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-   -   Chemical Resistance of Polyethylene (http://www.physicsforums.com/showthread.php?t=279539)

shinigami66 Dec14-08 01:11 AM

Chemical Resistance of Polyethylene
 
I'm just wondering, what gives polyethylene its property chemical resistance? Does it have something to do with the electronegativies between the C-H bonds and most chemicals are unable to break the bonds between C-H, therefore unlikely to take part in a chemical reaction?
Thank you

Edit: I think I'm asking too much questions...
hmm but how does chlorine atoms in PVC polymer prevents fire? And also how does the bonding make it water resistant???
This is like a research task and I couldn't think why these properties can be related in terms of bonding :(
Thank you so much!

wowolaf Dec15-08 02:10 PM

Re: Chemical Resistance of Polyethylene
 
There are a number of reasons polyethylene has strong chemical resistance. Most of these stem from polyethylene's makeup - it's a long, long chain composed entirely of carbon and hydrogen.

Because of this, it isn't a very polar substance, so there's nothing on the molecule that interacts readily with water (a very polar molecule). Being aliphatic, it's also largely unaffected by interactions with aromatic solvents. It's lacking in any functional groups (esters, amides, etc.) that would be susceptible to nucelophilic attack or oxidation, so those sorts of reactions are out too.

Basically, it all boils down to the simplicity of polyethylene's construction. If you've taken ochem, you probably know that C-H bonds are fairly difficult to break (hydrogen is a terrible leaving group), and that's all polyethylene is.

I'm at work now, so I haven't confirmed this, but off the top of my head, I'd guess, simply, the chlorine in PVC prevents fire by reacting with the many radicals present in flame and stopping the exothermic reactions from propagating.

If you have any questions, I can try to clarify later; in the meantime, a google search on halogenated flame retardants might shed on some light on the mechanics behind your PVC question.


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