Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1997-12-23
2001-07-03
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S061000
Reexamination Certificate
active
06255359
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to compositions having variable, controllable or differential porosities and/or permeabilities, methods for preparing such compositions and method for the use of such compositions as membranes, filters or the like.
More particularly, the present invention relates to polymeric compositions having a desired permeability and/or porosity or a desired variation in permeabilities and/or porosity where the compositions are made by dispersing one or more (at least one) pore-forming agent in a polymer matrix, optionally force developing gradients in concentrations of the agents in the composition and subsequently leaching the dispersed agents from the matrix to form the composition and methods for using the compositions.
2. Description of the Related Art
Porous and/or permeable polymeric materials find application in a wide range of applications including permeable and semi-permeable membranes, filters, biomedical applications, chromatography media, and other applications where porosity and/or permeability are characteristics that effect the performance of a given material in a given application.
Several patents have dealt with synthetic composition and articles made therefrom that related to membranes, implants or other porous and/or permeable compositions including the United States Patents described herein.
U.S. Pat. No. 5,102,917 discloses a porous polysulfone membrane made by blending polysulfone with a particulate solid or with the particulate solid and a second polymer, extruding the resultant blend to form an article and leaching the particulate solid and second polymer from the article and is incorporated herein by reference.
U.S. Pat. No. 4,969,906 discloses a microporous implant comprising a hydrophilic polymeric material having pores where the pores are formed by: (a) dispersing water-dissolvable salt in the monomer; (b) polymerizing the monomer; (c) subjecting the resulting polymeric material with salt crystals dispersed therein to an aqueous solution; and (d) shaping said polymeric material and is incorporated herein by reference.
U.S. Pat. No. 4,634,720 discloses a process for the preparation of a composite material by polymerizing in situ an N-carboxyanhydride of an a-amino acid in the presence of a powdered calcium phosphate biomaterial where the polymerization taking place in an inert organic solvent and is incorporated herein by reference. The process also includes the additional step of adding a pore-forming agent to the composite material.
U.S. Pat. No. 4,386,129 discloses a porous film made by a process comprising the steps of: (a) dispersing in a resinous polymer, a nucleating agent capable of producing beta-spherulites; (b) forming by extrusion a film with a thickness from the molten product of step (a); (c) cooling the film below the crystallization temperature of the polymer to form beta-spherulites; and (d) removing the beta-spherulites from the cooled film product of step (c) by an extracting solvent to form the porous film product and is incorporated herein by reference.
U.S. Pat. No. 4,196,070 discloses a method for forming a microporous fluorocarbon sheet membrane comprising: (a) mixing an aqueous dispersion of fluorocarbon polymer with a pore-forming agent comprising a water-soluble crystallizable metallic organic salt; (b) forming a wet sheet from the aqueous dispersion; (c) concentrating the aqueous dispersion; (d) drying the crystal-containing sheet; (e) sintering the dry sheet; and (f) leaching the salt crystals from the sheet in an aqueous medium and is incorporated herein by reference.
U.S. Pat. No. 3,770,537 discloses a method of making a microporous film comprising: grinding a milled mixture comprising a thermoplastic polyurethane resin and a plurality of water-soluble particles; heat-forming the ground mixture to form a film; heat treating the film under a pressure of less than 10 p.s.i.; and leaching said particles from said heat-formed film and is incorporated herein by reference.
Although these patents relate generally to microporuos film, there is still a need in the art for cost effective and efficient methods for making polymer compositions that have controlled permeability and/or porosity or controlled variable permeability and/or porosity.
SUMMARY OF THE INVENTION
The present invention provides polymer compositions having a desired degree of permeability and/or porosity across a region or cross-section of an article made therefrom or a desired variation in permeability and/or porosity across a region or cross-section of an article made therefrom. The compositions and articles made therefrom can have permeabilities and porosities that range from substantially impermeable and/or non-porous to highly porous and highly permeable or any combination of permeability and porosity. The compositions and the articles made therefrom have potential use as separation media, open and closed foams, filters, permeable and semi-permeable membranes, implants or the like.
The present invention also provides methods for making composition having a substantially uniform, variable and/or differential permeability and/or porosity. Broadly, the method includes mixing into a polymer matrix having a first density, at least one pore-forming agent having a second density.
During or after the mixing, the agents can be allowed to anisotropically distribute throughout the polymer matrix or portions thereof due to the action of an external force such as gravity. This anisotropic distribution of agents in the matrix results in formation of compositions with variable permeabilities or porosities. After mixing and optional force development, the pore-forming agents are removed, leached or extracted from the matrix yielding a porous and/or permeable composition.
The method can also include agitating the polymer matrix containing the pore-forming agents so that void spaces formed in the polymer matrix will be generally larger than the actual physical size of the pore-forming agents, at least for solid pore-forming agents. The amplitude, direction and frequency of the agitation will control to some extent the size and shape of the void places formed in the composition after removal of the pore-forming agents. Preferentially, the mixing is carried out under controlled conditions where the controlled conditions include air-flow and optionally temperature, pressure, gas composition and/or humidity. Alternately, the mixing step can be the agitation step where the composition is mixed by vibronic agitation and not by other mixing techniques such as stirring, extruding, masticating, or the like.
Force development (anisotropic distributions of particles in the polymer matrix caused by the application of an external applied force) of the composition is preferably continued until a desired degree of variation in porosity and/or permeability is achieved. In a most severe case, one portion of the composition is rendered substantially impermeable and non-porous. Of course, combinations of force development, agitation, and mixing can be used to prepare compositions of the present invention as well with varying permeability and porosity characteristics.
This invention also provides methods for making composites having differential or variable permeability and/or porosity by adhering or affixing a first composition having a first permeability and/or porosity to a second composition having a different permeability and/or porosity. Such composites can have simple or complex differential permeabilities and/or porosities. The first and second compositions can be substantially uniform composition made by the method of the present invention or commercially available or can be different compositions of this invention having variable permeability and/or porosity.
Thus, composite structures can be prepared having complex arrays of porosities and/or permeabilities, either static or variable within regions of or throughout the entire composite structure. In fact, one part or region of the structure could allow permeat
Agrawal C. Mauli
Athanasiou Kyriacos A.
Board of Regents of the University of Texas System
Foelak Morton
Strozier Robert W
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