A buoyant carbonaceous fibrous structure coated with a water insoluble hydrophobic material

Abstract: A buoyant article which can be used for floatation and/or insulation comprising a fibrous structure of a multiplicity of resilient, shape reforming, elongatable, nonlinear carbonaceous fibers and a coating for said carbonaceous fibers comprising a water insoluble, hydrophobic, cured or set material.

Description: The present invention relates to a buoyant, low density, open celled, carbonaceous fibrous structure having good sound and thermal insulating properties. More particularly, the invention relates to lightweight, fibrous structures comprising a multiplicity of nonlinear carbonaceous fribers which are coated with a water insoluble hydrophobic material. The coated fibrous structures are useful in clothing articles, particularly jackets, jump suits, sleeping bags, floatation equipment, and the like, to provide buoyancy as well as sound and thermal insulation, particularly when used for aeroplane insulation. The invention further relates to a buoyant insulation for floating articles including a boat or a ship comprising the coated fibrous structure of the invention. Advanced thermal protection provided by articles which use insulating materials will have to meet higher demands for meeting the requirements for protecting the environment. Flammability, smoke toxicity, mold and mildew formation, loss of insulation performance when wet, dust and other irritants are only a short list of the problems found with the current materials used as insulation for personal articles such as garments, sleeping bags, and the like. The prior art discloses numerous insulating materials such as fowl down (Eider duck or goose) and feathers, asbestos, wool, cotton, polyester and polypropylene fibers, as well as various foam materials such as polyurethane foam, as thermal insulation for many applications. Fowl down is the most effective lightweight thermal insulation material. Current thermal insulating materials most commonly used as substitutes for down are thermoplastic fibrous materials which provide a fair to adequate thermal insulation at the cost of some additional weight, but are less than acceptable because they are flammable, melt when subjected to a modest amount of heat, and can generate toxic fumes when burned. In addition, such prior art materials absorb moisture and water and none have the capabilities of forming buoyant, lightweight structures even when coated with water repellent materials. There is a further need for a buoyant, lightweight, nonwettable insulation in aircraft which is also effective to provide thermal insulation under drastic temperature changes as well as sound absorbency. Current use of coated fiberglass results in additional weight for the aircraft and does little to help maintain the buoyancy of an aircraft when forced to conduct an emergency landing in an open body of water. U.S. Patent No. 4,167,604 to William E. Aldrich discloses the use of crimped hollow polyester filaments in a blend with down or feathers in the form of a multiple ply carded web which is treated with a thermosetting resin to form a batting having thermal insulating characteristics. The web is not flame resistant and does not have any buoyancy or moisture repellent characteristics. In effect, the web suffers from the serious disadvantages of being flammable, of being nonbuoyant and of retaining moisture. U. S. Patent No. 4,321,154 to Francois Ledru relates to high temperature thermal insulation material comprising insulating mineral fibers and pyrolytic carbon. To make the insulation lightweight, an expanding agent or hollow particles such as microspheres are utilized. Although lightweight, this material is not buoyant and will absorb moisture. European Patent Publication No. 0199567, Published October 29, 1986, to F. P. McCullough, et al entitled, "Carbonaceous Fibers with Spring-Like Reversible Deflection and Method of Manufacture," discloses nonlinear carbonaceous fibers which are suitably utilized in the buoyant structures of the present invention. U. S. Patent No. 4,371,585 to Memon, discloses a process for applying a silicone or siloxane coating which may be utilized in the present invention. A publication of the Dow Corning Corporation entitled, "Dow Corning Materials For High Technology Applications," 1986, discloses silicone products including silicone elastomers, organo-functional silanes, chlorosilanes, and the like, which can be used as coating materials in preparing the buoyant structures of the invention. In accordance with the present invention there is provided an open celled, buoyant fibrous structure adapted for use as a floatation article comprising a multiplicity of nonlinear, substantially irreversibly heat set, resilient, shape reforming, elongatable, carbonaceous fibers, said fibers having a reversible deflection ratio of greater than 1.2:1 and an aspect ratio (l/d) greater than 10:1 and a coating for said carbonaceous fibers comprising a water insoluble, hydrophobic material. The carbonaceous fibers contain at least 65 percent by weight of carbon and preferably posses a sinusoidal or a coil-like configuration or a more complicated structural combination of the two in order to provide the compression reforming characteristics required in the invention. The fibrous structure is open celled or porous and therefore has a low bulk density even when coated with a water insoluble, hydrophobic material. The fibrous structure possess both excellent thermal and sound insulation, and good reversible compressibility. The term fibrous structure herein applies to articles such as a wool-like fluff, a nonwoven web, batting, felt, fabric or cloth, or the like. Preferably, the structure is in the form of a wool-like fluff, a non-woven batting, felt or web and has a bulk density of from 4.8 to 32 kg/m³. Surprisingly, articles of the invention require less than about 10 percent by weight of the coating material in order to achieve buoyancy. Although a greater amount of the coating material can be utilized, it is not necessary for achieving the buoyancy requirements of the invention. Depending upon the hydrophobic coating material that is utilized and the utility of the fibrous structure, it has been unexpectedly found that only the outer surface of the fibrous structure need be coated in order to achieve desirable floatation characteristics. The coating materials which can be used in the present invention may consist of any lightweight, water insoluble material that can be deposited onto the fibers so as to adhere to the fibers. The coating materials include suitable compositions such as high molecular weight waxes, haloaliphatic resins, thermoset and thermoplastic resins, ionomers, silicone products including rubbers and elastomers, polysiloxanes, and the like. Some of the known water insoluble, hydrophobic, polymeric materials require that they be set or cured. Preferred coatings include the silicone products, polysiloxanes, polytetrafluoroethylene, polyvinylidene fluoride, and polyvinyl chloride. It is understood that the term "open-celled" fibrous structure means that the porosity of the structure is maintained and that the structure can still be opened. The carbonaceous fibers which are used in the invention may be prepared by heat treating a suitable stabilized carbonaceous precursor material such as that derived from an assembly of stabilized polymeric materials or pitch based materials (petroleum or coal tar). The polymeric material can be made into a nonflammable, carbonaceous fiber or fiber structure or configuration which is thermally stable. For example, in the case of polyacrylonitrile (PAN) based fibers, the fibers are formed by melt or wet spinning a suitable fluid of the precursor material having a normal nominal diameter of from 4 to 25 µm (microns). The fibers are then collected as an assembly of a multiplicity of continuous filaments in tows, and are stabilized (by oxidation in the case of PAN based fibers) in the conventional manner. The stabilized tows (or staple yarn made from chopped or stretch broken fiber staple) are thereafter formed into a coil-like and/or sinusoidal form by weaving or knitting the fibers, tows or yarn into a fabric or cloth. The fabric or cloth is thereafter heat treated, with the fibers in a relaxed and unstressed conditions, at a temperature of from 525°C to 750°C, in an inert atmosphere for a period of time to produce a heat induced thermoset reaction wherein additional cross-linking and/or a cross-chain cyclization reaction occurs between the original polymer chain. At the lower temperature range of from 150°C to 520°C, the fibers are provided with a varying proportion of temporary to permanent set while in the upper range of temperatures of from 525°C and above, the fibers are provided with a substantially permanent or irreversible heat set. It is to be understood that higher temperatures may be employed of up to about 1500°C, but the most flexible and the smallest loss of fiber breakage, when carded to produce a wool like fluff, is found in those fibers that are heat treated to a temperature of from 525°C to 750°C. Preferably, the method of carbonaceous fiber manufacture is as described in the aforementioned European Patent Publication No. 0199567. Carbonaceous fibers that are derived from nitrogen containing polymeric materials, such as an acrylic based polymer, generally have a nitrogen content of from 5 to 35 percent by weight, preferably from 16 to 25 percent by weight, more preferably from 18 to 20 percent by weight. The "electrical resistance" of a carbonaceous fiber is determined by measurement on a 6K tow of fibers with the individual fibers having a nominal diameter of from 7 to 20 µm (microns). The "specific resistivity" is calculated by measurements as described in European Patent Application No. 0 199 567. The carbonaceous fibers which are utilized in the fibrous structures of the invention can be classified into three groups, depending upon the particular end use and the environment that the structures in which they are incorporated are placed. In a first group, the carbonaceous fibers have a carbon content of greater than 65 percent by weight but less than 85 percent by weight and are electrically nonconductive and possess no antistatic characteristics, i.e., they are not able to dissipate an electrostatic charge. The nonconductive fibers have an electrical resistance of greater than 4 x 10⁶ ohms/cm and, correspondingly, a specific resistivity of greater than 10⁻¹ ohms-cm. When the nonconductive fibers are selected from an acrylic polymer, it was determined that the nitrogen content of such fibers was greater than about 18 percent by weight. Such fibers when formed into a wool-like fluff, batting and the like, and coated according to the invention are suitable as insulation for sleeping bags, boats, floatation devices and the like. In a second group, the carbonaceous fibers are slightly or partially electrically conductive and can be classified as being antistatic, i.e., having the ability to dissipate an electrostatic charge. These fibers have a carbon content of greater than 65 percent by weight but less than 85 percent by weight and an electrical resistance of from 4 x 10⁶ to 4 x 10³ ohms/cm. Preferably, when the carbonaceous fibers are derived from precursor stabilizedacrylic fibers, i.e., polyacrylonitrile based fibers, the percentage nitrogen content is from 16 to 20 percent by weight and preferably from 18 to 20 percent by weight. These particular fibers when coated are excellent for use as insulation for personal articles where antistatic properties are desirous as well as insulation and buoyancy. The coated battings of the second group of fibers are useful as insulation in flight suits, jackets, in aircraft to provide insulation, sound proofing as well as buoyancy, in sports garments, floatation equipment, and the like. In a third group are carbonaceous fibers having a carbon content of at least 85 percent by weight. Preferably, the fibers which are utilized are derived from stabilized acrylic fibers and have a nitrogen content of less than 10 percent by weight. As a result of the still higher carbon content, the fibrous structures of the invention have a higher electrical conductivity, i.e., an electrical resistance of less than 4 x 10³ ohms/cm and, correspondingly, a specific resistivity of less than 10⁻¹ ohms-cm. The nonlinear carbonaceous fibers, when formed into a structure such as a batting, or the like, provide better insulation against high temperatures as compared to an equal weight of linear carbonaceous fibers. As a result of their higher carbon content, these fibers have superior thermal insulating characteristics. The fibrous structure in the form of a wool-like fluff, even when coated with a hydrophobic material, provides good compressibility and resiliency while maintaining buoyancy, thermal and sound insulating efficiency, as well as electrical shielding and/or electrical grounding capability. Preferred polymeric precursor materials are stabilized acrylic fibers selected from acrylonitrile homopolymers, acrylonitrile copolymers and acrylonitrile terpolymers. The copolymers preferably contain at least about 85 mole percent of acrylonitrile units and up to 15 mole percent of one or more monovinyl units copolymerized with styrene, methylacrylate, methyl methacrylate, vinyl chloride, vinylidene chloride, vinyl pyridine and the like. Also, the acrylic filaments may comprise terpolymers, preferably, wherein the acrylonitrile units are at least about 85 mole percent. The fibrous structure of the invention may be treated either before or after coating with an organic or inorganic binder, needle punched, bagged or adhered to a flexible or rigid support using any of the conventional materials and techniques depending upon the ultimate use and environment of the structure. The coating compositions which may be utilized to form the coating on the fibrous structure may be applied by any conventional means such as by dipping, spraying, application with rollers and the like. The coating composition when applied need not cover the entire open structure throughout but preferably should be uniformly distributed. Suitably buoyant articles have been obtained wherein only the surface area or a portion thereof is coated by spraying the coating material in an aerosol form onto the fibrous structure. It is understood that all percentages as herein utilized are based on weight percent. Exemplary of the present invention are set forth in the following examples. Example 1: A. Preparation of Batting A stabilized polyacrylonitrile PANOX™ (R. K. Textiles) continuous 3K (3000 filaments) or 6K (6000 filaments) hereafter referred to as OPF, tow having nominal single fiber diameters of about 12 microns, was knit on a flat bed knitting machine into a cloth having from 3 to 4 loops per centimeter. Portions of this cloth were heat set at 750°C in a nitrogen atmosphere over a 6 hour period. When the cloth was deknitted, it produced a tow which had an elongation or reversible deflection ratio of greater than 2:1. The deknitted tow was cut into various lengths of from 5 to 25 cm, and fed into a Platts Shirley opener. The fibers of the cut tow were separated by a carding treatment into a wool-like fluff, that is, the resulting product resembled an entangled wool-like mass or fluff in which the fibers had a high interstitial spacing and a high degree of interlocking as a result of the nonlinear configuration of the fibers. B. Coating Procedure The batting of Part A was spread out and sprayed with an aerosol spray containing a fluoroalkane resin in a solvent comprising 1,1,1-trichloroethane sold under the trademark "SCOTCHGARD™" by Household Products Division/3M. About 90 percent of the outside surface of the batting was coated. The batting was then air dried to cure the coating and weighed. The batting, when placed in water for two hours, floated. After two hours, the batting was shaken, squeezed and weighed. There was about 0.1 percent water absorbency. The coated batting is suitable for use as a floatation aid and insulation for jackets and jumpsuits. Example 2 A 3K OPF PANOX™ stabilized tow was knit on a Singer flat bed knitting machine at a rate of 4 stitches/cm and was then heat treated at a temperature of 950°C. The cloth was deknitted and the tow (which had a coil elongation or reversible deflection ratio of greater than 2:1) was cut into 7.5 cm lengths. The cut tow was then carded on a Platt Miniature carding machine to produce a wool-like fluff having fibers ranging from 2.5 to 6.5 cm in length. The wool-like fluff had a high electrical conductivity (a resistance of less than 4 x 10³ ohms/cm) when tested over any length of up to 60 cm. The fluff was coated by dipping into a bath containing a 20 percent solution of polyvinylidene fluoride in 1,1,1-trichloroethane. The fluff was removed and air dried. The dried fluff when placed into a water bath floated. Example 3 The coated wool-like fluff material of Example 2 was introduced as a filling into a thermal jacket. The jacket employed about 140 g of the fluff as the sole fill for the jacket. The jacket had an insulating effect similar to that of a down (feathers) jacket having from 420 to 710 g of down as the insulating fill. The jacket when placed into a water bath floated. Example 4 Two other jackets were filled with the coated fluff of Example 2. In a first jacket the fibers used were a blend of the carbonaceous fibers of Example 2 and 25 percent of a synthetic polyester binder fiber which was thermally bonded to the carbonaceous fibers. In a second jacket, the fibers used were the carbonaceous fibers of Example 2 with 20 percent of a thermally curable epoxy resin which was thermally cured. Both of the jackets contained about 420 g of insulation material. Both jackets when worn and the wearer placed in a pool of water were buoyancy aids.

Claims: An open celled fibrous structure comprising a multiplicity of non-linear, substantially irreversibly heat set, resilient, shape reforming, elongatable, carbonaceous fibers having a carbon content of at least 65% by weight, said fibers having a reversible deflection ratio of greater than 1.2:1 and an aspect ratio greater than 10:1, characterized in that said open celled fibrous structure has a coating of a water insoluble, hydrophobic material, and that said structure is buoyant and adapted for use as a floatation article. The structure of claim 1, wherein said carbonaceous fibers are derived from acrylic precursor fibers selected from acrylonitrile homopolymers, acrylonitrile copolymers and acrylonitrile terpolymers, wherein said copolymers and terpolymers contain at least 85 mole percent acrylic units and up to 15 mole percent of one or more monovinyl units copolymerized with another polymer. The structure of claim 2, wherein said precursor fibers have a diameter of from 4 to 25 micrometers. The structure of claim 1, 2 or 3, wherein said carbonaceous fibers have a carbon content of at least 85 percent by weight, are electrically conductive and have an electrical resistance of less than 4x10³ ohm/cm, and a specific resistivity of less than 10⁻¹ ohms-cm. The structure of claim 1, 2 or 3, wherein said carbonaceous fibers have a carbon content of from 65 to 85 percent by weight, are electrically non-conductive or do not possess any electrostatic dissipating characteristics, and have an electrical resistance of greater than 4x10⁶ ohm/cm and a specific resistivity of greater than 10⁻¹ ohms-cm. The structure of claim 1, 2 or 3, wherein said carbonaceous fibers have a carbon content of from 65 to 85 percent by weight, have a low electrical conductivity and electrostatic dissipating characteristics, and have an electrical resistance of from 4x10⁶ to 4x10³ ohm/cm. The structure of any one of the preceding claims, wherein the carbonaceous fibers are permanently heat set and have a sinusoidal and/or coil-like configuration. The structure of any one of the preceding claims, wherein said multiplicity of carbonaceous fibers are in the form of a fibrous structure selected from a wool like fluff, a non-woven web, batting, felt, fabric and cloth. The structure of claim 8, wherein said fibrous structure is in the form of a woollike fluff, a non-woven batting, felt or web and has a bulk density of from 4.8 to 32 kg/m³. The structure of any one of the preceding claims, wherein said water insoluble, hydrophobic coating is selected from an ionomer, a thermoset resin, a thermoplastic resin, a haloaliphatic resin, a silicone elastomer, silicone rubber, polysiloxane, or a high molecular weight wax. The structure of claim 10, characterized in that said water insoluble, hydrophobic coating is present in an amount of less than 10% by weight, based on the total weight of the structure. A buoyant insulated article selected from a jacket, a sleeping bag, or blanket, characterized in that the insulation comprises the coated, fibrous structure of any one of the preceding claims. A buoyant insulation for an aircraft, characterized by the coated, fibrous structure of any one of claims 1 to 11. A buoyant insulation for floating articles, including a boat or ship, characterized by the coated fibrous structure of any one of claims 1 to 11.

Inventors: MCCULLOUGH FRANCIS P JR, SNELGROVE R VERNON, MCCULLOUGH, FRANCIS P., JR., SNELGROVE, R. VERNON
Applicants: DOW CHEMICAL CO, THE DOW CHEMICAL COMPANY
Application year: 1988
Main classification: D01F11
IPC codes: D01F9, D01F11, D06M15, D06M101