Effects of molecular weight distribution (Md) on the performances of the polyethersulfone (PES) ultrafiltration membranes

• PES membranes with different structures can be obtained by blending.
• Wider Md leads to higher flux and lower rejection at similar Mn of PES.
• Wider Md leads to lower flux and rejection at similar Mw of PES.
• Membranes showed similar performances irrespective of Md as Mη is similar.

In this study, effects of molecular weight distribution (Md) on the performances of polyethersulfone (PES) ultrafiltration membrane were studied. PES samples with similar weight average molecular weight (Mw), number average molecular weight (Mn), or viscosity average molecular weight (Mη) but different Md, were obtained by blending. The thermodynamic and the kinetic factors were studied through ternary phase diagram and shear viscosity data, respectively. Experimental results showed that PES membranes with different structures can be obtained by blending. This can be due to the combined effects of the thermodynamic factor and kinetic factor of casting solution. The filtration experiments showed that wider Md would lead to higher permeability and lower rejection when the Mn values of PES were similar, and on the other side, wider Md could lead to lower permeability and rejection when the Mw values of PES were similar. In addition, under conditions of similar Mη values of PES, the membranes showed similar performances irrespective of the Md.

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