A strip resonance technique for measuring the ultrasonic viscoelastic parameters of polymeric sheets with application to cellulose

An acoustic strip resonance apparatus that measures the viscoelastic response of polymeric sheets over the temperature range of 100–400°K and at frequencies from 20 to 100 kHz is described. This is a computer‐controlled instrument which uses the resonant frequency and the quality factor of standing waves in strips to calculate the ratio of complex Young's modulus to density. Results are presented for cellophane and paper samples. These are consistent with measurements reported by others at lower frequencies. That is, (1) a single predominant secondary relaxation process which corresponds to the γ relaxation occurring at 200°K and 1 Hz is found in dry samples at 260°K and 60 kHz; (2) as moisture is added, the γ relaxation weakens and a higher temperature, β, relaxation appears; and (3) at low temperature, moisture addition initially increases the mass specific Young's modulus. The effects of methanol on the viscoelastic parameters of cellulose were also measured and found to be similar to those of water.