Effects of sodium and zinc neutralization on large deformation hysteresis of an ethylene methacrylic acid butyl acrylate copolymer

The mechanical hysteresis and recovery behaviors of an elastomeric ethylene methacrylic acid butyl acrylate (EMAABA) copolymer, its sodium-neutralized (EMAABANa) and zinc-neutralized (EMAABAZn) counterparts are evaluated and compared under large strain loading conditions. Experiments at different rates, under cyclic loading conditions and in relaxation indicate two major hysteresis mechanisms: a characteristic viscoelastic mechanism operative at all strains and a microstructural evolution/breakdown mechanism incurred during large strains. Loading-unloading cycles show large rate-dependent hysteresis loops with significant recovery of strain upon unloading, revealing a highly dissipative yet resilient behavior. The microstructure breakdown mechanism occurs during the initial strain excursion as revealed by subsequent loading cycles showing a significantly more compliant behavior and dramatically reduced hysteresis loops. The neutralized materials are found to be significantly stiffer, stronger and more dissipative compared to the neat material while still retaining the same level of recovery. Therefore the neutralization of this material provides an excellent means to tune stiffness and dissipation while retaining resilience, providing mechanical performance properties attractive for abrasion, impact and puncture resistant applications.