Question

5. A. What characteristics describe a traditional elastomer? Be sure to consider transition temperatures, molecular configurations, and conformational morphology. (6 pts) B. How does rubber elasticity differ from elasticity in thermoplastics such as polyethylene or polystyrene? Be sure to describe the molecular-level origin of elasticity for both rubbers and thermoplastics (1.e. what produces the restoring force when strained)? (6 pts) C. The theoretical stress-strain relationship for rubber elasticity is described by o=nRT1a-a) where o is stress, RT is the gas constant times absolute temperature, n is a material constant, and is the extension ratio, i.e. length/initial length (LIL). What happens to the Young's modulus as the temperature increases? This is not typical for other materials, so why does this happen for elastomers? (Hint: Think how temperature affects Gibbs free energy.) (4 pts) D. Describe the structure of a thermoplastic elastomer. How does it differ from traditional elastomers? (4 pts)

Answer 1

Answer (5) (A).

(i) Elastomers composed of long chain molecules which are cross linked each other. Sometimes called rubber or rubbery materials. They are  usually thermosets (requiring vulcanisation) and also thermoplastic.

(ii) It shows a large  elastic elongation power of 200% and also can be stretched then suddenly goes back to normal length once we release the load.

(iii) Elastomers shows amorphous polymeric nature with segmental motion if temperature raised above glass transition temperature.So it can use as a seals, adhesives, tires, springs and etc.

(iv) The cross-linking agents are essential for creating the crosslinks to interconnect at molecular level thus enlightening the strength and elasticity.Thus the conventional elastomers shows high molecular weight with low elasticity and strength.

(v) Through preparation, long chain molecules and chemically attach each other, establishing new connections and converting the material as a elastic solid.

Answer (5) (D). Thermoplastic elastomers (TPE), sometimes mentioned as thermoplastic rubbers, are a TYPE of copolymers or a mixture of polymers (generally a plastic and a rubber) that comprised of materials with both thermoplastic and elastomeric properties.