Note: Descriptions are shown in the official language in which they were submitted.
10~3~Z
This invention concerns the neutralization of
sulfonated, normally solid polymers with a gaseou neut-
ralizing agent such as ammonia.
It is known that exposure to gaseous ammonia
S or immersion in aqueous ammonia will neutralize a sulfonated
or chlorosulfonated surface of resinous material and
that water or steam may be used after gaseous ammoniation
to wash water-soluble sulfur-containing compounds from
plastic articles. See United Sta~eQ Patent 3,625,751
to Wilhe}m E. Walles, issued December 7, 1971. This
patent also teaches that a mixture of steam and gaseous
ammonia may be used to neutralize sulfonated polymers.
The prior art treatments of sulfonated surfaces
of resinous polymers to neutralize the acid groups are
slow or require additional processing which create~ a
bottleneck in the manufacture of these items. Spraying
or rinsing these ~urfaces with a liquid neutralizing
reagent necessitates the addition of a drying step to
the manufacturing process. Treatment of the surface
with gaseous ammonia involves a relatively lengthy ex-
posure period to complete neutralization even if an
atomsphere of pure ammonia is utilized. The use of an
atmosphere of pure ammonia is an inefficient and waste-
ful use of the reagent. -
This invention provides a process for neutraliz-
ing sulfonated normally solid polymers with a gaseous
mixture of an inert gas and ammonia or an organoamine in
the presence of an hydroxyl compound characterized in
that substantially comple~e neutraiization is accelerated
by contacting the sulfonated polymer with an inert gas
1~ 130-F -1-
1093242
containing a vaporous hydroxyl compound without rendering
the sulfonated polymer visibly moist. The amount of
vaporous hydroxyl compound employed is preferably sufficient
to accelerate the rate of neutralization by at least 25
percent relative to the rate of neutralization achieved
by the prior art method of vapor phase neutralization
in the absence of the hydroxyl compound, but does not
render the sulfonated polymer visibly moist. The sulfonated
polymer may be contacted with the vaporous hydroxyl com-
pound either prior to or contemporaneous with the substan-
tially complete neutralization.
Surprisingly, the practice of the present
invention greatly accelerates the rate, e.g., as much
as from 100 to 400 percent of the normal rate in absence
of hydroxyl compound, at which the gaseous neutralizing
agent neutralizes the sulfonated polymer. The sulfonated
polymer is unexpectedly more easily neutralized by the
method of this invention to a degree sufficient to elimi-
nate hy(Jroscopic properties. In contrast, the prior art
practice of neutralizing a surface with dry gaseous
neutralizing agent neutralizes the sulfonic acid groups
to a degree insufficient to eliminate the hygroscopic
character of the surface of the sulfonated polymer.
The method of the present invention is useful
for the production of sulfonated polymers which may be
employed as containers for hydrocarbon or other organic
materials which permeate untreated non-aromatic polymers.
The method is also useful in the production of sulfonated
polymers to be electrostatically spray coate~.
18,130-F -2-
~.093242
One especially preferred embodiment of this
invention wherein great utility is achieved is in the
manufacture of a sulfonated polymeric enclosure member
for the containment of a hydrocarbon fluid such as gaso-
line, kerosene, diesel fuel, and other similar fuels.
In such embodiment, the enclosure member preferably exists
in the form of a molded container such as, for example,
a gasoline tank, oil drum or barrel.
The polymers to which this invention is appli-
cable can be classed as sulfonatable, normally solid
- polymers. A sulfonatable polymer must have a plurality
of replaceable hydrogen atoms bonded to carbon atoms near
the surface. The following groups or classes exemplify
such sulfonatable polymers:
a. aromatic polymers such as, for example,
polystyrene, polyvinyltoluene, poly(phenylene),
and poly(p-xylene);
b. polyolefins such as, for example,
polyethylene, polypropylene, polyisobutylene,
polybutene-l, and poly(methylpentenes);
c. polyacrylic esters such as, for example,
poly(methyl acrylate), and poly(ethyl meth-
acrylate);
d. poly(vinyl esters) such as, for example,
poly(vinyl acetate), and poly(vinyl butyrate);
e. polyvinylidene halides such as, for example,
polyvinylidene chloride and polyvinylidene
fluoride,
f. halogenated polyolefins such as, for example,
chlorinated polyethylene and chlorinated poly-
propylene;
18,130-F -3-
10932~2
,
g. polyvinyl halides such as, for example,
polyvinyl fluoride and polyvinyl chloride;
h. polycarbonates such as, for example,
poly(bisphenol-A) carbonate; and
i. polyesters such as, for example, poly-
(ethylene terephthalate).
Blends of the aforementioned polymers and copolymers
of the related monomers are also included in the scope
of the invention. The preferable sulfonated polymers
for use with the method of this invention are the poly-
(monoolefins~ such as the high and low density polyethylenes,
polypropylene, ethylene/propylene copolymers, ethylene/butene-l
copolymers and blends thereof.
Central to this invention is the unexpected
discovery that the presence of a gaseous hydroxyl com-
pound such as water vapor or a gaseous organic hydroxyl
compound, e.g., methanol, ethanol, or ethylene glycol,
accelerates the rate at which a gaseous neutralizing
agent such as ammonia or a gaseous organoamine, e.g.,
methyl amine, will effect substantially complete neutrali-
zation of a sulfonated surface of a normally solid polymer.
Substantially complete neutralization has been effected
when a strip of litmus paper dampened with distilled water
and placed in contact with the sulfonated surface indicates
a pH of at least 5, preferably a pH in the range of ~ to 7
and more preferably from 5.3 to 7.
It is preferred that the hydroxyl compound
or the neutralizing agent used in accordance with this
invention be of low molecular weight because of the
gen~rally higher vapor pressures low molecular weight
18.130-F _4_
~093242
species possess. Accordingly, such a low molecular
weight organic hydroxyl compound is one that achieves
the concentration in moles hydroxyl compound per liter
gas necessary to accelerate neutralization at operating
S conditions suitable for the practice of this invention.
Exemplary preferred compounds include methanol, ethanol,
and ethylene glycol. A low molecular weight neutralizing
agent is an organoamine that achieves the concentration
in moles organoamine per liter gas necessary to neutralize
the sulfonated polymer in a short time period in accordance
with this invention. Exemplary preferred compounds
include methylamine, dimethylamine, and ethylamine. It
is preferable that the necessary concentrations be achieved
with vapor phase organoamines and hydroxyl compounds,
but a suspension of fine droplets of the compound in an
inert gas can also be used if the droplets are small
enough that the sulfonated polymer is not wetted visibly
during contact.
This invention is most preferably practiced
using water vapor and gaseous ammonia because these
reagents more rapidly and completely neutralize the
surface in accordance with this invention and because
these reagents are inherently more economical to use than
organic, hydroxyl compounds or gaseous organoamine neutra-
lizing agents. For the sake of brevity and because the
teaching of the method of the invention does not depend on
the reagents used, the invention will be described in
terms of the preferred reagents, water vapor and ammonia.
The method by which the polymers are sulfonated
is not critical. The preferred method of sulfonating
18,130-F
1093~ ,
the polymer is to immerse them at room temperature in
a tank containing a dry inert gas with about 0.1-25 percent
by volume of sulfur trioxide (SO3) mixed therein for a
time varying from 0.1-20 minutes. Examples of the inert
gases to be used in this process are nitrogen, carbon
dioxide, sulfur dioxide and air. It is desirable to
exclude water vapor from the above gases by a conventional
drier tube since in the presence of water in a liquid
or vapor form the SO3 is converted to droplets of sulfuric
acid of varying concentration and the sulfonation of the
polymer is either inhibited or prevented.
The sulfonation of a polymer produces water-
-soluble sulfur-containing compounds as well as the
sulfonic acid groups that are bonded to the polymer.
In applications in which the presence of these water-
-soluble compounds does not affect the suitability of
the sulfonated polymer for its intended purpose, these
compounds, though they are not removed by subsequent
gaseous neutral~zation, need not be rinsed from the surface.
An example of such an application is a fuel tank in
which the insolubility of these compounds in gasoline
makes it unnecessary that they be rinsed from the polymer.
If no rinsing is necessary, the drying step normally
required if an aqueous neutralization solution were
employed can be eliminated by practicing the neutra-
lization method of the present invention. Even where
the sulfonated polymer is to be used in an application
which makes it desirable that these soluble compounds
be rinsed from the surface, the use of the neutralization
method of the instant invention may be preferable to
18,130-F -6-
109324~
the use of an aqueous solution for neutralization because
of the ease with which unused ammonia may be recycled
and the ease with which bulky articles of unusual con-
figuration may be neutralized.
The acceleration of the rate of neutralization
of s~llfonated polymers observed in accordance with this
invention is not dependent upon the degree of sulfonation.
For example, any concentration in the range of sulfonate
group concentrations typically employed to enhance
barrier properties of sulfonatable polymer, i.e., from
0.015 to 50 milligrams of sulfur trioxide equivalents
per square centimeter, can be advantageously neutralized
in the practice of this invention. The time savings to
be derived from this invention may be less where the degree
of sulfonation is less than above, but some advantage
persists even at very low degrees of sulfonation, e.g.,
as low as 0.001 milligram of sulfur trioxide equivalents
per square centimeter.
While the concentration of water vapor in
inert gas can exceed the saturation point of the inert
gas in accordance with the method of this invention, it
is generally less desirable to exceed the saturation
point because under such conditions condensation often
occurs. ~xcessive condensation is undesirable because
it necessitates a drying step which otherwise might be
eliminated in many instances. More importantly, if the
sulfonated polymer is not neutralized immediately
following or concurrent with the exposure to water
vapor, sulfuric acid is formed in the reaction of water
with the water-soluble, sulfur-containing compounds
18,130-F -7-
1093242
deposited on the polymer surface during sulfonation.
The acid can damage the polymer and other adjacent
surfaces and hinder the effective and rapid neutrali-
zation of those sulfonated surfaces insulated from
contact with neutralizing gas by the acidic condensa-
tion. It is therefore preferable that the concentra-
tion of water vapor in inert gas employed in the practice
of this invention does not exceed the saturation point
of the inert gas in contact with the sulfonated polymer.
If the atmosphere of air containing water vapor
but not ammonia to which the sulfonated polymer is exposed
is at a pressure of one atmosphere of 21C, it is pre-
ferable in the practice of this invention that the gas
mixture has a relative humidity in the range from 20 to
100 percent, more preferably 50 to 100 percent, most pre-
ferably 85 to 100 percent. The preferred ranges of relative
humidities at a pressure of one atmosphere at 21C corres-
pond to a preferred concentration in mole of water vapor
per liter of gaseous mixture from 0.005 to 0.024, the
more preferred from 0.012 to 0.024, and the most preferred
from 0.020 to 0.024. The lower limits of the foregoing
preferred, more preferred, and most preferred concentra-
tions of water vapor are applicable to the practice of
this invention independent of whether the neutralization
follows the exposure to the humidified atmosphere or occurs
contemporaneously and independent of the temperature and
pressure so long as the conditions are suitable for the
practice of this invention. The upper limit of the fore-
going preferred range of concentrations is governed by
the saturation point of the humidified atmosphere at the
1~,13~-F -8-
10~3Z~2
temperature, pressure, and composition of the atmosphere
employed in the practice of this invention. If the neutrali-
zation is to occur contemporaneously with the exposure
to water vapor, the gas mixture will also contain ammonia
and the foregoing preferred concentrations are applicable
to the mixture of gases including ammonia.
Neutralization of the sulfonated polymer with
ammonia by the method practiced in this invention can
follow exposure to water vapor, can occur contemporaneously
with exposure to water vapor, or can occur in both of
these time frames as when ammonia is used to purge water
vapor from contact with the surface and is used to neutra-
lize the surface. If the method of neutralization com-
prises contacting the sulfonated polymer simultaneously
with water vapor and ammonia, the molar ratio of ammonia
and water vapor concentration, NH3:H2O, is an important
parameter in effecting the most rapid and material
efficient neutralization. The most preferred range of
ratios is 1:1 to 3:1. But, even at higher, less preferred-
ratios (the upper limit being 10:1), an inert atmosphere
saturated with water vapor will noticeably accelerate
neutralization. The lower limit of the preferred ratios
that produce an unexpected acceleration of the rate of
neutralization with a water saturated inert atmosphere
is usually a ratio of NH3:H2O of about 4:5. The limits
set by the preferred range of water concentrations and
the preferred ratios of the concentrations of ammonia
to water vapor during contemporaneous exposure determine
that the ammonia should comprise roughly 1 to 20 percent
by volume of the preferred neutralizing atmosphere when
18,130-F -9-
1093Z9Z
contemporaneous contact of the sulfonated polymer with
ammonia and water vapor is carried out in the practice
of this invention.
The ratio of the concentration of ammonia
and water vapor is not particularly critical when the
sulfonated polymer is exposed first to an inert gas con-
taining water vapor followed by expos~re to an inert
gas containing ammonia. In the successive exposure of
the sulfonated polymer to water vapor and ammonia atmo-
spheres at one atmosphere at 21C, the neutralizing
atmosphere can preferably contain from 5 to 100 voiume
percent ammonia, more preferably 50 to 100 volume percent
ammonia, and most preferably 85 to 100 volume percent
ammonia. Mixtures of 16 to 25 volume percent ammonia
in air are potentially explosive, hence it is desirable
to avoid such mixtures in the practice of this invention.
The foregoing preferred ranges of the percentage ammonia
by volume in the neutralizing atmosphere when compared to
the water vapor content of a saturated atmosphere at
the same temperature and pressure determine preferred
mole ratios of ammonia and water vapor from 1.9:1 to 38.5:1,
more preferred mole ratios from 19.2:1 to 38.5:1, most
preferred mole ratios from 32.7:1 to 38.5:1. The preferred
range of concentrations of ammonia for the neutralization
of a sulfonated polyrner immediately after exposure to a
humidified atmosphere by the method of this invention
as calculated from the foregoing volume percentages of
ammonia at a pressure of one atmosphere at 21C is
from 0.002 to 0.04, more preferably from 0.034 to 0.04,
mole of ammonia per liter of the inert gas-ammonia mixture.
The lower limits of the foregoing preferred ranges of
18,130-F
10~3242
concentrations of a~monia are applicable when the humidi-
fied atmosphere precedes the neutralized atmosphere to
the practice of this invention at all temperatures and
pressures suited to the practice of this invention.
The upper limit of the preferred and most preferred range
- of concentrations of ammonia is governed by the concen-
tration of an atmosphere of pure ammonia gas at the
operating temperature employed.
The methods by which the sulfonated polymer
may be ~rought in successive or concurrent contact with
water vapor and ammonia in accordance with this inven-
tion will generally be obvious to the skilled artisan
and are not part of this invention. The sulfonated
polymer can be transported through the treating atmo-
lS sphere(s). The sulfonated polymer may be placed in a
vessel and the atmosphere surrounding the sulfonated
polymer is then displaced or modified to the neutralizing
atmosphere of this invention. Alternatively, a stream
of inert gas containing suitable amounts of the reagents
may be directed over the surface of the sulfonated
polymers for a sufficient span of time to achieve virtuall~
complete neutralization. In the case of a sulfonated
surface on the internal side of a normally solid polymeric
enclosure member, the complete enclosure may itself be
used as a neutralization chamber. It is preferred that
- whatever method is utilized that intimate contact of
the sulfonated polymers with the water and ammonia
vapors over the duration of exposure be insured.
The mixtures of gases utilized in the foregoing
methods can readily be prepared by methods known to the
18,130--F
~09324~
art. ~n atmosphere saturated with water vapor can be
produced by bubbling the inert gas through water. The
preferred ratio of concentrations of ammonia and water
vapor can be produced by bubbling the inert gas through
an aqueous solution containing a suitable concentration
of ammonia. The concentrations of ammonia and water
vapor can be reduced by mixing the inert gas previously
bubbled through the aqueous solution with dry inert gas.
There exist other methods to regulate the concentrations
of ammonia and water vapor, for example, the use of
flowmeters or laminar flow valves to regulate the injection
of these gases into a stream of inert gas of a known flow
rate. The practice of this invention is not limited to
any specific techniques utilized to produce mixtures of
ammonia and/or water vapor in inert gases of a concen-
tration suitable for the neutralization of sulfonated
polymers by the method of this invention.
Temperature is not critical in practicing the
foregoing methods of neutralization, but it is advantageous
to carry out the methods in the temperature range of
4C to 93C, preferably 21C to 82C. If the temperature
is in the lower part of the above range the vapor pressure
or partial vapor pressure of the water vapor is too low
to promote most efficient neutralization of the sulfonated
surface. If the temperature of the atmosphere saturated
with water vapor exceeds that of the sulfonated polymer
condensation often occurs. Steam or heated water vapor
can be used in the practice of the method claimed, but are
not preferred because precautions, such as heating the
polymer prior to neutralization, must be taken to prevent
18j130-F -12- -
10~324~ -
condensation of the steam or heated water vapor on the
sulfonated surface.
The pressure at which the surface is neutralized
by the above methods is also not critical. While for
reasons of convenience it is preferable to carry the
treatment out at atmospheric pressures, the neutralization
methods advantageously can be carried out at pressures
in the range of 0.1 to 5 atmospheres. However, excessive
pressure may lead to undesirable condensation of water
vapor. Very low pressure may result in concentrations
of ammonia too low for most efficient neutralization.
When the neutralization proceeds contempor-
aneously with exposure to the water vapor, i.e., when
the ammonia and water wapor are present in the same
atmosphere, the duration of contact between the
sulfonated polymer and the above atmosphere is pref-
erably governed by the time required for substantially
complete neutralization of the sulfonated polymer. If
the exposure is concurrent, for a given mole ratio of
ammonia and water vapor concentrations the time required
for néutralization will generally decline as the con-
centration of ammonia is increased. Under preferred
conditions the typical time necessary for relatively
complete neutralization of a sulfonated polymer by
simultaneous exposure to ammonia and water vapor is
- 20 to 30 seconds.
If the contact with water vapor precedes ex-
posure to ammonia, the duration of the contact between
the sulfonated polymer and the atmosphere containing
the water vapor is that period of contact necessary to
18,130-F -13-
1093242
accelerate neutralization. While the duration of contact
with water vapor can advantageously be as little as 5
seconds, exposure from 20 to 90 seconds is preferred.
A period from the initiation of the contact with water
vapor to the initiation of neutralization lonyer than
about 180 seconds can result in a deterioration of the
surface due to the formation of sulfuric acid in the
reaction of water with the water-soluble sulfur-containing
material on the surface of the sulfonated polymer. The
time necessary for relatively complete neutralization
~f the sulfonated polymer after contact with an atmosphere
saturated with water vapor for the preferred period can
be as little as 20 seconds if the neutralization atmosphere
is pure anhydrous ammonia.
The following examples are presented to il-
lustrate but not in any manner limit the invention.
Example 1
A series of high density polyethylene bottles
(16-ounce (497.6 gram) capacity) are connected in turn
to an apparatus which permits the bottles to be purged
with any of the following vapor phase mixtures: sulfur
trioxide in nitrogen, nitrogen bubbled through an aqueous
solution of ammonia, nitrogen bubbled through distilled
water, anhydrous ammonia, or anhydrous nitrogen. The
bottles are each sulfonated by purging them for three
minutes with the sulfur trioxide and nitroge~ mixture
produced in a 65 to 70 percent oleum bubbler. The sul-
fonation is followed by a one minute purge with dry nitro-
gen. The bottles were neutralized by one of three methods.
18,130-F -14-
1093Z4Z
Method 1 involves the neutralization of the
bottles with mixtures of anhydrous ammonia and nitrogen
of various concentrations. Method 1 is consistent with
prior art methods.
In Method 2 the bottle is purged with dry
nitrogen bubbled through aqueous ammonia solutions at a
number of different concentrations. The purging gas
is assumed to be a saturated vapor and the volume-percent
of each component is calculated on this basis.
Under Method 3 the bottle is first purged for
varying durations Wit}l nitrogen saturated with water
vapor and is followed by a purge with anhydrous ammonia.
A ratio of ammonia to water vapor concentrations is cal-
culated though the reagents do not contact the sulfonated
polymer contemporaneously.
A piece of litmus paper wetted with distilled
water can be used to determine when the surface is well
neutralized.
All of the foregoing operations are carried
out at 22C and 1 atmosphere. The neutralization times
required by the afoxementioned methods of neutralization
are set out in Table I.
18,130-F -15-
~3Z42
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18 ,130-F -16-
1093242
.
It appears from the data presented in Table I
that exposure of the sulfonated polymer to water vapor
and ammonia simultaneously or successively as in Methods
2 and 3 respectively results in great acceleration of
neutralization over the prior art treatment of the sur-
face with gaseous ammonia as depicted in Method 1. In
particular, neutralization by Method 2 is not only faster
but more efficient with respect to the utilization of
ammonia than the prior art method. Neutralization by
Method 3 is much faster than neutralization without p,re-
treatment of the surface with water vapor in all reported
tests except Sample No. A5. The five-second pretreatment
,~ of the surface with water vapor in Sample No. A5 was
i insufficient at the experimental pressure, temperature,and concentration of water vapor in the pretreatment
atmosphere to produce an acceleration of neutralization.
Example 2
, A series of 12-gallon (45.4 l) high density
polyethylene (HDPE) containers suitable for use as auto- '
mobile fuel tanks are sulfonated to the same degree so
as to provide a barrier for the containment of hydrocarbon
fluids such as gasoline. A stream of dry air containing
30 percent anhydrous ammonia by volume and flowing at
a rate of 9.6 standard cubic feet per minute is utilized
to neutralize some of the sulfonated'HDPE tanks in accord-
ance with the prior art method. Addition of atomized
water at the rate of l/60 gallon per minute is made to
the foregoing gas stream. The humidified stream is also
used to neutralize some of the sulfonated tanks. Provision
is made to permit some of the larger water droplets to
18,130-F -17-
1~932~2' '
condense out of the gas flow before the humidified stream
is directed into the sulfonated tank.
After continuous treatment for a period of
ninety seconds, tanks purged with a stream of anhydrous
ammonia and air retain high surface acidity, a pH of 2.
The humidified gas flow achieves substantially complete
neutralization of the sulfonated polymer, a surface pH
of 6.5 to 7.0, in a period of 25-30 seconds.
18,130-F -18-
