Chitin Microstructure Formation by Rapid Expansion Techniques with Supercritical Carbon Dioxide

Rapid expansion techniques (of supercritical solution (RESS) and into a liquid solvent (RESOLV)) with supercritical carbon dioxide are used to form chitin microstructures. The effect of the pre-expansion conditions, temperature (40−60 °C), pressure (104−208 bar), chitin concentration (1−6 mg/mL), and nozzle diameter (100−500 μm), on the morphology and the size of the chitin microstructures formed with both RESS and RESOLV are studied. Depending on the experimental conditions, it is found that spherical microparticles, with average diameters of 1.7−5.3 μm, are obtained with RESS, while continuous microfibers, with average diameters of 11.5−19.3 μm, are obtained with RESOLV. For both RESS and RESOLV it was observed that the pre-expansion temperature−pressure conditions studied here have practically no effect on the average diameters of the formed material. On the contrary, it is shown that concentration and nozzle diameter directly influence the morphology and size obtaining that lower concentrations and smaller diameter nozzles lead to the production of smaller diameter microstructures and closed-size distributions.