Using High Glass Transition Polymers to Suppress Irreversible Volume Expansion of High Explosive Crystals in PBXs

The explosive TATB has a graphitic, plate-like crystal structure that imparts texture to the compacted material. This is also true for TATB-containing composites, inducing anisotropy to the mechanical and thermal properties of these composites. The plate-like TATB crystals possess high anisotropic CTE values, the through-plane direction being 10-20 times greater than the two in-plane directions. Although the mechanism is not well-understood, in solid compactions the highly anisotropic CTE gives rise to an irreversible volume expansion that accompanies thermal cycling, called “ratchet growth”. The ratchet growth of neat TATB and a TATB-based PBX with FK-800 as the binder have been studied extensively. Previous studies indicate the FK-800 restricts irreversible volume expansion of TATB crystals. It has been suggested that the ratchet growth of the TATB crystals could be suppressed further if a higher Tg polymer were used in the formulation (FK-800 Tg = 28°C). For this study, two high Tg polymers were selected and formulated with TATB to create molding powder for each composite materials and were die-pressed into right cylinders to approximately 98% TMD for each material. Specimens were thermal cycled to various hot and cold temperatures using a TMA to measure the strain changes after thermal excursions. The results are compared to the response of neat TATB and TATB/FK-800 composite measured in previous studies to highlight the role of different Tg binders in the ratchet growth phenomenon. LA-UR-25-20929