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Natural and Synthetic Rubber - Coggle Diagram
Natural and Synthetic Rubber
Introduction
Thermoset Elastomer(Thermoset Rubber)
Undergo a chemicall change during vulcanization to become permanently insoluble and infusible.
Crosslilinked rubber
Thermoplastic Elastomer (TPE)
Rubber
"Rubber" is originated from 'rub away' because it was used to 'rub away' pencil marks.
Latex (natural product harvested from the rubber tree.
Elastomer
Polymer that displays elastic properties.
Rubbery materials.
"Elastomer" derived from 'elastic polymer'.
Natural Rubber Harvesting and Processing (Vulcanisation)
Process stages
Molding
Extrusion
Calendering
Coating
Molding & Casting
Heating
Increased temp to speeds up vulcanisation process
C-5 bond replaces C-H bond linking chain
Mixing crude rubber with about 5-30% of sulphur + Addtives (activator, accelerator, coagulants, anti-oxidants, color pigments, etc.)
Improvisation by vulcanisation
Elasticity
Tear strength
Tensile strength
Abrasion resistance
Hardness
Insoluble in solvents
Thermoset Rubber
Trans-polyisopropene
Obtained free radical polymerization of isoprene
Trans-configuration
Highyly zig-zag chain - cannot be stretched
Neoprene
High tensile strength, resilence, oil and flame resistence, resistance to degration by oxygen and ozone
High cost limits
Produced by polymerization of chloroprene
Used in manufacture of hoses, stoppers, conveyor belts and insulator
SBS Rubber
Polubutadiene - rubbery
Polystyrene - tough hard plastics
Polystyrene chains tend to clump together - able to retain its shape after stretch
Hard rubber - shoes and threads
Nitrile rubber (BUNA-N)
Resistant to he action of petrol, lubricating oil and organic solvents
Used in making oil seals, hoses and tank linings
Obtained by copolymerization of 1,3 - butadiene and acrylonitrile (presence of peroxide catalyst)
Butyl Rubber
Excellent impermeability & good flexibility
Used in speaker, protective clothing & gas masks
Co-polymer of isobutylene and isopropene
Synthetic Rubber
Benefits
Creates longer life
Better Physical range
Ability to stretch and return to its original shape
Application
Shoe soles
Insulating coating for electrical wire
Conveyor belts
Film stock
Processed like thermoplastics
Examples
Kraton
Pibiflex
Thermolast
Hytrel
Possess properties of rubber
Differences
Vulcanised rubber
Insoluble in organic solvents & oxidising agents
High resistance to abrasion
Low water absorption capacity
Can be used over wide temperature
High wear & tear resistance
High tensile strength & high elasticity
Hard & non-sticky
Thermoset
Natural rubber
Low resistance to abrasion
Soluble in organic solvents
Large water absorption capacity
Can be used over a narrow temperature range
Low wear & tear resistance
Low tensile strength & low elasticity
Soft & Sticky
Thermoplastic
Natural Rubber and Latex
Recovering rubber from Latex
Coagulum is squeezed and reduced thickness
The sheets are dropped over wooden frames and dried
Coagulation (12 hours) by adding Formic Acid
Coagulated rubber on separation and drying gives crude rubber
Low tensile strength
Low elasticity
Soft, sticky & thermoplastics
Latex
Contains small amounts of proteins, lipids, HC and mineral substances.
Part of lipids & proteins is surrounded by rubbery particles
Colloid system having the rubber particles dispersed in water
Modification
Sedimentation
Water evaporation
Centrifugation
Electrodecantation
Natural rubber
Occurs naturally as a milky colloidal suspension
Does not have straight chain but has a coiled structure
Elastic HC polymer
Has elastic properties
Natural polymer of isopropene
Prepared from colloidal solution of rubbr in water