Effect of heat treatment on pervaporation separation of aqueous salt solution using hybrid PVA/MA/TEOS membrane

• Heating favours completion of crosslinking reaction among PVA, MA and TEOS.
• Increasing heating temperature/time reduces the swelling and water uptake.
• Increasing heating temperature/time reduced water flux but increased salt rejection.
• There is a strong correlation between water flux and FFV of the hybrid membrane.
• Both NaCl and water diffusivity increased exponentially with decreasing 1/FFV.

Heat treatment is believed to be an important step in controlling the morphology and properties of polymer based membranes. In this study, hybrid organic–inorganic membrane based on poly(vinyl alcohol) (PVA), maleic acid (MA) and tetraethyl orthosilicate (TEOS) was synthesised via a sol–gel route. The effects of heating temperature and heating time on pervaporation separation performance of aqueous salt solution were studied in relation to swelling and hydrophilic properties, the free volume, salt transport properties, and water diffusivity of the membrane. The free volume of the hybrid membrane under different heat treatment conditions were well correlated with the pervaporation testing results. With increasing heating temperature or time, the fractional free volume of the hybrid membrane was reduced due to a more compact structure by crosslinking among PVA, MA and TEOS. As a result, the water flux decreased and the salt rejection increased. The salt transport properties followed a similar trend as the water uptake, indicating the hydrated NaCl was solvated by water in the membrane phase.