Solid Rocket Propellant Photo-Polymerization with an In-House LED-UV Prototype

Abstract

Composite solid propellants have used cast molding production technology for many decades, with intrinsic limitations on production flexibility, promptness, and grain geometry, as well as environmental implications on toxicity and global carbon footprint. This traditional method involves the use of toxic chemicals, has a long processing time, requires high temperature, and the products have limited geometries. To overcome those issues, different photo-curable resins have been evaluated as possible matrices. In fact, the UV-curing process is fast and has low energy consumption. The photocuring reaction parameters of six different pristine formulations were evaluated by Fourier transform infrared spectroscopy analysis. After finding the optimal curing parameters, different composites were prepared by adding 75 or 80 wt% ammonium sulfate particles used as an inert replacement for the oxidant. The thermomechanical properties and thermal resistance of the UV-cured composites were characterized via dynamic thermal-mechanical and thermogravimetric analysis. Subsequently, the mechanical properties of the inert propellants were investigated by tensile tests. The most promising resin systems for the production of solid rocket propellants were then 3D printed by an in-house developed illumination system and the obtained object micro-structure was evaluated by X-ray computed tomography.

Rheological and Mechanical Characterization of 3D-Printable Solid Propellant Slurry

“…The UV curing system was characterized using a Delta Ohm HD2102 radiometer with the LP471UVA probe, as it differs from the one utilized in the previous work [ 4 ]. The use of a 3D-printed support for the sensor allows for the collection of data relating to various levels, i.e., distances from the illuminating head.…”

“…For multilayer samples used for tensile tests, once the first single layer was exposed to UV light, another mask was stacked on top of the first one in the mold to enable the application of a second layer and further exposure until the required overall thickness was achieved with each layer being cured with a given time as specified in the following. In the previous research phase [ 4 ], the production of multilayer samples for tensile tests was carried out using bolted stainless steel molds. To enhance the specimen production rate and optimize the process, filmogenic release agents (polyvinyl alcohol) were tested to facilitate extraction from the metal mold.…”

“…In line with previous works [ 4 ]: A test speed of 0.3 mm/s was set; The geometry of the multilayer specimen followed the DIN_53504_1994 standard [ 27 ]; In order to have a better clamping to the testing machine and to avoid the specimen breakage in the terminal gripping part, an alternative clamping system based on a metal joint made of an eyelet–carabiner series was set up. …”

“…In comparison to our previous work [ 4 ], the present project involved a redesign of the sample molds for tensile tests. Specifically, the old method, which relied on a basic metal plate and several screwed-on masks onto which the slide was then placed, proved to be costly in terms of production time and also presented significant problems in the extraction process: one of the encountered challenges was that once the structure was unscrewed, the individual layer sometimes remained attached to one side by the mask but not on the other.…”

“…It is within this context that a patented manufacturing process based on deposition and UV-activated polymerization for solid rocket motors was developed [ 20 ]. The initial phase of the project focused on the applicability of UV photopolymerization to create solid grains with suitable mechanical and physical properties [ 4 , 21 ]. Various photocurable resins were considered as binders for highly loaded composite propellants.…”