WO2012030610A1

WO2012030610A1 - Bi-component particle-loaded fiber and method for making

Info

Publication number: WO2012030610A1
Application number: PCT/US2011/049099
Authority: WO
Inventors: Atanas Valentinov Gagov; James W Zimmerman
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2010-08-30
Filing date: 2011-08-25
Publication date: 2012-03-08
Anticipated expiration: 2013-02-28

Abstract

A bi-component fiber with a plurality of island portions formed from particle-loaded material, the island portions encompassed within a sea of non-loaded material. The particle-loaded island portions include inorganic particles bound together by a first organic binder, where the inorganic particles comprise a particle density of greater than 30% by volume of the particle-loaded island portions.

Description

BI-COMPONENT PARTICLE-LOADED FIBER AND METHOD FOR MAKING

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. § 1 19 of U.S.

Provisional Application No. 61/378,202 filed on August 30, 2010 the content of which is relied upon and incorporated herein by reference in its entirety.

FIELD

[0002] This disclosure generally relates to fibers having inorganic particles loaded in an organic binder.

BACKGROUND

[0003] Processes and compositions for the production of highly porous ceramic articles for filter and substrate applications are disclosed, for example, in U.S. Patent Publication No. 2009-0220734 Al . Such processes and compositions employ at least one raw material that is fibrous, and which acts as a microstructural template during reactive firing and produces an anisotropic micro structure in the final, fired ceramic article. However, raw materials are generally significantly more expensive to obtain in fibrous form than in powdered form, and the use of fibrous raw materials can therefore be economically unattractive.

SUMMARY

[0004] In one aspect, embodiments of bi-component particle-loaded fibers are described. One embodiment of a bi-component fiber has an islands- in-sea cross-section and includes a plurality of island portions comprising particle-loaded regions encompassed within a sea portion of non-loaded material. In one implementation, the particle-loaded regions are comprised of inorganic particles bound together by a first organic binder, wherein the inorganic particles comprise a particle density of greater than 30% by volume of the particle- loaded regions, and wherein the particle-loaded regions have an average diameter less than about 150 μιη. The sea portion encompassing the island portions comprises a second organic binder. [0005] In another aspect, methods for producing bi-component particle-loaded fibers are described. In one embodiment, a method for producing a bi-component particle-loaded fiber comprises preparing a particle-loaded composition comprising a first organic binder and inorganic particles, wherein the inorganic particles are greater than 40% by weight of the composition; and co-extruding the particle-loaded composition through a spinneret with a second organic binder to form a bi-component fiber having a first diameter, the extruded particle-loaded composition defining a plurality of island fibers longitudinally aligned within the extruded second organic binder, the island fibers having a diameter of less than 150 μιη..

[0006] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0007] It is to be understood that both the foregoing general description and the following detailed description present embodiments that are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the principles and operations of the embodiments, and are incorporated into and constitute a part of this specification.

DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 A is a schematic illustration of a bi-component fiber having a plurality of highly particle-loaded 'island" regions that are continuous in the axial direction and encompassed within a "sea" of non-loaded material, as described herein.

[0009] FIG. IB is a schematic illustration of a single particle-loaded island region (or alternately "particle-loaded island fiber") as described herein.

[0010] FIG. 2 is a schematic illustration of one system that can be used to produce bi- component particle-loaded fibers described herein.

DETAILED DESCRIPTION

[0011] Reference will now be made in detail to example embodiments which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. [0012] This disclosure describes a bi-component fiber having an "islands-in-sea" cross- section. The "island" portions of the bi-component fiber comprise highly particle-loaded regions that are continuous in the axial direction and encompassed within a "sea" of non- loaded material. In one embodiment, the island portions comprise inorganic particles bound by an organic (e.g., polymer) material and the sea portion comprises an organic material different from the organic material of the island portions. The island portions can be greater than 15 volume percent, greater than 30 volume percent, or even greater than 60 volume percent of the volume of the bi-component fiber (i.e., combined island and sea portions). Volume percent of the island portions may alternately be expressed as a percentage of the cross-sectional area of the bi-component fiber. In some embodiments, fibers as described herein may be used as raw materials in the production of ceramic products such as cordierite and aluminum titanate.

[0013] FIG. 1A is a schematic representation of a bi-component fiber 10 according to the present disclosure. The bi-component fiber 10 comprises an elongated body 12 having a plurality (2 or more) of island portions 14 encompassed within a sea portion 16. Island portions 14 are comprised of regions of highly particle-loaded material that are continuous in the axial direction (defined by longitudinal axis 18) and encompassed within sea portion 16 of non- loaded material. That is, the island portions 14 of highly particle-loaded material define a plurality of discrete particle-loaded fibers within the non- loaded sea portion 16. Although the body 12 of bi-component fiber 10 and island portions 14 therein are depicted in FIG. 1A as having a generally circular cross-sectional shape, fiber 10 and the island portions 14 therein may have any suitable cross-sectional shape, including irregular cross-sectional shapes.

[0014] Island portions 14 of highly particle-loaded material are described in greater detail below with reference to FIG. IB. The non-loaded material forming sea portion 16 comprises one or more organic binder(s) having any suitable composition as described herein. In one embodiment, the organic binder(s) of sea portion 16 comprise a thermoplastic (e.g., polymer) material. Exemplary thermoplastic materials suitable for use as the material of sea portion 16 include, but are not limited to, polyesters, polyolefins, polycarbonates, polyamides, or mixtures thereof. In some embodiments, the organic binder(s) of sea portion 16 may include rheology modifiers and plasticizers to obtain the desired material properties. In some embodiments, a thermoplastic material for use as sea portion 16 may have a melt flow index (MFI) ranging from 5-120 g/10 min.

[0015] FIG. IB is a schematic representation of a single particle-loaded island portion 14 of the bi-component fiber 10 in FIG. 1A. The particle-loaded island portion 14 is formed of a plurality of inorganic particles 24 bound together by one or more organic binders 26. In some embodiments, all or a portion of the inorganic particles 24 may be encapsulated (i.e., wholly contained) within the organic binder(s) 26. In some embodiments, a portion of the inorganic particles 24 may be only partially encapsulated in the organic binder(s) 26. In one embodiment, the particles 24 are distributed generally uniformly throughout the particle- loaded island portion 14. In one embodiment, the inorganic particles 24 comprise greater than 40% by weight of particle-loaded island portion 14. In other embodiments, the inorganic particles 24 comprise greater than 50% by weight, greater than 60% by weight, greater than 70% by weight, or even greater than 80% by weight of particle-loaded island portion 14.

[0016] The inorganic particles 24 of the particle-loaded island portion 14 may include metals, intermetallics, metal oxides, ceramics, glasses, minerals, etc. For example, the inorganic particles 24 may comprise one or more of alumina, ceria, zirconia, zeolite, silica, titanium dioxide, cordierite, aluminum titanate, silicon carbide, and silicon nitride, to name a few. In one embodiment, particles 24 in particle-loaded island portion 14 comprise a single inorganic material. In another embodiment, particles 24 in particle-loaded island portion 14 comprise more than one inorganic material.

[0017] Inorganic particles 24 may be characterized on the basis of their size. In one embodiment, particles 24 have a median particle size (D₅₀) greater than about 20 nanometers, greater than about 500 nm, or even greater than about 50000 nm. As used herein, the median particle size (D₅₀) represents the median or the 50th percentile of the particle size distribution, as measured by volume. That is, the D50 is a value on the distribution such that 50% of the particles have a size of this value or less. Particle size may be accurately determined by any commercially available particle sizing equipment which uses, for example, dynamic light scattering, laser light diffraction, or electrical sensing methods. In another manner of characterizing the size of particles 24, the particle size may be described in relation to the diameter of the particle-loaded island portion 14, which diameter may be less than about 200 μιη, less than about 150 μιη, less than about 100 μιη, or even less than about 50 μιη. For example, in some embodiments, the median particle size is more than 20% of the diameter of particle-loaded island portion 14, more than 30% of the diameter of particle-loaded island portion 14, more than 40% of the diameter of particle-loaded island portion 14, or even more than 50% of the diameter of particle-loaded island portion 14. For example, in one embodiment, the particle-loaded island portion 14 has a diameter smaller than about 100 μιη when the inorganic particles 24 have a median particle size greater than about 20 nanometers.

[0018] The one or more organic binder(s) 26 of particle-loaded island portion 14 may have any suitable composition as described herein. In one embodiment, the organic binder 26 comprises a thermoplastic (e.g., polymer) material. Exemplary thermoplastic materials include, but are not limited to, polyesters, polyolefins, polycarbonates, polyamides, or mixtures thereof. In some embodiments, the organic binder 26 may include rheology modifiers and plasticizers to obtain the desired material properties. In some embodiments, a thermoplastic material for use as binder 26 may have a melt flow index (MFI) ranging from 5-120 g/lO min.

[0019] In some embodiments, one or more aspects of the organic binder(s) 26 of particle- loaded island portion 14 are substantially the same as the organic binder(s) of sea portion 16. For example, the organic binder(s) 26 of particle-loaded region 14 and the organic binder(s) of sea portion 16 may have melt flow indexes that match or are substantially similar to allow co-extrusion of the materials. In some embodiments, the one or more aspects of the organic binder(s) 26 of particle-loaded island portion 14 are different than the organic binder(s) of sea portion 16. For example, the organic binder(s) of sea portion 16 may be selected so that subsequent to formation of bi- component fiber 10, the material of sea portion 16 can be removed without removing the organic binder(s) 26 of particle-loaded island portion 14. For example, organic binder(s) of sea portion 16 may be water soluble while organic binder(s) 26 are insoluble in water.

[0020] The bi-component fiber 10 as described herein is manufactured by methods that involve the bi-component extrusion of a thermoplastic melt stream through a spinneret die, and optionally drawing the resulting bi-component fiber 10 to a smaller diameter. The inorganic particles 24 are entrained within the thermoplastic melt stream of binder(s) 26 as it is delivered to the spinneret and extruded through the plurality of orifices of the spinneret to create a plurality of particle-loaded island portions 14. Streams of the extruded particle- loaded material exiting the orifices of the spinneret are generally aligned because of viscous flow. The organic binder(s) that form sea portion 16 are coextruded with the particle-loaded island material as is known in the art, and the viscosities of the island and sea materials are substantially matched (such as by controlling temperature and/or flow rate of one or both materials). As the bi-component fiber 10 is extruded, the extruded fiber is optionally placed on a rotary winder to draw down the bi-component fiber diameter.

[0021] The bi-component fiber 10 so produced may be considered a "green" fiber which can optionally be subjected to a pyro lysis and sintering process that removes the organic binder(s) and densifies the inorganic materials 24 to form a completely inorganic fiber.

Therefore, in one embodiment, particles 24 may include sintering aids, such as transitional metal salts, organo-metallics, clays, high surface area metal oxides, magnesium oxide, silicone, silicon dioxide, rare earth oxides and transitional metal carbides, borides and nitrides.

[0022] In one embodiment, bi-component fiber 10 may be further processed to separate particle-loaded island portions 14 from the fiber 10. For example, if the binder material of sea portion 16 is water soluble and binder(s) 26 of island portions 16 are not water soluble, sea portion 16 may be dissolved in water to leave the plurality of separate particle-loaded island portions 14 as discrete particle-loaded fibers, where such particle-loaded fibers can be used in further processes, such as a pyro lysis and sintering process that removes the organic binder(s) and densifies the inorganic materials 24 to form a completely inorganic fiber.

[0023] FIG. 2 is a schematic diagram of one system 100 that can be used to produce bi- component fibers 10 as described herein. System 100 includes at least one organic binder source 102 and at least one inorganic particle source 104. Binder source 102 and particle source 104 deliver binder 26 and particles 24 (e.g., a mixture that is 40-80% by weight particles), respectively, to a first extruder 106' (e.g., a twin screw extruder) in which the particles 24 and binder 26 are mixed to form a generally homogenous composition. The composition of particles 24 and binder(s) 26 is heated above the melting temperature of the thermoplastic, extruded by first extruder 106 through a first die 108 (e.g., a 2 mm die orifice), cooled (e.g., by air or in a water bath), and then pelletized or powderized. After drying, the pelletized or powderized composition is fed into a second extruder 110 (e.g., a single screw extruder), heated above the melting temperature of the thermoplastic, and co-extruded through a second die 112 (e.g., a spinneret) with an organic binder from organic binder source 103 providing the non- loaded material for sea portion 16. In one embodiment, the resulting bi-component fiber 10 has a diameter less than about less than about 1000 μητ, less than about 500 μιη, or even less than about 400 μιη. In one embodiment, the island portions 14 within bi-component fiber 10 have diameters less than about 100 μιη, less than about 50 μιη, or even less than about 20 μιη. In some implementations, extruded bi-component fiber 10 may optionally be drawn to an even smaller diameter (e.g., such that island regions 14 have a diameter of about 10 μιη) using rotary winder 114. The system 100 may be operated in a continuous manner to produce a highly loaded bi-component fiber 10.

[0024] Although the illustrated system 100 depicts a single binder source 102 for island regions 14, a single binder source 103 for sea portion 16, and a single particle source 104, it should be understood that other systems may include more or fewer binder sources and/or more than one particle source. Similarly, although only a single bi-component fiber 10 is depicted, it should be understood that other systems may produce more than one bi- component fiber at the same time. In some embodiments, bi-component fibers 10 may be optionally coated with a material to prevent the bi-component fibers 10 from adhering to themselves, e.g., methylhydroxypropylcellulose, for example.

EXAMPLES

[0025] The following non-limiting examples are provided to illustrate the principles described herein. The Examples describe particle loadings in terms of weight percent of the particles, which can be translated into volume percent of the extruded and drawn fiber using the relationships described above, specifically:

v P fiber _w , ₌

' particle " particle ^ fifer

P particle )]

where V_particie is the volume percent of particles in the fiber, p_/¾_er is the density of the fiber, Pparticie is the density of the particles, and particle is the weight percent of the particles, n is the number of batch components and i is the individual components, is the density of the component i, and W; is the weight percent of the component i.

Example 1:

[0026] A particle-loaded fiber was produced using an apparatus similar to that in FIG. 2. Polypropylene (melt flow index of 35 g/10 min) was mixed with 66 weight percent aluminum oxide in a twin screw mixer. The median diameter (d50) of the aluminum oxide was 2.6 micrometers. The mixture was extruded into a two millimeter diameter filament which was cooled and pelletized. The pellets were fed into a heated single screw extruder and pumped at 10.6 cubic centimeters per minute. A second heated single screw extruder pumped polylactic acid (PLA) at a rate of 57.6 cubic centimeters per minute. The two melts were merged into a bi-component die containing 196 spinnerets with each spinneret configured to produce sixteen island portions. The die temperature was heated to 240°C and the bi- component fiber was extruded at a diameter of approximately 350 micrometers and then pulled at 130 meters per minute. The final diameter of the bi-component fiber so-produced was approximately 100 micrometers, and the sixteen island portions in each bi-component fiber each had diameters of approximately 10 micrometers. A yarn containing 196 bi- component fibers was collected on a spool and then chopped into 800 micrometer length staple. The material (PLA) forming the sea portions of the bi-component fibers was removed from the staple using a 1 : 1 ammonium hydroxide - water solution heated to 60°C. The resulting 10 micrometer diameter particle-loaded fibers (island portions) were rinsed and dried.

[0027] The present disclosure describes a bi-component fiber having a plurality of island regions of inorganic particles highly loaded in an organic binder, and a sea region

encompassing the island regions. The fiber and fiber producing methods described herein beneficially use low cost precursors (i.e., inexpensive polymers and inorganic particles). The methods permit a continuous fiber making process, and allow fiber diameter control. The methods are also conducive to using any inorganic material without generating chemical byproducts other than pyro lysis gasses of the organic binder when the green fiber is optionally subjected to a pyro lysis and sintering step which removes the organic binder and densities the inorganic materials to form an inorganic fiber. The present disclosure thus provides a highly versatile fiber making process and fibers that meet the needs for fibrous precursors for ceramic articles such as particulate filters, catalytic substrates, and refractory insulation. In some embodiments, precursors may be selected such that the above-described process can be used to generate high strength fibers as may be desired for reinforcement fibers.

[0028] While the article and method have been described with respect to several embodiments and examples, various modifications, additions, and variations will become evident to persons of skill in the art without departing from the spirit and scope of the invention as it is claimed. Thus it is intended that the present disclosure cover such modifications and variations provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A bi-component fiber having an islands-in-sea cross-section, the bi-component fiber comprising:

a plurality of island portions comprising particle-loaded material, the particle-loaded island portions comprised of inorganic particles bound together by a first organic binder, wherein the inorganic particles comprise a particle density of greater than 30% by volume of the particle-loaded island portions, and wherein the particle-loaded island portions have an average diameter less than about 150 μιη; and

a sea portion encompassing the island portions, the sea portion comprising a second organic binder.

2. The bi-component fiber of claim 1, wherein the island portions comprise greater than 15% by volume of the bi-component fiber.

3. The bi-component fiber of claim 1, wherein the inorganic particles comprise a particle density of greater than 50% by volume of the particle-loaded island portions.

4. The bi-component fiber of claim 1, wherein the particle-loaded island portions have an average diameter less than about 100 μιη.

5. The bi-component fiber according to claim 1, wherein the inorganic particles have a median particle size of greater than about 20 nanometers.

6. The bi-component fiber according to claim 1, wherein the inorganic particles have a median particle size in the range of about 20 nanometers to about 10 μιη.

7. The bi-component fiber according to claim 1, wherein at least one of the first organic binder and the second organic binder comprises a thermoplastic material.

8. The bi-component fiber according to claim 7, wherein at least one of the first organic binder and the second organic binder comprises at least one of a polyester, a polyolefin, a polycarbonate, or a polyamide.

9. The bi-component fiber according to claims 1, wherein the first organic binder is a different material than the second organic binder.

10. The bi-component fiber according to claim 1, wherein at least one of the first organic binder and the second organic binder further comprise organic rheology modifiers and plasticizers.

11. The bi-component fiber according to claim 1 , wherein the inorganic particles comprise at least one of alumina, ceria, zirconia, zeolite, silica, titanium dioxide, cordierite, aluminum titanate, silicon carbide, and silicon.

12. The bi-component fiber according to claim 1, wherein the inorganic particles comprise one or more sintering aids.

13. A method of producing a bi-component particle-loaded fiber, comprising:

preparing a particle-loaded composition comprising a first organic binder and

inorganic particles, wherein the inorganic particles are greater than 40% by weight of the composition; and

co-extruding the particle-loaded composition through a spinneret with a second organic binder to form a bi-component fiber having a first diameter, the extruded particle-loaded composition defining a plurality of island portions longitudinally aligned within the extruded second organic binder, the island portions having a diameter of less than 150 μιη.

14. The method of claim 13, wherein the first diameter of the bi-component fiber is less than about 500 micrometers.

15. The method of claim 13, further comprising drawing the extruded bi-component fiber from the first diameter to a smaller second diameter.

16. The method of claim 15, wherein the smaller second diameter is less than about 200 micrometers.

17. The method of claim 16, wherein after drawing the bi-component fiber to the second diameter, the island portions have a diameter less than about 20 μιη.

18. The method of claim 13, wherein the total cross-section of the island portions comprises greater than 15% of the cross-sectional area of the bi-component fiber.

19. The method of claim 13, wherein the first organic binder comprises a thermoplastic material.

20. The method of claim 13, wherein preparing the particle-loaded composition comprises:

compounding the first organic binder and inorganic particles in a first extruder;

performing at least one of pelletizing and powderizing of the compounded first

organic binder and particles; and

providing the pelletized or powderized compound to a spinneret for extruding into the island portions.

21. The method of claim 13, wherein the inorganic particles are greater than 60% by weight of the particle-loaded composition.

22. The method of claim 13, further comprising:

removing the second organic binder to separate the plurality of island portions.