US20110165811A1

US20110165811A1 - Article Formed From Electrospinning A Dispersion

Info

Publication number: US20110165811A1
Application number: US13/061,232
Authority: US
Inventors: Randal M. Hill; Eric J. Joffre; Donald T. Liles; Bonnie J. Ludwig
Original assignee: Dow Corning Corp
Current assignee: Dow Silicones Corp
Priority date: 2008-08-29
Filing date: 2009-08-28
Publication date: 2011-07-07
Also published as: WO2010025381A3; CN102187022B; CN102187022A; TW201016909A; IL211432A0; WO2010025381A4; WO2010025381A2; KR20110058827A; CA2735440A1; JP2012501390A; EP2318575A2; MX2011002221A

Abstract

An article of fibers includes a cured compound. The fibers are formed from electrospinning a dispersion. The dispersion includes a liquid and a condensation curable compound. A content of the liquid in the dispersion is reduced such that the condensation curable compound cures. The article is formed from a method of manufacturing which includes the step of forming the dispersion. The method also includes the step of electro spinning the dispersion to reduce the content of the liquid such that the condensation curable compound cures.

Description

FIELD OF THE INVENTION

The present invention generally relates to an article and a method of manufacturing the article. More specifically, the method includes forming a dispersion including a liquid and a condensation curable compound and electrospinning the dispersion to manufacture the article.

DESCRIPTION OF THE RELATED ART

The development of fibers having micro- and nano-diameters is currently the focus of much research and development in industry, academia, and government. These types of fibers can be formed from organic and inorganic materials such as polyaniline, polypyrrole, polyvinylidene, polyacrylonitrile, polyvinyl chloride, polymethylmethacrylate, polythiophene, and iodine-doped polyacetylene. Fibers of this type have also been formed from hydrophilic biopolymers such as proteins, polysaccharides, collages, fibrinogens, silks, and hyaluronic acid, in addition to polyethylene and synthetic hydrophilic polymers such as polyethylene oxide.
Many of these types of fibers can be formed through a process known in the art as electrospinning. Electrospinning is a versatile method that includes use of an electrical charge to form a mat of fibers. Typically, electrospinning includes loading a solution into a syringe and driving the solution to a tip of the syringe with a syringe pump to form a droplet at the tip. Electrospinning also usually includes applying a voltage to the needle to form an electrified jet of the solution. The jet is then elongated and whipped continuously by electrostatic repulsion until it is deposited on a grounded collector, thereby forming the mat of fibers.
Fibers that are formed via electrospinning may be used in a wide variety of industries including in medical and scientific applications. More specifically, these types of fibers have been used to reinforce certain composites. These fibers have also been used to produce nanometer tubes used in medical dialysis, gas separation, osmosis, and water treatment.
In some applications, fibers are formed from electrospinning various types of two- and three-phased systems such as emulsions. The electrospinning techniques that are used with these systems typically produce fibers that exhibit undesirable mechanical characteristics rendering the fibers brittle and fragile. Accordingly, there remains an opportunity to form articles of fibers that are formed from dispersions and that exhibit improved stress and strain properties. There also remains an opportunity to develop a method of forming such articles.

SUMMARY OF THE INVENTION AND ADVANTAGES

The present invention provides an article of fibers and a method of manufacturing the article. The fibers include a cured compound and are formed from electrospinning a dispersion. The dispersion includes a liquid and a curable compound. The method includes the steps of forming the dispersion and electrospinning the dispersion. In one embodiment, the method includes the step of curing the curable compound.
Electrospinning the dispersion allows the fibers that are formed to exhibit characteristics typical of the cured compound and exhibit improved stress and strain properties. This formation of fibers allows for more efficient and accurate production of a variety of materials to be used in medical, scientific, and manufacturing industries. The use of the dispersion also allows for a variety of types of condensation curable compounds to be utilized to form products that can be manipulated based on desired physical and chemical properties.

BRIEF DESCRIPTION OF THE DRAWING

Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein FIG. 1 is a scanning electron microscope image of an article including fibers of the instant invention including fiber-fiber junctions and spherical defects.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides an article including fibers (i.e., an article of fibers), as shown in FIG. 1. The present invention also provides a method of manufacturing the article. The method, which includes a step of electrospinning, is described in greater detail below.
The article may include a single layer of fibers or multiple layers of fibers. As such, the article may have a thickness of at least 0.01 μm. More typically, the article has a thickness of from about 1 μm to about 100 μm and most typically has a thickness of from about 25 μm to about 100 μm. The article is not limited to any particular number of layers of fibers. The article may be woven or non-woven, and may exhibit a microphase separation. In one embodiment, the fibers and the article are non-woven and the article is further defined as a mat. In another embodiment, the fibers and the article are non-woven and the article is further defined as a web. Alternatively, the article may be a membrane. The fibers may also be uniform or non-uniform and may have any surface roughness. The article may be waterproof, water resistant, fire resistant, electrically conductive, self-cleaning, water draining, drag reducing, and combinations thereof. In one embodiment, the article is a coating. It is also contemplated that the article may be a fabric, a breathable fabric, a filter, or combinations thereof. Further, the article may be used in a variety of industries such as in catalysts, filters, solar cells, electrical components, transdermal patches, bandages, drug delivery systems, and in antimicrobial applications. Another potential application for the article may be use as a superhydrophobic porous membrane for oil-water separation or for use in biomedical devices, such as for blood vessel replacements and uses in burn bandages to provide non-stick breathability.
The article may be a superhydrophobic fiber mat and may exhibit a water contact angle of greater than about 150 degrees. In various embodiments, the article exhibits water contact angles of from 150 to 180, 155 to 175, 160 to 170, and 160 to 165, degrees. The article may also exhibit a water contact angle hysteresis of below 15 degrees. In various embodiments, the article exhibits water contact angle hysteresis of from 0 to 15, 5 to 10, 8 to 13, and 6 to 12. The article may also exhibit an isotropic or non-isotropic nature of the water contact angle and/or the water contact angle hysteresis. Alternatively, the article may include domains that exhibit an isotropic nature and domains that exhibit a non-isotropic nature.
The fibers may also be of any size and shape and are typically cylindrical. Typically, the fibers have a diameter of from 0.01 to 100, more typically of from 0.05 to 10, and most typically of from 0.1 to 1, micrometers (μm). In various embodiments, the fibers have a diameter of from 1 nm to 30 microns, from 1-500 nm, from 1-100 nm, from 100-300 nm, from 100-500 nm, from 50-400 nm, from 300-600 nm, from 400-700 nm, from 500-800 nm, from 500-1000 nm, from 1500-3000 nm, from 1000-5000 nm, from 2000-5000 nm, or from 3000-4000 nm. The fibers also typically have a size of from of from 5 to 20 microns and more typically have a size of from 10-15 microns. However, the fibers are not limited to any particular size. The fibers are often referred to as “fine fibers”, which encompasses fibers having both micron-scale diameters (i.e., fibers having a diameter of at least 1 micron) and fibers having nanometer-scale diameters (i.e., fibers having a diameter of less than 1 micron). The fibers may also have a glass transition temperature (T_g) of from 25° C. to 500° C.
The fibers may also be connected to each other by any means known in the art. For example, the fibers may be fused together in places where they overlap or may be physically separate such that the fibers merely lay upon each other in the article. It is contemplated that the fibers, when connected, may form a web or mat having pore sizes of from 0.01 to 100 μm. In various embodiments, the pore sizes range in size from 0.1-100, 0.1-50, 0.1-10, 0.1-5. 0.1-2, or 0.1-1.5, microns. It is to be understood that the pore sizes may be uniform or not uniform. That is, the article may include differing domains with differing pore sizes in each domain or between domains. Further, the fibers may have any cross sectional profile including, but not limited to, a ribbon-like cross-sectional profile, an oval cross-sectional profile, a circular cross-sectional profile, and combinations thereof. In some embodiments, “beading” of the fibers can be observed, which may be acceptable for most applications. The presence of beading, the cross-sectional profile of the fiber (varying from circular to ribbonous), and the fiber diameter are functions of the conditions of a method in which the fibers are formed, to be described in further detail below.
In some embodiments, the fibers may also be fire resistant, as introduced above. Fire resistance of the fibers, particularly the non-woven mat including the fibers, is tested using the UL-94V-0 vertical burn test on swatches of the non-woven mat deposited onto aluminum foil substrates. In this test, a strip of the non-woven mat is held above a flame for about 10 seconds. The flame is then removed for 10 seconds and reapplied for another 10 seconds. Samples are observed during this process for hot drippings that spread the fire, the presence of afterflame and afterglow, and the burn distance along the height of the sample. For non-woven mats including the fibers in accordance with the instant invention, intact fibers are typically observed beneath those that burn. The incomplete combustion of the non-woven mats is evidence of self-quenching, a typical behavior of fire-retardant materials and is deemed excellent fire resistance. In many circumstances, the non-woven mats may even achieve UL 94 V-0 classification. Without intending to be bound by any particular theory, it is believed that the fire resistance is typically attributable to a low ratio of organic groups to silicon atoms in the fibers. The low ratio of organic groups to silicon atoms is attributable to the absence of organic polymers and organic copolymers in the fibers. However, it is also contemplated that the fire resistance may be due to factors other than the low ratio of organic groups to silicon atoms in the fibers.
The fibers are formed from a dispersion. As is known in the art, dispersions include one phase of matter that is immiscible with, and dispersed in, another phase of matter, i.e., a dispersed phase in a continuous phase. In the instant invention, the dispersion includes a liquid and a curable compound, described in greater detail below. In one embodiment, the liquid is a non-polar liquid. In another embodiment, the liquid is a polar liquid such as an alcohol, an ionic liquid, or water. Typically, the liquid is water. The water may be tap water, well water, purified water, deionized water, and combinations thereof and may be present in the dispersion in varying amounts depending on the type of dispersion. The liquid may be either the dispersed phase or the continuous phase. In one embodiment, the dispersion includes solid particles as the dispersed phase and the liquid as the continuous phase. In another embodiment, the dispersion includes a non-polar liquid as the dispersed phase and a polar liquid as the continuous phase. In various embodiments, the liquid may be present in amounts of from 20 to 80, of from 30 to 70, of from 40 to 60, or in an amount of about 50, parts by weight per 100 parts by weight of the dispersion, so long as a total amount of the dispersion does not exceed 100 parts by weight.
The dispersion may be further defined as a “colloid” or “colloid dispersion,” terminology which can be used interchangeably. Typically, colloids include particles of less than 100 nanometers in size dispersed in the continuous phase. Colloids may be classified in numerous ways. For purposes of the instant invention, the colloid may also be classified as a gel (a liquid dispersed phase and a solid continuous phase), an emulsion (a liquid dispersed phase and a liquid continuous phase), and/or a foam (a gas dispersed phase and a liquid continuous phase). The colloid may be reversible (i.e., exist in more than one state) or irreversible. Further, the colloid may be elastomeric or viscoelastic.
In one embodiment, the dispersion is further defined as an emulsion, as first introduced immediately above. Emulsions are typically classified into one of four categories according to a chemical nature of the dispersed and continuous phases. A first category is an oil-in-water (O/W) emulsion. O/W emulsions typically include a non-polar dispersed phase (e.g., oil) in an aqueous continuous phase (e.g. water) which forms droplets, which are typically referred to as emulsion particles. For purposes of the instant invention, the terminology “oil” includes non-polar molecules and may include the curable compound. A second category of emulsion is a water-in-oil (W/O) emulsion. W/O emulsions typically include a polar dispersed phase in a non-polar continuous phase thereby forming an inverted emulsion. A third category is a water-in-oil-in-water (W/O/W) emulsion. These types of emulsions include a polar dispersed phase in a non-polar continuous phase which is, in turn, dispersed in a polar continuous phase. For example, W/O/W emulsions may include water droplets entrapped within larger oil droplets that in turn are dispersed in a continuous water phase. A fourth category is a water-in-water (W/W) emulsion. These types of emulsions include aqueous solvated molecules in a continuous aqueous solution wherein both the aqueous solvated molecules and the continuous aqueous solution include different molecules that are water-soluble. Without intending to be bound by any particular theory, it is believed that the aforementioned types of emulsions depend on hydrogen bonding, pi stacking, and/or salt bridging of both the dispersed and continuous phases. In this invention, the dispersion may be further defined as any one of these four types of emulsions.
As is also known in the art, dispersions are, to a certain degree, unstable. Typically, there are three types of dispersion instability including (i) flocculation, where particles of the dispersed phase form clumps in the continuous phase, (ii) creaming, where the particles of the dispersed phase concentrate towards a surface or bottom of the continuous phase, and (iii) breaking and coalescence, where the particles of the dispersed phase coalesce and form a layer of liquid in the continuous phase. The instant dispersion may exhibit one or more of these types of instability.
The dispersion of the instant invention may include particles of varying sizes. In one embodiment, the dispersion includes particles of from 1 nm to 10 μm, more typically of from 1 nm to 1 μm, and most typically of from 1 to 100 nm. In another embodiment, the dispersion may be classified as a nanoemulsion. The dispersion may include particles smaller or larger than the sizes described immediately above, depending on the desire of those of skill in the art.
As first described above, the dispersion also includes the curable compound. The curable compound may any organic or inorganic compound known in the art that can be cured. Non-limiting examples of suitable curable compounds include compounds that cure by free-radical mechanisms, hydrosilylation, condensation, addition reactions, ultraviolet light, microwaves, and heat. Examples of such curable compounds include, but are not limited to, peroxides, amides, acrylates, esters, ethers, imides, oxiranes, sulfones, ureas, urethanes, compounds with ethylenically unsaturated bonds, and combinations thereof. In one embodiment, the curable compound is selected from the group of silanes, siloxanes, silazanes, silicones, silicas, silenes, silsesquioxanes, and combinations thereof. In this embodiment, the curable compound typically cures via free radical, condensation, and/or hydrosilylation mechanisms. In various embodiments, the curable compound may be present in amounts of from 20 to 80, of from 30 to 70, of from 40 to 60, or in an amount of about 50, parts by weight per 100 parts by weight of the dispersion, so long as a total amount of the dispersion does not exceed 100 parts by weight.
Alternatively, the curable compound may be further defined as a condensation curable compound. As is known in the art, condensation curable compounds cure via condensation reactions. Condensation reactions are chemical reactions in which two molecules combine to form a new single molecule, together with the loss of a small molecule, such as water. When water is lost, the condensation reaction may also be known as a dehydration reaction. For descriptive purposes only, a general condensation (dehydration) reaction scheme is set forth below:
wherein R is an organic or inorganic moiety. The condensation reaction is not limited to loss of water and instead may include a loss of an organic or inorganic compound or a molecule of hydrogen. The condensation reaction may also occur where one or more Si atoms in the reaching scheme is replaced by a carbon (C) atom.
The condensation curable compound may include monomers, dimers, oligomers, polymers, pre-polymers, co-polymers, block polymers, star polymers, graft polymers, random co-polymers, macromonomers, telechelic oligomers, nanoparticles, and combinations thereof. The term “oligomer” as used herein includes identifiable chemical groups, including dimers, trimers, tetramers and/or pentamers, linked together through reactive moieties capable of condensation. Examples of preferred organic reactive moieties capable of condensation that may be included in the condensation curable compound include, but are not limited to, hydrolyzable moieties, hydroxyl moieties, hydrides, isocyanate moieties, amine moieties, amide moieties, acid moieties, alcohol moieties, amine moieties, acrylate moieties, carbonate moieties, epoxide moieties, ester moieties, and combinations thereof. The condensation curable compound may also include inorganic moieties including, but not limited to, silicones, siloxanes, silanes, transition metal compounds, and combinations thereof. In addition to the condensation reactions, articles of the instant invention can also be formed by various addition reactions such as free radical additions, Michael reactions, hydrosilylation reactions, and/or Diels Alder reactions. Ring opening polymerizations can also be used.
In one embodiment, the condensation curable compound may be any compound of U.S. Provisional Application No. 61/003,726 filed on Nov. 20, 2007, which is expressly incorporated herein by reference. In another embodiment, the condensation curable compound may include organic and inorganic polymers such as polyesters, polyamides, polyimides, polyureas, polyethers, polyamines, polyurethanes, aramides, polycarbonates, carbonates, and combinations thereof. Alternatively, the condensation curable compound may cure to form a compound selected from the group of polyesters, nylons, polyurethanes, aramides, carbonates, and combinations thereof.
The (condensation) curable compound may be substantially free of silicon (i.e., silicon atoms and/or compounds containing silicon atoms). It is to be understood that the terminology “substantially free” refers to a concentration of silicon of less than 5,000, more typically of less than 900, and most typically of less than 100, parts of compounds that include silicon atoms, per one million parts of the condensation curable compound. It is also contemplated that the (condensation) curable compound may be totally free of silicon.
Alternatively, the (condensation) curable compound may include a polymerization product of at least a silicon monomer and an organic monomer. It is contemplated that the organic monomer and/or silicon monomer may be present in the (condensation) curable compound in any volume fraction. In various embodiments, the organic monomer and/or silicon monomer are present in volume fractions of from 0.05-0.9, 0.1-0.6, 0.3-0.5, 0.4-0.9, 0.1-0.9, 0.3-0.6, or 0.05-0.9.
The organic monomer may include any organic moiety described above. The terminology “silicon monomer” includes any monomer that includes at least one silicon (Si) atom such as silanes, siloxanes, silazanes, silicones, silicas, silenes, silsesquioxanes, and combinations thereof. It is to be understood that the silicon monomer may include polymerized groups and remain a silicon monomer so long as it retains an ability to be polymerized. In one embodiment, the silicon monomer is selected from the group of silanes, silsesquioxanes, siloxanes, and combinations thereof.
In an alternative embodiment, the (condensation) curable compound is selected from the group of an organosilane, an organopolysiloxane, and combinations thereof. In this embodiment, the organopolysiloxane may be selected from the group of a silanol terminated siloxane, an alkoxylsilyl-terminated siloxane, and combinations thereof.
The (condensation) curable compound may be linear or non-linear and may include hydroxyl and/or organosiloxy groups (—SiOR) and may include hydroxyl terminated polydimethylsiloxane. The (condensation) curable compound may include the general structure:
wherein each of R¹and R²independently include one of a hydrogen, a hydroxyl group, an alkyl group, a halogen substituted alkyl group, an alkylenyl group, an aryl group, a halogen substituted aryl group, an alkaryl group, an alkoxy group, an acyloxy group, a ketoximate group, an amino group, an amido group, an acid amido group, an amino-oxy group, a mercapto group, and an alkenyloxy group, and n may be any integer.
Alternatively, the (condensation) curable compound may include hydrocarbylene and/or fluorocarbylene groups. Hydrocarbylene groups include a divalent moiety including carbon and hydrogen. Fluorocarbylene groups include a hydrocarbylene moiety with at least one of the hydrogens replaced with at least one fluorine atom. Typical fluorocarbylene groups include partially or wholly fluorine substituted alkylene groups. The (condensation) curable compound may also include olefinic moieties including acrylate moieties, methacrylate moieties, vinyl moieties, acetylenyl moieties, and combinations thereof.
If the (condensation) curable compound includes a hydroxyl group, the (condensation) curable organopolysiloxane may include siloxanes having at least one terminal silanol group or one hydrogen atom bonded to silicon or a hydrolyzable group which, upon exposure to moisture, forms silanol groups. Terminal or pendant silanol groups, or their precursors, allow for condensation.
Alternatively, the (condensation) curable compound may be further defined as an elastomer or as a curable elastomer. As is known in the art, “elastomers” are compounds that exhibit elasticity, i.e., an ability to deform under stress and return to an approximately original shape. In the instant invention, the terminology “elastomer” is not limited to polymer or monomers and may include one or both. Additionally, the elastomer may include any of the aforementioned (condensation) curable compounds. In one embodiment, the curable elastomer is commercially available from Dow Corning Corporation of Midland, Mich. under the trade name of Dow Corning 84 Additive.
In one embodiment, the curable compound has a number average molecular weight (M_n) of greater than 5,000 g/mol and more typically of greater than 10,000 g/mol. However, the curable compound is not limited to such a number average molecular weight. In another embodiment, the curable compound has a number average molecular weight of greater than about 100,000 g/mol. In various other embodiments, the curable compound has number average molecules weights of from 100,000-5,000,000, from 100,000-1,000,000, from 100,000-500,000, from 200,000-300,000, of higher than about 250,000, or of about 150,000, g/mol. In yet another embodiment, the curable compound has a number average molecular weight of greater than 50,000 g/mol, and more typically of greater than 100,000 g/mol. In alternative embodiments, the curable compound may have a number average molecular weight of at least about 300 g/mol, of from about 1,000 to about 2,000 g/mol, or of from about 2,000 g/mol to about 2,000,000 g/mol. In other embodiments, the curable compound may have a number average molecular weight of greater than 350 g/mol, of from about 5,000 to about 4,000,000 g/mol, or of from about 500,000 to about 2,000,000 g/mol.
In addition to the curable compound, the dispersion may also include one or more surfactants. In various embodiments, the dispersion includes a (first) surfactant and a second surfactant or multiple surfactants. The surfactant may be combined with the liquid, with the curable compound, or with both the liquid and the curable compound, prior to formation of the dispersion. Typically, the surfactant is combined with the liquid before the dispersion is formed. Surfactants are also known as surfactant active agents, surface active solutes, emulsifiers, emulgents, and tensides. Relative to this invention, the terminology “surface active agent”, “surface active solutes”, “surfactants”, “emulsifiers”, “emulgents”, and “tensides” may be used interchangeably. Surfactants reduce a surface tension of a liquid by adsorbing at a liquid-gas interface. Surfactants also reduce interfacial tension between polar and non-polar molecules by adsorbing at a liquid-liquid interface. Without intending to be bound by any particular theory, it is believed that surfactants act at these interfaces and are dependent on various forces including, excluded volume repulsion forces, electrostatic interaction forces, van der waals forces, entropic forces, and steric forces. In the instant invention, the surfactant may be chosen or manipulated based on one or more of these forces.
The surfactant, first and second surfactants, or first/second/and multiple surfactants may independently be selected from the group of non-ionic surfactants, cationic surfactants, anionic surfactants, amphoteric surfactants, and combinations thereof. Suitable non-ionic surfactants include, but are not limited to, alkylphenol alkoxylates, alcohol ethoxylates including fatty alcohol ethoxylates, glycerol esters, sorbitan esters, sucrose and glucose esters, including alkyl polyglucosides and hydroxyalkyl polyglucosides, alkanolamides, N-alkylglucamides, alkylene oxide block copolymers such as block copolymers of ethylene oxide, propylene oxide and/or butylene oxide, polyhydroxy and polyalkoxy fatty acid derivatives, amine oxides, siloxane based polyethers, and combinations thereof.
Suitable cationic surfactants include, but are not limited to, interface-active compounds including ammonium groups such as alkyldimethylammonium halides and compounds having the chemical formula RR′R″R′″N⁺X⁻ wherein R, R′, R″, and R′″ are independently selected from the group of alkyl groups, aryl groups, alkylalkoxy groups, arylalkoxy groups, hydroxyalkyl(alkoxy) groups, and hydroxyaryl(alkoxy) groups and wherein X is an anion. Suitable anionic surfactants include, but are not limited to, fatty alcohol sulfates. Further non-limiting examples of suitable anionic surfactants include alkanesulfonates, linear alkylbenzenesulfonates, and linear alkyltoluenesulfonates. Still further, the anionic surfactant may include olefinsulfonates and di-sulfonates, mixtures of alkene- and hydroxyalkane-sulfonates or di-sulfonates, alkyl ester sulfonates, sulfonated polycarboxylic acids, alkyl glyceryl sulfonates, fatty acid glycerol ester sulfonates, alkylphenol polyglycol ether sulfates, olefin sulfonates, paraffinsulfonates, alkyl phosphates, acyl isothionates, acyl taurates, acyl methyl taurates, alkylsuccinic acids, sulfosuccinates, alkenylsuccinic acids and corresponding esters and amides thereof, alkylsulfosuccinic acids and corresponding amides, mono- and di-esters of sulfosuccinic acids, acyl sarcosinates, sulfated alkyl polyglucosides, alkyl polyglycol carboxylates, hydroxyalkyl sarcosinates, and combinations thereof. Suitable amphoteric surfactants include, but are not limited to, aliphatic derivatives of secondary and/or tertiary amines which include an anionic group, betaines, and combinations thereof.
Additionally, the surfactant and/or first and second surfactants may independently include aliphatic and/or aromatic alkoxylated alcohols, LAS (linear alkyl benzene sulfonates), paraffin sulfonates, FAS (fatty alcohol sulfates), FAES (fatty alcohol ethersulfates), alkylene glycols, trimethylolpropane ethoxylates, glycerol ethoxylates, pentaerythritol ethoxylates, alkoxylates of bisphenol A, and alkoxylates of 4-methylhexanol and 5-methyl-2-propylheptanol, and combinations thereof. Typically, the surfactant is present in an amount of from 0.1 to 100, more typically of from 0.01 to 5, even more typically of from 0.5 to 5, and most typically of from 1.5 to 5, parts by weight per 100 parts by weight of the dispersion.
The dispersion may also include a thickener. As is known in the art, thickeners increase a viscosity of the dispersion at low shear rates while maintaining flow properties of the dispersion at higher shear rates. Suitable thickeners for use in the instant invention include, but are not limited to, polyalkylene oxides such as polyethylene oxide, polypropylene oxide, polybutylene oxide, and combinations thereof. In one embodiment, the thickener is selected from the group of algenic acid and its derivatives, polyethylene oxide, polyvinyl alcohol, methyl cellulose, hydroxypropylmethyl cellulose, alkyl and hydroxyalkyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, guar gum, gum arabic, gum ghatic, polyvinylpyrrolidone, starch, modified starch, tamarind gum, xanthan gum, polyacrylamide, polyacrylic acid, and combinations thereof. The thickener may also include a nanoparticle such as titanium dioxide and/or a nanoclay such as betonite. The thickener may also be conductive, semi-conductive, insulating, magnetic, or light-emitting. Alternatively, the thickener may include a conductive polymer such as polypyrrole, polyaniline, and/or polyacetylene. The thickener may also include biological components such as proteins or DNA.
The thickener may be combined with the liquid, with the curable compound, or with both the liquid and the curable compound before the dispersion is formed. Typically, the thickener is combined with the liquid before the dispersion is formed. The thickener is typically present in an amount of from 0.001 to 25, more typically of from 0.05 to 5, and most typically of from 0.1 to 5, parts by weight per 100 parts by weight of the dispersion.
As is also known in the art, dispersions typically have two different types of viscosities, a total viscosity and a viscosity of the dispersed phase. The dispersion of the instant invention typically has a total viscosity of at least 20 centistokes at a temperature of 25° C. In various embodiments, the dispersion has a viscosity of at least 20 centistokes, more typically from about 30 to about 100 centistokes, most typically from about 40 to about 75 centistokes at a temperature of 25° C. using a Brookfield rotating disc viscometer equipped with a thermal cell and an SC4-31 spindle operated at a constant temperature of 25° C. and a rotational speed of 5 rpm. The viscosity of the dispersed phase is not limited and is not believed to affect the total viscosity. In one embodiment, the dispersed phase is solid and has an infinite viscosity.
The dispersion may also have a zero shear rate viscosity of from 0.1 to 10, from 0.5 to 10, from 1 to 10, from 5 to 8, or about 6, PaS. Further, the dispersion may have a conductivity of from 0.01-25 mS/m. In various embodiments, the conductivity of the dispersion ranges from 0.1-10, from 0.1-5, from 0.1-1, from 0.1-0.5, or is about 0.3, mS/m. The dispersion may also have a surface tension of from 10-100 mN/m. In different embodiments, the surface tension ranges from 20-80, or from 20-50, mN/m. In one embodiment, the surface tension of the dispersion is about 30 mN/m. The dispersion may also have a dielectric constant of from 1-100. In various embodiments, the dielectric constant is between 5-50, 10-70, or 1-20. In one embodiment, the dielectric constant of the dispersion is about 10.
The dispersion may also include an additive. The additive may include, but is not limited to, conductivity-enhancing additives, salts, dyes, colorants, labeling agents, and combinations thereof. Conductivity-enhancing additives may contribute to excellent fiber formation, and may further enable diameters of the fibers to be minimized, especially when the fibers are formed through electrospinning. In one embodiment, the conductivity-enhancing additive includes an ionic compound. In another embodiment, the conductivity-enhancing additives are generally selected from the group of amines, organic salts and inorganic salts, and mixtures thereof. Typical conductivity-enhancing additives include amines, quaternary ammonium salts, quaternary phosphonium salts, ternary sulfonium salts, and mixtures of inorganic salts with organic ligands. More typical conductivity-enhancing additives include quaternary ammonium-based organic salts including, but not limited to, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, phenyltrimethylammonium chloride, phenyltriethylammonium chloride, phenyltrimethylammonium bromide, phenyltrimethylammonium iodide, dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethylammonium iodide, tetradecyltrimethylammonium chloride, tetradecyltrimethylammonium bromide, tetradecyltrimethylammonium iodide, hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, and hexadecyltrimethylammonium iodide. The additive may be present in either the continuous or dispersed phase of the dispersion in any amount selected by one of skill in the art so long as the amount of the additive allows the curing of the curable compound to occur. In various embodiments, the amount of the additive is typically of from about 0.0001 to about 25%, more typically from about 0.001 to about 10%, and more typically from about 0.01 to about 1% based on the total weight of the fibers. In one embodiment, the additive includes methylaminomethylpropanol.
Referring now to the method of manufacturing the article, the method includes the step of forming the dispersion, described above. The dispersion may be formed by adding the curable compound and the liquid together and mixing. In one embodiment, the method includes the step of adding the condensation curable compound and the liquid together and mixing. The step of mixing may include mechanical mixing using ribbon mixers, plow mixers, fluidizing paddle mixers, sigma blade mixers, tumble blenders, vortex mixers, feed mixers, vertical mixers, horizontal mixers, rotor-stator mixers, sonicators, Speedmixers®, and combinations thereof.
The instant invention is not limited to any particular order of addition. In one embodiment, the dispersion is formed by combining the thickener and water to form a mixture and adding the mixture to the curable compound. Alternatively, the dispersion may be formed by any method known in the art.
The method also includes the step of electrospinning the dispersion. In one embodiment, this step reduces a content of the liquid (e.g. water) such that the condensation curable compound cures. Without intending to be bound by any particular theory, it is believed that electrospinning causes at least partial evaporation of the liquid, such as water, such that the condensation curable compound cures. Loss of solvent may allow the curable compounds to blend, i.e. come into intimate contact, allowing for cure. Without intending to be limited by any particular theory, it is believed that the force of an electric field, used in electrospinning, may align functional groups such that they are more readily in contact. The step of electrospinning may be conducted by any method known in the art. A typical electrospinning process includes use of an electrical charge to form the fibers. Typically, the dispersion used to form the fibers is loaded into a syringe, the dispersion is driven to a tip of the syringe with a syringe pump, and a droplet is formed at the tip of the syringe. The pump enables control of flow rate of the dispersion used to form the fibers to the spinning head. Flow rate of the dispersion used to form the fibers through the tip of the syringe may have an effect on formation of the fibers. The flow rate of the dispersion through the tip of the syringe may be from about 0.005 ml/min to about 0.5 ml/min, typically from about 0.005 ml/min to about 0.1 ml/min, more typically from about 0.01 ml/min to about 0.1 ml/min, and most typically from about 0.02 ml/min to about 0.1 ml/min. In one specific embodiment, the flow rate of the dispersion through the tip of the syringe may be about 0.05 ml/min.
The droplet is then typically exposed to a high-voltage electric field. In the absence of the high-voltage electrical field, the droplet exits the tip of the syringe in a quasi-spherical shape, which is the result of surface tension in the droplet. Application of the electric field results in the distortion of the spherical shape into that of a cone. The generally accepted explanation for this distortion in droplet shape is that the surface tension forces within the droplet are neutralized by the electrical forces. Narrow diameter jets of the dispersion emanate from the tip of the cone. Under certain process conditions, the jet of the dispersion undergoes the phenomenon of “whipping” instability. This whipping instability results in the repeated bifurcation of the jet, yielding a network of fibers. The fibers are ultimately collected on a collector plate. The liquid, such as water, is believed to rapidly evaporate from the dispersion during the electrospinning process, leaving behind the solids portion of the dispersion to form the fibers and cure the curable compound. The collector plate is typically formed from a solid conductive material such as, but not limited to, aluminum, steel, nickel alloys, silicon wafers, Nylon® fabric, and cellulose (e.g., paper). The collector plate acts as a ground source for the electron flow through the fibers during electrospinning of the dispersion. As time passes the number of fibers collected on the collector plate increases and the non-woven fiber mat is formed on the collector plate. Alternatively, instead of using the collection plate, the fibers may be collected on the surface of a liquid that is not part of the dispersion, thereby achieving a free-standing non-woven mat. One example of liquid that can be used to collect the fibers is water.
In various embodiments, the step of electrospinning comprises supplying electricity from a DC generator having generating capability of from about 10 to about 100 kilovolts (KV). In particular, the syringe is electrically connected to the generator. The step of exposing the droplet to the high-voltage electric field typically includes applying a voltage and an electric current to the syringe. The applied voltage may be from about 5 KV to about 100 KV, typically from about 10 KV to about 40 KV, more typically from about 15 KV to about 35 KV, most typically from about 20 KV to about 30 KV. In one specific example, the applied voltage may be about 30 KV. The applied electric current may be from about 0.01 nA to about 100,000 nA, typically from about 10 nA to about 1000 nA, more typically from about 50 nA to about 500 nA, most typically from about 75 nA to about 100 nA. In one specific embodiment, the electric current is about 85 nA. Typically, when electrospinning, the dispersion is at a temperature within 60° C. of ambient temperature. More typically, when electrospinning, the dispersion is at a temperature within 60° C. of a processing temperature.
The step of electrospinning is believed to at least partially cure the condensation curable compound. In one embodiment, the step of electrospinning completely cures the condensation curable compound. In other embodiments, the step of electrospinning does not completely cure, or even partially cure, the curable compound such that an additional curing step is needed. The method may include the step of drying to more completely cure the curable compound. When the curable compound is further defined as the condensation curable compound, it is hypothesized that the step of drying removes the liquid (e.g. water) and drives the condensation reaction to the right, i.e., towards completion.
The method may also include the step of curing the curable compound, as first introduced above. The step of curing may be implemented independent of, or in combination with, the step of electrospinning. This step may include any curing step known in the art including, but not limited to, those related to free-radical curing, hydrosilylation curing, condensation curing, UV light curing, microwave curing, heat curing, and combinations thereof.
The method may also include the step of annealing the fibers. This step may be completed by any method known in the art. In one embodiment, the step of annealing may be used to enhance the hydrophobicity of the fibers. In another embodiment, the step of annealing may enhance a regularity of microphases of the fibers. The step of annealing may include heating the article. Typically, to carry out the step of annealing, the article is heated to a temperature above ambient temperature of about 20° C. More typically, the article is heated to a temperature of from about 40° C. to about 400° C., most typically from about 40° C. to about 200° C. Heating of the article may result in increased fusion of fiber junctions within the article, creation of chemical or physical bonds within the fibers (generally termed “cross-linking”), volatilization of one or more components of the fiber, and/or a change in surface morphology of the fibers.

EXAMPLES

A series of fibers and a non-woven mat (i.e., the article of the instant invention) are formed according to the present method. The non-woven mat includes the fibers formed from the dispersion including a silicone elastomer as a condensation curable compound.
More specifically, 2 g of 2.5% polyethylene oxide (2,000,000 number average molecular weight) solution in water is added to 10 g of a dispersion including 63% by weight of Dow Corning 84 Additive in water. Dow Corning Additive 84 includes a mix of silica and cross-linked silicone rubber including functional groups that can undergo a condensation cure. The polyethylene oxide and the dispersion are stirred to form a translucent white dispersion. The dispersion is then delivered by a syringe/syringe pump to a stainless steel tube with inner diameter of 0.040 inches in preparation for electrospinning. An electric field is applied between the stainless steel tube and a piece of grounded aluminum foil. As the electric field is applied, a droplet at a tip of the stainless steel tube is electrospun into thin white fibers which are deposited onto the grounded aluminum foil. The step of electrospinning is performed at a plate gap of 30 cm, a tip protrusion of 3 cm, an applied voltage of 22 kV, and a flow rate of 1 mL/hr. The electrospinning is performed for one hour. The resultant fibers are one to five microns in diameter and tend to have fiber-fiber junctions. Spherical defects are present within the fibers, as shown in FIG. 1.
After electrospinning for one hour, the fibers form an opaque white membrane with a thickness of approximately 200 microns. After 24 hours, the membrane is peeled off the aluminum foil and tested to determine tensile properties (stress/strain) at a breaking point using an Alliance RT/5 Tensile Tester commercially available from RTS. More specifically, a “dog-bone” shaped sample of the membrane having a width of 0.1 inches is tested in a 10 N maximum load cell at a pull rate of 100 mm/min. A stress-strain curve is also generated. The peak stress measurement of the fibers is approximately 19 psi and the strain measurement is approximately 120 percent. Additionally, the stress-strain curve is approximately linear suggesting that the fibers are elastomeric at the breaking point.
The fibers formed in the aforementioned Example evidence that electrospinning a dispersion allows fibers to be formed that exhibit characteristics of the dispersed phase, i.e., the condensation curable compound, as opposed to the continuous phase. The fibers formed in this Example exhibit elastomeric stress and strain properties and an elastomeric stress-strain curve. The formation of these types of fibers allows for more efficient and accurate production of a variety of materials to be used in medical, scientific, and manufacturing industries. The use of the dispersion also allows for a variety of types of curable compounds to be utilized thus forming new products. The use of, for example, a dispersion in which a continuous phase is water, allows for an electrospinning process to be done through evaporation of a non-hazardous volatile liquid. The use of an active material, for example a bacteria, in the continuous phase, may allow for the creation of biologically functionalized fibers that are curable in a one-step process.
The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings, and the invention may be practiced otherwise than as specifically described.

Claims

1. A method of manufacturing an article comprising fibers formed from a dispersion, said method comprising the steps of:

A. forming the dispersion comprising;

(i) a liquid, and

(ii) a condensation curable silicone rubber, and

B. electrospinning the dispersion to reduce a content of the liquid such that the condensation curable silicone rubber cures via condensation.

2. A method as set forth in claim 1 wherein the dispersion further comprises a surfactant.

3. A method as set forth in claim 2 wherein the surfactant is combined with the liquid before the dispersion is formed.

4. A method as set forth in claim 2 wherein the surfactant is present in the dispersion in an amount of from 0.5 to 5 percent by weight based on a weight of the condensation curable compound.

5. A method as set forth in claim 1 wherein the dispersion further comprises a thickener.

6. A method as set forth in claim 5 wherein the thickener is further defined as polyethylene oxide.

7. A method as set forth in claim 5 wherein the thickener is combined with the liquid before the dispersion is formed.

8. A method as set forth in claim 5 wherein the thickener is present in the dispersion in an amount of from 0.05 to 5 percent by weight based on a weight of the dispersion.

9. (canceled)

10. (canceled)

11. (canceled)

12. (canceled)

13. A method as set forth in any one of claims 1-8 wherein the dispersion further comprises a condensation curable organic compound.

14. A method as set forth in any one of claims 1-8 wherein the dispersion comprises from 20 to 80 parts by weight of the condensation curable silicone rubber per 100 parts by weight of the dispersion so long as a total amount of the dispersion does not exceed 100 parts by weight.

15. A method as set forth in claim 14 wherein the dispersion comprises from 20 to 80 parts by weight of the liquid per 100 parts by weight of the dispersion so long as a total amount of the dispersion does not exceed 100 parts by weight.

16. A method as set forth in any one of claims 1-8 wherein, the liquid is further defined as water.

17. A method as set forth in claim 16 wherein the condensation curable silicone rubber is dispersed in the water.

18. A method as set forth in any one of claims 1-8 further comprising the step of drying the fibers to further reduce a content of the liquid such that the condensation curable silicone rubber.

19. A method as set forth in claim 1 wherein the dispersion comprises a dispersed phase comprising the condensation curable silicone rubber and a continuous phase comprising the liquid, a surfactant, and a thickener.

20. A method as set forth in any one of claims 1-8 wherein the fibers have a stress of at least 15 psi at break and a strain of at least 100 percent at break.

21. An article of fibers comprising a cured compound and formed from electrospinning a dispersion comprising:

A. a liquid; and

B. a condensation curable silicone rubber;

wherein a content of said liquid is reduced such that said condensation curable silicone rubber.

22. An article as set forth in claim 21 wherein said dispersion further comprises a surfactant.

23. An article as set forth in claim 22 wherein said surfactant is combined with said liquid before said dispersion is formed.

24. An article as set forth in claim 22 wherein said surfactant is present in said dispersion in an amount of from 0.5 to 5 percent by weight based on a weight of said condensation curable silicone rubber.

25. An article as set forth in claim 21 wherein said dispersion further comprises a thickener.

26. An article as set forth in claim 25 wherein said thickener is further defined as polyethylene oxide.

27. An article as set forth in claim 25 wherein said thickener is combined with said liquid before said dispersion is formed.

28. An article as set forth in claim 25 wherein said thickener is present in said dispersion in an amount of from 0.05 to 5 percent by weight based on a weight of said dispersion.

29. (canceled)

30. (canceled)

31. (canceled)

32. (canceled)

33. An article as set forth in any one of claims 21-28 wherein said dispersion further comprises a condensation curable organic compound.

34. An article as set forth in any of claims 21-28 wherein said dispersion comprises from 20 to 80 parts by weight of said condensation curable silicone rubber per 100 parts by weight of said dispersion so long as a total amount of said dispersion does not exceed 100 parts by weight.

35. An article as set forth in claim 34 wherein said dispersion comprises from 20 to 80 parts by weight of said liquid per 100 parts by weight of said dispersion so long as a total amount of said dispersion does not exceed 100 parts by weight.

36. An article as set forth in any one of claims 21-28 wherein said liquid is further defined as water.

37. An article as set forth in claim 21 wherein said dispersion comprises a dispersed phase comprising said condensation curable silicone rubber and a continuous phase comprising said liquid, a surfactant, and a thickener.

38. An article as set forth in claim 37 wherein said condensation curable silicone rubber comprises a silicone elastomer present in an amount of from 20 to 80 parts by weight per 100 parts by weight of said dispersion, said liquid is further defined as water and is present in an amount of from 20 to 80 parts by weight per 100 parts by weight of the dispersion, said surfactant comprises methylaminomethylpropanol present in an amount of from 0.5 to 5 parts by weight per 100 parts by weight of said dispersion, said thickener is further defined as polyethylene oxide and is present in an amount of from 0.05 to 5 parts by weight per 100 parts by weight of said dispersion.

39. An article as set forth in any one of claims 21-28 that is further defined as a non-woven mat.

40. A method of manufacturing an article comprising fibers formed from a dispersion, said method comprising the steps of:

A. forming the dispersion comprising;

(i) a liquid, and

(ii) a condensation curable silicone rubber,

B. electrospinning the dispersion to form the fibers; and

C. curing the condensation curable silicone rubber.

41. A method as set forth in claim 40 wherein the dispersion further comprises a surfactant and a thickener.

42. A method as set forth in claim 41 wherein the surfactant is present in the dispersion in an amount of from 0.5 to 5 percent by weight based on a weight of the condensation curable silicone rubber.

43. A method as set forth in claim 41 wherein the thickener is further defined as polyethylene oxide.

44. A method as set forth in claim 41 wherein the thickener is present in the dispersion in an amount of from 0.05 to 5 percent by weight of the dispersion.

45. (canceled)

46. (canceled)

47. (canceled)

48. A method as set forth in any one of claims 40-44 wherein the dispersion comprises from 20 to 80 parts by weight of the liquid per 100 parts by weight of the dispersion so long as a total amount of the dispersion does not exceed 100 parts by weight.

49. A method as set forth in any one of claims 40-44 wherein the liquid is further defined as water.

50. A method as set forth in claim 49 wherein the condensation curable silicone rubber.