Determination of Activation Energy of Relaxation events in composite solid propellants by Dynamic Mechanical Analysis

Abstract

The shelf life of a composite solid propellant is one of the critical aspects for the usage of solid propellants. To assess the ageing behavior of the composite solid propellant, the activation energy is a key parameter. The activation energy is determined by analysis of visco-elastic response of the composite solid propellant when subjected to sinusoidal excitation. In the present study, dynamic mechanical analyzer was used to characterize six different types of propellants based on hydroxyl terminated polybutadiene, aluminium, ammonium perchlorate cured with toluene diisocyanate having burning rates varying from 5 mm/s to 25 mm/s at 7000 kPa. Each propellant sample was given a multi-frequency strain of 0.01 percent at three discrete frequencies (3.5 Hz, 11 Hz, 35 Hz) in the temperature range -80 °C to + 80 °C. It was observed that all the propellants have shown two relaxation events (α-and β-transition) in the temperature range -80 °C to +80 °C. The α-transition was observed between -66 °C and -51 °C and β-transition between 7 °C and 44 °C for the propellants studied. The activation energy for both transitions was determined by Arrhenius plot from dynamic properties measured at different frequencies and also by time temperature superposition principle using Williams-Landel-Ferry and Arrhenius temperature dependence equations. The data reveal that the activation energy corresponding to α-transition varies from 90 kJ/mol to 125 kJ/ mol for R-value between 0.7 to 0.9 while for β-transition the values are from 75 kJ/mol to 92 kJ/mol. The activation energy corresponding to β-transition may be used to predict the useful life of solid propellant.

Viscoelastic behavior of carboxyl-terminated (butadiene-co-acrylonitrile)-based composite propellant binder containing polyglycidyl-type bonding agent

“…where: W d -sample weight before immersed in toluen, W g -sample weight after two days in toluen and Kratio of the densities of the solvent to the polymer. The density of toluene is 0.86 g/cm 3 , and those of cured propellant binder samples were in the range from 0.953 to 0.956 g/cm 3 , measured following Archimedes principle [9].…”

“…where: ν r -volume fraction of the binder in the swollen gel, χ -Flory-Huggins polymer-solvent interaction parameter, V 1 -molar volume of the solvent, N -network density of the tested binder sample. The value of Flory-Huggins polymer-solvent interaction parameter (χ) taken for polybutadiene-toluene system and the value of molar volume V 1 of swelling solvent are: 0.35 and 106 cm 3 •mol -1 , respectively [8]. The DMA measurements were carried out in the torsion deformation mode by using a mechanical spectrometer model "RMS-605" manufactured by the former Rheology Business Unit of company Rheometric Scientific Inc., Piscataway, NJ, USA.…”

“…Four CTBN-based composite propellant binder compositions (Table 1) selected for this study consisted of 100 phr of CTBN (1300×15, BF Goodrich, viscosity at 25 °C: 66.2 Pa s, carboxyl functionality: 1.9, number-average molecular weight: 3800 g/mol, specific gravity at 23 °C: 0.931 g/cm 3 , glass-liquid transition temperature, T g : -63.3 °C), 1.7 phr of antioxidant (2,2'-methylen-bis(4--methyl-6-tertbutyl phenol), commercially available as a product called AO 2246 and under a lot of other brand names (Fluka AG, Switzerland) and 0.44 phr of cure catalyst (iron(III)-acetylacetonate, (Fe(acac) 3 , Merck-Schuchardt, Germany). Mix ratio of propellant binder ingredients is expressed in phr, this means parts per hundred of resin based on 100 parts of CTBN.…”

Viscoelastic properties of carboxyl-terminated (butadiene-co-acrylonitrile)-based composite rocket propellant containing tris (2,3-epoxypropyl) isocyanurate as bonding agent

“…Bihari et al in their article have demonstrated that the interpretation of viscoelastic relaxation strength in polymers depends on the tangent of the phase lag angle (tan δ) or real (in-phase) or imaginary (out-of-phase) components of the storage and loss modulus, respectively [26]. The glass transition temperature (T g ) of a material also referred as α-transition is normally observed as a peak of tan(δ) considering the variation of tan(δ) with temperature ( Figure 7).…”

Applying modified hyperbranched polyester in hydroxyl‐terminated polyether/ammonium perchlorate/aluminium/cyclotrimethylenetrinitramine (HTPE/AP/Al/RDX) composite solid propellant

“…3,26 Stress relaxation performance is another vital aspect of viscoelastic properties and reflects the time-and temperature-dependent behavior of any polymeric composite material. 27 It can be seen from Fig. 14 that the stress relaxation modulus of both the blank and the MHBPE modified HTPE/AP/Al/RDX propellant decreases as time evolves at −40°C, 20°C and 70°C.…”