Study of the compatibility of plasticizers with poly(vinyl chloride) by dielectric spectroscopy

Abstract

Dielectric spectroscopy has been applied for studying the compatibility of plasticizers with poly (vinyl chloride) as well as for detecting the phase-inhomogeneities of plasticized systems. Commercial plasticizers having different polarity and compatibility with the polymer have been investigated. The effect of insufficient processing as well as storage and annealing on the physical structure of the compounds are also discussed. For obtaining dielectric spectra, the real and imaginary parts of the dielectric permittivity of liquid plasticizers and plasticized compounds were recorded continuously as a function of temperature in the range from −170 up to +200°C at fixed frequencies and heating-cooling rates. Exudation, the weight loss of the plasticizer, as well as mechanical properties were measured comparatively. It is a generally accepted fact that the compatibility of a plasticizer with a given polymer depends upon their dielectric properties. According to our observations, the temperature dependence of the dielectric permittivity of the plasticizer is of great importance from this point of view, especially in the range of application of the plasticized system. Comparing the dielectric dispersion spectrum of a liquid plasticizer to that of the corresponding plasticized compound, conclusions about the compatibility can be derived. A special polarization is found to be originated from the phase-separation and from the inhomogeneities. Besides the dielectric polarization arising from the polymer chain and plasticizer dipoles, the dielectric spectra show the existence of an interfacial, Maxwell-Wagner type polarization, which is found to be dependent on the inhomogeneities of the texture of the compound.