The Pressure-Volume-Temperature PVT Relation

For thermoplastic polymers, the equation of state is of the type v v(P, T), and is usually represented as a PVT diagram that gives the specific volume, v, as a funetion of temperature T and pressure P. The most commonly used equation is the Tait equation (van Krevelen 1976 Zoller et al. 1989 Zoller and Fakhreddine 1994)  

Differentiating the equation allows one to obtain the isothermal compressibility, K, and the coefficient of volume expansion, y  

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