(33d) Tying Formulation and Extensional Rheology to Processability in the Manufacturing of Ultrafine Fibers Via Electrospinning

Ultrafine fibers, those with a diameter less than approximately 5 mm, play a starring role in new product research in the fiber and textile industry, both for conventional textiles such as clothing and furnishing and for technical textiles in electronics, bioengineering, sensors and more. The frontrunner in manufacturing technology for ultrafine fibers is electrospinning, a technology similar to dry spinning in conventional fiber production, but where the pulling force is provided by an electric field, rather than mechanical intervention. Due to its relatively low productivity and high cost, electrospinning is most attractive for high value-add products such as cell growth scaffolds, pharmaceutical products, and electronics. Yet, high value-add products typically come with complex product specifications and designing a solution that can be electrospun, but contains all of the components for functionality in high value products, is challenging. To better understand how the material components of the solution effect the ability to form fibers, we focus on the response of the fluid to the extensional stress encountered during electrospinning. In complex fluids, there are viscoelastic stresses, microstructural transitions and extensional viscosities that alter free surface flows and processability. We use dripping-onto-substrate (DOS) extensional rheometry to examine polymer solutions with different compositions, including polymers of different molecular weights and stiffnesses and tie their rheological properties to the electrospinnability. We show that the extensional rheology can be used to predict the three different regimes of electroprocessing, formation of beads, beads-on-string and smooth fibers, for a given polymer solution and begin to tie polymer properties to spinnability. By understanding how complex formulation properties impact the ability to form fibers via electrospinning, we can rapidly respond to consumer needs as new products are developed for high value applications, including biomedical and electronic textiles.