US3592683A - Flame resistant materials and method of making same - Google Patents

Abstract

PROCESS FOR FLAMEPROOFING MATERIALS, MORE PARTICULARLY COTTON TEXTILE FABRICS, COMPRISING IMPREGNATING THE MATERIAL WITH A PHOSPHORUS COMPOUND, SUCH AS TRIALLYL PHOSPHATE, AND A COMONOMER, SUCH AS N-METHYLOL ACRYLAMIDE, AND THEREAFTER EXPOSING THE MATERIAL TO IIONIZING RADIATION AT A DOSE LEVEL TO CAUSE PRODUCTION OF A SOLID COPOLYMER OF THE PHOSPHORUS COMPOUND AND THE COMONOMER IN SITU IN THE MATERIAL. THE PREFERRED TRIALLYL PHOSPHATE AND N-METHYLOL ACRYLAMIDE ARE PRESENT IN THE IMPREGNATING BATH IN A RATIO AND CONCENTRATION SUCH THAT FLAME RESISTANCE IMPARTED TO THE MATERIAL IS RETAINED THROUGH AT LEAST FIFTEEN LAUNDERINGS UNDER STANDARDIZED CONDITIONS. THE FLAMEPROOFED MATERIALS PREPARED BY THE PROCESS, WHICH ARE DURABLE AGAINST AT LEAST FIFTEEN LAUNDERINGS, ARE DISCLOSED.

Description

United States Patent OifiC 3,592,683 Patented July 13, 1971 3,592,683 FLAME RESISTANT MATERIALS AND METHOD OF MAKING SAME Thomas D. Miles, North Randolph, Mass., and Armando C. Delasanta, Woonsocket, R.I., assignors to the United States of America as represented by the Secretary of the Army No Drawing. Filed Sept. 25, 1969, Ser. No. 861,163 Int. Cl. B4411 5/00; D06m 13/26, 15/16 US. Cl. 117-9331 10 Claims ABSTRACT OF THE DISCLOSURE Process for flameproofing materials, more particularly cotton textile fabrics, comprising impregnating the material with a phosphorus compound, such as triallyl phosphate, and a comonomer, such as N-methylol acrylamide, and thereafter exposing the material to ionizing radiation at a dose level sufficient to cause production of a solid copolymer of the phosphorus compound and the comonomer in situ in the material. The preferred triallyl phosphate and N-methylol acrylamide are present in the impregnating bath in a ratio and concentration such that flame resistance imparted to the material is retained through at least fifteen launderings under standardized conditions. The flameproofed materials prepared by the process, which are durable against at least fifteen launderings, are disclosed.

The invention described herein may be manufactured, used, and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

This invention relates to a process for flameproofing inflammable materials, such as cellulosic yarns and fabrics. More particularly, the invention relates to a process for making inflammable materials durably flameproof so that they will retain the flameproofness developed therein after numerous launderings.

In recent years many phosphorus-containing compounds have been found to be useful as flame retardants or flameproofing agents for various types of materials which are normally inflammable in the absence of a flameproofing agent or treatment. Among the more promising of these phosphorus-containing flameproofing agents have been the halogenated alkylene phosphates, especially certain brominated alkylene phosphates and polymers thereof. However, not all alkylene phosphates are effective for flameproofing. For example, triallyl phosphate not only is not a flame retardant for cellulosic materials; but, when present on such materials, actually increases their flammability. Polymerized triallyl phosphate has flame retardant properties; but polymerization thereof heretofore has required such drastic conditions as to render the application of triallyl phosphate to cellulosic materials and the polymerization thereon impractical because of resulting damage to the cellulosic material by the severe polymerization conditions heretofore found necessary.

It is, therefore, an object of the present invention to provide a method for accomplishing the flameproofing of materials which are normally inflammable by impregnating or otherwise incorporating in the material a phosphorus compound, such as triallyl phosphate, along with a comonomer and thereafter causing the phopshorus compound to copolymerize with the comonomer in situ in the material under conditions which do not seriously harm the tensile and other physical properties of the material.

Another object is to flameproof cellulosic materials by polymerizing triallyl phosphate with a comonomer absorbed therein under the influence of relatively low doses of ionizing radiation.

A further object is to provide a practical method for flameproofing cellulosic fabrics with triallyl phosphate at sufliciently low doses of ionizing radiation to obtain a high degree of polymerization of the triallyl phosphate in situ in the fabric without harming the physical properties of the fabric while markedly improving it from the standpoint of flameproofness and durability with respect to laundering.

Other objects and advantages will appear from the following description of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

The method of the invention is carried out by impregnating or otherwise incorporating in an inflammable material a polymerizable phosphorus compound, such as triallyl phosphate,and a comonomer, such as N-methylol acrylamide, and subjecting the material to high energy ionizing radiation at a dose of a level such that copolymerization occurs between the phosphorus compound and the comonomer forming a copolymer of the phopshorus compound and the comonomer in situ in the material, but at a level low enough so that relatively little or no reduction in the tear strength and other physical properties of the material occurs as a result of the exposure thereof to the ionizing radiation.

The preferred polymerizable phosphorus compound for use in accordance with the present invention is triallyl phosphate. However, other polymerizable phosphorus compounds, such as diallyl phosphate, monoallyl phosphate, or dimethyl hydrogen phosphite may be used.

The comonomers which have been found to be particularly effective with triallyl phosphate in the production of copolymers thereof for imparting flameproofness to cellulosic and other normally inflammable materials in accordance with this invention are N-methylol acrylamide, acrylamide, acrylic acid, and acrylonitrile. These materials may all be considered structurally closely related in possessing terminal double-bonded unsaturation. They are either acrylic acid or derivatives or precursors thereof.

The low dose level of ionizing radiation employed in accomplishing copolymerization of the triallyl phosphate with the selected comonomer is preferably about 2 megarads, but conveniently may be up to 6 megarads or even higher, but to avoid excessive damage to the fabric or other material, should be no higher than about 25 megarads. Such doses of ionizing radiation may be applied to the material from any convenient source of ionizing radiation, such a 60 Co source or a linear electron accelerator. In general, it is preferred to employ a linear electron accelerator as a source of the ionizing radiation since this type of equipment can be made to produce a high dose rate, thus making possible a given dose over a shorter period of time with less exposure of the material to ionizing radiation while it is exposed to an oxygen atmosphere. Also, the shorter times required for the irradiation in a linear electron accelerator make a continuous treatment of fabrics in commercial facilities more practical from an economic standpoint.

In general, the durability of flame resistance of a cotton fabric treated with triallyl phosphate and N-methylol acrylamide and thereafter irradiated with 2.0 megarads of ionizing radiation in accordance with the invention is dependent on the amount of add-on and the ratio of the triallyl phosphate to the N-methylol acrylamide comonomer. About 15.0 percent add-on is about the lower limit of add-on when a ratio of 8.3 parts of triallyl phosphate to 1.0 part by weight of N-methylol acrylamide is employed, in order to obtain good flame resistance which is retained after 15 launderings. Within the add-on range of 1533 percent, in order to obtain durability of flameresistance to laundering 15 times, it is necessary to employ a ratio of trially phosphate to N-methylol acrylamide of at least about 2 to l by weight. A lower ratio may produce initial flame resistance and varying degrees of retention of such flame resistance after laundering, but lack of resistance to 15 launderings. It is thus apparent that widely varying degrees of flame resistance and durability of flame resistance with respect to repeated launderings are possible by varying the ratio of triallyl phosphate to comonomer and varying the add-on of the solid polymer produced from the triallyl phosphate and the selected comonomer.

In testing fabrics treated in accordance with this invention to impart flame resistance and laundering durability with respect to flame resistance thereto, the flame resistance test which has been employed is the Vertical Bunsen test (Method 5903, Federal Specification CCC- T-191). The laundering method employed to determine durability of the flameproofness imparted to the fabrics to repeated launderings is Method 5556 of Federal Specification CCC-T-191, which consists of a series of suds and rinse cycles using a detergent and sour. The highest temperature during the wash cycles was 140 F.

Add-on is defined for the purposes of this invention as the diflerence between the final dried and conditioned weight of the treated material and the initial dried and conditioned weight of the material before treatment thereof divided by the initial dried and conditioned weight of the material before treatment thereof, multiplied by 100 to convert to percentage. It generally describes the percentage increase in weight of the treated material due to the solid polymer formed in situ thereon as a result of the irradiation of the material impregnated with the phosphorus compound and the comonomer.

Having described in general terms the conditions under which the flame resistant material of the present invention is prepared, we will now proceed to disclose specific examples of the production of flame resistant materials in accordance with the above-described principles.

It will be understood, of course, that the above-described principles and other advantages of our invention may also be accomplished by suitable variations of the detailed method steps, about to be set forth below, which are intended to be for illustrative purpoes, and not for the purpose of limiting the scope of our invention.

EXAMPLE I A 9 x 12 in. sample of 8.2 oz. cotton sateen fabric was immersed in a solution containing 125 cc. of triallyl phosphate and 25 cc. of N-methylol acrylamide (60% aqueous solution by weight). In this proportion, 8.3 to 1 of triallyl phosphate to N-methylol acrylamide by weight, the two chemicals are miscible. The sample was squeezed to a wet pick-up of 100 to 125% by weight, placed in a sealed 4 mil. polyethylene bag and exposed to 2 megarads of irradiation in air at room temperature using a 24 mev., 18 kw. electron LINAC as the source of radiation, Electron irradiation consisted of scanning the sample with an electron beam approximately 3-4 cm. in area as the sample moved through the beam path on a conveyor. The scan width was 16 in. and the dose rate, while the pulsed beam was on, was rads/sec. The repetition rate was 60 pulses/sec. and the pulse duration was 5 micro-sec. The sample was held in a vertical position during irradiation. The sample was then rinsed in hot water (40 C.) for 2 min. and dried at 100 C. in an oven. The add-on of dry solids on the fabric was percent by weight. Flame tests were made using the Vertical Bunsen test (Method 5903 of Federal Test Method Std. No. 191) both before and after laundering according to Method 5556 of the same Test Method Standard. Initially the after-flame was 0 sec. and the char length was 5.8 in, After 15 launderings, the after-flame was 0 sec. and the char length was 5.0 in.

EXAMPLE II The same type of fabric of the same sample size as in Example I was treated with the same ratio of chemicals as used in Example I and then exposed to 4 megarads of irradiation in air at room temperature using a 1.25 10 Ci Co isotope source. Gamma irradiation was under ambient conditions with a dose rate of 2.843.86 10 rads/min. After the radiation exposure, the sample was rinsed in hot water (40 C.) for 2 minutes and dried at 100 C. in an oven. The add-on of dry solids on the fabric was 26 percent by weight. Flame tests initially were 0 sec. after-flame and 5.0 in. char length; after 15 launderings 2 sec. after-flame and 5.5 in. char length.

EXAMPLE III The same type of fabric of the same sample size as in Example I was immersed in a solution of 10 gms. of acrylamide, 10 cc. of triallyl phosphate, 5 cc. of water and 10 cc. of methanol. The sample was exposed in the same manner as in Example II, but to 6 megarads of irradiation. After rinsing and drying as in Example I, the flame resistance of the treated fabric was 0 sec. afterfiame and 3.9 in. char length.

EXAMPLE IV The same type of fabric of the same sample size as in Example I was immersed in a solution containing 10 cc. acrylonitrile by weight aqueous solution) 10 cc. of triallyl phosphate, 5 cc. of water and 5 cc. of methanol. The sample was exposed in the same manner as in Example II, but to 6 megarads of irradiation, After rinsing and drying, as in Example II, the flame resistance of the treated fabric was 0 sec. after-flame and 7.1 in. char length.

EXAMPLE V The same type of fabric of the same sample size as in Example I was immersed in a solution comprising 20 cc. of triallyl phosphate and 20 c. of acrylic acid. The sample was exposed in the same manner as in Example II to 4 megarads of irradiation. After rinsing and drying as in Example II, the flame resistance of the treated fabric was 0 sec. after-flame and 4.6 in. char length.

EXAMPLE VI The treating solution containing triallyl phosphate and N-methylol acrylamide in a weight ratio of 4.8 to 1 contained in a polyethylene bag was subjected to 3 megarads of irradiation in the same manner as Example I. The product was a water insoluble polymer which did not propagate flame when exposed to and withdrawn from a Meeker burner flame.

EXAMPLE VII The same type of fabric of the same sample size as in Example I was immersed in a solution of 15 cc. of dimethyl hydrogen phosphite and 15 cc. of n-methylol acrylamide (60% aqueous solution by weight). The sample was subjected to 4 megarads in the same manner as in Example II. The add-on of dry solids on the fabric was 18 percent by weight. After rinsing and drying as in Example I, the flame resistance of the treated fabric was 0 sec. after-flame and 6.1 in. char length.

While the invention has been described above in terms of first treating a material with a phosphorus compound, such as triallyl phosphate, and a comonomer, such as N-methylol acrylamide, followed by irradiating the material with ionizing radiation to produce a copolymer of the phosphorus compound and the comonomer in situ on the material, it will be understood by those skilled in the art that the material may be irradiated with ionizing radiation first and thereafter treated with the phosphorus compound and the comonomer to produce a copolymer thereof on the material. It is believed that the copolymerization of the phosphorus compound and the comonomer within a short time is brought about due to the presence of free radicals produced in the material by the ionizing radiation and that such free radicals may be produced either before or subsequent to the treatment of the material with the phosphorus compound and the comonomer with substantially equally effective results. It may be desirable to exclude oxygen or to maintain the material at a relatively low temperature during and after irradiation if the irradiation is carried out prior to the application of the phosphorus compound and the comonomer in order to retain a maximum number of free radicals in the material for a given dose of irradiation until the reactants are applied thereto. Other methods known in the art for producing free radicals in a material, such as the application of free radical producing compounds, may also be used to treat the material either before or after application thereto of the phosphorus compound and the comonomer to produce a copolymer having durable flame retardancy characteristics in situ on the material.

One of the great advantages of the present invention resides in the fact that very good flame retardancy in cotton fabrics, as well as other normally inflammable materials, can be obtained with relatively low add-on and without the application thereto of high temperatures. Further in this regard, the dosages of ionizing radiation required are relatively low so that relatively slight degradation of the fabric or other material is caused by the treatment. But most importantly, the flame resistance imparted to the fabrics or other treated materials is very durable with respect to standardized laundering procedures.

Although the tear strengths of fabrics treated in accordance with the invention are somewhat less than those of the untreated fabrics, they are still sufficiently high to make the fabrics fiame-proofed in accordance with the present invention very useful wherever flameproofness is required in a fabric. This is especially true with respect to many fabric uses by the Armed Forces since the elimination of inflammability from clothing, shelter, and other normally inflammable items is considered a primary objective and the durability of flameproofing treatments to repeated laundering is most important, especially in clothing items, for the maintenance of flameproofness of such items without the necessity of retreatment during normal lives thereof.

We wish it to be understood that We do not desire to be limited to the exact details described for obvious modifications will occur to a person skilled in the art.

We claim:

1. A process for flameproofing an inflammable material comprising impregnating said material with a phosphorus compound selected from the group consisting of triallyl phosphate, diallyl phosphate, monoallyl phosphate, and dimethyl hydrogen phosphite and a comonomer selected from the group consisting of N-methylol acrylamide, acrylamide, acrylic acid, and acrylonitrile and thereafter irradiating said impregnating material with a dose of ionizing radiation sufl'lcient to produce a copolymer of said phosphorus compound and said comonomer on said material.

2. A process as set forth in claim 1, wherein the addon of said copolymer on said material is at least about 15 percent by weight.

3. A process as set forth in claim 1, 'wherein said phosphorus compound is triallyl phosphate and said comonomer is N-methylol acrylamide and the add-on of said copolymer on said material is from about 15 to about 33 percent by weight.

4. A process as set forth in claim 3, wherein the ratio by weight of said triallyl phosphate to said N-methylol acrylamide is at least about 2 to l.

5. A process as set forth in claim 1, wherein said dose of ionizing radiation is from about 2 to about 25 megarads.

6. A flame resistant material having a copolymer of a phosphorus compound selected from the group consisting of triallyl phosphate, diallyl phosphate, monoallyl phosphate and dimethyl hydrogen phosphite and a comonomer selected from the group consisting of N-methylol acrylamide, acrylamide, acrylic acid, and acrylonitrile deposited substantially uniformly on said material.

7. A flame resistant material as set forth in claim 6, wherein the add-on of said copolymer on said material is at least about 15 percent by weight.

8. A flame resistant material as set forth in claim 6, wherein said phosphorus compound is triallyl phosphate and said comonomer is N-methylol acrylamide and the add-on of said copolymer on said material is from about 15 to about 33 percent by weight.

9. A flame resistant material as set forth in claim 8, wherein the ratio by weight of said triallyl phosphate to said N-methylol acrylamide is at least about 2 to 1.

10. A flame resistant material as set forth in claim 6, wherein said copolymer is formed on said material by exposure of said material to a dose of ionizing radiation of from about 2 to about 25 megarads with said phosphorus compound and said comonomer absorbed on said material.

References Cited UNITED STATES PATENTS 2,660,543 11/1953 Walter et a1. 117-136 2,714,100 7/1955 Fontoy et a1 117---161X 3,934,555 4/1960 OBrien et a1 1l7l36X 2,998,329 8/1961 SoVish et a1 117-9331 ALFRED L. LEAVITI, Primary Examiner K. P. GLYNN, Assistant Examiner US. Cl. X.R.

117-136, 161P, 161UN, 161UZ; 204-15922; 2528.1