Note: Descriptions are shown in the official language in which they were submitted.
1058356
Field of Invention
The in~ention relatcs to improvements in the art of rendering
cellulosic materials flame retardant. More part;cularly ~t relates
to the treatment of cellulosic materials such as paper, wood, cotton,
rayon and the like, with effect~ve fire retardant amounts of a
reaction product of aqueous solutions of phosphoric acid or an acid
ammonium salt thereof with an alkylene oxide.
Back~round of the Invention
Cellulosic ~aterials such as paper, wood, and cotton
textiles, are highly flammable substances and once ignited continue
to burn. Methods for the flame proofing of these materials are known
but such methods are either too costly for general commercial use,
relatively ineffective, or give rise to products having poor surface
character.
lS With particular reference to paper, methods involving the
application of salts of phosphoric acid, boric acid and sulfamic acid
are, or have been, usedt These methods while commercially attractive,
costwise, are troublesome due to the crystallization of such salts on
the treated material after dr~ing. Further, the salts crystallize
on the application equipment necessitating the frequent shut down of
such equipment for cleaning.
Organo phosphorus compounds, such as tetrakis-(alpha
hydroxyethyl) phosphonium chloride and various derivatiYes thereof,
have also been suggested for the flame proofing of cellulosic
materials. Such compounds provide a level of flame retardancy which
is at least equiYalent to that obtained with the aforementioned
phosphate and borate salts. Moreover, the organo phosphorus compounds
provide a durable fla~e retardant character which withstands repeated
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laundering and dry cleaning. Such compounds, however, because of their
relatively high cost, are economically feasible salts only where a durable
finish is required.
Accordingly it can be seen that a need exists for a low cost
effective method for rendering cellulosic materials fire retardant which
methods do not deleteriously affect the surface characteristics of the
treated material.
Objects of the Invention
It is, therefore, a principal object of this invention to devise
improved fire retardant cellulosic materials.
Another object is to provide a process for treating cellulosic
materials to render them non-corrosive and non-irritating as well as flame
retardant.
A particular object is to devise compositions comprising a
cellulosic material and an effective fire retardant amount of a reaction
product of aqueous phosphoric acid and an alkylene oxide intimately
associated therewith.
These and other objects of the present invention will be obvious
from the following description.
Brief Summary of Invention
In accordance with the present invention, cellulosic materials
are rendered fire retardant by intimately admixing the material with an
effective fire retardant amount of a reaction product of an aqueous phos-
phoric acid or an acid ammonium salt thereof, which contains from about 1
to about 85 percent by weight of phosphoric acid or the equivalent amount
of an acid ammonium salt thereof and an alkylene oxide at a temperature of
0-100C. in a weight ratio of alkylene oxide to phosphoric acid (100%) of
0.5-1.5:1. The resultant product is preferably rendered neutral in char-
acter and thereafter dried to yield a product which not only is surprising-
ly fire retardant, non-corrosive and non-irritating in character but also
has a pleasant surface character, i.e., "hand".
By "effective flame retardant amount" is that amount of
said reaction product which suffices to impart flame retardant
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character to the cellult)sic material as defined by the American
Society of Testing Materials Test Standard D-777-46 and/or TAPPI
Standard Test T 461,
The term "~xygen Index" as used herein belo~J is that
value determined in accordance with the testing procedure described
in "The Oxygen Flame Flammability Test" ~. L. Isaacs, J. Fire and
Flan~ability Vol. l (January 1970, page 36 et seq.).
The materials treated in accordance with the present inven-
t10n may be formed ;n part or in whole of cellulosic materials such as
paper, wood, cotton and rayon and may be in various forms such as
wood pulp, texti1e fibers or sheet goods. The materials can also be
in comminuted form e.~., paper pulp, cotton fibers, etc. non-woven
form, e.g. paper sheets, ~ood boards, woven form, e.g., cotton or
rayon textile sheeting, and the like. Accordingly although, hereinafter,
primary reference will be made to the treatment of sheets of paper,
this is not to be taken as a limitation as other forms of cellulosic
material may be utilized as the materials treated in accordance with
the present invention.
Detailed Description of the Invention
In accordance with a preferred mode of carrying out the
present invention cellulosic materials, as above defined, are intimately
associated with an effective flame retardant amount of a reaction product
of an aqueous solution of phosphoric acid or an acid ammonium salt
thereof and an alkylene oxide. Thereafter the treated material is
contacted with an alkaline material, e.g., ammonia, ammonium hydroxide,
organic amines such as ethyl amine, ethylene diamine and the like, to
render the treated material substantially neu~ral, i.e., a pH of about
6 to 7.5. Alternatively the reaction product, prior to association
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itll the cellulosic material, may he neutralized and thereafter
utilized as a substantially ne~tral solution.
The fire retardant treatment of the invention can be
accomplished by several means. For example~ the cellulosic material,
in finished or unfinished condition, can be immersed, padded, sprayed,
dipped or othe~se admixed ~lith the a~ueous reaction product, the tho-
roughly ~etted or intimately associated mixture dried to remove excess
moisture and then exposed to gaseous ammon;a vapors until the treated
material reacts substantially neutral. The treated cellulosic material
may be heated to below its decomposition temperature without significant
effect on the treatment.
Alternatively the material can be intimately associated ~ith
an aqueous solution of the substantially neutral reaction product to
thoroughly impregnate the cellulosic material. Thereafter the treated
material containing an effective fire retardant amount of the neutralized
reaction product can be dried in any convenient manner.
The reaction product used in the process of this invention is
a complex mixture of unknown composition and is obtained by react;ng
an alkylene oxide e.g., ethylene oxide, 1,2-propylene oxide, 2,3-
butylene oxide, and the like with an aqueous solution of a phosphoric
acid, such as ortho phosphoric acid, meta phosphoric acid, pyrophosphoric
acid, and the like, or an acid ammonium salt thereof such as mono-
ammonium ortho phosphoric acid, diammonium ortho-phosphoric acid, mono-
ammon~um meta-phosphoric acid, and the like.
The preferred reactants are ortho phosphoric acid or
diammonium acid ortho phosphate, and ethylene oxide because of
their overall effectiveness and low cost.
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Aqueous solutions of the phosphoric acid or acid a~monium
salts thereof are used. Such solutions may contain from about 5 to
about 85 percent by weight of 100% phosphoric acid (or the equivalent
amount of the acid armonium phosphate) althou~h preferably dilute
solutions containing from about 7 to about 25 percent of lOOX phosphoric
acid are used.
To carry out the preparation of the said reaction product,
an aqueous solution of the phosphoric acid or acid a~onium salt ,
thereof is placed in a suitable reactor which may be equipped ~ith an
agitator and the alkylene oxide is bubbled into the solution. The
initial exotherm may be controlled by cooling the mixture and/or
by adjusting the rate of addition of the alkylene oxide. The temp-
erature of the reaction is adjusted to from about 0 to about 100
centigrade and preferably from about 10 to about 80 centigrade
and an amount of ~he alkylene ox1de which is from about one-half ~o
about one and one half times the ~Jeight of lO0 percent phosphoric
acid, or its equivalentj present. Preferably from about one to about
one and one-half the ~eight of 100% phosphoric acid equivalent is
added. The resultant solution can be used directly but preferably
it is neutralized to a pH of about 6.0 to about 7.5 or higher, with
ammonia or other alkaline reacting substances, as defined above.
The result~ng a~ueous solution of the reaction product is
a rather complex mixture ~hich does not crystallize on standing or on
evaporation, or if crystals do form they are rather minimal in amount.
Thus the reaction product is a liquid to a fluid slurry even after drying.
The reaction product is substantially neutral or can be rendered neutral
1n s1tu or after application to the cellulosic material. Such a
composition is e~inently advanta~eous since it can be mcre effectively
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applied to and distriluted throughout the material than a com~osition
tlich crystallizes on drying and thus deposits isolated crystals
on the material thereby affecting the surface character, e.g.9
"hand", of the treated material.
l~lithout being bound by any theory or explanation of
the reactions which take place during the formation of the reaction
product of the aqueous phosphoric acid or acid amnlonium salt thereof
and alkylene oxide, it is believed that 1lhen reacting, for example,
ethylene oxide and aqueous ortho phosphoric acid a major amount of a
hydroxy ethyl ester of ortho phosphoric acid is formed toaether with
lesser amounts of ethylene glycol and other phosphorus containing
organic compounds. Also there may be more or less amounts of unreacted
phosphoric acid ions present ~Ihich upon neutralization ~lith ammonia
or ammonium hydroxide form ammonium phosphates. Such a complex
mixture, fortuitously, resists crystallization even ~Ihen dried to a
low ~Jater content, and thus provides not only an effective fire retardant
agent, but also a non-irritating, i.e., non-acidic, which can be
readily applied to cellulosic materials and dried thereon ~ithout
affecting the surface properties, e.g., "hand", of the thus treated
material.
The present invention can be most adYantageously utilized
for imparting flame retardant character to paper and paper products
either at the pulp stage or finished stage in such products as crepe
or tissue paper used for decorative purposes and the like. The aqueous
reaction product can also be used to treat Christmas trees by dipping,
spraying and the like, to make the trees fire retardant. Further
as has been discovered by another, the aqueous solution is a highly
effective flame retardant material ~rhictl can be used to combat forest
fires. In such applications, additives such as jaguar gums to regulate
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viscosity " /etting agents, iron oxides and other coioring agents,
other flame retardant additives such as anti~ony oxides, can be dissolved
or suspended in the aqueous solution. This then can be used to spray
the burning area and/or limit the burning area by spraying the area
adjacent thereto and thereby to prevent or to limit the fire. On
evaporation of the water from the solution a viscous liquid remains
which adheres to and coats the trees and effectively renders them
flame retardant.
The following examples will illustrate the present invention.
Parts and percentages are by weight and temperatures are given in
degrees centigrade.
Example 1 - Preparation of Reaction Product of ~queous Phosphoric
_Acid and Ethylene Ox_de
A mixture of 58.5 parts of 85% ortho phosphoric acid was
diluted to 500 parts with water. The solution has a specific gravity
of 1.055 at 25 degrees. Ethylene oxide was bubbled into the solution
for about 10 minutes. The solution gained 75.7 parts in weight and
had a specific gravity of 1.073 at 25 degrees. This was a 15% solution
of the reaction product.
The above procedure was repeated but ethylene oxide was
bubbled into the solution for only about four minutes. The resulting
solution gained only 37.0 parts and had a specific gravity, at 25 degrees,
of 1.064. This was a 7X solution of the reaction product.
In a similar manner, ethylene oxide was bubbled into a
lOX phosphoric acid solution for about three minutes to give a gain
in weight of 20.5 parts and a specific gravity (25 degrees) of 1.0595.
Th1s was a four percent aqueous solution of the reaction product.
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In a similar manner, ethylene oxide was bubbled into a 10~
aqueous solution of phosphoric acid for about eight minutes, to give
an eleven percent solution of the reaction product. The gain in weight
was 54.9 parts, final temperature 77 degrees, and the specific gravity
(25 degrees) was 1.068.
Example 2
A two inch wide strip of tissue paper ("Kim-Wipe"oD) was immersed ~-~
in an aqueous solution of the reaction product of ortho phosphoric acid
and ethylene oxide containing four percent of said reaction product and
prepared as described in Example 1 above. The impregnated tissue paper
was laid on a metal plate and covered with a piece of filter paper and
a paper towel. The "sandwich" was squeezed "dry" by rolling. The tissue
paper was then placed in a 70~ oven until dry. The tissue paper was
tested according to ASTM D-777-46 and found to be fire retardant (char
length 4 inches). The hand of the treated tissue paper was excellent
and its strength was practically unaffected by the treatment.
Example 3
Swatches of cotton cheese cloth and cotton sheeting were
immersed in an aqueous solution of the reaction product of phosphoric
acid and ethylene glycol containing 15% of the reaction product and
prepared as described in Example 1 above. The solution was neutralized
to a pH of 6.9 with ammonium hydroxide. The swatches were squeezed out
manually and then dried in a 70 degree oven.
The Oxygen Index of the treated cotton swatches was 35-36
(01 of untreated cotton is 19) and strips of each of the treated cotton
swatches exposed to a vertical flame was self-extinguishing with a -
3-3 1/2 inch char length.
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Example 4 ::
To a solution of 58.5 parts of 85~ ortho phosphoric
ac~d diluted to 500 parts with ~later, ethylene oxide was added. The
latter was bubbled into the acid solution at such a rate that the
temperature did not exceed about 50 degrees. After the addition of
about 75 parts of ethylene oxlde, the addit1On was completed. The
reaction mixture was agitated for about five minutes and then
rendered neutral (pH of about 7) by the addition of ammonium hydroxide.
Tissue paper was impregnated with this solution by placing
a sheet of the paper on a six inch metal plate and lowering the plate
into a tray containing the solution. The paper swelled and floated in
the solution. Thereafter the metal plate was raised with a slight
slant to remove the impregnated paper. The tissue paper was covered
with a sheet of filter paper and then several paper towels were laid
on the filter paper. The resulting "sandwich" was rolled with a
heavy roller to squeeze excess solution out of the tissue paper. The
tissue paper was placed in a 40 degree oven for about one hour and then
hung in the air at about 23 degrees and 51% R.H. for about one hour. The
treated dried and equilibrated tissue paper was then tested for flame
retardancy according to TAPPI-T-461 and found to be flame retardant.
The tests were made with strips of treated paper cut both parallel
and perpendicular to the screen. Single thickness and double thîckness
tissue papers were tested and found to be flame retardant.
Example 5
A solution of 50 parts of diammonium acid phosphate in 450
parts of water was cooled to about 0 degrees in an ice bath. Ethylene
oxide was bubbled ~nto the solution until about 50 parts were added.
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The ethylene oxide was absorbed rapidly and the temperature of the
aqueous reaction mixture rose to ahout 13 degrees. The solution ~las
placed in a stoppered bottle and permitted to stand for about 24
hours at ambient terlperature. The solution renained clear and free of
crystals. A small portion of the a~ed solution ~as placed on a metal
plate and evaporated in an oven. The solution did not crystallize
and a thick oily mass remained.
Strips of tissue paper were impregnated with the aged
solution by the method described in Example 4 above and then tested
for flame retardancy accordin~ to TAPPI-T-461. The treated tissue paper
as found to be flame retardant by this standard test procedure.
The invention has been described in the aLove specification
and illustrated by reference to specific emhodiments in the illustrative
examples. However, it is to be understood, that this not be so limited
since changes and ~odifications in the specific details disclosed
hereinabove can be made w~thout departiny from the scope or spirit
of the inventions disclosed herein.
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