PVT of amorphous and crystalline polymers and their nanocomposites

Abstract

The Pressure–Volume–Temperature ( PVT) of polystyrene (PS), polyamide-6 (PA-6) and their clay-containing polymeric nanocomposites (CPNC) were determined at T = 300–600 K and P = 0.1–190 MPa, thus in the molten, glassy and semicrystalline phase. The melt and glass behavior was interpreted following the Simha–Somcynsky (S–S) cell-hole free volume theory while that of the semicrystalline phase using S–S and the Midha–Nanda–Simha–Jain (MNSJ) cell theory describing crystalline quantum interactions. The theoretical analysis yielded two sets of the interaction parameters, one from the S–S and the other from the MNSJ model. The derivative properties: the compressibility, κ, and thermal expansion coefficient, α, were computed as functions of T, P and clay content, w. These functions, crossing several transition regions, were significantly different for the amorphous PS than for the semicrystalline PA-6. The isobaric PS plots of κ and α vs. T detected secondary transitions at T β/ T g ≈ 0.9 ± 0.1 and at T c/ T g = 1.2 ± 0.1. Addition of clay severely affected the vitreous phase (physical aging). In PA-6 systems the behavior was distinctly different than in PS, viz. κ = κ( T) followed a similar function across the melting zone, while α = α( T) dependencies were dramatically different for the solid and molten phase. The theoretical functions in reduced variables κ ˜ = κ P ∗ = κ ˜ ( T ˜ , P ˜ ) ; α ˜ = α T ∗ = α ˜ ( T ˜ , P ˜ ) provided good basis for explanation of the observed dependencies.