Coating of particles - pushing the size limit through a solvent-less technique

Coating of solids is an essential process for a diverse group of industries including the chemical, pharmaceutical, agricultural, cosmetic, electronic, and food. Unfortunately, most industrially relevant coating processes require use of solvents and are not generally suitable for coating very fine particles without significant agglomeration. Here, we 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. In this novel dry-polymer-coating method, high intensity vibratory mixing device is used to first form an ordered mixture consisting of a particulate substrate, which is subsequently processed further to form a conformal polymeric film. As an example, challenging material such as ascorbic acid (AA) that is brittle and cannot withstand very large mechanical forces is considered. AA particles, ranging in size from 50 μm to 500 μm are successfully coated with a micronized polymer, polyethylene (PE) wax. Polymer coatings were able to prolong the dissolution time of ascorbic acid from seconds to hours depending on the coating thickness.