Frederico Muylaert Margem

Thermogravimetric Stability of Polymer Composites Reinforced with Less Common Lignocellulosic Fibers - an Overview

Environmental, economic, and technical reasons justify research efforts aiming to provide natural materials with possibility of replacing synthetic fiber composites. Commonly known lignocellulosic fibers, such as jute, sisal, flax, hemp, coir, cotton, wood, and bamboo have not only been investigated as reinforcement of polymeric matrices but already applied in automobile components. Less common fibers, such as curaua, henequen, fique, buriti, olive husk, and kapok are recently being studied as potential reinforcement owing to their reasonable mechanical properties. The relatively low thermal stability of these fibers could be a limitation to their composites. The works that have been dedicated to analyze the thermogravimetric stability of polymer composites reinforced with less common lignocellulosic fibers were overviewed.

The dynamic-mechanical behavior of epoxy matrix composites reinforced with ramie fibers

The exceptional tensile strength of ramie fiber has motivated investigations on its application as reinforcement in polymeric composites. In this study the temperature variation of the dynamic-mechanical parameters of epoxy matrix composites incorporated with up to 30% in volume of ramie fiber were investigated by DMA tests. The parameters were the storage modulus, loss modulus and tangent delta. The investigation was conducted in the temperature from 20 to 200°C in an equipment operating in its flexural mode at 1 Hz under nitrogen. The results showed that the incorporation of ramie fiber tends to increase the viscoelastic stiffness of the epoxy matrix. It was also observed sensible changes in the structure damping capacity when the fraction of fiber is increased in the composite. These results indicate that the segmental mobility of the epoxy chains is affected by interaction with ramie fibers in the composite.

Ballistic Efficiency of an Individual Epoxy Composite Reinforced with Sisal Fibers in Multilayered Armor

Sisal fibers are among the natural lignocellulosic ones with great impact resistance for potential use in polymer composites. This work evaluates the ballistic efficiency of the distinct individual components of a multilayered armor. These include the front ceramic, the back metallic sheet and the intermediate layer as either the conventional aramid fabric or a novel sisal fiber reinforced epoxy composite. Sisal fibers incorporated in epoxy resin plates with volume fraction of 30% were ballistic tested using the 7.62 caliber ammunition. The fibers were embedded under pressure in the epoxy resin matrix and cured at room temperature for 24 hours. The tested specimens were examined by scanning electron microscopy.

Thermogravimetric Stability Behavior of Less Common Lignocellulosic Fibers - a Review

A review on the thermogravimetric behavior of some less-common natural lignocellulosic fibers is presented. The review was limited to works analyzing results on the weight loss variation with temperature by means of the thermogravimetric (TG) curve and its derivative (DTG) for uncommon fibers such as curaua, rice, wheat straw, henequen, piassava, fique, date palm, buriti, artichoke, grass, okra, sponge gourd, caroa and olive husk. Relevant parameters obtained from corresponding TG/DTG curves were discussed to highlight distinctions and similarities in the thermal stability of these fibers. The concept of fiber thermal degradation is critically examined in view of the decomposition stages associated with the main constituents: water, hemicellulose, lignin and cellulose. The effect of fiber thermal degradation on possible application as polymer composite reinforced is remarked.

Dynamic-Mechanical Behavior of Malva Fiber Reinforced Polyester Matrix Composites

Dynamic-mechanical (DMA) tests have not yet been conducted in malva aligned fiber reinforcing polymeric composites. In this work, the temperature dependence of the DMA parameters in polyester matrix composites reinforced with up to 30% in volume of continuous and aligned malva fibers was investigated. These parameters were the storage and the loss modulus as well as the tangent delta. The investigation was conducted in the temperature interval from-20 to 180°C using a Perking-Elmer DMA equipment operating in flexural mode. The results showed that the incorporation of malva fibers tends to increase the viscoelastic stiffness of the polyester matrix. Sensible modifications in the glass transition temperature and the damping capacity of the structure were found with the amount of fiber in the composite. The molecular mobility of the polyester matrix is affected by its interaction with the malva fibers.

Interfacial Shear Strength in Lignocellulosic Fibers Incorporated Polymeric Composites

Lignocellulosic fibers have been recognized as attractive fillers for different types of matrices in polymeric composites. Their advantages such as recyclability and renewability are unique characteristics for composites used as automobile components and building structural panels. In view of the hydrophobic behavior of most polymers and the hydrophilic nature of lignocellulosic fibers, poor adhesion is observed between lignocellulosic fibers and the polymeric matrix, which results in lower mechanical properties. Pullout tests have been successfully used to determine the interfacial shear stress in synthetic fiber-reinforced composites, but little has been reported in the case of lignocellulosic fiber–polymer composites. This chapter presents an overview on the determination of the interfacial strength of lignocellulosic fibers–polymer matrix composites including some obtained by the authors on Brazilian fibers such as curaua, ramie, and piassava, considered as reinforcement for composites. Concluding remarks and suggestions indicate some future works.

Effect of the Fiber Equivalent Diameter on the Elastic Modulus of Eucalyptus Fibers

Environmental, economical, societal and technical advantages are today favoring natural lignocellulosic fibers over glass fiber. However, natural fibers are not as uniform in their dimension and properties as compared to synthetic ones. In recent works, it was found that the variation in strength could be correlated to the diameter for several lignocellulosic fibers, including that obtained from the eucalyptus wood. The present work investigated a possible correlation of the diameter with changes in the elastic modulus of eucalyptus wood fibers. Precise measurements of the equivalent diameter, conducted in a profile projector, were correlated with the elastic modulus by means of the Weibull statistic analysis. The results showed that an inverse correlation with the diameter applies for the elastic modulus with a reasonable degree of precision. SEM observation of the eucalyptus fiber, both it its structure and fracture aspects, strongly indicates that defects and microfibrils participation could be responsible for the inverse correlation.

Dynamic-Mechanical Analysis of Polyester Composites Reinforced with Giant Bamboo (Dendrocalmus giganteus) Fiber

To investigate the variation with temperature of the dynamic-mechanical parameters for the polyester matrix composites incorporated with up to 30% in volume of giant bamboo fiber was the motivation of this work. The analyzed parameters were the storage modulus, the loss modulus and the delta tangent. The investigation was conducted in the temperature interval from 25 to 195°C in a DMA equipment operating at 1 Hz of frequency under a flow of nitrogen. The results showed that the incorporation of long and aligned giant bamboo fibers tends to increase the viscoelastic stiffness of the polyester matrix. By contrast, only minor changes occurred in both the glass transition temperature and the damping capacity of the structure as measured by the tan δ peaks. These are indications that the polyester molecular mobility is not sensibly affected by interaction with the bamboo fibers in the composites.

Tensile Strength of Polyester Matrix Composites Reinforced with Giant Bamboo (Dendrocalmus giganteus) Fibers

Fibers of the giant bamboo (Dendrocalmus giganteus) are amongst the strongest lignocellulosic fibers. Although studies have been already performed, limited information exists on the mechanical properties of polymeric composites reinforced with continuous and aligned giant bamboo fibers. This work evaluates the tensile strength of this type of composite. Standard tensile specimens were fabricated with up to 30% of fibers aligned along the specimen length. The fibers were press-molded with a commercial polyester resin mixed with a hardener and cured for 24 hours at room temperature. The specimens were tensile tested in an Instron machine and the fracture surface analyzed by scanning electron microscopy. The tensile strength increased significantly with the amount of giant bamboo fiber reinforcing the composite. This performance can be associated with the difficult of rupture imposed by the fibers as well as with the type of cracks resulting from the bamboo fiber/polyester matrix interaction, which prevents rupture to occur.

Characterization of Banana Fibers Functional Groups by Infrared Spectroscopy

A number of methods are available for characterization of the structural, physical, and chemical properties of natural fibers. Various methods are used for fiber identification like microscopic analysis, solubility, heating and burning technique density, staining etc. End-use property characterization methods often involve use of laboratory techniques which are adapted to simulate actual application as composite reinforcement. One of the techniques used on this kind of studies is the infrared spectroscopy. In fact, Fourier Transform Infrared (FTIR) spectroscopy is a valuable tool in the determination of functional groups actively interacting within a fiber. In this work, the banana fiber was evaluated by FTIR to reveal these functional groups and compare to similar works on other different types of banana fibers.