Hydrophobic modification of poly(phthalazinone ether sulfone ketone) hollow fiber membrane for vacuum membrane distillation

New hydrophobic poly(phthalazinone ether sulfone ketone) (PPESK) hollow fiber composite membranes coated with silicone rubber and with sol–gel polytrifluoropropylsiloxane were obtained by surface-coated modification method. The effects of coating time, coating temperature and the concentration of silicone rubber solution on the vacuum membrane distillation (VMD) properties of silicone rubber coated membranes were investigated. It was found that high water permeate flux could be gotten in low temperature and low concentration of silicone rubber solution. When the coating temperature is 60 °C, the coating time is 9 h and the concentration of silicone rubber solution is 5 g L−1 the water permeate flux of the silicone rubber coated membrane is 3.5 L m−2 h−1. The prepolymerization time influence the performance of polytrifluoropropylsiloxane coated membranes, and higher prepolymerization time decrease the water permeate flux of the membrane. The water permeate flux and the salt rejection was 3.7 L m−2 h−1 and 94.6%, respectively in 30 min prepolymerization period. The VMD performances of two composite membranes during long-term operation were studied, and the results indicated that the VMD performances of two composite membranes are quite stable. The salt rejection of silicone rubber coated membrane decreased from 99 to 95% and the water permeate flux fluctuated between 2.0 and 2.5 L m−2 h−1. The salt rejection of polytrifluoropropylsiloxane coated membrane decreased from 98 to 94% and the water permeate flux fluctuated in 1 L m−2 h−1 range.