Patent Publication Number: US-2015079390-A1

Title: High Surface Area Fiber and Method of Construction Thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/877,727, filed Sep. 13, 2013, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates generally to fibers having a high surface area and to their method of construction. 
     2. Related Art 
     Traditionally, round fibers are used in the textile art. The cross-sectional shape of a round fiber is circular. As such, round fibers have an outer surface area of that is minimal, defined by (3.14)×(fiber diameter)×(fiber length), and the two ways to increase the surface area of a given length of a round fiber is to increase its diameter, thereby resulting in the fiber occupying a larger amount of space and having an increased weight, or by using many small round fibers to increase the surface area while using the same amount of weight. This is where nanofibers or electrospun technology has its benefits. The smaller the fibers the more surface area there is in a given volume, which in turn gives more filtration effect. In many applications, space and weight are tightly controlled, thereby requiring use of a fiber with the highest surface area possible. 
     Non-round fibers having an increased surface area relative to round fibers are known. Such fibers have multiple lengthwise extending legs, with each leg extending radially outwardly from a central axis of the fiber to form lengthwise extending channels on the surface of the fiber. Although the known legs provide an increased surface area to the fiber, lending to improving the filtration, sound and fluid absorbency and capillary action, further improvements in accordance with the invention provide significant increases in the surface area of fibers, thereby further enhancing their filtration, sound and fluid absorbency characteristics. 
     Small diameter fibers are commonly made with the “islands in the sea” design. This is where many small fibers made up of one material are extruded within another sacrificial material, so that once the outer sacrificial material is washed away, what remains are many small individual diameter fibers. This allows the encapsulated plurality of fibers to be stretched when cooled while still maintaining their inner shape, but allowing for smaller diameter, individual fibers to be made. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, a high surface area fiber is provided. The high surface area fiber includes an inner fiber extending along a longitudinal central axis. The inner fiber has a plurality of legs extending lengthwise in generally parallel relation with one another and with the central axis. Each of the legs extends radially away from the central axis to a first peak. First channels are formed between adjacent legs. The first channels extend in generally parallel relation with one another and with the central axis. At least some of the legs have protrusions extending laterally outwardly therefrom. The protrusions extend lengthwise in generally parallel relation with one another and with the central axis. 
     In accordance with a further aspect of the invention, each leg has opposite first sides, wherein each of the opposite first sides having a plurality of the protrusions extending laterally outwardly therefrom. 
     In accordance with a further aspect of the invention, the opposite sides of each leg converge toward their respective peak. 
     In accordance with a further aspect of the invention, each protrusion extends to a second peak, wherein each of the protrusions has opposite second sides converging toward their respective second peak. 
     In accordance with a further aspect of the invention, the inner fiber is formed from a first material extending coincident with the central axis, and an outer sheath, separate from the inner fiber, is formed from a second material that encapsulates the first material, wherein the first and second materials are different. 
     In accordance with a further aspect of the invention, the second material is dissolvable in a solvent. 
     In accordance with a further aspect of the invention, the second material can be provided to dissolve in water. 
     In accordance with a further aspect of the invention, a method of constructing a high surface area fiber is provided. The method includes extruding an inner fiber having a longitudinal central axis and a plurality of legs extending lengthwise in generally parallel relation with one another and with the central axis, with each of the legs extending radially away from the central axis to a first peak to form first channels between adjacent legs, wherein the first channels extend in generally parallel relation with one another and with the central axis. The method further includes extruding protrusions simultaneously with the legs, with the protrusions extending laterally outwardly from at least some of the legs and extending lengthwise in generally parallel relation with one another and with the central axis to form second channels between adjacent protrusions. The method further includes co-extruding an outer sheath about the inner fiber from a second material that is different from the first material, such that the outer sheath at least partially fills the first and second channels. 
     In accordance with a further aspect of the invention, the method further includes extruding each leg having opposite first sides, and extruding a plurality of the protrusions extending outwardly from each of the opposite first sides. 
     In accordance with a further aspect of the invention, the method further includes extruding the opposite sides of each leg converging toward the peak. 
     In accordance with a further aspect of the invention, the method further includes extruding each protrusion extending to a second peak, and extruding each of the protrusions having opposite second sides converging toward the second peak. 
     In accordance with a further aspect of the invention, the method further includes providing the second material as being dissolvable in a solvent. 
     In accordance with a further aspect of the invention, the method can further include providing the second material as being dissolvable in water. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects, features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description of presently preferred embodiments and best mode, appended claims and accompanying drawings, in which: 
         FIG. 1  is a perspective view of a high surface area fiber constructed in accordance with one embodiment of the invention; 
         FIG. 2A  is a cross-sectional view taken generally along the line  2 - 2  of  FIG. 1 ; 
         FIG. 2B  is a view similar to  FIG. 2A  with an outer sheath of the extruded fiber having been dissolved away; 
         FIG. 3A  is a cross-sectional similar to  FIG. 2A  of a fiber constructed in accordance with another embodiment of the invention; 
         FIG. 3B  is a view similar to  FIG. 3A  with an outer sheath of the extruded fiber having been dissolved away; 
         FIG. 4  is an enlarged partial view of the fiber of  FIG. 2B ; 
         FIG. 5  is an enlarged partial view of the fiber of  FIG. 3B ; and 
         FIG. 6  is a partial perspective view of a plurality of high surface areas fibers constructed in accordance with another aspect of the invention shown coextruded within a sacrificial sheath. 
     
    
    
     DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS 
     Referring in more detail to the drawings,  FIG. 1  illustrates a high surface area filament, and referred to hereafter as fiber  10 , constructed in accordance with the invention. The fiber  10  can be formed having any suitable continuous length and diameter, as desired. The fiber  10  includes a continuous inner fiber  11  that extends lengthwise along a longitudinal central axis  12 . The inner fiber  11  has a plurality of legs  14  extending lengthwise in generally parallel relation with one another and with the central axis  12 . Each of the legs  14  extend radially outwardly in branched fashion away from a central body  16  of the inner fiber  11 , and thus, away from the central axis  12  to a first peak  18 . With the legs  14  extending in parallel relation with one another, a plurality of continuous first channels  20  are formed by the legs  14 , wherein each of the channels  20  is formed as a continuous valley between adjacent legs  14 . As such, the first channels  20  extend in generally parallel relation with one another and also with the central axis  12 . At least some of the legs  14 , and shown here as each of the legs  14 , have elongate ridges and also referred to as lobes, ridges, fingers, protrusions or arms  22 , extending laterally outwardly therefrom. Each of the arms  22  extends radially outwardly to a second peak  24 . The arms  22  extend lengthwise continuously in generally parallel relation with one another and with the central axis  12 , and thus, continuous second channels  26  are formed between adjacent arms  22 . The lengthwise extending legs  14  and arms  22  of the inner fiber  11  provide the inner fiber  11  with an increased surface area, as compared to a cylindrical monofilament, which in turn enhances the ability of the fiber  10  to filter and absorb sound and/or fluid when woven, knit, braided, or otherwise formed into a fabric. Accordingly, a textile fabric formed with the fibers  10 , whether the fibers  10  are interlaced via weaving, knitting, or braiding, also referred to as interlaced yarns or filaments, or whether the fabric is formed as a nonwoven material, having a web formed at least in part including small fibers  10 , is able to function with an increased capacity to filter and/or absorb particulate, sound, and fluid. 
     The fiber  10  is initially formed as a bi-component co-extrusion, with the inner fiber  11  being extruded from a first material having the geometric features described above extruded coincident with the central axis  12 , and with an outer sheath  28  being simultaneously extruded, referred hereafter as coextruded, from a second material about the first material. The outer sheath  28  can fully encapsulate or partially encapsulate the inner fiber  11  to either completely fill or at least partially fill the first and second channels  20 ,  26 , wherein the first and second materials are different types of material. The first material can be extruded from a standard thermoplastic resinous material, such as polypropylene, polyester, nylon, polyethylene, thermoplastic urethanes, co-polyesters, or liquid crystalline polymers, by way of example and without limitation. The second material is extruded from a sacrificial, dissolvable resinous thermoplastic, such as, but not limited to, polyactide (PLA), co-polyester (PETG), polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer (EVOH), or a water-soluble thermoplastic polymer resin. As such, upon extruding the bicomponent fiber  10 , and allowing the extruded fiber  10  to solidify, the outer sheath  28  can be readily dissolved, when desired, including immediately thereafter, or after forming the desired end product, such as a textile material, whether woven, knit, braided, or a nonwoven. Accordingly, the fiber  10  can first be processed as a generally standard monofilament having a generally circular cross-section, or otherwise, including a generally oval or flatted cross-section, and then after forming the end product, the outer sheath  28  can be dissolved to exposed the encapsulated inner fiber  11 . As such, processing the inner fiber  11  into the textile fabric can be made easy, as with a standard monofilament, and thereafter, the more complex shape of the inner fiber  11  can be exposed by dissolving the outer sheath  28  away from the inner fiber  11 . To dissolve the outer sheath  28 , any suitable solvent can be used, depending on the material content of the second material, such as NaOH, acids, or in the case of a water-soluble polymer such as Exceval, water can be used to dissolve the outer sheath  28 . 
     As shown in  FIG. 6 , to improve manufacturing efficiencies, a plurality of the fibers  10  can be coextruded within a single sacrificial outer sheath  28 , whereupon dissolving the outer sheath  28 , the plurality of individual fibers  10  are exposed for individual use. 
     The central body  16  of the inner fiber  11  can be formed having any desired cross-sectional geometry, including round, oval, or otherwise. The legs  14  extend radially outwardly from the central body  16  along the entire length of the central body  16  and have opposite sides, referred to hereafter as first sides  30 . The opposite first sides  30  of each leg  14  converge toward the first peak  18 . Each of the opposite first sides  30  have at least one, and shown as a plurality of the arms  22  extending laterally outwardly therefrom. Each arm  22  extends along the entire length of the leg  14  from which it extends, and each arm  22  has opposite sides, referred to hereafter as second sides  32 , converging toward the second peak  24 . Accordingly, the surface area of each leg  14 , as compared to a leg not having arms extending outwardly therefrom, is increased by the additional surface area provided by the sides  32  of each arm  22  extending outwardly therefrom. It should be recognized that the legs  14  and arms  22  can be configured having any desired shape or contour, such as shown in  FIGS. 2A ,  2 B, wherein the legs  14  are generally serpentine or zig-zag shaped, as a result of the sinuous pattern of the arms  22  extending outwardly therefrom, and also as shown in  FIGS. 3A ,  3 B, wherein the legs  14  are generally triangular in shape and the arms  22  extend outwardly from the opposite sides  30  in generally minor relation with one another. It should also be recognized that the number of legs  14 , arms  22  and associated first and second channels  20 ,  26  can be provided as desired, and further, that legs  14 , arms  22  and associated first and second channels  20 ,  26  are nano-sized in width and height, such as between about 200-1000 nanometers, depending on the application. 
     Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that the invention may be practiced otherwise than as specifically described, and that the scope of the invention is defined by any ultimately allowed claims.