WO2000022222A1 - Methods for reducing the flammability of cellulosic substrates - Google Patents

Abstract

Methods of rendering celluosic materials fire retardant, and articles of manufacture including the materials, are disclosed. The methods involve applying to the material a composition including a carboxylic acid-containing compound and a suitable catalyst for coupling the compound to some or all of the hydroxy groups present on the material, and esterifying the hydroxy groups. The advantages of this fire-retardant composition include a relatively low level of toxicity, and the stability of the ester bond to conventional steam cleaning and other carpet cleaning methods. In a preferred embodiment, the fire-retardant cotton-fiber composition is used to prepare cotton carpets or raised surface apparel.

Description

METHODS FOR EDUCING THE FLAMMABILITY OF CELLULOSIC SUBSTRATES

FIELD OF THE INVENTION

The present application relates to methods for reducing the flammability of cellulosic substrates, including cotton fiber carpets and raised surface apparel.

BACKGROUND OF THE INVENTION

Cotton, like most textile fibers, is combustible. Whenever cotton is in the presence of oxygen and the temperature is high enough to initiate combustion (360- 420°C), untreated cotton will either burn (flaming combustion) or smolder (smolder combustion). The degree of flammability depends on the fabric construction.

Fabrics have different flammability requirements depending on the particular end use. Cotton fabrics, without the use of special flame-retardant finishes, meet practically all of these requirements for most existing end-uses. However, some new cotton product developments require special constructions or finishes to reduce their flammability. This is especially true in certain countries, such as the United States, which have strict regulations governing the flammability of these products.

Resistance to burning is one of the most useful properties that can be imparted to cotton fibers and textiles. Some end uses for cotton in textiles for apparel, home fiirmshings, and industry, can depend on its ability to be treated with chemical agents (flame-retardants) that confer flame resistance (FR). End uses requiring flame-retardant finishes include protective clothing (e.g., foundry workers apparel and fire fighters uniforms), children's sleepwear, furnishing/upholstery, bedding, carpets, curtams/drapes, and tents.

Chemical agents for reducing the flammability of products containing cotton fiber and other cellulosic fibers are well known and generally grouped into two categories: durable and non-durable. The durable type tend not to be removed in conventional washes and the non-durable type are typically removed in conventional washes.

The variable manufacturing cost of a typical durable flame-retardant treatment is about $ 1-2 per yard, depending on fabric weight and other factors. This can be a major limitation. The flammability and flame resistance of cotton has been studied extensively and several comprehensive reviews ot the subject are available.

Cotton is not currently the raw material of choice in the carpet industry. The carpet fiber business in the U.S. is roughly a 7,000,000 bale/year market, and cotton is less than one percent of this overall market. One reason that cotton has been almost excluded from this large market for fibers is the difficulty in complying with the Flammable Fabrics Act. This regulation requires that all carpets which are six feet by four feet or larger and are sold for residential use pass a flammability test. This test is commonly referred to as the "Pill Test". It calls for igniting a methenamine pill, which is placed in the center of a nine-inch by nine-inch carpet specimen. The specimen fails if the flame spreads to within one inch of a metal template containing an eight-inch diameter hole, which is placed on top of the carpet specimen prior to igniting the pill. The specimen passes if the flame does not spread to within one inch of the metal template.

For a residential carpet to be saleable, at least seven out of eight specimens must pass the test. Furthermore, if the carpet has been treated with a flame-retardant (with the exception of alumina trihydrate added to the back coating), then the carpet must be washed ten times as described in AATCC 124-1967 prior to testing.

There are numerous man-made fiber carpets which are currently available, many of which do not require any special treatments to pass federal flammability requirements because of the nature of the test. Many synthetic carpet fibers will melt away from the burning pill during the pill test, such that the pill eventually self extinguishes. The fuel load provided by these carpets in a fire, which is already burning, is not considered by the test method.

Other synthetic fiber carpets, such as polypropylene, require a flame- retardant such as alumina trihydrate. Alumina trihydrate is often added to a backcoating (or backing), as opposed to application directly to the carpet fibers. Synthetic thermoplastic fibers such as polypropylene melt quickly when exposed to a flame, for example, during the pill test. The burning pill then quickly falls, due to gravity, onto the backing. The backing typically includes three layers: a thermoplastic (usually polypropylene) primary backing layer, a latex adhesive layer (which may contain the flame-retardant) and a secondary thermoplastic (usually polypropylene) backing layer. Since the primary backing is also a low melting point thermoplastic, it quickly melts and allows the burning pill to come into direct contact with the latex. Since the latex often includes a flame-retardant, it can then suppress the spread of flames.

Certain other fibers, such as wool and modacrylic, are inherently flame resistant. These can be made into carpets which require no special treatments to pass the required pill test.

Cotton carpets can also be made which require no special treatments to pass the pill test. For example, a cut pile carpet can be made from a 3/2 Ne yam composed of 90 percent cotton and 10 percent low melt thermoplastic fiber. The low melt fiber is allowed to melt, typically prior to tufting of the carpet. A carpet which includes 12 stitches per inch, 1/11-inch gauge, and VA inch pile height can be constructed from this yam. Such a carpet is generally dense enough, with a sufficiently low pile height, that it will pass the pill test without any additional treatment.

A disadvantage of relying on such low pile height constructions when m-mufacturing cotton carpets is that it is very limiting from a design and marketing standpoint. The consumer in the U.S. today has become accustomed to a wide variety of choices when selecting a carpet. Substantially limiting the choices of carpet construction is not a practical option for a successful marketing program.

Another disadvantage of attempting to reduce the flammability of a cotton

(or cellulosic) carpet by construction alone is that achieving reduced flammability often means increasing the area density (oz./ square yard) of the carpet. As the area density of the carpet increases, the cost also generally increases. This approach is therefore very restrictive and would limit the market to the small, upper price end.

Alumina trihydrate, which is effective on certain thermoplastic fiber carpets, is not typically effective on cotton-containing carpets. On cotton-containing carpets, the cotton yarn which is under and in the vicinity of the burning pill will tend to char but maintain sufficient integrity to support, insulate and separate the burning pill from the carpet backing. There is not a sufficient heat flux reaching the alumina trihydrate contained in the latex backing for the alumina trihydrate to be effective at suppressing the flame.

The use of flame-retardant low melt fibers in place of the typical non-flame- retardant low melt fiber used in the ya has been attempted. The low melt fiber, in general, offers the advantages of improved resilience and tuft definition and minimizes shedding of loose fibers from the tufts. Testing has shown that flame retardant low melt fiber used in the yam is not effective. Although various explanations have been offered, the mechanism is not understood. Since federal law in the U.S. requires that any carpet which has a flame- retardant treatment (other than alumina trihydrate) be laundered ten times prior to flammability testing, any such flame-retardant which is apphed for that purpose must remain effective after the ten home launderings. Because home launderings are rather effective at removing materials which are not chemically bonded to the fibers, durable flame retardants are generally the most effective.

There have been many techniques for imparting durable flame resistance properties to cellulosic substrates described in the literature. However, there are relatively few that are practiced today, due to commercial availability of the chemicals, safety concerns, process control issues or other reasons. Durable flame retardants are typically more complex, more expensive and more difficult to apply than non-durable treatments. The main flame retardant finishes used on cotton are phosphorus-b ased.

Two of the more common phosphorous-based systems which are used to provide durable flame resistance to cotton substrates are the "pre- condensate"/ammonia process and the reactive phosphorous process.

In the "pre-condensate" /NH₃ process, the flame-retardant agent exists as a polymer in the fibrils of cotton fibers and is not combined chemically with OH groups in the cotton fiber. This process imparts durable flame resistance to 100% cotton fabrics when apphed under proper application procedures. It produces fabrics with a good hand and strength retention. Proper application of pre-condensates to cotton fabrics requires adequate fabric preparation, proper padding/uniform application, proper phosphorus add-on relative to fabric properties, appropriate moisture control prior to arnmoniation, control of the ammoniation step to ensure adequate polymer formation, and effective oxidation and washing of the treated fabric. This process is very useful for specialty applications that can command a very high price, such as protective clothing for fire fighters and other workers who may be exposed to fire or excessive heat. It is generally not practical for cotton carpets or raised surface apparel that will be sold to the average consumer. The problems associated with this process include the high cost, the special equipment needed (ammoniation chamber) which is not generally available, and the two drying steps which are required.

Reactive phosphorus-based flame retardants are compounds (e.g., N- methylol dimethyl phosphonopropionamide (MDPPA)) that react with cellulose, the main constituent of cotton fiber. These compounds can be used both for cotton and for cotton blends with a low synthetic fiber content. The finish, usually applied to the fabric after the coloring stage, promotes char formation. The durability of the finish makes the resulting treated fabric suitable for curtains, upholstery, bed linen and protective clothing.

The reactive phosphorus-based flame retardants are typically applied using a pad/dry/cure method, in the presence of phosphoric acid catalyst. The finish is sometimes applied with a methylated melamine resin to increase the bonding/fixation of the agent to cellulose, which enhances the flame retardancy. Afterwashing is generally required, often with an alkali such as soda ash, followed by further rinsing and drying. The afterwashing helps to reduce loss of fabric strength. The reactive phosphorous-based process has the advantage of not requiring specialized equipment such as an ammonia cure unit, and has less affect on dyes than the pre-condensate process. However, this process can cause more strength loss than the pre-condensate process. Further, there can be a durability problem associated with some wash treatments if the instructions of the chemical suppher are not followed.

6 - Reactive phosphorus based flame retardants can be unsuitable for certain end uses, such as cotton or cotton blend carpets. This is especially true when the products contain formaldehyde, because of concerns about the human health effects of exposure to certain volatile organic compounds (NOC's) which may have been released from carpeting or carpet backing in past years. Because of this, most carpet manufacturers generally consider even very low levels of formaldehyde to be unacceptable. Another issue is that these products are generally designed to be afterwashed as part of the application procedure. While the toxicity of such materials is generally low, there are significant concerns about the exposure of babies or small children to residual unfixed chemicals left on the carpet.

Another phosphorous-based approach has been to apply a flame-retardant cyclic phosphonate ester and tetrakis-(hydroxymethyl)phosphorιium sulfate (THPS) to polyester/cotton fabrics. The components are applied simultaneously and then cured (U.S. Patent No. 4,842,609 to Johnson). The phosphonate ester bonds to the polyester, and the THPS bonds to the cotton fibers. The minimum amount of polyester when this composition is used is 35% by weight. The treated fabrics can purportedly be washed numerous times and also have an acceptable hand. A limitation of the chemistry is that it requires such a large percentage of polyester in the blend, and also that phosphorous compounds can be problematic, as discussed above. Other organophosphorous-based treatments include those described in U.S. Patent No. 4,167,603 to Sistrunk, U.S. Patent No. 3,897,584 to Swidler et al., U.S. Patent No. 3,970,425 to Leblanc and LeBlanc, U.S. Patent No. 4,040,780 to Gamer, U.S. Patent No. 3,650,820 to DiPietro et al., and U.S. Patent No. 4,765,796 to Harper and Beninate.

A non-phosphorous approach for rendering cotton fire retardant has been to incorporate a water-insoluble, solid particulate mixture of brominated organic compounds and metal oxides, optionally with a metal hydrate, into the carpet fiber

7 - (U.S. Patent No. 4,600,606 to Mischutin). However, a limitation of the chemistry is that the metal oxide compounds may be rendered soluble when washed if the pH of the solution is on the acid side. Also, particles of brominated organic compounds may be irritating to people coming into contact with them, and may be harmful if ingested.

Another non-phosphorous approach has been to prepare a solution of boric acid, ammonium sulfate, borax, hydrogen peroxide, and optionally a surfactant and/or an alkyl phthalate ester, and apply this as a coating on cellulosic materials. A major limitation of this chemistry is the water-solubility of the components, which results in the composition being substantially removed during conventional washing.

U.S. Patent Nos. 4,820,307, 4,936,865 and 4,975,209 to Welch et al, and U.S. Patent No. 5,221,285 to Andrews et al, the contents of which are hereby incorporated by reference in their entirety, disclose using carboxylic acid-containing compositions to crosslink fibrous cellulosic textiles and provide the textiles with wrinkle resistance, smooth drying properties and durability to repeated laundering in alkaline detergents (see, for example, the Abstracts of each of the patents).

It is not known in the art that wrinkle-resistant carboxylic acid treatments impart fire retardance to the resulting textiles. In fact, U.S. Patent No. 4,979,533 to Moreau et al. discloses that phosphono-dicarboxylic acids can be applied to cellulosic textiles to impart both flame retardancy and wrinkle resistance. The phosphono groups were used for their ability to impart flame retardancy to the textiles, and the carboxyl groups were used for their ability to impart wrinkle resistant properties to the textiles.

Because wrinkle resistance is not usually a sought after property for carpets, carpets have not been treated with the carboxylic acid treatments described in the Welch and Andrews patents. Further, with respect to cotton-based raised surface apparel, the relatively high concentration necessary to impart wrinkle resistance would also be expected to adversely affect the "hand" of the resulting fabrics. When used in a concentration which would provide acceptable hand to cotton-based raised surface apparel, the wrinkle resistance would not be acceptable.

There is a need for fire retardants for cotton fiber, especially when the fiber is used in a cotton carpet or in raised surface apparel, that survives a certain number of washings, including steam cleanings. The present invention provides such materials.

SUMMARY OF THE INVENTION

Methods for providing cellulosic fibers with reduced flammabiUty, and articles of manufacture prepared from the resulting fire-resistant cellulosic fibers, are disclosed. The methods involve applying to a cellulosic fiber a composition including a mono-, di-, tri- or polycarboxylic acid, and reacting some or all of the carboxyl groups with some or all of the hydroxy groups present on the cellulosic fiber. Cotton is a preferred cellulosic fiber. Other cellulosic fibers include flax, jute, hemp, ramie, Lyocell™, Tencell™ and regenerated unsubstituted wood celluloses such as rayon.

Suitable carboxylic acids include aliphatic, alicyclic and aromatic acids which preferably contain at least two carboxyl groups. Examples of suitable aliphatic carboxylic acids include maleic acid, malic acid, fumaric acid, tartaric acid, citric acid, citraconic acid, itaconic acid, tricarballylic acid, trans-aconitic acid, 1,2,3,4-butanetetracarboxylic acid, all-cis-l,2,3,4-cyclopentane tetracarboxylic acid, mellitic acid, oxydisuccinic acid, thiodisuccinic acid, and the like. Examples of polycarboxylic acids useful for reacting with the cellulosic substrate include polymaleic acid, polyacrylic acid, poly(meth)acrylic acid, carboxymethyl cellulose

9 - and copolymers and blends thereof. Also suitable are carboxymethyl cellulose fixed with an external crosslinker and gluconic acid fixed by an external crosslinker.

The carboxylic acids and hydroxy groups are linked via ester linkages. The esterification can be performed using a catalyst and heat. Suitable esterification conditions are disclosed in U.S. Patent No. 4,820,307 to Welch et al., the contents of which are hereby incorporated by reference. Suitable catalysts include alkali metal salts of phosphorous containing acids, which include phosphorous acid, hypophosphorous acid, and polyphosphoric acids, and also include alkali metal mono- or dihydrogen phosphates and hypophosphites. The esterification can optionally be carried out using other catalyst systems, such as metal alkoxides, metal carbonates or bicarbonates, alkali metal acetates or other alkali metal acid salts, ammonium phophatex, ammonium halides, alkali metal hydroxides and alkali metal borates. Combinations of catalysts can also be effective.

The catalyst is preferably present in a concentration between 0.3 to 11% by weight of the carboxylic acid solution, and, preferably, the normality of the catalyst does not exceed about 80%, more preferably, about 65% of the normality of the carboxylic acids in the solution. However, when relatively low concentrations of acid are present, higher amounts of catalyst are required.

When the composition is applied to the cellulosic substrate, the percent by weight of the fire retardant solution which is applied to the cellulosic substrate is typically between about 5 and 100 percent by weight, preferably between about 10 and 50 percent by weight, and more preferably, about 15 percent by weight of the fiber to be treated. These ranges vary depending on the mode of application and the cellulosic substrate to be treated. For example, for raised surface apparel, larger amounts of the fire retardant solution may be required to achieve adequate fire resistance. This same general principal, of adjusting the solution concentration based on the total wet add-on, applies to other substrates as well, such as fiber fill or upholstery.

More conventional esterification conditions, for example, forming acid halides and reacting the acid halides with the hydroxy groups on the cellulosic material in the presence of a tertiary amine, can be used but are less preferred, in part due to the higher cost of the raw materials.

The resulting cellulosic fiber is fire resistant and the ester linkages between the carboxyl groups and the hydroxy groups on the cellulosic fiber are stable to most conventional washings, including the ten home launderings specified in 16 C.F.R. 1630 and 1631 for carpets which have been treated with a flame retardant.

The treated fiber can be present alone or as blends of cotton and other commercially available fibers, including polyester. The fibers can be used to prepare suitable articles of manufacture, including carpets, raised surface apparel, other garments, upholstery, and other articles which have acceptable fire resistance based on required tests for that particular use. In a preferred embodiment, the fiber is cotton and the article of manufacture is a cotton-based carpet or raised surface apparel. The treated cotton carpets can have a density between about 20 oz/yd² and 120 oz/yd², preferably between about 30 oz/yd² and 80 oz/yd².

The compositions can optionally include additional components, such as other fire retardants, dyes, wrinkle resist agents, foaming agents, buffers, pH stabilizers, fixing agents, stain repellants such as fluorocarbons, stain blocking agents, soil repellants, wetting agents, softeners, water repellants, stain release agents, optical brighteners, emulsifiers, and surfactants.

11 - DETAILED DESCRIPTION OF THE INVENTION

Methods for providing cellulosic fibers, in particular, cotton fibers, with reduced flammability, and articles of manufacture prepared from the resulting flame resistant cellulosic fibers, are disclosed. The methods involve applying to a cellulosic fiber a composition including a mono-, di-, tri- or polycarboxylic acid, a suitable esterification catalyst and a suitable solvent, and reacting some or all of the carboxyl groups with some or all of the hydroxy groups present on the cellulosic fiber.

Depending on the density of the cellulosic substrate, the substrate alone, such as a cotton carpet or raised surface apparel, can be nearly fire resistant enough to meet the U.S. requirements for flammability. A small increase in fire resistance can be sufficient to meet the U.S. guidelines. Accordingly, the use of conventional fire retardants such as organophosphorous compounds, halogenated aromatics, and metal carbonates, which impart fire resistance but which each have inherent problems associated with their use, can be avoided.

Definitions

The following definitions are used herein:

The term "pill test" as used herein is a test used to determine whether a carpet is sufficiently fire resistant for use in the home. It calls for igniting a methenainine pill, which is placed in the center of a nine-inch by nine-inch carpet specimen. If the flame spreads to within one inch of a metal template containing an eight-inch diameter hole, which is placed on top of the carpet specimen prior to igniting the pill, the specimen fails. If the flame does not spread to within one inch of the metal template, then the specimen passes. For a residential carpet, as described above, to be saleable, at least seven out of eight specimens must pass the test. Furthermore, if the carpet has been treated with a flame-retardant (with the exception of alumina trihydrate added to the back coating), then the carpet must be washed ten times as described in AATCC 124-1967 prior to testing.

The term "45 degree angle test" as used herein refers to the flammability test for wearing apparel outlined in the Code of Federal Regulations Title 16, Part 1610. This test method determines the flammability of fabrics with raised surface fibers such as fleece. It calls for placing the specimen to be tested at a 45 degree angle and igniting it by exposing the surface to an open flame for one second. The flame must be one inch from the tip of the flame to the gas nozzle. The rate and intensity of the spread of the flame will categorize the flammability of the fabric.

The term "acceptable hand" as used herein refers to the feel of the resulting substrate after it has been treated with the fire retardant composition.

The term "cellulosic substrate" as used herein refers to substrates that include cellulosic fibers, such as cotton, jute, flax, hemp, ramie, Lyocell™, Tencell™, regenerated unsubstituted wood celluloses such as rayon, blends thereof, and blends with other fibrous materials in which at least about 25 percent, preferably at least about 40 percent of the fibers are cellulosic materials. The term "fiber" relates to fibers present in a substrate such as a carpet, raised surface apparel, upholstery, woven, knit, and nonwoven fabrics, and the like.

The term "flame retardant" as used herein refers to the chemical apphed to the cellulosic substrate. The term "flame resistant" refers to the treated cellulosic substrate. The terms "flame resistant" and "reduced flammability" as applied to substrates are not intended to imply that the materials are fireproof, or that they will not bum. The term "effective fire retardant amounfrefers to an effective amount such that the treated substrate passes the required flammability test for that particular substrate.

The term "degree of substitution" refers to the number of hydroxy groups in the cellulosic substrate which are esterified, on average, per glucose moiety. For example, fire resistance can be obtained by esterifying a relatively low number of hydroxy groups on average on the cellulosic substrate.

The term "catalyst" is typically understood to mean a compound that facilitates a chemical reaction but which is regenerated, allowing further chemical reactions to take place. As used herein, the term "catalyst" also includes compounds which facilitate the coupling of carboxylic acid groups to hydroxy groups on a cellulosic substrate, even if the catalyst also eventually reacts with the substrate in some manner.

I. The Fire Retardant Composition The fire-retardant composition includes at least three elements, a carboxylic acid-containing moiety, a suitable catalyst for coupling the moiety to the fiber, and a suitable solvent.

A. Carboxylic Acid-containing Moieties

Any aliphatic, alicyclic, or aromatic mono-, di-, tri- or polycarboxylic acid can be used. The compounds can optionally include other reactive functional groups, for example, carbon-carbon double bonds, halides, amines, phosphorous esters, monosaccharides, disaccharides, polysaccharides, amides and i ides. The presence of olefins can allow further crosslinking, and the presence of halides can provide additional fire resistance. Perfluoroalkyl and perfluoroaryl groups can impart stain resistant properties to the composition. Hydroxy groups, which can be present, may not be preferred as they may interfere with the desired coupling chemistry and also cause some yellowing in the treated fiber compositions.

Preferably, the compounds include at least two carboxyl groups, so as to effectively bond to at least a portion of the hydroxy groups on the cellulosic material. However, the mechanism of flame resistance, conceivably, is through the decarboxylation of the carboxylic acid during combustion. Some of the dicarboxylic acids also contain hydroxyl groups that may be released as water vapor during combustion. The acids may also promote char formation. Since the ester linkages appear to function by releasing carbon dioxide when the material catches fire, it can be sufficient to use monocarboxylic acids to achieve adequate fire resistance, alone or in combination with the di-, tri- and polycarboxylic acids.

In one embodiment, the compounds are C₂.₂₀ straight, branched or cyclic di-, tri- or polycarboxylic acids, wherein an oxygen or sulfur atom is optionally present in one or more places on the molecule. Examples of such compounds include maleic acid, malic acid, fumaric acid, tartaric acid, citric acid, citraconic acid, itaconic acid, tricarballylic acid, trans-aconitic acid, 1,2,3,4-butanetetracarboxylic acid, all-cis-l,2,3,4-cyclopentane tetracarboxylic acid, mellitic acid, oxydisuccinic acid, thiodisuccinic acid, and the like, or anhydrides or acid halides of these acids.

In another embodiment, the compounds are polymers which include at least three carboxyl groups. Examples of such compounds include poly(methyl)maleic acid, carboxymethyl cellulose, poly(meth)acrylic acid, polymaleic acid, polyacrylic acid, copolymers and blends thereof, and anhydrides or acid halides of these acids. Also suitable are carboxymethyl cellulose fixed with an external crosslinker and gluconic acid fixed by an external crosslinker. Preferably, in aliphatic polycarboxylic acids, each carboxyl group is two or three carbons away from another carboxyl group. Preferably, in aromatic polycarboxylic acids, each carboxyl group is ortho to another carboxylic group.

B. Coupling Catalysts There are several types of catalysts which can be used to esterify the cellulosic materials. Examples of suitable catalysts include alkah metal salts of phosphorous-containing acids, including phosphorous acid, hypophosphorous acid, and polyphosphoric acid, and also include alkah metal mono and dihydrogen phosphates and hypophosphites. The most active catalysts of this type appear to be the alkali metal hypophosphites.

The polyphosphoric acids used to prepare the alkali metal polyphosphates include the cyclic oligomers trimetaphosphoric acid and tetrametaphosphoric acid, and acyclic polyphosphoric acids containing between 2 and 50 phosphorous atoms per molecule. Examples include disodium acid pyrophosphate, pentasodium tripolyphosphate, tetrasodium pyrophosphate, sodium trimetaphosphate and sodium tetrametaphosphate.

Suitable alkah metal dihydrogen phosphates include hthium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate.

Other catalysts which can be used include metal oxides, metal alkoxides, metal carbonates or bicarbonates, alkah metal acetates or other alkah metal acid salts, ammonium phosphate, ammonium halides, alkali metal hydroxides and alkali metal borates. Combinations of each of these catalysts can also be used. C. Suitable Solvents

Preferably, the catalyst and carboxylic acid are present in an aqueous solution, suspension or dispersion. However, other volatile solvents which are inert to the coupling chemistry and in which the carboxylic acid and catalyst are soluble or uniformly dispersible can be used.

The catalyst is preferably present in a concentration between 0.3 to 11% by weight of the carboxylic acid solution, and, preferably, the normality of the catalyst does not exceed about 80%, more preferably, about 65% of the normality of the carboxylic acids in the solution. The composition can be in the form of a solution or an emulsion.

D. Optional Components

Additional components can optionally be added to the fire-retardant composition. These include, but are not limited to, other fire retardants, dyes, wrinkle resist agents, foaming agents, buffers, pH stabilizers, fixing agents, stain repellants such as fluorocarbons, stain blocking agents, soil repellants, wetting agents, softeners, water repellants, stain release agents, optical brighteners, emulsifiers, and surfactants.

Suitable additional fire retardants include, but are not limited to, metal oxides, metal carbonates, halocarbons, phosphorous esters, phosphorous amines, phosphate salts, other phosphoms containing compounds, aluminum trihydrate, and nitrogen-containing compounds.

π. Cellulosic Substrates

Any cellulosic substrate which includes hydroxy groups can be treated with the above-compositions. Cotton is a preferred cellulosic fiber. Other cellulosic fibers include flax, jute, hemp, Tencell™, Lyocell™, ramie and regenerated

17 - unsubstituted wood celluloses such as rayon. The material can be a blend of fibers, such as a blend of cotton and a polyolefin such as polypropylene, a polyester or polytrimethyl terephthalate (PTT). The fiber composition is preferably at least 25, and, more preferably, at least 40 percent by weight cotton.

Any area density of carpet, raised surface apparel, or other woven, knit or nonwoven fabrics, can be constructed and used which is practical from a manufacturing standpoint. For carpet, an area density between 20 and 120 oz/yd², preferably between 30 and 80 oz/yd², is suitable.

πi. Articles of Manufacture Prepared from the Composition The treated fiber compositions can be used for several purposes, including cotton carpets, raised surface apparel, articles of clothing, etc. Cotton carpets are a preferred article of manufacture. Raised surface apparel are also a preferred article of manufacture. When used in carpets, the fiber preferably has a density of between 20 oz/yd² and 120 oz/yd², more preferably between 30 oz/yd² and 80 oz/yd².

IV. Methods of Manufacturing the Carboxylic Acid-Containing Compounds

The carboxylic acid-containing compositions described herein are either commercially available or can be prepared using known methodology.

V. Methods of Treating the Cellulosic Substrate

Methods for covalently linking a hydroxy group and a carboxyl group are well known to those of skill in the art. Conventional means involve forming an acid halide or anhydride, and reacting those with the hydroxy groups. These methods are not preferred, however. Acid hahdes can be prohibitively expensive, and require the use of non-aqueous solvents. Anhydrides which are not formed in situ also require the use of non-aqueous solvents. A preferred method for forming the ester linkages is to impregnate the fiber to be treated with a solution including the carboxylic acid-containing compound and a suitable esterification catalyst. Many of the catalysts disclosed herein appear to function via the in situ production of anhydrides, which then react with the hydroxy groups. In situ production of anhydrides from an aqueous solution of carboxyhc acids is preferable to using anhydrides in a non-aqueous solution, since it avoids the use of non-aqueous solvents.

The solution is added in any suitable proportion, but preferably, the amount of the solution is between 5 and 100 percent by weight of the fiber to be treated, more preferably, between 10 and 50 percent by weight, and most preferably, about 15 percent.

An amount of about 15 percent by weight is particularly well suited for spray application, foam application or other low, wet pickup methods commonly used for treating carpets with fluorochemicals. The use of these methods and types of solutions helps to avoid adding excess water which will have to removed during drying. Then, the material is heated at a sufficient temperature and for a sufficient time to drive off the solvent. Then, the material is heated at a sufficient temperature and for a sufficient time to esterify all or a portion of the hydroxy groups on the material. The material can then optionally be rinsed to remove residual, unreacted chemicals, and then dried. However, since the carboxyhc acids and catalysts used typically do not provide the carpet with odor or toxicity, subsequent rinsing may not be desired. Further, any unreacted carboxyhc acid or other functional groups may be used to attach other types of molecules, for example, via the formation of ester or amide linkages.

For carpets, there are a variety of application techniques which can be used to apply the fire retardant solutions. These include immersion, dipping, dripping, cascading, liquor circulation throughout the substrate, padding, kiss rolls, and doctor blades. These techniques may be used alone or in conjunction with vacuum, squeeze rolls, centrifuge, air knives, gravity drainage or other techniques. The application can be done via a continuous or batch method.

The application(s) of the carboxyhc acid(s) may be done to the fiber, yam or carpet, either before, after, or in conjunction with other manufacturing or processing steps, such as dyeing, winding, cabling, heat setting, tufting or weaving.

For raised surface apparel, or any other apparel that may benefit from a reduction in flammability, the application may be done by any of the above mentioned techniques in fiber, yam, fabric or garment form. Spraying, foaming, dipping or the "Metered Addition Process" are particularly suitable for garment application. The total amount of solution added to the substrate and the required concentration of carboxylic acid in the solution will be dependent on many factors including the flammability test method, the weight and construction of the substrate, and blend levels of the many possible fibers in a blend.

The concentration of carboxylic acid required to be effective, based on both the weight of the solution and on the weight of the substrate, will be dependent on the factors mentioned above for all substrates including raised surface apparel, carpets, upholstery, and any other substrate where it is desirable to reduce the flammability. Any of the application techniques which are mentioned above, or which are used to apply other chemical treatments to fibrous substrates, are considered suitable to be used herein for any cellulosic substrate where it is desired to reduce the flammability.

Where liquor ratios of the treating bath or solution are greater than 1:1 (i.e. greater than one pound of treating solution per pound of substrate), pre-treatment

- 20 - techniques, such as cationic pre-treatments can be used to encourage the treatment chemicals, for example: carboxylic acids, to exhaust or move out of the solution and onto the cellulosic substrate.

Although the temperature required to effectively form the ester linkages would be expected to vary somewhat depending on the nature of the substrate to be treated and the anhydride, a typical range of temperatures is between about 100 and 240 °C, more preferably between 110 and 200 °C. The temperature is preferably less than would otherwise be required to scorch the substrate. Excessive heating can cause yellowing of the substrate fibers, so care should be taken to control the reaction temperatures.

Suitable reaction times are typically between approximately one minute and five hours. However, the reaction times relate in part to the pH of the fire retardant solution. At a pH greater than 4, cure times are generally longer. However, there appears to be less of a change in the dye shade of dyed carpets when a pH greater than 4 is used.

Carpets typically have a polypropylene backing layer, which tends to melt at temperatures above 120°C. For this reason, it is preferable that this temperature not be exceeded when this type of carpet is treated. However, raised surface, apparel, upholstery, fiber fill, and carpets with non-thermoplastic backings may not have this type of temperature limitation. When these types of substrates are treated, the reaction temperature may be elevated as required, consistent with the scorching and/or yellowing temperature of these materials. One of skill in the art can readily determine an appropriate set of temperatures for a particular substrate to be treated.

It can be difficult to prepare anhydrides in situ when monocarboxylic acids are used. For these materials, it may be desirable to use conventional chemistry, such as the formation of acid halides or anhydrides and application of these materials to the carpet, rather than forming anhydrides in situ.

Those of skill in the art can readily determine an appropriate set of reaction conditions (amount of fire retardant solution to add and suitable temperatures and reaction times) to form ester linkages between the cellulosic substrate and the fire retardant composition.

In those embodiments in which the carboxylic acid-containing compound includes carbon-carbon double bonds, these bonds can be polymerized before, simultaneous with, or after forming the ester linkages with the hydroxy groups on the cellulosic substrate. The additional crosslinking provides additional fire resistance to the overall product. Methods for crosslinking carbon-carbon double bonds are well known to those of skill in the art, and typically involve the addition of a free radical polymerization initiator, such as t-butyl peroxide, persulfates, or azobisisobutyronitrile (AEBN).

IV. Methods of Evaluating the Fire Retardant Cellulosic Compositions

The suitability of the fire retardant composition for an intended use will depend on the ability of the treated cellulosic substrate to pass various standard flammability tests. The currently accepted test for carpets is the pill test. The currently accepted test for raised surface apparel is the 45 degree angle test.

The testing protocol for these tests is well known to those of skill in the art. Using these tests, with a suitably prepared reduced flammability cellulosic fiber composition, one can readily determine the efficacy of the fire retardant composition for its intended use. EXAMPLES

Example 1 : The Effect of Carboxylic Acids on the Flammability of Cotton Carpets

Additions of various dicarboxylic acids on cotton carpets were found to reduce the flammabihty of the carpets. These finishes on cotton carpets have proven durable to home laundering as well as to Hexapod treatments as judged by pill test results.

Samples of cotton carpet were produced by Strike-Off, batch number CD 98- 039, from cotton/low melt polyester (90/10). The carpet was intentionally constructed to fail the pill test. The details of the construction are given in Table I.

TABLE I Carpet Construction (Cut Pile)

The carpet samples were sprayed with mixtures of different dicarboxylic acids as shown in Table π, with 15% target add-on (wet-on-dry) by weight. The treated samples were dried at 220°F (104°C) and cured at 250°F (121 °C) for 5 minutes, except as follows. Sample N14/1B, N14/3B and N40/1 were cured at 300°F (149°C) for 5 minutes. The cured samples were evaluated for changes in hand, odor, and yellowing. The treated carpets were tested for flammabihty before

23 - and after washing and after being subjected to simulated wear in a Hexapod tester. The washing procedure was conducted using the AATCC 124-1996 test method with a minor modification: the samples were washed with the AATCC standard detergent 10 times prior to a tumble dry cycle.

TABLE π

Carboxyhc Acid Bath Formulations*

**l,2,3,4-Butanetetracarboxylic Acid

The treated samples were also subjected to Hexapod treatments to simulate the wear and tear caused by foot traffic. The Hexapod treatments were conducted according to ASTM D-5252 procedure. The carpets were subjected to 3 lb. Hexapod for 8000 cycles. The worn carpets were evaluated for weight loss and pile surface appearance. Then the carpets were tested for flammability using the pill test method.

- 24 - The flammability test was conducted according to the Code of Federal Regulations (CFR) title 16 part 1630 test method (Code of Federal Regulations, Title 16 Part 1630, p. 632 (1995).

The carboxylic acids used were: maleic acid (c.5-butenedioic acid), tartaric acid (2,3-dihydroxybutanedioic acid), citric acid (2-hydroxy- 1,2,3- propanetricarboxylic acid), and BTCA (1,2,3,4-butanetetracarboxylic acids). All carpet samples cured at 250 °F (121 °C) did not show any adverse change in hand, odor or color, as shown in Table HI. This indicates that the addition of carboxylic acids (or their by-products) and curing at 250°F (121 °C) did not change the appearance nor caused any yellowing on the bleached carpets. Some yellowing, however, was seen in the carpet samples treated with citric acid and cured at 300 °F (149°C). The mechanism of yellowing is still unclear, but it is conceivably due to the by-product formation during the curing of citric acid at a high temperature. Citric acid may decompose on heating to produce aconitic acid, which causes the yellowing of cotton (Welch, M. C, Peters, J. G.; Text. Chem. and Col., 29, n. 3, p. 22 (1997)).

TABLE HI

Physical Evaluation of Treated Carpet

Note: Samples N14/1B, N14/3B and N40/1 were cured at 300°F (149°C)

A slight yellowing on carpet was seen on sample N14/1B. This carpet was treated with tartaric acid and cured at 300 °F (149 °C). A possible source of this shght yellowing may be due to the addition of the fluorocarbon (Scotchgard FX1367™). Sample N14/1 was treated with Scotchgard FX1367™ and cured at

300°F (149°C) without carboxylic acid. The carpet showed slight yellowing similar to that of sample N40/1B. Therefore, this shght yellowing may be the result of the fluorocarbon addition or from residual acetate from bleaching instead of the byproduct of the acid.

The flammability of the treated carpet has shown a remarkable improvement from the untreated carpets. All the unwashed treated samples passed the pill test. The mode of flame extmguishing by the carboxylic acid is likely via decarboxylation of the acid. This resulted in formation of incombustible gases, such as carbon dioxide. Furthermore, the hydroxyl groups in tartaric and citric acids may be released as water vapor during combustion, which in turn, further absorbs energy from the area of combustion around the burning pill.

After 10 washes, samples 9/1 and 9/2 passed the pill test, and sample 9/4 showed improvement in fire resistance. Samples N14/1A and N14/3A, which failed the pill test, were treated with tartaric acid and citric acid, respectively, in conjunction with sodium phosphate, monobasic (NaH₂PO₄) as the catalyst and cured at 250°F (121 °C). This result indicates that the tartaric and citric acids, catalyzed with monosodium phosphate, did not effectively esterify the hydroxy groups on the cotton. The other tartaric acid-treated carpet, sample N9/2, however, passed the pill test after 10 washes. This sample was treated with tartaric acid catalyzed by sodium hypophosphite and cured at 250°F (121 °C). This shows that the sodium hypophosphite is a better fixation catalyst for tartaric acid onto the cellulose than the monosodium phosphate. U.S. Patent No. 4,820,307 to Welch et al., have demonstrated that the sodium hypophospite (NaH₂PO₂) can effectively catalyze the reaction of polycarboxylic acids with cotton. Furthermore, the presence of the hydroxyl groups in tartaric acid may impede the esterification of the cellulose. Samples treated with BTCA, N9/4, gave a marginal result. A possible reason may be the insufficient fixation of the acid on cellulose.

The durability of dicarboxylic acid fixation on cotton is possible via ester linkages between the acid and cellulose. The fixation may not necessarily result in the crosslinking of the cellulose. The reaction between the cellulose and the acid is believed to occur through the cychc anhydride intermediary. The catalytic formation of cyclic anhydride appears to occur by dehydration of the acid during the curing stage. The cyclic anhydride is readily reacted with the hydroxyl groups of the cellulose. The ease. of the cyclic anhydride formation varies with type of acid as well as the catalyst. The role of the catalyst is important in aiding the formation of the cyclic anhydride. As indicated earlier, sodium hypophosphite is believed to be the most effective catalyst for carboxylic acids.

All treated carpet samples subjected to Hexapod passed the pill test, as shown in Table rv. The Hexapod treatment was done to simulate the wear and tear of carpet due to foot traffic. The changes in appearance of the tufted surface were evaluated using the Carpet and Rug Institute (CRI) TM-101 method, reference scale F. The evaluation results are tabulated in Table V. All treated samples showed a weight loss between 1.34 - 2.37% after the Hexapod. The appearance of each carpet after Hexapod was evaluated against the control sample carpet. All treated carpet samples showed a remarkable resiliency to wear.. They showed similar wear and tear to that of untreated carpets.

27 - TABLE IV

Flammability: Pill Test Results

Note: P - Pass; F - Fail

Samples N14/1A and N14/3A cured at 250F

TABLE V

Physical Evaluation of the Carpet after Hexapod

Dicarboxylic acids can be fixed onto cellulose via formation of the ester linkages. This linkage has been shown to be effective and durable. The addition of the carboxylic groups on cotton has been shown to reduce the flammability of the cotton carpet. This finish on cotton carpet is durable to 10 washes and to Hexapod treatments. All treated samples showed remarkable endurance to simulated foot traffic. One of the advantages of these dicarboxylic acids, such as tartaric acid, is lower toxicity compared to many conventional FR finishes. Example 2: Evaluation of Lower Concentration of Carboxylic Acids on the Flammability of Cotton Carpets

The experimental approach is similar in this series of experiments: Solutions containing dicarboxylic acids, catalyst, fluorocarbon and non-rewetting wetting agent were prepared.

Carpet samples were sprayed with the solutions to 15% (w/w) target add on. Treated carpets were dried at 220°F (104°C) and cured at 250°F (121 °C). The treated carpet samples were tested for flammability using the pill test. The cotton carpets treated with lower concentration of dicarboxylic acids did not pass the flammability test after 10 washings. Only those carpets treated with 5% or higher concentrations of maleic acid in the solution passed the pill test before and after 10 washes.

Cotton carpet treated with solutions containing 10% by weight of the dicarboxylic acids showed reduced flammability. This type of finish has proved to be effective and durable to 10 home launderings. The detailed construction of the carpet is listed in

Table T. The formulation and the amount of dicarboxylic acids in bath and on carpet samples are shown in Tables VTI and VTfl.

TABLE VI Carpet Construction (Cut Pile)

TABLE Vπ

Carboxylic Acid Bath Formulations Percent On Weight of Bath (OWB)

TABLE VHI

Actual Concentrations of Carboxylic Acids on Carpets (Percent by Weight)

Samples Dicarboxylic acids

N27/1 0.81

N27/2 0.38

N27/3 0.81

N27/4 0.36

N27/5 1.01

N27/6 0.51

N27/7 0.00

The treatments on the carpet did not produce any changes in odor, hand, or appearance. These results are listed in Table IX.

TABLE LX

Physical Evaluation of Treated Carpet

31 - The flammability results of the treated carpets are listed in Table X. Only carpets treated with maleic acid with bath concentration of 5% passes the pill test before and after 10 washings. Two specimens were tested for each condition.

TABLE X

Flammabihty: Pill Test Results

Note: P = Pass; F = Fail

The low pH of the treated carpets was a concern. The low pH may cause irritation on sensitive skin. Lowering the concentration of the acids in the bath may raise the pH. As demonstrated in Table XI, those carpets treated with 2% dicarboxylic acids have reasonably high pH, above 4.00. Carpets which have pH higher than 4.00 passed the USP methyl orange test.

TABLE XI pH of Solutions and Treated Carpets and Results of USP pH Test (as Used for Pharmaceutical Grade Cotton Fiber) on Treated Carpets

Pass; F = Fail; NM = Not Measured

Modifications and variations of the methods and compositions described above will be obvious in view of the description of the invention. Such modifications are intended to be within the scope of the claims.

Claims

We claim:

1. A method for preparing cellulosic fibers with reduced flammability comprising: a) preparing a composition comprising carboxylic acids and a suitable esterification catalyst; b) applying an effective, fire retarding amount of the composition to a substrate to be treated which comprises a cellulosic fiber or a blend of a cellulosic fiber with another fiber; and c) esterifying the carboxyl groups with a sufficient quantity of the hydroxy groups on the fiber to be treated such that the resulting treated fiber has an acceptable degree of fire resistance for the intended use.

2. The method of claim 1, wherein the carboxylic acid-containing composition comprises a C₂.₂₀ straight chain, branched or cyclic alkane that includes at least one carboxylic acid moiety, and which is optionally substituted with a functional group selected from the group consisting of carbon-carbon double bonds, halides, perfluorinated groups, amines, phosphorous esters, monosaccharides, polysaccharides, i ides, and amides.

3. The method of claim 1, wherein the carboxylic acid-containing composition comprises a polymer that includes at least one carboxylic acid moiety, and which is optionally substituted with a functional group selected from the group consisting of carbon-carbon double bonds, halides, amines, phosphorous esters, monosaccharides, disaccharides, polysaccharides, amides and imides.

4. The method of claim 3, wherein the polymer is selected from the group consisting of polymaleic acid, poly(meth)acrylic acid, carboxymethyl cellulose, polyacrylic acid, and poly(meth)acrylic acid.

5. The method of claim 1, wherein the degree of substitution on the cellulosic substrate is between about 0.003 to 0.5.

6. The method of claim 1, wherein the degree of substitution on the cellulosic substrate is between about 0.005 to 0.025.

7. The method of claim 1 wherein the fiber is a cotton fiber.

8. The method of claim 7, wherein the cotton is in the form of a cotton carpet.

9. The method of claim 7, wherein the cotton is present in raised surface apparel.

10. The method of claim 1, wherein the fiber is a blend of cotton and another fiber selected from the group consisting of polyesters, polyamides, polytrimethyl terephthalate (PTT) wool, acrylic, modacrylic, rayon, acetate, triacetate, polyolefins, Tencell™, and Lyocell™.

11. The method of claim 1, wherein the fire-retardant composition further comprises an additional fire retardant selected from the group consisting of metal oxides, metal carbonates, halocarbons, phosphorous esters, phosphorous salts, phosphorous amines, aluminum trihydrate, and nitrogen-containing compounds.

12. The method of claim 1, wherein the composition further comprises a component selected from the group consisting of other fire retardants, dyes, wrinkle resist agents, foaming agents, buffers, pH stabilizers, fixing agents, stain repellants stain blocking agents, soil repellants, wetting agents, softeners, water repellants, stain release agents, optical brighteners, emulsifϊers, and surfactants.

13. The method of claim 1 wherein the fiber is selected from the group consisting of Lycell™, Tencell™ and rayon.

14. A method for preparing cellulosic fibers with reduced flammabihty comprising: a) selecting a suitable cellulosic substrate, b) pre-treating the substrate with a cationic pre-treatment, c) optionally removing excess pre-treatment, d) adding an effective, fire retarding amount of a composition comprising carboxylic acids and optionally including a suitable esterification catalyst to the pre- treated substrate, wherein the ratio by weight of the solution to the substrate is greater than 1:1.

15. The method of claim 14 further comprising a dyeing step prior to the pre- treatment step.

16. The method of claim 14 further comprising esterifying the carboxyl groups with a sufficient quantity of the hydroxy groups on the substrate to be treated such that the resulting treated substrate has an acceptable degree of fire resistance for the intended use.

17. A carpet comprising cotton fiber in which a portion of the hydroxy groups on the cotton fiber have been esterified with a carboxylic acid-containing moiety.

18. The carpet of claim 17, wherein the carboxyhc acid-containing moiety is a C₂.₂₀ straight chain, branched or cyclic alkane that includes at least one carboxylic acid moiety, and which is optionally substituted with a functional group selected from the group consisting of carbon-carbon double bonds, hahdes, amines, phosphorous esters, monosaccharides, disaccharides, polysaccharides, amides and imides.

19. The carpet of claim 17, wherein the carboxylic acid-containing moiety is a polymer that includes at least one carboxylic acid moiety, and which is optionally substituted with a functional group selected from the group consisting of carbon- carbon double bonds, halides, amines, phosphorous esters, monosaccharides, disaccharides, polysaccharides, amides and imides.

20. The carpet of claim 19, wherein the polymer is selected from the group consisting of polymaleic acid, polyacrylic acid, poly(meth)acrylic acid, and carboxymethyl cellulose.

21. The carpet of claim 17, wherein the degree of substitution on the cotton fiber is between about 0.003 to 0.5.

22. The carpet of claim 17, wherein the degree of substitution on the cotton fiber is between about 0.005 to 0.025.

23. The carpet of claim 17, wherein carpet further comprises a second fiber selected from the group consisting of polyesters, polyamides, polytrimethyl terephthalate (PTT) wool, acrylic, modacryhc, rayon, acetate, triacetate, polyolefins,

- 36 - Tencell™, and Lyocell™.

24. The carpet of claim 17, wherein the carpet further comprises an additional fire retardant selected from the group consisting of metal oxides, metal carbonates, halocarbons, phosphorous esters, phosphorous --mines, phosphorous salts, aluminum trihydrate, and nitrogen-containing compounds.

25. Raised surface apparel comprising cotton fiber in which a portion of the hydroxy groups on the cotton fiber have been esterified with a carboxylic acid- containing moiety.

- 37 -