FlarryF Bader

Combustibility of nitrilediffers fromnatural latex

Sonic manufacturesare switchingover to nitrite latexfront natural rubber latex asan answerto the proteinallergy problem which is inherent toproductsmadefrom Ni? latex.Althoughnitrite latexis notextremelydifficult toprocessit is differentand thereforehasa differentsetofproblemsto overcome.

H ow doesthe combustibility ofnitrile differ from naturallatex?Underwhat conditions?

Temperatures?NarayanaMurthy

-ChennaiAt Akron RubberDevelopmentLabo

ratoryInc. we recentlyperformeda DSCDifferential ScanningCalorimetry anaysis on films from both NIt andnitritelatex. We establishedthe melting pointof NIt at 216.7°Candnitrite at 283.4°C.Unlike neopreneboth NR and nitritefilms, once ignited, will continueto burn. Consideringthe differencein meltingpoints nitrile is unlikely to presentthesamedangerof spontaneouscombustionclaimedto be presentin Nit films.

I n a nitrile dip for examinationgloves, the latex on the formerfollowing thedip appearsto have

beadsof coagsweatcomingthroughthe latexthatdrop into the latexdiptank andcauseagglomerationof latex that requiresconstantskimmingof the tank. The sweat causesweakspots.Pleasecomment

MaheshJam-Ahmedabad

This problem,called sinteresis,occurswhenthe coagulationis so fastandso tight that water is squeezedfrom thelatex. This is usually accompaniedbyrather severeshrinkageof the film.sometimesas much as 2 inchesdownthe form. It is sometimesaccompaniedby rupture of the film small cracks,which laterare seenas pin holes.

This problem can be avoidedor atleastminimizedby adjustingfive processconditions.

1. Reducethe coagulantconcentration.Nitrite manufacturersare recoinmending as high as 36% calcium nitrate. A concentrationof 24% or lessshouldbe sufficient.

2. Decreasethe coagulanttemperature.However, bewareof wet coagulantconditions.

3. Increasethe surfactantin the coagulant by 0.25 to 0.5 per cent.

4. Increasethe stability of the latex bylowering the temperatureto 21±0C2°C.

5. Increasethe stability of the latex byincreasingthe stabilizer by 0.25 to0.5 parts.

All this will slowdown thecoagtlationand thereby reduceor eliminate theproblems.

I n a natural latex dip tank forcondoms- thereare tiny bubblesof 2 to 4 mIcron thatarc invisible

to the nakedeyebut causepinholes.What advicecanyou give?

Ramanathan-Bangalore

I am not sure how you know thereare ‘invisible" bubblesin the latex.Haveyou viewedthe liquid latex undera microscope?Assumingyour diagnosisiscorrectandsmall bubblesare present,Isuggestyou took for the source.

If you are milling your own dispersions andmaking your own compound,the sourceis likely to be in the dispersion milling process.Dispersionsshouldbe viewed undera microscopeto seeifthey are the source of the bubbles."Bubble busters"should be addedtoyour dispersionrecipe.Thesearereadilyavailable from your chemical supplier.Manufacturersare CrusaderChemicalsInc. or Mr ProductsInc.

If your are buying compound,presentthe problemto your supplierandhavehim searchfor the source.

Pleasesee ‘The I.atex Doctor" column in the Jan/Feb98 issueof RubberAsia for moresuggestionsfor solvingthe"pinhole" problem.

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Mr. Hariy FBader, Vice-President,LatexServices,AkronRubberDevelopmentLaboratory inAkron, USA,and a worldauthority onlatex, answersqucstionsanddoubtsofreaderson latexand latexproducts.

Send your questionsto:

‘The Latex Doctor’Rubber Asia,Ohanam House,Cochin - 682 020,Kerala, India Fax:94-484-317872

RubberAsia * May-June 1998 25