The synthesis and characterization of polyimide/polylactide blends of varying compositions were studied in order to control the size and size distribution of the PLA phase within the polyimide matrix. The PLA phase was then quantitatively extracted from the PI matrix to create pores of varying sizes and size distribution. Both ex-situ and in-situ preparation methods were used to determine the most desirable microstructure and properties. Membranes were prepared by solution casting with 1-Methyl-2-Pyrrolidone (NMP) and Tetrahydrofuran (THF) as the co-solvent.
The concentrations of PAA and PLA (PAA/PLA) used in the ex-situ preparation of polymer blends were 90/10 (V:V), 80/20 (V:V), 70/30 (V:V) and 60/40 (V:V). The concentration for PAA/PLA used in the in-situ preparation of polymer blends were 95/5 (V:V), 90/10 (V:V), 80/20 (V:V)and 60/40 (V:V). The curing temperatures for the membranes used ranged from 120°C to 275°C.
The PAA/PLA blends were synthesized and fully characterized. Rheological tests performed using a simple shear method show that the addition of PLA to the PAA matrix lowers the viscosity of the system. Newtonian flow was observed for all compositions. Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) show that the blends act as a two phase system. No significant changes in the chemical and physical properties of the polyimide occurred as a result of blending with PLA.
FTIR results before and after a water absorption test show that the absorption of water is slightly enhanced by the presence of PLA. The hydroxyl peak absorption in the IR spectrum of PAA/PLA blends is enhanced in all compositions. The water absorption test shows that the addition of a small amount of PLA into the polyimide matrix increases the absorption of water. This is true for membranes prepared by in-situ and ex-situ preparation methods.
Scanning electron micrographs were taken to confirm the extraction of PLA from the polyimide matrix. Extraction studies were carried out at various temperatures including 200°C 250°C and 275°C in order to determine the optimal conditions for the extraction of PLA. The in-situ polymer blend preparation method permitted a more systematic control of pore sizes and pore size distribution from sub millimeter to nanometer size scale. These pores could be filled with other polymers depending on what type of selectivity membranes that are trying to be obtained.