The Latex Doctor - ardl.com · The Latex Doctor QWhat is the effect of particle size of corn- ......
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The Latex Doctor Q What is the effect of particle size of corn- * pounding ingredients sulphur, accelerators and znO on the curing tharatteristics and vulcanisate properties of NR latex product? Can the dosage of chemicals be reduced by the use of smaller particle size chemicals say, less than ‘1 micron since the available surface area Is more? when I took a trial using perl-milled chemical particle size ci micron, instead of ball-milled chemical particle size 6-9 micron, the results were encouraging. Even with a 10% lesser dos age of slurry. I got better ageing properties for rubberized coir mattress. Pradeep Kuinar P. Jo Kurlon Ltd. y our observations are similar to what I have experienced. However, I’ve also en countered some problems you should con sider. * Ball-milled or attrition mill.prepared dis persions of latex chemicals should be 2-5 mi crons. I would expect problems with 6-9 mi cron dispersions. * Although good quality latex films can be obtained from compounds having as little as 5%of the normal PHDR ofasmaliparticle size chemical, the results are frequently not uniform from batch to batch. * I’m not sure of the reasons for this. It may be that small quantities require more or better mixing to ensure uniform distribution through out the compound of critical ingredients which are in very small quantities.’ * Maturing can be much slower and may require longer elevated temperatures. Particle size of compounding chemicals Harry F Bader. Vice-President, Latex Services, Akron Rubber Development Laboratory. Akron, USA, and a world authority on latex, answers questions and doubts of readers on latex and latex products. Send your questions to: The Latex Doctor Rubber Asia, Dhanam House, cochin 682 020, Kerala, India Fax :91-484-2317872 E-mail: dhanrubberethnet JULV-AGST 2006 * Vulcanisation is different. Experiment ation is required to determine the optimum conditions of time and temperature. * Also, experimentation is needed to establish the surface area ratio which produces the optimum results. * Are your ageing results possibly due to an original undercure condition? How do unaged properties compare? I believe there is need for more experimen tal work to ensure uniform material prepara tion and to ensure uniform compounding and process control. Latex quality and finished products we are finding differences in our finished prod uct properties when the latex we are using comes from different sources. How and why does this happen? SM. Pande and others, IColkata Q ur.chemical testing/analysis experts think that though they cart find differences in latex coming from varying sources, much fur ther testing plus experimental compounding and dipping would be needed to match those differences with varying results in finished products. I agree with that opinion. Also, you should be performing ASTM L 1076 testing on incoming shipments to ensure the latex meets the D 1076 requirements possibly and more importantly match the sup pliers’ data sheet indicating their D 1076 resulj Many years ago I experienced problel similar to what you are having when we We making medical-type gloves on automatic eQUi* ment having fixed times and temperatures f leaching, drying and curing. We eventually found that we had to alter P compounding and latex maturing processes ensure that the latex going on the line was same precure level, percentage solids, visc w and temperature, regardless of the cOI1ll of origin of the latex or the time of the yeal latex was tapped. When all conditions were the same, dipped products showed the same pr hb02
Transcript of The Latex Doctor - ardl.com · The Latex Doctor QWhat is the effect of particle size of corn- ......
The Latex DoctorQ What is the effect of particle size of corn-
* pounding ingredients sulphur, acceleratorsand znO on the curing tharatteristics andvulcanisate properties of NR latex product? Canthe dosage of chemicals be reduced by the useof smaller particle size chemicals say, less than‘1 micron since the available surface area Ismore?
when I took a trial using perl-milled chemicalparticle size ci micron, instead of ball-milledchemical particle size 6-9 micron, the resultswere encouraging. Even with a 10% lesser dosage of slurry. I got better ageing properties forrubberized coir mattress.
PradeepKuinar P. Jo Kurlon Ltd.
y ourobservationsaresimilarto whatI haveexperienced.However, I’ve also en
counteredsomeproblemsyou shouldconsider.
* Ball-milled or attrition mill.prepareddispersionsof latex chemicalsshouldbe 2-5 microns. I would expectproblemswith 6-9 microndispersions.
* Althoughgood quality latex films canbeobtainedfrom compoundshaving as little as5%of the normalPHDRofasmaliparticlesizechemical,theresultsare frequentlynotuniformfrom batchto batch.
* I’m notsureof thereasonsfor this. It maybe thatsmall quantitiesrequiremore or bettermixingto ensureuniform distributionthroughoutthecompoundof critical ingredientswhicharein very small quantities.’
* Maturing can be much slower and mayrequirelongerelevatedtemperatures.
Particle size ofcompoundingchemicals
Harry F Bader.Vice-President, LatexServices, Akron RubberDevelopment Laboratory.Akron, USA, and a worldauthority on latex,answers questionsand doubts of readers onlatex and latex products.Send your questions to:The Latex DoctorRubber Asia, DhanamHouse, cochin 682 020,Kerala, IndiaFax :91-484-2317872E-mail: dhanrubberethnetJULV-AGST 2006
* Vulcanisationis different. Experimentation is requiredto determinethe optimumconditionsof timeandtemperature.
* Also, experimentationis neededtoestablishthesurfacearearatio which producestheoptimum results.
* Are your ageingresultspossiblydue to anoriginal undercurecondition? How do unagedpropertiescompare?
I believethereis needfor more experimental work to ensureuniform materialpreparation and to ensureuniform compoundingandprocesscontrol.
Latex quality andfinished productswe are finding differences in our finished product properties when the latex we are usingcomes from different sources. How and whydoes this happen?
SM.Pandeandothers,IColkata
Q ur.chemicaltesting/analysisexpertsthinkthat thoughthey cart find differencesin
latexcomingfrom varyingsources,muchfurther testing plus experimentalcompoundingand dipping would be neededto matchthosedifferenceswith varying results in finishedproducts.I agreewith that opinion.
Also, you shouldbe performingASTM L1076 testingon incomingshipmentsto ensurethe latex meetsthe D 1076 requirementspossiblyand moreimportantlymatchthe suppliers’ datasheetindicatingtheir D 1076resulj
Many yearsago I experiencedproblelsimilar to what you arehaving when we We
makingmedical-typegloveson automaticeQUi*menthavingfixed timesandtemperaturesf
leaching, drying andcuring.
Weeventuallyfound thatwehadto alterPcompoundingandlatexmaturingprocessesensurethat the latex goingon the line wassameprecurelevel, percentagesolids,visc
w and temperature,regardlessof the cOI1ll
of origin of the latexor the time of theyeallatexwas tapped.
Whenall conditionswere the same,dippedproductsshowedthe samepr
hb02
I suggestyouevaluatethe compoundwhenit isreadyto go on line. Any differenceswill likelyresultin differentoutcomeof the final physicalproperties.
Problems in blending twonitrile latex gradesWe have made products by blending twogrades of nitrile latex because we get goodfilm properties and the modulus is all right.We have a few problems and we want toeliminate them,
1. Tear properties are poor.
2. The dipped product was taken from the trialbatch. For the first three days, the product wasfine in stripping and the film was perfect. Afterthree days, the films developed cracks on stresspoints of moulds. How can we make latex morestable and avoid precuring?
3. Also, can tensile strength be improved?
Manoj GoswainyNewDethi
M y experiencewith nitrile latex is mainlywith Dow Reichhold.I’ve successfully
used their Types68074 and 68075. If you arenot using Dow Reichhold,ask yoi.ir supplieraboutequivalentsto thosetypes-
2. Your experienceindicatesan overcureproblem as you havesaid, Have you done aprecurecheckusing N butyl alcohol insteadof chloroformwhich is usedfor naturallatex?This would be amethodfor trackingprecure.If you reducethe heathistory, precureshouldbe slower,
3. If you cancontrol the precure,the tensilestrengthshouldbe improved.
prevulcanised latticesWhat are prevulcanised lattices used for andwhy?
Anonymous- InternationalLatexConference
M ostlatex dippedproductsand foamproductsaremadefrom latexwhich hasbeen
maturedto some level of prevulcanisation.Precureis prevulcanisation.
It is difficult to hold a compoundedlatex to a ‘1’ level of precure.Therefore,manufacturersset their processfor a higherlevelof precure including total’ pre-vulcanisation.
This is to maintainuniform good quality oftheproduct. I am not awareof latex productswhich cannotbe made at some level of prevulcanisation.
Residual acceleratorsin medical glovesWhat are the typical levels of residual accelerators in medical gloves?
Anonymous- InternationalLatexConference
L evelsareimproving. Wenow find that mostglovessubmittedfor testingshow ‘below
detection’limits. This limit varieson theacceleratorsystemwhich is used,However, below1.0 ppm is usual.
Leaching of dipped goodsIn dipped products, how do you know if you areleaching, the product well enough or longenough?
KenRozarlo,Manila
T hefinal answeris the testingfor residualacceleratorcontentand for residualpro
teinsor Nil latex allergens.
However, if you operateyour leachsystemat,say,65°C; havea high degreeof water turbulence;maintaina reasonablewaterthroughputto avoid turbidity andcontinuethe leaching for a reasonabletime for the product,youare likely to besuccessful.
consult before making a claimcan a latex compound be considered foodgrade if the raw materials are listed in theCode of Federal Regulations. Title 21 Food andDrugs?
Anonymous- InternationalLatexConference
yes.However,therearemanyconditionswithin CFR21 which mustbemet, Theseinclude
theamountof the listedcontents;theconditionsof use; and the passingof testsfor extractionlevel.
I would suggestthatbeforemaking a claimregardinga productsuitability for food contactuse,anexperiencedsourceof testingandfamiliarity with themany sectionsof CFR21 beconsulted. *
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