Preparation and characterisation of PE films of carbon nanotube/polyaniline (PAN) composite mixture

ABSTRACT

Polyaniline (PAN) composites filled with nanotube were prepared by twin-screw extruder in order to study the influence of PE reinforcing effect on the mechanical behaviour of the nanotube/polyaniline (PAN) composites. The mechanical property tests of the composites with and without PE were performed. The tensile and flexural strength of nanotube/polyaniline (PAN) composites with polyethylene (PE) was improved. In conclusion, the addition of PE favoured the improvement of the higher interface strength and so had good effect on improving the tensile and flexural properties of the composites. The dielectric strength was slightly increased with the PE content increasing and then decreased gradually. The hybrid film with 2 wt.% of PE shows the dielectric strength of 199 MV/m, which is about 6% higher than that of nanotube/polyaniline (PAN) film (188 MV/m).     

Manufacture and research of TPS/PE biocomposites properties

In this paper the process of native starch preparing for modification by extrusion and manufacture of biocomposites is presented. The first aim of this study was to determine the mixing and granulating condition of native starch to obtain granulated native starch. For mixing and granulation of native starch Intensive Mixer manufactured by Maschinenfabrik Gustav Eirich was used. Mixing and granulation in a single process is a new method of preparation of powders for other processing. The main task of granulation is the elimination of dust emissions and the increase in density of powders. Granules are easy for dosage and more handy for transport and storage than powders, which is important from a technological point of view.The second aim of this study was to manufacture TPS/PE biocomposites. At first thermal modification of waxy maize starch was carried out with the use of a co-rotating twin screw extruder. During extrusion native starches have been deprived of their crystallinity and the obtained starch (TPS) has fully amorphous structure. XRD analysis revealed that semi crystalline phase of native starch after extrusion disappeared. During extrusion crystal structure of native starch is transformed into amorphous structure of thermoplastic starch (TPS), which was confirmed by XRD analysis.Reactive extrusion of obtained thermoplastic starch and high density polyethylene (HDPE) in the presence of polyethylene-grafted maleic anhydride (PE-g-MA) was done. To modify properties of TPS/PE blend polycaprolactone (PCL) was added in amount of 5 and 10 wt.%. The mass flow rate, static mechanical properties, thermal properties and morphology of obtained biocomposites were examined. The results show that the increased amount of TPS caused an increase in tensile strength and modulus of elasticity of prepared biocomposites. Addition of PCL to TPS/PE blends decreased tensile strength and modulus of elasticity. Moreover, higher amount of TPS and PCL in TPS/PE blends caused decrease of the elongation at break. On the other hand, using of PE-g-MA in TPS/PE blends cause increasing phase compatibility, which was confirmed by mechanical properties and morphology measurements.Biocomposites filled with higher TPS content (45 and 60 wt.%) possess lower resistance to hydrolytic degradation, which cause decrease of mechanical properties.It was found that higher amount of TPS in TPS/PE blends have small effect on mass flow rate and thermal properties estimated by differential scanning calorimetry (i.e. melting temperature, degree of crystallinity, melting enthalpy). This phenomenon have significant influence on processing of obtained biocomposites.     

Biodegradable starch-based composites: effect of micro and nanoreinforcements on composite properties

Thermoplastic starch (TPS) matrix was reinforced with various kenaf bast cellulose nanofiber loadings (0–10 wt%). Thin films were prepared by casting and evaporating the mixture of aqueous suspension of nanofibers (NFs), starch, and glycerol which underwent gelatinization process at the same time. Moreover, raw fibers (RFs) reinforced TPS films were prepared with the same contents and conditions. The effects of filler type and loading on different characteristics of prepared materials were studied using transmission and scanning electron microscopies, X-ray diffractometry, Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and moisture absorption analysis. Obtained results showed a homogeneous dispersion of NFs within the TPS matrix and strong association between the filler and matrix. Moreover, addition of nanoreinforcements decreased the moisture sensitivity of the TPS film significantly. About 20 % decrease in moisture content at equilibrium was observed with addition of 10 wt% NFs while this value was only 5.7 % for the respective RFs reinforced film.     

Solute-homogenization model and its experimental verification in Mg-Gd-based alloys

Composition homogenization in solid solution is important for industrial alloys. In the present work, a solute homogenization model is proposed based on the chemical short-range-order tendency in Mg-Gd-based alloys. After a calculation using the cluster-plus-glue-atom model, the stable Mg-Gd structural unit is derived, [Gd-Mg₁₂]Mg₆, where one solute Gd is nearest-neighbored with twelve Mg atoms to form the characteristic hcp cluster [Gd-Mg₁₂] and this cluster is matched with six Mg glue atoms. Such a local unit is then mixed with [Mg-Mg₁₂]Mg₃, the stable unit for pure Mg. Assuming that the Gd-containing units are arranged in fcc- or bcc-like lattice points and the Mg units in their octahedral interstices, three proportions between the two units are obtained, 1:1, 2:3, and 1:3, which constitute three solute homogenization modes. The prevailing Mg-Gd-based alloys are consequently classified into three groups, respectively exemplified by GW103 K (Mg-10Gd-3Y-0.4Zr, wt%), GW83 K (Mg-8Gd-3Y-0.4Zr), and GW63 K (Mg-6Gd-3Y-0.4Zr). Mg-Gd-Y-Zr alloys were designed following the model (where Y and Zr were also added in substitution for Gd) and prepared by permanent-mould casting. According to their mechanical properties, the 1:3 alloy (Mg-5.9Gd-1.6Y-0.4Zr) shows the best comprehensive properties (ultimate tensile strength 305 MPa, yield strength 186 MPa, elongation 9.0%) in solution plus ageing state.     

Preparation and characterization of PEG–PPG–PEG copolymer/pregelatinized starch blends for use as resorbable bone hemostatic wax

In this study, polymer blends between PEG–PPG–PEG copolymer mixtures and pregelatinized starch at various compositions ranging from 0 to 3 % by weight were prepared and evaluated for potential use as novel resorbable bone hemostatic wax. It was found that the prepared samples had sufficient smearability for use as a bone wax. An addition of pregelatinized starch increased the hardness, smoothness and consistency of the texture while decreasing the adherence to glove. Thermal analysis indicated that the heat of fusion slightly decreased with increasing pregelatinized starch content. Compressive stiffness tended to decrease with increasing starch content for concentrations lower than 20 %, but re-increased at higher starch levels. In contrast, adherence deformation increased initially, but then decreased with increasing starch content. This behavior was related to the dependence of softening or reinforcing effect on the level of starch concentration in the samples. Adherence load and energy decreased with the addition of pregelatinized starch implying the decrease in adhesiveness of the samples. Furthermore, increasing the pregelatized starch amount also increased the liquid sealing duration of the samples at both 23 and 37 °C. Cytotoxicity tests against osteoblasts using a MTT assay revealed that the all the prepared samples and their raw materials did not show any cytotoxic potential. Formulations containing pregelatinized starch content between 20 and 30 % were found to show optimized performance.     

Nitrogen doping of ZnTe for the preparation of ZnTe/ZnO light-emitting diode

Nitrogen-doped p-type zinc telluride (p-ZnTe) films are prepared by sputtering in a mixture of nitrogen/argon plasma. The effect of doping level N (ratio of N₂ flow rate to that for the mixed gas) in the range 0–10 % on the films properties is investigated. Heterojunction diodes are prepared on stainless steel flexible substrate from the p-ZnTe (doping level, N = 5 %) and solution-grown n-ZnO films. The junction parameters and light-emission properties of diodes are investigated. Doping level beyond N = 1 %, changes the cubic crystal structure of ZnTe to hexagonal and reduces the size of crystallites. At the doping level N = 2–4 %, films with the highest hole density of 2.5 × 10¹⁸ cm^?3 and lowest band gap energy of 1.4 eV are obtained. The diodes junction built-in potential and the donor density in n-ZnO films are found to be in the range 0.4–0.7 V and 1.5 × 10¹⁷–1.4 × 10¹⁸ cm^?3, respectively. Diodes exhibit electroluminescence in the UV and visible regions due to the band edge and defect emissions in ZnO.     

Prediction of Powder Stickiness along Spray Drying Process in Relation to Agglomeration

The spray drying process consists of a fast convective drying of liquid droplets by hot air. Initially, the water activity (a_w) of a drop is close to 1. During drying, the drop surface a_w decreases while viscosity increases until reaching a sticky rubbery state before further drying. This can be observed for products such as carbohydrates, leading to particles sticking on walls (product losses) or to adhesion between particles leading to agglomeration. In this study, particle stickiness was investigated in a cocurrent pilot spray dryer by measuring drying air properties (temperature and relative humidity) at different positions. This allowed describing the evolution of temperature and mean water content of the drying drops. Two model products (maltodextrin DE12 and DE21) were spray dried varying process parameters liquid flow rate (1.8, 3.6, and 5.4 kg/h), air temperature (144°, 174°, and 200°C), airflow rate (80–110 kg/h), and rotary atomizer speed (22,500–30,000 rpm). The two products exhibit different drying behaviors in relation to their affinity towards water (sorption isotherms) and glass transition temperature evolution with a_w (stickiness). Depending on drying conditions and product, the drop stickiness was observed very rapidly, close to the atomizer, or later, along the chamber. This approach can be used to identify conditions and positions corresponding to sticky particles.     

Interfacial Thermal Resistance and the Solidification Behavior of the Al/SiCp Composites

The objective of this investigation is to study the effects of applied pressure on the solidification time and interfacial thermal resistance of A356/10% SiC_p during squeeze casting. Samples were prepared for various but constant squeeze pressures up to 130 MPa while maintaining the melt and mold temperatures at 800°C and 400°C, respectively. It was observed that the solidification time was 60 s when no squeeze pressure was applied but it decreased to 42 s when the squeeze pressure was maintained at 130 MPa. The results also showed that the cooling rate increased with squeeze pressure. The solidification time calculated from one-dimensional heat flow theory was found to be close to that obtained from the experimental cooling curves. The interfacial thermal resistance between the mold and the casting was calculated and it decreases when the squeeze pressure increases.     

Low-temperature preparation of transparent conductive Al-doped ZnO thin films by a novel sol–gel method

We developed a novel sol–gel method to prepare transparent conductive Al-doped ZnO (AZO) thin film at low temperature. The AZO nanocrystals were prepared by a solvothermal method and then they were dispersed in the monoethanolamine and methanol to form AZO colloids. A (002)-oriented ZnO thin film was used as a nucleation layer to induce the (002)-oriented growth of AZO thin films. The AZO thin films were prepared on Si(100) and fused quartz glass substrates with the (002)-oriented ZnO nucleation layer and annealed at 400 °C for 60 min. All AZO thin films showed (002) orientation. For electrical and optical measurements, the films deposited on glass substrates were post-annealed at 400 °C for 30 min in forming gas (100 % H₂) to improve their conductivity. These samples had high transparency in the visible wavelength range, and also showed good conductivity. A 0.2 mol L^?1 AZO solution with 3 at.% Al content was heated in a Teflon autoclave at 160 °C for 30 min to form AZO nanocrystals, and then the AZO nanocrystals were suspended in the MEA and methanol to obtain the stable AZO colloid. The Al content in the AZO nanocrystals was 2.7 at.%, and the high Al doping coefficient was mainly attributed to the formation of AZO nanocrystals in the autoclave. The AZO thin film using this colloid had the lowest resistivity of 3.89 × 10^?3 Ω cm due to its high carrier concentration of 3.29 × 10²⁰ cm^?3.     

Nanospheres Containing Urea: Photothermic Properties

In the present research, nanospheres of chitosan (CS), maltodextrin, and sodium tripolyphosphate (STPP), loaded with urea, were synthesized by using an ionic gelation technique. In the nanosphere synthesis was used a central composite experimental design, obtaining nanospheres with an average size of 275?±?32 nm and 27.5 mV zeta potential. The nanospheres were characterized by their hydrodynamic diameter, polydispersity index, nitrogen content, and thermal properties such as thermal diffusivity (α), effusivity (e), and conductivity (k); also melting temperature was obtained by differential scanning calorimetry. The thermal properties of nanospheres show that the sample with the smallest size has a thermal diffusivity value of (14.4?±?0.4)?×?10^?8 m²·s^?1 and a thermal conductivity value of (6.4?±?0.1)?×?10^?1 W·m^?1·K^?1, and the obtained melting temperature was 157 °C. Higher concentrations of CS increase the values of these thermal properties, probably because chitosan interacts ionically with STPP forming a reticular network due to the opposite charges of both molecules.     

Orientation-dependent microwave dielectric properties of Ba0.6Sr0.4TiO3 thin films prepared by sol–gel method

Barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thin films have been prepared on the (100) LaAlO₃ single-crystal substrates by sol–gel technique. The X-ray diffraction study indicated that the thin films exhibited (100) preferred orientation and random orientation depending upon the concentration of precursor solution. The nonlinear dielectric properties of the BST films were measured using an interdigital capacitor. The temperature dependence of dielectric constant of the BST thin films was measured at 1 MHz in the temperature range from ?100 to 80 °C. The Curie temperature T _c of the films derived from 0.1, 0.2 and 0.3 M was found to be ?18.5, ?32.5 and ?39.9 °C, respectively. The tunability of BST films with the (100) preferred orientation was 30.74 %, which was much higher than that of thin films with random orientation at the frequency of 10 kHz with an applied electric field of 80 kV/cm. The microwave dielectric properties of the BST thin films were measured by a vector network analyser from 1 to 10 GHz.     

Optimization of Tablet Formulations Based on Starch/Lactose Granulations for Use in Tropical Countries

Abstract

Several granulations consisting of α-lactose monohydrate 200 mesh and native starch (corn, potato, rice or tapioca) were prepared. The influence of starch concentration, storage temperature and relative humidity on the physical properties of the tablets prepared from these granulations was estimated. Two granulations, which resulted in tablets with adequate initial values of crushing strength and disintegration time and with an acceptable physical stability were selected as standard granulations. The selected standard granulations were evaluated by incorporating a drug (diazepam, 2 mg or mebendazole, 100 mg). The tablet properties were determined one day after preparation. The crushing strength, the disintegration time and the microbiological quality were also measured after storage under tropical conditions. Both selected formulations proved to be adequate for the preparation of tablets by wet granulation, suitable for use in tropical countries.     

Facile fabrication of activated carbonized horseweed-based biomaterials and their application in supercapacitors

Carbonized horseweed was prepared for the first time using KOH as activating agent and employed as an electrode material. Varying the KOH/C weight ratio had a dramatic effect on the electrochemical capacitance of this electrode material. The obtained results showed that the sample prepared using a KOH/C weight ratio of 5/1 exhibited the highest specific surface area of 1469 m² g^?1, with average pore diameter of 3.18 nm. Further, this sample also exhibited the highest specific capacitance (184.2 F g^?1) at a current density of 0.4 A g^?1 in 6 M KOH electrolyte. In addition, the sample retained 97.6 % of its initial specific capacitance even after 1000 cycles, owing to the formation of a microporous/mesoporous structure by the activation process, the structure which provided suitable sites for charge transport and electrolyte diffusion. Thus, activated microporous carbon materials derived from horseweed could be effective as electrode materials in supercapacitors.     

Effects of sintering temperature on dielectric and piezoelectric properties of KNN-LS-BF-0.4mol%CuO lead-free piezoelectric ceramics

KNN-LS-BF-0.4mol%CuO piezoelectric ceramics were prepared by the traditional sintering method. The effects of sintering temperature on the dielectric and piezoelectric properties of KNN-LS-BF-0.4mol%CuO ceramics were studied. The results reveal that the sintering temperature has significant influence on the microstructure and the properties of KNN-LS-BF-0.4mol%CuO ceramics. With the increase of sintering temperature from 1,040 to 1,080 °C, the grains become more homogeneous and more tight-arrangement, resulting in the higher relative density as well as the best dielectric and piezoelectric properties. However, the properties of the samples would be deteriorated as they are sintered over 1,080 °C.     

Ba<Subscript>1−x</Subscript>La<Subscript>x</Subscript>Fe<Subscript>12</Subscript>O<Subscript>19</Subscript> (x = 0.0, 0.2, 0.4, 0.6) hollow microspheres: material parameters,magnetic and microwave absorbing properties

Ba_1?xLa_xFe₁₂O₁₉ (x = 0.0, 0.2, 0.4, 0.6) hollow ceramic microspheres (HCMs) have been prepared by combining self-reactive quenching method with heat treatment. Their material parameters, magnetic and microwave absorbing properties were investigated. It was observed that after doping of lanthanum, the material parameters showed a little change except hexagonal crystal disappearing. And the magnetic properties of HCMs were decided by lanthanum content and material parameters. With the lathanum increases from 0.0 to 0.6, the saturation magnetization (Ms) values initially increased, and then decreased sharply to a minimum value, and increased again, moreover, the coercive force (Hc) values were reduced first, and then increased, and decrease to a minimum value. Absorbing properties tests indicate that after La³⁺-doped, at 2 mm thickness, the effective absorbing band (<?10 dB) was reduced to 4.7, 5 and 4.4 GHz, respectively, the minimum reflectance would decrease in low substituted level (x ≤ 0.4) and increase in high level (x = 0.6), and the frequency shifts to low frequency with the increasing of doping content. In 1.5–3 mm range, with the increasing of thickness, the absorption peak of Ba_1?xLa_xFe₁₂O₁₉ (x = 0.2, 0.4, 0.6) HCMs shifts to low frequency and the absorption intensity increases, the effective absorbing band can up to 10, 8.1 and 8 GHz, respectively.     

Major effects on microstructure and electrical properties of ZnO-based linear resistance ceramics with MgO changes

The ZnO-based linear resistance ceramics were fabricated from ZnO–Al₂O₃–MgO–TiO₂ at 1,340 °C. The effect of the different doping amounts of MgO on the microstructure and electrical properties were investigated in detail. The optimal sample with the MgO concentration of 7 wt% possesses an energy density of 812 J/cm³ and a resistance temperature coefficient reaches 0.4 × 10^?3/°C, which are improved by 8 and 103 %, respectively. Spontaneously, the nonlinear coefficient maintains about 1.15 and the resistivity reaches to 778 Ω cm, increased by 33 %.     

Study on the efficiency of nanosized magnetite and mixed ferrites in magnetic hyperthermia

Magnetic materials, which have the potential for application in heating therapy by hyperthermia, were prepared. This alternative treatment is used to eliminate cancer cells. Magnetite, magnesium–calcium ferrites and manganese–calcium ferrites were synthesized by sol–gel method followed by heat treatment at different temperatures for 30 min in air. Materials with superparamagnetic behavior and nanometric sizes were obtained in all the cases. Thus, these nanopowders may be suitable for their use in human tissue. The average sizes were 14 nm for magnetite, 10 nm for both Mg_0.4Ca_0.6Fe₂O₄ and Mg_0.6Ca_0.4Fe₂O₄ and 11 nm for Mn_0.2Ca_0.8Fe₂O₄. Taking into account that the Mg_0.4Ca_0.6Fe₂O₄ and Mg_0.6Ca_0.4Fe₂O₄ treated at 350 °C showed the lower coercivity values, these nanoparticles were selected for heating tests and cell viability. Heating curves of Mg_0.4Ca_0.6Fe₂O₄ subjected to a magnetic field of 195 kHz and 10 kA/m exhibited a temperature increase up to 45 °C in 15 min. A high human osteosarcoma cell viability of 90–99.5 % was displayed. The human osteosarcoma cell with magnesium–calcium ferrites exposed to a magnetic field revealed a death cell higher than 80 % in all the cases.     

微孔壳聚糖保鲜膜的制备及保鲜效果研究

以壳聚糖为基材,采用不同成孔方式制备壳聚糖微孔膜,并将其应用于圣女果保鲜中。采用扫描电镜、红外光谱、光学显微镜等表征技术对膜的微观结构进行了研究,同时对膜的性能和保鲜效果进行了评定。研究结果表明：在壳聚糖中添加致孔剂纳米氧化锌、聚乙二醇或者通入氮气,均能获得性能较好的微孔膜;其中纳米氧化锌质量分数为4%、经水洗处理的微孔膜其氧气透过系数为37.90×10-15 cm3·cm/(cm2·s·Pa)接近市场PE保鲜膜透气系数;其对圣女果保鲜效果优于市场PE保鲜膜,相较于空白组其保鲜期延长了6 d。     

Development of Suspending Agent from Sodium Carboxymethyl Mungbean Starches

ABSTRACT

Three sodium carboxymethyl mungbean starches (SCMMSs) were selected, based on the physicochemical profiles and evaluated as potential pharmaceutical suspending agent in comparison with a sodium carboxymethyl tapioca starch and other five commercial suspending agents. Ibuprofen suspension was employed as a model formulation with 0.5, 1.0, and 2.0% w/v of suspending agents. Evaluation parameters included the determination of sedimentation volume ratio, redispersibility, viscosity and rheological properties and content uniformity studies. The results revealed that a high-viscosity modified mungbean starch, MMS-M-04, possessed suitable properties as a suspending agent and, at 1% concentration, was as effective as sodium carboxymethylcellulose and xanthan gum, two most-commonly used suspending agents. This modified starch could be further developed and employed as a new commercial suspending agent in the pharmaceutical industry.     

Effects of low-temperature carbonization temperature and time on morphology of carbon particles from maize starch

Carbon particles retaining the morphology of native maize starch were prepared successfully in nitrogen by low-temperature carbonization (LTC) treatment and subsequent carbonization at 600 °C for 1 h. The as-prepared carbon particles were characterized by FESEM and the process of LTC was investigated by XRD, FTIR, DSC, TGA, and elemental analysis. The results indicate that the LTC treatment is mainly the process of starch dehydration and the LTC condition has crucial effects on the morphology of final carbon particles. When the maize starch was treated with proper LTC process, the carbon content of treated maize starch is more than 51 %, and the final carbon particles show good dispersity.