Effect of the hydroxyl content and molecular weight of polyvinyl butyral on tape properties

Despite the desire to replace organics with water in tape casting systems, thick films often use solvent in order to speed up drying rates. Polyvinyl butyral having hydroxyl contents ranging between 11 and 20% and molecular weights between 40,000 and 120,000 g/mol was plasticized with butyl benzyl phthalate at solids contents between 62 and 75 vol.% La0.5Sr0.5CoO3 once the toluene/ethanol solvent was evaporated. High-hydroxyl content was more important than high molecular weight in increasing the Young's modulus, yield strength, and tensile strength of the tapes at room temperature. Annealing tapes at low temperatures (65 °C) for short times (10 min) relaxed stresses and tended to equalize modulus, strength, and ductility. Low hydroxyl content and low molecular weight enhanced particle packing, which resulted in cracking as tape thickness increased from 0.2 mm to 0.7 mm at higher solids contents. Crack-free tapes were made at all solids contents when the hydroxyl content was greater than 18%. Lower molecular weight at high-hydroxyl content, along with high solids content, was important for minimizing the amount of solvent used.