Synthesis and powder generation of powder coatings using supercritical carbon dioxide

This paper reports an integral continuous process of polymerization and micronization of powder coatings using supercritical CO2 as solvent. Combining different process steps into one single process, using ultra short production chains, can be one future use of supercritical fluids. This contribution is therefore an example of how such integral processes can be designed and how the development of new products can look like using supercritical fluids. An acrylic resin consisting of glycidyl methacrylate, methyl methacrylate and styrene was chosen as polymer system for use of thermosetting material for acrylic powder coating application. The reaction was performed in a tubular reactor. A monomer conversion of more than 96% was achieved with short reaction times of about 30 min at a temperature of 135 degrees C and at a pressure of 30 MPa in a homogeneous CO2 phase. The resulting polymer has a number average molecular weight of about 2500 g/mol with a narrow polydispersity index of 1.6. In this process, the synthesis step in compressed carbon dioxide was followed by a high pressure micronization using the well-known PGSS process. Thus, small particles of about 25 mu m were obtained. Simultaneously, residual monomers were removed from the polymer product with the escaping CO2-gas, achieving a high purity grade. The process is designed as a straight forward process combining synthesis, micronization and purification of a polymer without depressurization between the unit operations and demonstrates the benefits which supercritical fluid technologies offer for product and process development. (C) 2014 Elsevier B.V. All rights reserved.