Determination of thermodynamic interactions of poly(l-lactide) and biphasic calcium phosphate/poly(l-lactide) composite by inverse gas chromatography at infinite dilution

Inverse gas chromatography at infinite dilution was applied to determine the thermodynamic interactions of poly(l-lactide) (PLLA) and the composite of biphasic calcium phosphate and PLLA (BCP/PLLA). The specific retention volumes, V0g , of 11 organic compounds of different chemical nature and polarity (non-polar, donor or acceptor) were determined in the temperature range of 308–378 K for PLLA and 308–398 K for BCP/PLLA. The weight fraction activity coefficients of test sorbates, Ω∞1 , and the Flory–Huggins interaction parameters, χ∞12 , were estimated and discussed in terms of interactions of the sorbates with PLLA and BCP/PLLA. Also, the partial molar free energy, ΔG∞1 , the partial molar heat of mixing, ΔH∞1 , the sorption molar free energy, ΔGS1 , the sorption enthalpy, ΔHS1 , and the sorption entropy, ΔSS1 , were analyzed. A different chromatographic behavior of the two investigated samples, PLLA and BCP/PLLA, was observed. The values of Ω∞1 indicated n-alkanes, diethyl ether, tetrahydrofurane (THF), cyclohexane, benzene, dioxane (except for 338 K), and ethyl acetate (EtAc) (except for 338 K) as non-solvents, and chloroform (CHCl3) as good solvent (except for 378 K) for PLLA. For BCP/PLLA, CHCl3, EtAc (for 378 K), dioxane (except for 378 K), and THF were indicated as good solvents