US3816068A - Flame retardant for cellulosic fabrics - Google Patents

Abstract

Flame retardants for cellulosic fabrics, especially polyester blends, comprise a limited phosphine oxide class of N-methylol propionamides, particularly N-methylol-3(dimethylphosphinyl)propionamide, closely related structurally to N-methylol-3-(dimethyl phosphono)propionamide, but markedly more effective as a flame retardant.

Description

United States Patent 1191 Rivlin June 11, 1974 1 FLAME RETARDANT FOR CELLULOSIC FABRICS [75] Inventor: Joseph Rivlin, Greensboro, N.C.

[73] Assignee: Burlington Industries, Inc.,

Greensboro, N.C.

[22] Filed: July 12, 1971 [21] Appl. No.: 161,867

[52] US. Cl. 8/ll5.7, 8/116 P, 8/184, 8/D1G. 4, 106/15 FP, 117/136, 252/8.1,

260/56] R, 260/6065 P, 260/DIG. 24

[51] Int. Cl. D06m 13/28, D06m 15/54 [58] Field of Search 8/1 16.3, 116 P, 115.7, 8/184; 106/15 FP; 252/8.1

[56] References Cited UNITED STATES PATENTS 2,691,567 10/1954 Kvalnes et a1 8/116 P 3,639,532 1/1972 Oerter et a1. 8/116 P 3,639,539 2/1972 Nachbar et a1 8/116 P 3.766.252 10/1973 Schmidt et a1 252/8.I

OTHER PUBLICATIONS Anon., Textile World, p. 132, November, 1968.

Primary Examiner-George F. Lesmes Assistant Examiner-J. Cannon Attorney, Agent, or FirmCushman, Darby and Cushman [5 7] ABSTRACT 6 Claims, No Drawings FLAME RETARDANT FOR CELLULOSIC FABRICS BACKGROUND OF THE INVENTION (dimethyl phosphono)-propionamide, 15,

O O (03:30)! CHgCHgPJNHCHgOH has achieved considerable commercial success under the proprietary name of Pyrovatex CP. It is particularly effective because it bonds both phosphorus and nitrogen chemically to the cellulose molecule. Being reactively bonded rather than merely physically coated onto the cellulose, it holds more tenaciously than nonreactive coatings and plasticizers. Besides this advantage Pyrovatex CP, unless it is'combined with textile resins, has far less stiffening effect on fabrics than do the various kinds of coating agents.

Pyrovatex CP is not, however, without faults. As a phosphonate ester, it has a potential for hydrolysis under conditions of extended use, as during laundering, weathering, steam ironing, and the like. More important, the efficiency of the reaction between Pyrovatex CP and cellulose is low, thus resulting in considerable loss of expensive reagent during application to fabric. This low efficiency of reaction further manifests itself in the fact that only limited amounts of Pyrovatex CP can be added to cellulosic fibers, a fact which seriously diminishes its utility in fabric blends such as the popular 50/50 polyester/cotton. Being inert to polyester and incapable of heavy add-on to cellulose, Pyrovatex CP cannot be taken up by the blends in amounts sufficient to flameproof them adequately.

I SUMMARY OF THE INVENTION It is an object of this invention to provide a class of flame retardants having a high capacity for bonding chemically with cellulosic fabrics. 1

A further object of the invention is to provide a class of flame retardants effective on polyester/cotton blends.

A further object isv to provide flame retardants with exceptional resistance to laundering.

l havg found that new compounds, particularly where R, and R are methyl, ethyl, or porpyl radicals, and X is hydrogen or a methyl radical, are remarkably effective as flame-retardant reagents for cellulosic fabrics and fibers. The most preferredof these reagents is (CH ),P(O)CH,CH C(O)NHCH OH. Although obvi ously analogous to Pyrovatex CP in structure, it is surprisingly different from it in function and efficiency.

As shown hereinafter, the compounds of my invention exhibit high degrees and efficiencies of add-on to cellulosic fabrics and thereby confer a high level of flame resistance upon them. N-methylol-3- (dimethylphosphinyl)propionamide adds so well that it is effective even on 50/50 polyester/cotton blend fabrics.

DETAILED DESCRIPTION This invention comprises a new class of phosphine oxide derivatives of N-methylol propionamides of the general formula R1 0 X 0 \II E g /BCH1 H NHCHzOR R:

where R represents hydrogen or alkyl of up to six carbon atoms, X represents hydrogen or a methyl radical, and R, and R represent methyl, ethyl, or propyl radicals.

Preferred compounds are those having the formulas where R R and X are as defined above. The most preferred compound is N-methylol-3-(dimethylphosphinyl )propionamide:

CH\3R O rornomii'miomon C IV These new compounds may be made by reaction of suitable Grignard reagents with dialkyl phosphites, the resulting disubstituted phosphine oxides, also known as phosphinous acids, being thereafter treated with acrylamide methacrylamide, and after that with formaldehyde, undergoing reactions comparable to those described in the aforementioned U. S. Pat. No. 3,374,292.

Two particularly surprising features distinguish the phosphine oxide compounds of this invention from compounds known in the art: the high efficiency of their reaction with cellulose, and their superior flame retardant properties. Although neither of these advantages could have been anticipated, they are believed to work together to produce the remarkable overall superiority of these products. From a practical standpoint, the outcome of its particularly favorable combination of properties is that the preferred embodiment of this invention, N-methylol-3-(dimethylphosphinyl)propionamide, hereafter referred to for convenience as MDMP, works effectively as a flame retardant even for 50/50 polyester/cotton blends, an application where Pyrovatex CP falls far short of adequacy.

The aforementioned superior flame retardant capabilities of these phosphine oxide compounds are believed to derive from several factors. The principal of these is the fact, taking MDMP versus Pyrovatex CP as an example, that MDMP has so much the greater capacity for bonding to cellulose. This capability is amply demonstrated in the examples. A further factor, perhaps less clearly marked in effect, is the fact that the mode of action of MDMP under the influence of flame seems considerably different from that of Pyrovatex CP. This too is treated further in the examples.

In addition to the foregoing unexpected advantages, these compounds, having no hydrolysis-susceptible phosphonate groups, and being members of the class of phosphine oxides, among the most stable phosphorus compounds known, are free from the potential of many phosphorus-containing flame retardants, including Pyrovatex CP and its homologs, for forming strong and deleterious phosphorus acid groups on exposure to laundering, ironing, weathering, and like hydrolytic influences.

At the same time, these compounds retain all of the advantages mentioned earlier for Pyrovatex: chemical rather than physical bonding to cellulose, simultaneous addition of both nitrogen and phosphorus in a single reagent, and absence of stiffening and like defects commonly associated with flame-retardant coatings.

These compounds may be applied to substrates such as fabrics, yarns, and other forms of cellulose by any known means, such as spraying, dipping, padding, and the like, with preferably aqueous solutions of said compounds. The most convenient, and preferred, is padding, followed by drying in the case of aqueous application. Application to the substrate is followed by a curing of cross-linking step, to effect chemical reaction of the compounds hereof with free hydroxy groups in the substrate. This is preferably followed with a washing step to remove any of the compounds not chemically bound to the substrate. Typically, the reaction or curing step is brought about by application of heat, although other suitable reaction or curing mechanisms may also be utilized. Heat is normally most convenient and therefore is presently preferred. The amount and duration of heat treatment will normally depend on local practice, the type of substrate being treated, etc., and are not presently believed to be critical to the success of this invention. Usually a temperature of from about l50l75C for from about one to several minutes will suffice for the heating step.

It has not as yet been possible to provide reasons for the most truly unexpected advantages of the products of this invention, their remarkable efficiency or their extent of reaction with the fabric substrate. Considering the apparent similarity of the structures of Pyrovatex CP and these compounds, particularly MDMP, it would be expected that Pyrovatex and MDMP would react with cellulosic materials in essentially the same way. The structures differ by only the presence of two extra oxygen atoms in Pyrovatex, and even these are at the opposite end of the molecule from the functional -CH OI-I group. However, the data given below show clearly that there is a remarkable difference in reactivities, in favor of the compounds of this invention.

Not only are differences in reactivities apparent, but

even at comparable add-ons and phosphorus contents,

blend fabrics treated with MDMP are markedly more resistant to flame than those treated with Pyrovatex CP. It is apparent that, despite their close structural resemblance to each other, MDMP and Pyrovatex CP are actually very dissimilar in effectiveness, and presumably in mechanism of flame-proofing action. These facts are particularly evident when one compares their effects on 50/50 polyester/cottom blends.

It should be recognized that, while the primary emphasis herein is on fabrics of various types including percent cotton, 100 percent rayon, blends of such cellulosics with various man-made fibrous materials, and particularly in blends with polyester, it is understood that thess treatments are equally applicable to a broad variety of substrates where flame retardancy may be desired, including yarns, fibers generally, paper, I

and other cellulose-containing materials, whether these be made from cotton, rayon, wood pulp, or other sources of cellulose, and whether the articles in which they are incorporated are intended for use in apparel, home furnishings, intermediate, or industrial type products.

In assessing the flame retardancy of both the compounds of this invention and of earlier known products, two methods of evaluation have been utilized. One is the vertical flame test, Fire Resistance of Textile Fabrics," AATCC No. 34-1966. Greater reliance has been placed in this specification on the measurement of the Limiting Oxygen Index, LOI, because it offers more potential for indicating the extent of differences between test specimens, particularly those which fail, i.e., burn entire length (BEL), in the vertical test and therefore cannot be compared in terms of char length. It has been found, in general, that fabrics having LOI values above the range of about 0.240-0260 usually pass the vertical test; i.e., they are selfextinguishing to the degree that they do not burn their entire length, but instead have measurable char lengths.

The LOI values recorded herein were measured on a slightly modified General Electric Oxygen Index Flammability Gage, Cat. No. A4990A, following Instruction Manual 454 l KZS-OOIB. (See also ASTM Test D-2863, the standard LOI test used for plastics.) The application of the LOI test to fabrics is discussed in a paper by J. J. Willard and R. E. Wondra, Textile Research Journal, 40, 203-2l0 (1970).

Modiflcationslo the standard GE instrument (see ASTM Test D-2863 FIG. 1, for the meaning of the following apparatus terms) were as follows: inside diameter of glass cylinder 3 inches instead of 3% inches; distance from top of screen (4) to top of cylinder 11% inches instead of 6 inches; distance from bead surface (6) to screen (4) 6% inches instead of 3 inches; fabric length 6 inches instead of 5 inches; cover plate removed.

Flow rate was set at 4 cm./sec.

Further details of this invention are given in the following examples.

EXAMPLE 1 As an illustration of the invention, N-methylol-3- (dimethylphosphinyl)propionamide, MDMP, was synthesized as follows: Dimethylphosphine oxide was prepared by the method of Hays, J. Org. Chem., 33, 3690 (1968), and distilled before use. To a stirred solution of 271.7 g, 3.48 mol, dimethylphosphine oxide and 247.1 g, 3.48 mol, acrylamide in 319 ml ethanol was added dropwise a freshly prepared solution of sodium ethoxide, made from 8.4 g, 0.365 atom, sodium and 193 ml ethanol. After about one-fourth of the base had been added a vigorously exothermic reaction began. When the reaction subsided the addition was continued at a rate which maintained a temperature of 7080C. The resulting white slurry was stirred 2 hours longer without heating, cooled, "filtered, and the solid 3- (dimethylphosphinyl)-propionamide separated and dried. The yield of product melting l909lC was 483 Analysis:

Calcd. for C H NO P: C 40.2, H 8.05, N 9.39, P 20.8

% Found: C 39.9, H 7.84, N 9.36, P 21.7

A 95.1-g portion, 0.638 mol, of this intermediate was treated with 157 g, 1.9 mol, of 36.6 percent formaldehyde solution at 60C. The pH was held at 8-9 during the reaction by addition of a few small drops of 50 NaOl-l. After 2.5 hours the free formaldehyde content, measured by the sodium sulfite method, was constant. After overnight stirring at room temperature, the solution was analyzed, it being found that the content of N- methylol-3-(dimethylphosphinyl)-propionamide, MDMP, was 0.562 moles in the 141 g of solution.

EXAMPLE 2 To illustrate the utility of the invention, in this and following examples the procedure employed was to pad an aqueous solution of reagent, 1 percent curing catalyst (2-amino-2-methylpropanol hydrochloride), and 0.1 percent detergent (nonylphenylpolyethyleneoxyethanol) onto weighed samples of bleached or normally scoured, but otherwise untreated 100 percent cotton sheeting, 50/50 polyester/cotton sheeting, or other eel; lulosic fabric in a laboratory padder at 30 psi; dry 4 minutes at 93C; cure 3 minutes at 175C; process wash fi'minutes with water containing 0.001 percent detergent in a home washing machine set on warm; tumble-dry; and condition overnight at 72F and 65 percent relative humidity in preparation for final weighing and testing. Except when otherwise indicated, test fabrics were 100 percent cotton sheeting, 3.75 oz/yd, 95 X 84 count, and 50/50 polyester/cotton sheeting, 3.68 oz/yd, 96 X 88 count. Samples for treatment were usually about 10 X inches, weighing before treatment about 18 g for 50/50 polyester/cotton and 16 g for 100 percent cotton. The treatment cycle was repeated more than one time when ever it was desired to increase the extent of modification (add-on) beyond the maximum obtainable in a single treatment. The most superior results were generally obtained when using freshly prepared padding baths.

EXAMPLE 3 For comparative purposes, samples of 50/50 polyester/cotton fabrics were padded with 40 percent aqueous solutions of Pyrovatex CP and MDMP by the procedure of Example 2. Though noneof the once-treated samples passed the vertical test, those padded with MDMP had slightly but significantly higher L01 readings, as may be seen by comparison of the one-cycle entries in Tables 1 and 2. Two and even three cycles of Pyrovatex CP had almost no further effect on increasing the add-on and the L01, and all specimens burned their entire lengths in the vertical test. The L01 of the original fabric for all of the samples was 0.168.

TABLE 1 50/50 Polyester/Cotton Sheeting Padded with 40% Pyrovatex CP No. Phos- Vertical Padding phorus 7c Char Sample Cycles I 7! Add-on L01 Length A 1 1.32 9.1 0.223 BEL B l 1.21 9.3 0.220 BEL C 2 10.7 0.231 BEL D 2 11.0' 0.231 BEL E 3 1.72 12.5 0.231 BFL F 3 1.87 13.9 0.234 BEL Note: *BEL=Burned Entire Length TABLE 2 50/50 Polyester/Cotton Sheeting Padded with 40% MDMP No. Fhos- Vertical Padding phorus Char Sample Cycles 7c Add-on L01 Length A l 1.44 9.6 0.229 BEL B 1 1.25 7.8 0.231 BEL C 2 2.46 13.4 0.264 7.5" D 2 2.73 20.9 0.254 7.5" E 2 2.52 18.3 0.256 7.7" F 2 2.14 14.0 0.247 BEL G 2 2.19 1.50 0.251 3.8" H 2 2.67 15.5 0.243 7.1" 1 2 2.52 15.0 0.236 8.1"

Surprisingly, when MDMP was applied the second time, the additional add-on was usually equal to and sometimes even greater than the original, and the L01 readings were increasing materially. Most significant of all, from a practical standpoint, was the fact that the L01 rose into the 0240-0260 range, and that the majority of the test specimens no longer failed the vertical test. (A few did fail, but this was taken as verification of the known imprecision of the vertical test.)

It is obvious, from the results in these tables, that MDMP displays a remarkably greater capability for bonding with and flameproofing polyester/cotton blends.

EXAMPLE 4 To determine what range of polyester/cotton fabrics could be flameproofed with MDMP, samples of 65/35 polyester/cotton sheeting were treated twice with 40 percent MDMP and Pyrovatex CP solutions by the standard procedure of Example 2. Results are given in Table 3.

lts significantly higher L01 values showed that MDMP had effected a significantly greater increase in flame resistance than did Pyrovatex CP.

EXAMPLE For comparative purposes, the procedure of Example 4 was repeated, but this time by padding twice onto 65/35 rayon/polyester sheeting at 40 percent concentration according to the method of Example 2. Two MDMP treated samples gave LO1 readings of 0.252 and 0.242. and both samples passed the vertical flame test, giving char lengths of 6.3 and 4.6 inches.

EXAMPLE 6 1n using relatively expensive flame retardants such as Pyrovatex CP and MDMP, it is important to achieve a high degree of bonding of the solution padded onto the fabric. Anything removed by the process wash after curing is essentially non-recoverable and wasted. The degree of bonding is expressed as the efficiency, this being calculated from the equation:

Retardant retained after washing/Retardant padded on X 100 efficiency Samples of 100 percent cotton sheeting were put through one cycle of the process of Example 2, being padded with Pyrovatex CP and MDMP solutions of different concentrations. Data obtained are shown in Table 4.

TABLE 4 Efficiency of Addition to 100% Cotton of Pyrovatex CP and MDMP at Different Concentrations From these results it is apparent that the efficiency of addition of M DMP approaches 100 percent at low concentration, while that of Pyrovatex CP peaks at around 55 percent.

Similar results, shown in Table 5, were obtained when solutions of a range of concentrations were padded onto /50 polyester/cotton sheeting in the same manner.

TABLE 5 Efficiency of Addition to 50/50 Polyester/Cotton of Pyrovatex C P and MDMP at Different Concentrations TABLE 5 4 Continued "/7; 7n Retardant Concn. Add-on P [5111- L01 ciency Do. 8.1 1.15 74 0.223 D0. 11 6.0 0.97 83 0216 Do. 6.3 0.91 92 0.218

These results show conclusively that MDMP. despite the similarity of its structure to that of Pyrovatex C P, possesses a radically different degree of affinity for cotton, this greater affinity making it capable of greater add-ons with less waste of reactant.

EXAMPLE 7 1t became apparent from L01 measurements of a large number of test samples that at roughly equivalent phosphorus contents, MDMP-treated fabrics were proving statistically more resistant to burning than comparable Pyrovatex-treated fabrics. A series of both groups of fabrics were therefore submitted to burning in beakers in the LOl apparatus in oxygen concentrations at or above their LOl values. The chars were weighed and analyzed, and the percentage of the original phosphorus remaining in each char was calculated. Data are summarized in Tables 6 and 7.

TABLE 6 Retention of Phosphorus in Char from Retention of Phosphorus in Char from MDMP-Treated Cotton and 50/50 Polyester/Cotton Sheeting Original Samples '71 P in 71 P Retention L01 7: P Char by Char 100% Cotton 50/50 Polyester/Cotton From inspection of the last columns of Tables 6 and 7 it is immediately apparent that there is a very large difference of kind in the retention of phosphorus by Pyrovatex-treated versus MDMP-treated fabrics. Over twice as much Pyrovatex-added phosphorus remains behind. This is interpreted as showing that the mode of flameproofing by MDMP is such that a far higher percentage of the agent operates in the vapor phase when the fabric is subjected to burning. Evidently this different and wholly unexpected mode of action makes each amount of MDMP somewhat more effective as a flame retardant than a comparable amount of Pyrovatex CP.

Though it is not desired for this invention to be bound by the limits of any mechanism, it appears probable that the phosphorus liberated into the vapor phase above the burning fabric diminishes the flammability of the vapors, reducing their tendency to engulf the whole fabric in flame. This effect seems particularly advantageous where, as in the present invention, a significant portion of the retardant released by the cotton seems to be in a form more capable of affording maximum protection to the polyester portion of the blend.

EXAMPLE 8 Samples of MDMP-modified cotton and 50/50 polyester/cotton sheeting were subjected to multiple washings in a home washing machine set on hot, in the presence of 0.l percent TIDE. home detergent. The phosphorus analyses and LO! readings, before and after laundering, are shown in Table 8. It is evident that not only the phosphorus content but also the flame resistance remained constant, within the errrors of measurement of the methods.

1 claim:

1. A process for increasing the flame retardency of a cellulosic textile material which comprises impregnating the material with a solution containing an acidic catalyst and a product of the formula:

where R represents hydrogen or alkyl of up to six carbon atoms, X represents hydrogen or a methyl radical, and R and R represent methyl, ethyl or propyl radicals and thereafter curing the impregnated material under heating conditions.

2 Theprocess of clai rn l wherein tliecellulo sic tex tile material is a 50/50 polyester/cellulose blended textile fabric, X is hydrogen and R is hydrogen.

3. The process of claim 1 where the c ellulosic textile material is a polyester/cellulose blended textile material.

4. T he process of claim 3 where i s hydrogen and X is hydrogen or a methyl radical.

5. The process of claim 3 where X is hydrogen.

ti The product produced by the product of claim 11 -w qTEIi STATES PATENT OFFICE (s/ss) CERTIFICATE OF CORRECTIUN Patent No. 3,816,068 Dated. Juue 11, 1974 Inventor-(s) Joeeph Rivlin It is certified that error appears in the above-identified p atent and that said Letters Patent are hereby eorrected as shown below:

Column 1, line 61, "porpyl" should read -propyl- Column 2, lines 51-52, "acrylamide methacrylamide" should read --acry1amide or methacry1amide Column 5, line 51, "when ever" should read -whenever Column 6, line 29, in the fourth column, l. 50"

should read --15.o--

Column 6, line 57, "CO" should read -CP- Column 9, line 25, "NDMP" should read --M DMP-'- Signed and sealed this 29th day of October 1974.-

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSI IALL DANN Attesting Officer I commissloner of Patents P -w I RTEo STATES PATENT- OFFICE CERTIFICATE OF CORRECTION Patent No. 3,816,068 Dated June 11, 1974 Inventm-( Joseph Rivlin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby eorrected as shown below:

Column 1, line 61, "porpyl" should read -propyl Column 2, lines 51-52, "acrylamide methacrylamide" should read -aerylamide or methacrylamide Column 5, line 51, "when ever" should read whenever- Column 6, line 29, in the fourth column, "1. 50" v 2 should read -l5.0,- I

Column 6, line 57, "CO" should read --CP Column 9, line 25, "NDMP" should read -M.DMP-'- Signed and sealed this 29th dayof October 1974.-

(SEAL) Attest:

McCOY M. GIBSON JR. c. MARs ALL DANN Attesting Officer Commissloner of Patents

Claims (5)

1. 2. The process of claim 1 wherein the cellulosic textile material is a 50/50 Polyester/cellulose blended textile fabric, X is hydrogen and R is hydrogen.
2. 3. The process of claim 1 where the cellulosic textile material is a polyester/cellulose blended textile material.
3. 4. The process of claim 3 where R is hydrogen and X is hydrogen or a methyl radical.
4. 5. The process of claim 3 where X is hydrogen.
5. 6. The product produced by the product of claim 1.