Infinite dilution activity coefficient of solvents in poly-3-hydroxybutyrate from inverse gas chromatography

Over the past few years, there has been an increase in the production of biopolymers, including poly(3-hydroxybutyrate) P(3HB). However, finding compatible solvents for these new materials can be a challenging task. The infinite dilution activity coefficient (IDAC) is a thermodynamic property that indicates the level of interactions between two substances and can be determined from experiments of inverse gas chromatography (IGC). In this work, IGC was used to determine IDAC of 12 solvents in P(3HB). The substances studied were 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), 1,2-dichloroethane, 2,2,2-trifluoroethanol, 2-butanone, 2-heptanone, benzene, chloroform, cyclohexane, dimethyl carbonate, ethyl acetate, isooctane and toluene. HFIP was found to be the most compatible solvent with P(3HB) with IDAC values smaller than 1. Isooctane presented the highest IDAC value, in agreement with the well known incompatibility between hydrocarbons and P(3HB). In addition, P(3HB) crystallinity was determined through IGC technique, enabling the calculation of the IDAC of amorphous phase only, where vapor-liquid equilibrium can be assumed. The degree of crystallinity obtained with HFIP analysis in P(3HB) was 68%, a value close to that previously reported in the literature.