Poly(lactic acid)/coplasticized thermoplastic starch blend: Effect of plasticizer migration on rheological and mechanical properties

Polylactic acid (PLA) and thermoplastic starch (TPS) are known as bio‐based and biodegradable thermoplastic polymers that can be used in different applications owing to their inherent physical and mechanical properties. In order to reduce the higher costs of PLA and tuning its physical and mechanical properties suitable for short life packaging applications, blending of PLA with the TPS, more economical biodegradable polymer, has been considered in academic and industrial researches. However, melt blending of PLA with TPS without compatibilization process caused some drawbacks such as coarsening morphology and declining mechanical properties and ductility because of thermodynamic immiscibility, which may restrict its usage in packaging applications. Subsequently, our approach in this research is compatibilization of PLA/TPS blends by utilization of primary well tuning of TPS formulation with a combination of sorbitol and glycerol plasticizers. In this work, the wide composition range of melt mixed PLA/TPS blends was prepared using a laboratory twin screw extruder. The effects of microstructure on the rheological and mechanical properties of PLA/TPS blends were studied using different methods such as scanning electron microscopy (SEM) images, contact angle, oscillatory shear rheological measurements, and tensile and impact strength mechanical tests. The rheological and mechanical properties were interpreted according to the morphological features and considering the possibility of plasticizer migration from TPS to PLA phase during melt blending. Reduction in complex viscosity and storage modulus of PLA matrix samples indicates the improved melt processability of blends. Finally, in comparison with mechanical results reported in literature, our simple approach yielded the blends with elastic modulus and ductility comparable with those of chemically compatibilized PLA/TPS blends.     

Non-Fluorinated Polymer Composite Proton Exchange Membranes for Fuel Cell Applications – A Review

The critical component of a proton exchange membrane fuel cell (PEMFC) system is the proton exchange membrane (PEM). Perfluorosulfonic acid membranes such as Nafion are currently used for PEMFCs in industry, despite suffering from reduced proton conductivity due to dehydration at higher temperatures. However, operating at temperatures below 100 °C leads to cathode flooding, catalyst poisoning by CO, and complex system design with higher cost. Research has concentrated on the membrane material and on preparation methods to achieve high proton conductivity, thermal, mechanical and chemical stability, low fuel crossover and lower cost at high temperatures. Non-fluorinated polymers are a promising alternative. However, improving the efficiency at higher temperatures has necessitated modifications and the inclusion of inorganic materials in a polymer matrix to form a composite membrane can be an approach to reach the target performance, while still reducing costs. This review focuses on recent research in composite PEMs based on non-fluorinated polymers. Various inorganic fillers incorporated in the PEM structure are reviewed in terms of their properties and the effect on PEM fuel cell performance. The most reliable polymers and fillers with potential for high temperature proton exchange membranes (HTPEMs) are also discussed.     

Spectrophotometric determination of bismuth in water samples after preconcentration of its thiourea-bromide ternary complex on activated carbon

A simple, accurate, sensitive and reliable method for the selective extraction and spectrophotometric determination of Bi(III) was developed. Bi(III) was collected on activated carbon after complexation with thiourea and bromide ion in acidic media. The complex retained on activated carbon was then desorbed with the bromide solution in N,N-dimethylformamide (DMF) and determined spectrophotometrically at 375 nm. The linear calibration ranges and limit of detection for the proposed method was 1.00×10⁻⁹-1.50×10⁻⁷ and 8.00×10⁻¹⁰ mol l⁻¹, respectively. The influence of the interfering cations and anions on the determination of bismuth was investigated. The method was successfully applied to the extraction and determination of bismuth in natural water samples.     

Fluctuation-induced conductivity and dimensionality in the new Y-based Y<Subscript>3</Subscript>Ba<Subscript>5</Subscript>Cu<Subscript>8</Subscript>O<Subscript>18-</Subscript><Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> superconductor

The fluctuation conductivity measurement on the new Y-based Y₃Ba₅Cu₈O_{18- x} superconductor is presented. The dimensional crossovers between different temperature regimes were analyzed with Aslamazov-Larkin (AL) theory and a good quantitative agreement was achieved for the experimental data. For our data, the mean field regime is dominated by 2D AL fluctuations. Our results reveal the occurrence of critical fluctuation regime in consistent with the prediction of the full dynamic 3D XY model. We found the dynamical critical exponent to be z = 3.4 for our data. We analyzed also the excess conductivity data by Hikami-Larkin theory and estimated the phase relaxation time.     

An efficient diastereoselective synthesis of spiro pyrido[2,1-b][1,3]oxazines via a novel pyridine-based three-component reaction

The zwitterions generated from pyridine and dialkyl acetylenedicarboxylate (DAAD) reacted with benzofuran-2,3-diones to form highly substituted spiro pyrido[2,1-b][1,3]oxazines in good to high yields without using a catalyst.     

Pentafluorophenylammonium triflate (PFPAT): An efficient, metal-free and reusable catalyst for the von Pechmann reaction

Pentafluorophenylammonium triflate (PFPAT) is used as an efficient catalyst in the von Pechmann condensation of phenols with β-ketoesters leading to the formation of coumarin derivatives. Short reaction times, easy and quick isolation of the products, excellent chemoselectivity, excellent yields and ease of catalyst recovery with consistent activity makes this protocol efficient and environmentally benign.     

N,N'-dipyridoxyl Schiff bases: synthesis, experimental and theoretical characterization

Three N,N'-dipyridoxyl Schiff bases (L1, L2 and L3) have been newly synthesized and characterized by IR, (1)H NMR, mass spectrometry and elemental analysis. Their optimized geometries together with the theoretical assignment of the vibrational frequencies and the (1)H NMR chemical shifts of them have been computed by using density functional theory (DFT) method. In the optimized structures of the Schiff bases, two pyridine rings are not in a same plane; however the substitutions are essentially in the same plane with the pyridine rings. Also, the benzene ring(s) in the bridge region is (are) not in the same plane with the pyridine rings and azomethine moieties. In all the species, engagement in intramolecular-hydrogen bonds causes to weakness of the phenolic O-H bonds. Consistency between the theoretical results and experimental evidence confirms suitability of the optimized geometries for the synthesized Schiff bases.     

Microstructure and Thermal Properties of Ethylene/Vinyl Chloride Copolymers

Abstract

The microstructure of ethylene/vinyl chloride (E/VC) copolymers, prepared by partial reduction of PVC with a variety of reagents, was analyzed using carbon-13 NMR spectroscopy. The effect of the reduction mechanism on the microstructure and stereochemistry of the copolymers was studied. The reduction with tri-n-butyltin hydride (TBTH) produced copolymers with higher degrees of alternating monomer units than copolymers obtained by reduction with lithium aluminum hydride (LAH). Reduction with lithium triethylborohydride (SH) produced blockier copolymers. The correlation of monomer sequence and distribution with thermal stability and dehydrochlorination rate in these copolymers was investigated. Partial reduction of PVC by all reagents was shown to produce E/VC copolymers with improved thermal stability compared to PVC. In the series of copolymers produced by TBTH reduction, improvement in thermal stability increased with an increase in E content and reached a maximum at 40% E content but dropped steadily thereafter. All copolymers from SH reduction showed a considerable drop in their dehydrochlorination rate compared to PVC. The stabilization effect reached a maximum at ～7 mol% E content and stayed constant throughout.