Patent Publication Number: US-2021189620-A1

Title: Fibers with absorbent particles adhered thereto, methods for their production and articles thereof

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to U.S. Provisional Application No. 62/936,067, filed Nov. 15, 2019, which is incorporated by reference herein in its entirety. 
    
    
     ACKNOWLEDGMENT OF GOVERNMENT FUNDING 
     This invention was made with government support under grant number FA8750-14-D-0003 awarded by the U.S. Air Force Research Laboratory. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     Fabrics containing particles that can absorb compounds or microbes have many desirable uses. For example, such fabrics can be used for air filtration or for protective clothing. Examples of protective clothing with incorporated particles are combat uniforms for war theaters where chemical warfare is a potential threat. Such uniforms need to be comfortable while offering sufficient protection; this meaning that they need to be light, drapable and breathable while offering the mechanical properties needed for this demanding environment in addition to inhibiting the chemical threat from being absorbed by the skin. 
     Currently uniforms exist that include an outer fabric, an inner fabric, and a core composite where a fabric is coated with a mixture of a binder and activated carbon particles. Activated carbon particles have limitations for this application and the use of a binder binds a significant percentage of the particles&#39; surface, therefore reducing the capacity of the particles to absorb compounds. 
     Fabrics containing particles that can release compounds have also many desirable uses. For example, they can be used to release a fragrance or health beneficial compound into a stream of air. 
     Methods to attach particles onto a fabric without using a binder have been described. U.S. Pat. No. 6,024,813 describes blending absorbent particles (e.g. activated carbon or zeolites) with bicomponent fibers that typically have sheath:core cross sections. In this approach, the sheaths of the bicomponent fibers were heat activated and adhered to the outside of the particles. In this approach, the particles were typically significantly larger than the diameter of the fibers, resulting in significant tangling where multiple fibers were connected together by the particle, locking it in place. U.S. Pat. No. 5,786,059 describes a similar approach of using sheath:core bicomponent fibers to lock larger aerogel particles in place to form composite fabrics. 
     A disadvantage of these approaches is that they require relatively large particles, therefore limiting the surface exposed to the outside environment. This typically reduces the absorption capacity by weight of the absorbent particles. 
     There is thus a need for fibers and textile composites or fabrics that have greater absorption capacity and are breathable. The composites, fibers, and methods disclosed herein address these and other needs. 
     SUMMARY 
     In accordance with the purposes of the disclosed materials and methods, as embodied and broadly described herein, the disclosed subject matter, in one aspect, relates to compositions and methods of using the compositions. In specific aspects, the disclosed subject matter relates to multicomponent synthetic fibers decorated with particles, wherein the particles are smaller than the fiber diameter, and wherein the particles are adhered to the fibers. Composites where nonwoven fabrics of such fibers with adhered particles are also disclosed. In some examples, then composites have a majority (greater than about 75%) of the particles adhered to only one fiber are also disclosed. Further, composites where the web porosity is at least about 90% are disclosed. Methods of making the disclosed composites are also disclosed. 
     Additional advantages will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the aspects described below. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention will be more readily understood from a reading of the following specification and by reference to the accompanying drawings forming a part thereof: 
         FIG. 1  is an example of a process to bring the hot particles in contact with the nonwoven comprising multi-component fiber nonwoven. 
         FIG. 2  is a picture taken at 500× of PP/PE Island-in-the-Sea filaments with MOF particles. 
         FIG. 3  is a picture taken at 500× of CoPET/PET Sheath:Core bicomponent fibers coated with MOF particles. 
         FIG. 4  is a picture taken at 250× of CoPET/PET Sheath:Core bicomponent fibers coated with MOF particles. 
         FIG. 5  is a picture taken at 250× of PE/PET Sheath:Core bicomponent fibers from highloft nonwoven coated with MOF particles. 
         FIG. 6  is a picture of the system used to coat Sample  5 . 
         FIG. 7  is a picture taken at 250× of PE/PET Sheath:Core bicomponent fibers from highloft nonwoven coated with MOF particles by processing the web in a bed of hot particles. 
         FIG. 8  is a picture taken at 300× of PE/PET Sheath:Core bicomponent fibers from high loft nonwoven coated with MOF particles by incorporating the particles into the nonwoven using vibrations, then activating the sheath of the fibers by exposure in an oven at 170° C. and followed by removal of the particles that had not adhered. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the inventions are shown. Preferred embodiments of the invention may be described, but this invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The embodiments of the invention are not to be interpreted in any way as limiting the invention. 
     Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the descriptions herein and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. 
     Also, throughout this specification, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed matter pertains. The references disclosed are also individually and specifically incorporated by reference herein for the material contained in them that is discussed in the sentence in which the reference is relied upon. 
     Definitions 
     In this specification and in the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings: 
     Throughout the description and claims of this specification the word “comprise” and other forms of the word, such as “comprising” and “comprises,” means including but not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps. 
     As used in the description and claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly indicates otherwise. For example, reference to “a fiber” includes a plurality of such fibers. 
     Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges, and are also encompassed, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included. 
     The term “fiber” herein is intended to include staple fibers as well as continuous filaments. 
     As used herein, a “nonwoven fabric” means a fabric having a structure of individual fibers or filaments that are interlaid but not necessarily in an identifiable manner as with knitted or woven fabrics. 
     As used herein, the term “adhered” is meant to describe a close proximate association between different materials that is primarily attributed to chemical forces, e.g., electrostatic, hydrogen, covalent, ionic, van der Waals bonding, or physical attachment between the materials. An adhered particle, as described herein, is not associated with a fiber primarily because of physical entrapment by multiple fibers, as can be visually confirmed by microscopy, but rather by adhesive forces or physical attachment between the particle and a single fiber. 
     Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. All terms, including technical and scientific terms, as used herein, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs unless a term has been otherwise defined. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning as commonly understood by a person having ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure. Such commonly used terms will not be interpreted in an idealized or overly formal sense unless the disclosure herein expressly so defines otherwise. 
     Composites 
     Disclosed herein is a composite or nonwoven fabric that comprises synthetic fibers with particles adhered to the fibers. The composite can comprise multicomponent synthetic fibers, those fibers having one or several exposed surfaces of a component that melts at a lower temperature than other component(s) of the fibers. The composite also comprises at least one type of active particles having apparent diameters that are mostly smaller than the fiber diameters, the particles being adhered to the fibers by direct adhesion to polymer forming an exposed part or parts of the fibers having the lower melting point. The particle is adhered to the part of the fibers with the low melting temperature by heating the particles above the melting point of the low melting point component of the fibers, bringing those particles in contact with the fabric, and subsequently cooling this fabric under the melting point of any of its constituents. The results being a nonwoven composite with several of the multicomponent fibers being decorated with particles adhered to them. 
       FIG. 1  illustrates an exemplary method for bringing particles into contact with a fabric, e.g., a nonwoven. Another approach could include pre-heating the fabric prior to bringing it in contact with the particles, preheating the particles prior to bringing them in contact with the fabric, or pre-heating the particles and pre-heating the fabric before bringing them in contact with one another. Another approach could include loading the fabric with particles, heating this composite, and then removing the particles that have not adhered to the fiber. Further, at any step of the process the mixture of the fabric, fibers, and particles can be vibrated to aid distribution of the particles. In any of these methods care should be taken to maintain the integrity of the fibers while making a significant share of its surface tacky or adhesive in order to capture and retain a large quantity of the particles and achieving a good coverage. 
     Fibers 
     The fibers for use herein are synthetic multicomponent fibers. Such fibers have two or more different polymer components where at least one polymer is primarily exposed to the environment (external). The multicomponent fibers can be bicomponent, tricomponent, or have four or more components. The multicomponent fibers can have various different configurations. For example, the multicomponent fiber can be sheath:core (concentric sheath:core or eccentric sheath:core), island-in-the-sea, side-by-side (50/50 or unequal side-by-side), segmented pie, or tipped trilobal type fiber. For the sheath:core and other configurations the cross section is not limited to be round; options include trilobal, ribbon-shaped, oval, and others known in the art. Generally, a cross section that provide a higher surface by gram of fiber may be more desirable for some applications. The multicomponent fiber should have a significant amount of its surface comprised of a polymer that can be heat activated to adhere to the particles. 
     The synthetic multicomponent fibers can be from about 5 to about 100 microns in diameter. In certain examples, the diameter of the multicomponent fibers is from about 5 to about 10 microns, from about 10 to about 20 microns, from about 20 to about 50 microns, from about 50 to about 100 microns, from about 5 to about 10 microns, from about 5 to about 20 microns, from about 5 to about 30 microns, from about 5 to about 50 microns, from about 5 to about 100 microns, from about 10 to about 30 microns, from about 30 to about 50 microns, or from about 50 to about 100 microns. In specific examples, the multicomponent fibers are from about 15 to about 30 microns. The length of the multicomponent fibers need not be limited and can be a continuous fiber or a cut or staple fiber. 
     In the synthetic multicomponent fibers, at least one of the polymer components on an exposed surface of the fiber has a melting point that is at least 20° C. lower than any other components (polymers) of the fiber. In some examples, at least one of the polymer components on an exposed surface of the fiber has a melting point that is at least 30° C., 40° C., 50° C., or more lower than any other components (polymers) of the fiber. In some examples, the difference between the melting points of at least two polymers in the fiber can be 20° C. or more, e.g., a 30° C., 40° C., 50° C. or greater than 50° C. difference. Melting point is defined herein as the peak temperature achieved when a polymer formulation melts as measured by differential scanning calorimetry or DSC. 
     In certain examples, the multicomponent fiber comprises thermoplastic polymers. In certain examples, the polymer components can comprise a thermoplastic polymer selected from the group consisting of nylon 6, nylon 6/6, nylon 6/10, nylon 6/11, nylon 6/12, nylon 11, nylon 12, polyolefins such as polypropylene or polyethylene, polyesters, polyamides, co-polyesters, copolyetherester elastomers, polyacrylates, thermoplastic liquid crystalline polymers, and others. 
     An example of suitable multicomponent fiber is the sheath:core bicomponent fibers where the core comprises a polymer formulation having a significantly higher melting point temperature polymer formulation than the sheath. For example, this could be a bicomponent fiber having a core made from polyester (PET) and a sheath made from lower melting point co-polyester (Co-PET) or even polyethylene. Another example would be a bicomponent fibers made from a polypropylene core and a polyethylene sheath. 
     In other specific examples, the multicomponent fibers can be an island-in-the-sea fiber having from about 2 to about 100 islands (internal components). In certain embodiments, the multi-component fiber can have from about 30 to about 40 islands. In other embodiments, the multi-component fiber can have from about 2 to about 100 islands, from about 10 to about 80 islands, from about 20 to about 60 islands, from about 30 to about 50 islands, from about 2 to about 10 islands, or from about 5 to about 30 islands. The sea component can be the polymer that has a melting point lower than that of the polymer used to make the islands. For example, islands can be made from polyester (PET) and the sea can be made from lower melting point co-polyester (Co-PET) or even polyethylene or vice versa. Another example would be a bicomponent fibers made from a polypropylene islands and a polyethylene sea or vice versa. 
     Those are not restrictive examples and many other combinations are possible, as long as they provide an exposed part of the fiber having a lower melting temperature that can be heat activated than the other components of the fiber. 
     The multi-component fibers can form the complete nonwoven or they can be blended with other fibers selected for their properties (e.g. large diameter fibers to provide resilience). 
     Nonwovens 
     The nonwovens useful herein can be made by different methods as long as they comprise multicomponent fibers as described herein. These include spunbonds, carded webs, airlaid webs or wetlaid webs that can be thermally bonded by point bonding or thru-air bonding, or they can be needled or, they can be hydro-entangled or they can be stabilized by any combination of these methods. In a specific example is an opened web that is easily penetrated by the particles prior to bonding. Examples of suitable webs are carded webs comprising a majority of multicomponent fibers that are through-air bonded, or spunbond made from self-crimped filaments that are thru-air bonded or point bond using a bonding pattern that optimizes loft (e.g. using a quilted bonding pattern). A way to describe the well-opened structure of the preferred nonwoven is by its web porosity. Particularly suitable nonwoven used for the disclosed composites would have a web porosity above about 90%, e.g., above about 92%, above about 95%, or above about 99%. 
     Web porosity W p  is defined as the % of a nonwoven volume not occupied by the fibers or: 
         W   p =100*[1−(WD/FD)]
 
     where WD is the density of the web in grams per cubic centimeter and FD is the fiber density expressed in grams per cubic centimeter. 
     WD is calculated from the basis weight BW expressed as grams per square meter and the thickness T 1  of the fabric expressed in mm as measured under a load of 0.41 KPa 
       WD=BW/( T   1 ×10 3 )
 
     FD for a bicomponent fiber can be calculated from the weight faction of each polymer (F x ) and the solid density of the polymer PD x  expressed in grams per cubic centimeter. For a bicomponent fiber comprised of polymer a and b, FD can be calculated as follow: 
       FD=( F   a ×PD a )+( F   b ×PD b )
 
     Particles 
     In the disclosed composites, the relative size of the particles to the cross-sectional dimension of the fibers to which they are attached is a significant parameter. Small particles offer more surface per gram of particles than larger ones. Also, the composite should contain a maximum load of particles, and as much of the surface of the fiber should be covered with the particles as possible. Thus, without wishing to be bound by theory, it is believed that more than about two thirds (66%) of the particles attached to the fibers should have an average apparent diameter that is equal or smaller than about 100% the average apparent diameter of the fiber, and preferably smaller than about 75% the average apparent diameter of the fiber, and preferably smaller than about 50% the average apparent diameter of the fiber, even more preferably smaller than about 33% the apparent diameter of the fiber and finally, more preferably smaller than about 25% the apparent diameter of the fiber. 
     Average apparent diameter of the particle is the diameter of a smallest sphere that can contain entirely the particle. When smaller particles agglomerate into larger ones, the agglomerate is considered a “particle” as used herein. 
     Average apparent diameter of the fiber is the average width of the fibers as measured at random for several fibers with a microscope. This applies to non-round fibers where the standard deviation may be greater as the orientation of the fiber change. 
     A result of having a majority of the particles smaller than the fiber diameter is that most of the particles are attached to only one fiber at a time, e.g., more than about 75%, 85%, or 95% of the particles can be attached to only one fiber at a time. This is a difference with prior methods and reflects the high particle surface to fiber surface ratio for the disclosed composites. 
     Another aspect is the loading of particles onto the fibers and into the composite. The disclosed composites can have at least about 10% of the composite weight made-up of the active particles, preferably at least about 20%, most preferably at least about 30%, most preferably at least about 40%, and most preferably at least about 50%. 
     The particles that can be used herein can have an average diameter of from about 0.1 to about 100 microns, from about 5 to about 10 microns, from about 10 to about 20 microns, from about 20 to about 30 microns, from about 30 to about 50 microns, from about 50 to about 100 microns, from about 0.1 to about 1 microns, from about 0.1 to about 5 microns, from about 0.1 to about 15 microns, from about 0.1 to about 50 microns, from about 1 to about 100 microns, from about 1 to about 15 microns, from about 15 to about 50 microns, or from about 50 to about 100 microns. 
     In specific examples, the particles can be absorbent or reactive particles. For example, the particles can be carbon, zeolites, fumed silica, alumina, titania, zirconia, clay, zeolitic imidazole framework (ZIF), polyoxymetalates, or metal organic frameworks (MOFs). MOFs are crystalline inorganic materials, examples of which include UiO-66, UiO-66-NH 2 , ZIF-8, or ZIF-7. While individually very small, MOFs aggregate to particles within suitable size ranges disclosed herein. 
     EXAMPLES 
     The following examples are set forth below to illustrate the methods and results according to the disclosed subject matter. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative methods and results. These examples are not intended to exclude equivalents and variations of the present invention, which are apparent to one skilled in the art. 
     General Methods 
     For Examples 1 to 4, MOFs were put in a beaker that was immersed in a heated oil bath. The oil was heated and the temperature of the powder was raised above 130° C. as measured with a thermocouple inserted in the powder. A powder temperature of from about 130° C. to about 140° C. was reached. A strip of cut fabric was dipped into the heated powder with one side facing down and moved slowly. Then the fabric was dipped again with the other side facing down. After that, the fabric was shaken to remove loosely attached particles. In a few instances, a jet of air provided by a compressed air canister was used to remove loose particles. 
     Example 1 
     A spunbond made from Island-in-the-Sea filaments having 37 islands made from polypropylene and a sheath of polyethylene was used in the general method. The picture of the resulting fiber taken with a Keyence digital microscope VHX-950F is found in  FIG. 2 . This figure shows a partial coverage of the filaments with particles. 
     Example 2 
     The fabric used was made from sheath:core bicomponent fibers having a sheath made from low melting point co-polyester and a core made from higher melting point polyester. This fabric was made by carding the fabric and through-air bonding while pressed between two metallic mesh belts. It had a nominal basis weight of 0.5 osy or 17 gsm (gram per square meter). This fabric was used in the general method and the picture of the resulting fibers taken with a Keyence microscope is found in  FIG. 3 . 
     Example 3 
     The fabric used was made from sheath:core bicomponent fibers having a sheath made from low melting point co-polyester and a core made from higher melting point polyester. This fabric was made by carding the fabric and through-air bonding while pressed between two metallic mesh belts. The basis weight was 0.8 osy or about 27 gsm.  FIG. 4  is the picture taken with the microscope of the resulting fibers. It shows very good coverage of the fibers by the MOF particles. 
     Example 4 
     A fabric of a high loft nonwoven made by carding a web from bicomponent sheath:core fibers having a sheath made of polyethylene and a core of polyester was used in the general method. This web was through-air bonded without compression; therefore, it had a high bulk and could easily be penetrated by the MOF particles during the coating process. This web had a basis weight of approximately 76 gsm.  FIG. 5  is a microscopy picture of the coated fibers and illustrates the level of coverage achieved. 
     Example 5 
     For this example, the fabric was coated using an apparatus that comprises a V-shaped well immersed in a bath of heated oil (see  FIG. 6 ). This well contained the heated MOF particles (typically the volume of particles in the well was from about 1 to about 2 liters of particles). A fabric having a width of from about 250 mm to about 275 mm was unwinded from a mandrel and slowly passed into the bed of heated powder particles before being winded on a mandrel on the opposite side. While the fabric was immersed into the bed of hot particles, those were pressed against the fabric with the help of a metallic spoon to help them to penetrate into the fabric pore (This was done to simulate what nip rolls could do in a larger scale process). This was done twice with different sides of the fabric facing toward the bottom of the well. The oil temperature, the residence time, and the amount of work performed to press the hot powder into the pores of the fabric could be varied depending on the desired product or preference. At the end, the excess powder that had not adhered to the filaments was removed by shaking the fabric and blowing it with compressed air. 
     The fabric used for this example was a sample of B4302G nonwovens manufactured by Berry Global. It is a high loft through-air bonded carded nonwoven made bicomponent fibers having a sheath made of polyethylene and a core of polyester (A 50:50 ratio of PE and PET was assumed). The oil temperature was controlled at 200° C. and the residence time of the fabric in contact with the hot particles was at least 90 seconds.  FIG. 7  shows one side of this sample after coating with MOF particles. Very little shrinkage of the fabric was observed during the coating process. Large coated pieces of the fabric were weighted after the excess powder that was not attached to the fibers was removed by shaking and blowing with compressed air. For a fabric having a basis weight of about 60 gsm, a gain in basis weight of about 72 gsm or a gain in weight of about 120% was observed. 
     Example 6 
     In this example MOF particles were poured into a metallic deep pan and a pneumatic vibrator (Vibco model VS-130) was attached to the wall of the pan. The fabric used for this example was B4302G made by Berry Global. This carded and through-air bonded fabric is made from sheath:core bicomponent fibers where the sheath is made of polyethylene and the core is made of polyester. A piece of that fabric was put in the pan and covered with MOF particles while the pan was vibrated with high intensity. The energy delivered by the vibration helped the particles penetrate into the fabric structure. This piece of fabric loaded with MOF particles was then deposited onto a non-stick cookie sheet and covered with a fluoropolymer coated non-stick fabric. This pan was then heated in an air-circulated oven for 15 minutes at about 170° C. After being retrieved and while still hot, the loaded sample on the non-stick pan and covered by the non-stick fabric was gently compressed with a rolling pin. The purpose of the latter was to help getting the MOF particles embedded into the polymer forming the sheath of the fibers. The particles that were not adhered to the fibers were shaken off and blown away using compressed air. The results were that the sample of fabric that had an original basis weight of 64 gsm, was measured at 124 gsm after this operation; therefore, it had gained about 60 gsm of MOF particles. This is a weight gain of about 94%. This sample is shown in  FIG. 8 . 
     Other advantages which are obvious and which are inherent to the invention will be evident to one skilled in the art. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.