Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2002-08-23
2004-03-23
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C521S028000
Reexamination Certificate
active
06710093
ABSTRACT:
1. FIELD OF THE INVENTION
This invention relates to processes for immobilizing ion exchange particles within porous materials, and the products of those processes.
2. BACKGROUND OF THE INVENTION
The exchange of ions in solution with those bound to an insoluble solid—a process referred to as “ion exchange”—has numerous applications in industry, research, and medicine. Examples of applications include, but are not limited to, water softening, chromatography, natural product purification, metal recovery, and blood filtration. The insoluble solid materials typically used in ion exchange applications consist, comprise, or are made from ion exchange resins, which are typically functionalized porous polymeric materials. The functional groups bound to the surfaces and interiors of these materials are, or contain, an ionic moiety that can exchange with a solvated ion with which it comes in contact.
The chemical composition, form, and size of an insoluble solid used for ion exchange depends upon the particular ion exchange application. For example, U.S. Pat. Nos. 5,080,646 and 5,147,296 disclose porous membranes made from ethylene vinyl acetate (EVA) and ion exchange resin. The membranes, which are allegedly useful in some drug delivery applications, are formed using melt processing or solvent casting. U.S. Pat. No. 5,169,383 discloses an ion exchange membrane which is also made using melt processing or solvent casting.
A number of other ion exchange membranes have been disclosed. For example, U.S. Pat. No. 5,346,924 discloses a membrane made by heating, under pressure, granules or pellets of ion exchange resin and a binder. The binder is either linear low density polyethylene or high molecular weight polyethylene. U.S. Pat. No. 5,531,899 also discloses an ion exchange membrane made from high molecular weight polyethylene and ion exchange particles (i.e., particles of ion exchange resin). The membrane is formed by mixing the polyethylene with a porogen (diluent), heating the mixture, adding ion exchange particles, and forming, shaping, and quenching the final product.
Ion exchange resins have also been incorporated into non-membrane materials. For example, an epoxy ion exchange resin was reportedly adhered to a layer of EVA on a silica substrate. Chanda, M. and Rempel, G. L.,
Chem. Engin. Sci.
54:3723-3733 (1999). In most applications, however, ion exchange resin is simply poured into a column through which solutions can be passed. Although simple, this approach can be inefficient. One source of inefficiency is the formation of channels through the resin or along the walls of the column. Once such channels have formed, solutions passed through the column will avoid the bulk of the resin. It is thus desirable to immobilize particles of ion exchange resin in a porous solid through which solutions can pass.
Until this invention, the need for a process that can immobilize ion exchange resin has not been adequately met. In particular, processes such as those used to prepare typical ion exchange membranes allow little control over the porosity, ion exchange efficiency, and strength of the resulting ion exchange material. For example, methods that comprise melt processing can leave individual particles or even large chunks of ion exchange resin entirely coated with the polymers used to immobilize them, thereby rendering these pieces of resin useless. Conventional processes used to immobilize particles of ion exchange resin further do not allow the facile immobilization of resins that decompose at high temperatures. Consequently, new processes of immobilizing of ion exchange particles are desired, as are the products of those processes.
3. SUMMARY OF THE INVENTION
A first embodiment of the invention encompasses a process for immobilizing ion exchange particles in a polyolefin matrix. This method comprises sintering a mixture comprised of ion exchange and polyolefin particles, wherein the polyolefin particles are substantially spherical. Preferably, a substantial portion of the ion exchange particles do not decompose during the sintering.
In a preferred embodiment, the average size of the polyolefin particles is about the same as the average size of the ion exchange particles.
In a preferred embodiment, the polyolefin particles are thermal fined. In another preferred embodiment, the polyolefin particles are made using underwater pelletizing.
In another preferred embodiment, the mixture of particles is comprised of from about 90 to about 30 weight percent, more preferably from about 70 to about 40 weight percent, and most preferably from about 60 to about 50 weight percent ion exchange particles.
In another preferred embodiment, the polyolefin has a melting temperature that is less than the degradation temperature of the ion exchange resin. In a more preferred embodiment, the polyolefin has a melting temperature of less than about 125° C., more preferably less than about 115° C., and most preferably less than about 105° C.
In another preferred embodiment, the polyolefin has a melt-flow index of from about 10 to about 0.5, more preferably from about 8 to about 0.5, and most preferably from about 3 to about 1.
In another preferred embodiment, the polyolefin is selected from the group consisting of, but not limited to: ethylene vinyl acetate; ethylene methyl acrylate; polyethylenes such as, but not limited to, low density polyethylene, linear low density polyethylene, high density polyethylenes, and ultra-high molecular weight polyethylene; polypropylenes; ethylene-propylene rubbers; ethylene-propylene-diene rubbers; and mixtures and derivatives thereof. In a more preferred embodiment, the polyolefin is ethylene vinyl acetate comprising from about 30 to about 2, more preferably from about 20 to about 5, and most preferably from about 15 to about 6 weight percent vinyl acetate.
In a specific preferred embodiment, the polyolefin particles are ethylene vinyl acetate particles and the mixture is sintered at a temperature of from about 120° C. to about 75° C., more preferably from about 110° C. to about 80° C., and most preferably from about 100° C. to about 95° C. The sintering can optionally be conducted under pressure; preferred pressures are from about 1 psi to about 10 psi.
In another preferred embodiment, the mixture comprised of ion exchange and polyolefin particles further comprises a filler. Specific fillers include, but are not limited to, carbon black, cellulose fiber powder, siliceous fillers, polyethylene fibers and filaments, and mixtures thereof.
A second embodiment of the invention encompasses a process of immobilizing ion exchange particles in a hydrogel. This process comprises the formation of a mixture comprised of a solvent, ion exchange particles, and a material capable of forming a hydrogel, and heating and cooling the mixture under conditions sufficient to form a physically crosslinked hydrogel.
In a preferred embodiment, the mixture is comprised of from about 97 to about 60 weight percent, more preferably from about 96 to about 80 weight percent, and most preferably from about 95 to about 90 weight percent ion exchange particles.
In another preferred embodiment, the material capable of forming a hydrogel is poly(vinyl alcohol). In another preferred embodiment, the solvent is water, more preferably deionized water.
In another preferred embodiment, the conditions sufficient to form a physically crosslinked hydrogel comprise the heating and cooling of the mixture from about 1 to about 20, more preferably from about 5 to about 15, and most preferably from about 8 to about 12 times. In more specific embodiments of the invention, the mixture is cooled to a temperature of from about −60° C. to about −20° C., more preferably from about −50° C. to about −25° C., and most preferably from about −35° C. to about −30° C., and heated to a temperature of from about 25° C. to about 60° C., more preferably from about 25° C. to about 45° C., and most preferably from about 30° C. to about 35° C.
In another preferred embodiment, the mixture comprised of a solven
Arthur Michael Gerald
Greene, IV George W.
Yao Li
Lipman Bernard
Pennie and Edmonds LLP
Porex Corporation
LandOfFree
Immobilized ion exchange materials and processes for making... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Immobilized ion exchange materials and processes for making..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Immobilized ion exchange materials and processes for making... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3265944