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:star: Natural and Synthetic Rubber :star:, photo_2024-04-23_23-23-04,…
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Natural and Synthetic Rubber
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Synthetic Rubber
Thermoplastic Elastomer (TPE)
Benefits
Ability to stretch to moderate elongation and return to its near original shape
Creating a longer life
Better physical range than other materials
Uses
Shoe soles
Athletic footwear
Automotive components (corner panels)
insulation coating (electrical wire)
Example
Thermoplast
Hipex
Dryflex
Mediprene
Kraton
Processed like thermoplastics but their applications are those of an elastomer
Thermoset Rubber
Butyl Rubber (IIR)
IIR - isobutylene isoprene rubber
Produced by polymerization of 98% isobutylene, 2% of isoprene
Excellent impermeability, good flexibility
Rubber stopper (medicine vials & bottles)
Chewing gum
Insulating glass window
SBS Rubber (Poly(styrene-butadiene-styrene)
Hard rubber that is used to make:
sole of shoes
tire treads
product where durability is important
Tough hard plastic that gives SBS its durability
When one styrene group of SBS molecule joins one clump, other polystyrene chain of the same SBS molecule join another clumps, the different clump become tied together with rubbery polybutadiene.
Trans-polyisoprene
Obtained by the free radical polymerization of isoprene
The rubber so formed has all trans- Configuration
So, synthetic rubber has a highly regular zig-zag chain (cannot be stretched)
Neoprene (Polychloroprene)
Produced by polymerization chloropene
High tensile strength, resilience, oil and flame resistance, & resistance to degradation by oxygen / ozone, however its high cost limits
Used in manufacture of hoses, gasket, shoe steel, stoppers
Nitrile rubber (BUNA-N)
Obtained by copolymerization of 1,3- Butadiene & acrylonitrile in presence of peroxide as catalyst
Resistant to the action of petrol, lubricating oil & organic solvents
Used in making oil seals, hoses, tank linings etc
Natural Rubber
An elastic hydrocarbon polymer that occurs as a milky colloidal suspension in the sap of the rubber tree.
A natural polymer of isoprene (2-methyl-1,3-butadiene)
Uses
Gloves.
Latex modified to have higher dry rubber content.
Foam rubber
Glues
Structure - coiled, where it gets elastic properties.
Modification method
sedimentation
water evaporation thickening
centrifugation
electrodecantation
Dry rubber content is increased in latex and impurities and non-rubbery additives are removed from rubber
Vulcanisation Process
cross linking process in which individual molecules of rubber are converted into a three dimensional network of interconnected polymer chains through chemical cross links.
Sulphur is the original crosslinking agent
Elastomers must contain chemical unsaturation for sulfur cross linking.
Amount of sulphur used determines the extent of hardness of the cured rubber.
The addition of other chemicals and fillers can enhance the eventual properties of the finished rubber item
Properties of rubber improved by vulcanization
hardness
tensile strength
elasticitiy
tear strength
abrasion resistance
resistance to solvents
Differences
Vulcanized & Natural Rubber
Natural & Synthetic Rubber
