Preparation and vacuum membrane distillation performance of a superhydrophobic polypropylene hollow fiber membrane modified via ATRP

Superhydrophobic polypropylene hollow fiber membranes were fabricated using single- and multi-step atom transfer radical polymerization methods. The degree of grafting was improved by intermittently adding equal doses of monomers. Membrane morphology and anti-wetting properties of the membranes produced using the two methods were thoroughly investigated to understand the influence of structure on vacuum membrane distillation (VMD) performance. Initial monomer dosages of 20% and 30% facilitated the production of superhydrophobic modified membranes with water contact angles of 167.9° and 179.0°, respectively. The samples with the highest liquid entry pressure were produced using an initial monomer dosage of 20%, and were selected for the VMD experiments. Testing was conducted for 21 h and indicated that the modification method significantly affected VMD performance. This was attributed to the prominent differences in morphology and pore distribution. The average flux of the membrane produced with 20% monomer using the single-step method was 11.01 kg/m2h, which was 4.53 kg/m2h higher than that of the unmodified membrane; the long-term stability was superior. Although the membrane produced using the multi-step method exhibited an excellent average flux of 12.71 kg/m2h, the performance was highly unstable, and flux suddenly dropped after 6 h. Furthermore, the rejection performance was unsatisfactory. Overall, the two new membranes showed pronounced distinctions in VMD performances, which agrees well with our hypotheses.