Ultrafine Cellulose Acetate Fibers with Nanoscale Structural Features

Nano-structural features were introduced to ultrafine cellulose acetate (CA) fibers by electrospinning of its mixtures with either poly(vinyl pyrrolidone) PVP or β-cyclodextrin (β-CD) in DMF, followed by dissolution of the added PVP or β-CD. The presence of the charge-holding PVP enabled fiber formation from CA below its entanglement chain length and improved the electrospinning efficiency to produce bicomponent fibers with wide ranging diameters from 30 to 650 nm. At up to 50% contents, the PVP in the bicomponent fibers was phase-separated from CA and, upon removal, resulting in highly angulated fiber surfaces with nanometer-size spherulites and sub-micron size ridges and grooves. Adding β-CD to CA enabled fiber formation at concentrations below the chain entanglement concentration Ce (16.5%). Hydrogen bonding between β-CD and CA, as evident by FTIR, helped to distribute β-CD as individual molecules in the CA matrix and producing more uniform and finer (130–150 nm in diameters) fibers, irrespective of their β-CD contents. Removal of β-CD from the fibers originally containing 40% β-CD, generated nanoporous fibers with 2-nm nanopores and 70% increase in specific surface and doubled pore volume.