MECHANICAL HYSTERESIS OF A POLYETHER POLYURETHANE THERMOPLASTIC ELASTOMER

The mechanical hysteresis of a polyether polyurethane thermoplastic el astomer was studied as a function of temperature, percent strain, and deformation energy. Hysteresis values remained small at low temperatur es when the extent of the sample deformation did not disrupt the glass y matrix. This was readily evident at temperatures below the glass tra nsition temperature, T(g), of the polymer where the material did not f ormally yield. At temperatures above the T(g) of the polymer, hysteres is remained small even at substantial strains levels and demonstrated the capabilities of the hard segment domains to act as physical crossl inks. At elevated temperatures, percent hysteresis increased as the hy drogen-bonded hard segment domains weakened. When mechanical hysteresi s was considered on the basis of constant deformation energies, hyster esis values reached a maximum in the vicinity of the T(g) of the polym er. These maxima existed as a consequence of two opposing trends: the decreasing resiliency of the polymer as it becomes a glass and the inc rease in the resistance of that glass to undergo deformations sufficie nt to cause plastic flow. Finally, a hysteresis response sur-face cons tructed as a function of deformation energy and temperature was found to be sensitive to both the strain-induced crystallization of the rubb ery soft segment matrix and to the strain-induced yielding of the glas sy soft segment matrix.