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J. $oc.CosmeticChemists, 1, 85-98 (Feb. 4, 1970)

MicroencapsulationechniquesApplications nd ProblemsHERMAN NACK, B.Ch.E.*

PresentedMay 8, 1969, New York City

$ynopsis--A number of techniques have been developrid for cncapsulating small particlesanging in size from a few microns or less to about 2000 /z. In addition, there are otherfactors which must be given careful consideration n the development of suitable micro-encapsulatedproducts, such as: physical and chemical properties of the core materialand wall material; post-treatment of capsules; interaction of capsules and substrate;storage conditions; release mechanisms; and economics.MICROENCAPSULATIONrocesses f interest in the cosmeticsield include: aqueous phaseseparation, nonaqueous phase separation, interfacial polymerization, multiorifice rotatingcylinder, fluidized-bed spray-coating,melt prilling in a fluidized bed, spray drying, dif-[usional exchange,and meltable dispersion.

1 NTRODUCTIONInterest in the application of microencapsulation echnology na wide variety of fieldscontinues o run high. Recent research ctivitiesand commercial applicationspublicly disclosed nclude: detoxicantsfor treatmentof uremia (1); flavorand aromaconstituentsn foods (2);dye precursorsor graphic products (3); slow-release harmaceuticals(4, 5); slow-releaseertilizers (6); and perfumes (7). Undoubtedly,there are many applications hat have not been disclosed, ut have beenand are being studied in laboratoriesall over the world.This paper has been prepared with the objective of providing in-formationon someof the significant lements nd physical nd chemicalfactors f concernn microencapsulationrocessesnd systems.Descrip-tions of selectedprocessesnd discussion f some of the problems andpotentials f this technology re presented.

Battelle Memorial Institute, 505 King Avenue, C'lumbus, Ohio.85

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86 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTSTherearenumerouseasonsor consideringicroencapsulationora given roblem ndsome f these re: to changehephysicalharac-

teristicsf a corematerial forexamplerom iquid o "powder");oprovide ontrolledelease f capsuleontents;o permitmixingandstorage f reactiveor incompatiblematerials; o mask asteor color;andto reducevolatility.MAJOR ELEMENTSOF MICROCAPSULE YSTEMS

CoTeThe corephase,ndconsequentlyhe capsuletself,may epresenta wide ange f possibleonfigurations.ome f these reshownn Fig.

1. Operationshatmaybe requiredn preparation f suitable oresclude: spheroidization,rilling,emulsification,rinding, nd atomiza-tion. Selectionf the preferredechniquef corepreparation aybeof considerablemportances heconfigurationf the esultingapsulemaystronglynfluenceheperformancef thecapsularroductn theend useapplication.A. LIQUIDor GASEOUS ORE

SPHERICALSOLIDALLORESOLID CORE

IRREGULARSOLIDALLARTICLEC. LIQUID SLURRY CORE

LIQUIDHASESUSPENDEDSDLIDS SOLID WALLD. SPHEROIDIZED OLID CORE

SOLIDATRIXDISPERSEDSOLIDS SOLID WALLE. MULTIPLE WALL CAPSULESO FIRSTHELL'ORESECOND SHELL

Figure 1. Capsule onfigurations

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MICROENCAPSULATION TECHNIQUES 87Wall

The selectionof the proper wall material or materials or a givenproductapplication s often determinedby the requirementsof thesystem nder consideration. For example, f the capsularproduct mustresist the leachingaction of an aqueousmedium, the wall materialselected hould be hydrophobicn nature and provide a good waterbarrier. Since the wall deposited ends to follow the contour of thecore (as ndicated n Fig. 1), the final form of the capsular roduct salTected y the core configuration. Dependingupon the encapsulationprocessmployed, t may be more or lessdifficult to coat uniformly coreparticleswhose urfaces ossessharppeaksand depressions uch ike theproblems ncounteredn conventionalpainting or plating.

MicroencapsulationProcessSelectionThe selection f the preferredmicroencapsulationrocessor a givenapplication s not alwaysa simple task for there are a large number ofprocessesrom which to choose. One must be concerned with such[actorsas: whether the core is solid or liquid; the solubility charac-teristicsof the core; the reactivity of the core with candidatewall ma-terials and solvents; he sizeof the desiredcapsule; he method of attach-ing the capsule o the desiredsubstrate; he method of core release;andprocess nd producteconomics.A detailed discussion f the above actors s beyond he scopeof thispaper. Some of the more important aspects re discussedn a latersectionn whichmicroencapsulationrocessesre described.

CapsulePost-TreatmentIn many instanceshe capsulesmade by a given processequire ad-ditional treatment to impact the desired properties. Post-treatmentmay involve chemicaland/or physicalmethods. Hardening of gelatin

capsulewalls by treatment with formaldehyde s employed in capsulesused for carbonless arbon paper. Polymer wall films deposited romorganicsolventsolutionsmay be hardenedby treatment with a selectednonsolvent or the wall material. Heat-fusible wall materials depositedon core particlesmay be improved in barrier propertiesby a suitableheat treatment. Thin coatingsof liquids and finely divided solids maybe applied to the capsulewall surface o reduce the tendencyof capsulesto adhere to each other and to improve barrier properties in selectedenvironments.

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88 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTSCapste-Substratenteraction

Although there are instanceswhere capsules, s produced,are useddirectly in a product, n numerouscaseshe capsulesmust be fastenedto a substrate r suspendedn a nedium for proper functioning n theend use. For example, encapsulated erfume is attached to papertissuesso that pressure elease may be instigated when the tissue scrumpled n use. Food flavorcapsulesmay be suspendedn a matrix ofjelly in a tart and must remain stableuntil release s effectedby heatingin the toaster or oven.Here two problensare encountered: the need for a method ofapplying capsuleso substrateand the need to avoid adverseeffectsof

substrate n capsule tability in storage. The method selected or apply-ing the capsuleso the substratemust avoid the use of solvents hat tendto leach core naterial through the capsulewall during the applicationperiod. In addition, the presence f the binder employed o fastencap-sule to substrateshould not significantly nterfere with subsequentcap-sularrelease. Productswhich require suspensionf capsulesn a natrixmust be designedso that the capsulecontentsand wall remain intactduring the time the product s storedprior to consumption. If the cap-sule is surrounded by an aqueous medium (for example, in a foodproduct) the wall material (which nay be a fatty material) must limitthe rate of leachingof core so that sufficientactive core material remainsat the time release is desired.

StorageConditionsunder which capsules nd productscontainingcapsulesare stored vary widely. Factors of concern include temperature, hu-midity, pressure, ight, or other forms of radiation and air pollutants.Capsules ontaining volatile materials or certain reactive chemicalsmust

be protected from excess emperature to avoid premature evaporationor decomposition f the core contents. If the core is hygroscopic,ap-stilesmay absorbwater from a high humidity atmosphere o the pointof wall rupture, in some cases. Conversely,capsulescontaining somewater in the core may lose water by evaporation in a low humidityenvironment, thereby reducing the reactivity of the capsularsystem.Excessivepresstireon capsules n storage,such as certain slow releasefertilizers, may causeblocking or welding together of the capsules othat the product s no longer ree-flowing. Stackingof capsule-containing

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MICROENCAPSULATION TECHNIQUES 8O

products aycause rematureuptureof capsulesn the bottom ayersot: the stack.Release and Reaction

Capsular ore eleasemaybe instigated y suchmethods s: pressureand shear o rupture he wall, heatto melt wall material,dissolution t:the wall by a so]vent, nd extractionof the core contentsby leachingthrough hewall. The mechanismelecteds governed y the end useap-plicationot: he product.Releaseof core contentss usually ollowedby somechemical eac-tion with a materialadjacent o the capsule, r a physical ffectsuchasevaporation r wetting. The elficiency f release nd mixing with aco-reactants important o minimize he quantityof capsulesequired,hencecost. If speedof reaction s important,releaseshould nvolveintimate contact with a co-reactant and avoid losses of core material tosubstrateor surroundings.

Product PerJormancePerhaps he most mportant criterion for judging the over-allper-formanceof a capsular roduct elates o economics.As usual,one mustcome o gripswith the question: "Is the consumerwilling to pay for

the extra costof microencapsulation?"Here one must take into con-siderationnot only the productnoveltyaspects f the problem, but alsosuchmarketing actorsasconsumer ducation,distribution patterns,andprice consciousness. nfortunately, there are no pat answers o thisproblemespecially ince heremay not be a similar established roductto serveasa point of reference. It is evident that sucha situationcallsfor carefulproductdevelopment nd market studies.MICROENCAPSULATION PROCESSES

There are a large number of microencapsulation rocessesnd modi-ficationsof processeshat have been disclosedn the literature andpatents. Processesf potential interest in the cosmeticsield wereselectedor discussionn this paper.AqueousPhaseSeparation

In aqueous hase eparation rocessespolymericor macromolecularwall material is dissolved, r dispersed s a sol, in water. The core ma-terial to be encapsulated, hich must be immiscible with water, is dis-persed n particulate orm throughout he aqueousphaseby stirring.

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JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTSWall formation occurs when the dissolved wall material is caused to"phaseout" and "wrap" around the core particlesby a suitable systemchange. Possiblesystemchanges nclude: reduction in temperature,addition of chemicalprecipitatingagent,or pH alteration.A highly successfuldaptationof aqueousphaseseparation s calledaqueous hase oacervation, hich hasbeenapplied to the encapsulationof such materials as carbonless arbon paper reactants, lavor oils, andperfumes (3). In this process he macromolecularwall material (i.e.,gelatin) is phasedout of aqueoussolution as a concentrated iquid phase(coacervate) which forms a uniform liquid coating around the coreparticle. On further processing hardened solid (gelatin) wall isformed around the core material. The method is outlined in Fig. 2.

Makenmulsionf llnd a gellable colloidaqueousolCoacervatey!ditionf1n aqueous salt solution(Steps above are performed at atemperature above meltingpoint of the colloid sol )

Gelheolloidyouringoacervate mixture in coolsalt solutionWash wth water and filterto remove the salt

Harden fdter cake withsoluhon of formaldehydein water

Washwithwater nd ilterto remove residualformaldehyde

Adjustateroncentrationo desired amountFigure 2. Aqueousphase separation

Aqueousphaseseparation rocessesave been applied to both liquidand solid cores. Capsulesizesmay vary from a few microns to severalmillimeters. The capsulewall may be treated o presenta goodbarrierto oily or hydrophobicmaterials,but it is usuallya poor barrier to wateror hydrophilicmaterials.

NonaqueousPhaseSeparationNonaqueousphaseseparation s the inverse of the aqueousphaseprocessn that the continuouswall-containing hase s organicor hy-drophobic in nature, and the core material is usually water-miscible(hydrophilic). In the process hown n Fig. 3, the core liquid (calledpolar solventsolution) s suspendedn droplet form by stirring in poly-mer solution (wall material). Phasingout and core wrapping of the

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MICROENCAPSULATION TECHNIQUES 01

I Solventorpolymer -,

DispersingrJ separationJ

meJ

} Disperseolarolution1Polarolventolution as aHmdalroplets-- rpolymer soluhanPrecipitateolymerround1 Liquidsmbleithspersedpolar solution o polymersoluhon butform suspension f mcrocopsules non-solvent or polymer_

1 raduallyardenicrocapsulesy uccessiveashingsn iquid [ Non-solventor olymerixtures decreasing in amountsof solvent for polymerJSeparate,crocapsules

JndlfferentoatingDisperseicrocapsulesedium in coating medium?Dry nderJ reducedJPRODUCT

I Depositnsubstrate

PRODUCT

Figure 3. Nonaqueous haseseparation

wall material is causedby the addition of a liquid (nonsolvent) that ismiscible with the organic solvent but immiscible with both the coreparticlend hepolymericallmaterial. he processaybemodifiedto include a coacervation tep and suitable measures or hardening thecapsulewalls (8).Both liquid and solid core particles may be encapsulatedby non-aqueous hase echniques. Capsulesizesmay be varied over a wide rangefrom a few microns o millimeters,and a variety of wall materialsmay beemployed. This process as been applied to suchdiversecore materialsas reactive chemicals,glycerine,urea, and pigments.Interfacial PolymerizationThe formation of a polymer at the interface between two liquidphasess known as interfacial polymerization. This film-forming tech-nique hasbeenused o makecapsules ith either hydrophilicor hydro-phobiccores. Capsules ith polyamide (nylon) wallscan be made by aprocessn whichan aqueous ore iquid containing n aliphaticdiamine(i.e., hexamethylenediamine)s dispersedn droplet orm in an organicsolvent i.e., chloroform-cyclohexane,:4). When a solutionof a dicar-boxylicacidhalide(i.e., sebacoylhloride n the abovemixed solvent) s

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2 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

addedwith stirring, the nylon walls of the capsules re formed. The re-action can take placeat room temperatureand dependson the fact thatacid halidesof this kind are nearly insoluble n water, while the properdiamines have an appreciablepartition coefficient owards the organicphase. The polymer s formed n the organicphase, nd since he rate o[polymer ormationexceedshe rate of diffusionof the diamineout of theaqueous hase, he nylon wall is deposited lmostentirely at the interface(9). Productapplications ave ncludedcore materialssuchas dye pre-cursors, ils,proteins,and enzymes.

Multiorifice Rotating CylinderA multiorifice encapsulation eviceutilizescentrifugal force to formcapsulesrom fluid wall formulations. The wall formulation is hardenedby appropriatemeans fter the capsulesre formed.

Core material, Wallaterial

Figure 4. Multiorifice rotating cylinder device

Orificesaroundperiphery

ohardeningbath

The apparatusconsists f a rotating cylinder having orifices ocatedabout its periphery. As shown n Fig. 4, the wall material is fed to twointernal grooves rom which it flows by centrifugal force to the indi-vidual encapsulatingorificeswhere membranesare formed. The corematerial is fed onto a concentrically otating disc and is projectedontothe membranes. When the combined mass of core and wall materialis such that centrifugal force overcomes he cohesive orce of the wallmaterial, ndividual capsules reak oose nd are projectedoutward. Themembranes e-form, and the next capsules re formed. Capsulesize sinversely proportional to rotational speed. Good size uniformity isclaimed, sincethe capsules o not break loose rom the orificesuntil agiven masss reached (10).

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MICROENCAPSULATION TECHNIQUES 93

The wallsot he tormed apsules ay be hardenedby variousmeansincluding hemicaleaction, vaporationf a solvent, nd cooling. Theprocess ouldappear o be suitable or makinga varietyof productsn-volvingprimarily iquid cores. It may have imitationswhen capsulesbelow about 100 t are required. It is expected hat scale-upof theprocess ight havesomemechanicalimitations. However,high pro-duction atesare claimed or someproducts. Applications nclude cap-sules ontainingwater,solvents,wax solutions, nd pesticides.

Fluidized-Bed Spray-CoatingMicroencapsulationt:core particles hat can be fluidizedby a gas

may be accomplishedy spraying coatingagent (wall) onto the sur-faceot: he particles. The wall may be formedby congealing t:a mol-ten material,by chemical eactionon the surface, r by evaporation ta solvent rom a coatingsolution. The solvent s removedwith the gasleaving the bed. Coating thicknessmay be easily controlled by theamount otwall material applied. A conventional luidized-bedspray-coatingunit is shownon the left in Fig. 5 (11).COATING SOLUTION

DENSE-PHASEFLUID BED

VERTED CONE

J' FLUIDIZINGIRCONVENTIONAI- MODI FI ED

Figure 5. Fluidized-bedspray-coating nits

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JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

Conventional luidized-bedspray-coatingmethodsare generally em-ployed n the encapsulation t5 olid particles,and a minimum capsulesize ot5about 100 g is the usual rule. Liquids may be encapsulated fthey can be frozen n particulate orm and coatedat temperatures elowtheir freezingpoint (12). Fluidized-bedencapsulation asyielded suchproductsas: slow release ertilizer, coated iron particles,seeds,salts,and clays.

Deagglomerating-JetSpray-CoatingNumerous modifications of the conventional fluidized-bed micro-

encapsulation oncepthave been developed o satisfy he needsof par-ticular problems. A deagglomeratinget unit wascreated o coat coreparticlesot5 mallsize (less han about 100 g) which tend to agglomeratein a conventional luidized bed. Here the key feature is the use ot5ahigh velocitygas et and a conicalconduit in a fluidized bed to deagglom-erate the partially coatedparticlesbefore additionalcoatingmaterial isapplied from the coating spray nozzle. This method is shown on theright in Fig. 5 and may be employed o encapsulate olid particlesdownin the 10-gsize ange. It doesnot lend itself to liquid coresnor to solidcore particles arger than about 300 g (5). Products nclude pharma-ceuticals,esincatalysts,norganicsalts,and pigmentedplastics.

Melt Prilling in a FluidizedBedThis processs illustrated in Fig. 6. Here the wall material mustbe in solid particle form so that it can be fluidizedby a gas. The corematerial is heatedand is in liquid form for atomization rom a nozzle oyield dropletsot5 he desiredsize. The dropletsof core material fallinto the fluidized bed and are simultaneously ooledand coatedwith thewall material particles. The heat liberated from the core droplets istransferred o the wall material particlescausing hem to melt, adhereto the core surface,and flow together to form a coherentcapsulewailstructure. A mixture ot5 apsules nd bed material is removed from thefluidizing column and the capsules re separatedby screening. The ex-cess ed material is returned to the system. The process as been madecontinuousby providing for continuouscapsule emoval and bed ma-terial make-up (13).Capsulesizes ossible y this processange from about 300 to 3000 .Both liquid and solid core capsules an be made; however, he core ma-terial must be able to withstand he temperature equired to provide the

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MICROENCAPSULATION TECHNIQUES 95-Heaterii..rixtebil:.'i':.'-Fluidizedoating:.:// materiali:il Distributorplate

-- Plenum--AirnletFigure 6. Melt prilling in fluidizedbed

energy or fusingthe wall material particles ogether. Applicationsofthis process ave yielded slow-releaseertilizers,glycerinecapsules, ndbiologically ctiveencapsulatedroducts.Miscellaneous Processes

There are a number of additional microencapsulation rocesseshatmight be included n this paperbut, in the interestof brevity, can onlybe mentioned here."Spraydrying" encapsulations an old processhat hasreceivednew

interest in recent years (14). It involves the atomization and spraydrying ot:an emulsion n which the core is the discontinuous haseandthe wall material is a constituent f the continuousiquid phase.In a process nown as "meltable-dispersion,"he wall material in amolten stateand the corematerial are dispersedn a medium (in whichboth are insoluble) at a temperaturehigh enough to maintain the wallmaterial in liquid form. By means of agitation and use of wettingagents,he wall material s causedo envelop he coreparticles, nd solidi-fieson-cooling o completecapsule ormation (15).

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96 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTSIn the "diffusional xchange" rocesses,previously ormedcapsulewith a porous oating s mmersedn a preferred iquid so hat the origi-

nal core contents re diffusedout of the capsule nd the liquid diffusedin. The resultingencapsulatediquid is then overcoated r subjectedto a treatment hat imparts he desireddegreeof wall impermeability(16).Another aqueousphaseseparationprocess mploysa processluidsuch as mineral oil. An emulsion of a flavor oil, for example, in anaqueous elatinsolution s dispersedn the processluid and the mixtureis cooled o phaseout the gelatin. The capsulesmay be hardenedbydehydrationof the water with anhydrous lcohol (17).PROBLEMS

As in many areasof science nd technology, racticalor appliedde-velopments ave outrun an understanding f the fundamental actorsofmicroencapsulation. This situation has probably been accentuated ythe proprietaryaspects f many of the applications f interest. It is notsurprising, herefore, that the literature in this field is primarily con-cerned with methodologyand productsrather than with underlyingprinciples. It is a truism in the field of microencapsulationhat ex-perience s the best teacher,and that even the most proficient practi-tioner learns somethingalmost every time he goes nto the laboratory.Perhapsone of the mostdifficult technicalproblems s to control thepropertiesof the capsulewall. Here one tries to extrapolate he avail-able knowledgeon formation and propertiesof polymer films and or-ganic and inorganic coatings o the encapsulationprocessof interest.The resultsof suchattemptsoften leave much to be desired,since hereis usuallyonly a slightresemblance etween he conventionalilm form-ing operations nd those n microencapsulation. In general,someof thefactors that should be considered include: formulation of wall material,solvents nd nonsolvents mployed, emperature,and rate of deposition.A problem that is common o many microencapsulation rocessessthe agglomeration f capsules uring wall formation. As the wall ma-terials change rom liquid to solid form they often go through a stickystagewhich makesagglomerationdifficult to avoid. The problem be-comesmore pronouncedas particle size is reduced. Various methodswhich may be employed o minimize this difficulty nclude the use ofchemicalhardening agents,careful selectionof wall materials and of sol-vents,addition of parting agents,and application of mechanicaldevicesto physically eparate apsules.

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MICROENCAPSULATION TECHNIQUES 97

The evaluation o[ capsules nd capsularproducts s sometimesasmuch o[ a problemas is the making ota product. In the early stages,one usuallyemploys elativelysimpleand rapid screeningmethodswhichhope[ully relate to the eventual real world situation. It satis[actoryprogresss made, the evaluatorymethods end to becomemore complexuntil, finally, actual use conditionsmust be employed. This phaseottestingmay be quite time consumingand costly. Thus, the design otthe evaluationprocedures an be critical as regards he over-allprogresso[ a given program.

SUMMARYThe potential applicationsot microencapsulationall into widelydifferent areassuchas the biomedical,agricultural, [ood, and pharmaceu-tical fields. SuccessJulroduct development equirescareJulattentionto many actors oth technical nd economic. There are a wide varietyotmicroencapsulationrocessesvailable [or use in specificproblems,and no singleprocess an be applicableto all typesotsituations. Mostprocessesre subject o certaincommonproblemssuchas agglomeration

o[ capsules uring wall deposition.At times t is difficult o seewhat the future holds or microencap-sulation. Certainly, there is a need [or additional basicand appliedknowledgeon the phenomena nvolved and, if this knowledge s [orth-coming,one might expectan upsurge n practical applications. Un-doubtedly,novel microencapsulation rocessesill be developed,whichmay also increase he scopeo[ commercialproducts. In addition, ascompetences increasedn existingprocesses,ostsshould be reducedand the competitivepositiono[ encapsulated roducts mproved. Al-ready, he technique asyieldedsome ather unique solutionso complexproblems. Perhaps concise ssessmentt he picture s one otcautiousoptimism,hat s, progress,ut not withouthard work.

(ReceivedMay 21, 1969)REFERENCES

(1) Chang,T. M. S., "Semipermeablequeousmicrocapsules,rans. Am. Soc.ArtificialInternal Organs,12, 13-9 (1966).(2) Microencapsulationps flavor of onion powder,Food Processing-Marketing,6-7(Sept.,1967).(3) Green,B. K., U.S. PatentReissue4,899 November 9, 1960).(4) Wurster,D. E., U.S. Patent2,648,609August 1,1953).(5) Grass, . M., andRobinson, . J., u.s. Patent3,237,596March1, 1966).

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98 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS(6) Rindt, D. W., Blouin, G. M., and Getsinger,J. G., Sulfur coating on nitrogen fer-

tilizer to reducedissolution ate, J. Agr. Food Chem., 16, 773-8 (1968).(7) Soloway,S., U.S. Patent 3,137,131 June 16, 1964).(8) Reyes,Z., U.S. Patent 3,173,878 March 16, 1965).(9) Chang, T. M. S., Macintosh,F. C., and Mason,S. G., Semipermeable queousmicro-capsules, Can. J. Physiol. Pharmacol, 44, 115-28 (1966).(10) Massoth,F. E., Hensel, W. E., Jr., and Harlowe, W. W., Jr., Basic studiesof theencapsulationrocess,nd. Eng. Chem.,Process esignDevelop., , 6-13 (1965).(11) Flinn, J. E., and Nack, H., Advances n microencapsulationechniques,BattelleTech. Rev., 16, 2-8 (Feb., 1967).(12) Sachsel,G. F., and Nack, H., U.S. Patent 3,202,533 August24, 1965).(13) Nack, H., U.S. Patent 3,036,338 May 29, 1962).(14) Evans,R. B., and Herbst,W., U.S. Patent 3,159,589December , 1964).(15) Herbig, J. A., and Hanny, J. F., U.S. Patent 3,161,602December15, 1964).(16) Flinn, J. E., and Nack, H., What is happening n microencapsulation,hem.Eng., 74,171-8 (Dec.4, 1967).(17) Balassa,L. L., and Brody, J., Microencapsulationhe Balchem way, Food Eng., 40,88-91 (Nov., 1968).