Use of Batch Mixing To Investigate the Continuous Solvent-Free Mechanical Synthesis of OLED Materials by Twin-Screw Extrusion (TSE)

Mechanochemical synthesis has the potential to change the way in which chemistry is conducted, particularly with regard to removing or dramatically reducing the need for solvents. Recently, it has been demonstrated that mechanochemistry can be carried out continuously and on large scale through the use of twin-screw extrusion (TSE). TSE has successfully been applied to the synthesis of co-crystals, Metal Organic Frameworks (MOFs), Deep Eutectic Solvents (DESs), metal complexes and organic condensation reactions. However, whilst TSE provides a route for mechanochemical synthesis to be developed into a continuous, high volume manufacturing process, little is currently understood about how to best optimise the various process parameters involved. Herein, we investigate the use of a batch mixer that has been previously used in polymer processing, to optimise mechanochemical reactions performed by extrusion. In particular, reactions between 8-hydroxyquinoline (Hq) and metal acetate salts of zinc or aluminium to give quinolinate complexes Znq2 and Alq3, which are of interest for organic light emitting diode (OLED) applications, have been investigated. The manner in which the progress of the reaction correlates with the machine torque, temperature and specific mechanical energy (SME) imparted by the batch mixer have been elucidated. Significantly, this knowledge enabled optimisation of the mechanochemical reactions by TSE through the key parameters of screw speed, feed rate, temperature and particle size.