Coating of hydrophobic hollow fiber PVDF membrane with chitosan for protection against wetting and flavor loss in osmotic distillation process

This research studied the coating of hydrophobic membrane PVDF with chitosan, a highly hydrophilic polymer, for protection against wetting by oils from fruit juice and for reduction of flavor losses in osmotic distillation process (OD). FTIR and SEM results indicated that chitosan was well coated on PVDF membrane surface. The protection against wetting of the membranes was tested by OD of oil solution (limonene 2%, v/v) for 5 h. The results indicated that the coated membrane was able to protect the membrane against wetting-out and could maintain stable flux. An uncoated membrane was obviously wetted which was supported by the existence of CaCl2 in the retentate solution and the decrease of the permeate flux.Coating of membrane with chitosan resulted in membrane with higher water flux. For the membrane coated with chitosan crosslinked by formaldehyde, water flux decreased with increasing formaldehyde concentration. In OD of flavors (ethyl acetate and ethyl hexanoate)–limonene–water mixtures, when limonene concentration was increased, water flux decreased significantly while flavor fluxes and flavor losses increased. Coated membranes not only gave higher water flux but they also gave lower flavor flux. The results suggested that the coated membrane was appropriate for feed containing high limonene oil.