CA1105176A - Compositions comprising polyalkylenepolyamines and four-component inorganic salt fire retardant formulations - Google Patents

Abstract

A B S T R A C T

The present invention is directed to a fire--retardant composition for cellulosic substrates comprising a polyalkylenepolya??ne having a number average molecular weight of at least 1,000 and preferably between 25,000 and 100.000, and a four-component inorganic salt formulation consisting of ammonium sulfate, boric acid, and two components from the group consisting of a zinc halide, an alkali metal dichromate, diammonium phosphate and an alkali metal tetra-borate.
The claimed compositions not only impart fire retardancy to the cellulosic substrate, but also possess considerable resistance to leaching of salts from the substrate and are less hygroscopic than previous known formulations.

Description

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This inven-tion relates to fire re-tardant com-positions. In one aspect, this invention relates to com-positions comprising a polyalkylenepolyamine and a four-component inor~anic salt fire retardant formulation. In another aspect, this invention relates to a method of imparting fire retardancy to cellulosic substrates by treating same with said composi.tions.
Various inoryanic sa].t formulations are well-known, standardized fire retardants for cellulosic substrates.
However, many of these formulations contain components which are highly hygroscopic, thus causing such Eormulations to have limited utility. For example, ammonium sulfate is a common component in many of these formulations. If exposed to 81 percent relative humidity at 20C, it will absorb sufficient water vapor to reach saturation. Wood treated with an ammonium sulfate formulation and exposed to similar conditions also reaches saturation, primarily due to the hygroscopicity of such salts. Consequently, these formulations, or components -thereof, migrate (leach) to the surface of the treated substrate and the resulting dripping not only depletes the salt content of the wood, rendering it less fire resistant, but also severely disfigures the surface~ especially if finishedO If the treated substrate is exposed to running water or rainfall, this leaching is accelerated.
Strother, in U.S. Patent 3,565,679, teaches imparting fire retardancy to cellulosic substrates by treatlng same with a complex of a polyalkylenepolyamine and a condensation product of phosphorus pentoxide and ammonia.
Brown, et al., in U.S. Patent 4,038,451 teach that com-:
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: 18,328-F -1-'7~i positions comprising polyalkylenepolyamines and a mixture of mono- and diammonium phosphates can be used as fire retardants for cellulosic substrates.

According to this invention, a composition comprising a polyalkyleneopolyamine having a number average molecular weight of at least l,OOO and a four-component ~ire retardant formulation consisting o~:

a) ammonium sul~ate, b) boric acid, and c) two compnents selected from the group consisting of zinc halide, alkali metal dichromate, diammonium phosphate and alkali metal tetraborate not only imparts fire retardancy to various cellulosic substrates, but also demonstrates surprising leach resistance, even at elevated humidity.

The present invention is also directed to a method of imparting fire retardancy to a cellulosic subs-trate comprising treating the substrate with a ~ire retardant amount of an aqueous solution of any of the compositions of the present invention described above.

Both branched and linear polyalkylenepolyamines are useful in this invention. The linear polyalkylene-polyamines are known compounds consisting of n randomly joined unites (I, II) and are readily prepared by the ring-opening polymerization of substituted oxazolines or similar compounds (III~, ~ollowed optionally by hydrolysis.

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- 2a -(I) ~N- (CHR) x-CH2t C-R' o (II) tN- (CHR)X-cH2t H

(III) ~ O\
R' ( HR) x N

The substituents and subscripts are hereinafter defined.
The ring-opening polymerization is generally conducted in the presence of a cationic polymerization catalyst :~ :
t: !

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~: .. . - : : -at a reaction temperature of about 0-200C. Typical catalys-ts include strony mineral acids, or~anic sulfonic acids and their es-ters, acidic salts s~ch as ammonium sulfate, Lewis acids such as aluminum trichloride, stannous tetrachloride, boron trifluoride, and organic diazoniumfluoroborates and dialkylsulfates. Thi.s ring-opening polymerization is further described by Tomalia et al., J. Polymer_Sc~ence, 4, 2253 (1966); Bassiri et al., Polymer Letters, 5, 871 (1967); and Seeliger, Ger. 1,206,585.
The pre-hydrolyæed po.Lymers thereby obtained are linear, N-acylated polyalkylenepolyamines having a molecular structure consisting essentially of repeating units I. These polymers are easily deacylated by acid, . base or neutral hydrolysis. Hydrolysis is best controlled under acidic conditions and acid hydrolysis is thus preferred.
The partially deacylated polyalkylenepolyamines have a molecular structure consisting essentially of the randomly joined units I and II, illustratively depicted as:
(IV) ~N-(CHR)x-CH2) (N-(CHR) -CH2t C-R' h H x n-h O
wherein:
: n is the total`number of units;
:h is the number of acylated units; and : n-h is the num er of deacylated unitsO
"Deacylated polyalkylenepolyamines" here includes both:the fully~and partially deacylated polymers.
~ ~ Partlally deacylated polyalXylenepolyamines have at : : least;~one secondary amine group (-N-) per polymer chain H
, :
, : :

18,328-F ~ _3~

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., as in IV where n-h is at least 1. Preferably, the polyalkylenepolyamines here used are at least about 50 percent deacylated (n-h is at least about 50 percent of n~ and more preferably at 1eas-t about 90 percent deacylated (n-h is at least abou-t 90 percent of n).
Fully deacylated polyalkylenepolyamines (n-h is ~lbout 100 percent of n) are most preferred.
The branched polyalkylenepolyamines (V) include those obtained from reacting an alkylenepolyamine (e.g. r 10 - ethylenediamine, 1,2~propylenediamine, diethylenetriamine, te~raethylenepentamine, etc.) with a difunctional chain-extending and cross-linking agent (e.g., 1,2 dichloroethane, epichlorohydrin, etc.).
~V) ~CH2CH2-N-CH2cEl2 NH CH2CH2 ,CH2 Cll , 2 HN-CH2C~I2-NH-CH2CH2'-N-CH2CH2-NHt ,C~2 ::
~15 Of course, acylated polyalkylenepolyamines are not generated by these preparations and the branched poly-alkylenepolyamines~are thus without acyl groups, or in the language of line~ar polyalkylenepolyamines, they are fully deacylated. Also included within the term 2Q ~ 'Ibranch0d polyalkylenepolyamine" is polyethylenimine, generally~produced by the polymerization o~ ethylenimine in~the~presence af an acid catalyst, and the corresponding po~lypropylenimines. Polyethylenepolyamines, ~specially the polyethylenimines, are preferred for reasons of commercial availability.

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As regards the other substituents and subscripts in the above formulae, R is hydro~en or Cl-C3 alkyl, R' is hydro~-Jcn or alk~l having up to abou-t 18 carbon a-toms or an inertly-substituted derivative thereof, and x is l or 2.
By "inertly-substituted" is meant that the substituents do not reduce the polyalkylenepolyamines anti~hygroscopic properties. Illustrative inert substituents include halogen, ethylenic unsaturation, ether oxygen, carbonyl and ester. Exemplary R substituents include hydrogen, methyl, e-thyl and propyl, and exemplary R' substituents (alkyl) include methyl, ethyl, propyl, pentyl, cyclohexyl, - dodecyl, octadecyl, and the various halogenated and ethylenically unsa-turated derivatives of each. Fully deacylated polyethylenimines (x is l~ wherein R is hydrogen are the preferred linear polyalkylenepolyamines. Branched polyethylenimines are most preferred.
~ Polyalkylenepolyamines having a number average molecular weight of at least about l,000, as determined by gel permeation chromatography, are used in the practice of this invention. Typically these compounds have an average number molecular weight of at least about 20,000 :
and preferably of about 25,000. Practical considerations~
such as preparation, mechanical application, and the like are the only limitations upon these compounds' average : :
maximum molecular weight although convenience prefers a ~ :
maximum of ~out 200,000, and most preferably of about ` 100 ,000 .
Thle four-component Eire retardant formulations here used consist of:
a) ammonium sulfate, :

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b) boric acid, an(l c) two components selectecl from -the group consistiny oE zinc halide, alkali metal dichrornate, diammonium phosphate and alkali me-tal tetraborate.

Preferred ~inc ha)ides are zinc chloride and zinc bromide with zinc chloride especially preferred. Preferred alkali metal dichromates include sodi~l and potassiwm dichromate with sodium dichromate especially preferred.
Preferred alkali metal tetraborates include sodium and potassium tetraborate with sodium tetrabora-te especially preferred. Any suitable formulation of these ma-terials can be used but preferred formulations consist of ammonium sulfate, boric acid, zinc chloride and sodium dichromate~
Most preferred formula~iuns consist of, by weight:
a) 32 to about 38 percent ammonium sulfate, based on nitroyen and sulfur, b) 23 to about 27 percent boric acid, based on boron, c) 32 to about 38 percent zinc chloride, based on zinc, and d~ 3 to about 7 percent sodium dichromate.
The respective concen-trations of polyalkylene-polyamine and fire retardant formulation in the composition of this invention can vary widely, the exact amounts of each depending upon the substrate and the degree of both fire retardancy and hygroscopicity suppression desired.
A polyalkylenepolyamine concentration of at least abou-t

2 weight percent, and preferably of about 5 weight percent~
is generally satis~actory. A maximum polyalkylenepolyamine concentration o about 50 weight percent, and preferably ' 18,3~8-F -~_ : : . .

5~7~i oE about ~0 w~.:igh-t percen-t, i.s used for economic reason~.
Of course, the remaininy weigh-t pexcents consist of the fire retardant formulati.on, i.e., a minlmum of about 50 weiyht percent, and preferably about 80 weiyht pe.rcent, and a maximum of ab~ut 98 weiyht percent, and preferably about 95 weight percent~ respective].y.
The composi-tion of t:his inven-tion is applied to a cellulos.ic substrate in any convent.ional manner, e.g~, spraying, painting, dipping, roll coating, reverse roll coating~ pressure or vacuum treating, precipitation on fiber slurries or impregnation. Typically, the composition is dissolved in an aqueous medium which is then applied to the cellulosic substrate. Sufficient composition is generally dissolved to form an aqueous solution having a concentration of at least about 5 weight percent, and preferably about 10 weight percent, solids basis. A maximum aqueous concentration of about 50 weight percent, and preferably of about 20 weight percent, is used because of both economics and the composition's general solubility. The aqueous medium can be water per se or can be an aqueous solution or dispersion comprising other materials, such as pigments and sealers.
The dissolved, aqueous composition is generally applied to the substrat~ in an amount sufficient to either thoroughly :~
wet the surface of the substrate~or thoroughly impregl~ate the ~ubstrate, depending upon the method of application and the degree of protection desired. As regards surface ~:
application, on a solids basis, the substrate is usually : contacted with at least about 0.005 pound (2.3 g.), and preferaoly of a :out 0.01 pound ~4.5 g.)~ of composition per '' :
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square foot (0~093 m.2) of substra-te surface. Prac-tical considerations, such as economy, etc., are the only limita-tions upon the maximum amount of co~lposition that is con-tacted with the substrate, although convenience prefers about O.OS pound (23 g.), and most preferably about 0.03 pound (13.6 g.), oE composition per square foo-t (0.093 m?) of substrate surface. Regarding imprec3ncltion of the substrate, again on a ~olids basis, the su~s-tra-te is usually impregnated with the composition to at least about 5 weight percent and preferably to about 10 weiyht percent of the substrate's untrea-ted weight. Similar -to the surface application, practical considerations are the only limitations upon the maximum amount of composition that can be impregnated into the substrate, although convenience prefers impregnating with the composition to a maximum of about 70 weight percent, and most preferably to a maximum of 50 weight percent, of the substrate's untreated weight. After application, the treated substrate is normally dried at elevated temperatures to remove the solvent (water).
"Cellulosic s~strates" include wood, wood composites, wood-derived products and combinations thereof.
Any cellulosic substrate capable of receiving an application of an aqueous composition of polyalkylenepolyamine and ire retardant formulation can be used in the practice o this invention. Typical examples include: wood, such as pine, cedar or oak; wood composites, such as particle and fiberboard and plywood; and wood-derived products, such as veneer and paper; and combinations thereof,~such as paper-coated hardboard and particle board, or veneer-surfaced particle board.
:

18,328-F ~ -8-.

~5~6 The Eollowing examples ;llus-trate the lnvention.
Each control and example were conducted in duplicate, and unless o-therwise notecl all parts and percentages are by weight~
Control A:
Individual componen-ts (which were subsequently combined in the Eollowing embodiments) were evaluated as follows:
Three samples each oE PEI 600 (branched polyethylenimine havin~ a number average molecular weight of from 40,000 to 60,000),fire-retardant formulation Type D
(described by the American Wood Preservers1 Association Standard P10-68 as 35 percent zinc chloride, 35 percent ammonium sulfate, 25 percent boric acid and 5 percent sodium dichromate), and untreated, air dry, ponderosa pine wafers were individually exposed to relative humidities of 66, 75 and 93 percent. The samples were exposed to equilibrium and subsequently analyzed for moisture gain (moisture reyain with respect to the treated wafer) in percent of material weight. The results are hereinafter tabulated.
Example 1:
PEI 600 and Type D were formulated into a composition comprising 15 parts by weight PEI 600 and 85 ::
~25 parts by weight Type D. Three comparable samples of this composition~were individually exposed to varying relative humidlties per Control A and subsequently analyzed for :: :
~ ~ moisture gain. The results are also hereinafter tabulated~

.

18,328-F -9~

Control B:
Type D was indlvidually diluted to bo-th 10 and 15 percent by weight (solids basis) aqueous solutions ancl each solu-tion was individually applied by vacuum treat-ment -to six, oven-dried~ untreated ponderosa pine wa~ers.
The wafers were air driecl for 24 hours and then dried in a constant temperature oven to less than 1 percent water con-tent. I'he wafers were then indlviclually e~posed to -the relative humidities per Control A and sllbsequently analyzed for mois-ture regain. Again, the resul-ts are hereinafter tabulated.
Example 2:
, Control B was repeated excep-t that the six, oven-dried ponderosa pine wafers were individually treated with 10 and 15 percent by weight, solids basis, aqueous solutions of the composition o~ Fxample 1. The results are tabulated below.

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r ~ O ~ ~ 0 r l O ~ a o ~~ a ~ ~ O r--I rl S l h ~ O 11) a) (U 1~1~1 1~1 ¢1 E~l ~ ~ ~r~ U~
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The results oE Control A demor1strake -that both PEI 600 and Type D are hygroscopic materials, e.g., at 66 percent relative humidi-ty, PEI 600 absorbed water vapor to 62 percent of i-ts original clry weight.
!he an-ticipated clata of Example l (and similarl~
of Control B and Example 2) was computed by multiplying the moisture gain of PEI 600 by O.lS and the moisture gain of Type D by 0.85, both at the same given humidity, and-then summing the products. For example, at 66 percent relative humidity, the calculation is:
PEI 600: 62 x 0.15 = 10 TYPE D : 41 x 0.85 = 34 ANT. PEI 600/TYPE D: 44 The percent difference data was calculated, of course, by subtracting the actual data from the anticipated data and dividing the difEerence by the latter, i.e., at 66 percent relative humidity, 44 - l9 - 25, 25 . 44 = 56.8 This Example l data demonstrates the profound and un-expected effect PEI 600 has on suppressing the hygroscopicity of Type D.
The Control B data demonstrates that the hygro-scopicity of Type D is suppressed upon its application to a wood substrate.
In each ins-tance, the results of Example 2 shows an improved hygroscopicity suppression of Type D
as compared to the reported results of Control B.

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Claims (14)

1. A composition comprising a polyalkylene-polyamine having a number average molecular weight of at least 1,000 and a four-component fire retardant formulation consisting of:
a) ?mmonium sulfate, b) boric acid, and c) two components selected from the group consisting of zinc halide, alkali metal dichromate, diammonium phosphate and alkali metal tetraborate.

2. The composition of Claim 1 wherein the zinc halide is zinc chloride, the alkali metal dichromate is sodium dichromate, the alkali metal tetraborate is sodium tetraborate, and the polyalkylenepolyamine has a number average molecular weight between 20,000 and 200,000.

3. The composition of Claim 2 wherein the formulation consists essentially of:
a) ammonium sulfate, b) boric acid, c) zinc chloride, and d) sodium dichromate.

4. The composition of Claim 3 wherein the formulation consists essentially of about:
a) 32 to 38 weight percent ammonium sulfate, based on nitrogen and sulfur;
b) 23 to 27 weight percent boric acid, based on boron;
c) 32 to 38 weight percent zinc chloride, based on zinc; and d) 3 to 7 weight percent sodium dichromate.

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5. The composition of Claim 4 wherein the polyalkylenepolyamine is branched.

6. The composition of Claim 5 wherein the polyalkylenepolyamine is polyethylenepolyamine.

7. The composition of Claim 6 wherein the polyethylenepolyamine is a polyethylenimine having a number average molecular weight between 25,000 and 100,000.

8. The composition of Claim 7 comprising between about 2 and 50, inclusive, weight percent polyethylenimine and between 98 and 50, inclusive, weight percent fire retardant formulation.

9. The composition of Claim 7 comprising between 5 and 20, inclusive, weight percent polyethylenimine and between 95 and 80, inclusive, weight percent fire retardant formulation.

10. A method of imparting fire retardancy to a cellulosic substrate comprising treating the substrate with a fire retardant amount of an aqueous solution of the composition of Claim 1.

11. The method of Claim 10 wherein the substrate is treated with 0.005 to 0.05 pound of the composition, on a solids basis, per square foot of substrate surface.

12. The method of Claim 10 wherein the substrate is impregnated with the composition, solids basis, to 5 to 70 weight percent of the substrate's untreated weight.

13. The method of Claim 10 wherein the treating is with a composition comprising a polyalkylenepolyamine having a number average molecular weight between 25,000 and 100,000.

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14. The method of Claim 13 wherein the treating is with a composition comprising branched polyethylenimine and a fire retardant formulation consisting essentially of about:
a) 32 to 38 weight percent ammonium sulfate, based on nitrogen and sulfur;
b) 23 to 27 weight percent boric acid, based on boron;
c) 32 to 38 weight percent zinc chloride, based on zinc; and d) 3 to 7 weight percent sodium dichromate.

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