Methods for producing drug particles in the sub-micrometer or nanometer range are one option for enhancing the therapeutic effectiveness of a drug. The using of polymers as a drug coating material widespread in pharmaceutical production for surface modification because it can help improve the circulation and controlled release of the drug in the blood vessels. However, with drug coating/production by conventional methods, such as spray drying and emulsion techniques, high temperature treating could lead to the degradation of the drug. Supercritical fluid techniques have been developed to produce fine drug particles to overcome the problem. The drug (solute) is first dissolved in the supercritical fluid. Subsequently, the solution is rapidly expanded and depressurized through a nozzle, leading to supersaturation of the solution and the consequent precipitation of solid products with free solvent. This technique could be used with low temperature decomposition substances. In this research, menthol represents the drug and polyethylene glycol with molecular weight 6,000 (PEG6000) was used as the coating material, with the effects of RESS parameters be being investigated. The experimental results revealed that the obtained menthol particles exhibited a nominal size in a range of 0.5 to 60 micron with pressure in a range of 10 - 20 MPa, temperature in a range of 303 - 333 K and ethanol concentration in a range of 0 – 30 wt%. The RESS parameters which were pre-expansion temperature and pre-expansion pressure affected morphology, particle size and particle size distribution. It was also found that ethanol could help control morphology, particle size and particle size distribution.
