Development of environmentally friendly pyrotechnic colored flame compositions

Conventional fireworks compositions show excess smoke production when ignited. Furthermore, these compositions often contain perchlorates as these function both as an oxidizer and chlorine donor, but are harmful to the environment. TNO was challenged to change this situation and performed research to obtain perchlorate free and reduced smoke pyrotechnic compositions for firework applications.
A large variety of color compositions were looked into and optimized regarding pyrotechnic performance parameters including dominant wavelength, color emission purity, burn rate and smoke production. This research encompassed all colors produced for fireworks displays, with the following colors as main targets: red, green, blue, orange, lemon, white and purple. Highly nitrated cellulose was used in this research as a smokeless fuel. The targeted minimum amount of nitrocellulose (NC) in each color composition was 80 wt.% ensuring at least a significant reduction in smoke production compared to conventional fireworks compositions.
All optimization work regarding the color compositions was performed on small scale. Approximately 7 grams of each composition was mixed using a LabRAM (Laboratory Resonant Acoustic Mixer) and 1.5 gram, 10 mm ‡ cylindrical pellets were pressed subsequently. The pellets were ignited and the color performance was determined using spectrophotometry. Combinations of several chlorine donors and different color generators were tested in various mass ratios to obtain the best performing composition per color.
The compatibility of ingredients required attention in the formulation of chemically stable pyrotechnic compositions. Compatibility was primarily tested using a pressure vacuum stability test (PVST). In addition, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used for compatibility testing. Besides the compatibility of the ingredients, also the thermal stability had to be tested as NC is an intrinsically instable product and the main ingredient in the developed compositions.
Stabilizers were found that were able to stabilize the composition without influencing color performance properties. Finally, outdoor dynamic tests were performed with single shot devices launching so called comets up to 1.5” to observe the overall performance of the optimized color compositions.