WO2008046047A1

WO2008046047A1 - Low power heating elements using exothermic polyphenylene sulfide compounds

Info

Publication number: WO2008046047A1
Application number: PCT/US2007/081242
Authority: WO
Inventors: Maziyar Bolourchi
Original assignee: Polyone Corp
Current assignee: Avient Corp
Priority date: 2006-10-13
Filing date: 2007-10-12
Publication date: 2008-04-17
Anticipated expiration: 2009-04-13

Abstract

Heating elements are disclosed, made with an exothermic additive in a polyphenylene sulfide compound. The heating elements are highly efficient and use a small amount of power to generate temperatures ranging from about 30°C to about 250°C. The heating elements can be used in any electrical appliance for industrial or consumer use.

Description

LOW POWER HEATING ELEMENTS USING EXOTHERMIC

POLYPHENYLENE SULFIDE COMPOUNDS

CLAIM OF PRIORITY

[0001] This application claims priority from U.S. Provisional Patent

Application Serial Number 60/829,505 bearing Attorney Docket Number 12006020 and filed on October 13, 2006, which is incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention concerns the use of polyphenylene sulfide compositions as high efficiency heating elements.

BACKGROUND OF THE INVENTION

[0003] All consumer devices are or should be concerned with power management and energy consumption. Efficient use of energy, whether powered by fossil fuels or alternative energy sources, is or ought to be a goal of all product development.

[0004] Thermoplastic polymers have many advantages in material science, as compared with metals: relatively low cost, relative ease of manufacturing to final form, lack of oxidation which leads to corrosion. Heating elements such as metal rods or plates are commonly used to provide resistive heating, whether within an oven or as a cooking surfaces. [0005] U.S. Pat. No. 6,086,791 (Miller) discloses coatings and films of a non-metallic electrically conductive coating composition effective in emitting heat without break-down when connected to a source of electricity, which comprises: (a) a binder; (b) electrically conductive flake carbon black of particle size between about 5 and 500 micrometers; (c) electrically conductive flake graphite of particle size between about 5 and 500 micrometers; (d) a volatile solvent; wherein the weight amount of (b) and (c) together ranges from between about 10 and 75 weight percent based on the non-volatile solids content of the coating composition. U.S. Pat. No. 6,818,156 (Miller) also discloses coating and films using carbon-based materials having particle sizes in the nanometric and micrometric range for emitting heat.

[0006] U.S. Patent Application Publication 2005/0070658 (Ghosh et al.) discloses electrically conductive compositions that contain a greater amount of graphite than nanosized conductive filler or carbon fibers, between 6 and 80 times as much.

SUMMARY OF THE INVENTION

[0007] Unfortunately, films and coatings such as those disclosed by

Miller are present only at the surface of an article. Such films and coatings can chip, delaminate, or flake leaving the article untreated.

[0008] Unfortunately, the compounds such as those disclosed by Ghosh et al. utilize far more graphite than nanosized conductive filler, such as carbon black or nanotubes, or carbon fibers. The resistive heating taught by Ghosh et al. must overcome the considerable amount of graphite which is less electrically conductive than carbon black or nanotubes or carbon fibers.

[0009] What the art needs is a new type of heating element for consumer and industrial devices that is highly efficient in its use of energy. In order to provide a new type of heating element, one needs a compound that melts or degrades only at very high temperatures yet is exothermic throughout the bulk of the compound to deliver heat of a desired temperature. Because the compound is exothermic throughout its bulk, there is no possibility of loss of the thermally conductivity because of loss of a treatment on the surface of the component.

[00010] The present invention solves that problem in the art by providing a polypheny! ene sulfide compound that is exothermic throughout its bulk when connected to a source of electrical energy. [00011] Unexpectedly, it has been found that the polyphenylene sulfide compound is very efficient in its use of electrical energy, making it a new type of heating element for consumer and industrial devices. [00012] One aspect of the present invention is a heating element comprising a polymer compound having an energy efficiency of at least about 80 percent, wherein the compound comprises polyphenylene sulfide and an exothermic additive comprising electrically conductive particles and, optionally, less electrically conductive particles, wherein the amount of electrically conductive particles in the compound is same or greater than the amount of less electrically conductive particles, if any are present. f 00013] Another aspect of the present invention is an electrical appliance having a heating element of the polymer compound described above that can operate at plateau temperatures ranging from about 30⁰C to about 250⁰C. An advantage of the present invention is that the heating element can achieve those temperatures efficiently, generally more than about 80% efficiency. [00014] "Heating element" for purposes of the present invention means a component of a device, made from a polymer compound comprising polyphenylene sulfide, that is designed to operate at a temperature greater than ambient temperature to perform work, including without limitation, heating an enclosed space, altering chemical or physical properties of a substance, cooking food, etc.

[00015] "Exothermic additive" for purposes of this invention means one type of electrically conductive particles or a combination of that type of electrically conductive particles and less electrically conductive particles that can be engineered to provide a specific temperature when the polyphenylene sulfide compound is formed into a heating element and is powered by electricity. For clarity, the less electrically conductive particles comprise graphite. [00016] "Plateau temperature" means the temperature after resistive heating in which the compound reaches a steady state of heat dissipation vs. power consumption while functioning in ambient conditions.

[00017] Because the melting or other degradation point of polyphenylene sulfide is higher than the temperature desired for the components of the electronic device, it is possible to engineer any specific temperature of heat emitted from a thermoplastic article of the present invention.

[00018] For purposes of this invention, power consumption, as a first approximation, will be described as Watts, also known as Joules/second. It is true that with alternating current, a power factor may be needed to convert volt*amps to Watts. However, using the equipment to conduct the experiments of this invention and report the results, the alternating current in volt*amps does approximate Watts because the power factor has been addressed.

[00019] Advantages of the invention are explained with reference to the following embodiments with reference to the following drawings.

[00020] BRIEF DESCRIPTION OF DRAWING

[00021] Fig. 1 is an image showing a heating element of the present invention before a raw egg is placed on its surface, wherein the heating element is electrified to be at a temperature of 121°C.

[00022] Fig 2. is an image captured from a video at time zero (To), showing the raw egg being placed on the surface of the heating element.

[00023] Fig 3. is an image captured from a video at To plus thirty seconds

(T_{30 sees.}) showing the raw egg as it cooks on the surface of the heating element.

[00024] Fig 4. is an image captured from a video at To plus one hundred fifty seconds (T 150 sees. ) showing the raw egg as it cooks on the surface of the heating element.

[00025] Fig 5. is an image captured from a video at To plus two hundred ten seconds (T₂₁0 sees.) showing the fully cooked fried egg on the surface of the heating element. EMBODIMENTS OF THE INVENTION [00026] Polvphenylene Sulfides

[00027] Polyphenylene sulfides are polymers containing a phenyl moiety and one or more sulfides bonded thereto. Those skilled in the art will recognize the variety of commercially available polyphenylene sulfides are suitable for use in the present invention. Non-limiting examples of such commercially available polyphenylene sulfides ("PPS") include Ryton brand PPS powders in various grades from Chevron Phillips Chemical Co. of The Woodlands, Texas. Any of the patents in the literature known to those skilled in the art are appropriate for determining a suitable choice, without undue experimentation. [00028] Exothermic Additive

[00029] In one embodiment, the exothermic additive for the present invention can be a single form of carbon, preferably carbon black or substitutes for carbon black. In this embodiment, no graphite is needed or desired. [00030] An acceptable commercially available carbon black is Printex

XE2 super conductive carbon black particles having a particle size of about 35 run, from Degussa of Akron, Ohio, among other locations. Other types of carbon black particles include, without limitation, Corax^®' and Purex^® brand carbon blacks, also from Degussa, Ketjenblack^® brand carbon blacks from Akzo Nobel, Black Pearls^® brand carbon blacks from Cabot Corporation. Useful grades of carbon black as described in RUBBER TECHNOLOGY 59-85 (1995) range from Nl 10 to N990.

[00031] Therefore, average diameter particle size of the carbon black can be any size within the nanometric region, and more particularly from about 15 to about 900 nm. and preferably from about 20 to about 80nm. The aspect ratio of the carbon black can be any range customarily found, preferably ranging from about 1 :1 for spherical particles to about 5:1.

[00032] Rather than carbon black, other electrically conductive carbon particulate materials can be used. Non-limiting examples of substitutes for carbon black include nanotubes (single- walled and multi -walled), nanofibers, and other forms of carbon that have a high aspect ratio and are electrically conductive.

[00033] The cumulative amount of carbon black or its substitute as the exothermic additive can range from about 1 to about 75 weight percent of the total thermoplastic compound, and desirably less than about 18 weight percent, preferably less than about 15 weight percent, and most preferably less than about 10 weight percent. Generally, the greater the concentration of carbon black, the more exothermic the thermoplastic compound at a given amount of applied electrical energy.

{00034] In another embodiment, the exothermic additive can be a combination of two different forms of carbon, preferably a combination of particles of carbon black and particles of graphite. The carbon black is more electrically conductive than graphite. In this embodiment, the amount of carbon black exceeds the amount of graphite, in order to maximize the electrical efficiency of heating elements made from this embodiment.

[00035] When used in combination with carbon black or other electrically conductive carbon particulate material, an acceptable commercially available graphite is No. 2939 Thermally Pur. Flake graphite having a particle size of less than about 20 microns, from Superior Graphite

(www.superiorgraphite.com).

[00036] Both the Printex XE2 carbon black and No. 2939 graphite are disclosed in the Miller patents.

[00037J The size of the two different forms of carbon can be any size within the nanometric or micrometric region. The aspect ratio of the two different forms of carbon can be any range customarily found in the various forms of carbon useful for the present invention, such as almost 1:1 for spherical particles to about 20,000:1 for nanotubes.

[00038] For reasons explained in U.S. Pat. No. 6,086,791 (Miller) and

U.S. Pat. No. 6,818,156 (Miller), the combination of carbon black particles and graphite particles generate heat in a manner that can be engineered to provide a specific temperature resulting from a specific amount of electrical energy applied to a specific forrmilation of the thermoplastic compound. Without undue experimentation and beginning with the disclosures of the Miller patents identified above, one skilled in the art can add an amount of carbon black particles and an amount of graphite particles to produce a compound that is electrically conductive and exothermic when connected to a source of electrical energy.

[00039] A balance of carbon black particles and graphite particles can provide both electrical conductivity via the carbon black particles to transport electrical energy throughout the bulk of the polyphenylene sulfide and while also generating heat because of the less conductive or resistive nature of the graphite particles. Unexpectedly from the disclosures of the Miller patents, the combination of two different forms of carbon can be dispersed into bulk of an article formed from a polyphenylene sulfide compound to provide electrical conductivity and exothermic properties. The Miller patents do not disclose polyphenylene sulfide as a suitable binder for his coatings and films. [00040] The ratio of more conductive: less conductive portions of carbon forms in the exothermic additive can range from about 1.1 :1 to about 3:1. Generally at a constant ratio of more conductive/less conductive carbonaceous particles, the greater the concentration of exothermic additive, the more exothermic the thermoplastic compound at a given amount of applied electrical energy.

[00041] The cumulative amount of exothermic additive can range from about 1 to about 75 weight percent of the total thermoplastic compound. Generally at a constant ratio of more conductive/less conductive carbonaceous particles, the greater the concentration of exothermic additive, the more exothermic the thermoplastic compound at a given amount of applied electrical energy. [00042] Optional Other Polymers

[00043] The compound of the present invention can include additional polymer resins to alter the morphology or rheology of the compound. The other polymers can be compatible with PPS in order to form blends or incompatible with PPS in order to form a continuous/discontinuous two-phase polymeric system.

[00044] Non-limiting examples of other optional polymers include polyolefins, polyamides, polyesters, polyhalo-olefins, and polyurethanes.

Presently preferred among these optional polymers are polyolefins such as polyethylenes, and more preferably high density polyethylenes (HDPE), in order to reduce brittleness of molded parts made from compounds of the present invention.

[00045] The cumulative amount of optional other polymers can range from 0 to about 50 weight percent of the total thermoplastic compound.

[00046] Optional Additives

[00047J The compound of the present invention can include conventional plastics additives in an amount that is sufficient to obtain a desired processing or performance property for the compound. The amount should not be wasteful of the additive nor detrimental to the processing or performance of the compound. Those skilled in the art of thermoplastics compounding, without undue experimentation but with reference to such treatises as Plastics Additives

Database (2004) from Plastics Design Library (www.williamandrew.com), can select from many different types of additives for inclusion into the compounds of the present invention.

[00048] In compounding PPS, other compounding ingredients are desirably incorporated into the PPS to produce compounding formulas. Other compounding ingredients can include fillers, pigments and colorants if desired, processing lubricants, impact modifiers, uv-stabilizers, other processing aids, as well as other additives such as biocides or flame retardants. [00049] Fillers ordinarily are used to reduce cost and gloss and can include conventional calcium carbonates, clay, talc, mica, and diatomaceous earth fillers. Useful pigments and colorants can be organic, but preferably mineral such as titanium dioxide (which also serves as a uv-stabilizer). [00050] Impact modifiers are useful in PPS to increase toughness and can include chlorinated polyethylenes, ABS, acrylic polymers and copolymers, or methacrylic copolymers such as methylmethacrylate-butadiene-styrene (MBS) or olefins functionalized with carboxylic acids anhydrides or epoxides. [00051] Other processing aids for extruding PPS in complex profiles include acrylic or styrene-acrylonitrile copolymers to prevent edge tear in the extrusion of complex profiles or configurations.

[00052] Lubricants can be used to reduce sticking to hot processing metal surfaces and can include polyethylene, paraffin oils, and paraffin waxes in combination with metal stearates. Other lubricants include metal carboxylates, and carboxylic acids.

[00053] The cumulative amount of optional additives can range from 0 to about 40 weight percent of the total thermoplastic compound, depending on the type of additive and desired processing or performance property to be changed from the compound without such additive(s) therein. Without undue experimentation, one skilled in the art can determine the appropriate amounts using statistical techniques such as Design of Experiments. [00054] Processing

[00055] The preparation of compounds of the present invention is uncomplicated to those skilled in the art of thermoplastic compounding. The compound of the present can be made in batch or continuous operations. [00056] Mixing in a continuous process typically occurs in an extruder that is elevated to a temperature that is sufficient to melt the polymer matrix with addition either at the head of the extruder or downstream in the extruder of the solid ingredient additives. Extruder speeds can range from about 50 to about 500 revolutions per minute (rpm), and preferably from about 100 to about 300 rpm. Typically, the output from the extruder is pelletized for later extrusion or molding into polymeric articles.

[00057] Prior to extruding at temperatures sufficient to melt the PPS, the ingredients are physically mixed together using a Henschel mixer. Contrary to the disclosures of the Miller patents which teach grinding the carbon black particles with the graphite particles, the processing of the present invention begins with mixing of carbon black with the PPS followed by addition of the graphite. This order of mixing improves dispersion of both constituents of the exothermic additive within and throughout the bulk of the extruded PPS article.

[00058] Mixing in a batch process typically occurs in a Banbury mixer that is also elevated to a temperature that is sufficient to melt the polymer matrix to permit addition of the solid ingredient additives of any optional additive. The mixing speeds range from 60 to 1000 rpm and temperature of mixing can be ambient. Also, the output from the mixer is chopped into smaller sizes for later extrusion or molding into polymeric articles.

[0Θ059] Compounds can be formed into powder, cubes, or pellets for further extrusion or molding into polymeric heating elements of the present invention.

[00060] Subsequent extrusion or molding techniques are well known to those skilled in the art of thermoplastics polymer engineering. Without undue experimentation but with such references as "Extrusion, The Definitive

Processing Guide and Handbook"; "Handbook of Molded Part Shrinkage and

Warpage'¹; "Specialized Molding Techniques"; "Rotational Molding

Technology"; and "Handbook of Mold, Tool and Die Repair Welding", all published by Plastics Design Library (www.williamandrew.com), one can make articles of any conceivable shape and appearance using compounds of the present invention.

[00061] Heating Elements

[00062] Compounds of the present invention can be formed by extrusion or molding techniques into heating elements to provide a highly efficient source of resistive heating. To appreciate the advantages of the invention, the physics of resistive heating needs to be understood,

[00063] The physics of resistive heating is based on the reality that heat generation rate of an heating element equals power generated less heat dissipated to the environment.

[00064] Therefore, resistive heating can be represented by the following equation (I):

[00065] mC_p(ΔT/Δt) = (V²/R) - U(T_F-T_A) (I)

[00066] where V= voltage applied to the heating element , R= resistance within the heating element, m= the mass of the item to be heated. C_p ^~ heat capacity of the heating element, U- heat transfer coefficient (heat loss) of the heating element, T_A= ambient temperature, and Tp = final or plateau temperature of the heating element.

[00067] The geometry of the heating element influences its plateau temperature and efficiencies including such factors as its various aspect ratios, overall physical dimensions, distance between electrodes, surface area, and the like.

[00068] However, once thermal equilibrium is reached for the heating element, the heat generation rate becomes zero, resulting in the equality of power generated and heat dissipation to the environment, as represented by equation II:

[00069] (V²/R) = U(TF-TA) (II)

[00070] Experimental results allow calculation of U for any given formulation of compounds of the present invention, operating with an established geometry and at a given ambient temperature. Equation II, which expresses a steady state condition, assumes no essential change in ambient temperature either by the heating element or some outside influence.

[00071] Energy efficiency of a heating element of the present invention is determined by experimental results using such techniques as bomb calorimetry, which takes into consideration such factors as mass of water, specific heat of water (4.18 J/g-°C), power to the system, initial and final temperature of water, and duration of the experiment. Because there is no heat dissipation into the environment in a bomb calorimetry apparatus, Equation I is transformed into

Equation III:

[00072] mC_p(ΔT/Δt) = (V²/R) (III)

[00073J Using bomb calorimetry and Equation III, it has been found that energy efficiency for compounds of the present invention is at least about 80% and often exceeding 85%. Stated another way, for each Joule of electrical energy introduced into the heating element, 80% of that energy is converted into heat.

[00074] In addition to energy efficiency, overall power consumption is dramatically lower than employed for conventional heating elements such as metal rods or plates which use resistive heating to emit heat.

[00075] Compounds of the present invention heat to temperatures of between about 33 and 219 ⁰C using power consumption at steady state of

Equation II of between about 0.077 and 4.128 Watts, respectively. Moreover, the temperatures are reached by using voltages that seem far less than power consumption of appliance operating with conventional household voltages of

110 volts used for most consumer appliances or even 220 volts for electrical ovens or dryers.

[00076] Any article that needs to be heated, in whole or in part, can benefit from a heating element of the present invention, especially when considering those articles which presently use metal rods or wires. Particularly, consumer appliances benefit. Non-limiting examples of consumer appliances include heating blankets, heating ovens, heating dryers, milk warmers, hot plates and grills, etc.

[00077] Even more beneficially, because temperature can be generated using voltages less than household voltages, it becomes feasible for articles to be powered by batteries, including automobile batteries which can range in voltage from 6 to 56 volts and most often 12 volts. Also, any article can be powered via a transformer to reduce voltage from household voltage to any desired lower voltage for powering the heating element to reach a desired plateau temperature according to Equation I above.

[00078] Demonstration of the practicality of the present invention is shown in Figs. 1-5. Each of the Figs, is an image from a digital video showing the process of frying an egg on a surface made from a compound of the present invention. Within the space of 90 seconds, the surface (pre-heated to a plateau temperature of 121 ⁰C) fried the egg, while consuming power of 21.33 Watts in 90 seconds. Thus, a total of 1919.7 Joules was used to fry the egg.

USEFULNESS OF THE INVENTION

[00079] One can connect a source of electrical energy via electrodes to a heating element made from a compound of the present invention, to generate heat sufficient to raise the temperature of the heating element to a desired amount. The temperature can be controlled by a rheostat which controls electrical energy input to the thermoplastic article. The electrical energy can be alternating current or direct current.

[00080] Heating elements can be extruded as wires having diameters ranging from about 0.1 to about 0.25 cm or as rods having diameters ranging from about 0.25 to about 1.5 cm. Additionally, because the heating element is a thermoplastic polymer, heating elements can be molded into any desired three dimensional shape to provide a source of high efficiency, low power heat to any other material. It is not inconceivable for the shape of the final molded article to conform around the material to be heated, whether the material be a gas, a liquid, or a solid. Because the heating element is thermoplastic, very complex shapes can be achieved, using molding techniques known to those skilled in the art.

[00081] If there is any concern about the amount of electrical energy that is being delivered to the heating element, one can also include any type of current arrestor, such as an inline fuse, to assure that no more than a specific amount of electrical energy is to be delivered to the exothermic thermoplastic heating element of the present invention. An inline fuse would forestall excessive electrical energy being delivered to the article that would otherwise generate such heat as to degrade or melt the polyphenylene sulfide in the heating element or harm any component of any device such as an appliance that includes the heating element or a device or article in the vicinity of the heating element.

[Θ0082] Any form of electrode is suitable for connecting articles of the invention to the source of electrical energy. Ranging from alligator metal clips from a consumer retail outlet such as Radio Shack stores to pressure sensitive electrodes from a commercial wholesale outlet such as 3 M Company, the goal of the electrode is to connect the article to the source of electrical energy without excessive loss of energy. Electrodes can be insert-molded as well as integral to the part.

[00083] The amount and type of exothermic additive in the compound establishes the plateau or final temperature at which the heating element remains, according to Equation I above, given the environment within which the article containing the heating element resides.

[ΘΘ084] Contrasted with a coating or film as disclosed in the Miller patents, which might be susceptible to chipping or flaking from the exposed surface of the article, having the exothermic additive dispersed throughout the bulk of the thermoplastic polyphenylene sulfide compound assures continued performance even if the exposed surface of the article is scratched or marred. [Θ0Θ85] Depending on the geometry of the article, one may need to provide more than one set of electrodes to the article, perhaps providing the electrical energy to various sections of the article.

[00086] Moreover, it is quite possible to engineer the article to have different sections made from different compounds having different concentrations of exothermic additive dispersed therein, thereby resulting in different temperatures in the different sections by design. [00087] Examples further explain the invention.

EXAMPLES

[00088] Examples 145

[O0089] Samples of compounds of the present invention were compounded, extruded, and molded into test plaques and tested for exothermic and physical properties. Table 3 below shows the formulations, physical properties and exothermic properties caused by resistive heating.

[00090] The carbon black was dry-mixed in a Henschel mixer for about 2 minutes followed by addition of PPS and mixing for about 2 minutes, followed by addition of the graphite, if any, and continued mixing for about 2 minutes.

Then the dry-blend of the compound was introduced into a Century 30 extruder, with the settings and results shown in Table 1.

[00091] The extrudate was pelletized for later molding.

[00Θ92] Using a 33 Cincinnati Millacron molding machine, the following settings were used to mold plaques and tensile test bars of the compound of the present invention.

[00093] To measure exothermic properties, two holes were drilled into a conventional tensile test bar at opposite ends approximately 4.5 inches apart in order to attach brass screws. Probes from a Variac voltage rheostat were then attached to the brass screws to create a voltage loop. An IR gun was affixed at approximately 8 inches above the tensile bar to measure surface temperature at the center of the bar.

[00094] Table 3 shows the formulations, exothermic properties, and physical properties of the test bars.

[00095] Current was calculated using resistance at plateau temperature after multiple cycles of energizing. It was found that resistance decreased after the first energizing and then stabilized thereafter.

[0Θ096] Table 3 shows several unexpected results based on the following factors. Plateau temperature is dependent on both formulation and voltage. Resistance is nearly constant at a given voltage (15 volts) over the temperature range during resistive heating. Current draw is dependent on resistance at plateau temperature for a given voltage and that voltage. Power consumption is dependent on voltage and current at plateau temperature. [00097] With these factors and viewing especially the results of Example

14, it is unexpected to learn that one can generate as much as 250⁰C in temperature using electrical energy operating at 70 volts, drawing less than 0.2 amps and consuming less than about 13 Watts. Stated another way, for 1/8 of the wattage of a standard 100 Watt incandescent light bulb, compounds of the present invention can establish a steady state condition with their environment at a temperature 2.5 times the boiling point of water. The sheer ability for one skilled in the art to use data from Table 3 to engineer a heating element to operate at any temperature above ambient to as much as 25O⁰C is totally unexpected in the field of electric appliances designed to heat objects within them or the ambient space around them. [00098] Examples 16 and 17

[00099] Bomb calorimetry using water was performed on two different samples of the compound of Example 2. The specific heat of water is known to be 4.184 Joules/grams*temperature (⁰C). By using Equation III and a homemade bomb calorimetry machine, the exothermic properties and efficiency of the compound of Example 2 compound was measured in two different tests. The bomb calorimetry machine was a container made of foamed polystyrene having inside a large beaker nearly filled with water sitting atop of magnetic stirring device. The tensile test bar used in the experiment was submerged in the water in the beaker but not touching any portion of the beaker. Beneath the submerged tensile test bar was a magnetic stirrer, energized by the magnetic stirring device to circulate the water in the beaker about the submerged tensile test bar.

[00010©] At about 600 second intervals, the temperature of the water in beaker was measured using a mercury thermometer extending through the styrene container and into the water in the beaker. Table 4 reports the results.

*(Cp* ΔT* mass of water) / (time)

[Θ00101] With the space confined, no dissipation of heat was possible. As seen, the compound of Example 2 had more than 80% energy efficiency.

1000102] Example 18

[000103] The compound of Example 9, having been molded into a plaque was tested for its ability to fry a chicken egg.

[000104] Fig. 1 shows the image of the test plaque, about 1 1.43 cm in diameter and about 0.32 cm thick, having electrodes attached and energized with 45 volts to reach a plateau temperature of 121 ⁰C. The current measured at the plateau temperature was 0.47 amps, and the rate of power consumption was

21.3 Watts. [000105] Fig. 2 shows an image of the chicken egg being broken and spilled onto the surface of the test plaque operating at the plateau temperature of

121⁰C. This image establishes the commencement of the test, to be measured in seconds.

[000106] Fig. 3 shows the cooking of the egg after 30 seconds from the image of Fig. 2. It is apparent that the albumin is beginning to turn opaque white.

[Θ001Θ7] Fig. 4 shows the cooking of the egg after 150 seconds from the image of Fig. 2. It is apparent that the albumin is fully cooked and the yolk is firm.

Ϊ000108] Fig. 5 shows the completion of the cooking of the egg after 210 seconds from the image of Fig. 2.

[000109] The compounds of the present invention can replace metallic surfaces to literal])' fry an egg.

[00011ΘJ The invention is not limited to the above embodiments. The claims follow.

Claims

What is claimed is:

1. A heating element comprising a polymer having an energy efficiency of at least about 80 percent, wherein the polymer comprises:

(a) a polyphenylene sulfide, and

(b) an exothermic additive comprising electrically conductive particles and, optionally, less electrically conductive particles, wherein the amount of electrically conductive particles in the compound is same or greater than the amount of less electrically conductive particles, if any are present,

2. The heating element of Claim 1, wherein the less electrically conductive particles are graphite.

3. The heating element of Claim 1, wherein the heating element operates at a plateau temperature.

4. The heating element of Claim 1 , wherein the electrically conductive particles are carbon black particles.

5. The heating element of Claim 1, wherein the electrically conductive particles are carbon nano tubes or carbon nanofibers.

6. The heating element of Claim 1 , wherein the electrically conductive particles is present in an amount from about 1 to about 75 weight percent of the heating element.

7. The heating element of Claim 2, wherein the weight percent ratio of electrically conductive particles and less electrically conductive particles ranges from about 1.1 :1 to about 3: 1.

8. The heating element of Claim 1, further comprising a second polymer, wherein the second polymer is selected from the group consisting of polyolefins, polyamides, polyesters, polyhalo-olefins, and polyurethanes.

9. The heating element of Claim 1, further comprising additives selected from the group consisting of fillers, colorants, processing lubricants, impact modifiers, uv-stabilizers, processing aids, biocides, and flame retardants,

10. An electrical appliance having a heating element of any of Claims 1-9, wherein the heating element can operate at temperatures from about 30⁰C to about 250⁰C.