Rubber, viscoelastic behavior glass temperature

As we have seen above, the transition that separates the glassy state from the viscous state is known as the glass-rubber transition. This transition attains the properties of a second-order transition at very slow rates of heating or cooling. In order to clearly locate the region of this transition and to provide a broader picture of the temperature dependence of polymer properties the principal regions of viscoelastic behavior of polymers will be briefly discussed. 

Rubber is a viscoelastic solid formed by crosslinking a polymer, which is initially a viscoelastic liquid. In spite of this difference there still are some common issues in understanding the physics of the glass temperature and the viscoelastic mechanisms in the softening dispersion (i.e., called the glass-rubber transition zone in Ferry (1980). A case in point can be taken by comparing the viscoelastic behavior of the neat epoxy resin Epon lOOlF (Plazek and... 

Viscoelastic Response far above the Glass Temperature Tg The Fluid State. From Figure 10 or Figure 12 one can see the fluid state response of the polymer. This is the portion of the curve at long times or high temperatures from the rubbery plateau to the end of relaxation where the polymer would take the shape of whatever container held it, ie, it is a liquid. There are several fundamental aspects to polymer behavior in this region. On the rubbery plateau, the polymer chains behave as if they were part of a three-dimensional network and their response can be described from modern rubber elasticity theories. This behavior is beyond the scope of the current review and the reader is referred to... 

The time and temperature dependent properties of crosslinked polymers including epoxy resins (1-3) and rubber networks (4-7) have been studied in the past. Crosslinking has a strong effect on the glass transition temperature (Tg), on viscoelastic response, and on plastic deformation. Although experimental observations and empirical expressions have been made and proposed, respectively, progress has been slow in understanding the nonequilibrium mechanisms responsible for the time dependent behavior. 

Considering melt flow of BC, it is usually assumed that the test temperature is UCST > T > T, where T stands for glass transition temperature of the continuous phase. However, at Tg < T < T g (T g is Tg of the dispersed phase) the system behaves as a crosslinked rubber with strong viscoelastic character. At UCST > T > T, the viscosity of BC is much greater than would be expected from its composition. The reason for this behavior is the need to deform the domain structure and puU filaments of one polymer through domains of the other. Viscosity increases with increase of the interaction parameter between the BC components in a similar way as an increase of the interfacial tension coefficient in concentrated emulsions causes viscosity to rise [Henderson and Williams, 1979]. 

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