Este trabalho tem por objetivo a busca por técnicas alternativas para diminuir a incidência de vazios em resinas poliméricas e, por consequência, em materiais compósitos. Foram produzidas formulações diferentes utilizando resina epóxi à base de éter diglicidílico do Bisfenol A, endurecedor de poliamina alifática com e sem a adição de diferentes aditivos desaerantes a base de éteres e ésteres modificados. As formulações produzidas foram submetidas a condições extremas de agitação e processamento, sendo posteriormente avaliadas quanto a incidência de bolhas e vazios, densidade, propriedades mecânicas, morfológicas e térmicas. Os resultados foram bastante positivos quanto à diminuição da quantidade e do tamanho de poros pela utilização de técnicas de desgaseificação a vácuo e pelo uso de aditivos desaerantes.

This study aims alternative techniques to reduce the incidence of voids in polymeric resins and in composite materials. Different formulations were prepared using epoxy resin based on bisphenol A diglycidyl ether and an aliphatic polyamine hardener, with and without the addition of different degasing agents based on modified esters and ethers. The formulations produced were subjected to extreme agitation and processing conditions and we evaluated the incidence of bubbles and voids, density, mechanical, morphological and thermal properties. The results were very positive. We observed the decrease in number and size of pores by the use of vacuum degassing techniques and degasing agent additives.

A presença de vazios é um importante fator a afetar as propriedades de compósitos poliméricos. Existem várias causas para a formação de vazios, entre elas, o aprisionamento de gás (frequentemente gás úmido) durante o processo de impregnação dos reforços fibrosos com resina e os voláteis gerados durante a formulação da resina. A quantidade de bolhas de ar aprisionadas pode ser, por vezes, reduzida se o sistema de resina é sujeito a um processo de desgaseificação por vácuo ou pelo uso de aditivos químicos especiais. O objetivo deste trabalho é investigar o efeito de um agente desaerante nas propriedades finais de compósitos de resina epóxi moldados pelo processo de RTM utilizando como reforço mantas e tecidos de fibras de vidro. Os compósitos produzidos foram avaliados quanto as suas propriedades de tração, flexão, dureza, short beam e análise dinâmico mecânica (DMA). Em geral, a utilização do aditivo desaerante não provocou alterações significativas nas propriedades mecânicas, tais como resistência e módulo de tração e flexão, as quais são determinadas principalmente pelo tipo e fração volumétrica de fibras. Contudo, os resultados de resistência ao cisalhamento e de dureza mostram um efeito positivo com a inclusão do agente desaerante, levando à melhora na qualidade dos compósitos.

The presence of voids is an important factor to affect the properties of polymer composites. There are several causes for void formation, such as gas entrapment (most often wet air) during impregnation of the fibrous reinforcement with resin and volatiles arising from the resin system itself. The amount of entrapped air bubbles can sometimes be reduced if the resin system is subjected to a degassing process (e.g. aided by vacuum) or by using special chemical additives. The aim of this research is to investigate the effect of a degassing agent on the final properties of epoxy composites molded by RTM using glass-fiber mats or plain-weave cloths. The produced composites were evaluated under tensile, flexural, hardness and short beam testing, along with dynamical mechanical analysis (DMA). In general, the use of the additive did not ensure significant improvement in those mechanical properties that are primarily determined by the type and content of the fibrous reinforcement, such as tensile and flexural strength and modulus. However, the short beam strength and hardness results showed a positive effect with the inclusion of the additive, leading to better quality composites.

The aim of this work is to obtain polymer precursors based on styrene copolymers with distinct degrees of sulfonation, as an alternative material for fuel cell membranes. Acetyl sulfate was used to carry out the sulfonation and the performance of the polyelectrolyte was evaluated based on the content of acid polar groups incorporated into the macromolecular chain. Polymeric films were produced by blending the sulfonated styrene-indene copolymer with poly(vinylidene fluoride). The degree of sulfonation of the polymer was strongly affected by the sulfonation reaction parameters, with a direct impact on the ionic exchange capacity and the ionic conductivity of the sulfonated polymers and the membranes obtained from them. The films produced with the blends showed more suitable mechanical properties, although the conductivity of the membranes was still lower than that of commercially available membranes used in fuel cells.

Estudou-se a agregação de surfactantes aniônicos em soluções aquosas diluídas de (hidroxipropil)celulose (HPC) sob moderada força iônica (NaCl 0,1 mol L-1). Empregaram-se os surfactantes colato de sódio (CS), deoxicolato de sódio (DC) e dodecil sulfato de sódio (SDS). Observou-se decréscimo da concentração de agregação crítica (C1) para SDS e DC em comparação à concentração micelar crítica (CMC), enquanto ocorreu aumento para CS, a 298 K. A viscosidade relativa apresentou um máximo para o sistema SDS/HPC, mas permaneceu constante para CS/HPC ou DC/HPC. Houve aumento da temperatura de turbidez para todos os sistemas. Utilizando-se espalhamento de luz dinâmico, verificou-se que, a baixas concentrações de surfactante, o modo rápido da HPC relaciona-se a agregados surfactantes/HPC e cadeias poliméricas curtas; a altas concentrações, a micelas livres. O modo lento relaciona-se a complexos surfactante/HPC ou a "clusters" de HPC. Nos sistemas sais biliares/HPC, o mecanismo de agregação pode ocorrer em duas etapas.

The aggregation of different anionic surfactants in dilute aqueous solutions of (hydroxypropyl)cellulose (HPC) under moderate ionic strength (NaCl 0.1 mol L-1) was studied. The surfactants were sodium cholate (CS), sodium deoxycholate (DC) and sodium dodecylsulphate (SDS). By fluorescence probing, the critical aggregate concentration (C1) decreased for SDS and DC in comparison to the critical micelle concentration (CMC) whereas it increased for CS at 298 K. The relative viscosity reached a maximum for SDS/HPC but remained constant for CS/HPC and DC/HPC. By light scattering, cloud points were verified to increase. By dynamic light scattering, it was concluded that, at low surfactant contents, the fast mode of HPC is related to surfactant/HPC aggregates and shorter HPC chains; at high contents, to free micelles. The slow mode is linked to interchain polymer-surfactant complexes and HPC clusters. For the bile salts/ HPC systems, the mechanism of aggregation may occur in two steps.

This paper reports the encounter of five lice species on a specimen of tinamou in Petrópolis city, Rio de Janeiro state. These only two of them, Strongylocotes complantus and Kelloggia ribeiroi, had been previously told in this host species. The others species (Megapeostus petersi; Heptapsogaster mandibularis; Discocorpus microgenitalis) were reported at first time on this bird species.

Fluorescence probing, viscosity and light scattering measurements have been combined to study the aggregation of different anionic surfactants mainly in dilute solutions (0.5% w/v) of (hydroxypropyl)cellulose (HPC MW 173,000), in moderate ionic strength (NaCl 0.1 mol.L-1). The set of surfactants includes natural cholesterol derivatives, sodium cholate (CS) and sodium deoxycholate (DC), and the alkylsulphate, sodium dodecylsulphate (SDS). At 298 K the critical surfactant concentration related to aggregate/HPC formation (C1) decreases for SDS and DC whereas it increases slightly for CS. At 312 K the C1 values for CS and DC are slightly shifted toward higher values whereas it is not changed for SDS. All surfactant/HPC systems increase C1 values as the HPC concentration increases to 1.2%. Above C1 the viscosity increases for all surfactant/HPC systems but it is sharper in the increasing order CS, DC and SDS. The hydrodynamic behavior indicates that CS induces higher diffusion to HPC than SDS and DC. The aggregation in the surfactant/HPC systems is analyzed through the feature of surfactant/aggregate structure (size, charge density, etc).