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Author Question: Explain why copolymers of ethylene and propylene can be elastomers when the pure polyethylene and ... (Read 75 times)

bb

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on: Aug 19, 2018
Explain why copolymers of ethylene and propylene can be elastomers when the pure polyethylene and pure polypropylene are not elastomeric. Discuss whether you would expect a blend (instead of a copolymer) of polyethylene and polypropylene to be elastomeric.
 
  What will be an ideal response?

Question 2

Explain why a rubber band fails after having been wrapped very tightly around an object for several months.
 
  What will be an ideal response?


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ilianabrrr

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Reply #1 on: Aug 19, 2018
Answer to Question 1

The homopolymers of ethylene and propylene are nonelastomeric because they both have high crystallinity. Even low molecular weight polyethylene has considerable crystalline content. However, when the materials are copolymerized, the ability of the polymers to pack together tightly is significantly reduced when compared with the homopolymers.

Answer to Question 2

The elasticity of the chains decreases as they are in constant tension. This consistency in tension causes creep to happen within the material and the elastic ability of the original material degrades and often becomes brittle and breaks.


bb

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Reply 2 on: Aug 19, 2018
Gracias!

xiaomengxian

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Reply 3 on: Yesterday
Wow, this really help

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