Viscoelastic properties of poly(vinyl chloride) gels: Effect of plasticizer type

Viscoelastic behavior of PVC gels/sols in a wide range of PVC concentration c was examined in various plasticizers having different solubility toward PVC. The gel point c(g) decreased with decreasing solubility, possibly due to enhanced formation of PVC crystallites (crosslinking points in the gels) in poorer plasticizers. The exponent characterizing the power-law behavior of the critical gel (G ' similar toG " similar to omega "), n = 0.75, was insensitive to the plasticizer solubility. The exponent z (= 2.52 +/- 0.14), characterizing the equilibrium modulus G(e) of the well developed gels (G(e) similar to epsilon (z) with epsilon = \c - c(g)\/c(g)) was also insensitive to the plasticizer solubility. However, the magnitude of the normalized modulus c(-1)G(e) was smaller in poor plasticizers, suggesting some heterogeneity in the gel network structure therein. The other exponent gamma characterizing the viscosity eta of the sols (eta-epsilon (gamma)) moderately increases from 1.2 to 1.9 with increasing solubility. Comparison of the normalized viscosity and compliance in different plasticizers suggested that the sol structure was heterogeneous and this heterogeneity sensitively increased with decreasing solubility.