# Why does a 1:1 mixture of Polyvinyl Alcohol (PVA):H2O decompose/carbonize during heating?

I bought a powder of Polyvinyl Alcohol (PVA from Sigma Aldrich). I mixed the powder with water in a mixture 1:1 to place a droplet on a hot plate. To figure out the melting temperature of the PVA, I heated it, meanwhile the water should be evaporated. According to Wikipedia or other chemical databases, partially hydrolysed grades of PVA melt between $150-180\ ^\circ C$ .

My questions:

1. Why did my mixture decomposed/carbonized above $120\ ^\circ C$ (its color changed from transparent to brown, so I guess it decomposed)?
2. The mixture did not melt between $150-180\ ^\circ C$ . Why?
3. Did I make any general mistake at all?