanotubes is not decreased by polymer processing, as often occurs for prior art conductive carbon blacks, such as acetylene blacks. Because of this, and also because carbon nanotubes produce electrical conductivity at lower addition levels and with little or no reduction in impact properties, the major application of carbon nanotubes in polymer composites so far is for conductive plastics. Although carbon nanotubes can be effectively dispersed by conventional polymer mixing methods, such as internal mixers or extruders, the high cost of carbon nanotubes means that even a modest improvement in dispersion of the carbon nanotubes is economically significant. Nanoclay composites are an exciting new development in polymer composite technology. In most of these materials, quaternary ammonium or phosphonium ions are added to an aqueous dispersion of a negatively charged clay mineral, such as momtmorillonite, hectorite, saponite, stevensite, or beidelite; the organo-onium ion is exchanged for the metallic ions (typically sodium, potassium, magnesium, and calcium cations) that separate the planar layers in these clays. Because the quaternary ions are bulkier, this ion exchange pries the lamellae of the clay apart slightly. After this chemical modification, it is possible to exfoliate the nanoclay using high shear-rate mixing with solvents or polymers. Following is a quote from Southern Clay Products Company's website explaining the utility of these materials: "Cloisite® additives consist of organically modified nanometer scale, layered magnesium aluminum silicate platelets. The silicate platelets that Cloisite® additives are derived from are 1 nanometer thick and 70 - 150 nanometers across. The platelets are surface modified with an organic chemistry to allow complete dispersion into and provide miscibility with the thermoplastic systems for which they were designed to improve. Cloisite® additives have been proven to reinforce thermoplastics by enhancing flexural and tensile modulus while lowering

CLTE. Cloisite® additives have also been proven to be effective at improving gas barrier properties of thermoplastic systems. The surface char formation and flame retardance of thermoplastic systems have also been improved by incorporating Cloisite® nanoparticles

into the structure. There are some unique application areas where Cloisite® additives have been proven to improve the physical properties of the plastic products. Cloisite® additives have been shown to improve the properties of injection molded pieces for the automotive industry, of flexible and rigid packaging such as films, bottles, trays, and blister packs, and also of electronics plastics such as wire and cable coatings."

It has proved difficult, however, to actually exfoliate these nanoclays in elastomers. Ordinary rubber mixing equipment does not achieve the desired results; part of the explanation is that the shear rates imposed by conventional rubber mixing equipment are too low. For example the maximum shear rate imposed by a Banbury or Shaw Intermix mixer is less than 300 radians/second.. The prior art method to achieve exfoliation is with a twin-screw extruder, which applies maximum shear rates around 2000 radians/second or less. More typically the shear rate imposed by extruders used for mixing polymeric compounds is 1000 radians/second or less.

The Drais Gelimat Compounder is an ultra high speed thermokinetic mixing, fluxing and compounding system for processing of both virgin and recycled polymers, as well as highly loaded compounds and masterbatches. A similar device is the K-Mixer, which was produced for many years by Synergistics Industries Ltd of Saint-Remy, Quebec (Canada); there are still many K-Mixers in service. "TK mixer" is used herein to describe any such thermokinetic mixer. The high rotational shaft speed of TK mixers provides an extremely efficient and super fast processing cycle for polymer compounds. Examples of usage of TK mixers include use for highly filled mica/polypropylene compounds (US patent 4442243), pigment dispersions (US patent 4759801), lignocellulosic fibers/plastic compounds (US patent 6133348), and silicone rubber compounds (US patent 6913380). Another major application of the TK mixer is in mixing and heating materials rapidly to a uniform discharge temperature. For example, see US patents 4272474 on molding UHMW polyethylene, 4420449 on molding PTFE, 4407987 on molding PVC powders, and 4489587 on surface grafting to polymeric powders. Both the shearing and uniform heating effects of the TK mixer are important in the preparation of the flax/polyolefm composites of US Patent 6133348. TK mixers have not been reported to have been used in the prior art to prepare dispersions of polyaramid or other small diameter chopped synthetic fibers. TK mixers have also not been used in the exfoliation of nanoclays in polymer matrices.

US patent 4442243 describes exfoliation and grinding of mica in a TK mixer

during mixing with polypropylene. Reportedly, the degree of grinding and exfoliation of mica achieved during polymer mixing in the TK mixer is similar to that which occurs in wet grinding of mica. If so, this implies that mica is not exfoliated down to the level of individual platelets, because wet grinding does not take mica down to individual platelets.

US patent 4759801 describes simultaneous mixing and drying of wet pigment filter cake in the TK mixer. Note that in this case the water is present merely because it saves a process step to simultaneously dry and disperse the pigment into a polymer (the pigment is manufactured in water); water is not being deliberately added to the mixer to control temperature or to extend the mixing time for better dispersion.

SUMMARY OF THE INVENTION

Polyaramid short fibers and pulp, carbon nanotubes, and various other short man- made fibers can be efficiently dispersed in many different neat polymers, ranging from elastomers to thermoplastics. The dispersion can be accomplished with a thermokinetic ("TK") mixer such as the Gelimat from Draiswerke, Inc., Mahwah, NJ. The main features of this type of mixer that make it work for dispersing such short man-made fibers and pulp and carbon nanotubes is believed to be the large number of mixer rotations during a typical mix cycle, and the high shear rate and shear stress that is applied to the material during mixing. Another factor that is significant especially for low bulk density fibers such as polyaramid pulp is that only around 7-15% of the available volume in a TK mixer is filled with the polymer/fiber composition once the composition is well-mixed (i.e., the "fill factor" is only 7-15%, compared to typically 70-85% for a Banbury or Shaw Intermix mixer for example); the large available free volume inside the TK mixer makes it possible to load in a large quantity of low bulk density fiber before the mixer is taken up to mixing speed. This is a substantial advantage compared to a Banbury or Shaw Intermix internal mixer, because the fiber can be added all at once to the TK mixer whereas in a Banbury for example, it must be added several times to avoid overfilling the mixer. The fill factor in the TK mixer depends very importantly on the gap between the mixer blade and the wall, which is also the parameter that most effects the shear rate during mixing. If the gap is half as wide, the shear rate is twice as high (shear rate = rate of blade tip motion/shear gap). The fill factor for effective mixing also goes down as the gap narrows, but not in direct proportion, as does the shear rate. Thus,

optimization of a TK mixer for a particular dispersion problem may require optimizing the gap between blade tip and the wall of the mixer to give the highest fill factor consistent with producing good dispersion or exfoliation of the product.

Other mixing devices could potentially work in the same way, provided they expose the polymer/fiber blend to a similar large number of at least about 400 mixer rotations (as is the case for multiple pass mixing on many different kinds of equipment), and shear rate of at least about 2000 radians/second that is applied many times to each element of the polymer/fiber mixture. Other than the TK mixer, the other places where polymeric compounds are routinely exposed to shear rates above 2000 radians per second are in injection molding (when compound passes through narrow gates), and in some extrusion dies. However, these prior art processes are not generally applied to improving dispersion of polymer compounds. Also, these prior art methods that apply shear rates above 2000 radians per second are generally incapable of mixing polymer with fiber or fillers. Also, platy layered silicate minerals ("nanoclay") such as chemically treated montmorillonite clay (for example the Cloisite™ products from Southern Clay Products, Inc., Austin, TX) can be effectively exfoliated in a thermokinetic mixer. In this case, it is believed to be the unusually high shear stress and shear rate (typically about 3,000- 12,000 radians/second, depending mainly on the gap between the blade tips and the mixer wall) that leads to efficient exfoliation of the nanoclays.

Further, the addition of water to the mixture in a thermokinetic mixer provides benefits in those cases where water does not hydrolyze or damage the polymers being mixed. The thermokinetic mixing process is so intense in terms of mechanical energy input rate per volume of polymer composite being mixed that conventional cooling through the wall of the mixer is not effective. It has been found that addition of water directly into the mix chamber in a controlled way can provide effective cooling. Ideally, the system used to inject water for evaporative cooling should interface with the motor controller (which provides frequent updates on power consumption) and the infrared temperature probe in such a way that water injection is actively controlled to maintain temperature control. One advantage of water injection is that the mix cycle can be extended to provide additional high shear mixing without overheating or degrading the polymer or fiber. Another advantage that is seen specifically for the case of exfoliating nanoclays is that the added water appears to directly aid the process of exfoliation. A

third advantage which may be relevant in some particular cases is that during the evaporation of the steam from the mix chamber, residual monomers and other low molecular weight contaminants in the polymer are also removed by "steam distillation." When water cooling is used, it is important that steam generation should not commence until loose powders and fibers are sufficiently incorporated into the polymer that they will not be carried out of the mixer with the high velocity steam that exits the TK mixer through the steam port (which in the factory TK mixer used for many of the examples is a half inch pipe that vents one end of the TK mixer)

The invention features a process of using a thermokinetic mixer to form dispersions of fine denier (fiber diameter less than about 20 microns) chopped synthetic fibers with elastomers or other flowable polymers under conditions such that at least about 400 machine rotations occur during the mix cycle, and a shear rate of at least about 2000 radians/second is applied to the material being mixed.

The invention also features a composition of matter containing both man-made fibers with fiber diameter less than about 20 microns and a flowable polymer matrix phase prepared in a TK mixer. In one embodiment of the invention, polyaramid pulp, which is very difficult to disperse normally, is dispersed into a variety of different polymer systems, which can be accomplished with a thermokinetic mixer operated under conditions such that at least about 400 machine rotations occur during the mix cycle, and a shear rate of at least about 2000 radians/second is applied to the material being mixed. These novel dispersions can then be let down (blended) into additional polymer in conventional polymer mixing equipment such as internal mixers and extruders.

Another embodiment of the invention contemplates dispersions of exfoliated nanoclay with elastomers or other flowable polymers. These can be made using a thermokinetic mixer to exfoliate the nanoclay, which may be ion-exchanged montmorillonite clay, such as the Cloisite™ products from Southern Clay Products Company. The exfoliation can take place under conditions such that at least about 400 machine rotations occur during the mix cycle, and a shear rate of at least about 2000 radians/second is applied to the polymer and nanoclay materials being mixed.

Definitions for certain terms used herein:

"Polyaramid" refers to any synthetic polymeric fiber containing amide linkages in the main chain in which both the dicarboxylic acid and the diamine used to form the

linkage were aromatic monomers. Specific examples include Kevlar™ and Nomex™ from DuPont, Twaron™ from Teijin Twaron USA Inc., and Kermel™ polyaramid/polyimide fiber from the Kermel Company of France.

"FKM" means an elastomeric copolymer of vinylidene fluoride and at least 25% hexafiuoropropene, optionally containing up to 60% by weight of other fluorinated comonomers such as tetrafluoroethylene and various perfluoroalkyl vinyl ethers. "MEK" means methylethylketone, a common solvent

"Pulp" refers to a multifilamentous fiber material with complex interconnections among the individual fiber strands, in which the individual strands are on the order of 0.1-10 microns across. Natural fiber pulps are well known from the paper industry.

Synthetic fiber pulps are generally produced by hammer-milling or similar impact milling applied to cut fibers of certain liquid crystalline polymers (especially para-aramid fiber and other liquid crystalline polymers such as PEEK (polyetheretherketone), Vectran™ and PBO fiber (Zylon™ p-phenlyline-2, 6-benzobisoxazole), or to wet processing during fiber formation, as in the polyacrylonitrile (PAN) fiber pulps from Sterling Fibers, Inc.

"Carbon nanotubes" are very small diameter fibers composed primarily of carbon atoms arranged in curved graphitic layers. Carbon nanotubes can be either single layer or multilayer; that is, the hollow tube wall can consist of only one curved graphitic sheet, or several curved graphitic sheets which are nested together. "Nanoclay" means any clay mineral that has previously been intercalated with organic molecules that separate the clay layers somewhat compared to naturally occurring clays. The major commercially available examples of organically intercalated clays at present are various grades of Cloisite™ treated momtmorillonite clays from Southern Clay Products, but various other platy minerals can also in principle be organically intercalated and subsequently exfoliated, such as hectorite, saponite, stevensite, beidelite, or a double-layered metal hydroxide. Various types of nanoclays are described in US Patent 6849680, which is incorporated herein by reference.

"Thermoplastic polymer" means a polymer that in normal usage is a solid, either crystalline or glassy or both, but which is normally processed in a molten state, above both its glass transition temperature and its melting point

"Elastomer" is a processable polymer with glass transition temperature below room temperature, which is crosslinked after shaping via chemical crosslinking reactions "Flowable polymer" means either a thermoplastic polymer above its melting and

glass temperatures, or an uncrosslinked elastomer.

"Engineering thermoplastic" refers to any thermoplastic that retains useful mechanical properties above 150° C.

"Thermoplastic fluoropolymer" refers to any conventionally extrudable and injection moldable thermoplastic polymer containing more than 33% fluorine.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows stress-strain curves for four green (uncured) nanoclay/NBR compounds, two of which were made according to the invention; Figures 2 and 3 are electron micrographs at different magnifications of Cloisite

30B/NBR made by the process of the invention; and

Figure 4 shows tensile properties of three of the compounds of Fig. 1 after crosslinking (vulcanization).

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The special characteristics of the thermokinetic mixer make possible various well-dispersed composites of polyaramid pulp with polymers. For composites of polyaramid pulp in elastomers, the techniques of the present invention reduce the cost of preparing these composites versus prior art methods involving water-based or solvent- based mixing techniques. Also, mixtures of engineering thermoplastics with polyaramid pulp will benefit by the invention, hi particular, engineering thermoplastics such as polyphenylene sulfide (PPS), which are particularly brittle, stand much to gain from reinforcement with polyaramid pulp rather than the traditional glass fibers. The thermokinetic mixer is also useful for preparing mixtures of fine-denier chopped synthetic fibers with elastomers. In one particular case, it was found that 6 millimeter long chopped Twaron™ fiber (1.5 denier) could be well dispersed in EPDM, NBR, or CR in less than a minute; dispersing the same fiber using a rubber mill took more than an hour of milling time. The thermokinetic mixer has also proved to be effective at exfoliating nanoclay in polymers. We have dispersed and partially exfoliated organo-functionalized montorillonite clay in numerous different elastomers.

We have also found that water can be directly added to the TK mixer to maintain

temperature control, and in some cases the water enhances mixing, dispersion, and/or exfoliation. Water cooling via the water jacket is not effective because of the high intensity of mixing; there simply is not enough time to conduct much of the heat generated in the TK mixer away in the short time of mixing at near peak power consumption, especially in the larger mixers. Water that is directly injected, or added with the batch, is more effective than water that moves through cooling channels in the mixer wall at removing heat. Extending the mix time by adding water that boils off during mixing in this manner is preferable to remixing the batch, since mixing twice extends the total time the mixer is occupied. It is possible to calculate how much additional mixing time that a material can stay in the TK mixer prior to reaching its dump temperature when water is added using the following data from standard "steam tables" found in many engineering texts:

28.06 Enthalpy of liquid water at 60 degrees F (BTU/lb)

1150.5 Enthalpy of saturated steam at 212F (BTU/lb.)

1122.4 Enthalpy change/pound of water boiled

3794 BTU/kw-hr

1065 kilowatt-seconds (kilojoules)/lb water boiled off

17.75 kilowatt-minutes/lb water boiled off

hi the case of the 200 horsepower factory TK mixer (described below in Example

1), maximum power draw was about 150 kilowatts; during this peak mixing time, adding one pound of water to the batch which is converted completely to steam removes all the heat of mixing for about 8 seconds (depending somewhat on motor efficiency), thus extending mixing by about 8 seconds. In the smaller 30 horsepower lab TK mixer, one pound of water extends mix time at peak power by about 56 seconds. We have found that in some cases, adding water at the outset of mixing is appropriate (for example in the case of course NBR granulate mixing with Cloisite 30B), whereas when using pelletized EPDM plus either polyaramid pulp or nanoclay, adding water at the outset interferes with initial incorporation of the fiber or clay into the polymer. On the other hand, if water is added after the powder or fiber is incorporated into the polymer, it does not seem to slow down the dispersion process.

Examples of the Invention

The formulations for the first examples of this invention are shown in Tables 1 and 2. These are mixtures of nanoclay with NBR elastomer. Table 1 shows the masterbatch recipe (first stage mix), where most of the intensive mixing occurred. The masterbatch recipe of Table 1 was used to prepare four separate Examples (1 to 4) using an open roll rubber lab mill (Example 1), a Brabender mixer (Example 2), and a factory scale TK mixer in both dry mix mode (Example 3), and wet mix mode (Example 4). Table 2 gives the formulations for the final stage thermosetting compounds (Examples 5 to 7).

Table 1 : Non-Curing Masterbatch Formulations Used in Examples 1 to 4

Table 2: Final Stage Compounds (Examples 5 to 7))

(Nipol 1401 LG is from Zeon Chemicals L.P., Louisville, KY; Naugard 445 is from Chemtura Corporation, Middlcbury, CT; Cloisite 30B is from Southern Clay Products Inc,; TAIC DLC-A is from Natrochem Inc., Savannah, GA; DBPH-50 is from R.T. Vanderbilt Company, Inc., Norwalk, CT)

Preparation of masterbatches: The open roll mill mixing of comparative Example 1 occurred on a laboratory two-roll mill, without cooling. The mill rolls were pre-heated to about 40° C by milling a warm-up compound before beginning the lab mix procedure. The mixing took about 15 minutes total, including about eight minutes to thoroughly

incorporate the nanoclay. After the mixture was no longer dusty, it was passed through the mill endwise twelve times. At the end of the mixing cycle, the stock temperature was approximately 70° C.

Mixing of comparative Example 2 occurred in a Brabender Prep Center Mixer with a 68% fill factor, using Banbury mixing blades. The mixer was loaded with previously mill mixed Example 1, starting from room temperature, and was operated without cooling at 50 RPM for 8 minutes after the mixer was loaded. During mixing the maximum stock temperature was approximately 110° C. After mixing in the internal mixer, Example 2 was banded on the rubber mill and sheeted off. Mixing of Examples 3 and 4 of the invention occurred in our factory scale TK mixer. This mixer is a Gelimat G-80 mixer from Draiswerke made in 1964, but modified to serve as a pilot production-scale TK production machine. The basic dimensions of the mix chamber and shaft are as follows: chamber diameter 18 inches, length 19.25 inches, rotor shaft diameter 6 inches. The free volume inside the mixer is about 68 liters, and a typical fill factor for the mixer is from 7-10%. The rotor blades are arranged in two opposed rows of four blades, arranged in a helical pattern. Clearance between the blade tips and the wall is about 0.1875 inches, which implies a shear rate in the gap between the blade tips and the wall of about 5025 radians/second at 1000 RPM. Most of our modifications have to do with how the TK mixer is loaded and unloaded, and are not relevant to the present discussion. One particular modification we made is relevant: we installed a modern variable frequency control drive that gave us the ability both to vary the speed from 50-1150 RPM, and to monitor and totalize energy input to the batch during mixing. We did not connect the water cooling to the body of the TK mixer; it was operated adiabatically or nearly so during dry mixing. During wet mixing, the process was nearly adiabatic except for the vaporization of the water, which escaped through a steam vent. Our machine did not have the ability to routinely drop the batch on the basis of batch temperature from an IR probe, as in modern Gelimat TK mixers (see US patent 4332479), so we used energy totalization (as is often used in controlling other types of internal mixers, such as Banbury mixers) to trigger automatic opening of the discharge door.

Example 3 was loaded into the factory TK mixer at low rotation speed (60 RPM), then the mixer was closed and mixed at 1000-1100 RPM until the target mixing energy was attained; at that time the outlet door opened automatically. Our target drop

temperature was 185° C, and batches that came out above 200° C were scrapped. After being flung out of the mixer, the batch was rapidly cooled on an 80 inch factory open roll rubber mill (this was true for Example 4 as well). At steady state were able to dry mix a 15.4 pound batch (which when fully consolidated and dispersed occupies around 8.5% of the available volume inside the mix chamber) of Example 3 in about 40 seconds after the RPM was increased to 1000 RPM, during which time we input 60 kilowatt-minutes of power, and the machine rotated 666 times. This corresponds to an average heat capacity for the polymer/clay system of 0.65 joule/g-degree C, a realistic value that we did not test via laboratory methods such as DSC. We mixed approximately 30 batches of Example 3 in the factory TK mixer. Several samples were evaluated for green strength, and the particular sample upon which we report data herein was close to the median of all these samples.

We also experimented with adding 1.7 pounds of water to each batch to extend mix time. Example 4 contained 15.4 pounds of the first stage mix of Table 1, but also had 1.7 pounds of added water in each batch in the factory TK mixer. Mixing energy at equivalent drop temperature increased to 90 Kw-minutes, which extended the mix time by about 12-15 seconds. This is consistent with theoretical calculations, since 1.7 pounds of water should take 30 Kw-minutes to boil at atmospheric pressure. The wet mixed NBR/nanoclay prepared in this way was Example 4. We mixed approximately 30 batches of Example 4 in the factory TK mixer. Several samples were evaluated for green strength, and the particular sample upon which we report data herein was close to the median of all these samples.

For the particular dimensions of the factory TK mixer we used for Examples 3 and 4, the following table gives the shear rate as a function of shear gap at 1000 RPM. radians/second αap, mm αao, inch

47878 0.5 0.020

23939 1 0.039

11969 2 0.079

7980 3 0.118

5985 4 0.157

4788 5 0.197

3990 6 0.236

3420 7 0.276

2992 8 0.315

This table covers a range of shear gaps from 0.5 to 8 millimeters; the actual gap in our machine is about 4.75 millimeters, which implies a shear rate of about 5025 radians/second. We have observed that it is difficult to control the factory TK mixer when the gap is less than about 2 millimeters. Therefore, the preferred range of shear rates for the processes of the present invention is between around 2000 to 3000 radians per second at the low end, to around 12,000 or just more than that radians per second at the high end.

The green strengths of Examples 1 to 4 were evaluated on open-roll milled samples that were banded on a 6x13 inch rubber lab mill, and then cut off as sheets. The rubber lab milled sheets of Examples 1, 2 and 3 were also used for making crosslinked rubber formulations (Examples 5, 6, and 7), which were made via the recipe of Table 2 by mill mixing the masterbatches (Examples 1, 2, or 3, respectively) with curatives in the rubber mill.. These thermosetting second stage compounds were all prepared on the mill in much the same way as reported above for Example 1, though the incorporation of the TAIC and peroxide occurred more quickly than the incorporation of the nanoclay into Example 1. Examples 5, 6, and 7 were cured for 15 minutes @ 180° C underpressure, using an 8cm x 8cm x 1.5 mm window mold with chromed steel plates; these plaques were used for tensile experiments.

Both the green strength measurements and the tensile properties were measured on 7 mm wide strips of material (either cured or uncured) cut from rubber sheets. For the cured compounds, the samples were cut from approximately 1.5 millimeter thick slabs that were molded in a release-coating treated mold for 15 minutes at 180° C. The uncured samples were sheeted off the mill at approximately 2 mm thickness, and then let sit over night before cutting 7 mm width strips from smooth regions of the milled sheet. Figure 1 is a stress-strain curve of green strength measurements on the Examples 1-4 uncured nanoclay/NBR samples.

The green strength measurements show that an elongational type of deformation appears to clearly distinguish the extent of exfoliation in the samples. Note that the green strength of the TK mixer samples (Examples 3 and 4) is much higher than the green strength of conventionally mixed samples (Examples 1 and 2). Also, Example 4 (wet mixed) shows more exfoliation than Example 3 (dry mixed).

Figures 2 and 3 are electron microscope pictures of Example 3. Figure 2 shows that most of the initial large clay particles (>2 microns) have been broken down in the

TK mixer, and Figure 3 shows that at least some of the nanoclay has been exfoliated into quite thin sheets that are flexible (there are bent sheets in the micrograph about the thickness of a single clay platelet).

The stress-strain properties of the crosslinked compounds (Examples 5, 6, and 7; all mixed according to the formulation of Table 2) derived from the NBR/nanoclay masterbatches rank in the same order as the green strength measurements, but the differences are not as pronounced. Data is presented in Figure 4. Example 5 is based on masterbatch Example 1, which was mill mixed; Example 6 is based on masterbatch Example 2, which was mixed in the Brabender mixer; Example 7 is based on masterbatch Example 3, which was mixed in the TK mixer.

Examples 8-14 compare polyaramid pulp dispersions in ethylene/vinylacetate (EVA) polymer prepared in a conventional internal mixer versus the TK mixer. The particular grade of EVA we used (Elvax™ 265) is partially crystalline, and melts at 75° C; this material is very common in crosslinked wire and cable jacketing applications, which are evaluated in comparing Examples 12, 13, and 14. Elvax™ 265 is also a thermoplastic polymer, so evaluating the reinforcing properties of para-polyaramid pulp in a thermoplastic as a function of mixing method can also be accomplished by comparing Example 8 with comparative Examples 9 and 10 (prepared in a Brabender mixer). We have prepared numerous dispersions of polyaramid short fiber and pulp in various elastomers. In general, the results obtained are similar to those for Elvax™ 265. In most applications of para-polyaramid pulp in elastomers, the usage level is around 2-6 phr; in Examples 12-14 we evaluate the various dispersions (Examples 8, 9, 10) in such a way that the final compound has 5.0 phr of para-polyaramid pulp. Example 8 is a dispersion of the present invention. This dispersion was formed in a one liter lab TK mixer (Gelimat S-Series, Model G-I), using a batch factor of 0.92 (corresponding to a compound volume of 87 ml, about a 9% fill factor by volume of the mixer). This mixer has a feed screw, which is not appropriate for feeding fibers according to our experience. Because of this, we loaded the lab TK mixer by removing the faceplate on the main body of the mixer, putting in the entire weighed batch, and reattaching the faceplate with 6 machine screws prior to turning on the lab TK mixer. We followed this procedure for all lab TK mixer batches reported herein. Energy totalization is not available on this mixer, which has a variable speed DC motor drive. It is equipped

with an IR probe which theoretically can trigger the opening of the exit door at a preset temperature, but this has not proved to be reliable in our fiber composite experiments. The machine also has a gage that shows "% of maximum torque." In general, preliminary experiments not reported here in detail were performed to determine the optimum batch size so that the TK mixer achieves a maximum torque close to 100% of its rated capacity at full speed (3500 RPM).

Example 8 used 5 ml of injected water for cooling. This water was injected at 3000 RPM just as the torque was rising to its maximum value. This is only enough water to cool the lab TK mixer for about 0.6 seconds at maximum power consumption of about 21 kilowatts, but it served to demonstrate the feasibility of injecting water directly into a TK mixer spinning at full speed. The water was injected into the feed screw with a syringe and was effectively conveyed into the lab TK mixer via impingement on the rotating feed screw blades. The steam exited the lab TK mixer via the feed screws.

Example 8 was mixed about 7 seconds beyond the observed maximum torque, and came out of the mixer at about 240° C. Maximum torque was observed about 15 seconds after the speed was increased to 3500 RPM, so that the total time the lab TK mixer was mixing at 3500 RPM was about 22 seconds, which corresponds to 1280 machine rotations. Comparative Examples 9 and 10 were prepared in a Brabender Prep Center mixer with Banbury Blades; the starting temperature of the mixer was 75° C. The batch factor for Examples 9 and 10 was 2.7, corresponding to a 68% fill factor in the Brabender mix chamber. Example 9 was mixed for 10 minutes after the pulp was fully incorporated, at 75 RPM. Example 10 was mixed for 20 minutes after the pulp was fully incorporated, at 75 RPM. The final temperature for Examples 9 and 10 was 110-120° C. A direct comparison of the EVA/para-polyaramid pulp thermoplastic compound of this invention (Example 8) with the two EVA/para-polyaramid pulp thermoplastic compounds prepared in the Brabender (Example 9) was made by pressing sheets of these materials, then testing tensile properties. Although this sort of an EVA/para-polyaramid compound is not used in commerce, it is a valid means to show that the process of this invention leads to superior para-polyaramid dispersions in a common thermoplastic. These are the results of the testing of these EVA/para-polyaramid compositions:

Calculated Specific Gravity: 1.062 1.062

Average Tensile Strength,

Mpa 25.19 21.85

Average Tensile Elongation: 10.79% 9.53%

Stress at 10% elongation 25.66 25.92

These results to show improved properties for the EVA/para-polyaramid Example 8 over the Brabender-mixed Example 9.

Example 11 is used in the preparation of the final mill blend Examples 12 to 14, and was made in the Brabender Prep Center mixer, then sheeted out on the lab rubber mill. Examples 12 to 14 were prepared in the small Brabender mix head with roller blades, with a 68% fill factor (total available volume in the mixer = 60 ml), with initial temperature 70° C 5 and final temperature below 100° C.

Table 3: Para-Polyaramid Pulp Dispersions in EVA

Example Number

(Elvax 265 is a 28% vinylacetate EVA copolymer, and Kevlar™ 1F543 NGP Pulp is a fibrillated chopped para-polyaramid fiber from DuPont Corporation, Wilmington, DE; TAIC DLC-A is from Natrochem Inc., Savannah, GA; DBPH-50 is from R.T. Vanderbilt Company, Inc., Norwalk, CT)

Table 4 gives results for tensile properties of Example 12 and comparative Examples 13 and 14. These examples are all carbon black reinforced EVA compounds with 5 phr of polyaramid pulp. Example 12, which uses the TK mixer-produced para- polyaramid pulp dispersion (Example 8), has significantly higher tensile strength and elongation than either Example 13 or 14, which are based on Brabender-mixed para- polyaramid pulp dispersions. (Example 9, mixed for ten minutes in the Brabender, goes into comparative Example 13, and Example 10, mixed for 20 minutes in the Brabender, goes into comparative Example 14). The tensile strength and elongation to break for Example 12 are both significantly higher than for the controls, Examples 13 and 14. The last line of Table 4 is the product of (tensile strength) (elongation), which is an estimate of energy to break or toughness; when comparing Example 12 to control Examples 13 and 14 in this way, the toughness of Example 12 is nearly twice as high as the controls (Examples 13, 14).

Table 4: Tensile Properties of EVA Compounds Containing 5 phr of Polyaramid Pulp

Examples 15-18 compare carbon nanotube dispersions prepared in a conventional internal mixer versus the TK mixer. The initial dispersions (Examples 15, 16) were prepared at a 10% concentration. Table 5 shows these FKM/nanotubes dispersion recipes that were formed by two different methods. The carbon nanotube type used in these experiments is a multiwalled tube which is produced by a catalyzed growth process involving metallic particulate catalysts (US patent 7,125,534); in the final product, the catalyst particles remain; however the Nanocyl-7000 contains at most 10% metallic catalyst particles. We used a milled grade (hammer milled) supplied by Nanocyl.

Table 5: Carbon Nanotube Dispersions in FKM Elastomer

(Dai-El G902 is an FKM terpolymer from Daikin America, Inc. of Orangeburg, NY; Nanocyl-7000 is a multiwalled carbon nanotube from Nanocyl, S.A. of Sambreville, Netherlands; TAIC DLC-A is from Natrochem Inc., Savannah, GA; DBPH-50 is from R.T. Vanderbilt Company, Inc., Norwalk, CT)

Theoretically, the TK mixer could either improve the properties of a carbon nanotube by improving dispersion, or reduce properties by breaking the fibrils. To avoid fiber breakage, the loose carbon nanotubes were milled into the FKM rubber first, and then the milled sheet containing the carbon nanotubes was placed into the TK lab mixer to improve the dispersion of the polymer/nanotubes mixture. A significant increase in the difficulty of cutting the 10% Nanocyl/FKM mixture was noted after the milled sheet used to make Example 16 had gone through the TK mixer. A modest improvement in tensile properties was noted as a result of mixing in the TK mixer, as shown in Table 5. Example 19 and comparative Example 20 compare mixtures of para-polyaramid pulp with a fluoroplastic, THV-200G from Dyneon, LLC. This is a partially crystalline copolymer of tetrafluoroethylene, hexafluoropropene, and vinylidene fluoride with a melting point around 120° Celsius. Para-polyaramid pulp is rarely used in thermoplastics

of any kind because it has proved extremely difficult to wet the submicron fibrils and to disperse them in plastics using conventional mixing equipment such as twin screw extruders. Para-polyaramid short fibers also have not been found to reinforce plastics, probably because of a lack of bonding to the thermoplastic matrix, but they are used in some plastic bushings to increase wear and/or reduce friction. Theoretically, a para- polyaramid pulp could reinforce plastics if it is sufficiently dispersed so that individual fibrils in the pulp have been wetted by the matrix polymer.

Table 6 gives the recipes and simple tensile results on hot-pressed plaques. There were obvious differences in the mix quality that could be seen readily on the plaque surface. The Brabender-mixed plaque (Example 20) had visible inclusions of undispersed para-polyaramid pulp, whereas the TK mixed Example 19 was very smooth and uniform in its surface appearance.

Table 6: Mixtures of Synthetic Fibers with a Thermoplastic Fluoropolymer

Example number: Mixer used: INGREDIENT:

(THV-200G has since been renamed THV-220; it is supplied by Dyneon LLC of Saint Paul, MN; Kevlar pulp and rovings are from DuPont Corporation ofWilmington, DE; Kuralon polyvinyl alcohol (PVA) is from Kuraray Company, LTD of Tokyo, Japan; this sample was chopped to 6 mm fiber length by Engineered Fibers Technology, LLC of Shelton, CT.)

Although specific features of the invention are shown in some figures and not others, this is for convenience only, as some features may be combined with any or all of the other features in accordance with the invention.

Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless

otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein.

The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illustrate the invention and does not pose a limitation on the scope of the invention.

A variety of modifications to the embodiments described herein will be apparent to those skilled in the art from the disclosure provided herein. Thus, the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. What is claimed is: