Structure and characteristics of chitosan-based fibers containing chrysotile and halloysite

With the use of the methods of X-ray diffraction and electron microscopy, chitosan fibers prepared by coagulation into an alcohol-alkali mixture are shown to possess a two-phase structure containing C- and O-type crystallites. These fibers and composite fibers containing halloysite and Mg chrysotile nanotubes are characterized by anisotropic structure, i.e., by the orientation of both chitosan crystallites and Mg chrysotile particles along the fiber axis. A comparison of the rates of shear induced by passing of a polymer solution through a die and the data of rheological studies allows the conclusion that the structuring of chitosan solution under the applied field of shear stresses and the orientation of polymer macromolecules and filler nanotubes occur. An increase in the draw ratio during fiber spinning does not assist orientation of polymer crystallites but, in contrast, increases surface defectiveness and leads to the nucleation of longitudinal cracks; as a result, the strength of fibers decreases. The introduction of 5 wt % Mg chrysotile into the chitosan matrix markedly increases the mechanical characteristics of the composite fibers owing to the reinforcing action of oriented filler nanotubes.     

Preparation and Barrier Properties of Chitosan-Layered Silicate Nanocomposite Films

Summary: In this study, chitosan nanocomposite films were prepared using a solvent-casting method by incorporation of an organically modified montmorillonite (Cloisite 10A). The effect of filler concentration on the water vapor permeability, oxygen permeability, mechanical and thermal properties of the composite films was evaluated. The structure of nanocomposites and the state of intercalation of the clay were characterized by XRD. The water vapor permeability of pure chitosan films was measured as a function of relative humidity (RH). It was found that the permeability value increased with an increase in RH. The water vapor and gas permeability values of the composite films decreased significantly with increasing filler concentration. Permeation data was fitted to various phenomenological models predicting the permeability of polymer systems filled with nanoclays as a function of clay concentration and aspect ratio of nanoplatelets. According to the XRD results, an increase in basal spacing was obtained with respect to pure clay for chitosan/clay nanocomposites. This demonstrated the formation of intercalated structure of clay in the polymer matrix. Tensile strength and elongation at break of the composites increased significantly with the addition of clay, however the thermal and color properties of the films were not much affected by the intercalation of clay into polymer matrix.     

Conductive macroporous composite chitosan-carbon nanotube scaffolds

Multiwalled carbon nanotubes (MWCNTs) were used as doping material for three-dimensional chitosan scaffolds to develop a highly conductive, porous, and biocompatible composite material. The porous and interconnected structures were formed by the process of thermally induced phase separation followed by freeze-drying applied to an aqueous solution of 1 wt % chitosan acetic acid. The porosity was characterized to be 97% by both mercury intrusion porosimetry measurements and SEM image analysis. When MWCNTs were used as a filler to introduce conductive pathways throughout the chitosan skeleton, the solubilizing hydrophobic and hydrophilic properties of chitosan established stable polymer/MWCNT solutions that yielded a homogeneous distribution of nanotubes throughout the final composite matrix. A percolation theory threshold of approximately 2.5 wt % MWCNTs was determined by measurement of the conductivity as a function of chitosan/MWCNT ratios. The powder resistivity of completely compressed scaffolds also was measured and was found to be similar for all MWCNT concentrations (0.7-0.15 Omega cm powder resistivity for MWCNTs of 0.8-5 wt %) and almost five times lower than the 20 k Omega cm value found for pure chitosan scaffolds.     

Synthesis of Electrolyte Polymer Based on Natural Polymer Chitosan by Ion Implantation Technique

This research is conducted to make solid-state electrolyte based on natural polymers, as an alternative material for energy storage such as battery. Natural polymers as materials of solid state batteries have various benefits, such as unlimited abundance, biodegradable, unleakage, stable form, excellent process, and electrochemical stability, compare to the liquid ones. In this study, a solid state polymer electrolyte based on natural polymer such as chitosan was synthesized by incorporating various ion salts (Li, Cu, Ag) in the polymer matrix. The synthesis of solid-state electrolyte polymer was carried out by casting method to make a thin polymer film. Then the ionic (Li, Cu, Ag) doping with various implant dose will be applied to the thin polymer film matrix by ionic implantation technique. The implanted polymer electrolytes are then characterized their conductivities, micro structures, and crystal structures by high precision LCR, scanning electron microscopy-electron dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD), respectively. The measured of conductivities showed that thin film polymers after implanted with ionic Li, Cu or Ag were increased the conductivity, meanwhile elemental analisys by electron dispersive spectroscopy indicated that ionic implant to chitosan was success. The modification of chitosan polymer to become electrolyte polymer can be concluded.     

Specific features of chitosan-montmorillonite interaction in an aqueous acid solution and properties of related composite films

The rheological properties of chitosan solutions in a 2% aqueous solution of acetic acid with added montmorillonite nanoparticles and the mechanical properties and structural organization of chitosan-based composite films are studied. The interaction between the polymer functional groups and surface charges of nanoplatelets is confirmed by conductometric and potentiometric measurements. With the use of a X-ray diffraction analysis, it is shown that the nanoparticles in films are in the exfoliated and intercalated states. The incorporation of up to 10 wt % modified montmorillonite nanoparticles into the chitosan matrix results in a successive increase in rigidity and a decrease in the elongation at break.     

Stabilisation of the Secondary Structure of Chitosan Gels during the Preparation of Composites

Summary: Zeolite-chitosan composites have been prepared by encapsulation of zeolites by a gelling solution of chitosan or by in-situ synthesis of zeolites inside a chitosan gel. The preparation of the composite implies modifications of both components. Zeolites are dealuminated by the acid solution in which chitosan is dissolved and the morphology of the chitosan fibrils is stabilized by iniorganic species issued from the dealumination of the zeolites or from their synthesis medium. Zeolite-bearing chitosan xerogels present surface area and porosity similar to the textural properties of chitosan aerogels.     

手性拆分l-脯氨酸分子印迹聚合物的制备及其性能

以壳聚糖(CTS)为功能基体,以L-脯氨酸(L-Pro)为模板分子,采用分子印迹技术,在水溶液中合成了在空间结构和结合位点上与L-脯氨酸匹配的分子印迹聚合物(L-Pro-M IPs)。利用红外、扫描电镜和热失重分析,对相关化合物进行了表征,并对合成机理进行初步探索;通过对pH值、反应时间、交联剂用量的调节,获得最佳的反应条件为:制备壳聚糖-L-脯氨酸复合物的pH=10.7,干复合物1.0 g,交联剂8 mL,室温下反应18 h。结果表明,在水相中,L-Pro-M IPs对L-Pro具有良好的吸附选择性和高效分离特性,分离因子为4.67。     

Synthesis and characterization of a new conducting polymer composite

Organic conductive composite films have been synthesized by electropolymerization of pyrrole in the presence of chitosan and p-toluene sulfonic acid sodium salt. The obtained conductive polymer composite films have been characterized by Fourier Transform Infrared spectroscopy, dynamic mechanical analysis, scanning electron microscopy, X-ray diffraction and conductivity measurements. The prepared polymer composite films had the amorphous structure and exhibited the enhanced conductivity and mechanical properties due to the presence of chitosan in the composite films.     

聚合物-二氧化硅复合基材中CdS纳米晶的合成

本文报道在Sol-gel基材中制备由聚合物稳定的CdS纳米晶的新方法， 即通过甲基丙烯酸镉与甲基丙烯酸羟乙酯共聚合合成了含有Cd 2+的聚合物微凝胶, 在聚合物微凝胶网络中原位聚合正硅酸乙酯形成聚合物互穿的Sol-gel复合基材. 再向该聚合物/二氧化硅复合基材中通入H2S气体得到CdS纳米晶. 在聚合物网络中原位聚合正硅酸乙酯可以降低纯二氧化硅材料的脆性; 另一方面, 二氧化硅可以作为增强剂增加聚合物材料的强度. 因此, 在我们合成的聚合物/二氧化硅复合基材中制备的CdS纳米晶将具有很好的应用前景.     

原位沉析法制备有序排列四氧化三铁/壳聚糖纳米复合材料的研究

生物矿物由于具有完美结构及独特的生物活性,使其成为制备新型有彬无机杂化纳米复合材料的思想来源,在目前制备的有机／无机纳米复合材料中,纳米粒子在聚合物基质中大部分是无规分散的,但无机纳米颗粒在有机物中的有序排列是生命体中的一种根本体现,有序排列会使材料的性能更加优异。人骨的主要成分是纳米羟基磷灰石晶体和胶原,羟基磷灰石晶体是沿着胶原纤维的长轴方向有序排列的,这使得人骨不仅具有生物活性,而且具有非常好的力学性能。     

Preparation of agarose/chitosan composite supermacroporous monolithic cryogels for affinity purification of glycoproteins

Supermacroporous agarose/chitosan composite monolithic (AC CM) cryogels were prepared for affinity purification of the major egg white glycoproteins, ovalbumin (OVA), and ovotransferrin (OVT). The supermacroporous AC CM cryogels were produced by cryocopolymerization of agarose/chitosan blend solutions using glutaraldehyde as the cross-linker. The 3-aminophenlyboronic acid ligand was immobilized by covalent binding to epoxy-group-coupled supermacroporous AC CM cryogels. The microstructure morphologies of these cryogels were analyzed by scanning electron microscopy. The supermacroporous AC CM cryogels contained a continuous interpenetrating polymer network matrix with interconnected pores of 10-100 μm in size. The composite cryogels offered high mechanical stability and had specific recognition for glycoproteins. The maximum binding capacity of OVA adsorption from aqueous solutions was 55.6 mg/g. The matrix could be reused 11 times without significant loss in OVA adsorption capacity. The recovery yields of OVA and OVT from egg white were estimated to be 89 and 93%, respectively.     

Precise control of microstructure of functionalized polypropylene synthesized by the ansa‐zirconocene/ MAO catalysts

We inclusively investigated polymerization behavior and structure of copolymer in the copolymerization of propylene and alkylaluminum‐protected polar allyl monomers. The control of the arrangement of polar group in the copolymer was discussed. It was proved that the location of polar group could be controlled by zirconocene catalyst and a kind of polar monomer. The indenyl or the 2‐methylindenyl ligands of zirconocene were favored to produce end‐functionalized polymers. It was also found that the trimethylaluminum‐protected allylamine and triisobutylaluminum‐protected allylmercaptan had superior ability in the synthesis of end‐functionalized polypropylene. On the other hand, the 2‐methyl‐4‐phenylindenyl ligand produced the copolymers containing both the end‐polar unit and inner‐polar unit at the polymer chains. Terpolymerization of propylene, polar allyl monomer, and 5‐hexen‐1‐ol was also conducted. The NMR study of the terpolymer revealed that both the 5‐hexen‐1‐ol and the polar allyl monomer were incorporated into the polymer chain. It has also become apparent that the polar allyl monomer units predominantly occupied the chain end, while the 5‐hexen‐1‐ol units were located at the inner of main chain. Consequently, we have achieved the synthesis of functionalized polypropylene in which the arrangement of polar group was precisely controlled. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1738–1748, 2008     

A study on the bioactivity of chitosan/nano-hydroxyapatite composite scaffolds for bone tissue engineering

In order to increase the biocompatibility and bioactivity of chitosan, hydroxyapatite had been in situ combined into chitosan scaffolds. The bioactivity of the composite scaffolds was studied by examining the apatite formed on the scaffolds by incubating in simulated body fluid and the activity of preosteoblasts cultured on them. The apatite layer was assessed using scanning electronic microscope (SEM), X-ray diffraction (XRD), Fourier-Transformed Infrared spectroscopy (FTIR) and weight measurement. Composite analysis showed that after incubation in simulated body fluid on both of the scaffolds carbonate hydroxyapatite was formed. With increasing nano-hydroxyapatite content in the composite, the quantity of the apatite formed on the scaffolds increased. Compared with pure chitosan, the composite with nano-hydroxyapatite could form apatite more readily during the biomimetic process, which suggests that the composite possessed better mineralization activity. Furthermore, preosteoblast cells cultured on the apatite-coated scaffolds showed different behavior. On the apatite-coated composite scaffolds cells presented better proliferation than on apatite-coated chitosan scaffolds. In addition, alkaline phosphatase activities of cells cultured on the scaffolds in conditioned medium were assessed. The cells on composite scaffolds showed a higher alkaline phosphatase activity which suggested a higher differentiation level. The results indicated that the addition of nano-hydroxyapatite improved the bioactivity of chitosan/nano-hydroxyapatite composite scaffolds. On the other hand, that is to say composition of substrates could affect the apatite formation on them, and pre-loaded hydroxyapatite can enhance the apatite-coating. It will also be significant in preparation of apatite-coating polymer scaffolds for bone tissue engineering.     

Effects of the polymer-support on the synthesis of 2,4-dibromophenyl allyl ether in a triphase catalysis

The synthesis of 2,4-dibromophenyl allyl ether by reacting allyl bromide with 2,4-dibromophenol in an organic solvent/alkali solution by triphase catalysis was studied. A macroporous polymer pellet which served as the support of the catalyst was prepared by reacting styrene monomer with chloromethyl styrene and divinylbenzene through suspension polymerization. Tri-n-butylamine was immobilized on the surface of the polymer pellet to form the triphase catalysts. Immobilization of the catalyst on the polymer support carried out in a mechanical agitator was suggested to obtain a high catalyst reactivity. In the three-phase reaction, the effects of agitation speed, and the characteristics of the catalyst pellet which affect the conversion of allyl bromide in the three-phase catalytic reaction were examined in detail. Based on the experimental data, the optimum operating parameters for preparing the triphase catalyst to get a high yield of 2,4-dibromophenyl allyl ether were: using a low degree of polymer crosslinking (2%), and small particle size. The yield of the product obtained from the present study is higher than that which was obtained in a two-phase reaction. © 1993 John Wiley & Sons, Inc.     

Characterization and antibacterial activity of chitosan‐based composites with polyester

The effects of replacing poly(butylene succinate adipate) (PBSA) with acrylic acid‐grafted PBSA (PBSA‐g‐AA) on the structure and the properties of a PBSA/chitosan composite were investigated. The properties of both PBSA‐g‐AA/chitosan and PBSA/chitosan were compared using Fourier transform infrared (FTIR), ¹³C nuclear magnetic resonance (NMR), X‐ray diffraction (XRD), and an antibacterial activity test. With PBSA‐g‐AA in the composite, the compatibility with chitosan and, consequently, the properties of the composite became greatly improved due to the formation of ester and imide groups that conferred better dispersion and homogeneity of chitosan in the matrix. Composites containing PBSA‐g‐AA/chitosan exhibited superior mechanical properties due to greater compatibility between the two components. Moreover, chitosan enhanced the antibacterial activity of the composites. Composites of PBSA‐g‐AA or PBSA that contain chitosan have better antibacterial activity. The functionalized PBSA‐g‐AA/chitosan composites showed markedly enhanced antibacterial properties due to the carboxyl groups of acrylic acid, which acted as coordination sites for the chitosan phase, allowing the formation of stronger chemical bonds. Copyright © 2011 John Wiley & Sons, Ltd.     

Comparative study of Cu(II) catalytic sites immobilized onto different polymeric supports

The catalysts with copper(II) ions stabilized onto different polymeric matrixes are prepared on either bulk (Cu/chitosan, Cu/polyethyleneimine-polyacrylic acid (PPA), and Cu-diiminate-impregnated polystyrene, polyarylate, or polymethylmethacrylate) or composite supports (egg-shell type Cu/chitosan/SiO₂ and Cu/PPA/SiO₂). The morphology of the samples and peculiarities of Cu(II) cationic sites are studied by SEM and ESR methods, and the catalyst activities are compared in oxidation of o- and p-dihydroxybenzenes by air in water. The catalytic activity of Cu(II) centers is governed by the coordination of isolated copper ions: for the most active catalysts, i.e., Cu/chitosan and Cu/PPA, the symmetry of isolated Cu²⁺-sites approximates a coordinatively unsaturated square-planar structure. At the same time, accessibility of active sites to water differs for different polymers, so the contribution of hydrophilicity to the reaction pattern cannot be excluded. Redox transformations of the active sites in the course of catalytic tests do not cause copper leaching from the polymer matrix. The binary composite systems with a film of low-loaded hydrofilic Cu-polymer supported on macroporous SiO₂ demonstrate substantially higher activity in oxidation of hydroquinone and 3,4-dihydroxyphenylalanine, as compared with the bulk Cu/polymer samples. In turn, the specific activity of Cu/chitosan/SiO₂ exceeds significantly that of Cu/PPA/SiO₂ due to stabilization of a thinner and more uniform film of chitosan at the surface of silica.     

Solid-state synthesis of amphiphilic chitosan-polyethylene systems by the maleinization of both components

N-acylated chitosan modified by maleic anhydride was prepared by the method of the solid-state synthesis (Bridgman anvils, semipilot extruder). In contrast to the synthesis under homogeneous conditions, solid-state acylation is accompanied by the reaction of imidization of the formed amic acid as well as by reaction through double bonds, thus leading to the formation of derivatives of succinic anhydride. By simultaneous or subsequent interaction of chitosan modified with maleic anhydride with a PE matrix, either modified or not modified with maleic anhydride, new chitosan-polyethylene composite materials are prepared, and these composites are characterized by the combined valuable medicinal and biochemical properties of chitosan and high mechanical characteristics of the polyolefin component. The above composites are of obvious interest as amphiphilic sorbents, which are highly resistant to the action of aggressive media, as well as antimicrobial and biodegradable PE-based materials.     

Crosslinked chitosan composite membrane for the pervaporation dehydration of alcohol mixtures and enhancement of structural stability of chitosan/polysulfone composite membranes

Chitosan composite membranes having a microporous polysulfone substrate were prepared and tested for the pervaporation dehydration of aqueous isopropanol mixtures. When the composite membrane experienced excessive swelling at the feed mixture of high water content, the composite membranes were found to be segregated in structure due to the opposite characteristics to water of chitosan and polysulfone. Efforts to enhance the structural stability under various pervaporation operational conditions were made. The polysulfone substrate was immersed into hydrophilic binding polymer solutions such as polyvinyl alcohol, polyacrylic acid, and hydroxyethylcellulose before the casting of chitosan layer to increase the affinity between the thin chitosan layer and porous polysulfone layer which resulted in increased geometrical stability of the chitosan/polysulfone composite membranes. The chitosan layer was crosslinked with glutaraldehyde and H₂SO₄ in acetone solution to control the permselectivity.     

Synthesis of core-shell structured polymers with inserted thioether from a multi-functional scaffold

The synthesis of a thioether inserted, core-shell structured polymer from the scaffold of hyperbranched polyglycerol (PG) was described. PG was first allyl functionalized, and in the presence of AIBN, the allyl groups further underwent radical addition to thiol compounds, thus thiol functional polyethylene oxide monomether (MPEO) were grafted onto PG. Similarly, 2-mercaptoethy-lammonium chloride was introduced onto PG via thiol addition, and the residual amino groups were further quaternized with decyl bromide, leading to an amphiphilic core-shell structure polymer.     

Nanocomposites based on modified chitosan and titanium oxide

The effect of primary amino groups and molecular mass of chitosan on the stability of suspensions based on nanoscale TiO₂ dispersions in acidic solutions of various concentrations at pH 2.5 was studied. In the case of chitosan prepared according to a commercialized process, the stability of TiO₂ suspensions was low and depended on the concentration of the polymer solution. Solutions of low-molecular-mass highly deacetylated chitosan prepared by solid-phase synthesis stabilized a dispersion of nanosized TiO₂ particles for a very long time. Nanocomposites based on a chitosan-PVA graft copolymer and TiO₂ were prepared, in which the initial filler dispersion is retained up to very high filling ratios. A potential use of these nanocomposites in photocatalytic processes is discussed. The results of this study can be used for refining engineering procedures and processes for the manufacture of new biocompatible, bioactive, and biodegradable functional composite materials based on chitosan and synthetic polymers.