Polyvinyl alcohol (PVA) is a synthetic polymer belonging to the family of polyvinyl esters. It is a water-soluble resin that is primarily used as a water-soluble film in various applications. The type of PVA can vary based on its degree of polymerization and degree of hydrolysis.
- Degree of Polymerization (DP): The degree of polymerization refers to the average number of monomer units (vinyl alcohol monomers) linked together in the polymer chain. Higher DP values indicate longer polymer chains. PVA can have various DP values, typically ranging from hundreds to several thousand.
- Degree of Hydrolysis (DH): The degree of hydrolysis is a measure of the extent to which the acetate groups on the polyvinyl acetate precursor have been converted to hydroxyl groups. This process converts polyvinyl acetate (PVAc) into polyvinyl alcohol (PVA). DH is expressed as a percentage, where 100% DH means all acetate groups have been hydrolyzed to hydroxyl groups, resulting in fully hydrolyzed PVA. Partially hydrolyzed PVAs with DH values below 100% are also available.
The specific type of PVA is often denoted using these two parameters. For example:
- PVA 1788: PVA with a relatively high degree of polymerization (usually DP around 1700-1900) and high degree of hydrolysis (typically around 98-99%).
- PVA 217: PVA with a lower degree of polymerization (DP around 200) and a lower degree of hydrolysis (around 87-89%).
The choice of PVA type depends on the intended application, as different types of PVA have varying properties, such as solubility, film-forming characteristics, and mechanical strength. PVA is used in diverse applications, including adhesives, coatings, packaging films, textiles, paper coatings, and more.