Preparation and characteristics of reprecipitated chitin: a new morphological form easy to manipulate with versatile utility

With the object of effectively destroying the rigid crystalline structure of chitin and thereby preparing an amorphous form with enhanced reactivity, chitin was dissolved in methanol saturated with calcium chloride dihydrate and reprecipitated under appropriate conditions. Chitin in the solution was first precipitated in deionized water, and the mixture was subjected to dialysis followed by freeze-drying. As an alternative method, the chitin solution was directly dialyzed and freeze-dried. Judging from the appearances of the products, the latter method was much superior, giving rise to the formation of highly fluffy cotton-like chitin. Compared to β-chitin, α-chitin was suitable as a starting material because of the adequate solubility in the solvent system. The resulting reprecipitated chitin exhibited higher reactivity as confirmed by the adsorption of copper(II) and acetylation reaction. The method was quite simple and convenient to prepare reprecipitated chitin that will have high potential as a new form from the practical viewpoint.     

Amorphous silicon–carbon based nano-scale thin film anode materials for lithium ion batteries

The buffering effect of carbon on the structural stability of amorphous silicon films, used as an anode for lithium ion rechargeable batteries, has been studied during long term discharge/charge cycles. To this extent, the electrochemical performance of a prototype material consisting of amorphous Si thin film (∼250 nm) deposited by radio frequency magnetron sputtering on amorphous carbon (∼50 nm) thin films, denoted as a-C/Si, has been investigated. In comparison to pure amorphous Si thin film (a-Si) which shows a rapid fade in capacity after 30 cycles, the a-C/Si exhibits excellent capacity retention displaying ∼0.03% fade in capacity up to 50 cycles and ∼0.2% after 50 cycles when cycled at a rate of 100 μA/cm² (∼C/2) suggesting that the presence of thin amorphous C layer deposited between the Cu substrate and a-Si acts as a buffer layer facilitating the release of the volume induced stresses exhibited by pure a-Si during the charge/discharge cycles. This structural integrity combined with microstructural stability of the a-C/Si thin film during the alloying/dealloying process with lithium has been confirmed by scanning electron microscopy (SEM) analysis. The buffering capacity of the thin amorphous carbon layer lends credence to its use as the likely compliant matrix to curtail the volume expansion related cracking of silicon validating its choice as the matrix for bulk and thin film battery systems.     

Linear viscoelastic behavior of poly(ethylene terephtalate) above Tg amorphous viscoelastic properties Vs crystallinity: Experimental and micromechanical modeling

Linear viscoelastic behavior of amorphous and semicrystalline poly(ethylene terephtalate), (PET), was experimentally investigated. PET’s samples with different crystallinities (Xc) were prepared and viscoelastically characterized. Based on our experimental results (properties of the amorphous PET and semicrystalline polymers), micromechanical model was used to, first predict the viscoelastic properties of the semicrystalline polymers and second predict the changes on the viscoelastic properties of the amorphous phase when the crystallinity increases. For the micromechanical modeling of semicrystalline material’s viscoelastic properties, difficulties lie on the used numerical methods (Laplace-Carson transformation) and also on the actual physical and mechanical properties of the amorphous phase. In this paper we tried to simplify the Laplace-Carson-based method by using a pseudo-elastic one that avoids the numerical difficulties encountered before. The time-dependant problem is so replaced by a frequency-dependant set of elastic equations. Good agreement with low crystallinity fraction was found however large discrepancies appear for medium and high crystallinity. The poor agreement raises the issue of which amorphous mechanical properties should be taken as input in the micromechanical model? According to the dynamic mechanical analysis (DMA) experimental data, multiple amorphous phases with different glass transition temperatures were observed for each tested semicrystalline sample. For each sample, new glass transition temperature related to an equivalent amorphous phase was determined. DMA tests done at 1 Hz help estimating the mechanical properties of the new amorphous phase based on its new glass transition temperature. Using the new micromechanical approach developed in this paper, the changes occurring on the viscoelastic behavior of the amorphous phase upon crystallization were estimated. Good agreement was found after comparing the micromechanically estimated amorphous behavior with the experimentally estimated one leading to believe that the physical and mechanical properties of the amorphous phase change upon crystallization and taking on account this phenomenon is a key to a good prediction of the semicrystalline behavior using micromechanical models.     

Effect of molecular orientation on the crystallization and melting behavior in poly(ethylene terephthalate)

Amorphous poly(ethylene terephthalate) fibers in which the skin was removed were studied to expressly study the effect of amorphous molecular orientation on crystallization behavior. Thermal analysis was carried out on fibers with a wide range of molecular orientation using differential scanning calorimetry (DSC) under constrained and unconstrained conditions. The thermal behavior was correlated with structural characteristics such as amorphous orientation determined using wide-angle X-ray diffraction. We show for the first time a quantitative inverse linear relationship between the degree of amorphous orientation and the cold crystallization temperatures and heat of crystallization. Crystallization begins at a critical amorphous orientation of 0.18, and extrapolation shows that even at modest amorphous orientation of 0.27, the cold crystallization can start spontaneously at T_g and with no change in free energy.     

非晶态合金催化剂的研究进展

介绍了非晶态合金用作催化材料的研究成果，比较了几个研究阶段的特点。负载型非晶态合金有可能成为一种新型的工业用催化剂。     

Role of the Amorphous Morphology in Physical Properties of Ultra High Molecular Weight Polyethylene

The role of amorphous layer in the physical properties of ultra high molecular weight polyethylene (UHMWPE) was investigated. It revealed that the thicker amorphous layer would promote the toughness of polyethylene, but make a negative effect on the rigidity of the polymer. Furthermore, it would be easier for semicrystalline polymers with less entangled chains to bring out the interlamellar slippage that would absorb more energy during the deformation. Finally, promotion of the physical properties of UHMWPE was also achieved with the assistant of nano-modification and an excellent relativity between the physical properties and the amorphous thickness (la) was obtained.     

UV‐cured natural polymer‐based membrane for biosensor application

Chitosan, a natural product, is inherently biodegradable, biocompatible, and nontoxic. These properties make chitosan ideal for inclusion in matrices designed for use in enzyme immobilization for clinical analysis. This study demonstrates the feasibility of using chitosan in electrochemical biosensor fabrication. The enzyme sulfite oxidase (SOX) was covalently immobilized onto the matrix of chitosan–poly(hydroxyethyl methacrylate) (chitosan–pHEMA), a natural/synthetic polymer hybrid obtainable via UV curing. p‐Benzoquinone, which served as an electron transfer mediator, was coupled onto the polymer network for activation of the chitosan–pHEMA copolymer, after completion of the photo‐induced polymerization reaction. The biological activity of the immobilized SOX and the electroactivity of the coupled p‐benzoquinone were investigated. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 466–472, 2001     

Chitin derivatives. II. Time–temperature–transformation cure diagrams of the chitosan amidization process

The transformation of the salts of chitosan with acetic and propionic acid, chitosonium acetate and chitosonium propionate, into chitin or the respective homolog of amidized chitosan has been described on the basis of time–temperature–transformation (TTT) cure diagrams. The time to vitrification at various isothermal cure temperatures (T_c) was determined using dynamic mechanical thermal analysis. The time to full cure was derived using a T_g–T_c cure time relationship according to the method of Peng and Gillham, as well as by an extrapolation procedure. Consequently, TTT cure diagrams describing the temperature-driven regeneration process include full cure and vitrification curves. As in thermosets, this transformation displays an S-shaped vitrification curve, and the time to full cure increases with decreasing cure temperature. The time to full cure is very remote from the time to vitrification, and this is attributed to the tendency of vitrification to prevent full cure from being attained. The activation energies for vitrification of chitosonium acetate and chitosonium propionate derived from an Arrhenius equation are similar. This suggests that the same mechanism governs glass formation in the N-acetyl and N-propionyl-glucosamine derivatives. Additionally, the morphology of amidized chitosan and native chitin was examined using X-ray diffraction and FTIR analysis. X-ray diffraction results indicate that amidized chitosan is an amorphous material, whereas native chitin is crystalline. FTIR suggests the existence of hydrogen-bonded amide groups in native chitin but not in amidized chitosan. This difference in morphology between amidized chitosan and native chitin is accounted for in terms of the influence of glass formation in the former. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1879–1889, 1999     

Properties of chitosan‐based biopolymer films with various degrees of deacetylation and molecular weights

An increase in the depolymerization of chitosan was found with an increased concentration of sodium perborate. Acetic anhydride was added to reacetylated chitosan in a molar ratio per gulcosamine unit, and the amide I band of IR spectra changed with the addition of acetic anhydride. Sixteen chitosans with various molecular weights (MWs) and degrees of deacetylation (DODs) were prepared. X‐ray diffraction patterns indicated their amorphous and partially crystalline states. Increases in the chitosan MW and DOD increased the tensile strength (TS). TS of the chitosan films ranged from 22 to 61 MPa. However, the elongation (E) of chitosan films did not show any difference with MW. TS of chitosan films decreased with the reacetylation process. However, E of chitosan films was not dependent on DOD. The water vapor permeabilities (WVPs) of the chitosan films without a plasticizer were between 0.155 and 0.214 ng m/m² s Pa. As the chitosan MW increased, the chitosan film WVP increased, but the values were not significantly different. Moreover, the WVP values were not different from low DOD to high DOD. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3476–3484, 2003     

Reinforced mechanical properties of plasma-sprayed Fe-based amorphous composite coatings by in-situ TiNx/TiOy

Ceramic particle-reinforced Fe-based amorphous coatings have received extensive attention due to their excellent strength and wear resistance. In this paper, TiN_x/TiO_y -enhanced Fe-based amorphous coatings were prepared by reactive plasma spraying technology, and the effect of eggshell-like TiN_x/TiO_y on the comprehensive mechanical properties of Fe-based amorphous coatings was systematically studied. The results showed that the hardness of the composite coating was significantly higher than that of the amorphous single-phase coating. Moreover, indentation experiments showed that TiN_x/TiO_y effectively confined crack growth in the amorphous phase. Though the bonding strength of the composite coating was lower than that of the pure amorphous coating, but still maintained a high bonding force of 20.68 MPa. Through the wear experiment, it was found that the wear scar of the composite coatings appeared plastic deformation, the friction coefficient and wear mass loss were both greatly reduced, and the optimal wear performance appeared in the composite coating with 15% Ti addition. In addition, SEM, EDS analysis, and the first-principles simulation results demonstrated the good bonding between Ti-containing compounds and Fe-based alloys.     

Preparation and characterization of porous scaffold composite films by blending chitosan and gelatin solutions for skin tissue engineering

Biodegradable polymers have significant potential in biotechnology and bioengineering. However, for some applications, they are limited by their inferior mechanical properties and unsatisfactory compatibility with cells and tissues. In the present investigation blends of chitosan and gelatin with various compositions were produced as candidate materials for biomedical applications. Fourier transform infrared spectral analysis showed good compatibility between these two biodegradable polymers. The composite films showed improved tensile properties, highly porous structure, antimicrobial activities, low water dissolution, low water uptake and high buffer uptake compared to pure chitosan or gelatin films. These enhanced properties could be explained by the introduction of free ? OH, ? NH₂ and ? NHOCOCH₃ groups of the amorphous chitosan in the blends and a network structure through electrostatic interactions between the ammonium ions (? NH³⁺) of the chitosan and the carboxylate ions (? COO^?) of the gelatin. Scanning electron microscopy images of the blend composite films showed homogeneous and smooth surfaces which indicate good miscibility between gelatin and chitosan. The leafy morphologies of the scaffolds indicate a large and homogeneous porous structure, which would cause increased ion diffusion into the gel that could lead to an increase in stability in aqueous solution, buffer and temperature compared to the gelatin/chitosan system. In vivo testing was done in a Wistar rat (Rattus norvegicus) model and the healing efficiencies of the scaffolds containing various compositions of chitosan were measured. The healing efficiencies in Wistar rat of composites with gelatin to chitosan ratios of 10:3 and 10:4 were compared with that of a commercially available scaffold (Eco‐plast). It was observed that, after 5 days of application, the scaffold with a gelatin to chitosan ratio of 10:3 showed 100% healing in the Wistar rat; however, the commercial Eco‐plast showed only a little above 40% healing of the dissected rat wound. Copyright © 2012 Society of Chemical Industry     

Electrodeposition of amorphous gold alloy films

The process for electroplating amorphous gold-nickel-tungsten alloy that we developed previously based on the addition of a gold salt to a known amorphous Ni-W electroplating solution was investigated further using the X-ray diffraction (XRD) method for the purpose of quickly surveying the effects of various experimental variables on the microstructure of the alloy. In this system the gold concentration in the plating bath was found to be critical; i.e., when it is either very low or very high, the deposit becomes crystalline to XRD. The deposit composition varies linearly with the mole ratio of Au to Ni in solution, and the alloy deposit is amorphous to XRD when the atomic ratio of Au/Ni in the deposit is between 0.5 and 1.5. At suitable concentrations of the metal ions, the deposit contains essentially no tungsten. By extending the work on the Au-Ni-W system, an amorphous Au-Co alloy plating process was also developed.     

Application of chitosan solutions gelled by melB tyrosinase to water‐resistant adhesives

An investigation was undertaken on the application of dilute chitosan solutions gelled by melB tyrosinase‐catalyzed reaction with 3,4‐dihydroxyphenethylamine (dopamine). The tyrosinase‐catalyzed reaction with dopamine conferred water‐resistant adhesive properties to the semi‐dilute chitosan solutions. The viscosity of the chitosan solutions highly increased by the tyrosinase‐catalyzed quinone conversion and the subsequent nonenzymatic reactions of o‐quinones with amino groups of the chitosan chains. The viscosity of chitosan solutions highly increased in shorter reaction times by addition of melB tyrosinase. Therefore, in this study, the gelation of a chitosan solution was carried out without poly(ethylene glycol) (PEG), which was added for the gelation of chitosan solutions using mushroom tyrosinase. The highly viscous, gel‐like modified chitosan materials were allowed to spread onto the surfaces of the glass slides, which were tightly lapped together and were held under water. Tensile shear adhesive strength of over 400 kPa was observed for the modified chitosan samples. An increase in either amino group concentration of the chitosan solutions or molecular mass of the chitosan samples used effectively led to an increase in adhesive strength of the glass slides. Adhesive strength obtained by chitosan materials gelled enzymatically was higher than that obtained by a chitosan gel prepared with glutaraldehyde as a chemical crosslinking agent. In addition, the use of melB tyrosinase led to a sharp increase in adhesive strength in shorter reaction times without other additives such as PEG. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Development, characterization and stabilization of amorphous form of a low Tg drug

The objective of the present study was to develop a stable amorphous form of model drug carvedilol (CAR). The amorphous material produced by melt quench technique was subjected to physico-chemical characterization. Chemical stability of the drug during preparation of glass was tested by HPLC and IR spectroscopy and presence of amorphous form was confirmed by DSC and XRPD. The rate of dissolution and magnitude of the apparent solubility were found to be significantly higher for amorphous CAR than for crystalline CAR, at 25 °C. However at 37 °C, it was observed that dissolution of the amorphous form did not show a noticeable improvement over pure CAR over the period of 60 min, due to formation of cohesive supercooled liquid state. This observation was supported by enthalpy relaxation study, which indicated increase in enthalpy recovery and structural relaxation of amorphous form towards the supercooled liquid region. This indicated the functional inability of amorphous CAR from stability point of view and suggested the need for elevation of T_g. Hence combination of solid dispersion (SD) and surface adsorption techniques was attempted to overcome the functional limitations of amorphous CAR. SD in the ratio of 1:2:2 parts by weight of CAR, PVP (for elevation of T_g) and Aerosil^® 200 (as adsorbent) respectively presented dramatic improvement in rate and extent of drug dissolution. During accelerated stability studies with SD 1:2:2 the dissolution characteristics were slightly decreased over the period of 3 months and no crystallization events were observed. Thus, to exploit the functional advantage of amorphous form of low T_g drugs, formation of ternary SD system is recommended.     

Rubber toughening of an amorphous polyamide by functionalized SEBS copolymers: morphology and Izod impact behavior

Rubber toughening of an amorphous polyamide (Zytel 330) using combinations of triblock copolymers of the type SEBS and a maleic anhydride functionalized version, SEBS-g-MA, was investigated and the results compared with those of nylon 6 and nylon 66. The effects of rubber content and the type of extruder on the morphology, Izod impact behavior and the ductile-brittle transition temperature were explored. The shape and sizes of the rubber particles in blends with this amorphous polyamide were found to be more similar to those in nylon 6 than in nylon 66 blends. The twin screw extruder produced smaller particles with a more narrow distribution of sizes than the single screw extruder. Higher rubber contents generally yielded tougher blends; there is a critical rubber particle size above which the ternary blends are brittle at 20 wt% total rubber. The ductile-to-brittle temperature was found to decrease with increased rubber content and decreased rubber particle size. In general, the trends for this amorphous polyamide are rather similar to those reported earlier for semi-crystalline nylon 6 and nylon 66.     

Evaluation of wool nanoparticles incorporation in chitosan/gelatin composite films

The aim of this work was to develop chitosan/gelatin composite films embedded with various amounts of wool nanoparticles, which were produced by an environmental friendly process. Films loaded with wool nanoparticles were subjected to physiochemical, biological, and mechanical characterization. The obtained results showed that incorporation of wool nanoparticles into chitosan/gelatin composite led to a reduction in swelling, moisture content and dissolution degree of the films. In vitro degradation test revealed that the nanoparticles‐embedded composites had a lower degradation rate than that of chitosan/gelatin composite. Besides, composite films containing wool nanoparticles showed an improvement in the stability in phosphate buffered saline. On the other hand, tensile strength and elongation at break decreased upon loading the films with wool nanoparticles. The biocompatibility of the produced composites was also confirmed by MTT test. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40294.     

Electrodeposition of amorphous Au-Ni alloy film

It was found that, by choosing an optimum bath composition, amorphous Au-Ni alloy containing up to 40 at.% of Au with respect to the sum of Au and Ni can be electrodeposited from a bath prepared by excluding tungsten from the Au-Ni-W bath that we developed previously. Elemental analysis showed that the deposit contains 15-20 at.% of carbon and 2 at.% of nitrogen. Hardness of this deposit is almost three times as high as that of the conventional hard gold. The electrical contact resistance measured against a pure gold wire is comparable to that of the hard gold. The amorphous structure of the Au-Ni deposit is stable at temperatures up to 300 °C for at least 1 h. The amorphous tungsten-free Au-Ni deposit is worthy of consideration for applications in the fabrication of micro- and nano-scale electrical contacts.     

Determination of the reactive component of fly ashes for geopolymer production using XRF and XRD

Geopolymers are a class of versatile materials that have the potential for utilisation as a cement replacement, fireproof barriers, materials for high temperatures, and biological implant applications. This study investigated methods for determining the formulation for manufacturing geopolymers made with fly ash from coal-fired power stations. The accepted method of determining the formulation of geopolymers to get the desired matrix chemistry uses the bulk composition of the feedstock materials. This formulation method is widely used in investigations using feedstock materials that almost completely react during processing. It is widely considered that amorphous components of fly ash are the reactive components in the geopolymerisation reaction. However, quantification of the amorphous components is challenging and generally avoided with the concomitant problem that the formulation is far from optimum. For the work presented here, the composition of the amorphous part is determined accurately and this information utilised to synthesise geopolymers. The bulk composition is first determined using X-ray fluorescence spectroscopy (XRF) and then the amorphous composition determined using XRF and quantitative X-ray diffraction (QXRD). Formulating the mixture based on amorphous composition produced samples with a significantly higher compressive strength than those formulated using the bulk composition. Using the amorphous composition of fly ash produced geopolymers with similar physical properties to that of metakaolin geopolymers with the same targeted composition. We demonstrated a new quantitative formulation method that is superior to the accepted method.     

The effect of amorphous chalcogenides on mechanical and anticorrosive properties of protective organic coatings containing high amounts of zinc metal particles

The objective of this paper concerns reduction of zinc metal content in organic coatings while preserving their high anticorrosive efficiency. The two goals can be achieved by using amorphous chalcogenides as components of the protective coating. Special attention was paid to materials containing Ge₂₀Se₈₀, Ge₃₀Se₇₀ and Ge₄₀Se₆₀, which were characterized by physico-chemical properties. An epoxy ester resin was used as binder for the investigated organic coatings. Organic coatings were prepared by combining zinc metal with amorphous chalcogenides. The resistance of the prepared films was evaluated using the results of mechanical tests. The anticorrosive efficiency of the prepared films was evaluated using the results of direct corrosion tests. Thus the following conclusion can be made from the results of anti-corrosive tests: the higher the pigment volume concentration of amorphous chalcogenides in the coatings, the higher the protective performance of the paint against corrosion.     

Chitosan as Scaffold Materials: Effects of Molecular Weight and Degree of Deacetylation

In this study, we investigated in vitro the role of the degree of deacetylation and molecular weight on some biological properties of chitosan films. The influence of different degree of deacetylation and molecular weight of chitosan on the hydrophilicity, degradation, mechanical properties and biocompatibility were evaluated. The results showed that the degree of deacetylation affected the hydrophilicity and biocompatibility of the chitosan films. The molecular weight, on the other hand, affected the rate of degradation and the mechanical properties. Chitosan with higher degree of deacetylation and molecular weight was more suitable for tissue engineering applications. Alginate could be added into chitosan to modify the rigidity and hydrophilicity of chitosan. Higher hydrophilicity, biocompatibility, and elongation were found after modification.