Film forming SGP

Film forming starch-hydrolyzed polyacrylonitrile graft copolymer and latex composition.

This invention relates to absorbent film forming compositions. More 
particularly, this invention relates to combinations of starch-hydrolyzed 
polyacrylonitrile graft copolymer and a latex selected from nonionic or 
anionic latices. When dried from aqueous dispersions, this combination 
forms films which adhere to fabrics or other substrates while retaining 
the absorbency of the starch-hydrolyzed polyacrylonitrile graft copolymer. 
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, Ill. 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. 3,035,099 
shows 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 it 
weight. Washing the copolymer before drying with alcohol increases its 
absorbency to 800 to 1000 times its weight. 
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. 
Some of the major problems in using the copolymer is that the dry copolymer 
films are extremely brittle and adhere poorly to substrates. The copolymer 
in powder form is difficult to hold in position. 
SUMMARY OF THE INVENTION 
It has now been found that from aqueous dispersions of starch-hydrolyzed 
polyacrylonitrile graft copolymers and an anionic or non-ionic latex, 
films can be cast which vary in handleability from flexible to brittle. In 
addition these films readily adhere to substrates such as fabrics. 
The composition useful in making absorbent adhesive film comprises about 2 
to 98% by weight starch-hydrolyzed polyacrylonitrile graft copolymer and 
about 2 to 98% by weight acrylic, styrene, vinyl, or butadiene type latex. 
The components are dispersed in water. The amount of water is not critical 
inasmuch as it is a suspending vehicle and during drying evaporates away 
from the resulting film. 
DETAILS OF THE INVENTION 
By the term latex is meant a heterogeneous fluid composed of small globules 
or particles of natural or synthetic rubber or plastic suspended in a 
continuous aqueous phase. The anionic or non-ionic character of latices is 
determined by the anionic or non-ionic nature of the emulsifier used to 
maintain the globules or particles in suspension. Examples of anionic 
emulsifiers are sodium alkyl ether sulphate, sodium salt of alkylauryl 
polyether sulfonate, sodium salt of alkylauryl polyether sulfate, 
phosphate surfactant potassium salt, dioctyl sodium sulfosuccinate, sodium 
high ethoxy ether sulfate, and sodium lauryl sulfate. 
Examples of non-ionic emulsifiers include a series of compounds formed by 
addition of propylene oxide to an alcohol, followed by the addition of 
ethylene oxide. Examples of the results are polyethylene glycol ether of 
linear alcohol, nonylphenol polyethylene glycol ether, and octyl-phenoxy 
polyethoxy ethanol. 
Examples of monomers commonly polymerized to form polymers suspended in 
latices are styrene, methyl methacrylate, butylacrylate, acrylic acid, 
vinyl acetate, dibutyl maleate, combinations of stearic acid and 
butadiene, stearic acid and acrylic acid. The latices may be the self 
cross-linking type, the type to which a cross-linker is added, or a 
noncross-linking type. Useful latices are those having glass transition 
points between about 20.degree. F. to 110.degree. F. 
The blend of starch-hydrolyzed polyacrylonitrile graft copolymer and the 
latex can be obtained by mixing the components together. The 
starch-hydrolyzed polyacrylonitrile graft copolymer can be placed in a 
blender with about 20 to 40 times its weight of water and mixed until the 
copolymer is dispersed in the water and the dispersion has a smooth 
appearance. The latex can then be added slowly and mixing continued. 
Generally a homogenous white color indicates the dispersion is 
sufficiently uniform for the purposes of making absorptive films. The 
dispersion is then spread onto a surface such as paper, plastic, or fiber 
and dried. Drying can be conducted at temperatures from about 10.degree. 
C. to 110.degree. C. for a period of about 10 minutes to several days. The 
dried film or coating exhibits greater absorbency than films of 
starch-hydrolyzed polyacrylonitrile graft copolymer alone. 
The handleability of the final films varies from very flexible to brittle 
depending upon the glass transition point of the latex used. For example, 
acylic latices having the following compositions: 
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Parts by Weight 
Sample No. I II III 
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Deionized Water 57.17 57.17 57.17 
Sodium alkyl ether sulphate anionic 
liquid, 25% conc. 3.05 3.05 3.05 
Lauryl mercaptan (chain transfer agent) 
1.15 1.15 1.15 
Ammonium persulfate (polymerization 
catalyst) 0.19 0.19 0.19 
Ethyl acrylate 20.83 13.85 6.94 
Methyl methacrylate 
13.85 20.83 27.74 
Acrylic acid 3.51 3.51 3.51 
Formalin (Activator for catalyst) 
0.25 0.25 0.25 
Glass transition point (tg) 
18.degree. C. (64.degree. F.) 
40.degree. C. (104.degree. F.) 
0.degree. C. (32.degree. F.) 
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display the following properties. Sample I which is also shown in Example 
II produces a brittle film when incorporated with starch-hydrolyzed 
polyacrylonitrile graft copolymer. Sample II produces a very hard and 
brittle film with the copolymer. Sample III produces a soft film with the 
copolymer. Conversely the acrylic copolymer latex sold under the tradename 
Rhoplex AC-388.RTM. by Rohm and Haas Company, believed to contain methyl 
methacrylate, butyl acrylate and acrylic acid, produces a flexible film as 
shown in Example I. 
The films shown below in Examples I through IV all adhered to the substrate 
when cast on fabric. In addition, the films when submerged in water 
absorbed approximately the same amount of water as the starch-hydrolyzed 
polyacrylonitrile graft copolymer component absorbed alone.

EXAMPLE I 
Starch-hydrolyzed polyacrylonitrile graft copolymer in an amount of 8.333 
g. on an as is basis was dispersed in about 250 ml. water by mixing in a 
blender until smooth. To this was slowly added 8.334 g. of nonionic 
acrylic latex, sold under the tradename Rhoplex AC-388.RTM. by Rohm and 
Haas. Mixing was continued during and after the addition of the acrylic 
emulsion until the blend had a homogeneous white color. The mixture was 
spread in a 50 mil film on a tetrafluoroethylene cloth using a Boston 
Bradley Adjustable Blade. 
One portion of the film was dried for three hours at a temperature of 
100.degree. F. and another portion was dried for four days. Both portions 
were flexible and appeared to be very much alike. Both portions could be 
rolled up and placed in a sample bottle. The films appeared to hydrate and 
swell rapidly in deionized water. They were both cloudy in appearance. 
EXAMPLE II 
Following the procedure of Example I, anionic latex shown on page 4 of the 
specification was combined with starch-hydrolyzed polyacrylonitrile graft 
copolymer. The film appeared flexible before completely dry but overnight 
became brittle and broke up when placed in a sample bottle. 
EXAMPLE III 
Following the procedure set out in Example I, a film was made from 
starch-hydrolyzed polyacrylonitrile graft copolymer and an acrylic 
emulsion slurry sold under the tradename HA-8 by Rohm and Haas Co. 
Starch-hydrolyzed polyacrylonitrile graft copolymer in an amount of 8.333 
grams on an as is basis were slurried in 250 ml. of deionized water in a 
one quart blender. To the slurry was added 9.17 g. of the acrylic 
emulsion. A free film was cast on tetrafluoroethylene sheeting with a 
spreader bar with an 0.05 inch nip. The film was dried overnight at a 
temperature of 100.degree. F. The dried film was flexible enough to roll 
up with some cracking. 
EXAMPLE IV 
Following the procedure of Example I, two films were made using two 
different acrylic latices: Rhoplex B-5.RTM. and Rhoplex B-15.RTM. sold 
under those tradenames by Rohm and Haas Co. 
The ingredients used are listed below: 
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Components Sample 1 Sample 2 
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Water 250 ml. 250 ml. 
Rhoplex B-15.RTM. solids 
4.17 gm. 
Rhoplex B-5.RTM. solids 4.17 gm. 
Graft Copolymer 
8.33 gm. 8.33 gm. 
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The starch-hydrolyzed polyacrylonitrile graft copolymer was mixed in 250 
ml. of deionized water in a one quart blender. Care was taken to maintain 
minimum aeration. The acrylic latex was added and mixing was continued. 
The respective films were then cast on tetrafluoroethylene sheets with an 
0.05 inch draw down bar. The films were dried overnight at a temperature 
of 100.degree. F.