THERMAL ENERGY STORAGE MATERIALS

Abstract: A polymer structure includes a phase change material within pores of the polymer structure. The polymer structure is prepared via a process including spinodal decomposition. Thermal energy storage units include the polymer structure and a carrier supporting the polymer structure.

Description: THERMAL ENERGY STORAGE MATERIALS Background of the Invention This invention relates to thermal energy storage materials, and more particularly to novel processes and compositions useful for the preparation of such materials including polymer structures containing a phase change material . A phase change material (PCM) , also known as a latent thermal energy storage material, is used for thermal energy storage. Upon freezing and melting, a phase change material absorbs and releases substantially more energy per unit weight that a sensible heat storage material that is heated or cooled over the same temperature range. This is because in phase change materials the latent heats of fusion are greater than their sensible heat capacities. Latent heat of fusion is the amount of energy absorbed or released by a material to change its phase from liquid to solid or vice versa while maintaining its characteristic melting temperature. Sensible heat is the thermal energy absorbed or released by a material through a change in temperature that does not involve a phase change. Efficient phase change materials generally are characterized as having a high latent heat of fusion, high thermal conductivity, and the ability to repeatedly undergo thermal cycling without degrading. Depending on its melting temperature, a phase change material can be used to heat or cool a particular system. For example, a phase change material which has been heated above its melting point can be used to warm a thermal environment of a temperature less than the melting temperature of the phase change material . In such a system, the phase change material releases sensible heat until the melting temperature of the phase change material is reached, after which there is a thermal plateau until all of the phase change material has undergone a phase change to the solid phase. After solidification, the phase change material undergoes sensible heat transfer until thermal equilibrium with the environment is reached. A phase change material which has been cooled below its freezing point can be used to cool a thermal environment of a temperature greater than the crystallization temperature of the phase change material . In such a system, the phase change material absorbs sensible heat until the melting temperature of the phase change material is reached, after which there is a thermal plateau until all of the phase change material has undergone a phase change to the liquid phase. After melting, the phase change material undergoes sensible heat transfer until thermal equilibrium with the environment is reached. Phase change materials are superior to sensible heat materials for heat storage. Phase change materials due to their high latent heats of fusion, have higher heat storage capacities. In addition, because there is a thermal plateau at phase change, phase change materials function isothermally for prolonged periods of time. Because of their ability to absorb, store and isothermally release thermal energy, phase change materials have been used in a number of applications. Illustrative examples include, the incorporation of phase change materials into building materials such as drywall and floor boards to lessen building heating and cooling requirements. Phase change materials have also been incorporated into cups, glasses, tableware, and food storage items to keep food and beverages at the desired temperature for extended periods of time. Phase change materials have also been incorporated into fibers for use in clothing, bedding, wraps, cushions or other articles utilizing woven or nonwoven fibers, especially those for use in cold environments . Numerous methods have been devised for incorporating phase change materials into polymer structures such as fibers. Salyer, U.S. Patent No. 5,053,446 discloses a method for impregnating a polyolefin fiber with a phase change material. A thermally form stable, cross linked polyolefin fiber is immersed in a melt bath of the phase change material for a time sufficient to absorb at least 10% by weight of the phase change material . In addition to requiring a two step process, the method disclosed requires that the degree of cross linking be carefully balanced to provide thermal form stability and yet still allow sufficient phase change material to be absorbed. In U.S. Patent No. 4,908,166, Salyer describes a method for the production of a phase change material -containing polyolefin by creating a melt mix of a polyolefin and phase change material which is then extruded. Phase change material concentrations of up to 25% are said to be achieved with this method. Because the product is not produced by induction of spinodal decomposition, the product does not have a three-dimensional cellular structure. In U.S. Patent No. 5,804,266, Salyer discloses production of a continuous polymer fiber containing a phase change material. In this process, the fiber is produced by melting together a polymer, silica and a compatible phase change material. The resulting melt is then extruded in a continuous process to form a fiber. Silica is included in the melt to absorb the phase change material . Absorption of the phase change material by silica is necessary to prevent loss of the phase change material from the fiber when the material is heated and the phase change material is converted to the liquid state. Although necessary to prevent oozing of the phase change material, the inclusion of silica or some other absorbent, by necessity, limits the amount of phase change material that can be incorporated into the fiber. Phase change materials have also been directly incorporated into polymeric fibers. U.S. Patent No. 5,885,475 to Salyer discloses a fiber in which the phase change material is incorporated as either an alternating unit of a polymer, a repeating unit of the polymer, or the polymer itself. Incorporation directly into the fiber polymer limits the choice of phase change material that can be utilized to those which react with the polymer without significantly lessening its structural strength. What is needed is a polymer structure, such as a fiber or sheet, incorporating a phase change material which can be used in a variety of applications, is lightweight, easy to produce, and can incorporate a high percentage of a wide variety of phase change materials. The current invention meets this need. Summary of the Invention The present invention provides novel thermal energy storage units including a polymer structure having a phase change material within pores of the polymer structure, and a carrier supporting the polymer structure. The polymer structure is formed in a manner that provides many enclosed cells containing phase change material throughout at least the interior stratum of the structure. A significantly greater amount of phase change material is incorporated into the polymer structure as compared to conventional thermal storage materials because the phase change material is enclosed within the cells as the polymer structure is formed. The incorporation of larger amounts of phase change material provides greater thermal energy storage capacity within the unit as compared to the conventional materials. Also, the phase change material is intimately dispersed within the polymer structure at a submicron scale to provide uniform heating or cooling across a surface. In another embodiment, the polymer structure has a relatively low permeability outer stratum or "skin structure" which prevents leakage of phase change material from the polymer structure. Such a structure is particularly useful when the polymer structure includes passageways interconnecting cells which may contact the outer surface of the polymer structure, rather than enclosed cells of phase change material. It may be impractical to encase such a polymer structure to prevent leakage of phase change material, as when the polymer structure is in the form of loose fiber fill or a lofted fibrous polymer batt. The polymer structures of the invention are useful in thermal energy storage units for a multitude of diverse applications, including building materials (e.g., drywall, floor boards, insulation, and carpet pads) , paving materials (e.g., concrete, bricks, and cement), roadbeds, planting medium, containers and covers (e.g., mulch, soil, planters, and solar covers for outdoor plants) , food service, storage, transport and preparation materials (e.g., glassware, tableware and food storage containers), clothing (e.g., coats, pants, gloves, socks, and hats) , shoes, shoe liners, bedding, wraps (e.g., medical wraps, blankets, and surgical drapes), furniture, surgical cushions, and seat cushions. Briefly, therefore, the present invention is directed to a thermal energy storage unit comprising a polymer structure including a phase change material within pores of the polymer structure, and a carrier supporting the polymer structure. The phase change material is capable of absorbing, storing and releasing energy, and the carrier being capable of transmitting energy to or from the phase change material . The polymer structure is formed by first preparing a single phase liquid mixture comprising a polymer and the phase change material at a temperature at which the phase change material is fully miscible with the polymer in the relative proportions of phase change material and polymer contained in the liquid mixture. The phase change material is at least partially immiscible with the polymer in such proportions at a temperature below the mixing temperature. A nascent structure comprising the single phase liquid mixture is formed. The nascent structure is quenched to cause spinodal decomposition of the single phase liquid mixture into separate liquid phases comprising a continuous liquid phase comprising the polymer. The nascent structure is further cooled to solidify the continuous phase comprising the polymer, thereby forming the polymer structure . Another aspect of the invention is directed to a thermal energy storage unit comprised of a fibrous polymer batt, and a carrier supporting the batt. Fibers of the batt comprise a phase change material within pores of the fibers. The phase change material is capable of absorbing, storing and releasing energy, and the carrier is capable of transmitting energy to or from the phase change material. Yet another aspect of the invention is directed to a thermal energy storage material comprising polymer fibers comprised of more than 25 wt . % phase change material. The phase change material is within pores of the fibers, is capable of absorbing, storing and releasing energy, and is the only liquid within the polymer fibers. Still another aspect of the invention is directed to a method for increasing the thermal energy storage capacity of a product by incorporating the thermal energy storage material into the product . Another aspect of the invention is directed to a thermal energy storage unit comprised of polymer fibers comprising more than 25 wt . % phase change material, and a carrier supporting the fibers. The phase change material is within pores of the fibers and is capable of absorbing, storing and releasing energy. The carrier is capable of transmitting energy to or from the phase change material . Other objects and features will be in part apparent and in part pointed out hereinafter. Brief Description of the Drawings Fig. 1 is an illustrative phase diagram for a system comprising a polymer and a phase change material with which 'the polymer is fully miscible at a temperature above the melt temperature of the polymer; Fig. 2 is a plot of temperature vs. time in an outer stratum of a film from which a polymer structure is produced in accordance with the process of the invention; and Fig. 3 is a schematic illustration of an apparatus useful in carrying out the process of the invention. Corresponding reference characters indicate corresponding parts throughout the drawings. Description of the Preferred Embodiment Thermal energy storage materials of the invention contain a polymer structure which includes at least one phase change material within pores of the structure. The polymer structure preferably includes phase change material distributed substantially uniformly throughout a polymer matrix. The phase change material is enclosed in cells within the polymer matrix. This cellular structure results from inducing spinodal decomposition in a single phase liquid mixture of polymer and phase change material to cause liquid-liquid phase separation followed by quenching to solidify the polymer. As discussed below, the size of the phase change material areas, and associated interconnections, if any, can be controlled by altering the parameters used to produce the structures . In an embodiment of the invention, the phase change material is enclosed in cells within the polymer matrix and within passageways that interconnect some of the cells. When the polymer structure includes such passageways in the outer stratum of the structure, it is preferred that the structure includes a low permeability outer stratum or "skin structure" having a higher polymer concentration than does the structure's inner core. Depending on the conditions selected, the transition from the polymer outer layer to the inner core can be abrupt such that the structure possesses an outer skin of essentially pure polymer or there can be a gradient in which the concentration of polymer decreases from the outer surface to the inner core. The cellular polymer structure has the advantage of retaining large amounts of phase change material without the loss or "oozing" of phase change material from the structure during the repeated process of melting and solidifying the phase change material. This reduction in phase change material loss is especially apparent in the embodiment comprising a high polymer content outer stratum. The polymer structure of the present invention can be formed into a variety of shapes . For example and without limitation, it can be formed into films, blocks, pellets and filaments such as fibers by methods such as casting, molding, extruding and spinning. In one preferred embodiment, the polymer structure is formed into a fiber and more particularly a fibrous batt. Thermal energy storage units of the invention contain the polymer structure and a carrier supporting the polymer structure. The carrier is selected depending upon the intended end use of the thermal energy storage unit as is described below. The carrier is capable of transmitting energy to or from the phase change material, and is generally in the form of a cloth, a covering, a thread, a sheet, a film, a fiber, a pellet, a container, a rigid foam, a planting medium, a building material, a roadbed, or a paving material. For example, if the unit is to be used as building insulation, the polymer structure may be in the form of a fibrous batt supported by a carrier comprising a paper sheet . Illustrated in Fig. 1 is a phase diagram typical of compositions useful in the process of the invention. Such compositions comprise a thermoplastic polymer Ε> 1 and a phase change material O λ with which the polymer is at least partially immiscible at ambient temperature but fully miscible at elevated temperatures, typically above the melting point or glass transition temperature of the polymer. The coordinates for point C on the diagram are the critical composition for solutions of polymer P x in phase change material D x , i.e., the composition of P l and D x which exhibits the highest spinodal decomposition temperature, and the critical temperature, i.e., the spinodal decomposition temperature for the critical composition. The coordinates for point E are the eutectic composition and the melting point of the eutectic. Plotted to the left of the eutectic are the spinodal and binodal phase separation curves, and, below these, the polymer solidification line. Plotted to the right of the eutectic is the freezing point (or glass transition temperature) depression curve for the polymer in the P I /D- L system. As illustrated in the drawing, for compositions useful in the process of the invention, the phase diagram comprises a critical point C that is preferably joined to the eutectic by a binodal phase separation line without intervening nodes or inflections. In accordance with the process, a single phase liquid mixture is prepared having the composition and temperature of point A, i.e., having a P x content C a above the critical composition but below the eutectic, and a temperature T a at which Pi and O 1 are fully miscible. When forming an anisotropic or asymmetric polymer structure, the phase change material has sufficient volatility to be vaporizable from compositions ranging from C a to the eutectic composition C e or higher, at temperatures between T a and a temperature significantly lower than T a , e.g., T b , the temperature at point B, or below. The single phase composition is formed into a structure comprising a nascent structure, e.g., a film, fiber, or annular (hollow) filament. In an embodiment of the invention, anisotropic structures are produced such that the outer stratum of the polymer structure has a higher polymer concentration than does the inner bulk structure. The polymer concentration in an outer liquid stratum of the nascent structure, extending inwardly from the surface thereof, is increased by evaporation of a vaporizable phase change material from the surface to form an anisotropic polymer structure. The polymer concentration in the outer liquid stratum is thereby increased to a value higher than that in the bulk of the structure. Preferably, the surface and outer liquid stratum are cooled by the evaporation, driving the temperature/composition co-ordinates of the single phase liquid mixture toward the binodal and spinodal separation lines. Alternatively, evaporation can be promoted by transferring heat to the outer margin sufficient to maintain its temperature substantially constant, or in some instances to increase. In any event, evaporation conditions are controlled so that the rate of removal of vaporizable phase change material is greater than the rate of diffusion of phase change material from the bulk of the film or filament to the outer stratum, i.e., phase change material is evaporated from the outer stratum at a rapid rate. Advantageously, the evaporation is effected at subatmospheric pressure, for example under a modest vacuum of up to about 50 mmHg, typically about 10 to about 30 mmHg. As illustrated in both Figs. 1 and 2, evaporative cooling rapidly reduces the temperature of the outer stratum of the structure to T b and increases the concentration therein to C b , the coordinates of point B in Fig. 1. Preferably, evaporation is terminated at a point such as point B, at which the temperature remains high enough so that the composition of the nascent structure within the outer stratum remains a single phase liquid prior to quenching of the structure. The increase in concentration by evaporation is preferably sufficient so that C b is closer to the eutectic composition C e than to the critical composition C c . Although preferably close to the eutectic where the spinodal decomposition and solidification equilibrium lines are converging, point C b is also at a composition for which the spinodal decomposition temperature still exceeds the solid/liquid equilibrium temperature. The temperature co-ordinate of point C b is preferably as close to the binodal equilibrium as feasible, e.g., not more than about 40°C above the binodal line, more preferably not more than about 20°C above the binodal line, most preferably not more than 5° to 10°C above the binodal line. As noted, it is preferred that concentration C b be close to a point where the loci of binodal equilibrium, spinodal decomposition, and solidification equilibrium are converging toward the eutectic. Thus, it is preferred that the temperature at point B, i.e., at the end of the evaporative cooling step be no greater than about 30 degrees C, more preferably no more than about 20 degrees C, higher than the spinodal decomposition temperature, and that the spinodal decomposition temperature at the outer surface composition be no greater than about 50 degrees C higher, preferably no greater than about 20 degrees C higher, than the solidification temperature. The nascent structure is thereafter quenched to rapidly lower the temperature below the binodal, spinodal, and polymer solidification lines. As the mixture cools below the spinodal decomposition line, the single phase mixture separates into a liquid phase predominantly comprising phase change material, typically containing less than about 0.5% by weight polymer, and a second liquid phase predominantly comprising polymer. In an embodiment of the invention, the phase change material forms a discontinuous phase if the amount of polymer within the single phase mixture is great relative to the amount of phase change material in the mixture. In another embodiment of the invention, both phases are continuous, forming interpenetrating continuous liquid phase networks within the nascent structure. As quenching proceeds below the solidification line, the phase predominantly comprising polymer solidifies, in some instances with further expulsion of phase change material, forming a continuous crystalline or amorphous solid polymer phase extending from the surface substantially throughout the bulk of the structure, including the aforesaid outer stratum. Typically, spinodal phase separation may occur within a temperature range of about 100°C to about 200°C, more typically about 150°C to about 200°C. Solidification of the polymer phase is obtained on further cooling. Phase change material remaining in the structure imparts open cell porosity to the continuous polymer phase. If the mixture is quenched without significant evaporation of phase change material from the outer strata, the polymer structure is substantially isotropic, and typically has a phase change material fraction between about 50% and about 80% and an average pore size between about 0.2 and about 200μ, preferably between about 0.2 and about 20μ, and more preferably between about 0.2 and about 2μ . Some of the cells containing the phase change material may be interconnected by passageways containing phase change material if a discontinuous phase is present during quench. The passageways typically have an average diameter of about one-tenth that of the average pore size of the structure. Typically overall thickness is generally between about 50μ and about 500μ. In an anisotropic or asymmetric polymer structure, the residual phase change material concentration is significantly lower in the outer liquid stratum from which phase change material has been evaporated. Therefore, the porosity, i.e., the phase change material fraction, in the porous outer stratum is significantly lower than the phase change material fraction in the bulk of the solidified polymer structure or in other strata interior thereof. Average pore size is also typically smaller due to both the lower phase change material fraction and the relatively low temperature of the spinodal phase separation in the concentrated outer liquid stratum. As a result, a sheet, fiber, hollow filament, or other structure is produced having highly anisotropic, typically asymmetric, configuration and properties. A dense but porous outer stratum or skin is formed which is effective for retaining phase change material within the structure even when the phase change material is in a molten state. The phase change material fraction in the outer strata is typically between about 5 and about 50%, with an average pore size between about 0.5 and about 0.05μ. The bulk of the polymer structure, and the other strata within the interior thereof, typically have a phase change material fraction between about 50% and about 80% and an average pore size between about 0.2 and about 200μ, preferably between about 0.2 and about 20μ, and more preferably between about 0.2 and about 2μ. Some of the cells containing the phase change material may be interconnected by passageways containing phase change material if a discontinuous phase is present during quench. The passageways typically have an average diameter of about one-tenth that of the average pore size of the structure. Thus, a highly efficient thermal energy storage material may be produced by the method of the invention in an overall thickness of between about 50μ and about 500μ. Polymer structures for thermal energy storage may be produced in accordance with the process of the invention from a wide variety of thermoplastic polymers. Any thermoplastic polymer that is miscible with the phase change material at the mixing temperature, but immiscible with the phase change material at a temperature below the mixing temperature, can be used, including by way of example: polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyamides such as Nylon 6, Nylon 11, Nylon 66, and Nylon 13; polyolefins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylbutyral , chlorinated polyethylene, acrylonitrile/butadiene/styrene , styrene/acrylonitrile , polybutylene, styrene/butadiene, ethylene/vinyl acetate, polyvinyl acetate, and polyvinyl alcohol; acrylics such as poly(methyl methacrylate) , poly(methyl acrylate), poly(ethyl acrylate) , ethylene/acrylic acid and ethylene acrylic ester copolymers, and ethylene/acrylic ionomers ; polycarbonates; and polysulfones . Preferred polymers are microwave active polymers such as polyvinylidene fluoride. As used herein microwave active means a material that absorbs microwave energy and releases thermal energy. When such polymers are used to form the thermal energy storage materials of the invention, no additional liquid need be present in the material other than the phase change material , reducing the size and weight of the material as compared to traditional microwave-activated energy storage materials. Of course, blends of one or more polymers may be utilized in the practice of the present invention. Particular combinations of polymer and phase change material will depend on a number of factors known to those skilled in the art, and include, the anticipated use, the cost and availability of the materials, and the ability of the combinations of polymer and phase change materials to form operable mixtures. More specifically, any phase change material can be used so long as at a particular mixing temperature, the phase change material and the polymer will form a single phase liquid mixture, and that upon cooling will undergo phase separation by liquid-liquid separation rather than liquid-solid separation. In general, when the polymer involved is non-polar, non-polar phase change materials with similar solubility parameters at the mixing temperature will more likely be useful . When such parameters are not available for the mixing temperature, one may refer to more readily available room temperature solubility parameters for general guidance. Similarly, with polar polymers, polar phase change materials with similar solubility parameters should be initially examined. In addition, with hydrophobic polymers, useful phase change materials will typically have little or no water solubility. On the other hand, polymers that tend to be hydrophilic will generally require a phase change material having some water solubility. When blends of one or more polymers are used, useful phase change materials must typically be operable with all of the polymers included. However, some polymer blends will have characteristics such that the phase change material need not be operable with all the polymers used. For example, where one or more polymers are present in such relatively small amounts as to not significantly affect the properties of the blend, the phase change material used need only be operable with the principal polymer (s) . Choice of phase change material will also depend on the intended use of the thermal energy storage unit and more particularly, the temperature sought to be maintained. Thus, the phase change material used should have a melting temperature within the range sought to be maintained. Phase change material liquids used should remain in the liquid state at the quenching temperature. Suitable vaporizable phase change materials preferably have a vapor pressure sufficient for relatively rapid evaporation from the single phase liquid mixture at atmospheric or subatmospheric pressure and above the binodal decomposition line in the concentration region between the critical concentration and the eutectic. Lists of phase change materials and their characteristics can be found in a number of sources known to those skilled in the art and include, without limitation, Hall, et al . , Thermal State-of -Charge in Solar Heat Receivers, National Aeronautics and Space Administration, 1998; Hall et al . , Parametric Analysis of Cyclic Phase Change and Energy Storage in Solar Heat Receiver, National Aeronautics and Space Administration, 1997; Ibrahim et al . , Experimental and Computational Investigations of Phase Change Thermal Energy Storage Canisters, National Aeronautics and Space Administration, 1996; Dinter et al . , Thermal Energy Storage for Commercial Applications : A Feasibili ty Study on Economic Storage Systems, Springer- Verlang, 1991; Lauf and Hamby, Metallic Phase-Change Materials for Solar Dynamic Energy Storage Systems, Oak Ridge National Laboratory, 1990; Winter, Solar Collectors, Energy Storage, and Materials, MIT Press, 1990; Garg et al . , Solar Thermal Energy Storage, Kluwer Academic Publishers, 1985; and Lane, Solar Heat Storage : Latent Heat Materials, CRC Press, 1983. Commercially available phase change materials include hydrated salts, eutectic salts, and paraffins. As with polymers, it will be apparent to those skilled in the art that combinations of phase change materials may be used within the scope of the present invention. Furthermore, additional materials can be included. In many cases, it will be preferred that the additional materials be operable with the polymer (s) and phase change material (s) used. In some applications, however, it may be preferable that the additional material included be operable with either the polymer (s) or the phase change material (s), but not both. Examples of additional materials that may be added, include, but are not limited to, fire retardants or diluents. If a diluent is used, it can remain in the finished product or it can be removed by, for example, evaporation . If the thermal energy storage material is incorporated into a seat cushion, sleeping pad or other product used to provide warmth, the phase change material used preferably will have a melting temperature in the range of about 40°C to about 60°C and more preferably between about 53 °C and 57°C. Examples of phase change materials with melting temperatures within this range include Shellwax 100 (42- 44°C) , Shellwax 120 (44-47°C) , Shellwax 200 (52-55°C) , Shellwax 300 (60-65°C) (all products of Shell Oil Co.), boron R-152 (65°C) (Standard Oil of Ohio) , Union SR-143 (61°C) (Union Oil Co.), Witco 128 (53°C) (Witco Corp.), TH58 (58°C) (PCM Thermal Solutions of Naperville, Illinois) , paraffin 150 (61°C) , tristearin (56°C) , myristic acid (58°C) , elaidic acid (47°C) , and oxasoline wax-ES-254 (50°C) . If the thermal energy storage unit of the present invention is to be in close contact with the body, phase change materials with a melting temperature in the range of about 35 to 40°C are desired with a more desirable range being 36 to 38°C. Examples of phase change materials with melting temperatures in this range include n-eicosane (36.7°C)and sodium hydrogen phosphate dodecahydrate (36°C) . The thermal energy storage material of the present invention can also be incorporated into materials to keep substances at low or high temperatures. For example in the food industry, the thermal energy storage material can be used in products to keep perishable foodstuffs at low temperatures normally in the range from -70 to 10°C and more preferably within -20 to 5°C. In another food related application, the thermal energy storage units can be used to keep food stuffs at serving temperature normally within the range of 70 to 105°C. Examples of phase change materials with melting temperature within these ranges include TEA-4 (-4°C) , TEA-10 (-10°C) , TEA-16 (-16°C), TEA-21 (-21°C), TEA- 31 (-31°C) , TH89 (89°C) (all from PCM Thermal Solutions of Naperville, Illinois), n-tetradecane (5.5°C), carrobend eutectic (70°C) , barium hydroxide octahydrate (78°C) , methyl fumarate (102°C) , and acetamide (81°C) . The thermal energy storage materials of the present invention can also find application in the construction industry. They can be incorporated into building materials to provide insulation to structures. Films of the thermal energy storage materials can be used as an air infiltration barrier in addition to providing thermal energy storage capacity. Another example is incorporation of the present invention into roadways and sidewalks to help prevent icing. The present invention can also be used in agricultural applications. For example, a fibrous batt of the present invention can be used as a mulch or as a component of plant containers to maintain soil temperature. In these applications melting points for suitable phase change materials are generally within the range of 5 to 40°C. Examples of phase change materials with melting points within this range include polyethylene glycol 600 (carbowax) (20-25°C) , TH29 (29°C) (PCM Thermal Solutions of Naperville, Illinois) , n-escosane (37°C) , n-octadecane (28°C) , n-hexadecane (17°C) , n-tetradecane (5.5°C), gallium (30°C) , lithium nitrate trihydrate (30°C) , sodium hydrogen phosphate dodecahydrate (36°C) , and acetic acid (17°C) . If an anisotropic or asymmetric structure is desired, the single phase liquid mixture preferably comprises a diluent which is of higher volatility than the phase change material . Preferably, the phase change material is substantially non-volatile in the temperature range in which the evaporative cooling step of the process is conducted. By selection of a diluent of known volatility and controlling the relative proportions of diluent and phase change material with respect to each other and with respect to the proportion of polymer, the porosity and average pore size of both the porous outer stratum and bulk polymer structure can be controlled in a desired and predictable manner. Unlike a phase change material/polymer system, in a phase change material/polymer/diluent system comprising a vaporizable diluent, the residual diluent in the porous outer stratum can be predetermined to a large extent, thereby providing a predictable asymmetric structure. More particularly, such mix of diluent and phase change material may be selected to establish an especially sharp gradient in phase change material fraction and average pore size transversely of the polymer structure. The difference in volatility between the vaporizable diluent and the nonvolatile phase change material and the relative concentrations of the diluent and phase change material in the single phase liquid mixture are such as to yield a substantial difference in porosity and average pore size between the "skin" or porous outer stratum and the bulk polymer structure, and a substantial difference between the outer stratum porosity and average pore size vs. the porosity and average pore size of any other stratum in the structure, particularly any other stratum in the structure interior. Such difference affords high separation efficiency at modest pressure drop. A "pore size differential" may be defined as the difference between the average pore size of the outer margin and the bulk average pore size, or the difference between the average pore size of the skin and that of another particular stratum in the interior of the polymer structure. In accordance with the process of the invention, the pore size differential of a polymer structure produced with a combination of volatile diluent and non-volatile phase change material is generally greater than that of a polymer structure produced in a conventional manner. The pore size differential of a polymer structure produced with a combination of volatile diluent and non-volatile phase change material is generally also greater than that of a reference polymer structure obtained by processing a film or fiber containing only the phase change material under evaporative cooling and quenching conditions otherwise substantially identical to the conditions under which the polymer structure containing both the diluent and phase change material is processed. The vaporizable diluent and phase change material of lower volatility are miscible with the thermoplastic polymer at temperatures above the melting point of the polymer. The diluent can, but need not, be miscible with the phase change material . Preferably, the polymer is substantially insoluble in the diluent and phase change material at ambient temperature. Such diluents may typically have an atmospheric boiling point between about 650° and about 250°C. Exemplary vaporizable diluents include glycerol esters, salicylaldehyde, benzyla ine, methyl benzoate, N,N- dimethylaniline, methyl salicylate, and tolylamines. The preferred initial composition of the single phase liquid mixture depends on the configuration of the phase diagram for a system consisting of the components of the mixture. For non-crystalline polymers, one may refer to a temperature vs. concentration plot of the glass transition temperature as an alternative to referring to a phase diagram. Typically, the composition initially contains between about 15% and about 40% by weight thermoplastic polymer, up to 15%, preferably between about 5% and about 15%, by weight vaporizable diluent, and more than 25%, preferably between about 60% and about 85%, more preferably between about 70% and about 85%, by weight relatively nonvolatile phase change material . Appropriate phase diagrams or other plots for determining such concentrations can be developed by known techniques, for example, those set forth in Castro, U.S. Patent No. 4,247,498 and references cited therein, herein incorporated by reference in their entirety. Other functional considerations may also be taken into account in determining the proportions used for a particular system. For example, the strength characteristic of the resulting polymer structure may dictate the maximum amount of phase change material that should be utilized. To prepare the polymer structures of the thermal energy storage units of the invention, the single phase liquid is prepared by heating an agitated slurry of particulate thermoplastic polymer in the liquid phase change material, or liquid phase change material/diluent mixture, under moderate agitation to a temperature above the binodal phase separation line at the composition C a of the mixture. The resulting liquid mixture is then formed, conveniently by casting, molding or extrusion, into a film, pellet, molded article, or filament having the configuration of the solid polymer product to be produced. In one preferred embodiment, the nascent structure is formed into fibers by extrusion, melt spinning, melt blowing or other suitable method. These fibers can, in turn, be incorporated into woven or nonwoven products or formed into a nonwoven batt. Although films and fibers are the principal forms of polymer structures, the terms "polymer structure" and "nascent structure" are intended to encompass other configurations that may exist or be devised. The nascent structure is formed at a temperature at which the phase change material and polymer are fully miscible, but preferably under conditions which prevent flashing of phase change material as it is formed. More particularly, in the case of extrusion, the temperature of the structure and the ambient temperature, pressure and mass transfer conditions at the exit of the extrusion die are controlled so as to minimize flashing at the exit of the die. After the single phase liquid mixture has been formed into the shape of the desired article, evaporation, such as evaporative cooling, can be conducted to concentrate the polymer in the outer stratum of the film or filament to form an anisotropic or asymmetric structure. Evaporation preferably reduces the temperature of the outer stratum, typically from a temperature such as T a of Fig. 1 to a temperature that is above but preferably near to the binodal phase separation line for the composition reached in evaporative concentration, i.e., T b as shown in the phase diagram of Fig. 1 and the cooling curve of Fig. 2. Evaporation of vaporizable phase change material increases the concentration of polymer in the outer stratum from C a to C b _ i.e., the operating line of the evaporative cooling step extends from point A to point B along a path such as designated by the line L of Fig. 1. In the course of the cooling step, the temperature declines with time along a line such as illustrated in Fig. 2. It will be understood that, where the single phase liquid mixture comprises a phase change material and diluent, the phase diagram comprises more than two dimensions and the "curve" L may comprise more than two dimensions. However, where the phase change material and diluent are miscible with the thermoplastic polymer and with each other over the concentration and temperature range of the evaporative cooling step, and especially where such relationships prevail down to the spinodal decomposition lines, the process may be effectively illustrated by use of a two dimensional phase diagram, with the phase change material concentration parameter representing the combined concentrations of the phase change material and diluent . Evaporative cooling may be conducted by introducing the nascent structure into an oven and establishing a relative flow of stripping gas such as air over the surface of the structure. The stripping gas is at elevated temperature, typically above the spinodal and binodal phase separation lines, but below the boiling point of the single phase liquid mixture within the outer stratum at the pressure of the stripping gas. In the case of a fiber, e.g., the liquid filament comprising the nascent structure may pass through a heated pipe containing stripping air at the appropriate temperature. Alternatively, the surface of the film or fiber may be exposed to a rarified gas at a pressure below atmospheric but above the pressure at which the phase change material or diluent flashes from the outer stratum of the structure. Vacuum concentration is conducted with the temperature of the outer liquid stratum in a range wherein the vapor pressure is a substantial fraction of the total pressure but insufficient for the phase change material or diluent to flash. In the case of an annular fiber as may be used in forming a woven sheet for thermal energy storage, evaporation is ordinarily effected at the external surface of the annulus, ultimately forming a low porosity and low average pore size marginal stratum at that surface. In some instances it may be desirable and feasible to evaporate phase change material or diluent from the internal surface for formation of a low porosity and low average pore size margin or skin in the stratum extending toward the interior of the fiber wall from the surface bordering the hollow core. Alternatively, if a pore size and/or porosity gradient is desired in the latter stratum, it may be provided by use of a core fluid effective for extraction of diluent therefrom. To obtain the desired average pore size differential, the proportion of phase change material or diluent removed from the outer stratum is preferably sufficient to significantly increase the concentration of thermoplastic polymer in that stratum. It is further preferred that removal of phase change material or diluent be sufficient so that the ratio of the weight % concentration of polymer in the outer stratum to the weight % concentration of polymer in the bulk of the polymer structure be at least about 1.5, typically about 1.5 to about 3. In evaporative cooling, the requisite concentrating effect requires that the temperature of the outer stratum be lowered significantly. For example, the single phase mixture (at composition C a ) is initially heated to a temperature (T a ) that is at least about 5°C, more typically between about 10° and about 30°C, higher than the temperature on the binodal phase separation line at the concentration (C b ) . The temperature decrease obtained by evaporative cooling (T a - T b ) may vary substantially with the shape of the spinodal decomposition curve and the position of C b in relation to that curve; but in any case, the temperature T b achieved by evaporative cooling is preferably close to but above the binodal phase separation line at C b , as discussed herein above. Optionally, the outer stratum may be cooled evaporatively to a temperature below the binodal equilibrium line, either between the binodal and spinodal line, below the spinodal line, or even below the solidification line, but if any phase separation occurs, it is necessary to immediately quench the film or fiber to avoid formation of undesired structures in the outer stratum or bulk structure. Quenching of the nascent structure is preferably effected immediately following the evaporative cooling step for anisotropic or asymmetric polymer structures, or the forming step for substantially isotropic polymer structures. In the quenching step, as illustrated in Fig. 2, the temperature of the nascent structure should be reduced very rapidly through the spinodal decomposition line to a temperature below the solidification line at which the polymer rapidly crystallizes or assumes a relatively rigid or at least dimensionally stable amorphous structure. The nascent structure is preferably quenched from the temperature at the end of the evaporative cooling or forming to a temperature below the solidification equilibrium in the outer stratum at a rate of at least about 10°C per minute, preferably between about 10°C and about 50°C per minute. Quenching can be accomplished in various ways known to the art. Advantageously, quenching can be effected simply by exposure of a film or fiber to ambient air. Alternatively, the structure can be quenched on a chill roll or by immersion in a liquid bath, e.g., an aqueous liquid, with which the polymer is not miscible. In an embodiment of the invention, the time in which the temperature of the mixture is between the binodal and spinodal separation lines and between the spinodal and polymer solidification lines is minimized during quenching to avoid coarsening and obtain a monodisperse porous structure. Such as structure comprises interpenetrating networks defined by a first continuous liquid phase constituted predominantly of phase change material, and a second continuous liquid phase constituted predominantly of pol mer. Rapid cooling through the spinodal decomposition and solidification lines further conduces to a narrow distribution of pore size within the outer marginal stratum, and within other strata, in the solid polymer structure. The nascent structure is preferably quenched from the temperature at the end of the evaporative cooling or forming to a temperature below the solidification equilibrium in the outer stratum at a rate of at least about 10°C per minute, preferably between about 10°C and about 50°C per minute. A narrow pore size distribution can be obtained when the nascent structure is quenched from the temperature at the end of the evaporative cooling or forming to a temperature below the solidification equilibrium in the outer stratum at a rate of at least about 1,200°C per minute, and most preferably at least about 1,400°C per minute. Referring again to Figs. 1 and 2, in a preferred embodiment of the invention the combined cooling and quenching steps of the process comprise forming a nascent structure in a desired geometrical configuration, typically by extrusion into a thin film or fiber from a single phase liquid having the composition C a at temperature T a , and causing the film or fiber to be contacted by cooling air having a temperature F . As illustrated in Fig. 3, the single phase liquid may be extruded through a spinneret to produce a fine filament or fiber comprised of the homogeneous liquid, and drawing the fiber downwardly into cooling air. In the system of Fig. 3, a polymer solution is prepared in or charged to a spinneret feed vessel 1 positioned within a larger chamber 3. Polymer solution is agitated with an anchor or paddle mixer 5. Heat supplied by transfer from a heating fluid passing through coils 7 maintains the solution at a select controlled temperature corresponding to point A on the phase diagram of Fig. 1. The head space of vessel 1 above the polymer solution liquid level is in gas flow communication with a source of inert gas, e.g., nitrogen, for pressurizing the vessel to cause discharge of solution from a bottom outlet 9 of the vessel through a spinneret 11 below outlet 9 where a nascent single liquid phase fiber is formed. As the polymer solution passes through the spinneret 11, it is contacted at junction 13 by high velocity, heated air currents which move from a heater (not shown) through channels 15 in the spinneret 11. The temperature of the heated air currents is typically between about 150°C and about 220°C, depending on the polymer used. The heated air currents draw the nascent fiber from the spinneret 11. As the fiber exits the spinneret, cooled air currents moving along outer surfaces 17 of the spinneret 11 quench the nascent fiber to form a solid polymer fiber. Ambient air may be sufficient to cool the nascent fiber in a small scale production line, but a mechanically-generated source of cooled air may be needed on larger lines. The fibers are typically drawn and quenched within about six to eight inches of the tip of the spinneret, depending upon the polymer selected. The environment in chamber 3 outside vessel 1 is controlled at a temperature and pressure suited for evaporation of phase change material or diluent from the outer surface of the nascent fiber exiting spinneret 11. Optionally, the pressure in the chamber may be controlled below atmospheric to promote evaporation of phase change material or diluent. The combination of temperature and pressure in chamber 3 is controlled to avoid flashing of phase change material or diluent from the nascent fiber exiting the spinneret. As the fiber passes through the air or other stripping gas atmosphere between the exit of the spinneret and the surface of the take-up screen 19, phase change material or diluent is lost by evaporation from the outer surface to concentrate the outer liquid stratum as described above. In an anisotropic or asymmetric fiber, evaporation preferably causes cooling of the outer stratum to the temperature of point B as illustrated in Figs. 1 and 2. Quenching results in spinodal decomposition which provides a fine porous uniform cell structure containing phase change material. The quenched, porous solid fiber impinges against and is collected on a rotating takeup screen 19 to form a continuous web or fibrous batt. Fiber entanglement and surface attraction of the small fibers as they impinge on the take-up screen result in self-bonding; however, with the use of continuous filaments, self-bonding is not necessary to form the batt . Continuous fibers are formed from low viscosity polymer solutions, such as those between about 200 and about 2,000 centipoise. Thickness of the resulting batt will depend on the size of the fibers produced and the speed of the takeup screen. The exact thickness desired will vary with the particular application for which the batt is to be used and will be readily apparent to those skilled in the art. The thickness of the batt can be increased by wrapping the continuous strip of fibrous batt until a suitable thickness is obtained for maintaining a temperature over a desired time period. Fibers produced by a similar melt-blowing process are described in U.S. Patent No. 4,666,763, which is incorporated herein by reference in its entirety. The fibrous polymer structure formed in the process has a relatively highly porous bulk structure that is formed from the composition at point A and a porous outer stratum, if present, that is much "tighter," i.e., of lower porosity and pore size due to its formation from the high polymer content composition at point B. The porous outer margin not only has a relatively low specific pore volume, but is comprised of fine uniform pores obtained by spinodal phase separation at the relatively low spinodal decomposition temperature and correspondingly high viscosity of the composition C b which is significantly closer to the eutectic than composition C a at point A. Quenching produces a porous polymer structure in which the open pores of the bulk structure and skin structure, if any, are substantially occupied by the phase change material liquid. The polymer structure produced typically possesses the structure and properties described herein above. The bulk structure inward of the outer margin or skin structure may be substantially isotropic, or may have a degree of anisotropy resulting from diffusion of phase change material or diluent during evaporative cooling. The polymer structure may optionally be annealed to relieve stresses in the structure formed in the cooling process so long as the thermal expansion coefficient of the polymer corresponds to the annealing temperature. For certain applications, especially biomedical applications, the structure may be sterilized before use, for example by exposure to γ-radiation. It will be readily apparent to those skilled in the art that the polymer structures of the present invention can be used in a number of applications. For example and without limitation, the fibrous batts of the present invention can be incorporated into bedding such as blankets, sheets, pillow cases and mattress covers, or used to produce mattresses or cushions . More particularly the fibrous batts can be incorporated into sleeping pads as used in camping or into seat cushions as used in stadium seats. In addition, the batt can be used as a filler for sleeping bags. When used in cushions, pads, sleeping bags, etc., the loft of the batt provides cushioning and additional insulating capacity in addition to the heat released by the phase change material. The carrier for supporting the batt in such applications is generally a textile or polymeric sheet such as a fabric or vinyl covering, or a rigid foam such as polyurethane foam. The fibers or batts of the present invention also have use in items of apparel such as providing filling for coats, pants, and coveralls as well as being incorporated into caps, mittens, gloves, socks and shoes. It will be readily apparent that the fibrous batts of the present invention can be incorporated as a part of the garment or may be used as a separate item in conjunction with the garment, for example, as a shoe or glove liner. The fibrous batts of the present invention are particularly useful in these applications because the lofted nature of the batt performs like a traditional insulating material in addition to the effect of the phase change material. The carrier in such applications is generally the apparel article or a liner for the apparel article. For example, the polymer structure can be supported by a fabric for lining a coat, or by the fabric, leather or polymeric sheet used to make the coat. The present invention has multiple uses in the medical and veterinary fields. For example, the fibers of the present invention may be incorporated into surgical drapes, medical wraps or pads for surgical tables or gurneys . In such uses the presence of the phase change material can be used to maintain, raise or lower a patient's body temperature. As used herein, the term patient includes domestic and non-domestic animals as well as humans. For example, a surgical pad incorporating the present invention, alone or in combination with a surgical drape can be used to help maintain a patient's body temperature during surgical procedures involving opening of a major body cavity where significant heat loss can be expected to occur. Likewise, pads, blankets, wraps, etc., incorporating a batt of the present invention can be use to raise a patient's body temperature in cases of hypothermia or lower a patient's temperature in cases of hyperthermia (fever) . Additionally, the fibrous batts of the present invention can be used in medical and veterinary wraps to provide localized heating or cooling. When used for medical or veterinary purposes, articles incorporating the fibrous batts of the present invention may be sterilized by any method compatible with the materials used to form the batts, for example and without limitation, gamma irradiation or ethylene oxide gas sterilization. The carrier for the batt or other polymer structure form in these applications is typically the material from which the medical wrap, pad, blanket, or surgical drape is made. The polymer structure can also be supported by a fabric or polymeric sheet and enclosed between two layers of the material from which the wrap, pad, blanket or drape is made. The present invention is also useful in the food service industry. The polymer structure of the present invention can be incorporated into articles used to maintain the serving temperature of food (hot or cold) or used to maintain a low temperature for perishable foodstuffs. The polymer structure can be incorporated directly into the serving or storage container. Alternatively, the polymer structure may be incorporated into a separate item into which the food serving or storage container is placed, for example, a cup, can or bottle holder, or a container in which to transport food such as a pizza carrier. In such applications, the carrier for the polymer structure is typically the container, cup, can or bottle holder itself, or a polymeric sheet supporting a batt or film of the invention. The thermal energy storage material of the present invention has widespread application to the construction industry. The fibrous batts can be placed in floor, wall and ceiling cavities of buildings where the lofted nature of the material will function like traditional insulation. In addition, the phase change material incorporated will respond to changes in environmental thermal energy to either absorb or release heat and so maintain a more constant temperature within the structure. The fibrous batt can also be used in wall covering and particularly in floor coverings such as carpet pads. In addition, when formed into a film the polymer structure can serve as both an air infiltration barrier and a means for increasing thermal energy storage capacity of a structure. The carrier for the polymer structure in such applications is typically a paper sheet as generally used to support traditional building insulation, carpet padding, dry wall, or underlayments for a floor, wall, ceiling or other building structure. The polymer structure can also be incorporated into cementitious materials, for example as pellets or fibers. Typical examples of useful cementitious materials are hydraulic cements such as Portland cement, gypsum, plaster of Paris, lime, white cements, air entrained cements, high alumina cements, masonry cements and concretes. Concretes are mixtures of hydraulic cements and aggregates, including conventional coarse aggregates (e.g., gravel, granite, limestone, and quartz sieve) and so-called fine aggregates (e.g., sand and fly ash) . The cementitious compositions of the present invention also include concrete and plaster compositions useful in the manufacture of pre-formed materials, such as concrete blocks, dry wall, and the like, as well as in forming poured concrete structures as used in forming the walls, floors, floor pads, and partitions of buildings . The compositions can also be used as a thermal bank surrounding the energy source in an underfloor heating system. The carrier for the polymer structure in such applications is typically the cementitious material which surrounds the polymer structure . The polymer structure in the form of fibers or pellets can also be incorporated into unfired clay bricks or other porous medium such as foams. In addition to their thermal properties, the fibers and pellets of the present invention can also provide a structural component by helping to hold the material together. In addition, the polymer structures of the present invention are useful in roadway, runway, and bridge deck construction where icing may be prevented by incorporating phase change material for thermal energy storage during the day, and release of thermal energy during the night to prevent freezing of the water on the surface. When used in this manner, the polymer structure can be incorporated directly into the paving material or can be used as an underlayment , for example, between the roadbed and the paving material. In such applications, the roadbed, paving material or an underlayment acts as the carrier supporting the polymer structure . The thermal energy storage materials of the invention can also be used in refrigeration systems and other cooling systems required in building construction. The polymer structures of the invention is also useful when incorporated in small enclosures, such as those used for telecommunications devices that cannot be cooled by assisted means such as air conditioners or air-to-air heat exchangers due to the enclosure size or power requirement. The thermal energy storage materials can also be used in place of sensible heat sources in thermal management of larger outdoor enclosures that typically house switching/signal processing equipment, batteries for powering telephone switching systems or other telecommunication devices sensitive to outdoor temperature variations. The materials of the invention can also replace any passive cooling component for electronics. For example, the polymer structure can be incorporated into pin fins, plate fins, or other traditional heat sinks for high power electronic components such as integrated circuits and microprocessors. In such applications, the enclosure or heat sink is generally the carrier for the polymer structure . The thermal energy storage materials of the present invention is also useful in agriculture. In the cultivation of plants, batts, films or pellets can be used as a mulch on top of the soil or incorporated into the soil. In this application biodegradable polymers and phase change materials are preferred. In an alternative embodiment, the fibrous batts can be incorporated into plant containers such as flower pots, used to surround such plant containers, or used to cover plants during periods of low temperature such as at night. When used in this application, the phase change material in the polymer structure would, for example, absorb solar energy during the day and then release thermal energy at night . When used in this way, products incorporating the present invention would hasten seed germination and lessen plant damage due to low temperatures. In such applications, the soil, container or a plastic sheet generally supports the polymer structure. The polymer structures can also be used in the heating or cooling of commercial and residential greenhouses, barns and stables. When used in animal care, the polymer structure, especially when in the form of a fibrous batt, could be used to help maintain the body temperature of newborn animals or serve as bedding to provide warmth to animals housed in unheated structures during inclement weather. The carrier in such applications is typically a wrap, blanket or sheet composed of a fabric or a waterproof textile. Additional uses within the scope of the present invention will be apparent to those skilled in the art. In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained. As various changes could be made in the above compositions and processes without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims: What is claimed is: 1. A thermal energy storage unit comprising: a polymer structure comprising a phase change material within pores of the polymer structure, the phase change material being capable of absorbing, storing and releasing energy; and a carrier supporting the polymer structure, the carrier being capable of transmitting energy to or from the phase change material, wherein the polymer structure is formed by a process comprising: preparing a single phase liquid mixture comprising a polymer and the phase change material at a temperature at which the phase change material is fully miscible with the polymer in the relative proportions of phase change material and polymer contained in the liquid mixture, the phase change material being at least partially immiscible with the polymer in such proportions at a temperature below the mixing temperature; forming a nascent structure comprising the single phase liquid mixture; quenching the nascent structure to cause spinodal decomposition of the single phase liquid mixture into separate liquid phases comprising a continuous liquid phase comprising the polymer; and further cooling the nascent structure to solidify the continuous phase comprising the polymer, thereby forming the polymer structure . 2. The unit as set forth in claim 1 wherein the polymer structure is isotropic. 3. The unit as set forth in claim 1 wherein the vapor pressure of the phase change material is sufficient for evaporation thereof from the mixture within a temperature range between the mixing temperature and the temperature at which spinodal decomposition of the single phase mixture may be initiated on cooling thereof; the process includes, before the quenching step, the step of evaporating the phase change material from an outer liquid stratum of the nascent structure extending inwardly from a surface thereof, thereby increasing the concentration of polymer in the outer liquid stratum to a concentration higher than the concentration of polymer in the bulk of the nascent structure; and the polymer structure is anisotropic and comprises a porous outer stratum having an average pore size smaller than the average pore size of another stratum in the interior of the polymer structure . 4. The unit as set forth in claim 3 wherein spinodal decomposition of the single phase liquid mixture occurs in the interior of the nascent structure during the quenching step. 5. The unit as set forth in claim 4 wherein spinodal decomposition of the single phase liquid mixture occurs in the outer stratum during the quenching step . 6. The unit as set forth in claim 3 wherein evaporation of the phase change material from the outer liquid stratum comprises establishing a relative flow of a stripping gas over the surface of the nascent structure . 7. The unit as set forth in claim 6 wherein evaporation of phase change material from the outer liquid stratum comprises passing a stripping gas over the surface of the structure at a temperature below the boiling point of the composition of the outer liquid stratum at the pressure of the stripping gas . 8. The unit as set forth in claim 7 comprising passing the nascent structure through an oven heated to a temperature above the binodal phase separation line at the concentration of polymer achieved in the outer liquid stratum by evaporation of phase change material therefrom, as indicated on the phase diagram for a system comprising the polymer and the phase change material . 9. The unit as set forth in claim 3 wherein evaporation of phase change material from the outer liquid stratum comprises passing the structure through a heated drum. 10. The unit as set forth in claim 3 wherein the rate of evaporation of the phase change material from the outer liquid stratum is greater than the rate of diffusion of phase change material from the bulk of the structure to the outer liquid stratum. 11. The unit as set forth in claim 1 wherein the phase change material is mixed with the polymer at a temperature above the melting point of the polymer. 12. The unit as set forth in claim 1 wherein the phase diagram for a system consisting of the components of the single phase liquid mixture comprises a critical point and a eutectic at which the concentration of the polymer is higher than at the critical point, the co-ordinates of the critical point comprising a critical concentration and a critical temperature constituting the maximum temperature at which spinodal decomposition occurs, the binodal equilibrium temperature at the critical concentration being joined to the eutectic by a binodal phase separation line without intervening nodes or inflections, the polymer concentration in the single phase liquid mixture lying between the critical concentration and the concentration at the eutectic . 13. The unit as set forth in claim 12 wherein the polymer concentration in the single phase liquid mixture lies between the critical concentration and the concentration at which spinodal decomposition occurs before solidification. 14. The unit as set forth in claim 12 wherein evaporative cooling of the outer stratum increases the concentration of polymer in the outer liquid stratum to a concentration closer to the eutectic than to the critical point. 15. The unit as set forth in claim 14 wherein evaporative cooling of the surface reduces the temperature of the outer liquid stratum to a temperature near the binodal phase separation line. 16. The unit as set forth in claim 15 wherein evaporative cooling of the surface reduces the temperature of the surface to a temperature not more than about 40°C greater than the binodal phase separation temperature. 17. The unit as set forth in claim 12 wherein a line defining the locus of spinodal decomposition temperatures on the phase diagram is higher than a line defining the locus of solidification equilibrium temperatures over a range of compositions above the critical point. 18. The unit as set forth in claim 17 wherein the phase diagram comprises a eutectic at a polymer concentration higher than the critical concentration, and the spinodal decomposition temperature is greater than the solidification temperature at all concentrations between the critical point and the eutectic. 19. The unit as set forth in claim 17 wherein the spinodal decomposition temperature is higher than the solidification temperature at the concentration obtained at the outer surface of the nascent structure after evaporative cooling thereof . 20. The unit as set forth in claim 19 wherein the spinodal decomposition temperature is not more than about 50°C higher than the solidification temperature at the outer surface concentration . 21. The unit as set forth in claim 20 wherein the spinodal decomposition temperature is not more than about 20 °C higher than the solidification temperature at the outer surface concentration. 22. The unit as set forth in claim 3 wherein the temperature obtained at the outer surface of the nascent structure by evaporative cooling thereof is not more than about 40°C higher than the binodal equilibrium temperature at the surface concentration. 23. The unit as set forth in claim 22 wherein the temperature obtained by evaporative cooling at the outer surface is not more than about 50°C higher than the spinodal decomposition temperature at the surface concentration. 24. The unit as set forth in claim 23 wherein the surface temperature is no more than about 30°C higher than the spinodal decomposition temperature. 25. The unit as set forth in claim 3 wherein the surface temperature is closer to the spinodal decomposition line after evaporative cooling than before. 26. The unit as set forth in claim 3 wherein the nascent structure is quenched from the temperature at the end of evaporative cooling to a temperature below the solidification equilibrium in the outer stratum at a rate of at least about 10 °C per minute. 27. The unit as set forth in claim 3 wherein the nascent structure is quenched from the temperature at the end of evaporative cooling to a temperature below the solidification equilibrium in the outer stratum at a rate between about 10°C and about 50°C per minute. 28. The unit as set forth in claim 5 wherein the interior stratum is substantially isotropic. 29. The unit as set forth in claim 2 wherein diffusion of phase change material during evaporation results in an asymmetric structure of the interior stratum. 30. The unit as set forth in claim 3 wherein diffusion of phase change material during evaporation results in an asymmetric structure of the interior stratum. 31. The unit as set forth in claim 1 wherein the nascent structure is produced by extrusion of the single phase liquid mixture through an extrusion die. 32. The unit as set forth in claim 1 wherein the polymer structure is a fiber, a sheet, or a pellet. 33. The unit as set forth in claim 1 wherein the carrier is a cloth, a covering, a thread, a sheet, a film, a fiber, a pellet, a container, a rigid foam, a planting medium, a building material, a roadbed, or a paving material. Q→ μ- I- 1 C Φ 3 rt H- Cfl TJ H 0 Ω φ n CQ Φ Q 39. The unit as set forth in claim 38 wherein the phase change material and the diluent are miscible with each other and with the polymer at temperatures above the melting point of the polymer, and the polymer is substantially insoluble in the phase change material and the diluent at room temperature . 40. The unit as set forth in claim 38 wherein the phase change material is essentially non-volatile under the conditions prevailing during evaporation of diluent from said outer stratum. 41. The unit as set forth in claim 38 wherein the diluent has an atmospheric boiling point between about 150° and about 250°C. 42. The unit as set forth in claim 38 wherein the diluent is selected from the group consisting of glycerol esters, salicylaldehyde, benzylamine, methyl benzoate, N,N- dimethylamiline, methyl salicylate and tolylamines . 43. A thermal energy storage unit comprising: a fibrous polymer batt wherein fibers of the batt comprise a phase change material within pores of the fibers, the phase change material being capable of absorbing, storing and releasing energy; and a carrier supporting the batt, the carrier being capable of transmitting energy to or from the phase change material . 44. The unit as set forth in claim 43 wherein the phase change material is the only liquid within the polymer batt. 45. The unit as set forth in claim 43 wherein the carrier is a cloth, a covering, a thread, a sheet, a film, a fiber, a pellet, a container, a rigid foam, a planting medium, a building material, a roadbed, or a paving material. 46. The unit as set forth in claim 43 wherein the fibers contain from about 15 wt . % to about 40 wt . % of the polymer and from about 60 wt . % to about 85 wt . % of the phase change material . 47. The unit as set forth in claim 46 wherein the fibers contain from about 15 wt . % to about 30 wt . % of the polymer and from about 70 wt . % to about 85 wt . % of the phase change material . 48. The unit as set forth in claim 43 wherein the polymer is selected from the group consisting of olefin/vinyl alcohol copolymers, polyesters, polyamides, and polyolefins. 49. The unit as set forth in claim 43 wherein the polymer is a microwave activated polymer. 50. A thermal energy storage material comprising polymer fibers comprised of more than 25 wt . % phase change material, wherein the phase change material is within pores of the fibers, is capable of absorbing, storing and releasing energy, and is the only liquid within the polymer fibers. 51. The material as set forth in claim 50 wherein the fibers contain from about 15 wt . % to about 40 wt . % of the polymer and from about 60 wt . % to about 85 wt . % of the phase change material . 52. The material as set forth in claim 51 wherein the fibers contain from about 15 wt . % to about 30 wt . % of the polymer and from about 70 wt . % to about 85 wt . % of the phase change material . 53. The material as set forth in claim 50 wherein the polymer is selected from the group consisting of olefin/vinyl alcohol copolymers, polyesters, polyamides, and polyolefins . 54. The material as set forth in claim 50 wherein the polymer is a microwave activated polymer. 55. A thermal energy storage unit comprising: polymer fibers comprising more than 25 wt . % phase change material, the phase change material being within pores of the fibers and being capable of absorbing, storing and releasing energy; and a carrier supporting the fibers, the carrier being capable of transmitting energy to or from the phase change material . 56. The unit as set forth in claim 55 wherein the phase change material is the only liquid within the polymer fibers. 57. The unit as set forth in claim 55 wherein the carrier is a cloth, a covering, a thread, a sheet, a film, a fiber, a pellet, a container, a rigid foam, a planting medium, a building material, a roadbed, or a paving material. 58. The unit as set forth in claim 55 wherein the fibers contain from about 15 wt . % to about 40 wt . % of the polymer and from about 60 wt . % to about 85 wt . % of the phase change material . 59. The unit as set forth in claim 58 wherein the fibers contain from about 15 wt . % to about 30 wt . % of the polymer and from about 70 wt . % to about 85 wt . % of the phase change material . 60. The unit as set forth in claim 55 wherein the polymer is selected from the group consisting of olefin/vinyl alcohol copolymers, polyesters, polyamides, and polyolefins. 61. The unit as set forth in claim 55 wherein the polymer is a microwave activated polymer. 62. A method for increasing the thermal energy storage capacity of a product comprising incorporating the thermal energy storage material as set forth in claim 50 into the product . 63. The method as set forth in claim 62 wherein the product is a seat cushion, a medical or veterinary wrap or pad, a surgical drape, bedding, a hand warmer, a mattress, a sleeping bag, clothing, outerwear, a shoe, a shoe liner, a food storage or serving container, tableware, glassware, mulch, soil, a planter, an insulator, a building material, a roadbed, a heating or cooling system, an outdoor enclosure, an electronics or telecommunications enclosure, or a paving material . 64. The method as set forth in claim 63 wherein the building material is a floor, ceiling or wall covering. 65. The method as set forth in claim 63 wherein the paving material or building material is concrete, brick, cement, plaster, a foam, or dry wall.

Inventors: STERNBERG SHMUEL, STERNBERG, SHMUEL
Applicants: BAXTER INT, BAXTER INTERNATIONAL INC.
Application year: 2000
Main classification: H02K
IPC codes: C09K5, E04B1, F28D20