PVA 88 - Polyvinyl Alcohol — Frequently Asked Questions

Because the residual acetate groups disrupt crystallinity. A fully hydrolysed chain is a regular sequence of hydroxyls that hydrogen-bond strongly to neighbouring chains, packing into crystalline regions water cannot penetrate at room temperature. Leaving about one acetate in eight prevents that close packing, so water gets between the chains and the polymer dissolves cold.

It is the film. A pod must hold its contents securely in the pack and then dissolve completely and quickly in cold or warm wash water, leaving no residue on fabric. Cold water solubility is the defining requirement, and the partially hydrolysed grade provides it where the fully hydrolysed grade would not dissolve until the wash was nearly over.

Its partly hydrophobic acetate segments anchor onto the growing polymer particle while the hydroxyl-rich segments extend into the water phase, providing a steric barrier that keeps particles from coalescing. The 88 percent grade is used because it has enough acetate to adsorb onto the particle and enough hydroxyl to stay water-soluble.

Disperse it into cold water with agitation first, then heat if required, rather than adding it to hot water. Added to hot water it forms lumps with a gelled skin that resists further hydration, and those lumps never fully dissolve. Even for the cold-soluble grade, slow addition to well-agitated water is essential.