Dynamic Viscoelastic Behavior of Model Poly(vinyl chloride) Blends Characterized at Small Deformation in Shear Oscillation

Abstract

ABSTRACT:In the present study, dynamic shear oscillation measurements at small strain were conducted on four model blends of equal amounts (50/50 by weight) of poly(vinyl chloride) (PVC) with three compatible and one incompatible polymers. The compatible polymers were nitrile rubber containing 30% acrylonitrile (NBR-30), poly(B-caprolactone) (PCL), and copolyester thermoplastic elastomer (trademark HYTREL). The incompatible one was nitrile rubber containing 22% acrylonitrile . Double logarithmic plots of loss modulus G"(w) against storage modulus G'(w) were employed as a systematic, practical way of treating the data. The JogG"(w)-logG'(w) scheme was shown to enable one to characterize and interpret the viscoelastic behavior of the blends related to the mixing history and morphological changes.KEY WORDS Poly(vinyl Chloride) (PVC) / Nitrile Rubber (NBR) / Poly-(B-caprolactone) (PCL) / Copolyester Thermoplastic Elastomer (HYTREL) / Mechanical Blending/ Viscoelastic Behavior/ Shear Storage Modulus G'(w) / Shear Loss Modulus G"(w) / log G"(w)-log G'(w) Plot/ Dynamic mechanical measurements have been used for characterizing a wide range of polymeric materials. Common features of the dynamic mechanical measurements are to impose a periodic, uniform sinusoidal deformation on a specimen and then observe the storage (elastic) and loss (viscous) moduli of.the specimen.Dynamic mechanical analysis may be classified into two categories; the first is associated with the measurements involving free vibrations and in the second are those based on forced oscillations. 2 • 3 Among those falling in the second category, the dynamic shear oscillation measurement at small strain has been used to not only characterize the viscoelastic properties but also relate them to identify the differences in molecular structure and predict the behavior during processing. It is thus one of the most powerful techniques for studying the effect of not only molecular structure but also phase morphology on the physical properties and determining the processability and product performance, both of which are essential in component design.Among the dynamic viscoelastic parameters measured at small strain in shear oscillation, the shear storage modulus G' and shear loss modulus G" are of typical importance especially when elastic and viscous responses are needed to be rigorously separated. Both the storage and loss moduli can be obtained either as a function of temperature (at constant frequency; isochronal) or as a function of frequency (at constant temperature; isothermal).