Raw material from rubber tree (Hevea brasiliensis) is tapped every second day for its sap, known as latex, by making slanting cuts in the bark of the

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2 Rubbers/Elastomers

3 Raw material from rubber tree (Hevea brasiliensis) is tapped every second day for its sap, known as latex, by making slanting cuts in the bark of the tree. Latex is collected and acetic acid is added to it so as to precipitate out the rubber, which then hardens/coagulates. After being washed and dried, rubber is cured in special smokehouses to protect it against microbial attack. Natural Rubber (Polymer of isoprene-2-methyl-1,3- butadiene)

4 Vulcanization

5 Property Raw Rubber Vulcanized Rubber Elasticity Very high Low, depending on % S Tensile Strength 200 kg/cm kg/cm 2 Chemical resistance Very poor Higher Durability Less Higher Quality Inherent Can be controlled by vulcanization

6 Preparation, Properties and Uses of Commercial Rubbers

7 Buna-S Rubber/ Cold Rubber Copolymerization of butadiene & styrene carried out at 5 o C Good and tough mechanical properties Easily attacked by oxidizing agents, mainly ozone, organic solvents Uses: Manufacture of tyres, insulating wires and cables, adhesives

8 Polyurethane rubber/isocyanate rubber Ethylene glycol polymerizes with ethylene diisocyanate to form polyurethane rubber. Highly resistant to oxidation Resistant to organic solvents, attacked by acids and alkali Uses: surface coatings and manufacture of foams and fibers

9 Conducting Polymers Polymers are poor conductors of electricity, due to non-availability of large number of free electrons Today, they are synthesized at par to conductivities of metallic conductors Conductivity increases by decreasing the energy band gap Amount of energy needed to promote an electron from valence to empty band (conduction band) Polymers have large band gaps, with careful design of chemical structure of polymeric backbone band gap = 0.5 to 1eV

10 Conditions Polymer should consist of alternating single and double bonds called conjugated double bonds Polymer matrix has to be disturbed Either by removing electrons from them, Or inserting electrons into the material. The process is known as doping By doping with electron donor like alkali-metal ion or electron acceptor like Iodine & polymers turn conductive materials

11 Iodine molecule attracts an electron from polyacetylene chain and becomes I 3 - Polyacetylene molecule, now positively charged, is termed a radical cation, or polaron Lonely electron of the double bond, from which an electron was removed, can move easily. As a consequence, double bond successively moves along the molecule Conducting Polymers

12 Smart Materials Battery technology Conducting Polymers Telecommunication Aerospace

13 Self healing polymers Inspired from biological systems Wound healing Inherent ability of polymers to repair damage caused by mechanical usage over time Terminator Polymers Chemistry World posted a video of the product in action, showing someone cutting a piece of the polymer in two with a scalpel, pressing the pieces back together and leaving it on a table for two hours at room temperature. The person is unable to pull the material apart with their hands upon returning. This is the next generation breakthrough in polymers.

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15 Healing Process: A propagating crack ruptures the microcapsules, releasing the healing agent into the crack plane by capillary action. Polymerization is initiated by contact with the embedded catalyst or initiator, bonding the crack faces, and restoring structural continuity. At times, additional external stimuli such as heat or UV-radiation is required for the healing to occur.

16 Applications Nissan Motor Co. Ltd has commercialized world s first self-healing clear coat for car surfaces-trade name of this product is Scratch Guard Coat Self healing concretes in progress Self-healing materials are now used as composites in aircrafts.

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