Portal de Periódicos da CAPES

Observations on the structure of first generation polybenzimidazole reverse osmosis membranes

1984; Elsevier BV; Volume: 20; Issue: 2 Linguagem: Inglês

10.1016/s0376-7388(00)81329-0

1873-3123

Linda C. Sawyer, R. S. Jones,

Recycling and Waste Management Techniques

The structure-property relationships of polybenzimidazole (PBI) reverse osmosis (RO) membranes are important in process optimization. The membrane transport properties are influenced by the morphology which, in turn, is established by the process variables. Microscopical observation of the in situ porous textures of experimental membranes required development of special sample preparation methods. The preparation involves gradual replacement of water, and infiltration by an embedding resin, which permits thin sectioning for microscopical observation without collapse of the structure. p]Optical microscopy observations using the newly developed method provide an excellent overview useful for screening process variables. Scanning electron microscopy (SEM) was used to obtain useful three-dimensional fracture views of samples, although the membrane structure is somewhat collapsed during specimen preparation. Pore size and distribution, particularly in the region of the dense surface layer critical for effective separation properties (the active layer), were analyzed using transmission electron microscopy (TEM). Membrane surfaces were characterized using SEM and high resolution scanning electron imaging (SEI). Preliminary study revealed major morphological variation as flux levels varied. A study of high-flux as-cast and annealed first generation membranes revealed finger-like macrovoids below the top 500 nm layer. The top 20 nm has no resolvable pores (resolution limit about 10 nm, limited by sample thickness), whereas the bulk membrane exhibits pores about 100 nm across. The annealing process appears to shrink the membrane and reduce the pores to half the as-cast size.