Filter with electrostatic filtering function

Abstract

Filter media, tribocharged fibers thereof, and methods thereof are discussed. The filter media may include a first set of fibers and / or a second set of fibers. The first set of fibers may be triboelectrically charged by the second set of fibers. The first set of fibers and the second set of fibers may include polylactic acid fibers and acrylic fibers, respectively. The first group of fibers and the second group of fibers may further include acrylic fibers and polypropylene fibers, respectively. The filter media may include one or more charge additives. A method of making a filter media may include contacting a first set of fibers with a second set of fibers, wherein mutual contact of the first set of fibers and the second set of fibers triboelectrifies the first set of fibers.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 410,729 filed on September 28, 2022 and U.S. Provisional Patent Application No. 63 / 410,731 filed on September 28, 2022, the contents of which are incorporated herein by reference to the extent consistent with the present disclosure. Technical Field

[0003] The present description relates generally to electrostatic filtration media and, more particularly, to gas filters incorporating triboelectrically charged fibers. Background Art

[0004] Conventional filters, such as liquid filters and gas filters, generally use nonwoven materials (e.g., nonwoven and / or porous materials, fibers, textiles, sheets, meshes, etc.) that can or are configured to separate or remove pollutants or particles (e.g., dust, pollen, mold, bacteria, etc.) from the air, or are manufactured by them. Two types of filtration devices incorporating nonwoven materials include surface filters and deep filters. The role or function of surface filters (e.g., membranes or films) is to act as a barrier to prevent pollutants from passing through. Surface filters generally have submicron pore sizes, relatively narrow pore size distributions, and relatively high particle capture efficiencies. However, the pressure drop exhibited by surface filters is relatively high, resulting in a reduction in airflow through the filter. Surface filters also exhibit relatively low pollutant (e.g., particle) loading capacity, which greatly reduces the life of the filter. Therefore, the application of surface filters is generally limited. Deep filters have relatively moderate to high efficiencies, relatively low pressure drops, and relatively high pollutant loading capacity. Deep filters usually use one or more types of fibers in the form of nonwoven sheets to form a tortuous path between the fibers to trap or capture pollutants. Although traditional surface filters and deep filters are relatively effective in separating pollutants, the physical filtration of pollutants is often limited by aperture and / or the tortuous path formed in the nonwoven sheet. In view of this, the fibers of nonwoven materials or sheets are usually prepared from electrostatically charged fibers to prepare electrostatic or "electret" filter media to further separate pollutants via electrostatic interactions. Electrostatically charged filter media are described in U.S. Patents 10,571,137 and 9,802,187, and the disclosure of the above patents is incorporated herein by reference in the scope consistent with the present disclosure. Electrostatic or "electret" filter media improves filtration efficiency without increasing the force required to push air through the filter media.

[0005] Conventional methods of electrostatically charging fibers include, but are not limited to, treating the fibers, passing the fibers through a corona ("corona discharge"), hydro-charging, electrostatic fiber spinning, tribocharging, and the like. Tribocharging specifically involves rubbing or otherwise contacting two materials against each other and then separating them from each other. While filters utilizing tribocharged fibers have shown good promise, recent trends have attempted to increase the amount of charge or charge density that can be generated and maintained on the fibers without compromising filter life, load capacity, pressure drop, or flow through the filter. Summary of the invention

[0006] The following is only a simplified overview of some aspects of one or more embodiments of the subject matter discussed herein. Based on the detailed description provided below, more applicable areas of this subject matter will become apparent. This summary is not a broad overview, nor is it intended to be used to determine the key or important elements of the present invention, nor is it intended to limit the scope of this subject matter. On the contrary, its purpose is only to propose one or more concepts in a simplified form as a preface to the detailed description below.

[0007] The above aspects and / or other aspects and uses described herein can be achieved by providing a filter medium comprising a first group of fibers, wherein the first group of fibers are triboelectrically charged. The first group of fibers may comprise polylactic acid (PLA) fibers or acrylic fibers.

[0008] In one aspect, the filter media can include a second set of fibers. The first set of fibers can be triboelectrically charged by the second set of fibers.

[0009] In one aspect, at least a portion of the second set of fibers can include a tribo-negatively charged material.

[0010] In one aspect, at least a portion of the second group of fibers can include a tribopositively charged material. The tribopositively charged material can have a relatively lower positive charge than the first group of fibers.

[0011] In one aspect, at least a portion of the second plurality of fibers can include polypropylene (PP) fibers.

[0012] In one aspect, the polypropylene fibers can have an elongation of about 25% to about 100%, a tenacity of about 25 cN / tex to about 100 cN / tex, or a combination thereof.

[0013] In one aspect, the first group of fibers can include acrylic fibers.

[0014] In one aspect, the first set of fibers can include PLA fibers and at least a portion of the second set of fibers can include acrylic fibers.

[0015] In one aspect, the first group of fibers can also include polyhydroxyalkanoate (PHBV).

[0016] In one aspect, the weight ratio of the first group of fibers to the second group of fibers can be about 1 :1 by weight.

[0017] In one aspect, the first group of fibers and the second group of fibers can be nonwoven fibers.

[0018] In one aspect, the first set of fibers can be present in an amount of at least 10 wt %, based on the total weight of the filter media.

[0019] In one aspect, the PLA fibers can include poly-L-lactide (PLLA).

[0020] In one aspect, the first group of fibers, the second group of fibers, or a combination thereof can include about 2% or less spin finish.

[0021] In one aspect, the first group of fibers can include continuous fibers.

[0022] In one aspect, the first group of fibers can include non-continuous fibers.

[0023] In one aspect, the first group of fibers can have a diameter of about 0.1 μm to about 200 μm.

[0024] In one aspect, the first population of fibers can have a linear density of about 0.5 denier to about 50 denier.

[0025] In one aspect, the first group of fibers, the second group of fibers, or a combination thereof can include one or more nucleating agents.

[0026] In one aspect, the first group of fibers, the second group of fibers, or a combination thereof can include one or more charge additives configured to alter the charge on the first group of fibers, increase the stability of the charge on the first group of fibers, or a combination thereof.

[0027] In one aspect, the one or more charge additives may include one or more of the following: triphenylmethane, ammonium compounds, iminium compounds, ammonium fluoride compounds, fluorinated iminium compounds, dicationic acid amides, polymeric ammonium compounds, diallyl ammonium compounds, aromatic sulfide derivatives, phenol derivatives, phosphonium compounds, fluorinated phosphonium compounds, calix(n)arene, metal complexes, benzimidazolone, azine, thiazine, oxazine, or any combination thereof.

[0028] In one aspect, the one or more charge additives can include a nucleating agent.

[0029] In one aspect, the one or more charge additives can have an electronegative charge that is relatively greater than that of the first group of fibers or the second group of fibers.

[0030] In one aspect, the one or more charge additives can have a dielectric constant that is relatively greater than that of the first group of fibers or the second group of fibers.

[0031] In one aspect, the first population of fibers can include one or more charge control agents.

[0032] In one aspect, the filter media can be formed by carding and needling.

[0033] In one aspect, the first group of fibers and the second group of fibers can include a spunbond dielectric.

[0034] In one aspect, the first group of fibers and the second group of fibers can include a meltblown dielectric.

[0035] In one aspect, the first group of fibers can be triboelectrically charged by rubbing the first group of fibers with one or more machines. The one or more machines can include one or more of a carding machine, a needle loom, or a combination thereof.

[0036] In one aspect, the first set of fibers may include PLA fibers. The first set of fibers may be triboelectrically charged by hydrodynamic charging.

[0037] In one aspect, the second group of fibers can include one or more biodegradable fibers.

[0038] In one aspect, the one or more biodegradable fibers may include one or more of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), poly(adipate-co-butylene terephthalate) (PBAT), poly(3-hydroxybutyrate-co-e-hydroxyvalerate) (poly(3-hydroxybutyrate-co-e-hydroxyvalerate, PHBV), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), or any combination thereof.

[0039] In one aspect, the one or more biodegradable fibers can be selected from poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), poly(adipate-co-butylene terephthalate) (PBAT), poly(3-hydroxybutyrate-co-e-hydroxyvalerate) (PHBV), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), and combinations thereof.

[0040] In one aspect, the one or more biodegradable fibers can include PHBH.

[0041] The above aspects and / or other aspects and uses described herein may be achieved by providing an air filter product comprising any of the aforementioned filter media or the filter media described herein.

[0042] The above aspects and / or other aspects and uses described herein can be achieved by providing a method for manufacturing a filter medium. The method can include contacting a first group of fibers with a second group of fibers, and the first group of fibers can include polylactic acid (PLA) fibers or acrylic fibers. Contacting the first group of fibers with the second group of fibers can cause the first group of fibers to be triboelectrically charged.

[0043] In one aspect, the second set of fibers can include a tribo-negatively charged material.

[0044] In one aspect, the second group of fibers can include a tribopositively charged material. The tribopositively charged material can have a relatively lower positive charge than the first group of fibers.

[0045] In one aspect, the second group of fibers can include polypropylene (PP).

[0046] In one aspect, the first group of fibers can include acrylic fibers.

[0047] In one aspect, the first set of fibers can include PLA fibers. The second set of fibers can include acrylic fibers.

[0048] In one aspect, the first population of fibers can further include polyhydroxyalkanoate (PHBV).

[0049] In one aspect, the weight ratio of the first group of fibers to the second group of fibers is about 1:1.

[0050] In one aspect, the first group of fibers and the second group of fibers can be nonwoven fibers.

[0051] In one aspect, the filter media can include PLA fibers in an amount of at least 50 wt%.

[0052] In one aspect, the PLA fibers can include poly-L-lactide (PLLA).

[0053] In one aspect, the method can include combing a first set of fibers and a second set of fibers.

[0054] In one aspect, the method can include spunbonding a first population of fibers and a second population of fibers.

[0055] In one aspect, the method can include meltblowing the first group of fibers and the second group of fibers.

[0056] In one aspect, the method can include contacting one or more nucleating agents with the first group of fibers, the second group of fibers, or a combination thereof.

[0057] In one aspect, the method can include contacting one or more charge additives with the first population of fibers, the second population of fibers, or a combination thereof.

[0058] In one aspect, the method can include contacting one or more charge control agents with the first group of fibers, the second group of fibers, or a combination thereof.

[0059] The above aspects and / or other aspects and uses described herein can be achieved by providing an air filter product prepared according to any of the above methods.

[0060] Further areas of applicability of the present subject matter will become apparent from the detailed description provided hereinafter.It should be understood that the detailed description and specific examples, while indicating some typical aspects of the present subject matter, are intended for purposes of illustration only and are not intended to limit the scope thereof.

[0061] The description herein of desirable goals that may be achieved by various embodiments of the present specification does not mean, imply or indicate that any or all of these goals may appear as essential features, either individually or collectively, in the most general embodiment of the present specification or in any of its more specific embodiments. DETAILED DESCRIPTION

[0062] This specification and the accompanying drawings illustrate exemplary embodiments and should not be considered as limiting. The claims define the scope of this specification, including equivalents. Various mechanical, compositional, structural and operational changes can be made without departing from the scope of this specification and the claims (including equivalents). In some cases, well-known structures and technologies are not shown or described in detail to avoid blurring the specification. The same numbers in two or more figures represent the same or similar elements. In addition, the elements and related aspects described in detail with reference to one embodiment may also be included in other embodiments that are not specifically shown or described, as long as practical. For example, if an element is described in detail with reference to one embodiment, but is not described with reference to a second embodiment, it can still be claimed that the element is included in the second embodiment. In addition, the description herein is for illustrative purposes only and does not necessarily reflect the actual shape, size or dimensions of the system or illustrated components.

[0063] It should be noted that the singular forms "a", "an", and "the", as well as any singular use of any term, used in this specification and the appended claims, include plural referents unless expressly and unambiguously limited to one referent. The term "include" and its grammatical variations as used herein are intended to be non-limiting, such that the listing of items in a list does not exclude other similar items that can be substituted or added to the listed items.

[0064] Unless otherwise indicated, any quantitative values ​​are approximate, whether or not the words "about" or "approximately" are recited. The materials, methods, and examples described herein are illustrative only and not intended to be limiting.

[0065] As used throughout this disclosure, ranges are used as shorthand for describing each value within a range. It should be understood and appreciated that describing in range format is only for convenience and brevity and should not be construed as a rigid limitation on the scope of any embodiment or implementation disclosed herein. Therefore, the disclosed range should be construed as specifically disclosing all possible subranges and single values ​​within the range. Therefore, any value within the range can be selected as the endpoint of the range. For example, a description of a range such as 1-5 should be considered to specifically disclose subranges such as 1.5-3, 1-4.5, 2-5, 3.1-5, and individual values ​​within the range, such as 1, 2, 3, 3.2, 4, 5, etc. Regardless of the breadth of the range, this applies.

[0066] In addition, all numerical values ​​are "about" or "approximately" the indicated values, and take into account experimental errors and variations expected by a person of ordinary skill in the art. It should be recognized that all numerical values ​​and ranges disclosed herein are approximate values ​​and ranges, regardless of whether "about" is used in conjunction with them. It should also be recognized that the term "about" used in conjunction with a number herein means that it can be ±0.01% (inclusive), ±0.1% (inclusive), ±0.2% (inclusive), ±0.3% (inclusive), ±0.4% (inclusive), ±0.6% (inclusive), ±0.7% (inclusive), ±0.8% (inclusive), ±0.9% (inclusive), ±1.1% (inclusive), ±1.2% (inclusive), ±1.3% (inclusive), ±1.4% (inclusive), ±2.1% (inclusive), ±3.2% (inclusive), ±4.3

[0067] It should also be appreciated that when a numerical range is disclosed herein, any value falling within the range is also specifically disclosed.

[0068] As used herein, "free of" or "substantially free of" a material may refer to a composition, component or phase in which the material is present in an amount less than 10.0 wt%, less than 5.0 wt%, less than 3.0 wt%, less than 1.0 wt%, less than 0.1 wt%, less than 0.05 wt%, less than 0.01 wt%, less than 0.005 wt% or less than 0.0001 wt%, based on the total weight of the composition, component or phase.

[0069] All references cited herein are incorporated by reference in their entirety. In the event of a conflict in a definition in the present disclosure and that of a cited reference, the present disclosure controls.

[0070] The inventors surprisingly and unexpectedly found that polylactic acid (PLA) and / or its fibers exhibit and / or have relatively high tribopositive properties. Therefore, the inventors surprisingly and unexpectedly found that rubbing, manipulating or otherwise contacting PLA fibers with another fiber or material (e.g., tribonegatively charged fibers or materials) can produce or generate significant polarization and / or charge on the PLA fibers. The generation of charge can produce and / or enhance local electric field gradients on or inside the filter medium and / or PLA fibers, thereby increasing particle removal via electrostatic forces; thus improving the filtration efficiency of the filter medium. The inventors also surprisingly and unexpectedly found that the charge on the PLA fibers is still maintained after aging for several days. The inventors also surprisingly and unexpectedly found that fiber blends of PLA fibers and one or more biodegradable fibers (e.g., PHBV) can prepare completely or substantially biodegradable filter media. The present inventors have also surprisingly and unexpectedly discovered that fiber blends of PLA fibers and one or more biodegradable fibers exhibit improved filtration effectiveness compared to non-biodegradable conventional filter media.

[0071] Disclosed are filter media, filters, and / or fibers thereof that utilize electrostatic forces to capture particles. Exemplary filters may be or include, but are not limited to, gas filters, liquid filters, masks, CPAP filters, vacuum bags, cabin air filters, HVAC furnace filters, gas turbines, compressor intake filters, panel filters, household air filters, commercial air filters, and the like. In addition, systems and methods for manufacturing filter media, filters, and / or fibers thereof are disclosed.

[0072] The filter medium may include a variety of fibers. The fibers may be electret fibers. The term or expression "electret fibers" used herein may refer to fibers including dielectric materials having a quasi-permanent electrical polarization state. The various fibers of the filter medium may be formed into a substrate, such as a sheet, layer, film, porous film, mesh, netting, etc., or any combination thereof. The substrate may include one or more nonwoven materials. For example, the substrate may include fibers or threads that may be interwoven, interlocked, bonded, or otherwise connected. Exemplary nonwoven materials may be or include, but are not limited to, fibers, layers, sheets, or nets that are bonded or connected to each other via mechanical, thermal, and / or chemical means or methods. The substrate or nonwoven material may be meltblown, spunbonded, spunlace, thermally bonded, bonded combed, air-laid, wet-laid, co-formed, needle-punched, stitched, hydraulically wound, etc., or any combination thereof. The substrate may be flat or substantially flat. The substrate may be or include a porous sheet made from individual fibers, molten plastic or plastic film, or a combination thereof.

[0073] The fibers of the filter media can be coupled to each other mechanically (e.g., entangled), thermally, and / or chemically. For example, the fibers can be coupled to each other via thermal bonding (e.g., heating). In another example, the fibers can be coupled to each other via one or more chemical bonds. In at least one embodiment, the filter media or its fibers can include one or more binders, such as adhesives, that are capable of or configured to couple the fibers to each other.

[0074] The substrate and / or fiber can be or include a "high loft" nonwoven material. For example, the substrate and / or its fibers can be or include a high loft nonwoven material, including spunbonded and / or air-through bonded, combed nonwoven fibers. The term or expression "high loft" used herein can refer to a nonwoven material or fiber in which the volume of the void is relatively greater than the volume of the material or solid. It should be appreciated that in the combed nonwoven fibers of hot-air bonded, the loftiness or bulkiness of the substrate can be controlled by various methods known to those of ordinary skill in the art. For example, in one or more procedures (e.g., bonding), the bulkiness of the material and / or fiber can be increased by applying a relatively small compressive force to the filter medium or its fibers.

[0075] The substrate and / or its fibers can be or include knitted and / or woven materials. Knitted materials can include any knitting pattern suitable for the desired application, particularly filter applications. Knitted materials suitable for filter applications can be or include, but are not limited to weft knitting, warp knitting, knitted mesh panels, compressed knitted meshes, etc., or any combination thereof. Woven materials suitable for filter applications can be or include textile filter media, such as monofilament fabrics, multifilament fabrics, nylon nets, polyester nets, polypropylene nets, etc. For example, woven textiles can be used for screen filter press filter cloths, woven filter pads and other die-cut pieces, centrifugal filter bags, liquid filter bags, dust bags, bed dryer bags, rotary drum filters, filter belts, leaf filters, roller media, etc.

[0076] The filter media can include a variety of fibers that can be triboelectrically charged. It should be appreciated that the triboelectric effect (also known as triboelectricity, triboelectricity, triboelectrification, or tribocharging) describes the transfer of charge between two objects that slide, rub, or otherwise contact each other. It should also be appreciated that the extent of the triboelectric effect (e.g., the polarity and / or intensity of the generated charge) can depend at least in part on the respective materials and / or their properties, surface morphology (e.g., roughness, smoothness, etc.), temperature, strain (e.g., elastic strain), etc. It should also be appreciated that a triboelectric series can provide a list of materials sorted by one or more respective properties, such as the respective charge density of the materials (nC / cm 2). Increasing the relative distance or position of two materials in the triboelectric series indicates a corresponding increase in charge transfer between the two materials.

[0077] The filter medium or its fiber can be or include polylactic acid (PLA), non-PLA polymer or a combination thereof. For example, the fiber of the filter medium can be or include, but is not limited to polylactic acid (PLA) fiber, one or more non-PLA fibers or a combination thereof. Based on the total weight of the filter medium and / or its fiber, the amount of PLA fiber can be about 10wt% to 100wt%. For example, based on the total weight of the filter medium or its fiber, the amount of PLA fiber can be about 10wt%, about 20wt%, about 30wt%, about 40wt% or about 50wt% to about 60wt%, about 70wt%, about 80wt%, about 90wt%, about 95wt% or more. In at least one embodiment, at least about 10% of the fiber can be PLA fiber. Exemplary PLA fibers can be or include, but are not limited to racemic polylactic acid, such as poly-L-lactide (PLLA), poly-D-lactide (PDLA), poly-DL-lactic acid (PDLLA), etc., or a combination thereof. PLA polymers or copolymers can be prepared from lactic acid monomers. The lactic acid monomer may be or include one or more of the following: a lactic acid isomer, such as L-lactic acid, D-lactic acid, or a mixture thereof, an anhydride of any lactic acid isomer, including L-lactide, D-lactide, meta-lactide, or a mixture thereof, a cyclic dimer of such lactic acid and / or lactide, etc., or any combination thereof. In an exemplary embodiment, the PLA polymer may be a polymer prepared from an L-lactic acid monomer and a D-lactic acid monomer.

[0078] The term or expression "PLA-based surface" as used herein may refer to the surface of a fiber, fabric, film, etc., made or composed of at least 50% PLA-based resin. It should be appreciated that the remainder of the PLA-based surface may be or consist of other resins, such as polyhydroxybutyrate (PHB), other biodegradable materials, nucleating agents, antioxidants, charge enhancers, etc., or any combination thereof. In at least one embodiment, the fiber is entirely or substantially PLA resin. For example, the fiber may be greater than or equal to about 98% PLA resin, greater than or equal to about 99% PLA resin, or 100% PLA resin. In at least one embodiment, at least a portion of the fiber has a PLA-based surface. For example, the surface of one or more fibers includes at least 50% PLA-based resin.

[0079] The filter medium may include a first group of fibers and a second group of fibers. The first group of fibers may be or include PLA fibers, one or more non-PLA fibers, or a combination thereof. The second group of fibers may be or include PLA fibers, one or more non-PLA fibers, or a combination thereof. The first and second groups of fibers may be formed into substrates, such as sheets, layers, films, porous films, meshes, nets, etc. The substrate may include one or more nonwoven materials. The nonwoven material may have a structure in which a single fiber or thread may be interwoven. Exemplary nonwoven materials may be or include, but are not limited to, fibers, layers, webs, or combinations thereof that may be meltblown, spunbonded, bonded combed, airlaid, wetlaid, co-formed nonwoven structures, hydroentangled, etc. The substrate may also be or include, but are not limited to yarn, felt, knitted or woven fabrics, etc., or any combination thereof.

[0080] The first and second groups of fibers discussed herein may be included as part of a filter device that separates, captures, entraps, or otherwise absorbs contaminants. Exemplary filter devices may be or include, but are not limited to, liquid filters, gas filters for home and commercial air filtration, surgical masks or other face masks, and the like. Filter devices may be mechanical filters, absorption filters, sequestration filters, ion exchange filters, reverse osmosis filters, surface filters, depth filters, and the like, and may be designed to remove a variety of different types of contaminants from air, water, or other substances.

[0081] In an exemplary embodiment, the first and second groups of fibers may be incorporated into an air filter that can remove or otherwise separate particles and / or contaminants from air, such as a Minimum Efficiency Reporting Value (MERV) filter, a UV light filter, a washable filter, a media filter, a glass fiber filter, a pleated air filter, a non-pleated air filter, an activated carbon filter, a bag filter, a V-bank compact filter, a filter sheet, a flat cell filter, a filter cartridge, etc. The first and second fibers may comprise a filter media for an air filter and may be supported by a support layer, a scrim layer, or may be included in other layers or materials.

[0082] In at least one embodiment, the first group of fibers (i.e., "first fibers") may include PLA and / or its derivatives, or be composed thereof. In another embodiment, the first group of fibers (i.e., "first fibers") may include a blend or combination of PLA and one or more other materials or fibers (e.g., non-PLA materials or fibers). In yet another embodiment, the first group of fibers may include or be composed of one or more non-PLA materials or fibers (e.g., polypropylene fibers). Other materials or fibers may be or include, but are not limited to, one or more non-PLA melt-spun fibers, non-melt-spun non-PLA fibers in the form of continuous fibers, staple fibers, bicomponent fibers, acrylic fibers, etc., or any combination thereof. In at least one embodiment, PLA fibers or compositions thereof may include one or more of the following: amine stabilizers, compatibilizers, lubricants, antimicrobial agents, antiviral agents, dispersants, antioxidants, plasticizers, coupling agents, nucleating agents, charge enhancing additives, etc., or any combination thereof. The amount of PLA present in the first population of fibers can be at least about 30%, at least about 40%, at least 50%, at least 60%, at least 80%, at least 90%, or more based on the total weight of the first population of fibers.

[0083] In at least one embodiment, the first fibers may include a blend or combination of PLA fibers and polyhydroxyalkanoate (PHBV) fibers, wherein the amount of PLA present in the first group of fibers may be at least about 50% by weight of the first fibers. The charge density of the first fibers including a blend or combination of PLA fibers and PHBV fibers may be about 0.5 nC / cm 2 or higher.

[0084] In at least one embodiment, the first group of fibers comprises polypropylene (PP) fibers and the second group of fibers comprises acrylic fibers. Thus, the filter media or its fibers comprises a first group of fibers comprising PP fibers, a second group of fibers comprising acrylic fibers, and the filter media or its fibers further comprises one or more charge additives, as further discussed herein.

[0085] In at least one embodiment, the toughness or tensile strength of the first group of fibers and / or the second group of fibers is from about 25 cN / tex to about 100 cN / tex. For example, the toughness of the first fiber and / or the second fiber can be from about 25 cN / tex, about 35 cN / tex or about 45 cN / tex to about 50 cN / tex, about 70 cN / tex, about 80 cN / tex or about 100 cN / tex. In another example, the toughness of the first fiber and / or the second fiber can be from about 25 cN / tex to about 100 cN / tex, about 35 cN / tex to about 60 cN / tex or about 45 cN / tex. In at least one embodiment, the first group of fibers includes PP fibers, and the toughness of the first group of fibers or its PP fibers is from about 25 cN / tex to about 100 cN / tex, about 30 cN / tex to about 60 cN / tex or about 45 cN / tex. The term or expression "toughness" used herein can refer to the mass stress at break.

[0086] In at least one embodiment, the elongation of the first group of fibers and / or the second group of fibers is about 10% to about 150%. For example, the elongation of the first fiber and / or the second fiber can be about 10%, about 20%, about 30% or about 35% to about 40%, about 50%, about 70%, about 80% or about 150%. In another example, the elongation of the first fiber and / or the second fiber can be about 10% to about 100%, about 20% to about 70%, about 30% to about 40% or about 35%. In at least one embodiment, the first group of fibers includes PP fibers, and the elongation of the first group of fibers or its PP fibers is about 10% to about 150%, about 20% to about 100%, about 30% to about 40% or about 35%. The term or expression "elongation" used herein can refer to the amount of extension or stretching that a fiber withstands before breaking.

[0087] In an exemplary embodiment, the tenacity of the first group of fibers and / or the second group of fibers is about 25 cN / tex to about 100 cN / tex, about 30 cN / tex to about 60 cN / tex, or about 45 cN / tex, and the elongation is about 25% to about 100%, about 30% to about 50%, or about 35%. The inventors surprisingly and unexpectedly found that the fibers having a tenacity of about 30 cN / tex to about 60 cN / tex or about 45 cN / tex and an elongation of about 30% to about 40% or about 35% showed an improved effectiveness in maintaining and / or generating triboelectric charge. Without being bound by theory, it is believed that relatively high tenacity and / or relatively low elongation can cause the fibers to stretch more than typical fibers. It is believed that the relative increase in fiber stretching can affect crystallization. Specifically, it is believed that the relative increase in fiber stretching can increase the amount or percentage of crystallization, thereby producing more ordered or oriented crystals, and the orientation of the crystals causes the fibers to generate and / or maintain triboelectric charge with a relatively improved effectiveness.

[0088] In at least one embodiment, the first fiber and / or the second fiber may have a spin finish of 2% or less, preferably no or substantially no spin finish (e.g., bare fiber). As used herein, the term or expression "spin finish" may refer to a liquid, solid, or emulsion composition applied to the surface of a fiber in order to improve the processing of the fiber, such as in short fiber spinning or long fiber spinning.

[0089] The first group of fibers that can include PLA fibers can be continuous or discontinuous. Exemplary discontinuous fibers can be or include, but are not limited to staple fibers. The length of the first group of fibers (e.g., staple fibers and / or continuous fibers) can be from about 1mm to about 200mm, from about 5mm to about 150mm, or from about 30mm to about 70mm. The diameter of the first group of fibers can be from about 0.1 micron to about 200 microns or from about 5 microns to about 50 microns. The linear density of the first group of fibers can be from about 0.5 denier to about 50 deniers.

[0090] In at least one embodiment, the second group of fibers can be or include, but are not limited to, a tribo-negatively charged material or a tribo-positively charged material having a relatively low charge density compared to the first group of fibers (e.g., PLA fibers). As discussed above, the inventors surprisingly and unexpectedly discovered that PLA and its fibers are relatively high tribo-positively charged materials. For example, PLA is a material having a charge density of about 0.5-1.0 nC / cm 2 Thus, PLA is a relatively improved material for transferring charge with tribo-negatively charged materials, and rubbing or contacting a first set of fibers (which may include PLA fibers) with a second set of fibers (including fibers or materials positioned sufficiently away from PLA in the triboelectric sequence) results in significant polarization and charge on the PLA fibers.

[0091] The non-PLA fibers and / or the second group of fibers (ie, "second fibers") can be or include man-made fibers, natural fibers, or a combination thereof. Exemplary materials and / or fibers of the non-PLA fibers and / or second group of fibers may be or include, but are not limited to, polypropylene, polyester (PET), polyethylene naphthalate (PEN) polyester, polycyclohexanedimethylene terephthalate (PCT) polyester, polypropylene (PP), polybutylene terephthalate (PBT) polyester, copolyamide, polyethylene, high density polyethylene (HDPE), linear low density polyethylene (LLDPE), cross-linked polyethylene, polycarbonate, polyacrylate, polyacrylonitrile (PAN), polyfumaronitrile, polymers prepared from fumaronitrile, polystyrene (PS), maleic anhydride styrene, polymethylpentene, cyclic olefin copolymers, fluorinated polymers, polytetrafluoroethylene, perfluoroethylene and hexafluoropropylene or copolymers with PVDF, such as P(VDF-TrFE), or poly(vinylidene fluoride-co-trifluoroethylene) copolymers having a VDF molar content of 80%, or terpolymers, such as P(VDF-TrFE). TrFE-CFE), propylene, polyimide (PI), Kevlar, polyetherketone, cellulose ester, cotton, ramie, chitosan, wool, cuprammonium rayon (cupro), Lyocell, nylon, polyamide, silk, polyether-polyurea copolymer, Lycra, spandex, polymethacrylic polymer, poly(methyl methacrylate), polyoxymethylene, polysulfone, acrylic acid, modified polyacrylonitrile (modacrylic), styrenated acrylic acid, preoxidized acrylic acid, fluorinated acrylic acid, vinyl acetate, vinyl acrylate, ethylene-vinyl acetate copolymer, styrene-butadiene, ethylene / vinyl chloride, vinyl acetate copolymer, latex, polyester copolymer, carboxylated styrene acrylic or vinyl acetate, epoxy resin, acrylic multipolymer, phenolic resin, polyurethane, cellulose, polytetrafluoroethylene (PTFE), styrene, or any combination thereof. It should be appreciated that other conventional fiber materials may be considered.

[0092] The filter medium and / or its fibers can be biodegradable or substantially biodegradable. The term "biodegradable" as used herein can refer to materials or substances that can be decomposed by microorganisms. The filter medium and / or its fibers can also be bio-based or substantially bio-based. The term or expression "bio-based material" as used herein can refer to materials or substances made or prepared from substances derived from living organisms (or once living organisms). For example, bio-based materials can refer to materials and substances produced from plant or animal biomass. Exemplary bio-based materials can be or include, but are not limited to materials derived and / or prepared from starch, sugar, lipids or any combination thereof extracted from corn, sugar cane, sugar beets, vegetable oils, etc.

[0093] In at least one embodiment, the non-PLA fibers and / or the second group of fibers can be or include, but are not limited to, one or more bio-based and / or biodegradable fibers. For example, a portion of the non-PLA fibers and / or the second group of fibers can be or include one or more bio-based and / or biodegradable fibers. In another example, the non-PLA fibers and / or the second group of fibers can be substantially or completely bio-based and / or biodegradable fibers. Exemplary bio-based and / or biodegradable fibers can be or include, but are not limited to, one or more polymers and / or fibers made from or including: poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), poly(adipate-co-butylene terephthalate) (PBAT), poly(3-hydroxybutyrate-co-e-hydroxyvalerate) (PHBV), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), polybutylene caprolactone succinate (PCL-BS), polybutylene succinate adipate (PBSA), polyethylene terephthalate succinate (PETS), cellulose acetate (CA), one or more petroleum-based biodegradable polymers, derivatives thereof, copolymers thereof, or any combination thereof.

[0094] In an exemplary embodiment, the filter medium may include a first group of fibers and a second group of fibers, the first group of fibers including PLA fibers, which are bio-based and biodegradable, and the second group of fibers may include one or more other bio-based and / or biodegradable fibers. For example, the filter medium may include a blend of PLA fibers and one or more other bio-based and / or biodegradable fibers. In another example, the filter medium may include a blend of PLA fibers and other bio-based and / or biodegradable fibers (including one or more of PHBH, PHB, PBS, PBAT, PHBV, PHA or any combination thereof). In yet another example, the filter medium may include a blend of PLA fibers and one or more other bio-based and / or biodegradable fibers selected from PHBH, PHB, PBS, PBAT, PHBV, PHA and combinations thereof. In another example, the filter medium may include a blend of PLA fibers and PHBH.

[0095] The thickness or diameter of the non-PLA fibers and / or the second group of fibers or the second fibers may be from about 1 μm to about 10,000 μm, from about 1 μm to about 1,000 μm, or from about 10 μm to about 100 μm. For example, the diameter of the second fibers may be from about 0.1 μm to about 200 μm, or from about 5 μm to about 50 μm.

[0096] In an exemplary embodiment, the first group of fibers may be or include PLA and / or PLA fibers, and the second group of fibers may be or include polypropylene fibers, acrylic fibers, or a combination thereof. It should be appreciated that PLA has some properties or qualities similar to PP, PE, and PS, including but not limited to dielectric constant, tangent loss, and surface resistivity. However, when rubbed or contacted with PP fibers, PLA transfers relatively more charge than acrylic fibers. Similarly, when rubbed or contacted with acrylic fibers, PLA transfers relatively more charge than PP fibers. In view of this, the effectiveness of the filter medium is improved by using a first group of fibers including PLA or PLA fibers and a second group of fibers including one or more sufficiently tribo-negatively charged materials and / or tribo-negatively charged fibers, but without compromising other properties / quality of the filter medium, such as life, load capacity (e.g., dust holding capacity), pressure drop, airflow through the filter medium, etc., or any combination thereof. It should also be appreciated that compared to polypropylene (PP), PLA has a relatively high electrical resistance and a relatively low friction coefficient. PLA and its fibers are also hydrophobic. PLA is also biodegradable. PLA can be produced or prepared by existing production equipment, such as equipment for petrochemical industry plastics. Therefore, the production of PLA and / or its fibers is relatively cost-effective compared to other polymers (eg, PP, PS, PE, etc.).

[0097] The linear mass density of the first group of fibers and the second group of fibers can be the same, in denier or denier (D). The linear mass density of the first group of fibers and the second group of fibers can also be different. In at least one example, the linear mass density of the second group of fibers can be from about 0.5 denier or denier (D) to about 50D, from about 1D to about 10D.

[0098] The weight ratio of the first fibers to the second fibers present in the filter media can be about 10: 1 (e.g., about 10 to about 1), about 5: 1, about 3: 1, about 2: 1, about 1: 1, about 1: 2, about 1: 3, about 1: 5, or about 1: 10. In an exemplary embodiment, the weight ratio of the first fibers to the second fibers is about 1: 1.

[0099] The total surface area ratio of the first fibers to the second fibers present in the filter media can be about 10: 1, about 5: 1, about 3: 1, about 2: 1, about 1: 1, about 1: 2, about 1: 3, about 1: 5, or about 1: 10. In an exemplary embodiment, the total surface area ratio of the first fibers to the second fibers is about 1: 1.

[0100] PLA has several important properties similar to PP, such as dielectric constant, tangent loss and surface resistivity. However, more charge is transferred when PLA is rubbed with PP than when, for example, acrylic fiber is rubbed with PP. Similarly, more charge is transferred when PLA is rubbed with acrylic fiber than when, for example, acrylic fiber is rubbed with PP. In other words, the triboelectric charge density of PLA is higher than that of PP and acrylic fiber. Therefore, PLA will improve the overall effectiveness of the triboelectric charged filter without compromising its life, load capacity (e.g., dust holding capacity), pressure drop or other functions such as airflow through the filter. The term "pressure drop" used in this article to express a filter, medium or its material may refer to the pressure drop from the upstream side to the downstream side of the filter, medium or its material.

[0101] The PLA fiber and / or the second fiber can be continuous or discontinuous (e.g., staple fibers). In an embodiment, the diameter of the PLA fiber can be from about 0.1 micron to about 200 microns, or from about 5 microns to about 50 microns. The linear density of the PLA fiber can be from about 0.5 denier to about 50 denier.

[0102] The PLA fiber and / or the second fiber may include one or more nucleating agents that promote the formation of polymer crystals in the fiber. Suitable nucleating agents may be or include, but are not limited to, inorganic additives, organic additives, polymers, etc., or any combination thereof.

[0103] The filter medium and / or one or more fibers of the filter medium may include one or more charge additives or charge control agents (CCA). For example, the filter medium, its first group of fibers and / or its second group of fibers may include one or more charge additives or charge control agents. One or more charge additives can be or are configured to change (e.g., increase or decrease) the triboelectric charge of the filter medium and / or its one or more fibers. One or more charge additives can also be or are configured to increase the stability and / or duration of the triboelectric charge of the filter medium and / or its one or more fibers. One or more charge additives can or are configured to change the triboelectric charge, improve the stability of the triboelectric charge and / or extend the duration of the triboelectric charge without compromising other features or characteristics of the filter medium, including life, load capacity and / or pressure drop. In at least one example, the first group of fibers (which may include PLA fibers) and / or the second group of fibers may include one or more charge additives or charge control agents (CCA). In another example, the first group of fibers (which may include non-PLA fibers) and / or the second group of fibers may include one or more charge additives or charge control agents (CCA). In yet another example, the first group of fibers (which may include a combination of PLA fibers and non-PLA fibers) and / or the second group of fibers may include one or more charge additives or charge control agents (CCAs). The amount of charge additive present in the one or more fibers of the filter media may be about 0.02 wt % to 33 wt % based on the total weight of the filter media or the one or more fibers thereof.

[0104] The charge additive may be or include, but is not limited to, triphenylmethane, ammonium compounds, iminium compounds, ammonium fluoride compounds, fluorinated iminium compounds, dicationic acid amides, polymeric ammonium compounds, diallyl ammonium compounds, aromatic sulfide derivatives, phenol derivatives, phosphonium compounds, fluorinated phosphonium compounds, calixarenes, metal complexes, benzimidazolone, azine, thiazine, oxazine, etc., or any combination thereof. Exemplary charge additives may also be or include, but are not limited to, one or more nucleating agents having a surface charge opposite to the partial charge of the polymer, such as magnesium stearate (MgSt), phosphonium salts (e.g., triphenylphosphine, tributylphosphine, trimethylphosphine, dimethylphenylphosphine, methyldiphenylphosphine, tri(2-ethylhexyl)phosphine, tetrabutylphosphine hexafluorophosphate, tetrabutylphosphine sulfate, and tetrabutylammonium-phenylphosphonate), pyridinium salts (e.g., triphenylpyridinium tetrafluoroborate), pyrrolidinium salts (e.g., 1-butyl-1-methylpyrrolidinium bromide), sulfonium (e.g., triphenylsulfonium tetrafluoroborate), sulfonates (e.g., sodium octylsulfonate), phosphonic acid compounds (e.g., phosphonic acids, esters and salts; phosphinic acids, esters and salts; phosphoramides, phosphoramides), phosphonates (e.g., tetrabutylammonium-phenylphosphonate), the like, or any combination thereof. Exemplary charge additives may also include, but are not limited to, one or more high dielectric constant products such as CaCu3Ti4O12 , BaTiO3 and TiO2, products with stronger electronegativity than PP, such as PTFE and silicon, products with ultra-low dielectric loss tangent characteristics, such as silicon nitride, alumina, ceramics, high-density polyethylene, etc., or any combination thereof. Exemplary charge additives may also be or include, but are not limited to, aluminum or magnesium metal salts, lead zirconate titanate, potassium niobate, lithium niobate, lithium tantalate, sodium tungstate, unsaturated carboxylic acids or derivatives thereof, unsaturated epoxy monomers or silane monomers, maleic anhydride, monoazo metal compounds, alkyl acrylate monomers, alkyl methacrylate monomers, polytetrafluoroethylene, alkylene, arylene, arylene dialkylene, alkylene diarylene, oxydialkylene or oxydiarylene, polyacrylic acid and polymethacrylic acid compounds, organic titanates, quaternary phosphonium trihalogen zinc salts, organic silicone complexes, dicarboxylic acid compounds, macrocyclic polyethers or non-macrocyclic polyethers and cyclodextrins, Complex salts of amine derivatives, di-tert-butyl salicylic acid, potassium tetraphenylborate, potassium diborate, sulfonamides and metal salts, cycloalkyl, alumina particles treated with silane coupling, dimethyl silicone compounds, azo dyes, phthalates, quaternary ammonium salts, carbazole, diammonium and triammonium, hydrophobic silica and iron oxide, phenyl, substituted phenyl, naphthyl, substituted naphthyl, thienyl, alkenyl and alkyl ammonium complex salts, sodium dioctyl sulfosuccinate and sodium benzoate, zinc complexes, mica, monoalkyl and dialkyl tin oxides and polyurethane compounds, metal complexes of salicylic acid compounds, oxazolidinone, piperazine or perfluoroalkane, lecigran MT, Nigro black, fumed silica, carbon black, p-trifluoromethylbenzoic acid and orthofluorobenzoic acid, poly (styrene-co-vinyl pyridinium-toluenesulfonate), methyl or butyl triphenyl complex aromatic amine, triphenylamine dye and azine dye, alkyl dimethyl benzyl ammonium salt, etc., or any combination thereof. In an exemplary embodiment, the charge additive may include a product named FWM02 TM The electret additive can be purchased from Keimei Plastifizierung Technik (Yantai) Co., Ltd. in Shandong Province, China. FWM02 TM Increase the charge density on the fiber surface, thereby extending its charge retention time. Compared with fibers without charge additives, FWM02 TM Can improve the melt strength of the fiber. Use charge additive FWM02 TM Increasing the melt strength of the fiber can reduce the relative amount of defects (e.g., melt blowing, fiber breakage, etc.), thereby improving the fiber's ability to hold and / or generate an electrical charge. FWM02 TM The bulk density is about 0.50 g / cm 3 To about 0.55g / cm 3, a particle weight of about 60 ea / g to about 65 ea / g, a filter pressure value (FPV) less than or equal to 0.5 bar / g, a pressure rise value (PRV) less than or equal to about 0.5 Pa / g, and / or a melt flow index of about 650-655 g / 10 min. In another embodiment, the charge additive may include an electret additive under the trade name CON-CHARGE 01585, which can be purchased from CONSTAB Polyolefin Additives GmbH in Ruthen, Germany. Exemplary charge control agents may be or include, but are not limited to, one or more metal salts of aluminum or magnesium, lead zirconate titanate, potassium niobate, lithium niobate, lithium tantalate, sodium tungstate, unsaturated carboxylic acids or derivatives thereof, unsaturated epoxy monomers or silane monomers, maleic anhydride, monoazo metal compounds, alkyl acrylate monomers, alkyl methacrylate monomers, polytetrafluoroethylene, alkylene, alkylene based CCA, arylene, arylene based CCA, arylene dialkylene, alkylene diarylene, silicon nitride, PTFE, tourmaline, anhydride, maleic anhydride, alkylene glycol, polyethylene glycol, PDLA, Polyvel's CTL-01 and CN-L01, talc (Imerys's Jetfine or Lianiing Jinghua New Materials's SK-9900), N'1, N'6-dibenzoyl dihydrazide (Shanxi Chemical Research's TMC-306), aromatic sulfonate derivatives (Takemoto Oil and Fat Co. Ltd.'s LAK 301), sorbitol (SORB from Euro OTC Pharma Gmbh), polyethylene glycol, Sukano's NA S516, KRITILEN's NC PL830, Gabriel-Chemie's BIOL, dioctyl adipate, ethylene bis stearamide, zinc phenylphosphonate (PPZn), Nissan Chemical's ECOPROMOTE, etc., or any combination thereof. The one or more charge additives may also be or include, but are not limited to, MagIQ TM The electret additive can be purchased from Avient of Avon Lake, Ohio, USA. Other CCAs that can be used are described in U.S. Pat. No. 10,571,137, the contents of which are incorporated herein to the extent consistent with the present disclosure. The charge additive can include any combination of the above substances.

[0105] Based on the total weight of the filter medium, its first group of fibers and / or its second group of fibers, the filter medium, its first group of fibers and / or its second group of fibers include a charge control agent in an amount of about 0.02 wt % to about 33 wt %. For example, based on the total weight of the filter medium, its first group of fibers and / or its second group of fibers, the filter medium, its first group of fibers and / or its second group of fibers include a charge control agent in an amount of about 0.2 wt %, about 1 wt %, about 5 wt %, about 10 wt % or about 15 wt % to about 20 wt %, about 25 wt %, about 30 wt % or about 33 wt %.

[0106] The first group of fibers and / or the second group of fibers may include one or more waxes. Exemplary waxes may be or include, but are not limited to, one or more of the following: polyolefins, polyethylenes, functionalized waxes such as amines, amides, fluorinated waxes, mixed fluorinated waxes and amide waxes, such as esters, quaternary amines, carboxylic acid or acrylic polymer emulsions, chlorinated polyethylenes, natural or synthetic ester waxes, palm waxes, paraffin waxes, etc., or any combination thereof. One or more waxes may be fractionated or distilled to provide specific cuts that meet specific viscosity and / or temperature criteria.

[0107] The filter media, its first group of fibers, its second group of fibers, and / or its substrate may include one or more additives. Exemplary additives may be or include, but are not limited to, one or more antimicrobial agents or compositions, one or more antiviral agents or compositions, or combinations thereof. Exemplary antimicrobial and antiviral agents or compositions may be or include, but are not limited to, silver, zinc, copper, organosilicon, tributyltin, compounds thereof, complexes thereof, one or more organic compounds, such as organic compounds including one or more chlorine, bromine, fluorine, or any combination thereof.

[0108] The PLA fiber can be poly-L-lactide (PLLA), poly-D-lactide (PLDA) or a combination thereof. In at least one embodiment, the second fiber can be or include a tribo-negatively charged material. In at least one embodiment, the second fiber can include polypropylene (PP) and / or acrylic fiber.

[0109] In at least one embodiment, the weight ratio of the first fibers to the second fibers is about 1: 1. In at least one embodiment, the first fibers and / or the second fibers have about 2% or less spin finish, preferably no or substantially no spin finish.

[0110] The cross-section of the fibers can be one or more shapes, including but not limited to round, bean-shaped, dog-bone-shaped, trilobal-shaped, barbell-shaped, bow-tie-shaped, star-shaped, Y-shaped, etc. It should be appreciated that the cross-sectional shape of the fibers can be selected and / or can depend at least in part on one or more performance characteristics of the filter media and / or one or more fibers therein.

[0111] The filter medium and / or its fibers can be or have a gradient density. For example, the filter medium and / or its fibers can be prepared or configured as a filter medium and / or fiber sheet with a gradient density, wherein one or more of its characteristics can change (e.g., increase or decrease) from one side or surface to its opposite side or surface. For example, the pore size of the filter medium and / or its fibers can increase or decrease from the upper surface (e.g., the upstream side) to the lower surface (e.g., the downstream side). In an exemplary embodiment, the pore size of the filter medium and / or its fiber sheet decreases from its upper surface (e.g., the upstream side) to the lower surface (e.g., the downstream side). It should be recognized that changing the gradient density of one or more characteristics of the filter medium and / or its fibers can change (e.g., improve) the load capacity, effectiveness and / or efficiency of the filter medium or its fibers. Other characteristics of the filter medium and / or its fibers that can be changed according to the gradient can be or include, but are not limited to, the length of the fiber, the thickness or diameter of the fiber, the relative composition of each fiber in the blend, the charge density of the fiber, etc., or any combination thereof.

[0112] The filter medium and / or its fibers may include one or more bicomponent fibers. The term or expression "bicomponent fiber" used herein refers to a fiber comprising at least two materials bonded to each other or otherwise connected. For example, the filter medium and / or its fibers may be or include one or more bicomponent fibers. Bicomponent fibers may be prepared by extruding two materials (e.g., polymers) from the same spinneret. Exemplary material combinations of bicomponent fibers may be or include, but are not limited to, polypropylene (PP) / polyethylene (PE), polyethylene terephthalate (PET) / polypropylene (PP), etc., or any combination thereof. As further discussed herein, one or more fibers of the filter medium and / or its fibers (e.g., multiple fibers) may be connected to each other via thermal bonding, chemical bonding, and / or mechanical bonding (e.g., entanglement).

[0113] The method of making a filter medium may include providing or preparing a plurality of polylactic acid (PLA) fibers and tribocharging the PLA fibers. The method may include tribocharging the PLA fibers with a second group of fibers or second fibers.

[0114] The fibers may be made or prepared by any method including, but not limited to, air-laid, wet-laid, extruded, co-formed, needle-punched, stitched, hydraulically entangled, melt-blown, spunbonded, hydroentangled, thermally bonded, carded, spinneret, gel spinning, melt spinning, wet spinning, dry spinning, islands-in-a sea staple or spunbond, segmented pie staple or spunbond, electrospinning, etc., or any combination thereof. The above-mentioned method and / or other methods of preparing or manufacturing fibers are described in U.S. Patent Nos. 4,406,950, 6,338,814, 6,616,435, 6,861,142, 7,252,493, 7,300,272, 7,309,430, 7,422,071, 7,431,869, 7,504,348, 7,774,077, 9,522,357, 9,993,761 and U.S. Patent Publication No. 2009 / 266,759, the disclosures of which are hereby incorporated by reference into this document for all purposes and to the extent consistent with the present disclosure.

[0115] In an exemplary embodiment, the system, filter media and / or fibers thereof may include spunbond threads or fibers. Spunbond fibers or filaments may be prepared or formed by spinning a molten polymer into fibers or filaments and stretching the molten fibers. The fibers may be prepared into fiber bundles, which may be separated, spread and / or layered on a web to form a web. The fibers may also be bonded into a sheet or film form by thermal bonding and embossing.

[0116] In another exemplary embodiment, the system, filter media, and / or fibers thereof may include fibers prepared or formed using a meltblowing die. Examples of suitable meltblowing dies that can be used are discussed in detail in U.S. Pat. Nos. 6,972,104, 8,017,534, and 7,772,456, and U.S. Patent Application No. US2020 / 0216979A1, the entire disclosures of which are hereby incorporated by reference herein for all purposes and to the extent consistent with the present disclosure.

[0117] In an exemplary embodiment, a system for preparing a filter medium and / or its fibers may include one or more carding machines. For example, the system may include two carding machines placed in series with each other. Fibers with shorter fiber lengths may be processed into a continuous fiber web by fiber opening, fiber blending, and fiber reinforcement. The fiber web prepared by carding may be subjected to one or more other processes. For example, the fiber web may be subjected to a secondary bonding process to improve or increase the integrity and / or strength of the fiber web. It should be appreciated that the bonding process may be accomplished via chemical, thermal, and / or mechanical methods.

[0118] In at least one embodiment, the electrostatic or electret substrate prepared from the fibers can be a high loft triboelectric charged filter media prepared by carding and needle punching. In at least one embodiment, the method can include needle punching fibers. The method can also include carding fibers. In other embodiments, the method can include spunbond fibers. In other embodiments, the method can include meltblown fibers.

[0119] In at least one embodiment, the method may include contacting the first fiber and / or the second fiber with one or more nucleating agents, charge additives, charge control agents, or a combination thereof. For example, the method may include adding one or more nucleating agents to the first fiber and / or the second fiber, or contacting one or more nucleating agents with the first fiber and / or the second fiber in other ways. In another example, the method may include adding one or more charge additives to the first fiber and / or the second fiber, or contacting one or more charge additives with the first fiber and / or the second fiber in other ways. In yet another example, the method may also include adding one or more charge control agents to the first fiber and / or the second fiber, or contacting one or more charge control agents with the first fiber and / or the second fiber in other ways.

[0120] In at least one embodiment, the filter medium, the first group of fibers (e.g., PLA fibers) and / or the second group of fibers can be produced or prepared using a dual-beam meltblown system. The dual-beam meltblown system can be oriented at an angle so that the two fiber streams of the dual-beam meltblown system are mixed or otherwise contacted, and then one or more fibers are triboelectrically charged. For example, the two fiber streams of the dual-beam meltblown system can be mixed or otherwise contacted, so that one or more fibers are triboelectrically charged. It should be appreciated that the fibers (e.g., the first group of fibers and / or the second group of fibers) can be triboelectrically charged via needle punching, vibration generation, or hydraulic entanglement.

[0121] In such embodiments, the tribocharging method may be needling, vibration generation, or hydroentanglement.

[0122] In at least one embodiment, the filter media, the first group of fibers (e.g., PLA fibers), and / or the second group of fibers can be produced by meltblowing technology and then triboelectrically charged. For example, a low viscosity PLA resin can be extruded through a meltblowing die to prepare PLA fibers. Meltblown PLA fibers can be triboelectrically charged via a hydroentanglement (i.e., hydrodynamic charging) process, in which clean water acts as or is a second component that generates friction on the PLA fibers or their surfaces.

[0123] In at least one embodiment, the filter medium and / or its fibers may include bicomponent fibers, which include two or more materials. The bicomponent fibers may be spunbonded or meltblown. In an exemplary embodiment, the first material of the bicomponent fibers includes PLA. The second material of the bicomponent fibers may be selected from one or more materials disclosed herein. It should be appreciated that the bicomponent fibers may have different cross-sections, such as side-by-side cross-sections, segmented pie-shaped cross-sections, hollow segmented pie-shaped cross-sections, segmented ribbon-shaped cross-sections, etc., or any combination thereof. The bicomponent fibers may be triboelectrically charged via vibration, needle punching, hydroentanglement, etc., or any combination thereof.

[0124] In at least one embodiment, the filter medium and / or its fibers can be contacted or rubbed with any suitable material to triboelectrically charge the filter medium and / or its fibers. For example, a PLA article (e.g., a fiber, a film, or a fabric) can be rubbed against any suitable material disclosed herein, and friction energy (e.g., mechanical energy) can be converted into electrical energy. Such a system is generally referred to as a friction nanogenerator (TENG), which converts mechanical energy collected from the environment into electrical energy to power small devices such as sensors, air filtration, or charge consumer electronics. The triboelectrically charged PLA surface can be an excellent material for a TENG system because PLA has a high charge density for triboelectric charging.

[0125] The first and / or second fiber may include one or more polymers, which may include one or more charge additives, charge enhancers and / or charge control agents. Charge additives, charge enhancers and / or charge control agents are capable of or configured to maintain or enhance the triboelectric charge in the filter or its fibers. Charge additives may be added to the fibers in any suitable conventional manner. For example, just before the melt is extruded and fully mixed, a charge additive in particulate form (e.g., powder and / or granules) is mixed, combined, added together or otherwise contacted with the polymer melt, and the charge additive may be added to the polypropylene fiber. Therefore, the charge additive particles suspended and fully distributed in the melt appear on the surface of the fiber to a certain extent after extrusion.

[0126] The second fiber may include polypropylene (PP), acrylic polymer or a combination thereof. In at least one embodiment, the second fiber may include a blend of polypropylene (PP) and acrylic fiber. In another embodiment, the second fiber may include a blend of PP and other polymers. In yet another embodiment, the second fiber may include a blend of acrylic polymer and other polymers. Other polymers may be or include any polymer disclosed herein, including polymers disclosed with respect to the second fiber.

[0127] One or more fibers of the filter medium may include a homopolymer, a copolymer, or a heterofilament, which is a bicomponent fiber in which one component is an electret. In one example, the one or more fibers of the filter medium may include a homopolymer of PP. In another example, the one or more fibers of the filter medium may be PP fibers. In another example, the one or more fibers of the filter medium may be a bicomponent fiber including PP and another polymer and / or electret. For example, the one or more fibers of the filter medium may be a bicomponent fiber including PP and an electret.

[0128] The one or more fibers of the filter media may include non-melt-spun fibers in the form of melt-spun fibers or continuous fibers, staple fibers, bicomponent fibers, etc. In an exemplary embodiment, the one or more fibers of the filter media are staple fibers and have a spin finish of 2% or less, preferably no or substantially no spin finish (i.e., bare staple fibers).

[0129] In an exemplary embodiment, at least some of the fibers may include one or more polymers that may include charge additives, charge enhancers, or charge control agents, such as those described above, and at least some of the fibers may include PLA. For example, PLA fibers may include racemic PLLA (poly-L-lactide), regular PLLA, poly-D-lactide (PLDA), poly-DL-lactic acid (PDLLA), or a combination thereof. In addition, the PLA-based surface herein refers to the surface of a fiber, fabric, or film made of at least 50% PLA-based resin. The remainder or remainder of the composition may contain other resins, such as polyhydroxybutyrate (PHB), or other biodegradable materials, nucleating agents, antioxidants, charge enhancers, etc., or any combination thereof. In at least one embodiment, the fiber may include 100% PLA resin.

[0130] In at least one embodiment, the PLA fibers may include one or more charge additives. In another embodiment, the filter media may include a first fiber and a second fiber, the first fiber may include PLA, and the second fiber may include a charge additive. The second fiber may include any of the above fibers. In yet another embodiment, both the PLA fibers and the second fiber may include a charge additive.

[0131] In at least one embodiment, the filter medium and / or its fiber may include one or more nanoparticles. For example, one or more nanoparticles may be incorporated into substrate, filter medium and / or its fiber. At least one dimension of the nanoparticle is less than 1 micron or less than 100 nm. One or more nanoparticles can or are configured to increase the overall surface area of ​​the filter medium, thereby improving its filtration efficiency, and capturing submicron pollutants without significantly compromising other factors (e.g., pressure drop (i.e., airflow) through the filter). Nanoparticles can ensure that the efficiency of the filter medium remains relatively high, even after the electrostatic charge begins to decay over time. In addition, the connection between the fiber and the nanoparticles can be enhanced by the electrostatic charge, thereby allowing the nanoparticles to be deeply dispersed throughout the filter medium.

[0132] In at least one embodiment, the nanoparticles are "deeply" dispersed in the substrate or its fibers. As used herein, the term "deeply" refers to the dispersion of the nanoparticles beyond the first surface of the substrate so that at least some of the nanoparticles are placed between the first and second opposing surfaces and into the internal structure of the substrate or medium. In at least one embodiment, the nanoparticles are substantially dispersed throughout the medium from the first surface to the opposing second surface. In at least one embodiment, the nanoparticles are dispersed in a portion of the medium from the first surface to a position between the first surface and the second surface.

[0133] Nanoparticles having different triboelectric properties relative to the first and / or second fibers can be selected to further enhance particle removal using the triboelectric effect. In this way, the generated nanoparticles can be formed in an electric field and can be less contaminated by chemicals that can reduce the triboelectric effect. Nanoparticles having different adsorption properties or surface charge properties than the first and / or second fibers can also be used (for example, in oil or water filtration). This difference can be used to enhance or create a local electric field gradient within the filter medium to enhance particle removal. The nanoparticles and / or fibers can have different wetting properties.

[0134] The nanoparticles can be or include, but are not limited to, any suitable material, such as glass, biosoluble glass, ceramic materials, acrylic, carbon, metal, aluminum oxide, one or more polymers (e.g., nylon, polyethylene terephthalate, etc.), polyvinyl chloride (PVC), polyolefins, polyacetals, polyesters, cellulose ethers, polyalkylene sulfides, poly(arylene oxides), polysulfones, modified polysulfone polymers, polyvinyl alcohol, polyamides, polystyrene (PS), polyacrylonitrile, polyvinylidene chloride, polymethyl methacrylate, polyvinylidene fluoride, etc., or any combination thereof.

[0135] In at least one embodiment, the nanoparticles can be connected or bonded to the fibers via mechanical winding. This mechanical bonding can be assisted by an adhesive or a binder. In at least one embodiment, the nanoparticles may not be curled (i.e., in a relaxed state, they do not include obvious wavy shapes, curved shapes, curled shapes, coiled sawtooth shapes, or similar shapes associated with nanoparticles). In at least one embodiment, the nanoparticles may have a curled main structure with discrete lengths. For example, when these curled nanofibers with discrete lengths are attached to the fibers, they are entangled with each other and are entangled with the fibers by firmly attaching, entangled on the fibers and around the fibers to form modified fibers. In at least one embodiment, the attachment of nanofibers to the fibers can be achieved via electrostatic charge attraction and / or van der Waals attraction between the fibers and the nanoparticles. A more complete description of the filter medium incorporating nanoparticles can be found in the co-assigned, co-pending U.S. Provisional Patent Application Serial No. 63 / 328,970 filed on April 8, 2022, the complete disclosure of which is incorporated herein by reference in its entirety for all purposes.

[0136] The following numbered paragraphs disclose one or more exemplary variations of the subject matter of the present application:

[0137] 1. A filter media comprising a first set of fibers, wherein the first set of fibers comprises polylactic acid (PLA) fibers or acrylic fibers, wherein the first set of fibers are triboelectrically charged.

[0138] 2. The filter medium of paragraph 1, further comprising a second set of fibers, wherein the first set of fibers are triboelectrically charged by the second set of fibers.

[0139] 3. The filter media of paragraph 2, wherein at least a portion of the second set of fibers comprises a tribo-negatively charged material.

[0140] 4. The filter media of paragraph 2 or 3, wherein at least a portion of the second group of fibers comprises a tribopositively charged material, wherein the tribopositively charged material has a relatively lower positive charge than the first group of fibers.

[0141] 5. The filter medium of any of paragraphs 2-4, wherein at least a portion of the second group of fibers comprises polypropylene (PP) fibers.

[0142] 6. The filter medium of paragraph 5, wherein the polypropylene fibers have an elongation of about 25% to about 100%, a tenacity of about 25 cN / tex to about 100 cN / tex, or a combination thereof.

[0143] 7. The filter media of any of paragraphs 1-5, wherein the first group of fibers comprises acrylic fibers.

[0144] 8. The filter media of any of paragraphs 2-6, wherein the first group of fibers comprises PLA fibers, and wherein at least a portion of the second group of fibers comprises acrylic fibers.

[0145] 9. The filter media of any of paragraphs 1-8, wherein the first set of fibers further comprises polyhydroxyalkanoate (PHBV).

[0146] 10. The filter media of any of paragraphs 2-9, wherein the weight ratio of the first group of fibers to the second group of fibers is about 1:1 by weight.

[0147] 11. The filter media of any of paragraphs 2-10, wherein the first group of fibers and the second group of fibers are nonwoven fibers.

[0148] 12. The filter media of any of paragraphs 1-11, wherein the first set of fibers is present in an amount of at least 10%, based on the total weight of the filter media.

[0149] 13. The filter media of any of paragraphs 1-12, wherein the PLA fibers comprise poly-L-lactide (PLLA).

[0150] 14. The filter media of any of paragraphs 1-13, wherein the first group of fibers, the second group of fibers, or a combination thereof comprises about 2% or less spin finish.

[0151] 15. The filter media of any of paragraphs 1-14, wherein the first group of fibers comprises continuous fibers.

[0152] 16. The filter media of any of paragraphs 1-14, wherein the first group of fibers includes non-continuous fibers.

[0153] 17. The filter media of any of paragraphs 1-16, wherein the first population of fibers has a diameter of about 0.1 μm to about 200 μm.

[0154] 18. The filter media of any of paragraphs 1-17, wherein the first population of fibers has a linear density of about 0.5 denier to about 50 denier.

[0155] 19. The filter media of any of paragraphs 1-18, wherein the first group of fibers, the second group of fibers, or a combination thereof comprises one or more nucleating agents.

[0156] 20. A filter medium according to any of paragraphs 1-19, wherein the first group of fibers, the second group of fibers, or a combination thereof include one or more charge additives configured to change the charge on the first group of fibers, increase the stability of the charge on the first group of fibers, or a combination thereof.

[0157] 21. The filter medium of paragraph 20, wherein the one or more charge additives include one or more of triphenylmethane, ammonium compounds, iminium compounds, ammonium fluoride compounds, iminium fluoride compounds, dicationic acid amides, polymeric ammonium compounds, diallyl ammonium compounds, aromatic sulfide derivatives, phenol derivatives, phosphonium compounds, phosphonium fluoride compounds, calixarenes, metal complexes, benzimidazolone, azine, thiazine, oxazine, or any combination thereof.

[0158] 22. The filter medium of paragraph 20 or 21, wherein the one or more charge additives include a nucleating agent.

[0159] 23. The filter media of any of paragraphs 19-22, wherein the one or more charge additives comprise a relatively greater electronegative charge than the first group of fibers or the second group of fibers.

[0160] 24. The filter media of any of paragraphs 19-23, wherein the one or more charge additives comprise a relatively greater dielectric constant than the first group of fibers or the second group of fibers.

[0161] 25. The filter media of any of paragraphs 1-24, wherein the first group of fibers includes one or more charge control agents.

[0162] 26. The filter medium of any of paragraphs 1-25, wherein the filter medium is formed by carding and needling.

[0163] 27. The filter media of any of paragraphs 2-26, wherein the first group of fibers and the second group of fibers comprise spunbond charged media.

[0164] 28. The filter media of any of paragraphs 2-27, wherein the first group of fibers and the second group of fibers comprise a meltblown charged media.

[0165] 29. The filter medium of any of paragraphs 1-27, wherein the first group of fibers is triboelectrically charged by rubbing the first group of fibers with one or more machines, wherein the one or more machines include one or more of a carding machine, a needle loom, or a combination thereof.

[0166] 30. The filter media of any of paragraphs 1-28, wherein the first group of fibers includes PLA fibers, and wherein the first group of fibers are triboelectrically charged by hydrodynamic charging.

[0167] 31. The filter media of any of paragraphs 2-30, wherein the second set of fibers includes one or more biodegradable fibers.

[0168] 32. The filter medium of paragraph 31, wherein the one or more biodegradable fibers include one or more of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), poly(adipate-co-butylene terephthalate) (PBAT), poly(3-hydroxybutyrate-co-e-hydroxyvalerate) (PHBV), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), or any combination thereof.

[0169] 33. The filter medium of paragraph 31 or 32, wherein the one or more biodegradable fibers are selected from poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), poly(adipate-co-butylene terephthalate) (PBAT), poly(3-hydroxybutyrate-co-e-hydroxyvalerate) (PHBV), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), and combinations thereof.

[0170] 34. The filter media of any of paragraphs 31-33, wherein the one or more biodegradable fibers include PHBH.

[0171] 35. An air filter product comprising the filter medium of any of paragraphs 1-34.

[0172] 36. A method of making a filter media, the method comprising contacting a first group of fibers comprising polylactic acid (PLA) fibers or acrylic fibers with a second group of fibers, wherein contacting the first group of fibers with the second group of fibers causes triboelectric charging of the first group of fibers.

[0173] 37. The method of paragraph 36, wherein the second set of fibers comprises a tribo-negatively charged material.

[0174] 38. The method of paragraph 36, wherein the second group of fibers comprises a tribopositively charged material, wherein the tribopositively charged material comprises a relatively lower positive charge than the first group of fibers.

[0175] 39. The method of paragraph 36, wherein the second group of fibers comprises polypropylene (PP).

[0176] 40. The method of paragraph 39, wherein the first group of fibers comprises acrylic fibers.

[0177] 41. The method of paragraph 36, wherein the first group of fibers comprises PLA fibers and wherein the second group of fibers comprises acrylic fibers.

[0178] 42. The method of any of paragraphs 36-41, wherein the first group of fibers further comprises polyhydroxyalkanoate (PHBV).

[0179] 43. The method of any of paragraphs 36-42, wherein the weight ratio of the first group of fibers to the second group of fibers is about 1:1.

[0180] 44. The method of any of paragraphs 36-43, wherein the first group of fibers and the second group of fibers are nonwoven fibers.

[0181] 45. The method of any of paragraphs 36-44, wherein the filter media comprises PLA fibers in an amount of at least 50 wt%.

[0182] 46. ​​The method of any of paragraphs 36-45, wherein the PLA fibers comprise poly-L-lactide (PLLA).

[0183] 47. The method of any of paragraphs 36-46, further comprising combing the first group of fibers and the second group of fibers.

[0184] 48. The method of any of paragraphs 36-47 further comprising spunbonding the first population of fibers and the second population of fibers.

[0185] 49. The method of any of paragraphs 36-47, further comprising meltblowing the first group of fibers and the second group of fibers.

[0186] 50. The method of any of paragraphs 36-49, further comprising contacting one or more nucleating agents with the first group of fibers, the second group of fibers, or a combination thereof.

[0187] 51. The method of any of paragraphs 36-50, further comprising contacting one or more charge additives with the first group of fibers, the second group of fibers, or a combination thereof.

[0188] 52. The method of any of paragraphs 36-51, further comprising contacting one or more charge control agents with the first group of fibers, the second group of fibers, or a combination thereof.

[0189] 53. An air filter product prepared according to the method of any of paragraphs 36-52.

[0190] Example

[0191] The examples and other embodiments described herein are exemplary and are not intended to be limited to the full scope of the compositions and methods of the present disclosure. Within the scope of the present disclosure, equivalent changes, modifications and variations can be made to specific embodiments, materials, compositions and methods, and substantially similar results can be obtained.

[0192] Example 1

[0193] Exemplary fiber blends (1)-(3) comprising a blend of a first group of fibers and a second group of fibers were prepared, and the effectiveness of each in filtering particles in the air passing therethrough was evaluated. Specifically, each fiber blend (1)-(3) was evaluated to determine the average penetration rate of particles passing therethrough. It should be recognized that a relatively large or increased penetration rate of particles through a filter medium and / or a fiber blend indicates that the efficiency of the filter medium and / or the fiber blend is relatively small. Each fiber blend (1)-(3) includes a first group of fibers and a second group of fibers in a weight ratio of 1:1 (50 wt% to 50 wt%). Prior to combing, all fibers were conditioned at a relative humidity (RH) of about 30% for at least three days. The fibers were pre-weighed and hand-blended, then combed and needled to prepare the fiber blends. The fiber blends (1)-(3) were approximately 10"x10" (approximately 25.4 cm x approximately 25.4 cm).

[0194] The first fiber blend (1) includes a blend of acrylic fibers and polypropylene (PP) fibers. The second fiber blend (2) includes a blend of PLA fibers and acrylic fibers. The third fiber blend (3) includes a blend of PLA fibers and PP fibers. The PLA fibers do not have a spinning finish (i.e., do not contain a spinning finish).

[0195] At least three days after needling, the particle penetration rate was evaluated or measured using an ATI 100S device with 0.3 μm particles. The fiber blends (1)-(3) were evaluated using an ATI 100S device at 85 liters / minute (lpm) and 32 lpm. The average resistance of each fiber blend (1)-(3) was also evaluated / measured. It should be recognized that triboelectric charging of the fibers occurs during combing and / or needling. The basis weight of each fiber blend (1)-(3) was measured in grams / square foot (gsf), grams / square meter (gsm), and ounces / square yard (osy). It should be recognized that for ease of comparison, the observed values ​​were normalized to 134 gsm. Each fiber blend (1)-(3) was evaluated in duplicate, and the results are summarized in Tables 1 and 2, respectively.

[0196] Table 1

[0197]

[0198] Table 2

[0199]

[0200] As shown in Table 1, for the fiber blend (1) comprising acrylic fibers and PP fibers, the particles had a penetration rate of about 19.7% at about 85 lpm and a penetration rate of about 7.2% at about 32 lpm. For the fiber blend (2) comprising acrylic fibers and PLA fibers, the particles had a penetration rate of about 8.3% at about 85 lpm and a penetration rate of about 2.4% at about 32 lpm. In addition, for the fiber blend (3) comprising PP fibers and PLA fibers, the particles had a penetration rate of about 7.6% at about 85 lpm and a penetration rate of about 1.9% at about 32 lpm. The average resistance of fiber blend (1) was substantially the same as the average resistance of the remaining fiber blends (2) and (3). It should be appreciated that the average resistance is proportional to the pressure drop and inversely proportional to the air permeability. As shown in Table 2, similar results were observed when two evaluations were performed. Thus, it was surprisingly and unexpectedly discovered that fiber blends (2) and (3) incorporating PLA exhibited higher filtration effectiveness than fiber blend (1) not including PLA without compromising air permeability and / or pressure drop.

[0201] Example 2

[0202] The exemplary fiber blends (1)-(3) of Example 1 and another exemplary fiber blend (4) were each evaluated for their effectiveness in filtering airborne particles passing therethrough. Fiber blend (4) was prepared by adding a charge additive, namely FWM 02, to fiber blend (3). Specifically, the charge additive was added to PP fibers and blended with PLA fibers at a weight ratio of 1:1 to prepare fiber blend (4). The effectiveness was evaluated as described above for Example 1. It should be recognized that the observed values ​​were normalized to 126 gsm for ease of comparison. The results are summarized in Table 3.

[0203] Table 3

[0204]

[0205]

[0206] As shown in Table 3, the average penetration of particles in fiber blend (4) (including the charge additive) is similar to the penetration observed in fiber blends (2) and (3). In addition, although fiber blends (2)-(4) exhibit significantly lower particle penetration than fiber blend (1), the average resistance of each fiber blend (1)-(4) is essentially the same. Therefore, it is surprising and unexpected to find that fiber blends (2)-(4) incorporating PLA exhibit relatively higher filtration effectiveness without compromising air permeability and / or pressure drop compared to fiber blend (1) that does not include PLA.

[0207] Example 3

[0208] The effectiveness of the fiber blends (1)-(3) of Example 1 was evaluated after one and two weeks of aging. The results are summarized in Tables 4, 5, and 6.

[0209] Table 4: Day 0

[0210]

[0211] Table 5: Week 1

[0212]

[0213] Table 6: Week 2

[0214]

[0215]

[0216] As shown in Tables 4-6, the effectiveness and efficiency of fiber blends (1)-(3) were essentially the same after one week and two weeks. For example, after one week, for fiber blend (1), the particles had a penetration rate of about 21.8% at about 85 lpm and a penetration rate of about 7.6% at about 32 lpm (normalized values); for fiber blend (2), the particles had a penetration rate of about 12.7% at about 85 lpm and a penetration rate of about 3.4% at about 32 lpm; for fiber blend (3), the particles had a penetration rate of about 8.7% at about 85 lpm and a penetration rate of about 1.7% at about 32 lpm. As shown in Table 6, similar results were observed after two weeks.

[0217] Example 4

[0218] Flat plate filters (4)-(7) were prepared using tribocharged media or tribocharged fiber blends and their filtration effectiveness was evaluated. The fiber blends were prepared, carded and needle punched in a weight ratio of 1:1 with different scrims or supports. The PLA fibers were free of oil or non-spinning oil. The basis weight and net fiber weight were essentially the same. Flat plate filter (4) included a blend of PP fibers and acrylic fibers and a PP scrim. Flat plate filter (5) included PLA fibers and acrylic fibers and a PP scrim. Flat plate filter (6) included PLA fibers and acrylic fibers with an antimicrobial agent and a gas adsorbent additive. Flat plate filter (7) included PLA fibers and acrylic fibers and a PP scrim with a gas adsorbent additive. The results are summarized in Table 7.

[0219] Table 7

[0220]

[0221] As shown in Table 7, each of the filters (5)-(7) incorporating PLA exhibited improved filtration efficiency compared to the filter (4) comprising a PP blend. This improvement was observed at all three particle sizes (E1 = 0.3-1 μm, E2 = 1-3 μm, and E3 = 3-10 μm). It was surprising and unexpected to find that while the improved filtration efficiency was observed, a lower pressure drop was also exhibited. Specifically, the filters (5)-(7) incorporating PLA exhibited substantial improvements in particle size groups E1 and E2. For example, filter (5) comprising PLA fibers and acrylic fibers and a PP scrim improved filtration efficiency by more than 13 percentage points in group E1 (i.e., 53.1 vs. 66.5) and by more than 4 percentage points in group E2 (i.e., 86.6 vs. 90.9), while reducing pressure drop by almost 15% (i.e., 0.202 vs. 0.171). Filter (7) includes PLA fibers and acrylic fibers and PP scrim with gas adsorbent additives, which improves the filtration efficiency by more than 16 percentage points in the E1 group (i.e., 53.1 vs. 69.7) and by almost 3 percentage points in the E2 group (i.e., 94.7 vs. 97.2), while reducing the pressure drop by almost 5% (i.e., 0.202 vs. 0.1911).

[0222] Example 5

[0223] Exemplary fiber blends (8) and (9) comprising a first group of fibers and a second group of fibers were prepared and evaluated. Fiber blend (8) comprises acrylic fibers and PP fibers, but without a spinning finish; while fiber blend (9) comprises PP fibers and acrylic fibers and a charge additive (i.e., FWM 02), but without a spinning finish. The basis weight and net fiber weight of fiber blends (8) and (9) are substantially the same. The weight ratio of acrylic fibers to PP fibers in fiber blends (8) and (9) is about 1:1. The linear density of each fiber blend (8) and (9) is substantially the same, being about 1.7 decitex (dtex) to about 3.6 dtex. During the fiber spinning process, the charge additive is added to fiber blend (9). The fiber blend is processed by needle punching to solidify the fibers. The properties of PP fibers with and without the charge additive are summarized in Table 8.

[0224] Table 8

[0225] PP fiber with charge additive PP fiber without charge additives Average Dtex 2.59 2.46 Tenacity (cN / tex) 46.9 19.07 Elongation(%) 39 242 Fiber length (mm) 51 59

[0226] As shown in Table 8, the PP fibers used in fiber blend (9) include a charge additive and exhibit relatively lower elongation than the PP fibers used in fiber blend (8). The PP fibers used in fiber blend (9) include a charge additive and exhibit relatively greater toughness than the PP fibers used in fiber blend (8). Without being bound by theory, it is believed that the relatively higher toughness and relatively lower elongation allow the fibers to stretch more than PP fibers without a charge additive. It is believed that the relative increase in fiber stretching affects crystallization. Specifically, it is believed that the relative increase in fiber stretching increases the amount or percentage of crystallization, thereby producing more ordered or oriented crystals, and the orientation of the crystals relatively improves the effectiveness of the fibers in generating and / or maintaining triboelectric charges. It should be recognized that both PP fibers with and without charge additives were evaluated using scanning electron microscopy (SEM) to observe their physical properties and morphology. The SEM micrographs show that the surface roughness of the PP fibers treated with the charge additive is significantly higher than that of the PP fibers without the charge additive. Without being bound by theory, it is believed that the increase in surface roughness can contribute, at least in part, to the effectiveness of the PP fibers in generating, retaining, or maintaining a triboelectric charge. The SEM micrographs also show that the PP fibers treated with the charge additive exhibit relatively less inter-fiber alignment and more curling, kinking, and bending than the PP fibers without the charge additive, which were clearly aligned or parallel to each other.

[0227] The fiber blends (8) and (9) were aged for three days. Ten hand sheets of each fiber blend (8) and (9) were evaluated using an ATI 100s apparatus at 85 lpm and 32 lpm. The average penetration and resistance values ​​for 0.3 μm NaCl salt particles were evaluated. The results are summarized in Table 9.

[0228] Table 9

[0229]

[0230] As shown in Table 9, fiber blend (9) exhibits relatively improved filtration performance compared to fiber blend (8) which does not include a charge additive. It was surprisingly and unexpectedly found that the improved filtration performance did not compromise resistance and pressure drop, both of which remained essentially the same. Specifically, for fiber blend (8), the particle penetration rate was about 14.9%, while for fiber blend (9), the particle penetration rate was only about 8.6%. At 32 lpm, the particles penetrated about 4.1% of fiber blend (8), but only about 1.9% of fiber blend (9), thus improving performance by more than 200%. The resistance (mmH2O) of fiber blend (9) was essentially the same as that of fiber blend (8) at 32 lpm, and only slightly higher at 85 lpm. Therefore, compared to fiber blend (8), with essentially the same pressure drop, fiber blend (9) exhibits increased filtration efficiency.

[0231] Handsheets prepared from fiber blends (8) and (9) were aged under controlled temperature and humidity. Specifically, fiber blends (8) and (9) were aged at about 70°C and about 80% RH for about 24 hours, and then aged at about -20°C for about 24 hours. The aged fiber blends (8) and (9) were then evaluated for their filtration effectiveness. The results are summarized in Table 10.

[0232] Table 10

[0233]

[0234] As shown in Table 10, fiber blend (9) exhibited lower particle penetration after aging than fiber blend (8) while maintaining substantially the same resistance. Specifically, the average penetration of fiber blend (9) was about 9.6%, while the average penetration of fiber blend (8) was about 13.3%.

[0235] Example 6

[0236] Flat plate filters (10) and (11) were prepared from fiber blends (8) and (9) respectively to evaluate the fractional filtration effectiveness. Specifically, flat plate filters (10) and (11) were prepared from fiber blends (8) and (9) and measured at a headwind velocity of about 180 fpm. The particles were KCl salt particles (diameter 0.3 μm to 10 μm). The results are summarized in Table 11.

[0237] Table 11

[0238]

[0239] As shown in Table 11, for all three particle sizes, flat filter (11) exhibits improved filtration efficiency relative to flat filter (10). Although the pressure drop of flat filter (11) is relatively higher than that of flat filter (10), this increase in pressure drop is consistent with the decrease in thickness of flat filter (11) (i.e., the thickness of flat filter (11) is about 104.2 mm, compared to the thickness of flat filter (10) of about 111.7 mm). Specifically, flat filter (11) exhibits substantial improvement in particle size group E1 (about 57.9 vs. about 68.3). Particle group E1 is generally related to charge density.

[0240] Example 7

[0241] Exemplary fiber blends (12) and (13) comprising a first group of fibers comprising PLA fibers and a second group of fibers comprising poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) were prepared and evaluated for their respective effectiveness in filtering airborne particles passing therethrough. Specifically, each fiber blend (12) and (13) was evaluated to determine the average penetration rate of particles passing therethrough. The PLA and PHBH fibers did not contain a spinning finish. Fiber blend (12) included PLA fibers in an amount of about 50 wt% and PHBH fibers in an amount of about 50 wt%. Fiber blend (13) included PLA fibers in an amount of about 60 wt% and PHBH fibers in an amount of about 40 wt%. Prior to combing, all fibers were conditioned for at least three days at a relative humidity (RH) of about 30%. The fibers were pre-weighed, hand blended, and then carded and needle punched to produce fiber blends (12) and (13). The dimensions of fiber blends (12) and (13) were approximately 10" x 10" (approximately 25.4 cm x approximately 25.4 cm).

[0242] Fiber blends (12) and (13) were evaluated using an ATI 100S device at 85 liters per minute (lpm) and 32 lpm. The average resistance of each fiber blend (12) and (13) was also evaluated / measured. It should be recognized that triboelectric charging of the fibers occurs during the combing and / or needling process. The basis weight of each fiber blend (12) and (13) was measured in grams per square foot (gsf), grams per square meter (gsm), and ounces per square yard (osy). It should be recognized that the observed values ​​were normalized for ease of comparison. Fiber blends (12) and (13) were evaluated on the day of production and about four days later. The results are summarized in Table 12.

[0243] Table 12

[0244]

[0245] As shown in Table 12, the difference in average penetration between flow rates of 85 lpm and 32 lpm demonstrates that the PLA fibers of fiber blends (12) and (13) are tribocharged. Specifically, the average penetration at a lower flow rate of about 32 lpm is lower than the average penetration at a higher flow rate, indicating that the PLA fibers of fiber blends (12) and (13) are tribocharged. It also shows that the average penetration is substantially the same after aging for four days, demonstrating that the PLA fibers can retain their charge even after aging.

[0246] Although the apparatus, system and method have been described in detail herein according to certain preferred embodiments, many modifications and changes may be made thereto by those skilled in the art. Therefore, the above description should not be interpreted as limiting, but should be interpreted as covering the above obvious changes and being limited only by the spirit and scope of the appended claims.

Claims

1. A filter media comprising a first group of fibers, wherein the first group of fibers comprises polylactic acid (PLA) fibers or acrylic fibers, wherein the first group of fibers are triboelectrically charged.

2. The filter media of claim 1 further comprising a second set of fibers, wherein the first set of fibers are triboelectrically charged by the second set of fibers.

3. The filter media of claim 2, wherein at least a portion of the second set of fibers comprises a tribo-negatively charged material.

4. The filter media of claim 2 or 3, wherein at least a portion of the second group of fibers comprises a tribopositively charged material, wherein the tribopositively charged material has a relatively lower positive charge than the first group of fibers.

5. The filter media of any one of claims 2-4, wherein at least a portion of the second group of fibers comprises polypropylene (PP) fibers.

6. The filter medium of claim 5, wherein the polypropylene fibers have an elongation of about 25% to about 100%, a tenacity of about 25 cN / tex to about 100 cN / tex, or a combination thereof.

7. The filter media of any one of claims 1-5, wherein the first group of fibers comprises acrylic fibers.

8. The filter media of any one of claims 2-6, wherein the first group of fibers comprises PLA fibers, and wherein at least a portion of the second group of fibers comprises acrylic fibers.

9. The filter media of any one of claims 1-8, wherein the first group of fibers further comprises polyhydroxyalkanoate (PHBV).

10. The filter media of any one of claims 2-9, wherein the weight ratio of the first group of fibers to the second group of fibers is about 1:

1.

11. The filter media of any one of claims 2-10, wherein the first group of fibers and the second group of fibers are nonwoven fibers.

12. The filter media of any one of claims 1-11, wherein the first group of fibers is present in an amount of at least 10 wt%, based on the total weight of the filter media.

13. The filter media of any one of claims 1-12, wherein the PLA fibers comprise poly-L-lactide (PLLA).

14. The filter media of any one of claims 1-13, wherein the first group of fibers, the second group of fibers, or a combination thereof comprises about 2% or less spin finish.

15. The filter media of any one of claims 1-14, wherein the first group of fibers comprises continuous fibers.

16. The filter media of any one of claims 1-14, wherein the first group of fibers comprises non-continuous fibers.

17. The filter media of any one of claims 1-16, wherein the first group of fibers have a diameter of about 0.1 μm to about 200 μm.

18. The filter media of any one of claims 1-17, wherein the first population of fibers has a linear density of about 0.5 denier to about 50 denier.

19. The filter media of any one of claims 1-18, wherein the first group of fibers, the second group of fibers, or a combination thereof comprises one or more nucleating agents.

20. The filter media of any one of claims 1-19, wherein the first group of fibers, the second group of fibers, or a combination thereof include one or more charge additives configured to change the charge on the first group of fibers, increase the stability of the charge on the first group of fibers, or a combination thereof.

21. The filter medium of claim 20, wherein the one or more charge additives include one or more of triphenylmethane, ammonium compounds, iminium compounds, ammonium fluoride compounds, fluorinated iminium compounds, dicationic acid amides, polymeric ammonium compounds, diallyl ammonium compounds, aromatic sulfide derivatives, phenol derivatives, phosphonium compounds, fluorinated phosphonium compounds, calixarenes, metal complexes, benzimidazolone, azine, thiazine, oxazine, or any combination thereof.

22. The filter media of claim 20 or 21, wherein the one or more charge additives comprises a nucleating agent.

23. The filter media of any one of claims 19-22, wherein the one or more charge additives have a relatively more electronegative charge than the first group of fibers or the second group of fibers.

24. The filter media of any one of claims 19-23, wherein the one or more charge additives have a relatively greater dielectric constant than the first group of fibers or the second group of fibers.

25. The filter media of any one of claims 1-24, wherein the first group of fibers comprises one or more charge control agents.

26. The filter media of any one of claims 1-25, wherein the filter media is formed by carding and needle punching.

27. The filter media of any one of claims 2-26, wherein the first group of fibers and the second group of fibers comprise a spunbond tape dielectric.

28. The filter media of any one of claims 2-27, wherein the first group of fibers and the second group of fibers comprise a meltblown charged media.

29. The filter media of any one of claims 1-27, wherein the first group of fibers is triboelectrically charged by rubbing the first group of fibers with one or more machines, wherein: The one or more machines include one or more of a carding machine, a needle loom, or a combination thereof.

30. The filter media of any one of claims 1-28, wherein the first group of fibers comprises PLA fibers, and wherein the first group of fibers are triboelectrically charged by hydrodynamic charging.

31. The filter media of any one of claims 2-30, wherein the second group of fibers comprises one or more biodegradable fibers.

32. The filter medium of claim 31, wherein the one or more biodegradable fibers comprise one or more of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), poly(adipate-co-butylene terephthalate) (PBAT), poly(3-hydroxybutyrate-co-e-hydroxyvalerate) (PHBV), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), or any combination thereof.

33. The filter medium of claim 31 or 32, wherein the one or more biodegradable fibers are selected from the group consisting of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polyhydroxybutyrate (PHB), polybutylene succinate (PBS), poly(adipate-co-butylene terephthalate) (PBAT), poly(3-hydroxybutyrate-co-e-hydroxyvalerate) (PHBV), polyhydroxyalkanoate (PHA), polycaprolactone (PCL), and combinations thereof.

34. The filter media of any one of claims 31-33, wherein the one or more biodegradable fibers comprise PHBH.

35. An air filter product comprising the filter medium of any one of claims 1-34.

36. A method of making a filter media, the method comprising contacting a first group of fibers comprising polylactic acid (PLA) fibers or acrylic fibers with a second group of fibers, wherein contacting the first group of fibers with the second group of fibers causes triboelectric charging of the first group of fibers.

37. The method of claim 36, wherein the second set of fibers comprises a tribo-negatively charged material.

38. The method of claim 36, wherein the second group of fibers comprises a tribopositively charged material, wherein the tribopositively charged material has a relatively lower positive charge than the first group of fibers.

39. The method of claim 36, wherein the second group of fibers comprises polypropylene (PP).

40. The method of claim 39, wherein the first group of fibers comprises acrylic fibers.

41. The method of claim 36, wherein the first group of fibers comprises PLA fibers, and wherein the second group of fibers comprises acrylic fibers.

42. The method of any one of claims 36-41, wherein the first group of fibers further comprises polyhydroxyalkanoate (PHBV).

43. The method of any one of claims 36-42, wherein the weight ratio of the first group of fibers to the second group of fibers is about 1:

1.

44. The method of any one of claims 36-43, wherein the first group of fibers and the second group of fibers are nonwoven fibers.

45. The method of any one of claims 36-44, wherein the filter media comprises PLA fibers in an amount of at least 50 wt%.

46. ​​The method of any one of claims 36-45, wherein the PLA fibers comprise poly-L-lactide (PLLA).

47. The method of any one of claims 36-46, further comprising combing the first group of fibers and the second group of fibers.

48. The method of any one of claims 36-47, further comprising spunbonding the first group of fibers and the second group of fibers.

49. The method of any one of claims 36-47, further comprising meltblowing the first group of fibers and the second group of fibers.

50. The method of any one of claims 36-49, further comprising contacting one or more nucleating agents with the first group of fibers, the second group of fibers, or a combination thereof.

51. The method of any one of claims 36-50, further comprising contacting one or more charge additives with the first group of fibers, the second group of fibers, or a combination thereof.

52. The method of any one of claims 36-51, further comprising contacting one or more charge control agents with the first group of fibers, the second group of fibers, or a combination thereof.

53. An air filter product prepared according to the method of any one of claims 36-52.

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