Ultrafine fibrous cellulose membranes from electrospinning of cellulose acetate

Three solvents, that is, acetone, acetic acid, and dimethylacetamide (DMAc), with a range of solubility parameter delta, surface tension gamma, viscosity eta and boiling temperature were used to generate mixtures for electrospinning cellulose acetate (CA) (degree of substitution, DS=2.45). Although none of these solvents alone enables continuous formation of fibers, mixing DMAc with either acetone or acetic acid produced suitable solvent systems. The 2:1 acetone:DMAc mixture is the most versatile mixture because it allows CA in the 12.5-20% concentration range to be continuously electrospun into fibrous membranes. These CA solutions have eta between 1.2 and 10.2 poise and gamma around 26 dyne/cm and produce smooth fibers with diameters from 100 nm to similar to1 mum. Fiber sizes generally decrease with decreasing CA concentrations. The nature of the collectors affects the morphology as well as packing of fibers. Fibers collected on paper have more uniform sizes, smooth surfaces, and fewer defects, whereas fibers collected on water are more varied in size. Electrically conductive solid collectors, such as Al foil and water, favor more tightly packed and less porous membranes. Porous collectors, like paper and copper mesh, produce highly porous membranes. The pores in membranes collected on the Al foil and paper are much better interconnected in the planar directions than those in membranes collected on water. There is evidence that electrospinning induces order in the fibers. Deacetylation of CA membranes is more efficient and complete in NaOH/ethanol than in aqueous NaOH, producing DS values between 0.15 and 2.33 without altering fiber surfaces, packing, or organization. The fully regenerated cellulose membranes are similarly hydrophilic as commodity cellulose fibrous matrices but absorb nearly 10 times as much water. (C) 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2119-2129, 2002.