22

SURFACTANTS lit DETERGENTS

30

25

! 20

~"• to,0

0 14 " 16

Moles EO• Conventional cthoxylatc • Narrow range cthC/JIOylalC

Figure 1. Ethylene oxide nomolog di,tr1b4.rtlon (We cloud point etho.-ya.tes)

Properties, performance of nonionic surfactantsPclyoxyethylenated alcohols nan-ionic surfactants are more common-ly called alcohol erhoxytates (AE) iftheir hydrophobes are linear orbranched and alkyl phenol ethoxy-lares (APE) if they are based onalkyl phenol. These compounds andmany of their derivatives have beenan integral part of formulations usedin the consumer household. personal-care. industrial and institutionalmarkets for many years. They areused in virtually all cleaning pro-cesses and in industrial productionand manufacturing where thechemistry or process takes place atinterfaces between solid-solid,solid-liquid, liquid-liquid,liquid-air or solid-air. Some appli-cation areas include: detergents.dish wash. personal-care cleansingproducts. textile preparations andauxiliaries for dyeing. metalworkingfluids. adjuvants for pesticides andherbicides, processing agents andlubricants for fiber production, anddeinking compounds for paper andpaperboard.

The growth rate of the U.S. alco-hol etnoxytates market is forecast at4%/yr over the period 1993-2005(J.H. Houston. private communica-tion, 1994). The market for APE hasbeen under pressure from AE andfrom regulatory pressure driven bylegislation in Europe. The U.S.nonylphenol market is expected toremain essentially nat (J.H. Covill,Hoechst Celanese. internal commu-nication, 1994). The consumer

___ fitlllilku 'p,"'--I'orfo- CIoturJek_

ofli1oetu, --- AtyI NDttIottic Iiwfw"_ ..... f11Ol1G1"dforINFORM by Dr. ,.", A. ,.,.,. ... _ tlfJIPIIctItiot flltJlfll6er forHoecIut ~~ 4JJI "'-"'It..Dr.. C7wuf0&-. NC 28216.

detergent and personal-care indus-tries represent the largest share ofthe alcohol ethoxylate market whilethe industrial sector dominates theconsumption of nonylphenol erboxy-lates.

Given the wide spectrum of appli-cations and the many choices of AEsand APEs-which include the trade-marked products Genepcl. Hostapal(both from Hoechst AG). Neodol(Shell Chemical Co.), Tergitol(Union Carbid Inc.) and Alfonic(Vista Chemical Co.)--how does aformulator begin to select the AE,APE or non ionic surfactant combina-tions to achieve optimum perfor-mance?

Ethoxylation is done in the pres-ence of a variety of catalysts andresults in a homologous EO distribu-tion which is either termed conven-tional broad range or narrow range. Acomparison of conventional vs. narrowrange catalysis for an ethoxylated alco-hol is shown in Figure I. In the pres-ence of a narrow range catalyst, theEO distribution is peaked with a sub-stantially lower concentration of freealcohol compared to the conventionalerhcxylate. Nonylphenol erhoxytateEO distributions characteristically arepeaked regardless of the catalyst usedin ethoxytenon. These differences aswell as the large difference in linear.branched, and aryl hydrophobe struc-tures will have a substantial effect onthe physical and chemical propertiesexhibited by the surfactant.

The three families of surfactants tobe compared are:

Definition or StructureThe chemistry of ethoxylation issimply defined by the followingreaction:

o/ ,

ROH + (n)CHz -CHz -+ RO(CHzCHZO)nH

R ,. alcohothydrophobe or lipopnilc.n = number ofmolesof clhylcne o~idc(EO, which is hydrophilic)

INFORM. Vol. 6. no. 1 (Jonuory 1995)

Table 1Surfactant identification: comparison of HLB, cloud point

Alcohol Moles EO Hydroxyl Molecular HLB Cloud point,ethoxylate number weight 1% (OC)

26L3 3 171 328 8261A 4 145 387 926L5 5 134 419 1126L4S 6.3 117 480 12 45261..50 7 111 506 12 5026L60 7.3 108 520 12 6026L60N 7N 112 501 12 6026L75 8.3 100 561 13 7526L98N II.SN 80 701 14 100CII·030 3 185 303 8CII-OSO 5 143 392 11C11·070 7 117 480 13 53cu-oso 8 107 524 14 63en-no 11 86 652 15 95NP040 4 144 390 9NP060 6 120 468 12NP090 9 92 610 13 53NPIOO 10 86 655 13 63NPI30 13 71 790 15 85NPISO 15 64 877 15 93

• CII oxo alcohol (55% randombranching) with 3 to II moles EO;designated as CII-030 to CII-IIO,narrow range product includes an "N"following the moles of EO.

• CI2i14/16 coconut alcohol (100%linear) with I to 11.3 moles EO; desig-nated as 26L-J for nonwater solublewith one mole EO and 26LA5 for watersoluble with a cloud point of 45"C; nar-row range product includes an "N" fol-lowing the moles of EO or cloud point.

• Nonylpbenol (aryl) with 4-30 molesEO; designated as NP 040 - NP 300.

overall performance. Without somebasic knowledge of their interrelation-ships, achieving optimum performancecan be a very long and tedious process.

HL8 valueThe ratio of the hydrophile, EO, tohydrophobe or lipophile, alcohol isknown as the hydrophilic-lipophilicbalance or HLB. For polyoxyethylenenonionic surfactants, the HLB is equalto the total weight percent EO dividedby five.

A method of selecting the optimumemulsifier by matching the HLBs ofthe emollient and the emulsifier wasproposed by Griffin in 1950 (I). TheHLBs of many non ionic surractantsare available in McCutcheon s Emu/-sifters and Detergents (2) and havebeen commonly used as a startingpoint for surfactant selection. Wheremore than one emulsifier is applied,the HLB can be calculated:

HLBfinai = (W, x HLB t)

+ (Wl x HLBz)/(W, + W1)

whl':re;w, = the weight percent of emulsifier I and

W2 = the weight percent emulsifier 2.

There are limitations to thismethod since it does not allow for dif-ferences in HLB with changes in the

Hydroxyl numberTIle hydroxyl value or number is oftenused as a specification for ethcxylatesto follow the manufacturing process orto calculate the average molecularweight. The hydroxyl number isobtained experimentally by titratingwith KOH the excess acetic acidfonned as a result of acetylation of theterminal hydroxyl site with an excess ofacetic anhydride. From a blank titrationvalue, the amount of acetic anhydrideconsumed can be calculated. Thisamount is expressed in mg KOHIg. Thehydroxyl numbers, shown in Table 1for the 26L linear, CII cxo, and NPseries, decrease with an increase in theamount of EO on the alcohol. The aver-age molecular weight (MW) corre-spondingly increases and can be calcu-lated using the hydroxyl number:

PhysicaVchemical propertiesThe primary function of all surfucrantsis to reduce the interfacial tension orsurface tension at any interface. There-fore, ideally, only this property war-rants discussion. Unfortunately, themeasured values of interfacial tensionare strongly influenced by the surfac-tant's own structure and by its "totalenvironment," which, in turn, resultsin a variety of readily observed andmeasured behavior at end use. Froman applications point of view, wetypically assess the bulk of data on aseries of surfactant.s defined under lim-ited conditions, formulate the mostlikely product for success and evaluate

56,110 mg KOHlmoie

hydroxyl number (mg KOHlg)

= MW (glmole)

INFORM. Vol.6. no. 1 (January 1995)

23

24

SURFACTANTS a DETERGENTS

Table 2Comparison of HLB values

HLB value 26L ell Oxo NP General General Emulsinersolubility application

4 ,." Co-emulsifiers WIO5 26Ll.6 Oil-soluble emulsifier

7::M

Wetting. agentsNP 04{)

II 26L5 Cll·05026LAS26L50 NP060

12 ;~~N Detergents

? . Water-soluble O/w14 26L98N cu-oso NP 100 emulsifiers

c".n"IS en-no ~130NP

I· Sclubilizers17 NP300

surrounding conditions of the emulsi-fiers, i.e., the presence of additives,electrolytes, other surfuctants, or tem-perature at the point of application.Sowanda and McGowan (3) reviewedthe HLB system and, based on a ther-modynamic interpretation, concludedthat under Den ideal conditions theHLB is concentration-dependent. Themost optimum emulsifier(s) should beselected by determining the HLBexperimentally under use conditions.

Table 2 lists the HLB values for thethree series of nomoruc surfactantsand includes some general informa-tion on the range of solubility andfunction. Note that there are severalsurfactants with the same HLB value,so additional property data is helpfulin selecting the appropriate emulsifier.

Cloud pointA second method used to determinethe optimum surfactant choice isbased on selecting the emulsifier withthe appropriate HLB and then narrow-ing the choice by comparing the cloudpoint ar use. Cloud point is an indica-tion of a surfucrants solubility inwater. It is defined as the temperatureat which the water molecules associat-ed with the hydrophile acquire suffi-dent energy to break free of the sur-

factant molecule or desolvate. At thistemperature the surfactant is no longersoluble in water and the solutionbecomes hazy or cloudy. Above thecloud point, two distinct phases formconsisting of a surfactant-rich phaseand a clear dilute solution which con-tains essentially no micelles.

Theories on detergency and soilremoval have argued that optimumperformance is obtained in the vicinityof the cloud point. According toRosen (4), optimum detergency foroily soil is obtained at l5-30·C abovethe cloud point of the nonionic surfac-tant. The mechanism for oily soilremoval is based on the "roll-back" ofme oil and solubilization of the oil in asurfactant-rich separated phase. Solu-bilization is optimum above the cloudpoint in this "middle phase" in whichboth micelles and reverse micelles arebalanced. This occurs near the phaseinversion temperature (PIT) for water-in-oil (WID) or oil-in-water (O/W)emulsions. At the PIT the hydrophilicand hydrophobic properties of theemulsion are balanced. and the surfacetension and interfacial tension are at aminimum. This balance can be strong-ly affected by the presence of elec-trolytes and other additives in a deter-gent formulation or cleaning solution.

Therefore, an excess of nonionic sur-factant is usually needed to solubilizeoily soils and to prevent redeposition.

Cloud point data for the threeseries of nonicnic surfacrants areshown in Table I. The cloud pointincreases with an increase inhydrcphilicity or EO content withineach series. Similarly, the cloud pointalso increases with a decrease in themolecular weight of the hydrophobeat constant EO.

Surface tensionWhenever dealing with surfaceeffects, the properties at the solid-liq-uid, liquid-air, solid-air andliquid-liquid interfaces become moreimportant than the properties of thebulk liquid. In order to bringmolecules from the bulk interior to thesurface of a liquid, work must be doneto reduce the cohesive forces of theinterior liquid. Therefore, the surfaceporucn of liquids has a higher freeenergy than the bulk liquid. Theattractive force or internal pressureexerted by the molecules in the bulkliquid, which is defined as a force perunit length, is surface tension. Units ofsurface tension in the cgs system are

INFORM, VOl. 6, no. 1 (January 1995)

(continued on fWge 26)

26

SURFACTANlS a DETERGENlS

Table 3Surface tension and critical micelle concentration (25~C)

Alcohol ethoxylate Surface tension Surface tension CMC (mgfL)Wilhelmy plate Wilhelmy plate(dynes/em) 0..1% (dynes/em) 1.0%

26L3 25.41 24.81 7.9261A 27.59 27.51 8.226L5 27.29 27.35 8.626lAS 27.41 28.87 9.126LSO 28.59 29.16 9.4261.60 29.08 29.50 9.626L60N 31.70 31.75 6.526L75 31.04 32.01 10.626L98N 36.85 37.25 9.9CII-030 25.84 26.3i 41.0cn.oso 27.10 27.14 101.0CI1-070 27.51 27.94 142.0CII-080 27.39 28.13 160.0cu.uo 30.98 31.48 \85.0Ni'040 29.27 29.13 9.8NP060 29.67 29.47 14.5NP090 31.55 31.43 28.1NPIOO 32.12 31.28 30.5NPI30 42.5NPI50 70.7

(corrtinuedjrom page 24)

dynes/em or mN/m (5,6).Interfacial tension has the same

units as surface tension and describesthe work done 10 extend a surface at aboundary between any two phases.Recall that at the PIT, the surface ten-sion and interfacial tension approachzero. Therefore the temperature rangeof the specific application is veryimportant 10 consider in selecting theappropriate surfactant

Most solvents have surface ten-sions or 20-40 dynes/cm at room rem-perature. Water has an unusually highsurface lens ion of 72.75 dynes/em(2D°C), and mercury, also a liquid. hasa surface tension of 480 dynes/cm (7).Many surfacrants have the capacity toreduce the surface tension of water,bur nonionic surfactants typically canbe used at relatively low concentra-tions 10 reduce surface tension to the25-35 dynes/em range. Only the fluo-rosurfacrants reduce surface tensions10 about IS dynes/em. The surfactantmolecules orient and adsorb at theinterface or surface with thehydrophobic groups favoring the air.Since the cohesive forces of hydrocar-

bons are smaller than those of water,the surface tension of the aqueoussolution is appreciably lower than thatof water.

Surface tension reaches a minimumat the critical micelle concentration(CMC) of the surfactant At the CMC,colloidal particles or aggregates formfrom the unassociatcd molecules inaqueous solution. These aggregates,called micelles. have a defined struc-ture or shape (spherical. disk. cylindri-cal, lamellar sheets. ctc.) and have adirect impact on the physical proper-ties, (e.g., viscosity. cloud point andsolubilization) of oils. of a surfactantsolution. For non ionic surtactants.detergency performance with respectto solubilization of oil reaches a maxi-mum at 10-100 times the concentra-tion oll the CMC (4). CMC values foranionic surfactants are orders of mag-nitude greater than those typical ofnon ionic surfactants. Therefore, indilute solutions. non ionic surfactantscan solubilize oils much more readilythan ionic surfactants.

Surface tension and CMC valuesare given in Table 3 for the 26L.C II oxo and NP series. The surfacetension was measured at room temper-

arure at concentrations of 0.1 and 1%non ionic surfactant using the Wil-helmy plate method on a Kruss ten-siometer.

CMC values were also determinedat room temperature (25"C) in deion-ized water from least squares analysisof the surface tension vs. log concen-trauon curves. The CMC is recordedas the inflection point or point ofintersection of the two portions of thecurve, Notice in the table of CMCdata that the concentration of surfac-rant needed to reach the CMC increas-es with an increase in the number ofmoles of EO on the same hydrophobe.This may be attributed to a largerhydration radius and therefore anincrease in the space required foradsorption at the surface, Increases inthe chain length or number of carbonsin the hydrophobe will in generaldecrease the CMC (8), In addition.there is an appreciable difference inthe values of the CMC depending onthe structure of the hydrophobe. TheCMC values for the linear 26L seriesare generally an order of magnitudesmaller than those of the C IIbranched or NP aryl hydrophobeseries. A difference of one carbon

INFORM. Vol, 6. 1"10. 1 (January 1995)

27

Table 4Aqueous viscosities [Brookfield viscosity (cps) at 25°C, ·NA = solid at 25°C]

Weight Cll-070 Cll·08O CU·UO 26IAS 26L50 26L60 26L60N 26L75 26l..98N NP090 NP 100..20 \8 \3 \2 J3J 50 \7 12 9 8 69 2\30 77 87 49 1380 830 \86 BS 42 34 502 3\340 205 8'\ 297 8'\ get gel get gel gel gel "~I50 294 2680 get gel gel gel "~I gel gel gel gel60 gel 240 "~I "~I ,oJ "~I .oJ ,oJ "~I 2360 "~I70 gel 4690 4\9 get 7650 gel get gel get 5120 407080 get 115 175 "~I 4\800 5380 4670 6340 .oJ 896 52890 70 79 \20 87 96 99 333 123 \38 326 m

\00 66 73 'NA 50 " 70 60 'NA 'NA 307 'NA

would not be sufficient to explainsuch a large difference. The effectmay be due to the micellar structuresand the aggregation numbers, i.e.,number of monomers/micelle. charac-teristic of each of the surfactant series.

Addition of electrolytes to aque-cus solutions of polyoxyelhylenatednonlonics will also affect the CMC.The electrolyte is believed (0 interactwith water and contribute to a saltingin or salting out effect on thehydrophobic portion of the molecule(4). This phenomenon is often asso-ciated with the water structure of abulk liquid, i.e., electrolytes areeither water structure formers (salt-ing in) or water structure breakers(salting out) (9). For anionic surfac-tarns the hydrophilic portion of themolecule is more strongly affectedby the presence of electrolyte inaqueous solution. Surfactantmonomers salted out by the presenceof an electrolyte favor formation ofmicelles, an increase in bulk waterstructure and result in a lower CMC.When monomers are salted in andfully solvated by water molecules,micellization is not favored, bulkwater structure decreases and theCMC increases.

Families of CMC curves on mix-tures of surtacrarus or other additivescan be used to determine whether apositive synergism exists. For a spe-cific ratio of two components, a posi-tive interaction would be shown by asignificant lowering of the CMC forthe mixture compared to the CMCdeterminations for each of the single

surfactarus. The formation of mixedmicelles is thermodynamicallyfavored, and longer chained ncnionicsare typically found at a higher concen-tration in the micelle (4,8,9). Thiskind of data is valuable in determiningsurfactant choice(s) and optimizingthe performance of fully formulatedend-use products.

ViscosityViscosity is simply defined as "theinternal resistance to flow exhibitedby a fluid, the ratio of shearing stressto rate of shear" (10). The science ofdeformation of liquids with stress andstrain over time is called rheology(10). It is applicable to both the han-dling of liquids in processing and tothe formulation of end-use products inwhich a desired physical form isrequired. This is illustrated very wellby the relatively new liquid-gel auto-matic dish washing products whichflow very well after shaking (applyingshear) and then "gel" in the dispenser(at rest). These products are thixotrop-ic. Thixotropy also plays a veryimportant role in oil-well drilling flu-ids where aqueous clay suspensions,surfactants and polymers are alsoused.

Surfactant solutions are non-New-tonian liquids since the viscosities ofthese solutions are affected by shearrate, the structure of the surfactant.changes in temperature and pressure.and their shear history. In formulatedproducts, their viscosities measured inplain water may be further affected bythe total electrolyte concentration.

additives which modify the structureof water or the concentration of waterwith respect to the surfactant and in asense, the "general environment or thesolution." Viscosity of the bulk surfac-tant-containing liquid is also known toplaya significant role in defining thestability of foams and the hydrolyticstability of a formulated product.Foam stability affects the desired useprofile of the product, while hydrolyt-ic stability will strongly impact shelflife.

Absolute viscosity is expressed asforce/unit area.sec (dynes/cm/sec =poise). One poise equals 100 cen-tipcises (cP), IcP equals one milliPas·cal. sec (mPa.s). To place viscosity inperspective, at 25°C, water has a vis-cosity of 0.890 cps, a 20% sugar solu-tion has a viscosity of 1.710 cps and a60% sugar solution has a viscosity of44.02 cps (7, Il.12).

The data shown in Table 4 wasgenerated using a simple Brookfieldrotational digital viscometer at a con-stant shear rate of 50 rpm at roomtemperature. This data compares theviscosity/solution behavior of selectedwater-soluble ncnionics representativeof each of the series over the concen-tration range of 20-100%. If the solu-tions formed sols or gels, no viscositydata was available.

For all series the viscosity tendsto increase with concentration andthen pass through a gel range. Thebranched C 11 hydrophobe of theCll oxo series and the nonylphenolhydrophobe of the NP series areresponsible for the narrower gel

INFORM. Vol. 6, no. 1 (January 1995)

28

SURFACTANTS I:DETERGENTS

350 r--------------------,300~---------------

50

o

WettingWhen a gas-solid interface is replacedby a liquid-solid interface, the solidhas been wetted by the liquid. Gener-ally, a solid may be welted by spread-ing of the liquid. immersion of thesolid in the liquid or by adhesion ofthe liquid to the solid. Surface weltingby spreading occurs in paint andpainting. lubrication of metal parts,application of antistatic agents and inplating. Wetting by adhesion is illus-trated by the fogging of glass. waterrepellency and the adhesion ofbubbles in a Ilotauon process. Thewelling of textiles in washing anddyeing, dissolution of tablets andadsorption of moisture by powders areexamples of immersion wetting (4.9),

The Draves Welting lest (Draves.1939) is used to evaluate the speed atwhich a 0.1% surfactant solution willwet a standard waxed colton skein at25°C. This test has been used formany years as a benchmark for com-paring the wetting of textiles by sur-Iactants. This process is believed to bediffusion-controlled in the presence ofan excess of nonionic surfactant and ishighly dependent on the surfuctuntstructure and molecular weight (13).Thus more compact, lower molecularweight surfactants would be expectedto diffuse rapidly to the solid-airinterface. reduce the surface tension ofwater at that interface and permitwater to wet the cotton.

As welting of the substrate is thefirst step in the overall performance ofa cleaning solution, application of adye, dissolution of a powder, etc., usu-ally in a time-constrained process, fastwetting times are critical. In general.Draves welting times in an aqueousmedia of about ten seconds or less areconsidered very good.

Figure 3 compares the wettingtimes of the C II, 26L and NP series.The noniomcs are grouped by HLB.Those with low HLB and poor watersolubility tend to have long wettinglimes. Nonionics with increased EOcontent, very high molecular weightsand excessive water solubility alsotcnd to have longer wetting limes(HLB = 14---17). Ncnicnic surfacrarnsin the HLB range of 11-13 generally

(continued on (Xlge 30)

~ 2501-----------------::::---! 2001------------------~:::----e-.~>

1501------------

100~----

o 2 3Sodium Chloride (%)

4 5

• CII-070 • NP 090 Surfactant • 26L60 Surfactant

Figure 2. Viscosity with ult addlUons (O:E20% IUrfltCtant solution, spindle 12. 100 rpm,25"C)

60

so:['".g 30

~20

~ 10

o

r~H-I n r

u------uuuuuuAlcohol clooxylate5

Figure 3. Draves wetllng (25"C, 0.1% liurfaclant concentration, grouped by HLB vatuea,which are shown In parentheae')

range compared to that of the linear26L hydrophobe series. Followingthe gel range of most of these non-ionlcs. the viscosity is bimodal, i.e ..viscosity builds \0 II maximum and at90-95% concentration drops sub-stantially. Relatively low viscositiesat high actives thus make processhandling or pumping of the liquidsurfactants manageable at room tem-perature.

Should a Form ulmer wish toobtain a particular viscosity profilefor a finished product. we recom-mend viscosity measurements bedone following preparation and afterabout two or three days. We addedsodium chloride to 20% C 11-070.NP 090 and 26L·60 solutions 10observe the changes in viscosity with

addition of a simple electrolyte. Atsalt concentrations of 3-5%, viscosi-ty continued to increase slightly forabout two days.

Figure 2 compares the viscosity orthree nonionics commonly used indetergent formulations us a functionof salt concentration. The viscosityof 20% CII-070 is not significantlyaffected by sodium chloride. NP 090builds viscosity readily with addi-tions of sodium chloride. and 26L·60shows a moderate increase to 120cps when 5% sodium chloride isadded. Other surfactants and addi-lives will further affect the viscosityprofile of a final forrnulaticn. There-fore the cumulative effect on vlscosi-ty needs to be considered when for-mulating an end-use product.

INFORM. Vol. 6. no. 1 (January 1995)

30

SURFACTANlS a DETERGENtS

"r--------------------------------,E~20~--------~~~--_1~------..~__1.'§ 15 I----..-.-I::IHI-t---..-.-I-II---IHI-t-~~• 10 f-----1~~

u U U uAlcohol etho~yl8tcs

• Initial

§ c- '" "~"-0 0 0q~~

~q'" '" '" '" '""- "- -~ § § ~0

~~,

~" ~~"u z z

• Final (5 min)

Agure 4. Aoss-Mlles foam height (4g·C, 1% lurfactant concentraUon, grouped by HLB val-ues, whleh are shown In parentheses)

[continued from pi/8e 28)

exhibited good wetting speeds on cot-ton since they can readily diffuse tothe solid-air boundary and becausetheir cloud points are also slightlyhigher than the test temperature of25°C.

The ell series wets considerablyfaster than the 26L series over theentire HLB range with excellent 4-5 swetting speeds for the ell-050, Cll-079 and ell-OSO. These superior wet-ting limes can be explained by thecompact branched hydrophobe and themoderate molecular weights of thesenanionics.

The 26L60N, the narrow rangeethoxylate, wet faster than its conven-tional broad range counterpart, 26L60.This behavior is due to the absence ofimpurities in the form of unreactedalcohol and lower EO moieties whichwould be insoluble in water. Anyother narrow range hydrophobeswould exhibit faster wetting speedscompared to their conventional broadrange counterparts.

Overall, the nonylphenolhydrophobe (NP series) did not per-form as well as the CII branchedalcohol (Cll series) at these test con-ditions. The hydrophobe is large andbulky and would be expected to takelonger to migrate to the cotton sur-face.

FoamingIn water. nonicnic surfactants as aclass of compounds are generally con-

side red to be moderate to low foamerscompared to anionic surfactants.

Foam has been described as havinga honeycomb structure and is theresult of entrapping air or other gas ina film of an impure liquid. The pro-duction and persistence of a foamdepend largely on the ability of themonomolecular film imparted by thepresence of surfactant at theliquid-gas interface to resist the col-lapsing negative forces and the drain-ing of the "bulk liquid" of the bubble.This ability is commonly referred toas film elasticity and is directly relatedto surface tension. With the drainingof the "bulk liquid," the concentrationof the surfactant decreases causing acorresponding localized increase insurface tension. This behavior isknown as the Gibbs Effect. Addition-ally. the surface tension at the thinnedspot on the film immediately increasesfurther, prior to rcaching equilibrium,by diffusion of the surfactantmolecules back to the depleted orthinned area. This mechanism isknown as the Maragoni Effect. Shouldthe film reach a thickness of less than50-1OOA, it will collapse (4,9).

A persistent or stable foam requirespreservation of film elasticity and suf-ficient surfactant concentration toreplenish the thinned regions pro-duced by drainage. A sufficient sur-face tension gradient between the bulksolution and the thin film must also bepresent to repair the thinning film. Aswe approach the CMC of the surfac-tant, the surface tension of the solu-

tion does not vary significantly. In thiscase the surface tension gradient maynot be sufficient to repair the thin filmand rupture is possible throughmechanical shock or through rapiddiffusion of gas across the liquid-liq-uid boundaries of adjaccnt bubbles. Ifthe viscosity of the film is either veryhigh or very low. the foam will beunstable due to poor film elasticityand sluggish replenishment of the thinfilm. If the viscosity of the bulk solu-tion is high, foams generally tend tobe more stable (4, 14).

Transient or flash foams initiallymay be created by rapid migration ofthe surfactant to the liquid-air bound-ary. This also correlates with rapidreduction in surface tension. Thisfoam, however. breaks quickly. Rapiddiffusion of the surfactant disruptssurface film elasticity and thereforeminimizes foam stability.

The Ross-Miles Foam Height Test(ASTM 0 1173-53) and a number ofmodifications of the test have beenused extensively in an effort to corre-late foaming behavior with both sur-factant structure and end-use perfor-mance-d.etergency. At a given concen-tration and temperature, an ageddefined volume of surfactant isdropped into a jacketed cylinder. andthe foam height is measured bothimmediately and after five minutes.

Although polyoxycthylenated non-ionic surfactants are considered mod-erate foamers, foaming will increase.peak and decrease with increasing EOon a single hydrophobe. This behavioris shown in Figure 4. The water-solu-ble 26L conventional nonionic surfac-tants produce a moderate and morestable foam compared to their narrowrange counterparts or any of the elland NP nonionic surfacrants.

The branched chain and nonylphe-nol group are responsible for the tran-sient foams produced throughout thesetwo series. The narrow distributionassociated with the 26L60N and26L98N is responsible for the highinitial foam heights, but reduced foamstability. Data compiled by Crook etal. in 1964 (15) on single-cut alcoholethoxyfates is also consistent with thisbehavior. At or above the cloud pointsof all of these non ionic surfactantsfoaming decreases significantly due to

INFORM. Vol. 6. no. 1 (January 1995)

31

NOTICE OF THE ANNUAL BUSINESS MEETING

slower diffusion of the bulky micelleaggregates.

The physical properties and per-formance characteristics of poly-oxyethylenarcd ncnicnic surfactantsarc markedly affected by changes inthe relative ratios of hydrophilic tohydrophobic moieties and the chemi-cal structure of the hydrophobe. Non-ionic surfactant choices can be opti-mized by considering how they willbehave in defined aqueous systemsunder end-use conditions and judi-ciously observing and evaluating theeffects additives have on the formula-tion.

A basic understanding of the struc-ture-function relationships throughdefinition of HLB. CMC. surface ten-sion. viscosity. and wetting and foam-ing characteristics can lead to forme-lations exhibiting the desired end-useperformance properties across manyapplications.

Note: The alkoxylanon technologymentioned in this article may be cov-ered by one or more of the followingU.S. Patents--4,453.022; 4,453,023;4,727,199; 4,757,075; 4,820,673;4,873,017; 4,886,917: 4,902,658:4,946,984; 5,025,094; 5,104,575:5,112,788; 5.112,789; 5,114,900:5,118.650: 5,120,697; 5,136,106.

ReferencesI. Griffin. W.C., 1. Soc. Cosmetic

Chern. J :311 (1950).2. McCutcheon's Emulsifiers and

Detergents, McCutcheon Division,Manufacturing Confectioner Pub-lishing Co., Glen Rock, NJ, 1990.

3. Sowanda, R.. and lC. McGowan,Tenside Surf Det. 29(2): 109(1992).

4. Rosen, M.L Surfactonts andtnterfaciat Phenomena. JohnWiley & Sons Inc., New York,NY, 1989.

5. Moore. WJ., Physical Chemistry,Prentice-Hal! Inc .. EngelwoodCliffs, NJ, 1962, pp. 727-734.

6. Weser, C., "Measurement of Inter-facial Tension and Surface Ten-sion-General Review for PracticalMan," CIT Fochzeuschrift [ur dasLaboratorium. 24:642 and 24:734.Verlag, Darmstadt, Gennany, 1980.

7. Langes Handbook of Chemistry.

AcknowledgmentsSpecial thanks go to my colleaguesin the Surfactant Applications Labo-ratory at Hoechst Celanese Corp. inCharlotte, North Carolina, for acqui-sition and verification of the data onthe three series of nonionic surfac-lams and to Givens Ink for graphicssupport.

The annual business meeting of the American Oil CbemiSlS'Society wul be beld on Tuesday. May 9. 1995. a' 7:30 a.m. inthe South Banquet Hall of the Henry B. Gonzalez ConventionCenter in San Antonio. Te.... Routine business of the Societywill he conducted. including reports from the secretary.treasurer and president. and new oIfu:enwill he installed. /JCX:,S&

13th Edn., edited by J.A. Dean.McGraw-Hili Inc., New York, NY.1985. pp. 10, 92, 10I.

8. Surfoctants in Consumer Prod-uct s: Theory, Technologv ondApplication. edited by J. Falbe.Springer-Verlag, New York. NY.1987. pp. 139-142.

9. Nonionic Surfactants: PhysicalChemistry. edited by M.J. Schick.Marcel Dekker lnc., New York.NY. 1987.

10. Hawley's Condensed ChemicalDictionary, Eleventh Edition. edit-ed by N.I. Sax and R.J. Lewis, VanNostrand Reinhold Co., NewYork. NY, 1987, p. 1227.

II. Perry's Chemical EngineersHandbook. Sixth Edition, editedby R.H. Perry, D.W. Green andJ.D. Mahoney, New York. NY.1984. p. 5.

12. Dean, J.A., Handbook of OrganicChemistry, McGraw-Hill Inc ..New York. 1987. pp. 4-84.

13. Fowkes, F.M., 1. Phys. Chem .•57:98 (1953).

14. Oefoaming: Theory and IndustrialApplications, edited by P.R. Gar-rett, Marcel-Dekker Inc .. NewYork, NY, 1993.

15. Crook, E.H .• D.B. Fordyce andG.F. Trebbi. 1. Am. Oil Chern.Soc.4/:231 (1964).

INFORM, Vol. 6, no. 1 (January 1995)

33

SURFACTANTS a DETERGENTS

Use of peroxygens in ADD formulationsChemical bleaching has been prac-ticed since the introduction of sodiumhypochlorite in clothes laundering atthe end of the eighteenth century. Per-oxygen compounds have been usedfor more than 100 years. beginningwith the use of hydrogen peroxide(H202) in the 1880s. This was fol-lowed by the introduction of persaltsin washing powders. first in Europe,and more recently in the UnitedStates.

Like laundry detergents, autodish-washing detergents (ADDs) have fol-lowed a path from no bleach to chlo-rine bleach to peroxygen bleach.Chlorinated compounds were incorpo-rated as rinse aids 10 help eliminatewater spoiling and to improve Slainremoval. The most recent develop-ment in ADDs is the addition of per-oxygen bleach, incorporated into acommercial U.S. autodishwashing for-mulation in 1988.

Requirements for autodishwashingformulationsA typical autodishwashing formula-tion has to meet seve rul basic require-ments. It must remove soil, controlfoaming, inhibit corrosion. and pre-vent precipitation of water hardnessions to reduce spotting and streaking.Achieving these objectives requires acareful balance of ingredients:

• Polyphasphates enhance cleaningby dissolving soil. sequestering hard-ness ions and dissolving the precipi-tates that form in rinse water.

• Soda WI;" provides alkalinity forsoil dissolution and emulsification.

• Nonionic surfoctams remove soil.reduce spotting and filming. and sup-press protein soil foam.

" Chlorinated compounds removestains, reduce spotting and filming,and also act as sautuzcrs.

" Silicates protect against corrosionof china and metal parts and also helphydration.

A typical formulation has apH ;:: \1. to ensure soil dissolutionand emulsification of greasy foods.

While basic autodishwashing for-mulations have not changed substan-tially since the early 1980s, environ-

mental trends and consumer pressurestoday are forcing a new evaluation ofADD formulations.

Current trendsThe changes now taking place in theADD industry are similar to thoseaffecting laundry detergents: Productsmust be safer for the consumer. lesspolluting in the environment andeffective at lower wash temperatures.In order to meet these requirements.substantial product modification isnecessary.

Some of the challenges faced inreformulating these products include:

" Replacement of chlorinated COli/-

pounds. The use of such compoundshas been limited over the yearsbecause of their instability and theirincompatibility with other ADD ingre-dients. such as surfactants and fra-grances. More recently. the dischargeof chlorinated products in the sewagesystem has raised environmental con-cerns.

• Replacement of phosphates, Todate. phosphate bans have nor extend-ed to ADDs because of the smallervolumes used; however, the trendtoward more environmentally accept-able raw materials in all consumerproducts has increased interest indeveloping phosphate-free products.

" Reduction of alkalinity: From asafety standpoint. any product with ahigh pH can be considered a severehealth threat. The industry recentlyhas taken an initiative to switch frommetasilicate to the less alkaline disili-cate in autodishwashing fonnulations,and further changes to reduce alkalini-ty are highly desirable.

• Effectiveness at lower tempera-tures. The (rend toward energy conscr-

vadon has led to a drop of wash tem-peratures. not only in clothes launder-ing but also in autodishwashing. Thetarget set by the U.S. Department ofEnergy is 120°F (49°C) for ADD, butfurther initiatives arc expected to dropthe operating temperature further. Thenew formulations should perfonn wellat lower temperatures.

Current autodishwashing formula-tions perform an adequate cleaningjob. The challenge of reformulation isto find the combination of ingredientsthat maintains detergent performance,while improving safety to the con-sumer and the environment.

Percxygen compoundsManufacturers tried to eliminate chlo-rine in the 1970s but soon abandonedthe attempt when the revised formula-tions failed to clean as well. Today.however, chlorine alternatives exist inrbe form of solid peroxygen com-pounds or "perseus," and technologiesare available to compensate for themilder cleaning properties of thesecompounds.

Perseus, a solid form of hydrogenperoxide, include sodium perboratemonohydrate (PBSI) and sodium per-

PBSI

IHO,,/o - 0,,/OHI2'2"'+/, r »:

HO 0 0 OH

NaBOl"HzO

2NalCOl"3Hl~

Figure 1. Sodium perborate monohydrate(PBS1) Sodium percatbonate (peS)

(continued on ease 35)

INFORM. Vol. 6. no. 1 (January 1995)

35

SURFACTANTS a DETERGENtS

Com",,1 NOloo" (IS) NIci!<~te. N.l'oly· :ITPP(lO)2H~(15l .. .,1... CIS)

lngredleru cOIJCCRtrtltion('ll»

• PBSI 0 FBPCSAgure 2. Compatibility of persatts with bullderslseque.trants (Na2C03. NaCttrate· 2H20,and sodium polyacry.ate at 15% concentration; sodium tripolyphoaph.te at 30%, balanceof formulatlon Na2S0~; material stored In 2-oz bottles at 120"F for two weeks)

(continued/rom page 33)

carbonate (PCS) (Figure I). These dis-solve in water to generate H202-

Persalts can offer several advan-tages in ADD formulations:

• Greater compatibility with otheringredients. Compared to chlorinatedcompounds, persaJts are more compat-ible with surfactants, enzymes, per-fumes and colors. This permits a for-mulator to choose from among awider selection of perfumes and col-ors, and allows the incorporation ofenzymes to increase cleaning efficien-cy. Also, it is not necessary to use themore expensive surfactants that resistinteraction with chlorine. since a widerange of surfactants retain their prop-erties when mixed with persalts.

• Lower allw.linity. The optimal pHfor persalt stability/performance is=9.5-10.5. This allows the ADD to beformulated at pH values lower thanII. This lower alkalinity enhancesenzyme stability and improves con-sumer safety,

• Reduced glass etching and metalcorrosion. The lower pH of persaltformulations decreases etching ofglass and porcelain, and protects metaltrim on porcelain and the dishwasheritself.

• Safety. In general. persans willnot damage fibers, fabrics, finishesand dyes, so accidental spillage cre-ates no problems on clothes or floors.

• Environmental friendliness. Afteruse, persalts decompose to innocuouscompounds: oxygen, water andrnetaborate (pBS I) or soda ash (PCS).

• Fast-dissolving. Both pes andPBS I dissolve quickly. At 60°F

(15°C), 95% dissolution is achievedafter 2.0 minutes and 0.5 minutes,respectively. Virtually instantaneousdissolution is expected at the highertemperatures used in dishwashing.This allows for immediate bleachingactivity and quick interaction with anactivator, if present in the formulation.

• Odorless. Persalts are odorless.eliminating the need for masking per-fumes.

«Easy 10 handle. minimal fines.Persalts are free-flowing powders thatare easy to use and handle in bulk.They have a minimum amount offines and a high resistance to attrition.which helps prevent generation offines during handling. The narrowparticle size distribution reduces seg-regation and improves formulationcompatibility, while the near absenceof fines improves safety and availableoxygen stability.

Balancing a persalt formulationThe replacement of chlorinated com-pounds with persalts in aurodisbwash-ing formulations does pose some chal-lenges. First, persans have lessbleaching activity, which tends toreduce cleaning performance. Second,persalts do not help control spottingand streaking as much as the chlori-nated products. Fortunately, there arebalancing factors. Despite a trendtoward cooler wash water, dish wash-ing temperatures still remain highenough for a good stain removal per-formance. In addition, organic activa-tors that generate a peracid ill situ, canbe used to increase persalt bleaching

oConlrOl ""yd, iJri!c>il

Mc, .. U(J) H24(15)

Ingredient eoncentration ('II)

• PBSI 0 FBPCSFIgure 3. Compatibility of persalls with sUi-cates (anhydrous metaslllcate at 5%concentration; Briteall H24 at 15%, balanceof formulation Na2S04; material slored In 2-cz bonles at 120°F for two weeks)

activity.Other formulation ingredients can

compensate for lost functions thatwould be provided by chlorinatedproducts. One of the best ways tomaintain detergent performance is touse enzymes, which enhance removalof starch and protein, reduce spotting,and improve overall cleaning.Enzymes also can compensate for theloss of detergent efficacy when lessaggressive chemicals are incorporatedin the formulation. Sequesteringagents can further reduce spotting bycontrolling water hardness and pre-venting protein redeposition. Andalthough persalts cost more than chlo-rinated compounds, the use of less-expensive surfactants and perfumesmay offset this expense. Severalpatents for persalt-containing ADDshave been issued. Most supplementthe formulation with enzymes (usual-ly protease and amylase) and usebuilders other than phosphate. ThepH of these formulations tends to besubstantially lower than typical chlo-rinated ADDs, in the range of9.5-10.7 (1-7). Many patents alsocontain an activator such astetraacetylethylenediamine (TAED)(4,7). Several autodishwashing for-mulations containing persalts insteadof chlorinated products already havebeen commercialized both in Europeand the United States.

Persall stabilitySuccessful incorporation of persalts indishwashing powders requires a carefulselection of formulation ingredients.

INFORM, Vol. 6, rIO. 1 (January 1995)

36

SURFACTANlS 8< DETERGENtS

~ 100 ,---------,

!so·f.~ 60

~ 40" 20~ o ......

Do Control • PBSI FBPCS

Figure 4. Compatibility of enzymes withpersalts (each lonnuiation contaIned 1% ofenzyme tested, 15% persall, balanceNa2S0.; materialatored in 2-oz eetaee atl00"F lor eight weeks)

This includes nOI only the type ofmaterial used, but also its quality. Thelevel of moisture and transition metalsin a product can playa crucial role informulation stability, Another impor-tant factor is the temperature at whichthe persalt is mixed with the otheringredients. The base has to be cooledbefore addition of persalt. Incorpora-lion of a stabilizer such as a phospho-nate can funher improve persalt stabili-ty, both in the pack and in use.

Laboratory studies show that per-salts are compatible with a variety ofingredients used in ADD formula-tions, including soda ash, sodiumtripolyphosphate, disilicates and non-ionic surfnctnrus. Compatibility testswere carried out in plastic containersat l20"F and ambient humidity fortwo weeks. In this accelerated decom-position test. 85% residual available

100 r---------,~80e" (i().~g 40

] 20

oT<tmOm~1 E<p<no;e

o ADD formula wi!haull'ersalt

• ADD formula with Persall

Agure 7. Stability of e~mes In ADO fOf"-mulation containing sodium percarbonate(ADO formula with persan contained 15%persall, each formula had 1% eachTermamyl and Esperase, material stored in2-oz bottles at 100'F lor eight weeks)

I'IJSt FB PCS

o ADD formula wlo enzymes• ADD formula w/enZYlllCs

Figure 5. Stability Of enzymes In ADD for-mulation (1% each Termamyl andEsperase in ADD formula with enzymes,both formulations contained 15% persall,material stored In 2-oz bottles at 100'F foreight weeks)

oxygen is considered acceptable.Wherever enzymes were incorporatedin the formulation, testing was done atlOO"F for eight weeks.

First. testing was done individuallywith every ingredient, with the bal-ance of the material being sodium sul-fate. Figure 2 shows compatibilitywith a variety of builders. In all cases,residual available oxygen was above95% after two weeks.

Figure 3 shows compatibility withsilicates. Pcrsalts in general are morecompatible with disilicates than withanhydrous metasilicate. If anhydrousmetasilicate must be used, a lowerconcentration (e.g., 5%) appears 10maintain persalt stability.

Figure 4 shows compatibility ofPBS I and FB sodium percarbonatewith enzymes. Persalts were dry-blended with the high-alkaline pro-

T.........,.I ~

D ADD formula without Persalr• ADD formula with Persalt

Figure 6. Stability Of e~mes In ADD for-mulation containing sodium perboratemonohydrate (ADD formula wnh persallcontained 15% persan, each formula had1% each Termamyl and Esperaa.e, malerialatored in 2-oz bottles at 100"F for eightweeks)

tease "Esperase" and the amylase"Termamyl," using a balance of anhy-drous sodium sulfate. The resultsshow excellent retention of enzymeactivity after eight weeks at lOO"F inz-oz bottles.

Nonphosphate persatt formulationwith enzymesFollowing guidelines from publishedliterature, a nonphosphate ADD usingpersalts was formulated by dry blend-ing all the ingredients (Table I). Thisgave a mix.with a low moisture content.

Enzymes were incorporated to helpbreak down some of the soil and actsynergistically with the bleach. To fur-ther reduce spotting and streaking with-out phosphates, the builder systemincluded a combination of carbonate,polycarboxylate and silicate. Finally,persalt activity was boosted by adding

[continued 011 page 38)

% STPI'I:Na2COJ.1lCA(I%) 0 PBS(5%)

Figure 8. Stain removal performance of a chlorlneted ADD compared to a persall contain-Ing ADD (40 g ADDI6.2L H20; S5'C; cleaning scale: 10 = best cleaning)

INFORM, Vol. 6, no. 1 (January 1995)

38

SURFACTANTS lit DETERGENTS(continued from page 36)

an activator to improve bleaching per-formance and a stabilizer to minimizeavailable oxygen loss. Table I showsthe composition of this ADD.

This formulation was tested for themutual compatibility of perseus andenzymes by storing the formulation inplastic bottles at 100°F for eightweeks. The results, shown in Figures5-7, indicate the excellent stability ofboth persalts and the two enzymestested. PBS I was slightly more stablethan pes, bUI the residual availableoxygen level for PCS was consideredvery acceptable.

Chlorinated ADD \IS.PBS ADDWichelhaus and Andree (8) comparedthe bleaching performance of two ADDformulations-cone containing the chlo-rine bleach trichloroisocyanuratc(TICA) and the other containingPBSI----on tea-stained white porcelain.The results (Figure 8) indicate consider-able variation depending on the ratio ofsodium triphosphate (STP) and sodaash. It appears that peroxygen com-pounds offer a viable alternative to cur-rent chlorinated formulations.

To summarize, incorporation of per-salts in autodishweshing formulationscan produce stable products that pro-vide equivalent cleaning performanceplus greater safety for glass and porce-lain, metal trim, the consumer and the

Table 1New phosphate ADD formulation using persaHs

a Sample provided by BurtinglOO Chemical; b Britesil H24 sample provided by \hf:! PQ CorporIIIion;" sample pro-vidM by Shell C«pofDtioo; d sample provided by Warwict International LId.. e""",pIe provided by Monsanto

Corporation;! sample provided by NO\'o Nordisk.

Ingredient

Na2COl (anhydrous)Polyacrylate (Bcrcosperse AP)<,Na citrate dihydrateDisilicate (Britesil H24)bNonionic surfactant (Neodol 23-6.5)CPersall (PBS I or FB PCS)Activator (TAED-Mykon ASD)dPhosphonate stabilizer (Dequest 2041)~Protease (Espera~YAmylase (TermamylY

environment. The use of persalts inADDs also broadens the range of sur-factants and perfumes that can be used,and allows the incorporation ofenzymes.

Effective formulation requiresselecting compatible ingredients, min-imizing moisture content, eliminatingtransition metals and other contami-nants, and creating a suitable pH.

ReferencesI. World International Property

Organization Patent 93/07252.Church & Dwight.

% (w/w)

27.08.0

20.020.02.5

15.0,0.'II

2. European Patent Application414197 A2, Benckiser.

3. European Patent Application530870, Unilever.

4. World International PropertyOrganization Patent 92/09680.Procter & Gamble.

5. European Patent Application516553 A2, Colgate Palmolive.

6. European Patent Application504091 AI, Viking Industries.

7. Japanese Patent 01198699 A2,Kao.

8. Wichelhaus, W., and H. Andree,TensideSurf oe, 27:51 (1990) .•

Proceedings of the World Conferenceon lauric Oils:

Sources, Processing, and ApplicadonsThomas H. Applewhite, Editor

Hardbound. 192 pages. 1994ISBN 0-935315-56-XItem #IWC94List: $135.00AOCS Member: $1.08.00

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