Comparison of melt extrusion and thermokinetic mixing methods in poly(ethylene terephthalate)/montmorillonite nanocomposites

The scope of this study consists in studying the effects of processing type on thermal stability of poly(ethylene terephthalate) (PET) and its nanocomposites prepared with organically modified clays. To achieve this goal, an intercalating agent was synthesized and montmorillonite type of clay modified with this intercalating agent was mixed with the PET by using melt extrusion and high‐shear thermokinetic mixing method. According to the results, manganese in the raw clay—though chemically bound—was found to be responsible for the decreased intrinsic viscosity (IV) values, i.e. decreased molecular weight in PET/organoclay nanocomposites. Besides, it was revealed that working on the thermokinetic mixer provided substantial contributions such as shorter processing times in comparison to the melt extrusion method, elimination of drying step before melt processing, which has been accepted as an inevitable process for PET so far, less thermal degradation because of short processing times, and more homogeneous and better dispersion of the clay particles in PET matrix phase. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Performance analysis of dual-hop fixed-gain AF relaying systems with OSTBC over Nakagami-m fading channels

In this paper, we present outage probability and symbol error rate (SER) performance analyses of a dual-hop transmission using fixed-gain amplify-and-forward relaying in flat Nakagami-m fading channels. The system under consideration is equipped with multiple antennas at source and destination adopting orthogonal space-time block coding to provide transmit diversity and maximum ratio combining to provide receive diversity, respectively. For integer and half-integer m values, closed forms of exact outage probability and moment generating function (MGF) expressions are derived through cumulative distribution function (CDF) of the overall system signal-to-noise ratio. Closed-form exact SER expressions based on the overall CDF are obtained for binary phase shift keying, binary frequency shift keying and M-ary pulse amplitude modulation. Exact SER expressions based on the MGF method are also obtained for binary differential phase shift keying, M-ary phase shift keying and M-ary quadrature amplitude modulation. Moreover, the asymptotic diversity order analysis is performed through derivations of asymptotic outage probability and SER. Theoretical analyses are validated by Monte Carlo simulations showing perfect match between each other.     

Synthesis and characterization of novel poly(dimethylsiloxane)/polyindole composites

A series of composites of polyindole (PIN) and poly(dimethylsiloxane) (PDMS) were synthesized chemically using FeCl₃ as an oxidant agent in anhydrous media. The composites were characterized by FTIR and UV‐visible spectroscopies, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X‐ray diffraction (XRD), elemental analysis, inductively coupled plasma‐optic emission spectroscopy (ICP‐OES), magnetic susceptibility, stress–strain experiments, and conductivity measurements. The conductivities of PIN at different temperatures were also measured and it was revealed that their conductivities were slightly increased with increasing temperature. Moreover, the freestanding films of PDMS/PIN composites were prepared by casting on glass Petri dishes to examine their stress–strain properties. From thermogravimetric analysis results it was found that PDMS/PIN composites were thermally more stable than PIN. Thermal stabilities of PDMS/PIN composites increased with increasing PIN content. It was found that the conductivities of PDMS/PIN composites depend on the indole content in the composites. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of structural parameters on compressibility and soiling properties of machine woven carpets

Compressibility performance of the machine woven carpet after a static or dynamic loading expresses the texture deformation tendency of the carpet. This study is an experimental attempt to investigate the effects of pile height and pile density on compressibility and soiling property by dynamic loading, prolonged heavy static loading, compression recovery and artificial soiling tests. In this study, a total of 12 carpet samples with three different pile heights and four different pile densities were tested. As a result of this study, it was seen that higher pile density provides a lower thickness loss and so a lower level of texture deformation. On the other hand, pile height has a preventing effect for texture deformation for static loading and compression recovery tests whereas there is no considerable effect on dynamic loading test. There is no considerable difference between the soiling properties of the samples.     

Single-Laboratory Validation for the Determination of Aflatoxin B1, B2, G1, and G2 in Foods Based on Immunoaffinity Column and Liquid Chromatography with Postcolumn Derivatization and Fluorescence Detection

This study presents a method validation procedure for the determination of aflatoxin B₁, B₂, G₁, and G₂ in hazelnut, hazelnut paste, walnut, peanut, pistachio, corn, and wheat. The method consisting of clean-up with immunoaffinity column, high performance liquid chromatography with postcolumn derivatization and fluorescence detection was validated in accordance with Commission Regulation 2004/882/EC. The selectivity, linearity, decision limit, detection capability, detection and quantification limits, precision, recovery, ruggedness, and measurement uncertainty of the method were determined. The limit of detection and limit of quantification values (μg/kg) were: aflatoxin B₁, 0.02, 0.07; aflatoxin B₂, 0.01, 0.02; aflatoxin G₁, 0.02, 0.07; and aflatoxin G₂, 0.01, 0.03. The relative standard deviation values for the repeatability and within-laboratory reproducibility were below 4 and 5 %, respectively. The recovery values of the spiked samples ranged from 80 to 105 %. These results complied with minimum performance criteria established by regulation 2006/401/EC. Therefore, the procedure can be implemented for the routine analysis of aflatoxins in the studied matrices.     

Effects of Nanoparticles on Film Properties of Waterborne Acrylic Emulsions

Waterborne acrylic emulsion was obtained by using methyl methacrylate, ethyl and butyl acrylate monomers. Emulsions containing nanoparticles were prepared by blending the stable dispersions containing SiO₂ or MMT nanoparticles. The films were prepared from emulsions and coating tests were applied. The physical properties of prepared emulsions are better than the commercial emulsions. The addition of the nanoparticles especially SiO₂ have positive effect on the resistance to environmental conditions of emulsions. Waterborne acrylic emulsions containing nanoparticles prepared in this study can be used in the manufacturing of the semi-lustrous emulsion type nano paint with low cost, high performance and environmentally friendly.     

Analysis of Physical and Thermodynamic Properties of Poly(2-Phenyl-1,3-Dioxolane-4-Yl-Methyl-Methacrylate-Co-Styrene) Polymer with Inverse Gas Chromatography

In this study, physical and thermodynamic properties of poly(2-phenyl-1,3-dioxolane-4-yl-methyl-methacrylate-co-styrene) (PDMMA-ST) were investigated by using inverse gas chromatography. Two groups of solvents with different chemical natures and polarities were used to obtain information about PDMMA-ST-solvent interactions: alcohols and alkanes. The specific retention volume (V_g ⁰), the sorption enthalpy (ΔH₁ ^S), sorption free energy (ΔG₁ ^S), sorption entropy (ΔS₁ ^S), the weight fraction activity coefficients of solute probes at infinite dilution (Ω ₁ ^∞), and Flory-Huggins interaction parameters (χ ₁₂ ^∞) between polymer and solvents were determined for the interactions of PDMMA-ST with alcohols and alkanes by inverse gas chromatography in the temperature range of 333–473 K. Also, the solubility parameters of PDMMA-ST at infinite dilution were found by plotting the graph of [(δ ₁ ²/RT) - χ ₁₂ ^∞/V₁] versus solubility parameters, δ ₁, of probes.     

Design and manufacturing of a V-type Stirling engine with double heaters

Under the consideration of the solar energy potential of Turkey, a V-type Stirling engine having two heaters was designed, optimized and then manufactured. The prototype engine was tested in laboratory condition using an electrical heating system. Tests were conducted within the temperature range of 650–1000 °C with 50 °C increments. The pressure ranged from the ambient value to 2 bar with 0.5 bar increments at each stage of temperature. The maximum power was obtained at 950 °C and 1.0 bar charge pressure as 118 W.     

Determining the best type of heat exchangers for heat recovery

It is a common problem to choose the most appropriate heat exchanger configuration for heat recovery. In this study, a new model has been developed for determining the area and type of the most appropriate waste heat recovery heat exchanger for maximum net gain. A non-dimensional E number has been defined based on known technical and economic parameters such as the life-time, unit area cost of the heat exchanger, lower heating value of the fuel, overall heat transfer coefficient of heat exchanger, boiler efficiency, operation time per year, heat exchanger effectiveness, ratio of heat capacities, annual variation of the temperature of fluids supplied to the heat exchanger and present worth factor. The non-dimensional E numbers has been demonstrated in graphical forms as a function of NTU and ratio of heat capacities and corresponding heat exchanger area giving maximum net gain can easily be obtained from these graphs. The best heat exchanger type and its area can be determined comparing net gains or effectiveness of heat exchangers at NTU_max. Application of the new method has been given with a case study as a sample calculation.     

Experimental investigation of drying shrinkage cracking of composite mortars incorporating crushed tile fine aggregate

Drying shrinkage is generally classified as an important hardened concrete property. It expresses the strain occurring in hardened concrete due to the loss of water. During the drying process, free and absorbed water is lost from the concrete. When the drying shrinkage is restrained, cracks can occur, depending on the internal stresses in the concrete. The ingress of deleterious materials through these cracks can cause decrease in the compressive strength and the durability of concrete. In this study, being as a fine aggregate in mortars, crushed tile (CT) effect on drying shrinkage and drying shrinkage cracking is investigated. Thus, compressive and flexural strength, modulus of elasticity, and free and restrained drying shrinkage tests are conducted on mortar specimens produced with and without crushed tile fine aggregate. The ring test has been used in order to investigate the cracks induced by restrained drying shrinkage. In this way, free drying shrinkage strain, along with the number and development of drying shrinkage cracks, of the crushed tile fine aggregate mortar composites are quantified and observed.