Rubber nanofibrous membranes obtained by electrospinning: preparation, functionalization, and application as filters for oil/water separation

Offshore oil spills, industrial oily wastewater, and domestic oil pollution are some of the most serious global challenges and are leading environmental causes of morbidity and mortality. The development of effective methods to separate oils from water surfaces and oil/water mixtures is thus crucial. Electrospinning is a unique technique to produce nonwoven membranes formed by fine submicrometric fibers from polymer solution or melt through the application of high electrostatic forces. Electrospun nanofibrous membranes are considered a promising candidate for oil/water separation, with competitive advantages including a large specific surface area, high porosity, good pore channel connectivity, facile tunability of surface wettability, and easily scalable fabrication from various materials. In particular, the fabrication of rubber nanofibrous membranes by electrospinning has recently attracted significant attention owing to their interesting properties, such as high elasticity, extensibility and abrasion resistance, low hysteresis loss and excellent resilience. This research work concerns the preparation and functionalization of rubber electrospun membranes for oil/water separation. Suspension electrospinning (i.e., electrospinning of a stable dispersion of polymer micro-/nano-particles in water using a small quantity of an easily electrospinnable water-soluble polymer acting as a template) of a styrene-butadiene rubber (SBR) latex and polyethylene oxide (PEO) as template polymer is carried out. Then, a thiol-ene photo-induced chemical crosslinking process of the fibrous membranes is applied to inhibit the movement of the polymeric macromolecules and thus prevent the collapse of the fibers due to cold flow. This combination of processes allows the easy production of stable and insoluble rubber nanofibrous membranes exhibiting high hydrophobicity (contact angle with water &#8776;100°) and oleophilicity (contact angle with hexadecane <10°). After a few minutes of continuous contact with water, however, the membranes become gradually hydrophilic, losing their oil/water separation capacity. To overcome this limitation, a surface functionalization of the electrospun rubber membranes is designed and developed with the aim of tuning and stabilizing their wettability. In particular, a vinyl terminated polydimethylsiloxane (PDMS) is used as functionalizing agent. In order to study and optimize the membranes functionalization process, characterization techniques such as FT-IR, optical microscopy and FE-SEM analyses were used. In addition, quantitative tests were conducted to evaluate the wettability properties and the oil/water separation efficiency of the functionalized membranes. The developed PDMS-functionalized rubber nanofibrous membranes are demonstrated to maintain their hydrophobicity with time (water contact angle of 123° after 30 minutes, and water-in-oil contact angle of 121° after 24 hours) and to successfully separate oil from water (efficiency of separation of 99.31 %), showing an outstanding application potential for the treatment of polluted oily water.