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Fluid Characteristic of Triblock Copolymer PLA-PEG-PLA in Supercritical System

Author: LiuMin
Tutor: JiangYanBin
School: South China University of Technology
Course: Chemical Engineering
Keywords: PLA-PEG-PLA supercritical anti-solvent phase behavior process parameters
CLC: O631.3
Type: Master's thesis
Year: 2011
Downloads: 65
Quote: 0
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Abstract


Poly（lactic acid）/Poly（ethylene glycol）/Poly（lactic acid）（PLA-PEG-PLA） is a class of amphiphilic triblock copolymer, its thermodynamic and hydrodynamic characteristics are decided by the different mass ratio and molecular weight of PLA and PEG in the PLA-PEG- PLA. In this paper, PLA-PEG-PLA was chosen as a model compound to study its phase behaviors and thermodynamic properties in different supercritical systems using supercritical equilibrium technology. The Supercritical anti-solvent （SAS） process was used to prepare PLA-PEG-PLA particle.Solubility data were measured for PLA-PEG-PLA in supercritical systems of CO2 +Dichloromethane and CO2+EtOH+Dichloromethane using a Super Phase Monitor. The effects of temperature, the mass fraction of DCM （or DCM+EtOH）, the PEG mass fraction in PLA-PEG-PLA, and the molar ratio of DCM/EtOH on cloud-point pressure were discussed in detail. The results show the supersaturation of the PLA-PEG-PLA+DCM+CO2 ternary system increase with the decrease of DCM concentration. For the PLA-PEG-PLA+DCM+EtOH+ CO2 quaternary system, the cloud point pressure decreased but the bubble point increased as the addition of EtOH. The single-phase region shrunk in two systems as the PEG content decreased. Both of the two systems exhibited typical lower critical solution temperature （LCST） phase behavior in SCF mixtures.Single factor experiments were arranged to investigate the effects of parameters on the formation of PLA-PEG-PLA particle using SAS, including solvent, the pressure, temperature, CO2 flow rate, solution flow rate and solute concentration. Unfortunately, no ideal PLA-PEG- PLA microparticle was prepared in the selected condition. But only some favorable results attained, i.e., DCM is suitable solvent for this system due to its excellent volatility, the near-critical temperature （30℃） and middle pressure（140bar） were good for the precipitate of the solute, there should be a correspond relationship among CO2 flow rate, solution flow rate and solute concentration. Also there is no ideal progress even when PLA or hydroxy- camptothecine（HCPT） used as crystallization seed.

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CLC: > Mathematical sciences and chemical > Chemistry > Polymer chemistry ( polymer ) > Polymer physics and physical chemistry of polymers > The chemical nature of polymers
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