# Why does clear vinyl airline tubing turn white?



## ObiQuiet (Oct 9, 2009)

Do I just have a cheap variety, or is there some way to keep it clear and invisible?

Thank you,
-ObiQuiet


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## TarantulaGuy (Apr 15, 2009)

Are you running CO2 through it?


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## ObiQuiet (Oct 9, 2009)

Thanks for the response! 

No, no CO2. It's just a short piece sitting in the tank holding a plant in place. 

I've seen it happen when I boiled the same kind of tubing to sterilize it, but that's different.


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## grak70 (Jan 5, 2010)

Two mechanisms:

- CO2 reacts with the resin or plasticizer, forming a skin of higher Tg plastic that crystallizes.
- By diffusion (heat, soaking, etc), the plasticizer leaves the resin causing the base material to partially crystallize. Heat and stress by themselves can also crystallize plastics.

Either way, the crystallites that form in the plastic are opaque to light, making the tubing appear milky. You'll also notice that it's more brittle which is why plasticizers are added in the first place.


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## ObiQuiet (Oct 9, 2009)

Ah! That makes a lot of sense. Is there a kind/brand of tubing which is more stable in this regard?


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## grak70 (Jan 5, 2010)

This black stuff:

http://www.marinedepot.com/ps_viewi..._campaign=mdcsegooglebase2&utm_content=CO1511

I don't know what it's made of. Maybe polyurethane? Also, the brand name Tygon reportedly works well.


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