Patent Application
20070282053
The emulsification process of water and STF was found to require a pretreatment of the highly viscous fluid and certain amount of energy that can be achieved from an ultrasonic bath, horn sonication, or heavy duty blending.
STFs are known in the art and are disclosed in Wagner et al, U.S. Ser. No. 11/260,742 and Wagner et. al., PCT application no. US06/04581 filed Feb. 9, 2006 which are again incorporated by reference in their entirety.
The stabilization process was aided by a surfactant. Surfactants are disclosed in the following references which are incorporated by reference in their entirety: (Kirk-Othmer Encyclopedia of Chemical Technology “Surfactants”, by Tharwat Tadros Copyright© 2006 by John Wiley & Sons, Inc., DOI: 10.1002/0471238961.1921180612251414.a01.pub2, Article Online Posting Date: Jul. 14, 2006) and Flick, Ernest W., “Industrial Surfactants” 2nd edition, © 1993, publisher, William Andrew Publishing/Noyes (Flick, “Industrial Surfactants”).
The preferred surfactants are those that have a suitable hydophilic/lyophilic balance (HLB), preferably from 8 to 18 and more preferably typically around 15. (Kirk-Othmer Encyclopedia of Chemical Technology, “Emulsions” by Edward Kostansek, Rohm and Haas Co.,Copyright© 2003 by John Wiley & Sons, Inc. All rights reserved.DOI: 10.1002/0471238961.0513211206180902.a01.pub2, Article Online Posting Date: Jul. 18, 2003
These include, but are not limited to Pluronic™ L64 and others from the Pluronic™ family of similar or higher HLB (BASF), Triton-X705 or others from the Triton™ family with similar HLB (Dow). Other nonionic, anionic, cationic or zwitterionic surfactant suitable for forming aqueous emulsions of insoluble oils may be used depending upon the specific STF carrier fluid composition. Similarly, nonionic, anionic, or cationic polymers may also be employed, again depending on the specific STF carrier fluid composition. Stability can also be achieved through the use of particles, commonly known as a pickering emulsion. These particles may be the same as those comprising the STF, or may be specifically chosen to stabilize the oil-water interface. Other “Surfactants can be chosen from among those recommended by standard industrial practice handbooks, such as Flick “Industrial Surfactants”.
In the case of a water like system, the surfactant would have an HLB of about 8 to about 20, preferably around 15. In the case of an oil like system, the surfactant would have an HLB of about 3 to about 8, (See Kirk-Othmer Encyclopedia of Chemical Technology, “Emulsions” by Edward Kostansek, Rohm and Haas Co.,Copyright© 2003 by John Wiley & Sons, Inc..DOI: 10.1002/0471238961.0513211206180902.a01.pub2, Article Online Posting Date: Jul. 18, 2003
Water like, would include water and aqueous soluble solvents such as alcohols.
The materials that can be used are conventional body armor or ballistic material. Conventional body armor materials are typically comprised of many layers of polyaramid poly(phenylene diamine terephthalamide) fabric, sold by DuPont under the registered name of KEVLAR®, with optional ceramic tile inserts.
One type of material would include reactive polymeric materials that cure or crosslink to form solids. Reactive polymers include polyurethanes that cure through the chemical reaction of components polyols and isocyanates), epoxies that cure through the addition of a catalyst, and UV curable resins. A preferred second material of this type would be from the class of elastomeric or elastomeric gel materials, such as silicone rubber (cross-linked PDMS) or silicone gels and the like, which can be relatively low viscosity liquids prior to cross-linking, whereafter they form resilient materials with good rebound characteristics. A variety of elastomers exist to provide a wide range of properties such as chemical and solvent resistance, temperature resistance, and hardness (durometer). These materials could be mixed with shear thickening fluids at room temperature to disperse the shear thickening fluids adequately and to achieve the desired composite morphology or shear thickening fluid droplet size. The liquid-like second material could subsequently be cured, or the curing could be accelerated through heating or the addition of additional components that catalyze the reaction and transform the second material into a solid. Curing could be accomplished by UV. Further, the liquid could be gelled by physical and or chemical crosslinking of polymers or by the addition of structure forming agents, such as fumed silica.
Another type of materials would include melt processable polymers or thermoplastic elastomers (TPE). Melt processable polymers include but are not limited to polyolefins such as polyethylene and polypropylene, nylon, polymethylmethacrylate, polyvinylchloride, polyethylene, polyesters such as but not limited to terephthalate (PET), polycarbonate and the like. Thermoplastic elastomers would include such as materials as those sold under the trade names Santoprene™ (Exxon Mobil Chemical), Hytrel® (DuPont Company), and Engage™ from DuPont-Dow Elastomers. In this instance, increased temperature is used to liquefy a polymeric material. At the processing conditions required to achieve the desired melt flow properties of the polymer second material, the shear thickening fluid would be compounded with the polymer melt to achieve the desired level of mixing and microstructure. The temperature would subsequently be reduced to generate the solid polymer-shear thickening fluid composite.
The pre-treatment of the STF involved dissolving the STF in a co-solvent such as but not limited to alcohol, alkanes, such as heptane and hexane, or toluene. Any soluble or partially material that does not adversely affect the STF properties can be employed.
This boiling point of this co-solvent needs to be lower than the boiling point of the solvent component of the STF, which in this case, is a silicone oil. The amount of co-solvent should also be minimized, but sufficient to enable the STF to be emulsified. A preferred amount of co-solvent is around 10% by volume in order to avoid any significant processing issues and to ease the evaporation of the co-solvent.
As a specific example, 150 mL of STF (50% 450 nm silica particles (Shokubai, KEP-50, Nissan Chemical) dispersed in polytrimethicone(PTM-20, ISP, Inc.) and 15 mL of heptane (reagent grade, Fischer Scientific) were mixed by hand-shaking the container for 1 minute and subsequently, placing the container on a roll-mixer for 10 minutes. In a separate stock solution container, 0.5 g of a surfactant (Pluronic L64, BASF) was dissolved in 1000 mL of deionized water. To ensure that the surfactant fully dissolved in the water, the stock solution was placed in the ultrasonic bath for 1 hour under heating to 35° C. 585 mL of the water/surfactant mixture was then added to the STF/heptane mixture. This mixture was then placed in an ultrasonic bath at approximately 35° C. for 1 hour. The mixture was then hand-shaken for 1 minute after sonication. The result is shown in
The emulsion as prepared appears uniform for approximately 5-10 minutes, where upon a dense layer appears to form at the bottom, while a clear layer of water forms at the top. These phases continue to grow at the expense of the emulsion. Some emulsion is still evident after 24 hours. Upon shaking or stirring, the emulsion can be regenerated.
As a specific application of the above mixture, the emulsion as prepared was placed in a dip coating pan for STF-fabric manufacturing. A standard procedure, previously published was followed. (Egres, et al., STAB PERFORMANCE OF SHEAR THICKENING FLUID (STF)-FABRIC COMPOSITES FOR BODY ARMOR APPLICATIONS, Proceedings of SAMPE 2005: New Horizons for Materials and Processing Technologies. Long Beach, Calif. 1-5 May 2005). The fabric used was a 15″×15″ sheet of Twaron (1011-123.0-1002, provided by Barrday, Inc.). The fabric was submerged in the emulsion for 1 minute and then drawn through a set of 2 rubber nip-rollers to remove excess fluid. The sheet was then hung-dried for 30 minutes upon which it was further dried in an oven at 80° C. for 30 minutes. The final weight addition of STF to the fabric was 24%. The STF-Twaron composite was then cut into four 7.5″×7.5″ pieces which were stacked for quasistatic (QS) spike resistance testing. Four untreated sheet were also tested for comparison. An Intron 4201 was used to measure load. An NIJ-standard spike was used as the impactor and pushed into the fabric sample at 5 mm/min. Backing material is a multilayer foam and witness paper support, the details of which is outlined in NIJ Standard 0115.0.
All the references described above are incorporated by reference in its entirety for all useful purposes.
While there is shown and described certain specific structures embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described.
This application claims benefit to US Provisional Application No. 60/811,339 filed Jun. 6, 2006, and is incorporated by reference in its entirety for all useful purposes.
| Number | Date | Country | |
|---|---|---|---|
| 60811339 | Jun 2006 | US |
