ABSTRACT:The mechanical properties of epoxy networks based on diglycidyl ether of bisphenol A epoxy resin cured with various linear aliphatic amines, such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and cyclic amines such as 1-(2-aminoethyl)-piperazine and isophorone diamine, were studied. General characteristics such as T g , density, and packing density, were determined and related to the structure and funcionality of the curing agent. Dynamic mechanical spectra were used to study both the a and b relaxations. Tensile and the flexural tests were used to determine the Young's and flexural modulus, and fracture strength all in the glassy state. Furthermore, linear elastic fracture mechanics was used to determine K IC . As a rule, isophorone diamine network presented the higher tensile and flexure modulus while 1-(2-aminoethyl)piperazine gave the highest toughness properties.

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ABSTRACT:We developed a conductive epoxy/amine system containing polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA). The curing behaviors of diglycidyl ether of bisphenol A with triethylenetetramine (TETA), PAni.DBSA, and both amine compounds at different concentrations were investigated by differential scanning calorimetry (DSC). Epoxy/TETA systems containing PAni.D-BSA presented two distinct exothermic peaks at 90°C due to the cure by TETA as a hardener and at 236°C related to PAni.DBSA as the curing agent. The presence of PAni.DBSA in the systems constituted by epoxy/hardener in stoichiometric proportions resulted in a decrease in the glass-transition temperature of the epoxy matrix, as indicated by DSC and dielectric analyses. Electrical conductivity was determined in the epoxy/amine networks, with the TETA concentration kept constant and also in stoichiometric proportions of mixed hardener (TETA ϩ PAni.DBSA) to epoxy resin. The last condition resulted in a higher electrical conductivity.

ABSTRACT:The compatibilizing effect of mercapto-modified ethylene-vinyl acetate (EVALSH) was investigated in vulcanized nitrile rubber (NBR)/ethylene-vinyl acetate (EVA) copolymer blends. EVALSH increased the ultimate tensile strength, mainly in blends containing larger amounts of NBR. In addition, an accelerating effect of this functionalized copolymer was observed in blends vulcanized with the sulfur system. This behavior was confirmed with oscillating disk rheometry and differential scanning calorimetry analyses. The improvement of the mechanical performance was attributed to the interfacial action associated with the increase in the crosslink density of the NBR phase promoted by the mercapto groups in EVALSH. The effects of EVALSH on the morphology and dynamic mechanical properties were also studied.

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