Cellulose acetate

Abstract: Diffusion and distribution coefficients of water and sodium chloride have been measured in cellulose acetate osmotic membranes. These coefficients have been found to vary with the degree of acetylation of the cellulose ester. The diffusion coefficient of water varies from 5.7 × 10−6 to 1.3 × 10−6 cm.2/sec., and the diffusion coefficient of salt varies from 2.9 × 10−8 to 3.9 × 10−11 as the acetyl content is increased from 33.6 to 43.2 wt.-%. A homogeneous diffusion model is proposed which describes the observations in terms of Fick's law.

Abstract: Three solvents, that is, acetone, acetic acid, and dimethylacetamide (DMAc), with a range of solubility parameter δ, surface tension γ, viscosity η 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 η between 1.2 and 10.2 poise and γ around 26 dyne/cm and produce smooth fibers with diameters from 100 nm to ∼1 μm. 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. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2119–2129, 2002

Abstract: The application of different ionic liquids (IL), namely 1-N-butyl-3-methylimidazolium chloride ([C(4)mim](+)Cl(-)), 3-methyl-N-butyl-pyridinium chloride and benzyldimethyl(tetradecyl)ammonium chloride were investigated as solvents for cellulose. The ILs used have the ability to dissolve cellulose with a degree of polymerization in the range from 290 to 1 200 to a very high concentration. Using [C(4)mim](+)Cl(-), no degradation of the polymer appears. By (13)C NMR measurement it was confirmed that this IL is a so-called non-derivatizing solvent. [C(4)mim](+)Cl(-) can be applied as a reaction medium for the synthesis of carboxymethyl cellulose and cellulose acetate. Without using any catalyst, cellulose derivatives with high degree of substitution could be prepared.(13)C NMR spectrum of cellulose dissolved in the IL [C(4)mim](+)Cl(-) (top). The (13)C NMR spectrum of cellulose dissolved in DMSO/tetrabutylammonium fluoride trihydrate is shown for comparison (bottom).