Solventless polymer coating of microparticles

Solventless coating technologies have recently emerged to improve upon the processing inefficiencies and practical limitations of solvent-based polymer film coating. The purpose of this study was to introduce a dry-coating methodology by which microparticles can be coated with polymers without the use of solvents, plasticizers, or heat treatments and is applicable to particles including those <100 μm, noted as major improvements upon solvent-based and current dry-polymer coating technologies. Using a vibratory mixing device, the dry-polymer-coating method developed here first forms an ordered mixture consisting of a particulate substrate, ascorbic acid, ranging in size from 50 μm to 500 μm coated with a micronized polymer, polyethylene (PE) wax. Surface energy measurements accurately predicted that PE wax particles would strongly adhere to ascorbic acid through van der Waals induced attractive forces indicating a simple approach for predicting substrate–polymer compatibility. Due to vibration, subsequent particle–particle collisions between constituents of the ordered mixture deform the polymer layer into a continuous film resulting in encapsulation of the ascorbic acid. Discrete and continuous polymer coating could be discriminated based on SEM imaging, dissolution testing, or dispersive particle size measurements. Furthermore, polymer coatings were able to prolong the dissolution time of ascorbic acid from seconds to hours depending on the coating thickness. This novel dry-polymer-coating technique, operating in dry state without solvents, plasticizers, or heat treatments while also avoiding particle breakage and agglomeration, can reasonably be extended to a wide variety of applications ranging from the control release of pharmaceutical microparticles to protective coatings for metal powders.