Design and fabrication of lotus-root-like multi-bore hollow fiber membrane for direct contact membrane distillation

Highly constrained by the requirements of high porosity and large pore sizes, traditional single-bore hollow fiber membranes often suffer from easy breakage and performance instability during long-term operations of membrane distillation (MD). In this work, a multi-bore PVDF hollow fiber (MBF) membrane with a lotus root-like geometry was designed and successfully fabricated via the specially designed spinneret and optimized spinning conditions. Various effects of spinning parameters including bore flowrate, dope flowrate and take-up speed were investigated on the membrane macro- and micro-structure, mechanical properties and direct contact membrane distillation (DCMD) performance. The tensile strength characterizations have proven the excellent mechanical rigidity and elasticity of MBF membranes. Even for the MBF membrane with a thin wall of around 40 μm, the maximum load was as high as 2.4 N. Most importantly, the performance of the DCMD of the MBF membrane was only slightly lower or even comparable to that of single-bore membranes. In addition, the MBF membranes exhibited superior stability in terms of vapor permeation flux and salt rejection during the continuous DCMD experiment with robust operational conditions. We believe this work may have profound implication to the development of mechanically durable membranes not only for membrane distillation MD but also for other membrane applications.