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The use of vegetable fibers in the modern engineering industry represents a worldwide need for sustainable low-cost materials with desirable mechanical characteristics, such as high strength, modulus of elasticity and strain capacity. In order to be used as a reinforcement in composite systems, the Curauá fibers' durability and interface characteristics with the different matrices should be improved. The present work aims to characterize and compare the behavior of curauá filaments both in natural and treated conditions focusing on increasing their durability and bond performance. To minimize the degradation and high water absorption, two types of polymeric coatings were impregnated in the fibers: aluminum oxide and sand. Direct tensile tests were performed and correlated to the morphological observations of the fiber structure by SEM images. The adhesion between matrix and fiber was evaluated by pull-out tests. Volumetric changes due to the wetting and drying of the fibers were also analyzed. The results indicated an improvement of the fiber-matrix bond, fiber tensile strength and stiffness after the surface treatments. Additionally, the coating had a positive effect on the hydrophilic nature of the fiber, decreasing its water absorption capacity.

With growing environmental concerns over synthetic polymers, natural polymeric materials, such as hemicellulose, are considered a good sustainable alternative. Curaua fibers could be an excellent source of biopolymer as they have a relatively high hemicellulose content (15 wt%) and only a small amount of lignin (7 wt%). In this work, hemicellulose was extracted by an alkaline medium using KOH and the influence of the alkali concentration, temperature, and time was studied. A hemicellulose film was produced by water casting and its mechanical, thermal, and morphological properties were characterized. The results show that the best method, which resulted in the highest hemicellulose yield and lowest contamination from lignin, was using 10% (w/v) KOH concentration, 25 °C, and time of 3 h. The hemicellulose film exhibited better thermal stability and elongation at break than other polymeric films. It also exhibited lower rigidity and higher flexibility than other biodegradable polymers, including polylactic acid (PLA) and polyhydroxybutyrate (PHB). [ABSTRACT FROM AUTHOR]

Microfibrillated cellulose (MFC) employed as reinforcement of polymeric matrices can increase elastic modulus, stiffness and strength of a composite. In this work, the assessment of the mechanical, thermal properties and tensile tests assisted by digital image correlation (DIC) was performed for curaua fiber MFC-reinforced polylactic acid (PLA) composites as a function of MCF content. First, MFC was incorporated into PLA using a solvent exchange technique and subsequent polymer solubilization to produce master batch composites. Then, more PLA was added to obtain composites with 0.5 and 1.5 wt% MFC by using double screw extrusion and injection molding. As a result, the addition of MFC caused the flexural, tensile, indentation, impact and modulus strengths to increase compared to those of pure PLA. The deformation gradient obtained from DIC verified that the 0.5 wt% MFC/PLA composite presented greater homogeneity in relation to load dispersion, corroborating the higher rigidity, maximum stress, and Poisson's ratio.

The use of vegetable fibers in the modern engineering industry represents a worldwide need for sustainable low-cost materials with desirable mechanical characteristics, such as high strength, modulus of elasticity and strain capacity. In order to be used as a reinforcement in composite systems, the Curauá fibers' durability and interface characteristics with the different matrices should be improved. The present work aims to characterize and compare the behavior of curauá filaments both in natural and treated conditions focusing on increasing their durability and bond performance. To minimize the degradation and high water absorption, two types of polymeric coatings were impregnated in the fibers: aluminum oxide and sand. Direct tensile tests were performed and correlated to the morphological observations of the fiber structure by SEM images. The adhesion between matrix and fiber was evaluated by pull-out tests. Volumetric changes due to the wetting and drying of the fibers were also analyzed. The results indicated an improvement of the fiber-matrix bond, fiber tensile strength and stiffness after the surface treatments. Additionally, the coating had a positive effect on the hydrophilic nature of the fiber, decreasing its water absorption capacity. [ABSTRACT FROM AUTHOR]

The polypropylene with load of reinforcement of curauá fiber (PP-curauá) is a compound developed to be applied in the process of injection of automotive plastic parts. Polypropylene composites reinforced with mineral fillers (talc) or glass fibers have been widely applied in this segment. However, natural fibers are an important alternative considering the aspects of sustainability, recyclability, abundance and low cost, when compared with glass fibers, and industrial talc. This study was prompted by the growing need for materials that meet the constant cycles of use, disposal and reuse, and avoid the harmful effects on the environment. The mechanical properties of a curaua fiber and polypropylene-based ecocomposite reprocessed one, three and five times were assessed, since reprocessing is known to change the strength of these materials. Pure polypropylene (0%) and ecocomposites with 10 and 30 wt% of fiber were submitted to tensile and three-point bending tests. The results showed that polypropylene ecocomposites with 30% curaua fibers exhibited a higher modulus of elasticity. Moreover, reprocessing did not significantly affect the ecocomposite properties, demonstrating their viability for reuse. [ABSTRACT FROM AUTHOR]

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.

This work manufactured prepregs by impregnating discontinuous curaua fibers with B-stage epoxy resin. The prepreg layers were then stacked to produce laminates by hot compression. Alkaline treatments were previously applied to the curaua fibers to improve their interface with the polymer matrix. Then, the prepregs and the final composites were studied regarding their thermal, dynamic mechanical, mechanical, and morphological behavior. The treatments promoted defibrillation by removing lignin and hemicellulose from the fibers, which allowed better impregnation of the treated fibers with epoxy resin. In general, laminates that used treated fibers exhibited the largest storage modulus in the glassy region. The mechanical results showed the laminates produced with treated fibers prepregs presented a highest tensile and flexural resistance than those manufactured with untreated fibers and neat epoxy resin. The NaOH-treated curaua/epoxy laminate exhibited high tensile strength (56.2 MPa) and modulus (3.3 GPa). Overall, fracture morphology indicated better fiber adhesion for the treated fiber composites. The results demonstrate that natural fibers prepregs can be successfully produced and present proper physical and mechanical behavior in components. [ABSTRACT FROM AUTHOR]

The objective of this study was to obtain nanowhiskers from bleached and milled curaua fibers. Nanowhiskers were obtained via a TEMPO system. TEM micrographies proved the fibers were obtained. FTIR analysis showed characteristic peaks of the oxidation products for the samples submitted to the treatment, suggesting that the it was effective for cellulose. The results show that the TEMPO method increased crystallinity and decreased the degree of polymerization. As for thermal stability, the nanowhiskers were more thermally stable than the other samples. Based on our findings, the use of nanowhiskers may be suitable for a variety of applications, such as the production of nanocomposites.

Supercritical carbon dioxide (scCO2) has been used as a physical blowing agent to produce polymer expanded materials. Firstly, a statistic study was performed to determine the neat polystyrene (PS) expansion parameters, using the ANOVA and response desirability approach. The results suggested that the optimal parameters are 120 °C (temperature), 2500 psi/17.23 MPa (pressure), and 2 h (residence time). Secondly, defibrillated curauá fibers (CF) were used as reinforcement in the PS matrix, in three different proportions (1.0, 2.5, and 5.0% (w/w)), to produced expanded composites. The results showed that CF acted as a nucleating agent, facilitating scCO2 to sip into the composite due to the reinforcement/matrix interface. The expanded composites were characterized by SEM, apparent density, cell population density, void volume fraction, and mechanical properties by the compression test, water uptake, dye absorption and, water contact angle (WCA). CF incorporation in the composite increased the compressive strength value and modified the expanded composite final morphology, decreasing the cell size and increasing void content and density. The PS/CF 5.0% sample showed higher water and organic dye absorption and the addition of CF on the expanded composite slightly decrease WCA. [ABSTRACT FROM AUTHOR]

With growing environmental concerns over synthetic polymers, natural polymeric materials, such as hemicellulose, are considered a good sustainable alternative. Curaua fibers could be an excellent source of biopolymer as they have a relatively high hemicellulose content (15 wt%) and only a small amount of lignin (7 wt%). In this work, hemicellulose was extracted by an alkaline medium using KOH and the influence of the alkali concentration, temperature, and time was studied. A hemicellulose film was produced by water casting and its mechanical, thermal, and morphological properties were characterized. The results show that the best method, which resulted in the highest hemicellulose yield and lowest contamination from lignin, was using 10% (w/v) KOH concentration, 25 °C, and time of 3 h. The hemicellulose film exhibited better thermal stability and elongation at break than other polymeric films. It also exhibited lower rigidity and higher flexibility than other biodegradable polymers, including polylactic acid (PLA) and polyhydroxybutyrate (PHB).

The objective of this study was to obtain nanowhiskers from bleached and milled curaua fibers. Nanowhiskers were obtained via a TEMPO system. TEM micrographies proved the fibers were obtained. FTIR analysis showed characteristic peaks of the oxidation products for the samples submitted to the treatment, suggesting that the it was effective for cellulose. The results show that the TEMPO method increased crystallinity and decreased the degree of polymerization. As for thermal stability, the nanowhiskers were more thermally stable than the other samples. Based on our findings, the use of nanowhiskers may be suitable for a variety of applications, such as the production of nanocomposites. [ABSTRACT FROM AUTHOR]

Natural fibers are increasingly used as composite reinforcement in different fields of engineering. Caraua fiber stands out for its good mechanical properties and adherence to resin; however, little is known about its behavior in the manufacture of a composite or whether classic failure theory applies in this case. The present study assesses the mechanical properties of two laminas reinforced with unidirectional curaua fiber containing fiber volume fractions of 30 % and 22 %, and compares the results with the values obtained for four failure criteria, using analysis of variance (ANOVA). To that end, tensile tests were conducted along the fiber direction and at other loading angles, in addition to iosipescu shear tests. The results show that the Hashin criterion was the best and the maximum stress criterion does not represent the failure behavior of these materials.

Over the last few years, great interest has been shown by researchers in presenting alternative proposals for the design and fabrication of materials with good mechanical properties and low cost for a variety of applications. With this in mind, a study was carried out on the addition of curaua fibers in a polypropylene (PP) matrix. These were extruded in the pellets form with curaua fiber content of 5, 10 and 20% (mass percentage). An injector was used to make the test specimens from these pellets, which were then subjected to mechanical tests (tensile and three point bending), physical and thermal tests (fluidity index and HDT). As a consequence, it was noted that the incorporation of fibers in composites of PP with curaua resulted in an increase in the elastic modulus and tensile strength improving therefore the mechanical properties of these materials. Another important point was to check if there was an increase in heat deflection temperature as the fibers were added. As a result, it has been found that it is feasible to use these materials in industry, facilitating its recycling and improving its final mechanical properties.

Graphical abstract Highlights • Curaua fibers treated with cellulase and pectinase for biocomposite preparation. • Enzyme treatments on lignocellulosic fibers to standardize fiber quality. • Eco-friendly fibers treatments for improved polymeric biocomposite performances. Abstract The aim of this work is to elucidate the reinforcing potential of enzymatically treated curaua fibers in biodegradable poly(butylene succinate) (PBS)-based composites. The effect of two different enzymes, i.e. cellulase and pectinase, was evaluated. Untreated and enzymatically treated curaua fibers were characterized in terms of thermal stability (TGA), crystallinity (XRD) and surface morphology (SEM). The composite characteristics were investigated by mechanical test (tensile and flexural resistance), thermal stability and SEM micrographs of the fractured surfaces. Enzymatic treatments resulted in a significant change in morphology of curaua fibers, while their thermal stability and crystallinity were not affected much. SEM investigation of tensile fractured surfaces of composites showed strong adhesion between fibers and matrix. [ABSTRACT FROM AUTHOR]

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.

Microfibrillated cellulose (MFC) employed as reinforcement of polymeric matrices can increase elastic modulus, stiffness and strength of a composite. In this work, the assessment of the mechanical, thermal properties and tensile tests assisted by digital image correlation (DIC) was performed for curaua fiber MFC-reinforced polylactic acid (PLA) composites as a function of MCF content. First, MFC was incorporated into PLA using a solvent exchange technique and subsequent polymer solubilization to produce master batch composites. Then, more PLA was added to obtain composites with 0.5 and 1.5 wt% MFC by using double screw extrusion and injection molding. As a result, the addition of MFC caused the flexural, tensile, indentation, impact and modulus strengths to increase compared to those of pure PLA. The deformation gradient obtained from DIC verified that the 0.5 wt% MFC/PLA composite presented greater homogeneity in relation to load dispersion, corroborating the higher rigidity, maximum stress, and Poisson's ratio. [Display omitted] • Microfibrillated cellulose is incorporated into PLA using a solvent exchange technique and then masterbatch. • The innovative technique of PLA composites with digital image correlation (DIC) coupled with tensile property analysis. • Experimental results for flexural, impact, indentation, dynamical-mechanical, and thermal behavior. [ABSTRACT FROM AUTHOR]

The use of lignocellulosic fibers as reinforcement in polymer composites has increased worldwide recently. Vegetal fibers have low cost and they are commonly available in Brazil. The curaua fibers in particular are of great importance for the development of the Amazon region. The mechanical behavior of the composites reinforced with fibers depends on the effectiveness of the transfer of the applied load by the matrix to the fibers, which is determined by the magnitude of the interfacial bonding between fiber/matrix phases. In this paper, curaua fibers were treated with 0.25-2% (w/v) NaOH solution under tensile loading to improve fiber-matrix adhesion in curaua fibers/epoxy laminates. Composites with 40 vol.% curaua fibers were obtained. Maximum improvement in the composite properties was observed for those containing curaua fibers treated with 0.5% NaOH under tensile loading. Composites with good bending properties were obtained by using a simple, low cost and environmental friendly method for curaua treatment. This method employed low concentration of chemical solutions, which are neutralized during the process, and no need of heating. [ABSTRACT FROM AUTHOR]

This study evaluated the mechanical, thermal, rheological, and morphological properties of virgin and recycled matrices and their composites with 20 wt % of curaua fiber. The recycling process of postconsumer polystyrene was carried out by grinding and extrusion. It was found that the recycling of expanded polystyrene did not have a major influence on the mechanical properties; however, the thermal stability was increased. The addition of curaua fibers led to increases in the tensile strength, modulus of elasticity, rigidity, thermal stability and melt viscosity of the composites. The composites made with the recycled matrix revealed higher thermal stability and melt viscosity than those made with the virgin matrix. Scanning electron microscopy characterization showed empty spaces where the curaua fibers had pulled out of the matrices in the fractured regions, indicating poor interfacial adhesion without the use of a coupling agent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Curaua nanofibers extracted under different conditions were investigated. The raw fibers were mercerized with NaOH solutions; they were then submitted to acid hydrolysis using three different types of acids (HSO, a mixture of HSO/HCl and HCl). The fibers were analyzed by cellulose, lignin and hemicellulose contents; viscometry, X-ray diffraction (XRD) and thermal stability by thermogravimetric analysis (TG). The nanofibers were morphologically characterized by transmission electron microscopy (TEM) and their surface charges in suspensions were estimated by Zeta-potential. Their degree of polymerization (DP) was characterized by viscometry, crystallinity by XRD and thermal stability by TG. Increasing the NaOH solution concentration in the mercerization, there was a decrease of hemicellulose and lignin contents and consequently an increase of cellulose content. XRD patterns presented changes in the crystal structure from cellulose I to cellulose II when the fibers were mercerized with 17.5% NaOH solution. All curaua nanofibers presented a rod-like shape, an average diameter (D) of 6-10 nm and length (L) of 80-170 nm, with an aspect ratio (L/D) of around 13-17. The mercerization of fibers with NaOH solutions influenced the crystallinity index and thermal stability of the resulting nanofibers. The fibers mercerized with NaOH solution 17.5% resulted in more crystalline nanofibers, but thermally less stable and inferior DP. The aggregation state increases with the amount of HCl introduced into the extraction, due to the decrease of surface charges (as verified by Zeta Potential analysis). However, this release presented nanofibers with better thermal stability than those whose acid hydrolysis was carried out using only HSO. [ABSTRACT FROM AUTHOR]

Polyurethane composites reinforced with curaua fiber at 5, 10 and 20% mass/mass proportions were prepared by using the conventional melt-mixing method. The influence of curaua fibers on the thermal behavior and polymer cohesiveness in polyurethane matrix was evaluated by dynamic mechanical thermal analysis (DMTA) and by differential scanning calorimetry (DSC). This specific interaction between the fibers and the hard segment domain was influenced by the behavior of the storage modulus E′ and the loss modulus E″ curves. The polyurethane PU80 is much stiffer and resistant than the other composites at low temperatures up to 70°C. All samples were thermoplastic and presented a rubbery plateau over a wide temperature range above the glass transition temperature and a thermoplastic flow around 170°C. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A well‐known treatment applied in vegetable fibers in both paper and cellulose industry is named hornification. This treatment consists in soaking and drying cycles aiming promoting a reducing in the water absorption capability of the fibers, which causes a stiffening in the cellulosic structure increasing the dimensional stability and consequently their mechanical properties. In this work is presented an analysis of the effect of alkaline hornification, using a calcium hydroxide (CH) 0.7% w/v solution, after 01, 05, and 10 cycles of soaking and drying on the structure changes, mechanical answer, durability performance, and adherence behavior of curaua fibers in the cementitious matrix. The fiber structure as well as their physical and chemical characteristics are evaluated before and after hornification treatment by X‐ray diffraction (DRX), Thermogravimetry (TGA), Fourier Transformade Infrared (FTIR), and Scanning Electronic Microscope (SEM), while their mechanical answer is evaluated by direct tensile tests. The obtained results indicate that the hornification treatment alters the morphological, physical, and chemical fiber properties, improving their mechanical properties. However, when the number of cycles is excessive, this kind of treatment may cause a decreasing in fiber mechanical properties. [ABSTRACT FROM AUTHOR]