An extended duration operation for solid hollow fiber membrane-based cooling crystallization

It was recently demonstrated that the technique of solid hollow fiber membrane-based cooling crystallization can be employed to achieve continuous polymer precipitation from a solution and subsequent polymer coating/encapsulation of sub-micrometer particles/drug crystals as well as nanoparticles in suspension. In this technique, there is no need for high pressure as in supercritical solvent-based anti-solvent crystallization; further, there is easy scale-up and production of free-flowing polymer-coated particles. There is a concern however, whether this crystallization method can be applied for an extended duration since the earlier studies were run for only about 10 min. In this work, the duration of the cooling crystallization-based coating process has been greatly extended from 10 min to 60 min and 120 min. Eudragit RL 100 was chosen as the coating polymer and Cosmo 55 (550 nm silica particles) was the host for the coating process in an acetone solution. Scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) were employed to characterize the coated samples. The results showed that the solid hollow fiber membrane-based cooling crystallization performed successfully as a continuous crystallizer during extended time running operation. Characterization of the products by SEM and TGA indicated a stable product consistent with a uniform spherical shape. The coating thickness of the samples tended to be essentially identical for the extended-duration coating process as long as solvent loss by volatilization and uneven distribution of host particles in the feed solution-suspension was kept to a minimum.