Carbon dioxide sorption and diffusion in poly(3-hydroxybutyrate) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

摘要

CO2 sorption and diffusion in poly(3-hydroxybutyrate) and three poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymers were investigated gravimetrically at temperatures from 25° to 50°C and pressures up to 1 atm. The sorption behavior proved to be linear for all the copolymers studied. An additional set of measurements performed in a pressure decay apparatus at 35°C showed that the linearity could be extrapolated to pressures up to 25 atm. The sorption results obtained from both techniques were in good agreement. The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) sorption kinetics were increasingly non-Fickian at the higher temperatures, thus preventing the calculation of diffusion coefficients above 35°C. Interestingly, this was not the case for poly(3-hydroxybutyrate), and diffusion coefficients and permeabilities could be calculated at all of the investigated temperatures. The 35°C permeabilities were fairly low, which is attributed to the high degree of crystallinity of this polyester family. Finally, the poly(3-hydroxybutyrate) barrier properties against CO2 are successfully compared with those of some selected common thermoplastics.