Effect of tris (2,3-epoxypropyl) isocyanurate on dynamic modulus of CTBN-based composite rocket propellant

The influence of tris(2,3-epoxypropyl) isocyanurate as a bonding agent on viscoelastic dynamic modulus of carboxyl- terminated (butadiene-co-acrylonitrile)-based composite propellant was investigated. Strain amplitude sweep tests have been run at the room temperature. Frequency dependencies of rheological behaviour parameters (storage and loss modulus) were also analyzed. Based on the frequency dependencies of the storage and loss modulus, in the temperature range from -80 °C to 40 °C, the master curves were created, reaching broader frequency interval in comparison to that used in the measurements. This enables a prediction of the material response at various frequencies, usually unobtainable experimentally. Williams- Landell-Ferry (WLF) equation constants were determined for different reference temperatures. Further, material constants, fractional free volume at the glass transition temperature and thermal coefficient of free volume expansion were calculated. The data obtained from WLF analysis of the tested composite propellants showed that the values of the thermal coefficient of expansion of free volume and the fractional free volume at the glass transition temperature decrease with increasing content of tris(2,3-epoxypropyl) isocyanurate. Also, the apparent energy for viscoelastic relaxation increases, because of the increased intermolecular hydrogen interactions.