Dispersion polymerization of acrylonitrile using a poly(ethylene glycol)-b-polyacrylonitrile macro-RAFT agent

Polyacrylonitrile (PAN) nanoparticles were successfully prepared by dispersion polymerization of acrylonitrile (AN) in water using 10 and 20 wt% of the poly(ethylene oxide)-b-PAN macromolecular RAFT (PEO-b-PAN macro-RAFT) agent (M _n=5,600 g/mol, PDI=1.15). The degrees of polymerization of the PEO and PAN blocks were 113 and 16, respectively. The PAN nanoparticles had a crumpled spherical appearance and their sizes ranged from 50–80 nm. The degree of crystallinity of the PAN particles was 23 %. The M _n values of the PAN nanoparticles prepared with 10 and 20 wt% of the PEO-b-PAN macro-RAFT agent were 33,900 and 25,800 g/mol, respectively. The existence of the PEO block on the surface of the PAN nanoparticles was confirmed by ¹H NMR spectroscopy and XPS.     

Structure and performance of fibers prepared from liquefied wood in phenol

The fibers from liquefied wood in phenol (WPFs) were spun by adding hexamethylenetetramine as synthetics and cured by soaking in solution containing hydrochloric acid and formaldehyde as main components. The chemical structure of WPFs remarkably changed from that of liquefied wood was identified by FT-IR spectrometer. WPFs with the average diameter of 27∼42 μm, tensile strength of 230∼356 MPa, and modulus of 15∼31 GPa were obtained using spinning speed of 0.72 μm min⁻¹, hydrochloric acid concentration of 18.5 %, heating rate of 10 °C h⁻¹, and curing time of 4 h. These WPFs showed a high thermal stability and a complex thermal decomposition process by TG(thermogravimetric) analysis. It was also found that the two obvious weight loss temperatures of WPFs were 510°C and 748°C.     

Facile fabrication of carbon nanotubes/polystyrene composite nanofibers for high-performance electromagnetic interference shielding

Polystyrene (PS) composites with nanofibrous structure consisting of multi-walled carbon nanotubes (MWCNTs) with 0-10 wt.% of nanofiller have been fabricated via electrospinning technique. The surface morphology and thermal properties of the composites were evaluated by scanning electron microscopy (SEM) and thermo-gravimetric analysis (TGA). The SEM analysis of the composite nanofibers samples revealed that the average diameter of the nanofibers increases with increasing MWCNTs content. The resultant MWCNTs/PS composite nanofibers diameters were in the range of 391±63 to 586±132 nm. The thermal stability of composites was increased after addition of MWCNTs to PS matrix. The electrical conductivity of the composites with different weight percentage of MWCNTs was investigated at room temperature. Electrical conductivity of MWCNTs/PS composite nanofiber followed percolation theory having a percolation threshold V _c= 0.45 vol% (~0.75 wt. %) and critical exponent q=1.21. The electrical conductivity and thermal properties confirmed the presence of good dispersion and alignment MWCNTs encapsulated within the electrospun nanofibers. The electromagnetic interference (EMI) shielding effectiveness of the MWCNTs/PS composites was examined in the measurement frequency range of 8.2-12.4 GHz (X-band). The total EMI shielding efficiency of MWCNTs/PS composite nanofibers increased up to 32 dB. The EMI shielding results for MWCNTs/PS composite nanofibers showed that absorption loss was the major shielding mechanism and reflection was the secondary mechanism. The present study has shown the possibility of utilizing MWCNTs/PS composite nanofibers as EMI shielding/absorption materials.     

Conductive polymer-coated threads as electrical interconnects in e-textiles

An organic polymer electrical interconnect is demonstrated. The ionomer mixture poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS; 1:2.5, w:w) was cast onto silk fibers from a 50:50 (v:v) ethylene glycol solution by a dip-coating process. Dynamic mechanical analysis (DMA) results show that Young’s modulus and mechanical strength are maintained during the coating process from acidic solution (pH ∼1). DMA dynamic temperature scans reveal two new thermal transitions once PEDOT:PSS is applied to the silk fiber, and they are assigned to the glass transition temperature (59 °C) and melting point (146 °C) of the ionomer pair. Electrical conductivities of 8.5 S/cm were achieved with four cycles of the dip-coating process, only 10x less than Ag-coated thread control samples. SEM imaging of the PEDOT:PSS-coated fibers show slight texturing to the fibers due to the coating, as well as significant charging in the uncoated samples when compared to PEDOT:PSS-coated samples. The conductive fibers fabricated by this process were successfully applied as electrical interconnects in flexible, fully functional 555 timer circuits stitched into fabric substrates.     

Thermal Characterization of Alkali Treated Kenaf Fibers and Kenaf-Epoxy Composites

Chemical treatment of natural fibers is a well-defined means of mechanical property improvement in natural fiberreinforced composites. An understanding of mechanical and thermal properties in these media is essential for evaluating heat transfer, thermal degradation, and overall performance of these composites over their product lifetime. However, very little information is available illustrating the effect of such treatment on the thermal properties of kenaf composites. Also, no study to date has reported the thermal conductivity of individual kenaf fibers. This study reports the effects of fiber treatment (in 6 % NaOH) on thermal transport in unidirectionally oriented kenaf-epoxy composites and individual kenaf fibers. The effective thermal conductivities and thermal diffusivities of chemically treated fiber composites show a general increase over untreated fiber composites (0.210 to 0.232 W/m/K at 28 °C, 0.206 to 0.234 W/m/K at 200 °C). This improvement may be attributed to improved interfacial contact between the fibers and epoxy matrix shown in microstructural images after chemical treatment. The thermal conductivity of individual fibers was evaluated at room temperature using two techniques. Results from both techniques showed slight increases after chemical treatment (0.58±0.53 to 1.0±0.13 W/m/K and 1.2±0.54 to 1.6±0.28 W/m/K) but lacked statistical significance. Any improvement in surface crystallinity after chemical treatment does not appear to affect overall fiber thermal conductivity. A better understanding of thermal transport in kenaf fibers and composites enables better estimation of the performance of these composites in different applications. Moreover, the thermal conductivities of individual fibers are useful in understanding the fiber’s contribution to conduction in different fiber reinforcement configurations.     

Synthesis and characterization of boron doped alumina stabilized zirconia fibers

Boron doped PVA/Zr-Al acetate nanofibers were prepared by electrospinning using PVA as a precursor. The effect of calcination temperature on morphology and crystal structure was investigated at 250, 500, and 800 °C. The study also establishes the effect of boron doping on the morphology of PVA/Zr-Al acetate nanofibers at various calcination temperatures. The measurements showed that the conductivity, pH, viscosity and the surface tension of the hybrid polymer solutions have increased with boron doping. In addition, the fibers were characterized by FTIR, DSC, XPS, XRD and SEM techniques. The addition of boron did not only increase the thermal stability of the fibers, but also increased the average fiber diameters, which gave stronger fibers. The DSC results indicated that the melting temperature (Tm) of the fibers was increased from 256 to 270 °C with the addition of boron. XRD peak patterns showed that after further heat treatment at 800 °C, zirconia exists in two phases of tetragonal and monoclinic modifications. Moreover, alumina does not transform into the γ-Al₂O₃ and θ-Al₂O₃ phase at 800 °C. The SEM appearance of the fibers showed that the addition of boron resulted in the formation of crosslinked bright surfaced fibers.     

The role of Na-montmorillonite on thermal characteristics and morphology of electrospun PAN nanofibers

Polymer organic-inorganic hybrid nanofibers constitute a new class of materials in which the polymeric nanofibers are reinforced by uniformly dispersed inorganic particles having at least one dimension in nanometer-scale. In the present study, polyacrylonitrile (PAN) and PAN/Na-montmorillonite (PAN/Na-MMT) nanofibers were conducted via electrospinning process. Electrospun PAN and PAN/Na-MMT fibers with the respective mean fiber diameter of about 220 and 160 nm were prepared. The influence of the clay-montmorillonite on the morphology and diameter of nanofibers was investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The microscopic techniques propose that the PAN/Na-MMT composite nanofibers show lower mean fiber diameter than the neat PAN nanofibers. Besides, the difference in nanoclay-content has a slight effect on the distribution of fibers diameter. Thermogravimetric analysis (TGA) results suggest that introduction of clay-nanomaterials improves the thermal characteristics of fibers.     

Synthesis,analysis and simulation of carbonized electrospun nanofibers infused carbon prepreg composites for improved mechanical and thermal properties

This paper reports the fabrication, characterization and simulation of electrospun polyacrylonitrile (PAN) nanofibers into pre-impregnated (prepreg) carbon fiber composites for different industrial applications. The electrospun PAN nanofibers were stabilized in air at 270 °C for one hour and then carbonized at 950 °C in an inert atmosphere (argon) for another hour before placing on the prepreg composites as top layers. The prepreg carbon fibers and carbonized PAN nanofibers were cured together following the prepreg composite curing cycles. Energy dispersive X-ray spectroscopy (EDX) was carried out to investigate the chemical compositions and elemental distribution of the carbonized PAN nanofibers. The EDX results revealed that the carbon weight % of approximately 66 (atomic % 72) was achieved in the PAN-derived carbon nanofibers along with nitrogen and lower amounts of nickel, oxygen and other impurities. Thermomechanical analysis (TMA) exhibited the glass transition regions in the prepreg nanocomposites and the significant dependence of coefficient of thermal expansion on the fiber directions. The highest value of coefficient of thermal expansion was observed in the temperature range of 118-139 °C (7.5×10^-8 1/°C) for 0 degree nanocomposite scheme. The highest value of coefficient of thermal expansion was observed in the temperature range of 50-80 °C (37.5×10^-6 1/°C) for 90 degree nanocomposite scheme. The test results were simulated using ANSYS software. The test results may be useful for the development of structural health monitoring of various composite materials for aircraft and wind turbine applications.     

Sugars Profiles of Different Chestnut (Castanea sativa Mill.) and Almond (Prunus dulcis) Cultivars by HPLC-RI

Sugar profiles of different almond and chestnut cultivars were obtained by high-performance liquid chromatography (HPLC), by means of a refractive index (RI) detector. A solid-liquid extraction procedure was used in defatted and dried samples. The chromatographic separation was achieved using a Eurospher 100-5 NH₂ column using an isocratic elution with acetonitrile/water (70:30, v/v) at a flow rate of 1.0 ml/min. All the compounds were separated in 16 min. The method was optimized and proved to be reproducible and accurate. Generally, more than 95% of sugars were identified for both matrixes. Sugars profiles were quite homogeneous for almond cultivars; sucrose was the main sugar (11.46 ± 0.14 in Marcona to 22.23 ± 0.59 in Ferragnes g/100 g of dried weight), followed by raffinose (0.71 ± 0.05 in Ferraduel to 2.11 ± 0.29 in Duro Italiano), glucose (0.42 ± 0.12 in Pegarinhos two seeded to 1.47 ± 0.19 in Ferragnes) and fructose (0.11 ± 0.02 in Pegarinhos two seeded to 0.59 ± 0.05 in Gloriette). Commercial cultivars proved to have higher sucrose contents, except in the case of Marcona. Nevertheless, chestnut cultivars revealed a high heterogeneity. Sucrose was the main sugar in Aveleira (22.05 ± 1.48), Judia (23.30 ± 0.83) and Longal (9.56 ± 0.91), while glucose was slightly prevalent in Boa Ventura (6.63 ± 0.49). The observed variance could serve for inter-cultivar discrimination.     

The demonstration of a dense and stable circumferential layer in the subsurface of polyacrylonitrile fibers for carbon fibers

The radial structure of polyacrylonitrile (PAN) copolymer fibers was investigated quantitatively by etching layer by layer in an improved permanganic etchant; meanwhile the effect of the etchant on the fiber surface was taken into consideration. The aggregated structure (crystal size, crystallinity, orientation and density) and thermal stability of each circumferential layer of PAN fibers were determined in detail according to a model proposed in the study. A denser layer with a thickness of about 1 µm was observed in the subsurface (2 µm from the PAN fiber surface), possessing a greater crystal size and crystallinity as well as a relatively higher thermal stability than other layers. This layer was considered to be a barrier for the diffusion of oxygen into PAN fibers during the stabilization and accelerated the formation of a core-shell structure in the resulting carbon fibers.     

Rheological and thermal properties of acrylonitrile-acrylamide copolymers: Influence of polymerization temperature

An attempt was made to correlate the polymerization temperature and rheological and thermal properties of acrylonitrile (AN)-acrylamide (AM) copolymers. The copolymers were synthesized at different polymerization temperature. The copolymer structure was characterized by gel permeation chromatography (GPC) and Infrared spectrum (IR). The rheological and thermal properties were investigated by a viscometer and differential scanning calorimeter-thermogrametric (DSCTG) analysis, respectively. When the polymerization temperature increased from 41 °C to 65 °C, the molecular weight ([`(M)] <sub>w</sub> )(\overline M _w ) of copolymers decreased from 1,090,000 to 250,000, while its conversion increased from 18% to 63%, and the polymer composition changed slightly. To meet the requirements of carbon fibers, the rheological and thermal properties of products were also investigated. It was found that the relationship between viscosity and [`(M)] _w\overline M _w was nonlinear and the viscosity index (n) decreased from 3.13 to 2.69, when the solution temperature increased from 30 °C to 65 °C. This suggests the dependence of viscosity upon [`(M)] _w\overline M _w is higher at lower solution temperature. According to the result of activation energy, the sensivity of viscosity to solution temperature is higher for AN-AM copolymers synthesized at higher polymerization temperature. The result of thermal analysis shows that the copolymers obtained at higher polymerization temperature are easier to cyclization evidenced from lower initiation temperature. The weight loss behavior changed irregularly with polymerization temperature due to irregular change of liberation heat.     

Influences of organic-modified Fe-montmorillonite on structure, morphology and properties of polyacrylonitrile nanocomposite fibers

The Fe-montmorillonite (Fe-MMT) combined catalysis effects of Fe ion with barrier effects of silicate clays, was firstly synthesized by hydrothermal method, and then was modified by cetyltrimethyl ammonium bromide (CTAB). The organic-modified Fe-montmorillonite (Fe-OMT) was dispersed in the N, N-dimethyl formamide (DMF) and then compounded with polyacrylonitrile (PAN) solution which was dissolved in DMF. The composite solutions were electrospun to form PAN/Fe-OMT nanocomposite fibers. The influences of the Fe-OMT on the structure, morphology, thermal, flammability and mechanical properties of PAN nanocomposite fibers were respectively characterized by X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM), Thermogravimetric analyses (TGA), Micro Combustion Calorimeter (MCC) and Electronic Single Yarn Strength Tester. It was found from XRD curves that there was not observable diffraction peak of silicate clay, indicating that the silicate clay layers were well dispersed within the PAN nanofibers. The HRTEM image indicated that the multilayer stacks of nanoclays could be found within the nanofibers and were aligned almost along the axis of the nanofibers. The SEM images showed that the diameters of nanocomposite fibers were decreased with the loading of the Fe-OMT. The TGA analyses revealed that the onset temperature of thermal degradation and charred residue at 700°C of PAN nanocomposite fibers were notably increased compared with the pure PAN nanofibers, contributing to the improved thermal stability properties. It was also observed from MCC analyses that the decreased peak of heat release rate (PHRR) of the PAN nanocomposite fibers reduced the flammability properties. The loadings of Fe-OMT increased the tensile strength of PAN nanocomposite fibers, but the elongation at break of PAN nanocomposite fibers was lower than that of the PAN nanofibers.     

Volatile Compounds and Antioxidative Activity of <Emphasis Type="Italic">Porophyllum tagetoides</Emphasis> Extracts

Porophyllum tagetoides is an annual warm-weather herb that has an intense typical smell. Its leaves are commonly used in soup preparation and traditional medicine for treatment of inflammatory diseases. Its volatile compounds and antioxidant properties were evaluated in crude, aqueous and ethanol leaf extract and an oil emulsion using different antioxidant assays in vitro, such as: DPPH radical scavenging activity, redox potential, polyphenol content, reducing power and optical density. A high antioxidative activity was found when comparing leaves with stems. The crude extract from leaves showed a very high reducing power (2.88 ± 0.20 O.D.) and DPPH radical-scavenging activity (54.63 ± 4.80%), in concordance with a major concentration of vitamin C (23.97 ± 0.36 mg/100 g). Instead, the highest polyphenol content (264.54 ± 2.17 mg GAE/g of sample) and redox potential (561.23 ± 0.15 mV) were found by the ethanol and aqueous extract, respectively. Aldehydes and terpenes such as nonanal, decanal, trans-pineno, β-myrcene and D-limonene were the major volatiles found. This study suggests that Porophyllum tagetoides extracts could be used as antioxidants.     

The effects of blend composition and blending time on the ester interchange reaction and tensile properties of PLA/LPCL/HPCL blends

PLA/LPCL/HPCL blends composed of poly(lactic acid) (PLA), low molecular weight poly(ε-caprolactone) (LPCL), and high molecular weight poly(ε-caprolactone) (HPCL) were prepared by melt blending for bioabsorbable filament sutures. The effects of blend composition and blending time on the ester interchange reaction by alcoholysis in the PLA/LPCL/HPCL blends were studied. Their thermal properties and the miscibility due to the ester interchange reaction were investigated by¹H-NMR, DSC, X-ray, and UTM analyses. The hydroxyl group contents of LPCL in the blends decreased by the ester interchange reaction due to alcoholysis. Thus, the copolymer was formed by the ester interchange reaction at 220 °C for 30–60 minutes. The thermal properties of PLA/LPCL/HPCL blends such as melting temperature and heat of fusion decreased with increasing ester interchange reaction levels. However, the miscibility among the three polymers was improved greatly by ester interchange reaction. Tensile strength and modulus of PLA/LPCL/HPCL blend fibers increased with increasing HPCL content, while the elongation at break of the blend fibers increased with increasing LPCL content.     

Depositon of ZnO on polyacrylonitrile fiber by thermal solvent coating

In this study, the surface functionalization of polyacrylonitrile (PAN) fibers was achieved by depositing ZnO nanoparticles using thermal solvent coating. surface morphology, crystalline structure, surface chemistry, thermal stability and washing stability of the ZnO coated PAN fibers were investigated by scanning electron microscope (SEM), X-ray diffractometer (XRD), Fourier transform Infra red spectroscopy (FT-IR), Thermo-gravimetric analyses (TGA) and washing stability test, respectively. In addition, the weight changes after coating and washing were studied at different coating and washing conditions. The SEM images revealed that the ZnO was well coated on the surface of the PAN fibers and the coating was obviously affected by the experimental temperature. The FT-IR spectra indicated the chemical features of the deposited ZnO nanostructures. The XRD patterns showed that there was a typical crystalline structure of ZnO nanogains formed on the PAN fibers after coating. The TGA results revealed that the thermal stability of the PAN fibers was improved by the ZnO coating. The experimental results of washing stability revealed the effect of temperature on the washing stability. Weight measurements indicated that the amount of ZnO deposited on PAN fibers increased with the increasing of coating temperature from 60 to 70 °C. Weight measurements also revealed that the weight of the ZnO coating on fibers decreased with the increase in washing temperature and washing time.     

Synthesis and properties of acrylonitrile-methyl itaconate copolymers as spun carbon fiber precursors

Acrylonitrile-methyl itaconate (AN-MIA) copolymers were successfully prepared by free-radical solution copolymerization, and then were spun into precursors of carbon fibers by one-step wet-spun method in this study. Effect of methyl itaconate(MIA), itaconic acid (IA) and methyl acrylate (MA) on the characteristics of the copolymers and precursors were studied in contrast. The monomer reactivity ratios for AN/MIA system were determined by Kelen-Tudos (K-T) method with r ₁=0.65, r ₂=1.80. The viscosity test shows that using MIA as a co-monomer is an effective way to decrease the viscosity of PAN solution. During the spinning and stretching processes, polyacrylonitrile (PAN) copolymer with MIA as co-monomer can reach the higher total draw-ratio of 12.0 folds, while PAN copolymer with IA as co-monomer can reach only 8.5 folds. The fineness and elongation at-break of the PAN precursors with MIA as co-monomer improve, but the tenacity decreases. DSC test shows MIA is less effective in improving the thermal property than IA.     

The modification of Kevlar fibers in coupling agents by <Emphasis Type="Italic">γ</Emphasis>-ray co-irradiation

Kevlar fibers were treated in three kinds of coupling agents’ solutions by Co⁶⁰ γ-ray co-irradiation. After the treatment, the interlaminar shear strength (ILSS) values of Kevlar fibers/epoxy composites were all improved. Surface elements of the fibers were determined by energy dispersive X-ray microanalysis (EDX). X-ray photoelectron spectroscopy (XPS) indicated that the oxygen/carbon ratio of the treated fibers was increased and Fourier transform infrared (FT-IR) spectrum confirmed the increase in the polar groups at the fiber surface. The tensile strength of the fibers was evaluated by statistical analysis using the Weibull distribution. The wettability of the fiber surface was also enhanced by the treatment. The possible mechanisms of γ-ray co-irradiation treatment are proposed by the radical reactions. The results indicated that γ-ray co-irradiation technique modified the physicochemical properties of Kevlar fibers and improved the interfacial adhesion of its composites.     

The effect of growth regulators on meristem tip development and in vitro multiplication ofSolanum tuberosum L. plants

Summary We studied the effect of β-indoleacetic acid (IAA), α-naphthylacetic acid (NAA), kinetin (K), 6-benzylaminopurine (BAP) and gibberellic acid (GA₃) on development of isolated meristems of four potato cultivars (subsp. tuberosum). GA₃ had a stimulating effect on in vitro meristem growth. The differences among the cultivars are presented. K+IAA+GA₃ induced formation of multiple shoots. We describe a method of continual plant multiplication under in vitro conditions and propose the produce for maintenance, multiplication and virus eradication of potato germplasm and cultivars.

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Zusammenfassung Von vier Kartoffelsorten (Blanik, Cira, Nora und Radka) wurden die Meristemspitzen entnommen. Der N?hrboden enthielt Makround Mikroelemente gem?ss Murashige & Skoog (1962), Vitamine entsprechend B-5 (Gamborg et al., 1968), 100mg/l Inositol, 30 g/l Saccharose und 8 g/l Agar. Wir untersuchten die Wirkung von β-Indolessigs?ure (IAA), α-Naphytlessigs?ure (NAA), Kinetin (K), 6-Benzylaminopurin (BAP) und Gibberellins?ure (GA₃). Auf den N?hrb?den mit IAA und NAA wurde mangelhaftes Triebwachstum und unvollst?ndige Blattentwicklung (Abb. 1) festgestellt; die Pflanzen konnten nicht in Erde versetzt werden. K (0.1 μM) induzierte vollst?ndige Pflanzenentwicklung (Tabelle 1), w?hrend BAP (0,1μM) die Triebenentwicklung anregte, worauf die Bewurzelung auf N?hrboden mit 0,1 μM IAA (Abb. 2) erfolgte. Alle GA₃-Konzentrationen hatten einen vorteilhaften Einfluss auf die Entwicklung von Pfl?nzchen aus Meristemspitzen (Abb. 1 und Tabelle 1). Optimales Wachstum und rasche Entwicklung der Pflanzen aller vier Sorten wurde mit dem N?hrboden mit IAA+K+GA₃ erreicht. Mehrfache Triebbildung erfolgte auf den Medien mit erh?hten GA₃-Konzentrationen (5 und 10 μM), speziell bei den Sorten Cira und Blanik (Abb. 3). Die Pflanzen aus der Meristemspitzenkultur konnten unter sterilen Bedingungen in Perlit, das mit der Hoagland's-L?sung und mit einem Zusatz von 0,1 μM IAA ges?ttigt war, fortlaufend vermehrt werden. Die Pflanzen entwickeln sich aus Achselknospen. Ein Steckling aus einem Meristem ist f?hig, 5–8 Pflanzen in zwei Monaten hervorzubringen. Der Artikel beschreibt das System der mehrfachen Triebbildung und die laufende Fortpflanzung in vitro zur Erhaltung und Vermehrung von Kartoffel-Keimplasma (Westcott et al., 1977) und virusfreien Züchtungen (Abb. 4).

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Résumé Des méristèmes apicaux ont été prélevés sur quatre variétés de pommes de terre: Blanik, Cira, Nora et Radka. Le milieu de culture contenait des macro-et microéléments d'après les indications de Murashige & Skoog (1962), des vitamines B-5 (d'après Gamborg et al., 1968), 100 mg/l d'inositol, 30 g/l de sucrose et 8 g/l d'agar. Nous avons étudié l'action de l'acide β-indoleacetic (IAA), de l'acide α-naphtylacétique (NAA), de la kinétine (K), de la 6-benzylaminopurine (BAP) et de l'acide gibberellic (GA₃). Sur les milieux contenant de l'IAA et du NAA, nous avons observé un développement imparfait des pousses, et un développement partiel des feuilles (fig. l); les plantes ne pouvaient pas être transplantées en terre. K (0,1 μM) a induit un développement complet des plantes (tableau 1) tandis que le BAP (0,1 μM) a stimulé le développement des pousses suivi de leur enracinement dans le milieu contenant 0,1 μM d'IAA (fig. 2). Toutes les concentrations de GA₃ ont eu un effet bénéfique sur le développement des plantules issues de méristèmes apicaux (fig. 1 et tableau 1). La croissance optimale et le développement rapide des plantes des 4 variétés ont été observés sur le milieu contenant IAA+K+GA₃. Des pousses multiples se sont formées sur les milieux contenant des concentrations élevées en GA₃ (5 et 10 μM), notamment sur les variétés Cira et Blanik (fig. 3). Les plantes obtenues à partir de culture de méristèmes apicaux ont p? être continuellement propagées en conditions stériles dans de la perlite saturée d'une solution de Hoagland avec addition de 0,1 μM de IAA. Les plantes se développent à partir des bourgeons axillaires; une plantule d'origine méristématique est capable de donner naissance à 5 à 8 plantes en 2 mois. L'article décrit le système de formation des pousses multiples et la propagation continue in vitro pour la maintenance et la multiplication de variétés de pommes de terre indemnes de maladies (Westcott et al., 1977) et de virus (fig. 4).

     

Studies of electrospinning process of zirconia nanofibers

Eletriospinning process was used to fabricate Zirconia nanofibers and polyvinyl pyrrolidone (PVP) was employed in this procedure. SEM, TGA, FT-IR and XRD were used to investigate the electrospinning process. Pure PVP was electrospun at the same conditions as comparisons. The results indicated that the fibers had an average diameter about 80 nm with smooth surface. FT-IR spectrum and TGA curve proved that PVP was removed from the fibers after a thermal treatment. It was found that the crystal structure of Zirconia changed at different calcination temperature. The use of PVP, bicomponent solvent of water and ethanol and inorganic salt had positive effects on the morphology of the fibers.     

Antihyperglycemic,Antioxidant and Antiglycation Activities of Mulberry Leaf Extract in Streptozotocin-Induced Chronic Diabetic Rats

In Thailand, beverages containing mulberry leaf (Morus alba L.) are believed to promote good health, especially in people with diabetes. We examined the effects of long-term administration of an ethanolic extract of mulberry leaf (MA) on blood glucose, oxidative damage, and glycation in streptozotocin-induced diabetic rats. Daily administration of 1 g/kg MA for six weeks decreased blood glucose by 22%, which was comparable to the effect of 4 U/kg insulin. Lipid peroxidation, measured as malondialdehyde and lipid hydroperoxide concentrations (3.50 ± 0.33 and 3.76 ± 0.18 μM, respectively) decreased significantly (P < 0.05) compared to nontreated control diabetic rats (8.19 ± 0.45 and 7.50 ± 0.46 μM, respectively). Hemoglobin A_1C, a biomarker for chronic exposure to high concentration of glucose, was also significantly decreased in the MA-treated group (6.78 ± 0.30%) in comparison to untreated group (9.02 ± 0.30%). The IC₅₀ of in vitro antiglycation and free radical scavenging activities of MA were 16.4 ± 5.6 μg/ml and 61.7 ± 2.1 μg/ml, respectively. These findings support that long-term administration of MA has antihyperglycemic, antioxidant and antiglycation effects in chronic diabetic rats, which may be beneficial as food supplement for diabetics.