Dynamic Mechanical Properties of Polyoxymethylene, IV

Abstract

Dynamic mechanical measurements are made with a torsion pendulum apparatus over about three decades of frequency in the α relaxation region of the single crystals of polyoxymethylene. Real and imaginary parts of complex rigidity are measured in each of the three specimens, that is, a mat of single crystals prepared by gradual cooling; a rod of isothermally crystallized single crystals and a heat-treated sample of the single crystal mat. The composite relaxation curves are made by superposing the dispersion curves of real and imaginary parts of complex rigidity on each of the specimens. The composite relaxation curve of loss tangent is also made by superposing the loss tangent curves for the single crystal mat. The activation energies of the α relaxation evaluated from the temperature dependence of the horizontal shift factor are 37 kcal/mol (T<40°C), 25 kcal/mol (40°C<T<90°C) and 38 kcal/mol (T>90°C) respectively. The magnitude of vertical shift along the logarithmic rigidity axis is independent of temperature above about 100°C and 115°C for the single crystal mat and the piled rod of the single crystals, but the magnitude varies linearly with increasing temperature above about 50°C for the heat-treated sample of the mat.