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Paraffin has been identified as a promising alternative for use in propellant grains for hybrid rocket motors. Studies have been conducted using grain as fuel paraffin or liquid hidroxylated polybutadiene polymer (HTPB) due to the high thrust generated during firing. However, in consequences the low mechanical properties of pure paraffin, this study aims to evaluate the kinetics of degradation of a mixture composed of paraffin particles (PP) and HTPB compared with grain fuel pure paraffin and pure HTPB. For this we used a thermal analysis technique thermogravimetric in conjunction with the application of kinetic methods based on ASTM E1641 and Vyazovkin theory. Based on these results we can say the activation energy results are in agreement with the literature and the mixture PP / HTPB presents intermediate activation energy values as expected.

Ammonium dinitramide (ADN) has been considered the potential substitute for ammonium perchlorate in solid green propellants. However, it has also some drawbacks due to its high hygroscopicity and chemical incompatibility with some of the components present in composite propellant formulations. On the other hand, ADN melts at temperatures below degradation, which makes emulsion crystallization an important method to prepare spherical ADN particles that benefit both propellant slurry processing and casting. Spherical ADN particles were prepared by emulsion crystallization to be used for the microencapsulation studies, and whose method was assessed to better understand which parameters may affect the ADN particles formation. Microencapsulation protects ADN particles as it addresses hygroscopicity besides the given protection from chemical incompatibility. Polyurethane made of hydroxyl-terminated polybutadiene was selected as a coating material because of its common use in propellants as a binder. Also, the good performance of methylene diphenyl diisocyanate as a curing agent was such that it was used in the whole study. The number of layers and the processing time played important roles in the formation of the capsule as seen in the impermeability tests. Besides, drying at 50°C for 168 h showed to be even more beneficial on average for the capsule protective property. Chemical compatibility between the capsule and ADN was confirmed at 60°C which allows it to be used as a protective coating. However, the obtained average coating thickness of ten microns has to be reduced yet with more efficient protective coating materials.

Paraffin-based hybrid propellants have been developed due to their high burning rate. However, they have some disadvantages such as inadequate mechanical properties and unstable burning. In this work, paraffin fuel grains with carbon black were evaluated to study the possible effects of this additive on the mechanical, thermal and ballistic properties of these grains, besides the already known effect of minimizing the thermal radiation inside the motor. The grains with carbon black showed significant changes in the thermal degradation profile and substantial improvement in burn stability.

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