Calcium alginate gel fibers: Influence of alginate source and gel structure on fiber strength

The low-deformation extension modulus was measured for Ca–alginate gel fibers prepared from alginates of different compositions and molecular weights. The modulus showed an increase with increasing molecular weight for alginates of the same composition and sequence parameters. Fibers prepared with an inhomogeneous polymer concentration profile showed higher moduli than did fibers with a homogeneous polymer concentration profile. The higher modulus observed for fiber prepared from an alginate with low Ca²⁺ affinity is tentatively explained as resulting from a higher degree of polymer chain alignment. © 1994 John Wiley & Sons, Inc.     

New insights into sodium alginate fouling of ceramic hollow fiber membranes by NMR imaging

Ceramic hollow fiber membranes are investigated with respect to the fouling behavior. Constant pressure dead‐end filtration experiments have been performed using alginate as model substance for extracellular polymeric substances. In addition to the evaluation of the filtration data using conventional cake filtration model, nuclear magnetic resonance imaging (MRI) was used to elucidate the influence of Ca²⁺ on the fouling layer structure for alginate filtration within ceramic hollow fiber membranes. To visualize the alginate layers inside the opaque ceramic hollow fiber membranes by means of MRI, specific contrast agents were applied. Supplementary to multi slice multi echo imaging, flow velocity measurements were performed to gain more insight into the hydrodynamics in the fouled membranes. MRI reveals the structure of the alginate layers with the finding that the addition of Ca²⁺ to the alginate feed solution promotes the formation of a dense alginate gel layer on the membrane's surface. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2459–2467, 2016     

Strontium ion substituted alginate-based hydrogel fibers and its coordination binding model

Sr-alginate and Ca-alginate hydrogel fibers were fabricated via microfluidic spinning technology, and various analytical methods were adopted to characterize fibers and disclose the coordination model of Sr²⁺ binding with alginate molecule chain. For both fibers, the more crosslinking sites of Sr²⁺ with alginate molecule were illustrated in comparison with that of Ca²⁺. The more robust mechanical performance of Sr-alginate fibers than Ca-alginate counterpart was a strong indication of the more strong binding of Sr²⁺ with alginate molecular chain. FTIR and electric conductivity disclosed the chelation type of Sr²⁺ with alginate macromolecule being similar to that of Ca²⁺, which was core-shell of the analogous “egg-box” structure. Circular dichroism spectroscopy further certified the extra coordination sites for Sr²⁺ with alginate molecule than Ca²⁺. Research on the coordination model will be more beneficial to optimizing the physicochemical properties of alginate fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48571.     

Ultrafiltration recovery of alginate: Membrane fouling mitigation by multivalent metal ions and properties of recycled materials

Recovery of alginate extracted from aerobic granular sludge (AGS) has given rise to a novel research direction. However, these extracted alginate solutions have a water content of nearly 100%. Alternately, ultrafiltration (UF) is generally used for concentration of polymers. Furthermore, the introduction of multivalent metal ions into alginate may provide a promising method for the development of novel nanomaterials. In this study, membrane fouling mitigation by multivalent metal ions, both individually and in combination, and properties of recycled materials were investigated for UF recovery of sodium alginate (SA). The filtration resistance showed a significantly negative correlation with the concentration of metal ions, arranged in the order of Mg²⁺ < Ca²⁺ < Fe³⁺ < Al³⁺ (filtration resistance mitigation), and the moisture content of recycled filter cake showed a marked decrease. For Ca²⁺, Mg²⁺, Fe³⁺, and Ca²⁺+ Fe³⁺, the filtration resistances were almost the same when the total charge concentration was less than 5 mmol⋅L^–1. However, when the total charge concentration was greater than 5 mmol⋅L^–1, membrane fouling mitigation increased significantly in the presence of Ca²⁺ or Fe³⁺ and remained constant for Mg²⁺ with the increase of total charge concentration. The filtration resistance mitigation was arranged in the order of Fe³⁺ > Fe³⁺ + Ca²⁺ > Ca²⁺ > Mg²⁺. Three mechanisms were proposed in the presence of Fe³⁺, such as the decrease of SA concentration, change in pH, and production of hydroxide iron colloids from hydrolysis. The properties of recycled materials (filter cake) were investigated via optical microscope observation, dynamic light scattering, Fourier transform infrared, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. The results provide further insight into UF recoveries of alginate extracted from AGS.     

Identification of fiber misalignment in continuous fiber composites

Misaligned fibers are invariably present in nominally unidirectional high‐performance composites. Such misaligned fibers are known to affect key mechanical properties of the composite, such as the longitudinal compressive strength, longitudinal tensile modulus, fatigue endurance, shear strength, and delamination resistance (1). In this paper we present a method for the automated detection of large angle fiber misalignment (θ > 40°) in continuous fiber‐reinforced composite materials. The method relies on the application of a series of geometrical criteria based upon measurements routinely obtained during optical scanning of polished sample cross‐sections. As such, the technique is ideal for the automated identification of highly misaligned fibers in large‐area (∼ cm²) specimens that may contain several millions of individual fiber images. The criteria applied take into account the fact that prepared cross‐sections of such materials contain many damaged fibers as a result of attrition during polishing. Data obtained from three pultruded unidirectional rods reinforced with continuous carbon filaments are used to illustrate the effectiveness of this method in identifying regions where large angle misalignment occurs.     

Effects of counter cations on the water vapor sorption properties of alginic acid and alginates

In this study, the water vapor sorption of four types of alginate, namely, alginic acid (Alg), Na-Alg, Ca-Alg, and NH₄-Alg, were measured, and the effect of differences in counter cations on water vapor solubility and crystallization mechanism associated with the arrangement of hydrogen bonds generated during humidification was investigated. The sorption amounts in the high-humidity region can be arranged as follows: Na-Alg > NH₄-Alg > Ca-Alg > Alg. All samples formed a (C)-type double helix structure before and after the sorption based on the results of Fourier transform infrared spectroscopy and wide-angle X-ray diffraction. The counter cation affects the arrangement of the hydrogen bonds in this structure. Only Ca-Alg possessed a pseudocrosslinking among the (C)-type double helix structures due to the divalent Ca²⁺ ions, which induced variations in the crystal arrangement behavior of the other three samples before and after sorption. Cases I–III show a case of how the orientation is aligned with a new hydrogen bond and classified for each sample.     

Development of the inorganic nanoparticles reinforced alginate-based hybrid fiber for wound care and healing

It is necessary for wound dressing constructed from fibers capable of overcoming external stretching and protecting injured skin. The limited mechanical performance of existing alginate fiber limits its biomaterial application. Herein, this issue can be addressed via incorporation of uniformly dispersed hydroxyapatite (HAP) and silica (SiO₂) nanoparticles (NPs) in alginate (Alg) by microfluidic spinning technique. These NPs serve as a reinforcing phase to help the alginate-based composite to develop outstanding mechanics. Both HAP-Alg and SiO₂-Alg hybrid fibers exhibited excellent breaking elongation, 67.56 ± 6.85% and 52.08 ± 5.20% respectively, while that of breaking strength were 7.04 ± 0.58 MPa and 4.96 ± 0.59 MPa. Furthermore, in vitro cytotoxicity was explored by studying on the proliferation and migration of keratinocytes and fibroblasts, which illustrated no obvious cytotoxicity of the resulting alginate fibers loaded with HAP and SiO₂ NPs. The artificial scratch assay demonstrated that the resulting alginate-based composite fiber can assist the injured skin regeneration. This work provides a significant progress in the conception of developing NPs reinforced alginate-based hybrid fiber which can withstand the large strain behavior and facilitate wound healing, making it an ideal candidate as wound dressings and fibrous scaffolds.     

Comprehensive Simulation of Ca2+ Transients in the Continuum of Mouse Skeletal Muscle Fiber Types

Mag-Fluo-4 has revealed differences in the kinetics of the Ca²⁺ transients of mammalian fiber types (I, IIA, IIX, and IIB). We simulated the changes in [Ca²⁺] through the sarcomere of these four fiber types, considering classical (troponin –Tn–, parvalbumin –Pv–, adenosine triphosphate –ATP–, sarcoplasmic reticulum Ca²⁺ pump –SERCA–, and dye) and new (mitochondria –MITO–, Na⁺/Ca²⁺ exchanger –NCX–, and store-operated calcium entry –SOCE–) Ca²⁺ binding sites, during single and tetanic stimulation. We found that during a single twitch, the sarcoplasmic peak [Ca²⁺] for fibers type IIB and IIX was around 16 µM, and for fibers type I and IIA reached 10–13 µM. The release rate in fibers type I, IIA, IIX, and IIB was 64.8, 153.6, 238.8, and 244.5 µM ms⁻¹, respectively. Both the pattern of change and the peak concentrations of the Ca²⁺-bound species in the sarcoplasm (Tn, PV, ATP, and dye), the sarcolemma (NCX, SOCE), and the SR (SERCA) showed the order IIB ≥ IIX > IIA > I. The capacity of the NCX was 2.5, 1.3, 0.9, and 0.8% of the capacity of SERCA, for fibers type I, IIA, IIX, and IIB, respectively. MITO peak [Ca²⁺] ranged from 0.93 to 0.23 µM, in fibers type I and IIB, respectively, while intermediate values were obtained in fibers IIA and IIX. The latter numbers doubled during tetanic stimulation. In conclusion, we presented a comprehensive mathematical model of the excitation–contraction coupling that integrated most classical and novel Ca²⁺ handling mechanisms, overcoming the limitations of the fast- vs. slow-fibers dichotomy and the use of slow dyes.     

Influence of K+ and Na+ ions on the degradation of wet‐spun alginate fibers for tissue engineering

A synthetic type of wet‐spun alginate fibers were immersed in simulated body fluid(SBF) composed of K⁺, Na⁺, and Ca²⁺ cations with various concentrations. Experimental measurements revealed that Na⁺ had a greater impact on degradability than that of K⁺ ion. The finding was further confirmed by the characterization of mass loss, ICP, XRD, and theoretical analyses. The degradation process and mechanism were demonstrated through the research on swelling behavior and mass loss. Besides, the wet‐spun alginate fibers were characterized by FT‐IR, XRD, and SEM. The results showed that the degradation mechanism could be attributed to the ion‐exchange between Ca²⁺ of the synthetic alginate fibers and Na⁺, K⁺ of the solutions under the osmotic pressure. The synthetic fibers were swelled and then degraded faster with the presence of Na⁺ ion presented greater influence on degradability compared with K⁺ ion. The degradation results of a mechanical rupture of fibers due to excessive water uptake without the occurrence of any chemical changes in the spun alginates structure. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44396.     

Preparation and properties of alginate superabsorbent filament fibers crosslinked with glutaraldehyde

Superabsorbent filament fibers based on sodium alginate were prepared using glutaraldehyde as a crosslinking agent. Alginate was extruded into an aqueous hydrochloric acid coagulation bath to form continuous alginic acid gel fibers via a wet‐spinning method. The alginic acid gel fibers were dehydrated by exchanging water with dioxane, crosslinked, then neutralized for better absorbency. Crosslinked alginate filaments exhibited a high saline solution and synthetic urine absorbencies, maintaining the integrity of the fiber structure. Maximum synthetic urine absorbency was obtained with the fiber crosslinked at a lower glutaraldehyde concentration compared with that required for maximum saline solution absorbency. This appears to be due to the crosslinking effect of calcium ions in the synthetic urine solution being absorbed. Strain and tenacity of the crosslinked alginate fibers decreased with an increasing amount of glutaraldehyde used in the crosslinking reaction. The decrease in tenacity was not significant while the strain showed an extensive decrease. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1797–1804, 2000     

The preparation of high performance silk fiber/fibroin composite

An all-silk composite, in which uniaxially-aligned and continuous-typed Bombyx mori silk fibers were embedded in a matrix of silk protein (fibroin), was successfully prepared via a solution casting process. The structure, morphology, mechanical and thermal properties of such silk fiber/fibroin composites were investigated with X-ray diffraction, scanning electron microscopy, tensile and compression tests, dynamic mechanical analysis and thermogravimetric analysis. The results demonstrated that the interface adhesion between silk fiber and the fibroin matrix was enhanced by controlling the fiber dissolution through 6 mol L⁻¹ LiBr aqueous solution. Compare to those of the pure fibroin counterparts, the overall mechanical properties as well as the thermal stability of such silk fiber/fibroin composites were significantly improved. For example, the composite with 25 wt% fibers showed a breaking stress of 151 MPa and a breaking elongation of 27.1% in the direction parallel to the fiber array, and a compression modulus of 1.1 GPa in the perpendicular direction. The pure fibroin matrix (film), on the other hand, typically had a breaking stress of 60 MPa, a breaking elongation of 2.1% and a compression modulus of 0.5 GPa, respectively. This work suggests that such a controllable technique may help in the preparation of animal silk based materials with promising properties for various applications.     

High-flux CO2-stable oxygen transport hollow fiber membranes through surface engineering

The influences of bulk diffusion and surface exchange on oxygen transport of (La_0.6Ca_0.4)(Co_0.8Fe_0.2)O_3-δ (LCCF) hollow fiber membranes were investigated. As an outcome, two strategies for increasing the oxygen permeation were pursued. First, porous LCCF hollow fibers as support were coated with a 22 μm dense LCCF separation layer through dip coating and co-sintering. The oxygen permeation of the porous fiber with dense layer reached up to 5.10 mL min^?1 cm^-2 at 1000 °C in a 50 % CO₂ atmosphere. Second, surface etching of dense LCCF hollow fibers with H₂SO₄ was applied. The surface etching of both inner and outer surfaces leads to a permeation improvement up to 86.0 %. This finding implies that the surface exchange reaction plays a key role in oxygen transport through LCCF hollow fibers. A good long-term (>250 h) stability of the asymmetric hollow fiber in a 50 % CO₂ atmosphere was found at 900 °C.     

Fabrication,structure, and properties of chitin whisker‐reinforced alginate nanocomposite fibers

Calcium alginate yarn (30 fibers) and calcium alginate nanocomposite yarn (30 fibers) containing 0.05–2.00% w/w chitin whiskers were both prepared by wet spinning process. The whiskers were prepared by acid hydrolysis of chitin from shrimp shells. The average length and width of the whiskers were 343 and 46 nm, with the aspect ratio being ～ 7.5. Incorporation of a low amount of the whiskers in the nanocomposite fibers improved both the mechanical and the thermal properties of the fibers significantly, possibly a result of the specific interactions, i.e., hydrogen bonding and electrostatic interactions, between the alginate molecules and the homogeneously dispersed chitin whiskers. Biodegradation of the calcium alginate fibers and the nanocomposite fibers was tested in Tris‐HCl buffer solution and the same buffer solution that contained lysozyme. The addition of the chitin whiskers in the nanocomposites fibers accelerated the biodegradation process of the fibers in the presence of lysozyme, whereas the presence of Ca²⁺ ions in the Tris‐HCl buffer solution helped to improve the tenacity of both the alginate and the nanocomposite fibers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effective Cd2+ chelating fiber based on polyacrylonitrile

A reusable chelating fiber containing polyamino–polycarboxylic acid ligands was prepared via the stepwise modification of polyacrylonitrile fiber with diethylenetriamine and chloroacetic acid. The amination and carboxylmethylation conditions were optimized, and the modified fiber was characterized by elemental analysis, XRD, SEM and FTIR. For Cd²⁺ in water, this chelating fiber has prominent adsorption abilities such as low adsorption limitation (0.001 mg/L), high adsorption capacity (1.34 mmol/g) and fast response speed (half-saturation adsorption time less than 0.5 min based on 1 mg/mL Cd²⁺). The effectiveness of this chelating fiber has been proved by using it to treat actual sewage water, where the concentration of Cd²⁺ was reduced from 0.540 to below 0.001 mg/L. This level easily meets drinking water standards (0.003 mg/L) issued by the World Health Organization. Moreover, this chelating fiber is also very effective at treating other metal ions such as Cu²⁺, Ca²⁺, Zn²⁺, Mg²⁺, Pb²⁺, Ni²⁺, Ag⁺ and Hg²⁺.     

Analysis of physical properties of PET/CD‐PET polyblend hollow fiber and its kinetics of alkaline hydrolysis

Cationic dyeable poly(ethylene terephthalate) (CD‐PET) was formed by copolymerizing dimethylterephthalate (DMT),5‐sodium sulfonate dimethyl isophthalate (SIPM) with a molar ratio of 2% and ethylene glycol (EG). Blends of regular poly(ethylene terephthalate) (PET) and CD‐PET were spun into hollow fibers. The fibers were then treated with aqueous NaOH. This study investigated the physical properties of PET/CD‐PET polyblend hollow fibers and their kinetic behavior of alkaline hydrolysis using differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), the density gradient method, a gel permeation chromatograph (GPC), a rheometer, and regression analysis of the statistical method. For the alkaline hydrolysis kinetics equation of PET, CD‐PET, and PET/CD‐PET polyblend materials: ? dW/dt = KC^αA^β, β values of chip and POY/ FOY hollow fibers are equal to 1. Moreover, R² of the kinetics equation of chip/POY/FOY for a from 1.09–1.35/1.08–1.32/1.06–1.29 were better than those of a = 1. Experimental results indicate that the rate constant of alkaline hydrolysis was CD‐PET hollow fiber > PET/CD‐PET polyblend hollow fibers > PET hollow fiber and FOY > POY > > Chip. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3601–3610, 2002     

Blend membranes from carboxymethylated chitosan/alginate in aqueous solution

The blend membranes were satisfactorily prepared by coagulating a mixture of O‐carboxymethylated chitosan (CM‐chitosan) and alginate in aqueous solution with 5 wt % CaCl₂, and then by treating with 1 wt % HCl aqueous solution. Their structure and miscibility were characterized by scanning electron micrograph, X‐ray diffraction, infrared spectra, differential thermal analysis, and atomic absorption spectrophotometer. The results indicated that the blends were miscible, when the weight ratio of CM‐chitosan to alginate was in the range from 1 : 1 to 1 : 5. The polymers interpenetration including a Ca²⁺ crosslinked bridge occurred in the blend membrane, and leads to high separation factor for pervaporation separation of alcohol/water and low permeation. The tensile strength in the wet state (σ_b = 192 kg cm⁻² for CM‐chitosan/alginate 1 : 1) and thermostability of the blend membranes were significantly superior to that of alginic acid membrane, and cellulose/alginate blend membranes, owing to a strong electrostatic interaction caused by —NH₂ groups of CM‐chitosan with —COOH groups of algic acid. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 610–616, 2000     

Continuous and high throughput production of alginate fibers using co-flow in a millifluidic T-junction

We present a new technique for continuous production of alginate fibers using off-the-shelf millifluidic components and syringe pumps. The components are quickly assembled to form a T-junction to deliver co-flowing streams of sodium alginate and calcium chloride allowing formation of hydrogel fibers in the exit channel. We vary the flow rates of the two streams, calcium chloride concentrations and length of exit channel and identify conditions where fibers of uniform and nonuniform thickness are produced. We find that uniform fibers can be produced at a maximum total flow rate of 10 mL min⁻¹. As expected, for uniform fibers, we observe that the fiber diameter increases with increase in alginate solution flow rate, and we propose a simple model that predicts the fiber diameter as a function of flow rate ratio. We investigate the source of fiber nonuniformity and explain it using an empirical model that involves crosslinking time and gel strength. Our approach features easy device assembly and operation and enables continuous fiber production without clogging risks. Fiber production rates in the order of 10 m min⁻¹ are achievable using our approach. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47120.     

Cationic latex interaction with pulp fibers. II. Modification of sheet properties by styrene butadiene latex with quaternized amino groups

Unbeaten kraft fibers covered with experimental cationic latexes were formed into sheets in which direct fiber-fiber bonds are replaced by polymeric bonds. The effect on sheet properties—breaking length, elongation at break, folding endurance, opacity, and light scattering—was evaluated as a function of latex composition. The composition was altered by either the ratios of styrene to butadiene in the polymer or by mixing soft film-forming and hard nonfilming latex. It is shown that, regardless of latex composition and mechanical properties of the polymeric film, all the latexes can modify the sheet properties to a similar extent, providing that the sheets are heated above the polymer's glass transition temperature. An improvement of tensile strength is accompanied by increased elongation. As a probable mechanism of reinforcement, it is suggested that the polymer acts as a filler of the fiber's surface irregularities, thus providing a larger contact area between fibers and an improved stress transfer between them.     

海藻酸纤维对铜离子的吸附性能

为了研究不同各类的海藻酸纤维对铜离子的吸附性能,用盐酸及硫酸钠水溶液处理海藻钙纤维,分别得到海藻及海藻酸钙钠纤维,把三种纤维分别与含铜离子的水溶液接触后,在不同的时间段测试溶液中铜离子的深度,结果表示：海藻酸、海藻酸钙及海藻酸钙钠纤维对铜均有较好的吸附性能,其平衡吸附容易分别为68.6mg/g,81.7mg/g和71.0mg/g,海藻酸钙纤维的吸附容量在三种纤维中最高,由于海藻酸钙钠纤维遇水后可以很快地吸水膨胀,其吸附速度较其它两种纤维快.