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

CO2 sorption and diffusion in poly(3-hydroxybutyrate) and three poly(3-hydr oxybutyrate-co-3-hydroxyvalerate) copolymers were investigated gravimetrica lly at temperatures from 25 degrees to 50 degrees C and pressures up to 1 a tm. The sorption behavior proved to be linear for all the copolymers studie d. An additional set of measurements performed in a pressure decay apparatu s at 35 degrees C showed that the linearity could be extrapolated to pressu res up to 25 atm. The sorption results obtained from both techniques were i n good agreement. The poly(3-hydroxybutyrate-co-3-hydroxyvalerate) sorption kinetics were increasingly non-Fickian at the higher temperatures, thus pr eventing the calculation of diffusion coefficients above 35 degrees C, Inte restingly, this was not the case for poly(3-hydroxybutyrate), and diffusion coefficients and permeabilities could be calculated at all of the investig ated temperatures. The 35 degrees C permeabilities were fairly low, which i s attributed to the high degree of crystallinity of this polyester family. Finally, the poly(3-hydroxybutyrate) barrier properties against CO, are suc cessfully compared with those of some selected common thermoplastics. (C) 1 999 John Wiley & Sons, Inc.