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The growing environmental awareness in the last few decades has driven the research and development of composites reinforced with natural fibers as an alternative to replace synthetic fiber composites. However, their hydrophilic character and surface heterogeneity may be considered a challenge to allow reliable and wide application of these materials. One way to overcome this drawback is the modification of the surface of the fiber by chemical and/or physical treatments. Among these treatments, the graphene oxide (GO) has stood out due to its amphiphilic character. In the present work, the influence of GO-treatment in piassava fiber was investigated. The interfacial adhesion between the piassava fiber, both untreated and with GO, and the epoxy resin was evaluated by pullout tests. Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were also performed to verify the effectiveness of the GO-treatment on the piassava fiber. The fiber’s surface morphology was further investigated by scanning electron microscopy (SEM). The GO-treatment of the piassava fiber enhanced the interfacial shear strength by ∼171% more than untreated fibers. This could allow new applications of these eco-friendly composites as high-performance materials.

Novel nanocomposites of polyamide-11 (PA11) reinforced with commercial graphene nanoplatelets (GNP) in amounts of 1.0, 2.5, and 5.0 wt.% were prepared and characterized for their thermal stability and aging performance. The processing of the nanocomposites was carried out by mixing PA11 in the molten state employing a double screw mini-extruder at 200 °C under 60 rpm screw speed, with a residence time of 7 min. The incorporation of GNP increased the thermal stability of PA11, particularly in the amount of 1.0 wt.%, as observed by thermogravimetric analysis. X-ray diffraction indicated that the composites' crystallinity increased with 1.0 and 2.5 wt.% of GNP. Evidence of agglomerates formation in the sample with 5.0 wt.% of GNP suggests it to be less dispersed in the PA11 matrix and associated with reduction in crystallinity. The dynamic mechanical analysis showed that GNP promoted an increase in the storage and loss moduli. The increase of GNP in the PA11 matrix enhanced the water contact angle and, therefore, provided greater hydrophilicity of the nanocomposite. The GNP reinforcement prevents the decrease in the molar mass of PA11, estimated by the corrected inherent viscosity (CIV) measured with aging time into water at 85 °C, when compared to the performance of neat PA11. All nanocomposites had CIV values above 1.20 dL/g before and after the aging test. Therefore, using the lowest GNP content of 1.0 wt.% proved to be the more efficient for application in flexible oil/gas pipelines.

Polycaprolactone (PCL) bionanocomposites reinforced with microfibrillated cellulose (MFC), either plain or modified with 2 wt% of zinc oxide (ZnO) nanoparticles, were first time developed for possible application as multifunctional packing. The MFC was obtained by an alkali treatment, a steam explosion process, and ZnO modification applied to parchment (PAR), a husk waste from the coffee industry. X-ray diffraction (XDR), thermogravimetric analysis (TGA/DTG), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), tensile tests, and CO2 permeability characterized the MFCs and the bionanocomposites. As for the MCFs, the crystallinity index of 50.6% measured by XRD for the plain PAR fiber increases with the combined alkaline treatment and steam explosion (CFA/EXP) to 68.2%, and further with ZnO modification (ZnO-CFA/EXP) to 80.1%. TGA/DTG displays a rising onset of thermal degradation from 214 to 306 °C, as well as maximum degradation rate from 330 to 350 °C, for PAR and ZnO-CFA/EXP, respectively. Regarding the nanocomposites, the addition of 3 wt% of alkali/steam explosion and ZnO-modified CFA/EXP contributes to enhancing thermal stability. Tensile tests disclosed improved mechanical properties of the novel nanocomposites as compared to the PCL matrix. In particular, Young's modulus rose from 88.5 to 169.5 MPa for the plain PCL and PCL reinforced with 3(ZnO-CFA/EXP), respectively. SEM images evidenced the participation of cellulose micro and nanofibrils in the PCL matrix. Approximately 20% reduction in the CO2 permeability coefficient of both PCL and its 3CFA/EXP nanocomposite compared with 3(ZnO-CFA/EXP) proved that the ZnO nanoparticles provide a gas barrier to the nanocomposite, a convenient property for food packing.

Among the natural fibers, the hemp fiber extracted from the stem of Cannabis sativa is, after sisal, the second most applied as reinforcement of polymer composites and increasingly used from automotive to civil construction industries. Polypropylene (PP) is the most common hemp fiber-reinforced matrix. Despite numerous papers on the application of natural fibers reinforcing polymer composites for ballistic protection, only one was so far dedicated to hemp fibers/PP with this purpose. In the present work, the main objective is for the first time to investigate the ballistic performance of the epoxy matrix reinforced with up to 30 vol% of hemp fabric. Epoxy is recently emerging as another strong alternative for the hemp fiber/fabric matrix. Due to the great variability in properties, a preliminary investigation was conducted on the basic mechanical and thermal behavior of the composites. The 30 vol% reinforcement with hemp fabric increased by 7.5 times the Izod impact energy as well as by more than 60% the tensile strength and 80% of the elastic modulus as compared to the neat epoxy. For all composites, a decrease of 20% in thermal temperatures (Tonset and Tmax) occurred in comparison to neat epoxy. The absorbed ballistic energy from the impact of 0.22 ammunition was significantly higher (95–108.5 J) than that previously reported of 36 J for hemp fabric/PP composite and others natural fiber/epoxy composites.

As an alternative for ordinary Portland cement, geopolymers are cost effective materials that can be prepared with relatively low energy consumption and substantial reduction of CO2 emissions. In the present study the characteristics of novel hybrid composite of geopolymer foam (GPF)/polylactic acid (PLA) and their efficiency in removing copper(II) and zinc(II) to treat high volumes of polluted water are investigated. Contrary to the conventional methods for removing heavy metals, the newly developed composites are ecological, low-cost, easily available, and economically viable alternatives providing good physical-chemical stability, ion-exchange properties, and a porous structure. Based on the sustainable advantage to produce geopolymers from recycled materials, GPFs were obtained from blast furnace slag (BFS) by reacting 20 ml of an 8 M alkaline solution of sodium metasilicate (Na2SiO3) with BFS particles and later addition of hydrogen peroxide. GPFs were produced with a stoichiometry of 1.4 and 1.6 g/L between BFS/alkali solution with a 1.6 ml solution of hydrogen peroxide 50% to develop porosity into the materials. Finally, the GPFs were coated with PLA. Specimens of GPF/PLA composites were characterized by X-ray fluorescence spectroscopy, Fourier transformed infrared spectroscopy, thermogravimetric analysis, dynamic mechanical analysis, and field emission gun scanning electron microscopy. Adsorption analysis of Cu(II) and Zn(II), as well as ion-exchanges from aqueous solution through the composite with 1.4 and 1.6 stoichiometry, were performed using deionized water containing 0.80% Cu(II) or Zn(II). The test resulted in high performance for retaining Cu(II) and Zn(II). Under CO2 pressure at 50 bar, the gas permeation tests confirmed porous formations into the geopolymer foams coated with molten PLA.

In the present work, two types of composites were produced, both reinforced with 30 vol% of curaua fibers (CF). In the first type, only the fiber was functionalized with graphene oxide (GO), producing the GOCF/EM composite. While in the second, only the epoxy matrix (EM) was functionalized, producing the CF/GOEM composite. The objective of the work was to investigate the influence of functionalization with GO on the tensile properties of these produced composites. In comparison with the non GO-functionalized composite, as control CF/EM, the results revealed an increase in yield strength (64%), tensile strength (40%), Young's modulus (60%) and toughness (28%) of the CF/GOEM composite. The GOCF/EM composites for which the fibers were functionalized with GO also performed better than the CF/EM composite. The ANOVA and Tukey tests confirm this increase. As for ductility, within the standard deviation, no change was observed between samples functionalized by GO and those from the control. For the first time, comparing the results of the composites, it was demonstrated that a polymer matrix functionalized by GO offers superior tensile performance compared to the other types, keeping the same GO concentration in the composite. This fact is corroborated by the analysis of the corresponding fracture mechanisms. Preliminary results of composite with simultaneous functionalization of both fiber and epoxy matrix failed to present superior properties. This might be attributed to high amount of GO, which is apparently not a good reinforcement as the curaua fiber.

The arapaima is a large Amazonian freshwater fish and an example of a natural protective system against predators such as the piranha fish. In this work, both the plain scales and a 30 vol% of arapaima scales reinforced epoxy composite were characterized for their structure, composition and morphology. The characterization was performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The SEM images showed that the surface morphology of the scales was not altered by the flattening process applied before composite manufacturing. The EDS results confirm that the percentage of calcium is higher in the scale outer layer, which also shows the presence of phosphorous. The evidence of collagens in the plain scales as well as the presence of hydroxyl groups and absorption bands related to the epoxy group in the composites were revealed by FTIR. Mechanical bend tests disclosed the toughening contribution of arapaima scales to the composite epoxy matrix. Nanoindentation testing confirms the higher hardness of the scale outer layer associated with calcium participation. These experimental results provide, for the first time, an initial view of the arapaima scales potential for use as reinforcement in novel polymer composites.

Natural lignocellulosic fibers have been studied as cost-effective reinforcements in composites for engineering applications that, in some cases, may require exposure to temperatures above ambient. In the present work a promising fiber extracted from a Brazilian palm tree, the piassava fiber both neat as well as graphene oxide (GO) functionalized, had their thermal behavior analyzed jointly with corresponding epoxy composites. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were for the first time employed to assess the thermal properties of the GO-coated piassava fiber. Dynamic mechanical analysis (DMA) investigated innovative epoxy matrix composites reinforced up to 30 vol% of both neat and GO-coated piassava fiber. TGA/DTG results indicate a limit of thermal stability of about 200 °C for the neat piassava fiber. On the other hand, the hemicellulose and lignin maximum degradation rates occurred at relatively higher temperatures for the GO-coated piassava fibers. The DSC analysis revealed an endothermic peak at about 125 °C for the neat piassava fiber associated with the breakage of molecular bond, which was not found for the GO-coated fibers within the maximum interval of temperature analyzed. The DMA parameters revealed notable changes attributed to the effect of GO coating on the piassava fibers regarding the viscous stiffness and damping capacity of the epoxy composite.

In the aluminum industry, the initial operation comprises the production of its oxide, Al2O3 (alumina) from ores, mainly the bauxite. The Bayer process is, in practice, the only used to produce alumina generating a huge amount of hazardous waste known as red mud. Among the proposed alternatives to consider red mud a useful by-product, the incorporation into clay ceramics allows large quantities to be reutilized as construction products. Several research works investigated this alternative but were limited to single clay incorporation without specific application in building construction products. In the present work the possibility of producing bricks and roofing tiles for building construction with plain red mud and incorporations separately, in two different clays, with low and high plasticity, was for the first time investigated. Both red mud and clays were characterized. Corresponding ceramics fired at 850, 950 and 1050°C were evaluated for their technological properties. The results indicated that plain red mud fired at any of these temperatures might be used as bricks according to the Brazilian standards. It could also be used for roofing tiles production when fired at 1050°C. Application in bricks for building construction and a preliminary environmental assessment were for the first time presented. Keywords: Red mud ceramic, Plain ceramic, Clay incorporated ceramic, Bricks and tiles

The aim of this work is to characterize properties and microstructure of AISI 316L stainless steel used as a coating on welding of carbon steel sheets. Two carbon steel plates were set as the metal base and the stainless steel coating was applied on the weld bead. The applied process used was the submerged arc welding (SAW) and tests were carried out for the tensile strength and Vickers hardness, in addition to observation of the microstructure by optical microscopy. The results indicated that the stainless-steel coating applied on the weld bead provided relatively high values of tensile strength. Moreover, the hardness values suggest that the investigated innovative material can be applied in corrosive environments. Keywords: Carbon steel, Stainless steel, Coating, Welding

Engineering applications involving polymer composites reinforced with natural lignocellulosic fibers (NLFs) have greatly increased in recent decades due to advantages associated not only with favorable composite properties but also fiber sustainability and cost-effectiveness. A search for less common NLFs is currently an endeavor for the development of novel composites with improved properties. In particular, for applications above room temperature, the thermal resistance must be characterize. In the present work composites reinforced with up to 30 vol% fabric made of buriti, a relatively unknown natural fiber from Brazil, with limited reported information, were characterized by thermogravimetric/derivative (TG/DTG) and dynamic mechanical analysis (DMA). Preliminarily, the plain buriti fiber was investigated in terms of X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and TG/DTG analysis. XRD pattern allowed, for the first time, the evaluation of a microfibril angle of 7° and crystallinity index of 63%. FTIR bands for buriti fibers were also obtained with expected results. TG/DTG results indicate for the buriti fiber a limit degradation temperature around 200 °C and for the buriti fabric epoxy composites at about 250 °C. Dynamic mechanical analysis of composites disclosed similar viscoelastic stiffness values but an increasing glass transition temperature with the amount of buriti fabric. Keywords: Buriti fabric, Epoxy composites, Natural fiber composites, Thermal analysis, Structural characterization

The ballistic performance of multilayered armor system (MAS) with front ceramic tile, followed by a laminate of up to 50 vol.% of fique fabric-reinforced epoxy matrix and back by a 5062H34 aluminum alloy was evaluated. The backface signature (BFS) caused by the bullet in a block of clay witness behind the target was used to evaluate the MAS ballistic performance according to international standards. The results using high-velocity 7.62 mm ammunition show a BFS similar to a MAS second layers of Kevlar™ laminate with the same thickness. The Weibull analysis statistically provides the reliability of BFS test results. Fracture examinations by scanning electron microscopy (SEM) revealed that the epoxy-fique fabric composite has different types of energy dissipation mechanisms. These are the same capture of ceramic fragments by a mechanic of incrustation presented in Kevlar™ laminate. Among the tested materials, the 40 vol.% fabric composite was found to be a better alternative to replace Kevlar™. The lower cost of the epoxy-fique fabric composite is an additional advantage that favors its substitution for the aramid fabric. Keywords: Fique fiber, Natural fiber composite, Weibull analysis, Ballistic performance

Reinforcement of polymer matrices with natural lignocellulosic fibers (NLFs) is today presenting great potential for the reduction of both product weight and cost in many industrial sectors as well as the advantage of being renewable and eco-friendly materials. For some industrial applications, especially in ballistic armor, the materials are expected to meet technical and mechanical requirements in terms of impact behavior, which motivate the present work. This work conducted a notch toughness assessment by Izod and Charpy impact tests of epoxy matrix composites reinforced with different volume fractions of fique fabric, up to 50 vol%. Statistical analyses indicated significant differences between composites with distinct amount of fique fabric. Failure mechanisms were analyzed by scanning electron microscopy (SEM). The results revealed that composite reinforced with 40 vol% of fique fabric presented the best notch toughness performance. Composites with 15 and 30 vol% of fique fabric display predominantly brittle fracture associated with lower impact energies. With higher amount, 50 vol%, of fique fabric reinforcement both Izod and Charpy impact energy suffered a small decrease according to the Roger and Plumtree model. Keywords: Fique fabric, Impact tests, Epoxy matrix, Natural fiber composite

A spent tire without the legal possibility of running is classified as unserviceable tire waste. In this work, incorporation of rubber tire waste (RTW) in clay ceramics used in the production of bricks and roofing tiles was for the first time evaluated. The raw materials were initially characterized in terms of its mineralogical and chemical composition by X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. Physical and mechanical properties of RTW incorporated ceramics such as bulk density, water absorption, linear shrinkage, flexural and compressive strength were determined. Besides, thermal analyses by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were carried out in the plain RTW. Different ceramic compositions were prepared with amounts of 0.5; 1; 1.5 and 2 wt% RTW incorporated into the clay ceramic. Prismatic specimens were prepared by uniaxial pressing and then sintered at 850 and 950 °C. The results indicate that the investigated waste contributes to a saving in energy during the ceramic sintering due to its high amount of carbon. An increase in the ceramic porosity above 1.5 wt% of RTW was responsible for increasing the water absorption. Within standard deviations, both the shrinkage and strength were not impaired. The clay ceramic with 1 wt% of RTW sintered at 950 °C was the most suitable condition observed. Hence, these results showed a viable alternative to RTW, turning it into an environmentally friendly by-product for civil construction materials. Keywords: Tire waste, Waste incorporation, Clay ceramic, Physical properties

Fiber-reinforced composites are among the most investigated and industrially applied materials. Many studies on these composites using fibers, especially with natural fibers, were made in response to an urgent action for ambient preservation. A particularly relevant situation exists nowadays in the area of materials durability. In this respect, no studies on water-immersion-accelerated aging in fique fiber–epoxy composites are reported. This work aimed to fill this gap by investigating the epoxy matrix composites reinforced with 40 vol% fique fabric. The epoxy matrix and the composite, both unaged and aged, were characterized by weight variation, water absorption, morphology, colorimetry (CIELAB method), Fourier transform infrared spectroscopy (FTIR) and dynamic–mechanical analysis (DMA). The main results were that degradation by water presents appearance of complex microfibril structures, plasticization of epoxy resin, and debonding of the fique fiber/epoxy matrix. The most intense color change was obtained for the water-immersion-aged epoxy by 1440 h. Cole–Cole diagrams revealed the heterogeneity of the materials studied.

The titica vine fiber (TVF) (Heteropsis flexuosa) is a natural lignocellulose fiber (NLF) from the Amazon rainforest that was, for the first time, investigated in terms of its basic properties such as dimensions, porosity, and density as well as its chemical composition, moisture content, crystallinity, and microfibrillar angle. In this study, the apparent density of TVF was determined as one of the lowest-ever reported for NLFs). Using both the geometric method and Archimedes’ principle, density values in the range of 0.5–0.6 g/cm3 were obtained. The moisture content was measured as around 11%, which is in accordance with the commonly reported values for NLFs. The TVF exhibited a high porosity, approximately 70%, which was confirmed by SEM images, where a highly porous morphological structure associated with the presence of many voids and lumens was observed. The crystallinity index and microfibrillar angle were determined as 78% and 7.95°, respectively, which are of interest for a stiff NLF. A preliminary assessment on the mechanical properties of the TVFs revealed a tensile strength, Young’s modulus, and elongation of 26 MPa, 1 GPa, and 7.4%, respectively. Furthermore, the fiber presented a critical length of 7.62 mm in epoxy matrix and an interfacial shear strength of 0.97 MPa. These results suggest the TVFs might favors applications where lighter materials with intermediate properties are required.

Cements from alkali-activated reactions are unleashing opportunities for the future application of inorganic polymers, known as geopolymers. These materials are eco-friendly, since their manufacturing process does not involve carbon dioxide (CO2) emission and it makes possible the use of industrial waste as raw material. In this work, a geopolymeric cement concrete (GCC) was developed through adequate portions of geopolymer components. Its characteristics were compared with Portland cement concrete (PCC), through the establishment of some parameters of design such as consumption of binders, water/aggregates ratio and cement content. The mechanical performance of these concretes was evaluated with emphasis on the fatigue behavior. The results showed a better fatigue performance of CCG in comparison with PCC in several parameters. Better matrix/aggregate adhesion in the CCG in comparison with PCC was also observed in the microstructural analysis, which may explain its superior fatigue performance. Keywords: Geopolymer, Concrete, Fatigue

This paper aims to present a comparison on the use of different heat treatment conditions in association with welding of a HSLA-80 steel. This investigation was carried out by multipass welding using the coated electrode process in different heat treatment conditions, with or without pre- or post-weld heating, in order to compare effects on the mechanical properties and microstructure for each condition. After welding was performed, procedures to identify microstructural phases and characterize the mechanical behavior were carried out. The results of mechanical tests and metallographic analysis were conclusive that heat treatments are not necessary to complement welding procedures of this steel. This is especially the case of the post-welding heat treatment. In fact, the application of these treatments did not significantly affect neither the microstructure nor the mechanical characteristics of the material. Keywords: Mechanical properties, Heat treatment, Microstructure, Mechanical testing

Ceramic armors are frequently used for protection against high energy projectiles, such as the 7.62 mm and 5.56 mm. Recently, it has been demonstrated that a modification in the geometry of the impact face, from flat to convex, enlarges the stress distribution zone created by the projectile-target interaction. This effect raises the projectile's energy absorption and might improve the user's safety. In the present work, the objective is to characterize ceramic armor plates with convex impact face, by means of the NIJ-0101.06 (2008) standard methodology, aiming to provide an eventual application in armor vests. The characterization is based on the measurement of the backface signature, a deformation behind armor imprinted in a reference material that simulates the consistency of the human body. The results showed significant improvement in the ballistic performance after the impact geometry modification. Keywords: Ballistic test, Ceramic armor, Multilayered armor system, Impact geometry

The mallow fiber (Urena lobata, linn) is demonstrating a great potential as reinforcement in polymer matrix composites. The difficulty in the use of the mallow, as in other natural lignocellulosic fibers (NLFs), is its hydrophilic compatibility with polymeric matrices that are typically hydrophobic. In order to improve the adhesion between the fiber surface and polymeric matrices, mallow fibers were subjected to mercerization treatment. In this work composites were produced with epoxy matrix reinforced with 30 vol% of mallow fibers, both untreated and mercerized. By means of XRD analysis it was verified the variation of crystallinity in fibers treated with different NaOH solutions as well as immersion times and agitation. After this XRD preliminary analysis, a treatment of 5% NaOH solution for 24 h without agitation was selected. The objective was to compare the Charpy impact energy of composites specimens produced with untreated mallow fibers and treated for the higher crystallinity obtained after the selected mercerization. For the analysis of impact energy the Tukey test was applied from which it could be assured, with a confidence level of 95%, that the epoxy specimens reinforced with 30 vol% of untreated mallow fibers, had the best performance. Keywords: Mallow fibers, Epoxy composite, Mercerization, Charpy impact test

The several advantages of natural lignocellulosic fibers (NLFs), such as, economical, technical, environmental and social, make these fibers an alternative to replace synthetic fibers in composite materials. The application of NLF as reinforcements in polymeric composites has increased in many industrial sectors from civil construction to automobiles. This demands the characterization of promising fibers, such as those extracted from leaves of pineapple (PALF) and the mesocarp of coconut fruit (coir fiber), for possible application in composites. In the present work, pullout tests were performed to compare the interfacial adhesion with epoxy resin of these two fibers that have greatly different characteristics. Results showed a critical length 70% higher for the coir fiber in comparison to PALF and a interfacial strength 3.5 times smaller, which indicates stronger adhesion of PALF with epoxy resin. This may be justified by the distinct morphological aspects, particularly the rougher surface of PALF. Mechanical tests were also performed in both coir fiber and PALF composites. In these tests, it was observed the superiority of mechanical properties for the composite reinforced with 30 vol% of PALF. Additionally, ballistic tests were carried out. In this evaluation, composites were used in a MAS type III against the 7.62 mm ammunition. The results revealed a relatively low depth of penetration (18.2 mm) for the MAS with PALF composite as well as a depth of penetration (31.6 mm) for MAS with coir composite, both considered efficient according to the personal body armor standard. Therefore, all these results highlight the potential of these fibers as polymer composites reinforcement in ballistic armors. Keywords: Pullout test, Natural lignocellulosic fibers, Critical length, Interface adhesion

Dynamic mechanical analysis (DMA) is one of the most common methods employed to study a material’s viscoelastic properties. The effect of thermal aging on plain epoxy and a fique fabric-reinforced epoxy composite was investigated by comparing the mass loss, morphologies, and DMA properties of aged and unaged samples. In fact, thermal aging presents a big challenge for the high-temperature applications of natural fiber composites. In this work, both plain epoxy and fique fabric-reinforced epoxy composite were found to have different molecular mobility. This leads to distinct transition regions, with different changes in intensity caused by external loadings from time-aging. Three exponentially modified Gauss distribution functions (EMGs) were applied to loss factor curves of fique fabric-reinforced epoxy composite and plain epoxy, which allowed identifying three possible mobility ranges. From these results it was proposed that the thermal degradation behavior of natural fibers, especially fique fiber and their composites, might be assessed, based on their structural characteristics and mechanical properties.

Titica vine (Heteropsis flexuosa) is a typical plant of the Amazon region commonly used for making baskets, bags, brooms and furniture, owing to its stiff fibers. In spite of its interesting properties, there is so far no reported information regarding the use of titica vine fibers (TVFs) in engineering composite materials. In this work, the TVF and its epoxy composites were for the first time physically, thermally and mechanically characterized. Additionally, the effect of two kinds of chemical treatments, one with sodium carbonate and one with calcium lignosulfonate, as well as different volume fractions, 10, 20, 30 and 40 vol%, of TVF-reinforced composites were assessed for corresponding basic properties. The thermogravimetric results of the composites reveal enhanced thermal stability for higher TVF content. In addition, the composite incorporated with 40 vol% of TVFs treated with sodium carbonate absorbed 19% more water than the composites with untreated fibers. By contrast, the calcium lignosulfonate treatment decreased water absorption by 8%. The Charpy and Izod impact tests showed that the composites, incorporated with the highest investigated volume fraction (40 vol%) of TVF, significantly increased the absorbed energy by 18% and 28%, respectively, compared to neat epoxy. ANOVA and Tukey statistical analyses displayed no direct influence of the chemical treatments on the energy absorption of the composites for either impact tests. SEM images revealed the main fracture mechanisms responsible for the performance of TVF composites.

Polymer composites reinforced with natural fabric have recently been investigated as possible ballistic armor for personal protection against different levels of ammunition. In particular, fabric made of fique fibers, which is extracted from the leaves of the Furcraea andina, was applied as reinforcement for polymer composites used in a multilayered armor system (MAS). The superior performance of the fique fabric composites as a second MAS layer motivated this brief report on the determination of the absorbed energy and capability to limit velocity in the stand-alone ballistic tests. The single plates of epoxy composites, which were reinforced with up to 50 vol% of fique fabric, were ballistic tested as targets against 7.62 mm high-speed, ~840 m/s, impact ammunition for the first time. The results were statistically analyzed by the Weibull method and ANOVA. The absorbed energies of the 200–219 J and limit velocities of 202–211 m/s were found statistically similar to the epoxy composites reinforced with the fique fabric from 15 to 50 vol%. Predominantly, these findings are better than those reported for the plain epoxy and aramid fabric (KevlarTM) used as stand-alone plates with the same thickness. Macrocracks in the 15 and 30 vol% fique fabric composites compromise their application as armor plates. The delamination rupture mechanism was revealed by scanning electron microscopy. By contrast, the integrity was maintained in the 40 and 50 vol% composites, ensuring superior ballistic protection compared to the use of KevlarTM.

Natural fiber reinforced polymer matrix composites are gaining attention as engineering materials for advanced applications, including components of high performance ballistic armors. This requires superior mechanical properties, such as tenacity. Composites reinforced with jute fiber are currently being investigated as possible advanced engineering materials. Therefore, the objective of the present work was to evaluate the impact resistance of epoxy matrix composites reinforced with up to 30 vol% of continuous and aligned jute fibers. This evaluation was performed by measuring the Charpy absorbed impact energy of standard ASTM notched specimens. The results indicated a significant increase in the absorbed impact energy with the volume fraction of jute fibers. The microstructural mechanism related to this performance was revealed by scanning electron microscopy analysis. Keywords: Jute fiber, Epoxy composites, Charpy, Impact test

The fibers extracted from the stem of the giant bamboo plant have been investigated as possible composite reinforcement due to their relatively high tensile strength. A dimensional characterization of the distribution and the effect of diameter on the mechanical resistance of bamboo fiber of the species Dendrocalmus giganteus has not yet been performed. The present work characterized the distribution of a bundle of this bamboo fiber. Based on this characterization, diameter intervals were set and the dependence of the tensile strength of these fibers with a corresponding diameter was analyzed by the Weibull method. The results indicated an inverse dependence, in which the highest tensile strength was obtained for the thinnest fibers. Moreover, a mathematical hyperbolic relationship was found to adjust well this inverse correlation. An investigation of the microstructure by means of scanning electron microscopy revealed a potential mechanism for this correlation. Keywords: Giant bamboo, Fiber diameter, Tensile strength, Weibull analysis

For personal protection against high kinetic energy projectiles, multilayered armor systems (MAS) are usually the best option. They combine synergistically the properties of different materials such as ceramics, composites and metals. In the present work, ballistic tests were performed to evaluate multilayered armor systems (MAS) using curaua non-woven fabric epoxy composites as second layer. A comparison to a MAS using aramid (Kevlarâ¢) fabric laminates was made. The results showed that the curaua non-woven fabric composites are suitable to the high ballistic applications, and are promising substitutes for aramid fabric laminates. Keywords: Composite, Natural fiber, Curaua fiber, Non-woven fabric, Aramid laminate, Ballistic test

The fibers extracted from the sugarcane bagasse have been investigated as possible reinforcement for polymer matrix composites. The use of these composites in engineering applications, associated with conditions such as ballistic armor, requires information on the impact toughness. In the present work, Charpy tests were performed in ASTM standard specimens of polyester matrix composites, reinforced with 10, 20 and 30 vol% of continuous and aligned sugarcane bagasse fibers, in order to evaluate the impact energy. Within the standard deviation, the composite absorbed impact energy increased with the volume fraction of sugarcane bagasse fiber. This toughness performance was found by scanning electron microscopy to be associated with the fiber/matrix delamination. Keywords: Sugarcane bagasse fiber, Polyester composites, Charpy test, Impact toughness

The mechanical behavior and the strengthening mechanism of stainless steel welded joints at 600 °C have been investigated. The welds were composed of AISI 304 stainless steel, as base metal, and niobium containing AISI 347 stainless steel, as weld metal. The investigation was conducted by means of creep tests. The welded specimens were subjected to both high temperature (600 °C) and long periods (up to 2000 h) under constant load, and both mechanical properties and microstructural changes in the material were monitored. It was found that the exposure of the material at 600 °C under load contributes to a strengthening effect on the weld. The phenomenon might be correlated with an accelerated process of second phase precipitation hardening. Keywords: Stainless steel, Weld, AISI 304, Precipitation hardening

Stainless steels are well known by their corrosion resistance. The austenitic types, in particular, are also applied as structural components in engineering systems operating at high temperatures such as nuclear reactors, petrochemical furnaces and turbines. For these applications operational temperatures may go up to 800ºC. Under constant load applications the main mechanism of failure, which would limit the material's life, is creep. In the present work creep parameters were evaluated in the high temperature interval of 600 to 800ºC for an AISI 316 austenitic stainless steel. Dislocation substructures were observed by transmission electron microscopy in creep ruptured specimens. Two distinct mechanisms of dynamic strain aging and dynamic recovery associated with different values for the power law exponent n and the Arrhenius activation energy Q for creep were verified below and above 700ºC, respectively.

Multilayered armor systems (MAS) composed of relatively lighter materials with capacity to provide personal ballistic protection are being extensively investigated and used in armor vests. A typical MAS to stand high impact energy 7.62 mm bullet has a front ceramic followed by an aramid fabric laminate, such as Kevlar™. Since both the army and municipal police personnel might need to wear an armor vest, a large number of vests needs to be supplied. In the case of Kevlar™, one of the most expensive MAS material with an expiration time of 5 years, the possibility of its replacement by an equally ballistic efficient low cost material and more durable could be a relevant economical advantage. Natural fibers composites have recently been investigated as possible alternatives for Kevlar™. In particular, the fiber extracted from the coconut fruit, known as coir fiber, normally disposed as waste, could be a low cost material for this purpose. Therefore, the present work investigated the possibility of using coir fiber mantle, with different volume fraction, reinforcing epoxy composites as MAS second layer. It was found that 30 vol% of coir fiber composite displayed similar ballistic performance as compared to Kevlar™ with substantial economical advantage.

The fique is a plant typical of the Colombian Andes, from which relatively common items are fabricated. One of these is woven fabric extensively applied in sackcloths. The mechanical strength of fique fabric have motivated recent investigations on possible reinforcement of polymer matrix composites. For this purpose its thermo-mechanical behavior was unveiled. In particular, dynamic mechanical analysis (DMA) of fique fabric reinforced polyester matrix composites disclosed improved viscoelastic behavior in association with change in the glass transition temperature. The present work extends this investigation to epoxy matrix, which is one of the most employed thermoset polymer for composite matrix. Fique fabric volumetric fractions of up to 50% are for the first time incorporated into epoxy composites. It was found that these incorporations significantly increased the viscoelastic stiffness of the composite, given by the storage modulus (E’), in the temperature interval from -50 to 170°C. An accentuated softening in viscoelastic stiffness was revealed for all composites above 75°C. Peaks in both the loss modulus (E”) and tangent delta (tan δ), respectively associated with the lower and upper limits of the glass transition temperature, were shifted towards higher temperatures with increasing amount of fique fabric.

Waste incorporation into clay ceramic is a worldwide accepted recycling procedure for environmentally friendly reuse of spent industrial materials. In the present work a clay ceramic from the city of Campos dos Goytacazes, Brazil, was, for the first time, investigated with different amounts, up to 10 wt%, of a solid waste generated from the “Sulfatreat” natural gas treatment process. Both the waste and the incorporated ceramic were characterized by X-ray fluorescence and X-ray diffraction as well as vibratory sieving, gas chromatography and sedimentation method. Ceramic samples were prepared by uniaxial pressing at 18 MPa and sintered at 850°C. Physical and mechanical properties of these ceramics such as linear shrinkage, apparent density, water absorption and flexural strength were evaluated. Microstructure of the incorporated ceramics was analyzed by optical microscopy. The results showed that, within the standard deviation, the linear shrinkage and apparent density of the clay ceramic were not affected by the waste incorporation. However, the water absorption is benefitted, by decreasing above 5 wt% incorporation, while the flexural strength is impaired for any incorporated amount. Porosity and larger waste particles observed in microstructure are proposed reasons for these advantages and shortcomings.

Multilayered armor systems (MAS) with a front ceramic layer backed by a relatively unknown Amazonian guaruman fiber-reinforced (Ischnosiphon koem) epoxy composites, as second layer, were for the first time ballistic tested against the threat of 7.62 mm rifle ammunition. The amount of 30 vol% guaruman fibers was investigated in three distinct configurations: (i) continuous aligned, (ii) 0–90° cross-laid, and (iii) short-cut randomly dispersed. Additionally, single-target ballistic tests were also carried out in the best MAS-performed composite with cross-laid guaruman fibers against .22 caliber ammunition. The results disclosed that all composites as MAS second layer attended the US NIJ standard with corresponding penetration depth of (i) 32.9, (ii) 27.5, and (iii) 29.6 mm smaller than the lethal limit of 44 mm in a clay witness simulating a personal body. However, the continuous aligned guaruman fiber composite lost structural integrity by delamination after the 7.62 projectile impact. By contrast, the composite with cross-laid guaruman fibers kept its integrity for subsequent shootings as recommended by the standard. The single-target tests indicated a relatively higher limit velocity for .22 caliber projectile perforation, 255 m/s, and absorbed energy of 106 J for the cross-laid guaruman fibers, which are superior to corresponding results for other less known natural fiber epoxy composites.

In recent decades, the unique characteristics of natural fibers have promoted their use as reinforcement in polymeric composites. This is verified in several industrial sectors, from packaging to automotive and civil construction. Among the natural fibers, the raffia fiber extracted from the palm tree Raphia vinifera and introduced in the Amazon region a long time ago; started to be considered for the production of polymeric composites only in recent years. For the first time, the effect of raffia fiber length and its alkali treatment on the mechanical properties of a polymer composite was disclosed. Tensile tests were performed in composites with raffia fibers randomly dispersed into terephthalate-based unsaturated polyester resin. The results showed an increase in the Young’s moduli, confirmed by ANOVA, for the composite with both untreated and alkali-treated fibers in comparison to the plain polyester, which characterizes a stiffening effect. The composites with alkali treated fibers exhibited similar tensile strength values for all lengths; however, their strengths are lower than those for the untreated condition due to a weak raffia fiber/polyester matrix adhesion. Therefore, this work fills the current knowledge gap on raffia fiber incorporation in polyester matrix and valorizes this abundant Brazilian resource, providing additional information towards the use of raffia fiber in polymer composites.

The replacement of synthetic fibers by natural fibers has, in recent decades, been the subject of intense research, particularly as reinforcement of composites. In this work, the lesser known tucum fiber, extracted from the leaves of the Amazon Astrocaryum vulgare palm tree, is investigated as a possible novel reinforcement of epoxy composites. The tucum fiber was characterized by pullout test for interfacial adhesion with epoxy matrix. The fiber presented a critical length of 6.30 mm, with interfacial shear strength of 2.73 MPa. Composites prepared with different volume fractions of 20 and 40% tucum fiber were characterized by tensile and Izod impact tests, as well as by ballistic impact energy absorption using .22 ammunition. A cost analysis compared the tucum fiber epoxy composites with other natural and synthetic fiber reinforced epoxy composites. The results showed that 40 vol% tucum fiber epoxy composites increased the tensile strength by 104% and the absorbed Izod impact energy by 157% in comparison to the plain epoxy, while the ballistic performance of the 20 vol% tucum fiber composites increased 150%. These results confirmed for the first time a reinforcement effect of the tucum fiber to polymer composites. Moreover, these composites exhibit superior cost effectiveness, taking into account a comparison made with others epoxy polymer composites.

Natural-fiber-reinforced polymer composites have recently drawn attention as new materials for ballistic armor due to sustainability benefits and lower cost as compared to conventional synthetic fibers, such as aramid and ultra-high-molecular-weight polyethylene (UHMWPE). In the present work, a comparison was carried out between the ballistic performance of UHMWPE composite, commercially known as Dyneema, and epoxy composite reinforced with 30 vol % natural fibers extracted from pineapple leaves (PALF) in a hard armor system. This hard armor system aims to provide additional protection to conventional level IIIA ballistic armor vests, made with Kevlar, by introducing the PALF composite plate, effectively changing the ballistic armor into level III. This level of protection allows the ballistic armor to be safely subjected to higher impact projectiles, such as 7.62 mm caliber rifle ammunition. The results indicate that a hard armor with a ceramic front followed by the PALF/epoxy composite meets the National Institute of Justice (NIJ) international standard for level III protection and performs comparably to that of the Dyneema plate, commonly used in armor vests.

A novel class of graphene-based materials incorporated into natural lignocellulosic fiber (NLF) polymer composites is surging since 2011. The present overview is the first attempt to compile achievements regarding this novel class of composites both in terms of technical and scientific researches as well as development of innovative products. A brief description of the graphene nature and its recent isolation from graphite is initially presented together with the processing of its main derivatives. In particular, graphene-based materials, such as nanographene (NG), exfoliated graphene/graphite nanoplatelet (GNP), graphene oxide (GO) and reduced graphene oxide (rGO), as well as other carbon-based nanomaterials, such as carbon nanotube (CNT), are effectively being incorporated into NLF composites. Their disclosed superior mechanical, thermal, electrical, and ballistic properties are discussed in specific publications. Interfacial shear strength of 575 MPa and tensile strength of 379 MPa were attained in 1 wt % GO-jute fiber and 0.75 wt % jute fiber, respectively, epoxy composites. Moreover, a Young’s modulus of 44.4 GPa was reported for 0.75 wt % GO-jute fiber composite. An important point of interest concerning this incorporation is the fact that the amphiphilic character of graphene allows a better way to enhance the interfacial adhesion between hydrophilic NLF and hydrophobic polymer matrix. As indicated in this overview, two basic incorporation strategies have so far been adopted. In the first, NG, GNP, GO, rGO and CNT are used as hybrid filler together with NLF to reinforce polymer composites. The second one starts with GO or rGO as a coating to functionalize molecular bonding with NLF, which is then added into a polymeric matrix. Both strategies are contributing to develop innovative products for energy storage, drug release, biosensor, functional electronic clothes, medical implants, and armor for ballistic protection. As such, this first overview intends to provide a critical assessment of a surging class of composite materials and unveil successful development associated with graphene incorporated NLF polymer composites.

Natural lignocellulosic fibers and corresponding fabrics have been gaining notoriety in recent decades as reinforcement options for polymer matrices associated with industrially applied composites. These natural fibers and fabrics exhibit competitive properties when compared with some synthetics such as glass fiber. In particular, the use of fabrics made from natural fibers might be considered a more efficient alternative, since they provide multidirectional reinforcement and allow the introduction of a larger volume fraction of fibers in the composite. In this context, it is important to understand the mechanical performance of natural fabric composites as a basic condition to ensure efficient engineering applications. Therefore, it is also important to recognize that ramie fiber exhibiting superior strength can be woven into fabric, but is the least investigated as reinforcement in strong, tough polymers to obtain tougher polymeric composites. Accordingly, this paper presents the preparation of epoxy composite containing 30 vol.% Boehmeria nivea fabric by vacuum-assisted resin infusion molding technique and mechanical behavior characterization of the prepared composite. Obtained results are explained based on the fractography studies of tested samples.

The growing interest in natural lignocellulosic fibers (NLFs) is associated not only with environmental benefits but also with technical, economical and social advantages. Among the NLFs, the coir fiber and pineapple leaf fiber (PALF) are low-cost and widely available waste materials. The present work investigated the dynamic mechanical properties, by means of DMA tests, of these two different fibers as reinforcement of epoxy matrix composites. The influence on DMA properties of composites by the volume fraction and the configuration form, mat or aligned coir fiber, were also evaluated. The results showed higher E’ and E” moduli values and an increase in Tg with the incorporation of PALF in epoxy matrix, which indicate a superior dynamic mechanical properties for this composite in comparison to the neat epoxy resin. The experimental data also revealed a stronger interfacial interaction of PALF/epoxy when compared to coir fiber/epoxy. It was also found a lower tan δ value exhibited by higher volume fractions of aligned coir fibers in epoxy matrix.

Multilayered armors with a front ceramic followed by aramid fabric (Kevlar™) are currently used against high velocity ammunition. In these armors, a front ceramic layer that shatters and spalls the bullet is followed by an intermediate layer, usually plies of aramid fabric, which dissipates both the bullet and ceramic fragments energy. In the present work, the intermediate aramid fabric layer was replaced by an equal thickness layer of 30 vol% jute fabric reinforced epoxy composite. Ballistic impact test with 7.62 caliber ammunition revealed that both the plain epoxy and the jute fabric composite have a relatively similar performance of the Kevlar™ and also attended the NIJ standard for body protection. The energy dissipation mechanisms of jute fabric composite were analyzed by scanning electron microscopy and found to be the rupture of the brittle epoxy matrix as well as the interaction of the jute fibers with the post-impact fragments. This latter is the same mechanism recently disclosed for aramid fabric. However, the lightness and lower cost of the jute fabric composite are additional advantages that favor its substitution for the aramid fabric.

Composites with sustainable natural fibers are currently experiencing remarkably diversified applications, including in engineering industries, owing to their lower cost and density as well as ease in processing. Among the natural fibers, the fiber extracted from the leaves of the Amazonian curaua plant (Ananas erectifolius) is a promising strong candidate to replace synthetic fibers, such as aramid (Kevlar™), in multilayered armor system (MAS) intended for ballistic protection against level III high velocity ammunition. Another remarkable material, the graphene oxide is attracting considerable attention for its properties, especially as coating to improve the interfacial adhesion in polymer composites. Thus, the present work investigates the performance of graphene oxide coated curaua fiber (GOCF) reinforced epoxy composite, as a front ceramic MAS second layer in ballistic test against level III 7.62 mm ammunition. Not only GOCF composite with 30 vol% fibers attended the standard ballistic requirement with 27.4 ± 0.3 mm of indentation comparable performance to Kevlar™ 24 ± 7 mm with same thickness, but also remained intact, which was not the case of non-coated curaua fiber similar composite. Mechanisms of ceramic fragments capture, curaua fibrils separation, curaua fiber pullout, composite delamination, curaua fiber braking, and epoxy matrix rupture were for the first time discussed as a favorable combination in a MAS second layer to effectively dissipate the projectile impact energy.