Electrospinning based on benign solvents: current definitions, implications and strategies

Electrospinning evolved as a powerful technology to produce membranes consisting of nano- to micron-scaled fibers offering unique membrane properties due to the extremely high surface-to-volume ratio and high membrane porosity. However, this technology is often far removed from a green and environmentally-friendly process, as it employs solvents with issues such as high flammability, toxicity, difficult disposal, or energy-intensive synthesis. Indeed, the most commonly used solvents in the electrospinning field are halogenated (e.g. chloroform, trifluoroethanol) and toxic solvents (e.g. dimethylformamide), the use of which is now restricted by the Chemical Control Regulation in the European Union (REACH). This is especially important when considering the commercialization of electrospun products due to the more limited solvent choice. In order to render electrospinning more attractive as a commercial technique and further improve scalability, solvent alternatives and other green routes have to be established, which adhere to societal and legal restrictions especially in regard to the environmental and health impact. Therefore, this review provides the current ecological and economical context of this technology, and summarizes recent approaches towards green electrospinning. Since electrospinning from solutions and dispersions constitutes the predominantly used form of this technique both in research and industry, the focus of this work is set on the use of solvents or solvent mixtures classified exclusively by the term "green". The approaches presented comprehensively cover the production of polymeric fibers via solution, emulsion, suspension, and in situ cross-linking electrospinning.