Fluorescent fibers and polymer films containing them

Abstract

An optical element is provided. The optical element includes a polymer film having at least one layer comprised of fibers containing a plurality of fluorophores. The fluorophores have a quantum yield greater than 20 percent.

Description

FLUORESCENT FIBERS AND POLYMER FILMS CONTAINING THEMCROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to U. S. Application No. 63 / 721,043, filed November 15, 2024, the content of which is incorporated herein by reference in its entirety.FIELD OF THE DISCLOSURE

[0002] The present invention is directed to a novel kind of fluorescent films and woven or nonwoven fluorescent fibers and combinations of such films and fibers.BACKGROUND OF THE DISCLOSURE

[0003] Fluorescence can provide benefits in a wide range of applications, including art, design, energy production, and controlled environment agriculture. More generally, fibers may provide an avenue for imparting spectral functionality in composite materials such as films, fabrics, coatings, metals, ceramics, polymers, and other compounds. For example in agriculture, achieving optimal plant growth occurs by controlling all growth parameters such as temperature, humidity, light quality and quantity, irrigation and fertigation. Utilizing greenhouses to cultivate plants is one method that can provide control over all growth parameters. As overall use of greenhouses has expanded worldwide, many improvements in control of specific growth parameters remain desirable and continue to receive ongoing research and exploration, including control over the light environment provided to the plants. Advances in light emitting diode-based horticultural lighting has allowed for better understanding of the impact of the light environment on growing plants and most high-tech greenhouses utilize technologies such as shade curtains and supplemental lighting to decrease or increase the total light provided to a plant in a day. It has also been well proven that light spectrum can be used to control plant morphology.

[0004] One objective of the present invention is to provide a variety of novel materials useful in fluorescence applications, such novel materials capable of increasing plant yields within the greenhouse. Optimized light spectra can be achieved through use of these novel composite materials.SUMMARY OF THE DISCLOSURE

[0005] In one aspect of the invention, an optical element is provided that includes a polymer film having multiple layers. At least one of the multiple layers is composed of fibers containing a plurality of fluorophores. The fluorophores have a quantum yield greater than 20 percent.

[0006] In another aspect of the invention, a fiber is provided comprising an extruded polymer including at least one layer and containing a plurality of fluorophores. The fluorophores have a quantum yield of greater than about 20 percent. The fiber provides sunlight transparency of at least 50 percentBRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1. shows pictures of QD fibers in (a) EVOH, (b) LDPE, (c) LDPE-MAH, and (d) nylon polymers in ambient light, (e)-(h) show corresponding QD fibers in UV light.

[0008] Figure 2. shows a schematic of QD fibers reinforced (a) 3-layer and (b) 5-layer films.

[0009] Figure 3. shows a schematic of QD fibers reinforced 7-layers. Where P is at least one of a polyethylene, polypropylene, ethylene vinyl alcohol, nylon, polyethylene grafted with maleic anhydride, polyester or thermoplastic polyurethane film. The oxygen barrier includes ethylene vinyl alcohol, nylon, polystyrene or polyethylene terephthalate.

[0010] Figure 4. shows pictures of (a) and (b) EVOH-QD fibers sandwiched between layers of polyethylene films in ambient and in UV light and (c) and (d) nylon-QD fibers sandwiched between layers of polyethylene films in ambient and in UV light.

[0011] Figure 5. shows photostability data of CuInS2 / ZnS QDs fibers in different polymers (a) ethylene vinyl alcohol, (b) nylon, (c) low density polyethylene, (d) low density polyethylene grafted maleic anhydride, (e) ethylene vinyl acetate, and (f) thermoplastic polyurethane

[0012] Figure 6. shows photostability data of CuInS2 / ZnS QDs fibers in (a) ethylene vinyl alcohol, (b) thermoplastic polyurethane, (c) low density polyethylene grafted maleic anhydride, (d) lowdensity polyethylene, and (e) ethylene vinyl acetate and sandwiched between two sheets of ethylene vinyl alcohol.

[0013] Figure 7. shows (a) a schematic of QD fiber reinforced 5-layer films and (b) a schematic cross-section of a QD fiber including QDs in a polymer fiber core and covered with a second polymer providing oxygen barrier properties. The second polymer providing oxygen barrier properties is ethylene vinyl alcohol, nylon, polystyrene or polyethylene terephthalate

[0014] Table 1. Optical and mechanical properties of QD fibers in different polymersDEFINITIONS AND ABBREVIATIONS

[0015] The following explanations of terms and abbreviations are provided to better describe the present disclosure and to guide those of ordinary skill in the art in the practice of systems, methodologies and compositions disclosed herein.

[0016] As used herein, “comprising” means “including”, and the singular form “a” or “an” or “the” includes plural references unless the context clearly indicates otherwise. Unless the context clearly indicates otherwise, the term “or” is inclusive, and thus refers to both a single element of stated alternative elements and a combination of two or more of those elements.

[0017] Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one or ordinary skill in the art to which this disclosure relates. Suitable methods and compositions are described herein for the practice or testing of the systems, methodologies and compositions described herein. However, it is to be understood that other methods and materials similar, or equivalent to, those described herein may be used in the practice or testing of these systems, methodologies and compositions disclosed herein. Consequently, the systems, methodologies, compositions and examples disclosed herein are illustrative only, and are not intended to be limiting. Other features of the present disclosure will be apparent to those skilled in the art from the following detailed description and the appended claims.

[0018] Unless otherwise indicated, all numbers expressing quantities of components, percentages, temperatures, times, and so forth as used in the specification or claims are to be understood as being modified by the term “about”. Unless otherwise indicated, non-numerical properties such as colloidal, continuous, crystalline, and so forth as used in the specification or claims are to be understood as being modified by the term “substantially”, meaning to a great extent or degree. Accordingly, unless otherwise indicated implicitly or explicitly, the numerical parameters and / or non-numerical properties set forth herein are approximations, and the optimal values of these properties and parameters may depend on the desired properties sought, the limits of detection under standard test conditions or methods, the limitations of the processing methods, and / or the nature of the property or parameter. When directly and explicitly distinguishing embodiments from disclosed prior art, the embodiment numbers are not approximations unless the word “about” is recited.DETAILED DESCRIPTIONI. Definitions

[0019] Carcinogen: A material that has been shown to directly or indirectly cause cancer in any mammal.

[0020] Colloidal suspension: A mixture consisting of a disperse phase (the suspended particles) and a continuous phase (the liquid medium of suspension), wherein the mixture either does not settle, or would take a very long time to settle appreciably.

[0021] Dispersibility: The ability of QDs to form a colloidal suspension.

[0022] Emission spectrum: Those portions of the electromagnetic spectrum over which QDs (or a composition containing them) exhibit photoluminescence (PL) (in response to excitation by a light source) whose amplitude is at least 1% of the peak PL emission.

[0023] Flocculation: A process whereby the disperse phase in a colloidal suspension forms aggregates and comes out of suspension.

[0024] Nanoparticle: A nanoscale particle of a solid material. The nanoparticles disclosed herein are preferably crystalline and have a size of less than 500 nanometers in dimension. The nanoparticles disclosed herein may form a colloidal suspension. Embodiments of the disclosed nanoparticles may be of a single material or may include an inner core and an outer shell of differing materials. The nanoparticles may further include a plurality of ligands bound to the nanoparticle outer surface. Exemplary nanoparticles which may be utilized in the compositions, systems and methodologies described herein may comprise metals, metal oxides, metal chalcogenides, semiconductors, and insulators. Nanoparticles may be crystalline (i.e., nanocrystals), amorphous, or mixtures thereof.

[0025] Photoluminescence (PL): The emission of light (electromagnetic radiation, in the form of photons) after the absorption of light. It is one form of luminescence (light emission) and is initiated by photoexcitation (excitation by photons).

[0026] Polar solvents: A polar solvent is any solvent containing an electric dipole. Exemplary polar solvents include acetone, ethanol, water, ethanol / water mixtures, isopropanol, isopropanol / water mixtures, methanol, methanol / water mixtures, dimethyl sulfoxide, diethyl sulfoxide, tetrahydrofuran, and tetrahydrofuran / water mixtures.

[0027] Polymers (as well as polar polymers): A large molecule, or macromolecule, composed of many repeating subunits. Polymers range from familiar synthetic plastics such as polystyrene or poly (methyl methacrylate) (PMMA), to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many smaller molecules, e.g., monomers. Exemplary polymers include poly (methyl methacrylate) (PMMA), polystyrene, silicones, epoxy resins, and the like.

[0028] Polar polymers: Polar polymers are polymers that contain a permanent electric dipole. Polymers containing only carbon and hydrogen atoms are non-polar polymers. Polar polymers typically contain other atoms such as chlorine, fluorine, oxygen, nitrogen, and sulfur whereby the polymer will contain a permanent electric dipole. Exemplary polar polymers include poly vinylalcohol, an ethylene vinyl alcohol copolymer, polyvinyl acetate, polyurethane, ethylene vinyl acetate, an acrylic polymer, polyvinyl butyral, and polyamides, e.g., nylons.

[0029] Quantum Dots: A nanoparticle that exhibits size dependent electronic and optical properties due to quantum confinement. The quantum dots disclosed herein preferably have at least one dimension less than about 50 nanometers. The disclosed quantum dots may be colloidal quantum dots. Some of the quantum dots which may be utilized in the compositions, systems and methodologies described herein are made from a binary semiconductor material having a formula MX where M is a metal and X is typically selected from sulfur, selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, or mixtures thereof. Exemplary binary quantum dots which may be used in the compositions, systems and methodologies described herein include CdS, CdSe, CdTe, PbS, PbSe, PbTe, ZnS, ZnSe, ZnTe, InP, InAs, Q12S, and In2S3. Other quantum dots which may be utilized in the compositions, systems, and methodologies described herein are ternary, quaternary, and / or alloyed quantum dots including, but not limited to, ZnSSe, ZnSeTe, ZnSTe, CdSSe, CdSeTe, HgSSe, HgSeTe, HgSTe, ZnCdS, ZnCdSe, ZnCdTe, ZnHgS, ZnHgSe, ZnHgTe, CdHgS, CdHgSe, CdHgTe, ZnCdSSe, ZnCdSeTe, ZnHgSeTe, ZnHgSSe, CdHgSSe, CdHgSeTe, CUA1S2, CuAlSe2, CuFeSe2, CuFeSe2, CuInS2, CuAlSexS2-x, CuInS2, CuInSe2, CuInGaSe2, CuInZnS2, CuZnSnSe2, CuInSexS2-x, CuInZnSexS2-x, AgInS2, AgInSe2, AgInGaSexS2-x, and AgInSexS2-xwhere 0 < x < 2. Embodiments of the disclosed quantum dots may be of a single material or may include an inner core and an outer shell of differing materials. The outer shell may be a thin shell or layer formed by any suitable method, such as cation exchange. The quantum dots further include a plurality of ligands bound to the quantum dot surface.

[0030] Ligand: A ligand is an ion or molecule that binds to another, usually larger, molecule. In general, a ligand bonds to a metal atom, which in the case of the present disclosure, is part of a quantum dot and / or nanoparticle. A ligand may be configured to bind to a particular receptor, interact with various types of matter in prescribed ways, and / or the like. Capping ligands are configured to stabilize the interface where nanoparticles, such as quantum dots, interact with their surrounding medium.

[0031] Solubility: When used in reference to QDs, the ability of QDs to form a clear colloidal suspension without haze caused by formation of aggregates.

[0032] Toxic: Denotes a material that can damage living organisms due to the presence of phosphorus or heavy metals such as cadmium, lead, or mercury.

[0033] As mentioned previously, the present invention describes a number of fluorescent films and fibers. There are a number of parameters of the films and fibers that may be controlled and / or optimized to achieve optimal performance. For example, it is generally preferred for the fluorophores to have a quantum yield of greater than 20 percent. Also, it is preferred and desirable that the fluorophores emit a spectrum of light having a maximum intensity at wavelengths greater than 400 nm. It should be appreciated that the fluorophores are preferably quantum dots and the loading of the quantum dots within the films or fibers is at least 0.1 percent.

[0034] Among other desirable characteristics can be the spacing of fibers from one another in the optical element where the fibers are generally at least 1 mm apart. The fibers within the optical element can be arranged parallel from each other or can cross each other, and such crossing can often be at angles of at least 5 degrees. It should also be noted that the fibers generally have a diameter of at least 10 microns.

[0035] The fibers have other desired properties, e.g., the fiber preferably has a tensile strength at break of at least 18 MPa, an elongation at break of at least 300 percent, a tear resistance of at least 2000 g / mm and a tear drop resistance of at least 500 g All such properties aid in avoiding unwanted breakage of the fibers.

[0036] The optical elements can be vulnerable to degradation from a number of sources Both oxygen and water vapor (moisture) can impact the films so that oxygen and moisture barriers can be employed. Aso, additives can be employed in the fibers and films to help avoid or reduce degradation from some light or heat.

[0037] The following examples are non-limiting and are merely intended to further illustrate the compositions, systems and methodologies described herein.Example 1

[0038] Preparation of QD liquid concentrate (QDLC) in bis(ethylhexyl) sebacateIn a typical process, CuInS2 / ZnS quantum dots (from Strem, catalogue no: 29-8510; 29-8520 & 29-8530) were dissolved in bis(ethylhexyl) sebacate at 70-95% QD concentration by weight to produce QD liquid concentrate in bis(ethylhexyl) sebacate.Example 2

[0039] Preparation of QD liquid concentrate (QDLC) in octadeceneIn a typical process, CuInS2 / ZnS quantum dots (from Strem, catalogue no: 29-8510; 29-8520 & 29-8530) were dissolved in octadecene at 70-95% QD concentration by weight to produce QD liquid concentrate in octadecene.Example 3

[0040] Twin screw extrusion of QD fibers in LLDPEIn a twin extruder, linear low density polyethylene (LLDPE) pellets were introduced through the hopper and in another port, QD liquid concentrate from each individual sample from examples 1 & 2 was introduced (LLDPE to QDLC ratio varied from 2% to 50%) into the extruder at 180 °C and the resultant strands were stretched while hot to form QD fibers. The thickness of the fibers were varied from 10 pm to 500pm. (Figure 1)Example 4

[0041] Twin screw extrusion of QDs fibers in EVAIn a twin extruder, ethylene vinyl acetate (EVA) pellets were introduced through the hopper and in another port, QD liquid concentrate from each individual sample from examples 1 & 2 was introduced (EVA to QDLC ratio varied from 2% to 50%) into the extruder at 150 °C and the resultant strands were stretched while hot to form QD fibers. The thickness of the fibers were varied from 10 pm to 500pm.Example 5

[0042] Twin screw extrusion of QDs fibers in EVOHIn a twin extruder, ethylene vinyl alcohol (EVOH) pellets were introduced through the hopper and in another port, QD liquid concentrate from each individual sample from examples 1 & 2 was introduced (EVOH to QDLC ratio varied from 2% to 50%) into the extruder at 220 °C and the resultant strands were stretched while hot to form QD fibers. The thickness of the fibers were varied from 10 pm to 500pm. (Figure 1)Example 6

[0043] Twin screw extrusion of QDs in maleic anhydride grafted LDPE (PE-MAH)In a twin extruder, linear low density polyethylene (PE-MAH) pellets were introduced through the hopper and in another port, QD liquid concentrate from each individual sample from examples 1 & 2 was introduced (PE-MAH to QDLC ratio varied from 2% to 50%) into the extruder at 180 °C the resultant strands were stretched while hot to form QD fibers. The thickness of the fibers were varied from 10 pm to 500pm. (Figure 1)Example 7

[0044] Twin screw extrusion of QDs in maleic anhydride grafted EVA (EVA-MAH)In a twin extruder, linear low density polyethylene (EVA-MAH) pellets were introduced through the hopper and in another port, QD liquid concentrate from each individual sample from examples 1 & 2 was introduced (EVA-MAH to QDLC ratio varied from 2% to 50%) into the extruder at 150 °C and the resultant strands were stretched while hot to form QD fibers. The thickness of the fibers were varied from 10 pm to 500pm.Example 8

[0045] Twin screw extrusion of QDs in thermoplastic polyurethane (TPU)In a twin extruder, linear low density polyethylene (LLDPE) pellets were introduced through the hopper and in another port, QD liquid concentrate from each individual sample from examples 1 & 2 was introduced (LLDPE to QDLC ratio varied from 2% to 50%) into the extruder at 150 °C and the resultant strands were stretched while hot to form QD fibers. The thickness of the fibers were varied from 10 pm to 500pm.Example 9

[0046] Twin screw extrusion of QDs in nylonIn a twin extruder, linear low density polyethylene (LLDPE) pellets were introduced through the hopper and in another port, QD liquid concentrate from each individual sample from examples 1 & 2 was introduced (LLDPE to QDLC ratio varied from 2% to 50%) into the extruder at 180 °C and the resultant strands were stretched while hot to form QD fibers. The thickness of the fibers were varied from 10 pm to 500pm. (Figure 1)Example 10

[0047] Lamination of QD fibers to form reinforced 3 -layer filmsEach of the QD fibers from examples 5 and 9 were hot pressed or hot laminated between two sheets of polyethylene and the resultant reinforced films were rolled and taken for characterization. Figure 2a & Figure 4.Example 11

[0048] Lamination of QD fibers to form reinforced 5-layer filmsEach of the QD fibers from examples 5 and 9 were hot pressed or hot laminated between two sheets of polyethylene and maleic anhydride grafted polyethylene bilayer films. The resultant reinforced films were rolled and taken for characterization. Figure 2b.Example 12

[0049] Lamination of QD fibers to form reinforced 7-layer filmsEach of the QD fibers from examples 3-9 were hot pressed or hot laminated between two sheets of polyethylene and maleic anhydride grafted polyethylene and an oxygen barrier (i.e., ethylene vinyl alcohol, nylon, polystyrene or polyethylene terephthalate trilayer films). The resultant reinforced films were rolled and taken for characterization. Figure 3.Example 13

[0050] Photostability measurements of QD fibersThe QD fibers from each of examples 3 to 9 were put in a photostability chamber at 50 °C and illuminated using light characterized by a wavelength of 400 nm. The photoluminescence (PL) intensity was collected as a function of time. Figure 5 shows a graph of PL intensity over the time.Example 14

[0051] Photostability measurements of QD fibers reinforced 3-layer filmsThe QD fibers from example 10 were put in a photostability chamber at 50 °C and illuminated using light characterized by a wavelength of 400 nm. The photoluminescence (PL) intensity was collected as a function of time. Figure 6 shows a graph of PL intensity over the time.

[0052] Although the present invention has been described with reference to specific details, I is not intended that such details should be regarded as limitations upon the scope of the invention. Various modifications, substitutions, combinations, and ranges of parameters may be made or utilized in the compositions, and methodologies described herein.

Claims

CLAIMSWhat IS CLAIMED IS:Claim 1: An optical element comprising: a polymer film having at least one layer comprised of fibers containing a plurality of fluorophores, said fluorophores having a quantum yield greater than 20 percent.Claim 2: The optical element of claim 1 wherein said fluorophores emit a spectrum of light having a maximum intensity at wavelengths greater than 400 nm and less than 800 nm.Claim 3: The optical element of claim 1 wherein said fluorophores are quantum dots of a material selected from the group of CuInS2, CuInSe2, AgInS2, AgInSe2, CuGaS2, CuGaSe2, CuAlS2, CuAlSe2, AgGaS2, AgGaSe2, ZnS, ZnSe, and alloys thereof.Claim 4: The optical element of claim 1 wherein said fibers are comprised of a polymer selected from the group consisting of ethylene vinyl alcohol, ethylene vinyl acetate, polyethylene, polyester, thermoplastic polyurethane, and nylon, said fibers further including quantum dotsClaim 5: The optical element of claim 4 wherein the quantum dots loading in said fibers is at least 0.1 percent or at least 1%.Claim 6: The optical element of claim 1 wherein said fibers are comprised of either single strands or multiple strands.Claim 7: The optical element of claim 1 wherein said fibers are woven or non-woven.Claim 8: The optical element of claim 1 wherein said fibers are spaced apart from one another by at least 0.1 mm.Claim 9: The optical element of claim 1 wherein said fibers are oriented parallel to one another or oriented crossing one another.Claim 10: The optical element of claim 1 further comprising at least two distinct fibers in said film containing fluorophores having different maximum intensities at wavelengths separated by at least 50 nm.Claim 11: The optical element of claim 1 wherein said fibers have diameters of at least about 1 micron or at least about 10 microns.Claim 12. The optical element, of claim 1 wherein said fibers are optically transparent, semi¬ transparent, or opaque.Claim 13: The optical element of claim 1 wherein said fibers are either single stranded or co¬ axial.Claim 14: The optical element of claim 1 wherein said polymer film further includes at least one layer of an oxygen barrier material and at. least, one layer of a moisture barrier’ material.Claim 15. The optical element of claim 1 wherein said polymer film further includes at least one layer containing additives for stabilizing said polymer film against light or thermal degradation.Claim 16. A fiber comprising an extruded polymer including at least one layer and containing a plurality of fluorophores, said fluorophores having a quantum yield of greater than about 20 percent.Claim 17: The fiber of claim 16 wherein sai d fluorophores emit a spectrum of light, having a maximum intensity at wavelengths greater than 400 nm and less than 800 nm.Claim 18: The fiber of claim 16 wherein said fluorophores are quantum dots of a material selected from the group of CuInS2, CuInSe2. AgInS2, AgInSe2, CuGaS2, CuGaSe2, CuAlS2, CuAlSe2, AgGaS2, AgGaSe2, ZnS, ZnSe, and alloys thereof.Claim 19: The fiber of claim 16 further comprising a polymer selected from the group consisting of ethylene vinyl alcohol, ethylene vinyl acetate, polyethylene, polyester, thermoplastic polyurethane, and nylon, said fibers further including quantum dotsClaim 20: The fiber of claim 16 wherein the quantum dots loading in said fibers is at least 0.1 percent or at least 1 percent.Claim 21. The fiber of claim 16 wherein the fiber has a tensile strength at break of at least 18 MPa.Claim 22. The fiber of claim 16 wherein the fiber has an elongation at break of at least 300 percent.Claim 23 The fiber of claim 16 wherein the fiber has a tear resistance of at least 2000 g / mm.Claim 24. The fiber of claim 16 wherein the fi ber has a tear drop resistance of at least 500 g.

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