Note: Descriptions are shown in the official language in which they were submitted.
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1032-34-00
TITLE: ALKALI METAL BOROHYDRIDE CONCENTRATE
BACK&ROUND OF THE INVENTION
The use of alkali metal borohydrides such as sodium
borohydride and potassium borohydride as blowing agents
in connection with the production of cellular articles
is well known. For example, United States Patellt Number
2,951,819 utilizes an alkali metal borohydride in connec-
tion with the manufacture of cellular articles. United
States Patent No. 3,167,520 relates to cellular articles
prepared from polystyrene by extruding polystyrene resin
containing an alkali metal borohydride which decomposes
during extrusion to form a cellular article. The inven-
tion of this application is directed to an improvement
to the technique of aforesaid United States Patent No.
3,167,520.
SUMMA~Y OF T~E INVENTION
The invention involves the use of alkali metal
borohydrides such as sodium and potassium borohydride as
blowing agents useful in connection with the production
of articles having a foamed or cellular structure. One
particularly advantageous embodiment of the invention .in-
volves the use of a stable borohydride concentrate mixture
containing from about 0.5% to 20% by weight of an alkali
metal borohydride with a dry inert resinous polymer. The
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concentrate should contain no more than about 0.1% ad-
sorbed water or the borohydride will hydrolyze. Such
water may be adsorbed on.the surface of the borohydride
and/or on the surface of the resinous polymer.
The concentrates of the invention may be made by
dry blending from 0.5% to 20% by weight of powdered
alkali metal borohydride with a dry inert resinous polymer
to form a mixture containing less than about 0.1% by
weight wa-ter; heating the mixture to a temperature above
that of the melting point o~ the resin to form a molten
mixture; extrudin~ the molten mixture and then cooling
the e~trusion to form a solid, stable concentrate; and
then forming the cooled extrusioned concentrate into pel-
lets by conventional techniques such as chopping, grinding
and the like.
Another aspect of the invention comprises a method
for making cellular articles by contacting a mixture of
alkali metal borohydride and a resinous polymer with a
high surface area silica activating agent having a proton
source adsorbed on its surface so as to cause said alkali
metal borohydride to hydrolyze thereby causing said
resinous polymer to have a foamed cellular structure. The
alkali metal borohydride may be in the form of the con-
centrate described above or as neat powdered alkali metal
borohydride.
DETAILED DESC~IPTION OF THE IN~ENTION
The concentrates of the invention may be used to
incorporate low levels of alkali metal borohydride i.nto
the same or different resins with the object of using
the incorporated borohydride to foam -the resin where an
additional protonic activator such as wa.ter, alcohol or
acid is also added to the resin to react with the boro-
hydride to produce hydrogen.
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When used as a blowing agent for ~hermoplastic
resins, up to 0.5% NaBH4 may be incorporated into the
resin ~rom the concentrate. The preferred range is up
to 0.25%.
The use of concentrates to incorporate low levels
oi borohydride into resins has several advantages. First
of all, the concentrates protect the borohydride irom
adventitious hydrolysis during ha~dling and may be stored
for peri.ods on the order of a year without the occurrence
of signi~icant hydrolysis. Secondly, it is much easier
to incorporate the borohydride at very low levels such as
less than 1 wt.% into the resin by using the concentrates.
Thirdly, overall handling such as weighing and making
uniform mixtures is much easier using the concen~rates
than using neat borohydrid~. Because such highly reactive
material has been concentrated and rendered substantially
inert, employee safety is enhanced. In addition, very
uniform dispersions of borohydride in the resin are ob-
tained using the concentrates.
The s-table borohydride concentrate of the invention
comprises from about 0.5% to 20% by ~eight of an alkali
metal borohydride, less than about 0.1~ adsorbed water,
balance essentially being dry inert resinous polymer. The
0.5% lower limit for borohydrides was selected primarily
because lower concentrations would necessarily involve the
use o~ excessive amounts of the concentrate and the 20%
upper limit was selected because higher levels would re-
quire excessively small amounts of the concentrate and
thereby hamper the attainment of uniform dispersion in
the thermoplastic polymer to be foamed. It is preferred
to include the alkali metal borohydride in amounts be-
tween 2 and 10% because such range permits let-down ratios
on the order o~ about 20:1 as are normally desired in the
industry. Sodium and potassium borohydrides are contem-
~lated for use in connection with the invention. The
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concentrate should contain no more than about 0.1% by
weight o~ adsorbed water, preferably not more than
about 0.01%, in order to prevent hydrolysis of the
borohydride. Thus, the borohydride and resin must be
very dry when mixed to ~orm the concentrate and moisture
pick-up should be avoided during such mixing.
The inert resinous polymer component o~ the con-
centrate compriæes resi~s in which reactive pxotonic
hydrogen atoms are substantially absent. Such resins
include polyolefins, polydienes, polystyrene, polyphenylene-
oxide-styrene,polyacrylates, polyvinylchloride, polyvinyl-
acetate and the like.
The alkali metal borohydride concentrates of the
illvention are prepared by dry blending from about 0.5%
to 2070 by wei~ht o~ the borohydride with the inert resinous
polymer to ~orm a dry mi~ture thereof. The mixture should
contain less than about 0.1% o~ adsorbed water. The mix-
ture is then treated to a temperature in excess of the
melting point o the re~in, extruded, cooled, and ormed
i~to pellets.
As mentioned previously, the alkali metal boro-
hydride has utility as a blowing agent in connection with
the manufacture of cellular or ~oamed resinous articles.
Typical res,inous polymers that may be foamed wi$h use of
the concentrate include but are not limited to polyolefins,
polydienes, po]ystyrene, polyphenyleneoxide-styrene,poly-
acryletes, polyvinylchloride, polyvinylacetate and the
like.
Cellular articles may be manufactured by mixing
~he alkali metal borohydride concentrate mentioned above
with a resinous polymer and an e~-fective amount o an
activating agent capable of donating an acidic proton
to the alka].i metal borohydride so as to hydrolyze
substantially all of the alkali metal borohydride while
the resinous polymer is molten and thus ~orm a cellular
article. The activating agent may comprise a fi~ely
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divided high surface area solid having a proton source
adsorbed on its surface. A preferred activating agent is
finely divided high surface area silica.
An example of a form of silica suitable for use in
the invention is that manufactured by Cabot Corporation
under the designation "CAB-O-SIL'~ Such type of silica
is manufactured by fumin~. It is pre~erred to utilize
silica having a surface pH of less than 7 because acidic
mater:ials aid in the decomposition of alkali metal boro-
hydrides. It is especially preferred to have a pH in
the range of 4 or lower. Finely divided, high surface
area activating agents function to provide nucleation
sites for foam to form. These materials have a very
high capacity for adsorbing liquids such as water and yet
remain a free-~lowing solid so as to thereby aid in the
promotion of uniformity during the blending or mixing
stage of the process.
Suitable proton sources include water, mineral
acids, carboxylic acids, alcohols,sulfonic acids, poly-
acrylic acid~ polystyrene sulfo~ic acid and li~e materials.
Water is preferred due to its relative cost, availability,
and low corrosivity.
It has also been discovered that the silica acti-
vators described above may also be used in combination
with alkali metal borohydride materials other than the
concentrate described above. ~or example, powdered
alkali metal borohydrides may be utilized in combination
with the silica activators to produce foamed polymers.
As in the case of the concentrate additions, the alkali
metal borohydride and a resinous polymer are contacted
with a sufficient amount of activating agent to cause
substantially all of the borohydrides to hydrolyze.
The following examples further illustrate the
practice o~ the invention.
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Example 1
Sodium borohydride was concentrated in polypropylene
by the following procedure. Ninety parts by weight of pre-
viously dried, powdered, unstabilized polypropylene resin
(melt index 12) and 10 parts by weight of NaBH4 that was
previously dried 24 hrs at 100~C, were thoroughly mixed in
a dry blender. The resultant mixture was extruded through
a 1/8 inch diameter die at about 450F. The extruded rod
was pelle~ized in line with the extruder. The extruded con-
centrate was examined with a low power microscope and an ex-
tremely uniform dispersion of minute borohydride particles
was found. Virtually no gas bubbles were observed in the
resin pellets.
Example 2
Sodium borohydride was concentrated in NORYL resins in
the following manner. Ninety parts by weight of dry NORYL~3
r~sin FN 215, a proprietary General Electric Co. blend of poly-
phenylene oxide and po~ystyrene in pellet form, was mixed with
0.1 part ~y weight of mineral oil and 10 parts by weight of
NaBH4 powder, that was previously dried at 100C for 8 hrs.
The resultant dry blended mixture was then extruded at about
450F and pelletized as described in the previous example.
The concentrate pellets were e~uivalent to the pellets of
Example 1.
Example 3
Sodium borohydride was concentrated in polystyrene with
use of the following procedure. Ninety parts by weight of pre-
viously dried high impact polystyrene pellets was blended with
0.1 part of mineral oil and 10 parts by weight of dry NaBH4
powder. The resultant mixture was then extruded at about 450F
and pelletized as described in Example 1. As in Example 1,
an excellent dispersion of minute particles o~ NaBH4 in the
resin was produced with virtually no gas bubbles observed.
Example_
An activating agent concentrate was prepared by-the
~ollowing procedure. 2806 parts by weight of CAB-O-SIL fumed
silica was intensively mixed with 71 parts by weight of a
solution (65% solids) of polyacrylic acid in water for five
minutes with use of a Henschel mixer. The resultant mixture
was a "dry" free flowing powder.
Example 5
The procedure described in Example 4 was also used to
prepare an activator concentrate containing 71.4 parts by
weight of water. The water was added slowly to 28.6 parts
by weight of CAB-O-SIL fumed silica while mixing. The con-
centrate handled as a "dry" powderO
Example 6
Polypropylene foamed fibers were prepared as follows. The
series of blends of polypropylene resin powder, sodium boro-
hydride, and CAB-O-SIL whose compositions are shown in Table
I were prepared. The polypropylene powder was not dried
prior to blending, but rather was blended in the "as-received"
condition.
TABLE I
Polypropylene 99.89 99.75 99.5 99.95 99.92
NaBH4 0.1 0.25 0.5 0.05 0.075
CAB-O-SIL 0.001 0.0025 0.005 0.005 0.00075
These mixtures of Table I were extruded through a 3/4 inch
diameter die at 430-440F to form filaments with varying amounts
of oriented foamed cells. A 3 1/2:1 compression ratio was em-
ployed. The moisture present on ~he NaBH~ and the resin was
sufficient to activate the release of hydrogen to foam the
fibres as they passed thrcugh the melt phase in the extruder.
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Example 7
Foamed polypropylene structural parts were prepared by
the following procedure. Blends of undried polypropylene
resin powder, sodium borohydride, powdered stearic acid and
CAB-O-SII. were prepared in a Henschel Mixer. Stearic acid func-
tioned as the activator and CAB-O-SIL as the nucleating agent
for bubble formation in this system. This system was limited
to 1~ stearic acid activator due to the limited solubility
of the acid in the solid resin and because the lubricity in
the barrel of the extruder provided by $he molten stearic acid
causes slippage of the screw Although good foams were pre-
pared with good density reduction, stearic acid and other fatty
acids are less than ideal activators because of the above
mentioned factors. In any e~ent, structural foam parts of
good quality were produced on a reciprocating screw L/D 16:1,
100 ton, 5 oz. injection molding machine equipped with a cut
off nozzle. The compositions shown in Table II were so pro-
duced. All percentages are based on the weight of polypropylene
resin.
TAB~E II
SBH Fumed Silica Stearic Acid % Wt. Reduction
% % ~ of Part Due to Foam
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0.06 0.1 1.0 20.2
0.13 0.1 1.0 27.3
0.25 0.1 1.0 34.4
~.~ 0.1 1.0 37.3
1.0 0.1 1.0 33.7
Example 8
Foamed polystyrene structural parts were prepared by
the following procedure. Polystyrene resin powder, the sodium
borohydride concentrate prepared in Example 3, and either the
activatox of Example 4 or Example 5 were blended in the pro-
portion shown in Table III. All percentages are based upon
the weight of the resin.
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TABLE III
~ Conc. of % Conc. of
E~le 3 % Conc. of Example 4
NaBH4 Chemical E~le 5 Polyacrylic % Part
Blowlng Agent H20 Activator Acid Ackivator Wt. Reduction
1 0.56 16
1 0.28 15.1
2 0.28 18.4
4 2.24 26.8
8 2.24 25.5
~15 140
1 0.14 12
~ 0.56 23.3
0.7 2~.6
Excellent quality foams having very fine uniform pore size
w~re produced with use of a structural foam injection machine.
Density reductions of about 25% using only 49~ of the blowing
agent concentrate (0.4% NaBF~4) and 2.24~6 of the silica/water
activator concentrate are unusually high and very desirable
for this type of structural foam. Normally, with nitrogen in-
jection to provide cells, density reductions of less than 20%
are achieved. Moreover, the borohydride blown foam was unusu-
ally white, whereas the nitrogen blown foams have a slightly
yellow cast. These Activator concentrates such as water,
organic acids, alcohols, etc. adsorbed on colloidal silica
serve as ideal activators and nucleating agents for these sys-
tems because the activators can be premixed with blowing agent
concentrates in the desired ratio with no reaction occurriny.
This mixture can then be blended with the resin to be foamed
in the desired ratio and fed into the foaming machine to pro-
duce the foamed article.
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~ Example 9
Extruded foamed sheets of NORYL resin were manufactured
by the following technique. NORYL resin was blended with the
sodium borohydride blowing agent concentrate of Example 3 and
an organic acid according to the percentages listed in Table
IV. All percentages are based on the weight of NORYL resin.
These mixtures were extruded with a 3~4 inch~diameter extruder.
TABLE I'~
Chemical% Chemical Acid/Sodium
Blowing Blcwing AcidBorohydride
A~ent Agent Activator Mole Ratio De~ree of Foam
E~le 3 1.0 Oleic 4/1 Highly foamed
E~le 3 1.0 Octanoic4/1 Highly foamed
Neat NaBH4 0~1 Octanoic4/1 Highly foamed
E~ple 3 ~1.0 Stearic 4/1 Highly foamed
mple 3 1.0 - - Very slight
It can be observed from this example that practically no foaming
occurs where the chemical blowing agent is used in the absence
of an activator. Furthermore, the NaBH4 concentrates are just
as efficient as an equivalent amount of Neat NaBH~ for blowing.
Neat NaBH4 suffers many other deficiencies previously described
which ar~ overcome by th~ concentrates of the invention~
