Rheological characterization of nitrocellulose gels

Various nitrocellulose, NC, based propellant formulations need to be processed using new and more environmentally friendly solvent combinations on the one hand and using continuous processing methodologies on the other hand. A detailed understanding of the significant changes that take place in the structure and hence the rheological behavior of NC based formulations during manufacture is required to minimize the use of organic solvents and to revert to safer and green solvents. Towards achieving these objectives, experimental methodologies were developed for the first time to enable the accurate characterization and thus fingerprinting of the rheological behavior of NC gels. In these methodologies linear viscoelastic measurements are employed. The concentration of the solvents existing in the gel sample during rheological characterization is concomitantly monitored to allow the documentation of the major source of error associated with the rapid loss of the typical solvents, which generally exhibit relatively high vapor pressures. These measurements have indicated that the source of the NC fibers and the treatment method alter the rheological behavior and can be tracked. The rheological properties of the NC gels can be linked to their manufacturability and such data can be used to pinpoint optimum geometries and processing conditions. The processability of the NC based formulations can also be tailored on the basis of rheological characterization, allowing the manufacturers greater latitude for reducing costs and environmental footprint during manufacture, as well as improving the quality of their NC based energetic formulations.