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Description  |
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This invention relates to a resilient starch graft polymer-polyhydric
alcohol product. A resilient, soft, shock absorbent type material is
formed by heating a mixture of a starch-hydrolyzed polyacrylonitrile
copolymer dispersed in a polyhydric alcohol such as glycerol. The material
is useful for seat pads, artificial limb pads, toys and other applications
where resilient, soft, shock absorbent or foam like type materials find
utility.
BACKGROUND OF THE INVENTION
Starch-hydrolyzed polyacrylonitrile graft copolymers exhibiting the
capacity to absorb from about 300 to 1000 times their weight of deionized
water are known at this time. The development of these compositions was
carried out by the Northern Regional Research Laboratory, Peoria,
Illinois. The starch-hydrolyzed polyacrylonitrile graft copolymer is
produced by exposure of starch, either gelatinized or ungelatinized, to a
catalyst such as ceric ammonium nitrate which acts as a catalyst to
generate free radicals in the starch chain. Polyacrylonitrile chains
become attached to these free radicals by copolymerization. A wide range
of substitution in these copolymers is known in the art. For example, U.S.
Pat. No. 3,935,099 and the divisional applications thereof, now U.S. Pat.
Nos. 3,981,100, 3,985,616, and 3,997,484, show the preparation of
copolymers in which the starch to polyacrylonitriles molar ratios range
from 1:1.5 to 1:9. The variations in molar ratio of the components of the
copolymer is not critical to the practice of this invention. The resulting
material is then saponified in sodium hydroxide to hydrolyze the
polyacrylonitrile chains to carboxy amide and alkali metal carboxylate
groups mixed with metal salts. Drying the hydrolyzed material can be
accomplished by tumble air drying or vacuum drying. After drying, the
material can absorb about 300 to 400 times its weight. Washing the
copolymer before drying with alcohol increases its absorbency to 800 to
1000 times its weight.
These copolymers are now commercially available one of these being sold
under the trademark SGP by Henkel Corporation. In addition, the product is
sometimes referred to as "Super Slurper". The copolymer can be made as
film, flakes, powder or mat. These forms take up water, swelling but not
dissolving and hold it in expanded duplications of their own dry shapes.
Films extend and thicken in all dimensions. Powders become piles of water
textured like crushed ice. A flake expands to a clear, angular piece of
water. The swollen forms shrink in dilute acid, expand again in dilute
alkali solution. They also shrink as they dry and expand again when
absorbing water.
The copolymer, with these properties, can be mixed with or coated on a wide
variety of materials including, for example, sand, straw, sawdust, seeds
and roots, natural or synthetic fibers, flour, gelatin, and starch. It can
hold water in soils, animal bedding and kitty litter, toweling and
diapers, bandages, surgical pads, and dental absorbents.
SUMMARY OF THE INVENTION
It has now been discovered that starch-hydrolyzed polyacrylonitrile graft
copolymer when dispersed in a polyhydric alcohol, such as glycerol,
combines to form a resilient, soft, shock absorbent type material after
heating. The product contains about 5% to 60% by weight of the starch
graft copolymer and about 95% to 40% by weight of the polyhydric alcohol
based on the total weight of graft copolymer and polyhydric alchol.
DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS
The starch-hydrolyzed polyacrylonitrile graft copolymers are well known and
commercially available as indicated in the "Background of the Invention"
above. In the examples to follow the product employed was the commercially
available product SGP 502S which is typically a dry powder having a
moisture content in the range of about 3-6% by weight, a methanol content
of about 1% by weight and a fluid absorbency of a 1% saline solution of
about 80-90%. The powder is available in varying granulations, the
granulation of the material used in the examples to following being a -100
mesh.
The commercial product may also be described generally as a polymer
composed of a naturally occurring polymer (starch) and a synthetic polymer
(acrylamide and alkali metal acrylate). Proportions of starch and acrylic
polymer are about 2:3 while the proportion of acrylate and acrylamide are
about 3:1.
The polyhydric alcohols employed are those commonly referred to as the
sugar alcohols which bear a close relationship to the simple sugars from
which they are formed and from which their names are often derived. These
polyols contain straight carbon chains in which each carbon atom bears a
hydroxyl group. The sugar alcohols may also be defined by the general
formula:
HOCH.sub.2 (CHOH).sub.n CH.sub.2 OH where n is 2-5.
Among these alcohols are glycerol, erythritol, xylitol, sorbitol, mannitol
and dulcitol with glycerol, erythritol, xylitol and sorbitol being most
preferred or desirable for the purposes of this invention.
Based on the total weight of the starch graft copolymer and the sugar
alcohol, the product will be prepared generally using about 5-60% of the
starch graft copolymer and about 95-40% of the polyhydric alcohol. This
will depend somewhat on the particular sugar alcohol employed. More
desirably about 10 to 40% starch graft copolymer and 90 to 60% sugar
alcohol is employed with the preferred amounts being about 20% starch
graft polymer and 80% sugar alcohol.
The product is prepared by dispersing the starch graft polymer in a sugar
alcohol, such as glycerol, in the desired weight ratio and heating above
room temperature (about 23.degree. C.) up to temperatures of 120.degree.
C. A soft, resilient, though sometimes sticky, material results after
heating which is useful for seat pads, artificial limb pads, toys and
other applications where resilient, soft, shock absorbent or foam-like
materials find utility.
In the following examples, all parts and percentages are by weight unless
otherwise indicated.
EXAMPLE I
Eighty (80) grams of glycerol was weighed into a 150 ml. beaker to which
was added 20 grams of a starch-hydrolyzed polyacrylonitrile graft
copolymer (SGP.RTM. 502S). The copolymer and glycerol was stirred with a
glass mixing rod and the mixture placed in a forced air oven set at
80.degree. C. overnight. Upon initial mixing the mixture took on a
greenish tint. After heating the mixture was a tough, rubbery, sticky
mass.
EXAMPLE II
In this example mixtures of varying amounts of the starch graft copolymer
and glycerol were studied. Mixtures were prepared in beakers using a
stirring rod as follows:
______________________________________
Starch Copolymer
Glycerin
Sample (grams) (grams)
______________________________________
1 20 180
2 40 160
3 60 140
4 80 120
5 50 50
6 30 20
7 40 10
______________________________________
All of the mixtures were heated to 90.degree. C. for 2 hours and allowed to
cool to room temperature. Sample 1 settled out before it could set. The
material in the bottom of the beaker had the soft, resilient sticky
characteristics. Samples 2, 3 and 4 were sticky, rubbery mats, sample 2
being the softest, stickiest and most resilient. Sample 4 was hard and
barely sticky. Sample 5 was a chunk of consolidated granules which could
be broken up into sticky granules. Samples 6 and 7 were granular materials
which tend to stick together and not flow. When placed in water it does
not block but absorbs slowly.
EXAMPLE III
One hundred (100) grams of starch graft copolymer were added to 400 grams
of glycerol in a 1 quart blender cup. To this was added 5 grams of
paraformaldehyde (5% based on the starch copolymer.) Agitation was
continued until all ingredients were thoroughly mixed. The mixture was
poured into a dish coated with a mold release agent and placed in a forced
air oven at 80.degree. C. for 2 hours. The product had the same properties
as that of Example I i.e. sticky and rubbery with slow hydration in water.
The foregoing was repeated using 25 grams of paraformaldehyde. After 2
hours at 80.degree. C. the product was rubbery but had much less stretch
and snapped if pulled too far. The product was placed in an oven at
110.degree. C. for 2 hours after which the oven was turned off and the
product left overnight. The next morning the product was a dense, smelly
foam which has expanded in every dimension by an estimated 10-20%. When
placed in water it absorbed without swelling and produced a transparent,
colorless, brittle gel.
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