NATURAL RUBBER

SUBMITTED BY:NITHUSHA.KMSC.BPSROLL NO:17 1

•Rubber is a type of polyisoprene made up of 5 carbon isoprene units.

• The 5 carbon units could be linked in the cis or trans conformations resulting in polymers with very different physical properties.

• Rubber is composed of all cis-linked isoprene units, forms an amorphous structure that is highly elastic.

• Gutta percha is a polyisoprene compound made of all trans-linked isoprene units, forms linear strands but are not elastic.

INTRODUCTION

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•NR is a high molecular weight polymeric substance with viscoelastic properties. it shows all the reactions of an unsaturated polymer.

•Vulcanization converts the viscous nature of raw rubber into elastic.

•Vulcanized rubber will have very high tensile strength and comparatively low elongation.

•Its hardness and abrasion resistance also high when compared to raw rubber.

•The main use of natural rubber is in automobiles. 3

STRUCTURE OF NR

• Structurally it is cis 1,4-polyisoprene.

•Isoprene is a diene and 1, 4 addition leaves a double bond in each of the isoprene unit in the polymer. 4

• The commercial source of natural rubber latex is the Para rubber tree (Hevea brasiliensis).

• Other plants containing latex include:

• Gutta-percha • Rubber fig • Panama rubber tree (Castilla elastica)• Common dandelion• Parthenium argentatum (Guayule).• Russian dandelion

SOURCES OF NR

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PHYSICAL PROPERTIES

Specific gravity : 0.92 Refractive index : 1.52

Coefficient of cubical expansion : 0.00062/°C

Cohesive energy density : 63.7 Cal/cc.

Heat of combustion : 10547.084 Cal/g

Thermal conductivity : 0.00032 Cal/sec/cm/°C

Dielectric constant : 2.37

Power factor (at 1000 cycles) : 0.15-0.2

Volume resistivity : 1015 ohm.cm

Dielectric strength : 3937 V/mm 7

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• Crude rubber is a tough and an elastic solid,becomes soft and sticky as the temperature rises.

• Its specific gravity is 0.915.

• Raw natural rubber has elasticity over a narrow range of temperature from 10 to 60.

• Raw natural rubber has low tensile strength and abrasion resistant.

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• NR absorbs large quantities of water.

• It is insoluble in water, alcohol, acetone, dilute acids and alkalis.

• It is soluble in ether, carbon disulphide, carbon tetrachloride, petrol and turpentine.

• Pure rubber is a transparent, amorphous solid, which on stretching or prolonged cooling becomes crystalline

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MECHANICAL PROPERTIES

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•The latex will coagulate in the cups if kept for long. The latex has to be collected before coagulation.

•The collected latex, "field latex", is transferred into coagulation tanks for the preparation of dry rubber or transferred into air-tight containers with sieving for ammoniation.

•Ammoniation is necessary to preserve the latex in a colloidal state for longer periods of time.

•Latex is generally processed into either latex concentrate for manufacture of dipped goods or it can be coagulated under controlled, clean conditions using formic acid.

PROCESSING OF NR

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•The coagulated latex can then be processed into the higher-grade, technically specified block rubbers such as SVR 3L or SVR CV or used to produce Ribbed Smoke Sheet grades.

•Naturally coagulated rubber (cup lump) is used in the manufacture of TSR10 and TSR20 grade rubbers.

•The processing of the rubber for these grades is a size reduction and cleaning process to remove contamination and prepare the material for the final stage of drying.

•The dried material is then baled and palletized for storage and shipment in various methods of transportation.

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• Rubber is always compounded with additives to satisfy the given application in terms of properties, cost, and processability.

• Compounding adds chemicals for vulcanization.

• Mainly used reinforcing filler used in NR is carbon black.

• Other additives include antioxidants , antiozonants coloring pigments, plasticizers and softening oils, blowing agents in the production of foamed rubber and mold-release compounds.

COMPOUNDING OF NR

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Temperature Range:•Low Temperature Usage:-20° to -60° F | -29° to -51°C•High Temperature Usage: Up to 175° F | Up to 80°C.

Properties Affected by Compounds:•Hardness•Modulus•High Resilience•High Damping•Low Compression Set•Low Creep/Relaxation•Cross Link Density 14

• NR Composites and Nano composites based on Conventional Fillers:

i. Reinforced with Carbon Blackii. Reinforced with Silicaiii. Based on Carbon Nanotubesiv. Based on Graphene

• NR Composites and Nano composites Based on Natural Fillers:

i. Fiber-Reinforcedii. Starch-Reinforced iii. Reinforced with Natural Mineral Fillers

NR COMPOSITES

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• NR Composites and Nano composites Based on Metal or Metallic Compound Fillers

i. Metal nanoparticles and metallic compound powders are used to strengthen the polymers, and improve their thermal stability and gas barrier properties.

ii. NR is often reinforced with various kinds of metal nanoparticles and metallic compound powder.

• NR Composites and Nano composites Based on Hybrid Fillers

i. NR composites filled with hybrid fillers possess outstanding mechanical properties that are not caused by only one filler. 16

NR COMPOSITES AND ITS PROPERTIES

GLASS FIBERS BASED NR:

•Glass fibers have high tensile strength, low cost, high chemical resistance and excellent insulating properties.

•The disadvantages are relatively low tensile modulus and high density, high hardness, sensitivity to abrasion during handling which tends to decrease its tensile strength, relatively low fatigue resistance.

•Fiber-reinforced NR composites are manufactured by various processes, the most common being extrusion, injection molding and compression molding. 17

• E-glass fiber has better tensile properties than A-glass fiber.

• E-glass/NR composites will show better tensile properties than A-glass/NR composites.

• Increase in fiber content leads to an increase in the strength and modulus of a fiber reinforced polymer matrix composite.

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•Uses of NR in hoses.•Footwear,Batteryboxes,Foammattresses,Balloons,toys.•NR used in soil stabilization, in vibration absorption and in road making.•Catheters and surgical gloves•Consumer products (like golf or football balls and other recreational and sports goods, erasers, footwear).•Non-tyre rubber items include industrial products transmission and elevator belts, hoses and tubes, industrial lining, and bridge bearings.•Heavy Equipment Industry(like Shock mounts,Vibration isolators,Gaskets,Seals,Rolls,Hose and tubing).

APPLICATION OF NR COMPOSITES

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