Charged Cellulose Acetate Research Articles

Nanofibrous mats layer-by-layer assembled via electrospun cellulose acetate and electrosprayed chitosan for cell culture

Negatively charged cellulose acetate (CA) and positively charged chitosan (CS) were layer-by-layer (LBL) assembled together by the electrospinning–electrospraying hybrid technique via physical deposition and electrostatic force for the first time. The morphology of the mats indicated that all of them were of a good fiber shape and a three-dimension structure. The X-ray photoelectron spectroscopy results verified the existence of CS on the surface of the as-spun mats. The thermogravimetric analysis and differential scanning calorimetry results illustrated that the thermal properties of the mats were affected by their compositions. In addition, the cell culture experiment demonstrated that the scaffolds with the LBL structured polysaccharide films were of good cell compatibility and no cytotoxicity for the mouse lung fibroblasts cells. Moreover, the ability of cell adhesion and spreading was affected by the number of deposition layers and the composition of outermost layer.

LBL structured chitosan-layered silicate intercalated composites based fibrous mats for protein delivery

Organic rectorite (OREC) was used to prepare intercalated composites with chitosan. The negatively charged cellulose acetate (CA) fibrous mats were modified with multilayers of the positively charged chitosan or chitosan–OREC intercalated composites and the negatively charged bovine serum albumin (BSA) via electrostatic layer-by-layer (LBL) self-assembly technique. The morphology and protein delivery properties of the resultant samples were investigated by regulating the number of deposition bilayers, the outermost layer and the composition of coating bilayers. The thickness of LBL films coated CA mats increased as the number of bilayers was increased and OREC was added. X-ray photoelectron spectroscopy indicated that chitosan and OREC were deposited on CA fibers. Small angle X-ray diffraction patterns showed that OREC was intercalated by chitosan. The in vitro BSA encapsulation and release experiments demonstrated that OREC could affect the degree of protein loading capacity and release efficiency of the LBL films coating.

Polyelectrolyte Multilayer-Assisted Immobilization of Zero-Valent Iron Nanoparticles onto Polymer Nanofibers for Potential Environmental Applications

We report a facile approach to synthesizing and immobilizing zero-valent iron nanoparticles (ZVI NPs) onto polyelectrolyte (PE) multilayer-assembled electrospun polymer nanofibers for potential environmental applications. In this approach, negatively charged cellulose acetate (CA) nanofibers fabricated by electrospinning were assembled with multilayers of poly(diallyldimethylammonium chloride) (PDADMAC) and polyacrylic acid (PAA) through electrostatic layer-by-layer assembly. The formed PAA/PDADMAC multilayers onto CA nanofibers were then used as a nanoreactor to complex Fe(II) ions through the binding with the free carboxyl groups of PAA for subsequent reductive formation of ZVI NPs. Combined scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetry analysis studies demonstrate that the ZVI NPs are successfully synthesized and uniformly distributed into the PE multilayers assembled onto the CA nanofibers. The produced hybrid nanofibrous mats containing ZVI NPs were found to exhibit superior capability to decolorize acid fuchsin, an organic dye in dyeing wastewater. We show that the loading capacity of ZVI NPs can be tuned by changing the number of PE layers and the cycles of binding/reduction process. Increasing the number of the binding/reduction cycles leads to a slight bigger size of the ZVI NPs, which is not beneficial for improving the reactivity of ZVI NPs. The present approach to synthesizing and immobilizing ZVI NPs onto polymer nanofibers opens a new avenue to fabricating various fiber-based composite materials with a high surface area to volume ratio for environmental, catalytic, and sensing applications.

Polyelectrolyte multilayer film-assisted formation of zero-valent iron nanoparticles onto polymer nanofibrous mats

A facile approach that combines the electrospinning technique and layer-by-layer (LbL) assembly method has been developed to synthesize and immobilize zero-valent iron nanoparticles (ZVI NPs) onto the surface of nanofibers for potential environmental applications. In this approach, negatively charged cellulose acetate (CA) nanofibers fabricated by electrospinning CA solution were modified with bilayers composed of positively charged poly(diallyl-dimethyl-ammoniumchloride) (PDADMAC) and negatively charged poly(acrylic acid) (PAA) through electrostatic LbL assembly approach to form composite nanofibrous mats. The composite nanofibrous mats were immersed into the ferrous iron solution to allow Fe(II) ions to complex with the free carboxyl groups of PAA, and then ZVI NPs were immobilized onto the composite nanofibrous mats instantly by reducing the ferrous cations. Combined scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and thermogravimetry analysis demonstrated that the ZVI NPs are successfully synthesized and uniformly distributed into the polyelectrolyte (PE) multilayer films assembled onto the CA nanofibers. The present approach to synthesis ZVI NPs opens a new avenue to fabricating various materials with high surface area for environmental, catalytic, and sensing applications.

Polyoxometalate nanotubes from layer-by-layer coating and thermal removal of electrospunnanofibres

We have recently fabricated Keggin-type polyoxometalate(H4SiW12O40) nanotubes by calcining layer-by-layer (LBL) structured ultrathin hybrid film coated electrospunfibrous mats. The hybrid film coated electrospun fibrous mats were obtained from the alternatedeposition of positively charged poly(allylamine hydrochloride) (PAH) and negatively chargedH4SiW12O40 on the surface of negatively charged cellulose acetate (CA) nanofibres using the electrostaticLBL self-assembly technique. The fibrous mats were characterized by scanning electronmicroscopy, transmission electron microscopy, Fourier transform infrared (FT-IR) spectroscopy,and wide-angle x-ray diffraction (WAXD). It was found that the morphology of hybridPAH/H4SiW12O40 film coated fibrous mats was strongly influenced by the number of depositionbilayers and the pH of dipping solutions. The fibrous mats were contracted andH4SiW12O40 nanotubes with a wall thickness of about 50 nm can be fabricated after calcination at hightemperature. Additionally, the FT-IR and WAXD results indicated that the pureH4SiW12O40 nanotubes were obtained with a Keggin structure.

Layer-by-layer structured films ofTiO2 nanoparticles and poly(acrylic acid) on electrospun nanofibres

We report a new approach for fabricating layer-by-layer (LBL) structuredultrathin hybrid films on electrospun nanofibres. Oppositely charged anataseTiO2 nanoparticles and poly(acrylic acid) (PAA) were alternately deposited on the surface ofnegatively charged cellulose acetate (CA) nanofibres using the electrostatic LBL self-assemblytechnique. The fibrous mats were characterized by wide-angle x-ray diffraction, Fouriertransform infrared spectroscopy, scanning electron microscopy, transmission electron microscopyand Brunauer–Emmett–Teller (BET) surface area techniques. The crystalline phase of anataseTiO2 remained unchangedin the resultant TiO2/PAA films coated on CA fibrous mats. Moreover, theTiO2/PAA film coated fibres showed rough surfaces with grains due to the deposition of aggregatedTiO2 particles. The average diameter of the fibres increased from 344 to 584 nmand the BET surface area of the fibrous mats increased from 2.5 to6.0 m2 g−1 after coating withfive bilayers of TiO2/PAA films.

Distribution analysis of cellulose acetate phthalate by ion-exclusion-moderated size exclusion chromatography

Ion-exclusion is the electrostatic repulsive interaction between a charged polymer and charges of the same sign on the surface of a column packing. Controlled ion-exclusion allows compensation of hydrophobic adsorption in size exclusion chromatography of negatively charged cellulose acetate phthalate (CAP) polymers in acetone/water/LiCl (80/20) as a mobile phase. Properly selected low-ionic-strength conditions provide correct separation in size-exclusion mode also in binary solvent mixtures. Possible interfering effects related to light scattering at low-salt conditions are shown to be negligible if on-line concentration/light scattering detection is used. The absence of these interferences is easily checked by a comparison of experiments at two different low-salt concentrations. Molecular weight averages and distributions identical within the experimental error are obtained when both salt concentrations are properly selected.

Interactions in reverse osmosis of electrolyte/ charged surfactant solutions through porous membranes

Reverse osmosis experiments have been carried out using very weakly negatively charged cellulose acetate membranes and membranes made from sulfonated polysulfone which have cation—exchange properties. Experimental solutions consisted of hydrophobic charged surfactants and inorganic electrolytes. The rejection of the surfactants decreases markedly as the concentration of electrolytes increases and reaches negative values at low pressures. The volume flow in the presence of the surfactants also decreases. A membrane polymer/substrate interaction, e.g. adsorption, is proposed to account for this effect which is more pronounced with the ion—exchange membranes. However, at c.m.c. levels in the solution, the surfactant rejection increases and it appears to be related to a change in the activity.

Interactions in reverse osmosis of electrolyte/ charged surfactant solutions through porous membranes

Reverse osmosis experiments have been carried out using very weakly negatively charged cellulose acetate membranes and membranes made from sulfonated polysulfone which have cation—exchange properties. Experimental solutions consisted of hydrophobic charged surfactants and inorganic electrolytes. The rejection of the surfactants decreases markedly as the concentration of electrolytes increases and reaches negative values at low pressures. The volume flow in the presence of the surfactants also decreases. A membrane polymer/substrate interaction, e.g. adsorption, is proposed to account for this effect which is more pronounced with the ion—exchange membranes. However, at c.m.c. levels in the solution, the surfactant rejection increases and it appears to be related to a change in the activity.

Electrothermographic behaviour of corona charged cellulose acetate and the leucomalachite Green mixed system

Important electrothermographic characteristics such as charge acceptance, surface-potential decay with and without exposure to infrared radiations, retention of surface charge, contrast potential and residual potential of pure and sensitized cellulose acetate layers have been investigated. An attempt has been made to explain the results on the basis of electrical properties. Leucomalachite Green (LMG) is found to be very effective in controlling the thermosensitivity in the cellulose acetate layers. Cellulose acetate layer sensitized with 20% by wt of LMG shows a suitable high-contrast potential of 890 V with zero residual potential on heating its surface to 62° C and is a suitable material for electrothermographic and related applications.

Study of the surface potential decay characteristics in cellulose acetate films

The surface potential decay characteristics of corona charged cellulose acetate films have been investigated as a function of charging time, initial surface potential, thickness and voltage polarity. Some of these studies have also been performed on iodine doped (2% wt/wt) cellulose acetate films. The carrier mobility has been calculated from these measurements and comes out to be 1.96 × 10 −9 cm 2 V −1 s −1 for pure cellulose acetate films. It has been found that the carrier mobility increases to 6.0 × 10 −6 cm 2 V −1 s −1 by iodination.

Membrane/water distribution and diffusion of nickel ion in cellulose acetate membranes

In the framework of a study on the removal of metals from aqueous solutions by reverse osmosis, Ni ++ diffusion and distribution between weakly charged cellulose acetate (CA) dense membranes and aqueous NiSO 4 were determined. NiSO 4 solutions with concentrations from 10 -1 to 10 -3 were used. The values of diffusion coefficients were found to be 10 -13 cm 2/s and practically independent of salt concentration. Distribution coefficient data varied as a function of the external solution concentration, according to Anderson's treatment of electrolyte sorption. The experimental data were in satisfactory agreement with Glueckauf's physical model of distribution, at sufficiently high concentrations.