Engineering Science 1021A/B Lecture Notes - Lecture 31: Viscoelasticity, Thermoplastic, Vulcanization
17 May 2018
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Department
Professor
Common elastomers are made from highly coiled. Linear polymer chains
•
•
In their natural condition, elastomers behave in a similar manner to
thermoplastics (viscoelastic)
Applying a force causes the chains to uncoil and stretch, but also slide
past each other causing permanent deformation
This can be prevented by cross-linking the polymers chains
§
○
•
The process of vulcanization uses sulfur atoms to form cross-links between
chains
○
•
As more sulfur is added, more cross-links are formed and the elastomers
becomes more rigid
○
•
Vulcanized rubber is not recyclable (into new rubber)•
All deformation is elastomers is recoverable•
Thermoplastic Elastomers
Special class of elastomers•
Combination of hard and soft mers (a block copolymer)
○
Typically styrene "ends" and butadiene or isoprene "middles"
○
•
On cooling, the hard zones prevent chain sliding, but still allow elastomeric
middles to uncoil
•
They do not employ covalent cross-links to maintain their shape•
Are recyclable•
Elastomers
Common elastomers are made from highly coiled. Linear polymer chains•
•
In their natural condition, elastomers behave in a similar manner to
thermoplastics (viscoelastic)
Applying a force causes the chains to uncoil and stretch, but also slide
past each other causing permanent deformation
This can be prevented by cross-linking the polymers chains
§
○
•
The process of vulcanization uses sulfur atoms to form cross-links between
chains
○
•
As more sulfur is added, more cross-links are formed and the elastomers
becomes more rigid
○
•
Vulcanized rubber is not recyclable (into new rubber)•
All deformation is elastomers is recoverable•
Thermoplastic Elastomers
Special class of elastomers•
Combination of hard and soft mers (a block copolymer)
○
Typically styrene "ends" and butadiene or isoprene "middles"
○
•
On cooling, the hard zones prevent chain sliding, but still allow elastomeric
middles to uncoil
•
They do not employ covalent cross-links to maintain their shape•
Are recyclable•
Elastomers
