Boron-based polyelectrolyte complex and uses thereof

Abstract

The disclosure relates to a method for forming a flame-retardant coated substrate, the method comprising, among other things, exposing a substrate to the combined aqueous solution to give a treated substrate; and exposing the treated substrate to a buffer solution to produce a flame-retardant coated substrate, wherein a coating on the flame-retardant coated substrate comprises a polyelectrolyte complex formed between the polymeric, polycationic material and the polyborate salt.

Description

BORON-BASED POLYELECTROLYTE COMPLEX AND USES THEREOFCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority from U.S. Appl. No. 63 / 605,918, filed December 4, 2023, which is incorporated by reference as if fully set forth herein.TECHNICAL FIELD

[0002] This disclosure relates to the field of flame-retardant coatings for various substrates including engineered wood products, such as oriented strand board (OSB).BACKGROUND

[0003] In 2021 , there were over 1.35 million fires reported in the United States, resulting in 3800 civilian deaths, 14700 civilian injuries, and $15.9 billion in property damage. Specifically, home structure fires contributed to 27 % of fires, 75 % of civilian fire deaths, and 76 % of civilian fire-related injuries, while also accounting for 38 % of property damage. Wood is widely used as a building material for most home construction and outdoor structures due to its renewability, good mechanical properties, and aesthetic appeal. Nowadays, the use of engineered wood products, such as OSB, is becoming more and more popular, especially in residential and construction, including flooring, roofing, and ceiling / wall paneling. Compared to other construction materials, primarily cellulosic wood has a low ignition temperature (-300 °C), and when decomposed, it breaks down into small molecules and releases combustible volatiles that continue to fuel and propagate the fire. Given its inherent flammability, developing an effective flame-retardant (FR) treatment for OSB is crucial to impede or prevent the spread of flames upon exposure to an ignition source, reducing flammability and protecting lives and property.

[0004] Several environmentally benign FR treatments have been developed as alternatives to the traditional halogenated compounds and other toxic flame retardants. In recent years, the use of polyelectrolyte complex (PEC) coatings to deposit FR treatments on flammable substrates has gained great interest due to its versatility, environmental friendliness, ambient processing, and wide variety of chemistries available for use. Most PEC surface treatments are deposited via layer-by-layer (LbL) assembly, a water-based technique consisting of sequential immersions of a substrate into oppositely charged polyelectrolyte solutions, which typically interact through electrostatic attractions. This LbL deposition is impractical for the fire protection of wood, however, to the numerous processing steps and theheterogenous surface of wood, resulting in very slow diffusion of polyelectrolytes during each deposition step. An alternative approach to overcome the large number of processing steps is “one pot” PEC deposition, in which polycations and polyanions are mixed in one homogenous, aqueous solution. This is typically a two-step strategy that involves creating a stable solution of two polyelectrolytes by adjusting the pH so that one of the species remains relatively uncharged and then exposing it to a buffer solution to induce an entropy-driven complexation.

[0005] Among the variety of chemistries employed for reducing material flammability, intumescence-based systems have been among the most widely used in PEC coatings to treat wood. An effective intumescent system consists of three components: an acid source, a blowing agent, and a carbon source. In brief, the acid source catalyzes the premature dehydration of the carbon source (e.g., polyols), producing aromatic char that is then expanded by nonflammable gases (e.g., N2, H2O, and CO2) released during thermal degradation of the blowing agent. This process forms a thermally stable char layer that insulates the underlying material from the ignition source. On cellulosic substrates, this FR chemistry typically incorporates amine-rich molecules or polymers as blowing agents, along with phosphate-based compounds as acid sources. In particular, phosphorus- containing compounds are known to be excellent flame retardants, acting in both gas and condensed phases by releasing radicals that inhibit chain-branching reactions and phosphoric acid that promotes char formation. Unfortunately, some phosphorus-based chemistries have been banned due to concerns about persistence, bioaccumulation, and toxicity issues. It is for this reason that alternative intumescent chemistries need to be explored.SUMMARY

[0006] Boron and its derivative compounds, which can be widely found in nuts, grains, fruits, leafy vegetables, and saline environments, exhibit both condensed and gas-phase modes of FR action. When exposed to heat, the release of boric acid promotes char formation by the dehydration of polyols, similar to the flame retardant mechanism of phosphate-based compounds. Additionally, borates melt to form a glassy layer that insulates the underlying substrate from heat and oxygen. Additionally, during boric acid-catalyzed dehydration releases water and noncombustible gases that dilute fuel in the form of radicals and excess oxygen. Sodium polyborate, for example, has been shown to improve the FR behavior of various materials, including polyethylene terephthalate, ethylene-vinyl alcohol copolymers, polyurethane foam, cotton fabric, and wood.

[0007] The inventors have discovered the first-ever environmentally-benign PEC coating comprising a polyborate salt (e.g., sodium polyborate (SPB)) and a polymeric, polycationic material (e.g., polyethylenimine (PEI)) for the fire protection of substrates such as OSB. The claimed PEC treatment deposits conformally to the structure of OSB, adding little additional weight, while maintaining its mechanical properties (i.e. , the flexural modulus and strength). The flammability of OSB is reduced by the presence of, e.g., a PEI / SPB coating, dramatically decreasing the total smoke release by 79%, along with reducing the peak heat release rate and total heat release by 18 % and 21 %, respectively. Moreover, the PEC coating increases the time to ignition (+18 %) and char residue (+35%) relative to the untreated OSB, as measured by cone calorimetry.

[0008] While not being bound by any specific theory, the inventors believe that these findings, in conjunction with surface analysis and imaging of the char residue of the coated OSB, suggests a primarily condensed phase FR mechanism by the formation of char and bubbles via intumescence reinforced with a stable glassy layer. This boron-based coating can improve the fire resistance of OSB and other engineered wood products, which could expand their utility in home construction, promoting both safety and sustainability.DESCRIPTION OF THE DRAWINGS

[0009] The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed herein.

[0010] FIG. 1 is a schematic of PEC coating deposition and components for coating OSB substrates.

[0011] FIGS. 2A-2D are SEM images of (2A / 2B) uncoated and (2C / 2D) PEI / SPB (60, 10)-coated OSB.

[0012] FIGS. 3A-3C are 3A FTIR spectra of uncoated (black) and PEI / SPB (60, 10)-coated (red) OSB. XPS spectra of 3B uncoated and 3C PEI / SPB (60,10)- coated OSB surfaces.

[0013] FIGS. 4A-4B 4A Thermogravimetric analysis of mass loss (solid lines) and derivative mass loss (dashed lines) as a function of temperature under an air atmosphere and 4B differential thermograms for uncoated and PEI / SPB (60,10)- coated OSB.

[0014] FIGS. 5A-5I (Top left) Pre- and (top right) post-butane torch test samples: (5A / C) uncoated and (5B / 5D / 5E) PEI / SPB (60, 10)-coated OSB. SEM images of (5F / 5G) uncoated and (5H / 5I) PEI / SPB (60,10)-coated OSB char residue after the torch test.

[0015] FIG. 6 Representative heat release rate curves as a function of time for uncoated and coated OSB.

[0016] FIG. 7A-7C (7A) FTIR spectra of uncoated (blue) and coated (orange) OSB char residues. XPS spectra of (7B) uncoated and (7C) coated OSB char surfaces.

[0017] Unless otherwise indicated, all figures and drawings in this document are not to scale and are chosen for the purpose of illustrating different embodiments of the invention. The dimensions of the various components are depicted in illustrative terms only, and no relationship between the dimensions of the various components should be inferred from the drawings, unless so indicated. Although terms such as “top”, “bottom”, “upper”, “lower”, “under”, “over”, “front”, “back”, “up” and “down”, and “first” and “second” can be used in this disclosure, it should be understood that those terms are used in their relative sense only unless otherwise noted.DESCRIPTION

[0018] Reference will now be made in detail to certain embodiments of the disclosed subject matter. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter.

[0019] Systems and methods described herein can provide a simplified, scalable method to apply a flame-retardant coating to engineered wood products, such as oriented strand board (OSB), along with foams, fabrics, textiles, films, and other flammable substrates. Systems and methods described herein introduces a deposition process for creating a polyelectrolyte (PEC) coating that can impart flame-retardancy to substrates.

[0020] Systems and methods described herein can describe a combination that can include a polymeric, polycationic material and a polyborate salt to form a flame-retardant PEC coating. Phosphate-containing molecules (e.g., ammonium polyphosphate, polysodium phosphate, sodium hexametaphosphate, and melamine polyphosphate) can also be included in combination with a polymeric, polycationic material and a polyborate salt (e.g., in the combined aqueous solution of a first aqueous solution comprising polymeric, polycationic material, and a second aqueous solution comprising polyborate salt; see, e.g., ACS Applied Polymer Materials &. 5226-5234 (2024), which is incorporated by reference as if fully set forth herein) to form a flame-retardant PEC coating. The polyborate salt can be any suitable polyborate salt including sodium polyborate (e.g., CAS 183290-63-3), ammonium polyborate, disodium octaborate tetrahydrate, ammonium pentaborate, sodium pentaborate decahydrate, dicalciumhexaborates, and sodium-calcium pentaborates. The systems and methods described herein can have the potential to significantly improve the scalability and efficacy of flame-retardant treatments for engineered wood products. The coating method and system described herein can be an industrially attractive method to form a flame-retardant coating on a substrate without the need for a chemically reactive process, halogenated materials, or special equipment.

[0021] Systems and methods described herein can be used for coating a substrate with a flame-retardant coating to impart flame-retardant properties. A coating method can provide a substrate with a flame-retardant coating by depositing a coating on the substrate. The coating can comprise a polyelectrolyte complex formed between a polymeric, polycationic material and a polyborate salt. The coating can be between about 10 nanometers and about 100 microns thick.

[0022] The disclosure relates to a method for forming a flame-retardant coated substrate, the method comprising: preparing a first aqueous solution, comprising a polymeric, polycationic material; preparing a second aqueous solution, comprising a polyborate salt; combining the first aqueous solution and the second aqueous solution to form a combined aqueous solution; exposing a substrate to the combined aqueous solution to give a treated substrate; and exposing the treated substrate to a buffer solution to produce a flame-retardant coated substrate, wherein a coating on the flame-retardant coated substrate comprises a polyelectrolyte complex formed between the polymeric, polycationic material and the polyborate salt.

[0023] The disclosure also relates to a method for forming a flame-retardant coated substrate, the method comprising: exposing a substrate to a combined aqueous solution of a first aqueous solution comprising polymeric, polycationic material, and a second aqueous solution comprising polyborate salt to give a treated substrate; and exposing the treated substrate to a buffer solution to produce a flame-retardant coated substrate; wherein a coating on the flameretardant coated substrate comprises a polyelectrolyte complex formed between the polymeric, polycationic material and the polyborate salt.

[0024] The buffer solution can have any suitable pH, such as from about 2 to about 5 and can comprise any suitable acid, such as citric acid, acetic acid, and the like.

[0025] The flame-retardant coating can be applied to a wide range of substrate materials. In some instances, for example when the substrate is nylon / polyamide, additional ingredients may be required to form a fire-retardant coated substrate, such as a polyphosphate such as melamine polyphosphate. Substrates can include a textile, a fabric, a foam, a film, leather, a vinyl compound, plastic, wood(e.g., engineered wood, such as oriented standard board), a carpet, hook and loop fasteners, a non-foam padding, a film, or a combination thereof. Without limitation, examples of suitable fabric materials can include wool, linen, cotton, polyester, nylon, a polyester-cotton blend, a nylon-cotton blend, or a combination thereof. The substrate can include a hook and loop fastener (i.e., VELCRO®, which is a registered trademark of Velcro Industries, B.V.). The substrate can be a carpet, wherein a carpet can refer to a woven floor or wall covering having an upper pile layer attached to a backing. The substrate can include wood, a wood product, a particle board, balsa wood or the like. In some examples, non-foam padding can refer to a material that provides cushion against contact that does not include foam (e.g., feathers). The substrate can be positively charged, negatively charged, or neutral. Alternatively, or in addition, the substrate can comprise a multi-layered material comprising a combination of the substrates listed above.

[0026] The substrate can include a filmic substrate, such as, a polyester film, a polyethylene terephthalate (PET) film, a polypropylene film, a cellulose acetate film, a polyvinyl chloride (PVC) film, a polyethylene films, or a combination thereof.

[0027] The polyelectrolyte complex of the coating can be formed from a polymeric, polycationic material and a polyborate salt.

[0028] The polymeric, polycationic material can include polyethylenimine (PEI), branched polyethylenimine (BPEI), linear polyethylenimine, polyallylamine, polyvinylamine., cationic polyacrylamide, cationic poly diallyldimethylammoniumchloride (PDDA), poly(melamine-co-formaldehyde), polymelamine, a copolymer of polymelamine, polyvinylpyridine, a copolymer of polyvinylpyridine, or a combination thereof. The polymeric, polycationic material can include polymers with hydrogen bonding, such as, polyethylene oxide, polyvinylpyrrolidone, or a combination thereof. The polymeric, polycationic material can include, silicon based polymers, polyoligomeric silsesquioxane, carbon nanotubes, graphene, or a combination thereof.

[0029] The polymeric, polycationic material can include a colloidal particle, a nanoparticle, a nitrogen-rich polymer, or a combination thereof. The polymeric, polycation material can take the form of a powder, a flake, a liquid, a solution, a suspension, or a combination thereof.

[0030] The polyborate salt can include a boronic acid, a boron containing acid, or a combination thereof.

[0031] The coating method can involve preparing one or more aqueous solutions. The aqueous solution can be prepared by any suitable method, such as, direct dissolution, serial dilution, volumetric preparation, gravimetric preparation,sonication, manual mixing, magnetic mixing, shear mixing, static mixing, or a combination thereof.

[0032] The coating method can involve preparing two separate aqueous solutions. The first aqueous solution can include a polymeric, polycationic material, and the second aqueous solution can include a polyborate salt. The first aqueous solution can include from about 1.0 wt. % polymeric, polycationic material to about 50.0 wt. % polymeric, polycationic material, alternatively from about 0.01 wt. % polymeric, polycationic material to about 1.50 wt. % polymeric, polycationic material, alternatively from about 0.05 wt. % polymeric, polycationic material to about 1.50 wt. % polymeric, polycationic material, alternatively from about 0.01 wt. % polymeric, polycationic material to about 1 .00 wt. % polymeric, polycationic material, alternatively from about 0.01 wt. % polymeric, polycationic material to about 50.0 wt. % polymeric, polycationic material, alternatively from about 0.05 wt. % polymeric, polycationic material to about 30.0 wt. % polymeric, polycationic material, alternatively from about 1.0 wt. % polymeric, polycationic material to about 15.0 wt. % polymeric, polycationic material, and alternatively from about 1.0 wt. % polymeric, polycationic material to about 10.0 wt. % polymeric, polycationic material.

[0033] The second aqueous solution can include from about 1 .0 wt. % polyborate salt to about 50.0 wt. % polyborate salt, alternatively from about 0.01 wt. % polyborate salt to about 20 wt. % polyborate salt, alternatively from about 5 wt. % polyborate salt to about 15 wt. % polyborate salt, alternatively from about 10 wt. % polyborate salt to about 20 wt. % polyborate salt, alternatively from about 15 wt. % polyborate salt to about 20.0 wt. % polyborate salt, alternatively from about 10 wt. % polyborate salt to about 15.0 wt. % polyborate salt, alternatively from about 15 wt. % polyborate salt to about 18.0 wt. % polyborate salt, and alternatively from about 12 wt. % polyborate salt to about 19 wt. % polyborate salt.

[0034] The first aqueous solution can include a variety of chemical species, such as, water molecules, hydrogen ions, hydroxide ions, polymeric molecules (e.g., PEI), protonated polymeric molecules (e.g., protonated PEI), polycationic molecules (e.g., polycationic PEI), or a combination thereof.

[0035] The second aqueous solution can include a variety of chemical species, such as, water molecules, hydrogen ions, hydroxide ions, boronic acid molecules, or a combination thereof.

[0036] When both the first aqueous solution and second aqueous solution have been prepared, the first aqueous solution and second aqueous solution can becombined to form a combined aqueous solution. The combined aqueous solution can include a polymeric, polycationic material and a polyborate salt.

[0037] The combined aqueous solution can also be prepared in one step. For example, the combined aqueous solution can be prepared by including a polymeric, polycationic material and a polyborate salt. For example, the combined aqueous solution can contain a polymeric, polycationic material and a polyborate salt. The combined aqueous solution can include from about 1.0 wt. % polymeric, polycationic material to about 50 wt. % polymeric, polycationic material, alternatively from about 0.01 wt. % polymeric, polycationic material to about 1.50 wt. % polymeric, polycationic material, alternatively from about 0.05 wt. % polymeric, polycationic material to about 1.50 wt. % polymeric, polycationic material, alternatively from about 0.01 wt. % polymeric, polycationic material to about 1.00 wt. % polymeric, polycationic material, alternatively from about 0.01 wt. % polymeric, polycationic material to about 50.0 wt. % polymeric, polycationic material, alternatively from about 0.05 wt. % polymeric, polycationic material to about 30.0 wt. % polymeric, polycationic material, alternatively from about 1.0 wt. % polymeric, polycationic material to about 15.0 wt. % polymeric, polycationic material, and alternatively from about 1.0 wt. % polymeric, polycationic material to about 10.0 wt. % polymeric, polycationic material.

[0038] The combined aqueous solution can include from about 1.0 wt. % polyborate salt to about 50.0 wt. % polyborate salt, alternatively from about 0.01 wt. % polyborate salt to about 20 wt. % polyborate salt, alternatively from about 5 wt. % polyborate salt to about 15 wt. % polyborate salt, alternatively from about 10 wt. % polyborate salt to about 20 wt. % polyborate salt, alternatively from about 15 wt. % polyborate salt to about 20.0 wt. % polyborate salt, alternatively from about 10 wt. % polyborate salt to about 15.0 wt. % polyborate salt, alternatively from about 15 wt. % polyborate salt to about 18.0 wt. % polyborate salt, and alternatively from about 12 wt. % polyborate salt to about 19 wt. % polyborate salt.

[0039] The combined aqueous solution can include a variety of chemical species, such as, water molecules, hydrogen ions, hydroxide ions, polymeric molecules (e.g., PEI), protonated polymeric molecules (e.g., protonated PEI), polycationic molecules (e.g., polycationic PEI), polyborate salt(s), or a combination thereof.

[0040] The pH of the first aqueous solution, the second aqueous solution and / or the combined aqueous solution can be adjusted. The pH can be adjusted by any suitable means, such as, by adding an acid or a base. For example, the second aqueous solution can have a pH of at least 8, alternatively the second aqueous solution can have a pH of about 8 to about 10. The first aqueous solution can havea pH of not more than 6, alternatively the first aqueous solution can have a pH of about 4 to about 6. The combined aqueous solution can have a pH of about 8 to about 10, alternatively the combined aqueous solution can have a pH of 9.

[0041] The methods for forming a flame-retardant coated substrate described herein can further include rinsing the coated substrate with water (e.g., deionized water). In addition, the methods for forming a flame-retardant coated substrate described herein can further include drying the coated substrate..

[0042] Additives can be added to the coating on the substrate through the first aqueous solution, the second aqueous solution, the combined aqueous solution, or a combination thereof. The additives can be used for a variety of purposes, such as, ultraviolet (UV) light protection or abrasion resistance. An additive for UV protection can include titanium dioxide. An additive for abrasion resistance can include crosslinkers, such as, bromoalkanes, aldehydes, carbodiimides, amine active esters, acrylates, epoxides, or a combination thereof. A suitable aldehyde can include glutaraldehyde. A suitable carbodiimide can include1-ethyl-3-(3- dimethylaminopropyl) carbodiimide (EDC). A suitable amine active ester can include a N-hydroxysuccinimide ester, an imidoester, or a combination thereof. A crosslinker can provide resistance to washing and increased durability to the flame-retardant coating.

[0043] The coating can be deposited on the substrate at any suitable temperature. The deposition of the combined aqueous solution can occur at a temperature from about ambient temperature (e.g., 25 °C) to about 100 °C. Thus, for example, the first aqueous solution, the second aqueous solution, and / or the combined aqueous solution can be at about ambient temperature to about 100 °C.

[0044] The first aqueous solution, the second aqueous solution, and / or the combined aqueous solution can be deposited on the substrate by any coating method. The coating method can include any suitable water-based or solution coating technology. Examples of suitable coating methods can include dip coating, bath coating, immersion spray coating, roll-to-roll coating, slot coating, spin coating, curtain coating, gravure coating, reverse roll coating, knife over roll (e.g., gap) coating, blade coating, curtain coating, metering (e.g., Meyer) rod coating, air knife coating, or a combination thereof. In some examples, the coating can be deposited by spraying of the first aqueous solution, the second aqueous solution, and / or the combined aqueous solution onto the substrate.

[0045] The first aqueous solution, the second aqueous solution, and / or the combined aqueous solution can be deposited on the substrate for any suitable period to produce the flame-retardant coating. The substrate can be exposed tothe combined aqueous solution from about 1 second to about 24 hours, alternatively from about 1 second to about 10 minutes, alternatively from about 10 seconds to about 10 minutes, alternatively from about 1 second to about 1 hour, and alternatively from about 30 seconds to about 10 minutes.

[0046] The coating method can include a single exposure (e.g., dip) of the substrate to the first aqueous solution, the second aqueous solution, and / or the combined aqueous solution or multiple exposures to the first aqueous solution, the second aqueous solution, and / or the combined aqueous solution. Without being limited by theory, the first aqueous solution, the second aqueous solution, and / or the combined aqueous solution can cover the internal walls of any pores present in the substrate without blocking the pores.

[0047] A typical roll-to-roll coater, used for any dip coating of fabrics, can be modified with a drying tunnel and enough baths to scale this coating method for engineered wood products. For example, bath coating can be used to coat a foam, by passing the foam through a bath and squeezing between rolls to remove excess liquid. Additionally, and alternatively, spray coating can be used to coat the substrate.

[0048] The coating method can include rinsing and / or drying the coated substrate after exposure to the buffer solution to, among other things, remove excess buffer solution from the surface of the coated substrate. Without being limited by theory, the polyelectrolyte complex formation can function as an adhesion mechanism to the substrate, allowing the adherence of the coating to the substrate.

[0049] The drying step to enable evaporation of the combined aqueous solution can be accomplished by any suitable method. For example, the drying can include air drying at room temperature, air drying at ambient temperature, forced air drying, heat drying in an oven, infrared drying, applying pressure to the coated substrate, or a combination thereof. The drying gas can include any gas suitable for removing all or a portion of liquid from the coated substrate. For example, the drying gas can include air, filtered air, nitrogen, or a combination thereof. The coated substrate can be dried by the drying gas for any suitable period to remove all or a portion of the liquid.

[0050] Heating the coated substrate can be accomplished by any suitable means to evaporate, e.g., the buffer solution. For example, heating the coated substrate can include applying a heat source to the coated substrate. Any suitable heat source can be applied. The evaporation of the buffer solution can be performed at a temperature of 25-150 °C. The evaporation of the buffer solution can be performed at a temperature from about 50 °C. to about 200 °C., alternatively fromabout 50 °C to about 100 °C, alternatively from about 100 °C to about 200 °C, alternatively from about 70 °C to about 200 °C, alternatively from about 70 °C to about 100 °C, alternatively from about 25 °C to about 150 °C, and alternatively from about 50 °C. to about 70 °C

[0051] The evaporation of the buffer solution can be performed between about 10 seconds and about 2 hours, alternatively for about 24 hours, alternatively for about 5 seconds to about 20 minutes, alternatively from about 15 minutes to about 25 minutes, alternatively from about 10 seconds to 24 hours, alternatively from about 10 seconds to about 2 hours, alternatively from about 2 hours to 12 hours, alternatively from about 2 hours to 4 hours, and alternatively from about 5 seconds to about 500 seconds.

[0052] The substrate can have a varying thickness of the flame-retardant coating. For example, the coating can be between about 10 nanometers and about 100 microns thick, alternatively between about 10 nanometers and about 100 nanometers, alternatively between about 100 nanometers and about 1 micron, alternatively between about 1 micron and about 5 microns, alternatively between about 5 microns and about 10 microns, alternatively between about 10 microns and about 100 microns, alternatively between about 10 nanometers and about 1 micron, alternatively between about 100 nanometers and about 1 micron, alternatively between about 100 nanometers and about 10 microns, and alternatively between about 1 micron and about 100 microns.

[0053] As described herein, the weight gain (wt. %) of the substrate refers to the final weight of the substrate after drying as a percent of the weight of the uncoated substrate. For example, the coated substrate has between about 1.0 % and about 5 %, alternatively between about 1.0 % and about 3 %, alternatively between about 2 % and about 5 %, and alternatively between about 2 % and about 4 % of the weight gain.

[0054] The flame-retardant coating can be optically transparent or partially optically transparent. Optical transparency refers to the property of a material that allows light to pass through without significant absorption or scattering, enabling clear visibility of objects on the other side. The flame-retardant coating can impart additional optical properties to the substrate. The flame-retardant coating can be formulated to enhance or modify the optical characteristics of the underlying substrate. For example, the flame-retardant coating can be designed to increase light transmission, reduce glare, or alter the refractive index of the substrate. The flame-retardant coating can be engineered to provide specific color effects or UV protection to the substrate.

[0055] The coating method can result in a coated substrate that can pass the ASTM D6413 vertical flame test with a char length less than or equal to 4 inches, no after flame after 2 seconds, and no melting or dripping of the substrate.

[0056] The coating method can result in a coated substrate that can achieves a Class 1 or a Class 2 rating when tested according to NFPA 701 (Standard Methods of Fire Tests for Flame Propagation of Textiles and Films), with a char length less than 6.5 inches, an after flame time for less than 2 seconds, and the substrate has no flaming residue.

[0057] The coating method can result in a coated substrate that can pass the FMVSS 302 standard (Federal Motor Vehicle Safety Standard for flammability of interior materials), with a burn rate of less than 4 inches per minute and selfextinguishes in less than 60 seconds.

[0058] The coating method can result in a coated substrate that can pass the BS 5852 standard (British Standard for assessment of the ignitability of upholstered seating by smoldering and flaming ignition sources), with the substrate passing the smoldering cigarette test and the match flame equivalent test.

[0059] The coating method can result in a coated substrate that can achieve a pass rating when subject to the small open flame test as described in 16 CFR Part 1610 (Standard for the Flammability of Clothing Textiles), with an average burn time of less than 3.5 seconds.

[0060] The coating method can result in a coated substrate that can achieve an afterburn of less than 120 seconds (e.g., less than 100 second, less than 90 seconds, less than 60 seconds, less than 40 seconds; between 40 seconds and 120 seconds, between 60 seconds to about 120 seconds, between 40 seconds and 100 seconds or between 80 seconds and 120 seconds) and / or has a percent residue of at least 60% (e.g., at least 70%, at least 80%, at least 90%, at least 95%; between 60% and 95%, between 70% to 90%, between 75% to 90% or between 60% and 80%) in a torch test.

[0061] The coating method can result in a coated substrate having a weight gain of less than 6% (e.g., less than 5%, less than 4%, less than 3%, less than 2%; between 1 % and 6%, between 2% and 4%, between 3% and 5% or between 1 % to 5%) when compared to a weight of the substrate before coating.

[0062] The coating method can result in a coated substrate having a flexular modulus and / or flexular strength that is substantially the same as the substrate before coating. For example, the coating method can result in a coated substrate having a flexular modulus and / or flexular strength that changes less than 5%, less than 4%, less than 3%, less than 2%, less than 1%; between 0.1% to 2%, between0.1 % to 1%, between 0.1% to 0.5% or between 0.1 % and 0.3% relative to flexular modulus and / or flexular strength of the substrate before coating.

[0063] The coating method can result in a coated substrate having fire reaction parameters including a heat release rate (HRR), total heat release (THR), peak of heat release rate (pkHRR), total smoke release (TSR), and / or time to ignition (TTI) determined from cone calorimetry. Thus, for example, the coating method can result in a coated substrate (e.g., an engineered wood product such as OSB) having a total heat release (THR) that is decreased by at least 10% (e.g., by at least 15%, at least 20%, at least 30%, at least 40%, at least 50% or more; 10% to 50%, 15% to 40%, 10% to 40%, 30% to 60% or 25% to 50%) relative to uncoated substrate; a peak of heat release rate (pkHRR) that is decreased by at least 10% (e.g., by at least 15%, at least 20%, at least 30%, at least 40%, at least 50% or more; 10% to 50%, 15% to 40%, 10% to 40%, 30% to 60% or 25% to 50%) relative to uncoated substrate; a total smoke release (TSR) that is decreased by at least 50% (e.g., at least 60%, at least 70%, at least 80%, at least 90%, at least 95% or more; 50% to 80%, 50% to 75%, 65% to 90%, or 60% to 95%) relative to uncoated substrate; and / or a time to ignition (TTI) that is increased by at least 15% (e.g., by at least 20%, at least 30%, at least 40%, at least 50% or more; 15% to 50%, 15% to 40%, 10% to 40%, 30% to 60% or 25% to 50%) relative to uncoated substrate.

[0064] Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range were explicitly recited. For example, a range of “about 0.1 % to about 5%” or “about 0.1 % to 5%” should be interpreted to include not just about 0.1% to about 5%, but also the individual values (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1% to 0.5%, 1.1 % to 2.2%, 3.3% to 4.4%) within the indicated range. The statement “about X to Y” has the same meaning as “about X to about Y,” unless indicated otherwise. Likewise, the statement “about X, Y, or about Z” has the same meaning as “about X, about Y, or about Z,” unless indicated otherwise.

[0065] In this document, the terms “a,” “an,” or “the” are used to include one or more than one unless the context clearly dictates otherwise. The term “or” is used to refer to a nonexclusive “or” unless otherwise indicated. In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting. Further, information that is relevant to a section headingcan occur within or outside of that particular section. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

[0066] In the methods described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed step of doing X and a claimed step of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

[0067] The term “about” as used herein can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1% of a stated value or of a stated limit of a range.

[0068] The term “substantially” as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

[0069] The term “substantially no” as used herein refers to less than about 30%, 25%, 20%, 15%, 10%, 5%, 3%, 2%, 1%, 0.5%, 0.1 %, 0.05%, 0.001 %, or at less than about 0.0005% or less or about 0% or 0%.

[0070] Those skilled in the art will appreciate that many modifications to the embodiments described herein are possible without departing from the spirit and scope of the present disclosure. Thus, the description is not intended and should not be construed to be limited to the examples given but should be granted the full breadth of protection afforded by the appended claims and equivalents thereto. In addition, it is possible to use some of the features of the present disclosure without the corresponding use of other features. Accordingly, the foregoing description of or illustrative embodiments is provided for the purpose of illustrating the principles of the present disclosure and not in limitation thereof and can include modification thereto and permutations thereof.

[0071] The disclosure relates to, among other things, the following enumerated Embodiments, which listing does not represent an order of importance:

[0072] 1 . A method for forming a flame-retardant coated substrate, the method comprising:

[0073] preparing a first aqueous solution, comprising a polymeric, polycationic material;

[0074] preparing a second aqueous solution, comprising a polyborate salt;

[0075] combining the first aqueous solution and the second aqueous solution to form a combined aqueous solution;

[0076] exposing a substrate to the combined aqueous solution to give a treated substrate; and

[0077] exposing the treated substrate to a buffer solution to produce a flameretardant coated substrate,

[0078] wherein a coating on the flame-retardant coated substrate comprises a polyelectrolyte complex formed between the polymeric, polycationic material and the polyborate salt.

[0079] 2. A method for forming a flame-retardant coated substrate, the method comprising:

[0080] exposing a substrate to a combined aqueous solution of a first aqueous solution comprising polymeric, polycationic material, and a second aqueous solution comprising polyborate salt to give a treated substrate; and

[0081] exposing the treated substrate to a buffer solution to produce a flameretardant coated substrate;

[0082] wherein a coating on the flame-retardant coated substrate comprises a polyelectrolyte complex formed between the polymeric, polycationic material and the polyborate salt.

[0083] 3. The method of Embodiment 1 or 2, wherein the combined aqueous solution further comprises a phosphate-containing molecule.

[0084] 4. The method of Embodiment 3, wherein the phosphate-containing molecules comprise ammonium polyphosphate, sodium hexametaphosphate, polysodium phosphate, melamine polyphosphate or combinations thereof.

[0085] 5. The method of Embodiment 1 or 2 further comprising rinsing the coated substrate with water.

[0086] 6. The method of Embodiment 1 , 2 or 3 further comprising drying the coated substrate.

[0087] 7. The method of Embodiment 1 or 2, wherein the polyborate salt comprises sodium polyborate, ammonium polyborate, disodium octaborate tetrahydrate, ammonium pentaborate, sodium pentaborate decahydrate, dicalcium hexaborates, sodium-calcium pentaborates or combinations thereof.

[0088] 8. The method of Embodiment 1 or 2, wherein the pH of the buffer is from about 2 to about 5.

[0089] 9. The method of any one of Embodiments 1 to 8, wherein the buffer comprises citric acid.

[0090] 10. The method of Embodiment 1, wherein the first aqueous solution comprises from about 1.0 wt. % polymeric, polycationic material to about 50.0 wt. % polymeric, polycationic material.

[0091] 11. The method of Embodiment 1, wherein the second aqueous solution comprises from about 1.0 wt. % polyborate salt to about 50.0 wt. % polyborate salt.

[0092] 12. The method of any one of Embodiments 1 to 11 , wherein the combined aqueous solution comprises from about 1.0 wt. % polymeric, polycationic material to about 50 wt. % polymeric, polycationic material.

[0093] 13. The method of any one of Embodiments 1 to 12, wherein the combined aqueous solution comprises from about 1.0 wt. % polyborate salt to about 50.0 wt. % polyborate salt.

[0094] 14. The method of any one of Embodiments 1 to 13, wherein the coating is between about 10 nanometers and about 100 microns thick.

[0095] 15. The method of any one of Embodiments 1 to 14, wherein the substrate comprises an engineered wood product.

[0096] 16. The method of Embodiment 15, wherein the engineered wood product comprises oriented standard board.

[0097] 17. The method of any one of Embodiments 1 to 16, wherein the polymeric, polycationic material comprises a colloidal particle, a nanoparticle, a nitrogen-rich polymer, or a combination thereof.

[0098] 18. The method of any one of Embodiments 1 to 17, wherein the polymeric, polycationic material comprises polyethylenimine (PEI), branched polyethylenimine (BPEI), linear polyethylenimine, polyallylamine, polyvinylamine,, cationic polyacrylamide, cationic poly diallyldimethylammonium-chloride (PDDA), poly(melamine-co-formaldehyde), polymelamine, a copolymer of polymelamine, polyvinylpyridine, a copolymer of polyvinylpyridine, or a combination thereof

[0099] 19. The method of any one of Embodiments 1 to 18, wherein the polyborate salt comprises a boronic acid, a boron containing acid, or a combination thereof.

[0100] 20. The method of any one of Embodiments 1 to 19, wherein the polyborate salt comprises sodium polyborate.

[0101] 21. The method of any one of Embodiments 1 to 20, wherein the first aqueous solution has a pH of not more than 6.

[0102] 22. The method of Embodiment 21 , wherein the first aqueous solution has a pH of about 4 to about 6.

[0103] 23. The method of any one of Embodiments 1 to 22, wherein the flame-retardant coated substrate exhibits an afterburn of less than 120 seconds and / or has a percent residue of at least 60% in a torch test.

[0104] 24. The method of any one of Embodiments 1 to 23, wherein the flame-retardant coated substrate has a weight gain of less than 6% when compared to a weight of the substrate before coating.

[0105] 25. The method of any one of Embodiments 1 to 23, wherein the flame-retardant coated substrate has a flexular modulus and / or flexular strength that is substantially the same as the substrate before coating.

[0106] 26. The method of any one of Embodiments 1 to 25, wherein the flame-retardant coated substrate has a total heat release (THR) that is decreased by at least 10% relative to uncoated substrate.

[0107] 27. The method of any one of Embodiments 1 to 26, wherein the flame-retardant coated substrate has a peak of heat release rate (pkHRR) that is decreased by at least 10% relative to uncoated substrate.

[0108] 28. The method of any one of Embodiments 1 to 27, wherein the flame-retardant coated substrate has a total smoke release (TSR) that is decreased by at least 50% relative to uncoated substrate,

[0109] 29. The method of any one of Embodiments 1 to 28, wherein the flame-retardant coated substrate has a time to ignition (TTI) that is increased by at least 15% relative to uncoated substrate.

[0110] 30. An article comprising a flame-retardant coated substrate made by the method of any one of Embodiments 1 to 29.Examples

[0111] The disclosure can be better understood by reference to the following examples which are offered by way of illustration. The disclosure is not limited to the examples given herein.Materials

[0112] Branched polyethylenimine (PEI, Mw= 25 000 g / mol), boric acid (H3BO3, 99.5 %), sodium tetraborate decahydrate (Na2B4Oy10 H2O, Borax, 99.5 %), citric acid monohydrate (CA, reagent grade, 98 %), and sodium hydroxide (NaOH, ACS reagent, 97 %) were purchased from Sigma-Aldrich (Milwaukee, Wl). Oriented strand board (OSB, 7 / 16), made of wood strands with phenolformaldehyde and polyurea / polyurethane resin, was purchased at Home Depot (College Station, TX, USA) and cut into 2 x 4 in and 4 x 4 in pieces. These OSBcoupons were soaked in a stirring 18 MQ deionized (DI) water bath for 72 h and then dried and stored in a 70 °C oven.Preparation of PEI / SPB polyelectrolyte complex solution

[0113] The sodium polyborate (SPB) solution was prepared by dissolving 20 g of boric acid and 25 g of borax in 100 g DI water at 75 °C as described in Inorganic Chemistry Communications 10 20-22 (2007), which is incorporated by reference as if fully set forth herein. Aqueous solutions of 18 wt. % SPB and 2 wt. % PEI were prepared separately and allowed to remain at their natural pH. The PEC solution was prepared by mixing equivalent masses of 2 wt. % PEI and 18 wt. % SPB solutions and was used immediately after mixing. This mixture results in a stable and transparent solution. A 100 mM CA solution was prepared and adjusted to pH 3 by adding 5 M NaOH dropwise. All solutions were prepared with 18 MQ deionized (DI) water.Polyelectrolyte complex deposition

[0114] Prior to coating deposition, dried OSB pieces were immersed in a DI water bath for at least 12 h to hydrate cell walls. OSB samples were then immersed into the stirring PEC solution for a given length of time, referred to as the “dip time”. The deposited coating on the substrate was then cured by immersion into the stirring CA buffer solution for a given length of time, referred to as “cure time.” Next, the samples were immersed in stirring DI water for 1 h and then dried at 70 °C for 24 h before testing. The overall coating process and components used are shown in FIG. 1 .Characterization

[0115] Flame tests were performed with a homebuilt torch testing setup in a fume hood. OSB coupons (2 x 4 in) were held vertically and subjected to a butane torch flame (Bernzomatic precision torch ST2200T; Worthington Industries, Columbus, OH). The torch was aligned with the center of the samples and the torch nozzle was positioned 0.8 in away from them. The inner blue flame of the torch was approximately 0.8 in long. The OSB pieces were exposed to the butane torch flame for 4.5 min. After the flame was removed, the samples were allowed to burn until either the coating self-extinguished the flame or the fire burned itself out (i.e. , the afterburn time). Subsequently, the burned samples were allowed to cool down and then they were weighed to collect the remaining residue. Cone calorimetry was conducted to measure the flammability of the samples, in compliance with ASTM E-1354-12. Samples (4 x 4 x 0.5 in3), tested in triplicate, were placed in an aluminum foil pan and subjected to a heat flux of 35 kW m-2. Thermogravimetric analysis (TGA) was performed with a Q50 thermogravimetricanalyzer (TA Instruments, New Castle, DE) under air and nitrogen atmospheres. Samples (3-6 mg) were held at 100 °C for 20 min to remove residual water and then heated at a rate of 10 °C / min to 705 °C. Differential scanning calorimetry (DSC) was performed using a TA Instruments DSC Q20 (New Castle, DE) at a heating rate of 5 °C min-1, from 50 to 400 °C, under a nitrogen atmosphere. TGA coupled with mass spectrometry (TGA-MS) was carried out under an air atmosphere for uncoated and coated samples using a TA Instrument 5500 Thermogravimetric Analyzer with a Discover Mass Spectrometer (New Castle, DE). Samples were held at 100 °C for 20 min to remove residual atmospheric water and then heated at a ramp of 10 °C min'1to 705 °C. Gaseous products were detected from 10-200 amu. The surface morphologies of the uncoated and coated OSB samples were observed by sputter coating the samples with 5 nm of gold prior to imaging using a field emission scanning electron microscope (SEM) (TESCAN, Brno, Czechia). Fourier transform infrared spectroscopy (FTIR) was used to characterize uncoated and coated substrates using an attenuated total reflectance (ATR) fixture (Frontier Perkin-Elmer Inc. Shelton, CT). X-ray photoelectron spectroscopy (XPS) was performed using an Omicron XPS / UPS (Denver, CO), with a DAR 400 Mg / AI X-ray source and a 0.8 eV energy resolution detector. The mechanical properties of the OSB samples were measured with an MTS Insight Electromechanical Testing System (MTS Systems Corporation, Eden Prairie, MN, USA), utilizing a 30 kN load cell. The samples (5.1 x 10 x 1.3 cm3) were tested in a three-point bending arrangement, with a spacing of 5.1 cm between the lower points.Results and discussionPolyelectrolyte complex coating deposition and composition

[0116] The length of time the OSB is immersed in the PEC solution (dip time) and in the CA buffer (cure time) was evaluated to determine the optimal coating procedure. The variation in dip time was tested at a fixed cure time (10 min), while the cure time was investigated at a fixed dip time (60 min). As summarized in Table 1 , the coat weight is proportional to both the dip time and cure time. Due to the heterogeneous nature of OSB’s surface, the diffusion time of the coating tends to be slower compared to the time required to deposit similar coatings on other substrates (e.g., textile, paper, and foam). With short immersion times, only a small proportion of polyelectrolyte is diffused into the OSB, resulting in low weight gain. Alternatively, longer immersion times in both the PEC solution and CA buffer lead to higher weight gain.Table 1 Weight gain and torch test performance for OSB samples.PEC dip, Weight Afterburn Residue cure gain (%) (s) (%) time (min)Uncoated - 165 ± 19 23 ± 61. 10 1.0 ± 0.3 113 ± 24 62 ± 1110. 10 3.2 ± 0.8 49 ± 8 71 ± 260. 10 5.8 ± 0.6 6 ± 4 93 ± 360, 1 2.5 ± 0.6 29 ± 16 80 ± 460, 5 3.0 ± 0.2 20 ± 11 87 ± 7

[0117] The extent of the PEC diffusion into the OSB during the dipping and cure step was further investigated via TGA. Longer dip and cure times result in a greater char yield in both the external and internal strands. The fact that the decomposition pathway is changed in both external and internal locations suggests the polyelectrolytes are diffusing entirely through the OSB. SEM images reveal that uncoated OSB exhibits a highly porous and rough surface, as shown in FIGS. 2A and 2B. This can be attributed to the heterogeneous nature of the wood strand surface and the presence of the resin. After PEC deposition, the surface of OSB appears to be smoother, but its porosity and roughness are still maintained, indicating the coating deposits conformally to the substrate (FIGS. 2C and 2D).

[0118] The surface composition of uncoated and coated OSB samples was characterized using ATR-FTIR spectroscopy (FIG. 3A). Uncoated OSB exhibits a broad band at 3301 cm-1, representing cellulose's hydroxyl groups, along with absorptions at 2916, 1665, and 1020 cm-1, indicative of C-H stretching, O-H bending, and C-O-C asymmetrical stretching, respectively. Additionally, it displays absorptions characteristic of the phenol-formaldehyde and polyurea / polyurethane resin components at 1684, 1602, and 1263 cm-1, corresponding to C=O stretching, C=C stretching, and C-N stretching, respectively. While the spectrum of the OSB treated with PEI / SPB shows a reduction in the intensity of these bands, the distinctive peaks of PEI and SPB cannot be distinguished in the IR spectra due to signal overlap with cellulose. To further confirm the deposition of the PEC coating on OSB, XPS was carried out, as shown in FIGS. 3B and 3C. XPS reveals the presence of boron (from SPB deposition) and a decrease in the C / N ratio on the coated sample, indicating a greater nitrogen content through PEI deposition. This confirms that the coating components effectively interacted with the OSB, demonstrating successful deposition onto the substrate.Mechanical and Thermal behavior

[0119] The influence of the PEC treatment on the mechanical properties of OSB was tested in three-point bending. Table 2 shows the flexural modulus and flexural strength of both uncoated and (60,10)-coated OSB. The mechanical strength of both uncoated and coated substrates reveals that the PEC treatment has no significant impact. The thermal degradation and decomposition process for both uncoated and coated OSB was monitored using TGA under air and nitrogen atmospheres. FIG. 4A shows TGA curves, illustrating the distinct stages of mass loss in air. The first stage (210-360 °C) involves decomposition of the OSB’s resin followed by dehydration and decomposition reactions of cellulose, hemicellulose, and lignin, which produce nonflammable gases, aliphatic carbon, and levoglucosan. The second stage, around 400 °C, is attributed to the generation of H2O, CH4, CO, and CO2 as a result of oxidation of aromatic char.Table 2 Mechanical behavior of OSB samples obtained from three-point bend testing.Flexural FlexuralSample Modulus Strength

[0120] The thermograms demonstrate that the OSB decomposition pathway is changed by the deposition of the PEI / SPB coating. The presence of the coating slightly lowers the initial degradation temperature of OSB from 277 to 260 °C. This earlier onset of degradation can be attributed to the initial decomposition of SPB into boric acid around 215 °C, promoting the dehydration of cellulose and forming highly crosslinked char by cyclization and condensation reactions. The char layer produced from these reactions suppresses combustion and slows mass loss, protecting the underlying material from further decomposition. While the uncoated OSB completely degrades, the coated OSB yields a residue of approximately 11 wt. % (at 700 °C), suggesting condensed phase action.

[0121] This degradation event is also apparent in the derivative curves, indicating a roughly 63 % reduction in the mass loss rate compared to uncoated OSB. This reduction demonstrates that the coating decelerates OSB’s degradation, resulting in a reduced volatile contribution to fire propagation. This is supported by TGA-MS. No characteristic peaks of boron species were detected during TGA-MS, suggesting that the decomposition products of SPB remains inthe char. TGA curves for uncoated and coated OSB under nitrogen atmosphere reveal a single degradation step attributed to the depolymerization of cellulose and the OSB’s resin into volatile gases and char. Under pyrolysis conditions, the coated OSB leaves behind a greater residue (35 %) once the temperature reaches 700 °C.

[0122] The role of the condensed phase action and PEC coating degradation during pyrolysis was investigated with differential scanning calorimetry, as shown in FIG. 4B. The differential thermogram of uncoated OSB shows an endotherm at 258 °C indicating the heat absorption associated with the simultaneous thermal decomposition of the resin and depolymerization of cellulosic components into levoglucosan and volatile pyrolysis gases, followed by an exotherm at 336 °C, which represents the formation of tar and char. The incorporation of the PEC treatment results in shifting of these peaks to lower temperatures. Specifically, the new endotherm at 140 °C, and the early appearance of the endothermic event around 200 °C, is most likely due to desorption of water from SPB, followed by its degradation. The subsequent early exothermic event at 325 °C can be attributed to the complete decomposition of the PEI / SPB coating, during which boric acid catalyzes the dehydration of cellulose, leading to the formation of a more stable and conjugated system (e.g., aromatic char), without producing aliphatic carbon and combustible gases. The coated OSB results in an increase in the absolute energy balance, imparting a heat sink effect by cooling the substrate’s surface with the endothermic decomposition of SPB and the release of noncombustible gases from PEI.Flammability behavior

[0123] Flammability behavior of the OSB samples was evaluated by performing a homebuilt butane torch test where uncoated and coated substrates were exposed to a direct flame for 4.5 min. FIG. 5 shows images of uncoated and PEI / SPB (60,10)-coated OSB before and after flame testing, with the flame test results summarized in Table 1. Upon exposure to the flame, uncoated OSB (FIG. 5C) immediately ignites, and it continues to burn for an extended amount of time after the flame is removed (165 s), leaving little residue behind (23 %). In contrast, the PEI / SPB treatment alters the burning behavior of OSB by decreasing the afterburn time and increasing the sample residue. It should be noted that the flame performance of the coated OSB is directly proportional to the weight gain. The higher the weight gain, the shorter the afterburn times, and the higher the overall residue. Specifically, the OSB immersed into the PEC solution for 60 min and buffer cured for 10 min (60,10) performs the best, self-extinguishing in ~6 s after the flame is removed and yielding more than 90 % residue. SEM images of thechar residues for uncoated and PEI / SPB (60,10)-coated OSB are shown in FIGS. 5F-I. After ignition, the microstructure of the uncoated OSB char residue appears to be disrupted and destroyed, whereas the coated one is preserved, exhibiting a smoother surface with visible microbubbles and aggregates on top of the sample’s surface. The latter is indicative of a combination of micro-intumescence by the release of non-flammable gases from PEI (blowing agent) and glassy char formation by the decomposition products of SPB (e.g., boron trioxide).

[0124] Cone calorimetry was carried out to quantify the flammability of the uncoated and PEI / SPB-treated OSB. This standardized test can quantitatively explain the combustion process of materials in a well-defined fire scenario, through the use of oxygen consumption calorimetry. Fire reaction parameters such as heat release rate (HRR), total heat release (THR), peak of heat release rate (pkHRR), total smoke release (TSR), time to ignition (TTI), and the char yield are measured during testing. Representative heat release rate (HRR) curves for uncoated and coated OSB are displayed in FIG. 6, with results summarized in Table 3. The heat release curves for OSB samples exhibit a bimodal HRR peak, which is characteristic of a thermally thick charring material like wood. Both of these peaks are reduced by the presence of the coating. The PEI / SPB treatment provides fire protection to OSB by increasing the TTI by 19 % and decreasing both the pkHRR and THR by 18 % and 21 %, respectively. Interestingly, the PEC coating also significantly reduces the TSR (-79 %) and increases the char yield of OSB by 35 %, indicating that the char formed acts as a volatile barrier and inhibits heat and mass transfer.Table 3. Cone calorimetry data for OSB samples.Char analysis

[0125] Further insight into the condensed phase action and char composition was gained using XPS and ATR-FTIR spectroscopy. FIGS. 7B and 7C and Table S1 show the corresponding XPS spectra, XPS-derived atom percentages, and atomic ratios for both uncoated and coated OSB samples, along with their respective char residues. Upon exposure to the flame, the coated sampleexhibits an increase in the C / 0, B / N, and C / N ratios and a decrease in the C / B ratio. This observation indicates that the decomposition of cellulose releases water, carbon monoxide, and carbon dioxide, while PEI degrades mostly into nonflammable gas (e.g., N2and NH3). Additionally, there is an increase in the boron content after ignition, suggesting the presence of SPB degradation products, such as B2O3, within the char structure.

[0126] ATR-FTIR spectra of the char residues were obtained for both uncoated and coated samples. As shown in FIG. 7A, the char residues exhibit strong and broad bands from 3610 to 2365 cm-1, along with an absorption at 1710 cm-1. These bands are indicative of O-H stretching (3318 cm-1), C-H stretching (2912 cm-1), and C=O stretching (1710 cm-1), revealing the presence of carboxylic acid groups. Aromatic 0=0 stretching at 1580 cm-1and C-0 stretching around 1100 cm-1are also observed. Overtones and combination bands of aromatic compounds appears between 2134 and 1857 cm-1(Friedel and Carlson 1971). In general, the intensity of all these absorption bands increases in the coated sample, demonstrating an improvement in the formation of more a conjugated and stable system with heteroaromatic compounds. Moreover, the presence of new peaks at 1430, 1220, and 870 cm-1in the coated substrate can be attributed to the B-O-C stretching vibrations, which is further evidence of formation of borate ester groups bound to the aromatic char.Conclusions

[0127] A boron-nitrogen polyelectrolyte complex treatment was shown to reduce the flammability of OSB for the first time. The PEI / SPB coating was deposited in a simple two-step process, adding minimal weight and preserving both the visual aesthetics and mechanical properties of OSB. Coated samples achieved self-extinguishing behavior during a direct flame test, yielding more than 90 % residue. Cone calorimetry revealed that the treatment reduces the pkHRR and THR, while also significantly decreasing total smoke release. These results, along with char analysis, suggest that the FR action mostly occurs in the condensed phase through a combination of intumescence and thermal barrier mechanisms. The performance of this simple two-step coating creates an opportunity to produce safer wood products and extend their use into more building and architectural applications.

Claims

What is claimed is:

1. A method for forming a flame-retardant coated substrate, the method comprising: preparing a first aqueous solution, comprising a polymeric, polycationic material; preparing a second aqueous solution, comprising a polyborate salt; combining the first aqueous solution and the second aqueous solution to form a combined aqueous solution; exposing a substrate to the combined aqueous solution to give a treated substrate; and exposing the treated substrate to a buffer solution to produce a flameretardant coated substrate, wherein a coating on the flame-retardant coated substrate comprises a polyelectrolyte complex formed between the polymeric, polycationic material and the polyborate salt.

2. A method for forming a flame-retardant coated substrate, the method comprising: exposing a substrate to a combined aqueous solution of a first aqueous solution comprising polymeric, polycationic material, and a second aqueous solution comprising polyborate salt to give a treated substrate; and exposing the treated substrate to a buffer solution to produce a flameretardant coated substrate; wherein a coating on the flame-retardant coated substrate comprises a polyelectrolyte complex formed between the polymeric, polycationic material and the polyborate salt.

3. The method of claim 1 or 2, wherein the combined aqueous solution further comprises a phosphate-containing molecule.

4. The method of claim 3, wherein the phosphate-containing molecules comprise ammonium polyphosphate, sodium hexametaphosphate, polysodium phosphate, melamine polyphosphate or combinations thereof.

5. The method of claim 1 or 2 further comprising rinsing the coated substrate with water.

6. The method of claim 1 or 2 further comprising drying the coated substrate.

7. The method of claim 1 or 2, wherein the polyborate salt comprises sodium polyborate, ammonium polyborate, disodium octaborate tetrahydrate, ammonium pentaborate, sodium pentaborate decahydrate, dicalcium hexaborates, sodiumcalcium pentaborates or combinations thereof.

8. The method of claim 1 or 2, wherein the pH of the buffer is from about 2 to about 5.

9. The method of claim 1 or 2, wherein the buffer comprises citric acid.

10. The method of claim 1 or 2, wherein the first aqueous solution comprises from about 1.0 wt. % polymeric, polycationic material to about 50.0 wt. % polymeric, polycationic material.

11. The method of claim 1 or 2, wherein the second aqueous solution comprises from about 1.0 wt. % polyborate salt to about 50.0 wt. % polyborate salt.

12. The method of claim 1 or 2, wherein the combined aqueous solution comprises from about 1.0 wt. % polymeric, polycationic material to about 50 wt. % polymeric, polycationic material.

13. The method of claim 1 or 2, wherein the combined aqueous solution comprises from about 1.0 wt. % polyborate salt to about 50.0 wt. % polyborate salt.

14. The method of claim 1 or 2, wherein the coating is between about 10 nanometers and about 100 microns thick.

15. The method of claim 1 or 2, wherein the substrate comprises an engineered wood product.

16. The method of claim 15, wherein the engineered wood product comprises oriented standard board.

17. The method of claim 1 or 2, wherein the polymeric, polycationic material comprises a colloidal particle, a nanoparticle, a nitrogen-rich polymer, or a combination thereof.

18. The method of claim 1 or 2, wherein the polymeric, polycationic material comprises polyethylenimine (PEI), branched polyethylenimine (BPEI), linear polyethylenimine, polyallylamine, polyvinylaminexcationic polyacrylamide,cationic poly diallyldimethylammonium-chloride (PDDA), poly(melamine-co- formaldehyde), polymelamine, a copolymer of polymelamine, polyvinylpyridine, a copolymer of polyvinylpyridine, or a combination thereof19. The method of claim 1 or 2, wherein the polyborate salt comprises a boronic acid, a boron containing acid, or a combination thereof.

20. The method of claim 1 or 2, wherein the polyborate salt comprises sodium polyborate.21 . The method of claim 1 or 2, wherein the first aqueous solution has a pH of not more than 6.

22. The method of claim 21 , wherein the first aqueous solution has a pH of about 4 to about 6.

23. The method of claim 1 or 2, wherein the flame-retardant coated substrate exhibits an afterburn of less than 120 seconds and / or has a percent residue of at least 60% in a torch test.

24. The method of claim 1 or 2, wherein the flame-retardant coated substrate has a weight gain of less than 6% when compared to a weight of the substrate before coating.

25. The method of claim 1 or 2, wherein the flame-retardant coated substrate has a flexular modulus and / or flexular strength that is substantially the same as the substrate before coating.

26. The method of claim 1 or 2, wherein the flame-retardant coated substrate has a total heat release (THR) that is decreased by at least 10% relative to uncoated substrate.

27. The method of claim 1 or 2, wherein the flame-retardant coated substrate has a peak of heat release rate (pkHRR) that is decreased by at least 10% relative to uncoated substrate.

28. The method of claim 1 or 2, wherein the flame-retardant coated substrate has a total smoke release (TSR) that is decreased by at least 50% relative to uncoated substrate,29. The method of claim 1 or 2, wherein the flame-retardant coated substrate has a time to ignition (TTI) that is increased by at least 15% relative to uncoated substrate.

30. An article comprising a flame-retardant coated substrate made by the method of claim 1 or 2.

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