A novel method for removing residual acetone from gelatin microspheres

Purpose. To develop a method for removing residual acetone from gelatin microspheres. Methods. Free-flowing gelatin microspheres were either heated under vacuum or subjected to a stream of humidified air in a specially designed apparatus for removal of the residual acetone. To understand the removal mechanism, hygroscopic and thermal properties of the microspheres were examined. Results. Heating the gelatin microspheres under vacuum did not reduce the acetone level below 2%, but the use of humidified air under fluidizing condition reduced the residual acetone in gelatin microspheres by an additional two orders of magnitude. The rate of acetone removal was a strong function of the relative humidity (RH) of the air stream; higher RH accelerated acetone removal. Other variables influencing the acetone removal rate are the mean particle diameter and the linear velocity of the humidified air. Under high relative humidities, significant amounts of moisture were absorbed into gelatin microspheres, reducing their glass transition temperature below 25degreesC. Conclusion. The residual acetone in gelatin microspheres can be efficiently removed when exposed to air of high RH. Mechanisms of water-dependent acetone removal are proposed.