Abstract Introduction Alkaline treatments extract hemicellulose from the fibers, which can be reused in the manufacture of other materials, and the cellulosic portion can be applied as reinforcement in a composite. This way, all components of the fibers are utilized. Method In this work, curaua fibers (Ananas erectifolius) were treated with potassium hydroxide (KOH) to solubilize part of the hemicellulose and lignin, and the cellulose-rich fibers were used to manufacture composites with unsaturated polyester, which were characterized to investigate the effect of the treatment on their properties. Result The alkaline treatment removed large portions of hemicellulose and significantly degraded the crystalline cellulose and lignin, resulting in a small increase (2.4%) in overall crystallinity and with a negative impact on their thermal stability. SEM images showed defibrillation of the treated fiber and fibril separation, increasing roughness and surface contact area. Conclusions In all, although the alkaline treatment substantially modified the fibers and no significant changes were observed in the mechanical properties of the composite, the total removal of hemicellulose was found to affect the integrity of cellulose fibers making harder their application as reinforcement. However, the higher cellulose content could be useful for other applications.
Resumen Introducción Los tratamientos alcalinos extraen hemicelulosa de las fibras, las cuales pueden ser reusada en la manufactura de otros materiales, de la cual la fracción celulósica puede ser aplicada como un refuerzo en un compósito. De esta manera, todos los componentes de las fibras son utilizados. Método En este trabajo, las fibras de curaua (Ananas erectifolius) se trataron con hidróxido de potasio (KOH) para solubilizar la parte de la hemicelulosa y lignina, en donde las fibras ricas en celulosa se emplearon para fabricar compósitos con poliésteres insaturados, los cuales se caracterizaron para investigar el efecto del tratamiento en sus propiedades. Resultados El tratamiento alcalino remueve grandes porciones de hemicelulosa y degradaron de manera significativa la celulosa cristalina y la lignina, resultando en un ligero incremento en la cristalinidad total (2.4%) y con un impacto negativo en su estabilidad térmica. Las imágenes de SEM mostraron la desfibrilación de las fibras tratadas y la separación fibril, aumentando la rugosidad y el área de superficie de contacto. Conclusiones Resumiendo, aunque el tratamiento alcalino modifica sustancialmente las fibras, ningún cambio significativo se observa en las propiedades mecánicas del compósito, además, se encontró que la remoción total de la hemicelulosa afectaba la integridad de las fibras de celulosa, dificultando su aplicación como un refuerzo. Sin embargo, el mayor contenido de celulosa podría ser útil para otras aplicaciones.
Vinyl ester resins are widely used in sandwich composite structures. Because of their good resistance to chemicals, flexibility and easy processing, these sandwich are extensively applied in the marine sector. These composites are typically manufactured by liquid molding processes, especially infusion. In this study, RTM light was used to inject the polymeric resin into the mold cavity, flowing in the space between the impermeable core and the mold walls, where the fibrous medium was. In this process, viscosity, gel time and curing time of the resin are very important parameters. This work addressed the curing and post-curing characteristics of a vinyl ester resin, and also the characteristics of neat and reinforced vinyl ester using dynamic mechanical analysis (DMA). The increase in shear rate did not significantly influence resin viscosity within the studied range. Differential scanning calorimetry showed the efficiency of the post-curing stage, with the decrease in residual enthalpy. With DMA, it was possible to determine gel time and gel temperature, which yielded similar values to those found by the SPI (Society of the Plastics Industry) method, indicating that the simpler SPI method can be reliably used for that.
The interest in the use of vegetable fibers (e.g. jute, sisal and curaua) for more noble applications, such as reinforcement in polymeric composite materials, has increased over the years due to a variety of aspects, especially those related to environmental legislation and community awareness regarding the life cycle of products. In this context, the aim of this work is to develop hybrid interlaminate curaua/glass/insaturated polyester composites by hot compression molding and to analyze their mechanical properties as a function of the thickness of the laminate. The short beam strength of the thickest sample decreased due to its higher void content. Furthermore, the thinnest sample showed lower hardness, and lower impact, tensile and Iosipescu shear strength, partly attributed to its lower fiber volumetric fraction. Thus, in general, the most adequate laminate was the one comprising eight layers, four of which were of glass fiber and four of curaua fiber, but only if flexural loading is not critical.
O interesse do uso de fibras vegetais (ex. juta, sisal e curauá) para aplicações mais nobres, como em reforço de materiais compósitos poliméricos, vem aumentando com o passar dos anos devido a aspectos diversos e, em especial, à legislação ambiental e à conscientização sobre o ciclo de vida dos produtos. Diante deste contexto, o objetivo deste trabalho é obter materiais compósitos híbridos interlaminares curauá/vidro/poliéster insaturado por moldagem por compressão à quente e analisar a dependência das suas propriedades mecânicas com a espessura. A resistência short beam da amostra mais espessa diminuiu devido ao seu maior teor de vazios. Além disso, a amostra mais delgada apresentou menor dureza, e resistência ao impacto, à tração e ao cisalhamento Iosipescu, atribuído em parte a sua menor fração volumétrica de fibras. De modo geral, o laminado considerado mais adequado foi aquele formado por oito camadas, sendo quatro de fibra de vidro e quatro de curauá, desde que esforços fletores não sejam críticos.
Nanocomposites based on epoxy and a mixture of clays and multi-walled carbon nanotubes (MWCNT) were produced by casting, and also molded by RTM using glass fibers as reinforcement, yielding a hybrid multi-scale micro/nanocomposite material. Two types of montmorillonite clays were used, natural (MMT-Na) and organophilic (MMT-30B). Higher viscosity was obtained for the mixture with MMT-30B and it was observed that this clay did not perform as well as the MMT-Na in helping the dispersion of the carbon nanotubes (CNT). The glass transition temperature (Tg) of the nanocomposites increased in up to 6 °C with the addition of MWCNT and up to 10 °C with the addition of MMT-30B, differently from the MMT-Na which did not alter the Tg of the material. By transmission electron microscopy, it was verified that more homogeneous dispersions and more intercalated structures were obtained with the MMT-30B than with the MMT-Na. Finally, the low clay content used and, especially, the very low MWCNT content, did not significantly alter the studied flexural properties.
Resin Transfer Molding (RTM) is a manufacturing process in which a liquid resin is injected into a closed mold pre-loaded with a porous fibrous preform, producing complex composite parts with good surface finishing. Resin flow is a critical step in the process. In this work, the numerical study of the resin flow in RTM applications was performed employing a general Computational Fluid Dynamics software which does not have a specific RTM module, making it necessary to use the Volume of Fluid method for the filling problem solution. Examples were presented and compared with analytical, experimental and numerical results showing the validity and effectiveness of the present study, with maximum difference among these solutions of around 8%. Besides, based on the computational model for the RTM process, a new computational methodology was developed to simulate Light Resin Transfer Molding (LRTM). In this process, resin is injected into the mold through an empty injection channel (without porous medium) which runs all around the perimeter of the mold. The ability of FLUENT® package to simulate geometries which combine porous media regions with open (empty) regions was used. Two specific cases were simulated, showing the differences in time and behavior between RTM and LRTM processes.
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.
In this work, a varied amount of acetone was employed to dissolve an epoxy resin and then a route was followed to remove the acetone, simulating a frequently used method to disperse nanofillers in thermoset matrices. Analyses were then carried out to address the influence of residual acetone on the curing process and on the epoxy properties. The results showed a detrimental effect on the mechanical properties of the cured epoxy due to the presence of residual acetone and also a less brittle-like fracture of the specimen. Fourier transform infrared spectroscopy and thermogravimetric analyses were additionally used to characterize the cured resins and have also indicated the presence of a small amount of acetone. Nevertheless, rheological measurements indicated that 10.0 wt.% acetone addition on the resin causes a significant decrease in viscosity (around 50%) which may promote a better dispersion of nanofillers.
Flexible multilayer plastic films may be used for the thermoforming of packages for meat products. In this case, the packages must meet the technical requirements of medium or high barrier to oxygen, depending on the characteristics of the food product, in order to avoid contamination during its shelf-life and consequently risk to human health. However, the thermoforming process alters the original characteristics of the plain films, which could render them inadequate to use, especially in the deepest corners of the packages, which are the critical points. This work addressed the thermoforming effects on the properties of two multi-layered plastic films, called medium barrier (MB), comprising PP/tie/PA6/tie/PA6/tie/LDPE, and high barrier (HB), where the central adhesive (tie) layer was replaced by a layer of ethylene vinyl alcohol copolymer (EVOH). The characterization of the films included investigations of thickness, oxygen permeability, and mechanical and optical properties.
Filmes plásticos flexíveis multicamadas podem ser utilizados como embalagens termoformadas de produtos alimentícios à base de carne, sendo que para esta aplicação, necessitam apresentar especificações técnicas de média ou alta barreira ao oxigênio, dependendo das características do produto a ser embalado, de forma a evitar sua contaminação e risco à saúde humana durante seu tempo-de-prateleira. No entanto, o processo de termoformação altera as características dos filmes planos originais. O processamento pode fazê-los não mais atender às especificações exigidas, principalmente nos cantos das embalagens, que são os pontos críticos. Neste trabalho, foram avaliados os efeitos da termoformação em propriedades de filmes plásticos multicamadas denominados de média barreira, compostos de PP/Adesivo/PA6/Adesivo/ PA6/Adesivo/PEBD, e de alta barreira, onde a camada intermediária de adesivo foi substituída por uma camada de copolímero de etileno-álcool vinílico (EVOH). A caracterização dos filmes incluiu investigações de espessura e taxa de permeabilidade ao oxigênio, além das propriedades mecânicas e óticas.