US3556840A

US3556840A - Method for improving the flame retardant properties of a cellulosic material

Info

Publication number: US3556840A
Application number: US713317A
Authority: US
Inventors: Giuliana C Tesoro
Original assignee: JP Stevens and Co Inc
Current assignee: JP Stevens and Co Inc
Priority date: 1968-03-15
Filing date: 1968-03-15
Publication date: 1971-01-19
Anticipated expiration: 1988-01-19
Also published as: FR2004039A1; GB1258652A; DE1913137A1

Abstract

CELLULOSIC TEXTILE MATERIALS ARE RENDERED FLAME-RETARDANT BY TREATING THE TEXTILE MATERIAL WITH AN N-(OXYMETHYL)-3(DIALKYLPHOSPHONO)PROPIONAMIDE, E.G., N-(HYDROXYMETH YL)-3(DIETHYLPHOSPHONO)PROPIONAMIDE, AND AN ACID CATALYST AND HEATING TO INSOLUBILIZE THE AMIDE COMPOUND AND THEREAFTER TREATING THE MATERIAL WITH A POLY(OXYMETHYL) MELAMINE, E.G., TRIS(HYDROXYMETHYL) MELAMINE, AND A PEROXIDE SUCH AS HYDROGEN PEROXIDE AND HEATING TO INSOLUBILIZE THE MELAMINE COMPOUND. THE RESULTING PRODUCT, WHICH DESIRABLY CONTAINS 0.5 TO 1.8 WEIGHT PRECENT PHOSPHORUS, BASED UPON THE CELLULOSE, AND SUFFICIENT NITROGEN TO RENDER THE CELLULOSE FLAME-RETARDANT, RETAINS THE SOFT HAND, STRENGTH AND AIR PERMEABILITY CHARACTERISTIC OF THE UNTREATED TEXILE.

Description

United States Patent 01 3,556,840 Patented Jan. 19, 1971 METHOD FOR IMPROVING THE FLAME RETARD- AN T PROPERTIES OF A CELLULOSIC MATERIAL Giuliana C. Tesoro, Dobbs Ferry, N.Y., assignor to J. P. Stevens & Co., Inc., New York, N.Y., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 672,412, Sept. 15, 1967, which is a continuation-in-part of application Ser. No. 620,109 Mar. 2, 1967. This application Mar. 15, 1968, Ser. No. 713,317

Int. Cl. C09k 3/28; C09d 5/18 US. Cl. 117-137 8 Claims ABSTRACT OF DISCLOSURE This application is a continuatiomin-part of copending application Ser. No. 672,412 filed Sept. 15, 1967, which in turn was a continuation-in-part of applicationSer. No. 620,109 filed Mar. 2, 1967, now abandoned.

This invention relates to flame-retardant cellulosic textiles and to methods for their production. More particularly this'invention relates to cellulosic fabrics which compound and the amide and the melamine compounds amount of nitrogen which is required increases as the phosphorus content decreases.

Because very few phosphorus-containing compounds also contain nitrogen in amounts sufficient to aid flame retardancy at low total add-on, it has been found necessary to employ organo-nitrogen compounds having high nitrogen contents, such as the poly(oxymethyl)melamines, in combination with the phosphorus-containing compound. One problem with the use of such organonitrogen compounds has been their tendency to cross-link the cellulose and thereby adversely affect properties such as hand, strength and the like. It has been discovered in accordance with the present invention that a desirable degree of flame retardance can be obtained without adverse effect on cellulosic properties when an N-(oxymethyD phosphonopropionamide is employed as the phosphorus-containing are applied to the cellulose in a specific sequence.

Briefly, the method of the present invention comprises treating cellulose with an N-(oxymetihyl)phosphonopro pionamide in an amount suificient to provide the desired have been rendered filame-retardant with little adverse effect on the physicalproperties of the fabric.

-It has long been known that'flame-retardant properties maybe imparted to celluloseyparticularly in a textile able due to series degradation of the cellulose as Well as lack of durability of the treatment.

phosphorus content, insolubilizing the amide by acidcatalyzed reaction with the cellulose, and thereafter treating the cellulose with a poly(oxymethyl)melamine in an amount sufficient to provide the desired degree of flame retardance and insolubilizing the melamine compound,

preferably a poly(hydroxymethyl)melamine, by wet fix-i ation employing a peroxide.

By the term oxymethyl, as employed in the present. application, is meant hydroxymethyl or lower alkoxy-' methyl. By the terms lower alkyl and lower alkoxy,

are meant linear or branched chain alkyl and alkoxy: groups containing up to about 6 carbons, and preferably up to about 2 carbons, such as methyl, ethyl, isopropyl, tert-butyl, methoxy, ethoxy, isopropoxy, tert-butoxy and the like. By the term lower alkenyl is meant alkenyl' groups of up to 6 carbons, preferably allyl. By the term halogen is meant a halogen having an atomic number of 17 to 53, inclusive, with chlorine being preferred.

sN-(oxymethyl)phosphonopropionamides which are em- 5 ployed in accordance with the present invention are reprei sented by the formula:

'More recently treatments employing organophosphoru's compounds have been developed in an effort to provide flame retardance Without concurrent damage to the cellulose and to render the phosphorus-containing agent -resistant to removal during laundering. Although many of these-treatments are commercial-use today, none has been completely successful due to the high cost of the or'ganophosphorus compound and the high degree ofadd-on of organophosphorus compound required to provideflanie-retardant properties." 7

Still more recently, it has been discovered that organic nitrogen is a synergist for phosphorus-induced flame retardance in cellulose, and thus allows the use of reduced amountslof organophosphorus compound. For example, when 6- to Ill-ounce cotton fabric is treated with an organophosphorus compound little or no flame-retardant eifect is observed until at least about 1.5 weight percent phosphorus, based on cellulose, is present, and acceptable flame-retardant properties are not achieved until the phosphorus content is'at least about 2 percent. By incorporating sufiicient organic nitrogen into the treatment, however, excellent flame-retardant properties can be obtained at phosphorus contents as low as about 0.2 weight percent, despite thefact that organic nitrogen compounds alone are not flame-retardant agents. In such treatments the lower alkyl or lower alkenyl; R is and R are preferaby hydrogen.

Illustrative compounds include:

N- (hydroxymethyl) -3- (dimethylphosphono propion- V amide,

A N-(hydroxymethyD-3-[bis(2-chloroethyl)phosphono] propionamide,

N- (methoxymethyl -3 diethylphosphono) propionamide, N-(ethoxymethyl)-3-(diethylphosphono)propionamide,

N- (prop oxymethyl) -3 diethylpho sphono propionamide, N- (isobutoxymethyl) -3 (diethylpho sphono) propionamide,

N-(butoxymethyl)-3-(diethylphosphono)propionamide, I

N (hydroxymethyl -N-methyl-3 diethylpho sphono) propionamide, and

l I- (allyloxymethyl 3 diethylphosphono) propionamide.

The amides of Formula I are readily produced by 5 reaction of the corresponding N-unsubstituted amide with formaldehyde, optionally in the presence of an alcohol,

in a neutral or alkaline aqueous medium at temperatures of from about 40 to about 60 C. The N-uns ubstituted a:

(1) wherein R is lower alkyl or halogen-substituted lower alkyl; R is hydrogen or lower alkyl; and R? is hydrogen,-

perferably alkyl and R amide, in turn, can be obtained by the reaction of a dialkylphosphite with acrylamide in the presence of a basic catalyst as described in U.S. Pat. 2,754,319.

The poly(oxymethyl)melam-ines which are employed in accordance with the present invention contain at least two oxyrnethyl groups and are represented by the formula:

3 3( 2)x( 2 )y[ 2 )2]z wherein C N represents the s-triazine nucleus; each of x, y and z is an integer having a value of from 0 to 3, with the proviso that the sum of x, y and z is 3 and the compound contains at least two oxymethyl groups; and R is hydrogen or lower alkyl, preferably hydrogen.

P Illustrative of the poly(oxymethyl)melamines are:

N ,N ,N -tris (hydroxymethyl) melamine,

hexakis (methoxymethyl melamine,

bis (hydroxymethyl) melamine,

tetrakis (hyd roxymethyl) melamine,

pentakis (hydroxymethyl) melamine,

bis (methoxymethyl melamine,

tetrakis (ethoxymethyl) melamine,

pentakis (isobutoxymethyl) melamine, and

tris hydroxymethyl) tris (methoxymethyl) melamine.

In the first step of the process of this invention cellulose is treated with the N-(oxymethynphosphonopro pionamide and an acidic catalyst to promote reaction of the phosphonopropionamide with the cellulose. Suitable acidic catalysts include hydrochloric acid, sulfuric acid and formic acid. The phosphonopropionamide and acid catalyst are preferably applied to the cellulosic substrate in aqueous solution, and when aqueous media are employed suitable catalysts include salts of strong acids and weak bases which upon hydrolysis yield acids. Ammonium halide, e.g., chloride, and various amine hydrohalides (hydrochlorides) are preferred. Other suitable catalysts are ammonium sulfate, zinc nitrate, zinc tetrafluoroborate,

zinc chloride, magnesium chloride, aluminum chloride.

hexahydrate, ammonium oxalate and ammonium lactate. The amounts of phosphonopropionamide and catalyst present in the aqueous solution are not critical to this invention, and will depend upon the desired phosphorus content of the treated cellulose and the quantity of solution applied to the cellulose. In general, however, solutions containing from about to about 35 weight percent propionamide and from about 0.5 to about 5 weight percent catalyst have been found suitable.

Insolubilization of the propionamide is elfected by subjecting the thus-treated cellulose to conditions under which the propionamide reacts with the cellulose, as by heating the treated cellulose at an elevated temperature, for example, a temperature of about 150 C. to about 200 C. The heating is carried out for a period of time sufficient to effect insolubilization, usually 1 to 10 minutes. When the amide and catalyst are applied in solution, the solvent is preferably evaporated oif prior to effecting insolu'bilization.

After insolubilization of the propionamide, the fabric is washed to remove unreacted amide, and in particular, to remove the acidic catalyst which, if left on the cellulose, would promote cross-linking of the cellulose by the poly(oxymethyl)melamine. Such cross-linking adversely affects the properties of cellulosic materials such as strength, hand and the like.

The washed fabric is then treated with the poly(oxymethylhnelamine compound and a peroxide, preferably hydrogen peroxide. This treatment, like the treatment of the first step, is preferably carried out by the use of aqueous solutions of melamine and peroxide. The concentration of melamine compound in such a solution is not narrowly critical, but should be enough to provide sufficient nitrogen to the cellulose to impart flame-retardant properties thereto, and concentrations of from about 2 to about 25 weight percent have been found useful. Catalytic amounts of peroxide are normally in the range of from about 0.1% to about 0.5%.

Insolubilization of the melamine compound is ordinarily effected by means of Wet fixation of the thus-treated material. In a preferred technique, the cellulose already modified in the first step is padded to 100% i30%-wet pick-up with an aqueous solution containing both melamine compound and hydrogen peroxide, partially dried to a moisture content of about 10 to about 30 weight percent and then treated with steam for a period of time sufiicient to insolubilize the melamine compound. Ordinarily-times of from about 1 minute to about 1 hour are required.

As noted previously, the amounts of nitrogen and phosphorus necessary to give a specified degree of flame retardance are inversely related. With reference to the compounds empioyed in the process of this invention this rerelationship is defined by the expression: M

wherein N is the 'weight percent nitrogen, based upon expression because chlorine assists the nitrogen-phosphorus synergism with respect to flame retardance. Be-.

cause the presence of halogen may adversely affect the treated cellulose its presence is not preferred.

In general it is preferred to employ relatively low phosphorus contents in the cellulosic product. The preference for low phosphorus concentrations is based in part upon the relatively high cost of the phosphonopropionamide as. compared with melamine compound. In addition it has been found that the efficiency of the insolubilization of the phosphonopropionamide increases as the degree of addon of the phosphonopropionamide decreases. For example, as is illustrated by Example 6, the efliciency ofutiliza tion increases from about 40% at a nominal'add-on of 35 weight percent of amide to about 73% at a nominaladd-on of about 16% amide. Finally, when the treatmentof this invention is applied to textile products it has been found that air permeability decreases with increasing phosphorus content, and when preservation of air permeability is desired, the phosphorus content should not be in excess of about 1.8 Weight percent and is desira-bly less than 1.2%. To provide effective flame re" tardance without excessive add-on of melamine cornpound, the cellulose should contain at least about 0.2%

and preferably at least about 0.5% phosphorus.-

When phosphorus content is within the range of 0.5 to about 1.8% the nitrogen content of the cellulose should be in the range of from 10% to about 1.7%, and preferably from about 8% to about 5% The cellulose which is treated in accordance with'this invention can be from any of various sources, for instance, from seed hairs, as native cotton, from bast fabrics, as flax (linen), ramie, juteand hemp, and from regenerated cellulose, as viscose rayon. This invention also" can be applied to yarns and to fabrics which are cellu s losic blends, as cotton-rayon blends containing from about 10% to about 60% cotton and from about to about 1 40% rayon. Furthermore, the invention is applicable to'. cellulosic yarns which' then may be woven, knitted or bonded into a flame-retardant fabric with a minimum degree of impairment to characteristic properties. 'An additional application includes treatment of a rayon yarn 'or fabric which is subsequently used to manufacture a" carbon yarn or fabric having improved properties and/or:

improved yield.

The following examples are illustrative. In the examples the following analytical and test methods were ernployed:

( 1) Analyses:

(a) Chlorine: Saponi'fication by means of potassium A hydroxide in ethylene glycol, followed by'argentometric titration of chloride ion.

(b) Nitrogen: Kjeldahl digestion followed by titration of distilled ammonia.

Phosphorus: Kjeldahl digestion followed by colorimetricanalysis employing acetone-water to intensify the phosphornolybdate color [Bernha'rt ,et al., Anal. Chem.,

vol. 27, 440(1955)].

.(2) ,Airpermeability: Federal Specifications for Tex-.

tile Test Methods, CCCT-1 9,1b., Method 5450, reported in cubic feet per'minute per square foot.

(3) Crease recovery: ASTM D l295-60T, reported as the sum of the angles, in degrees, in Warp (W) and filling (F) directions.

(4) Flame retardancy (vertical test): AATCC 34- 1966, reported as char length in inches. BEL means burned the entire length.

(5) Flex abrasion resistance: ASTM D l175-44T (0.5-pound head weight and 2-pound toggle tension on Stoll Flex Abrader), reported in cycles.

weight of the fabric (OWF) resulting immediately after padding are shown in thetable. After padding, .the samples were framed to the original dimensions, dried at 60 C., heated at 165 C. for 5 minutes to insolubilize the amide, washed, dried and conditioned as before. Weight gains were measured, and were .corrected for moisture regain.

Next, N ,N ,N -tris (hydroxymethyl)melamine s m s s) was applied in a second step to increase the nitrogen content of the fabric by padding the samples resulting from the first step with aqueous solutions which contained both tris(hydroxymethyl)melamine (in varying amounts) and 0.3% hydrogen peroxide. Then the samples were dried to 20-30% moisture content, steamed in a laboratory steamer for 8 minutes (to hasten wet fixation), washed, dried and conditioned as before.By the procedure of wet fixation, tris(hydroxymethyl)melaminewas insolubilized substantially quantitatively.

The results of these experiments (Samples A-G) are U summarized in Table I, together with the results of an (6) Laundering: AATCC 88A-1964T, Test III, hometype washer, S-pound load, full cycle, 60 0., synthetic experiment in which the cotton sheeting was treated with a mixture of the amide and the melamine compound employing Catalyst XRF to insolubilize the reagents (Sample H). The pad-cure procedure was used in applying the mixture in a single step.

TABLE I *Assumed.

detergent; tumble drying. The number of launderingdrying cycles (10 or is indicated by 10L or 50L, respectively.

'(7). Laundering with bleach: 0.25 pint (0.5 cupful) of All of the samples treated with the amide and the melamine compounds possessed acceptable flame 'retard+ra ancy. Sample H, 1' howeven which'. was obtainedmby the? commercial beads based on potassium'peroxymonosulfate (K 50 was added per 16 gallons.

(8) Stiffness: (Cantilever), ASTM D 1388-64, reported in mg.-cm. p,

(9) Tear strength: (Elmendorf), ASTM D1424- S9, reported in pounds. All parts and percentages are by weight unless stated otherwise. Q

EXAMPLE 1 Samples of all-cotton sheeting in a plain weave (bleached, desized and weighing 4.3 ounces per square yard) were conditioned at a relative humidity of 65;L2% at 2121 C. for at least 16 hours and weighed. Except for a control sample which was juntreated, the

sampleswere padded with an aqueous solution containing N (hydroxym'ethyl) 3 (diethylphosphono)propionamide (C H NO P) and, as the catalyst, an amine hydrochloride in the formof an aqueous 30% solution marketed by Millmaster Onyx Corp. under the trade name Catalyst XRF. The concentration of Catalyst XRF on the weight of the bath was 3.0%. Concentrations of the reagents were varied, and the percentages on the I single-step procedure, possessed a considerably increased stiffness (366 rug-cm.) when compared'with theuntreated control (97 ,mg.-cm.) or the products of the two-step procedure of this invention (101-136 mg.-cm;). For sheet--- ing of the type employed in this example, the stiffness should be less than about 250 mg.-cm. I The elfect ofincreasing amounts of phosphorus on air permeability is evident from SamplesA-G; Thus, at 0, i to. 0.79% phosphorus-theair permeability was 52-.

f t /min./ft. whereas phosphorus contents of about I and 2% gave values of about 44larid 37, respectively.Be- I cause the permeability of the treated sheeting is desira-bly at'least about of the natural permeability, or-about .42 ft. /min./ft. it can be seenthat phosphorus contents in excess of about 1.8 percent should be avoided.

EXAMPLE 2 "News Employingv the general procedureof Example 1, I that the b is(2,-chloroe thyl) ester was usedf ins'tead'of the" diethyl ester of -N- (hydroxymethyl) 3-phosphonopropion amide, two samples were treated by the two-ist'epfmethodi of this invention. The data for these experiments are slimmarized in Table II, together'with the data for'an unnli treated control. p j I TABLE II Air , permea- OWF, percent Found in fabric bility sample, percent h Char Stlliness on. it./*

1st step, 2d step, length, (overall), min.

Cotton sheeting sample CaHmClzNOsP CeHizNsOs 01 N I inches rug-cm. sq. it.

BEL 97 60 Assumed.

' EXAMPLE 3 these experiments are summarized in Table III, together 20 with the data for an untreated control.

that the two-step process of this invention results in greater abrasion resistance and greater tear strength than does the single-step process. Evidence that cross-linking occurs to an appreciable extent in the single s tep treatment is provided by the data for crease recovery, for crease recovery angles are significantly higher in the productsobtained from the single-step process (Samples C and D) than for a corresponding add-on of chemicals in the two- TABLE III Found Air in fabric permea- OWF, percent sample, bility, percent Char Stifiness cu. it./ Rayon challis 1st step, 2d step, length, (overall), m1n./

sample CaHmNO P CQHIZNGOI! N P inches rug-cm 7 sq. it

A 24 7. 5 4.32 1.69 5. 9 80 81 B 13 13. 3 6. 48 0. 59 6. 5 124 98 C 23 8.0 4. 46 1. 23 5. 7 290 94 D 7. 6 16. 0 7. 0. 72 6. 9 361 91 Control *0 "0 BEL 43 162 Assumed.

EXAMPLE 4 I erties which are typical of the two-step process are ob- Employing the two-step procedure of Example 1, several 5 samples were prepared and then laundered repeatedly with tained without loss in char length or whiteness in comparison with those of the single-step process.

TABLE V Total of Found in crease fabric recovery OWE, percent sam angles War Warp Cotton percent Char (W+F), Tear abrasion sheeting 1st step, 2d step, length, rength, resistance, Whitesample C3H15NO5P CgHrsNuOs N P inches Dry Wet cycles ness 28 56 4. 2 218 179 1. 6 425 +82 2 78 4. 5 133 212 1. 5 290 +79 62 4. 3 269 244 0. 9 245 +78 36 4. 2 275 233 0. 4 200 +81 "0 BEL 173 147 .3. 1 950 +83 v v p EAssurned. v or without persulfate bleach. To evaluate the durability of EXAMPLE 6 the treatment the vertical flame test was carried out before laundering and after 10 cycles. The data for these ex periments are summarized in Table IV;

Samples of the same all-cotton sheeting identified at the beginning of Example 1 were padded with a variety of con- TABIJE IV After 10 I launderings, found in Found fabric OWF, Percent in sample, After 10 Cotton w fabric Cher percent. launderings, sheeting 1st step, 2d step, sample length, oharlength, sample C H1 NO P GtHlZNflOJ N inches Bleach N P inches 10.4 19. 7.77 5.0 None"--- 7.30 0.85 4.7 10.4 12.5 5.28 4.8 K2805".-. 5.12 1.01 5.4 10.4 19.3 7.39 as Kzsosuu; 7. 1.01 4.1

it 4.8 inches'after 50 launder-lugs.

The general procedure "of Example 1 was followed to compare the eflects on fabric properties resulting from the two-step process and from the simultaneous treatment with N-(hydro'xymethyl)+3 (diethylphosphono)propionamide and t'ris(hydroxyrnethyl) melamine. The resulting samples (all rnade using the same type of all-cotton sheet- I ing identified in Example 1)" were subjected to several tests to evaluate" the fabric treated under the different sets centrations of N,-(hydroxymethyl) 3 e (di m ethylphosphono)propionamide (C H NO P) at a'fairly uniform wet pick-up (106i2% WPU) so a range was obtained in plication (percentage OWF) withefiiciency of utilization, upon insolubilization by heating for 4 minutes at'approxif conditions, By referring to Table V, below, it is evident mately C. The data summarized in Table VI demonstrate that efficiency of utilization (measured here by the ratio of the percentage of phosphorus found in the fabric after curing to the percentage of phosphorus OWF before curing) is greater at lower levels of application. This economic feature is used to advantage in the present invention, which enables flame retardancy to be obtained at very low levels of pohsphorus (under 1.8%) with concomitant benefits in other properties.

Calculated by multiplying the values in the preceding column by 0.1467, because 14.67% by weight of CGHHNOEP is phosphorus.

After curing (4 minutes at approximately 170 0.), washing to rdermove C H NOsP which did not condense with the cellulose, and

*The ratio of percentages expressed more fully is (P in the fabric after curing) (P OWF before curing).

What is claimed is:

1. In a method for improving the flame-retardant properties of a cellulosic material by the insolubilization of an N-(oxymethyl) 3-phosphonopropionamide and a poly (oXymethyDrnelamine on said cellulosic material, the improvement of insolubilizing said amide in the presence of an acidic catalyst and thereafter insolubilizing said melamine in the presence of hydrogen peroxide.

2. A method according to claim 1 wherein said propionamide is represented by the formula:

wherein R is lower alkyl or halogen-substituted lower alkyl; R is hydrogen or lower alkyl; and R is hydrogen, lower alkyl, or lower alkenyl, and said melamine is represented by the formula:

wherein C N represents a triazine ring; each of x, y and g is an integer having a value of from to 3 with the proviso that the sum of x, y and z is 3, and there are at least two oxymethyl groups; and R is hydrogen or lower alkyl.

3. A method according to claim 2 wherein R is lower alkyl, each of R R and R is hydrogen, and x is O.

4. A method according to claim 3 wherein said propionamide is employed in an amount sufiicient to provide from about 0.5 to about 1.8 weight percent phosphorus, based upon cellulose, and said melamine is employed in an amount sufficient to provide from about 1.7 to about 10 percent nitrogen based upon cellulose, the nitrogen content being at least 94P wherein P is the Weight percent phosphorus, based upon said cellulose.

5. A method according to claim 4 wherein the phosphorus content is not more than about 1.2 percent and the nitrogen content is from about 5 percent to about 8 percent.

6. A method according to claim 2 wherein said propionamide is N-(hydroxymethyl) 3 (dimethylphosphono) propionamide and said melamine is N N N -tris(hydroXymethyDmelamine.

7. A method according to claim 2 wherein said propionamide is N-(hydroxymethyl) 3 (diethylphosphono) propionamide and said melamine is N N N -tris(hydroxymethyl)melarnine.

8. A method according to claim 2 wherein said propionamide is N-(hydroxymethyl) 3 [bis(2 chloroethyl) phosphono]propionamide and said melamine is N N N -tris(hydroxymethyl)melamine.

References Cited UNITED STATES PATENTS 2,530,261 11/1950 Morton et al. 8-116.2 2,781,281 2/1957 Berger 117-136 3,276,897 10/1966 Reeves et al. 106-15X 3,436,250 4/1969 Yamaguchi et al. l17-l36X WILLIAM D. MARTIN, Primary Examiner H. I. GWINNELL, Assistant Examiner US. 01. X.R. 117-136, 143, 144

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,556,8 LO Dated January 19, 197i Inv Giuliana C. Tesoro It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, Table IV, right-hand column, "5. should reac 5.1 and "4.1" should read 4H Column 9, line 1 the formula should read C N NH Signed and sealed this 28th day of September 1971.

3 3 NHCHZOR [N(cH 0I R (SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Acting Commissioner of Pat.