Flame-retardant fiber blend

[57] ABSTRACT

Flame-retardant yarns and fabrics of a combination of (1) fibers of a polyester resin of at least 75 mol % of ethylene-2,6-naphthalene dicarboxylate units and flame-retardant amount of an organic bromine or chlorine compound physically mixed therewith and (2) flame-retardant cellulosic fibers. Preferably, one or more specified metal compounds are also physically mixed with the polyester resin and halogen compound.

Claims, No Drawings

3,874,155

FLAME-RETARDANT FIBER BLEND

The most commercially important polyester textile fibers have been those prepared from polyethylene terephthalate resins. Because of their commercial importance and the great concern for flame-retardant textile fabrics, attempts have been made to provide flameretardant properties for these flammable polyester materials. One of the methods used required the physical incorporation of flame-retardant chemicals in the polymer composition. Organic halogen compounds and combinations of halogen compounds and metal compounds have been incorporated in polyester resins. However, in the case of textile fibers, the high amounts of flame- retardant chemicals necessary to impart the degree of flame- retardancy required by stringent federal regulations embrittles the fibers and detrimentally affects the physical properties thereof.

The need for a polyester fiber which has good physical properties and high flame-retardancy is most critical for yarn and fabric blends of polyester fibers and cellulosic fibers. Polyester-cellulosic fiber blends provide textile fabrics having the highly desirable wear characteristics of polyester fabrics with highly desirable comfort characteristics of cellulosic fabrics. Polyester fibers are thermoplastic and when exposed to a flame, burn and melt away from the flame, thus extinguishing themselves. If polyester fibers are blended with flammable cellulosic fibers and exposed to a flame, the polyester is more likely to continue burning even when melting since the burning cellulose fiber continuously ignites it. If polyester fibers are blended with flameretardant cellulosic fibers and the blend ignited, the flame-retardant cellulosic fibers burn only in the area of flame contact. However, the flame-retardant cellulosic fiber prevents the polyester fiber from shrinking and dripping away from the flame and the polyester continues to burn.

It is a primary object of this invention to provide more useful flame-retardant yarns and fabrics of blends or combinations of polyester fibers and cellulosic fibers.

It is another object of this invention to provide yarns and fabrics of good physical properties from blends of flame-retardant polyester fibers and flame-retardant cellulosic fibers which yarns and fabrics will meet more stringent flame- retardant requirements.

Polyesters as employed herein have reference to fiber- forming polymers of glycols and dicarboxylic acids, hydroxycarboxylic acids, and combinations thereof.

These and other objects are attained in accordance with this invention which comprises flame-retardant yarns and fabrics of a combination of (1) fibers of a polyester resin of at least 75 mol % of ethylene-2,6naphthalene dicarboxylate units and up to 25 mol % of other ester units, and at least one organic bromine or chlorine containing compound having a total content of bromine, chlorine or mixture thereof of at least 40% based on the weight of the compound, the halogen compound being present in an amount sufficient to improve the flame-retardant properties of the polyester resin, and (2) flame-retardant cellulosic fibers.

The organic halogen compound is heat stable up to a temperature of at least the melt temperature of the polyester resin and preferably to at least 300°C. At the ignition temperature of the polyester resin, bromine or chlorine is liberated from the compound to provide flame-retardancy. If desired, more than one bromine or chlorine compound can be employed in combination as long as the total halogen content is at least 40% based on the weight of the total halogenated compounds employed. It is preferred that the organic halogen compound or compounds are present in the composition in an amount sufficient to provide from at least 5 up to about 25% halogen, more preferably from about 10 to about 20%, based on the weight of the polyester resin. Aromatic bromine compounds are preferred based on their generally better flame-retardant performance.

Examples of halogen compounds useful for this invention are included in the following formula:

<img file="US3874155A_D0001.tif" />

Y n

where X is chlorine or bromine, Y is —R, —OR, or —OROR, where R is an alkyl radical having from 1 to 10 carbon atoms, an aryl radical having from 6 to 24 atoms, an aralkyl radical having from 6 to 16 atoms and the halides thereof, R' is an alkylene radical having from 1 to 6 carbon atoms, n and m are positive integers satisfying the expression 6S 1, 5δ/ι §0.

Examples of halogen compounds useful for this invention include polybrominated diphenyls, polybrominated diphenyl ethers, polybrominated diphenyl carbonates, tetrabromophthalic anhydride, tetrabromophthalic-imide, tetrabromobisphenol A difatty acid ester, tetrabromobisphenol S di-fatty acid ester, hexabromobenzene, polybrominated poly (pentaerythritol) (see U.S. Pat. No. 3,700,625), polybrominated carbonates containing neopentyl groups (see U.S. Pat. No. 3,688,001), brominated polyethers (see U.S. Pat. No. 3,645,962), polybrominated terphenyls, polybrominated anthracenes, pentabromo toluene, pentabromo benzyl bromide, polybrominated diphenoxyalkanes, tetrabromobisphenol A dimethyl ether (see U.S. Pat. No. 3,658,634). The bromine radicals are replaced with chlorine radicals to provide corresponding chlorine containing compounds.

These compounds are used alone or in combination to supply the required amount of halogen for the composition. Preferably, the compounds contain at least 60% by weight of bromine or chlorine in order to permit the incorporation of less of the organic halogenated compound in the polyester resin composition for optimum flame-retardancy and physical properties.

In a preferred embodiment of this invention, a metal compound, from the group including antimony oxides, e.g., antimony trioxide; antimony salts of a-hydroxycarboxylic or a, β-dicarboxylic acid, zinc oxide and alumina, is also included in the resin composition, if desired, in an amount sufficient to provide improved flame-retardancy, generally in amounts ranging from about 3% to about 60%, preferably 7 to 35% of the metal, based on the weight of the halogen present. Combinations of these compounds are also employed either alone or on supports, e.g., a mixture of antimony

3,874,155 trioxide and alumina on silica gel. These metal compounds, as is well known, enhance the flame-retardant effectiveness of the organic halogen compounds. Antimony salts of α-hydroxycarboxylic or α,/3-dicarboxylic acids as flame-retardants is disclosed in Ger. Offen. No. 2,121,186.

Likewise, other flame-retarding materials which will not detrimentally affect the polyester, can be used in conjunction with the halogen compound in amounts sufficient to improve the flame-retardant property of the fibers. Examples of flame- retardant phosphorous compounds useful for this invention include polyphosphonates (see W. R. Sorenson and T. W. Campbell, “Preparative Methods of Polymer Chemistry, ” 2nd Edition, Wiley Interscience, New York, pages U.S.), organic phosphine oxide- Lewis acid complexes (see U.S. Pat No. 3,600,350), pentaerythritol phosphites (see U.S. Pat. No. 3,412,051), cyclic phosphites and phosphates (see U.S. Pat. Nos. 3,293,327, 3,281,381 and 3,310,609), phosphine oxides in combination with polyamides (see U.S. Pat. No. 3,629,365), and polymers such as poly (2,2-bis-4-hydroxy-3,5dichlorophenyl propane pentaerythritol diphosphite) (see U.S. Pat. No. 3,406,224).

While fibers prepared from ethylene-2,6naphthalene dicarboxylate homopolymer resin are preferred for this invention, up to 25 mol % of other ester units are randomly placed in the polyester chain with ethylene-2,6-naphthalene dicarboxylate units to obtain thermoplastic resins for fibers having improved or varied characteristics. The other ester units are usually derived from other diacids and diols and include, for example, terephthalic acid, bibenzoic acid, sulfoisophthalic acid, diphenoxyalkane dicarboxylic acids, malonic acid, glutaric acid, and the like; hydroxyalkoxybenzoic acids, adipic acid, and alkylene glycols having from 3 to 12 carbon atoms, gem-dialkyl glycols, bis(hydroxymethyl jcyclohexane, diethylene glycol and the like. The diacids and/or diols can be halogenated to provide additional flame-retardant properties for the resin.

There are various known methods for the preparation of filament-forming polyester resins. Of these, the two most commonly employed are the so-called transesterification method and the direct esterification method. In the former, a lower alkanol diester is reacted with a diol and the product polycondensed while in the latter, the diacid is reacted directly with a diol and the product polycondensed. Any method for preparing high molecular weight poly (ethylene-2,6naphthalene dicarboxylate) is suitable for this invention.

The polyester and copolyester resins used for this invention are those having an intrinsic viscosity of at least 0.2 and preferably 0.4 (determined in a 60 weight % phenol and 40 weight % tetrachloroethane solution) at 30°C.

The polyester resin of the fiber blend of this invention can have incorporated therein various additives for improving the resin properties including, for example, heat and ultraviolet light stabilizers, antioxidants, antistatic agents, plasticizers, dyes, pigments and the like along with the flame-retardant.

The physical mixture of polyester resin and flameretardant material is conventionally prepared by mixing the resin, the halogen containing organic compound and, preferably, a metal oxide to obtain a sub4 stantially homogeneous product. The constituents can be premixed by tumbling, rolling or other mixing means and when fibers are produced by melt extrusion, a more homogeneous mass results during the processing. Alternatively, the halogen containing compound, metal oxide or both can be injected into the polyester melt prior to spinning into fibers.

Polyester fibers or filaments are usually formed by melt extrusion of the resin composition through a multihole spinneret in a conventional manner. The as-spun yarn is then conventionally oriented to produce textile yarn of the continuous filament or staple fiber type.

Flame-retardant cellulosic fibers preferably include cotton, rayon or cellulose acetate fibers which have been combined, impregnated or coated with flameretardant chemicals which provide substantially permanent flame-retardant properties therefor without degrading the physical properties of the fiber. That is, the cellulosic fibers or fabrics produced therefrom should be capable of withstanding periodic washing or cleaning with conventional dry cleaning solvents without losing much of their flame-retardant properties. Many flame-retardant treatments for cellulosic fibers are known and several have been found to produce substantially permanent flame-retardancy. It is preferred, in the case of artificially prepared cellulosic fibers such as rayon and cellulose acetate, that the flame-retardant chemical be incorporated into the cellulosic spinning solution thereby providing cellulosic fibers having the flame-retardant “locked in”the cellulosic matrix. Examples of the preparation of these types of cellulosic fibers are found in U.S. Pat. Nos. 2,816,004, 3,266,918, 3,321,330, 3,455,713, 3,645,936 and 3,704,144.

One preferred form of this invention involves the use of the flame-retardant regenerated cellulose filaments or fibers described in U.S. Pat. No. 3,455,713. These fibers have been found to have excellent physical properties and permanent flame-retardancy. In brief, they are regenerated cellulose filaments having dispersed therein a substantially water-insoluble, liquid phosphonitrilate polymer having the general formula

<img file="US3874155A_D0002.tif" />

wherein R and R' are the same or different alkyl or alkenyl radicals having from one to six carbon atoms and n is an integer of at least three.

These filaments are preferably prepared by incorporating a flame-retarding amount of the phosphonitrilate polymer in filament-forming viscose, and spinning and regenerating filaments.

In another aspect of the invention, the flameretardant cellulosic fibers are cellulose acetate fibers prepared by incorporating compounds such as tris(2,3-dibromopropyl)phosphate or similar compounds as disclosed in U.S. Pat. No. 3,321,330 into the acetate spinning dope and wet or dry spinning the fibers.

The blended or combined flame-retardant polyester and cellulosic fibers are used in various fiber and fabric constructions including, for example, spun staple yarns,

3,874,155 mixed or tangled continuous filament yarns, novelty yarns, knit, woven and non-woven fabrics.

The flame-retardant polyester fibers and cellulose fibers described herein can also be blended with or combined in a fabric with normally flame-retardant fibers including, for example, glass fibers, polyvinyl chloride fibers, asbestos fibers, metal fibers, modacrylic fibers such as available under the trademark Dynel and Verel, and aromatic ring polyamide fibers such as available under the trademark Nomex. The yarn or fabrics of this invention will generally contain from about 10 to about 90, preferably about 20 to about 80 weight % of the flame-retardant polyester fibers and about 90 to about 10, preferably about 80 to about 20 weight % of the flame-retardant cellulosic fibers.

The following examples are set forth to demonstrate this invention.

EXAMPLE

A resin composition or mixture A was prepared by dry mixing 139.2 grams of poly(ethylene-2,6naphthalene dicarboxylate) having an intrinsic viscosity of 0.42 with 9.0 grams of octabromobiphenyl (6.5% based on the weight of the polyester, 5.0% bromine based on the weight of the resin) and 1.8 grams of antimony trioxide (20% based on the weight of the octabromobiphenyl). This mixture was charged to a 150 cc. vertical cone reactor equipped with a 10 hole spinneret at the bottom. The mixture was heated at 290°-295°C. with stirring for 15 minutes, pressurized under 20 p.s.i. of nitrogen and spun into a yarn of 254 denier per 10 filaments. The yarn was drawn at a ratio of 5.0 to 1.0 with the input godet and the platens at 121°C. and the output godet at ambient temperature. The yarn was designated yarn A.

This drawn yarn was plied with a flame-retardant regenerated cellulose yarn to provide a yarn blend of 50 parts by weight of polyester and 50 parts by weight of flame-retardant regenerated cellulose (rayon). A knitted fabric of this yarn blend was designated Fabric A.

In the same manner, a polyethylene terephthalate yarn containing the same amount of octabromobiphenyl and antimony trioxide was prepared as mixture B. This mixture was charged to the same 150 cc. vertical cone reactors-spinning unit. The mixture was heated at 280°C. with stirring for 15 minutes, pressurized under nitrogen and spun into a yarn of 258 denier per 10 filaments. The yarn was drawn at a temperature of 121°C. and at a ratio of 3.96 to 1.0. (70% of breakdraw ratio). This yarn was designated yarn B.

A yarn blend of this polyester yarn B was prepared in the same manner as above to provide a yarn of 50 parts by weight of polyester and 50 parts by weight of flame-retardant rayon. A knitted fabric of this yarn blend was designated Fabric B.

The flame-retardant regenerated cellulose yarn referred to above in both cases was prepared in accordance with the teaching of U.S. Pat. No. 3,455,713 to Godfrey and provided regenerated cellulose filaments having about 15% of liquid polymer of di-n-propyl phosphonitrilate dispersed therein.

The yarn blends were each knitted to a fabric of the same construction on a Lawson knitting machine.

The flammability of the test fabrics were quantitatively determined using the flammability testing apparatus as defined by the United States Department of Commerce Standard FF 3-71. In addition, the fabrics were tested in the Standard Method of Test for Flammability of Plastics using the Oxygen Index Method, ASTM-D-2863-70. The higher the Oxygen Index value, the higher the expected flame-retardant properties of the test sample.

The results of these tests are reported in the following tables:

Table I

<td> Fabric</td><td> Vertical Flammability Test (3 second bone dry)</td><td> LOI</td>

<td> A</td><td> 3 samples, 1 sec. AF', 2.38” CL</td><td> 25.7</td>

<td> B</td><td> 1 sample, 84 sec. AF¹, 10.00” CL</td><td> 24.4</td>

•AF = after flame, meaning material continued to burn after flame source was removed ^CL = char length, original sample is 10, thus a 10 CL would indicate complete charring of the test fabric

The above results indicate Fabric A to be clearly superior in flame-retardancy when compared with Fiber B.

The fact that only one burning evaluation was performed on Fabric B is quite significant. This was due to the limited quantity of yarn B that could be processed. This shows that mixture A is clearly superior in processability to that of mixture B, in spite of the higher operating temperatures for the former.

In order to demonstrate the excellent physical properties of yarn of poly(ethylene-2,6-naphthalene dicarboxylate) resin containing the high amount of flameretardant additive as described above, as compared to polyethylene terephthalate yarn containing these same amounts of flame-retardant additives, the data in the following tables are set forth:

Table II

Resin Mixture A and Mixture B and

Properties Yarn A Yarn B

<td> I.V. (resin)</td><td> 0.42</td><td> 0.60</td>

<td> I.V. (fiber)</td><td> 0.47</td><td> 0.47</td>

<td> Free carboxyl groups (resin)</td><td> 11 meq./kg.*</td><td> 20 meq./kg.</td>

<td> Free carboxyl groups (fiber)</td><td> 33 meq./kg.</td><td> 56 meq./kg.</td>

<td> Bromine (found)</td><td> 3.4%</td><td> 4.6%</td>

<td> Antimony (found)</td><td> 1.02%</td><td> 1.0%</td>

<td colspan="2"> * — Milliequivalcnts per kilogram</td><td></td>

The above data indicate that fiber produced from mixture A, containing poly(ethylene-2,6-naphthalene dicarboxylate), exhibits unexpectedly superior chemical properties when compared with mixture B, containing poly(ethylene terephthalate), in the presence of the same additive compounds.

Table III

<td> Yarn Composition</td><td> Tenacity, g./d.</td><td> Elongation, %</td><td> Initial Modules, g./d.</td>

<td> 1) Polyethylene terephthalate (no additive)</td><td> 3.42</td><td> 39.2</td><td></td>

<td> 2) Yarn B (Polyethylene terephthalate + Octabromobiphenyl + Sb,O_:1 )</td><td> 1.7</td><td> 19.8</td><td></td>

3,874,155

Table Ill-Continued

<td> Yarn Composition</td><td> Tenacity, g./d.</td><td> Elongation, &lt;7&lt;</td><td> Initial Modules, g/d.</td>

<td> 3) Poly(ethylene2,6-naphthalene dicarboxylate) (no additive)</td><td> 3.3</td><td> 28.1</td><td> 108.9</td>

<td> 4) Yarn A [Poly (ethylene-2,6dicarboxylate) + Octabromobiphenyl + Sb₂O_:1]</td><td> 5.67</td><td> 24.5</td><td> 158.2</td>

In the above table, the resins of the same chemical identification were obtained from the same resin batch and had the same initial intrinsic viscosity.

The data from the above tables indicate that fabrics prepared from blended yarn of this invention will meet stringent flame-retardant standards and maintain good physical properties. Yarn blends containing fibers of polyethylene terephthalate resin physically mixed with amounts of flame-retardant chemicals sufficient to provide flame-retardant properties are physically weaker and as a result will not give the wear performance typical of a polyester fiber.

Various changes and modifications may be made in practicing the invention without departing from the spirit and scope thereof and, therefore, the invention is not to be limited except as defined in the appended claims.