(668d) PE/PEO Cocontinuous Polymer Blends with Application In Gas Separation Membranes

The microporous support layer for gas separation membranes provides mechanical strength and prevents the rupture of the selective layer under the incoming gas pressure. Therefore, average pore size, pore size distribution, pore wall functionality and thickness of the support layer play a vital role in the overall performance of the membrane. This study will focus on the design of a microporous membrane support layer derived from cocontinuous polymer blends.  The effect of blend composition, shear rate, residence time, and annealing time on the cocontinuous morphology of polyethylene (PE)/ polyethylene oxide (PEO) blends was investigated. Porous PE sheets were generated by solvent extraction of PEO and used as a support layer for gas separation membranes.

The PE/PEO blends using non-functional and maleic-anhydride functional PE (PE-g-MA) were mixed in batch microcompounder and pilot plant scale co-rotating twin-screw extruder. The effect of residence time on the cocontinuous morphology in the twin-screw extruder was studied by varying screw geometry, mixing speed, and the zone of PEO introduction.

The morphology and phase size of the blends was examined using SEM (scanning electron microscopy) and LSCM (laser scanning confocal microscopy). In order to satisfy the LSCM requirements of specimen transparency and fluorescence of one phase, hydroxyethyl(methacrylate) (HEMA) stained with rhodamine B dye was polymerized inside of the pores of the porous PE sheet. Approximately 100 2D images per sample were acquired, deconvolved and binarized prior to the 3D image reconstruction. A triangular mesh representation of the interface was generated using marching cubes algorithm, and the specific interfacial area and characteristic length were calculated.¹

Rheological characterization of the blends with droplet and cocontinuous morphologies was performed. The rheology of droplet blends was fit to the Palierne viscoelastic droplet model to quantify the equilibrium interfacial tension of PE/PEO blends using both PE and PE-g-MA.  Cocontinuous blend rheology was investigated over annealing time to predict coarsening behavior. 

The gas separation membranes were prepared by solvent casting a THF solution of PS-PIL-PS ionic gel into porous PE sheets.² The effect of type of processing, pore size, film thickness, and pore wall functionality on the performance of the membranes is discussed and compared.

1. Lopez-Barron, C.; Macosko, C. W. Langmuir 2009, 16, 9392-9404.

2. Gu, Y.; Lodge, T.P. Macromolecules 2011, DOI/ma2001838.