CA2137555A1 - Method of thickening of water, and its use - Google Patents

Abstract

The method proposed for increasing the viscosity of water is charcterized in that, for the instantaneous production of increased-viscosity water which does not lose its viscosity characteristics on storage, a slurry is prepared containing 1-9 %, preferably 2-5 %, of high-disperse synthetic, preferably pyrogenic, silicic acid in water with only a small amount of added ethers of fatty alcohols or saccaric alcoohols or esters of fatty acids with poly(ethylene glycol) or poly(propylene glycol) with a molecular weight between 250 and 50,000, at a concentration of 0.005 to 1.5 %, poly(ethylene glycol) or poly(propylene glycol) with a molecular weight between 600 and 50,000 at a concentration of 0.05 to 1.5 %, poly(ethylenimine) at a concentration > 0.003 or poly(N-vinyl-2-pyrrolidone) at a concentration of 0.05 to 0.5 %.
Characteristic of this system is its marked rheopexic properties which are shown instantaneously under the action of shear forces. Under such conditions, the viscosity increases and a stable, homogeneous terminal state is produced. The increased-viscosity water thus produced can be used as, for instance, a fire extinguishant, a carrier for crop sprays and cleaning agents or as the liquid in water beds.

Description

~2137) jrj PCT / DE 9 3 / O 0 512 L~5HNERT, BUIL
Method of Thickening of Water, and its ~se.

Thickening of liquids is of technological significance for controlling flow properties, for instance, for avoiding losses and running when employed as a means ofdepositing or transport,for retaini~g sedimentable particles in a homogeneous mixture, for fixing the liquids to surfaces in order to ohtain longer lasting effectivity or in order to improve the behavior of the liquids as hydrostatic media for pressure distribution, for example, by reducing or eliminating ~ave propagation.
Due to its non-toxicity, capacity as a solvent, compatibility, lcw cost and good availability, water is an excellent liquid medium. On the other hand, its quick, uncon~rollable a sp~lci~'n~ runnin ~ its adhesion to surfaces as only thin films of J water, the~sedimentation ofsolids if present and its strong wave propagation are often disadvantageous for technological application. This is the case when it is used as a fire extinguishant, as a liauid carrier of cleansing or plant protection agents but also in exploiting its very good pressure distribution properties.
The production of thickened water to fulfill the mentioned technological ohjects, in particular, in a lasting, controllable manner and in order to avoid diminishing its advantageous properties by adding minimal amounts of accessory agents is, therefore, often a challenge. For this purpose, various tec;~nological paths reflecting the respective specific needs have been embarked upon.
Orsanic viscosity-increasing agents, suc;n as gelatin~
- starches or cellulose derivatives~ nat~r l polysaccharides (gums) or synthetic, water-soluble high polymers alter the properties of water in a manner that is disadvantageous for the mentioned technological applications by producing sticky or thread-drawing properti~s-, o~-d~e-to poor - stability (oxidative or microbial d c~mposition, cf. Kirk-Othmer, Encyclopedia of Chemical T~chnology, 3rd. ed., vol. 18, p~ 623).
If on the other hand, inorganic viscosity-increasing agents such as crystalline silicates (bentonite, attapulgibe or mica) are solely utilized as a stable viscosity-increasing agent for water, the required concentrations are distinctly abnve~-iG~ in order to obtain technologically exploitable viscosity-increasing results as is known from the forest-fire-fighting application of thickened water using bentonite or attapulgite (lit., e.g., C.E. Hardy, Chemicals for Forest Fire 7 ~ cJ ~

_, .
Fighting, 3rd. ed., Boston, 1977). Crystalline layered silicates, such as bentonite often for~ undesirable, difficult-to-remove residues after evaporation of the water.
All mentioned viscosity-increasing agents for water have in common that they require considerable time (ranging from hours to days), due to t~eir swelliny behavior, to achieve the desired maximum viscosity, which is difficult to control by outside influences and which requires handling that is often complicated. Silicic gels produced by the gelling of unstabilized silicic sols or by neutralization of water glass can generate a thickening effect even in low concentrations, however, they continuously separate water from the gel (syneresis) due to polycondensation of the silicic acids resulting from neutralization, causing the gel to shrink. Evaporation of the water results in a hardened residue which is very difficult to remove from surfaces, vessels or devices, pipes or the like consequently eliminating ~he use of water the viscosity of which has been increased in this manner, e.g., for fire extinguis~ers, plant-protection spray~rS or as a filling medium, e.g., for water~eds. ~oreover, the gelling time of silicic acid in low concentrations n water is difficult to control even when auxili--y agents such as salts are added.
Although:~_ghly-disperse, amorphous, synthetic si1icic acid does not show the latter-me~tioned disadvantageous properties, they are employed as visccsity-increasing agents predominantly for organic, hydrophobic fluids, because due to their hydrophilic properties, they show a distinctly weaker Pffect as a viscosit~-increasing agent in low concentrations in water. This aiso is true for other liquid hydrophilic media, such as, e.g., glycerin.
R.K. Iler also confirms, e.g., in "The Chemistry of Silica", Wiley, New York, 1979, p. 336, that dispersions of pyrogenically produGed silicic acid form sols in an aqueous so ution,~-which do not form st-ong gels and, therefore, are-only of little usa as lnorganic binders.
, The present invention`~J~ound as a solut~on to the object of instantaneous p~oduction of stable, th ckened water, that th~ viscosity of a lowly-concentrated silicic sol which can be prepared from highly-disperse synthetic, preferably from-pyrogenic silicic acid in water by slurrying in-water, e.g., sluFries of 1-9~, preferably 2-5~ pyrogenic silicic acid in water with only a small amount of added specific water soluble organic compoundsr notably et~ers of fatty alcohols or saccharic alcohols or -3- 2 1 3 7 ~ J ~

esters of fatty~acids with poly(ethylene glycol) or poly tpropylene glycol) with a molecular weight o~
>250 - 50,000, in a concentration from 0.005 to 1.5~, poly(ethylene glycol) or poly(propylene glycol) with a molecular weight of >600 - 50,000 in a concentration from 0.05% to 1.5%, of poly(ethylenimine) in a concentration from >0.003 or of poly(N-vinyl-2-pyrrolidone) in a concentration from 0.05 to 0.5%, can be instantaneously and stably increas2d. Characterizing and differing from the other mentioned thickening methods for water is that in this thickening method, in particular, the marked rheopexicbehavior of the system which are shown instantaneously under the action of shear forces, such as, e.g., being stirred with an electric stirrer (800-1600 rpm), passing through centrifugal pumps or being sprayed through nozzles. Thickening and a homo~eneous and a very stable thickening effect is produced.
The mentioned organic compounds can be employed in K sclely the mentioned concentrations~r in combination. The range of application for poly(ethylene glycol) or its mentioned derivatives is limited to a pH-range of 1-9. If the pH-values are higher, dilution to a thin watery consistency prior to being added occurs. In the case of poly(ethylenimine), this dilution can be detected below a pH-value of 3. A com~ination of the two additives permits increasing the ~iscosity in a correspondingly larger pH-range. The synthetic amorphous silicic acid can also be mixed dry with the mentioned organic compounds prior to adding the water. This mixture can be stored until use and then mixed with the amount of water required to reach the needed concentration. The silicic acid and the mentioned organic additivies can also be mixed directly with the water.
The thickened slurry of synthetic, amorphous silicic acid of low concentration in water (" thickened water") produced in this manner Gan, e.g., be very succPssfully utilized as a fïre~egtinguishant for class A fires (in particular for hard-to-extinquish fires of tires or other synthetic materials), because they massively adhere to hydrophobes or hot surfaces and thus permit keeping thick water layers at dis~osal on horizontal, vertical or even downward~~X~nng surfaces of any kind. I~ is suited as a drilling fluid, because it is stable against shear forces under pressure and at high temperatures. It can also be used as-~ carrier for clsaning agents, such as antiliming a~ents, because, e.g., organic acids such as citric, tartaric or malic acids can be dissolved in it, which can be applied to calcified surfaces to produce a lasting effect.

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The use of the invented viscosity-increased water is also very advantageous as a hydrostatic, pressure-equalizing filling for waterbeds or cushions or gel saddles with the advantage of eliminating wave reflections. Development of microorganisms in the thickened water is not observed in theflexible cushions even over a period of several months, whereas similar cushions filled with watPr had slimey deposits, probably algae, on the inner walls after the same period of tim~.
The invented thickened water demonstrates compatibility with the salts of anorganic and organic acids dissolved in it even in higher c~ncentrations (e.g.
an addition of 30% of potassium acetate or potassium lactate) so that frost resistance (e.g. at -30C) is achieved. Sugar or its derivatives sucn as sorbito~;
glycol orglycerol can also be dissolved in any concentration in viscosity-increased water without diminishing the viscosity. Therefore, .he viscosity-increased water can also be employed as a reu~eable, liquid filling for cooling pillows, cooling cells or cooling bags. Due to the good handlins properties, these mixtures can be refilled as desired and thus reused. This is usual'y not possible with fillings of this type produced with organic gel formers~
Moreover, the stable thickening permits the incorporation and stable suspension of sedimentable mineral or organic insolu~le materi~ls, even proteins, wh~ch is useful for analytic, but also synthetically preparative purposes, such as separation of materials.
For the use as fire-extinguishants~rcm concentrats can be added to the ffiscosity~increased water (e.g., of the AFFF type), with thethi~ng as well as foamability being retained. A thickene~ foam is produced that contrary to foam which is only made with AFFF has considerably better adhesion-to-surface properties-so that uncontrollable running of the foam is ~ --avoided and fighting fires of solid materials (class A)-and of flammable liquids (class B) is permitted.
The ~ollowing examples make the present invention more apparent without the intention of limi~ing the spirit or. - ~
scope of the invention: -2137. . ~

Example 1 --

2.2 liters of a 15~ dispersion of an amorphous, synthetic silicic acid (Wacker ~DK KD 150, reg. trademark, Wac~er Chemie GmbH, Munich3 are mixed with 7.8 liters of water. 20 grams of poly(ogyethylene lauryl ether) with a molecular weight of approximately 380 (Mulsifan CPA, reg. trademark, of Zschimmer and Schwarz, Lahnstein) are mixed with the watery dispersion which has a flow time of 10 seconds in a DIN 53 211 cuP. The mixture has a flow viscosity of 11 seconds immediately following the addition. A 500 ml part of the mixture is filled into a spray-pump bottle and is sprayed onto a vertical, smooth aluminum sllrface. The thickeninqf the mix-ure increases immediately due to the spraying forces so that the mixture remains sticking completely to the metal surface.
Another 500 ml part o~ the thinly liquid mixture is st~red in a vessal for a few seconds with an electric stirrer (Phllips Elektroquirl, 800/1600 rpm, cutting knlre diameter approx.
4 cm). The mixture continues to thicken instantaneously and then a.flow viscosity of approximately 29 seconds is measured in the ~low beaker. (A small part of the mixture does not flow out of the cone of the beaker).
Similar thic~ening can be obtained by pumping the mi~ture through an electric centrifug~l pump (flow rate:
68 liter/min). (Flow viscosity approx. 26 sec.).
Instantaneous thickening and very good adhesion of the thickened water to surfaces of any kind is also found when spraying with plant-protection agent "sprayers"(Gloria, types 172 RTG and 176 T, various spray nozzles). Good adhesion to plants is also found, in particular, where water pearls off the s~rface of the plants due to surface hydrophobicity. Thus, for example, use for low-loss applica~ion of water in thick layers onto plants, is also possible which maY cont-.in other additives which leads to improved prevention of frost damage or can be utilized for applying plant-protection agents. By - spraying with water the applied layers can be removed again, if need be.
Instead of poly(oxyethylene lauryl ethers), poly(ethylen glycol) with a molecular weight of approximately 4220 or poly(oxyethylene sorbitan monostearate) with a molecular weight of approximately 1200 or PEG-120 jojoba alcohol and PEG-120 jojoba acid (molecular weight approx. 5400) or poly(ethylenimine) or poly(N-vinyl-2-pyrrolidone) were tried and yielded the same results. A viscosity-increasing effect which increases due to the influence of shear forces can already be found with added amounts of only 0.05% of the ~entioned low-molecular poly(oxyethylene) derivates, poly(ethylene glycol), poly(~-vinyl-2-pyrrolidone), or only 0.00~ of poly~oxyethylenimine), -6- 2137`;~

and the viscosity is correspondingly lcwer. The polyethers have an upper action limit of approximately 1.5%, poly(N-vinylpyrrolidone) one of approximatel~ 1% with regard to the overall mixture, above which slurries of the silicic acid in water return to their initial ~hinly liquid state.

Example 2 Thickened water produced according to example 1 is employed to extinguish a fully developed fire with 6 burnins automobile tires. It is applied using a commercial 10 liter water-fire extinguisher according to DIN. The fire was completely extinguished with 5 liters of the viscosity-increased wa~er, wi~hout re~indling. On the other hand, the same fire could not be extinguished using 12 kg quenching powder, because rekindling recurred after temporary axtinguishing of the flames -~ith the powder.

Example 3 Thickened water produced according to example 1 was filled into a cushion holding 5 li.ers and another cushion of the same type was filled wi.h pure water. The filling with the thickened water completely a7~oided wave reflections, whereas in the cushion that was only filled with pure water long~lasting "wave motion"
occurred. Comparison also revealed distinctly improved sitting comfort due to the a~oidancP of "wave motion'l.
Both cushions were emptied after 6 months, and examination of the interior revealed formation of slimey, greenish deposits only in the cushion that was filled with pure wa~e~, whPreas the interior of the cusnion filled with -viscosi~y-increased water showed no changes.
A waterbed Prod. "Kuss", DLM Mfg. Co, Findlay, Oh., U.S.A., unstabilized) was filled wlth appro~imately 500 1 of-the--thickened water according to example 1.
So-l-ely by this means, 100% stabilization of the waterbed was achieved, which is indicated by a -eflection period of <1 second following a shoc~ impulse at the edge of the water~ed. An unstabilized waterbed onl~ filled with water has, on the other hand, a reflection period of 30 econds. Thus, considerable improvement of reclining comfort is obtained without the mechanical stabilizing systems that are commonly used with waterbeds.

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Example 4 Viscosity-increased water produced according to ex~mple 1 was mixed with 30 weight per cent of potassium acetate, which dissolves in it. Po~ass~um acetate is described as so-called "loaded stream agent" in Kirk-Othmers Encyclopedia of Chemical technology, Supplement, p. 454, 1985 for use as an antifreeze in loaded stream water fire extinguishers and for little effective class B fires.
The thickening effect is retained even with this additive. The mixture was cooled for 2~ hours to -300C, with the homogeneous, thick-flowing consistency being ~etained. Freezing was not observed. After warming, the thickened starting consistency was retained, decomposition or coagulation was not obser~ed. The procedure can be multiply repeated.
In a small-scale extinguishing test using pine roof slates, very good flame extinguishing proper~ies were determined with this viscosity-increased mixture, also indicated by the good adhesion on the inflammable s~rfaces. The test was repeated with potassium acetate bein~ repla~ed by potassium lactate and yielded corresponding results.
In other tests, it was discovered that a high concentreted, approximately 30% solu~ion of potassium acetate or potassium lactate in water ~ithout the additives des~ribed in example 1 can increase the viscosity of this mixture by adding approximately 3.3 weight in per cent of synthetic ~morphous silicic acid, with adhesion to flat surfaces (plastic, rubber) not being as good as with the same mixture with the addition of the organic compounds mentioned in example 1. Contrary to the orga~ic additives -in example 1, this incre~se in viscosity occ~lrs only if h~gh concentrations of both mentioned organic-salts are employed.

Example 5 Thickened water produced according to example 1 is mixed in 3 tests with 2~, 3~ and 6~ of a commercial AFFF foam concentrate without the synergists contained in it of the poly(oxyethylene fatty alcohol ether) type. The mixtures proved to be foamable with a foam nozzle, yielding, in compar-ison to foam formation with non-thickened water or to the non-thickened slurr~ o~si-licic acid in water, without the thickening addit~e a thickened foams.
Contrary ~o the aforementioned '~non- thickened"
foam~,this foam adheres to surfaces.These "thickened"
fo2ms obtained in this manner are suited for -8- 2i~J7 j5~

extinguishing fires of liquid hydrocarbons. Moreover, they are also very effective in fighting fires of solid materials as they adhere to the latterO
With approximately 5 liters of a foam ~hickened in this manne containing 6~ of the AFFF ~oam concentrates permits extlnguishing a fire of pine slates measnring 270cm x 50 cm ~ 7 layers respectively, cross-section 2cm x 4cm). Practically no rekindling was discovered.

~x~mple 6 A slurry of 150g pyrogenic silicic acid ~Aerosil 200, reg.
trademark, Degussa3 in 4850ml of water is mixed with lOg of poly(N-vinvyl-2-pyrrolidon~3 (Sokal~n HP 50 or HP 53, reg. trademark, BASF) and stirred with a glass rod. A
slight increase in viscosity occurs, i~dicated by a flow period in a DIN 53 211 cup Erom 9 seconds (without Sokalan) to 20 seconds (with Sokalan). If the mixture is sllbsequently brie~ly sheared (1 sec.) ~ith a stirrer (Philips _le~troquirl, 800/1600 rpm, c ameter of the cutting k~ife 4cm), the viscosity incr~ases to a value at which a pastelike consistency is o~tai~d which has a strong property to form layers on wall and stic~s to the cone of the flow beaker and thus no longer permits determining the viscosity in the cup. . The mixture shows very good stability of the homogeneity, adhesion to surfaces, sl~ch as poly(ethylene`, glass, metal, as well as lasting stability against shearing forces even at 95C. HoweYer, it still can be sprayed very well through nozzles of commercial fire extinguishers or plant-protection agent sprayers.The mixture~5:~ows a much delayed releasa of water when comi~ intQ-direct oontact with sucking substrates, such as, e.g., soil.
This is advantageous in the use of water whose viscosity has been increased in this manner for extinguishing garabage dump fires, because application-of~~the extinguishant by injection is possible without-uncontrolled penetration. Unthic~ened ~ater, on th~ other hand, penetrates ~uickly and uncontrollably and, therefore, is quickly lost as an extinguishant for the fire-endangered zones.

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Example 7 An amount of 30g of pyrogenic silicic acid is mixed with 500ml of water and 470g of a solution of sorbi~ol syrup (70%
in water3. Adding 2g of poly(N-vinyl 2-pyrrolidone) and blendins ~with an electric stirrer at 8Q0 rpm yields a pourable paste which can be utililzed as a filling for cooling bags. The mass is sufficiently mouldab].e to conform to uneven surfaces even at -20C. It can be repeatedly frozen and thawed, and therefor can be multiply reused.

E~ample 8 A visocisty-increased slurry of pyroge~ic silicic acid such as described in example 1 is mixed with 2% o~E citric or t~rtaric or malic acid, and 50Qml OI this mixture is used to clean calcified stone or plastic surfaces.
Thorough material-saving cleaning of the calcified surfaces is achieved due to the adhesive effect.

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Claims (5)

AMENDED CLAIMS
[(filed with the International Office on 22 November 1993 (22/11/93); original claims 1-3 replaced by amended claims 1-5 (2pages)]

1. A method for the production of thickened water by preparing a slurry of 1 - 9% weight per cent of high-disperse synthetic, preferably pyrogenic silicic acid in water with a only small amount of additives, characterized by providing 0.05 - 0.5 weight per cent of poly(N-vinyl-2-pyrrolidone) (PVP) as said additive.

2. A method according to claim 1, characterized by using PVP in mixture with the state-of-the-art additives of ethers of fatty alcohols, saccharic alcohols, or esters of fatty acids of poly(ethylene glycols) or poly(prolylene glycol) of molecular weights from >6000 - 50,000 or of poly(ethylenimine).

3. A method according to claim 1 or 2, characterized by achieving intensification of the thickening effect by vigorous stirring, shearing action or by spraying processes.

4. Thickened water, characterized by being obtained according to at least one of the claims 1 to 3.

5. Use of said thickened water according to claim 4 as a binding medium or carrier substance for pigments, cleaning agents, plant-protection agents, drilling fluids, extinguishants or as a filling for waterbeds or cushions.