Natural and synthetic rubber

Natural and synthetic rubber

1. NATURAL AND
SYNTHETIC RUBBER

2. What is Rubber
■Rubberisamaterial,whichcanstretchandshrink.
■Itisapolymer.
■Itcanbeproducedfromnaturalsources(e.g.naturalrubber)orcanbesynthesisedonan
industrialscale.

3. Natural Rubber
■Naturalrubberisanaturallyoccurringpolymerobtainedfromthelatexofrubbertrees.
■Latex,amilkyliquidpresentineitherthelatexvessels(ducts)orinthecellsofrubber-
producingplants
■Theliquidis30-40%rubberparticles,55-65%water,andsmallamountsofprotein,
sterolglycosides,resins,ash,andsugars.

4. Rubber tapping
■Rubbertappingistheprocessbywhichlatexiscollectedfromarubber
tree.
■Thelatexisharvestedbyslicingagrooveintothebarkofthetreeata
depthofone-quarterinchwithahookedknifeandpeelingbackthebark.
■Itiscollectedinacupmountedoneachtree.

5. Processing of natural rubber
■Productionofrubberisfollowedbyprocessingintofinalproducts
consistsof:
1.Compounding
2.Mixing
3.Shaping
4.Vulcanizing
■Processingtechniquesfornaturalandsyntheticrubbersarevirtuallythe
same,differencesbeinginthechemicalsusedtoeffectvulcanization.

6. Compounding
■Compoundingaddschemicalsandotheradditivestorawrubberinorder
toobtaindesiredproperties.
■Chemicalsaddedduringcompoundingreactwiththerubberduringthe
vulcanizingprocesstostabilizetherubberpolymers.
■Mainlyusedreinforcingfilleriscarbonblack.Carbonblackincreases
rubber’stensilestrengthandresistancetoabrasionandtearing.
■Otheradditivesincludeantioxidants,antiozonantscolouringpigments,
plasticizersandsofteningoils.

7. Mixing
■Theadditivesmustbethoroughlymixedwiththebaserubbertoachieve
uniformdispersionoftheingredients.
■Thehighviscosity(resistancetoflow)oftherubbermakesmixing
difficulttoaccomplishwithoutraisingthetemperatureoftherubberhigh
enough(upto300degreesFahrenheit)tocausevulcanization.
■Topreventprematurevulcanization,themixingusuallytakesplaceintwo
stages.

8. ■Duringthefirststage,additiveslikecarbonblackaremixedintothe
rubber.Thismixtureisreferredtoasamasterbatch.
■Oncetherubberhascooled,thechemicalsforvulcanizationareadded
andmixedintotherubber.
■EquipmentformixingincludestheTwo-rollmillandinternalmixerssuch
astheBanburymixer.

9. Shaping
■Shaping processes for rubber products can be divided into four basic categories
1.Extrusion: Extrusion consists of forcing highly plastic rubber through a series
of screw extruders.
2.Calendering: Calendering passes the rubber through a series of increasingly
smaller gaps between rollers.
3.Coating: Coating uses the calendering process to apply a coat of rubber or to
force rubber into fabric or other material.
4.Molding and Casting: Molding is also a step in making tires. Three primary
methods of molding rubber are compression molding, transfer molding and
injection molding.

10. Vulcanization
■Vulcanizationcompletestherubber-productionprocess.Itisachemical
processinwhichtherubberisheatedwithsulphur.
■Vulcanizationcreatesthecross-connectionsbetweenthepolymersof
rubber.
■Increasingcross-connectionsdecreaseselasticity,Withoutvulcanization,
rubberwouldremainsticky

11. Application of Natural rubber
■Themainuseofnaturalrubberisinautomobilestyresandtubesabout60
%ofthetotalnaturalrubberproduction.
■Inheavydutytyres,themajorportionoftherubberusedisNR
■UsesofNRinhoses,footwear,batteryboxes,foammattresses,balloons,
toysetc.,arewellknown.
■NRnowfindsextensiveuseinsoilstabilization,invibrationabsorption
andinroadmaking.

12. ■Articlesforuseinthemedicalandhealthsector.
■Consumerproducts(likegolforfootballballsandotherrecreationaland
sportsgoods,erasers,footwearandotherapparel)

13. Synthetic Rubber
■Syntheticrubbersarecomplexchemicalcompoundsformedthroughthe
polymerizationofmonomers.
■Typicalmonomersusedforproductionfeedmaterialincludebutadiene,
styrene,isoprene,chloroprene,acrylonitrile,ethyleneorpropylene.
■Syntheticrubberproductionstartswiththerefiningprocessofoil,coalor
otherhydrocarbonswithnaphthaasoneofthedesiredproducts.

14. Styrene Butadiene Rubber (SBR)
■Styrene-Butadienerubber(SBR)derivedfromthecopolymerizationof
styreneand1,3-butadiene.
■Styrenecontentintherangeof10-25%andbutadieneunitiscomposed
approximately60to70%.

15. ■TherearetwomajortypesofSBRwithdifferentpropertiesbasedon
theirmanufacturingprocess.
■EmulsionSBR(e-SBR)–HotSBRorColdSBR.Itcanbeproducedby
free-radicalemulsionpolymerizationofstyreneandbutadieneeitherat50
to60C(hotemulsionSBR)oratabout5C(coldemulsionSBR).
■SolutionSBR(s-SBR).SolutionSBRisproducedbytermination-free*,
anionicsolutionpolymerizationofstyreneandbutadienewithalkyl
lithiuminitiator(e.g.,butyllithium)inahydrocarbonsolvent,usually
hexaneorcyclohexane.

16. Uses of SBR
■ThemajoruseofSBRisintheproductionoftires,particularlycarand
lightweightvehiclestires.
■ColdemulsionSBRisespeciallyusedinlighterdutytires.
■SBRcanalsobefoundinindustrialapplicationsasbelting,insulationfor
wireandcabling,haul-offpads,rollcoverings,hoses,gaskets,seals.
■SBRisincludedinshoesoles,carpetbackingadhesive,andinmolded
rubbergoods.

17. Nitrile Butadiene Rubber –NBR
■NitrileRubber(NBR)isaco-polymerof75%butadieneand25%
acrylonitrilemonomer.
■Areemulsifiedinwaterandthenpolymerized(theirsingle-unitmolecules
linkedintolarge,multiple-unitmolecules)throughtheactionoffree-
radicalinitiators.
■Nitrilerubber,alsoknownasBuna-N,Perbunan,acrylonitrilebutadiene
rubber.

18. Application of NBR
■Nitrilerubberispopularinapplicationsrequiringoilresistance,
performanceunderextremetemperatures,andpersonalprotection.
■Usedinautomotiveindustry,usefulforgaskets,oilseals,o-rings,engine
hoses.
■Usedtomaketherollsintheprintingindustrythatspreadinks.
■Usedintextilestowaterprooffabricandimprovethefinish.
■Nitrileglovescanrangefromheavy-dutygloves,footwear,floormats,
sponges,andahostofmoldedgoods.

19. Silicone rubber
■Siliconerubber(orSiRubber)isthemostcommonlyusedsyntheticruuberorpolymer
■similarbondstructureasfoundinglass,sandandquartz.
■Composedofsilicone-whichisitselfapolymer-togetherwithhydrogen,carbon,and
oxygen.
■Madefromacross-linkedpolymerthatisreinforcedwithsilica.

20. Application of silicon rubber
■Electronicsinsulatingtape,sealant,varnish,lubricants,keyboards,and
housings.
■Aerospacesiliconerubberisusedinspacesuitfabrics,toolingmaterials,
sealsandgaskets.
■Constructionusessiliconerubberforadhesives,sealants,andcoatings
■Inconsumermaterialincludeanti-stickbakeware,foodcontainers,
utensils,toys,andjewelry
■Medicalsiliconerubbercanbefoundintubing,adhesives,and
defoamers.

21. Draw back of synthetic rubber
■During the vulcinization of synthetic rubber, soot is produced. Soot is a
carbon particle that contributes to climate change.