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Name: Nicklas
Status: student
Grade: 9-12
Country: Sweden
Date: N/A 


Question:
Why is plastic a good thermal insulator? Is this true of all polymers?



Replies:
Plastics, and most other polymers, are not good thermal conductors because the glassy structure of the polymer chains tend to disperse the motions of the constituent molecules. Good thermal conductors tend to get the molecules to all move in the same direction at the same time. That happens with crystalline substances (metals for example). Thermal conduction is a complicated subject, so this short answer is about all a format like NEWTON BBS can handle. You might do a web search on the term "thermal conductivity" for more information.

Vince Calder


Hi Nicklas,

In the simplest terms, thermal conductivity is functionally equivalent to electrical conductivity. Anything that doesn't conduct electricity as freely as metals do, air is one example, is considered a good thermal insulator. That's why double paned windows are good thermal insulators.

-Alex Viray


Nicklas,

Electrical conductivity is possible in plastics - in fact, my graduate thesis was in the production of electrically conductive polymers. However, such polymers have to be specially designed. In order for an organic polymer to be electrically conductive, the electrons within the polymer have to be mobile - they have to be able to move across the polymer chain, and be able to "jump" across chains. This can be achieved by producing polymers that have carbon-carbon double bonds. If the double bonds are conjugated (separated only be one single bond), the electrons can become delocalized (they do not stay around just one or two carbons) - and as such the electrons become mobile. This flow of electrons is current.

In the normal or average plastic, the polymer is made up of mostly single carbon-carbon bonds where the electrons remain around the same carbons. The electrons are not mobile. As such, there is no good mechanism to allow the flow of electrons or current.

Greg (Roberto Gregorius)
Canisius College



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