SBR COMPOSITES REINFORCED WITH N-ISOPROPYL-N'PHENYL-P-PHENYLENEDIAMINE-MODIFIED CLAY

SBR compounds including the N-isopropyl-N'-phenyl-p-phenylenedianfine-modified clay (organoclay) were prepared. Effects of modified clay and antioxidant (IPPD) contents on mechanical and rheological properties of SBR composites were studied. FTIR results confirmed that the clay was chemically modified by IPPD and changed into an organoclay. X-ray diffraction (XRD) results confirmed the increase in interlayer distance of the clay due to the insertion of IPPD. Rheological and cure characteristics of SBR compounds were determined using RPA (Rubber Process Analyzer) and rheometer. Scorch time and cure time of SBR compounds decreased with introduction of the organoclay. Mechanical properties and heat aging resistance of the SBR composites were improved significantly by incorporation of the organoclay.     

Consumption of fruit and vegetables among elderly people: a cross sectional study from Iran

Background  

There is substantial evidence that low consumption of fruit and vegetables (FV) is a major risk factor for many chronic diseases. The aim of this study was to assess FV consumption and the variables that influence it among elderly individuals in Iran aged 60 and over.     

Synthesis and characterization of highly soluble and thermally stable new polyimides based on 3,5-diamino benzoyl amino phenyl-14H-dibenzo[a,j]xanthene

A new xanthene-containing diamine monomer was successfully synthesized in four steps by the condensation of β-naphthol and 4-nitrobenzaldehyde in the presence of p-toluenesulfonic acid catalyst, reduction of the nitro intermediate, the nucleophilic substitution reaction of amine compound and 3,5-dinitrobenzoyl chloride, and subsequent reduction of the dinitro compound. The diamine monomer could be obtained in quantitative yield. A series of novel organosoluble aromatic polyimides were prepared by direct polycondensation of synthesized diamine with four tetracarboxylic dianhydrides via a conventional two-step polymerization process. The polymers were obtained in quantitative yields with inherent viscosities of 0.20–0.74 dL/g. Most of the polymers dissolved in N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide and dimethyl sulfoxide. The resulting polyimides exhibited good thermal stability; no weight loss was detected before a temperature of 450 °C in nitrogen. Wide-angle X-ray diffraction measurements showed that these polyimides were predominantly amorphous.     

Numerical simulation of heat and moisture transfer through bulky PAN nanofiber mats

In this study, the coupled heat and moisture transfer of polyacrylonitril nanofiber mats were investigated by theoretical and experimental methods. A mathematical model was used to describe and predict the coupled heat and moisture transfer of nanofiber mats. Based on the results obtained by scale analysis method, order of magnitude of heat transfer by radiation is negligible for nanofiber mats but heat transfer by convection is important. In this investigation, the coupled heat and moisture transfer including convection heat transfer was solved numerically by finite difference method. Comparison between numerical results and experimental data shows good agreement, which indicates the high accuracy of the numerical results.     

High-Performance and Biobased Polyamide/Functionalized Graphene Oxide Nanocomposites through In Situ Polymerization for Engineering Applications

In this study, biobased polyamide/functionalized graphene oxide (PA-FGO) nanocomposite is developed using sustainable resources. Renewable PA is synthesized via polycondensation of hexamethylenediamine (HMDA) and biobased tetradecanedioic acid. Furthermore, GO is functionalized with HMDA to improve its compatibility with biobased PA and in situ polymerization is employed to obtain homogeneous PA-FGO nanocomposites. Compatibility improvement provides simultaneous increases in the tensile strength, storage modulus, and conductivity of PA by adding only 2 wt% FGO (PA-FGO2). The tensile strength and storage modulus of PA-FGO2 nanocomposite are enhanced dramatically by ≈50% and 30%, respectively, and the electrical conductivity reached 3.80 × 10^–3 S m⁻¹. In addition, rheology testing confirms a shear-thinning trend for all samples as well as a significant enhancement in the storage modulus upon increasing the FGO content due to a rigid network formation and strong polymer-filler interactions. All these improvements strongly support the excellent compatibility and enhanced interfacial interactions between organic–inorganic phases resulting from GO surface functionalization. It is expected that the biobased PA-FGO nanocomposites with remarkable thermomechanical properties developed here can be used to design high-performance structures for demanded engineering applications.     

Biosynthesis of xanthangum‐coated INPs by using Xanthomonas campestris

Synthesis of iron nanoparticles (INPs) with a biocompatible coating usually is a multistep process which requires harsh, special and protected reaction conditions. In the current experiment, the authors used Xanthomonas campestris cells to develop a facile method for fabrication of biocompatible INPs. Bacterial cells were supplied with ferric citrate as an iron precursor. Transmission electron microscopy micrographs exhibited that xanthan gum‐coated INPs are synthesised and deposited on the surface of X. campestris cells and produced nanoparticles were 20–80 nm in diameter with 41.7 nm mean particle size. Xanthan gum coating with about 7 nm thickness formed a clear hollow around each nanoparticle. According to thermogravimetric analysis, the coating was about 13.4% of the total INPs weight. Prepared particles had a zeta potential of −114 mv which is an ideal surface charge to make particles colloidally stable in aqueous matrixes. Xanthan gum‐coated INPs were non‐crystalline with low saturation magnetisation value of about 0.26 emu/g.Inspec keywords: nanoparticles, nanofabrication, iron, microorganisms, transmission electron microscopy, particle size, electrokinetic effects, surface charging, magnetisation, organic compoundsOther keywords: biosynthesis, xanthan gum‐coated INPs, Xanthomonas campestris cells, iron nanoparticles, biocompatible coating, bacterial cells, ferric citrate, transmission electron microscopy micrographs, mean particle size, thermogravimetric analysis, zeta potential, surface charge, saturation magnetisation, size 20 nm to 80 nm, Fe     

Investigation and Comparing the Effects of CNTs and Ag Nanoparticles Doping on YBCO Superconductor Properties

In this work, we investigate and compare doping effects of Ag nanoparticles and carbon nanotubes (CNTs) on the properties of Y₁Ba₂Cu₃ O _7?δ (YBCO) high-temperature superconductor. The YBCO samples were prepared using sol-gel method and characterized by resistivity versus temperature (ρ–T), the electrical field versus current density (E–J), x-ray diffraction (XRD) and scanning electron microscope (SEM) analysis. The results show that the orthorhombic phase of superconductivity was formed for all the prepared samples. Also, we found that the crystalline size of the YBCO samples decreases from 62 to 33 nm by adding CNTs and Ag nanoparticles to the compound. The pinning energy, critical current density and critical temperature of the samples increase by adding CNTs and Ag nanoparticles to YBCO compound, but CNTs play a more effective role than Ag nanoparticles in this compound.     

Effects of Mixing the Steel and Carbon Fibers on the Friction and Wear Properties of a PMC Friction Material

Friction, fade and wear characteristics of a PMC friction material containing phenolic resin, short carbon fiber, graphite, quartz, barite and steel fiber were investigated through using a small-scale friction testing machine. Four different friction materials with different relative amounts of the carbon fiber and steel fiber were manufactured and tested. Comparing with our previous work which contained only steel fiber as reinforcement, friction characteristics such as fade and recovery and wear resistance were improved significantly by adding a small amount of carbon fiber. For the mixing of carbon and steel fiber, the best frictional and wear behavior was observed with sample containing 4 weight percentage carbon fiber. Worn surface of this specimen was observed by optical microscopy. Results showed that carbon fibers played a significant role in the formation of friction film, which was closely related to the friction performance. The brake pad with Steel fibers in our previous work, showed low friction coefficient and high wear rate. In addition, a friction film was formed on the surface with a relatively poor quality. In contrast, the samples with mixing the steel and carbon fiber generated a stable friction film on the pad surface, which provided excellent friction stability with less wear.     

Direct electrochemistry of chemically modified catalase immobilized on an oxidatively activated glassy carbon electrode

Catalase (Ct) was modified using Woodward’s reagent K (WRK) as a specific modifier of carboxyl residues. The modified Ct was immobilized on an oxidatively activated glassy carbon electrode surface to investigate its direct electrochemistry. Using cyclic voltammetry an irreversible reduction peak was obtained at approximately −0.362 V vs. Ag/AgCl in buffer solution, pH 7, and at a scan rate of 0.1 V s⁻¹. The electrochemical parameters, including charge-transfer coefficient (0.27), apparent heterogeneous electron transfer rate constant (13.51 ± 0.42 s⁻¹) and formal potential of the Ct film (−0.275 V) were determined. The prepared enzyme electrode exhibited a response to H₂O₂.     

Poly(lactic-co-glycolic acid): The most ardent and flexible candidate in biomedicine!

Among all polymers, without doubt, poly(lactic-co-glycolic acid) (PLGA) is the most popular one in biology and biomedicine fields. Having a tunable structure, a controllable and desired release profile, huge capacity of functionalization with various agents besides an incredible biosafety and biocompatibility, which led to its food and drug administration (FDA) approval, is among some outstanding features of this polymer. Cancer treatment using PLGA-based vehicles carrying anticancer agents, delivery of various active compounds from drugs to peptides and vaccines, tissue regeneration, and treatment of central nervous system disorders, all shows the potential of this polymer in this area. Nowadays, the focus of most investigations is on designing the most efficient PLGA formulation and improving its effectiveness with various synthesis and postsynthesis modifications. The aim of this review is to mention some recent investigations directed to improve PLGA efficiency in biomedical area.