Polymeric coatings may act as a physical barrier between the aggressive ions and the metal substrate. However, prolonged exposure may cause damage to the polymer coating, leading to a continuous reduction of the barrier effect and consequently loss of the corrosion protection. The objective of this study is to determine the effect of aminopropyltriethoxysilane (APS), cellulose and polyaniline emeraldine-salt (PAni ES) in an epoxy coating on the corrosion protection of mild steel. Microcrystalline cellulose (MCC) and cellulose nanowhiskers (CNW) functionalized or not with PAni ES were used and compared. The coating properties were investigated by electrochemical impedance spectroscopy (EIS), salt spray test and scanning electron microscopy (SEM). The surface of the carbon steel, after 1000 h of exposure, did not present evidence of superficial corrosion. Polymer coatings using CNW and PAni ES showed improved corrosion protection properties even after 90 days of immersion in 3.5 wt% NaCl solution. The greatest increase in the corrosion resistance of the coating was found by EIS for the epoxy coating reinforced with CNW functionalized with PAni ES, revealing a synergistic effect of the electroactivity of a conducting polymer and nanosized cellulose particles.

Resumo Neste trabalho foram desenvolvidas espumas flexíveis de poliuretano com a adição de celulose de Pinus nas concentrações de 0,5; 1 e 2% (m/m). A celulose foi submetida ao processo de fibrilação mecânica e posterior secagem por aspersão (spray dry) sendo caracterizada quanto a sua morfologia por MEV e MET. As espumas foram produzidas pelo método de batelada (one-shot) com a adição e mistura da fibra junto ao poliol. As espumas foram caracterizadas por MEV, densidade aparente e resistência à compressão. Os principais resultados indicam que a fibrilação mecânica promove a obtenção de fibras em escala nanométrica, porém durante a secagem, ocorre aglomeração ocasionando aumento para escala micrométrica. As propriedades mecânicas da espuma obtiveram acréscimos de 40 e 50% na resistência à compressão com a adição de 0,5 e 1% de celulose, respectivamente, evidenciando seu potencial como aditivo alternativo para o desenvolvimento de espumas de poliuretano.

Abstract In this work, flexible polyurethane foams were developed with the addition of Pinus cellulose at concentrations of 0.5; 1 and 2 wt%. The cellulose was subjected to mechanical fibrillation process and subsequent dried by spray dry process. It was characterized morphologically by SEM and TEM. The foams were produced by one-shot method by adding and mixing the fiber with the polyol. The foams were characterized by SEM, apparent density and compression strength. The main results indicate that the mechanical fibrillation promotes the obtainment of nanoscale fibers, but during the drying process, agglomeration occurs causing an increase reaching the micrometer scale. The mechanical properties of the foam increased by 40 and 50% in compressive strength with the addition of 0.5% and 1% of cellulose, respectively, showing its potential as an alternative additive for the development of polyurethane foams.

AbstractPolymer coatings have been used for the corrosion protection of metal surfaces acting as a physical barrier against several corroding media. In spite of the good efficiency of these coatings their resistance is limited due to the presence of localized defects which give place to localized corrosion. Aiming to improve the barrier properties of these coatings this work has proposed the use of nanocomposites as powder coatings based on a standard formulation of a commercial powder varnish. Nanocomposites with 2 and 4 wt% contents of organophilic montmorillonite (OMMT) were obtained in the molten state through of a co-rotating twin-screw extruder. The application of the nanocomposite coatings was performed by electrostatic pulverization on mild steel panels. The coatings were characterized to determine their structure using X-ray diffraction (XRD). The morphologies of the coatings were assessed using transmission electron microscopy (TEM). Gloss and adhesion measurements and the flexibility and impact resistance of the coatings were included in the physical assessment of the coatings. The corrosion performance was evaluated by the salt spray test and by electrochemical impedance spectroscopy (EIS). The coatings with clays presented predominantly exfoliated structures, with good dispersion of OMMT in the epoxy matrix. The addition of OMMT reduced the impact resistance, flexibility and gloss but increased the barrier properties of the coatings. The best corrosion performance in NaCl solution was achieved for 4 wt% OMMT.

ResumoNeste estudo foram desenvolvidos compósitos utilizando PEAD, pó de madeira (Pinus taeda), alumina calcinada e dois diferentes tipos de agentes compatibilizantes para avaliação das propriedades morfológicas e mecânicas dos mesmos. Para aumentar a interação entre a matriz polimérica e o pó de madeira foram utilizados 2% de polietileno graftizado com anidrido maleico em todas as formulações. Para efeito comparativo foi desenvolvida uma formulação com viniltrietoxisilano como compatibilizante para a alumina calcinada. O teor de cargas variou de 4% a 33% para os compósitos de carga única e mantiveram o percentual de 28% para os compósitos com as duas cargas. A interação entre a matriz polimérica e as cargas, proporcionada pelo agente compatibilizante anidrido maleico, foi observada nas micrografias da interface da matriz/carga. A utilização do silano não proporcionou efeito adicional nas propriedades mecânicas dos compósitos. Os compósitos isentos de alumina apresentaram maior resistência à tração, porém na resistência à flexão a presença da alumina contribuiu para o aumento desta propriedade provavelmente devido à pequena interação existente entre a interface do seu grão e a matriz polimérica.

AbstractThis work aims at the evaluation of morphological and mechanical properties of HDPE composites developed with wood flour (Pinus taeda), calcined alumina and two different types of compatibilizing agents. In order to improve the interaction between the polymer matrix and wood flour 2% maleic anhydride-grafted polyethylene was used in all formulations. For comparison a formulation with triethoxyvinylsilane as compatibilizer for the calcined alumina was developed. The filler content ranged from 4% to 33% for the single filler composite while the percentage of 28% was kept as such for the two-fillers composites. The interaction between the polymer matrix and fillers, provided by the maleic anhydride compatibilizer agent, could be observed in the micrographs of the matrix / filler interface. The silane did not improve the mechanical properties of the composite. Free alumina composites showed higher tensile strength, but concerning flexural strength the presence of alumina contributed to increased values in this property. This was probably caused by the reduced interaction between the interface of its grain and the polymer matrix.

Neste trabalho avaliou-se a influência do tratamento alcalino das fibras de curauá, nas concentrações de 1, 5 e 10%(m/v) de NaOH, nas propriedades dos compósitos com matriz de PHBV e 20% m/m de fibras de curauá. Os compósitos foram moldados por extrusão e injeção e avaliadas suas as propriedades morfológicas, térmicas e mecânicas. Os resultados de FTIR mostraram que o tratamento alcalino promoveu modificações na estrutura das fibras de curauá, comprovadas pela remoção da hemicelulose e da lignina, evidenciadas pela ausência das bandas típicas destes compostos. Nos compósitos com fibras de curauá tratadas com solução de NaOH na concentração de 5% apresentaram um aumento de 30% na resistência à flexão e 12% na resistência ao impacto, quando comparados aos compósitos com fibras sem tratamento. Estes resultados indicam que o tratamento alcalino promoveu uma melhoria na adesão das fibras na matriz, o que melhorou significativamente as propriedades mecânicas dos compósitos.

This study investigate the influence of alkaline treatment applied to Curauá fibers, at concentrations of 1, 5 and 10% (w/v) NaOH, on the properties of the composite of PHBV matrix with 20 wt % Curauá fiber. The composites were molded by extrusion and injection and their morphological, thermal and mechanical properties were evaluated. The results showed that alkali treatment caused modifications in the structure of the Curauá fibers by the removal of hemicellulose and lignin, as evidenced by the absence of the typical bands of these compounds in FTIR analysis. It was found an increase of 30% in flexural strength and 12% in impact resistance for the composites with fibers treated in 5% NaOH solution, in relation to composites with fibers without treatment. These results indicate that the alkaline treatment promoted an improvement in the adhesion of the fibers to the matrix, which significantly improved the mechanical properties of the composites. However, concentrations of NaOH solution different from 5% may have a deleterious effect on the mechanical properties of the fibers and composites.