Thermal Characterization of Ammonium Perchlorate with Acrylonitrile Butadiene Styrene or Polylactic Acid Supports for Additively Manufactured Solid Rocket Propellant

With the popularity growth of rapid prototyping methods, namely 3D printing, there is increased interest in 3D printed molds. Understanding the thermal limitations of common thermoplastics is critical since any geometric deformation in the mold directly compromises the propellant grain’s internal surfaces, when casting propellant. In this experimental work, the objective was to determine the effect of exposing a hot viscous casting medium at 110◦C on the structural integrity of Fused Deposition Modeling (FDM) 3D printed cylindrical propellant casting molds. Material and wall thickness for the molds were varied, and a nonreactive viscous surrogate material, representative of AP composite propellant, was used to simulate AP casting conditions. This experiment used a 2 × 4 general factorial design to evaluate two material types (PLA and ABS) and 4 different wall thicknesses (0.2 mm, 0.4 mm, 0.6 mm, and 0.8 mm) and statistical analysis was applied to determine appropriate parameters for future studies. The analysis of the results showed a statistically significant interaction between the wall thickness and the material (p < 0.001). The results showed that ABS showcased a high dimensional stability at every wall thickness whereas PLA showed severe plastic deformation at lower wall thicknesses given the lower glass transition temperature of the material. The experiment concludes that for AP composite propellant with a pour temperature of 110◦C, ABS molds are more appropriate selection than PLA. Moreover, the range of minimum mold wall thickness when using ABS in this application was determined. ABS works well at 0.2mm wall thickness but a higher wall thickness, such as 0.8mm, is still recommended so the mold maintains the desired shape. This work also revealed a path for future research to determine suitable mold wall thicknesses for PLA molds in this high temperature application.