Plasticization of poly(vinyl butyral) by water: Glass transition temperature and mechanical properties

The effect of plasticization by water on the mechanical properties of additive‐free poly(vinyl butyral) (PVB) was investigated. PVB is hygroscopic and the amount of absorbed water was measured in various environmental conditions. Two kinds of interactions with hydrophilic sites was demonstrated. The thermal and thermomechanical studies (differential scanning calorimetry and dynamic mechanical thermal analysis) showed that water decreases the glass transition temperature thus acting as a plasticizer. This gives the material larger deformation capability and increased toughness. Surprisingly, the modulus remains high and this was explained by a structure consisting in two phases with different levels of plasticization, reflected by a double peak of relaxation associated to multiple phases with different glass transition temperature. Atomic force microscopy measurements on samples with high level of hydration shows evidence of nanometric hydrated domains acting as an elastomeric phase and thus inducing toughening of the material.