Dimitrios Samios

A d.s.c. kinetic study on the effect of filler concentration on crosslinking of diglycidylether of bisphenol-A with 4,4′-diaminodiphenylmethane

Abstract The kinetics of formation of epoxy resin composites was studied using an epoxy matrix of diglycidylether of bisphenol-A (DGEBA) and 4,4′-diaminodiphenylmethane (DDM) as curing agent in the presence of quartz flour as filler. The curing reactions of these systems were kinetically followed by differential scanning calorimetry (d.s.c.) at different scanning rates. The activation energies of the curing reactions were obtained using non-isothermal methods: the single scanning rate method of Barrett as well as the multiple scanning rate methods of Kissinger, Osawa and half-width. The crosslinking process is characterized by an average activation energy of 54.2–62.7 kJ mol −1 despite different methods or filler concentrations being used to obtain it. The reaction rate for the systems with filler concentrations higher than 10 wt% showed a considerable decreasing at higher temperatures at conversions higher than 50%.

Self-assembly of amphiphilic di and triblock copolymers of styrene and quaternized 5-(N,N-diethylamino) isoprene in selective solvents

Self-association of highly asymmetric block copolymers of styrene and quaternized 5-(N,N-diethylamino)isoprene was studied. After quaternization with dimethyl sulfate, the di and triblock copolymers consisted of a long block of polystyrene (PS) with a short poly[5-(N,N,N-diethylmethylammonium)isoprene][methyl sulfate](PAI) block at one or both chain ends, respectively. The aggregates were prepared by first dissolving the copolymers in an organic solvent and then adding water to induce the segregation of the PS chains. Pure DMF, THF or dioxane was used as the organic solvent, as well as DMF/THF mixtures. The critical water content (cwc) and the morphologies were studied as a function of the common solvent, initial copolymer concentration and architecture (di or triblock) by static light scattering and by Transmission Electron Microscopy (TEM), respectively. It was found that both, the cwc and the morphologies of the aggregates are most strongly affected by the nature of the common solvent. Some unexpected behaviors were found for the triblock copolymer. Morphologies of a triblock copolymer in various mixtures of DMF and THF, quenched at determined water contents, were investigated in order to study the degree of morphological control that can be achieved solely as function of the organic solvent composition. Multiple morphologies have been found including equilibrium morphologies and kinetically trapped ones. Finally, the stability of primary micelles prepared in DMF was studied by DLS, upon dilution with DMF and water, and a possible mechanism for the destabilization of the aggregates is proposed.

Analysis and comparison of the Barrett, Freeman-Carrol and the time-temperature-transformation (TTT) superposition methods: The case of a high Tg diamine/epoxy system

Abstract In the present work the curing process of the epoxy system diglycidylether of bisphenol A (DGEBA) with 4,4′-diaminodiphenylmethane (DDM) has been studied by differential scanning calorimetry (DSC) techniques. Dynamic methods (Barrett and Freeman-Carrol) and the isothermal time-temperature-transformation (TTT) superposition method were applied in order to obtain kinetic features of the curing process. The time-temperature evolution of the glass transition temperature (Tg) and the extent of reaction (α) were used as parameters in order to monitor the curing process. Three different reaction ranges have been observed: the initial range of cure (0.05

Thermal stability of soy-based polyurethanes

New types of polyurethanes were prepared by reacting diisocyanates and formiated soy polyols with different OH functionalities. Thermal properties and degradation kinetics were investigated by TGA. All prepared PUs showed at least two-weight loss steps, the first one, around 210 °C. Thermal stability of these PUs depends strongly on urethane groups per unit volume and an increase in the weight loss was observed as a result of the increased amount of urethane groups. Degradation kinetics behavior of the soy-based polyurethanes was investigated according to the Flynn method. Different average activation energy values were obtained from isothermal and isoconversional curves, 140.6 KJ/mol and 62.8 KJ/mol, respectively, indicating the complexity of the PUs degradation process.

Removal of Cd+2 from aqueous solutions onto polypyrrole coated reticulated vitreous carbon eletrodes

The development of simple methods for removal of heavy metals from aqueous samples is a relevant field of research. In this connection, the electrodeposition of the Cd+2 ion, one of the most toxic species for animals and human beings, was investigated in aerated pH 4.8 sulfuric-sulfate solutions. In potentiostatic conditions, the maximum rate of cadmium deposition at a neutral polypyrrole (PPy0) coated reticulated vitreous carbon (RVC) working electrode occurs at -3.0 V vs. the saturated calomel reference electrode (SCE). Moreover, the conversion rate depends both on the applied potential and on the mass transport regime, and, for solutions containing 10 mg L-1 of Cd2+, the highest removal efficiency achieved is 84% after 90 min of electrolysis. The concentration decay of the Cd+2 ion in the solution was monitored by anodic stripping voltammetry (ASV) at a hanging mercury drop electrode. Besides, metallic cadmium deposited onto the polypyrrole modified RVC electrode was evidenced by Scanning Electron Microscopy (SEM) analysis using the backscattered electron image (BEI) technique and by Energy Dispersive Spectrometry (EDS).

Time–temperature dependence of the thermo-oxidative aging of polychloroprene rubber: The time–temperature-transformation (TTT) superposition method and the lifetime prediction

Abstract The time–temperature dependence of the thermo-oxidative aging of polychloroprene rubber (CR) was studied using the time–temperature-transformation (TTT) superposition method and the IEC-216 norm. Aging of the material was performed inside temperature-controlled oven under circulated air temperature. The samples were characterized by gravimetry (G), thermogravimetric analysis (TG) and Shore A hardness before and after aging. It was demonstrated that the basic idea of Wisanrrakkit and Gilham for the TTT treatment of DSC thermal analysis data can be applied in the studies of CR aging processes. A quantitative relation between aging temperature, aging time, Shore A hardness and mass loss variation was demonstrated, which permits the prediction of lifetime under thermo-oxidative condition of CR.

Thermomechanical behaviour of semicrystallinepolymers submitted to plane-strain compression

Abstract High-density polyethylene (HDPE) and poly(vinylidene fluoride) (PVF2) were submitted to plane-straincompression at temperatures between the glass transition temperature (Tg) and the melting point (Tm) by using a deep channel die; this device allowed compression along the Z-axis, elongation along the X-axis and no dimensional change along the Y-axis. The thermomechanical and morphological changes occurring during the plastic deformation process and relaxation of the deformed materials were investigated by thermomechanical analysis, differential scanning calorimetry and density measurements. The results show that the deformation process affects the thermodynamic properties of polymers, introducing different characteristics into the material. An increase of amorphous phase was registered in both materials. The plastically deformed semicrystalline polymers showed non-regular linear thermal expansion behaviour in the deformation directions (X and Z). The relaxation process, which is obtained by heating the deformed materials, is characterized by ‘shape and temperature memory’.

SONOCHEMICAL DEGRADATION OF 1,4- CIS-POLYISOPRENE USING PERIODIC ACID-SOLVENT AND TEMPERATURE EFFECT

Abstract The influence of solvent and temperature on cleavage of 1,4-polyisoprene using ultrasonic radiation (40 kHz), chemical degradation with periodic acid (H 5 IO 6 ) and sonochemical degradation (H 5 IO 6 /40 kHz) was studied. The reactions were performed in toluene, n -hexane and chloroform at different temperatures. The results were discussed in terms of dielectric constants and solvent vapour pressure. Chemical and sonochemical degradation depend on solvent and temperature. The degradation is more efficient in chloroform than in toluene and less efficient in n -hexane. Increase in temperature causes a significant increase in chemical degradation reaction and decrease in ultrasonic degradation. Ultrasonic irradiation accelerates the chemical degradation process and permits to obtain products with lower molecular weight.

Preliminary characterization of anhydrous ethanol used in Brazil as automotive fuel

This work reports preliminary studies on the characterisation of anhydrous ethanol (AEA) used as an automotive fuel mixed with gasoline in Porto Alegre (South Brazil). Pre-concentration of the impurities contained in 1000 ml of AEA was carried on through solid-phase extraction using XAD4 resin. The main compounds in the extract were identified by means of spectral data from the library of the equipment. The concentrate was then fractionated using a preparative liquid chromatographic column filled with activated silica gel and the elution procedure was carried out with, n-hexane, n-hexane-benzene (1:1, v/v) and dichloromethane. Prior to analysis by GC-MS, each fraction was reduced to 1 ml with a gentle stream of nitrogen. Saturated linear hydrocarbons and aromatic hydrocarbons eluted in the first fraction and oxygenated compounds such as aldehydes. ketones and alcohols, eluted in the second one. were the main compounds detected in the sample.

Análise exploratória aplicada a espectros de reflexão total atenuada no infravermelho com transformada de Fourier (ATR-FTIR) de blendas de biodiesel/diesel

In this study, hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to classify blends produced from diesel S500 and different kinds of biodiesel produced by the TDSP methodology. The different kinds of biodiesel studied in this work were produced from three raw materials: soybean oil, waste cooking oil and hydrogenated vegetable oil. Methylic and ethylic routes were employed for the production of biodiesel. HCA and PCA were performed on the data from attenuated total reflectance Fourier transform infrared spectroscopy, showing the separation of the blends into groups according to biodiesel content present in the blends and to the kind of biodiesel used to form the mixtures.