Lisete Cristine Scienza

Dynamic-mechanical and thermomechanical properties of cellulose nanofiber/polyester resin composites.

Composites of unsaturated polyester resin (UPR) and cellulose nanofibers (CNFs) obtained from dry cellulose waste of softwood (Pinus sp.) and hardwood (Eucalyptus sp.) were developed. The fiber properties and the influence of the CNFs in the dynamic-mechanical and thermomechanical properties of the composites were evaluated. CNFs with a diameter of 70-90 nm were obtained. Eucalyptus sp. has higher α-cellulose content than Pinus sp. fibers. The crystallinity of the cellulose pulps decreased after grinding. However, high values were still obtained. The chemical composition of the fibers was not significantly altered by the grinding process. Eucalyptus sp. CNF composites had water absorption close to the neat resin at 1 wt% filler. The dynamic-mechanical properties of Eucalyptus sp. CNFs were slightly increased and the thermal stability was improved.

Influence of the Addition of Montmorillonite in an Epoxy Powder Coating Applied on Carbon Steel

Polymer 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.

Behavior in simulated soil of recycled expanded polystyrene/waste cotton composites

Composites consisting of waste cotton yarn (CF) from the textile industry and postconsumer expanded polystyrene (EPS) was followed during 90 days of exposure in simulated soil. The mechanical properties, morphologies and chemical natures of the composites were determined before and after exposure in simulated soil. The composites were made using a single-screw extrusion, a twin-screw extrusion and injection molding. The composites showed an increase of the mechanical properties nearly 50% in relation to the recycled expanded polystyrene (rEPS). After exposure in simulated soil the composites presented losses of mechanical properties. Evidence of the oxidation of the samples was demonstrated by the increase in the values of the carbonyl index after 30 days of exposure in simulated soil. Changes in the color of the surface of the sample were observed after 90 days of exposure and are due to the fungi and bacteria colonization on the surface.

Epoxy-Montmorillonite Nanocomposites Applied to Powder Coatings

Abstract The wide range of applications associated with nanocomposites is due to their improved properties when compared to conventional composites. In this study, commercial epoxy-based powder coatings were formulated with 2 and 4% (w/w) of an organically modified montmorillonite (OMMT) by incorporation in the melt state (extrusion). These composites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and X-ray diffraction (XDR). The thermal behavior and stability of the epoxy nanocomposites were studied by TGA and DSC. The nanoparticle structure within the polymer matrix was analyzed by XRD and TEM. A predominantly exfoliated structure was observed by TEM, which was confirmed by XDR analysis. The study demonstrated that the nanoclay increases the glass transition and crosslinking temperatures and also enhances the thermal stability of the coating.

Avaliação das propriedades mecânicas e morfológicas de compósitos de PEAD com pó de Pinus taeda e alumina calcinada

Neste estudo foram desenvolvidos compositos utilizando PEAD, po de madeira (Pinus taeda), alumina calcinada e dois diferentes tipos de agentes compatibilizantes para avaliacao das propriedades morfologicas e mecânicas dos mesmos. Para aumentar a interacao entre a matriz polimerica e o po de madeira foram utilizados 2% de polietileno graftizado com anidrido maleico em todas as formulacoes. Para efeito comparativo foi desenvolvida uma formulacao com viniltrietoxisilano como compatibilizante para a alumina calcinada. O teor de cargas variou de 4% a 33% para os compositos de carga unica e mantiveram o percentual de 28% para os compositos com as duas cargas. A interacao entre a matriz polimerica e as cargas, proporcionada pelo agente compatibilizante anidrido maleico, foi observada nas micrografias da interface da matriz/carga. A utilizacao do silano nao proporcionou efeito adicional nas propriedades mecânicas dos compositos. Os compositos isentos de alumina apresentaram maior resistencia a tracao, porem na resistencia a flexao a presenca da alumina contribuiu para o aumento desta propriedade provavelmente devido a pequena interacao existente entre a interface do seu grao e a matriz polimerica.

Isolation and Characterisation of Cellulose Nanowhiskers from Microcrystalline Cellulose Using Mechanical Processing

In this study, the production of cellulose nanowhiskers (CNW) from microcrystalline cellulose (MCC) by a mechanical grinding process in a super mass colloider was evaluated. MCC and CNW samples were evaluated by thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The stress/strain characterisation of the films was performed by dynamic mechanical equipment. The morphological analysis showed the formation of a nanowhiskers/nanoscale structure in the CNW sample. The FTIR analysis of the CNW sample showed absorption band that is characteristic of cellulose. The XRD analysis indicated a small decrease in the crystallinity index and crystallite size, although the cellulose type-I structure was maintained. No changes were observed in the thermal stability of the CNW sample after the mechanical grinding process until 350 °C. A greater increase in the Young modulus was observed for the CNW sample.

Obtenção de espumas flexíveis de poliuretano com celulose de Pinus elliottii

Neste trabalho foram desenvolvidas espumas flexiveis de poliuretano com a adicao de celulose de Pinus nas concentracoes de 0,5; 1 e 2% (m/m). A celulose foi submetida ao processo de fibrilacao mecânica e posterior secagem por aspersao (spray dry) sendo caracterizada quanto a sua morfologia por MEV e MET. As espumas foram produzidas pelo metodo de batelada (one-shot) com a adicao e mistura da fibra junto ao poliol. As espumas foram caracterizadas por MEV, densidade aparente e resistencia a compressao. Os principais resultados indicam que a fibrilacao mecânica promove a obtencao de fibras em escala nanometrica, porem durante a secagem, ocorre aglomeracao ocasionando aumento para escala micrometrica. As propriedades mecânicas da espuma obtiveram acrescimos de 40 e 50% na resistencia a compressao com a adicao de 0,5 e 1% de celulose, respectivamente, evidenciando seu potencial como aditivo alternativo para o desenvolvimento de espumas de poliuretano.