Study On The Solubility Of Gases In Biodegradable Poly (lactic Acid)

Poly (lactic acid) (PLA) is a new kind of biodegradable polymer, which is non-toxic, non-irritative and good biocompatibility. The application of this polymer is very wide. However, some gases such as CO₂,H₂O,O₂ and N₂ appeared in the processes of synthesis,production of PLA, could affect the function of PLA. Therefore, modeling the gases solubility in PLA under pressure and temperature, are of significance in the application of PLA in industrial scale.The Peng-Robinson cubic equation of state (PR EoS) and Perturbed-Chain SAFT equation of state (PC-SAFT EoS) were used to calculate the solubility of gases in biodegradable PLA in this paper, which the gases were nitrogen,carbon dioxide,water,oxygen and ethylene.Firstly, the evaluation of the energy parameter a and co-volume parameter b of the pure PLA in the PR EoS were obtained by fitting the PVT and density data of PLA with a single set of (a/MW) and (b/MW) parameters for several MWs of PLA. The solubility of gases in PLA was calculated with the PR EoS combined with the van der Waals (vdW) and Wong-Sandier (WS) mixing rules, and the binary interaction parameters were optimized simultaneously. The three pure component parameters of the PC-SAFT EoS, segment number m, segment diameter s and segment energy parameters e/k were regessed by fitting the PVT and density data of systems with PLA. And the correlations of the three pure component parameters with MWs were obtained.Considered the effect of the difference of the volume and size between gases and PLA, an improved mixing rule was proposed based on the analysis of the former mixing rules. The PC-SAFT EoS was used to calculate the solubility of gases in PLA with Berthelot-Lorentz (B-L) mixing rule, Quadratic mixing rule and the proposed mixing rule, which the interaction parameters were optimized.The calculated results showed that the average absolute deviations of the PR EoS with WS mixing rule and vdW mixing rule were 6.05% and 7.31%, the PC-SAFT EoS with B-L mixing rule,quadratic mixing rule and the proposed mixing rules were 8.79%, 8.52% and 5.68%, respectively. Compared with the above results, the PC-SAFT EoS combined with the proposed mixing rules presented experimental data with well agreement.