US2012686A - Process for fire-proofing cellulosic materials - Google Patents

Description

Patented Aug; 27, 1935 unirao srA'rss FATE oFFicE PROCESS FOR FIRE-PROOFING CELLULOSIC MATERIALS Martin Leatherman, Hyattsville, MIL, dedicated to the free use of the Public of the United States of America No Drawing. Application May 2,1934, Serial No. 723,546

3 Claims.

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. {757) This application is in part a continuance of my application Serial Number 711,727, filed February 17, 1934.

This application is made under the act of March 3, 1883, as amended by the act of April 30, 1928, and the invention herein described, if patented, may be manufactured and used by or for the Government for governmental purposes also largely prevents the outof-door deteriora- 4 tion of cellulosic fabrics arising from the effects of certain general classes of treating materials,

when acted upon by sunlight.

It is well known that hydrated stannic oxide prevents flaming of cellulosic materials when properly placed therein. However, it has never.

been established as to why or how stannic oxide inhibits flaming of cellulosic fabrics when the said fabrics are exposed to an igniting flame. I have discovered the mechanism involved in this said 'flameproofing process and in order to make these specifications as complete as possible -I will briefly describe my discoveries and also the manner in which these discoveries were authenticated.

The three lines of investigation which I followed all tended to prove that stannic oxide flameproofs cellulose by setting up a catalytic dehydration of the cellulose under the influence of heat. In the first place, when untreated fabric samples and fiameproofed fabric samples were respectively heated in tubes at 325 C. in a stream of dry, CO2- free air, the exit gases obtained from the flameproofed fabric samples invariably showed much the larger percentage of C02. The samples in all cases were completely ashed before the air flow was stopped. The air and the gases swept out with it were all collected in a large evacuated bottle each time and aliquot samples of the collected gas were analyzed in a modified Orsat apparatus. The larger yield of CO2 from the treated samples indicated to me that with the treated, fiameproofed samples the products formed were largely CO2 and water, whereas with the'untreated samples the carbon was evolved as a constituent of volatile combustible compounds such as acetone; hydrocarbons, etc.

In the second phase of my investigations the carefully dried fabric samples were heated in tubes in a stream of dried oxygen-free nitrogen,

the tubes being immersed in a molten metal bath at 325 C. for 240 seconds. was filtered out of the exit gases and the evolved moisture was collected and weighed. The percentage of water evolved, based on the net weight of the fabric, was always much greater in the case of the samples treated with stannic .oxide.

The tarry matter The third-line of study was undertaken to eslo tablish beyond any doubt that the stannic oxide effects its flameprooflng action by splitting the cellulose into carbon and water; Treated and un-' treated samples were heated at 325 C. in tubes in a stream of dried oxygen-free nitrogen until most of the matter volatile at that temperature was driven off, the heating being continued the same length of time in all cases. The container tubes were then connected with an absorption train and the fabric residues were completely burned in a stream of oxygen. In this way the carbon in the residues was determined as carbon dioxide. Based on the net weight of carbon-in the,

original cellulose of the fabric samples, the percentage of carbon in the residues from the de-.

' structive distillation of the treated fabric was nearly twice as great .as in the identically obtained residues from the untreated fabric.

Thus it was definitely proved that stannic oxide flameproofs cellulose by catalytically splitting the cellulose carbohydrate into carbon and water and thereby preventing the formation of combustible gases. It now became possible to improve the action of stannic oxide by applying knowmprinciples of catalysis. In the first place, it has been shown by others that alkali acts as a catalyst poison. Therefore, if it were possible to precipitate stannic oxide in the cotton fabric under more acid conditions a more pronounced fiameproofing effect should be produced. The Perkin method Patent No. 856,906 of using fairly dilute ammonium sulfate solutions to decompose the sodium stannate on the fabric precipitates the stannic oxide under alkaline conditions because of the ammonia evolved.

If, for example, instead of. using ammonium sulfate as the precipitant for sodium stannate, ferric sulfate or chloride-is used, three effects are obtained. In the first place a solution of ferric sulfate or of ferric chloride is acid in reaction, as is ammonium sulfate, because of hydrolysis.

The reaction between sodium stannate and the ferric salt, if an excess of the latter is used, leaves the solution from which the stannic oxide is deposited still acid, unlike ammonium sulfate, and

this lessens the quantity of alkali which can be absorbed by the freshly precipitated, gel-like stannic oxide. In the second place, ferric oxide is precipitated in intimate contact with the stannic oxide and thereby exerts catalytic promoter effects. Many other oxides exert similar effects. In the third place, and most important, the iron oxide colors the fabric and this coloring exerts a preservative action on the fabric. This is true of other colored oxides such as those of chromium, manganese, copper, cobalt, nickel; etc. Stannic oxide alone in fabric accelerates deterioration of cotton fabric in sunlight.

The desirable catalytic action of stannic and other oxides in flameproofing of cellulose is accompanied by amost undesirable action. These oxides'are also catalysts for carbon combustion and after the dehydration mechanism liberates the carbon the oxide facilitates its combustion. Consequently fiameproofed fabrics glow vigorously even though they do not flame. For this reason, to produce a fully firepro'ofed fabric, after flameproofing with metallic oxides, it is necessary to use a supporting agent. From the standpoint of weather-resistance there is only one type of material which will sufilce. type of material is represented by chlorinated organic substances of various kinds. It is known touse the chlorinated vinyl resins in combination with tin oxide, but, while this treatment effectively fireproofs cotton, it is impracticable because both stannic oxide and chlorinated vinyl resin act very destructively on the fabric so that the fabric lasts only a short time. However,'1 have discovered that this destructive action is prevented by the presence of a coloring material.

In the past, the chlorinated resinous materials have all been objectionable because of cost or undesirable physical or chemical properties. I have found that certain cheap petroleum derivatives can be chlorinated to give materials which are very well suited as glowproofing agents for use in connection with oxide mixtures in cellulose fabrics for exposure to weather. The glowproofing effect results from the evolution of hydrogen chloride. at elevated temperatures. The chlorinated product must not decompose spontaneously when properly protected, that is, by a coloring material, and it must evolve hydrogen chloride within a definite temperature range. I have discovered that highly chlorinated paraflin wax answers these requirements but does not have the desired physical properties, that is, it stiffens the fabric too much: If, before chlorination, I mix with the paraffin approximately its own weight of certain light bodied partially unsaturated liquid parafiin oils of low lubricating power,

such as are used by filling stations for flushing crank cases, I can introduce a higher percentage of chlorine and still obtain a less plastic product which does not unduly stifien the fabric but results in a flexible, soft, fire-proofed material which is also highly water proofed. I prefer to have jin the finished chlorinated material fifty to seventy per cent of chlorine based on the total weight of product but the percentage of chlorine may, within the spirit of my invention, be less or more than this.

' It is well known that tin is a rare metal and that its cost must progressively increase. One of the further merits of my invention lies in the fact that by using promoter oxides, a part of the tin necessary for flameproofing may be replaced with cheaper metal oxides. An additional merit of my invention lies in the possibility ofassisting, with- ThiS I out deleterious results,'the fiameproofing effect of the oxides by using the above-mentioned resinous chlorinated petroleum derivatives, which besides glowproofing the fabric, markedly assist in A typical procedure which I may follow in producing a weather-resistant fireproofing treatment in cellulose fabrics is as follows: if the fabric is unbleached and water-resistant it is first soaked in a solution of a wetting agent of either the sulphonated type or of the sulfate ester type for about five minutes, such as a one per cent aqueous solution ofa metallic salt of a sulfate ester of an aliphatic alcohol, then squeezed out and rinsed thoroughly in water for about five minutes, after which it is again squeezed out and immersed in sodium stannate solution for about twenty minutes. When bleached and absorbent fabric is being treatedlthe wetting agent treatment is unnecessary. The sodium stannate solution con-i .tains about twenty parts or less of alphasodium colored precipitate, as in the case of titanium or vanadium salts, it is necessary to use a pre-' viously colored fabric or to introduce a pigment later, preferably with the resin treatment. It may also be desirable to mix enough ironor chromium salt with the titanium salt solution to produce a colored precipitate in the fabric.

After the precipitation of the stannate, the

fabric is squeezed and immersed in aqueous or gaseous ammonia to precipitate the balance of the iron or other metal which may have been used. This additional amount of colored oxide obtained by the ammonia precipitation is of great value in that it gives a deeper color than that provided when the colored metallic salts are washed out, and this deeper color is very effective in further preserving the fabric against deteriora-' tion. When the ammonia precipitation is used,

less washing of the fabric is required, in fact,

where the sodium and amonium salts are not objectionable the fabric need not be washed at all. However, ammonium salts tend to deteriorate the fabric in time and it will usually be desirable to wash them out. After drying, the fabric is ready for the treatment with the glowproofing agent.

I have found that certain of the chlorinated diphenyls act as excellent plasticizers in connection with my chlorinated petroleum derivatives, and, in fact, in connection with other chlorinated resinous materials. The best chlorinated diphenyl derivative is one which exists as a moderately viscous liquid but I may use a chlorinated diphenyl derivative which is less viscous or one which issolid. All of the derivatives obtained by chlorinating diphenyl are of value.

assist in preventing flaming in cellulosic materials butwhen used as I describe they appear to slightly assist the fiameand glow-proofing action of the material which they serve to plasticize.

The percentage of chlorinated diphenyl to be required as a plasticizing material will depend upon the physical properties of the said chlori- These materials by themselves do not materially nated diphenyl as well as upon other factors. I

may use as little as fifteen parts of chlorinated diphenyl to eighty-five parts of chlorinated petroleum derivatives and I may use enough to equal the weight of the chlorinated petroleum derivatives employed. I In general the total mixture impregnated into the fabric will not exceed thirty per cent of the total weight of the treated fabric, including precipitated oxides. For most purposes, twenty per cent of the total weight of the finished fireproofed fabric will be suiiicient.

As a plasticizing agent there may be substituted in the place of chlorinated diphenylsspecified charred portion of the fabric which has been.

subjected to an igniting flame. Having made a full disclosure of the function of the glowprooflng and assisting agent I will now give specific examples of compositions which are suitable for my purpose. 7

As a typical composition of the glowprooflng resin I may use 75 parts of chlorinated petroleum products, preferably a chlorinated mixture ofparafiin wax and low-viscosity, partially unsaturated, petroleum oils, said chlorinated mixture to contain approximately sixty per cent of chlorine based on total weight, and parts of chlorinated diphenyl. For my purpose I will ordinarily use as a plasticizer a chlorinated diphenyl which has a viscosity similar to that of heavy molasses. However, I do not restrict myself because I can use the chlorinated petroleum derivatives without any plasticizer at all or I can use chlorinated diphenyls of a wide range'of physical properties mixed with the chlorinated petroleum derivatives in widely varying proportions.

In coating or impregnating the flame-proofed fabric with the chlorinated resinous glowprooflng and assisting agent no definite solution concentrations can be specified because the proper and desired concentration will vary with the solvent employed, the pressure applied in squeezingout excess solution and with the percentage which it is desired to leave in the fabric. For a given concentration of solution, a high-volatile solvent like carbon tetrachloride will leave a higher percentage of resin in the fabric than will low-volatile solvents such as mineral spirit thinners. Also if the fabric is to be treated by dipping, the concentration will be different than if the resin solution is applied by brushing.

The proportions of the respective ingredients present in the finished flreproofed fabric may be varied considerably. For example, if the percentage of flameprooflng oxides is increased, the

percentage of glowprooflng resin can be decreased to a certain point. Also the glowprooflng resin solution may be made the vehicle for a pig--' ment, and a paint may thereby be prepared which is especially useful in preparing striped awnings or in home treating of canvas on farms or else- Fireproofed fabric denotes fabric whichwhere. As pigment any earthy material such as ochre, sienna, umber, etc., or any colored metallic oxide may be used.

In the treatment as outlined in these specifications there is no water-soluble constituent which can be leached out by rain and the pigmenting material stabilizes the chlorinated resinous constituent. The fabric retains its fireproof characteristics and does not rapidlylose its tensile strength as it will do when no pigment is present. The petroleum hydrocarbons furnish a cheap source of raw material for chlorination and the finished chlorinatedproduct is cheap enough to be used in low priced fabrics.

Having fully disclosed my invention, I claim:

cellulosic materials and fabrics which comprises immersing the fabric until thoroughly saturated in a one per cent aqueous solution of a metallic salt of a sulfate ester of an aliphatic alcohol, rinsing the cellulosic material thoroughly in water, pressing out as much of the water as possible; then impregnating the cellulosic material with sodium stannate, drying, and then immersing the dried cellulosic material in a water solution of a salt of a strong mineral acid with a weakly base-forming metal, the hydroxide of which is water-insoluble, then with only light squeezing immersing the wet cellulosic material in an ammonia solution, then washing the mate-- rial in water to remove soluble salts, drying the 1. The process of fire-proofing and-preserving material, impregnating the material with a chlorinated mixture of paraffln wax and lowviscosity, partially unsaturated petroleum oil plasticized with chlorinated diphenyl derivatives and containing coloring materials.

2. The process of fire-proofing and preserving cellulose materials and fabrics which comprises immersing the fabric until thoroughly saturated in a one per cent solution of a metallic salt of a sulfate ester of an aliphatic alcohol, rinsing the cellulosic material thoroughly in water, pressing out as, much of the water as possible; then impregnating the cellulosic material with sodium stannate, drying, and then immersing the dried cellulosic material in an aqueous solution of ferric sulphate, then with light squeezing immersing the wet cellulosic material in an ammonia solution, then washing the cellulosic material in water to remove soluble salts, drying the cellulosic material and impregnating it with a chlorinated mixture of paraflin wax and lowviscosity, partially unsaturated petroleum oil containing chlorinated-diphenyl derivatives.

3. The process of fire-proofing and preserving cellulosic materials and fabrics which comprises immersing the fabric until thoroughly saturated in a one per cent aqueous solution of a metallic salt of a sulfate ester of an aliphatic alcohol,

-rinsing the cellulosic material thoroughly in water, pressing out as much of the water as possible; then impregnating the cellulosic material with sodium stannate, drying, and then immersing the dried cellulosic material in a water solution of a salt of a strong mineral acid with a weakly base-forming metal, the hydroxide of.

which is water-soluble and colored, then washing the material in water to remove acid residues, drying the material and impregnating the material with a chlorinated mixture of paraflin wax and low-viscosity, partially unsaturated leum oil.

MARTIN LEATHERMAN.

pe o- CERTIFICATE or CORRECTION.

Patent No. 2,012,686. I August 21,1935.

MARTIN LEATHERMAN.

It is hereby certified that error appears in the printed specification. of, the

above numbered patent requiring correction as follows: Page 3, second, column,

line 67, claim 3, for "water-soluble" read water-insoluble; and that the said Letters) Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed t?" 5th day of November, A. D. 1935,

Leslie Frazer (Seal) v ABt iIIICOmIHi'SSIOH BI of'Patents