RHEOLOGY OF PVC PLASTISOL ― VII EXPLORATION ON NON-LINEARITY OF VISCOELASTIC BEHAVIOR

摘要

Non-linearity (strain-amplitude dependence) of viscoelastic behavior was examined with a plastisol made with a commercial PVC resin dispersed in DOP at 50 volume percent. The measurements were made in shear at room temperature in the frequency range of 10 ~(-1) ― 10~2 rad/s. The strain amplitude was from 0.02 to about 10. At a fixed amplitude, the complex viscosity, | η~*|, decreased with the increase of frequency (pseudo-plastic), reaching a viscosity minimum and then, increased (dilatancy). At a fixed frequency, the viscosity decreased with the increase of amplitude, reaching a minimum and then, increased, in some cases, going over a maximum. At a fixed amplitude, the storage modulus, G', increased monotonically with the increase of frequency. However, at a fixed frequency, the modulus decreased, reaching a minimum and then, increased, in some cases, going over a maximum. In general, the steady state viscosity, η, was higher than |η~* I, when compared at numerically equal value of frequency and shear rate. The shear-rate dependence of η exhibited both pseudo-plastic flow and dilatancy. The first normal stress difference, N_1, - was almost zero in the pseudo-plastic region, but about - 80 Pa in the dilatant region. The negative value implies that another normal stress difference, N _2, is present. Viscosities measured with a spindle rheometer were somewhat higher than those measured with a concentric-cylinder rheometer. The difference is attributable to the shear-induced migration in the former rheometer and the formation of the immobilized layer in the latter rheometer.