Harry F. Bader

Avoid over-curingto boost tear resistancein latex films

How canyou improvethetearresistanceof latex ruins?

Anonymous - InternationalLatex Conference,Akron

A generalanswer is to avoidover-curingof the film.

Both tensileandtearstrengthwilldeterioratewhen your producthas been over-cured.

An additive which wilt greatlyimproveresistanceto tearpropagation Trouser Tear is Tylac68060, a nitrile latex producedby Dow Reictthold.An 8-12 panadditionis generallysufficienttoincreaseTrouserTearproperties.

A wordof caution.Flexresistancewill decreasewith this addition.

ReducingviscosityWe are a rubberised coir

manufacturingcompany.Wewant to reduceviscosity in ourcompoundinglatexCL. Totalsolid contentsin CL is about54% wIthout changingTS,filler, chemicalssince we aresprayinglatexoncoconutfibre.If viscosity is l, penetrationof Spray will increaseour production. So kindly suggestasuitableIngredientor method.

11. RavindraNath ReddyHosurCoir Foam, India

I f solids contentis critical, theadditionof inorganice.g. so

dium hydroxideor sodium silicateand organicalkalinematerials ethylenediamine, urea,monoethylamine,diethanolamine or morpholinewill reduceviscositymoderately. The mosteffectivematerialis ethylenedi-

amine. Oneto threepartsaresuggestedandare usuallyaddedas a25% solution in water. Urea 1to 3 phr. may be addedas drycrystals or as a concentrated50% solution. Sodium silicate0.25 phr is particularly effective if high amountsof zincoxideare present.

As always, try this on a laboratory basisto ensurethe viscositydepressantdoesnot causeunforeseenstability problems.

Fillers to reducecostWe producedippedproducts,

mainly bladders.Pleaselet usknow if we canincorporateanyruler to reducecost e.g. whatratio is suitable without muchaffecting the original properties?as thetensilestrengthTSand elongation propertiesarevery critical in our product. TSup to 250 kg/cin.sq. and elongation up to 850 are required.

AshwaniMagonParadiseRubberIndustries

A soft clay suchas McNameeclay, supplied by RT

Vanderbilt, is commonlyusedforthepurposeyou haveoutlined, itwill reducecostand it will reducetensile strengthandelongation.

How much reductionof physical ptopertiesshould be establishedin your laboratory?I suggcst an addition of 10-20PHDRas a 50% slurry as a start forchecking changesin physicalproperties.

Lower JatexproteinJhnitWhat is the estimatedlower

limit for reducinglatex protein

The latex doctor

Harry F. Bader,Vice-President,LatexServices,AkronRubberDevelopmentLaboratoiy, Akron,USA, anda worldauthority on latex.answersquestionsanddoubtsofreaderson latexand latexproducts.

Send your questions to:

‘The Latex Doctor’Rubber Asia,Dhanam House.Cochin - 682 020,Kerala, IndiaFax: 91-484-2317872E-mail: danani@satyam.net.indhanwbber@eth.net

RubberAsia November-December2005 103

4-

relatedissuesthroughcombinationsof powderfreeandreduction technologies?

A.S.G - International LatexConference

"Dowder-free" technology1. doesnot reducelatexpro

tein. The absenceof powderpreventstheprotein in the latex filmfrom being ‘picked up" by thepowder and thus spreadingthroughout the area where thegloves arebeingused.

The lower limit which shouldbe consideredacceptableis "below the lower detectiOnlimit" ofthetestmethodsof ASTM D 5712or ASTM D 6499.

Residualaccelerators‘What arethe typical levelsof

residualacceleratorsin medicalgloves?

Anonymous - InternationalLatex Conference

Unfortunately, thereis no generafly acceptedtest methodto

determinethe level of residualacceleratorswhich canbeextractedfrom a naturalor syntheticlatexglove by humanperspiration.

One method being used is extraction with DI. water or PBSwith anHPLC analysisof theextract. Zero identifiedacceleratorresiduesis consideredacceptable.

Tackling crystallisation

Can the compounderaffectthedegreeto which a polychloroprene product will exhibitcrystallinity during low-temperatureexposure?

A delegate- InternationalLatex Conference.

T hevulcanisationtemperatureand the resulting "state of

cure" have a major effect oncrystallisationof polychloropreneproducts.Checkwith your chloroprenesupplierto find out whatcure temperatureand time youshould usewith his polymer toprevent or at least minimisecrystallisation.

Sulphur in the compoundcanreducecrystallisationas can theuse of some accelerators.Here

again, contact the chloroprenesupplierfor recommendations.

A 3rd factoris thechoiceof thechloroprenepolymer. Somepolymershavemuchgreaterresistanceto crystallisation. For completeinformation about the severalpolymers on the market, checkwith your chloroprenesupplierandalso with his competitors.Allchloroprenesare not the same;

Refer, if possible,to JohnCarl’sNeopreneLatex pages65-67.

Will blendinghelp?CanI reducetheeffect of cold

temperaturecrystallinity in mypolychloroprene product byblending in somenitrile latex?

Anonymous - InternationalLatex Conference.

p ossibly. However, that dependson the nitrile polymer

and the chloroprenepolymer aswell as thecure system, vulcanisation temperature,andthecompound recipe. It would be betterto addresstheproblemas outlinedin the reply to the queryabove.

Also it would probably be better to tackle the problemby opting for a chloroprene polymerwith a lower crystallisation rate.

A major difference is that thechloroform precuresystem

doesn’twork with polyisoprene.Therefore,a switch to a swollendiametersystemwhich works forboth polymers is a likely choice.

It is possibleto useN Butyl alcohol for polyisopreneand chloroform for NB., But theresultsaresomewhatdifferent in appearance.

Keepin mind that these"quickmix" testsare subjective.

The timing of the addition ofthe ‘solvent’ andthereadingmustalwaysbe thesame,the latex andsolventtemperaturesmustbe thesame and, most important, thepersonmaking thejudgementcallmust alwaysbe the same. *

A majordifferenceIs thereany differencein ma

turing polyisoprene latex andnatural rubber latex?

JanPeters- on email

104RubberAsla S Novewber- Oecember2005