WO2016186645A1

WO2016186645A1 - Fire-resistant cellulose material

Info

Publication number: WO2016186645A1
Application number: PCT/US2015/031410
Authority: WO
Inventors: Thomas C. Shutt
Original assignee: Nature Tech Llc
Priority date: 2015-05-18
Filing date: 2015-05-18
Publication date: 2016-11-24

Abstract

A fire-resistant cellulose material composed of a liquid acid fire-retardant chemical composition or salt derived therefrom, and methods of producing the cellulose material are disclosed.

Description

FIRE-RESISTANT CELLULOSE MATERIAL

FIELD OF THE INVENTION

[0001] Embodiments of the invention relate to fire-resistant cellulose products produced by applying a liquid acid fire retardant composition comprising an aqueous solution of one or more inorganic acids as the sole fire retardant component or, in embodiments, in combination with the application of a minor amount of powdered flame retardant, and methods of producing cellulose insulation and other products.

BACKGROUND OF THE INVENTION

[0002] Cellulose is the framework (skeleton) for all plant fibers. After harvesting, retting and drying, the cellulose fibers from trees and plants such as cotton, flax, hemp, kenaf and jute, among others, are used to manufacture paper, insulation, building products, containers and many other items. Many of these products benefit from and/or have higher value by being fire retarded. With some products it is mandatory that they are fire retarded. Examples of mandated fire retarded products include numerous building materials such as but not limited to cellulose insulation, fire doors and certain types of cellulose-based board materials (e.g., panels), as well as automobile fabrics, furniture, etc.

[0003] Burning or combustion of cellulose fiber materials such as paper, cardboard, etc., generally involves two different chemical processes: a) flaming, which results from ignition of gases released by the pyrolysis of the cellulose fiber, and b) smolder, a slow, high temperature, flameless combustion which results from the oxidation of the remaining carbon-rich material, as with charcoal in a barbeque. The basic difference between smoldering and flaming combustion is that smoldering combustion occurs on the surface of a solid rather than in the gas phase.

[0004] Cellulose insulation is flammable and prone to smoldering, and it is well known in the cellulose insulation industry that chemical additions to a paper source material will increase its resistance to burning. It is also known that some chemicals will extinguish flaming but not smoldering combustion. Examples of such chemicals include borax pentahydrate, hydrated magnesium sulfate and aluminum trihydrate, among others. It is further known that other chemicals can extinguish both flaming and smolder. Examples of these chemicals include ammonium sulfate, ammonium phosphate and boric acid.

[0005] Cellulose insulation is required to meet federal regulations and certain

government regulations have mandated that cellulose insulation should not support burning under normal environmental conditions. The test methods that assure this property are set forth in ASTM C-739. Testing for flaming is carried out using critical radiant flux (CRF) equipment. In that test, a "pass" is achieved if the cellulose material will not support surface flame while being subjected to radiation of 0.12 watts/cm² or greater. Smolder testing is performed using a smolder box. A loss in weight of less than 15% of the original cellulose weight constitutes a "pass." In Europe, various classifications are available ranging from Category A to Category F. Chemical loadings to allow cellulose to meet ASTM C-739 would also allow it to meet a Category B. To obtain a Category C listing lesser amounts of chemical are required than would be required to meet ASTM C-739.

[0006] In order to prevent flaming and smoldering combustion, most cellulose insulation is manufactured by applying fire retardant chemicals in powder form, such as hydrated borax, boric acid, ammonium sulfate, aluminum trihydrate (ATH), etc. In order to meet government standards for cellulose insulation, the loading of the powdered chemical is typically about 14 to 18 % by weight (wt%) of the final insulation product. However, those chemicals are relatively expensive and their inclusion significantly raises the costs associated with the manufacture of a cellulose insulation product. In addition, the powder material dusts the cellulose particle surface, with a large portion of the powder being present in the product as loose dust particles. There are growing concerns about potential adverse health effects associated with the use of and exposure to boric acid (borax, sodium borates), which, although providing fire retardant and insecticidal properties, is a respiratory irritant and has shown adverse reproductive effects in test animals.

[0007] By comparison, the application of a liquid form of the fire retardant chemical will penetrate the cellulose particles and requires a much lower loading of the fire retardant chemical, typically about 4 to 1 1 wt% of the final insulation product, which lowers raw material costs and results in appreciable cost savings. Liquid fire retardant compositions are described, for example, in USP 4,595,414 and USP 4,168,175 (Shutt). Examples of liquid fire retardant chemicals include aqueous solutions of ammonium sulfate, monoammonium phosphate, diammonium phosphate, ammonium tripolyphosphate, boric acid, ferrous sulfate, zinc sulfate, and mixtures thereof, dissolved in water. A disadvantage of currently known liquid fire retardant chemicals is that they can be corrosive or devolve ammonia through offgassing. In addition, as discussed above, exposure to boric acid (borax, sodium borates) has been linked to potential adverse health effects.

[0008] Accordingly, it would be desirable from an industry standpoint to provide a cellulose material that would overcome the foregoing disadvantages, and can be produced at a low cost with liquid chemical as the sole or, in embodiments, the principal flame retardant in combination with powdered chemical, and will possess the requisite level of fire retardance to meet government standards.

SUMMARY

[0009] The present invention provides a fire-resistant cellulose fiber material and cellulose products, and methods of production.

[0010] In embodiments, the cellulose material is produced by applying a liquid acid fire retardant composition comprising an aqueous solution of inorganic acid(s) as the sole flame retardant component. In embodiments, a minor amount of powdered flame retardant can be added to lower the amount of liquid component and thereby reduce drying cost and/or capital equipment cost.

[0011] The liquid acid fire-retardant composition is an aqueous solution that is applied to the cellulose fiber material to provide fire-resistance. In embodiments, the liquid acid fire-retardant composition is composed of an aqueous solution of one or more inorganic acids as the sole fire retardant chemical component. In embodiments, the liquid acid fire retardant composition comprises a fire retardant chemical component consisting of an aqueous solution of one or more inorganic acids. In embodiments, the inorganic acid is selected from the group consisting of sulfuric acid, phosphoric acid, and mixtures thereof. The liquid acid fire-retardant composition can further include optional non-fire retardant additives such as a surfactant. [0012] In an embodiment, the method comprises the steps of applying a liquid acid fire-retardant composition to a cellulose material to produce an acid fire retardant-soaked (i.e., moistened or wetted) cellulose material having the liquid acid fire retardant composition absorbed therein, the liquid acid fire retardant composition comprising a) a fire retardant chemical component consisting of one or more inorganic acids in an aqueous solution, and b) optionally, one or more additives; optionally, applying an aqueous solution of an alkali compound or aqueous slurry of an alkaline earth compound to the acid-treated cellulose material such that the cellulose material has a pH of at least 3.5, preferably pH 6 to 8; and reducing the cellulose material in size to produce the fire-resistant cellulose fiber material. In embodiments, the treated fire-resistant cellulose fiber material is composed of a salt adsorbed and/or adhered thereto, which is the reaction product of the liquid acid fire-retardant composition absorbed to the cellulose fibers with the alkali or alkaline earth compound. In embodiments, applying the liquid acid fire-retardant composition and the aqueous alkali solution or alkaline earth slurry is by spraying.

[0013] In embodiments, the invention is a fire-resistant cellulose fiber material comprising cellulosic fibers and a salt adsorbed and/or adhered thereto, the salt being derived through the reaction between a liquid acid fire-retardant composition absorbed to the cellulosic fibers and an aqueous solution of an alkali compound or slurry of an alkaline earth compound applied to the acid-treated fibers. In embodiments, the acid-derived salt is a sulfate or a phosphate. In embodiments, the fire-resistant cellulose fiber material comprises cellulosic fibers and an inorganic acid absorbed therein.

[0014] The cellulose fiber material produced according to the disclosure possesses the requisite level of fire retardance to meet government standards. In embodiments, the cellulose fiber material has a CRF value of 0.12 watts/cm or greater, as measured according to

ASTM C-739. In embodiments, a fire resistant cellulose insulation material has a settled bulk density of 1 to 2 lbs/ft³.

[0015] In an embodiment, the fire-resistant cellulose material (product) (e.g., insulation) comprises 94 to 85 wt% of cellulosic fibers, 4 to 1 1.8 wt% of the liquid acid fire-retardant chemical composition, 0 to 3 wt% of an alkali or alkaline earth compound, and 0 to 0.2 wt% surfactant, the amounts based on the total weight of the cellulose material, wherein the material has a pH of at least 3.5, and typically 6 to 8.

[0016] In embodiments, the cellulose fiber material comprises, based on the total weight of the cellulose fiber material, 94 to 85 wt% of cellulose fibers, 6 to 15 wt% of an acid derived salt, and 0 to 0.2 wt% surfactant. In embodiments, the acid derived salt is a sulfate or a phosphate. In embodiments, the cellulose fiber material is without the presence of an ammonium salt or ammonia residue therefrom. In embodiments, the cellulose material is without the presence of boric acid or salt thereof.

[0017] To attain a Category C listing in Europe, in an embodiment, the cellulose material comprises 98 to 92.8 wt% of cellulose fiber, 2 to 5 wt% of the liquid acid fire-retardant composition, 0 to 2 wt% of an alkali or alkaline earth compound and 0 to 0.2 wt% surfactant. The application of lower loadings of acid, alkali or alkaline earth and surfactant, in

embodiments, would require the addition of a powdered chemical, for example, in the amount of 2 to 10 wt%.

[0018] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as reaction conditions, and so forth as used in the specification and claims are to be understood as being modified in all instances by the term "about."

[0019] As used herein, the term "liquid acid fire retardant composition" and like terms, means an aqueous solution composed solely of one or more inorganic acids as the fire-retardant chemical component, without organic acids or powdered fire-retardant chemicals. A liquid acid fire retardant chemical composition can optionally include one or more non-fire retardant additives (e.g., surfactants).

[0020] "Composition" and like terms mean a mixture or blend of two or more

components.

[0021] As used herein, the term "fire" refers to the process of burning of cellulose by flame or smolder. The terms "flame" and "flammable" refer to the burning of gases resulting from pyrolysis due to heat. The term "smolder" or smoldering combustion refers to the burning of a carbon-rich material remaining after gases have devolved (e.g., as with charcoal in a barbeque). Both burning processes can be chemically tested by the methods, for example, as outlined in ASTM C-739 (Standard Specification for Cellulosic Fiber Loose-Fill Thermal Insulation) and as mandated by law.

[0022] As used herein, the term "lire resistant" means resistance to flaming and smoldering combustions. The term "fire-retardant chemical" refers to a chemical substance or mixture (other than water) that reduces flammability or smolder of a cellulose material.

[0023] Unless stated to the contrary, implicit from the context, or customary in the art, all parts and percentages are based on weight.

DESCRIPTION OF THE INVENTION

[0024] In embodiments, the present invention relates to a fire-resistant cellulose (e.g., paper-based) product composed of an absorbed inorganic acid component as the sole fire retardant compound, and methods of producing the cellulose product. In embodiments, the fire-resistant cellulose product is composed of a salt derived from the reaction of an inorganic acid absorbed to the cellulose fibers and an alkali or alkaline earth compound, as the sole or a majority weight percent (wt%) of the lire retardant compound, based on the total weight of the cellulose product.

[0025] In embodiments, the methods utilize a liquid acid fire retardant composition consisting of an aqueous solution of one or more inorganic acids as the sole fire retardant component to produce a cellulose product composed of cellulosic fibers containing the liquid acid fire-retardant composition absorbed therein and, in embodiments, an aqueous solution of an alkali compound or aqueous slurry of an alkaline earth compound to reduce the free acid and increase the pH of the product to 3.5 to 8. In embodiments, the resulting cellulose product comprises a salt resulting from the reaction of the inorganic acid and alkali or alkaline earth compound, which is absorbed and/or adhered to the cellulose fibers. The cellulose product of the invention possesses a high level of fire resistance at a much lower cost than other cellulose-based products. In preferred embodiments, the products and methods of the invention avoid the use of powdered (dry) fire retardant compositions. [0026] In embodiments, the invention utilizes an aqueous solution of one or more inorganic acids as the sole fire retardant component in the production of the fire-resistant cellulose product. In embodiments, in fabricating the cellulose product, no dry powdered fire retardant compounds need to be applied to or included in the cellulose material. The use of an aqueous inorganic acid solution as the sole fire retardant component of the liquid acid fire retardant composition (without the inclusion of organic acids or powdered fire retardant compounds) can lower costs in the manufacturing of the cellulose product, e.g., insulation, and also eliminate potential problems of corrosiveness and odor, which can occur in the use of conventional powdered fire retardants.

[0027] Processes for applying liquid fire-retardant compositions to cellulose materials are known in the art, as described, for example, in U.S. Patent No. 5,534,301 (Shutt).

Shredder

[0028] Briefly, a supply of cellulose-containing material can be loaded onto a feed table where the cellulose material can be sorted and separated from non-cellulose materials, and then conveyed into a shredding apparatus to physically reduce the cellulose material to a desired size (e.g., pieces of paper), for example, a typical average width and length of 0.5 to 2 inches (1.25 to 5 cm). Cellulose-containing materials typically comprise wood or other plant materials, for example, cotton, flax, hemp, kenaf and jute, among others, known and used in the art for producing cellulose-based materials, for example but not limited to, unused or used (recycled) paper such as newspaper, cardboard, fiberboard, paperboard, etc. The shredding apparatus may involve different types of standard systems known in the art.

Spray Booth

[0029] In embodiments, the liquid acid fire retardant composition is then applied to wet

(moisten) the reduced size cellulose material. In a preferred embodiment, the liquid acid fire retardant composition is delivered in a spray booth using a spraying system that can include one or more spraying nozzles connected to a source of the liquid acid fire retardant composition, e.g., a tank. Spray booths are well known in the art. The liquid acid fire retardant composition can be delivered onto the cellulose material in a fine mist composed of a plurality of droplets (e.g., droplets 40 to 200 microns in diameter). Application of the liquid acid fire retardant composition produces a fire retardant shredded cellulose material that is moistened (wetted) with the liquid acid fire retardant composition.

[0030] For some applications, immersion of the reduced size cellulose material in the liquid acid fire retardant composition is preferred, for example, when manufacturing insulation blankets from fibers such as flax and jute for use in the automobile market. In such an application, the reduced size cellulose material can be immersed in a bath containing the liquid acid fire retardant composition, and then dried. Optionally, to remove excess liquid prior to drying, the cellulose material can be passed through a dewatering device such as a vacuum screening apparatus or rollers.

Liquid acid fire retardant chemical

[0031] Although acids are destructive to paper, it was surprisingly found that the application of an aqueous solution of an inorganic acid onto a cellulose material, without the application of a conventional, powdered fire retardant chemical such as hydrated borax, ammonium sulfate, aluminum trihydrate (ATH), etc., and, in some embodiments, followed by the application of a liquid, aqueous solution of an alkali compound or an aqueous slurry of an alkaline earth compound, will render the cellulose material fire resistant to both flame and smolder combustion. Although not intended to be a limitation to the present disclosure, it is believed that the inorganic acid hydrolyzes the cellulose material through the donation of a proton (H⁺), which causes breaking of the covalent bonds that hold the glucose rings together, which in turn leads to a reaction (under heat) that provides a flame retarding effect and increases the fire resistance of the cellulose product, e.g., insulation. The application of an aqueous solution of an alkali compound or an aqueous slurry of an alkaline earth compound onto the acid-treated cellulose material counteracts the hydrolytic activity by the acid and produces a desired pH, i.e., a pH of 3.5 to 8, preferably a pH of 6 to 8. Modifying the acidity by the addition of the alkali or alkaline earth compound prevents an excessive degradation of the paper.

[0032] In general, the liquid acid fire retardant chemical composition can comprise any inorganic acid which imparts fire resistance to the cellulose materials. Preferred acids are those that are non-toxic. Examples of suitable acids include strong inorganic acids such as sulfuric acid and weak inorganic acids such boric acid and phosphoric acid. [0033] In embodiments, the liquid acid fire-retardant composition is composed of an aqueous solution of one or more inorganic acids as the sole fire retardant chemical component. In embodiments, the inorganic acid is sulfuric acid, phosphoric acid, or a mixture thereof. In embodiments, the liquid acid fire retardant composition is an aqueous solution comprising a fire retardant chemical component that consists of at least one of sulfuric acid and phosphoric acid. The liquid acid fire-retardant composition can further include optional non-fire retardant additives such as a surfactant.

[0034] In embodiments, the liquid acid fire-retardant composition comprises a fire retardant component that consists of an aqueous solution of sulfuric acid or phosphoric acid. In embodiments, the liquid acid fire-retardant composition comprises a fire retardant component that consists of a mixture of a major amount of sulfuric acid and a minor amount of phosphoric acid (i.e., less than 50 wt.% phosphoric acid based on the total weight of the inorganic acids). In embodiments, the fire retardant component consists of an aqueous solution of a mixture of a major amount of phosphoric acid and a minor amount of sulfuric acid (i.e., less than 50 wt.% sulfuric acid of the total weight of the inorganic acids). In embodiments, the fire retardant component consists of an aqueous solution of a major amount of phosphoric and/or sulfuric acid and a minor amount of boric acid, e.g., 0.1 to 3 wt% boric acid of the total weight of the inorganic acids.

[0035] The liquid acid fire-retardant composition is an aqueous solution of the inorganic acid as the sole fire retardant chemical component (i.e., without organic acids or powdered fire retardant chemical compounds), and optional additives. In embodiments, the concentration of the inorganic acid in the liquid acid fire-retardant composition (with optional additives) is greater than zero (>0), more typically at least 1.5 wt%, more typically at least 1.8 wt%, more typically at least 2 wt%, more typically greater than 2 wt%, more typically at least 5 wt%, more typically at least 10 wt%, more typically at least 15 wt%, up to 50 wt%, more typically up to 40 wt%, more typically up to 30 wt%, more typically up to 25 wt%, and more typically up to 20 wt%, based on the total weight of the liquid acid fire-retardant composition. In a preferred embodiment, sulfuric acid is present as the acid component in the liquid acid fire-retardant composition as a 15 wt% to 25 wt% aqueous solution, preferably as a 20 wt% aqueous solution. [0036] In embodiments, the liquid acid fire retardant chemical comprises an effective amount of the inorganic acid such that its application alone or in combination with an alkali or alkaline earth compound will provide a cellulose material with a Critical Radiant Flux (CRF) value of at least 0.12 watts/cm², which will pass testing requirements, for example, the requirements according to ASTM C-739 (Standard Specification for Cellulosic Fiber Loose-Fill Thermal Insulation). For example, as illustrated by the test data in Table 1 below, a cellulose material that was sprayed with 15 wt% inorganic acid ("acid load") from a 40 wt% aqueous inorganic acid solution had a "passing" CRF value (i.e., at least 0.12 W/cm²) except for the 40% glycolic acid application.

Table 1

[0037] The CRF values indicate the minimum radiant energy needed for a fire to sustain flame propagation, with a higher number indicating a more flame-resistant system, i.e.,

>0.45 W/cm² being better than 0.42 or 0.12 W/cm². A "pass" is achieved if the cellulose material will not support surface flame while being subjected to radiation of 0.12 watts/cm² or greater.

[0038] The results in Table 1 demonstrate the effectiveness of an inorganic acid as a flame retarding additive to cellulose material. The data also demonstrates that stronger inorganic acids (e.g., sulfuric acid) are more effective in flame retarding ability than weaker organic acids (e.g., acetic acid, citric acid). Additives.

[0039] In order to enhance the wetting or impregnation of the cellulosic fiber material by the liquid acid fire retardant composition, a conventional wetting agent or surfactant may be included in the solution, such as a polyoxyethylene alkyl phenol, e.g. TRITON X-100

(manufactured by Rohm & Haas Co.). In embodiments utilizing a wetting agent or surfactant, the liquid acid fire-retardant composition generally comprises 0.02 to 0.2 part of one or more wetting agents or surfactants, more typically 0.04 to 0.1 part, and more typically 0.1 part, based on 100 parts of water.

Application of liquid fire-retardant composition

[0040] In applying the liquid acid fire-retardant composition, it was found that the better the coverage of the cellulose material by the acid, the less acid is required to pass the CRF test. This was determined by spraying a liquid acid fire-retardant composition having a lower acid content/higher water content, which provided greater area coverage of the pieces of the cellulose material than a liquid acid fire-retardant composition having a higher acid content, e.g., a 40% versus a 10% aqueous solution of sulfuric acid (H₂SO4). This is illustrated by the test data summarized in Table 2 below, generated by using an aqueous solution of different

concentrations of sulfuric acid (H₂SO₄) applied to the cellulose material by spraying the shredded, size-reduced cellulose material in a spray booth.

Table 2

[0041] The application of the liquid acid fire-retardant composition preferably produces a wetted/moistened cellulose material that comprises an amount of the composition such that the wetted fibers contain at least 4 parts up to 12 parts, and more typically up to 8 parts of the inorganic acid as the fire resistant chemical per 100 parts of the cellulose fibers. The amount of inorganic acid that is applied will vary according to the acid, its strength and its dilution in aqueous solution, and should be sufficient to provide a CRF value of at least 0.12 W/cm , including, in embodiments, after the application of the alkali solution or alkaline earth slurry to the acid-treated fibers to form an acid-derived salt.

Application of Alkali or Alkaline Earth Compound(s).

[0042] The application of the inorganic acid to the cellulose material will generally cause the material to degrade. In addition, the use of inorganic acid as a flame retardant can lead to problems of metal corrosion upon use, e.g., after a cellulose insulation product is installed. To counteract the degradation of the cellulose material and eliminate problems with corrosion during use, a sufficient amount of an alkali or alkaline earth compound can be applied to the cellulose material after the application of the inorganic acid component to modify the acid pH.

[0043] In general, an aqueous solution of any water-soluble alkali compound or aqueous slurry of any alkaline earth compound can be applied to the acid-treated, cellulose material. The application of the alkali solution or alkaline earth slurry preferably produces a wetted/moistened cellulose material that comprises an amount of the alkali or alkaline earth compound sufficient to adjust the cellulose material to a final pH of at least 3.5, preferably a pH of 6.0 to 8.0, preferably a pH of 7.0.

[0044] In embodiments, in applications of a liquid acid fire-retardant composition containing greater than (>) 2 wt% of the inorganic acid (e.g., sulfuric acid, phosphoric acid), an aqueous alkali solution or aqueous alkaline earth slurry can be applied to the acid-treated cellulose material to moderate the pH of the acid-treated cellulose material to a pH of 3.5 to 8.

[0045] In embodiments, in applications of a liquid acid fire-retardant composition containing greater than (>) 0 wt% to less than or equal to (<) 2 wt% of the inorganic acid (e.g., sulfuric acid, phosphoric acid), application of an aqueous alkali solution or aqueous alkaline earth slurry to the acid-treated cellulose material may not be required to moderate the pH of the material. In such applications, a minor amount (e.g., up to 15 wt%, or up to 10 wt%, or up to 5 wt%, for example, 5 to 10 wt %) of a powdered fire retardant chemical can be applied to the dried, acid-treated cellulose materials to increase the level of fire retardance. [0046] In the use of phosphoric acid as the inorganic acid in the liquid acid fire-retardant composition, it was surprisingly found that the pH of the cellulose material remained higher than expected, e.g., at pH 5.5, which eliminated the need for applying the alkali or alkaline earth compound to modify the pH of the acid-treated cellulose material. Thus, in embodiments in the application of a liquid acid fire-retardant composition consisting of phosphoric acid as the fire retardant component, an aqueous solution of an alkali compound or aqueous slurry of an alkaline earth compound can be optionally applied to modify the pH of the acid treated cellulose material.

[0047] Preferred alkali compounds are those with high water solubility. Non-limiting examples of alkali compounds suitable for use include sodium carbonate, sodium hydroxide, potassium hydroxide, potassium carbonate, and mixtures thereof. Preferred alkali compounds include sodium carbonate and sodium hydroxide. Non-limiting examples of alkaline earth compounds include magnesium carbonate, calcium carbonate, dolomite (calcium magnesium carbonate), and mixtures thereof. Treatment of the cellulose material with an aqueous alkali solution or aqueous alkaline earth slurry will result in the production of the corresponding salt of the acid (i.e., acid-derived salt, or salt derivative), for example, sulfates and phosphates.

[0048] In embodiments, an aqueous solution of a water-soluble alkali or aqueous slurry of an alkaline earth compound can be sprayed onto the cellulose material after the application of the liquid acid fire-retardant composition, after a delay period to allow the acid to react with the cellulose fibers, generally after a 2 to 15 minute delay period. The amount of alkali or alkaline earth compound that is applied will vary according to the alkali or alkaline earth compound, its concentration in aqueous solution or aqueous slurry, and the acid and amount of acid applied.

[0049] In embodiments, the aqueous solution of the water-soluble alkali compound or the aqueous slurry of the alkaline earth compound comprises at least a 5 wt%, more typically at least a 10 wt%, more typically at least a 15 wt%, up to 50 wt%, more typically up to 40 wt%, more typically up to 30 wt%, more typically up to 25 wt%, more typically up to 20 wt%, of the alkali or alkaline earth compound. In a preferred embodiment, sodium carbonate is used as the alkali component as a 5 to 20 wt% aqueous solution, preferably as a 15 wt% aqueous solution. In another preferred embodiment, dolomite is used as the alkaline earth component as a 5 to

20 wt% aqueous slurry, preferably as a 15 wt% aqueous slurry. Dwell time

[0050] In embodiments, after the application of the liquid acid fire-retardant composition and after the application of the alkali solution or alkaline earth slurry, a "dwell" time (delay period) is allowed to elapse in order to ensure diffusion of the liquid fire retardant composition into the cellulose fibers and reaction of the alkali or alkaline earth compound to adjust the pH of the product to 3.5 to 8. For example, the wetted cellulose material can be held in a hopper or other containment vessel for a desirable time period, for example, up to 45 seconds to

120 seconds (up to 2 minutes) or longer, and in embodiments, from 2 to 15 minutes.

Drying

[0051] After the application of the liquid acid fire retardant, which in embodiments, is followed by the application of the aqueous alkali solution or aqueous alkaline earth slurry, the wetted cellulose material is dried to remove the added water from the applied liquids. Removal of the excess water through drying reduces the amount of dust produced in subsequent processing through the hammermill and/or fiberizer. In embodiments, the wetted cellulose material is transferred by a stream of air (e.g., heated air) into a drying chamber such as a rotary drier and a tumble drier, among others. In preferred embodiments, the dried cellulose material is "air dry" (e.g., 90 to 95% dry) having a 5% to 10% moisture content.

[0052] Although not preferred, in embodiments, a minor amount of a powdered flame retardant compound (e.g., up to 15 wt%, or up to 10 wt%, or up to 5 wt%, for example, 2 to 15 wt%, or 5 to 10 wt%) can optionally be applied to the dried cellulose fiber material in addition to the liquid acid fire retardant composition to lower the amount of liquid component and thereby reduce drying costs and/or capital equipment costs, and/or to increase the level of fire retardance. Examples of powdered flame retardant compounds include, but are not limited to, native gypsum, Epsom salts (magnesium sulfate), and aluminum trihydrate (ATH). It is preferred that a powdered flame retardant chemical is not applied to the cellulose fiber material in order to maintain a lower product density and reduce the amount of dust that is generated from the cellulose product during installation. In embodiments, a minor amount of a pest control additive can be added, e.g., 1 to 15 wt% based on the total weight of the cellulose material. For example, although not preferred, a powdered boric acid or salt thereof (e.g., sodium borate, borax) can be applied to the dried, acid-treated cellulose fiber in a minor amount, e.g., 1 to 5 wt% based on the total weight of the cellulose material, as a pest control additive (e.g., insecticide).

Fiber izer/Hammer mill

[0053] The dry, fire retardant-treated cellulose material can then be transferred, for example, by air flow, to a hammer mill, fiberizer or both, such as known and used in the art, to further reduce the size of the shredded material into smaller pieces, for example to an average length and width of 0.25 to 0.5 inches (0.6 to 1.25 cm). In embodiments, the cellulose material can be dried, for example, by applying heat to the wetted material prior to or during the transfer of the material.

[0054] Fiberizers and hammer mills are known and used in the art. The fiberizer, for example, is a mechanical device configured with rotating elements in close proximity to one or more sets of static or counter rotating elements such that when the cellulose material is conveyed through the device, a finely divided material is produced. Processing through the fiberizer reduces the size of the cellulose material to a desired, final reduced size, fluffy form. For. a cellulose insulation product, it is preferred that the final product will have a settled bulk density of 1 to 2 lbs/ft³ (e.g., 1.2 to 1 .6 lbs/ft³).

Dedusting

[0055] The size reduction processing in the fiberizer/hammer mill typically produces a substantial quantity of dust (i.e., material with very small particle size), which contains residues and chemicals that can be easily inhaled and pose significant problems such as lack of visibility and personal nuisance due to a high amount of air-borne dust particles, particularly when the material is pneumatically applied, for example, as an insulation.

[0056] In embodiments, the fire-retardant cellulose fiber material can be de-dusted to eliminate a major amount (i.e., at least 50% by volume or more) to substantially all (i.e., about 90-100% by volume) of the dust, and produce a low-dust fire-retardant cellulose fiber material that has functionally equivalent fire-retardant properties as the fire-retardant cellulose fiber material before de-dusting. The de-dusted product can be characterized by a substantial absence of detached fibrous residue which, if present, can increase its density.

[0057] Such a dust removal (de-dusting process is described in US 2010/0086780 (Shutt)

(issued as USP ). The de-dusting can be performed by any suitable process, for example, by screening, air classification, or other known separation techniques. Preferably, the de-dusting is performed by a screening technique or screening in combination with another separation technique.

[0058] In preferred embodiments, the screen has a mesh size that is suitable for effectively separating a sufficient amount of dust from the dried product, preferably to produce a substantially dust-free material by removing at least about 50% by volume of the dust content of the dried product, more preferably at least about 70%, and more preferably at least 90%, up to 100%, by volume of the dust. The mesh of the screen can range from about ^200 mesh to about 10 mesh, and is preferably about 40 mesh to about 14 mesh, more preferably about 30 mesh to about 20 mesh. An example of a suitable screening apparatus for use in the de-dusting process of the invention is a gyratory (vibratory), high capacity, production separator or sieve (e.g., Models VS0048 (single deck) and VS0060 (double deck)), available commercially from

VORTI-SIV®, a division of MM Industries, Inc., Salem, Ohio U.S.A.

[0059] A reduced-size dry cellulose product that has been processed according to the invention using a liquid fire-retardant chemical, will typically contain about 8-15 % by weight dust composed of about 7.5-14.5%) by weight cellulose-based (e.g., paper) dust with about 0.5-1.5% by weight of fire-retardant chemical adhered to the dust, and de-dusting according to the invention can remove a substantial amount of dust (up to 100% of the dust) from the reduced-size dry product with substantially no loss of fire-retardant properties.

Final Product / Packaging

[0060] In an embodiment, the final fire-resistant cellulose product, e.g., insulation, based on the total weight of the product, comprises:

A. Cellulose fibers, being at least 80 wt%, more typically at least 85 wt%, more typically at least 90 wt%, up to 94 wt%;

B. One or more acids, at up to 10 wt%, and at least 4 wt% (e.g., sulfuric acid), applied as a 10 to 40 wt% aqueous solution and then dried on the material;

C. Optionally, one or more alkali or alkaline earth compounds, at up to 8 wt%, more typically up to 4 wt%, more typically up to 2 wt% (e.g., Na₂C03), applied as a 10 to 20 wt% aqueous solution or slurry and dried on the material; and

D. Optionally, a surfactant, typically up to 0.2 wt%.

[0061] In an embodiment, the final fire-resistant cellulose product, e.g., insulation, based on the total weight of the product, comprises:

B. One or more acid derived salts, at up to 20 wt%, more typically up to 15 wt%, more typically up to 10 wt%, and at least 5 to 6 wt%;

C. Optionally, a surfactant, at up to 0.2 wt%.

[0062] Examples of acid derived salts (salt derivatives) include sulfates and phosphates.

In embodiments, the cellulose product is without the presence of an ammonium salt or ammonia residue therefrom and/or boric acid or salt thereof (e.g., borate).

[0063] In embodiments, the final cellulose product is treated with an amount of the inorganic acid component sufficient and effective to provide a level of fire retardance to meet federal standards for both the smoldering combustion test and the flame spread burn test, which for insulation is outlined in ASTM C-739 (Standard Specification for Cellulosic Fiber Loose-Fill Thermal Insulation). Where used, the amount of applied alkali or alkaline earth compound is sufficient and effective to provide the cellulose material with a final pH of at least 3.5, preferably pH 6.0 to 8.0, and more preferably pH 7.0. In embodiments, the cellulose fiber material has a CRF value of 0.12 watts/cm² or greater, as measured according to ASTM C-739. In embodiments, the final cellulose product is treated with an amount of the inorganic acid component sufficient and effective to provide a level of fire retardance sufficient to attain a Category C listing or higher in Europe.

[0064] The dried cellulose product can be deposited into a holding bin or conveyed to a bale press or baler or to a bagging apparatus, as known and used in the art, and packaged for transport and future use. In an installation process for insulation, the fire retarded cellulose insulation product can be placed into a hopper and mechanically fluffed-up, and then "blown" directly into an attic or stud spaces in an existing wall, among other applications.

[0065] The fire-resistant cellulose product of the invention can be used for producing fire-retarded products including building materials such as but not limited to cellulose insulation, fire doors and cellulose-based board materials (e.g., panels), as well as automotive fabrics, and furniture, among other articles.

[0066] In embodiments of the present invention, the only chemical used for imparting fire resistance is an inorganic acid(s), which is applied to the cellulose material exclusively as a liquid (without the presence of an organic acid or powdered fire retardant chemicals).

Surprisingly, the applied liquid acid fire retardant composition (and, in embodiments, the subsequently applied alkali or alkaline earth compound) provides a cellulose insulation and other products having the required level of fire retardance to meet federal standards for both the smoldering combustion test and the flame spread burn test, while significantly reducing the cost of manufacture of the fire-resistant cellulose material, e.g., insulation, compared to cellulose material produced using only a powdered or other liquid fire retardant chemical. The use of an aqueous inorganic acid component as the sole fire retardant chemical in place of more expensive fire retardant chemicals such as hydrated borax, ammonium sulfate, aluminum trihydrate (ATH), etc., significantly lowers manufacturing costs, avoids outgassing of ammonia, and eliminates potential health issues associated with the use of boric acid/borates.

[0067] Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover any adaptations or variations that operate according to the principles of the invention as described. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof. For purposes of United States patent practice, the contents of any referenced patent, patent application or publication are incorporated by reference in their entirety.

Claims

WHAT IS CLAIMED IS:

1. A fire-resistant cellulose fiber material, comprising cellulosic fibers containing a liquid acid fire-retardant composition absorbed therein or salt derivative thereof absorbed therein and/or adhered thereto, the liquid acid fire-retardant composition comprising:

a fire retardant chemical component consisting of an aqueous solution of one or more inorganic acids; and

optionally, one or more additives.

2. The cellulose fiber material of Claim 1 , having a CRF value to meet at least one of ASTM C-739, a Category C rating, and a Category B rating.

3. The cellulose fiber material of Claim 1 , having a CRF value of 0.12 watts/cm or greater, as measured according to ASTM C-739.

4. The cellulose fiber material of Claim 1 , having a CRF value to meet a Category C rating or higher.

5. The cellulose fiber material of Claim 1 , consisting essentially of the cellulosic fibers and an inorganic acid absorbed therein, wherein the inorganic acid is selected from the group consisting of phosphoric acid, sulfuric acid, and mixtures thereof, optionally with a minor amount of boric acid.

6. The cellulose fiber material of Claim 1 , consisting essentially of the cellulosic fibers and the salt derivative of the one or more inorganic acids adsorbed therein and/or adhered thereto.

7. The cellulose fiber material of Claim 6, wherein the salt derivative is selected from the group consisting of sulfates and phosphates.

8. The cellulose fiber material of Claim 1 , without the presence of an ammonium salt or ammonia residue.

9. The cellulose fiber material of Claim 1 , wherein the cellulose fiber material has no fire retardant chemical in powder form contained therein or situated thereon.

10. The cellulose fiber material of Claim 1 , comprising, based on the total weight of the cellulose fiber material:

94 to 85 wt% of cellulose fibers;

4 to 1 1.8 wt% inorganic acid;

0 to 6 wt% alkali or alkaline earth compound; and

0 to 0.2 wt% surfactant.

1 1 . The cellulose fiber material of Claim 1 , comprising, based on the total weight of the cellulose fiber material:

94 to 85 wt% of cellulose fibers;

6 to 15 wt% of an inorganic acid derived salt; and

0 to 0.2 wt% surfactant.

12. The cellulose fiber material of Claim 1 1 , wherein the inorganic acid derived salt is selected from the group consisting of sodium sulfate, potassium sulfate, sodium phosphate, potassium phosphate, and mixtures thereof.

13. The cellulose fiber material of Claim 1 , having a settled bulk density of 1 to 2 lbs/ft .

14. A fire-retarded insulation material comprising the cellulose fiber material of Claim 1.

15. A fire-retarded article comprising the cellulose fiber material of Claim 1.

16. The article of Claim 15, selected from the group consisting of fire doors, board materials automotive fabrics, and furniture.

17. A method of producing a fire-resistant cellulose fiber material, comprising: applying a liquid acid fire-retardant composition to a cellulose material to produce a wetted, fire retardant-treated cellulose material having the liquid acid fire-retardant composition absorbed therein, the liquid acid fire-retardant composition comprising a) a fire retardant chemical component consisting of an aqueous solution of one or more inorganic acids; and b) optionally, one or more additives;

optionally, applying an aqueous solution of an alkali compound or an aqueous slurry of an alkaline earth compound to the wetted, fire retardant-treated cellulose material such that the cellulose material has a pH of 3.5 to 8; and

reducing the cellulose material in size to produce the fire-resistant cellulose fiber material.

1 8. The method of Claim 1 7, wherein applying the liquid fire-retardant composition is by spraying.

19. The method of Claim 17, wherein the inorganic acid is selected from the group consisting of phosphoric acid, sulfuric acid, and mixtures thereof, optionally with a minor amount of boric acid.

20. The method of Claim 17, wherein the liquid fire-retardant composition comprises an aqueous solution of > 0 wt% to < 2 wt% of the inorganic acid, and

the method further comprises applying a minor amount of one or more powdered fire retardant chemicals to the fire retardant-treated cellulose material.

21. The method of Claim 20, wherein an amount of the powdered fire retardant chemical is applied to meet at least one of ASTM C-739, EP Category B, and EP Category C.

22. The method of Claim 21 , wherein 2 to 15 wt% of the powdered fire retardant chemical is applied to the fire retardant-treated cellulose material.

23. The method of Claim 21 , wherein 2 to 10 wt% of the powdered fire retardant chemical is applied to the fire retard ant-treated cellulose material.

24. The method of Claim 17, wherein an aqueous solution of an alkali compound or aqueous slurry of an alkaline earth compound is applied to the cellulose material.

25. The method of Claim 24, wherein the aqueous solution of the alkali compound or aqueous slurry of the alkaline earth compound is applied after a delay period of 2 to 15 minutes after applying the liquid acid fire-retardant composition to a cellulose material.

26. The method of Claim 24, wherein the liquid fire-retardant composition comprises an aqueous solution of > 2 wt% of the inorganic acid.

27. The method of Claim 24, wherein

the alkali compound is selected from the group consisting of sodium carbonate, sodium hydroxide, potassium hydroxide, potassium carbonate, and mixtures thereof; and

the alkaline earth compound is selected from the group consisting of magnesium carbonate, calcium carbonate, dolomite, and mixtures thereof.