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NATURAL AND SYNTHETIC RUBBER, Neoprene, SBS Rubber, ❖ Excellent…

- - - - A natural polymer of isoprene (2-Methyl -1, 3 – Butadiene).
        
        Also known as Cis-polyisoprene.
        
        Cis-polyisoprene does not have a straight chain but has a coiled structureso that it gets elastic property.
  - - - The preferred method of recovering rubber
        from latex : Coagulation
        
        Coagulation : adding an acid such as formic acid (HCOOH); coagulation takes about 12 hours.
        
        Vulcanisation process
        
        Vulcanization (curing, cross-linking) is one of the most important
        processes for most of rubber technologies.
        
        Vulcanization is a cross linking process in which individual molecules of rubber (polymer) are converted into a three dimensional network of interconnected polymer chains through chemical cross links.
        
        This crosslinking produces a net-like structure that gives a more stable elasticity than the purely electrostatic nature of the pre-vulcanisation bonds.
        
        Sulfur as vulcanizing agent has a limitation. The elastomers must contain chemical unsaturation (C=C double bonds) for sulfur cross linking.
        
        Determines the extent of hardness or
        toughness of the cured rubber.
- - - - ➢ Thermoplastic polymer that possesses the properties of a rubber.
      - ➢ TPEs are processed like thermoplastics, but their applications are those of an elastomer.
      - ➢ The benefit of using TPE is the ability to stretch to moderate elongations and return to its near original shape, creating a longer life and better physical range than other materials.
      - ➢ No tires of TPE
        
        Example of TPE:
        -Thermolast, Hipex
        -Copec For Tec E
        -Santoprene
      - ➢ Shoe soles, athletic footwear, automotive components such as fender extensions and corner panels, insulation coating for electrical wire, tubing for medical applications, conveyor belts, sheet and film stock.
- - - - ❖ Synthetic rubber (trans-polyisoprene) was obtained by the free radical polymerization of isoprene.
      - ❖ The rubber so formed has all trans- Configuration.
      - ❖ As a result of this, synthetic rubber has a highly regular zig-zag chain which cannot be stretched.