Fiber with reversible enhanced thermal storage properties and fabrics made therefrom

Abstract: A fiber with integral microspheres filled with phase change material or plastic crystals has enhanced thermal properties at predetermined temperatures. The fibers may be woven to form a fabric having the enhanced thermal storage properties,and articles of manufacture may be formed therefrom.

Description: This invention relates generally to the field of synthetic fibers, and articles of manufacture which incorporate an energy absorbing phase change or plastic crystal material which enables such articles to exhibit extended or enhanced heat retention or storage properties. The treatment of textiles and/or fibers with various substances in order to change the properties thereof is well known. For example, it is known that textiles may be waterproofed by coating them with natural or synthetic rubber. Substances have been developed which when sprayed onto fabrics introduce the property of stain resistance. In addition, it is known that fragrance delivery systems can be incorporated into fabrics. One such fragrance delivery system uses breakable fragrance filled microcapsules which are attached to the surface of a fabric or fiber and upon the introduction of an external force, the microcapsules break, releasing the fragrance over an extended time period. Fabrics have been given enhanced thermal properties by coating the fibers and the interstitial spaces between fibers with phase change materials and with plastic crystal materials (see the article entitled:- Fabrics given enhanced thermal properties, October 20, 1986; Chemical and Engineering News, Pages 15 and 16). The thermal properties of fabric are enhanced as it is impregnated with these materials. More specifically, materials such as water, undergo phase changes from solid to liquid to gas at well known temperatures. Similarly, other materials such as paraffin wax undergo phase change from a solid to a liquid (fusion). At the phase change temperature, a characteristic of the material during the heating cycle is to absorb and hold a large quantity of thermal energy at a constant temperature before changing to the next phase. Thus, the material can be used as an absorber to protect an object from additional heat as a quantity of thermal energy will be absorbed by the phase change material before its temperature can rise. The phase change material may also be preheated and used as a barrier to cold, as a larger quantity of heat must be removed from the phase change material before its temperature can begin to drop. However, the aforementioned surface mounted phase change materials are not without their deficiencies. For example, it was found that while somewhat effective, the phase change material was not durably bound to the fibers and laundering removed most of the material. Thus, the fabric lacked repeatability of thermal response as each laundering removed a portion of the phase change material, thus causing the fabric to exhibit a corresponding change in thermal properties which limited its usefulness. As a result, further work was undertaken to perfect a series of process steps for binding the phase change material to the fabric in order to extend the useful life of the enhanced thermal properties. Furthermore, as far as is known to the inventors, the usefulness of these fibers and fabrics has been applied to a broader temperature range which limits the thermal absorption or release at a specific temperature range. It is, therefore, an object of the present invention to provide a fiber with enhanced thermal energy retention or storage properties, the properties being maintained over an extended period of time. It is a further object of the invention to provide a fiber having enhanced thermal energy retention or storage properties which can be woven into a fabric from which articles of clothing and the like can be manufactured. According to the present invention there is provided a fiber with reversible thermal energy storage properties of the type generally disclosed in the aforesaid article, and as defined in claim 1. The fiber comprises a base material and a plurality of microcapsules. The microcapsules are integral with and are dispersed throughout the base material and contain a thermal energy storage means, i.e. a temperature stabilizing means, namely a paraffinic hydrocarbon phase change material or plastic crystals. Due to the presence of these microcapsules, the fiber exhibits enhanced resistance to temperature change when subjected to heat or cold. Whilst conventional microencapulated materials, such as perfumes, have to be released by rupturing the microcapsules, before they produce the required effect, this does not apply to temperature stabilizing materials. For this reason, the microcapsules containing temperature stabilizing materials are resistant to leakage or rupture and may be subjected to repeated external mechanical stresses with minimum changes in the thermal characteristics of the fiber. The fiber may include microcapsules containing different preselected phase change materials which increase the range of temperature stability of the fiber. The fiber may also be woven into a temperature adaptable fabric. Reference is also made to US-A-3,852,401, in that it discloses various processes for producing an artificial fiber containing a microencapsulated fiber modifier. However, the microcapsules are intentionally frangible or semi-permeable, since the modifier contained therein is of a type which must be released in order to confer the required effect on the fiber, for example a perfume or a fire-retardant. In order that the invention may be more readily understood, various embodiments will now be described. The base material of the fiber is preferably a synthetic polymer such as polyester, nylon, acrylic or modacrylic and the like. The microcapsules can range in size from one to 10 µm and are formed according to the methods described in any one of the following texts to which the reader is referred for an explanation on how to fabricate microcapsules: Books on Microencapsulation: 1. Vandergaer, J.E., Ed: Microencapsulation: Processes and Applications. Plenum Press, New York, 1974. 2. Gutcho, M.H.: Microcapsules and Microencapsulation Techniques. Noyes Data Corp., Park Ridge, New Jersey, 1976. 3. Ranney, M.W.: Microencapsulation Technology. Noyes Development Corp., Park Ridge, New Jersey, 1969. 4. Kondo, A.: Microcapsule Processing and Technology. Marcel Dekker, Inc., New York, 1979. 5. Nixon, J.R.: Microencapsulation. Marcel Dekker, Inc., New York, 1976. Articles on Microencapsulation: 1. Sparks, R.E.: "Microencapsulation", Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 15, 3rd Edition, John Wiley and Sons, Inc., 1981. 2. Thies, C.: "Physicochemical Aspects of Microencapsulation," Polym. Plast. Techno. Eng., vol. 5, 7 (1975). 3. Thies, C.: "Microencapsulation", McGraw-Hill Yearbook of Science and Technology, 1979, pp. 13-21. 4. Herbig, J.A.: "Microencapsulation", Encyclopedia of Polymer Science and Technology, Vol. 8, 719 (1968). The microcapsules contain a temperature stabilizing means which may be a paraffinic hydrocarbon phase change material such as eicosane or alternatively, plastic crystals such as 2,2-dimethyl-1,3-propanediol (DMP) and 2-hydroxymethyl-2-methyl-1,3-propanediol (HMP) and the like may be used as the temperature stabilizing means. When plastic crystals absorb thermal energy, the molecular structure is temporarily modified without changing the phase of the material. In another aspect of the invention, the composition of the phase change material may be modified to obtain optimum thermal properties for a given temperature range. For example, the melting point of a homologous series of paraffinic hydrocarbons is directly related to the number of carbon atoms as shown in the following table: Compound Name Number of Carbon Atoms Melting Point °C n-Octacosane 28 61.4 n-Heptacosane 27 59.0 n-Hexacosane 26 56.4 n-Pentacosane 25 53.7 n-Tetracosane 24 50.9 n-Tricosane 23 47.6 n-Docosane 22 44.4 n-Heneicosane 21 40.5 n-Eicosane 20 36.8 n-Nonadecane 19 32.1 n-Octadecane 18 28.2 n-Heptadecane 17 22.0 n-Hexadecane 16 18.2 n-Pentadecane 15 10.0 n-Tetradecane 14 5.9 n-Tridecane 13 -5.5 Each of the above materials can be separately encapsulated and is most effective near the melting point indicated. It will be seen from the foregoing that the effective temperature range of the fiber can, therefore, be tailored to a specific environment by selecting the phase change materials required for the corresponding temperature and adding microcapsules containing the materials to the fiber. In addition, the fiber can be designed to have enhanced thermal storage characteristics over a wide range of temperatures or at discrete temperature ranges through proper selection of phase change material. In fabricating the fiber, the desired microencapsulated phase change materials are added to the liquid polymer, polymer solution, or base material and the fiber is then expanded according to conventional methods such as dry or wet spinning of polymer solutions and extrusion of polymer melts. Embedding the microcapsules directly within the fiber adds durability as the phase change material is protected by a dual wall, the first being the wall of the microcapsule and the second being the surrounding fiber itself. Thus, the phase change material is less likely to leak from the fiber during its liquid phase, thus enhancing its life and repeatability of thermal response. In another important aspect of the invention, a fabric can be formed from the fibers described above by conventional weaving, knitting or nonwoven methods. For example, in a woven fabric any combination of the warp or weft with or without microcapsules can be used in order to obtain the desired texture and durability. This fabric may then be used to fabricate temperature adaptable clothing and other thermal barriers. For example, protective gloves can be made from the fabric. By choosing an appropriate phase change material, the gloves can be adapted for cold weather use. The gloves can be placed in a heating chamber prior to use to liquify the phase change material. When it is desired to use the gloves, they are removed from the chamber and they will remain warm for an extended period of time. Substantial cooling will not occur until the liquid phase change material has solified. Conversely, by selecting the appropriate phase change material, the gloves can be used to handle hot objects. In this situation the gloves are cooled and a phase change material is solified. When the gloves are exposed to a hot surface, the user will remain comfortable as he will perceive that they are remaining cool. This continues until the phase change material has liquified. The reader will note that this concept can be applied to numerous applications including items of clothing such as shoes, environmental suits as well as other applications which require shielding of individuals or machinery from the hot and cold.

Claims: A fiber with reversible thermal energy storage properties comprising: a base material, and a thermal energy storage means associated with the fiber so that the fiber exhibits enhanced resistance to temperature change when subjected to heat or cold, the thermal energy storage means comprising a paraffinic hydrocarbon phase change material, or comprising a plastic crystal material, characterised in that the thermal energy storage means is contained in a plurality of microcapsules integral with and dispersed throughout the base material. A fiber with reversible thermal energy storage properties according to claim 1, wherein the thermal energy storage means contained in the individual microcapsules is protected by a dual wall, the first wall being the wall of the microcapsule, and the second wall comprising the base material which surrounds the microcapsule, whereby the resistance to leakage of the thermal energy storage means when the fiber is subjected to repeated external mechanical stresses is enhanced. A fiber with reversible thermal energy storage properties according to claim 1 or 2, wherein said microcapsules range in diameter from 1.0 µm to 10 µm. A fiber with reversible thermal energy storage properties according to claim 1, 2 or 3, wherein the fiber includes at least two types of separately encapsulated thermal energy storage means. A fiber with reversible thermal energy storage properties according to any preceding claim, wherein the base material is a synthetic polymer base material. A fabric or article with reversible thermal energy storage properties including a plurality of fibers, at least some of which comprise fibers according to any preceding claim.

Inventors: BRYANT YVONNE G, COLVIN DAVID P, BRYANT, YVONNE G., COLVIN, DAVID P.
Applicants: TRIANGLE RES & DEV CORP, TRIANGLE RESEARCH AND DEVELOPMENT CORPORATION
Application year: 1988
Main classification: D01F1
IPC codes: F28D20, D01F1, D03D15, D06M23, D04H1, D06M101