Abstract:
Cellulosic substrates, e.g., wood, textiles, or paper, have increased fire resistance when there are added thereto one or more compounds of the formula ##STR1## wherein M and R are specified substituents.

Description:
BACKGROUND OF THE INVENTION 
     Numerous monophosphate derivatives are known to be effective fire-retarding agents. In general, however, polyphosphoric acid derivatives have not been used as fire-retarding agents. In particular partial esters of polyphosphoric acid have not been suitable because of the presence of residual acid functionality which is likely to adversely affect cellulosic materials with which it is brought into contact. 
     Furthermore, monophosphate derivative fire-retarding agents are generally regarded as nonpermanent. Such fire-retarding agents are susceptible to leaching from the cellulosic material upon contact with water. Cellulosic materials so exposed are thereby rendered less resistant to fire. In U.S. Pat. No. 3,565,679 a list of non-permanent fire retardants includes the phosphates. 
     SUMMARY OF THE INVENTION 
     According to the invention cellulosic materials that are resistant to fire are provided by incorporating therein fire-retarding amounts of a compound of the formula ##STR2## wherein, R is each occurrence the remnant of phenol, halophenol or a C 1-20  aliphatic or halogenated aliphatic monohydroxyl compound formed by removal of the hydroxyl group; 
     M is independently each occurrence an ammonium, substituted ammonium or metal cation having valance n; 
     m is an integer from zero to three; y is an integer equal to or greater than zero; and q, x and z are all integers greater than or equal to one selected such that (zn)+y=x(m+4)-q and q≦m+3. 
     Preferred are cellulosic compositions containing a fire-retarding amount of water-insoluble compound of the identified formula, for example aluminum-containing derivatives of polyphosphoric acid partial esters. It has been found that such compositions retain fire-resistant qualities even after exposure to water. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention comprises a method of treating cellulosic materials to render them resistant to fire. Included in the invention are such treated cellulosic materials that have been rendered resistant to burning by fire. By cellulosic material is included wood, paper, cardboard and other wood products such as chip board, plywood, cellulose insulation, etc. and fabrics comprised entirely or partially of cellulosic fibers. Examples are cotton, linen, and blends thereof with various synthetic fibers. 
     Accordingly, the above-described materials are treated by any convenient method so as to add to them fire-retarding amounts of the compounds of formula I. Such compounds are ammonium or metal-containing derivatives of partial esters of polyphosphoric acids. 
     By &#34;ammonium&#34; is meant not only the monovalent cationic derivative of ammonia formed by addition of a hydrogen ion thereto, but also C 1-20  aliphatic and aromatic amine derivatives formed in a similar manner by addition of a hydrogen ion to the respective amine compounds. Included are primary, secondary and tertiary amines. 
     The metal employed, if any, is not critical and such may be selected from alkali metal and alkaline earth metal elements, the transition elements and the elements of group 3a of the periodic table. Preferred are metals selected from K, Mg, Al, Na, Ca, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ag. Especially preferred are Al, K or Na. The electronic state of the metal species is not fully understood and the compounds in many ways exhibit the qualities of coordination complexes. 
     The compounds may be formed by reaction of certain hereinafter-described partial esters of polyphosphoric acids with ammonia or amine compounds, and with ammonium or substituted ammonium hydroxides, halides, carbonates or oxides as well as with the above-described neutral metals or their corresponding metal oxides, carbonates, hydroxides, halides, sulfates or nitrates. Mixtures of reactants and successive reactions of the partial esters with combinations of the above reactants, e.g., first reaction with a metal salt followed by neutralization of remaining acid functionality with ammonia or amine compounds may be employed. 
     The preferred compounds are those that are substantially water-insoluble. Cellulosic materials containing added quantities of such compounds have been found to retain their fire resistance even after exposure to water for extended periods of time. As an example of such a preferred compound are the aluminum-containing derivatives. 
     The partial esters of polyphosphoric acids useful in forming the compounds of the present invention are of the formula ##STR3## wherein R and m are as previously defined; and y&#39; and q&#39; are integers greater than or equal to one such that y&#39;=(m+4)-q&#39;. 
     Suitable monohydroxyl compounds from which R may be formed are phenol, halophenols or common aliphatic alcohols such as alkanols and halogenated derivatives thereof, alkyl or phenyl monoether derivatives of alkanediols and halogenated derivatives thereof and alkyl or phenyl monoether derivatives of (poly)alkylene glycols and halogenated derivatives thereof. The remnant portion after removal of the hydroxyl functionality may be described as being C 1-20  alkyl, phenyl, alkyl (poly)oxyalkylene, phenyl (poly)oxyalkylene radicals and halogenated derivatives thereof, the term (poly) referring to an optional multiplicity of oxyalkylene units. Preferred halogenated derivatives are bromine-containing derivatives. A mixture of the above suitable remnants of monohydroxyl compounds may also be used. 
     Most preferred are compounds of the above formula (I) wherein R is of the formula ##STR4## where R 1  is each occurrence hydrogen, methyl or halomethyl; R 2  is each occurrence C 1-6  alkyl or haloalkyl, phenyl or halophenyl and n is an integer from 1 to 4. 
     The partial esters of polyphosphoric acid are formed by the reaction of a stoichiometric deficiency of the above described monohydroxyl compounds with phosphorus pentoxide. The reaction technique is well-known being similar to that disclosed in U.S. Pat. No. 2,866,680. Accordingly, the monohydroxyl reactant is controllably added to a slurry comprising phosphorus pentoxide and an organic solvent such as the lower alkanes, aromatics or halogenated hydrocarbons. A preferred solvent is dichloromethane. 
     Addition of the monohydroxyl reactant is discontinued at or before the point where the ratio of monohydroxyl to phosphorus (R:P) is about 1:1. To compensate for possible water contamination of the monohydroxyl reactant, excess P 2  O 5  is preferably utilized, e.g., R:P ratios from 0.9:1 to 1:1, and most preferably from 0.95:1 to 1:1. The ratio of monohydroxyl remnant to phosphorus in the reaction product is desirably about 1:1. 
     The exothermic reaction causes heating of the reaction mass. Proper choice of a solvent allows the reaction to be maintained at a gentle reflux at moderately elevated temperatures. The reaction may be continued for several hours or longer until the P 2  O 5  is substantially completely reacted. Additional heating during the course of the reaction may be accomplished by conventional means. 
     The product, generally a light colored liquid, may be separated from any excess unreacted P 2  O 5  by decanting or filtration, and the solvent removed if desired by evaporation or other technique. 
     Reaction of the partial esters of polyphosphoric acid with the previously-described ammonia, amine or metal reactants is accomplished by contacting the two reactants optionally in the presence of an inert solvent which may be the solvent previously used for formation of the partial ester. Elevated temperatures may also be employed to increase the rate of reaction. 
     The resulting compounds are easily recovered in high purity by evaporation of the reaction solvent. Monophosphate or full ester contaminants are produced only in minor proportions during the reaction and are preferably present in an amount less than 10 percent by weight. Generally a mixture of the compounds is produced. 
     The metal-containing compounds are believed to exist as coordination complexes having the empirical formulas previously stated. Assignment of more definitive structural formulas to the various compounds cannot be attempted at the present time since the compounds exist as an intricate coordination network which is randomly oriented in three dimensions. 
     Treatment of cellulosic materials in order to render such materials resistant to fire is accomplished by any suitable means. According to one method the described compounds may be applied as a solution in an organic solvent to the cellulosic material by any suitable means, for example: dipping, painting, spraying, pressure impregnation, etc. The solvent is then removed, as for example by evaporation. The compounds are preferably employed in fire-retarding concentrations from about 1 percent to about 40 percent and most preferably from about 5 percent to about 30 percent by weight based on the dry weight of the cellulosic material. 
     An alternate method may also be utilized to produce the metal diphosphoric acid ester complexes used in treating cellulosic materials according to this invention. Accordingly, a metal alkoxide is first formed by alkoxide-exchange or by direct reaction of the hydroxyl-bearing compound or a mixture thereof with the metal. The metal alkoxide is then contacted with phosphorus pentoxide in the same manner previously-described to form the desired metal derivatives of polyphosphoric acid partial esters. The process is more fully described in Examples, 4, 5 and 6 which follow hereinafter. 
     SPECIFIC EMBODIMENTS OF THE INVENTION 
     The following examples are provided as further illustrative of the present invention and are not to be construed as limiting. 
    
    
     EXAMPLE 1 
     Preparation of bis(butoxyethyl)diphosphoric acid 
     Phosphorous pentoxide (270 g, 1.9 moles) was slurried under nitrogen in a reaction flask containing 500 ml CH 2  Cl 2 . Over approximately 2 hours 2-n-butoxyethanol (425 g, 3.6 moles reagent grade) was added from a dropping funnel causing a gentle reflux to occur. After complete addition only a small amount of unreacted P 2  O 5  remained. The flask contained a clear yellow colored solution. Reaction for an additional 24 hours resulted in complete conversion of P 2  O 5  and a darker colored solution. Analysis by  31  P nuclear magnetic resonance specroscopy indicated the product comprised greater than 90 percent of the diphosphoric acid half ester with minor amounts of other partial esters of polyphosphoric acids, plus monophosphates and full ester contaminants. 
     EXAMPLE 2 
     A portion of the product produced in Example 1 was neutralized by bubbling dry NH 3  into the solution at a rate sufficient to cause a gentle reflux. After about 90 minutes no further exotherm occurred indicating the reaction was complete. The solution was further diluted with CH 2  Cl 2  to a concentration of 15 percent by weight and used to treat several small strips of fir plywood, 1/4&#34;×1/2&#34;×3&#34; long. After immersion in the solution for between 2 and 8 hours, the strips were dried at 100° C. for about 4 hours and then humidified at normal room conditions for 2 days. When clamped at a 45° angle and ignited for 15 seconds with a bunsen flame, all the treated strips self-extinguished in an average of less than 20 seconds. By comparison untreated strips subjected to the same procedure are entirely consumed. 
     EXAMPLE 3 
     A portion of the solution produced in Example 1 was combined with metallic aluminum so that the ratio of polyphosphoric acid partial ester to aluminum was 3:1. The mixture was gently heated taking care not to exceed 150° C. to avoid decomposition of the diphosphoric acid partial ester. A trace of water or alcohol added to the mixture acted as a catalyst to initiate the dehydrogenation reaction. 
     After completion of the reaction as evidenced by cessation of gas evolution (approximately 1/2 hour), a viscous product comprised of coordination polymers of aluminum and diphosphoric acid remained. 
     Similar experiments utilizing a solvent (toluene) and substituting iron for aluminum have also produced the desired coordination complexes, although their formation generally required longer reaction times. 
     EXAMPLE 4 
     Preparation of aluminum complex by alkoxide exchange 
     Aluminum isopropoxide (20.4 g, 0.1 mole) was added to a solution of butoxyethanol (47.2 g, 0.4 mole) contained in 200 ml of CH 2  Cl 2 . After stirring to thoroughly mix the reactants, the solvent was removed by a Rotovac vacuum stripping apparatus and the remaining solution heated in vacuo over steam until all isopropanol formed during the reaction had volatilized. Remaining in the flask was a white waxy solid weighing 50.5 grams identified as having an empirical formula of HAl(OC 2  H 5  OC 4  H 9 ) 4 . 
     EXAMPLE 5 
     The product produced in Example 4 (0.1 mole based on aluminum) was dissolved in 200 ml of CH 2  Cl 2  and slowly added by means of a dropping funnel with stirring to a slurry of P 2  O 5  (28.5 g, 0.2 mole) in 200 ml CH 2  Cl 2 . The mixture slowly increased in viscosity which CH 2  Cl 2  refluxed due to the exothermic reaction. After complete addition a clear homogeneous gel was obtained. 
     EXAMPLE 6 
     Addition of dry NH 3  or an alkanolamine to neutralize the acid-functionality of the complex formed in Example 5 resulted in a low viscosity solution. Treatment of cellulosic materials with the solution may be accomplished in the same manner as Example 2. 
     EXAMPLE 7 
     Mixed alkoxide of aluminum 
     Aluminum tri(2-n-butoxyethoxide) was prepared by incremental addition of pure aluminum turnings to anhydrous 2-n-butoxyethanol. Accordingly, 2-n-butoxyethanol (944 g, 8.0 moles) was added to a 3-liter flask fitted with condenser, stirrer and inlet for dry N 2 . The flask and contents were heated to reflux temperature (approximately 160° C.) and approximately 5 grams of aluminum turnings were added. Evolution of H 2  gas was observed after 2 to 10 hours signifying the reaction had begun. 
     Once the reaction began additional portions of aluminum turnings were added every 5 to 10 minutes and the temperature of the reaction lowered to about 120° C.-130° C. A total of 63 grams, 2.33 moles of aluminum were reacted in this manner to provide a viscous liquid product. 
     At this point a different alcohol 2,2,2-tri(bromomethyl)ethanol (432 g, 1.33 moles), dissolved in about 500 ml CH 2  Cl 2  was added to the neat aluminum alkoxide to produce an equilibrium mixture of aluminum alkoxides in which 2-butoxyethoxy and 2,2,2-tri(bromomethyl)-ethoxy radicals were in a 6:1 ratio dissolved in CH 2  Cl 2 . 
     EXAMPLE 8 
     Diphosphate half esters of mixed alkoxides 
     In a 12-liter glass flask equipped with a stirrer, condenser and dry N 2  inlet, P 2  O 5  (700 g, 4.93 moles, 5 mole percent excess) was slurried with 5 liters of CH 2  Cl 2 . The mixed aluminum alkoxide prepared in Example 7 above dissolved in CH 2  Cl 2  was slowly added with stirring so as to maintain a gentle reflux. Complete addition of aluminum reactant was obtained over a period of 3-4 hours. The final product after all alkoxide reactant was added was saturated with NH 3  to break any viscous gels formed and diluted with CH 2  Cl 2  to a final volume of about 9 liters (approximately 21 percent of the phosphate complex by weight) for treating of wood panels for fire retardancy. 
     EXAMPLE 9 
     Preweighed strips of plywood (douglas fir 1/4&#34;×31/2&#34;×24&#34;) were loaded into a treating chamber and the chamber evacuated to a pressure of 1&#34; mercury for 30 minutes. The solution to be used in treating the strips was added to the evacuated chamber and pressure (200 lb/in 2 ) was applied by adding compressed nitrogen. 
     The pressure was released and the strips removed. Excess surface solution was wiped off. After drying under ambient conditions the strips were heated to 100° C. for several hours and finally rehumidified at 50 percent relative humidity and ambient temperature for several days. By comparing the weights of the strips initially and after the treatment and drying procedure a figure reflecting the percent fire retardant add-on, known as dry add-on percent, was obtained. Different concentrations of treating solutions can be utilized to produce strips having varying amounts of fire-retardant add-on. 
     EXAMPLE 10 
     The treating procedure of Example 9 was used to prepare a number of wooden strips. The solutions used had concentrations of the aluminum complex fire retardant of Example 8 of 21 percent, 16 percent and 12 percent, respectively, providing dry add-on percent values (calculated according to the procedure of Example 9) of from 20 to 8 percent. 
     Seven such strips selected over the range of dry add-on percent values were ignited in a two-foot tunnel designed to simulate the ASTM E-84, 25-foot (Steiner) tunnel test. Accordingly, flame spread is reported in comparison to that obtained on asbestos hardboard and a red oak hardwood standard to which the igniting flame is adjusted to produce maximum flame spread of 8-9 inches and 24 inches, respectively, after 4 minutes. When so tested the strips produced maximum flame spreads of from 15 to 17 inches to qualify as Class II rated fire retardants. 
     EXAMPLE 11 
     An additional number of strips produced in Example 10 having add-on values from 20 percent to 8 percent were subjected to weather testing according to a procedure similar to Underwriters&#39; Laboratory Test 790, a standard test for weathering of roofing and siding material. The test consisted of alternate cycles of 96 hours water spray (0.7 inches/hour) followed by 72 hours drying at 60° C. After 4 weeks the panels are removed, dried and rehumidified at 50 percent relative humidity. 
     After subjection to the weathering test the strips were ignited according to the procedure of Example 10. The results of the tunnel test on these specimens showed a maximum flame spread of from 16.5 to 18 inches for all the strips. By comparison untreated wood strips failed the test.