Document 138686

Cosmet,
Sd,, 58, 451-476 (July/August2007)
Semi-permanentsplit end mendingwith a
polyelectrolytecomplex
R. RIGOLETTO, Y. ZHOU, and L. FOLTIS, InternationalSpecialty
Products,
1361 AlpsRoad,Wayne,N.J. 07470.
Synopsis
Split endsform throughmechanical
stresses
duringgroomingprocedures
and aremorelikely to appearin
hair damagedasa resultof excessive
combingforces.Althoughthereare no conventional
systemsthat will
permanentlymendsplit ends,a semi-permanent
mendingcomposition
hasbeenachievedthrougha polyelectrolytecomplex.The complexis formed as a result of the ionic association
of a cationicpolymer,
Polyquaternium-28,and an anionic polymer, PVM/MA Copolymer.Hair tressescontaining tagged split
endsareusedin measuring
mendingefficacy.The taggingallowsthe fateof the split endsto be determined
afterdifferenttypesof treatmentregimenswhichtestthe durabilityof the mend.Monitoringof the repair
andmendingdurabilityis carriedout with the aid of a stereomicroscope.
Resultsobtainedwith this method
indicatethat the complexbothby itselfandwhenformulatedinto a simplelotionprovideda high levelof
split end mending not only after initial treatmentbut more importantlyafter combingshowingthe
durabilityof the mend.Cumulativeeffectsand durabilityto washingindicatethat the polymercomplex
doesnot build up on the hair and rinsesoff with shampoomakingpossibleits usageasa postshampoo
treatment.The formulatedlotion hashigherdurabilityperformance
ascomparedto a commercialproduct
with a split endmendingclaim.The proposed
mechanism
of actionentailsa crosslinking
microgelstructure
that infiltratesthe damagedhair sitesbindingthem together.This modelis supportedby the analysisof
phasebehavior,viscometry,
Scanning
ElectronMicroscopy,
andabsorption
of ionicdyes.
INTRODUCTION
The manifestationof damagedhair as seen macroscopically
as we view whole hair
attributes is basedon the state of each of the individual fibers taken collectively.
Different typesof damageare observedon a microscopicscaleusing scanningelectron
microscopyas a diagnostictool (1). These consistof transversefracturesthrough the
hair's cuticle, transversefractures of the whole fiber, delamination within the cuticle,
longitudinalsplitting of the hair shaft(split ends),and multiple longitudinalsplitting
of the hair shaft (trichorrhexis nodosa) (2). Each of these structural maladies when
multiplied by the numberof fibersis portrayedin wholehair attributessuchasdullness,
lack of manageabilityor stylability, rough texture,and poor combability.The hair as a
whole basedon the stateof the individual fiberslooksunhealthy.
There are multiple causesfor this damageand encompass
physical,chemical,and environmentalfactors.Versatilityof hair stylesis a majorcauseof the predominance
of hair
damage.Consumersdesireproductsthat allow them to expresstheir individuality and
personalstyleto a greaterextent.Keepingup with the latesthair stylefashionincludes
451
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JOURNAL OF COSMETIC SCIENCE
oxidativehair coloringand permanentwaving.Also styling agentsin combinationwith
stylingimplementssuchascurlingandflat ironsallowsoneto havea differenthair style
evenfrom oneday to the next. The resultof this increasedamountof styling hasits effect
on the quality and conditionof the hair. This is compoundedwith longerhair styles
sincethe endsof the hair are older and haveexperiencedmore weatheringaswell as the
aggressive
stylingtreatments.Eventuallythe hair becomes
dull, unmanageable,
coarseto
the touch,andhardto comb.When viewingthesedamagedfiberson a microscopic
scale
one realizesthe causeof what is observedon the macroscopic
scale.With the predominanceof aggressive
styling behaviorsit is clearthat there is a market needfor compositionsand productsthat are able to not just prevent hair damagebut, what is more
challenging,affectits repair.
One manifestationof damagethat affectswholehair attributesare fibersthat havesplit
longitudinally at their tip ends.The technicalterm for split endsis trichoptilosis.The
theory of split end formation as proposedby Swift is fully elaboratedin an article
entitled Mechanismof split--end formationin human headhair (3) and is depictedin
Figure l. A cluethat led to the theoryon the mechanismof split endformationwasfrom
an SEM of a split endfiber. It wasobserved
that the split occurredin sucha mannerthat
it formedparallelto the majoraxisof the hair diameter(4). Swift theorizedthat when
hair is combedthe elliptically shapedhair fiberspreferentiallyorientaresso that the
majoraxisis parallelto the surfaceof the combtooth. As the combtraverses
the hair,
shearstresses
are producedparalleland longitudinalto the major axisof the fiber. The
degreeof shearstressis distributedparabolicallyalongthe minor axisof the hair sothat
the shearplane sufferingthe most shearstresswould be that running parallel to the
major axisof the hair. When the shearforcebecomesgreat enoughtiny fracturesoccur
along this axis and eventuallywill propagateto the end of the fiber. As the comb is
pulled through the hair the bending is propagatedfrom root to tip; it is not a static
bend.As the combreachesthe tip end of the tressthe collectionof fiberstend to snarl
increasingthe shearstresses
to a greaterextent at the tip than anywhereelsealong the
fiber length. Fibersare dynamicallybent over 180 degreesas observedundera stereo-
Comb tooth
Major diameter
Shear stress
y axis
Figure 1. Mechanismof split end formationshowingthe distributionof shearstresses
in fiber during
combing.Depictionof theoryproposedby Swift (3)
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microscope
(Figure2). The major stressthen leadingto hair fractureis not just oneof
stretchingsuchas is measuredby tensilestrength,but ratherflexureor bending(5).
Combing,then, is the major route that fiberstend to split sincetheseshearforcesare
necessary
to fracturethe hair which eventuallywill lead to a split end. However there
are many factorswhich weakenthe hair that predispose
it to split during the combing
process(6). There are many references
on the effectsof UV on the degradationof the
differentstructuresof hair. One referenceis a reviewof our currentunderstandingof the
subjectandoptionsfor photoprotection
(7). Other damagingfactorsthat arenoteworthy
to mention are chemical processingsuch as bleaching (8), thermal (9), thermalmechanicaldamage(brushand blow dry) (10), and damagefrom surfactants
which can
be translatedto multiple shampooing
(11). Evenif hairhasnot beenpurposelydamaged,
the hair at the tip end beingolderthan at the root hassufferedmorewearand tearand
would tend to split during combing.It is necessary
thereforewhen designinga test
method that will be usedto test the efficacyof a compositionto mend split endsto
incorporate
into the procedurethe samecombingforcesthat arepresentduringeveryday
grooming.Without this the fibers will not be subjectedto the samedegreeof shear
forcesduring combingand the durability of the mendedfiber cannotbe assessed.
This aspectof testingthe durabilityof the split endmendhasbeenincorporated
into the
test method usedin this study. Subjectinghair to realisticcombingforcesallowsthe
assessment
of not only the initial mendingafter treatment,but more importantlythe
durability of the mend suchas a post combing treatment.With this method various
Figure 2. Dynamicbendingof hair as combis passedthroughtress.
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polymer systemswere testedfor their ability to mend split ends.The experimentation
evolvedfrom testingindividualpolymersto polymerblendswhereit wasdiscovered
that
a polyelectrolytecomplex,formed betweenthe ionic interactionsof two oppositely
chargedpolymers,providedpositiveeffectsin the mendingprocess.The novelcomposition wasfoundto havedurability to a postcombingtreatmentand wasstill able to be
washedoff the hair after a post shampootreatment. Basedon these featuresit was
characterized
as a semi-permanent
hair repaireffect.Besidesa descriptionof the polyelectrolytecomplexusedin this study, as well as test results,a proposedtheory of the
mechanismof mendingis described.This mechanismservesas a model for designing
other complexesthat will have the samehair mending effect.
MATERIALS
AND
METHODS
MATERIALS
Natural brown hair tressesare suppliedby InternationalHair Importersand are made
with their patentedswatchingprocessto be 3.5 gramsof loosehair, 6.5 inchesin length
from the bottom of the sewnend to the tip of the hair, and 1 3/4 inchesacross.Brand
of combsusedin the experimentsare Sally'sBeauty Supply. Fine teeth sectionof the
comb containseight teeth per centimeter.
The freeacidform of the copolymerof methyl vinyl etherandmaleicanhydride(INCI:
PVM/MA Copolymer)is suppliedby International SpecialtyProductsunder the trade
nameGantrez© S-97 BF Polymer.The copolymer
of vinyl pyrrolidoneandmethacrylamidopropyltrimethyl ammonium chloride (VP/MAPTAC Copolymer; INCI:
Polyquaternium-28)is supplied by International SpecialtyProductsunder the trade
nameConditioneze
© NT-20. This is a 20% (w/w) solutionin water.Theseingredients
are usedas suppliedand not purified or modified in any way. Figure 3 illustratesthe
structuresof thesecompounds.
A commercialproduct with a split end mending claim was usedas a benchmark.Its'
ingredientlabel is: Aqua/Water, Cyclopentasiloxane,
PropyleneGlycol, Hydroxypropyl
Guar, Phenoxyethanol,
Peg 40 HydrogenatedCastorOil, PEG/PPG-17/18 Dimethicone, BehentrimoniumChloride, Aminomethyl Propanol,Trideceth-12, Polyquaterium-4, Dimethiconol,Limonene,Linolool,BenzylSalicylate,Amodimethicone,
AlphaIsomethyl Ionene, Perea Gratissima/AvocadoOil, Carbomer, Potato Starch Modified,
Methyl Paraben, Butylphenyl Methylpropional, Citronellal, Cetrimonium Chloride,
Laureth-23,Laureth-4,PrunusArmeniaca/ApricotKernel Oil, Coumarin,Hexyl Cinnamol,Parrum/Fragrance,
F.I.L. C1638713
EQUIPMENT
© Nikon SMZ 1500 Stereomicroscope
© Linksys2.2 programfor digital imagery(Linksysfor Windows, Linkam Scientific
InstrumentsInc., 8 Epsom Downs Metro Center, Waterfield, Tadsworth,Surrey,
KT205HT,
U.K.)
ß Thermal/MechanicalStyling Apparatuscustombuilt at ISP to producetresseswith
split ends.
© Amray model 1820/D digital ScanningElectron Microscope(SEM) with a LaB6
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455
OCH3
I
CH
--CH2 --
CH
CH
I
I
O:C
C:O
I
OH
I
OH
INCI: PVM/MA Copolymer
CH•
-CH•
OH
I
I
CH
CH•
I
C--O
I
NH
CI
H•)•
I
H•C• N+---CH•
I
CH•
INCI' Polyquatemium-28,(VP/MAPTAC Copolymer)
Figure 3. Polymersusedto form complex.
electronsource,usedto obtainhigh resolutionimagesof fibers.The unit is capable
of magnificationup to 100,000x.
ß Malvern MastersizerS, usedto measureparticlesizedistributionof microgelsof the
complexin water.It determinesparticlesizedistributionof the liquid dispersions
by
using Mie laserlight scatteringtheory.Mie theory, unlike Fraunhofer,allowsconsiderationof particle refractiveindex, required for reliable results on particles
<10 pm.
METHODS
Production
ofsplitendsonhair tresses
with a thermal-mechanical
apparatus.
The hair obtained
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JOURNAL OF COSMETIC SCIENCE
from InternationalHair Importersis essentiallyreceivedundamaged.In order to start
the experimentation,hair needsto be damagedto createsplit endsfor repair.This is
accomplished
with a thermal/mechanical
styling apparatus.This apparatusconsists
of
two vent brushesthat are attachedto a cylindricalmixing blade.This is madeto rotate
with a mixer situatedin a horizontalinsteadof its' normalverticalposition.The mixer
is adjustedso that it is made to rotate at 75 rpm againsta hair tress.This treatment
equatesto approximately9,000 brush strokesan hour. Simultaneously,the hair is
subjectedto the hot air of a blow dryerwhichis situatedto keepthe hair againstthe
brushesduring rotation. This treatmentsimulateswhat a consumerdoesduring the
styling process.
This apparatushasbeenpreviouslyusedfor assessing
the ameliorating
effectsof conditioningagentsagainstthe damageincurredby both thermal and mechanicalstress(10). Prior to attachingthe hair to the apparatus
it is first dampenedby
rinsingfor 10 seconds
with warm tap water and combedthroughwith a plasticcomb
to removeanysnags.The hair tressis then put on the thermal/mechanical
apparatus.The
hair tressis subjectedto this thermal/mechanical
stressfor 1.5 hoursat 75 rpm. The hair
blowdryeris setat warmandlow fan andis pointedat the middleof the tress.The brush
is set to a positionto traverseat least3Aof the tresslength. At the end of the process,
the hair tressis examinedunderlow magnificationto confirmthat it is easyto find 20
split endsacrossthe hair tress.If not, then more brushingis doneuntil a satisfactory
number of split endsare produced.
Pretreatment
procedures.
A split end fiber is isolatedin the tresswith the useof a magnifyingglassandtweezers.The fiber is labeledat its root end.Split endfibersarechosen
uniformlydistributedthroughoutthe tress.A dot is drawnwith a redpermanentmarker
slightlybeforethe beginningof the split to later determineif the split brokeoff after
combing.This procedureis repeatedfor 20 split endsfor eachtress.A total of five tresses
aretaggedin this way for a total of 100 fibers.This is the quantityof split endsfor the
study of one formula and providesa statisticalbasisfor the results.
Picturesof eachsplit end are taken under the stereomicroscope
at 20x. The digital
pictures for all of the 100 split end fibers are savedand their files are labeledas
pretreatment.Data is tabulatedin a chart as is illustratedin Table I. The following
scoringsystemis usedfor futurequantificationof split end repair:end split = 1; no split
= 0; partial split = 0.5.
The differentdegreesof splitsare illustratedin Figure4. First thereis the majorsplit
which is termedprimary.A split end within a split is termedsecondary.
Finer splitsat
the tertiarylevelarealsoobserved
at the 20x magnification.Eachtype of split is scored
and tabulatedin eachstep of the process.In this experimentonly primary split end
mendingwill be reportedsincethis is observable
with the nakedeyeand hasthe most
effect on whole hair attributes.
Posttreatment
andwithouts•bjecting
thetress
to•vmbing.
The tresses
arefirst washedwith 3%
Ammonium Lauryl Sulfatesolutionfor one minute and then rinsed well. The excess
water is removedfrom the tressand 0.50 gramsof the test compositionis addedto each
tressand distributeduniformlywith the help of combing.The tressesare then allowed
to air dry. When the tresses
aredry they aregentlystrokedto breakany adhesionof the
fibersfrom the effectsof the treatment.As in the pretreatmentstep,picturesareagain
taken under the stereomicroscope
for eachof the 100 taggedfibers and their digital
picturesarefiled anddesignated
asposttreatmentbeforecombing.Split endmending
assessment
is again tabulatedin the chart in Table I.
2006 TRI/PRINCETON
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CONFERENCE
457
I
Tabulation of Data and Calculationof Mending for One Tress
After leave-on
After leave-on
treatment
Fiber#
Before treatment
P
treatment
(beforecombing)
(after combing)
S
T
P
S
1
1
0
1
0
0
T
0
1
P
0
S
T
0
2
1
0
0
0
0
0
0
0
0
3
4
1
1
0
1
0
0
0
0
0
0
0
0
0.5
0
0
0
0
0
5
6
1
I
2
1
0
0
0.5
0
0
0
0
1
0.5
0.5
0
0
0
7
1
1
0
0
0
0
0
0
0
8
1
0
0
0
0
0
0
0
0
9
1
0
0
0.5
0
0
0.5
0
0
0
10
1
0
0
0
0
0
0
0
0
11
1
0
0
0
0
0
0
0
0
12
1
1
0
0
0
0
0
0
0
13
14
1
1
1
1
0
1
0
0
0
0
0
0
1
0
0
0
0
0
15
1
0
0
0.5
0
0
1
0
0
16
1
0
0
0
0
0
0
0
0
17
1
0
0
0
0
0
0
0
0
18
1
0
0
0
0
0
1
0
0
19
1
0
0
0
0
0
1
0
0
20
1
0
0
0
0
0
1
0
20
7
3
1
90
95
0.5
85.7
92.8
8.5
50
57.5
0.5
85.7
92.8
Total split end
Complete mending (%)
Total mending (%)
0
100
100
Durability Index D
0.61
0
0
100
100
1
1
History of mendingfor eachfiber asobservedwith stereomicroscope
(1 = end split; 0 = intact end; 0.5 =
partial split; P = primary split; S = secondarysplit; T = tertiary split).
Durabilitystep--Posttreatment
with combing
thehair tress.
Eachhair tressis combedtwenty
times with the fine teeth of the comb. Picturesof the taggedfiber endsare again taken
under the stereomicroscope
and their files labeledas post treatment with combing.
During the observation
of eachfiber the permanentmark is identifiedasa landmarkto
make surethe end of the split fiber hasnot brokenoff to guardagainsta falsepositive
mending effect being recorded.Scoringis tabulatedas beforeas is seenin Table I.
CalcMationof split endmending
percentage.
The following two equationsare usedto calculatethe degreeof split end mending.
Total mending% =
Total # splitendsbeforetreatment- # splitendsaftertreatment
Total # splitendsbeforetreatment
x 100
Total percentmendingincludesthe assessment
of both completeand partial splits.
Scoring:1 = split end, 0 = mendedsplit, 0.5 = partially mendedsplit.
Total mending% after combing
Durability
Index
(D)=Total
mending
%before
combing
Therefore, the maximum D -- 1.0, and the minimum D -- 0.
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JOURNAL OF COSMETIC SCIENCE
:Fiber 2 before treatment
SecondarySplit
PrimarySplit
•' •90 urr•
Figure 4. Stereomicroscopic
view of fiber (20x) showingprimaryand secondary
levelsplits.
All of the resultsreportedin this study are basedon total mendingwhich includesthe
assessment
of both completeand partial mendingof the split end fiber. An exampleof
the calculationof the tabulateddata for oneof the five tresses
of a study is foundat the
bottom of Table I. Again, althoughthe secondaryand tertiary level splitsare assessed
as
well moreemphasisis placedon the primary splitssincetheseareapparentto the naked
eyeand their mendingwould afforda consumerperceivablebenefit.
Illustrationof complete
andpartial mending.
Figure 5 showsthe three stagesof the measurementcyclenamelypretreatment,post treatmentbeforecombing,and finally post
treatmentafter combing.The last step teststhe durability of the mend. The red dot
madewith the permanentmarkercanbe observedjust prior to the split end. This series
of photosin Figure 5A) servesto exemplifycompletemendingof the split end. Figure
5B) showsan examplewherethe fiber hasbeenpartially mendedafter treatmentand
stayspartially mendedafter the post combingprocess.In this casea scoreof 0.5 would
be assigned.Both completeand partial mending are taken into considerationin the
assessment
of mendingand is designatedas total mending.
Advantages
of the testmethod.
Sincethe tagged split end fibers are part of the trees,
applicationof the treatmentcanbe performedin a realisticfashionsimulatingconsumer
usage.In this experimentthe product is applied to damp hair and allowed to air dry.
However,the methodallowsthe studyof differentapplicationtechniquessuchasbrush
and blow drying or addingthe treatmentto dry hair for example.
The advantageof the taggingprocessallowsthe studyof the fate of the split end after
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B)
Pretreatnlent
Post treatment
beforecombing
Post treatment
.....
after combing
•
Figure 5. Examplesof the two typesof mendingthroughthe threestagesof measurement:
(A) Complete
mending:split end is completelymendedfrom startof fissureto endof fiber. (B) Partialmending:split end
is mendedfrom start of fissureto a fractionof the length to the end of the fiber.
treatmentand moreimportantlyto durability to combing.Sincethe fiber is still part of
the tressit canbe subjectedto normalcombingforcesor othertreatmentsto determine
the effectiveness
of the split end mendingproduct.In this casethe tressis subjectedto
twenty combingsafter applicationof the formulation.Combing was chosento test
durabilitysince,asdescribed
above,the majorcauseof split endformationis throughthe
shearstresses
generatedduring the combingprocess.
Also,the taggingprocess
allowsthe
study of other treatment variablessuchas survivabilityafter washing,the effect of
multiple treatments,or someother regimendesignedby the experimenterto test split
end mendingdurability.
Another advantageto the method is the increasein the depth of field that the stereomicroscope
possesses
overthe opticalmicroscope.
As canbe seenin Figure4, the whole
fiber end canbe focusedand observedunderlow magnification.In the figure it canbe
observedthat this split end hasa major bifurcationwhich is termedprimary, and two
minor splitswhich are termed secondary.
The stereomicroscope
alsoallowsthe observationof the fiber unhampered
by a coverslip whichmaydepress
the fiber to the point
wherethe split end will close.A slight shadowcanbe observedfrom the light source
abovethe specimenshowingthat the fiber is not laying flat on the stage.
PRODUCTION
OF POLYELECTROLYTE
COMPLEX
Table II comprises
the formulationusedin the test. Test formulasutilize the complex
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JOURNAL OF COSMETIC SCIENCE
Table
II
Formationof Complexand Formulationof Split End Mending Serum(6lB)
Ingredients
Phase
A
Deionized water
49.00
Xanthan gum (RhodicareT)
Phase
0.50
B
Deionized
water
Polyquaternium-28
(conditioneze© NT-20)
Phase
%w/w
36.00
9.00 (1.80 active)
C
Deionized
water
4.24
Sodiumhydroxide(10% Aq. Soln.)
PYM/MA copolymer(Gantrez© S-97 BF Polymer)
Propyleneglycol(and)diazolidinylurea(and) iodopropynylbutylcarbamate
(Liquid Germall© Plus)
0.56
0.20
0.50
100.00%
Percentactive complex= 2.00%.
Ratio of PVM/MA copolymertO Polyquaternium-28= 0.20:1.80.
at 2 percentactivewith a ratio of PVM/MA Copolymerto Polyquaternim-28of 0.20 to
1.80 respectively.
The procedurefor putting the full formula together(6lB) which
includesthe productionof the complexis as follows.
Procedure
for full formula
1. In main containerdisperseXanthan Gum into room temperaturewater with moderatepropelleragitation.When fully incorporatedswitch to moderatesweepagitation and mix until
uniform.
2. Add water of phaseB in a premix containerand mix with moderatepropeller
agitation.Add Polyquaternium-28(ConditionezeNT-20) and mix until uniform.
3. Add waterof phaseC to a separatepremix containerandmix with moderatepropeller
agitation.Add sodiumhydroxidesolutionandmix until uniform.SprinklePVM/MA
Copolymer(GantrezS-97 BF Polymer)into vortexandmix until uniform.AdjustpH
to 6.95 + 0.05 with sodium hydroxidesolution.
4. Increaseagitationof contentsof phaseB (-1000 rpm). Add phaseC to phaseB over
the courseof 20-30 seconds.
Mix with fastpropelleragitationfor ten minutes.
5. Add combinedphasesB and C to phaseA. Mix until uniform.
6. Dissolvepreservative
and mix until uniform.
7. Adjust pH to 7.1 + 0.1 with 10% citric acid solution.
It is importantto add the anionicpolymerto the cationicpolymerwhen formingthe
complex.Also,the complexshouldbemadeprior to its incorporation
into a formulation;
the stepsin the aboveprocedurefor making the complexare 2 through 4. When
incorporatingthe complexinto a formula the integrity of the complexis judged microscopically
to determineif it hasa typicalmicrogelstructurewhichis described
below.
This is a predictiveindicatorfor the efficacyof the complexto repairsplit ends.The
complexhas shownto be compatiblewith nonionicand mildly cationicand anionic
polymers.In this casethe complexis addedto the anionicpolymerXanthanGum to
makea serumproduct.One of the controlformulasis madeby addingthe complexalone
to water to obtain two percentactive.
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DISCUSSION
CHARACTERIZATION
OF POLYELECTROLYTE
MICROGEL
COMPLEX
There have been variousnamesfor polyelectrolytecomplexes.These consistof such
namesas polymer-polymercomplexes,or interpolyelectrolytecomplexes.Despite their
nomenclatureas used in the academicliterature they are describedas two speciesof
polymersthat caninteractwith eachother without the formationof covalentbonds.The
bondsinvolvedcouldbe electrostatic,
hydrogenbonding,Van der Waals interactions,or
a combinationof each.The polyelectrolytecomplexusedin this study is basedon the
electrostaticinteractionsof two oppositelychargedmolecules.It is not just a mixture of
two polymers.As canbe seenin Figure6 high molecularweight linearpolyanionicand
polycationicpolymerswhen combinedtogetherform a complexthrough the association
of their oppositecharges(12). There are numerousfactorsthat shouldbe briefly mentioned at this point that are important in the formationof the complex.Besidesconsideringthe weight ratiosof the two unlike chargedpolymersother factorsinvolvedin
the interactionaremolecularweights,chargedensities,pH and electrolytecontentof the
solvent,the solventtype, and the process'
of putting the two polymerstogether.Since
unlike chargesinteract on a molar basis,the stoichiometryand chargeratios are important in consideringtheir interaction.
The hypothesiswas that split end mending can be achievedwith a polyelectrolyte
complexmade through the interactionof two oppositelychargedpolymers.This is in
distinction to split end mending with a polymer-surfactantcomplexas patented by
Ramashandranet al. (13). They invented an ingenioushair rinse compositionthat
claimedwouldnot only conditionhair to providesuchpropertiesaswet detangling,but
also lend fixative propertiesand repair split ends. The three main ingredientsthat
comprisedthe rinse are quaternaryammonium salts(quat), water insolubleacrylic or
acrylate polymers and a solvent that comprisesa long chain alcohol and/or alcohol
ethoxylate.The solventis usedto help compatibilizethe quat and polymer. It was
theorizedthat the quat and polymerform a complexwith eachother in the solventand
Polyanion
Polycation
Polyelectrolyte
Complex
Figure 6. Ionic association
of polyelectrolytes
of differentchargethat formsa complex;adaptedfrom
reference(12).
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JOURNAL OF COSMETIC SCIENCE
aids the depositionof the anionicpolymer on the hair during the rinse cycle which
would otherwisebe washedaway.They alsotheorizethat split end mendingis achieved
by the adhesiveness
of the depositedpolymerwhich when dried formsa film that holds
the splits together.
Using the specializedtest methodasdescribedin the methodssectionaboveallowedthe
screeningof many typesof compositions
which led to the formationof the hypothesis.
Someindividualpolymersor mixturesof polymersgaveonly a poor to fair mending
durability efficacy.The compositiondiscovered
basedon a polyelectrolyte
complexwas
found to haveincreased/mending
durability efficacyover controlsystems.The anionic
polymer of this complexis PVM/MA Copolymer.The anionic contributionof this
moleculedependson pH since it has two carboxylicgroupsper monomer unit. The
cationic polymer component is Polyquaternium-28 or VP/MAPTAC Copolymer. Its
cationicityis from the quaternarygroupsand are positivelychargeddespitepH. The
electrostaticinteractionthen is betweenthe ionizedcarboxylicgroup of the anionic
polymerand the quaternarynitrogengroup of the cationicpolymer(14).
When the complexformsit canbe characterized
microscopically
asa microgelstructure.
Figure7 showsthe characteristics
of thesemicrogelsbasedon the polyelectrolyte
complex as observedunder an optical microscopeat 500x. It can be observedthat these
particlesare translucent,non-uniform in shape,and are dispersiblein the aqueous
..50.x!ens
ß
•30um•
Mi
ge!
.
:
2.00%
active
complex
cmprising
0.2ø&PVA
Cpolymer
1.8- Polyquatemmm-28
Figure 7. Microgel structureas observedunder optical microscope(500x)
2006 TRI/PRINCETON
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463
solvent.Stability showsthat a 4% activecomplexdispersionis stableat elevatedtemperaturesandmultiple freezethawcycles.The particlesarein the rangeof 5-10 microns
in sizeasmeasuredwith a Malvern particlesizeanalyzer.The particlesizedistribution
is illustrated in Figure 8.
By studyingthe phasediagramformedbetweenPVM/MA Copolymerand Polyquaternium-28 the phaseregionsof their interactionswereidentified.In building this phase
diagram variousweight ratios were usedin putting the two polymerstogether while
keepingothervariablesconstant.The variableskept constantwerethe solventwhichwas
water, pH of the PVM/MA Copolymerwhich wasadjustedto 7.00 + 0.05, and the type
of polymerwhichinherentlycontrolsthe molecularweight andotherintrinsicproperties
of the polymerssuchascationicchargedensity.The process
of putting the two polymers
togetherwasalsokept constant.The characterof the polymercombinationswere noted
and given a value againstset criteria.The phasediagramwasproducedby regression
analysiswith the help of statisticalsoftware(15). The resultantphasediagramis illustrated in Figure 9. The complexeswere characterizedmacroscopically
by appearance
wherethe value of 5 wasgiven to clearsolutions,1 wasgiven to opaquewhite dispersions,and 2 through4 for intermediatevaluesfor solutioncharacters;
seelegendin
Figure9. It wasfirst thoughtthat the opaquemilky white dispersions
designated1 only
.
,
,
i
,
.
ii]
.
0_1
,
!
i
i
.ll
!
lJl
.
]
i
.
i
i[
i
i,i
11111
i
[i
!
.
,
i
,
.!
i
i
1110_0
Figure 8. Malvernparticlesizeanalysisof microgelstructure.
.
!
464
JOURNAL OF COSMETIC SCIENCE
DESIGN-EXPERT
Plot
0.50
Phase
Behavior
O Des•jn Points
Phase
Run
Behavior = 1.564
0.38
X: A: Polyquaternium-28= 1 .80
Y: B: PVM/MA Copolymer = 0.20
'• 0.25
Solution
Character
ComplexTested
o
o
Legend:
I = Milky
• 0A3
2 = Very hazy
3 = Hazy
4 = Slightly hazy
5 = Clear
0.00
2.44
4.88
7.31
9.75
A: Polyquaternium-28
Figure 9. Phasebehaviorof polymersof differingcharge.
containedthe complex,but with further investigationunder the microscopeit was
observedthat all dispersionsother than the clear onescontainedmicrogels.It was
concluded
that the white opaquedispersions
thenhadthe highestintensityof microgels
formedand would be mostappropriatefor testingthe split end mendingbenefit.The
complextestedin this studyis identifiedin Figure9 and consists
of two percentactive
complexmadeby combiningPVM/MA CopolymerandPolyquaternium-28
at a weight
ratio of 0.2 to 1.8 respectively.
Polyelectrolyte
complexes
basedon otheranionicand cationicpolymercombinations
werestudiedin thiswaybut havenot beentestedformendingefficacy.
Complexes
using
PVM/MA Copolymerasthe anioniccomponent
havebeenformedwith Polyquaternium7, 10, and 11. Also,Vinylpyrrolidone/acrylates/laurylmethacrylate
copolymerservingas
the anionicpolymerhasbeencomplexedwith Polyquaternium-28.
The phasediagrambuilt in Figure9 is basedon weight ratiosof the two polymers.
However,the two polymersareactuallyinteractingon a stoichiometric
basisthrough
their chargeinteraction.To furtherelucidatethe interactionof thesetwo polymersthe
followingstudywasconducted
andis illustratedin Figure10. Variouslevelson a weight
basisof Polyquaternium-28were combinedwith 0.2% PVM/MA Copolymer.The
resultantviscositywas measuredusing a Brookfieldviscometerwith a small sample
adapterandthe viscosityplottedagainstthe calculated
moleratioof cationicmonomer
to anionicmonomer.The shapeof the curveis distinctlyparabolically
curvedcontaining
a minimum viscosity.It was discovered
that this minimum of viscosityoccursat a
2006 TRI/PRINCETON
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465
lOOO
Excess
polyanions;
Excess
polycations
lOO
ß PVM/MA0.2%
lO
..l•.
iEnd
point::C*/•'2
=1
1
o.oo
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
5.00
UnitmoleratioofPolyquaternium-28
to PVMIMA
Copolymer
Figure 10. Dependenceof viscosityon unit mole ratio cationicto anionicgroups.
stoichiometricchargeratio of oneto onewherethe stoichiometricequivalence
of cationic
and anionicchargesarethe same.This indicateda maximumin the amountof microgels
formedsincetheseare discreteparticlesthat are dispersedin solution.Polymer ratios
deviatingawayfrom the oneto onestoichiometricequivalence
would containpolymer
not associated
in a microgeland would increasethe viscosityof the solution.The lower
viscosityevidentfor the 1:1 ratio wasdue to the hydrodynamicvolumeof the complexed
chainsbeing smallerthan when free un-complexed
polymersare presentin solutionat
otherchargeratios.This charge-charge
interactioncontributesto the compactnatureof
the microgelstructureof the complexand exemplifiedthe stoichiometricinteractionof
the two polymers.It wasdeterminedthat the complexchosento repair split endshasa
cationicto anionicchargeratio of precisely1.14.
MENDING
TEST
RESULTS
OF MICROGEL
COMPOSITION
A screeningstudy showedthe efficacyof the polyelectrolytecomplexin split end
mendingdurability. The controlsystemswerebasedon the componentpolymersof the
complexusedalone and a clear 1:1 mixture of the two polymerswhere there are no
discretemicrogelspresent.All polymer and polymer combinationswere kept constant
at a total of 2.00% active.This screeningstudyconsistedof measuringtwenty tagged
fibersfor eachformulationinsteadof the usualonehundredand wasbasedon complete
mendingasobservedwith a magnifyingglass.Test resultsshowedthat the complexhad
increased
durability of mendingoverthe controlformulations.Test resultsare in Table
III.
When the complexwas usedalone at 2.00% active in a one hundredfiber study it
mended92 out of 100 fibersafter treatmentand beforecombing.After combingthe
tresstwenty times 68 fibersremainedmended.When the 2.00% activecomplexwas
formulatedinto a simple lotion formula thickenedwith Xanthan Gum approximately
466
JOURNAL OF COSMETIC SCIENCE
Table
III
ScreeningExperimentShowingEfficacyof ComplexOver SystemsUsed asControls
% Mending
after
% Mending
after
Durability
Formula type
treatment
combing
index
2.00% neutralizedPVM/MA copolymer
2.00 % Polyquaternium-28
2% Complex;0.20 neutralizedPVM/MA copolymerand
1.80 polyquaternium-28
1.00% neutralized PVM/MA copolymerplus 1.00%
polyquaternium28
90
75
15
0.17
4O
O.53
90
75
O.83
85
2O
0.24
the sameresultswere obtained.This providedevidencefor two things.First, that the
resultswere reproduciblegiving validity to the test method. Second,the complexcould
be formulatedinto a systemwithout lossof efficacy.Resultsareportrayedin Figure 11.
In both casesthe durability indicesof the mending after combingwas over 70%.
As mentionedin the procedurethere are 100 fiberstestedfor eachtreatment,twenty
fiberstaggedon one tresstimes five tresses.The data illustratedin Figure 12 showsthe
variability of mending for each tressfor both beforeand after combingon the full
formulation.The averageand standarddeviationof the mending resultsafter combing
of the five tresses
is 67.6 + 12.6%. Comparingthis mendingdatato a controlformula
containingjust the thickeningagentascanbe seenin Figure 13 showsthe significance
of the difference.From this it can be concludedthat the complexis responsible
for the
high mending scores.
Stereomicroscopy Results of Mending Efficacy
Primary Splits, Complete+partial Mending
100
92
93.3
80
ß
Complex
alone,
149A
Inafull
formula,
61B 1
.......
68 6716
................
/
40
20
0
I
before combing
after combing
Figure 11. Total percentmendingof complexaloneand in a frameworkformulaboth beforeand after
combing.
2006 TRI/PRINCETON
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467
Stereomicroscopy Results of Mending Efficacy
Primary Splits, complete+partial mending
lOO
95
92.5
95
Ave.
9o
= 93.3%
+/-
2.4%
8o
7o
average of 100 fibers,
6o
67.6%+/-12.6%
5o
mending
after combing
4o
3o
2o
lO
o
tress 1
tress 2
tress 3
tress 4
[] before combing El after
tress 5
combing
1
Figure 12. Varianceof mending efficacyfor five tressesusedin one experiment.
Complexesbasedon differentweight ratiosof cationicto anionicpolymerweretestedfor
split endmendingefficacy.It wasdiscovered
that althoughthereweremicrogelsformed
by the interactionof Polyquaternium-28and PVM/MA Copolymer,an optimalamount
of repair was evidentwhen the two polymerswere combinedwhen their chargeratios
were 1:1 as can be seenin Figure 14. Split end mendingefficacyis reducedas the
polymerratio deviatesfrom the one to one chargeratio. This is further evidencein
showingthe importanceof the polyelectrolytecomplexin mendingsplit ends.
The advantage
of thedeveloped
methodis to determinethe fateof the splitendsthrough
varioustreatmentsthat test the durabilityof the mend.Sincethe taggedsplit endfiber
is alwayspart of a tressit can be treatedin sucha way that it is exposedto realistic
treatments.In the previouscasethe tresswas subjectedto a controlledamount of
combingto testthe durabilityof the mend.Other treatmentregimenscanbe conceived
to test durability in a realisticfashion.A test was devisedto determinethe effectof
multiple treatmentsof the formulawith the complexand its removabilitywith shampoo. One cycleconsistedof treatmentwith the formula, drying, combing,and then
washing.Split end mendingwas assessed
after treatmentbeforecombing,after treatment after combing,and finally after washingfor one, two and five cyclesof the
treatment schedule.Resultsof the test are illustrated in Figure 15. First it can be
observed
that mendingis high after treatmentbut beforecombingfor treatmentcycle
onethroughfive. Durability to combingstressoverthe multiple treatmentcyclesstays
the sameand is approximately60%. Durability to washingis low and decreases
with
continueduse.It wasobserved
duringthe mendingtabulationthat the split endsbecame
moreseverewith continuedwashingwhichexplainsthe loweringof the percentmend-
468
JOURNAL OF COSMETIC SCIENCE
Stereomicroscopy Results of Mending Efficacy
primary Splits, complete+partial mending
lOO
93.3
90
80
70
•
67.6
[]before
comb
[] aftercombing
60
50.4
50
40
30
'
,,,
20
lO
,,,
o
with complex(11110-61B)
No complex(11203-152A)
Figure 13. Total percentmending of formulawith complexvs control.
ing scoresafter multiple washcycles.Measurements
taken beforeand after treatment
after one cycle are approximatelythe sameas the previousdata and show again the
reproducibilityof the data. The implicationsof theseconclusions
related to consumer
performanceincludethat the productcan be claimedthat it will not havethe negative
effectsof build up with continueduseand that productdirectionsshouldincludeadding
the productto the hair after everyshampooin order to obtain the desiredeffect.
There are few commerciallyavailableproductson the market that claim split end
mending.The onefoundwastestedasa benchmark
for performance
to the formulawith
the polyelectrolyte
complex.Althoughthe commercialproductwasable to mendsplit
endsinitially aftertreatment,the mendsfailedafterpostcombing.Total percentmending is considerably
loweraftercombingfor the commercialproductvs. the formulawith
the polyelectrolyte
complex(Figure 16A). Durability index of the commercialproduct
is muchlowerespecially
forprimarysplit ends(Figure16B).The mechanism
responsible
for temporarilymendingsplit endsin the commercialproductis probablythrougha
loweringof the surfaceenergyof the fibersafter treatment.The damagedpartsof the
fibersare then attractedthroughweakhydrophobic
bonds.Ingredientsresponsible
for
this are the blend of siliconesin the productsuchas cyclopentasiloxane,
dimethicone,
alkyl modified dimethicone,dimethiconol,and amodimethicone.Other ingredients
having the sameeffectare the cationicsurfactantsand organicoils; refer to methods
sectionfor ingredient labeling. This hydrophobicmechanism,although it providesa
high degreeof mending,fails to providedurability to the mend as exemplifiedin the
2006 TRI/PRINCETON
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CONFERENCE
469
Mending Efficacy vs. Charge Ratio of Polyquaternium-28 to
PVMIMA Copolymer
90
0.90
0.80
80
0.70
...
70
0.60
60
t.
50
0.50
•
0.40
.•.
"-
40
0.30
30
0.20
20
0.10
lO
........:....................
•................................ .
o
0.6
0.4
•,
•,
....
0.8
1
.....................
'•.................?........................
4 0.00
1.2
1.4
1.6
1.8
2
Charge Ratio
mending% before combing
m
mending% after combing
durability
---- ---- Poly. (durability)
Poly.(mending% after combing)
Poly.(mending% before combing)
Figure 14. Mendingefficacyvs chargeratio of cationicto anionJcpolymer.
B) Durability Index
A) Total % Mending of Primary Splits
lOO
60
.,0.60 ....
40
0
,
CycleI
,
Cycle2
Cycle5
G Total % Mending Before Combing
i• Total % MendingAfter Combing
I• Wash
0.40
0.20
.....
0.00.
,
CycleI
Cycle2
Cycle5
I•Durability
Index
Combing []Durability
Index
Wash
Figure 15. Ctmqulative
effectsandmendingdurabilityto washingoverthe courseof five cycles.(A) Total
percentmendingof primarysplits.(B) Durability index.
postcombingdurabilitytest.The hydrophobic
bondingof the components
of the split
fiber is not strongenoughto withstandthe stressof the combingprocess.
In our screeningexperimentsfor the polyelectrolyte
complexit wasfound that there
weremanycompoundsthat couldmend split endsprior to stressingthe tressto test the
durabilityof the mend.It wasthe ability of the complexto durablymendthe split ends
after this post combingprocessthat providesthis semi-permanent
mendingability.
Basedon the surfacecharacteristics
of damagedhair aswell asthe structureand chemical
interactionsof the polyelectrolytecomplexwith hair, a theory was proposedon the
possiblemechanismof this semi-permanent
split end mending.
PROPOSED
THEORY
OF SPLIT
END
MENDING
Hydrophilic
character
of damaged
hair. Human hair consistsof a centralcorecalledthe
470
JOURNAL OF COSMETIC SCIENCE
A) Total % Mending of Primary Splita
B) Durability Index
100
1
90
80
70
60
30
2o
02
lo
01
o
Commercial Product
Split End Mending Serum 61B
Commercial
Product
SplitEndMendingSerum61B
[[]Before
Combing
[]After
Combing]
Figure 16. Comparison
of mendingwith complex
vsa commercial
product.(A) Totalpercentmendingof
primary splits. (B) Durability index.
cortexcoveredby a sheathof severallayersof flattenedcuticle cells. Each of these
overlappingscalesis abouthalf micronthick and45 micronslong.The thin outermost
layer that formsa sheatharoundthe cuticlecell is known as the epicuticleand is
hydrophobic,
whereas,
the cortexis hydrophilic(16). The outerlayerof cuticlesurface
contains18-methyleicosanoic
acid (18-MEA) alsocalledthe F-layer,which makesthe
hair surface
hydrophobic.
18-MEA bindswith theA-layercontaining
cystinegroupsin
the cuticlecell.The mainfunctionof the cuticleis to providemechanical
protectionfor
substances
insidethe cortexlayersuchas preventingaminoacid and proteinsfrom
washingout throughthe hair surfaceor protectingit from furtherdamage.When hair
becomes
damagedtherearebothphysicalandchemicalchanges
to boththe surface
and
internalstructures
of the hair fiber.The morphological
changes
of a damagedhairfiber
areevidentasillustratedin Figure17. Besides
theobvioussplitin thefiberexposing
the
subassemblies
of the cortexit canbe observed
that the cuticleis partiallylifted aswell.
Fora damaged
hairfibercontaininga splitend,asshownin the SEMpicture,thecuticle
layersarechemicallydamagedaswell resultingin the hair fiberbeingmorehydrophilic.
Thismightbedueto theexposure
of thecortexaftercuticledamageand/ortheexposure
of theA-layerin cuticlecells.The A-layercontains
highlevelof cystinegroups(>.30%).
The disulfidebondin cystine,-R-S-S-R-, is veryreactiveandis in a stateto be oxidized.
One of the possible
oxidationproducts
of cystineis cysteicacid,R-SOj. Whenthe F
layer is strippedthe increased
levelsof cysteicacid on the damagedhair surfacewill
contributeto its increased
hydrophilicity.
A simpletestdemonstrates
that damaged
hairismorehydrophilicthanundamaged
hair.
A hair tip with a split end anda healthyhair tip weresoakedin a 0.03% cationicdye
solutioncalledSafraninusedin microbiologicalstainingfor 30 seconds
and rinsedin
runningwater.The hair fiberswerethen observed
undera stereomicroscope.
The microscope
imagein Figure 18 showsthat the split tip end turnsto a muchmorered color
than the healthyhair. This is dueto the higherinteractionof the cationicstainwith the
increased
numberof anionicsitesof the damagedfiberwhicharedueto the chemicaland
morphological
changes
in the hair surface.The positiveresponse
to stainingindicates
that the hair surfaceor cuticlecellsare damagedafter the hair fiber splits and is
consistentwith the SEM resultsin Figure 17 which showsthe cuticledamagecharacterizedby jaggededges.
Besidesthe stainingtest therehavebeenmany studiesthat showthat the hair surface
becomes
morehydrophilicor morenegativelychargedwhendamaged.
For example,it
hasbeenreportedthat the hair surface
becomes
hydrophilicbecause
of the exposure
of
uncovered
A-layerafter exfoliationof hydrophobic
F-layerby the actionof hydrogen
2006 TRI/PRINCETON
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471
.
..
Figure 17. SEM showingsplit end and cuticle lifting.
peroxideand alkali usedin hair coloring(17). Ruetschfoundthat when hair is subjected
to chemicaloxidationthat a positiveresponse
is obtainedby treatmentwith the cationic
fluorochrom,RhodamineB (18). Also, the dye response
wasfoundto be directlyproportionalto the treatmenttime. Cysteicacid wasrevealedto be the new specieson the
surfaceof the hair basedon chemicalanalysisthroughX-Ray photoelectron
spectroscopy.
FTIR hasbeenshownto haveutility in measuringthe hydrophilicnatureof damaged
hair (8). The disulfidebondwhenoxidizedby a damagingprocess
canbedetectedby the
shifting bandsin the IR spectrumas the chemicalfunctionalgroupschangeto more
hydrophilicspecies.
The oxidationproductsformedin hair dependon the natureof the
oxidizing agent. Joy et al. reportedthat when hair is treated with alkaline hydrogen
peroxide
solutions
theIR peakat approximately
1040cm
-• corresponding
to cyteicacid
is significantlychangedconfirmingdisulfide oxidation(19). It was also found in the
studyby Joy that cysteicacid contentincreases
from root to tip end of both naturally
weatheredand bleachedhair showingthe increaseof damageof the hair with age.
Another piece of evidenceshowingthe increasein the hydrophiliccharacterof the
surfaceof damagedhair is an increase
in surfaceenergy.Throughthe useof the Wihelmy
balancetechniquetestedon singlefibers,it wasfound that both oxidationand reduction
increased
the wettabilityof the hair (20, 21). They attribute theseincreases
to againthe
generationof hydrophilicgroupssuchassulfonicacidgroupsin the caseof oxidationand
thiol groupsin the caseof reduction.
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JOURNAL OF COSMETIC SCIENCE
Healthyhairtipend
-.
..
............
a
,.•::.:....•': •5.•':'•.........
Figure 18. Ionic dye reactionto damagedhair.
Structure-property
relationships
are importantfactorsto considerin the process
of either
choosingor designingingredientsto test for hair repair.One hasto theorizehow the
ingredientwill interactwith the fine structureand chemistryof hair in orderto determine if it is a candidatefor experimentation.A few experimentshavebeenshownin this
paperthat providesevidencethat therearechangesin the morphologyandchemistryof
hair during the damageprocess.
One thing that is essentialthereforein the repairprocess
is that the ingredienthas to havea cationicnature in order to bind to the anionichair
surfaceof the split fibers.Also, adhesiveeffectsare necessary
that are able to glue the
split subassemblies
of the fiberstogether.Lastlyand mostimportantlythe composition
needsto be ableto closethe split endsand smooththe lifted cuticlescalessoasto ensure
a durablemend especiallyafter combingor other stressfactorsduring for examplehair
styling. Consideringthe chemistryand morphologyof the microgelstructureand its
interactionwith the chemistryand morphologyof damagedhair, it seemsreasonable
that the polyelectrolyte
complexis able to meet all of thesecriteriafor the hair repair
process.Basedon this thinking a mechanismof actionfor the semi-permanent
split end
mending effect is proposed.
Proposed
mechanism
of splitendmending
with PEC microgel.
It hasbeenshownthat maximum mending was achievedfrom microgelsthat were formed from polyelectrolyte
complexesmadefrom combinationsof oppositelychargedpolymerscloseto a oneto one
stoichiometriccharge ratio. This charge ratio was shown through viscositymeasurementsto be the point of maximumcomplexation.It is believedthat althoughthischarge
ratio is balancedthere existsin the microgelresidualanionicand cationicchargesthat
2006 TRI/PRINCETON
CONFERENCE
473
havenot associated
together.This is because
of the sterichindrancethat preventsthe two
macromolecules
to completelyassociate
all of their unlike chargestogetherfor complete
neutralization.
Therearevariousaspectsto the proposedmechanismof actionof the hair repairprocess
with the polyelectrolytecomplex.First, the residualcationicchargeson the microgel
would tend to bind to the anionic sites of the damagedcortex through electrostatic
association.
To showthe cationicityof the complexthe anionicdye, Direct Red 80, was
usedas an indicator.Figure 19 showsa split end beforetreatmentwith the complex,
after treatment showingmending, and after treatment with Red 80 showinga positive
response
to the dye. The higherlevelof red towardsthe tip indicatesthe predominance
of complex.The red mark just prior to the split end again is the mark made with a
permanentmarker.
During the drying stagethe microgelcomplexis able to form a crosslinkingstructure
which bridgesthe subassemblies
of the fiber together.The microgelstructureand its
interactionwith hair are illustrated in Figure 20A. The crosslinkingadhesivestructure
of the microgelservesto glue the damagedpartsof the fiber together.Sincethe complex
is in the form of microgelsin the size rangeof 5-10 micronsthey are small enoughto
infiltrate the fissuresof the split cortexespeciallythoseas canbe seenmacroscopically
asa split end. The smallerparticlescan to a certainextentpermeatethe lifted cuticle
whichis alsopresentin damagedhair. After drying the microgelsform a cleardurable
film which tendsto bind thesedamagedpartsof the hair togetheras is illustratedin
A) Beforetreatment
B) After treatment
C) After treatmentplusRed 80
Figure 19. Anionic Direct Red 80 dye test indicatesmore microgeldepositionon tip end.
474
JOURNAL OF COSMETIC SCIENCE
Mendin•
serum
Microgel
absorption
Lifted cuticle
B)
drying
Mended
hair fiber
Split cortex
Figure 20. Proposed
mechanism
of splitendmending.(A) Microgelcrosslinking
structure.
(B) Bindingof
cuticle and split end during the drying process.
Figure 20B. The uniquefeaturesof the dried thin film ensurea durablemend that will
survivethe combingprocess.
Thesevariousaspects
of the mendingmechanism
provides
for an efficacious
level of mendingthat can endurea postcombingprocess
which is
typical of normal styling behavior.Visual effectsof this mendingcan be observed
throughSEM. In Figure21 it canbe observed
that the mendedfiber hasa smoothcuticle
where before treatment it was characterizedas lifted. Also, the seam of the weld is
evident where the split end usedto be.
Having an increased
understanding
of the formationand chemistryof polyelectrolyte
complexes
and their interactionwith the chemistryand morphologyof hair allowsthe
designof newcompositions
that couldfunctionin the samewayasthe complexstudied
here.
CONCLUSIONS
Hair stylingtrendshavecreateda needfor hair repaircompositions
that will attemptto
restoredamagedhair to its normalstate.Split endsareonemanifestation
of that damage.
A testmethodhasbeendevisedthat canassess
in a realisticfashionthe mendingof split
endsthroughvarioustreatmentregimens.The methodis realisticin that the tagged
split endfibersarepart of a tressthat canbe subjected
to normalcombingor washing
cycles.With this methodit has beendiscovered
that a polyelectrolyte
complexcan
semi-permanently
mend split endsin that split end hair treatedwith this composition
cansurvivethe stressof combing.The composition
is efficacious
especially
in comparisonto a commercialbenchmarkwith a split endmendingclaim.A proposed
mechanism
of actionhasbeenput forthandconsists
of the microgelstructureof thepolyelectrolyte
complexactingasa crosslinking
structurein the damagedsubassemblies
of the damaged
fiber.The understanding
of this mechanism
opensthe wayfor the development
of new
2006 TRI/PRINCETON
-•' ':.lendi;ng
,ei.a'm:treated.
CONFERENCE
475
Mended split
Smoothed
cuticle
Figure 21. SEM imageof hair fiber after mending,showingmendedsplit and smoothedcuticle.
combinationsof polymersthat form microgelstructuresafter complexationthat could
alsohavea positivebenefitin the areaof hair repair.
ACKNOWLEDGEMENTS
The authorswould like to thank Bill Thompsonof ISP for SEM andparticlesizeanalysis
andAlison Robinsonalsoof ISP for help with opticalmicroscopy
and imaging software.
REFERENCES
(1) A. C. BrownandJ. A. Swift, Hair breakage:The scanningelectronmicroscope
asa diagnostictool,J.
Soc.Cosmet.
Chem.26, 289-297 (1975).
(2) J. A. Swift, The mechanics
of fractureof humanhair, Int. J. Cosmet.
Sci.,21, 227-239 (1999).
(3) J. A. Swift,Mechanism
of split-endformationin humanheadhair,J. Soc.Cosmet.
Chem.,
48, 123-126
(1997).
(4) J. A. Swift,"Fundamentals
of HumanHair Science,"
Cosmetic
Science
Monograph
Number
One,p. 62, Fig.
36.
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