The Latex DoctorQ What is the effect of particle size of corn-

* pounding ingredients sulphur, acceleratorsand znO on the curing tharatteristics andvulcanisate properties of NR latex product? Canthe dosage of chemicals be reduced by the useof smaller particle size chemicals say, less than‘1 micron since the available surface area Ismore?

when I took a trial using perl-milled chemicalparticle size ci micron, instead of ball-milledchemical particle size 6-9 micron, the resultswere encouraging. Even with a 10% lesser dosage of slurry. I got better ageing properties forrubberized coir mattress.

PradeepKuinar P. Jo Kurlon Ltd.

y ourobservationsaresimilarto whatI haveexperienced.However, I’ve also en

counteredsomeproblemsyou shouldconsider.

* Ball-milled or attrition mill.prepareddispersionsof latex chemicalsshouldbe 2-5 microns. I would expectproblemswith 6-9 microndispersions.

* Althoughgood quality latex films canbeobtainedfrom compoundshaving as little as5%of the normalPHDRofasmaliparticlesizechemical,theresultsare frequentlynotuniformfrom batchto batch.

* I’m notsureof thereasonsfor this. It maybe thatsmall quantitiesrequiremore or bettermixingto ensureuniform distributionthroughoutthecompoundof critical ingredientswhicharein very small quantities.’

* Maturing can be much slower and mayrequirelongerelevatedtemperatures.

Particle size ofcompoundingchemicals

Harry F Bader.Vice-President, LatexServices, Akron RubberDevelopment Laboratory.Akron, USA, and a worldauthority on latex,answers questionsand doubts of readers onlatex and latex products.Send your questions to:The Latex DoctorRubber Asia, DhanamHouse, cochin 682 020,Kerala, IndiaFax :91-484-2317872E-mail: dhanrubberethnetJULV-AGST 2006

* Vulcanisationis different. Experimentation is requiredto determinethe optimumconditionsof timeandtemperature.

* Also, experimentationis neededtoestablishthesurfacearearatio which producestheoptimum results.

* Are your ageingresultspossiblydue to anoriginal undercurecondition? How do unagedpropertiescompare?

I believethereis needfor more experimental work to ensureuniform materialpreparation and to ensureuniform compoundingandprocesscontrol.

Latex quality andfinished productswe are finding differences in our finished product properties when the latex we are usingcomes from different sources. How and whydoes this happen?

SM.Pandeandothers,IColkata

Q ur.chemicaltesting/analysisexpertsthinkthat thoughthey cart find differencesin

latexcomingfrom varyingsources,muchfurther testing plus experimentalcompoundingand dipping would be neededto matchthosedifferenceswith varying results in finishedproducts.I agreewith that opinion.

Also, you shouldbe performingASTM L1076 testingon incomingshipmentsto ensurethe latex meetsthe D 1076 requirementspossiblyand moreimportantlymatchthe suppliers’ datasheetindicatingtheir D 1076resulj

Many yearsago I experiencedproblelsimilar to what you arehaving when we We

makingmedical-typegloveson automaticeQUi*menthavingfixed timesandtemperaturesf

leaching, drying andcuring.

Weeventuallyfound thatwehadto alterPcompoundingandlatexmaturingprocessesensurethat the latex goingon the line wassameprecurelevel, percentagesolids,visc

w and temperature,regardlessof the cOI1ll

of origin of the latexor the time of theyeallatexwas tapped.

Whenall conditionswere the same,dippedproductsshowedthe samepr

hb02

I suggestyouevaluatethe compoundwhenit isreadyto go on line. Any differenceswill likelyresultin differentoutcomeof the final physicalproperties.

Problems in blending twonitrile latex gradesWe have made products by blending twogrades of nitrile latex because we get goodfilm properties and the modulus is all right.We have a few problems and we want toeliminate them,

1. Tear properties are poor.

2. The dipped product was taken from the trialbatch. For the first three days, the product wasfine in stripping and the film was perfect. Afterthree days, the films developed cracks on stresspoints of moulds. How can we make latex morestable and avoid precuring?

3. Also, can tensile strength be improved?

Manoj GoswainyNewDethi

M y experiencewith nitrile latex is mainlywith Dow Reichhold.I’ve successfully

used their Types68074 and 68075. If you arenot using Dow Reichhold,ask yoi.ir supplieraboutequivalentsto thosetypes-

2. Your experienceindicatesan overcureproblem as you havesaid, Have you done aprecurecheckusing N butyl alcohol insteadof chloroformwhich is usedfor naturallatex?This would be amethodfor trackingprecure.If you reducethe heathistory, precureshouldbe slower,

3. If you cancontrol the precure,the tensilestrengthshouldbe improved.

prevulcanised latticesWhat are prevulcanised lattices used for andwhy?

Anonymous- InternationalLatexConference

M ostlatex dippedproductsand foamproductsaremadefrom latexwhich hasbeen

maturedto some level of prevulcanisation.Precureis prevulcanisation.

It is difficult to hold a compoundedlatex to a ‘1’ level of precure.Therefore,manufacturersset their processfor a higherlevelof precure including total’ pre-vulcanisation.

This is to maintainuniform good quality oftheproduct. I am not awareof latex productswhich cannotbe made at some level of prevulcanisation.

Residual acceleratorsin medical glovesWhat are the typical levels of residual accelerators in medical gloves?

Anonymous- InternationalLatexConference

L evelsareimproving. Wenow find that mostglovessubmittedfor testingshow ‘below

detection’limits. This limit varieson theacceleratorsystemwhich is used,However, below1.0 ppm is usual.

Leaching of dipped goodsIn dipped products, how do you know if you areleaching, the product well enough or longenough?

KenRozarlo,Manila

T hefinal answeris the testingfor residualacceleratorcontentand for residualpro

teinsor Nil latex allergens.

However, if you operateyour leachsystemat,say,65°C; havea high degreeof water turbulence;maintaina reasonablewaterthroughputto avoid turbidity andcontinuethe leaching for a reasonabletime for the product,youare likely to besuccessful.

consult before making a claimcan a latex compound be considered foodgrade if the raw materials are listed in theCode of Federal Regulations. Title 21 Food andDrugs?

Anonymous- InternationalLatexConference

yes.However,therearemanyconditionswithin CFR21 which mustbemet, Theseinclude

theamountof the listedcontents;theconditionsof use; and the passingof testsfor extractionlevel.

I would suggestthatbeforemaking a claimregardinga productsuitability for food contactuse,anexperiencedsourceof testingandfamiliarity with themany sectionsof CFR21 beconsulted. *

JULY-AUGUSt 2006 103hr