Effect of the sol fraction and hydrostatic deformation on the viscoelastic behavior of prestrained highly filled elastomers

Abstract

This study focuses on the relations between the microstructure and the viscoelastic behavior of an industrial solid propellant belonging to the class of highly filled elastomers. Precisely, the study aims at determining the impact on the viscoelastic behavior of the presence of the sol fraction inside the polymer network. The sol fraction is the part of the binder that a good solvent can extract. The solid propellant is swollen to various extents by solutions of plasticizer and polymer molecules. This swelling leads to a hydrostatic deformation of the polymer network, corresponding to an extension or contraction loading for each specimen. Prestrained dynamic mechanical analysis tests, superimposing a small oscillating strain on a prestrain, characterize the viscoelastic behavior. The degree of swelling of the network and the effective filler fraction drive the viscoelastic response. In addition, the mechanical behavior does not depend on the chemical nature of the introduced sol fraction. Moreover, a nonlinear behavior, i.e., an increase in both storage and loss moduli with increasing prestrain, is initiated at low prestrain. This nonlinearity depends on the contraction or extension of the network and could result from particles aligning with prestrain, which is expected in such highly filled materials.

Prestrained biaxial DMA investigation of viscoelastic nonlinearities in highly filled elastomers

“…The physical and mechanical interactions between the fillers and the binder or between the phases of the polymeric matrix are at the origin of the observed mechanical nonlinearities at the scale of the composite. These relations between the physical interactions and the macroscopic properties as a function of different input parameters have been extensively discussed in [15].…”

“…More precisely, the propellant consists of a cross-linked elastomeric matrix based on hydroxyterminated polybutadiene (HTPB) in which the fillers composed of ammonium perchlorate and aluminum particles are included (see Fig. 1 and described in detail, for example, in [15]). The mechanical properties of the composite will inherit the viscoelasticity of the matrix and stiffness of the inclusions.…”

Microstructure and deformation mechanisms of a solid propellant using 1 H NMR spectroscopy

“…The relations between the nonlinear mechanical behavior at the macroscopic scale and the microstructure at the scale of the fillers or the polymer chains have been explored [1][2][3][4][5][6]. However, direct experimental evidence of the physical mechanisms of deformation at the scale of the polymer network is difficult to obtain.…”

“…Consequently, the binder contains a significant amount of sol fraction, that is the fraction of the binder that can be extracted by swelling. The sol fraction is constituted of polymer chains and plasticizer and participate actively in the nonlinearity of the mechanical behavior [1][2][3]. Schematically, the propellant is composed of the fillers, the polymer network, and the sol fraction.…”

Influence of crosslinking and plasticizing on the viscoelasticity of highly filled elastomers

“…The incorporation of plasticizers before curing, denoted as preswelling, must be distinguished from the swelling of the cured polymer with plasticizers or diluents, denoted as postswelling . The effect of postswelling on solid propellants was considered in a previous study . The results show that the macroscopic viscoelastic behavior was modified according to the swelling or contraction of the network independently of the viscosity of the introduced liquid.…”