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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to polyester foam materials and, more
specifically, to resilient polyester foams.
2. Description of the Prior Art
Polyesters may be broadly defined as macromolecular compounds having a
plurality of carboxylate ester groups in their skeletal structures.
Polyesters, as so defined for use herein, are to be distinguished from
other ester-containing polymers (e.g. cellulose esters, polyvinyl esters,
and polyacrylates) wherein carboxylate groups are present in substituent
entities pendant from the backbone of the polymer. Polyesters have been
known to science for many years and have been used in recent years in such
diverse applications as coatings, films, fibers, molding and casting
compounds, and as intermediates in chemical reactions. Polyester foams
based on unsaturated acids and unsaturated monomeric cross-linking
materials have also been known and used. Foams made from polyesters whose
polymeric structure is not dependent for development on unsaturation
within its substituent monomers, however, have received scant if any
attention in the past. And the same is specifically true of resilient
foams made from such polyesters.
Most polyesters finding use today are linear polymers as opposed to three
dimensional polymers. Three dimensional polymers are, of course, polymers
having cross-links between the essentially linear polymeric structures
forming the skeletal backbones of the molecules. There can be some
branching within the skeletal backbones without having a departure from
essential linearity.
Polyesters have been synthesized in the past from a variety of reactants
through the use of several reaction schemes. The most direct synthesis is
the esterification of a dicarboxylic acid with a glycol. (Dicarboxylic
acids and glycols are sometimes referred to, respectively, as dibasic
acids and dihydroxy compounds). In this scheme, the dicarboxylic
acid/glycol mixture is heated until condensation occurs. The products of
the condensation reaction are polyester and water.
Polyesters can also be prepared by ester exchange reactions.
A third general method of preparing polyesters, and the one which is most
useful in the practice of the instant invention, is the polycondensation
of polyols with acyl halides such as diacid chlorides. The products of
this polycondensation reaction are, of course, the polyester and a
hydrogen halide such as hydrogen chloride. Depending upon the physical
properties of the reactants, the acyl halide-polyol reaction is frequently
conducted in the presence of an inert solvent such as chlorobenzene or a
chlorinated biphenyl. A stream of an inert gas is frequently passed
through the reaction system to remove the gaseous hydrogen halide. It is
also possible to conduct the acyl halide polyol reaction without the use
of solvents if the reactants are low melting compounds which can form a
homogeneous mixture. In either case, it is essential that all components
of the reaction system be free of moisture since water hydrolizes the acyl
halide thereby terminating the polymerization reaction.
SUMMARY OF THE INVENTION
Stable, three dimensional polyester foams are formed by reacting together
acyl halides, polyols, and polyhydroxy cross-linking agents in the
presence of alkali metal carbonates under such conditions as to form
foams. After formation, the polyester foams can be crushed so as to
rupture membranes between cells thereby producing interconnected networks
of cells and to aid in the release of entraped gaseous hydrogen halide.
It is an object of the present invention to prepare stable, resilient
polyester foams from acyl halides, polyols, and polyhydroxy cross-linking
agents reacted in the presence of alkali metal carbonate.
It is a further object of this invention to prepare stable, resilient foam
materials based on three dimensional polyesters prepared from acyl
halides, polyols, and polyhydroxy cross-linking agents.
It is a still further object of this invention to prepare stable, resilient
foam materials wherein the relative degrees of hydrophilicity are
controlled by the nature of the reactants used to prepare the resilient
foam materials.
It is a still further object of this invention to prepare absorbent,
resilient polyester foam materials.
It is an object of this invention to prepare polyester foam materials which
can be used in place of polyurethane foam materials. It is a further
object of this invention to prepare polyester foam materials which do not
produce the undesirable level of toxic gases produced when polyurethane
foam materials burn.
It is a still further object of this invention to prepare stable,
absorbent, resilient, polyester foam materials which are pharmacologically
acceptable for use in contact with the human body.
These and other objects will become readily apparent from the Detailed
Description of the Invention which follows.
DETAILED DESCRIPTION OF THE INVENTION
While this specification concludes with claims particularly pointing out
and distinctly claiming the subject matter regarded as the invention, it
is believed that the invention disclosed herein can be better understood
from the following detailed description.
As used herein, "stable" refers to materials which retain their physical
properties upon storage at ambient and near-ambient conditions for at
least several weeks. As used herein, "resilient" refers to the ability of
a material to essentially return to its original configuration after a
deforming force is removed. As used herein, "pharmacologically acceptable"
refers to the ability of a material to be used in intimate contact with
portions of the human body, such as skin or mucous membrane, without
producing deleterious results. Unless otherwise indicated, the terms
"foam," "polyester foam," and "polyester foam material" are used
interchangeably herein and refer to cellular structures the cell walls of
which are formed from solid polymeric material derived from polyesters.
The polyester foam materials of the instant invention are prepared from a
reaction mixture comprising four components: acyl halide, polyvol,
polyhydroxy cross-linking agent, and alkali metal carbonate.
While any suitable method of preparation can be used, a preferred method
for making polyester foams is similar to that used in the well-known
one-shot method of preparing polyurethane foams. The various reaction
components are supplied at a temperature of from about 20.degree. to about
65.degree. C to a mixing head wherein they are violently agitated for from
about 0.005 to about 0.5 minute at a temperature of from about 20.degree.
to about 65.degree. C and at a pressure of from about zero to about 7.03
kilograms per square centimeter (about zero to about 100 pounds per square
inch). The foamed mixture is then discharged onto a moving belt. The foam
is allowed to cure for from about 5 to about 1,000 minutes at a
temperature of from about 20.degree. C. to about 100.degree. C. Curing can
be accelerated through the addition of energy to the foam. The cured foam
is then ready for such further processing as is dictated by the use to
which the material will be put.
A very simple and effective batch method of preparation comprises mixing
the polyol and the polyhydroxy cross-linking agent and heating the mixture
to the desired temperature. To the above mixture, in a suitable container,
is added the alkali metal carbonate with vigorous mixing. Following a
mixing period, the acyl halide is added with mixing. The resulting mass,
which can optionally be placed in a suitable container, is allowed to cure
at ambient temperature. Infra-red radiation can optionally be used to
accelerate the curing of the surface of the foam mass.
Alternatively, any two or three of the reaction components can be
prereacted, in any desired proportions, and the product of this
prereaction then reacted with the balance of the reaction components as
indicated above.
Acyl halides (sometimes called polycarboxylic acid halides) useful in the
present invention are organic compounds containing at least two -COX
radicals wherein X is a halogen atom. Preferably, the acyl halides are
dicarboxylic chlorides having the general formula CLOC-R-COCL wherein R is
an aliphatic group defined as (CH.sub.2).sub.n wherein n is greater than
or equal to three. Examples of preferred dicarboxylic acid chlorides are
glutaryl chloride, adipyl chloride, pimelyl chloride, suberyl chloride,
azelayl chloride and sebacyl chloride. The most preferred acyl halide for
use in making stable, absorbent, resilient foams which can be used to
absorb body fluids is the diacid chloride of adipic acid, adipyl chloride.
Although in general a single acyl halide will be used, the use of mixtures
of two or more acyl halides is within the scope of this invention.
Polyols are organic compounds containing a plurality of hydroxyl groups.
Two different types of polyols serving two different functions are used
herein. For convenience, one is referred to simply as "polyol" and the
other is referred to as "polyhydroxy cross-linking agent." The distinction
between the two will become readily apparent from a reading of the
following paragraphs.
As used herein, "polyol" refers to an organic molecule having at least two
hydroxyl groups and an equivalent weight of at least about 1,000,
preferably at least 1,500. Preferably, the polyol is aliphatic. These
polyols serve primarily to make up the basic skeletal structures of the
polyester of this invention.
Diols (polyol compounds containing two hydroxyl groups) suitable for use in
the instant invention are the ethylene oxide-propylene oxide-propylene
glycol polymers such as Pluracol Polyol 686 made by BASF Wyandotte of
Wyandotte, Michigan. Pluracol Polyol 686 is an ABA block copolymer
containing about 80% ethylene oxide (A) and 20% propylene oxide (B). It is
a diol having a molecular weight of approximately 5,000 and a hydroxyl
number of 22.4 (Hydroxyl number is defined as the number of milligrams of
potassium hydroxide required to completely neutralize the hydrolysis
product of the fully acylated derivative prepared from one gram of polyol.
Mathematically, the hydroxyl number of a compound is equal to 56,100 times
the number of hydroxyl groups in the compound divided by the molecular
weight of the compound.)
An example of a suitable triol (polyol compound containing three hydroxyl
groups) is the liquid ethoxylated-propoxylated glycerin sold by The Dow
Chemical Company of Midland, Michigan under the tradename XC1421. This
material has a molecular weight of about 5,000, is about 65% ethylene
oxide, and has a hydroxyl number of about 33.7.
Quadrafunctional polyols are preferred for use in the instant invention.
(As used herein, "quadrafunctional" and "trifunctional" refer to compounds
having, respectively, four and three hydroxyl groups available for
reaction.) It has been surprisingly discovered that quadrafunctional
polyols produce a polyester foam which is more resilient than that
produced from other polyols. Examples of quadrafunctional polyols are
ethylene oxide-propylene oxide block copolymers based on either ethylene
diamine or on pentaerythritol. The former are sold under the Tetronic
tradename by BASF Wyandotte. The latter, having a molecular weight from
about 4,000 to about 30,000 and an ethylene oxide content of from about
5% to about 90%, are preferred for use in the instant invention in making
absorbent, resilient polyester foams useful in catamenial tampons.
Polyols based on ethylene oxide without propylene oxide present can be
used, but such polyols generally have a melting point too high for
convenient processing. Ethylene oxide contents greater than about 60% and
less than about 90% are generally preferred.
Mixtures of polyols can be used in this invention.
As used herein, "polyhydroxy cross-linking agent" refers to a propoxylated
derivative (adduct) of a polyhydric alcohol. These polyhydroxy
cross-linking agents contain secondary available hydroxyl groups. These
propylene oxide-based materials used in the instant invention must be at
least trifunctional, preferably quadrafunctional. They should have an
equivalent weight of less than about 250. Preferably, they should have a
molecular weight of less than about 500. Especially preferred are the
propylene oxide adducts of trimethylol propane and pentaerythritol.
Suitable materials are sold under the Pluracol tradename as TP340, TP440,
PEP450 and PEP550 by BASF Wyandotte. TP340 is the tripropoxylated
derivative of trimethylol propane while TP440 is the tetrapropoxylated
derivative. PEP450 and PEP550 are the tetrapropoxylated and
pentapropoxylated derivatives of pentaerythritol. Polyhydroxy
cross-linking agents serve primarily to introduce covalent cross-links
between essentially linear portions of the skeletal structure of the
polyester foam of this invention.
Mixtures of polyhydroxy cross-linking agents as well as a single
polyhydroxy cross-linking agent can be used to produce the polyester of
this invention.
The alkali metal carbonates useful in the instant invention are well known
inorganic compounds. Preferably, reagent grade sodium carbonate is used.
It has been discovered that some samples of technical grade sodium
carbonate will not function properly in this invention. However, heating
these samples to about 700.degree. C for several minutes has been found to
convert them to properly functioning materials. Preferably, the alkali
metal carbonate is finely ground. Particularly preferred is reagent grade
sodium carbonate ground so that 100% will pass through a 400 mesh screen.
Because of the aforementioned polymerization termination action of water,
the level of moisture in the total reaction system should be maintained
below about 0.1% by weight.
Further, it has been found that inorganic bases, such as sodium hydroxide,
do not function in the instant invention in place of the alkali metal
carbonates. Among other reasons for this is the fact that they are
hygroscopic and tend to introduce excessive amounts of water into the
system.
As used herein, "reaction system" encompasses the total quantity of
reaction components used to make the polyester foams of this invention.
Acid halide index is a measure of the amount of acid halide present in the
reaction system. It is defined as 100 times the ratio of the number of
acid halide equivalents present in the reaction system to the number of
equivalents of available hydroxyls present in the reaction system. An acid
halide index of 100 indicates the presence of stoichiometric quantities of
acid halide and available hydroxyls. An acid halide index greater than 100
indicates the presence of an excess of acid halide while an acid halide
index smaller than 100 indicates the presence of an excess of hydroxyls in
the reaction system.
The acid halide index of the reaction system useful in the instant
invention should be approximately 100. Systems having an acid halide index
greater than about 98 have been found suitable. A slight excess of acyl
halide (acid halide index greater than 100) is permissible and preferable.
Thus reaction systems having an acid halide index smaller than about 108
but greater than about 100 are preferred. Acid halide indicies between
about 98 and about 108 represent systems having a substantially
stoichiometric amount of acyl halide.
The amount of acyl halide present in the reaction system has a profound
effect on the density of the polyester foam produced. It has been
demonstrated that when the acid halide level increases from about 19% to
about 21% by weight of the reaction system, while the number of
equivalents of hydroxyls present is adjusted to maintain a constant acid
halide index, the density of the polyester foam decreases from about 10
pounds per cubic foot (0.16 gram per cubic centimeter) to about 4 pounds
per cubic foot (0.06 gram per cubic centimeter). For use in catamenial
tampons, as hereinafter described, resilient foams of low density are
preferred. For other uses, of course, other densities can be more
suitable.
The amount of polyhydroxy cross-linking agent present should be from about
15% to about 80% by weight of the polyol present, preferably from about
20% to about 40%.
The amount of alkali metal carbonate present should be from about 2% to
about 150%, preferably from about 25% to about 67%, by weight of the total
amount of polyol, polyhydroxy cross-linking agent and acyl halide present.
Small quantities of alkali metal bicarbonate, such as sodium bicarbonate,
are tolerated by the system. Alkali metal bicarbonate up to a level of
about 5% by weight of the total organic materials present can be added
without adverse effect.
Mixtures of acyl halides, polyols, and polyhydroxy cross-linking agents can
be used to prepare polyester foams if one follows the general reaction
scheme described in this specification. It has been discovered, however,
that the foams so prepared are unstable after curing; they tend to liquify
during storage at ambient conditions. It has been surprisingly discovered
that the addition of alkali metal carbonate to the reaction system leads
to the formation of foams having excellent stability even during prolonged
storage. It has also been discovered that low levels of alkali metal
bicarbonate in the absence of alkali metal carbonate improve the stability
of polyester foams over that of foams made without the inclusion of either
alkali metal carbonate or bicarbonate in the reaction mixture, but the
improvement in polyester foam stability engendered by alkali metal
bicarbonate is significantly less than that engendered by alkali metal
carbonate.
Without advancing a specific theory as to the function of the alkali metal
carbonate, it can be stated that this material neither appears to enter
into the reaction as by becoming a part of the polymer structure nor
appears to function as a blowing agent. Essentially all the alkali metal
carbonate can be recovered after the polymerization reaction is complete.
The hydrophilic/hydrophobic character of the polyester foams of this
invention is determined in large part by the nature of the reactants from
which the polyester is formed. For example, when propoxylated -
ethoxylated pentaerythritol having a molecular weight of more than 15,000
and an ethylene oxide content greater than 70% is used as the polyol, the
resulting polyester is hydrophilic whereas that made with a similar polyol
having an propylene oxide content of about 90% by weight in hydrophobic.
Also, increasing the length of the aliphatic chain in the acyl halide, as
by changing from glutaryl chloride to adipyl chloride, decreases the
hydrophilicity of the resulting polyester foam. It is well within the
ability of the skilled artisan having before him the teachings of this
specification to select reactants that will yield a polyester foam
material with the hydrophilic/hydrophobic character best suited for the
use at hand.
In addition to the four required components of the reaction mixture,
additional materials can be present so long as their presence does not
interfere with the fundamental polycondensation reaction. Examples of
optional materials include nonionic surfactants useful as uncured foam
stabilizers, catalytic surfactants, pigments, flame retardant chemicals,
and the like. Pluronic L-92, a nonionic surfactant having a molecular
weight of about 3,600 and a hydroxyl number of about 31, as made by BASF
Wyandotte, is particularly useful as a catalytic surfactant. (Catalytic
surfactants contribute to the structure of polyester, and polyurethane,
foams by reducing foam cell size and promoting uniform foam cell size.)
In order to more fully describe the present invention, and not by way of
limitation, the following examples are presented.
EXAMPLE I
A mixture consisting of 400 grams Pluracol Polyol 686 (polyol) and 144
grams Pluracol TP-340 (polyhydroxy cross-linking agent) was heated in a
stainless steel vessel to a temperature of 40.degree. C. This mixture also
contained 0.1 gram Pluronic L-92 (catalytic surfactant). The heated
mixture was transferred to a cylindrical paper container 8.9 centimeters
in diameter. To the mixture in the cylindrical paper container was added
100 grams sodium carbonate of which 100% would pass through an 80 mesh
screen and 50% would pass through a 200 mesh screen. The resulting mixture
was agitated for 25 seconds with a 6.1 centimeter diameter turbine blade
mixer. At the end of the initial mixing, 151 grams adipyl chloride was
added and the total reaction composition was agitated for an additional 10
seconds. The resulting resilient polyester foam was removed from the
cylindrical paper container and subjected to infra-red radiation to hasten
the curing of the surface. The resulting resilient polyester foam had a
density of 0.045 grams per cubic centimeter.
EXAMPLE II
A mixture consisting of 397.6 grams Dow XD 1421 (polyol) and 192.4 grams
Pluracol TP-440 (polyhydroxy cross-linking agent) was placed in a
stainless steel vessel. Four grams Pluronic L-92 (catalytic surfactant)
were also added to the mixture. The procedure of Example I was followed in
making a resilient polyester foam except that the initial mixture was
heated to 45.degree. C. The quantity of sodium carbonate used in this
example was 200 grams while 155 grams adipyl chloride was used. The
resulting resilient polyester foam had a density of 0.06 grams per cubic
centimeter.
EXAMPLE III
The absorbent, resilient polyester foam made in this example was based on a
polyol which was an ethylene oxide-propylene oxide block copolymer of
pentaerythritol and which had an ethylene oxide content of 73% and a
hydroxyl number of 14. A mixture consisting of 199.9 grams of the
aforementioned polyol and 73.1 grams Pluracol PEP-450 (polyhydroxy
cross-linking agent) plus 2 grams Pluronic L-92 (catalytic surfactant) was
placed in a stainless steel vessel and heated to 50.degree. C. The warmed
mixture was transferred to a paper cylinder 8.9 centimeters in diameter.
To the mixture in the paper cylinder was added 100 grams sodium carbonate
as used in Example I and the system was agitated for 20 seconds with a 7.6
centimeter diameter six-bladed mixer. Following the initial mixing, 74
grams adipyl chloride was added to the system and mixing was continued for
10 seconds. The total reaction system was poured into a 15.2 centimeter by
22.9 centimeter rectangular container and allowed to set. After the
surface of the polyester foam had been subjected to infrared radiation for
5 minutes to reduce surface tackiness, the foam mass was crushed between
opposing rollers. The resulting absorbent, resilient, open celled
polyester foam had a density of 0.06 gram per cubic centimeter. After
comminuting and washing with water, the absorbent, flexible polyester foam
of this example was eminently suitable for use in the catamenial aggregate
absorbent body described by Schaefer in U.S. Pat. No. 3,815,601.
For some applications, it is desirable that the polyester foam be open
celled. As used herein, the term "open celled" means that the individual
cells of the foam are interconnected by open channels. Cured polyester
foam can be converted to the open celled state by subjecting it to
sufficient compressive force to reduce its volume to about 20% of its
original value. This compression tends to rupture the membranes making up
the individual cell walls. In addition to forming an interconnected
network of channels and cells, this compression and the resulting membrane
rupture facilitates the release of gaseous hydrogen halide from the cured
foam mass.
For use in catamenial tampons, it is preferred that the polyester foam be
open celled and have from about 50 to about 400 cells per linear inch.
For some applications, it is desirable that the residual alkali metal
carbonate and hydrogen halide be washed from the polyester foam mass. This
washing can be readily accomplished by reducing the foam mass to
convenient sized particles (as by chopping or cutting) and agitating these
particles in a suitable solvent such as water. In most cases, the residual
alkali metal carbonate is more than sufficient to neutralize any residual
hydrogen halide present. Following washing, the polyester foam can be
dried in any convenient, known manner that will be readily apparent to
those skilled in the art.
The novel polyester foams of the instant invention find application in
numerous circumstances where soft, resilient, absorbent foam materials are
required. For example, the comminuted and washed foam of the instant
invention can be used in the catamenial aggregate absorbent body described
by Schaefer in U.S. Pat. No. 3,815,601 which was issued on June 11, 1974,
and which is incorporated herein by reference.
Further, the novel polyester foams of the instant invention can be used in
applications where polyurethane foams are now used. Such applications
include use in surgical bandages, household sponges, furniture pads, and
the like.
EXAMPLE IV
In this example, portions of two of the reaction components are prereacted
and the prereaction product is used in the formation of a polyester foam
of this invention.
One hundred fifty grams Pluralcol PEP-450 (polyhydroxy cross-linking agent)
was mixed with 35.7 grams adipyl chloride (96% purity) for 20 seconds at
room temperature and atmospheric pressure in a 500 milliliter beaker with
a 7.6 centimeter diameter turbine blade mixer. The resulting product was
allowed to degas for one hour at room temperature. A 105.7 gram aliquot of
the reaction product was mixed with 250 grams Pluracol Polyol 747 and 2.5
grams Pluronic L-92. Pluracol Polyol 747 is an ethylene oxide-propylene
oxide block copolymer of pentaerythritol, has an ethylene oxide content of
73% and a hydroxyl number of 14, and is manufactured by BASF Wyandotte. A
286.6 gram aliquot of this last described mixture, which had been heated
to 50.degree. C in a steel beaker, was mixed with 100 grams anhydrous,
reagent grade sodium carbonate for 20 seconds in a 0.95 liter cylindrical
paper can with the hereinbefore described mixer. To the mixture in the
cylindical paper can, 57.9 grams adipyl chloride (96% purity) was added
and mixed for 10 seconds. The resulting product exhibited a cream time of
30 seconds and a rise time of 1 minute 50 seconds.
After being allowed to cure for 5 minutes at room temperature, the
resulting polyester foam was open celled (i.e. required no reticulation to
produce open cells) and had an exceedingly fine cell structure. It had a
density of approximately 0.19 grams per cubic centimeter (11.7 pounds per
cubic foot).
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