| Abstract | The pressure-volume-temperature (PVT) surface of polyamide-6 (PA-6) was determined in the range of temperature T = 300–600 K and pressure P = 0.1–190 MPa. The data were analyzed separately for the molten and the noncrystalline phase using the Simha-Somcynsky (S-S) equation of state (eos) based on the cell-hole theory. At Tg(P) ≤ T ≤ Tm(P), the ‘‘solid’’ state comprises liquid phase with crystals dispersed in it. The PVT behavior of the latter phase was described using Midha-Nanda-Simha- Jain (MNSJ) eos based on the cell theory. The data fitting to these two theories yielded two sets of the Lennard-Jones interaction parameters: e*(S-S) = 34.0 ± 0.3 and e*(MNSJ) = 22.8 ± 0.3 kJ/mol, whereas v*(S-S) = 32.00 ± 0.1 and v*(MNSJ) = 27.9 ± 0.2 mL/mol. The raw PVT data were numerically differentiated to obtain the thermal expansion and compressibility coefficients, α and Κ, respectively. At constant P, j followed the same dependence on both sides of the melting zone near Tm. By contrast, α = α(T) dependencies were dramatically different for the solid and molten phase; at T < Tm, α linearly increased with increasing T, then within the melting zone, its value step-wise decreased, to slowly increase at higher temperatures. |
|---|
