FlarryF Bader Combustibility of nitrile differs from natural latex Sonic manufactures are switching over to nitrite latex front natural rub ber latex as an answer to the protein allergy problem which is inherent to products madefrom Ni? latex. Although nitrite latex is not extremely difficult to process it is different and therefore has a different set of problems to overcome. H ow does the combustibility of nitrile differ from natural la tex? Under what conditions? Temperatures? Narayana Murthy -Chennai At Akron Rubber Development Labo ratory Inc. we recently performed a DSC Differential Scanning Calorimetry ana ysis on films from both NIt and nitrite latex. We established the melting point of NIt at 216.7°C and nitrite at 283.4°C. Unlike neoprene both NR and nitrite films, once ignited, will continue to bu rn. Considering the difference in melting points nitrile is unlikely to present the same danger of spontaneous combustion claimed to be present in Nit films. I na nitrile dip for examination gloves, the latex on the former following the dip appears to have beads of coag sweat coming through the latex that drop into the latex dip tank and cause agglomeration of la tex that requires constant skimming of the tank. The sweat causes weak spots. Please comment Mahesh Jam -Ahmedabad This problem, called sinteresis, oc curs when the coagulation is so fast and so tight that water is squeezed from the latex. This is usually accompanied by rather severe shrinkage of the film. sometimes as much as 2 inches down the form. It is sometimes accompanied by rupture of the film small cracks, which later are seen as pin holes. This problem can be avoided or at least minimized by adjusting five process conditions. 1. Reduce the coagulant concentration. Nitrite manufacturers are recoin mending as high as 36% calcium ni trate. A concentration of 24% or less should be sufficient. 2. Decrease the coagulant temperature. However, beware of wet coagulant conditions. 3. Increase the surfactant in the coagu lant by 0.25 to 0.5 per cent. 4. Increase the stability of the latex by lowering the temperature to 21±0C 2°C. 5. Increase the stability of the latex by increasing the stabilizer by 0.25 to 0.5 parts. All this will slow down the coagtlation and thereby reduce or eliminate the problems. I na natural latex dip tank for condoms - there are tiny bubbles of 2 to 4 mIcron that arc invisible to the naked eye but cause pinholes. What advice can you give? Ramanathan -Bangalore I am not sure how you know there are ‘invisible" bubbles in the latex. Have you viewed the liquid latex under a mi croscope? Assuming your diagnosis is correct and small bubbles are present, I suggest you took for the source. If you are milling your own disper sions and making your own compound, the source is likely to be in the disper sion milling process. Dispersions should be viewed under a microscope to see if they are the source of the bubbles. "Bubble busters" should be added to your dispersion recipe. These are readily available from your chemical supplier. Manufacturers are Crusader Chemicals Inc. or Mr Products Inc. If your are buying compound, present the problem to your supplier and have him search for the source. Please see ‘The I.atex Doctor" col umn in the Jan/Feb 98 issue of Rubber Asia for more suggestions for solving the "pinhole" problem. Mn ihëIáte4octot 17 ye of ic li ar :1 :1. .0 -x It ‘S 9 7 Mr. Hariy F Bader, Vice- President, Latex Services, Akron Rubber Development Laboratory in Akron, USA, and a world authority on latex, answers qucstions and doubts of readers on latex and latex products. Send your questions to: ‘The Latex Doctor’ Rubber Asia, Ohanam House, Cochin - 682 020, Kerala, India Fax: 94-484-317872 RubberAsia * May-June 1998 25

Combustibility of Nitrile Differs from Natural Latex

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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.

ihëIáte4octot

17yeof

icliar:1

:1..0-xIt

‘S

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