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Author Topic: Reactivity of HDPE and PVC  (Read 4535 times)

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Doze

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Reactivity of HDPE and PVC
« on: October 24, 2011, 11:58:28 AM »

Hello Community,

I'm researching on water and waste water piping. Apparently according to   http://www.dynalabcorp.com/files/Physical%20Properties.pdf 1) HDPE is far more resistant to Ketones, Esters and Aldehydes?
2) HDPE absorbs a little less water than PVC?

1) Is this because of the non polar C-H bond in HDPE, or is it because of it crystallinity?
2) Is this because the PVC has a partial negative chlorine side group, and that attracts the Hydrogen?

Also unlike PVC, HDPE is weak to oxidizing agents (in the water disinfectants) such as Fluorine and can cause chain scissions in the polymer like in this picture (on the right):

That's bad to use then I guess

Why does it oxidize    relating to the chemical structure of HDPE?

Help would be much appreciated, thank you.
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marquis

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Re: Reactivity of HDPE and PVC
« Reply #1 on: October 27, 2011, 04:42:35 AM »

In regard to 1-Resistance to Ketones, etc.- HDPE is more resistant to ketones, etc.  This is because PVC is soluble (at least to some extent) in ketone, aldehydes, etc.  Cyclohexanone and THF are two common solvents used to dissolve PVC for lab testing.

As to 2- PVC doesn't absorb much in the way of water (my experience is with medical PVC applications, not waste water applications).  Then again HDPE won't either.  I wonder if it's a difference between absorbing  little water or very little water.  However, many PVC compounds include plasticizers, which may absorb water.

PVC degrades by forming hydrochloric acid and conjugated alternating single and double carbon bonds on the polymer backbone.  The free hydrochloric acid speeds up the dehydrohalogenation, generating more free HCl, which further speeds up the degradation, etc.  This is why PVC needs stabilizers and is prone to oxidation.

Hope this helps.
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