Porous polymer structures obtained via the TIPS process from EVOH/PMMA/DMF solutions

The thermally induced phase separation (TIPS) process was used to study the phase behavior of ternary solutions containing poly(ethylene-co-vinyl alcohol) (EVOH) with 38 and 32 wt.% of ethylene content, poly(methyl methacrylate) (PMMA) and N,N-dimethylformamide (DMF) and to prepare microporous membranes. EVOH/PMMA/DMF solutions, with 0.92 and 0.83 DMF volume fraction and variable volume polymer ratios, were submitted to experiments to determine the cloud temperature (Tcloud) by optical microscopy and the dynamic crystallization temperature (Tcd) by differential scanning calorimetry (DSC), related to liquid–liquid (L–L) and solid–liquid (S–L) phase separation, respectively. L–L phase separation takes place as the temperature decreases, an UCST behavior, followed by S–L phase separation due to EVOH crystallization. At room temperature the ternary solutions show two macroscopic phases, F1 and F2, whose compositions were determined by high resolution thermogravimetric analysis in order to determine the tie lines. The ternary solutions (phases F1 and F2) were slowly dried and the morphology of the resulting membranes were analyzed by scanning electronic microscopy (SEM). The membranes show a bi-layer structure, one dense layer richer in PMMA and another porous layer richer in EVOH. The connected porous structure probably derives from the phase separation through a nucleation and growth mechanism.