US3505087A - Flame-retardant rayon containing halogenated phosphonitrilate polymer - Google Patents

Description

United States Patent Ofifice 3,505,087 Patented Apr. 7, 1970 US. Cl. 106-15 9 Claims ABSTRACT OF THE DISCLOSURE Flame-retardant regenerated cellulose filaments and filamentary articles containing dispersed therein a flameretardant amount of a substantially water-insoluble, liquid, halogenated phosphonitrilate polymer, and a method of preparing the filamentary articles are disclosed herein.

This in a continuation-in-part application of eopending patent application Ser. No. 566,757, filed July 21, 1966, now Patent No. 3,455,713.

It is desirable for many textile purposes to provide cellulose fibers and yarns having greatly decreased flammability. The production of rayon which demonstrates acceptable flame-retardant properties for all textile requirements, using inexpensive and commercially suitable chemical flame-retardants, has not been satisfactorily accomplished to date.

The application of various organic and inorganic flameretardants to the surface of cellulose fibers and fabrics has not produced the desired result for a number of reasons. In many instances, the chemical flame-retardant is effectively removed when the fabric is washed with water or dry cleaned with solvents. Other flame-retardant chemicals which may be applied to the fabric surface and retained after washing are generally too costly. In other cases, the chemicals used may provide some lasting reduction in flammability but destroy fiber and fabric characteristics, such as tenacity, softness, whiteness, and dyeability, which are desirable and necessary for textile applications.

In the manufacture of rayon by the viscose method, it has been proposed to add various flame-retardant chemicals to the viscose prior to spinning. This approach presents many additional problems because of the particular chemistry of the viscose process. Accordingly, the flameretardant must be stable and inert with respect to the highly alkaline viscose and also with respect to the acid regenerating bath into which the viscose is extruded. It must not be extracted during spinning and processing. Furthermore, the added material must not interfere with the spinning process, i.e., cause clogging of the spinnerets. The rayon produced from the flame-retardant containing viscose must not be degraded in any of its properties and must have a substantially reduced flammability.

It is not an object of this invention to provide a flameretardant rayon fiber without appreciable degradation of any fiber properties.

It is a further object of this invention to provide a process for preparing a flame-retardant rayon fiber which retains substantially all of the properties of ordinary rayon.

These and other objects are achieved in accordance with this invention which comprises a regenerated cellulose filament having dispersed therein a substantially water-insoluble, liquid phosphonitrilate polymer having the following general formula:

wherein R and R are the same or different alkyl, alkenyl, arylalkyl or aryl radicals wherein the alkyl and alkenyl radicals have from one to six carbon atoms and the aryl groups have 6 to 10 carbon atoms and, at least one of the OR or OR' groups of the polymer has one or more halogen atoms attached to the carbon atoms of R or R, and n is an integer of at least 3. For example, R and R include halogen substituted and unsubstituted ethyl, propyl, isopropyl, butyl, isobutyl, arnyl, isoamyl, hexyl, allyl, crotyl, phenyl, naphthyl and cresyl radicals. Where R is methyl R must be a radical of a greater number of carbon atoms since the methyl radical is not readily halogenated and also tends to make the polymer more Water-soluble. In the preferred embodiment of this invention, R and R are both halogenated ethyl or propyl radicals since compounds where R and R are the same are more easily prepared, and phosphonitrilate polymers having fewer carbon atoms tend to be more water-soluble, whereas the presence of more carbon atoms provides products having a lower percentage of phosphorus thereby reducing their effectiveness. However, mixed esters wherein R and R are different radicals depending on the combination of substituent groups and halogens, may provide superior results. Furthermore, the halogen atoms included herein are chlorine, bromine and fluorine. Iodine is excluded since derivatives thereof are unstable.

The liquid phosphonitrilate polymer is a cyclic trimer, tetramer or higher cyclic polymer, or a linear polymer and is preferably employed as a mixture of these isomers for economic reasons. It has been found, however, that the pure polymeric isomer is effective for the purposes of this invention.

The amount of phosphonitrilate flame-retardant dis persed in the regenerated cellulose filament varies from about 5 to about 30% and preferably from 10 to 25%, based on the weight of the filament.

The method of this invention comprises incorporating the above described liquid phosphonitrilate in a viscose solution and spinning the viscose in the shape of one or more filaments into a coagulating and regenerating medium. The formed filaments are aftertreated using techniques well-known in the rayon field to provide continuous filaments, fibers and yarn, as well as staple fibers. These may then be used to prepare any known textile article in which the flame-retardant property is desirable.

The flame-retardant phosphonitrilate of this invention is a liquid of pumpable consistency which is preferably used as a crude reaction product, prepared, for example, in a known manner by the conversion of the corresponding polymeric phosphonitrilic chlorides to the specified esters, and then halogenated. Refined products such as the trimer are also quite useful. Halogenation, for example, may be carried out as shown by Hamalainen et al., Textile Research Journal, February 1956, pp. 14l 144, and U8. Patent 2,825,718. The esters or mixed esters may also be chlorinated or fluorinated similarly.

The halogenated esters are also former, for example, by reacting the liquid polymers of phosphonitrilic chloride with a compound which will form a halogenated ester of the phosphonitrilic chloride, for example, ethylene chlorohydrin and ethylene bromohydrin, or halogenated alkyl alcohols, for example, as shown in US. 2,681,295.

The product formed by these reactions is an oily liquid and may be incorporated in viscose as such or in suitable solutions or aqueous emulsions. Preferably a controlled amount of the flame-retardant halogenated phosphonitrilate is injected into the viscose just prior to its extrusion through the filament forming spinnerets. The viscose is then spun into an acid bath and processed in a conventional manner.

The following examples are set forth to demonstrate this invention.

EXAMPLE 1 295.5 grams (3.67 moles) of ethylene chlorohydrin was added dropwise over a 75 minute period to a stirred solution of 133.4 grams (2.3 mole equiv.) of the cyclic trimer of phosphonitrilic chloride in 1000 ml. of pyridine. Initially the reaction mixture was at 20 C., but the temperature rose rapidly reaching 38 C. after about 70 grams of ethylene chlorohydrin had been added. External cooling reduced the temperature to about C. where it was held for the remainder of the addition. The reaction mixture was then stirred at room temperature for 24 hours.

After the 24 hours of stirring, some excess of pyridine was distilled off under vacuum (150 minutes, 40-41 C.) and the residue poured onto ice water (1000 ml.). The product was extracted with chloroform (300 ml.) and the chloroform solution separated, washed twice with dilute hydrochloric acid (100 ml. per wash) and then twice with water (300 ml. per wash). The aqueous layers were extracted successively with chloroform (300 ml.) and the chloroform solutions combined, dried and filtered.

Evaporation of the chloroform on a rotary evaporator left an oily residue which was stirred under vacuum for 5.5 hours (40 C., 0.02 mm.). The final product was a straw colored oil (225.5 grams, 95%) with a faint mistiness which was not removed by filtering.

A nuclear magnetic resonance spectrum of this material showed a triplet 3.75 p.p.m. and a complicated, poorly resolved pattern at 1:1 ratio. This result was consistent with the formula for 2,2,4,4,6,6-hexa(2-chloroethoxy) cyclotriphosphazatriene or 2-chloroethyl hexaester of trimeric phosphonitrilic chloride, and there were no significant impurities. Analysis of the compound showed 22.8% carbon, 3.95% hydrogen, 34.7% chlorine, 7.54% nitrogen and 16.9% phosphorus. Theoretical requirements for the compound are 23.6% carbon, 3.95% hydrogen, 34.8% chlorine, 6.9% nitrogen and 15.2% phosphorus.

A compound prepared in this manner was injected into the viscose line supplying the spinnerets for manufacturing rayon in a metered amount based on the weight of the cellulose in the viscose. This viscose was spun into a conventional aqueous acid spin bath comprising 9.0% sulfuric acid, 2.0% zinc sulfate and sodium sulfate at 55 C. The resulting yarn was processed by passing it through a series of baths including water wash, desulfurization, bleaching, bleach acid, anti-chlorine, and soft finish baths. The yarn was dried and collected.

A yarn flammability test was conducted with yarn produced as described above. The test consisted of first preparing a yarn bundle by wrapping the yarn around the closed fingers of an extended hand to produce a bundle of 6000 denier and then removing it from the hand. The yarn bundle is twisted five times and then doubled on itself to produce an integrated yarn bundle, one and one-half inches long and of 12,000 denier size. The free ends of the yarn bundle are clamped in forceps, and the bundle, held in horizontal position, is passed through the tip of the flame of a Fisher burner in an oscillating motion at a rate of one pass per second. The burner flame is adjusted to a two inch height and a blue flame. The number of passes to induce flaming of the sample is determined. A control yarn bundle (yarn con- .tains no flame-retardant inflames in 1 or 2 passes and flame-retardant yarns are classified for inflammability as follows:

1-2 passes-poor 3-4 passes-fair 56 passes-good 7-9 passes-very good to excellent 10 or more passes-excellent Rayon yarn containing about 15 wt. percent of the 2-chloroethyl hexaester of trimeric phosphonitrilic chloride was rated excellent in the above test procedure with no evidence of after-glow. After-glow represents combustion without a visible flame.

Retention of the amount of flame-retardant in the yarn after the above. described complete processing of the spun yarn based on phosphorus analysis showed 91.0%. The yarns esthetic properties were substantially the same as ordinary rayon.

EXAMPLE II A similar procedure for preparing the chlorinated ester of the cyclic trimer of phosphonitrilic chloride as shown in Example I was carried out except that a mixture of phosphonitrilic chloride polymers obtained as the crude product from the preparation of the liquid phosphonitrilic chloride polymer was employed in place of the pure cyclic trimer. The mixture contained mostly trimer and tetramers with some higher cyclic and linear polymers of phosphonitrilic chloride. The yield was 85.4% and analysis of the product showed 23.3% carbon, 4.05% hydrogen, 34.9% chlorine, 16.0% phosphorus and 7.4% nitrogen.

The product of the above reaction was similarly injected into viscose and the viscose spun and processed as described in Example I. The yarn, containing about 15% by weight of the injected product, was subjected to the flame test and showed very good flame retarding with no after-glow. After exposure to ultraviolet light in a Fadeometer for 50 hours, the loss of yarn strength was not greater than conventional rayon.

EXAMPLE III The 2,3-dichloropropyl hexaester of the cyclic trimer of phosphonitrilic chloride was prepared by chlorination of the hexaallyl ester of phosphonitrilic chloride. This was injected into viscose and the viscose spun and processed. The yarn, containing 25% by weight of the chlorinated phosphonitrilate was flame-retardant.

Other water-insoluble, liquid halogenated polyphosphonitrilic esters, e.g. chlorinated, brominated and fluorinated allyl esters of polyphosphonitrilic chloride; adducts of bromoform and allyl ester of polyphosphonitrilic chloride; 2,3-dibromopropyl ester of polyphosphonitrilic chloride; 1,3-dichloropropyl ester of polyphosphonitrilic chloride; chlorophenyl ester of polyphosphonitrilic chloride; bromonaphthyl ester of polyphosphonitrilic chloride; halogenated or partially halogenated mixed esters, e.g. bromopropyl, ethyl ester of polyphosphonitrilic chloride; fluoropropyl, methyl ester of polyphosphonitrilic chloride; chlorophenyl, methyl ester of polyphosphonitrilic chloride; etc., can be injected into viscose to prepare rayon as shown in the foregoing examples.

As set forth in the statement of the invention, it is not necessary that the OR and OR groups attached to each phosphorus atom in the polymeric chain be halogenated. That is, for example, the hexaester of the cyclic trimer of phosphonitrilic chloride has six substituent groups. In accordance with this invention, from one to six of these groups can be halogenated.

Some of the halogenated esters will be more permanently retained in the yarn than others, some require addition in greater amounts to the viscose to obtain the desired flame-retardancy but the greatest advantage of the flameretardant of this invention is that it can be injected into viscose and spun into a yarn which retains its normal softness and hand. This is because the halogenated ester is a viscous liquid held within the regenerated cellulose matrix. Phosphonitrilic esters which are solids tend to produce harsh yarn and are difiicult to spin in viscose.

Those halogenated esters which are not permanently retained by fabric made of the rayon yarn after continued washing will be useful for rayon intended for use in disposable garments.

I claim:

1. Regenerated cellulose filaments and filamentary articles, said filaments having dispersed therein a flame-retardant amount of a substantially water-insoluble, liquid phosphonitrilate polymer having the following general formula:

wherein R and R are the same or different alkyl, alkenyl, arylalkyl or aryl radicals wherein the alkyl and alkenyl redicals have from 1 to 6 carbon atoms and the aryl radicals have from 6 to 10 carbon atoms and, at least one of the -OR or -OR groups of the polymer ha one or more halogen atoms attached to the carbon atoms of R or R, and n is an integer of at least 3.

2. The regenerated cellulose filaments of claim 1 containing from about 5 to about 30% based on the Weight of the cellulose, of the liquid phosphonitrilate polymer.

3. The regenerated cellulose filaments of claim 1 wherein R and R are both 2-chloroethyl radicals.

4. The regenerated cellulose filaments of claim 1 wherein R and R are both 2,3-dichloropropyl radicals.

5. The regenerated cellulose filaments of claim 1 wherein R and R are different radicals and one of said radicals is halogenated.

6. A method of preparing a flame-retardant regenerated cellulose filament which comprises mixing viscose and a fllame-retardant amount of a substantially water-inlNi wherein R and R are the same or diflerent alkyl, alkenyl, arylalkyl or aryl radicals wherein the alkyl and alkenyl radicals have from 1 to 6 carbon atoms and the aryl radicals have from 6 to 10 carbon atoms and at least one of the -OR or OR' groups of the polymer has one or more halogen atoms attached to the carbon atoms of R or R, and n is an integer of at least 3; shaping the mixture into a filament, and coagulating and regenerating said filament.

7. The method of claim 6 wherein the viscose is passed under pressure to a spinneret and extruded, and the liquid phosphonitrilate polymer is injected at a controlled rate into the viscose prior to extrusion. H

8. The method of claim 6 wherein about 5 to about 30% 0f the liquid phosphonitrilate is mixed with the viscose, based on the weight of the cellulose in the viscose.

9. The method of claim 6 wherein R and R are the same and each contain at least 2 carbon atoms.

References Cited UNITED STATES PATENTS 8/ 1966 Schappel et al. 7/1969 Godfrey.

US. Cl. X.R.