Cation exchange membranes based on semi interpenetrating network (sIPN) are prepared for diffusion dialysis (DD) using poly(vinylidene difluoride) (PVDF) and sodium p-styrenesullonate (SSS) as starting materials. Five membranes have been prepared by varying the content of PVDF and dosage of crosslinking agent. Ion exchange capacity (lEC), water uptake (W-R), swelling resistance and mechanical property of the membranes have been measured. These membranes show excellent thermal and alkali stability due to the high-performance PVDF matrix and sIPN morphology. The membranes have been successfully applied to alkali recovery. The base dialysis coefficients (U-OH) are in the range of 0,00080-0.0061 m/h and the separation factors (S) in the range 12.0-90.3 at 25-65 degrees C. Effect of PVDF content and cross-linking degree on ion permeability and selectivity has been discussed. 2013 Elsevier B.V. All rights reserved.