HarryF. Bader

Can zinc oxide activereplace ‘white seal’ gradein glove compounding?We regularly go through youreducative articles in RubberAsia. Pleaselet us know if zincoxide-active with specificationenclosed is likely to give any results in latex-natural compounding for gloves, latex thread andother products where Frenchprocesszinc oxide white seal isused. It is said that smaller dosagesof zinc oxide-activein placeof the normally used white sealvariety give better strength,physical appearanceand colourreflection. In view of its zincoxide-active higher surface areaand very, very low other metalcontents, how much reduceddosagecould he given, becausezinc oxide-activeis costlier thanthe white seal grade? Your detailed guidelines will be appreciated.Keralian Rubber Corporation

T here are several factors to beconsidered before deciding

whetherzinc oxide-activeZnOAT is a reasonablereplacementfor white-sealZnO.a Zinc oxideactive is 69-74%

ZnO while white-sealZnO is99.85%.

b Dispersionsshouldbegroundso thattheparticlesizeis 2 microns or less.

c Sulphuris themostdifficult togrind of the latex additives.ZuC is easy.

Considering thesefactors, I’mdoubtful of the claimed advantages.

1. Claim: Specific gravity and

apparentdensity of ZnO-ATare lower. Fact: After grinding, this changes.

2. Claim: The surface area iswider. Fact: Not after grinding.

3. Claim: It contains very fewharmful impurities. Fact: Impurity levels in the white-sealgradearesatisfactory.

4. Claim: As ZnO-AT is a finerparticle,it is superiorin its dispersion. Fact: Dispersinggrinding thewhite sealgradeis no problem.

5. Claim: Shorteningof vulcanization time. Fact: flow so?Acceleratorsandsulphur vulcanization limes are notchanged.

6. Claim: Generally, the consumptionof zincoxideactive‘ZnO-AT’ is about60 to 80%of generally usedWS in rubber dependingon the compound. So ZnO-AT can savevulcanizationcost.Fact: Thismustbeestablishedby experimentation.

7. Claim: The higher surfaceareaimparts highertensilemodulesand higher curing density.Fact: Too high a surfaceareaneeds more compoundingtime. After grinding, surfaceareadifferencesarenot an issue.

S Claim: The finer particlesincreasethemechanicalproperties like tensile strength, tearstrength, modulus and elasticbehaviourevenat lower doses

The latex doctor

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Harry F. Bader,Vice-President,LatexServices,AkronRubberDevelopmentLaboratory, ALTO!:,USA, anda worldauthorityon lotat,answersquestionsanddoubtsofreaderson latexand latexproducts.

Send your questions to:

‘The Latex DoctorRubber Asia,Dhanam House,Cochin - 682 020.Kerala, IndiaFax: 94-484-317872

RubberAsia S anuar February 2003 73

comparedwith normal WS ofcoarserparticlesize. Fact: After grinding,particlesizeis notanissue.

9. Claim: ZnO-AT, being verylow in lead content,causesnodiscolouration; otherwise, ittakesplacedue to the formation of blackleadsulphidebecauseof presenceof sulphurinvulcanizatesandhencecanbeusedin light colouri white colour articles of rubber. Fact:I’ve not seenthis asaproblem.What is theprice differential,in anycase?

In all cases,when a material issuggestedas areplacementfor onewhich you havebeenusing for along time, it is extremely important to proceedwith caution. Trialbatchesshouldbe madeaftersuccessftmllaboratoryexperiments.

...Thecoagulantsolution on our

glove line very quickly becomescontaminated with dirt particles, likely from the conveyorchain which holds the dippingformers. How can I solve thisproblemwithout frequently removing the tank for cleaning?

Anonymous

T he first thing to do is morefrequent chain cleaning.

However, therearewaysto removeparticlesfrom thecoagulant.

In all cases, the coagulantshould be agitated in somefashion to keepthe solution from stratifying, andwhena powdermouldrelease is present, to keep itmixed. A circulating pump willprovidethat agitation.

For a clearcoagulant,anin-linefilter works well. The coagulantis always freefrom contaminants.However, for a coagulantcontaining powder, thecirculating pumpreturn line should passthrougha#90 meshcheeseclothbagtiedovertheendof the return pipe.

The cheeseclothwill retain thedirt particles,but shouldallow thepowderto passthrough.

Oneof ourcustomersrequiresa membranewhich should resist to -65°C. In other words itsglass transition temperature

must be -65°C. My compound’s Tg is -S5°C. Is there anatural rubber which has lowerTg values than SMR?

Anonymous

rf herearetwo quicksuggestions for the -65°C Tg.

1. If there are hydrocarbonoilsin theconipound,replacethemwith Ester oils such as DOAdi-octyl-adipate. AshlandChemical is thesupplier.

2. Add Polybutadiene BunaC822, CB23, C824, orCB25. Theseall have a Tg -

109°C. CB25 is supposedtohavethebest "processability"with low temperatureflexibility. Bayer Corpn. is the supplier.

Another possibility is syntheticpolyisoprene.Goodyear Natsyn2200 has a Tg -98°C.

Hopethis helps.If not, askthemto submit acompleterecipefor arecommendation.

Pleaselet meknow thespecifictest to assessthequality of constant-viscosityNR.

SreeLakha

F or latex, ASTM D 1076, andfor dry rubber, ASTM D

1646.

Follow-up query from SreeLakha: What are the qualitycontrol testsfor dippedgoods?

There are no specific requirements for QC testing. For bothGMP and ISO 9001 Certifications, eachmanufacturerdecideswhatcontrolsareneededto ensurethat his product meetsthe finalspecification.

In many cases.QC is merelycheckingprocessparameterson aregular basis to ensureall conditions areasthey should be andtheprocessis in control. This, pluscertification of raw materialsbythesuppliers,resultsin high quality output.

Final product inspection willprovide the verification of theabove andwill also provide thefinal quality assurancedata. *

RubberAsla * 3enuar - February 2003

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