Patent Application
20110203720
Microporous membranes are prevalent in the chemical, food, pharmaceutical and medical industries where they are used to separate desired and undesired components of process streams, for example, to remove impurities by filtration or to separate and retain precious or useful particulate species. Microporous membranes are also used in custom apparel such as outerwear, where they provide breathability and yet protect the wearer from the elements such as wind and rain. They are also used in the fabrication of protective masks and apparel to help exclude toxic particulate species such as carcinogenic aerosols, spores and bacteria. In all of the aforementioned applications, performance is greatly limited by the largest pores in the membrane because the largest pore controls the size of the particulate that can be excluded and the majority of flow is relegated to the larger pores, such that the smaller pores may give a higher porosity number to the membrane but contribute little to overall flux. Since the separation performance and protective performance of a membrane is strongly affected by the largest pore size in the membrane, it is highly desirable that a membrane designed for separation or protection have a very narrow pore size distribution. The effect of pore size distribution of a membrane on its separation performance has been a subject of research over the years. For example Bowen and Welfoot have shown where the researchers show that total product recovery in an ultrafiltration membrane process is negatively affected by a wide pore size distribution (Bowen, W. R., Welfoot, J. S., Desalination, Vol. 147, pp 197-203, 2002). Thus it is highly desirable that membranes exhibit little or no variation in pore size.
Uniform pores in planar films can be created by many different fabrication techniques. For example, uniform capillary pores can be created by ion bombardment and track-etched processes. They can also be created using laser ablation, ion beam etching or optical lithography. But all these micro-fabrication processes are limited by one or more of a variety of factors such as cost, a limited number of suitable material substrates, the inability to create large-area membranes, and low porosity.
Membranes without open pores are used to separate chemical species by permitting diffusion of some and not others. Life itself is sustained by selective diffusion through cellular lipid membranes, desalination is used worldwide to make fresh or potable water from sea or brackish water; likewise, gas purification, kidney dialysis and many other chemical separations are known as entropic driven processes. Many materials that have high selectivity that could be used as membranes are not used as the materials themselves have poor physical properties that make them impractical to use as a large area membrane of commercial value.
Certain porous structures can also be formed by arranging or aligning cylindrical or other cross-section fibers along a single axis, partially bonding the fibers to each other such that the fibers hold together as a structure and then cutting the partially fused structure in a direction that is perpendicular to the axis of fiber alignment such that porous flat sheets are formed. In such planar structures, pores are created by the interstitial space formed between neighboring fibers, and there is no means of producing a well-defined, controllable pore size distribution. For example, in Japanese Patent Application 1996226060 (“JP 8-226060”), the inventors disclose a process of forming filters by arranging plurality of fibers parallel to each other, continuously partially fusing the fibers into a ribbon while maintaining the fibers parallel to each other, continuously folding and or pleating the partially fused ribbon in a partially consolidated block of fibers and then skiving the fibrous block to form porous planar sheets. It is important to note that in order to create the desired porous sheets having a density of around 0.05 g/cm3, the inventors only partially bonded the fibers to each other thereby creating void spaces of varying dimension in between the neighboring fibers. It is well known in the art that an alignment of fibers, when partially bonded, lead to a wide pore space distribution. Fibers can be packed more tightly to make voids more uniform, but only at low porosity When fibers are tightly packed, the porosity of the fibrous structure is significantly smaller that reported in JP 8-226060; see, for example, Tomadakis, M. M., Sotirchos, S. V., “Knudsen diffusivities and properties of structures of unidirectional fibers” (AlChE Journal Vol. 37 (8), pp 1175-1186, 1991. Thus, the membranes generated by the invention of JP 8-226060 are understood to exhibit a highly undesirable wide pore size distribution.
Another process for forming porous fiber on end structures is disclosed in U.S. Pat. No. 3,085,922, where Koller discloses a structure formed by aligning solid fibers in a preferential direction, partially infusing the space between the fibers with a liquid binder, solidifying the binder to partially bond the fibers to the neighboring fibers and then cutting the fibers perpendicular to the axis of alignment to produce an open porous structure. However, this porous sheet suffers from the same drawback of JP 8-226060 in that the porous sheet comprises, throughout the sheet, pores of a wide pore size distribution. Further, because of the limited number of bonds between neighboring fibers, membranes formed from such partially bonded fiber structures will lack the mechanical properties necessary for a large number of membrane applications.
Membranes and sheet structures with uniform pore size and exhibiting good mechanical properties can be created on a small scale (e.g., less than about a meter wide) from a “fiber-on-end” (FOE) process wherein multi-component fibers (sheath-core and islands-in-the-sea) with uniform micro-features are assembled in a preferred direction, consolidated, then cut or sectioned in a direction that is perpendicular to the orientation of the fibers, producing sheets with uniform micro-features. When the micro-features in the planer sheets are removed by a method such as preferential dissolution in a solvent, membrane with highly uniform capillary pores can be created. Membranes with uniform capillary pores may also be created by a similar process by aligning uniform hollow fibers and then carefully consolidating the fibrous structure such that there is little or no interstitial space left between neighboring fibers but the holes maintain their integrity, and then cutting the consolidated structure perpendicular to the fiber alignment direction producing porous membranes with very uniform size capillary pores.
Hand lay-up of above described fiber on end materials formed from either solid multi-component fibers or hollow fibers has been demonstrated, but for manufacturing large area membranes, for commercial scale applications, greater than about a meter wide, a hand lay-up process is not practical.
One method of making fully consolidated fiber-on-end materials is to arrange pre-cut thermoplastic fiber lengths into a cavity of a press die. The die is closed and heat and pressure are applied, so that the walls of the fibers soften and fuse together in such a way that there is essentially no interstitial space between fibers. Careful application of heat and a sufficient rate of heat transfer can allow one to avoid degrading, distorting or melting the cores of the outermost fibers while still allowing the fibers located near the center to fuse. However, making fiber-on-end materials with large dimensions, greater than about a meter wide, by the above described method is limited by heat transfer rates and would likely require careful control and choice of time and temperature.
In European Patent Application No. 195860 A1 parallel fibers are consolidated by winding the fibers on a drum and then bonding them into a solid that is later skived in a direction perpendicular to the parallel fibers. The fibers, having been arranged concentric to the surface of the winding drum, must be sliced in a radial direction with respect to their winding orientation. This is accomplished by cutting off the consolidated fiber layer, pressing it flat, cutting sections of the flattened layer, reorienting the sections by ninety degrees, fusing the sections together into a block, cutting the blocks again into trapezoids, arranging the trapezoids around the periphery of a support drum and skiving a layer, perpendicular to the fiber axis, to form a membrane. In European Patent Application No. 167094 A1, a solid cylinder of sea polymer is made at a temperature above the sea melting point, then cut axially into four segments which are pressed flat prior to making thin cuts into this flattened segment. This pressing flat of a thick fused polymer block, which is reinforced with small polymer cores, places high extensional stress on those cores on the smaller inside curvature of the quartered section and high compressional stress on cores nearer the outside larger curvature. This could impose high distortion to the cores and give non-uniform capillary structures. The methods disclosed in European Patent Application Nos. 195860 A1 and 167094 A1 require multiple handling steps and are not readily adaptable for large-scale, continuous or potentially automated operation. Heat transfer rates also limit how quickly each fusing step can be accomplished with thermoplastic or reactive bonding agents. These features limit the productivity of these methods and practical membrane size.
There thus remains a need for a process capable of making fiber-on-end materials of large planar dimensions, e.g., one meter wide or more, in a continuous or automated manner.
The invention disclosed herein provides a scalable process for making large area membranes and capillary arrays having uniform microfeatures or pore size, by arranging parallel fibers into a ribbon or fabric; folding the ribbon or fabric back and forth on itself; and applying heat and pressure to form a fully consolidated solid material, from which membranes and capillary arrays are skived.
One aspect of the present invention is a process for manufacturing articles from fibers arranged on end, comprising the sequential steps:
a. arranging a plurality of fibers parallel to each other, wherein the fibers are made from polymeric material and are hollow fibers or multicomponent fibers,
b. continuously thermally fusing the fibers into a ribbon or fabric while maintaining the fibers parallel to each other,
c. continuously folding or pleating the ribbon or fabric,
d. compressing and thermally fusing the folded or pleated ribbon or fabric into a fully consolidated solid billet such that there is essentially no interstitial void space left in between fibers, and
e. skiving fiber-on-end material of a desired thickness from the solid,
thereby forming a porous membrane or capillary array comprising uniform capillary pores.
Another aspect of the present invention is a process for manufacturing an article from fibers arranged on end, comprising the sequential steps:
a. arranging a plurality of fibers parallel to each other, wherein the fibers are made from polymeric material and are hollow fibers or multicomponent fibers,
b. producing a desired thickness of partially thermally fused fiber material by either:
c. allowing the roll to cool to ambient temperature,
d. slitting the at least partially fused fiber material,
e. removing the slit material from the cooled roll,
f. flattening it to form a flattened section,
g. optionally, repeating steps a through g to form additional flattened sections,
h. forming a stack comprising the flattened sections or sections cut from one or more flattened sections,
i. compressing and thermally fusing the stack into a fully consolidated solid billet such that there is essentially no interstitial void space left in between the fibers, and
j. skiving fiber-on-end material of a desired thickness from the billet,
thereby forming a porous membrane or capillary array comprising uniform capillary pores.
A further aspect of the invention is a process for preparing porous membranes and capillary arrays, comprising the sequential steps:
a. providing a fully consolidated shaped billet comprising thermally fused fibers on end such that there is essentially no interstitial void space between fibers,
b. cutting trapezoidal sections from the billet such that the fibers are oriented substantially perpendicular to the base of the trapezoidal section,
c. welding the trapezoidal sections together to form a billet that is two concentric polygons in cross-section,
d. mounting the billet formed in step c on a spindle,
e. continuously rotating the billet,
f. skiving fiber-on-end membrane from the continuously rotating billet, and
g. manufacturing an article comprising the skived fiber-on-end material.
A further aspect of the invention is a process for preparing porous membranes and capillary arrays, comprising the sequential steps:
a. providing a fully consolidated shaped billet comprising completely thermally fused fibers on end such that there is no interstitial void space between fibers,
b. cutting annular sections from the billet such that the fibers are oriented substantially perpendicular to the base of the trapezoidal section,
c. welding the annular sections together to form a billet,
d. mounting the billet formed in step c on a spindle,
e. continuously rotating the billet,
f. skiving fiber-on-end membrane from the continuously rotating billet, and
g. manufacturing an article comprising the skived fiber-on-end material.
The term “fiber-on-end” (FOE) as used herein refers to an arrangement of fibers substantially all of which are parallel to a common axis and perpendicular to an optional processing means. In one embodiment of the present invention, a plurality of fibers is arranged parallel to each other and formed into a fabric or ribbon, which retains the parallel fiber orientation. The fabric or ribbon is pleated and fused to form a fully consolidated solid block of material having essentially no interstitial void space in between neighboring fibers, referred to herein as a “billet.” The fibers are bound together by thermal fusing without using a chemically reactive binder or solvent bonding.
As used herein, the terms “fully consolidated,” “completely consolidated,” “complete consolidation,” and “having essentially no interstitial void space” equivalently mean that the density of the fused solid so described is at least 90% of its theoretical density. In an embodiment, the density is at least 95% of its theoretical density. In an embodiment, the density is at least 99% of its theoretical density. The theoretical density of a fully consolidated block made up of n materials can be calculated as
where Vi is the volume fraction of the i-th material and di is its density. The value for the density of the i-th material, if not determined experimentally, can be calculated using methods known in the art, taking into account any changes in crystallinity and amorphous content occurring during thermal fusing.
For a block of fused hollow fibers, the n materials are the polymer phase (i.e., the polymer(s) making up the fiber) and air. The total volume is the volume of the polymer phase (vp) plus the volume of the air in the fiber hollows (vair). The polymer phase volume fraction is then vp/(vp+vair). Because the density of air is so much smaller than typical polymer densities, the theoretical density of a fully consolidated block of hollow fibers is simply the volume fraction of the polymer phase times the density of the polymeric material making up the polymer phase.
The fused solid formed from “fibers on end” is further processed by removing a thin layer, typically though not necessarily perpendicular to the fiber orientation, with a sharp blade thus forming a membrane. This process is known as “skiving”. The term “membrane” as used herein is a discrete, thin structure that can moderate the transport of species in contact with it, such as gas, vapor, aerosol, liquid and/or particulates. Thicker sections may be desired to replicate the thickness of films and their distinctive end-uses, and still thicker may be desired to replicate, for example, leather or slit leather uses; cut into cubes, for example, such articles can be used as tablets that could contain materials such as pharmaceuticals. A porous membrane can be formed by using hollow fibers or multicomponent fibers in which a component is dissolved away after the membrane is skived from the billet. As used herein, the term “multicomponent fiber” denotes fibers containing two or more components (bicomponent, tricomponent, and so on). The term “porous membrane” as used herein denotes a membrane containing openings (pores) that may or may not completely traverse the membrane. The term “capillary array” as used herein denotes a membrane or sheet in which pores can be partially or completely filled with other species, for this invention.
The processes herein can be carried out continuously or partly continuously. One example of a continuous process is shown schematically in
Membranes and capillary arrays can be prepared by skiving layers from a fused block, the direction of the skiving typically perpendicular or close to perpendicular to the fiber axis and, optionally, dissolving one or more fiber components.
Fibers suitable for use in the embodiments of the invention can be made by any of various methods known in the art. Depending on the particular polymer(s) used, fibers can be spun from solution (for example, polyureas, polyurethanes) or from a melt (for example, polyolefin, polyamide, polyester). Materials, equipment, principles, and processes concerning the production of fibers are discussed in detail in Fourné, F., Synthetic Fibers, (Carl Hanser Verlag, 1999), translated and edited by H. H. A. Hergeth and R. Mears.
Hollow fibers are well known; their manufacture and applications are discussed in, for example, Fourné, p. 549 and by Irving Moop citch, Jr. in “Hollow Fiber Membranes,” Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition, Volume 13, pages 312-337 (John Wiley & Sons, 1996).
The production of bi- and multicomponent fibers (for example, islands-in-the-sea and sheath-core fibers) is discussed in, for example, Fourné, op cit., pp. 539-548 and 717-720. The term “islands-in-the-sea” as used herein denotes a type of bicomponent or multicomponent fiber also described as multiple interface or filament-in-matrix. The “islands” are cores or fibrils of one or more polymers imbedded in a “sea” (or matrix) consisting of another polymer. The matrix is often dissolved away to leave filaments of very low denier per filament. Conversely, the islands can be dissolved away to leave a hollow fiber. The term “sheath-core” as used herein denotes a bi- or multicomponent fiber of two polymer types or two or more variants of the same polymer. In a bicomponent sheath-core fiber, one polymer forms a core and the other surrounds it as a sheath. Multicomponent sheath-core type fibers of two or more polymers can also be made, containing a core, one or more inner sheaths, and an outer sheath. When the core is made as a hollow, more than one hollow may be present and more than one sheath may surround the hollow. Hollows may also have various shapes.
Many polymer materials can be used to create fiber-on-end membranes by the processes described herein. The appropriate choice of polymer materials will depend on several factors. One factor is the consolidation process and conditions for binding the fibers into a defect-free FOE billet. If elevated pressures and temperatures are to be used to sinter the neighboring fibers in a FOE bundle, then the polymer that makes up the outermost sheath or sea in a multicomponent fiber preferably has a melting point or softening point that is lower than the melting point of the polymer(s) that make(s) up the inner sheath, core or islands in the fiber. It may also be desirable that the glass transition temperature or the softening point or the heat deflection temperature of the inner sheath, core or island be higher than the melting point or the softening point of the outer sheath polymer or the sea polymer.
If one of the polymer components is later to be dissolved away to produce pores, then such a component should be readily soluble in a solvent. It is also desirable that the other polymer components or phases in the fiber are resistant to or insoluble in the solvent used to dissolve the soluble polymer component. Examples of soluble polymers and the solvents in which they are soluble in include, but not limited to, polyamides in formic acid, polyesters in strong alkali solutions, polyurethanes in polar solvents such as dimethylacetamide, polystyrene and its copolymers in aromatic solvents such as toluene and nonpolar solvents such as dichloromethane, and polyvinyl alcohol and some polyethers and polyether copolymers in water. Those skilled in the art know that certain polymers, although not soluble in pure solvents, are soluble in mixed solvents. These polymers may also be used as the soluble component in the multicomponent fibers used to create membranes made by the processes described herein.
Mechanical properties must also be considered when choosing polymer components. Enough mechanical flexibility is required for the fibers to survive being folded during the pleating process. When the fibers have been fused into a billet, the materials must be amenable to skiving by one or several skiving operations known to those skilled in the art.
The selection of the polymer components comprising the fiber will be determined in part by the end use of the FOE material created from the fiber. For example, if the fiber-on-end membranes produced by the processes described herein are to be used in the fabrication of chemical and biological protective garments, then the polymer components of the fiber should be intrinsically resistant and impermeable to toxic chemical and biological agents. If the membranes are to be used for filtration or purification of process streams in the chemical, biochemical or pharmaceutical industries, then the polymer components of the fiber are desirably resistant to the different species present in the process streams.
If the fiber-on-end membranes are used to create one or more hydrophobic but breathable layers in firefighter's turnout coat, then it may be desirable to select polymer components that have fire resistant properties. It is expected that there will be several other applications for the FOE membranes created by the processes described herein. Hence, polymer components of the precursor multicomponent fiber may be selected to provide the desired properties that are needed for that specific application.
Those skilled in the art will know that the multicomponent fibers may be spun from a wide variety of polymer materials. Examples of classes of suitable polymer materials include, but not limited to, homopolymers, copolymers and blends of: polyolefins, polyesters, polyamides, polyurethanes, polyethers, polysulfones, vinyl polymers, polystyrenes, polysilanes and polysulfides and fluorinated polymers. The copolymers within each class or between each class of aforementioned polymers can be random copolymers or block copolymers. Specific examples of polyolefins include, but not limited to, stereospecific and random homopolymers of ethylene and propylene; and their copolymers with butene, octene, tetrafluoroethylene, hexafluoropropylene, tetrafluoroethylene, methacrylic acid, acrylic acid, vinyl acetate, vinyl alcohol, and vinyl chloride, methyl acrylate, ethyl acrylate, butyl acrylate or maleic anhydride. Ionomers derived from polyolefin copolymers, such as DuPont™ Surlyn® ionomer resins (E. I. du Pont de Nemours & Company, Inc., Wilmington, Del., USA), can also be used as a component in the multicomponent fiber. Specific examples of fluorinated polymers include, but not limited to, homopolymers and copolymer of vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, and hexafluoropropylene. Specific examples of polyamides (PA) include, but not limited to, homopolymers and copolymers of PA-6, PA-66, PA-610, PA-611, PA-612 and PA-1212 and their N-alkylated analogs. Polyamides obtained from aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid and those obtained from aromatic diamines such as meta-xylene diamine and para-xylene diamine may be also be used for multicomponent fiber formation. Specific examples of styrenic polymers include, but not limited to, polystyrene, copolymer of styrene and 1,2 butadiene and 1,4 butadiene, isoprene, and isobutylene. These copolymers can be completely saturated, partially saturated on unsaturated. Partial or complete saturation is achieved by reduction of the double bonds in the polymer. Ionomers (e.g., from acids) and ionomer salts of styrenic materials are further examples.
Useful thermoplastic polyurethane elastomers that could be used to make fibers and then membranes include those prepared from a polymeric glycol, a diisocyanate, and at least one diol or diamine chain extender. Diol chain extenders are preferred because the polyurethanes made therewith have lower melting points than if a diamine chain extender were used. Polymeric glycols useful in the preparation of the elastomeric polyurethanes include polyether glycols, polyester glycols, polycarbonate glycols and copolymers thereof. Examples of such glycols include poly(ethyleneether)glycol, poly(tetramethyleneether)glycol, poly(tetramethylene-co-2-methyl-tetramethyleneether)glycol, poly(ethylene-co-1,4-butylene adipate)glycol, poly(ethylene-co-1,2-propylene adipate)glycol, poly(hexamethylene-co-2,2-dimethyl-1,3-propylene adipate), poly(3-methyl-1,5-pentylene adipate)glycol, poly(3-methyl-1,5-pentylene nonanoate)glycol, poly(2,2-dimethyl-1,3-propylene dodecanoate)glycol, poly(pentane-1,5-carbonate)glycol, and poly(hexane-1,6-carbonate)glycol. Useful diisocyanates include 1-isocyanato-4-[(4-isocyanatophenyl)methyl]benzene, 1-isocyanato-2-[(4-isocyanato-phenyl)methyl]benzene, isophorone diisocyanate, 1,6-hexanediisocyanate, 2,2-bis(4-isocyanatophenyl)propane, 1,4-bis(p-isocyanato,alpha,alpha-dimethylbenzyl)benzene, 1,1′-methylenebis(4-isocyanatocyclohexane), and 2,4-tolylene diisocyanate. Useful diol chain extenders include ethylene glycol, 1,3-propane diol, 1,4-butanediol, 2,2-dimethyl-1,3-propylene diol, diethylene glycol, and mixtures thereof. Preferred polymeric glycols are poly(tetramethyleneether)glycol, poly(tetramethylene-co-2-methyl-tetramethyleneether)glycol, poly(ethylene-co-1,4-butylene adipate)glycol, and poly(2,2-dimethyl-1,3-propylene dodecanoate)glycol. 1-Isocyanato-4-[(4-isocyanatophenyl)methyl]benzene is a preferred diisocyanate. Preferred diol chain extenders are 1,3-propane diol and 1,4-butanediol. Monofunctional chain terminators such as 1-butanol and the like can be added to control the molecular weight of the polymer.
Useful thermoplastic polyester elastomers include the polyetheresters made by the reaction of a polyether glycol with a low-molecular weight diol, for example, a molecular weight of less than about 250, and a dicarboxylic acid or diester thereof, for example, terephthalic acid or dimethyl terephthalate. Useful polyether glycols include poly(ethyleneether)glycol, poly(tetramethyleneether)glycol, poly(tetramethylene-co-2-methyltetramethyleneether)glycol [derived from the copolymerization of tetrahydrofuran and 3-methyltetrahydrofuran] and poly(ethylene-co-tetramethyleneether)glycol. Useful low-molecular weight diols include ethylene glycol, 1,3-propane diol, 1,4-butanediol, 2,2-dimethyl-1,3-propylene diol, and mixtures thereof; 1,3-propane diol and 1,4-butanediol are preferred. Useful dicarboxylic acids include terephthalic acid, optionally with minor amounts of isophthalic acid, and diesters thereof (e.g., <20 mol %).
Useful thermoplastic polyesteramide elastomers that can be used in forming the fibers and membranes include those described in U.S. Pat. No. 3,468,975. For example, such elastomers can be prepared with polyester segments made by the reaction of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 1,10-decandiol, 1,4-di(methylol)cyclohexane, diethylene glycol, or triethylene glycol with malonic acid, succinic acid, glutaric acid, adipic acid, 2-methyladipic acid, 3-methyladipic acid, 3,4-dimethyladipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, or dodecandioic acid, or esters thereof. Examples of polyamide segments in such polyesteramides include those prepared by the reaction of hexamethylene diamine or dodecamethylene diamine with terephthalic acid, oxalic acid, adipic acid, or sebacic acid, and by the ring-opening polymerization of caprolactam.
Thermoplastic polyetheresteramide elastomers, such as those described in U.S. Pat. No. 4,230,838, can also be used to make the fibers and membranes. Such elastomers can be prepared, for example, by preparing a dicarboxylic acid-terminated polyamide prepolymer from a low molecular weight (for example, about 300 to about 15,000) polycaprolactam, polyoenantholactam, polydodecanolactam, polyundecanolactam, poly(11-aminoundecanoic acid), poly(12-aminododecanoic acid), poly(hexamethylene adipate), poly(hexamethylene azelate), poly(hexamethylene sebacate), poly(hexamethylene undecanoate), poly(hexamethylene dodecanoate), poly(nonamethylene adipate), or the like and succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, terephthalic acid, dodecanedioic acid, or the like. The prepolymer can then be reacted with a hydroxy-terminated polyether, for example poly(tetramethylene ether)glycol, poly(tetramethylene-co-2-methyltetramethylene ether)glycol, poly(propylene ether)glycol, poly(ethylene ether)glycol, or the like.
A key challenge in the FOE process is to take the as-spun yarns and align the fibers side by side with high packing density, orienting the fibers so that they face a preferred direction, and then completely consolidating them into a solid block such that there are essentially no interstitial voids in between the fibers and then skiving the resulting solid block to produce a film. This completely consolidated block can take many forms depending on the desired final product. For example, a rectangular billet with the fibers oriented perpendicular to the skived surface will create individual sheets of film when linearly skived. In a like manner a cylindrical billet with the fibers oriented radially relative to the cylinder axis will produce a long, continuous film when rotary skived.
Proper alignment of the fibers will help produce a defect-free and void-free FOE solid structure which when skived and processed will yield a uniform and defect-free membrane. Fibers are preferably arranged parallel to each other in a direction referred to as the fiber direction or axis, with little or no fiber crossover. Fibers not aligned to parallel to the axis could conceivably cause structural defects or porous defects when the fibers are consolidated and then skived. There are several methods for aligning the fibers; the usefulness of each depends on the orientation method, consolidation method and the ultimate billet form to be produced and which is the most cost-effective manner. Typically, the as-spun yarns are first wound up on bobbins. Most (but not all) alignment methods use these bobbins as a feed supply. Examples of alignment methods include, but are not limited to, forming the fibers into a ribbon, weaving yarns into a unidirectional fabric, skein winding, and on a bobbin itself.
The term “ribbon” as used herein denotes a thin, flat arrangement of fibers that can be several inches to several feet wide but generally only a few fibers thick. It is desirable that the ribbon thickness be less than 0.2 inch (0.51 cm), but it is preferred that the thickness be less than 0.1 inch (0.25 cm), and it is more preferred that the thickness be less than 0.05 inch (0.13 cm). The fibers are lightly tacked together so that the ribbon can be handled without the individual fibers' coming loose. A common textile process for creating a ribbon of material is to take bobbins of yarn and assemble them into a creel, so-called beaming, with hundreds or even thousands of bobbins. The ends of each of these bobbins are combined in a comb and then wound up on a mandrel to form a beam. Once the beam is formed, the individual fibers that make up the beam can be tacked or bound together by one or more of several different means to create a sheet-like structure.
The appropriate yarn density of the beam, as defined by the number of yarn ends per unit width of the beam, will depend on several factors such as the number of fiber ends in a single yarn end and the denier of the filaments. For example if the denier of the filaments comprising a yarn end is small, a larger number of yarn ends will be required to create a beam where a few or all of the fibers are tacked to the neighboring filaments. Conversely, if the denier of the fibers is large, fewer yarn ends will be required to create a partially tacked fiber beam. Optimum yarn end density is desirable. Sparse yarn end density may create a poorly tacked beam and a very high yarn density will lead to a stiff beam, when tacked. Those skilled in the art will note that, in order to create a tacked fiber beam, the total number of yarn ends multiplied by the diameter of the yarn ends should be greater than the width of the beam.
In the process described herein, the fibers are bound together by thermal fusing. As used herein, the term “thermal fusing” denotes bonding using heat without a chemically reactive binder or a solvent used for solvent bonding. There are many ways to thermally fuse the fibers. For example, the beam comprising the fibers can be passed through or over a heating unit (radiant heater, hot air convection heater, microwave heater, etc.), thereby allowing the fibers to tack to each other. The fibers in the beam can also be tacked by passing the beam through one or more calendar rolls, which may or may not be driven. The beam may also be passed through heated or unheated nip rolls to control the thickness of the fiber beam. The heating method used depends on the type of fiber being fused and the beam density, as is well known in the art. It is desired that the fibers in the beam be tacked to only an optimum extent. If the fibers are weakly tacked to each other, they may come apart from the beam and break. Broken fiber or loose ends can lead to defects in the final fiber-on-end product. If the fibers are too strongly tacked to each other, the resulting beam may lose its flexibility and be difficult to process.
A ribbon can be formed from one type of fiber or from two or more types of fibers. The types of fibers can be differentiated in many different ways. For example, the fibers can vary in the size or shape of their cross-section, size, shape or the number of cores per fiber, polymer components comprising the fibers. The fibers can also vary in properties such as, for example, color, chemical composition, surface chemistry and electrical conductivity. The different types of fibers can be distributed randomly during the beaming operation, or they can be distributed in a desirable repeating or non-repeating pattern.
Another method of aligning the yarns is to weave them into a unidirectional fabric. The term “fabric” as used herein denotes a planar textile structure produced by interlacing yarns fibers or filaments. A “unidirectional fabric” is a fabric made with a weave pattern designed for directional strength in one direction only. The yarns can be woven in either the weft or warp direction. Each has different advantages. Weaving the yarns in the warp direction involves less setup since it can be fed from a single bobbin; also, the yarn density can be adjusted. Alternatively, placing the yarn in the weft direction (for “uni-weft” fabric) requires a large number of bobbins, similar to that for beaming; but the advantage is that, once the creel is set up, the fabric can be produced at a higher rate. In both cases, the cross axis yarn is a low melting point binder fiber woven in a loose weave that ties the fabric together. In one embodiment of the process described herein, a unidirectional weft (“uni-weft”) fabric is woven, having a high density of fibers in the weft direction but very sparse warp fibers, and the warp fibers are low melt temperature fibers that are melted after the weaving process and are thereby used to hold the weft fibers together.
As with ribbon, woven fabrics can comprise of one or more types of fibers. The different types of fibers can be woven randomly into the fabric or can be woven to create a specific repeating or non-repeating pattern.
A typical windup has a helix angle for winding where yarns cross lap each other at that angle. However, it is possible to wind the yarns at a very low angle such that the fibers lay essentially parallel to one another.
The fibers can be wound to an inch in depth or more; however a depth of from 1/16″ to ¼″ (1.6 mm to 6.4 mm) is advantageous for further processing. The fibers are bound together by thermal fusing. The fiber can be wound onto an unheated roll (i.e., bobbin), after which the roll can be placed into a heated oven where the fibers loosely fuse together. The oven temperature will depend on the fiber composition. Alternatively, the fibers can be wound onto a heated roll where they are lightly fused (see, e.g., Example 1 below). In both cases, the roll is allowed to cool and the fused fiber material is then cut off the bobbin and placed flat to form a unidirectional mat of fibers. For our tests, we had fused bobbins with 1/16″ (1.6 mm) and ⅛″ (3.2 mm) thick wound fiber on 6″ (15 cm) cores. The bobbins were heated in an oven at about 80° C. for 2 hours. After removal from the core, the mat of fibers was well tacked together with high fiber density, and it was thin enough to be easily laid flat for subsequent cutting into shapes.
As an illustration, fibers can be wound on a bobbin to a thickness in the range of 1/32″ (0.8 mm) and ⅛″ (3.2 mm). The temperature used to fuse the fibers on the bobbin is determined according to the melting point of the outer sheath of the fiber. It is desirable that fusing temperature be 15° C. above or below the onset of melting of the polymer that makes up the outer sheath. The onset of melting of a polymer can be obtained with the help of a differential scanning calorimeter. If the polymer does not have a melting point then the fusion temperature can be in the range of the softening temperature of the polymer.
The fibers can be wound on a skein winder to produce a loose coil of yarn. This yarn can then be placed directly into a mold as a hank of parallel fibers and consolidated under heat and pressure, to form a billet. Alternatively, the fibers may be bound together by coating the fibers with a binder or by solvent bonding.
Once the fibers have been oriented along a preferred direction and partially fused by any of the processes as described above, the oriented and partially fused fibers must now be fully consolidated to yield a solid structure that contains no void space between the neighboring fibers. The complete consolidation of the fibers is carried out under elevated temperature and pressure. Without being bound by theory, complete consolidation of fibers requires that the polymer that makes up the sheath or sea of a multicomponent fiber must soften or melt and flow in such a way that a) the interstitial void space between fibers is essentially completely filled in and b) the polymer interface between neighboring fibers disappears.
The temperature of complete consolidation will depend upon the composition of the fibers being consolidated. If the fibers being consolidated comprise sheath-core or islands-in-the-sea fibers, where the core or island is an amorphous polymer, then the consolidation temperature must be higher than the softening temperature of sheath polymer or the sea polymer but lower than the softening point of the core or island polymer. If the polymer material that makes up the core or island is a semi-crystalline polymer and the sheath or sea polymer is an amorphous polymer, then the consolidation temperature must be higher than the softening point of the sheath or sea polymer but lower than the melting point of the core or island polymer. If the polymer material that makes up the core or island is a semi-crystalline polymer and the sheath or sea polymer is also a semi-crystalline polymer, then the consolidation temperature must be higher than the melting point of the sheath or sea polymer but lower than the melting point of the core or island polymer. Thus, there may be a range of temperatures within which the oriented fibers be completely consolidated to yield a solid structure. Within a given temperature range, the optimal temperature for consolidation will depend on a variety of process and material factors (e.g., the molecular weight and viscosity of the sheath or sea polymer, the process used for complete consolidation, pressure used for consolidation and the time desired for complete consolidation) and is readily determined by one of skill in the art.
The pressure for complete consolidation will in general be significantly higher than atmospheric pressure; in one embodiment, the pressure is in the range of about 200 psi (1.38 MPa) to about 2500 psi (17.2 MPa). The optimal pressure for consolidation will depend on a variety of process and material factors (e.g., the temperature being used for consolidation; the molecular weight, viscosity and surface properties of the polymer that makes up the sheath or sea of the fiber, fiber cross-sectional shape); the diameter of the fibers; the process and equipment being used for consolidation; and the time required for complete consolidation) and is readily determined by one of skill in the art.
The pressure and temperature used for complete consolidation of the fibers can each vary over a range during the consolidation process. For example, the temperature of the fibers during consolidation may be varied in discrete steps or can be varied continuously. The increase in temperature can vary at a constant rate over a given time or at a non-constant rate. Similarly, pressure during consolidation can be varied in steps or in a continuous manner.
The time for complete consolidation will depend on several material and process factors (e.g., the temperature and pressure being used for consolidation; the molecular weight, viscosity and interfacial properties of the sheath or sea polymer; fiber cross-sectional shape, and the equipment being used for consolidation) and is readily determined by one of skill in the art. In general, the time for consolidation should be sufficient to allow for the sheath or sea polymer to completely fill the interstitial void space between fibers and form a solid bond with the neighboring fibers. Hexagonally shaped fibers, closely packed, will have less interstitial void to eliminate than round.
Several analytical tools or techniques may be used to indicate when complete consolidation has been achieved. For example, in some cases, the density of the block can be measured directly and compared to the theoretical density, as described above. The consolidated structure can also be subjected to X-ray tomography, a non-destructive, technique used to study the three dimensional microstructure of solid materials. The consolidated material can be skived to yield thin sections which may be analyzed under different microscopes to indicate the existence or disappearance of voids between fibers. The thin sections from the consolidated structure can also be subjected to hydraulic or gas permeability tests. Infinitely high resistance to flow of liquid or gas can indicate complete consolidation and absence of void space in the consolidated structure. Mercury porosimetry is yet another technique that can be used to indicate complete or insufficient consolidation.
Those skilled in the art of machine design and large scale manufacturing will know that several different kinds of equipment and machinery can be used for complete consolidation of the fibers. One form of equipment which is readily available at manufacturing sites is a heated hydraulic press which can supply varying levels of pressure to consolidate the fibers.
Since fiber consolidation may be carried out at elevated temperature and pressure, the fibers being consolidated may be confined in molds during the consolidation process. The shape and size of the mold will depend on the shape and size of the billet desired and the pressure and temperature being used for complete consolidation.
The final billet requirements are determined by the desired product and cost of assembly. For a billet that is to be skived into discrete sheets (linear skiving), all the fibers must be essential parallel and are usually oriented perpendicular to the skiving surface. In some applications, skiving at an angle to the fiber axis brings additional value to the membranes. For example, cutting off-axis gives the same capillary pore structure with preferred entry or exit angles into and out of the capillary pores. This type of skiving will produce sheets with the area of the surface to be skived. Billets suitable for linear skiving can be produced by a variety of methods, including, but not limited to, pleating followed by fusion and stacking followed by thermal fusion. A schematic of the process is illustrated in
A fused ribbon or fabric can be run through a continuous pleating operation in which the ribbon or fabric is repeatedly folded and then stacked together. This process is similar to the pleating process used to make folded filter media or pleats in fabrics. The process is illustrated in
Under heat and pressure, these pleats can be made to tack together to form a batt in which the fibers are typically now oriented substantially perpendicular to the batt surface. This batt can be used in several ways. It can be placed into a rectangular mold and then consolidated under heat and pressure to form a rectangular billet that can be skived into sheets Additionally, the batt or the rectangular billet formed therefrom can be sectioned into segments (for example, trapezoidal or other shapes) that can be assembled to orient the fibers radially in preparation for rotary skiving, as described below.
The pleating process can be adapted to make thin solids (see, for example,
Flattened sections of fused fiber material (i.e., ribbons, mats, plates) can be stacked together and then molded to create a billet. This billet can be skived to form individual sheets of film or the billet can be cut into sections that can be assembled into a cylindrical billet for rotary skiving. The flattened fused fiber material can also be cut into sections that can be assembled to orient the fibers in a radial direction. For example, the trapezoidal shaped sections 7 can be cut from a mat (
Any of the methods described above can be used to make a rectangular billet of FOE material. While these billets can be used in a linear skiving process to make individual sheets of film there are applications where a continuous roll of film is preferred. A continuous roll can be produced by rotary skiving, in which a cylindrical billet is spun on its axis, and skiving produces a film that is the width of the billet but of a very long length (
First, the billets are cut (typically machined) into sections. In one embodiment, the section is a trapezoidal section, as shown in
There are many ways to weld the cut sections together. The sections can be welded by heating in an oven with or without pressure. Most other known plastic welding techniques can also be used, including, without limitation, hot plate welding, vibration welding, and ultrasonic welding.
In some instances it is preferred to cap the machined surfaces prior to welding. Heat sealing a solid film 9 onto the surfaces (
The annular section shown in
The processes described herein makes it practical to manufacture porous membranes or capillary arrays of any desired width and length from fibers arranged on end using a continuous and/or automated process. Additionally, lower manufacturing costs are achievable as a result of continuous processing and the reduction in fabrication steps.
Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.
Additional processing steps and eventual applications will depend in part on the nature of the original fibers and the thickness of the skived layer. If the fibers used to make the fiber-on-end materials have special properties then the membrane or capillaries formed by skiving the material will also have special properties and unique value. Such properties may be, for example, a special distribution of hole sizes or a geometrical arrangement of different multicomponent fibers to form a unique array or selected values of conductivity or surface energy or surface chemistry or optical index, color, or species diffusion (selective permeation).
In one embodiment of the process of the present invention, porous membranes are produced. If the original fibers are hollow, then the layer or membrane skived from a fused block of fibers will be porous and have regularly spaced and uniformly sized holes with a properly prepared billet. If the original fibers are bicomponent fibers with a solid core that is made of a material that can be dissolved after spinning, then a porous membrane can be made after skiving by dissolving away the core to form holes. Similarly, if each fiber has multiple cores of the islands-in-the-sea type, having a number of smaller dissolvable fiber cores arranged within a sea of a different polymer, then the islands may be dissolved to form membranes with smaller pores, i.e., microporous membranes.
Many other variations are possible. For example, the original fiber could be tricomponent, with a central core that can be dissolved away, an inner sheath that is rigid and contributes a special functionality (e.g., hydrophilicity, hydrophobicity, conductivity), and an outer sheath that is fusible at a lower temperature than the inner sheath or core materials.
As another example, the original fiber could be a tricomponent fiber, with a central core that can be dissolved away, an inner sheath that is capable of changing volume in the presence of an external stimulus (i.e, temperature, chemical exposure, etc.) and an outer sheath that is fusible at a lower temperature than the inner sheath or core materials. A membrane created from such fibers would be capable of changing its pore size and hence its permeability whenever the external stimulus is applied or taken away.
As yet another example, a fiber on end sheet or membrane can be made in which the walls of the capillaries have active or reactive chemical moieties on the surface, such as carboxylic acid groups, hydroxyl groups, amine groups, epoxy groups, anhydride groups etc. The sheet or membrane can be made by fabricating an FOE billet using a multicomponent fiber comprising a central core that can be dissolved away, an innermost sheath containing the active or reactive chemical moieties at the surface after the central core is dissolved, and an outermost sheath that is fusible at a lower temperature than the innermost sheath or core materials. Alternatively, the fiber could be hollow and be made of an inner sheath with the desired moieties at the surface and an outer sheath that is fusible at a lower temperature than the innermost sheath. Membrane created from such fibers could be used for affinity separation of species as they flow through the capillaries of one or more FOE capillary arrays, such as the membrane chromatography applications described by R. Ghosh in “Protein separation using membrane chromatography: opportunities and challenges,” Journal of Chromatography, 952(1-2), pp 13-27, 2002. As is known to those skilled in the art of chromatography in general and membrane chromatography in particular, the active or reactive chemical moieties along the capillary wall may be used to attach or graft other reactive groups such as sulfonic acid groups, quaternary amine groups, metal ions, enzymes, proteins etc., which will selectively bind to specific biological and chemical species that need to be purified or removed from a process stream. Capillary pores of uniform size as produced by the processes described herein allow more uniform flow and more exposure of solution to the functional membrane wall.
Some applications may benefit from a bimodal, trimodal or other controlled distribution of pore or core sizes, with some holes functionalized, others not. This can be achieved by using a mixture of fiber diameters or fiber component diameters. For example, hollow fibers of the same outer diameter but different wall thickness, thus, different hole size, could be used.
Examples of uses for the FOE membranes described herein include without limitation filters for particle sizing with defined sized distribution (for example, monodisperse or, if fibers of two different diameters are used, bimodal), chromatography membranes, and adaptive membrane structures that change permeability in response to a stimulus and apparel, as described below.
The porous membranes can be used as the hole-containing components of adaptive barrier membrane structures as described in U.S. Pat. Nos. 7,597,855 and 7,625,624, and pending U.S. patent application Ser. Nos. 11/584,999 and 11/584,927, which are hereby incorporated by reference in their entirety. An adaptive membrane structure includes first and second membranes having holes, and means to respond to an actuating stimulus that moves the first membrane into contact with the second membrane in a position in which the holes of the first membrane are substantially out of registration, or are out of registration, with the holes of the second membrane, thereby change the permeability of the membrane structure. In an alternative structure, the porous membrane of the present invention is one of two adjacent membranes, the second membrane containing an array of protruding members, each protruding member shaped and positioned so as to be insertable in and enter a hole in the porous membrane when one or both membranes are moved toward each other in response to application or removal of a stimulus. As each protruding member enters its corresponding hole, it contacts the inner surface of the hole in such a way as to create a seal between the protruding member and its mating hole, thereby eliminating paths permeation, convection and/or diffusion. Examples of articles into which adaptive membrane structures can be usefully incorporated include without limitation apparel (e.g., a protective suit, a protective covering, a hat, a hood, a mask, a gown, a coat, a jacket, a shirt, trousers, pants, a glove, a boot, a shoe and a sock); an enclosure (e.g., a tent, a safe room, a clean room, a greenhouse, a dwelling, an office building or a storage container); and a valve for controlling the flow of gas, vapor, liquid and/or particulates).
Examples of articles into which adaptive membrane structures can be usefully incorporated include without limitation apparel(e.g., a protective suit, a protective covering, a hat or other head covering, a hood, a mask, a gown, a coat, a jacket, a shirt, trousers, pants, a glove, a boot, a shoe and a sock); an enclosure (e.g., a tent, a safe room, a clean room, a greenhouse, a dwelling, an office building or a storage container); and a valve for controlling the flow of gas, vapor, liquid and/or particulates. The protective covering could be a protective garment for chemical protection, biological protection, or both, including without limitation, a coverall, a protective suit, a coat, a jacket, a limited-use protective garment; a glove; a sock, a boot; a shoe or boot cover, trousers, a hood, a hat or other head covering, a mask, and a shirt, a medical garment, a surgical mask, a medical or surgical gown, or a slipper.
The membrane pores can also be functionalized chemically to impart particular properties, such as catalytic or enzymatic activity, reactivity, adsorptivity, hydrophilicity, hydrophobicity, and the like.
A porous membrane produced as described herein can also be used to support other inorganic, organic or biological materials either on its surface or inside its capillary pores. These materials may be physically supported or chemically grafted to the membrane. By the introduction of other materials on the membrane or inside its pores, a composite membrane may be formed which may be used for many different applications such as filtration, separation, purification, protection, sensing and diagnostics.
Porous membranes from this invention can also be used as templates for the synthesis or fabrication of advanced materials. The capillaries could be the sites for die casting or replication of reverse image structures. The uniform capillary pores of the membrane can be used as tiny reactors to synthesize materials such as microtubes and nanotubes. These advanced materials can be left in the pores to yield a composite membrane or can be recovered by dissolving away the membrane in a suitable solvent. When the advanced materials are such that are stable at very high temperatures, they can be recovered by incinerating or burning the outer membrane at high temperatures.
Membranes with Filled Pores or Capillaries
In another embodiment, the process described herein is used to produce membranes containing filled pores or capillaries. For example, the core material of sheath-core fibers used may be left undissolved if desired, and the core material could, depending on its composition, impart special functionality to the membrane, such as fire resistance, antimicrobial activity, thermochromic properties, and the like. For example, the core material could comprise a polymer that has been compounded with a sufficient level of flame retardant, antimicrobial agent, insecticide and insect repellants to impart that property to an article comprising the membrane. A few examples of flame retardants that could be incorporated in this manner are halogen- and phosphorous-containing flame retardants, including without limitation decabromodiphenyl oxide, cyclic phosphonate esters, triphenyl phosphate, poly(sulfonyldiphenylene phenylphosphonate) and ammonium polyphosphate. Surface properties can also be modified by using core materials comprising antistatic agents or electrically conductive materials, or hydrophobic or hydrophilic substances (e.g., polymers or oligomers.
If the fiber-on-end material is skived so as to from a thick layer, then long capillaries rather than shorter holes can be made. Such a capillary membrane can be used to selectively wick fluids or to store and dispense fluids in a controlled manner. Such a membrane could be used for controlled release of drugs in, for example, medical materials, devices, or implants, including without limitation a bandage, wound dressing, catheters, prostheses, pacemakers, heart valves, artificial hearts, knee and hip joint implants, vascular grafts, orthopedic fixtures, ear canal shunts, cosmetic implants, implantable pumps, hernia patches, and artificial skin. The membrane itself could be made from a material that is absorbed into the body longer term when implanted.
A capillary membrane could be impregnated with a variety of functional materials. The functional material could be a liquid itself, wicked into the holes by capillary action, or dissolved in a solution, wherein the solvent is evaporated after the solution impregnates the membrane. The functional material might also be spun as part or all of sheath or core components of the fibers used to make the membrane.
For example, paraffin waxes are examples of phase change materials used in heat regulation applications. Thus, a paraffin wax could be dissolved in methylene chloride and incorporated into a porous capillary membrane by wicking, after which the solvent would be evaporated, leaving behind the paraffin wax. An article comprising such a filled capillary membrane would demonstrate desirable heat regulation characteristics depending on the temperature of the environment. Representative examples of articles containing a capillary membrane that incorporates a phase change material include without limitation blankets, upholstery for the home and for automobile seating, bedding (such as pillows, pillow cases, sheets, comforters, bedspread, mattresses, mattress covers), exposure suits for underwater diving, footwear (such as shoes, boots, ice skating boots, sneakers, and slippers) midsoles and liners, gloves and mittens, hats, ski masks, jackets, coats, parkas, snowsuits, ski pants and other pants, thermal underwear and other intimate apparel, vests, shirts, blouses, sweaters, dresses, and potholders.
Antimicrobial and antiodor agents can also be incorporated as functional fillers in the present invention. An antimicrobial agent is a bactericidal, fungicidal (including activity against molds), and/or antiviral agent. These include, for example, chitosan and its derivatives, triclosan, cetyl pyrridinium chloride, polybiguanide-based compounds; and the alkyl (especially methyl, ethyl, propyl, and butyl) and benzyl esters of 4-hydroxybenzoic acid, which are commonly referred to as “parabens.” Use of a specific antimicrobial or antiodor functional filler with a specific capillary membrane structure will require a solvent that will dissolve the functional filler but not affect the membrane structure. The antimicrobial and antiodor articles of the invention find application in uses such as apparel, including without limitation liners and midsoles for footwear (such as boots, shoes, slippers, sneakers), gloves and mittens, hats, shirts and blouses, outer wear, sweaters, dresses, intimate apparel, and medical garments; healthcare, including medical drapes, antimicrobial wipes, handkerchiefs, and medical packaging.
Insecticides and insect repellants can also be used as functional fillers. Examples include but are not limited to N,N-diethyl-m-toluamide (“DEET”); dihydronepetalactone and derivatives thereof; essential oils such as citronella oil, backhousia citriodora oil, melaleuca ericafolia oil, callitru collumellasis (leaf) oil, callitrus glaucophyla oil, and melaleuca linarifolia oil; and pyrethoid insecticides, such as but not limited to permethrin, deltamethrin, cyfluthrin, alpha-cypermethrin, etofenprox, and lambda-cyhalthrin. Articles containing an insecticidal and/or insect repellant material or compound that are made from or incorporate a filled capillary membrane structure of the invention find application in uses such as apparel, including without limitation hats, hoods, scarves, socks, shoe liners, shirts and blouses, shorts, pants; tents, tarpaulins and bedding.
If the fibers are single core, or islands-in-the-sea type having a number of smaller fiber cores (“islands”) arranged within a sea of a different polymer, wherein the sea is dissolvable in a solvent that does not dissolve the islands, then the sea may be etched to form a surface that has many micro-projections or hairs. Such a surface can be made to possess super-hydrophobic properties, useful in, for example, self-cleaning surfaces or stay-dry materials.
All of the above examples are of higher value and utility than the fibers themselves. The FOE materials produced as described herein can find new applications in filtration, protective membranes, drug delivery, self cleaning super-hydrophobic surfaces and many other exciting new materials.
The present invention is further defined in the following Examples. It should be understood that these Examples are given by way of illustration only. From the above discussion and these Examples, one skilled in the art can ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various uses and conditions.
The meaning of abbreviations is as follows: “cm” means centimeter(s), “dpf” means denier per filament, “g” means gram(s), “h” means hour(s), “kg” means kilogram(s), “lb” means pound(s), “min” means minute(s), “mm” means millimeter(s), “MPa” means megapascal(s), “psi” means pounds per square inch, “rpm” means revolutions per minute, and “μm” means micrometer(s).
Surlyn® is a registered trademark of E. I. du Pont de Nemours and Company, Inc.
Elvamide® is a registered trademark of E. I. du Pont de Nemours and Company, Inc.
Nucrel® is a registered trademark of E. I. du Pont de Nemours and Company, Inc.
This example describes a laboratory-scale fiber-on-end process used to create microporous membranes.
Sheath-core fibers were spun on a continuous fiber spinning line. A schematic of the spinning line is shown in
Before fiber spinning, Surlyn® 8150 resin and Elvamide® 8061 nylon multipolymer resin were dried for 16 h at 60° C. in a vacuum oven with a dry nitrogen sweep. The dried polymers (12 and 13) were melted in two separate co-rotating twin screw extruders (14 and 15). The extruder that fed the molten ionomer was set at 255° C. and the one that fed the molten Elvamide® 8061 nylon multipolymer resin was set at 200° C. Both polymer melt streams from the respective extruders were fed to separate Zenith gear pumps, which then metered the molten polymers through to spin pack 16. The speeds of the two gear pumps were preset so as to supply 11.2 g/min of the ionomer and 4.8 g/minute of the Elvamide® 8061 nylon multipolymer resin respectively. These flow rates allowed the outer sheath in the sheath-core fiber to be nominally 70% by weight and the core to be nominally 30% by weight. The spin pack was heated to 244° C. using heated block 17. Both polymer streams were filtered through three 200 mesh and one 325 mesh screen in their respective partitions within the pack. After filtration, the copolyamide was metered through 0.015″ (0.38 mm) diameter orifices of 0.030″ (0.76 mm) length into a surrounding sheath pool of ionomer, which was metered for concentric placement by an offset of 0.004″ (0.10 mm), as measured from the flat metal surface containing the core orifices and the top of the plateau as described in U.S. Pat. No. 2,936,482. Sheath and core then flowed down a counterbore of 0.0625″ (1.6 mm) diameter and approximately 0.325″(8.26 mm) length until they reached a filament forming orifice of 0.012″ (0.30 mm) diameter and 0.050″ (1.3 mm) length. A total of 34 individual sheath-core filaments were created at the spinneret orifice outlets.
These 34 resulting filaments were cooled in ambient air (quench zone 18), given a water surface finish (19), and then combined in a guide approximately eight feet (2.4 meters) below the spin pack. The 34 filament yarn was pulled away from the spinneret orifices and through the guide by a pair of rolls 20 turning at approximately 1200 meters per minute. From these rolls the yarn was taken to a conventional winder 21 and wound onto several bobbins. The average denier per filament for the yarn was measured to be 3.6.
The sheath/core yarn was taken off the bobbins and wound onto a rotating heated roll that was set at 85° C. The rotational speed of the roll was set at approximately 58 rpm. The outer diameter of the roll was estimated to be 10.11″ (25.68 cm). As the yarn was being taken up by the rotating roll, it was also linearly traversed by an oscillating guide along a direction that was parallel to the axis of the rotating cylinder. The oscillating guide was manufactured by Mossberg Industries, Cumberland, R.I. The oscillating amplitude of the guide was set to 5 inches (13 cm) and this allowed the yarn to spread out over a distance of 5 inches (13 cm) on the heated roll. The linear speed of the guide was kept small to ensure that the helical angle for the winding was extremely small. Approximately 47,800 meters of the sheath-core yarn was wound onto the heated roll. After the winding was completed, the roll was allowed to cool to room temperature. This allowed each yarn winding to lightly fuse to its nearest neighbors and form a 5″ (13 cm) wide ribbon. This lightly fused ribbon was slit, taken off the roll and laid flat on table. The resulting ribbon was 31.75″ (80.64 cm) long, 5″ (13 cm) wide and approximately 0.03″ (0.76 mm) thick. It weighed 19.12 g and consisted of approximately 59,300 sheath-core filaments all running parallel to the longest axis of the ribbon. The density of the ribbon was estimated to be 0.49 g/cm3. The yarn density in the ribbon was estimated to be 349 yarn ends/linear inch. A total of 4 ribbons were created by this method. Using a sharp blade, each ribbon was slit into equal halves, yielding 8 ribbons, each having a length of 31.75″ (80.64 cm), a width of 2.5″ (6.4 cm) and a thickness of 0.03″ (0.8 mm).
Each ribbon was then manually folded over itself at a recurring distance of 2.25″ (5.72 cm) to form pleats. Pleating was carried out along the length of the ribbon, which was also the direction of orientation of the fibers that made up the ribbon. Each pleated ribbon was then compressed under an 8.5 lb (3.9 kg) weight for 30 minutes in a convection oven set at 85° C. This caused the fibers in the pleated ribbons to partially fuse to their neighbors. Marks were made on each plate to show the direction of the orientation of fibers. This process yielded a total of 8 partially fused plates that were approximately 2.5″×2.25″×0.45″ (6.4 cm×5.72 cm×1.14 cm). The 8 partially fused plates thus formed were stacked on top of each other making sure that the fiber orientation in all the plates was in the same direction. The entire stack was heated to 85° C. in a convection oven for 60 minutes. The heated stack of plates was removed from the oven and immediately sandwiched between two pre-heated aluminum plates and then compressed in between a heated Carver hydraulic press. The temperature of the press was set at 85° C. and the pressure for compression was 15 psi (0.10 MPa). After 30 minutes of compression, the heaters in the hydraulic press were turned off and the stack was allowed to cool to room temperature while still under 15 psi (0.10 MPa) of compression pressure. This process of compressing the stack of preconsolidated plates allowed them to fuse to form a single block of dimension 2.5″×2.25″×1.99″ (6.4 cm×5.72 cm×5.05 cm) with a density of 0.83 g/cm3. This block was trimmed to a final dimension of 1.98″×1.98″×1.99″ (5.03 cm×5.03 cm×5.05 cm with the help of a band saw. The block now weighed 105.7 g.
This preconsolidated block was placed in the cavity of a metal mold such that the direction of the oriented fibers in the block was perpendicular to the vertical wall of the mold cavity. The mold cavity was 2.0″×2.0″ (5.08 cm×5.08 cm) square and its height was 5″ (13 cm). Two metal rams were placed on the open ends of the mold cavity so as to sandwich the preconsolidated polymer block. The mold was placed in between a Carver hydraulic press and a pressure of 1000 psi (6.9 MPa) was applied on the rams. The outside wall of the mold was then heated with the help of tightly fitting circular Watlow band heaters that wrapped around the mold. The temperature of the mold was measured by a thermocouple inserted into the mold wall and the temperature of the mold was controlled by temperature controllers. Once the heaters were turned on, it took 40 minutes for the thermocouple to stabilize to 95° C. The polymer block was held at this temperature and 1000 psi (6.9 MPa) of pressure for 2 h, after which the heaters were turned off and the block was allowed to cool while still under 1000 psi (6.9 MPa) of pressure. When the block had cooled to room temperature, it was removed from the mold cavity. The final dimensions of the block were 2.0″×2.0″×1.64″ (5.08 cm×5.08 cm×4.17 cm). The density of the block was estimated to be 0.98 g/cm3. This density suggests that the block was completely consolidated with little or no void space present in the block.
Thin films of varying thickness were skived from the fully consolidated block, as shown in
Skived film samples were soaked in concentrated formic acid (90% by weight) between 5-10 minutes. Formic acid dissolved out the Elvamide® 8061 nylon multipolymer resin phase in each film and thereby created microporous membranes. The weight of film samples before dissolution and after dissolution of the Elvamide® 8061 nylon multipolymer resin phase was measured. Gravimetric analysis showed that the Elvamide® 8061 nylon multipolymer resin phase was about 30% by weight of the films. The density of Elvamide® 8061 nylon multipolymer resin is 1.07 g/cm3. Thus the porosity of the membranes was estimated to be 28%. Membrane samples thus created were analyzed under a scanning electron microscope (SEM). The SEM images showed cylindrical pores in the membranes (see
This example describes the formation of a solid billet by pleating and consolidating a unidirectional fabric.
Sheath-core fibers with Surlyn® 8150 resin sheath and Elvamide® 8061 nylon multipolymer resin core were spun as described in Example 1. The sheath-core fibers were woven into a unidirectional fabric with a plain weave. The count of the fabric was 5×35.6, its width was 18 3/16 in [46.2 cm] and its weight was 5.913 oz/yd2. The unidirectional fabric was cut along the direction of the fibers to from several fabric ribbons that were 2.5″ (6.4 cm) wide and about 18″ (46 cm) long. Using the same method as described in Example 1, each ribbon was then manually folded over itself at a recurring distance of 2.25″ (5.72 cm) to form pleats. Pleating was carried out along the direction of the fibers. Four such pleated ribbons were stacked on top of each other and compressed and tacked together at 90° C. for 30 minutes under an 8.5 pound weight. This process yielded a preconsolidated plate of density 0.42 g/cm3. Ten such preconsolidated plates were stacked on top of each other and tacked together under a hydraulic press at a temperature of 90° C. and an applied pressure of 60 psi (0.41 MPa). The resulting block had a density of 0.95 g/cm3. The block was trimmed to a dimension of roughly 2.0″×2.0″×2.17″ (5.1 cm×5.1 cm×5.51 cm) and further consolidated in a metal mold (as described in Example 1) at a temperature of 95° C. and a pressure of 1000 psi (6.9 MPa). The resulting block had a density of 1.0 g/cm3 and was completely consolidated.
In Examples 1 and 2, partially consolidated fiber ribbon and a unidirectional woven fabric were pleated by hand. Pleating and consolidation can also be done at continuously at much faster speeds using automated machines. In a commercial process, a continuous sheet of preconsolidated fiber beam or unidirectional woven fabric could be continuously fed into a heated zone where the sheet is heated to a desired temperature. The heated sheet can then be taken through a commercial oscillating knife pleating machine such as those manufactured by JCEM GmbH of Switzerland. The machine will create pleats in the sheet of desired amplitude. The pleated sheet could then we sent through a heated stuffer box where individual pleats would be pushed against the preceding pleat with desired force. The elevated temperature and pressure in the stuffer box will enable to tack together to form a solid sheet structure where the fibers run perpendicular to the plane of the sheet and the sheet thickness is equal to the amplitude of the pleats. The solid may then be cut into desired shapes, which can then be further consolidated at elevated temperature and pressure to form FOE billets for skiving.
Unidirectional fabric described in Example 2 was fed to an automated oscillating knife pleating machine. The pleating speed was set at 30 pleats a minute and pleat height was set at 0.5″ (1.27 cm). The resulting pleats were continuously bonded to their nearest neighbor on the same machine. The temperature for bonding was 80° C. and the applied pressure was 30 psi (0.21 MPa). The resulting consolidated structure was 18″ (45.7 cm) wide and 0.5″ (1.27 cm) thick.
The assembly of trapezoids is illustrated in
Each block had a capping film bonded to the two angled surfaces. The method for applying the film is shown in
The individual trapezoids were then welded together using a Branson vibration-welding machine, Model Kiefel 240G. This machine has an upper platen that is fixed in the vertical direction and vibrates horizontally. The lower platen moves vertically but is fixed in the horizontal direction. The welding of the trapezoids into a cylindrical billet occurred in two stages. First, three trapezoids were welded together to form a triplet (
To form a triplet, two trapezoids were placed in a specially designed fixture that was fixed to the lower platen. This fixture rigidly clamped the two trapezoids so that they could not move during the welding process. Each trapezoid was oriented with one angled surface horizontal and the other angled surface located such that a third trapezoid can fit snugly between the two trapezoids (
Once the trapezoids were clamped firmly into the fixtures, the lower platen rose and placed the trapezoids into contact where they were forced together with 1800 lb of force (8.0 kilonewtons), which resulted in a bonding pressure of 130* psi (0.90 MPa). The upper trapezoid was vibrated at 60 Hz with a 0.070″ (1.8 mm) amplitude for 10* seconds (
The triplets were then welded together using the same vibration-welding machine used to weld the trapezoids. Specially designed fixtures were mounted on the upper and lower platens to hold the triplets firmly during welding. These fixtures held the triplets in such a way that the angled surfaces of each triplet would contact each other when the lower platen rose.
Once the triplets were properly positioned and clamped, the lower platen rose and placed the triplets into contact with each other (
The center of the billet was bored out to 1.0″ (2.54 cm) diameter. A specially fabricated spindle 24 was designed that would drive the billet 23 without placing excessive load on the welded joints. The spindle fit snugly in the 1.0″ (2.54 cm) diameter hole and had a plate 25 that bolted onto the billet to drive it (
This is an example of the formation of a membrane from a hollow fiber with inner and outer sheath, where the outer sheath was thermally fused into a matrix while the inner sheath maintained the hollow shaped pore. This also illustrates that pores can have many cross sectional shapes. The outer sheath of the fiber was Nucrel® 0411HS ethylene copolymer, a thermoplastic ethylene acrylic acid and methacrylic acid copolymer made by E. I. du Pont de Nemours and Company, Inc. (Wilmington, Del., USA); and the inner sheath was 3.14 IV polycaprolactam, and their ratio was 40/60 respectively. Micrographs of the starting fiber cross sections are shown in
The fibers were wound onto a bobbin at 3500 meters/minute as a ten-fiber yarn of 45 denier. The spinneret was supplied polymer at 255° C. with a concentric sheath-core polymer configuration that passed through an orifice as illustrated in U.S. Pat. No. 5,439,626,
This example describes a laboratory scale method for forming a completely consolidated block of fiber-on-end material with no interstitial voids present.
Sheath core fibers comprising a Nucrel® 1214 polymer sheath and AQ55S water soluble polyester core were spun on equipment and by a method described in Example 1. Nucrel® 1214 is a copolymer of polyethylene and methacrylic acid manufactured by E. I. du Pont de Nemours and Company, Inc. (Wilmington, Del., USA). The AQ55S polyester was manufactured by Eastman Chemical Company (Kingsport, Tenn., USA). The density of Nucrel® 1214 polymer was 0.93 g/cm3 and the density of AQ55S was found to be 1.29 g/cm3.
The polyethylene copolymer was fed to the spinneret at the rate of 12.6 g/min while the water soluble polyester was fed at the rate of 5.4 g/min. The spinneret was designed to extrude 34 filaments. The spinning speed was set at 1500 meter/minute. At these spinning conditions the denier per filament was expected to be 3 and diameter of each filament was expected to be 20.6 micrometer. The diameter of the core of each filament was expected to be about 10 micrometers. At the above stated polymer feed rates the volume fractions of the sheath polymer and core polymer were calculated to be 0.77 and 0.23, respectively.
The resulting sheath-core yarn was wound on a small 4″ (10.2 cm) diameter lab scale skeiner. Several skeins were made in this way. The resulting skeins were carefully cut to yield a yarn bundle of 2″ (5.08 cm) segments. These segment were placed in a metallic rectangular mold with the inside dimensions of 2″×2″×5″ (5.08 cm×5.08 cm×12.7 cm). Care was taken to ensure that all filaments were pointing in the same direction in the mold. Once the mold was loosely filled with fiber, it was fitted with metal rams on both sides of the mold cavity so as to sandwich the fibers. The wall of the mold was surrounded by a Watlow band heater to heat the mold walls. The entire assembly was placed on a Carver hydraulic press with heated platens. A pressure of 100 psi (0.69 MPa) was applied to the rams of mold. The mold and platens of the press were heated to 92° C. while the pressure on the rams was held at 100 psi (0.69 MPa). After 1 h, the pressure on the rams was increased to 300 psi (2.07 MPa). The fibers in the mold were held at 92° C. and 300 psi (2.07 MPa) for 2 minutes. At the end of two minutes, the band heater on the mold and the heaters on the press were turned off and the mold was allowed to slowly cool to room temperature while the pressure on the rams was maintained for several hours. Then the pressure was also allowed to fall over night.
At the end of the above experiment, the fibers in the mold had fused together to yield a solid polymer block. The block was taken out of the mold and weighed. The weight of the block was 155 g and the dimensions of the block were 2″×2″×2.45″ (5.08 cm×5.08 cm×6.22 cm) with a volume of 161 cm3. The density of the block was calculated to be 1.036 g/cm3. Based on the volume fractions of the sheath polymer and the core polymer, the theoretical density of the block was calculated to be 1.02 g/cm3. Since the ratio of the measured density of the block and the theoretically calculated density of the block was close to 1, we can conclude that the block was completely consolidated with no interstitial void volume.
The resulting block was skived in a manner described in Example 1 to yield 0.005″ (0.127 mm) thick polymer sheets. Half of the sheets were left untreated (“as-prepared”) while the other half were soaked in hot water at 70° C. for 5 minutes to dissolve out the polyester cores. After the dissolution step, the membranes were washed in cold water and dried in a convection oven. The as-prepared polymer sheets and the membrane sheets with dissolved cores were inspected under an optical microscope. The as-prepared sheets showed no pores or defects while the membranes with dissolved cores exhibited almost uniform pores that were in the range of about 10 to 15 μm in diameter.
An as-prepared sheet and a membrane with dissolved cores were then analyzed for pore size distribution using mercury porosimetry. For the as-prepared sheet, no significant mercury intrusion was observed over the entire range of pore diameters, indicating there were no interstitial voids in the sample sheet. In the case of the membrane with dissolved cores, significant mercury intrusion in the range of 10 μm and 20 μm, with the maximum around a pore diameter of 13.5 μm, which is very close to the expected size of the original polyester cores.
This example describes a lab scale method for forming a fully consolidated block of fiber-on-end material which when skived yields a membrane with very uniform pores and no defects.
Islands in the sea yarn comprising Nucrel® 1214 ethylene copolymer sea and AQ55S polyester polymer islands was spun at Hills Inc, in Florida, USA. The weight fraction of both polymers in the fiber bundle was 0.5 and the volume fractions of the ethylene copolymer and the polyester polymer were 0.58 and 0.42, respectively. The yarn bundle contained 72 filaments. Each filament contained 36 islands. The denier of filament was determined to be 3 dpf.
The yarn was wound onto a rectangular 8″×5″ (21.6 cm×25.4 cm) metal plate using a lab scale card winder. The winding was carried out at a tension of 30 g and the yarn was wound to an approximate thickness of 0.2″ (0.51 cm). The metal plate with the wound fibers was then wrapped in Teflon® fluoropolymer coated aluminum foil and placed in between the heated platens of a Carver hydraulic press at a pressure of 40 psi (0.28 MPa) for 2 minutes. The platens were at 70° C. The heaters in the platens were then turned off and the heated plate with fibers was allowed to cool below 60° C. while fibers were still under pressure. When the metal plate was cooled and removed from the press, the fibers were lightly stuck to each other and also partially consolidated. The tacked fibers were then cut using a razor knife to yield 2″×2″ (5.08 cm×5.08 cm) plates comprising partially consolidated fibers. Twenty one such 2″×2″ (5.08 cm×5.08 cm) plates were stacked into the mold described in previous examples. The mold was assembled with rams on each side and a band heater to heat the walls of the mold as described previously. Then the fibrous plates were consolidated under the heated carver press as follows. The mold and press platens were heated to 70° C. while a pressure of 200 psi (1.38 MPa) was applied onto the rams of the mold. Then the pressure was slowly increased to 1000 psi (6.89 MPa) while increasing the temperature of the mold and platens to 90° C. After the desired temperature was achieved, the pressure on the rams was held constant at 1000 psi (6.89 MPa) for 1 h. Then the pressure was increased to 2000 psi (13.8 MPa) and held at that level for 2 minutes. After this the heaters were turned off and the mold was allowed to slowly cool to room temperature. As the mold cooled the pressure was allowed to drop on its own to zero.
At the end of the consolidation step, a solid block had been formed whose weight was measured to be 258 g and external dimension were measured as 2″×2″×3.7″ (5.08 cm×5.08 cm×9.40 cm). The density of the block was 1.06 g/cm3. The theoretical density of the block was calculated to be 1.08 g/cm3. The ratio of the actual density and the theoretical density of the consolidated block was 0.98. Thus it can be concluded that the block was completely consolidated with no interstitial void space present.
The consolidated block was skived to produce sample sheets 0.002″ (0.005 cm) thick. The sample sheets were then exposed to hot water in a manner similar to that described in Example 6 to dissolve out the polyester islands. The resulting porous membrane was analyzed for pore size distribution using a capillary flow porometer manufactured by Porous Materials, Inc. (Ithaca, N.Y., USA). The observed pore size distribution was extremely narrow, with about 60% of the pores having a diameter of 1.5 μm, and about 95% having a diameter between about 1.1 μm and about 1.8 μm.
This application is a continuation-in-part of U.S. application Ser. No. 11/828,606, filed Jul. 26, 2007, which in claims the benefit of U.S. Provisional Application No. 60/837,389, filed Jul. 28, 2006. The present invention is directed to processes for making fiber-on-end materials such as microporous membranes and capillary arrays.
| Number | Date | Country | |
|---|---|---|---|
| 60837389 | Jul 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11828606 | Jul 2007 | US |
| Child | 13104055 | US |
