Isothermal compression - Equations of state

Besides the volume increase by thermal expansion also the volume reduction by compression is an important data for the processing of polymers. 

On of the most useful expressions to represent the P(P,T)-behaviour of liquids, including polymeric liquids, is the Tait-relation (Tait 1888,1898 and Dorsey 1940)  

This purely empirical relation was derived by Tait as long ago as 1888 it is still one of the best approximations of the actual PVT-behaviour. Reference is usually made to the voyage made by HMS Challenger and the report of experiments undertaken by Tait into the compression of water. 

Simha et al. (1973) have shown that C is indeed almost constant (best average value C = 0.0894) and that the temperature dependent factor B(T) can be expressed by 

TABLE 4.14 Constants of the Tait-equation for polymer melts 

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