The latex doctorHarry F. Bader

How to make newanti-oxidants work

We have come across ready-made anti-oxidants in dispersionform made by Struktol Co.. Arethese effective as compared withour conventionalanti-oxidantsdispersionas they suggestto use0.75phr. of dispersiononly?

Ashwani MagonParadiseRubberIndustries

Struktol antioxidants perform aswell as those of other manufacturers.However,wheneveryouplanto introducea new antioxidantsyoushoulddo comparativetesting to ensurethat thenewmaterialworks wellwith your compound.

That is true even if the new antioxidant is the samechemicalas youarecurrentlyusing.

Chemicalswhicharesupposedto bechemicallythe same,sometimesdo notperform in an identical fashion.

...

We havejust startedoperationofa manufacturing unit for nitritelatex dipped gloves on cotton lining - plain stockinettefabric sewnor raisedor fleecevariety. Kindlyclarify a few points mentionedbelow:

1. What is the difference inactivity betweensodium laurylsulphonateandsodiumdodecytbenzenesulphonateor stabilizerandwhat is thepH rangewithinwhich thesefunction properly?

2. How does ammonium polyacrylate, PVA and CMC differ in their function asthicknessin carboxylatedNBR latex andwhat is the p11 range withinwhich they function properly?

.3. What is the ideal combination

- low pfl with low level of stabilizer orhigh pH with low levelof stabilizer?

4. How can we avoid drippingwhen no coagulant is used?How is dripping relatedto pH?

5. How can we avoid penetrationto the liner - andwhat aretheexact parametersto be used?

6. What explainsthe crackedsurface of coatedfilm as it comesout of the curing oven?

7. How couldwe maintainandtestthe MST and chemicalstabifityasprocesscontrol parameters?

B. Dutta

T herearemany"nitrile" polymers available.Themajormanufacturers provide technicalinformationin their ProductBulletin, which indicatesthe stabilizerswhich shouldbe usedand the recommendedpH.Reichhold recommendssodiumdodecyl benzenesulphonatefor alltheir nitriles. Theamountvaries.TherecommendedpH variesdependentonwhichnitrile you areusing.Theyalsorecommendthematerialyou shouldusefor pH adjustment.

2. Additions of CMC to a latex compound provide higher viscosities with changesin flow, thicknessof pick-up, etc., you expect from increasedviscosity.Additions of PVA or an acrylicthickenerprovide both increasedviscosity and increasedthixotrophy. Combinations of thetwo types of thickenersareusedto control fabric penetrationandfilm thickness.The pH of nitritecompoundshould be as recommended by the manufacturerintheir ProductBulletin.

Harry F. Bader,Vice-President,LatexServices,AkronRubberDevelopmentLaboratory. Akron.USA, and a worldauthority on latex,answersquestionsanddoubtsof readersonlatex and latexproducts.

Send your questions to:

‘The Latex Doctor’Rubber Asia,Dhanam House,Cochin - 682 020,Kerata, IndiaFax: 94-484-317872

RubberAsia U May - June 2002 75

3. 1 would not vary thepH verymuchfrom what themanufacturerrecommends for the type of nitrileyou areusing.

4. Dripping occurs when the latexpick-up is too great. This can becontrolledin severalways:* Reducetheform removalspeed.

* Reducetheform temperature.* Increasethe latex compound

thixotrophy.

* Increase the latex compoundviscosity.

* Rotatethe formers.

5. Sameansweras for Questionno.4.To provideexactparametersisnot possiblewhen I have no informationaboutyour processconditions or your latex compoundrecipe and its properties. I don’tevenknow which type of nitriteyou areusing.

6. The major reasonfor crackingisthat thefilm is not properly driedbefore it entersthe cure oven. Isuggestyou experimentwith formtemperaturesanddrying timesandtemperaturesto determinewhatconditionsarebest.Also checktheprecureof your latex compound.A high precurewill maketheproblem worse.

7. MST can be determinedby themethodin ASTM 0 1076, Section 16. Equipment is availablefrom;Atlas Electric DevicesCo., 4114N. RavenswoodAvenue. Chicago, IL 60613-1831Tel: 773-327-4520Fax: 773-327-5787

Chemical stability canbe measuredby theZOV methodZinc OxideViscosity. This measuresthe increaseinviscosity ofa latexcompoundduring acontrolledadditionof zincoxide.

Anothermeasureof stability is theprecure testas illustratedin theVanderbiltHandbook,but using N butyl alcoholratherthanchloroform.

I realize theseanswersare somewhat vague. However, I know nothing aboutyour latex compound,thefabric you areusing, theprocessyouhaveor the control of your processconditions. It is, therefore,impossible to recommendwhat you shoulddo to resolveyour problems.

What are the best techniques!methodsfor cleaningglovemoutdsin a factory? In a lab?

Anonymous - submittedat 2001Latex Conferencein Akron, Ohio,

"Best" is dependentuponcosts. Inhigh wagerate countries, automaticcleaningwith low labourinput wouldbe preferred. Labour savingswouldaffectmajor equipmentcosts.

However, in lower wageratecountries, savingsmight not be sufficientto affect major equipmentcosts.Mypersonal preferenceis Ultra-Soniccleaning.This equipmentcanbe installedon-line so that all glovedipping formuers are cleanedafter eachcycle of dipping.

In 1973, Ultra-Sonicequipmentwasinstalledonthe two glove linesof myfactory in OklahomaCity. In 1975,thesameequipmentwasincludedonthenewthird line. Fromthattime untiltheplant closedin 1980, we neverremoved glove formers for cleaning.First-gradequality during that timewasneverlessthan98%.

The sameequipmentwasusedin abatch system for the glove formersusedin themanualbatchproductionof industrial gloves.

During thatperiod, we usedglovefonnersfrom both GeneralPorcelainand RosenthalCeram-tec. We didnot experienceany formerporosity.

The solution in the Ultra-Sonicrankswas5% OakiteRustStripperinwaterat 70°C. For lab use, this solution could beusedwith brushscrubbing.

What Is the difference betweenthe process used to producecondoms and the processused toproducemedicalgloves?

Anonymous - submitted at the2001 Latex Conferencein Akron,Ohio.

Condomsare madeby the "straight" dipping method. Usually, two latexdips areused.Theprocessis asfollows;

* Condom dipping forms arecleanedandrinsed.

* Forms areair-dried andwarmedto a fixed temperature.

* Forms are dipped into the firstlatex tank.

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* Latexviscosity, total solids, precure level, etc. are controlled togive a requiredfirst-dip thickness.

* Fonns are removed,rotatedandspun to evenly distribute the tipdroplet,air-driedand warmedtoa fixed temperatureandmoisturecontent.

* Formsaredipped into thesecondlatextank. This maybe thesameas the first tank or the latex maybe somewhatdifferent. In eithercase,propertiesarecontrolled.

* Dropletcontrol is repeatedas thelatex is dried.

* A strippingaid is appliedanddrying andcuring is completed.

* Condoms are usually automatically stripped for further processing,inspectionandpacking.

* Medical gloves are sometimesmadeby thesame"straight" dipping processwith the latex properties being altered to produceathicker film. However, theusualprocessis "coagulant" dipping.The most popular coagulantdipping processis as follows:

* Glove dipping forms arecleanedandrinsed.

* Forms are air dried andwarmedto afixed temperature.

* Forms aredippedinto a coagulanttank.Thecoagulantrecipecanvaryconsiderably.The vehicle can bewater, ethanolor acetoneor a mixture of these. Water is themostpopular.To thevehicle, acoagulantsaltof a strongacid anda weakbaseusually Ca2NO3 is addedplus wetting agents.Therecipeiscontrolledas is the temperature.

* The coagulant film is air-drieduntil it is moist, but not wet, androtationandspin to distributefinger tip dropletsoccur.

* Forms aredippedinto a latextank.The latex is controlled as withcondoms.Thetime in the latexdwell time is alsocontrolled.

* The controlled properties of thelatex, the controlled coagulantrecipe, thedwell time andthe temperatureof the latex, the coagulant andthe forms determinethefilm thickness.

* Forms areremovedslowly fromthe latex, rotated and spun fordroplet control.

* Forms with the gelled latex film

areair-drieduntil thegel is strongenoughfor leaching.

* Gelledfilm is leached.

Leached film is dried, cured,releachedandcoatedwith a stripping aid, not necessarilyin thatorder.

* Gloves are usually manuallystripped for further processing,inspectionandpacking.

Cannaturallatex be blendedwithsynthetic latex? If so, what combinationswould be successful?

Anonymous - submittedat 2001Latex Conferencein Akron.

I havepersonalexperiencewithblendingnatural and synthetic latex that goesback 50 years. So theansweris yes.

As to what combinationswould besuccessfuldependson whatyou wishto achieve.Someof theblendswhichI considera successare;

* SBR/naturalfor foam pillows andmattresses- reducescost.

* Chloroprene/naturalfor householdandindustrial gloves- improvedoilresistance.

* Nitrile/natural for instanceswhereimprovedtearpropagationis wanted.

* Chloroprene/naturalfor instanceswhere reduced air permeation iswanted.

* Nitrile/natural for instanceswhereimprovedsolventresistarceis wanted.

Thepossibilitiesarevirtually endless.If you achievethepropertiesyou want,thecombinationis a success.

CLARIFICATION

The query in this columnMarch-April 2002 on"making a better glove" wasinadvertently attributed toMr. Andrew Tan, who isExecutive Director ofMARGMA, the prestigiousassociationof glove-makersofMalaysia. It was actually aquestion from one JosephineEscobar. Margma merelyforwarded it to RubberAsiafor Mr. Bader’s reply.

Editor

RubberAsia * May - June 2002 77