Polyvinyl alcohol is widely used in various industries due to its many excellent properties, for example:
I. Physical Properties
1. Solubility: Polyvinyl alcohol powder is soluble in water. Polyvinyl alcohol resin (PVA) with a degree of hydrolysis less than 95% can dissolve in water at room temperature, while polyvinyl alcohol resin (PVA) with a degree of hydrolysis greater than 99.5% can only dissolve in hot water above 95℃.
2. Thermal Stability: Polyvinyl alcohol softens when heated. Below 40℃, there is no significant change. Its glass transition temperature is 75~85℃. Heating above 100℃ causes it to slowly change color and become brittle. Above 160℃, prolonged heating will gradually cause it to color, dehydrate and etherify, losing its solubility. Above 220℃, it decomposes, producing water, acetic acid, acetaldehyde, and butenal. Above 250℃, it becomes a polymer containing conjugated double bonds.
3. Chemical Resistance: PVA is almost unaffected by weak acids, weak alkalis, or organic solvents, and has high oil resistance.
4. Storage Stability: PVA is a low-viscosity polymer, and its aqueous solution is very stable at room temperature. The aqueous solution will not deteriorate during storage.
5. Film-forming Properties: Due to the high adhesion between PVA molecules, PVA easily forms films. The resulting films are colorless and transparent, possess good mechanical strength, have a smooth, non-sticky surface, and good solvent resistance. The molecular films have good light transmittance, high moisture permeability, are non-charged, do not attract dust, and have good printability.
II. Chemical Properties
PVA can be considered a linear polymer with secondary hydroxyl groups. The hydroxyl groups in the molecule have high reactivity and can undergo typical low-alcohol chemical reactions, such as esterification, etherification, and acetalization. It can also react with many inorganic or organic compounds.
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