| MadSci Network: Chemistry |
Hi Awais,
Polyvinyl alcohol has a hydroxyl side chain while polyvinyl acetate has
an acetate side chain. See the Wikipedia pages below for structure
shorthands. Because hydroxyl groups are more polar, PVOH is more
hydrophilic and soluble in water than PVOAc.
Because PVOH is so water-soluble, it is used in things like the casing
for dishwasher detergent “pods.” When the pods are exposed to water in
the dishwasher, the PVOH readily dissolves, releasing the detergent
contents. It is also used as a thickener for water-based products.
The articles below also summarize some key properties of both polymers.
PVOH’s properties depend strongly on the humidity and water content.
Polyvinyl acetate (PVOAc) is the more common polymer found in glues
such as wood & paper glue. It is much less soluble in water, and forms
an emulsion rather than a solution in water. Though PVOH is also used
as an adhesive in some applications, I think those generally call for a
less permanent adhesive. PVOAc is actually used as a raw material in
the manufacture of PVOH.
Of the two polymers, PVOH has the higher melting point and glass
transition temperature. The melting point of PVOH, about 200 degrees C,
is actually higher than its thermal degradation temperature, ~200 degC.
Links:
http://cameo.mfa.org
/wiki/Polyvinyl_acetate
http://cameo.mfa.org
/wiki/Polyvinyl_alcohol
http://www.p
olymerprocessing.com/polymers/PVAC.html
http://www.p
olymerprocessing.com/polymers/PVOH.html
https://en.m.wikipedia.org/wiki/Polyvinyl_alcohol
https://en.m.wikipedia.org/wiki/Polyvinyl_acetate
-Alex Tobias
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