Natural Rubber
Natural Rubber•Sources, Plantation Economy•Coagulation & Processing of Coagulate•Structure & Composition•Properties of raw...
Sources•Many plants produce a milky sap, referred to as latex, which is a caoutchouc dispersion in an aqueous medium•Latex...
Plantation Economy•Early plantation economies used Ficus elastica,Funtumia, de Castilloa and Manihot plants•But were spoon...
Tapping          Page 5
Coagulation•Preferred method is Acid Coagulation (FormicAcid/acetic Acid)•Latex from different sources are blended inhuge ...
Processing of Coagulate•Coagulum is processed immediately to prevent changes inproperties under the influence of bacteria ...
Structure & Composition•Rubber Hydrocarbons + Impurities + Others•Average composition measured for latex crepe: 89-92%Rubb...
Structure      Chemical structure of      cis-polyisoprene, the main      constituent of natural      rubber.      Synthet...
Chemical Properties of raw NR•If heated above 300 ° C destructive distillation occurs•Double bond in the isoprene unit and...
Cont..•Since NR contains some amount ofantioxidants, it is stable for longer storageperiods in air at room temperature. BU...
Physical Properties of raw NR•Specific gravity: 0.934 @ 20°C•Specific heat: 0.502 @ 20°C•Purified NR after extraction with...
Cont..•Un-crosslinked NR can be extended to 800 to 1000% of itsoriginal length without breaking•As the temperature increas...
Cont..Behaviour in Solvents:•When in contact with organic liquids likebenzene, gasoline, vegetable oils, mineraloils, carb...
Compounding of NRBlends with NR:•NR is non-polar•Therefore NR can be readily blended with othernon-polar rubbers•NR has to...
Cont..Vulcanization Chemicals:•Sulphur & Accelerators: Suphur is predominantly used ascrosslinking agent eventhough peroxi...
Factice•Added to improve processability ( extrusionand calendaring operations)•Prevent deformations while curing•Improves ...
Cont.. •Activators: Many accelerator systems require additional activators like fatty acids or salts of fatty acids namely...
Cont..Protective Agents:•Since unsaturation in NR causes the material to degradedue to ageing, it has to be compounded wit...
Cont..Fillers:•Fillers are not necessarily used in NR to obtain high tensilestrength but to reach a level and range of pro...
Cont..Softeners:•Most important mineral oils including paraffinic toaromatic•Animal and Vegetable Oils are also used•Bloom...
Cont..Process Aids:•Important in facilitating the dispersion of fillers•Ensure smooth processing•In pure white or pastel c...
Processing of NR•Good processing properties•Viscosity stabilized grades of NR do not require premasticationbefore filler i...
Cont..•Viscosity is the most widely used measure ofprocessing quality•During mixing control of viscosity is essential fors...
Properties of NR vulcanizatesStrength:•TS of gum vulcanizates: 17 to 24 Mpa•TS of black filled vulcanizates: 24 to 32 Mpa•...
Cont..Dynamic Properties:•High resilience with values exceeding 90% + Good flexing properties•At large strains fatigue lif...
Uses of NR•Tires•Footwear•Engineering products•Mechanical goods                             Page 27
Competitive products of NREthylene Propylene Diene MonomerEPDM rubber is used in seals, glass-run channels,radiators, gard...
Competitive products of NRIsoprene Rubber is beneficial for the production ofgloves, medicalproducts, adhesives, tackifier...
Competitive products of NRStyrene Butadiene Rubber is used widely in pneumatictires, shoe heels and soles, gaskets and eve...
References•Rubber Technology Handbook, Werner Hoffman•Rubber Technology, Maurice Morton•Wikipedia                         ...
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Natural Rubber - Sources, Coagulation & Processing of Coagulate, Structure & Composition, Properties of raw NR Compounding, Processing of NR, Properties of NR vulcanizates, Uses of NR, Competitive products of NR

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Sources, Plantation Economy
Coagulation & Processing of Coagulate
Structure & Composition
Properties of raw NR
Compounding, Processing of NR
Properties of NR vulcanizates
Uses of NR
Competitive products of NR

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  • So today, i will be speaking about a typeof Rubber- Natural Rubber.
  • “CAW-CHoW-K”
  • 2.3 Text
  • Read 2.4.1.1 & 2Pg 13
  • Crystallization occurs due to orientation of polymer chain. Strain crystaliizationCrystallization enhances intemolecular attractive forces and reinforcess the strength of the polymer. Therefore high tensile strength in the direction of deformation and less in the perpendicular direction.
  • NR is non polar
  • Factice: oxides based on based on sulphur monochloride
  • Pri-plasticity retention ratio: ratio of plasticity of rubber exposed to 140deg for 30 min to the original plasticity of the ubberexprssed as %Smr standard Malaysian rubber
  • Gumvulc: without any filler :P
  • Absorb energy when subjected to elastic deformationFatigue life: The number of applied repeated stress cycles a material can endure before failure.
  • Natural Rubber - Sources, Coagulation & Processing of Coagulate, Structure & Composition, Properties of raw NR Compounding, Processing of NR, Properties of NR vulcanizates, Uses of NR, Competitive products of NR

    1. 1. Natural Rubber
    2. 2. Natural Rubber•Sources, Plantation Economy•Coagulation & Processing of Coagulate•Structure & Composition•Properties of raw NR•Compounding, Processing of NR•Properties of NR vulcanizates•Uses of NR•Competitive products of NR Page 2
    3. 3. Sources•Many plants produce a milky sap, referred to as latex, which is a caoutchouc dispersion in an aqueous medium•Latex producing plants are predominantly found in tropical climates•Not all caoutchouc producing plants are harvested for industrial purposes Page 3
    4. 4. Plantation Economy•Early plantation economies used Ficus elastica,Funtumia, de Castilloa and Manihot plants•But were spoon displaced by HeveaBrasiliensis, due to greater yield•Yield was improved by the stimulation of latexflow. Several chemicals, such as 2-amino-3,5,6-trichloropicolinic acid or 2-chloroethyl phosphoric acid were used, which after application, penetrates the bark and produce ethylene within the plant Page 4
    5. 5. Tapping Page 5
    6. 6. Coagulation•Preferred method is Acid Coagulation (FormicAcid/acetic Acid)•Latex from different sources are blended inhuge tanks in order to achieve good uniformity•Latex is diluted with water to a solids contentup to 12 to 18%•Iso-electric point is reached at a pH of 5.1 to4.8, which coagulates the latex Page 6
    7. 7. Processing of Coagulate•Coagulum is processed immediately to prevent changes inproperties under the influence of bacteria when exposedto air•When kept immersed in water or in its ownserum, impurities in the caoutchouc are decomposed bybacteria into gases, such as CO2, CH4 & Nitrogen containingcompoundsTwo Standard ways of Processing the coagulum: 1. Drying by exposure to wood smoke (Smoked Sheet) 2. Air drying (Pale Creep) Page 7
    8. 8. Structure & Composition•Rubber Hydrocarbons + Impurities + Others•Average composition measured for latex crepe: 89-92%Rubber HC, 2.5-3% acetone extractables, 2.5-3.5%protein, 2.5-3.5% moisture, 0.15-0.5% ash•Rubber HC content of NR consists of 99.9% cis-1,4-polysioprene. Presence of even small amount of transresults in greatly different properties•Average molecular weight ranges from 2,00,000 –4,00,000•Has a broad molecular weight distribution (results in greatprocess ability) Page 8
    9. 9. Structure Chemical structure of cis-polyisoprene, the main constituent of natural rubber. Synthetic cis-polyisoprene and natural cis-polyisoprene are derived from different precursors. Page 9
    10. 10. Chemical Properties of raw NR•If heated above 300 ° C destructive distillation occurs•Double bond in the isoprene unit and the α-methylenegroups are reactive for sulphur vulcanization•May also lead to age degradation due to the presenceof double bond(reacts with O2 or O3)•Other reactions with hydrogen leads to formation ofHydrogenated rubber•Reacts with Chlorine to form chlorinated rubber; reactswith HCl to form hydro-chlorinated rubber; cyclizationreactions also may occur Page 10
    11. 11. Cont..•Since NR contains some amount ofantioxidants, it is stable for longer storageperiods in air at room temperature. BUT Onstorage at high temperatures and on exposure tolight, NR oxidizes by forming hydroperoxidesthrough oxygen radicals•Unsaturation facilitates reaction with oxidizingagents like peroxides, peroxy acids, potassiumpermagnate, ozone, chlorine etc.. Page 11
    12. 12. Physical Properties of raw NR•Specific gravity: 0.934 @ 20°C•Specific heat: 0.502 @ 20°C•Purified NR after extraction with acetone hasrefractive index of 1.5215 to 1.5238•Electrical properties of NR are determined by its watersoluble impurities. For instance the specific resistivityof sheets is 10^15 and that of crepe is 2*10^15•When NR is stretched more than 80% of its originallength, crystallization occurs Page 12
    13. 13. Cont..•Un-crosslinked NR can be extended to 800 to 1000% of itsoriginal length without breaking•As the temperature increases forces required to deform thematerial becomes larger•At high rates of strain, deformations are completelyrecoverable, whereas at low strain rates some deformationmay remain. This deformation will however recover onheating or after some time. Because of this incompleterecovery the extension and retraction do not coincide. Thishysteresis leads to a heat build up, and is more pronouncedin the first heat cycle and less in the subsequent cycles. Page 13
    14. 14. Cont..Behaviour in Solvents:•When in contact with organic liquids likebenzene, gasoline, vegetable oils, mineraloils, carbon tetrachloride, swell raw rubber to aconsiderable amount to form a highly viscoussolution or gel.•Physical bonds are broken in this process Page 14
    15. 15. Compounding of NRBlends with NR:•NR is non-polar•Therefore NR can be readily blended with othernon-polar rubbers•NR has to be masticated so that it has the sameviscosity as the blend partner to achieve intimateblending of the polymers Page 15
    16. 16. Cont..Vulcanization Chemicals:•Sulphur & Accelerators: Suphur is predominantly used ascrosslinking agent eventhough peroxides/High energy radiationcan also be used to crosslinkFor lower S concentrations, large amount of Accelerators are usedand viceversaHigh concentrations of Sulphur may produce Ebonite•Metal Oxides: Used in a compound to develop the full potentialof acceleratorsEg: Zinc oxide, Lead oxide, Factice, MgO in the presence of acidiccompounding ingredients Page 16
    17. 17. Factice•Added to improve processability ( extrusionand calendaring operations)•Prevent deformations while curing•Improves the appearance of vulcanizates•Used in large conc. in compounding forpreparation of rubber erasers Page 17
    18. 18. Cont.. •Activators: Many accelerator systems require additional activators like fatty acids or salts of fatty acids namely stearic acid, zinc soaps or amine stearates •Vulcanization Inhibitors: Used to prevent scorch Pthalamide sulphinamide based Inhibitors are used when accelerators or acidic compounding ingredients doesnt provide sufficient scorch life Page 18
    19. 19. Cont..Protective Agents:•Since unsaturation in NR causes the material to degradedue to ageing, it has to be compounded with protectiveagents.•Most effective ones are aromatic amines such as p-phenylene diamine derivatives which also doubles up as anantidegradant from Ozone and heat & also against dynamicfatigue•PAN/PBN impart good fatigue resistance to NR•More effective PAs discolour light coloured vulcanizates soless effective PAs such as phenols, bisphenols, MBI are used Page 19
    20. 20. Cont..Fillers:•Fillers are not necessarily used in NR to obtain high tensilestrength but to reach a level and range of properties that arerequired for technical reasons( such as density, colour, price)•Reinforcing fillers enhance the already high tensile propertiesof NR, and the improve the abrasion and tear resistance+improves the processability, affects the hardness and reboundelasticity of NR vulcanizates•Less reinforcing fillers: n770, n990 ; Light inactive fillers:kaolin, ZnO, MgCO3,CaCO3, Kaolin Page 20
    21. 21. Cont..Softeners:•Most important mineral oils including paraffinic toaromatic•Animal and Vegetable Oils are also used•Blooming potential must be taken into considerationwhile selecting softeners for NRResins:•Added for improving building tack, so that they can befabricated•Rosin, tar, pitch Page 21
    22. 22. Cont..Process Aids:•Important in facilitating the dispersion of fillers•Ensure smooth processing•In pure white or pastel coloured articles, calcium soaps ofunsaturated fatty acids are preferred•Stearic acids, zinc and calcium soaps and residues of fattyacids Page 22
    23. 23. Processing of NR•Good processing properties•Viscosity stabilized grades of NR do not require premasticationbefore filler incorporation•For non-stabilized grades mastication is a common practice•Mastication is carried out below 80 degrees or above 120 degree•Chemical peptizers are used to carry out mastication at lowertemperatures•Break down behaviour is dependant on PRI values and on theinitial viscosity of the rubber•Latex grade rubbers such as RSS1 and SMR L (high PRI values)breakdown much faster than cuplump grades such as SMR 20 ( lowPRI values) and therefore require more mastication Page 23
    24. 24. Cont..•Viscosity is the most widely used measure ofprocessing quality•During mixing control of viscosity is essential forsmooth operation during processing such as extrusionand injection moulding•In Extrusion of a fully mixed batch, the batch viscosityis the main factor controlling the die swell and stressdeveloped•A masticated rubber has better extrusion propertiesthan a non masticated rubber of same viscosity Page 24
    25. 25. Properties of NR vulcanizatesStrength:•TS of gum vulcanizates: 17 to 24 Mpa•TS of black filled vulcanizates: 24 to 32 Mpa•Strength/tear resistance/cut growth resistance: Excellent ( dueto the ability to undergo crystallization)•Decreases with increase in TemperatureAbrasion & Wear:•Excellent abrasion resist., improved by blending with polybutadiene•Wear resistance: dependant on surface temperature•Below 35 deg. NR shows better wear than SBR•Above 35 deg. SBR is better Page 25
    26. 26. Cont..Dynamic Properties:•High resilience with values exceeding 90% + Good flexing properties•At large strains fatigue life of NR > SBR and vice versa for small strainsCompression Set:•Poor in NR compared to SR (Due to presence of non rubbersubstances in SR, and DPNR shows much improved properties)Ageing:•Heat-ageing resistance is given by choosing proper vulcanizatessystems and by use of amines or phenolic antioxidants•Ozone resistance is improved by adding Waxes and antioxidants ofthe p-phenylene diamine type Page 26
    27. 27. Uses of NR•Tires•Footwear•Engineering products•Mechanical goods Page 27
    28. 28. Competitive products of NREthylene Propylene Diene MonomerEPDM rubber is used in seals, glass-run channels,radiators, garden, tubing, pond liners, washers, belts,electrical insulation, O-rings, solar panel heat collectors,UV protection (for tubular motors in shutters) andspeaker cone surrounds.EPDM doesnt require maintenance with products toprotect it from ultraviolet light, like natural rubber does.EPDM rubber offers the same colour stability anddurability in heat as natural rubber but at a lower price. Page 28
    29. 29. Competitive products of NRIsoprene Rubber is beneficial for the production ofgloves, medicalproducts, adhesives, tackifiers, paints, coatings, andphotoresistors.They combine the key qualities of natural rubber such asgood mechanical properties and hysteresis with superiorfeatures such as high purity, excellent clarity, goodflow, low gel content, no nitrosamines, and no naturalrubber proteins! Page 29
    30. 30. Competitive products of NRStyrene Butadiene Rubber is used widely in pneumatictires, shoe heels and soles, gaskets and even chewinggum.SBR is more resistant to abrasion and oxidation thannatural rubber. Page 30
    31. 31. References•Rubber Technology Handbook, Werner Hoffman•Rubber Technology, Maurice Morton•Wikipedia Page 31
    32. 32. Page 32

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