FLUX DECAY AND REJECTION DURING MICRO-FILTRATION AND ULTRA-FILTRATIONOF HYDROPHOBICALLY-MODIFIED WATER-SOLUBLE POLYMERS

Crossflow filtration of anionic and cationic hydrophobically modified water-soluble polymers was studied using polyether sulphone membranes with varying pore sizes. New data on the permeate flux rates and rejec tions of these polymer solutions are presented. It was found that the pseudo-gel polarisation concentration increases with increasing polyme r solubility. The steady state permeate flux decays linearly with log (MWCO). A minimum molecular weight cut off (MMWCO) can be identified b y extrapolating the steady state permeate flux to zero. The MMWCO is w ell below the molecular weight cut off (MWCO) based on the random coil size of the macromolecule. It is shown that the MMWCO should be based on the size of the small axis of the rod-like extended molecule, whic h can orientate in the flow field during passage through the pores. Th is model also explains why the polymer rejection increases with increa sing permeate flux.