Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
--1
IMPROVED ALKENYL AROMATIC-OLEFINICALLY
UNSATURATED ACID FOAMS AND PROCESS FOR PREPARATION
Extruded plastic foams have become important
items of commerce utilized as ~hermal insulation and
decoration. Orle of the more populax extruded plastic
foams is polystyrene foam. It has been recognized that
it would be desirable to have improved styrene polymer
foam having a higher heat distortion temperature,
greater solvent resistance and having a wider latitude
in preparation. Extruded alkenyl aromatic poly~er
foams generally are prepared using substantial quanti-
ties of halocarbons as volatile fluid foaming agents.Depending on the particular volatile fluid foaming
agent or mixture employed, the halocarbon will sooner
or later diffuse from the foam and enter the atmosphere.
There has been considerable semiscientific speculation
as to the long term effects of such halogens being
released into the atmosphere. In view of the current
energy crisis, larger and larger volumes of extruded
plastic foam and thermal insulation will be desixed and
required. One convenient solution to the halo-hydrocarbon
problem would be to employ carbon dioxide as a blowing
C-27,~52A-F
.
.
--2--
agent. However, certain technical drawbacks exist
which make the use of carbon dioxide as a blowing agent
undesirable.
It would be desirable if there were available
an improved alkenyl aromatic polymer foam suitable for
thermal insulation and decoration.
It would be desirable if there were available
an improved process for the preparation of alkenyl
aromatic polymer foams which minimized the amount of
halo-hydrocarbons released into the atmosphere.
It would also be desirable if there were
available an improved process for the preparation of
alkenyl aromatic polymer foams which permitted an
increase in latitude in the opera~ing conditions.
These benefits and other advantages in accor-
dance with the present invention are achieved in an
improved alkenyl aromatic pol~mer foam, the foam having
a density of from 0.5 to 8 lb/ft3 (8-128 kg/m3),
the foam having a synthetic resinous thermoplastic body
comprised of a polymer having a weight average molecular
weight of from about 100,000 to about 350,000 gram
moles, the polymer having polymerized therein from
about 99 to 70 parts by weight of an alkenyl aromatic
monomer and fxom about 1 to 30 parts by weight of an
olefinically unsaturated acid selected from the group
consisting of acrylic acid, methacrylic acid, itaconic
acid and mixtures thereof, the body defining a plurality
of closed gas filled cells, the foam body having an
C-27,652A-F -2-
,, . ~, -
,2Y.,1~3
--3--
ion thereln, the ion being selec~ed from a g~oup con-
sisting of sodium, magnesium, zinc, ammonium and mixtures
thereof.
Synthetic resinous thermoplastic foams suit-
able for the practice of the present invention arepolymers containing polymers thereof alkenyl aromatic
monomer and olefinically unsaturated acid wherein the
al~enyl aromatic monomer is present in the proportion
of from about 99 to 70 parts by weight and the acid is
present in a proportion of from about 1 to 30 parts by
weight. Preferable for most applications, the alkenyl
aromatic monomer is present in a proportion of from
about 95 parts by weight to 80 parts by weight while
the acid is present in a proportion of from about 5 to
20 parts by weight. Advantageously, the weight average
molecular weight of the alkenyl aromatic monomer and
olefinically unsaturated acid containing polymer is
from about 100,000 to 350,000 gram moles as determined
by gel permeation chromatography, and preferably from
about 150,000 to 300,000 ~ram moles.
By the term "alkenyl aromatic monomer" is
meant an alkenyl aromatic compound having the general
formula
Ar - C = CH2
wherein Ar represents an aromatic hydrocarbon radical,
or an aromatic halohydrocarbon radical of the benzene
series, and R is hydrogen or the methyl radical.
C-27,652A-F -3-
'7~ ~U;~
--4--
Examples of such alkenyl aromatic monomers are styrene,
~-methylstyrene, o-methylstyrene, m-methylstyrene,
p-methylstyrene, ar-ethylstyrene, ar-vinylxylene,
ar-chlorostyrene or ar-bromostyrene and the like.
In the preparation of foams in accordance
with the present invention, the copolymers em~loyed
need not be limited only to two monomers such as styrene
and acrylic acid. A portion o the styrene may readily
be replaced with alkyl styrenes such as methylstyrene,
t-butylstyrene, bromostyrene, chlorostyrene and the
like; as well as acrylonitrile, methacrylonitrile,
methylmethacrylate in a proportion generally up to
about 20 weight percent of the total polymer. The
acrylic acid portion may be wholly or partially re-
placed with methacrylic acid, itaconic acid and thelike.
Blowing agents useful in the practice of the
present invention include sodium bicarbonate, magnesium
carbonate, ammonium carbonate, and zinc carbonate in a
proportion of 0.5 to 20 parts by weight per hundred
parts by weight of polymer, and combinations of sodium
bicarbonate with sodium metho~ide with hydrocarbons or
fluorocarbons.
Also useful in the practice of the present
invention are sodium carbona~e monohydrate, zinc aceta~e
dihydrate, zinc carbonate, ammonium carbonate, magnesium
carbonate hydrates incIuding basic magnesium carbonates.
Such foaming agents again may be used alone or in
combination with hydrocarbons or fluorocarbons. Suitable
volatile fluid foaming agents are well known in the
art.
C-27,652A-F -4-
--5--
Desirably the density of the ~oam in accor-
dance with the invention is from about 0.5 to about 8
pounds per cubic foot and preferably in the range of
about 1 to 5 pounds per cubic foot. Desirably the cell
size of the foam is from about 0.1 to about 5 millimeters
and advantageously from about 0.1 to about 2.5 millimeters.
Suitable styrene-acrylic acid Gopolymers for
the practice of the present invention are provided by a
coil polymerization technique set forth in u.S~ Letters
Patent 3,035,033 to W. K. Schweitzer. A like procedure
can be used to prepare other copolymers for the practice
of the present invention.
Generally, preparation of foam in accordance
with the present invention is accomplished by intimately
admixing particulate resin with the desired particulate
blowing agent, for example a styrene-acrylic acid resin
having a particle diameter of about 0.1 inch (0.25 cm)
and powdered sodium bicarbonate. In order to provide
uniform admixture it is often desirable to apply to
the resin an adhering aid such as a 1:1 by weight mix-
ture of dibutylphthalate and alphamethylstyrene.
Usually, the particulate resin if the resin is placed
into a suitable dry blender, the adhering aid added,
the ~aterial tumbled for a length of time generally
known only to those familiar with the particular dry
blender, the powdered foaming agent such as sodium
bicarbonate and then the added mixture further
tumbled to provide a dispersion of sodium bicarbonate
over a surface of the resin and because of the presence
of the adhered aid, stratification of th~ resin of
sodium bicarbonate does not occur under normal handling
conditions. The dry blend of resin and foaming agent
C-27,652A-F -5-
.
.
~7~X~
--6--
is then passed to an extruder whexe it is heat plasti-
fied, usually at a temperature of about 250C, thoroughly
mixed, cooled and extruded into a zone of lower pressure
where it foams and cools to a self-supporting shape.
Generally, it is de~irable to maintain the
heat plastified foaming agent containing resinous
composition under sufficient pressure that foaming is
prevented until the heated mobile gel is exposed to
atmospheric pressure. The preparation o~ foams such as
foam plank is well known and is set forth in the following
U.S. Letters Patents: 2,669,751; 2,740,157; 2,838,801;
3,751,377; 3,817,669; 3,954,929; 3,897,528; and 3,914,085;
the preparation of foamed sheet by extrusion is disclosed
in the following U.S. Letters Patent: 2,917,217;
3,151,192; 3,64~,462; 3,311,681; 3,391,051; 3,560,600.
All molecular weights are determined by gel permeation
chromatography.
The invention is further illustrated but not
limited by the following examples.
Employing a 3/4 inch (1.91 cm) extruder having
a feed zone heated to a temperature of about 210C, an
intermediate zone heated to about 180C, and a die heated
to about 150C, a first series of foam samples were pro-
duced utilizing a styrene-acrylic acid copolymer containing
8.0 weight percent acrylic acid and having a molecular
weight of about 260,000 gram moles; varying quantities
of sodium bicarbonate were employed as blowing agent
and varying screw speeds were utilized.
A second series of samples were prepared
using styrene-acrylic acid copolymer of abou~ 8 weight
C-27,652A-F -6-
.
,
--7--
percent acrylic acid, the remainder styrene and having
a molecular weight of 210,000 gram moles. Die temperature,
die pressure and screw speed were recorded; foam samples
were gathered, aged in air for a period of about a week
and the external skin removed prior to determining the
foam density which is recorded in pounds per cubic
foot. Cell size was measured using the procedure ASTM
D 3576 and the percentage of open cells was determined
by ASTM D 2856-A and the heat distortion temperature
was determined by modified ASTM Test D 2126-75. This
test employs a one hour exposure at each temperature
and the heat distortion temperature is the maximum
temperature giving a linear dimension change of less
than two percent. The results are set forth in Table I
wherein the following abbreviations are employed:
SAA Styrene acrylic acid copolymer
pph parts by weight per hundred parts of
polymer
C degrees Centigrade
rpm revolutions per minute
pcf pounds per cubic foot
mm millimeters
Temp. Temperature
C-27,652A-F -7-
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C-27, 652A-F -8-
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For purposes of comparison a pol~,Tstyrene
having a weight average molecular weight of about
200,000 gram moles was treated in a generally similar
manner. The results are set forth in Table II.
C-27,652A-F -9-
--10--
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C-27, 652A-F -10-
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Results show that a lower density foam having a
substan~ially closed cell structure and a higher heat
distortion temperature is achieved by expanding styrene/-
acrylic acid copolymer with sodium bicarbonate. On the
other hand, polystyrene is not expanded to a low density
foam by sodium bicarbonate and the polystyrene foam has a
high open cell content over the entire range of sodium
bicarbonate level.
A styrene-maleic anhydride copolymer containing
about 20 pexcent maleic anhydride polymerized therein,
with a solution viscosity of 5.6 centipoise at 25C in a
10 percent methylethylketone solution was foamed employing
sodium bicarbonate as well as a styrene-acrylonitrile
polymer which contained about 75 weight percent styrene
with 25 weight percent acrylonitrile were foamed for
comparative purposes. The styrene-maleic anhydride
copolymer being designated by the abbreviations SM~ and
styrene-acrylonitrile polymer, by SAN. These styrene
copolymers do not produce a low-density closed cell foam
as shown in Table III. From the results, it appears that
the response of the styrene-acrylic acid copolymer to the
sodium bicarbonate blowing agent is uni~ue.
C-27,652A-F
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A series of extrusions were made using an
8 percent acrylic acid, 92 percent styrene copolymer
having a molecular weight of about 210,000 gram moles
and varying levels of triclorofluoromethane (F-11) and
varying levels of sodium bicarbonate. The results are
set forth in Table IV.
C-27,652A-F -13-
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C-27, 652A-F -14-
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A similar experiment employing a volatile
fluid foaming agent was performed for comparative
purposes utilizing polystyrene and an 80/20 parts by
weight mixture of trichlorofluoromethane/pentane with
varying levels of sodium bicarbonate. The results are
set forth in Table V.
C-27,652A-F -15-
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C-27, 652A-F -16-
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A number of mixtures containing varying
quantities of sodium methoxide and sodium bicarbonate
were extruded to form foams with a copolymer of 8
weight percent acrylic acid and the remainder being
styrene having a weight average molecular weight of
about 210,000 gram moles. The results are set forth
in Table VI.
C-27,652A-F -17-
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C-27, 652A-F -18-
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--19--
A variety of other materials were extruded
with a copolymer of 8 weight percent of acrylic
acid and the remainder being styrene. The polymer
had a molecular weight of about 210,000 gram moles.
The results are set forth in Table VII.
C-27,652A-F -~19-
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C-27, 652A-F -21-
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Note that of the sodium carbonate, sodium
carbonate monohydrate and zinc carbonate, sodium car-
bonate and sodium carbonate monohydrate gave satisfactory
foams while with the addition of 7.5 parts per hundred of
trichlorofluoromethane, all three compounds work as an
effective secondary blowing agent.
A series of extrusions were performed e~mploying
styrene-acrylic acid copolymers of varying acrylic acid
content and varying sodium bicarbonate content. The
results are set forth in Table VIII which establishes
that good foams of low density and reasonable open cell
content can be obtained over a wide range of composi-
tions.
C-27,652A-F -22-
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C-27, 652A-F -23-
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-24-
A 8 weight percent acrylic acid styrene
copolymer was foamed under a variety of conditions
and ammonium bicarbonate levels with trichlorofluoro-
methane and ethyl chloride. The results are set forth
in Table IX, from which it can be seen that very little
bicarbonate is equivalent to a subs-tantial quantity of
the volatile fluid foaming agent.
C-27,652A-F -24-
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C-27, 652A-F -25-
-26-
In a manner similar to the foregoing illus-
tration, varying quantities of hydrated magnesium
carbonate were evaluated alone and in combination with
trichlorofluoromethane, (8 weight percent acrylic acid
resin, the remaining being styrene). The results are
set forth in Table X.
C-27,652A-F -26
--27--
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C-27, 652A-F -27-
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-28-
Foamed sheet was prepared using a one-inch
extruder and tubing die wherein the tube was inflated
with air to provide a foamed sheek of a desired thick-
ness. The die diameter was 1-1/4 inches and the die
gap was 0.025 inch. The blowing agent used was varying
amounts of sodium bicarbonate. The copolymer employed
was of styrene and acrylic acid which contained about
8 weight percent acrylic acid, the remainder being
styrene. The polymer was extruded at about nine
pounds per hour. The screw speed and temperatures
were adjusted for optimum results. The results are
set forth in Table XI.
C-27,652A-F -28-
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C-27, 652A-F -29-
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~ mploying the apparatus of the previous
illustration, foam was prepared from a copolymer of 92
weight percent vinyl toluene and 8 weight percent
a~rylic acid. The vinyl toluene was about 60 weight
percent meta-isomer and 40 weight percent para-isomer.
The polymer had a molecular weight of about 180,000
gram moles; 7 parts by weight of sodium bicarbonate
were employed as blowing agent to 100 parts by weight
of the resin. The die temperature was 150C, screw
speed was 30 revolutions per minute. The resultant
foam had a density of 4.54 pounds per cubic foot; the
cell size was about 0.45 millimeters and was 21.2
percent open cell. For a comparison, a homopolymer of
paravinyl toluene having a molecular weight of about
300,000 gram moles was similarly treated. The foam
with skin had a density of 6.11 pounds per cubic foot,
cell size of 0.62 millimeters, and was 37.8 percent
open cell.
In a manner similar to the foregoing illu-
strations, other foams are readily prepared employingsodium bicarbonate, hydrated magnesium carbonate, zinc
diacetate monohydrate alone or in combination with a
volatile fluid foaming agent to prepare foam plank or
foam sheet when the hereinbefore described styrene-acrylic
acid, styrene-methacrylic acid or styrene-itaconic acid
vinyl toluene acrylic acid copolymers are utilized.
C-27,652A-F -30-
