Functionalization of chitosan via single electron transfer living radical polymerization in an ionic liquid and its antimicrobial activity

In this work, single electron transfer living radical polymerization (SET‐LRP) was used to functionalize chitosan in a well‐controlled manner. The chitosan‐based macroinitiator was first synthesized and then initiated the SET‐LRP of methacryloyloxyethyl trimethylammonium chloride (DMC) in ionic liquid system, using Cu⁰/N,N,N′,N′,N′′‐pentamethyldiethylenetriamine as a catalyst. The grafting of PDMC brushes on chitosan was confirmed and analyzed by Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance. Transmission electron microscopy reveals that the chitosan copolymer showed self‐assembled behavior in acetone. Surface properties of the copolymer have been investigated by environment scanning electron microscopy analysis. The linear relationship between the ln([M]₀/[M]_t) and time, the linear increase of number‐average molecular mass with conversion as well as the low polydispersity index of the polymer confirmed the “living/controlled” features of the polymerization of DMC through SET‐LRP. Finally, the chitosan copolymer demonstrates its potential antibacterial application, showing excellent inhibitive capability against Escherichia coli. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42754.     

Dissolution and utilization of chitosan in a 1‐carboxymethyl‐3‐methylimidazolium hydrochloride ionic salt aqueous solution

1‐Carboxymethyl‐3‐methylimidazolium hydrochloride ([IMIM–COOH]Cl), a new ionic salt, is proposed as a green, promising solvent for dissolving chitosan. However, because of the optimal dosage of chitosan dissolved in [IMIM–COOH]Cl, a 12 wt % [IMIM–COOH]Cl aqueous solution was selected as an optimum solvent system for dissolving chitosan. The structures of the original and regenerated chitosan were characterized by Fourier transform infrared spectroscopy and X‐ray diffraction analysis. Scanning electron microscopy was used to visualize the morphological features of the reconstituted chitosan membranes. Meanwhile, the absorbance, tensile strength, and breaking elongation of the chitosan membranes were measured. The results reveal that 10–11 wt % was an optimal chitosan concentration for preparing membranes. Furthermore, the adsorption capacity for Cu(II) ion of the chitosan membranes was increased with the chitosan concentration decreased from 12 to 8 wt %. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41965.     

Dissolution and stability of chitosan in a sodium hydroxide/urea aqueous solution

Medium‐molecular‐weight chitosan (MMWC; 157.5 kDa) and low‐molecular‐weight chitosan (LMWC; 53.4 kDa) samples were dissolved in an NaOH/urea solution by freeze–thaw treatment. The factors affecting dissolution were optimized, and the stability of chitosan in the produced solution was investigated. NaOH and urea concentrations of 2 and 0.67 mol/L, respectively, and a treatment temperature of ?18°C were optimized as the dissolving conditions. MMWC and LMWC could be completely dissolved in the 2 mol/L NaOH/0.67 mol/L urea solution after six and five cycles of freeze–thaw treatments, respectively. Dissolution and storage in the 2 mol/L NaOH/0.67 mol/L urea solution slightly increased the deacetylation degree of chitosan and slightly decreased the molecular weight. The solution stability of LMWC was better than that of MMWC. MMWC tended to form a gel during storage. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39819.     

Preparation of oligochitosan via In situ enzymatic hydrolysis of chitosan by amylase in [Gly]BF4 ionic liquid/water homogeneous system

The preparation of oligochitosan with excellent performance via in situ enzymatic hydrolysis of chitosan by amylase in ionic liquid system is reported. It has been found that [Gly]BF₄ ionic liquid leads to the good solubility and assistant degradation for chitosan, as well as good biocompatibility for amylase. In the homogeneous system that contained 1.0 g chitosan (degree of deacetylation = 88.5%) and 99.0 g 2 wt % [Gly]BF₄ aqueous solution, oligochitosan with 2200 viscosity‐average molecular weight has been obtained after 0.12 g amylase being used for 3 h at 50°C and pH 5.0. This result is superior to that conducted in acetic acid system. Moreover, [Gly]BF₄ can be easily separated from the product and reused with only slight performance loss (oligochitosan product with 2700 viscosity‐average molecular weight has been obtained after [Gly]BF₄ being reused for five times). In addition, the mechanism for enzymatic hydrolysis of chitosan in [Gly]BF₄ ionic liquid has been described. The research on the moisture‐absorption, ‐retention, and antibacterial activity of oligochitosan product shows that the smaller molecular weight would bring the better moisture‐absorption and antibacterial properties. The oligochitosan product with 2200 viscosity‐average molecular weight exhibits preferable antibacterial properties to S. aureus and E. coli. At the same time, the moisture‐absorption and ‐retention capacity of the above product can reach 32% (relative humidity (RH) = 43%), 62% (RH = 81%), and 150% (RH = 43%), 35% (dry silica gel) respectively. The enzymatic preparation of oligochitosan through [Gly]BF₄ ionic liquid/water homogeneous system can be an efficient and environment‐friendly method for academics and industry. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41152.     

Evaluation of 1‐ethyl‐3‐methylimidazolium acetate based ionic liquid systems as a suitable solvent for collagen

Collagen, a prominent biopolymer, which is famous for its excellent biological activity, has been used extensively for tissue engineering applications. In this study, a novel solvent system for collagen was developed with an ionic liquid, 1‐ethyl‐3‐methylimidazolium acetate ([EMIM][Ac]), solvent system. A series of sodium salts were introduced into this solvent system to enhance collagen's dissolution procedure. The results show that the solubility of collagen was significantly influenced by the temperature and sodium salts. The solubility reached up to approximately 11% in the [EMIM][Ac]/Na₂HPO₄ system at 45°C. However, the structure of the regenerated collagen (Col‐regenerated) may have been damaged. Hence, we focused on the structural integrity of the collagen regenerated from the [EMIM][Ac] solvent system by the methods of sodium dodecyl sulfate–polyacrylamide gel electrophoresis, Fourier transform infrared spectroscopy, ultrasensitive differential scanning calorimetry, atomic force microscopy, X‐ray diffraction, and circular dichroism because its signature biological and physicochemical properties were based on its structural integrity. Meanwhile, a possible dissolution mechanism was proposed. The results show that the triple‐helical structure of collagen regenerated from the [EMIM][Ac] solvent system below 35°C was retained to a large extent. The biocompatibility of Col‐regenerated was first characterized with a fibroblast adhesion and proliferation model. It showed that the Col‐regenerated had almost the same good biological activity as nature collagen, and this indicated the potential application of [EMIM][Ac] in tissue engineering. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2245–2256, 2013     

Preparation and application of magnetic chitosan in environmental remediation and other fields: A review

Magnetic chitosan has received considerable attention over the decades due to its low cost, biodegradability, green sources, magnetic intensity. In this review, we reviewed the preparation methods of magnetic chitosan using co-precipitation, cross-linking and electrochemical. Therein cross-linking methodologies involved in the reaction of amino groups are facile to introduce additional reaction groups and improve anti-swelling of chitosan layers, mostly in an acidic environment. Besides, we focused on the applications of magnetic chitosan in various fields such as wastewater treatment, for example, removal of heavy metal ions, organic/inorganic dyes, fluorides, and pesticides. Moreover, magnetic chitosan also reveals great potential application in the field of medical, pharmaceutical, food and electronic screening. Above all, magnetic chitosan is economically and operationally beneficial as it can be easily separated and controlled with an external magnetic field and can be modified to maximize its functions.     

Functionalized chitosan with butylammonium ionic liquids for removal of Cr(VI) from aqueous solution

Environmental pollution by heavy metals is currently a problem of great concern for human health. In this context, this study aims to contribute with the synthesis and characterization of chitosan functionalized with three different ionic liquids (n-butylammonium acetate, sec-butylammonium acetate, and tert-butylammonium acetate) followed by its application in hexavalent chromium effluent treatment. The adsorbents synthesized (ChN, ChS, and ChT) were characterized by SEM, EDS, FTIR, BET, RDD, PSD, and XRD techniques. Afterward, the influences of temperature, contact time, and pH on the Cr(VI) adsorption process were evaluated. The solution with pH 3 displayed the highest adsorption capacities (107.31, 104.60, and 107.97 mg.g^-1 for ChN, ChS, and ChT, respectively). The kinetic data were better adjusted to the Weber-Morris kinetic model with an ideal time of 2 h. Furthermore, the influence of temperature was evaluated using the Freundlich and Langmuir isotherms, with maximum capacities of 142.05 (ChN), 131.58 (ChS), and 146.63 mg.g^-1 (ChT). The adsorbent displayed enhanced adsorption properties in comparison with raw chitosan by an intensification of the electrostatic interaction between amino groups and hexavalent chromium. Finally, the reusability was investigated, and significant results were observed (84.33 ± 4.87%) in the adsorption process after 4 cycles.     

Preparation of chitosan and carboxymethylcellulose-based polyelectrolyte complex hydrogel via SD-A-SGT method and its adsorption of anionic and cationic dye

The excellent properties of the polyelectrolyte complex hydrogels (PECHs) prepared with polysaccharides only, including polyampholyte, low toxicity, green, and clean production, have endowed them great application potentials as the adsorbents for dye-containing wastewater treatments. In the current study, the PECH of chitosan (CTS) and carboxymethylcellulose (CMC) was prepared by semi-dissolution acidification sol–gel transition (SD-A-SGT) method. The hydrogel was formed by the strong electrostatic interaction of cationic  NH₃⁺ groups of CTS and the anionic  COO⁻ groups of CMC. This simple but efficient means exhibited great potentials in constructing PECHs with uniform composition and controllable sol–gel transitions. Molecular dynamics simulation was first employed to predict the formation process and the microstructure of PECHs prepared by SD-A-SGT method. The structure and properties of the CTS-CMC PECHs were also characterized by Fourier transform infrared spectroscopy, SS ¹³C-NMR, scanning electron microscopy, mechanical tests, and rheological measurements, respectively. Taking the advantage of amphoteric polyelectrolyte properties, adsorption properties of anionic and cationic dyes were investigated using sunset yellow FCF and methylene blue as model dyes, respectively. The PECHs prepared in the present work had good adsorption capacity for both cationic and anionic dyes with maximum adsorption capacity of 212.83 mg/g for sunset yellow FCF and 167.35 mg/g for methylene blue. Therefore, this PECH would be a promising environmentally friendly adsorbent for the treatment of functional molecules with different charges.     

Behavior of cellulose liquefaction after pretreatment using ionic liquids with water mixtures

Ionic liquid (IL)‐water mixtures were applied in cellulose pretreatment experiment and the pretreated cellulose was used in subsequent phenol liquefaction process as a new application method. Cellulose recovery rate and the average molecular weight (M_w) of pretreated cellulose were investigated to understand the influence of these mixtures on cellulose structure. X‐ray diffraction, Fourier transform infrared, gel permeation chromatograph, and scanning electron microscope were used to clarify the changes of pretreated cellulose. The liquefied residues from untreated cellulose and pretreated cellulose were considered as significant index to determine the effect of IL‐water mixtures on cellulose. Moreover, liquefied residues were initially characterized by the variation of the average M_w. It was suggested that the lower M_w of cellulose obtained in IL‐water mixtures, and the crystalline structure was disrupted. So, some cracks were found on the cellulose surface obviously. The liquefied residues result suggested that the pretreated cellulose obtained the lower residues at the same time or the same amount of residues by using the less time. The behavior of cellulose liquefaction efficiency using IL‐water mixture pretreatment was discussed. The lower M_w of cellulose was the major factor, which accelerates the cellulose phenol liquefaction process efficiency. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40255.     

Preparation,characterization and antioxidant activity of acetylated garlic polysaccharide,and garlic polysaccharide-Zn (II) complex

Garlic polysaccharide (PS) was extracted from garlic by hot-water extraction. Acetylated garlic polysaccharide (AcPS) and garlic polysaccharide-zinc complex (ZnPS) were synthesized. The results of Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy analysis showed that the modifications were successful. The antioxidant activities of PS, AcPS, and ZnPS were further investigated in vitro, including scavenging superoxide anion and hydroxyl radicals, antilipid peroxidation capacity, and reducing power. The results showed that the scavenging abilities of AcPS and ZnPS on hydroxyl radical (The IC₅₀ of PS, AcPS, and ZnPS were 2.86, 1.62 and, 1.49 mg/ml, respectively,) and superoxide anion radical (The scavenging rate of PS, AcPS, and ZnPS were 1.5% and 1.8%, and 2.3%, respectively, when concentration was at 1.0 mg/ml.) were stronger than that of PS, and the inhibitory effect of AcPS on lipid peroxidation was significantly stronger than that of PS (The IC₅₀ of PS and AcPS were 1.05 and 0.53 mg/ml, respectively.). It indicated that the acetylation was a favorable way to enhance the antioxidant activity of garlic PS; ZnPS complex could be applied as potential candidate for antioxidant and Zn supplement.     

Production and isolation of chitosan from Aspergillus terreus and application in tin(II) adsorption

Fed‐batch fermentation was used for biomass and fungal chitosan production by Aspergillus terreus (BCRC 32068) grown in a potato dextrose agar medium. The polysaccharides were extracted by an alkali–acid treatment, and structural investigations by X‐ray diffraction, Fourier transform infrared analysis, and viscosity and thermal analysis were done. A high level of chitosan was extracted from A. terreus; this implied that it was feasible to produce chitosan from industrial waste mycelia. Fungal chitosan derived from A. terreus showed the highest adsorption capacity for Sn(II). The order of Sn(II) adsorption capacity for these chitosanaceous materials was Fungal chitosan > Chitin > Biomass. Fungal chitosan derived from A. terreus was well correlated with Langmuir's isotherm model. The maximum capacity for Sn(II) sorption deduced from the use of the Langmuir isotherm equation was 303 mg/g; this was significantly higher than that of A. terreus. Fungal chitosan is an easy and cost‐effective material for the abatement of pollution. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40436.     

Tunable wettability and tensile strength of chitosan membranes using keratin microparticles as reinforcement

Keratin particles with microscale are prepared by ball mill and its influences on the chitosan membrane is evaluated. Composite membranes with various content of keratin are fabricated, and their physical and chemical properties such as morphology, wettability, crystallization, thermal stability, tensile strength, and break elongation are investigated. Optical microscope and situ topographic scan mode of nano‐test system are used to examine the dispersion and aggregation of keratin on the surface of chitosan membrane. The result of contact angle (CA) and mechanical testing show that the incorporation of keratin particles decrease the CA from 98.1° to 58.2°. Tensile strength and break elongation of the composite membrane reaches a maximum of 65 ± 8 MPa and 15% when the keratin content is 6%, an increase of 80% and 88% compared with the pristine chitosan membrane. Both the increase in tensile strength and break elongation is result of the incorporation of keratin particles known for their excellent compatibility between keratin and chitosan matrix. These kind of composite material combines the antibacterial properties of chitosan with cell culture preference of keratin which may have potential biomedical application. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44667.     

High strength antibacterial membranes consisted of nanofibrous chitosan immobilized silver nanoparticles

Chitosan (CS) has biocompatibility and biodegradability, but the bulk CS hydrogel/membranes with its poor strength and limited antibacterial property could not satisfy the practical application. Here green dissolving/regeneration and in situ reduction strategy was combined to construct high strength antibacterial CS membranes. First nanofibrous CS hydrogels were constructed through dissolving CS in LiOH/KOH/urea aqueous system via freezing–thawing process followed regeneration. Then, Ag NPs were immobilized along CS nanofibers through in situ reductions of Ag + by the NH₂ group of CS. The obtained NCM-Ag composite dry membranes are easy for storing and can quick switch to nanofibrous hydrogels as absorbing water. Size of Ag NPs can be controlled to very small until 2 nm by concentration and limited space network. Fourier transform infrared spectroscopy and X-ray photoelectron spectrometer indicated the forceful grasp ability of CS nanofibers to Ag NPs for a stable binding, mechanical property was enhanced over 100Mpa as the nanofibrous structure and chain linked by Ag coordination. The NCM-Ag membranes had excellent antibacterial activities against both Staphylococcus aureus and Escherichia coli. Moreover, such nanofibrous CS membrane exhibited good adhesive ability to tissues. Combining all these properties, NCM-Ag membranes would be potential as antibacterial adhesion barrier to accelerate wound healing.     

Synthesis of a novel organosoluble,biocompatible, and antibacterial chitosan derivative for biomedical applications

Electrospun materials have a number of applications in the tissue engineering field. However, the limited solubility of chitosan (CS), especially in organic solvents, makes its electrospinning with other synthetic organosoluble polymers impossible. In this article, we report the synthesis of a novel organosoluble derivative of CS through the application of a simple synthetic methodology. CS was reacted with 1,3‐diethyl‐2‐thiobarbituric acid (DETBA) with triethylorthoformate in the presence of methanol and acetic acid (4:1). The functional groups in the synthesized materials were confirmed by Fourier transform infrared and solid‐state NMR spectroscopy, whereas X‐ray diffraction revealed the level of crystallinity. The CS derivative (CS–DETBA) was tested for its cytotoxic effects on human gastric adenocarcinoma AGS cells and was found to be nontoxic. The prepared derivative showed a much enhanced inhibitory effect on the growth of three bacterial strains, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, over that of CS itself. Overall, CS–DETBA showed good solubility in a range of organic solvents, such as dimethyl sulfoxide and N,N‐dimethylformamide, and was blended with polycaprolactone (PCL) to form films and electrospun nanofibers. The morphologies of the synthesized materials were analyzed by field emission scanning electron microscopy, and the fiber diameter was 360 nm under optimum conditions. This study demonstrated that the CS–DETBA–PCL blend could be a potential material for tissue engineering and biomedical applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45905.     

Kinetics of chitosan coagulation from aqueous solutions

In this study, we investigated the kinetics of chitosan hydrogel formation from aqueous chitosan solutions with sodium hydroxide (NaOH) as the coagulant. Two sets of experiments were performed, one in a parallelepiped cell and the other with cylindrical chitosan solution extrudates. The coagulation occurred by the neutralization of the protonated amino groups (? ) present in the chitosan chains, with the kinetics being controlled by NaOH transport toward the gelification zone. In this study, we confirmed the appropriateness of Fick's second law to describe NaOH transport, considering the instantaneous reaction between the NaOH and ? groups. The experimental data were used to determine the NaOH diffusion coefficient in gels having different chitosan concentrations. The diffusion coefficient values obtained from the cylindrical coagulation data were lower than those determined for linear coagulation because of the influences of transport geometry and gel structure, respectively. Accordingly, in fiber coagulation calculations, it is recommended to use diffusion coefficient values determined from cylindrical coagulation studies. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46062.     

Preparation of high-performance deproteinized natural rubber/chitosan composite films via a green and sulfur-free method

To solve the environment and health issues arose from the sulfur vulcanization, a facile and completely eco-friendly method of latex-assembly and in situ cross-linking is developed to prepare fully bio-based and high-performance rubber films. The films are featured by a “reinforced concrete” structure composed of dynamically cross-linked chitosan framework and unvulcanized deproteinized natural rubber (DPNR) matrix. The self-assembly of DPNR latex particles and chitosan, as well as the in situ cross-linking of chitosan in the film forming process are confirmed by transmission electron microscope and dynamic light scattering. As green rubbers without vulcanization, the as-designed composite films possess excellent mechanic properties comparable to those of the sulfur vulcanized DPNR film, whose tensile strength and toughness reach 15.2 MPa and 77.6 MJ m⁻³ respectively. Moreover, the films exhibited appropriate permeability to moisture and achievable reprocessing, which have potential applications in wearable devices.     

Enhanced adsorption and recovery of Pb(II) from aqueous solution by alkali‐treated persimmon fallen leaves

Persimmon fallen leaves were employed to prepare a renewable and low‐cost biosorbent named as NPFL. Effects of initial pH, contact time, initial Pb(II) concentration, coexisting metal ions, and ionic strength on adsorption of Pb(II) from aqueous solution by NPFL were studied in detail. Enhanced removal capacity of NPFL toward Pb(II) was observed, and the maximum adsorption capacity was evaluated as 256 mg g^?1 by Langmuir modeling calculation. The fast adsorption process and the well‐fitted kinetics data with pseudo‐second‐order model indicated that chemisorption is the main rate‐limiting step for the adsorption process. NPFL had superior adsorption selectivity for Pb(II) from aqueous solution with coexisting metal ions. Characterization of NPFL and adsorption mechanism (electrostatic attraction, ion exchange, and chelation) were performed using XRD, SEM‐EDS, FT‐IR, XPS, and TGA. The results suggested that NPFL could be utilized as a potential candidate for the preconcentration of Pb(II) recovery and its removal in practice. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43656.     

Effect of freeze‐thaw pretreatment on thermal drying process and physicochemical properties of chitosan

The effect of freeze‐thaw pretreatment on the thermal drying process and physicochemical properties of chitosan was investigated in this study. Results showed that the freeze‐thaw treatment changed the form of chitosan paste and reduced 75.6–77.7% of the water content. The freeze‐thaw treatment decreased the drying time of chitosan from 16–19 h to 2.75–4 h and the dried product was loosely packed powder. After freeze‐thaw treatment, the molecular weight of chitosan was unchanged during the thermal drying. The heat‐induced browning effect of chitosan during drying was greatly alleviated by the pretreatment. Furthermore, the pretreatment increased the 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) radical‐scavenging activity of dried product by 40.4–59.8%. The molecular weight, color, and DPPH radical‐scavenging activity of the pretreated dried chitosan product were close to those of freeze‐dried product. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41017.     

Preparation and hemocompatibility of electrospun O‐carboxymethyl chitosan/PVA nanofibers

Chitosan was deacetylated and carboxymethylated to prepare O‐carboxymethyl chitosan (CMC) for further electrospinning. CMC was characterized using FTIR, NMR, and chemical titration, indicating a degree of carboxymethylation of 51.4%. CMC was electrospun together with poly(vinyl alcohol) (PVA) to prepare membranes composed of nanofibers. The electrospinning conditions were optimized. The CMC/PVA membrane obtained at the conditions of 15.2 g/mL CMC 50 mL, 8 g/mL PVA 5 mL, 25 kV, and a distance of 23 cm, had nanofibers without beads, with diameters of 70–200 nm. The mats were crosslinked by glutaraldehyde before platelet adhesion measurement. The nanofibrous structure remained after crosslinking while the wettability decreased. CMC/PVA mats with higher CMC amount and fewer beads, had fewer adherent platelets and less platelets aggregation showing better hemocompatibility. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43565.