AN UPDATE ON THE ROUND ROBIN TEST TO EVALUATE THE NITROCELLULOSE SIZE EXCLUSION CHROMATOGRAPHY METHOD IN STANAG 4178 (ED. 2)

摘要

Nitrocellulose continues to be an important energetic material which is found in a wide range of propellants and other energetic formulations. As a polymeric material, acceptance testing commonly includes the measurement of solution viscosity as the indicator of degree of polymerisation and processability. However, many viscosity methods are used and results cannot be easily compared. STANAG 4178 "Assessing the Quality of Nitrocellulose Deliveries from one NATO Nation to Another" is being updated which provides an opportunity to incorporate size exclusion chromatography (SEC) or gel permeation chromatography (GPC) for the determination of mean molecular masses and the molar mass distribution. [1] This additional information should form the basis for a robust assessment of nitrocellulose samples in future. SEC is a well established analytical technique but nitrocellulose analysis is complicated by the inherent complexity of the material (resulting from a distribution of R-ONO_2 groups along each polymer chain) and its unusual solubility behaviour in organic solvents commonly used for analysis. The SEC method in STANAG 4178 (Ed. 2) was jointly developed at AWE Plc, Cranfield University and ICT. This method is being evaluated with a round robin test in which 9 laboratories (representing 8 participating Nations) were each provided with SEC columns, calibration standards and 4 nitrocellulose samples (courtesy of AWE Plc and Nitrochemie Wimmis, Switzerland). The selected nitrocellulose samples have different nitrogen contents covering the range 11.6-13.5 % (w/w). The preliminary reported results of the round robin test have been analysed for consistency and trends which can be attributed to sample preparation and the use of specific SEC equipment and/or data analysis software. The recommended conditions for SEC analysis, and the procedure for subsequent data interpretation, have also been reassessed where necessary.