CA1137080A - Surfactant-soluble cellulose derivatives - Google Patents

Abstract

SURFACTANT-SOLUBLE CELLULOSE DERIVATIVES

Abstract of the Disclosure Cellulose ethers containing an amount of hydroxypropoyl, hydroxyethyl, or methyl radicals such that they are normally water soluble are further modified with C12 to C24 hydro-carbon radicals to a level at which they are water insol-uble. These modified ethers are soluble in surfactants and effect substantial viscosity increases in solutions of surfactants. They also are highly effective emulsifiers in aqueous systems.

Description

This invention relates to a new class of modified water-solub}e polymers~ Specif isally, it relates to such polymers which have been modif ied to a state in which they : are no longer water-soluble but retaln s31ubility and S exhibit useful properties in detergent systems.
Nonionic water-soluble cellulose ethers are employed in a wid~ variety;of applications where their viscosifying :~ powers are desired. They are widely used j e . g ., as thicken-: ers, as water retention aids, and as suspension aids in certain polymeri2ation processes, among others. For some of these applications, specific cellulose ethers are required, but for many, di~ferent ethers can be employed, depending : ~ ~:
upon price and in~many cases simply o~ the preference of the user. Widely used~ commercially available nonionic cellulose ethers include methyl cellulosel hydroxypropyl . methyl cellulose,~hydro$yethyl cellulose, hydroxypropyl cellulose and ethyl hydroxyethyl cellulose.
As is generally the oase with high polymers, better thickening and viscosifying efficiency is realized with ~;.
20 higher molecular weight cellulose ethers. Production of ~.:
: very high molecular weight materials requires the use o~
: more expensive rellulose furnishes such as cotton linters in lieu of-the more common wood pulp types.: Moreover, even when very high molecular weight furnishes are employed, the etherification process is extremely harsh on the furnish and causes signi~icant reductions in the molecular weight ~ of the cellulose. High viscosity solutions then become ~: -.~ difficult to:obtain without resorting to follow-up steps such as crosslinking. This is not a practical alternative with nonionic cellulosics since good crosslinking techniques are not known and those that are known are : ~ .: ' , ~

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troublesome and inefficient. The on]y other way presently ~nown for attaining :~ high viscosity is to use high concentrations of the polymer. This technlque is frequently ineffiGient, impractical, or otherwise undersirable.
United Sta~es patent No. 4,228,277, filed February 12, 1979, discloses water-soluble cellulose ethers of greatly increased viscosifying power, compared to known water-soluble cellulose ethers of comparable molecular weight, comprising nonionic cellulose ethers which are further modified by substitution with specified amounts of C10 to C16 alkyl radicals. Such ethers ^ are substituted ~ith an amount of the long chain alkyl radical up to the amount which renders them water-insoluble. The thickening or viscosifying ability of these ethers on aqueous systems is increased even further in the presence of nonionic surfactants although at the higher levels of modification they are not soluble in such aqueous systems when such surfactants are presen~.
` In accordance with this invention, a class of nonionic cellulose : ::
ethers modlfied with C10 to C24 alkyl radicals have been fo~md which are water-insoluble but which are soluble in surfactants and surfactant systems.
~`~ The cellulose ethers of this invention are low to medium molecular weight cellulose ethers having a sufficient degree of nonionic substitution selected from the class consisting of methyl, hydroxyethyl, and hydroxypropyl radicals to cause them to be normally soluble and which are further substituted with a hydrocarbon radical having 10 to 24 carbon atoms in an amount sufficient to render them water-insoluble but less than about 8% by weight based on the total weight of the modified cellulose ether. The cellulose ether is preferably one whichJ prior to modifica~ion, has a molecular weight between about 20,000 and 500~000 (about 75 to 1800 D.P.~ and most preferably between about 20~000 and 80~000 ~75 to 300 D.P.).

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Cellulose ethers have heretofore been modified with small ~ .
hydrophobic groups such as ethyl, butyl~ benzyl and phenylhydroxyethyl groups.
Such modifications or such , -2a-., , ~' .

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modified products are shown in U.S. patents 3,091,542;
3,272,640; and 3,435,~27 inter alia. The~e modifications are usually effec~ed for the purpose of reducing the hydro-philicity and thus reducing the hydration rate of the cellu-lose ether. These modifiers have not been found to effectthe property improvements caused by the modifications con-templated by this invention. This is to say, there i5 no significant alteration of the rheological properties or the surface-active properties of the ether. Anotber ~odi~ica-tion of water-soluble cellulose derivatives is shown in U.S.
patents 3~824~085 and 3r96~5140 These patents disclo~e hydroxypropyl cellulose laurate and the use thereo~ for gelling hydrocarbons. The degree of substitution of the~e products is quite high and they ~re not water-soluble nor capable o~ affecting the viscosity of aqueous systems.
Any nonionic water-soluble cellulose ether can be em-ployed as the cellulose ether substrate to ~orm the products of this inventio~. Thus, e.g., hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, ethyl ~ydroxyethyl cellulose, and methyl hydroxyethyl cellulose can all be modifiedO The amount of nonionic substituent such as methyl, hydroxyethyl or hydroxypropyl does not appear to be critical so long as there is sufficient to assure that the ether is initially ~ 25 water-soIuble.
; The modified cellulose ethers of this invention are ;~ described as being water-insoluble. In the context of this invention, water~insoluble means soluble to the extent of less than 1% b~ weight or yielding a swollen gel at greater ~han 1~ concentration in water. Materials~of greater water solubility are frequently not soluble in surfactant systems and they form hazy or cloudy mixtures.
Modifier content (wt. ~) is determined using a modified Zeisel method. Ether-bound hydrophobe is cleaved by use of 35~ H~r in acetic acid. Brominated hydrocarbon reaction product i5 extracted with hexane and analyzed via a tempera-ture programmed flame ionization instrument.
The weight percent of modi~ier at which the cellulose . ;,, . :

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ether becomes water insoluble is influenced principally by the size of the long chain alkyl modifler and to a lesser extent by the molecular weight and the hydrophilicity of the cellulose ether substrate. The amount of modifier is best expressed in terms of the average number of modifiers per polymer chain~ It has been experimentally determined that or all nonionic water-soluble cellulose ethers, the rela-tionship between the amount which results in insolubility (NINS) and modifier carbon number n is defined by the formula:
log NINS = K - 0.07 ~ .005 C
The constant K varies from 1.4 to 2~1 and is a function of the hydrophilicity of the cellulo~e ether substrate. K is -~
about 1.5 to 1.8 for methyl cellulose, about 1.9 to 2.2 for hydroxyethyl cellulose and hydroxypropyl methyl cellulose.
Overall, NINS varies from about 1 to 25. A range can be calculated within this overall ranye for each water-soluble cellulose ether which is usable in the invention.
~-~Thus, for methyl cellulose ~X = 1.8) NINS is about 13 when a C10 hydrocarbon modifier is employed and about 3 when the modifier has 2~ carbon atoms. NINS for medium D.P.
hydroxye~hyl cellulose is about 25 with a C10 hydrocarbon modifier and about 5 with a C20 modifier.
Solubility in sur~actants is observed in an aqueous -~~5 solution thereof of about 5% by weight surfactant concentra-tion and greater, preferably 5 to 40% by weight solutions ~of the surfactant. ~he limits of concentration of modiied ;cellulose ether in the surfactant solution are related to the concentration of surfactant. In general, solubility appears to require a ratio of surfactant to cellulose ether of at least about 5 to 1.
;The modified cellulose ethers are soluble in all ;classes of water-soluble surfactants and aqueous solutions ~thereof. They are soluble in all nonionic, cationic, an ~--:~35 ionic and amphoteric surfactants which have water solubility .
greater than 5 grams per 100 grams water. Exemplary of sur-factant types that can be used wi~hin the various classes are the fatty acid esters of sorbitan, ethoxylated or - :
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~5--propoxylated sorbitan es~ers, ethylene and propylene glycol fatty acid esters, monoesters of ~lycerine, polyoxyethylene derivatives of lanolin, polyoxyethylene esters of resin acids, alkyl and aryl sulfonates, triethanolamine fat~y acid esters and salts, alkali metal lauryl sulfates, long chain alkyl quaternary salts, and alkali metal salts of unsatur-ated fatty acids.
The long chain alkyl modifier can be attaahed to the cellulose ether substrate via an ether, ester or urethane linkage. Preferred is the ether linkage as the reagents most commonly used to effect etherification are readily ob-~ tained, the reaction is similar to that commonly used for `~ the initial etherification, and the reage~ts are usually more easily handled than the reagents employed for modiEica-- 15 tion via the other linkages. The resulting linkage is also usually more resistant to further reactions.
Methods of preparing mixed ethers o~ cellulose, i.e., products having more than one etherifying modifier attached to the same cellulose molecule, are known to the art. The ; 20 products of this invention can be prepared via essentially the same methods. Brie-fly, the preferred procedure for pre- ;
paring the mixed ethers of this invention comprises slurry-ing the nonionic cellulose ether in an inert organic diluent such as a lowex aliphatic alcohol, ketone, or hydrocarbon and adding a solution of alkali metal hydroxide to the re-sultant slurry at a low temperature. When the ether is thoroughly wetted and swollen by the alkali, a C10 to C~4 halide, preferably a bromide, is added and the reaction is continued, with agitation, until complete. Residual alkali is then neutralized and the product is recovered~ washed with inert diluents, and dried. The etherification can al~o be e~fected with a Cl~ to C24 epoxide or halohydride but these are sometimes less reactive, less efficient.
Substantially the same preferred procedure is used to -` 35 attach the hydrocarbon modifier via the ester or urethane ~-linkage. Conventional slurry methods o~ reacting this type of modifier with cellulose ethers, i.e., without the alkali, are ineffectiv~. The alkali s~eep is required in order to :-., .

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~6--assure that the cellulose ether is swollen to the point that the modifier can react substantially uniformly on all cellu-lose ether molecules throughout. If reaction is not sub-~tantially uniform throughout the cellulose ether mass, the improved rheological properties are not realized.
Although ~he products of this invention are referred to as being "long chain alkyl qroup modified", it will be recogni2e~ that ex~ept in the case where modification is effected with an alkyl halide, the modifier iQ not a simple lony chain alkyl group. The group is actually an alpha-hydroxyalkyl radical in the case when an epoxide is used, a ; urethane radical in the case of an isocyanate, or an acyl radical in the case of an acid or acyl chloride. Nonethe-less, the~terminology "long chain alkyl group" is used since the size and effeot o~ the hydrocarbon portion of the modi-fyîng molecule substantially obscures any noticeable effect from the connecting group. Properties are not significantly different from those of the product modified with the simple long chain alkyl group.
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A slurry of 80 parts by weight of medium viscosity hydroxyethyl celIulose ( 2.5 M.S.) in 393 parts isopropanol wa~ prepared and degassed~by sparging wlth N2. To this was added 72 parts of an aqueous 35.5~ NaOH solution. This was agitated at O to 5C. in an nitrogen atmosphere.After abou~t 16 hours, 45 parts of C16 epoxide was charged to the slurry. The temperature was raised to 75C. and reaction was allowed to continue for six hours.
The reaction mass was neutralized with HN03, after which the p~ wa~ adjus~ed to 7 with acetic acid. The prod-uct was isolated b~ filtration and washed with 330 parts hexane. Hexane was removed and the modified polymer was dissolved in 80/20 methanol/water. The polymer was precip-itated with acetone, separated from the liquids and washed with acetone until it wa~ hard e~ough to be filtered, then .,~
-~- dried over~ight at room temperature.
The modified product contained 2.68~ C16 modifier and was less than 1% soluble in water.
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Examele 2 Low viscosity hydroxyethyl cellulose was treated as set forth in Example 1 except that only 23 parts of the C16 epoxid~ was used.
The modified product contained 6.3~ of C16 modifier and was less than 1.3% soluble in water.
~, A slurry of 80 parts by weight of low viscosity hydroxyethyl cellulose in isopropanol was prepared and de--10 gassed by sparging with nitrogen. To this was added 72 parts o~ 35.5% NaOH solution~ Tbis was agitated for about ~- 16 hours at 0 to 5C., at which time 45 parts of C16~
epoxide was added and the temperature was raised to 75C.
for 3.5 hours.
lS The reaction mass was neutralized with nitric acid and the p~ was adjusted to about 7 with acetic acid. The poly-mer was removed from the isoprbpanol reaction medium and ~ashed several times with hexane. Following removal of the hexane, the polymer was dissolved in 90/10 methanol/water mixture and the pol~mer was reprecipitated with hexane.
The hexane was removed by decantation and the polym~r was - washed with acetone~until it was hardened~sufficiently to be vacuum filtered. Residual acetone was removed by drying the polymer overnight under vacuum at room temperature.
The modi~ied polymer contained 3.05% C16 modifier and was less than 1~ soluble in water. ~ ~
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A solution (10 g.) of low molecular weight hydroxyethyl cellulose (2~5 U.S.) in 190 g. distilled dimethyl sulfoxide 30 (DMSO) was sparged with nitrogen to remove oxygen. To this `
was added 0.9 gram potassium t-butoxide in 15 ml. distilled - DMSO.
A dispersion of 0.4 g. of C16 epoxide in 5 ml. of DMSO was rapidly added with stirring to the reaction mixture at~room temperature. ~The temperature was raised to 80& .
oYer 40 minute~ and held there for 3 hours~ At the end of the reaction period, the mass had the appearance of a thick --, ,, f :
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gel. This was allowed to cool to room temperature and to stand overnight.
Acetone was added to the reaction mass and it was ground in a sealed blender. This step was repeated three S times with the acetone removed by decantation after each grinding. Finally, the solids were added to a large volume ~- of acetone stirred by a Cowles blade for 30 minutes, then ~- recovered by suction filtration and air dried.
The ~odified ether contained 3.5~ by weight of the C16 modifier and was less than 1% soluble in water.

The procedure of Example 4 was repeated using 2 g. of the C16 epoxide to produce a modified product containing about 5.8% modifier.
Example 6 A slurry o 80 parts by weight of low viscosity hydroxyethyl cellulose in 393 parts of isopropanol was pre-pared and degassed by sparging with nitrogen. To this was -~ added 72 parts of 35.5~ aqueous NaO~ solution. This was ~; 20 agitated for about 16 hours at 0 to 5C. 36 ~rams of C12 epoxid~ was added. The temperature was raised to about 70 to 75C. and~reaction was allowed to proceed for 3.5 hours with constant agitation~under an argon blanket.
The reaction mass was cooled to room temperature and neutralized to about pH 7 with nitric acid and then acetic acidO Removed from the isoprspanol, the polymer was washed -~ twice with hexanet then twice with 20% aqueous acetone, then dried under vacuum at room temperature.
The modified polymer contained 2.42% C12 modifier and was less than 1~ soluble in waterO
Example 7 The procedure set forth in ~xample 6 was repeated except the reaction was carried on for 4.5 hours. The water-insoluble product contained 3.4% C12 modifier.
~xample 8 The procedure of Example 6 was repeated using a C14 ~-~` epoxide, allowing the reaction to proceed for 3.5 hours.
" r i The water-insoluble product contained 2.~4% C14 modifierO

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g ~, 'r Exam~le_g Example 8 was repeated, allowing 5 hours' reaction time. The water-insoluble product contained 2.75% C14 r modifier.
The solubility of the modified cellulose ethers of the invention makes them useful as viscosifiers for shampoo formulations where many conventional water soluble gums are not compatible. For example, the current trelld in shampoos is toward low pH, low eye irritation products. This has ~ecessitated the elimination from the formulations of salts and amides whic~ have been employed heretofore as viscosi-fying constituents~ The incompatibility of conventional ~ums, as, e.g., hydroxyethyl cellulose, makes th~se formula-~ions particularly diffiGult to viscosify. The modified cellulose ethers of this invention are compatible with sur-actants in the concentration~ used in most shampoos and they effect substantial viscosity increases. The formula- -tions, in most cases, are crystal clear solutions.
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Low molecular weight hydroxypropyl cellulose was dis solved in 90% isopropanol with NaOH ~1.5N) and a hydrophobic epoxide. The thick ~olution was stirred for varying lengths of time, as listed in the table below, at 75C. The prod-uct was isolated by precipitation into hexane. All products -~ 25 in Table 1 are wa~er insoluble, but dissolve readily in a 10% solution of sodium tetradecyl sulfate in water.
Table 1 Epoxide Amount Time Wt~
Exam~le Carbon_No. (~rams) ~ L ~odification 10a 12 20 3 14 02 b 14 20 3.75 1.13 c 20-~4 20 4 1.43 d 16 20 3 0.93 e 14 36 3.5 1.90 f 20-24 ~0 3.5 2~75 ' :

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Exam~le 11 Methyl hydroxypropyl cellulose (Methocel A4C - Dow) was modified by reswelling in a caustic isopropanol slurry at 75C. for specified times with the levels of hydrophobic epoxide in Table 2. All of the products are water insoluble as recorded in Table 2 but dissolve readily in a 10% solu-tion of sodium tetxadecyl sulfate.
-~ Table 2 Epoxide ~nount Time Wt. ~
~ E~ Carbon No. ~ hours) Modification lla 1~ 36 5.5 2O90 b 14 36 5.5 2.60 c 20-24 36 5.5 2.60 Example 12 lS Example 11 was repeated substituting hydroxypropyl methyl cellulose (Methocel E-50 by Dow) for the methyl cell-ulose. All samples are water insoluble but soluble in 10%
sodium tetradecyl sulfate.
Table 2 Epoxide Amount Time Wt. %
E~ Carbon No. lgrams) ~ L Modification 12a 12 36 3.5 20 80 b 14 36 3.5 2.60 c ~ 15-1~ 3~ 3.5 2.10 Example 13 A low pH shampoo formulation* consisting essentially of the following ingredients was prepared:

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N-carboxymethyl-N-~(a -oxocarboxymethyl)-ethyl]-2-dodecyl imidazoline 12.0 parts Lauryl sulfate triethanolamine 3.7 parts Lauric diethanolamide 5.0 parts Ethyl dimethyl-(3-lanolin amide) ammonium ethyl sulfate 12.0 parts Water 22. 3 parts Propylene glycol 6.5 parts Cellulose ether dispersion 38.5 parts ~;~ 10 *See Soap, Cosmetics, and Che~ical ~pecialties, July 1978 The first four ingredients and the water were blended with heating to 70C. for 4 minutes. The water-insoluble cellulose ethers to be tested were dispersed in water at ; 15 about 70C. with stirring. The warm surfactant blend was : then stirred into the warm dispersion, followed by the pro-pylene glycol. The mass was then stirred for a time from about 15 minutes to one hour until the polymer was dissolved.
Pertinent data are recorded in the following table. .
Table 4 :~
Polymer Modifier and Conc. inViscosity :::
Concentration Mix (cps.) Appearance ::
, None - 56 Clear Hydroxyethyl Cellulose 2~ - Incompatible C16 ~ 2.7% 0.8% ~75 Clear Cl~ - 2.7~ 1% 3575 Some haze Cl~ - 2.7% 1.5~ 18,000 Cloudy C16 ~ 3% 2% 925 Clear C16 6.3% 2~ 1,250 Clear C14 - 2.4% 2% 335 Clear C14 - 2.75~ 2% 405 Clear - C12 - 2.4% 2~ 330 Clear :
C12 - 3,4% ~% 365 Clear The solubility of the modified cellulose ether in ~he surfactants and the substantial viscosity increases result-:~ ing therefrom are clear from the data in the table.

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: Despite their insolubility in water, the novel cellu-lose ethers of the invention are, themselves, highly effec-: tive emulsifiers in aqueous system~. This behaviour is demonstrated in the next example.
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Mixtures of 50 part~ water containing 1 part of hydroxyethyl cellulose modified wi~h C16 hydrocarbon, a~d 50 parts of a water-immiscible hydrocarbon oil wera prepared and homogenized vigorously with a manual homogenizer, Initially all of the systems were thorouyhly and completely dispersed when transferred from the homogeni7er, After one ~ day, the unmodified hydroxyethyl cellulose emulsion had sep-:~ arated an oil phase. All of the modified hydroxyethyl ~ cellulose emulsion showed no oil phase separation, although -.~ 15 some slight variances in creaming rates were noted.
Table ~
Poly % Oil Phase No,Oil M.W. C Separatlon `:~ 1Fractol medium 0 Yes 2Fractol low 0 Yes :~
3Fractol medium 2.01 No 4: Fractol medium 4.31 No Fractol : medium 6.7 No . 6Fractol low 3.1 No 7Fractol low 5.1 No 8Xylen~ low 0 Yes ~, 9~ Xylene medium 0 Yes 10XyIene medium Z.01 No 11Xylene medium 4.31 No 12Xylene medium 6.7 No 13Xylene low 3.1 No 14Xylene low 5.1 No 15Pine oil low 0 Yes 16Pine oil medium 0 Yes 17Pine oil medium 2.01 No 18Pine oil medium 4.31 No 19 Pine oil: medium 6.7 No 20Pine oil low 3.1 No 21Pine oil low S.l No :

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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A cellulose ether having a sufficient degree of nonionic substitution selected from the class consisting of methyl, hydroxyethyl, and hydroxypropyl radicals to cause it to be normally soluble in water and which is further substi-tuted with a hydrocarbon radical having 10 to 24 carbon atoms in an amount between that which renders said ether water-insoluble and about 8% by weight based on the total weight of the modified cellulose ether.

2. A water-insoluble cellulose ether of claim 1 wherein the normally soluble cellulose ether prior to modi-fication has a D.P. of about 75 to 1800.

3. A cellulose ether of claim 2 wherein the nonionic substitution is comprised of the hydroxyethyl radical.

4. A cellulose ether of claim 2 wherein the nonionic substitution is comprised of the hydroxypropyl radical.

5. A cellulose ether of claim 2 wherein the nonionic substitution is comprised of the methyl radical.