US2286726A - Process of flameproofing cellulosic material and products thereof - Google Patents

Description

Patented June 16, 1942 FFHQ PROCESS OF FLAMEPROOFING CELLULOSIC MATERIAL AND PRODUCTS THEREOF ware No Drawing. Application January 6, 1939, Serial No. 249,653

13 Claims. (Cl. 117-137) This invention relates to the flame-proofing of cellulosic materials and more particularly to the permanent, i. e., water-resistant, flameprooflng of cellulosic textiles.

The flame-proofing of textiles has been done for many years. Salts such as ammonium phosphate have been used for this purpose. The flame-proofing salt is, however, readily removed by simple washing. Flame-proofing with alkylamine borates, phosphates,- hydroiodides and hydrobromides, and alkylolamine phosphates is likewise not permanent to washing. A flameproofing process wherein the flame-proofing is resistant to water is desirable. Attempts have been made to provide such a process by precipitating stannic oxide on the textile but have been unsatisfactory since this promotes a strong afterglow. This can be eliminated by further coating with chlorinated hydrocarbons but this adversely affects the feel of the fabric. Attempts to use urea phosphate in combination with a thermosetting phenol-formaldehyde resin have likewise not led to a flame-proofing resistant to water. The products are also stifi.

This invention has as an object an improved flame-proofing process. A further object is to decrease the combustibility of organic materials. A further object comprises improved flameproofed cellulosic materials. Another object is the provision of a process for flame-proofing cellulosic materials so that they are also flameproof after washing. A further object is to provide flame-proofed cellulosic materials which are afterglow-proofed Without being substantially stiffened, hardened or altered in aspect. Other objects will appear hereinafter.

These objects are accomplished by the following invention wherein a cellulosic material, such as a fabric, is impregnated with ethylenimine, either monomeric or polymeric, and is then treated with an acidic fire-retardant i. e., one the aqueous solution of which has a pH less than 7.0.

Under proper conditions, cellulosic materials, e. g. fabrics. may be treated with ethylenimine or polyethylenimine so that the imine becomes permanently attached to the cellulosic material and is not removed therefrom by water, soap, acids, or alkalies. This may. for example, be

accomplished either by heating the cellulosic material under reflux for several hours in a solution of monomeric ethylenimine in an inert solvent such as water, or by impregnating the cellulosic material with polyethylenimine by immersing in an aqueous or alcoholic solution of the polymer, squeezing through rollers, drying, and baking to remove the solvent and fix the polymer to the cloth. Baking is not necessary when the monomer is used since the refluxing process effects a simultaneous polymerization and union with the cloth. Ethylenimine in itself shows no fire-retarding properties.

The cellulosic material containing ethylenimine is then treated with solutions of acidic materials;

which have fire-retarding properties. These may be monobasic acids, polybasic acids, or acidic salts of polybasic acids. merit, the cloth is thoroughly'rinsed in water and dried.

The following examples, wherein parts are by weight, illustrate the nature of the invention but in no way are intended to limit the scope thereof.

Example I Cotton broadcloth aggregating 200 parts is heated under reflux in a solution comprising 100 parts of ethylenimine and 150 parts of water for 24 hours. The cloth is removed, thoroughly rinsed in hot water, and dried. This treatment causes 8.6% of ethylenimine, based on the weight of the cloth, to become absorbed, and probably I reacted with the cellulose. This ethyleniminetreated cloth is then reacted with a 15% aqueous solution of phosphoric acid by immersing the cloth in the solution, wringing out, rinsing thoroughly in cold water, and drying An amount of phosphoric acid equal to approximately 20% of the initial weight of the cloth is reacted with the ethylenimine and fixed to the cloth by this process. When ,this product is exposed to the flame of a Bunsen burner, charring occurs at the point of contact with the flame, but no flame is propagated along the cloth regardless of whether the cloth is held vertically or horizontally; and no afterglow (fiameless combustion) is evident. The product is soft, pliable, and similar to an untreated sample in -feel and handle," and shows no stiffness or harshness. Upon being washed for half an hour in a 1% aqueous solution of the sodium salt of a sulfated long chain alcohol at C., and in a similar solution at the boiling point, the cloth remains substantially flame-proof as described above.

Example II Polyethylenimine is prepared by refluxing 250 parts of ethylenimine with 1.0 part of phosphoric acid in 209 parts of methanol for 42 hours. At the end of this time, the methanol and un- Following this treathour.

Similar results are obtained by using a solu tion of ten parts of polyethylenimine in twenty parts of ethyl alcohol.

Example III Cotton cloth is impregnated with a aqueous solution of polyethylenimine prepared as in Example II. The same is wrung out, dried, and baked at 100-110 C. for four hours. It is then soaked in a 15% aqueous solution of watersoluble calcium acid phytate, prepared as dis closed in copending application of Roger Adams and C. W. J. Wende, Serial No. 249,654, filed of even date herewith. After impregnation with the phytate, the cloth sample is rinsed and dried.

It neither propagates a flame nor shows an afterglow when exposed to the Bunsen flame, and retains these properties after half-hour treatments in water at 50 C. and at 100 0., respectively. The phytate is not removed by washing at 100 C. with a 1% aqueous solution of the sodium salt of a sulfated long chain alcohol. The fire-proofed product is soft and pliable, with no stiffness or harshness.

Example III above, in the use of ethylenimine,

' is an illustration of the present invention, and,

in the use of. a phytate as a fire-retardant, it is an exemplification of the invention of Adams and Wende, above identified.

Example IV Rayon yarn spun from a viscose solution containing 20% by weight of polyethylenimine is extracted in 4% sodium carbonate solution at 90 C. for half an hour to desulfurize the rayon and to remove the acids remaining from the coagulating bath. It is then thoroughly rinsed in hot water, immersed in a 15% aqueous solu tion of phosphoric acid for twenty minutes,

rinsed, and dried. The product thus obtained can be burned with some difficulty, but is markedly. less flammable than the untreated material. It remains difiicultly combustible after washing for half an hour in boiling water.

ethylenepentaminc. In these partial amine-acid addition salts, the amine or similar nitrogen base should contain a carbonrnitrogcn ratio of 2:1 or less. It will be understood, however, that the present invention is not concerned with that selection of such compounds which is proper if they are to have fire-retarding effects. It is only necessary that the compound used be a fireretardant and acidic, both of which, if not already known, are readily determinable.

It will similarly be recognized that the present invention, viz., the use of'ethylenimine to affix acidic fire-retardants to cellulosic materials, is not concerned with the amount of acidic fireretardant which will be required, but can be practiced in the affixing of whatever amount, as known from the prior art or as determinable by simple test, is required to impart the degree Of fire-retardance desired to the particular cellulosic material to be treated. The amount of ethylenimine to be used will be at least that which is stoichiometrically equivalent to the amount of acidic fire-retardant to be used, and an excess of 1020% is usually desirable. As an empirical guide, the amount of ethylenimine to be preliminarily applied to the cellulosic material will vary directly with the flame-proofing effectiveness (F. P. E.) of the acidic fire-retardant on the cellulosic material to be flame-proofed, and in- 1 gms. LXequiv. Wt. of F. R equiv. Wt. of E. I. F. P. E.

it being understood of course thatlesser amounts of ethylenimine are suitable if complete flameproofness is not necessary. For the more eifective acidic fire-retardants such as phosphoric Any acidic fire-retardant, i.'e., any monobasic i acid, polybasic acid, or acidic salt of a polybasic acid which functions to retardcombustion i. e., one the aqueous solution of which has a pH less than 7.0 may be used in conjunction with ethylenimine to impart the property of waterresistant fiame-proofness to cellulosic materials such as textiles. These include: fire-retardant monobasic acids, e. g., sulfamic acid, hydrobromic acid, and hydriodic acid; fire-retardant polybasic acids, e. g., phosphoric acid, phytic acid, boric acid, sulfuric acid, tungstic acid, and phosphotungstic acid; and acidic partial salts of the above and other fireretardant polybasic acids, the cations in such salts comprising hydrogen and a metal such as Ca, Al, Zn, Sn, or Mg, or a nitrogen base such as ammonia, urea, guanidine, dicyandiamidine, ethylenediamine, diethylenetriamine, triethylenetetramine, or tetraacid (which appears to function as a monobasic acid) and sulfamic acid, good results are obtained when the cellulosic material is impregnated with ethylenimine in an amount, based on the Weight of the material, of from 6% to 40% and preferably from 8% to 20%. However, a cellulosic fabric which has been impregnated with less than 6% ethylenimine and then treated with phosphoric acid will have a good feel and some degree of fire-retardance, though it Will not be completely flame-proof. A fabric which has been treated with 40% or more of ethylenimine and then with phosphoric acid is completely flameproof but may be somewhat less pliable than is desired. Less efiective acidic fire-retardants such as boric and phosphotungstic acids, require large amounts of ethylenimine. Phytic acid and acidic phytates as a rule require intermediate amounts. In the case of monomeric ethylenimine, optimum results are obtained with 8l0% ethylenimine and slightly less than a stoichiometrical amount of phosphoric acid, the preferred procedure being to heat the cellulosic material with a concentrated (20-40%) aqueous solution of the monomeric ethylenimine for 12 to 24 hours at refluxing temperature (-110 0.), whereby to polymerize the ethyl-cnirnine in .situ, rinse with hot water, immerse in a .l-25% aqueous solution of phosphoric acid for to 15 minutes at 20-40 C.,

rinse with cold water, and dry. In the case of polyethylenimine, optimum results are obtained with 12-18% polyethylenimine and an approximately stoichiometrical amount of a Water-soluble calcium acid phytate, the. preferred procedure being to impregnate the cellulosic material with a -20%, aqueous'solution of polyethylenimine, dry, bake at 90-l25 C, for 2-6 hours, immerse in a 10-20% aqueous solution of the phytate, rinse with cold water, and dry.

'I'he'examples show applications of the invention to cellulosic textiles. It is however useful for imparting fire-retarding or fire-resisting properties to any cellulosic material whatever in anyform whatever, particularly to those which may,-by the present invention, be made more permanently resistant to combustion are paper, cellulose derivatives, wood, hemp, excelsior, sawdust, kapok, and regenerated cellulose in sheet or thread form.

The process of the present invention is superior to any known method for flame-proofing textiles in that the fire-retardant substances are not leached out by cold water, by boiling water, or

by mild detergents such as the sodium salts of sulfated long chain alcohols. Furthermore, the cellulosic material is fiame-proofed and afterglow-proofed without, being stiifened or harshened, and is altered in color only slightly or not at all.

No other known flame-proofing method gives all these results. As is discussed above, stannateprocessed fabrics show a very strong afterglow unless they are treated with enough chlorinated hydrocarbon to impair the feel; and if treated by the sodium stannate-ferric chloride process they are colored brown. Amine phosphates, etc., are satisfactory fiame-proofers which have little or no efiect on the "feel of cloth, but fiameproofing agents of this type are water-soluble and may be leached out simply by dipping the cloth for a few seconds in cold water.

The above description and examples are intended to be illustrative only. Any modification of or variation therefrom which conforms to the spirit of the invention is intended to be included within the scope of the claims.

I claim:

1. Process which comprises treating with an acidic fire-retardant a cellulosic material impregnated with polyethylenimine.

2. Process which comprises impregnating a cellulosic material with polymeric ethylenimine', baking the same, and then impregnating the material with an acidic fire-retardant.

3. Process which comprises impregnating a cellulosic textile with 6 to 40% of its weight of polymeric ethylenimine, baking the same, and then impregnating the material with an amount, up to the stoichiometrical amount, sufiicient to retard combustion, of phosphoric acid.

4. Process which comprises impregnating a cellulosic textile with 8 to of its weight of polymeric ethylenimine, baking the same, and then impregnating the textile with an amount, up to the stoichiometrical amount, sufiicient to retard combustion, of phosphoric acid.

5. Process Which comprises impregnating a cellulosic textile with 6 to 40% of its weight of monomeric ethylenimine, polymerizing the same in the cellulosic textile, and then impregnating the textile with an amount, up to the stoichiometrical amount, sufficient to retard combustion,

of phosphoric acid.

6. Process which comprises impregnating a cellulosic textile, with a to 20% of its Weight of monomeric ethylenimine, polymerizing the same in the cellulosic textile, and then impregnating the textile with an amount, up to the stoichiometrical amount. sufficient to retard combustion, ofphosphoric acid.

'7. Process which comprises heating a cellulosic textile for 12-24 hours at refluxing temperature in an aqueous solution of ethylenimine oi 20-40% concentration and in such amount as to provide 810% ethylenimine based on the weight of the textile, rinsing with hot water, immersing in a 10 to aqueous solution of phosphoric acid for 5 to 15 minutes at 20 to C., rinsing with cold water, and drying.

8. A product comprising a cellulosic material impregnated with an acidic fire-retardant in amount at least sufficient to retard combustion, said fire-retardant being fixed to thematerial by polymeric ethylenimine.

9. A product comprising a cellulosic textile impregnated with an acidic fire-retardant in amount at least sufiicient to retard combustion, said fire-retardant being fixed to the textile by polymeric ethylenimine.

10. A product comprising a cellulosic textile, polymeric ethylenimine in amount equal to 6 to 40% of the weight of the cellulosic textile, and an amount, up to stoichiometrical amount, sufficient to retard combustion of phosphoric acid.

11. A product comprising a cellulosic textile, polymeric ethylenimine in amount equal to 8 to 20% of the Weight of the cellulosic textile, and an amount, up to stoichiometrical amount, sufficient to retard combustion, of phosphoric acid.

12. A product comprising a cellulosic textile and sulfamic acid in amount at least suflicient to act as a fire-retardant therefor, the sulfamic acid being afiixed to the textile by means of polyethylem'mine.

13. Process which comprises treating a cellulosic material impregnated with polyethylenimine with a fire-retardant acid.

WALLAQE .E. GORDON.