Dynamic mechanical properties of polyvinyl acetate

Abstract

The real and imaginary components of the complex compliance have been measured between 30 and 5100 cycles/sec. at nine temperatures between 50°C. and 90°C. on an unfractionated sample of polyvinyl acetate ( M n = 140,000, M w = 420,000). The results superpose by the method of reduced variables to give composite curves covering the transition from rubberlike to glasslike consistency as a function of frequency at 75°C. From these, the reduced curves for the real and imaginary parts of the complex shear modulus, and the real part of the complex viscosity, have been calculated. Earlier data of Mead and Fuoss on dielectric dispersion and dielectric loss of polyvinyl acetate have been reduced to 75°C. in the same manner, and the mechanical and electrical reduction factors are found to be identical. The apparent activation energy for mechanical and electrical relaxation increases sharply with decreasing temperature, as observed for other polymers. Distribution functions of mechanical relaxation and retardation times, and of electrical relaxation times, have been calculated from both real and imaginary components of modulus, compliance, and dielectric constant, respectively. The results of the approximation formulas of Williams and Ferry and of Schwarzl and Staverman are found to be closely similar. The electrical relaxation spectrum is somewhat flatter, and lies at shorter times, than the mechanical retardation spectrum.