I have seen on multiple chemical vendors' websites that partially hydrolyzed polyvinyl alcohol can be dissolved in water at room temperature, whereas fully hydrolyzed PVA needs to be dissolved at around 90C. What is the reason for this? I use PVA as a binder in aqueous ceramic slurries, and want to know how PVA behaves as a binder depending on the degree of hydrolysis?
I see. Often times, PEG is used as a plasticizer in slurries with pva. I imagine this also disrupts crystallization. Thanks for the help
In fact, one needs to heat incompletely hydrolysed PVA (88% saponification degree) to 90 - 100°C, too, to dissolve it at 5% concentration in water. This solution may be stored at room temerature for a long time, though PVA chains have a tendency to self-associate : it was shown by Sakurada et al. in 1950-ties. The residual acetate groups decrease this association by decreasing regularity of the chain structure. Besides, the acetates may possibly help to adhesion of the polymer to ceramics, due to hydrogen bond formation C=O ...HO-ceramics, similar to polyvinylacetate glues.
It's simply a case of H-bonding interactions. In fully hydrolysed PVAc the inter molecular H bonding is so 'extreme' it results in insolubility. partially hydrolysed PVAc (to some optimum degree) balances the H bonding with the desired aqueous solubility. There is extensive literature on this topic.
Actually, there is no difference in solubility per se but the RATE of dissolution of fully hydrolyzed PVA is slower due to the higher degree of crystallinity of this material.
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