Small deformation viscoelastic response of gum and highly filled elastomers

Abstract

Small deformation viscoelastic response has been investigated in a series of five elastomeric binders, both with and without nonreinforcing filler. The filled system were found nonlinear viscoelastic and thermorheologically complex. These behavior suggest the existence of a secondary relaxation process. The origin of this secondary process was modeled as an interphase of polymer weakly adsorbed on the filler surface. Decomposition of time-temperature shift factors for filled vs unfilled properties showed that the mechanical response of this interphase followed Arrhenius behavior. Measured activtion energies ranged from 24 to 76kJ/mole, depending on the cohesive-energy demsity of the elastomeric binder. Finally, these activation energies were related to the strain amplitude dependent nonlinear factor for the polymeric systems which contained no polar groups in their backbone, suggesting that in these systems both the nonlinear and thermorheologically complex nature of the filled materia ls' viscoelastic response originate from relaxations within this interphase

Viscoelastic behavior in a hydroxyl‐terminated polybutadiene gum and its highly filled composites: Effect of the type of filler on the relaxation processes

“…There is not a superposition of E ′ data at the lowest temperatures and highest frequencies for the HTPB1 propellant. This feature indicates a thermorheological complexity of the material under study, as previously observed in similar highly filled composite solid propellants 25, 26. Such thermorheological complex behavior is probably caused by the variation of the strength of filler–filler and filler–matrix interactions with temperature.…”

“…The temperature location of this relaxation is shifted to higher temperatures in the composite as a result of the mobility reduction caused by filler incorporation. Temperature shifts ranging from 3 to 8°C are common in similar systems 26…”

“…The nonlinear behavior and thermorheological complexity of these important materials have been considered in the literature 25–27…”

“…Despite the importance of HTPB‐based propellants for rocket engines and the obvious concern about structure and properties relationships, very few comprehensive investigations appear to be available in the open literature. There are only a few studies in which the viscoelastic response has been examined in an HTPB gum and propellants under small deformation by using dynamic mechanical analysis 25, 26. Stacer and Husband26 estimated the apparent activation energies of secondary relaxations induced by the presence of fillers from decomposition of the time–temperature shift factor for filled versus unfilled materials.…”

Aging of HTPB/Al/AP Rocket Propellant Formulations Investigated by DMA Measurements

“…HTPB‐based propellants show no simple thermo‐rheological behavior 5–7 due to the presence of secondary relaxation phenomena appearing at higher temperature. Each investigated AV0x formulation shows two apparent maxima.…”