Morphology transition in electrospinning polymers by a dual‐capillary system

An experimental investigation of the fiber morphology change of fibers prepared by a dual‐capillary electrospinning system, operated in the cone‐jet mode, was carried out for poly(vinyl acetate) polymers of three molecular weights. The substrate morphology of the electrospun poly(vinyl acetate) could be changed significantly when the polymer's molecular weight, concentration, solvent, and outer liquid flow rate were varied. The onset of bead‐to‐fiber transition was determined by the critical chain overlap concentration. For solutions with a high concentration, the fiber diameter and surface were significantly affected by the physical properties of the solvents. To produce fibers of small diameter, electrospinning with a higher conductivity solution was desirable. On the other hand, a high‐conductivity solution needed to be avoided to keep the fiber uniform in diameter and smooth on the surface. The comparison of electrospun fibers produced by both single‐capillary and dual‐capillary systems was also addressed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

High Stiffness Cellulose Fibers from Low Molecular Weight Microcrystalline Cellulose Solutions Using DMSO as Co‐Solvent with Ionic Liquid

There is a need to develop high‐performance cellulose fibers as sustainable replacements for glass fibers, and as alternative precursors for carbon filaments. Traditional fiber spinning uses toxic solvents, but in this study, by using dimethyl sulfoxide (DMSO) as a co‐solvent with an ionic liquid, a novel high‐performance fiber with exceptional mechanical properties is produced. This involves a one‐step dissolution, and cost‐effective route to convert high concentrations of low molecular weight microcrystalline cellulose into high stiffness cellulose fibers. As the cellulose concentration increases from 20.8 to 23.6 wt%, strong optically anisotropic patterns appear for cellulose solutions, and the clearing temperature (T _c) increases from ≈100 °C to above 105 °C. Highly aligned, stiff cellulose fibers are dry‐jet wet spun from 20.8 and 23.6 wt% cellulose/1‐ethyl‐3‐methylimidazolium diethyl phosphate/DMSO solutions, with a Young's modulus of up to ≈41 GPa. The significant alignment of cellulose chains along the fiber axis is confirmed by scanning electron microscopy, wide‐angle X‐ray diffraction, and powder X‐ray diffraction. This process presents a new route to convert high concentrations of low molecular weight cellulose into high stiffness fibers, while significantly reducing the processing time and cost.     

Electrospinning of solvent‐resistant nanofibers based on poly(acrylonitrile‐co‐glycidyl methacrylate)

This article reports on the preparation of novel solvent‐resistant nanofibers by electrospinning of poly(acrylonitrile‐co‐glycidyl methacrylate) (PANGMA) and subsequent chemical crosslinking. PANGMA nanofibers with diameters ranging from 200 to 600 nm were generated by electrospinning different solutions of PANGMA dissolved in N,N‐dimethylformamide. Different additives were added to reduce the fiber diameter and improve the morphology of the nanofibers. The as‐spun PANGMA nanofibers were crosslinked with 27 wt % aqueous ammonia solution at 50°C for 3 h to gain the solvent resistance. Swelling tests indicated that the crosslinked nanofibers swelled in several solvents but were not dissolved. The weight loss of all the crosslinked nanofibrous mats immersed in solvents for more than 72 h was very low. The characterization by electron microscopy revealed that the nanofibrous mats maintained their structure. This was also confirmed by the results of the pore size measurements. These novel nanofibers are considered to have a great potential as supports for the immobilization of homogeneous catalysts and enzymes. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mild condition dissolution of high molecular weight cotton cellulose in 1‐butyl‐3‐methylimidazolium acetate/N,N‐dimethylacetamide solvent system

To investigate the effective dissolution of high molecular weight (MW) cellulose macromolecules at ambient conditions, cellulose (DP > 4,000) derived from cotton fiber waste was dissolved in 1‐butyl‐3‐methylimidazolium acetate (BMIMAc)/N,N‐dimethylacetamide (DMAc) solvent in this study. High MW cotton cellulose achieves a solubility between 3% and 5% cellulose concentrations using BMIMAc/DMAc solvent at ambient conditions. Rheological studies showed that all cellulose/solvent solutions displayed a shear thinning behavior. Results from the physical characterization revealed that well‐dissolved cotton cellulose exhibited highly porous structure and the crystalline structure of cotton cellulose was highly disrupted during dissolution and regeneration processes. This study is the first to report on the ability of BMIMAc/DMAc solvent system to dissolve high MW cellulose under ambient conditions, which represents an energy‐saving and environmentally friendly approach. As cellulose used in this study was derived from low quality waste cotton fibers, the potential utilization of such cotton cellulose may create a competitive market for low quality cotton and target advanced applications of cellulose‐based products for green materials and energy. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45928.     

Preparation of high‐molecular‐weight poly(N‐vinylcarbazole) by the photoinduced low‐temperature solution polymerization of N‐vinylcarbazole in 1,1,2,2‐tetrachloroethane

For the preparation of high‐molecular‐weight (HMW) poly(N‐vinylcarbazole) (PVCZ) with a narrow molecular weight distribution, N‐vinylcarbazole (VCZ) was solution‐polymerized in 1,1,2,2‐tetrachloroethane (TCE) at ?20, 0, and 20°C with photoinitiation. The effects of the polymerization temperature and the concentrations of the polymerization solvent and photoinitiator on the polymerization behavior and molecular parameters of PVCZ were investigated. A low polymerization temperature with photoirradiation was successful in obtaining HMW PVCZ with a smaller temperature rise during polymerization than that for thermal free‐radical polymerization by azobisisobutyronitrile (AIBN). The photo‐solution‐polymerization rate of VCZ in TCE was proportional to [AIBN]^0.45. The molecular weight was higher and the molecular weight distribution was narrower for PVCZ made at lower temperatures. For PVCZ prepared in TCE at ?20°C with a photoinitiator concentration of 0.00003 mol/mol of VCZ, a weight‐average molecular weight of 920,000 was obtained, with a polydispersity index of 1.46, and the degree of transparency converged to about 99%. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2391–2396, 2003     

Spinning and drawing properties of ultrahigh‐molecular‐weight polyethylene fibers prepared at varying concentrations and temperatures

The concentrations and temperatures of ultrahigh‐molecular‐weight polyethylene (UHMWPE) gel solutions exhibited a significant influence on their rheological and spinning properties. The shear viscosities of UHMWPE solutions increased consistently with increasing concentrations at a constant temperature above 80°C. Tremendously high shear viscosities of UHMWPE gel solutions were found as the temperatures reached 120–140°C, at which their shear viscosity values approached the maximum. The spinnable solutions are those gel solutions with optimum shear viscosities and relatively good homogeneity in nature. Moreover, the gel solution concentrations and spinning temperatures exhibited a significant influence on the drawability and microstructure of the as‐spun fibers. At each spinning temperature, the achievable draw ratios obtained for as‐spun fibers prepared near the optimum concentration are significantly higher than those of as‐spun fibers prepared at other concentrations. The critical draw ratio of the as‐spun fiber prepared at the optimum concentration approached a maximum value, as the spinning temperature reached the optimum value of 150°C. Further investigations indicated that the best orientation of the precursors of shish‐kebab‐like entities, birefringence, crystallinity, thermal and tensile properties were always accompanied with the as‐spun fiber prepared at the optimum concentration and temperature. Similar to those found for the as‐spun fibers, the birefringence and tensile properties of the draw fibers prepared at the optimum condition were always higher than those of drawn fibers prepared at other conditions but stretched to the same draw ratio. Possible mechanisms accounting for these interesting phenomena are proposed.     

Preparations and properties of thermosensitive terpolymers of N‐isopropylacrylamide,sodium 2‐acrylamido‐2‐methyl‐propanesuphonate,and N‐tert‐butylacrylamide

Terpolymers based on N‐isopropylacrylamide, sodium 2‐acrylamido‐2‐methyl‐propanesulfonate, and N‐tert‐butylacrylamide were synthesized by free‐radical copolymerization with 2,2′‐azobisisobutyronitrile as an initiator. The lower critical solution temperatures (LCSTs) of the linear polymer aqueous solutions were determined by the measurement of the transmittance on UV at different temperatures. The influence of the polymer concentration, polymer composition, and ionic strength on the LCSTs of the linear polymers was investigated. The LCST decreased with increases in the hydrophobic monomer N‐tert‐butylacrylamide, polymer concentration, and ionic strength. The phase transition became sharp when the polymer concentration and ionic strength increased. Meanwhile, the crosslinked hydrogels were prepared with the same recipe used for the linear terpolymers, but a crosslinker was added to the reaction system. The swelling ratios of the hydrogels at various temperatures and salt solutions were determined. The hydrogels possessed both high swelling ratios and thermosensitivity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of water‐miscible solvents on the organic solvent‐resistant tyrosinase from Streptomyces sp. REN‐21

The effect of various water‐miscible organic solvents (ethanol, methanol, acetone, acetonitrile, N,N‐dimethylformamide (DMF) and dimethylsulfoxide (DMSO)) on the kinetics of 4‐tert‐butylcatechol (tBC) oxidation in the presence of different samples of organic solvent‐resistant tyrosinase (OSRT) has been studied. In contrast to mushroom tyrosinase the enzyme shows a high relative stability in solutions of organic solvents and increased activity toward the bulky and hydrophobic substrate, tBC, in respect to catechol. Rates of the studied OSRT‐catalyzed reactions are however reduced by the presence of organic solvents and for all studied samples of OSRT decrease exponentially with the content of an organic solvent. The effect has been satisfactorily described by the effect of organic solvents on the thermodynamic activity of tBC. The correlation of the inhibition parameters with the hydrophobicity of a particular solvent (log P), its intrinsic molar volume, V_i, and the Dimroth–Reichardt parameter, E_T(30), are shown. The results allow also the prediction of OSRT activity in aqueous solutions of water‐miscible organic solvents. Copyright © 2003 Society of Chemical Industry     

Development,optimization, and characterization of electrospun poly(lactic acid) nanofibers containing multi‐walled carbon nanotubes

Electrospinning of poly (L ‐D ‐lactic acid) (PLA) was investigated with the addition of multi‐walled carbon nanotubes (MWNT) for development of a scaffold for tissue engineering. Through this experiment, it was determined that the optimal concentration of PLA with weight average molecular weight (M_w) 250,000 g/mol is ～20 wt % as indicated by scanning electron microscopy. This concentration produces fibers with no beading or film formation. The preferred solvent system is a combination of chloroform and dimethyl formamide to alleviate the volatile action of chloroform. The optimum processing parameters for PLA are an electric field of 1 kV/cm which was determined by a surface response plot to minimize fiber diameter based on the applied voltage, working distance, and addition of MWNT. Fourier Transform infrared spectroscopy has indicated the removal of the solvent system. With the addition of MWNT, the fiber diameter was drastically reduced by 70% to form fibers with a mean diameter of 700 nm. This is believed to be due to an increased surface charge density for the MWNT/polymer solution. Transmission electron microscopy validated the alignment of the MWNT within the fibers. MWNT loading exhibited an increase in the conductance of the scaffold and the tensile modulus at an optimal loading level of 0.25 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Ultradrawing properties of ultrahigh‐ molecular‐weight polyethylene/carbon nanotube fibers prepared at various formation temperatures

The influence of formation temperature on the ultradrawing properties of ultrahigh‐molecular‐weight polyethylene/carbon nanotube (UHMWPE/CNT) fiber specimens is investigated. Gel solutions of UHMWPE/CNT with various CNT contents were gel‐spun at the optimum concentration and temperature but were cooled at varying formation temperatures in order to improve the ultradrawing and tensile properties of the UHMWPE/CNT composite fibers. The achievable draw ratio (D_ra) values of UHMWPE/CNT as‐prepared fibers reach a maximum when they are prepared with the optimum CNT content and formation temperature. The D_ra value of UHMWPE/CNT as‐prepared fibers produced using the optimum CNT content and formation temperature is about 33% higher than that of UHMWPE as‐prepared fibers produced using the optimum concentration and formation temperature. The percentage crystallinity (W_c) and melting temperature (T_m) of UHMWPE/CNT as‐prepared fiber specimens increase significantly as the formation temperature increases. In contrast, W_c increases but T_m decreases significantly as the CNT content increases. Dynamic mechanical analysis of UHMWPE and UHMWPE/CNT fiber specimens exhibits particularly high α‐transition and low β‐transition, wherein the peak temperatures of α‐transition and β‐transition increase dramatically as the formation temperature increases and/or CNT content decreases. In order to understand these interesting drawing, thermal and dynamic mechanical properties of the UHMWPE and UHMWPE/CNT as‐prepared fiber specimens, birefringence, morphological and tensile studies of as‐prepared and drawn fibers were carried out. Possible mechanisms accounting for these interesting properties are proposed. Copyright © 2010 Society of Chemical Industry     

Synthesis of ultrafine poly(styrene‐maleic anhydride) and polystyrene fibers by electrospinning

Fiber formation from atactic polystyrene (aPS) and alternating poly(styrene‐maleic anhydride) (PSMA) synthesized by free radical polymerization (AIBN, 90°C, 4 h) were investigated by electrospinning from various solutions. aPS was soluble in dimethylformamide (DMF), tetrahydrofuran (THF), toluene, styrene, and benzene, whereas PSMA was soluble in acetone, DMF, THF, dimethylsulfoxide (DMSO), ethyl acetate, and methanol. aPS fibers could be electrospun from 15 to 20% DMF and 20% THF solutions, but not from styrene nor toluene. PSMA, on the other hand, could be efficiently electrospun into fibers from DMF and DMSO at 20 and 25%, respectively. Few PSMA fibers were, however, produced from acetone, THF, or ethyl acetate solutions. Results showed that solvent properties and polymer–solvent miscibility strongly influenced the fiber formation from electrospinning. The addition of solvents, such as THF, generally improved the fiber uniformity and reduced fiber sizes for both polymers. The nonsolvents, however, had opposing effects on the two polymers, i.e., significantly reducing PSMA fiber diameters to 200 to 300 nm, creating larger and irregularly shaped aPS fibers. The ability to incorporate the styrene monomer and divinylbenzene crosslinker in aPS fibers as well as to hydrolyze PSMA fibers with diluted NaOH solutions demonstrated potential for post‐electrospinning reactions and modification of these ultrafine fibers for reactive support materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Cellulose fibers modified by hydrophobic‐type polymer

In the present research, we discuss the influence of a hydrophobic modifier on the properties of cellulose fibers. The commercially available fluorocarbon polymer water dispersion was introduced in different concentration ratios to the spinning dope to change the physical properties of cellulose fibers. Cellulose fibers from N‐methylmorpholine‐N‐oxide were prepared as a direct solvent. The fibers obtained contained up to 15% w/w of fluorocarbon polymer. To observe how the modifier influences the fibers' mechanical and thermal properties, fibrillation tendency and moisture absorption were examined. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 398–409, 2007     

Preparation of high molecular weight poly(N‐vinylcarbazole) in high yield by low‐temperature precipitation polymerization of N‐vinylcarbazole

To produce high molecular weight poly(N‐vinylcarbazole) (PVCZ) with high conversion, N‐vinylcarbazole (VCZ) was heterogeneously polymerized in methanol at 30, 40 and 50 °C using a low temperature initiator, 2,2′‐azobis(2,4‐dimethylvaleronitrile) (ADMVN), and the effects of polymerization temperature and concentration of initiator and solvent on the polymerization behaviour and molecular parameters of PVCZ investigated. Globally, experimental results correspond to predicted ones. Low polymerization temperature using ADMVN and a heterogeneous system using methanol proved to be successful in obtaining poly(N‐vinylcarbazole) (PVCZ) of high molecular weight and high conversion with small temperature rise during polymerization, although free radical polymerization by azoinitiator was used. The polymerization rate of VCZ in methanol at 30 °C is proportional to the 0.88th power of ADMVN concentration. The molecular weight is higher and the molecular weight distribution is narrower with PVCZ polymerized at lower temperatures. For PVCZ produced in methanol at 30 °C using an ADMVN concentration of 0.0001 mol/mol of VCZ, a weight average molecular weight of 1 750 000 g mol⁻¹ is obtained, with a polydispersity index of 1.82 © 2000 Society of Chemical Industry     

Temperature‐dependent transition of crystal phases in the electrospinning process of poly(vinylidene fluoride‐co‐hexafluoropropylene)

The temperature‐dependent transition of the crystal phases of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) was investigated in the electrospinning process. A solution of PVDF‐HFP in N,N‐dimethyl acetamide (DMAc) produced only the β‐phase‐dominant crystal up to 70 °C, irrespective of the spinneret temperature. In a mixed solvent of DMAc and acetone, however, the crystal phase of the electrospun fibers was dependent on temperature: β‐phase‐dominant at 30 and 50 °C and α‐phase‐dominant at 70 °C. The transition was related to a change of the coagulation rate during electrospinning, because the less perfect α phase is preferable to the β phase at a higher coagulation rate. The temperature‐dependent increase of the coagulation rate was more drastic in the presence of acetone, so the transition took place only in the mixed solvent. At elevated temperature, acetone not only raised the evaporation rate of the solvent but promoted the phase separation of the polymer resulting from the lower critical solution temperature behavior, which was rheologically traced. © 2019 Society of Chemical Industry     

Swelling–deswelling kinetics of poly(N‐isopropylacrylamide) hydrogels formed in PEG solutions

A series of poly(N‐isopropylacrylamide) (PNIPA) hydrogels was prepared by free‐radical crosslinking copolymerization of N‐isopropylacrylamide (NIPA) and N,N′‐methylenebisacrylamide (BAAm) in aqueous solutions of poly(ethylene glycol) of molecular weight 300 g/mol (PEG). The amount of PEG in the polymerization solvent, the crosslinker (BAAm) content, and the gel preparation temperature (T_prep) were varied in the gelation experiments. The hydrogels were characterized by the equilibrium swelling and elasticity tests as well as by the measurements of the deswelling–reswelling kinetics of the hydrogels in response to a temperature change between 25 and 48°C. The rate of deswelling of the swollen gel increases while the rate of reswelling of the collapsed gel decreases as the amount of PEG in the polymerization solvent is increased or as the crosslinker content is decreased. The T_prep effect on the swelling kinetics of the hydrogels was only observed if the PEG content of the polymerization solvent is less than 20%, which is explained with the screening of H‐bonding interactions in concentrated PEG solution. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 37–44, 2006     

Hierarchical Self‐Assembly of Poly(Urethane)/Poly(Vinylidene Fluoride‐co‐Hexafluoropropylene) Blends into Highly Hydrophobic Electrospun Fibers with Reduced Protein Adsorption Profiles

Electrospinning of blend systems, combining two or more polymers, has gained increasing interest for the fabrication of fibers that combine properties of the individual polymers. Here, a versatile method to produce hydrophobic fibers composed of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDFhfp) and polyurethane (PUR) is presented. PVDFhfp containing fibers are expected to reduce protein adsorption. In a one‐step process, blend solutions are electrospun into homogeneous nonwoven membranes with fiber diameters in the range of 0.6 ± 0.2 to 1.4 ± 0.7 µm. Surface fluorine concentrations measured by X‐ray photospectroscopy show an asymptotic dependency in function of the PVDFhfp to PUR ratio, reaching values close to pure PVDFhfp at a weight per weight ratio of 10% PVDFhfp to 90% PUR. This fluorine enrichment on the surface suggests a gradient structure along the fiber cross‐section. At increased surface fluorine concentration, the contact angle changes from 121 ± 3° (PUR) to 141 ± 4° (PUR/PVDFhfp). Furthermore, these highly hydrophobic fibers present significantly reduced fibrinogen or albumin adsorption compared to PUR membranes.     

Phase separation of poly(N‐isopropylacrylamide) solutions and gels using a near infrared fiber laser

We used a tunable near infrared fiber laser in the wavelength range of 1533–1573 nm to induce photothermal phase changes in poly(N‐isopropylacrylamide) (PNIPAM) aqueous solutions and hydrogels. The laser induces the hydrophilic to hydrophobic transition of the polymer by heating the surrounding water. We report our observations of the phase changes based on using a novel fiber backreflectance method coupled with visual cloud point measurements. At 1533 nm the phase transition was induced at the end of a single mode optical fiber with 9 mW of power at an ambient temperature of 24°C. We found that the power required to reach the lower critical solution temperature was inversely proportional to the absorption spectrum of water. In addition, phase changes in both solutions and gels occurred very rapidly (<1 s) as the laser was turned on and off. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Graft copolymerization of N‐vinyl‐2‐pyrrolidone onto sodium carboxymethylcellulose with azobisisobutyronitrile as the initiator

Graft copolymers of sodium carboxymethylcellulose with N‐vinyl‐2‐pyrrolidone were prepared in aqueous solutions with azobisisobutyronitrile as the initiator. The graft copolymers [sodium carboxymethylcellulose‐g‐poly(N‐vinyl‐2‐pyrrolidone)] were characterized with Fourier transform infrared spectroscopy, elemental analysis, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and scanning electron microscopy. The grafting parameters, including the graft yield of the graft copolymer and the grafting efficiency of the reaction, were evaluated comparatively. The effects of reaction variables such as the time, temperature, and monomer and initiator concentrations on these parameters were studied. The graft yield and grafting efficiency increased and then decreased with increasing concentrations of N‐vinyl‐2‐pyrrolidone and azobisisobutyronitrile and increasing polymerization temperatures. The optimum temperature and polymerization time were 70°C and 4.30 h, respectively. Further changes in the properties of grafted sodium carboxymethylcellulose, such as the intrinsic viscosity, were determined. The overall activation energy for the grafting was also calculated to be 10.5 kcal/mol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 936–943, 2007     

Effects of solvent basicity on free radical polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane initiated by barbituric acid

The polymerizations of N,N′‐bismaleimide‐4,4′‐diphenylmethane (BMI) initiated by barbituric acid (BTA) carried out in a variety of solvents at 130°C were studied. The nitrogen‐containing cyclic solvents such as N‐methyl‐2‐pyrrolidinone acted as a catalyst to promote the formation of the three‐dimensional crosslinked network structure. By contrast, the polymerization in a cyclic solvent that did not contain nitrogen such as γ‐butyrolactone resulted in nil gel content. The higher the solvent basicity, the larger the amount of insoluble polymer species formed. The molar ratio of BTA to BMI also played an important role in the polymerizations. The resultant polymers, presumably having a hyper‐branched structure, exhibited much narrower molecular weight distributions than those prepared by conventional free radical polymerizations. The BMI polymerizations using BTA as the initiator could not be adequately described by conventional free radical polymerization mechanisms. A polymerization mechanism that took into account the generation of a ketone radical pair between BTA and BMI and the subsequent initiation, propagation and termination reactions was proposed. It was concluded that the nitrogen‐containing cyclic solvents were capable of participating in the ketone radical pair formation process, thereby increasing the extent of polymer crosslinking reactions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of water‐soluble chitosan

An improved method of preparing water soluble chitosan was studied by N‐acetylation with acetic anhydride. Its merits were a simple processing technique, very short reaction time, little agent, high molecular weight of the product, and good water solubility. This article not only discusses the effect of several factors, such as the amount of reactants, concentration of hydrogen ions in the solution, and solvent system, on N‐acetylation but also some influential factors on the water solubility of N‐acetylated chitosan. Experiments showed that the amount of acetic anhydride was the most important factor affecting the N‐acetylation degree of the chitosan. The effect of the means of adding materials and the amount of solvent on the reaction could not be ignored. The solubility of half N‐acetylated chitosan was not changed with an increase in the molecular weight in water, and the water solubility decreased with increasing molecular weight in the alkaline region. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3497–3503, 2004