low-energy emulsification -applications in high internal phases emulsions

8/10/2019 Low-Energy Emulsification -Applications in High Internal Phases Emulsions

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j. Soc.Cosmet. hem., 35, 357-368 (November 1984)

Low-energy mulsification.Part VI: Applicationsn

high-internal haseemulsions

T. J. LIN, 628 Enchanted ay, PacificPalisades, A 90272, and

Y. F. SHEN, ShenHsiangTang Chemical o., Ltd. P.O. Box 150,

Talchung, aiwan.

Receivedecember2, 1983. Presentedt Annual Scientific eeting,

Societyf Cosmetichemists,ew York, December, 1983.

Synopsis

Low-energy mulsification LEE) is a novel emulsificationmethod by which thermal energy s selectively

applied o onlya portionof the externalor internalphasenstead f to the entireemulsion s n conventional

emulsification. lthoughLEE hasproven o be extremely nergy-efficientndverypractical n processing

a wide-range f commercial mulsions,t hasbeendifficult to apply he techniqueo emulsions ith large

internalphase olumesbecause f potential rreversible hase nversion.The inversion roblem s partic-

ularly acutewhen LEE is carriedout at relativelyhigh ratiosof unheated hase o heatedphase.

The modifiedLEE technique nvolveswithholdingof a portion of the internal phase iquid as well as a

portion of the externalphase.The emulsion s made n three stages,with applicationof thermal energy

only during the first-stage oncentrate reparation.

Tests on O/W emulsions stabilized with anionic and nonionic surfactants indicate that the new method

can effectivelypreventpermanentphase nversion n high-internalphaseemulsions nd allow LEE pro-

cessing t higher ratios of unheatedphase o heated phase han did the original LEE method. It was

discoveredhat mixing time and mixer rpm as well as the bulk temperature nd the sizeof the withheld

phasehave significanteffectson the mean droplet size of finishedemulsions.

INTRODUCTION

Low-energy mulsificationLEE), as originally ntroducedby Lin, involves two-stage

processing f emulsions 1). A portion of the emulsion'sntendedexternalphase luid

is withheld and an emulsionconcentrates first made with applicationof thermal

energy. Generally, the withheld phase alpha phase) s not heatedand serves o cool

the bulk during the second tageprocessing hich nvolves dilution of the emulsion

concentrate.Hence the greater he ratio of the unheatedwithheld phase o the heated

externalphase beta phase), he greaterwill be energyconservation nd cost-reduction.

In this work, o and [3 are definedas the weight fractionsof the unheated nd heated

phases espectively.Subscripts and e are used to denote the emulsion's nternal and

externalphases.

It has been demonstratedn pilot plants as well as in many manufacturingplants in

differentparts of the world that LEE canbe extremelyuseful n processing wide range

of cosmetic, ood, and pharmaceutical mulsionswith significant eductionof energy

and processing osts.The increasen productivity due to a reduction n the cooling

357


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358 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

time as he resultof adoptingLEE canbe very substantial.n somecases,he reduction

of cooling equirementsan be so great that the useof a refrigerated ystem an be

entirely eliminated n designinga new plant (2).

Previous xperimental ork indicated hat whencorrectly rocessed,he qualityof the

emulsionsmade with LEE was virtually indistinguishablerom that of the emulsions

made with conventional ot processing3). Although it is clear that the greater he

ratio of tx to [3, the greaterwill be the energyconservation,here is a practical imit

to the sizeof the alphaphase ecause f potential, rreversible hasenversion spointed

out in an earlier work (4).

Uncontrolledphase nversions nd the resulting reduction n emulsionstability or

coarsening f the emulsion extureare also he main reasons hy it hasbeendifficult

to apply LEE on emulsions ontaining elativelyhigh solidsor emulsions aving nternal

phases xceeding 0% of the total volume.Emulsions tabilizedwith nonionic urfac-

tants may undergophase nversionat temperatures ear he phase nversion emperature

(PIT). LEE processing ay lead to the formationof a coarse mulsion f phase nversion

is not controlled 5). On the otherhand, when the key variables reproperlycontrolled,

LEE can producevery fine emulsions aving significantly mallermeandroplet sizes

than the emulsions reparedwith a conventional igh-energymethod 6).

The purposeof this work was to test a new technique f doublewithholdingwhich

was designed o expand he utility of LEE beyond ow-internalphaseO/W emulsions

and also o allow LEE processingn a relativelyhigh tx range.

In the original LEE method, only a portion of either the externalor internalphase s

withheld during the initial emulsification rocess. he new techniquenow involves

withholding portions of both phases.To avoid confusion, he withheld, unheated

portionsof the internaland externalphases ill be designated s x, phase nd tx phase

respectively. imilarly, the heatedportionsof the internaland externalphases ill be

respectivelyeferred o as [3iphase nd [ephase.

In the original method, emulsification s carriedout in two stages, ncluding a con-

centrate reparation tageand a dilution stageas ndicated elow:

OriginalLEE

First Stage:ConcentratePreparation

Internal Phase heated) + [e EC (EmulsionConcentrate)

SecondStage:ConcentrateDilution

EC + txe - Ef (Final Emulsion)

The new LEE technique o be introduced ere nvolveswithholdingof both txiand tx

and hence equires three-stepoperation s indicatedbelow:

New LEE (DoubleWithholding)

First Stage:ConcentratePreparation

[i q- [e El (First EmulsionConcentrate)

SecondStage: Xe-Phase ddition

E1 q- Oe> E2 (SecondEmulsion Concentrate)

Third Stage: xi-Phase ddition

E2 + tx ---> Ef (Final Emulsion)

The advantage f the doublewithholding echnique an be readilyseen rom Figure

1. In this illustration, the internal phasevolume is approximately qual to one third


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HIGH INTERNAL PHASE LOW ENERGY EMULSIFICATION 359

EXTERNALHASEx CASEfA}

INTERNALHASE-

...... (A)-

......... (B}---

L

=0.33

.e: 0.67

CASE(B]

C.= 0.67

0.5

EMULSION

Figure1. Comparisonf twodouble ithholdingEEprocesses.n bothcasesnternal hase quals ne

thirdof external hase; qando arewithheldnternal ndexternalhasesespectively;3,and Be re

heatednternal ndexternalhasesespectively.ase is more nergyfficient ue o a largerwithheld

external hase%. Splittingof the internal hasento oqand[3,andusingonly 3, or the initial emulsi-

fication educehe dangerof phasenversion.

of the external hase olume.ForLEEprocessing,he external hases predividednto

withheldOLphase ndheated ephase.f the divisionof the external haseweremade

at Oe/lBe O.33/0.67as n theCaseA), indicated y a dashedine, thevolume f [e

phasewould be significantlyarger han the total internalphase nd generally here

wouldbe no greatdangerof phasenversion. o achieve vengreater nergy onser-

vation, he divisionof the external hasemay be madeat a highero/[3c atio. In Case

(B) shownwith a dotted ine, the OLJ[ratio is chosen t 0.67/0.33. This means hat

the [3cphases now roughly qual o the totalvolume f the internal hase. rom

phase olumeconsiderations,here s nowa greaterdangerof unintended hasenver-

sionduring he first stageof the emulsion oncentratereparation.

One way to minimize the chanceof unintendedphase nversion s to add the external

phase iquid slowlyto the internalphase iquid. In a plant-scale peration,however,

sucha method s not only time-consuming, ut may be unreliable.Controlling he

initial surfactantocation sproposedy Lin andLambrechts aybeusefuln borderline

cases, ut it is not a sureway to controlphase nversion7).

A bettermethodproposed ere s to divide the internalphase nto oqand 13i. f, for


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360 JOURNAL OF THE SOCIETYOF COSMETICCHEMISTS

example, he internalphaseweresubdividednto two equalpartsas shown n Figure

1, and f only the i phasewereused o preparehe emulsion oncentrate,he ratioof

the external haseo the nternal hase olumeor theconcentrateouldnowbeabout

two insteadof one for Case B). For Case A), the ratio would now be approximately

four. The substantialncreasen the ratio of the externalphase olume o the internal

phase olume n the first-stage oncentratereparation ill greatly educe he chance

of phasenversion uring his stage.Since he second tage perationnvolves nly the

additionof an external-phaseluid (o phase)here s little danger f phasenversion.

Although he third stageoperation equires dditionof the remaining nternalphase

(oqphase)here s no greatdanger f phasenversionince n additional mountof the

external-phaseluid wasadded o the bulk in the second tageoperation.Hence, the

new double-withholdingrocedureffectivelyeduceshe dangerof irreversiblehase

inversionduring the manufacturing rocess nd allowsLEE processing t relatively

high o/ ratios o achieve ubstantial nergyconservation.

EXPERIMENTAL

Experimentswere carried out in 250-ml glassbeakerswith no baffles.A six-blade

turbinemixer driven by a high-torque,variablespeedmotor wasused o prepare he

emulsions. he dimensions f the turbinesare indicated n Figure 2. Since he rate of

phaseaddition was found to affectphase nversion, he ratesof adding the o and oq

phases erecarefully ontrolled y introducinghe fluid through buretwith a constant

orifice.Other experimental etails, ncludingheatingandcombining he phases, ere

similar to thoseof the procedureused n previous eports 3-5). Droplet size distri-

butionswereobtained hotographically.he meandropletdiameter epresentsn arith-

meticaverage f approximately00 droplets. he e andi phases ereheated o 75C

before ddition, and the o and oqphases erekept at 26Cbefore ddition.

RESULTS AND DISCUSSION

EFFECTS OF % AND %

According o an earliertheoryadvanced y Ostwald, emulsionphase nversionoccurs

when the internal phasevolume exceeds 4.02% of the total volume (8). However,

this argument s basedon closelypackeduniform spheres,which doesnot necessarily

represent real emulsion. For non-uniformdroplets,the critical volume fractionof the

internalphase,4), may far exceedhe 0.7402 limit withoutphasenversion.

In commercial rocessing f emulsions,however,phase nversiondepends ot only on

phase olumebut alsoon manycomplex actors, ncludingsurfactant LB, processing

temperature,method of preparation,mixer geometry, mixer speed, and the rate of

phase ombination.Generally, he phase-inversionroblembecomes ore roublesome

to control n a plant operationwhen4) values xceed .4.

For our experiments, e selectedO/W formulations avingapproximately 0% internal

phasevolumes.One exampleof sucha formulation s in Table I.

Using the above ormulation, one hundredemulsionswere preparedwith o and oq

values anging rom 0 to 0.9. In this seriesof experiments, ll waxy substancesswell


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50MM

---.Ir2 MM I--'-

-t-

IOMM

- 6 MM --4

as the oil-soluble urfactants ere nitially placed n IBiphaseand the water-soluble

surfactantswell as he water-solubleolymerwereplacedn the IBe hase s ndicated

in Table I. Mineral oil and deionizedwater were divided into both o and [ phases.

The rateof additionof [3 phasewassetat 14 ml/min. and the mixerspeedwasset at

400 rpm. All otherprocessariables erecarefully ontrolledo assure good epro-

ducibility.The emulsionype or each un wasdetermined ith an electrical onduc-

tivity tester,and he results resummarizedn Table I.

The test formulation ontains 8.5% of the oil phaseby weight (>50% by volume).

By a deliberatehoiceo test heutility of themodifiedmethod, his ormulationoes

not lend tself o easyLEE processing.he datapresentedn the first row of Table


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9

.8

.7

.6

.4

.3

.2

.I

-.I

-.2

i

o/w

w/o

; = 1.2cx -0.15

i z J i i I ,

.2 .3 .4 .5 .6 .7 .8 .9 i

Figure 3. Relationshipbetweenamount of externalphasewithheld (%) and the minimum amount of

internal phasewhich must be withheld (oO to produceO/W emulsions.Emulsionsbelow line are W/O

and above are O/W.

The slopeof the line (1.2) in Figure3 reflects he effectivenessf the double-with-

holdingechnique.n thiscase,he smallerhe slope f the ine, the greaters the

effectivenessf withholdingq n preventinghasenversiono formW/O typeemul-

sions.

Clearly,when he y-intercepts zeroor greater,no O/W typeemulsion anbe formed

with either heconventionalmulsificationethod r theoriginal EEmethod t any

Oealue nd heuseof thedouble-withholdingechniqueecomesssentialn making

an O/W emulsion.

It is o benoted ere hat hedata n TableI representnly heemulsionypewithout

regardo emulsion ualityor droplet izes. EEprocessingt different e ndoqvalues


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0 I I i, I I

200 400 600 800 I000 1200 1400

MIXER SPEED (RPM}

Figure4. Meandroplet ize n a finalemulsionsa function f mixingspeed. representshe mean

dropletdiameterof a final emulsionhaving he composition hown n Table I, immediately fter he E2

emulsiononcentrateasmixedwith oq or 8 minutes t 27C.TheE2emulsiononcentratesere repared

identicallyat % = 0.2, oq = 0.8, and cooled o 27C before he additionof oq. The E2 emulsion

concentrate ad a meandropletsizeof 2.5 microns.)

represent significant ariation n processingonditions nd thusa largevariation n

the propertiesof the emulsionscan be expected. n addition to o values, emulsion

temperature,mixing time, and the rate of mixing can alsohavesignificant nfluence

on the final emulsion.

EFFECTS OF MIXING

The majordifference etweenhe modified EE and he originalLEE s the third-stage

operation n the new techniquewhich involves n additionof oqphase nto the emulsion

concentrate, 2. Althoughaddingoil into a preformedO/W emulsionmay represent

a radical departure rom a normallyemployedemulsificationmethod, there are no

theoretical roundso believehat such procedure ouldnotproduce commercially-

acceptable mulsion.

Actually, headditionof an oil into an O/W emulsions notreallyanunusualndustrial

practice ince n makingmosthandcreams,he cold ragrance ils are oftendirectly

added o preformedO/W emulsionst bulk temperaturesroundor below40C.


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5O

z

o

o

r-

Z

4O

3O

2O

I0

T = 27"C

= 300 RPM

=mmO 0RPM

R = moo0 IPM

0

o 2 4

6 8 I 0 12 14 16 18 20 22 24 :::)6 2_8

MIXING TIME, ,9 (MIN)

Figure 5. Meandropletsizeasa function f mixingspeed nd ime aftero addition. representshe

meandropletdiameter f a final emulsion aving he compositionhownn Table , immediatelyfter

the E2 emulsion oncentrate asmixedwith oqat mixer speedR and mixing time 0. The E2 emulsion

concentrates ere prepared denticallyat o -- 0.2, oq = 0.8, and cooled o 27C before he addition of

oq. The E emulsionconcentrate ad a meandropletsizeof 2.5 microns.)

The important uestion ere s how ongandat what speedhe final emulsion, l,

mustbe mixedafter he addition f the otiphase.Addition ndmixing n of the oti

phase esults n not only a sizereduction f emulsion ropletsbut alsomass-transfer

of surfactantsndother omponentsetweenhenewly ormednterfaces.icroscopic

examinationsndicate hat asotiphase s added o the E2 emulsion, he sizedistribution

initiallyshows ualpeaks.With furthermixing, he sizedistributionnitiallyshows

dual peaks.With furthermixing, the emulsion roplets hangeo a near-Gaussian

distribution.

The rateat whichdroplet-sizeeductionakesplacedependseavily n the mixing

conditions.s canbe seenromFigure , the mixerspeeds a very mportantactor,

asmixingof an E2 emulsion oncentrateelow300 rpm producedxtremelyoarse

final emulsions.n this example, owever,ncreasinghe mixer pm beyond ,000

does ot appearo accomplishurthersize eduction ithinan eight-minuteeriod.

Theeffect f mixingspeed anbealso eenrom hedatapresentedn Figure , which

showsoth herpmandmixing-timeffects. sexpected,ize eductions more apid

at a highermixing speed.Since he meandropletsizeof the E emulsionbefore he

addition f o wasabout2.5 microns,he data ndicatehat t would equire bout20


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366 JOURNALOF THE SOCIETYOF COSMETICCHEMISTS

25

z

0 I0 20 30 40 50 60 70

TEMPERATUREF E2 , T (C)

_

Figure 6. Effectof initial E2 temperature n meandropletdiameter. D representshe meandroplet

diameter f a final emulsion aving he compositionhownn Table , immediately fter he E2 emulsion

wasmixedwith % at 720 rpm for 5 minutes. he temperaturef theoqphase as26C.TheE2 emulsion

concentratesereprepareddentically t o = 0.2, % = 0.8, andcooledo 26C.EachE2 emulsion

concentrate asheatedor cooled o the temperaturendicated n the abscissaeforeoqaddition.The E2

emulsionconcentrate ad a mean droplet sizeof 2.5 microns.)

minutesof mixing time at 1,000 rpm to reduce qdropletso the same verage ize

as E2 droplets.

EFFECT OF TEMPERATURE

Temperatures, of course, very important actor n all emulsion rocessing.n

example howinghe effectof the initial temperaturef the E2 emulsion n the mean

droplet izeof the final emulsions shownn Figure6. It is interestingo note hat

the meandroplet izeshows minimum t an E2 temperaturef about 0C. t is

believedhat the existence f the minimumpoint is probably ue to a viscosityffect.

At a constantmixerrpm, size-reductions mostefficient t a moderatelyighviscosity

rangeora shear-thinning,ime-dependentmulsion. scanbeseenrom heviscosity

data n Figure , theviscosityf theemulsionrops harplyt around 0C, esulting

in a lowered hear ction y the mixer otating t a constantpm. On the otherhand,

as hetemperaturerops elow 0C, he ncreasediscositynd heyieldvalue rob-

ably make he mixing essefficient, esultingn the formation f coarsermulsions.


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HIGH INTERNAL PHASELOW ENERGY EMULSIFICATION 367

60

o

u

50

40

30

0

IO I I I I i i I I I I I ,

I O 0 :30 40 0 60 70

tEMPEr/TUrE, t { C)

Figure 7. Effectof temperature n the viscosity n an E2 emulsion oncentrate.Viscositys the scale

reading n a Brookfield ychrolectriciscometer, odelLVT,'spindle 4, at 0.6 rpm. TheE2emulsion

concentrateasprepared t o = 0.2, o, = 0.8, based n the compositionn Table I andcooledo

26C. The emulsionconcentrate asheatedor cooled o the indicated emperature eforeviscositymea-

surements.)

This is anotherexampleshowing probable easonwhy sometimes ne can make a

finer emulsionwith LEE than usinga conventionalot emulsification ethod 6).

CONCLUSIONS

Experimentalatapresentedere ndicatehat themodified EE echniqueanbeused

to process /W emulsions ith relatively arge nternalphases r to carryout LEE in

a higherot rangewithout encounteringhe usualcomplication f unintended hase

inversion.

Although ll experimentalatapresentederewereobtained n aboratorycale quip-

ment, somepilot plantwork on different ormulations ascarriedout to demonstrate

the feasibility f usingsuch technique n a commercialcale.When carried ut at

correct t and ote alues,emulsificationroceedederysmoothlyo yield stableemul-

sionswith very fine texture.

In addition to saving more energy, the new technique s even lesssusceptibleo

unintendedhasenversion, scanbe seen rom he data n Figure3; it canbe used


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to control he phase nversion roblem n a commercial peration ven f energycon-

servation s not the purpose.

The successf adopting he method, however,may be dependent n properselection

of the size of oteand oti as well as the mixing equipmentand mixing conditions.As a

rule, oteand oti valuesshouldnot be selected t points too close o the phase-inversion

boundary ine.

ACKNOWLEDGEMENT

The authorsgratefullyacknowledgehe experimental ssistancef C. S. Chiang in

connection with this research.

REFERENCES

(1) T. J. Lin, Low-energy mulsification: Principles nd applications,. Soc.Cosmet.hem., 9, 117-

125 (March 1978).

(2) T. J. Lin, Low-energy rocessingf cosmetic reams nd otions,Cosmeticsnd Toiletries,5, 51-56

(March 1980).

(3) T. J. Lin, T. Akabori, S. Tanaka, and K. Shimura, Low-energy mulsificationI: Evaluationof

emulsion uality,J. Soc.Cosmet. hem.,29, 745-756 (December 978).

(4) T. J. Li.n, T. Akabori, S. Tanaka, and K. Shimura,Low-energy mulsificationII: Emulsification

in higl-'-zange,osmeticsnd oiletries,5, 33-39 (December980).

(5) T. J. Lin, T. Akabori, S. Tanaka,and K. Shimura,Low-energy mulsificationV: Effectof emul-

sification emperature,Cosmeticsnd Toiletries,6, 31- 39 (June 1981).

(6) T. J. Lin, T. Akabori, S. Tanaka, and K. Shimura, Mechanismsf Enhancedmulsificationn Low-

Energy rocessing,aperpresentedt 12th .F.S.C.C. Congress, aris,France,September 982.

(7) T. J. Lin andJ. C. Lambrechts, ffectof initial surfactantocationon emulsionphase nversion, .

Soc.Cosmet. hem., 20, 185-198 (March 1969).

(8) P. Becher,Emulsions.'heorynd Practice,nd ed., (ReinholdPublishing orp., New York, 1965),

pp 101-104.

low-energy emulsification -applications in high internal phases emulsions

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