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HDPE chemical storage bottles 1

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kclim

Materials
Jul 2, 2002
168
AU
Hello,

Does anyone know if HDPE/LDPE has a finite lifetime? Reason we had a small HDPE bottle of methanol which suffered brittle fracture during use (kinda snapped apart in the users hands). The bottle had been used for at least 6 years. We've since replaced the bottles with Nalgene LDPE ones.

From what I can gather, both HDPE and LDPE are compatible with methanol, and can last indefinitely in the right situations. UV and oxidation are the biggest threats to the integrity of the plastic.

The LDPE is softer, so perhaps if it does fail, it won't shatter as did the HDPE bottle?

Any comments are appreciated
 
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You considered one aspect of material damage, i.e. environmental damage. How about mechanical damage? Could the HDPE have fatigued? Perhaps combined with environmental damage?

Regards,

Cory

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HDPE is very susceptible to Enviromental Stress Cracking (ESC) and is known to embrittle over time. LDPE is less susceptible

I would think that the bottles are so cheap that you could afford to replace them, say annually.

Regards,

Peter P
 
ESC may be defined as the accelaeration of stress cracking by contact with a fluid, without chemical degradation. Tehe mechanism is purely phisycqal. The interactions between the fluid , the stress, and the polymer include local yielding, fluid absortion, plasticisation, craze intiation, crack gowth, and fracture, without irreversible chemical change.

A very common cause of plastics product failure is the me"mechanical degradation" induced by modest levels of stress over long periods of time. Fluid accelarates thr mechanism.

polymer bracnhing, as you can find in LDPE, increase ESC resistance as well as molecular weight

 
Thank you all for your responses. My querry was more out of interest rather than a pressing safety investigation. We probably should replace the bottles every year or so.

ESC seems to be the failure mechanism... How can you tell if it is fatigue related? Would you expect to see striations on the fracture surface, as you go with metals?
 
kclim,

Yes, it is possible to see step-growth patterns on the fracture surface.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
 
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