Equations of state for polyamide-6 and its nanocomposites. II. Effects of clay

Abstract

The pressure-volume-temperature (PVT) dependencies of polyamide-6 and its nanocomposites (polymeric nanocomposites) were measured at temperatures T = 300–600 K and pressures P = 0.1–190 MPa, thus spanning the range of molten and “solid” phases. The Simha-Somcynsky (S-S) cell-hole equation of state (EOS) was used for describing the molten region. At Tg(P) ≤ T ≤ Tm(P), the “solid” phase is a mixture of the liquid polyamide-6 with dispersion of crystals. Accordingly, the PVT behavior in this region was described as a combination of the S-S EOS for the liquid phase and the Midha-Nanda-Simha-Jain (MNSJ) EOS for the crystalline one. These two theories based on different models yielded two sets of the characteristic reducing parameters, P*, T*, V* and the segmental molecular weight, Ms. Incorporation of 2 and 5 wt % clay increased P* and reduced T* and V*, but the effects were small. Fitting the combination of S-S and MNSJ EOS' to isobaric “solid” phase data yielded the total crystallinity, Xcryst, and the correcting excess specific volume, ΔVm,c. Both parameters were sensitive to pressure, P, and the clay content, w—the former increased with P and w, whereas the latter decreased. The raw PVT data were numerically differentiated to obtain the thermal expansion and compressibility coefficients, α and κ, respectively. At T Tm, the opposite effect was observed, most likely owing to the excess of intercalant in the polymeric nanocomposites samples. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 966–980, 2009