Release characteristics of four model drugs from drug-loaded electrospun cellulose acetate fiber mats

Ultra-fine fiber mats of cellulose acetate (CA; M_w ≈ 30?000 Da; degree of acetyl substitution ≈ 2.4) containing four different types of model drugs, i.e., naproxen (NAP), indomethacin (IND), ibuprofen (IBU), and sulindac (SUL), were successfully prepared by electrospinning from 16% w/v CA solutions in 2:1 v/v acetone/N,N-dimethylacetamide (DMAc). The amount of the drugs in the solutions was fixed at 20 wt.% based on the weight of CA powder. The morphology of the drug-loaded electrospun (e-spun) CA fiber mats was smooth, with the average diameters of these fibers ranging between 263 and 297 nm. No presence of the drug aggregates of any kind was observed on the surfaces of these fibers, suggesting that the drugs were encapsulated well within the fibers. After submersion in the acetate buffer solution at 37 °C for 24 h, the drug-loaded e-spun CA fiber mats swelled particularly well (i.e., 570-630%), while the corresponding solvent-cast film counterparts did not. The release characteristics of the model drugs from both the drug-loaded CA fiber mats and the drug-loaded as-cast CA films were carried out by the total immersion method in the acetate buffer solution at 37 °C. At any given immersion time point, the release of the drugs from the drug-loaded e-spun CA fiber mats was greater than that from the corresponding as-cast films. The maximum release of the drugs from both the drug-loaded fiber mats and films could be ranked as follows: NAP > IBU > IND > SUL.     

Electrospun cellulose acetate fiber mats containing curcumin and release characteristic of the herbal substance

Ultra-fine cellulose acetate (CA; M_w ≈ 30,000 Da; degree of acetyl substitution ≈ 2.4) fiber mats containing curcumin from the plant Curcuma longa L., widely known for its anti-tumor, antioxidant, and anti-inflammatory properties, were fabricated, for the first time, from the neat CA solution (17% w/v in 2:1 v/v acetone/dimethylacetamide) containing curcumin in various amounts (i.e., 5–20 wt.% based on the weight of CA powder) by electrospinning. Incorporation of curcumin in the neat CA solution did not affect the morphology of the resulting fibers, as both the neat and the curcumin-loaded CA fibers were smooth. The average diameters of the curcumin-loaded CA fibers ranged between 314 and 340 nm. The integrity of the as-loaded curcumin in the curcumin-loaded CA fiber mats was intact as indicated by the ¹H nuclear magnetic resonance spectrometric results and the ability of the as-loaded curcumin in maintaining its free radical scavenging ability. Investigation of the release characteristic of curcumin from the curcumin-loaded CA fiber mats was carried out by the total immersion and the transdermal diffusion through a pig skin method in the acetate buffer solution containing Tween 80 and methanol or the B/T/M medium at 37 °C. In the total immersion method, almost all of the curcumin loaded in the curcumin-loaded CA fiber mat specimens was released into the medium (90 to 95%), while considerably lower values were obtained when the curcumin-loaded CA fiber mats were placed on top of a piece of pig skin. Lastly, the curcumin-loaded CA fiber mats were proven non-toxic to normal human dermal fibroblasts.     

Structural studies of electrospun cellulose nanofibers

Non-woven mats of submicron-sized cellulose fibers (250-750 nm in diameter) have been obtained by electrospinning of cellulose solutions. Cellulose are directly dissolved in two solvent systems: (a) lithium chloride (LiCl)/N,N-dimethyl acetamide (DMAc) and (b) N-methylmorpholine oxide (NMMO)/water, and the effects of (i) solvent system, (ii) the degree of polymerization of cellulose, (iii) spinning conditions, and (iv) post-spinning treatment such as coagulation with water on the miscrostructure of electrospun fibers are investigated. The scanning electron microscope (SEM) images of electrospun cellulose fibers show that applying coagulation with water right after the collection of fibers is necessary to obtain submicron scale, dry and stable cellulose fibers for both solvent systems. X-ray diffraction studies reveal that cellulose fibers obtained from LiCl/DMAc are mostly amorphous, whereas the degree of crystallinity of cellulose fibers from NMMO/water can be controlled by various process conditions including spinning temperature, flow rate, and distance between the nozzle and collector. Finally, electrospun cellulose fibers are oxidized by HNO₃/H₃PO₄ and NaNO₂, and the degradation characteristics of oxidized cellulose fibers under physiological conditions are presented.     

Synthesis and characterization of interpenetrating networks from polycarbonate and cellulose acetate butyrate

Polycarbonates (PC) are currently used for organic optical glass; nevertheless they show a poor impact resistance which may be increased by combination with cellulose acetate butyrate (CAB) into a PC/CAB interpenetrating polymer network (IPN), without altering the material transparency as we show here. A series of rigid IPNs based on an aliphatic polycarbonate and CAB was prepared through in situ polymerization techniques. The kinetics of the formation of two networks in the IPNs were studied by FTIR spectroscopy. Effects of the CAB cross-linking and weight proportions of the two components in the IPNs were investigated by dynamic mechanical thermal analysis.     

Electrospinning of native cellulose from nonvolatile solvent system

Improving and understanding the electrospinnability of native cellulose in room temperature ionic liquids (RTIL) have been a hot issue in recent years. In this study, the electrospinning of cellulose in a highly efficient RTIL of 1-allyl-3-methylimidazolium chloride (AMIMCl) was investigated. The introduction of co-solvent dimethyl sulfoxide (DMSO), which significantly decreased the surface tension, viscosity and entanglement density of the network and increased the conductivity of the spinning dope, contributed to a continuous jet. The problems lying in nonvolatility and the high ionic strength of the RTIL, which unavoidably led to the standing up vertically, adhesion and contractions of the wet fibers during the electrospinning process, were successfully resolved using a rotating copper-wire drum as a collector and solidifying the jet under high relative humidity. The water vapor played an important role in leading to “skin formation” which helped to stabilize the fibrous morphology, and finally smooth ultra-thin regenerated cellulose fibers were obtained. The combination of solvent system and collecting apparatus and conditions provided not only an effective method of producing ultra-thin native cellulose fibers on a large scale, but also a fundamental solution to other electrospinning systems with high ionic strength and nonvolatility. Measurements on WAXD and FT-Raman indicated that the electrospun cellulose fibers were almost amorphous with a little crystallization presented the polymorph of Type-II, which was totally different from the native cellulose with the dominated polymorph of Type-I.     

Electrospun cellulose acetate fibers containing chlorhexidine as a bactericide

Submicron fibers with bactericidal properties were prepared from electrospinning of blends containing cellulose acetate (CA) as a polymer base, chlorhexidine (CHX) as a bactericidal agent, and organic titanate Tyzor^® TE (TTE) as a cross-linker. A small amount of high molecular weight poly(ethylene oxide) (PEO) was incorporated into the blends to facilitate the electrospinning, and its effect on the extensional properties and spinnability of the N,N-dimethylformamide (DMF) solutions were evaluated. The CHX-containing fiber meshes were cured by TTE in the presence of water vapor, which created covalent links between the CA and CHX. The immobilization of CHX on or within the fibers was confirmed by FTIR, Raman and XPS measurements. The resulting fiber meshes exhibited bactericidal properties on contact, due to the CHX immobilized on the fibers, and within a zone of inhibition (ZoI), due to the release of unbound CHX. The relationship of ZoI for the gram-negative Escherichia coli and the gram-positive Staphylococcus epidermidis to the amount of unbound CHX in the fibers is described by a simple diffusion model. The contact bactericidal capacity against both E. coli and S. epidermidis was assayed after complete removal of unbound CHX from the fibers. A post-spin treatment to attach CHX onto CA-PEO fibers via TTE linkers was also shown to be effective.     

Dielectric studies of cellulose and its derivatives: 1. Acetylation of cellulose

Dielectric conductivity (dc) and water absorption measurements are reported on a series of cellulose linter samples acetylated to varying degrees. The data illustrates the effects of the original structure of the cellulose linters both on the ease of acetylation and also on the subsequent dynamic characteristics of the polymer. It is only in the most forcing conditions that the primary fibrillar structure is destroyed. A change in properties is observed to occur at 40% acetylation of the hydroxyl groups, this coincides with the concentration of accessible groups as determined by deuterium exchange. A correlation is observed between the absorption and electrical observations on these systems.     

Electrospinning of hydroxypropyl cellulose fibers and their application in synthesis of nano and submicron tin oxide fibers

Synthesis of hydroxypropyl cellulose (HPC) fibers via electrospinning has been demonstrated, for the first time, in this investigation. The HPC solution in two different solvents, anhydrous ethanol and 2-propanol, has been utilized with two different tip-to-collector distance (10 and 15 cm) for synthesizing HPC fibers by varying applied voltage within the range of 10–30 kV. It has been shown that, nano (<100 nm) and submicron (>100 nm) HPC fibers can be obtained under the described electrospinning conditions. Average HPC fiber diameter and its bead formation tendency appear to be a function of nature of the solvent and the applied voltage. Characteristic features of electrospinning of HPC fibers appear to be in consonance with the established mechanism of polymer fiber formation via electrospinning. Use of electrospun HPC fibers in synthesizing and depositing highly porous network of nano and submicron tin oxide (SnO₂) fibers on microelectromechanical systems (MEMS) device has been demonstrated.     

Synthesis and characterization of cellulose acetate-polysulfone blend microfiltration membrane for separation of microbial cells from lactic acid fermentation broth

This work is focused on synthesis and characterization of a polymer blend microfiltration membrane for separation of microbial cells from lactic acid fermentation broth in a continuous process. The membranes were prepared by blending hydrophilic cellulose diacetate (CA) polymer with hydrophobic polysulfone (PSF) polymer in wet phase inversion method. Polymers were blended in N-methyl-2-pyrrolidone (NMP) solvent (70 wt.%) where polyethylene glycol was added as a pore former. The membranes were characterized in terms of morphology, porosity, flux and microbial separation capability. The best prepared membrane with PSF/CA weight ratio of 25/75 yielded a pure water flux of 1830 LMH (liter/m² h) and a fermentation broth flux of 1430 LMH at around 1.5 bar TMP (trans-membrane pressure). The membrane was successful in complete retention of microbial cells from the broth in a continuous crossflow membrane module integrated with the fermentor.     

Miscibility, free volume behavior and properties of blends from cellulose acetate and castor oil-based polyurethane

A series of blend films from cellulose acetate (CA) and castor oil-based polyurethane (PU) were prepared. Morphology, miscibility, free volume behavior and properties of such blend films were investigated by wide-angle X-ray diffraction (WXRD), infrared, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), positron annihilation lifetime spectroscopy (PALS), thermogravimetric analysis and tensile test. The results indicated that lager free volume cavities did not form at the interface of two polymers although a certain degree of phase separation was found by the studies of SEM and DSC. Strong intermolecular hydrogen bonding interactions at the interface, which was proved by Fourier transform infrared spectroscopy, favors even better molecular packing, that is, PU dispersed in CA continuous phase to form fine microphase separation domain in the CA-rich blends. Due to such special interactions in the fine microphase separation domain structure, optimized properties of tensile strength, breaking elongation and cold-resistivity were obtained in the blend film with 75 wt% CA. The toughness of all the blend films was significantly higher than that of the film CA, owing to the plasticizing of PU elastomer in the blends.     

Preparation of polyacrylonitrile and cellulose acetate blend fibers through wet‐spinning

Fibers containing both polyacrylonitrile (PAN) and cellulose acetate (CA) were prepared through wet‐spinning by using N,N‐dimethylformamide (DMF) as a solvent. Compatibility of PAN and cellulose acetate blend (PCB) fibers was investigated by means of scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and infrared (IR) spectrophotometry. The absorptive capacity and mechanical properties of the fibers were measured. It was observed that the surface and the cross section of PAN fibers were quite smooth and free from voids and microcracks, whereas cracks and voids were present on the surface and cross section of blend fibers, which increased with the incorporation of CA in the blend. Moisture regains of blend fibers were quite high while their tensile properties showed a partial decrease. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2000–2005, 2007     

Electrospinning and characterization of highly sulfonated polystyrene fibers

Nanofibers of highly sulfonated (IEC ∼4.5 meq/g) polystyrene (SPS) were successfully electrospun. To accomplish this, the process of electrospinning this difficult-to-spin material was studied in detail. Fiber quality was optimized by manipulating the process and solution variables to fabricate continuous bead-free fibers. Bead-free fibers (average diameter 260 nm) were electrospun from 25 wt% SPS (500 kDa) in DMF at an electrode separation of 10 cm, an applied voltage of 16.5 kV and a flow rate of 0.3 mL/h. With increasing solution concentration, and thereby the solution viscosity, the morphology changed from beads to bead-on-string fibers to continuous cylindrical fibers. Beaded fibers and continuous bead-free fibers of SPS (500 kDa) could be spun at ∼2 C_e and 3.5 C_e, respectively, where C_e is the entanglement concentration determined from solution-viscosity measurements. The onset of formation of beaded fibers coincided with a sharp transition in the scaling of the storage modulus-concentration relationship.     

The effect of the solvent on the morphology of cellulose acetate/montmorillonite nanocomposites

Nanocomposites of cellulose acetate and sodium montmorillonite were prepared using the solution intercalation method with different solvents. The effects of solvent type on the morphology, thermal and mechanical properties of the nanocomposites were investigated by X-ray microtomography and diffraction, field emission scanning electron microscopy, analytical transmission electron microscopy based on electron loss spectroscopy imaging and dynamical mechanical analysis. XRD and TEM results indicated that the dispersion and delamination of the clay are achieved when the solvent presents favorable interactions with the clay. In this case, the storage modulus and the glass transition temperature are significantly higher than those of pure cellulose acetate. The results show that the solvent has a major effect in controlling the morphology of cellulose acetate and cellulose acetate nanocomposite and could be used as a process parameter to produce films with a range of properties.     

Dielectric studies of cellulose and its derivatives: 3. Glycerol in cellulose acetate

Dielectric studies are reported on cellulose acetate doped with glycerol. The addition of glycerol initially leads to the generation of a strongly interacting layer manifest by an increase in the amplitude of the side chain motion of the cellulose acetate and also the appearance of a higher temperature relaxation. Further addition of glycerol allows development of a multilayer situation which has relaxation properties similar to that of pure glycerol and is essentially independent of the cellulose acetate matrix. The high temperature conductivity of the samples investigated is critically dependent on the concentration of the dopant, increasing markedly for concentrations above 2–3%. This change in behaviour appears to correlate with the fibrillar surface area and is associated with the generation of proton conduction in the system. The general characteristics of this behaviour are similar to those previously reported¹ for the addition of water to cellulose derivatives.     

Structure and properties of high quality natural cellulose fibers from cornstalks

We have developed a fiber extraction method that produces fibers from cornstalks with mechanical properties similar to that of the common textile fibers. The fiber extraction method developed results in partial delignification and produces fibers from cornstalks that are suitable for textile and other industrial applications. The structure of the fibers obtained was investigated using X-ray diffraction and scanning electron microscope. The structure and composition of the natural cellulose fibers obtained from cornstalks are different than that of the common bast fibers such as flax and kenaf. Tensile properties of the fibers were studied using an Instron tensile tester. This study found that cornstalk fibers have relatively lower percent crystallinity but similar microfibrillar angle as that of the common bast fibers. The structure and properties of cornstalk fibers indicate that the fibers are suitable for producing various textile products.     

Permeation of sodium dodecyl sulfate through polyaniline-modified cellulose acetate membranes

The preparation of polyaniline (PANi)-cellulose acetate (CA) blends by casting films from a suspension, is reported. Two membranes were prepared from different solvents, one with a homogeneous and the other a heterogeneous dispersion of PANi in CA matrices. The membranes were characterized by X-ray diffraction, SEM, DSC, and FTIR, and the results were compared with those obtained for pure CA and PANi films. The transport properties of water and sodium dodecyl sulfate (SDS) in membranes of the PANi-CA blends and of CA were analysed. The transport of SDS and water depends on both the bulk/polymer density and the PANi content. In the homogeneous blend, the interaction between SDS and the polymer plays an important role in the transport mechanism. An irreversible interaction is observed, which can be monitored by UV-vis spectroscopy. The spectra of homogeneous, highly transparent PANi-CA blends show a pronounced sensitivity to SDS concentration, with detection limits [SDS]≥0.1 mM for films with a PANi concentration of 0.05% w/v.     

Extrusion and characterization of functionalized cellulose whiskers reinforced polyethylene nanocomposites

The surface of ramie cellulose whiskers has been chemically modified by grafting organic acid chlorides presenting different lengths of the aliphatic chain by an esterification reaction. The occurrence of the chemical modification was evaluated by FTIR and X-ray photoelectron spectroscopies, elemental analysis and contact angle measurements. The crystallinity of the particles was not altered by the chain grafting, but it was shown that covalently grafted chains were able to crystallize at the cellulose surface when using C18. Both unmodified and functionalized nanoparticles were extruded with low density polyethylene to prepare nanocomposite materials. The homogeneity of the ensuing nanocomposites was found to increase with the length of the grafted chains. The thermomechanical properties of processed nanocomposites were studied by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA) and tensile tests. A significant improvement in terms of elongation at break was observed when sufficiently long chains were grafted on the surface of the nanoparticles. It was ascribed to improved dispersion of the nanoparticles within the LDPE matrix.     

Cellulose membranes for reverse osmosis Part I. RO cellulose acetate membranes including a composite with polypropylene

With the aim of obtaining RO membranes for brackish water desalination from purified celluloses (cotton linters and bleached bagasse pulp), two reactions (heterogeneous and homogeneous) were applied for the synthesis of cellulose acetate (CA). The efficiency of the membranes was measured and compared with those prepared from purchased CA and prepared CA by acetylation of imported high-grade viscose wood pulp. The effect of blending CA with polypropylene (PP), on the efficiency of the prepared RO membranes was also studied. Results showed that the method of preparation of CA plays a profound effect on the salt rejection and water flux of the RO membranes. The efficiencies of RO membranes formed from heterogeneously acetylated celluloses are higher than those prepared from homogeneous ones. Blending the acetylated cellulose with 9% PP wastes improves the efficiency of membranes prepared from the homogeneously acetylated celluloses.     

聚乙丙交酯和二乙酸纤维素化学共混物的制备和初步表征

以辛酸亚锡(SnOct2)为催化剂,将溶有二乙酸纤维素(CDA)的乙/丙交酯 (GA/LLA)熔体进行开环接枝反应,制得二乙酸纤维素和聚乙丙交酯的共混物,并提纯得到接枝共聚物CDA-g-Poly(LLA-co-GA)s.用IR和GPC对提纯所得接枝共聚物进行了初步表征,用TGA和DSC对共混物的玻璃化温度、熔点和热失重行为进行了测定,并与相应的机械共混物进行了比较.结果表明,接枝共聚物具有较短的聚L-丙交酯(PLLA)和聚乙交酯(PGA)侧链.共混物具有较好的热稳定性,玻璃化温度和熔点可通过改变投料比调节.通过化学接枝反应所得共混物的性能与机械共混物不同的原因可能是由于PLLA和PGA侧链的内增塑作用.     

Preparation and characterization of chitosan coatings onto regular cellulose fibers with ultrasound technique

Regenerated cellulose fibers—viscose fibers—were coated with chitosan using an ultrasound technique to improve their accessibility, reactivity and sorption properties. The main purpose of our research was to study the modification of viscose fibers and to determine the effect of the application of chitosan onto viscose fibers. Samples were obtained by treating the fibers with chitosan in a dilute acetic acid solution in an ultrasonic bath. The influences of the chitosan coating on the changes in morphology, supramolecular structure, sorption and tensile properties were studied. The spectra (FTIR analysis) of the treated viscose fibers showed changes and new absorption bands that revealed the existence of the chemical interactions with the chitosan. The scanning electron microscope images confirmed that the surface of the fibers was covered with the chitosan. A decrease in the water retention value and increase in the absorption and moisture content with an increasing concentration of chitosan was noted. Furthermore, the differences in tensile behavior were analyzed using an Instron tensile testing machine. The chitosan coating had no effect on the tensile strength of the viscose fibers, but influenced the tensile strain. Some changes, though not significant, were noted in the structure (crystallinity, orientation) of the treated viscose fibers.