2,810,659
`G. K. GREMINGER, JR., 1:-rm.
`Oct 22. 1957
`THERMOPLASTIC COMPOSITIONS OF WATER—SOLUBLE CELLULOSE ETHERS
`
`Filed Nov. 25, 1953
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`INVENTORS
`
`George K 6/-em Inger; Jr‘.
`M//es A. VI/ea;/er
`
`BY
`
`ATTORNEYS.
`
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`

`United States Patent Office
`
`2,810,659
`Patented Oct. 22, 1957
`
`
`2,810,659
`
`THERMOPLASTIC COMPOSITIONS OF WATER-
`SOLUBLE CELLULOSE ETHERS
`George‘ K. Greminger, Jr., Midland, and Miles A. Weaver,
`Ithaca, l\_/lich., assignors to The Dow Chemical Com-
`pany, Midland, Mich., a corporation of Delaware
`
`Application November 25, 1953, Serial No. 394,326
`6 Claims.
`(Cl. 106-181)
`
`This invention relates to thermoplastic, water-soluble
`compositions of certain cellulose ethers.
`Methods for fabricating useful articles from water-
`soluble cellulose ethers have been limited to casting and
`dipping from aqueous solutions. Because of the unique
`solubility characteristics of those ethers many difficulties
`arose when it was ‘attempted to use such methods. For
`example, the temperature of the solution had to remain
`below the gel point of the cellulose’ ether during the
`shaping operation. Another object was that the amount
`of cellulose ether in solution had to be restricted, be-
`cause the viscosity of the solution had to be low enough
`for casting or dipping operations.. A still further objec-
`tion was the difliculty in dissolving suflicient amounts of
`the higher viscosity grades of the ethers. Therefore, so
`that the cellulose ethers may be used in a wider variety
`of applications for which their properties are ideally suit-
`ed, it has long been desired to find a thermoplastic water-
`soluble cellulose ether composition which could be ther-
`mally fabricated. One such composition has been dis-
`closed by Silvernail
`in U. S. Patent 2,602,755. That
`composition consisted of a water-soluble -cellulose ether,
`propylene glycol, and glycerine in certain stated propor-
`tions.
`
`is an object of this invention to provide water-
`It
`soluble compositions of cellulose ethers, -which composi-
`tions are capable of being thermally fabricated.
`It has now been found that thermoplastic compositions
`may be prepared by mixing or blending certain water-
`soluble cellulose ethers with a plasticizer consisting of
`a mixture of an alkylene glycol and certain esters of
`citric acids as will be later -described. Although these
`compositions are especially well .adapted for thermal fab-
`rication,
`they may also be used in conventional casting
`and dipping operations.
`The cellulose ethers that are useful in the compositions
`of this invention are water-soluble alkyl, hydroxyalkyl,
`or alkyl hydroxyalkyl cellulose ethers in which the alkyl
`group may contain from 1
`to 3 carbon atoms and in
`which the hydroxyalkyl group may contain from 2 to 3
`carbon atoms. Of particular usefulness are methyl cel-
`lulose, hydroxypropyl cellulose, and methyl hydroxypro-
`pyl cellulose.
`It is no-t critical in the compositions of this invention
`that the aforementioned ethers exhibit thermoplasticity in
`themselves. The chief requirement for use in this inven-
`tion, besides the previously mentioned structural limita-
`tions,
`is water-solubility.
`It is well-known that methyl
`cellulose, and other cellulose ethers which are soluble in
`aqueous media, differ in their solubility properties de-
`pending on the extent to which they are etherified. The
`least etherified products are soluble only in dilute alkaline
`media, and often only at low temperatures. The some-
`what more highly etherified materials are soluble in
`water.
`In a few cases the fully etherified compounds
`become insoluble in water and are soluble only in or-
`ganic solvents. Also, certain alkyl hydroxyalkyl cellulose
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`ethers, such as those described in our copending applica-
`tion Serial No. 394,484, filed November 25, 1953, are
`soluble in both aqueous and organic media.
`Any of
`the commercially available viscosity grades
`of these cellulose ethers may -be employed. The viscosity
`grade used will depend chiefly on the properties desired
`in the fabricated article and on other practical considera-
`tions such -as
`the length of time required to blend the
`ethers with the plasticizers. The higher the intrinsic vis-
`cosity of the cellulose ether,
`the less fluid will be the
`composition and the longer will be the time required to
`mix’ in the plasticizer.
`the useful plasticizers for
`As previously mentioned,
`the compositions of this invention are mixtures of alkyl-
`ene glycols with certain‘ esters of citric‘ acid. Any alkyl-
`ene glycol or polyalkylene glycol with a degree of poly-
`merization no greater than‘ 4% may be used in accordance
`with this invention. Typical examplesof such glycols as
`ethyleneglycol, diethylene glycol, triethylene glycol, tetra-
`ethylene glycol, propylene glycol, tripropylene glycol, n-
`butylene glycol 1,2, n-butylene glycol’ 2,3, glycerine, pen-
`tanediol 2,4 and hexanetriol 1,2,6. Substituted alkylene
`glycols may also be employed. Thus, 2-amino, 2-ethyl-
`propanediol 1,3, and 2-ethoxymethyl 2,4-dimethyl pen-
`tanediol 1,5, are also useful.
`The esters which are suitable for use in" this inven-
`tion are those trialkyl esters of an acid selected from the
`group consisting of citric acid and acetylcitric acid in
`which each alkyl group contains no more than 6 carbon
`atoms. As typical examples of useful esters may be men-
`tioned the triethyl,
`tributyl, and trihexyl esters of both
`citric and acetylcitric acid.
`The proportions of the elements that make up the
`compositions are illustrated as being within the shaded
`area on the annexed drawing, in which apex A repre-
`sents the alkylene glycol, apex B represents the ester of
`citric acid and apex C represents the cellulose ether.
`It
`can be seen that the amount of alkylene glycol which
`may be used may vary from 17 to 51 percent, the amount
`of citric acid ester from 8 to 32 percent, and the amount
`of cellulose ether from 34 to 72 percent. When larger
`amounts of cellulose ether are used,
`the resulting ex-
`truded strips are too stiff and when smaller amounts are
`used the plasticizer spews and the strips are too soft.
`When larger amounts of citric acid ester are used,
`the
`plasticizer spews and the strips :are hazy and when smaller
`amounts are used the strips age poorly. The amount
`that is used in any particular composition will depend
`on the viscosity grade of the cellulose derivative, and on
`the intended use of the composition.
`It should be ob-
`vious that when the very high viscosity grades of cellu-
`lose ethers (4000 centipoises or higher) are used, high
`concentrations of the cellulose ether are impractical be-
`cause the resulting solutions are so viscous that
`they
`cannot be easily worked. Also, the fluidity of the plasti-
`cized composition that is necessary varies with the type
`of fabricating operation. For casting and dipping opera-
`tions, the solutions must have greater fluidity than with
`most thermal operations, such as injection molding or ex-
`-trusion. When reference is made herein to the viscosity
`grade of the cellulose ether, this is the viscosity in centi-
`poises of a 2 percent solution of that ether by weight in
`water at 20° C.
`’
`
`The compositions of this invention are an improve-
`ment over the previously known compositions contain-
`ing propylene glycol and glycerine because of the in-
`creased compatibility of the citrates as compared to glyc-
`erine. This increased compatibility gives fabricated ar-
`ticles having greater clarity, flexibility, and dimensional
`stability, and -lower plasticizer loss on aging. Also high-
`er ratios of citrates to propylene glycol than of glycerine
`Mylan v. Qualicaps, |PR2017—OO203
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`

`2,810,659
`
`3
`to propylene glycol can be employed where soft, flexible
`articles are desired.
`The compositions of the invention will be further de-
`fined by the following illustrative examples.
`Example 1
`
`A composition was prepared consisting of 40 parts by
`weight of a water-soluble methyl hydroxypropyl cellu-
`lose (100 cps. viscosity grade), 45 parts by weight of
`propylene glycol, and 15 parts by weight of triethyl ace-
`tylcitrate. The mixture was heated to 140° C. with agi-
`tation to effect solution. The resulting composition was
`uniformly clear with no evidence of gels.
`When the above composition was subjected to extru-
`sion conditions, a clear flexible strip was obtained.
`In a like manner similar compositions were prepared
`using diethylene glycol, n-butylene glycol 1,2, and pen-
`tanediol 2,4 in place of the propylene glycol. These com-
`positions could be extruded to produce clear and flexible
`strips or sheets.
`
`Example 2
`
`Similar compositions to those of Example 1 were pro-
`duced using trihexyl citrate in -place of the tributyl acetyl-
`citrate. The compositions could be extruded into a flex-
`ible strip from which pharmaceutical capsules could be
`prepared by vacuum drawing the strip in a cavity mold.
`The capsules compared favorably with the common gela-
`tin capsules.
`In a similar manner compositions were prepared using
`water-soluble methyl cellulose (50 cps. viscosity grade)
`and hydroxyethyl cellulose in place of the methyl hy-
`droxypropyl cellulose. The compositions were compres-
`sion molded into clear sheets from which capsules could
`be prepared by vacuum drawing the strip in a cavity
`mold.
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`We claim:
`1. A thermoplastic composition consisting of (a) from
`34 to 72 percent of a water-soluble cellulose ether select-
`ed from the group of alkyl cellulose, hydroxyalkyl cellu-
`lose, and alkyl hydroxyalkyl cellulose in which the alkyl
`group contains from 1
`to 3 carbon atoms and the hy-
`droxyalkyl group contains from 2 to 3 carbon atoms,
`(b) from 17 to 51 percent of an alkylcne glycol, and (c)
`from 8 to 32 percent of a trialkyl ester of an acid select-
`ed from the group consisting of citric acid and acetyl-
`citric acid in which the alkyl group contains from 1 to 6
`carbon atoms; the proportions of each constituent being
`chosen so as to be represented by any point within the
`shaded area on the annexed drawing.
`2. The composition as claimed in claim 1 wherein the
`cellulose ether is a water-soluble methyl cellulose.
`3. The composition as claimed in claim 1 wherein the
`cellulose ether is a water-soluble methyl hydroxypropyl
`cellulose.
`,
`4. The composition as claimed in claim 1 wherein the
`cellulose ether is a water-soluble hydroxyethyl cellulose.
`5. The composition as claimed in claim 1 wherein the
`ester is triethyl acetylcitrate.
`6. The composition as claimed in claim 1 wherein the
`ester is tributyl citrate.
`
`References Cited in the file of this patent
`UNITED STATES PATENTS
`
`_
`
`1,735,158
`2,322,013
`2,479,037
`2,602,755
`
`Carroll _____________ __ Nov. 12, 1929
`Gilbert _____________ __ June 15, 1943
`Chambers __________ __ Aug. 16, 1949
`Silvernail ____________ __ July 8, 1952
`
`Mylan v. Qualicaps, |PR2017—OO203
`QUALICAPS EX. 2008 — 3/3
`
`Mylan v. Qualicaps, IPR2017-00203
`QUALICAPS EX. 2008 - 3/3
`
`