Development of microporous membranes from Poly(Ether Ether Ketone) (PEEK); via thermally-induced phase separation (TIPS);

The fabrication of poly (ether ether ketone) based membranes via thermally-induced phase separation has been investigated. Microporous membranes were generated from solid-liquid phase separation of miscible polymer-polymer mixtures comprised of PEEK and polyetherimide, with subsequent extraction of the PEI diluent; the introduction of a high polymer diluent provides a number of advantages in terms of melt processing and ultimate membrane properties. The nature of the solid-liquid phase separation and corresponding PEI segregation was investigated as a function of crystallization temperature and diluent molecular weight using dynamic mechanical thermal analysis. DMTA studies revealed segregation of PEI to both interlamellar and interfibrillar/interspherulitic regions. PEI extraction with dichloromethane was found to be site specific, with diluent removal solely from the interfibrillar and interspherulitic regions; the retention of interlamellar PEI in the final article was reflected in a significant increase in the thermal resistance characteristics of the material. Scanning electron microscopy revealed a microporous morphology comprised of a spherulitic superstructure with two distinct pore size scales corresponding to PEI extraction from between fibrillar bundles and in interspherulitic regions, respectively. The presence of residual crystalline order in the melt enhanced heterogeneous nucleation, resulting in a dense morphology of compact spherulites and a narrow distribution of interfibrillar pores.; Pure water permeation studies of the blend membranes indicated a flux in the range of commercially available microfiltration membranes. Uniaxial stretching of the membrane precursors led to a highly fibrillar network; flux values for these membranes were increased 30 to 40 times as a result of stretching. Mercury porosimetry revealed a multimodal distribution in 25/75 PEEK/PEI blend membrane, with a pore size range of 0.05 to 0.4{dollar}mu{dollar}m. The membranes based on 50/50 PEEK/PEI displayed a narrow distribution of (interfibrillar) pores centered at 0.03{dollar}mu{dollar}m.