Hot stage extrusion of p-amino salicylic acid with EC using CO2 as a temporary plasticizer

The aim of the current research project was to explore the possibilities of combining pressurized carbon dioxide with hot stage extrusion during manufacturing of solid dispersions of the thermally labile p-aminosalicylic acid (p-ASA) and ethylcellulose 20 cps (EC 20 cps) and to evaluate the ability of the pressurized gas to act as a temporary plasticizer. The thermal stability of the p-ASA was investigated using DSC, TGA and HPLC. The compound decomposes completely upon melting. Below 110 °C and under atmospheric conditions, the compound is thermally stabile for 10 min.Pressurized carbon dioxide was injected into a Leistritz Micro 18 intermeshing co-rotating twin-screw melt extruder using an ISCO 260D syringe pump. Carbon dioxide acted as plasticizer for p-ASA/EC 20 cps, reducing the processing temperature during the hot stage extrusion process. HPLC showed that without carbon dioxide injection, approximately 17% of p-ASA degraded, while less than 5% degraded with CO2 injection. The experiments clearly showed that injecting pressurized carbon dioxide broadens the application of hot stage extrusion to thermally labile compounds in a one step process.