CA1039272A - Water soluble cellulose ethers - Google Patents

Abstract

METHOD OF DISSOLVING CELLULOSE ETHERS IN
HIGH BASIC MEDIA

ABSTRACT OF THE DISCLOSURE
Dispersibility of cellulose ethers containing hydroxy-ethyl groups is improved at high pH levels by treating the cellulose ether in particulate form with a solution of boric acid or a borate and thereafter drying the treated ether. Upon addition of this ether to a high pH aqueous system, for example, Portland cement, the ether dissolves readily without formation of lumps and without unduly long hydration time.

Description

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This inven-tion relates to water-soluble cellulose ethers and in particular to cellulose etI1ers which have a reduced ten-dency to agglomerate in high pH aqueous media.
Several water-soluble cellulose ethers are commercially available, but in several cases the rate of dissolution is very ~` -slow. This is caus~d by the fact that when such an ether parti-cle touches the water the outer surface will swell and form a gel which dissolves slowly. If a mass of particles touches the water more or less simultaneously, the particles swell and gel and stick to neighboring particles, thus forming an agglomerate which dissolves even slower than the gel formed by one particle alone.
It is known that treatment of water-soluble cellulose ethers with a cross-linkiny material such as an aldeh~cle or di-aldehyde improves the dispersibility of that ether in water.
When such a treated cellulose ether is added to water and stirred, there is a time interval from the moment the ether is added until the moment solution viscosity begins to develop.
This time, known as the hydration time, is thought to be a meas-ure of the time required for water to hydrolyze hemiacetal crosslinkages produced by interaction of the aldehyde or dialdehyde with the cellulose ether. During the hydration period, water penetrat~s to the interior of the individual particles without causing khe sur~aces to become sticky. r~hen these cross link-ages are broken, the cellulose ether dissolves, causing the solu-tion viscosity to increase. Complete solution of such an ether is evidenced by the attainment of a stable solution viscosity.
The aldehyde or dialdehyde treated cellulose ethers are known to dissolve with little or no tendency to lump or agglomer-ate in neu~ral, weakly alkaline or acidic aqueous media, and toattain stable solution viscosity, but in strongly alkaline or high pH aqueous systems, e.g., about pH 10 or equivalent, agglo-meration occurs and solution viscosity does not develop smoothly, probably because hydration occurs too rapidly.

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According to this invention, there is provided a method of im~
proving the dispersibility of a cellulose ether in an aqueous liquid having a pH greater than lO which comprises contacting particulate cellulose ether `~
with boric acid or a water-soluble borate in the presence of a solvent for said boric acid or borate, removing the solvent, drying the residue.
The cellulose ether may also have been mc~dified by treatment -~
with an organic compound which forms hemiacetal bonds with said cellulose ether as discussed above, depending on the results desired. The preferred hemiacetal bond forming organic compounds are polyfunctional aldehydes. The O most suitable organic compound is glyoxal.
The treatment of the cellulose ether with the boric acid or borate is carried out in nonacidic, preferably alkaline medium. In a suit-able method boric acid or a borate is added to a slurry of cellulose ether and organic liquid, and after mixing, the liquid is removed and the so1id ~ ~ ~
residue is dried. The preferred organic liquid is acetone, and an alkali ~ ~ ' such as sodium hydroxide or an amine such as monoethanolamine is preferably also present.
The treatment of a cellulose ether with both a polyfunctional aldehyde and boric acid or a borate should be carried out in a nonalkaline, preferably acidic, medium if the aldehyde is to have a useful effect. Pre-ferred methods of treatment are as follows:
(I) Boric acid or a borate is added with a polyfunctional aldehyde to a water-miscible organic liquid, a cellulose ether is then added and the whole mixed thoroughly, the supernatant liquid removed and the solid residue dried.
(II) A polyfunctional aldehyde is added to a cellulose ether/
acidified organic liquid slurry. After mixing, boric acid or a borate is added and the whole is further mixed, after which it is filtered and the solid residue dried.

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(III) A polyfunctlonal aldehyde is added to a cellulose ether/
acidified organic liquid slurry. The whole is mixed and the supernatant liquid is removed. Boric acid or a borate in solution is added to the moist residue and after mixing the resultant mass dried.
(IV) A polyfunctional aldehyde is added to cl cellulose ether/
acidified organic liquid slurry, the whole is mixed, fil~
tered and the residue dried. The treated residue is re- ~;
slurried with further water-soluble organic liquid, boric ; ~
acid or borate is added, the liquid is removed, and the ;
resultant mass dried. `
The preferred cellulose ether is hydroxyethyl cellulose.
Other examples are methyl cellulose, methylhydroxypropyl cellu-lose, methylhydrox~ethyl cellulose and ethylhydroxyethyl cellu-lose.
It is important that the boric acid or borate be added in solution form to the cellulose ether slurry and that the dis-~ . , solving liquid be removed substantially completely. The mechan~ism by which the unique and unexpected effect of this invention 20 takes place is unknown, i.e., whether it is a reaction between `
the borate and ether or simply a deposition of the borate on the particle. In either event, the effect takes place in or from solution only. Upon ~rying, the resultant product is readily soluble in high p~I aqueous systems without agglomeration. The treated and dried cellulose ether is normally ground to a fine particle size for use. ~;~
The borate will normally be a readily soluble borate, e.g., borax, potassium borate or ammonium borate, and the sol~
vent can be either water or a suitable organic solvent such as methanol. The ~referred dialdehyde is glyoxal and the prefer-red organic liquid is acetone. The dialdehyde is preferably water-soluble and used in aqueous solution for application to the cellulose ether slurry.
It is preferred that the dialdehyde be present in the ~ 039zr~z reaction mixture within the concentration range 0.005 to 5% by weight based on the cellulose ether, suitably 0.04 to 2.0~. It ;~
is preferred that the boric acid or borate be present within the concentration range 0.001 to 0.5% by weight based on the cellu~
lose ether, suitably 0.003 to 0.2~, when a dialdehyde is also used. T~hen ~oric acid or borate is used alone, the preferred maximum proportion is 5%, suitably 2%.
The invention is illustrated ~y means of the following examples. ::
Example 1 To 25 g. of hydroxyethyl cellulose (HEC) were added ~
60 cm.3 of acetone, 6.25 cm.3 of a solution of 40 g. borax in ~ -ldm3 of methanol, 8 cm.3 of 0.lM sodium hydroxide solution. The ;
whole was mixed and dried on a water bath. After grinding the dried product, it was added at 2~ concentration to the ~iltrate o~ a slurry of 250 g. of Portland cement in ldm3 of water and the hydration time and viscosity development of the mixture was ;~
observed. The filtrate of Portland cement had a pH ~12.
The hydration time was 7 minutes and no agglomeration was observed, the viscosity developing smoothly as soon as the treated hydroxyethyl cellulose was mixed with the high pH system.
The viscosity was measured with a Brabender Visco Corder Model VC-3.
Examples 2 to 4 The method used for each example was the same as in Example 1. The quantities used and the results obtained are as follows:
Borax Soln. Hydration Example HEC Acetone (cm3) 40 g/dm3 0.lM Time ;-No. (g) (cm3) in Methanol NaOH ~Mins.)

2 25 60 12.5 ~ 7

3 25 60 6.25 3.2* 6

4 25 60 4 8 4 *0.5M NaOH was used in this example In all cases no agglomeration was observed and the vis-cosity developed smoothly.

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Example 5 To 500 g. of moist hydroxyethyl cellulose were added 2 dm3 of acetone. The hydroxyethyl cellulose-~acetone system was acidified with acetic acid, the acid value (as hereinafter defined) being adjusted to 24, and the desired amounts of glyoxal and borax were added at 30C. The term "acia value" is defined as the number of cm.3 of 0.lM NaOH required to neutralize 100 cm.3 of acidified acetone. Glyoxal was added as a 40% aqueous solution, the amount added being 0.25% by weight of 100% glyoxal based on the weight of hydroxyethyl cellulose. A~ueous sodium borate was added as a 4.5% strength solution, the amount added being 0.1% by weight of borax as Na2B4O7.10H2O based on the weight of hydxoxyethyl cellulose. The mass was stirred for 30 minutes and then suction filtered. The treated hydroxyethyl : . ,, cellulose was dried on a steam bath at 90-100 for 2 hours.
After grinding the product, it was added to the filtrate o a slurry of 250 g. Portland cement, Grade A, in ldm3 of water, and the hydration time and viscosity development of the mixture was observed. The filtrate of Portland cement slurry had a p~
~12.
The hydration occurred immediately and no agglomeration was observed. The viscosity developed smoothly as soon as the ~ -treated hydroxyethyl cellulose was mixed with the high pH aque~
ous system. The viscosity was measured with a Brabender Visco Corder Model VC-3.
Examples 6 to 8 The method used was the same as in Example 1. The fol~
lowing results were obtained, the percentages of glyoxal and borax being based on the weight of hydroxyethyl cellulose.

30Example % ~ Hydration Time No. Glyoxal Borax Acid Valueat pH ~12 _

6 04 0.10 24 -

7 10 0.02 24.8 1/2 min.

8 .10 0.07 24.8 In all cases, no agglomeration was observed and the viscosity developed smoothly.

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Example 9 To 500 g. of moist hydroxyethyl cellulose were added 2 dm3 of acetone. 0.15~ by ~eight of glyoxal based on the weight of hydroxyethyl cellulose was added at 30C., the glyoxal being a 40% aqueous solution. The whole was mixed for 30 minutes and the supernatant liquid was siphoned off leaving a moisk cake of gly~
oxal treated hydroxyethyl cellulose.
Aqueous sodium boxate was added as a 4.5~ strength solu-tion, the amount added being 0.03~ by weight of borax as Na2B4O7.10H~O based on the weight of hydroxyethyl cellulose. The cake was aried on a steam bath at 90-100 for 2 hours.
After grinding the product, 25 g. was added to 200 cm.3 ;~
of the filtrate of a slurry of 250 g. Portland cement Grade ~ in ldm3 of water, and the hydration time and viscosity development of the mixture were observed. The hydration time was 2 minutes and the viscosity developed smoothly thereafter. No ag~lomera-tion was observed.
Example lO
To 400 g. of acetone was added a 2.25~ strength aqueous sodium borate solution and 40% glyoxal solution sufficient to give .0056% by weight of sodium borate and 0.1% by weight gly-oxal, both based on the weight of hydroxyethyl cellulose used.
To this mixture was added lO0 g. of hydroxyethyl cellulose and ~ -the whole mixed for 15 minutes. The supernatant liquid was siphoned off, the treated residue dried and pulverized. The pulverized residue was added to a sample of water at pH 12, pro- -duced by filtering a slurry of 250 g. of cement with ldm3 of water, and the hydration time (as hereinbefore defined) and solu-tion time were both measured with a Brabender Visco Corder Model VC-3. The solution time is the time taken to reach stable solu-tion viscosity. The solution viscosities were seen to develop smoothly with no observable agglomeration occurring.

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lIydration Time Solution Time % GlyoXal ~ Borax at p~ 12 at p~ 12 0.1 .0056 2.5 minutes 19.0 minutes Examples 11 to 15 The methods used were substantially the same as in Exam-ple 10. No agglomeration was observed in any example.
Results _ Hydration TimeSolution Time Example % % at p~ 12 at p~ 12 -~
10No. Glyoxal Borax (Minutes) (Minutes) 11 .12.0068 1.4 18.0 ; ;~
12 .16.0056 2.5 35.0 !
13 .24.0056 3.1 21.5 14 .28.0056 2.5 16.1 1.00.0034 1.3 25.5 Examples 16 to 20 -The methods used were substantially the same as in Exam-ple 10 except that hydroxyethyl cellulose samples of lower mol-ecular weight ~Examples 16 and 17 with a 2~ Brookfield viscosity 20 of 320 and Examples 18, 19 and 20 with a 2% Brookfield viscosity l ~ -of about 2000) were employed. No agglomeration was observed in ~-dissolving 5 g. of any of the treated samples in 200 ml. o -water having a pH ~12.

Hydration Solution Example HEC % % Time Time No. TypeGlyoxal BoraxMinutes Minutes 16 150 K1.0 0.07 0.5 20 17 150 K1.0 0.09 0.5 40 18 150 G1.2 0.1 0.5 11 3019 150 G1.0 0.22 0 90 150 G2.0 0.22 0 300 Example 21 ~ ~
To 50 g. of hydroxyethyl cellulose was added 100 cm3 o ~ -acetone and 1 cm3 of lM NaOH. The required amount of borax solu-tion was added as a 4.5% aqueous solution. The supernatant liq-uid was removed and the residue was dried at about 90C. Hydra-tion time was measured with a Brabender Visco Corder in aqueous solutions at pH 12. The pH 12 medium was provided by il-tering a slurry of 250 g. of Portland cement Grade A a~d ldm3 of water.

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This procedure was followed with 0.09, 0~18 and 0.27%
borax tbased on the hydroxyethyl cellulose). No agglomeration was observed and smooth viscosity development was achieved in all ;
cases. ;
The results are tabulated as follows:

Hydration Time at Hydration Time at ; `~
Amount of Borax *Alkali Value 10 *Alkali Value 20-`

0.09 2 minutes 1/2 minute 0.18 3 minutes 2 minutes 0.27 3 minutes 3-1/2 minutes *Alkali value is defined as cc. of 0.1M HCl required to neutralize 100 cc. of alkaline acetone Example 22 ~-Ten grams dry basis of hydroxyethyl cellulose was slur- ~ -ried in 100 ml~ of acetone at room temperature. Then 20 ml. of aqueous solution (prepared by mixing 6 ml. of 1~ borax (Na2B4O7.10H2O) solution with 14 ml. of water) was addecl drop-wise with stirring over 20 minutes. Agitation was continued for one hour at r-25C. Then excess liquid was removed by filtra-tion and the product was washed with three 50 ml. portions of acetone to remove water. Excess acetone was removed by filtra-tion and the product was dried in vacuo at 60C. for one hour.
The product had good dispersibility in 0.01N NaOH solu~
tion at pH 12. The hydration time was 1.2 minutes followed by a fast increase in viscosity to 880 cps. A maximum viscosity of 920 cps. was attained in about 20 minutes.
Example 23 . ' The procedure of Example 22 was repeated except that the 20 ml. of solution added dropwise was prepared by mixing 2.5 ml. ~-~
of boric acid solution with 17.5 ml. of water. After water was removed by washing with two 50 ml. portions of acetone, and ;
excess acetone removed by filtration, the product was dried in vacuo at 60C. for one hour.
The product had good dispersibility in 0.01N NaOH solu-tion at pH 12. The hydration time was one minute, followed by a _ g _ " ~ r~ :
fast increase in viscosity to 660 cps. in five minutes and 700 cps. in ten minutes. A maximum viscosity of 740 cps. was attained in about 35 minutes.
Example 24 The procedure of Example 22 was repeated except that the 20 ml. of solution added dropwise was prepared by mixing l ml. of ,~
lg6 glyoxal solution and 2 ml. of 1% borax solution wi-th 17 ml. of water. After removal of excess acetone by filtration, the prod- ;
uct was air dried overnight.
The product has good dispersibility in 0,01N NaOH solu-tion at pH 12 but dissolved slowly. The hydration time was about 12 minutes, followed by a very slow rise in viscosity to 150 cps. in 50 minu-tes. `~
Example 25 One hundred grams of hydrox"vethyl cellulose was slurried ~
in 100 grams of acetone (acetone:water 97:1). Dry boric acid ~ ;
(0.30% by weight on cellulosic) was added to this slurry. After stirring for 10 minutes monoethanol amine (0.30% by weight on the cellulose derivative) was added. After stirring fox another 20 minutes the product was dried in a ventilated oven at 70 C.
for 30 minutes. The hydration time of the product was 2 minutes, the dissolving time was 11 minutes at pH 13.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of improving the dispersibility of a cellulose ether in an aqueous liquid having a pH greater than 10 which comprises contacting particulate cellulose ether with boric acid or a water-soluble borate in the presence of a solvent for said boric acid or borate, removing the solvent, drying the residue.

2. The method according to claim 1 where the boric acid or borate is present within the concentration range of 0.001 to 5% by weight, based on the weight of cellulose ether.

3. The method according to claim 1 where the cellulose ether is treated also with a dialdehyde in the amount of 0.005 to 5% by weight based on the weight of cellulose ether.

4. The method according to claim 3 where the amount of boric acid or borate is about 0.003 to 0.2% by weight based on the weight of cellulose ether.

5. The method according to claim 4 where the dialdehyde is glyoxal.

6. A method of dispersing a cellulose ether in an aqueous liquid having a pH greater than 10 which comprises adding residue obtained by the method of claim 1, 2 or 3 to the aqueous liquid.