Dead sea mask

8/7/2019 Dead sea mask

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j. Cosmet.Sci., 57, 441-454 (November/December2006)

A facial mask comprisingDead Sea mudBASIM ABU-JDAYIL, Departmentof Chemicaland PetroleumEngineering,UnitedArab EmiratesUniversity,P.O. Box 17555,ALAin, UAE, and HAZIM A. MOHAMEED, DepartmentofChemicalEngineering,JordanUnivemityof Scienceand Technology,P.O.Box 3030, 22110 Irbid,Jordan.Acceptedfor publicationJune27, 2006.

SynopsisMany investigatorshaveprovedthat Dead Seasalt and mud are usefulin treating skin disordersand skindiseases.Therefore,the blackmud hasbeenextensivelyusedasa basefor the preparationof soaps,creams,and unguentsfor skin care.This studyconcernsa facial maskmademainly of Dead Seamud. The effectsof temperatureandshearingconditionson the rheologicalbehaviorof the facialmaskwereinvestigated.Themud facialmaskexhibiteda shearthinning behaviorwith a yield stress.It was foundthat the apparentviscosityof the maskhasa strongdependenceon the shearrate aswell ason the temperature.The facialmaskexhibiteda maximum yield stressand very shearthinning behaviorat 40C, which is attributed to thegelatinizationof the polysaccharideusedto stabilizethe mud particles.On the other hand, the mud maskexhibiteda time-independentbehaviorat low temperaturesand shearratesand changedto a thixotropicbehaviorupon increasingboth the temperatureand the shearrate. The shearthinning and thixotropicbehaviorshavea significantimportancein the ability of the facialmaskto spreadon the skin: the Dead Seamud maskcan breakdown for easyspreading,and the appliedfilm can gain viscosityinstantaneouslytoresist running. Moreover, particle sedimentation,which in this casewould negatively affect consumeracceptanceof the product,occursslowlydue to high viscosityat rest conditions.

INTRODUCTIONThe Dead Searegion is the major spa areain the Middle East for patientswith varioustypesof arthritis.The uniqueclimaticconditionsin this areaandbalneologictherapy--which is basedprimarily on mud packsand bathing in sulfur bathsand in Dead Seawater--combineto alleviatethe symptomsof arthritis (1).The Dead Seahas a salt contentof about 320 g/L, of which potassiumchloride,mag-nesiumchloride,calciumchloride,and sodiumchloride(with their respectivebromides)are the major components,comprising98% of the saltson a dry weight basis.Anothermineral-richconstituentof the Dead Seais its "blackmud" (rich in organicsubstances),alsoknown as "bituminoustar." The therapeuticeffectof processedDead Seamud is

Addressall correspondenceto BasiraAbu-Jdayil.441


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442 JOURNAL OF COSMETIC SCIENCErelatedto its high contentof mineralsand its ability to retain heat for many hours,thusstimulatingblood circulationand clearingthe skin of dead epidermalcells(2). It hasbeen shownthat Dead Seasalt and mud are usefulin treating skin disordersand skindiseasessuchas psoriasis(3), seborrheicdermatitis,xerosis,artopic dermatitis, stageIskin burns,and sensitiveskin (4). In addition, black mud hasbeenextensivelyusedasa basefor the preparationof soaps,creams,and unguentsfor skin care.The manufac-turersof thoseproductsclaim that the mud hasmajor effectson revitalizingand toningthe skin. DeadSeamud deepcleanses;it removesimpuritiesby deepwashingof the skin.It penetratesporesto absorbaccumulateddirt, makeupresidue,and excessfatty secre-tions like hardened sebum.The demand for Dead Sea (DS) cosmeticsis increasing.Dead Sea cosmeticsincludeshampoos,creams,lotions,masks. .. etc. They haveDead Seasalt and/ormud in theirformulas.Consumeracceptanceof Dead Seacosmeticsdependson the stability of theproductsand their ability to spreadon the skin, which is directly related to flowbehavior.Semisolidsystemsareusedwidely in the formulationof topicalpharmaceuticaland cosmeticpreparations.Rheologicalpropertiesof semisolidsare highly importantphysicalparametersin technicalmanufacturing(filling, storage)and in aestheticterms.The evaluationof semisolidcosmeticstructureand consistencyis, therefore,essentialinorder to determine, adjust, and perhapspredict the performanceof newly designedproducts(5). The rheologicalpropertiesof a semisolidsystemsignificantlydetermineitsquality, usefulness,and purpose.Therefore,rheologyhasalwaysplayedand will play arole in the preparation,development,and manufactureof any formulation. For thatmatter,rheologicaldeterminationsareindispensablein the analysisof its properties.Theimportanceof rheologicalpropertiesin semisolidpharmaceuticaland cosmeticformsissuch that theologicaland thixotropic studieshave becomecrucial tools from bothpharmacotechnicaland galenicpoints of view. In a similar way, rheologycan elucidatethe possiblemodificationsof the system,expressedas a functionof time and tempera-ture, from the variationin the hysteresisloopsof the apparentviscosity(areaunder thecurve)(6). Thus,pharmacotechnicalteststhat includethe determinationof organolepticproperties,pH, sign, and macroscopicand microscopicexaminationallow us to evaluatethe evolutionof the propertiesof the formulationsmentioned,accordingto the time,temperature, and gravity. As a rule, the rheologicalstudy and, more precisely, theevaluationof thixotropicproperties,allow us to obtaina correctpictureof the physicalpropertiesand structuralstability of semisolidsystems(7,8).This study aimed to use theologicalmeasurementsin the evaluationof a commercialfacial mask samplemade mainly of Dead Seamud.

MATERIALS AND METHODSMATERIALS

The facialmasksamplesweresuppliedby Ammon for Dead SeaSaltsand SoapProducts(Amman,Jordan).The componentsof the maskusedwereDead Seamud (solids)67.0wt%, glycerin7.0 wt%, and stabilizer(with a trade nameofpolysaccharide)1.0-1.5%.The remainderwas deionizedwater. The chemicalidentity of Dead Seamud is naturalsediment.It is a mixture of solid mineral clayswith an interstitial solutionof inorganic


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FACIAL MASK OF DEAD SEA MUD 443

saltsand sulfidecompoundsoriginatedfrom microbiologicalactivity (4). The particlesizedistributionof the mud solidsis 86-98% 20 pm.The stabilizer"polysaccharide"is a modified starchcontainingglucoseas the solemonomerwith a molecularmassof 5 to 6 million daltons.It is obtainedby fermentationof Sc/erotiumro//3iion a glucose-enrichedmedium. The fermentationmedium is filtered.After beingwashedwith alcohol,the productis againdissolved,filtered,and dried. Thetype of linkagesfoundin the moleculegivesit a high stability;polysaccharideaqueoussolutionsshow thereforea good resistanceto aging and most enzymaticdegradations.Polysaccharidedisplayeda good ability to stabilize the mud suspensiondue to itscapacityto increasein a significantand stableway the viscosityof the medium. Poly-saccharidecan be usedin suspensionsat a recommendeddosagelevel of 1.0-1.5 wt%.RHEOLOGICAL MEASUREMENTS

The rheologicalpropertiesof facial mud were measuredwith a concentric-cylinderHaake-VT 500 viscometer,which has an inner cylinder rotating in a stationaryoutercylinder.Three differentmeasuringsystemswere used:MV2, MV3, and SV1. MV2 andMV3 usedthe samecup,with a radiusof 21.0 mm, anddifferentbobs,with radii of 18.4and 15.2 ram, respectively.On the otherhand,the cupradiusof the SV1 systemis 11.55mm, while its bob radiusis 10.1 min. Sampleswereallowedto relax(morethan 10 min)prior to measurementof their viscosity.It shouldbe pointedout that the viscometeroperatedin the range where the laminar flow is dominant. The viscometerwas ther-mostaticallycontrolledwith a water circulator(Haake D8) at the desiredtemperaturewith a precisionof + 0.1 C.METHODOLOGY

The experimentsperformedto characterizethe shear-,time- and temperaturedepen-dencyof the flow behaviorof Dead Seamud consistedof a seriesof two measurements:Apparentviscosityversusshearrate.A freshsamplewas loadedinto the annulargap of theconcentric-cylinderviscometer.Sampleswere left to reachthe desiredtemperature.Theapparentviscositiesof facialmud weremeasuredin the temperaturerangebetween5.0and 60.0C by continuousincreasing(forwardmeasurements)and continuousdecreasing(backwardmeasurements)of the shearrate. The valuesof the shearrate and apparent-Iviscositywererecordedevery30 sec.The shearratewasvariedfrom 2.200 to 159.80 sThe flow curvesof the facialmud wasmodeledusingthe Herschel-Bulkley(H-B) model:

(1)where is the shearstress,'ro is the yield stress,m is the consistencycoefficient,and nis the flow behaviorindex. Typically, the Herschel-Bulkleymodel is usedfor manymaterials,asthe NewtonJan,shearthinning, shearthickeningand Binghamplasticmaybe consideredas specialcases.Apparentviscositymeasurementsas a fnction of time at constantshearrate.In transientmeasurements,a freshsamplewasshearedat constantshearrates,namelyat 2.20, 10.21,28.38,47.43,79.02and/or131.90s-, andtheapparentviscositywasmeasuredasa


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444 JOURNAL OF COSMETIC SCIENCEfunction of shearingtime until an equilibrium statewas reached.Most of the samplesreachedthe equilibrium state in 30 min. The procedurewas then repeatedwith otherfreshsamplesat othershearratesand temperatures.The time-dependentflow propertiescould be modeledby applyingthe structuralkinetic (SK) model, which is adoptedbyusing the analogywith chemicalreactions.The final form of the model (9) is:

= + (2)whereqqois the initial apparentviscosityat t = 0 (structuredstate),qFlis the equilibriumapparentviscosityas t --> oo(equilibrium state),t is the shearingtime, k -- k (/) is therate constant of structure breakdown, and o is the order of the structure breakdownreaction.Details and assumptionsof this model are reportedby Abu-Jdayil (9).Rheologicalexperimentswere carriedout in triplicate,and the reproducibilitywas + 5 %on average.The averagevalueswere usedfor analysis.

RESULTS AND DISCUSSIONFLOW CURVES

It shouldbe pointed out that no surfaceslip was observedin the viscometersystemsused.Figure 1 showsthe flow curvesof the facialmaskmeasuredwith differentsystems,which havedifferentgap widths. It is clearthat the shearstressvalues(which representalsothe apparentviscosityvalues)of the mud mask are independentof the measuring

250 FacialMaskT=25CI .wI v200i [--I MV2[.....................................................................:...................... V svu 7150 ......................................................................................................................

.......... ........................................................!.............................................,

50- I , i...................... 5 .............................................. ...............................................,I I I I I0 40 B0 120 160 {1/$)

Figure 1. Flow curvesof the facialmaskmeasuredwith differentmeasuringsystems.

200


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Facial Mask : ':::J A T=lSC :---, ..... ,............................... :......... :...... .... ...............

--

6--

,,........................................ : .............................................................................. ,,,,

,

,,,,.... I I i I i III i I I I I is[2 4 6 8 2 4 6 8i 10 100 (x/s)Figure 2. Flow curvesof the facial mask fitted to the Herschel-Bulkleymodel.

system.Sincethe slip conditionsencounteredin a viscometerare a functionof the gapwidth, the data pointspresentedin Figure 1 showthat the slip conditionsin our systemare not clear.On the other hand, the shearstress-shearrate curvesof the facial mask shownin Figure1 indicatea shear-thinningflow with yield stresses.Figure 2 showsthe flow curvesofthe mud maskat differenttemperatures,fitted to the Herschel-Bulkleymodel(equation1). The regressedvaluesof 7o, m, and n for the forwardmeasurementsare presentedinTable I. It is clear that the parametersof the H-B model are temperature-dependent,

Table IRegressedParametersof the Herschel-BulkleyModelTemperature(C) ro (Pa) m (Pa s") n

5 40.0 11.30 0.6310 38.0 10.43 0.6215 35.0 9.96 0.6220 29.5 9.17 0.6225 30.6 14.66 0.4930 40.7 21.92 0.3835 60.0 25.16 0.3240 70.0 30.34 0.2245 67.0 29.58 0.1850 56.1 8.34 0.4255 54.5 7.20 0.4560 52.3 5.53 0.45


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0.100

2 m

0.010 -- i8 --6 --

i

4 i

2 i

olysaccharidssolution%I wt/oI T: 5CA T = 15 CI T: 25C [] T: 35o..................._i........................................................... c_.....

I I I

0.001 I I I I I I I I iiiii i I I I I IIII2 4 6 2 4 6 8 2 4 6 810 100 1000 10000

Figure 3. Temperaturedependenceof the theologicalbehaviorof polysaccharide.

On theotherhand,Figure3 showsthatat highshearrates(above300s-) theapparentviscosityof the polysaccharidedecreaseswith temperature,which meansthat the gelstructureis destroyedunderthe effectof high shearing.The high temperaturesoftensthegranulesof the polysaccharide,and the stressesimposedon them are large enoughfordeformationand flow, which in turn resultsin the decreasein viscositywith tempera-ture.

The effect of temperatureon the rheologicalbehaviorof the Dead Sea facial mask isshownin Figures4-6. The investigatedfacialmaskdemonstratesan unexpectedbehav-ior with temperature.This behaviorcanbe dividedinto threestages.In the first stage,which coversthe temperaturerangeof 5C to 20C, the apparentviscosityof mudbehaveslike the normalliquid, i.e., the apparentviscositydecreasesasthe temperatureincreases(seeFigure 4).However,an interestingbehaviorhasbeenobservedin the secondstage,which coversthe temperaturerangeof 20Cto 40C.As shownin Figure5, the apparentviscosityofthe facialmaskincreaseswith temperature.Above40C,the mud maskbehavestypi-cally in that the apparentviscositydecreaseswith temperature.This stage is demon-stratedin Figure 6.It seemsthat the presenceof the stabilizer"polysaccharide"is responsiblefor the unusualbehaviorof the secondstage.It shouldbe statedhere,that the rheologicalmeasurementson the facialmaskwerecarriedout in the low regionof shearrate (below200 s-1)(compareFigures4-6). In this shear-rateregion,it hasbeenshownthat the polysac-charideviscosityincreaseswith temperature(seeFigure 3). This explainsthe atypicalbehaviorof the facialmaskwith temperaturein the secondstage.It can be concluded


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448 JOURNAL OF COSMETIC SCIENCElOO

4 6 8 2 4 6 81 10 100 (1/s)Figure 4. Effectof temperatureon the apparentviscosityof the facialmask(5-20C).

lOO

lO

Figure 5. Effbctof temperatureon the apparentviscosityof the facialmask(2040C).


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450 JOURNAL OF COSMETIC SCIENCE

100 8 --

6 --

4

FacialMaskForwardmeasurement/Back-wardmeasurement) T: 5 C.

2 4 6 8 2 4 6 81 10 100

Figure 7. Temperatureeffecton the hysteresisloopsof the flow curvesof the facialmask.

behavior.As shownin Figure7, at low temperaturesthe directionof the hysteresisloopsis counterclockwise,indicatingan anti-thixotropicbehavior,which meansthat there isan increasein the mud viscositywith shearingtinhe.In someconditions,the right kindof attractionbetweenparticlesof mud is given;shearingcan then promotetemporaryaggregationratherthan breakdown,due to the collisionof theseattractiveparticles.Thisresultsin anti-thixotropy(18). Like other similarsuspensions,thereis a rangeof flowconditions under which shear-enhanced collisions make structure rather than break it(18). However,this anti-thixotropicbehavioris relativelysmall (accordingto the sizeofthe hysteresisloop) and disappearsgradually with increasingtemperature.Above 25C, the facial mask showshysteresisloopswith a clockwisedirection, indi-cating a thixotropic behavior.The size of the hysteresisloops becomeswider as thetemperatureincreasesfrom 25 to 60C (seeFigure 7).It shouldbe pointedout that the shear-thinningand thixotropicbehaviorshaveindus-trial and commercialsignificance.For example,sincethe viscositydecreaseswith shearrate and shearingtime during the mixing process,this will lead to lesspowerconsump-tion. Moreover,particle sedimentation,which in this casewould negativelyaffecttheconsumeracceptanceof the product,will occurslowly due to high viscosityat restconditions.On the other hand, the shear-thinningand thixotropic behaviorshave asignificantimportancein the ability of the facialmaskto spreadon the skin,wheretheDead Seamud maskcanbreakdownfor easyspreadingand the appliedfilm cangainviscosityinstantaneouslyto resist running. Newtonian materials do not behavein thisway, becausewhenspreadon the skin they run very quickly,reducingthe thicknessofthe requiredfilm.


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In order to evaluatethe effectof shearingtime on the rheologicalbehaviorof the mudmask,the viscosity-shearrate relationshipwasdeterminedat differenttimes of shearing.Dead Seamud mask sampleswere shearedat differentvaluesof constantshearingrateand at differenttemperaturesfor 40 min. At 5C the mud mask samplesexhibit atime-independentbehaviorat low shearrate and a weak thixotropicbehaviorat highshearrate(seeFigure8). The weakbondingbetweenparticlescouldexplainthe strengthdrop observedwhen the temperatureand shearrate increase.However, the rate andextent of viscositydecaydependon both the applied shearrate and the temperature.Typical thixotropicbehaviorobtainedat differentshearratesfor the Dead Seamud maskat 45C is shownin Figure 9.The observedtime-dependentflow behaviorof the mud mask was modeledusing thestructuralkineticsapproach(9). This modelpostulatesthat the changein the rheologicalpropertiesis associatedwith shear-inducedbreakdownof the internal fluid structureinthe Dead Sea mud. Using the analogywith chemical reactions,the final form of thestructural breakdownprocesscan be expressedas in equation 2. For all mud masksamplesinvestigated,it was found that their apparentviscositydata at constantshearratescould be correlatedwith equation2, using o -- 2, i.e., with a 2nd order irreversiblekinetic model. A goodcomparisonbetweenthe model fitted results(solidlines)and theexperimentalapparentviscosity/timedata for the mud mask can be seenin Figures 8and 9.The rate constant,k, is a measureof the rate of thixotropicbreakdown.Meanwhile theratio of the initial to equilibrium viscosity,qqo/q%,can be consideredas a relativemeasureof the amount of structural breakdown, or in other words as a relative measure

lOO

2 i

I=,i,IM,$k"].............................::.............................'i- q- 2.201/sk .............................::.............................'71 47.431/

,

,

............................. 4............................. :............................. ............................

............ .............i ............. ............_i............. .............._> ,,_....................::....... ....... k - >!< ....... X- ......... ........... X ...........

I I I I5 15 25 350 10 20 30

Shearingtime (min)Figure 8. Dependenceof the facialmask'sapparentviscosityon shearingtime at 5C.


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452 JOURNAL OF COSMETIC SCIENCElOO

........................................................[ /__i__/! S-Kmodemi 28381s,-----' _ .............:..............?---S-Kmodel)___!._.. /' " 131.91/s

2

15 25o lO 2o 3oShearingtime (rain)5 35 4O

Figure 9. Dependenceof the facialmask'sapparentviscosityon shearingtime at 45C.

of the extentof thixotropy.The valuesof k and Xlo/Xlasa functionof the appliedshearrate and the temperatureare reportedin Table II. As one expectedfor a thixotropicstructuredmaterial, k generally increaseswith increasingshearrate and temperature.Thixotropy is the result of structuralbreakdownunder shearand manifestsitself as adecreasein the apparent viscositywith time. As time of shear elapses,the rate ofbreakdown will decrease,as a fewer structural bonds are available for breakdown. Struc-tural reformationmay take placeand the rate of this processwill increasewith time ofsheardue to the increasingnumberof bondingsitesavailable(15). Table II showsalsothat the amountof structuralbreakdown(Xlo/Xl)increasesalsowith temperatureandshear rate.

CONCLUSIONSThe temperatureand shearingconditionsdependencyof the apparentviscositywereinvestigatedfor a facial mask made mainly of Dead Sea mud. The mud facial maskbehavedlike a shear-thinningmaterial with a yield stressand generallyexhibited athixotropicbehaviorin the temperaturerange of 5 to 60C. This behaviorhas apracticalsignificancethat deceleratesparticlesedimentationdue to high viscosityat restconditions.In addition, the shear-thinningand thixotropicbehaviorshavea significantimportancein the ability of the facialmaskto spreadon the skinwith a controllablefilmthickness.The Herschel-Bulkleymodel fitted well the flow curvesof the mud facialmask.The effectof temperatureon the facialmask'sapparentviscositywasdividedintothree stages.In the first stage, 5-20C, the viscositydecreased,as expected,with


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Table IIDegreeand Extent of Thixotropy of Dead SeaMud Mask, Evaluatedat Different ShearRatesand Temperatures

T]oTemperature(C) 'y' (s ) k x 103 (rain-) 'qo/qq, (Pas)5 2.20 0.0 1.00 24.4

10.21 47 1.05 12.728.38 121 1.16 6.247.43 190 1.23 4.5

15 2.20 28 1.03 22.310.21 79 1.05 10.628.38 125 1.17 5.247.43 361 1.28 2.7

25 2.20 39 1.08 23.510.21 139 1.13 10.128.38 209 1.20 4.947.43 404 1.35 2.8

35 2.20 82 1.34 41.410.21 270 1.43 12.228.38 280 1.50 5.579.02 489 1.51 3.8

45 2.20 150 1.90 47.810.21 328 1.93 12.928.38 555 1.97 5.2

131.90 618 2.76 2.7

temperature.But increasingthe temperaturefrom 20 to 45C led to an increaseinviscosity.This behaviorwasattributedto the gelatinizationof the stabilizer.In the thirdstage,45-60C, the mud maskregainednormalbehaviorand its viscositydecreasedwith temperature.As far asthe effectof steadyshearingon the flow propertiesof a DeadSea mud mask is concerned,the secondorder structural kinetic model describeditsthixotropicbehaviorwell. The rate of structuralbreakdownincreasedwith both shearrate and temperature.

ACKNOWLEDGMENTSThe authorsare grateful to Dr. HussamEI-Haffar and Mrs. Aida Frehatt from AremortCo. for their kind cooperationand supplyof materials.

REFERENCES(1) K. Sukenik,Balneotherapyfor rheumaticdiseasesat the Dead Seaarea,lsr.J. Med. Sci. 32, S16-S19(1996).(2) M. Hagit, O. Esith, and W. Ronni, Balneotherapyin dermatology,Dermatol.Ther., 16, 132-140

(2003).(3) S. Halevy, H. Giryes,M. Friger,and S. Sukenik,Dead Seabath salt for the treatmentof psoriasisvulgaris:A double-blindcontrolledstudy,J. Eur. Acad,Dermato/.Venereo/.,9, 237-242 (1997).(4) Z. Maor, S. Yehuda,S. Magdassi,G. Meshulam-Simon,Y. Gavrieli,Z. Gilad, and D. Efron, CreamcompositioncomprisingDead Seamud, US Patent6582709 (2003).


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