Curing activity in the preparation of solid composite
propellants
determines the performance of solid rocket motors in operation. Limited
by the lack of effective monitoring tools, the complete curing behavior
and thermal-induced curing kinetics are rarely disclosed. It is still
a challenge to monitor in situ and in real-time the physical and chemical
cross-linking reaction during the curing of propellant. Herein, we
demonstrate a promising approach based on optical fiber capable of
being implanted inside the propellant to monitor the internal stress
evolution during the curing process, by taking hydroxyl-terminated
polybutadiene propellant as an example. Attributed to the strain and
temperature sensitivity of a pair of optical fiber gratings, the thermal-assisted
physico-chemical cross-linking states of curing process have been
demonstrated in detail. By tracking the stress-induced wavelength
shifts of fiber gratings and calculating the curing mechanism function,
the complete curing roadmap, including the viscous flow stage, gel
stage, hardening stage can be clearly revealed, and the curing completion
times are obtained as 154, 81, and 40 h, at the curing temperatures
of 60, 70, and 80 °C, respectively. The apparent activation energy
of this curing system obtained by calculation is 73.88 kJ/mol. This
flexible fiber-based sensor provides an effective tool for unraveling
the cure kinetic mechanism, and paves a universal pathway to guide
the preparation and applications of versatile composite materials
for solid rocket motors.