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Article

Characterization and Application of Different Types of Pineapple Leaf Fibers (PALF) in Cement-Based Composites

by
Julianna M. da Silva
1,
Adilson Brito de Arruda Filho
1,
Lidianne do N. Farias
2,*,
Everton Hilo de Souza
3,
Fernanda V. D. Souza
3,
Cláudia F. Ferreira
1,3 and
Paulo R. L. Lima
2,*
1
Campus Cruz das Almas, UFRB, Federal University of Recôncavo da Bahia, Rua Rui Barbosa, s/n, Centro, Cruz das Almas 44380-000, BA, Brazil
2
Technology Department, UEFS, State University of Feira de Santana, Avenida Transnordestina, s/n, Novo Horizonte, Feira de Santana 44036-900, BA, Brazil
3
Embrapa Cassava and Fruits, Rua Embrapa, s/n, Chapadinha, Centro, Cruz das Almas 44380-000, BA, Brazil
*
Authors to whom correspondence should be addressed.
Fibers 2025, 13(5), 51; https://doi.org/10.3390/fib13050051
Submission received: 28 February 2025 / Revised: 1 April 2025 / Accepted: 24 April 2025 / Published: 30 April 2025
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Abstract

:

Highlights

What are the main findings?
  • Pineapple fibers obtained from fruit genotypes exhibit acceptable physical and mechanical properties for use as reinforcement in composite materials.
  • Cementitious composites reinforced with pineapple fibers exhibited deflection-hardening behavior due to the good adhesion between the pineapple fiber and the matrix.
What are the implications of the main finding?
  • The utilization of agricultural waste from pineapple leaves for fiber production can add value to the material, reducing the economic and environmental costs of disposal and increasing the income of pineapple producers.
  • The production of cement-based building elements reinforced with residual pineapple fibers will help reduce the harmful environmental impact of the construction industry.

Abstract

The use of plant fibers as reinforcement in cement composites has gained significant interest due to their favorable mechanical properties and inherent sustainability, particularly when sourced from agro-industrial waste. In this study, six types of pineapple leaf fibers from commercial and hybrid varieties were characterized in terms of morphology, crystallinity index, water absorption, dimensional stability, and mechanical properties to evaluate their potential as reinforcement in cement-based composites. An anatomical analysis of the leaves was conducted to identify fiber distribution and structural function. Cement-based composites reinforced with 1.5% (by volume) of long and aligned pineapple leaf fibers were produced and tested in bending. The results indicate that the tensile strength of pineapple fibers, ranging from 180 to 753 MPa, surpasses that of fibers already successfully used in composite reinforcement. Water absorption values ranged from 150% to 187%, while fiber diameter varied between 45% and 79% as fiber moisture changed from the dry state to the saturated state. The flexural behavior of the composites modified with pineapple leaf fibers exhibited multiple cracking and deflection hardening, with increases in flexural strength ranging from 6.25 MPa to 11 MPa. The cracking pattern under bending indicated a strong fiber–matrix bond, with values between 0.41 MPa and 0.93 MPa. All composites demonstrated high flexural toughness and great potential for the development of construction elements.

1. Introduction

The use of fibers or fabrics as reinforcement in cement-based materials for the production of construction elements has increased in recent decades, mainly as a replacement for traditional ferrocement, which is reinforced with steel bars or meshes and presents inherent durability issues due to reinforcement corrosion [1]. Glass fiber- or polymer fiber-reinforced cementitious composites have been used in the production of façade elements, wall panels, and roofing components [2,3]. The ease of molding cement-based composites with short fibers also allows the production of construction elements with curved geometries and reduced thickness, ensuring greater cost efficiency and architectural freedom [4].
On the other hand, the search for more sustainable solutions has encouraged the replacement of manufactured fibers with fibers derived from waste, such as recycled PET [5], recycled tire fibers [6], and natural fibers, which come from renewable sources and have lower energy production costs and reduced CO2 emissions [7]. Natural fibers exhibit adequate mechanical strength, and their physical and chemical compatibility with cement-based materials has been achieved through the use of appropriate matrices and fiber treatment methods [8]. This has enabled the application of these composites in various construction systems, such as slab blocks [9], sandwich panels [10], pavement [11], and masonry reinforcement [12].
Various natural fibers, such as sisal, jute, hemp, and flax, have been used to reinforce cementitious or polymer composites. Among them, Curauá fiber, extracted from the leaves of an ornamental pineapple plant, stands out due to its high tensile strength, reaching approximately 600 MPa—significantly higher than other natural fibers [13]. In cement-based matrices, this natural fiber primarily functions to inhibit crack propagation in the brittle cementitious matrix, increasing ultimate deformation and toughness. However, these properties are influenced by the fiber content incorporated. Hadipramana [14] observed that the addition of pineapple short fibers reduced workability, requiring adjustments to the water–cement ratio for optimal concrete performance. Nonetheless, with proper fiber dosage and treatment, higher pineapple content can be incorporated, resulting in concrete with improved compressive and split tensile strength [15,16].
For extruded cementitious composites, Teixeira [17] found that incorporating Curauá fibers not only increased toughness and flexural strength but also led to higher porosity due to reduced workability in the fresh state and fiber dispersion challenges. The use of pineapple fiber in engineering cementitious composites (ECC)—a material with strictly controlled mix proportions—has demonstrated the possibility of developing high-strength and high-toughness materials suitable for structural applications [17,18,19]. Additionally, durability assessments of Curauá fiber-reinforced mortars indicate that the material meets the minimum requirements for resistance to aggressive chemical environments, qualifying it for use in wall and ceiling covering mortars [13].
The success of the application of Curaua fibers as reinforcement for cement-based matrices indicates great potential for the use of pineapple leaf fibers grown for food production. Most of the pineapple cultivation is dedicated to fruit production, with around 30 million tons of fruit being produced annually across various countries, including Indonesia, the Philippines, Costa Rica, and Brazil as the leading producers [20]. Each pineapple plant produces a single fruit before being uprooted for replanting. As a result, the pineapple agroindustry generates a significant amount of waste, typically including discarded leaves, roots, and farm stems [21]. With the growing global population and increasing pineapple consumption, finding efficient ways to utilize this waste is essential to making the pineapple agroindustry more sustainable.
Although considered solid waste in Brazil, residual leaves from fruit pineapple plants are utilized as a natural fiber source in several countries, particularly in the textile industry [22,23]. In polymer composites, pineapple leaf fiber (PALF) enhances material stiffness and mechanical strength, expanding its potential applications, as it provides greater rigidity and tensile strength than the polymer matrix itself [24].
The review of the literature indicates that pineapple fiber is generally referred to simply as PALF or Curauá, without a precise identification of the specific plant variety from which the leaves were extracted for fiber production. However, there are currently 2252 pineapple varieties released and circulating in the global market [25], resulting from crossbreeding and genetic improvements aimed at increasing yield and resistance to pests. Each genotype, however, has unique characteristics, with variations in its chemical composition [26], which consequently alters the physical and mechanical properties of the fibers extracted from the leaves [27] and affects their applicability in composite production.
The objective of this study is to characterize fibers extracted from the leaves of three genotypes of fruit pineapple and three ornamental genotypes for their potential use as reinforcement in cement-based composites. In order to achieve this, the fibers were extracted using a decortication process and characterized in terms of their physical, mechanical, and structural properties. Composites reinforced with each genotype were then produced and subjected to flexural testing to evaluate their mechanical behavior.

2. Materials and Methods

2.1. Pineappleplants

The fibers used in this study were obtained from three fruit-bearing pineapple genotypes (‘BRS Imperial’, ‘Pérola’, and ‘Smooth Cayenne’), one ornamental genotype (‘Curauá’), and two ornamental hybrids (‘BRS Boyrá’ and ‘BRS Potyra’), all available at the Pineapple Active Germplasm Bank or Genetic Breeding, located in Cruz das Almas, BA, Brazil, at Embrapa Mandioca e Fruticultura. The scientific nomenclature of these genotypes is presented in Table 1.
Figure 1 shows the different pineapple genotypes. All leaf samples were collected from the breeding and propagation fields of Embrapa Mandioca e Fruticultura in Cruz das Almas, Bahia.
Anatomical analyses were performed on median cross-sections of the leaf. The leaf sections were fixed in a solution of FAA 70% (formaldehyde, glacial acetic acid, and 70% ethanol in water) for 48 h, dehydrated in a graded ethanol series (35–100%), with each step lasting 6 h. They were then infiltrated and embedded using the Historesin kit (hydroxyethyl methacrylate, Leica, Heidelberg, Germany). The polymerization of the resin was carried out at room temperature for 48 h. Serial histological sections (5 µm) were obtained using a Leitz rotary microtome (model 1516, Ernst Leitz GmbH, Wetzlar, Germany), placed on histological slides, and stained with acid fuchsin (0.1% p/v), followed by toluidine blue (0.05% p/v) [28]. The histological sections were analyzed and photographed under a B × S1 fluorescence microscope (Olympus Latin America Inc., Doral, FL, USA). Morphometric measurements were calculated using the ImageJ 1.46r program.

2.2. Leaf and Fiber Characterization

The fibers were extracted from the leaves using the decortication process (Figure 2a), with the same equipment used for extracting sisal fibers. After extraction, the fibers were exposed to the sun for natural drying, as shown in Figure 2a. In the laboratory, the fibers were washed in hot water (50 °C) to remove impurities and surface grease, then dried in an oven at 80 °C for 24 h.
The fiber morphology was investigated using a JEOL JSM 6510 microscope (JEOL Ltd., Tokyo, Japan) with a low vacuum and an accelerating voltage of 2.5–15 kV. The D2 Phaser Bruker (Bruker Corporation, Karlsruhe, Country: Germany)—CuKα radiation = 1.544 Å—was used to perform the XRD.
For the water absorption test, a 2 g bundle of dry fibers was used. The fibers were immersed in water, and after a 24-h immersion period, they were removed, gently patted dry with a lint-free cloth, and weighed.
The dimensional variation of the fiber was evaluated by measuring the change in fiber diameter between the dry and saturated states. Using an optical microscope, the diameters of three fibers were measured after drying in an oven at 60 °C for 24 h. The fibers were then immersed in water for 24 h, and the diameters were measured again. The dimensional variation was determined by the change in diameter relative to the dry fiber diameter.
Tensile tests on pineapple fibers were conducted using a Shimadzu AG-X electromechanical (Shimadzu Corporation, Kyoto, Japan) testing machine equipped with a 1 kN load cell, at a displacement rate of 0.03 mm/s. For each genotype, 15 specimens of fibers with lengths of 30 mm, 50 mm, and 70 mm were tested. The fibers were glued to a paper template for better alignment and adhesion with the machine grips, as recommended by ASTM C1557 [29].

2.3. Cement-Based Matrix and Composite Production

In order to obtain a durable composite, part of the cement used must be replaced by mineral additives [30] that will consume the free calcium hydroxide and minimize the alkali attack on the plant fiber. In this regard, the matrix was produced with 50% Portland cement CP V ARI (ASTM Type III; suitable for the production of prefabricated elements), 40% fly ash, and 10% silica fume.
The characteristics of the fly ash (FA) and silica fume (SF), as shown in Table 2, indicate that these mineral additions can be classified as pozzolanic materials due to the content of SiO2, Al2O3, and Fe2O3 present in their chemical composition.
The natural aggregate used was a fine sand (NA) with a maximum diameter of 1.2 mm and fineness of 1.73. A third-generation superplasticizer (Glenium 51), with a solid content of 30.9% and a specific gravity of 1.1 g/cm3, was used to ensure self-compacting behavior of the matrix. A viscosity modifier admixture (VMA), Rheomac UW 410, with a specific gravity of 0.7 g/cm3, was added at a dosage of 0.05% by weight of the binder to avoid segregation during molding. The mortar matrix used in this study presented a mix design of 1:1:0.35 (cementitious material: sand: water, by weight). To ensure good flowability, the superplasticizer additive content was defined so that the matrix achieved a spreading of 400 ± 10 mm in the flow table test, without any drop.
Laminates with two layers of fiber (volume fraction of 1.5%) were produced using long fibers, each 24 cm in length. For the production of the composites, the mortar mix was placed in a steel mold using the hand lay-up technique, one layer at a time, followed by a layer of unidirectional aligned fibers (up to two layers) with a length of 280 mm. Figure 3 shows the molding sequence of the first layers of matrix and fiber. The laminate composite had nominal dimensions of 285 mm × 75 mm × 10 mm (length × width × thickness). After casting and curing in the mold for 24 h, the laminates were immersed in water for 28 days.
The composites were subjected to bending tests under a four-point bending configuration using a Shimadzu UH-F 100 kN machine. Displacement control was applied at a crosshead rate of 0.3 mm/min, with a 1 kN capacity load cell. Three specimens of each mixture were tested. From the load–deflection curves, three parameters were calculated to evaluate the effect of fiber reinforcement: (a) the first-cracking flexural strength (σcr) of the composite—determined from the maximum load carried by the composite at first cracking; (b) the maximum post-cracking flexural strength (σmax) of the composite—determined from the maximum load carried by the composite after the first cracking event; and (c) the toughness indices according to ASTM C1018 [31].
By evaluating the cracking patterns at regular time intervals, the development of cracks throughout the load cycle of the bending test was recorded using a Canon digital camera at 30 s intervals. Photographs of the tensile face in bending tests were used to measure crack formation during the bending test. Similar procedures were carried out by Melo Filho [32], with a photo acquisition time of 60 s. A shorter acquisition time was used in the present work to ensure greater accuracy.

3. Results

3.1. Pineapple Leaf Fibers

3.1.1. Foliar Anatomy and Fiber Morphology

Figure 4A shows median cross-sections of the leaf from a pineapple variety.
The plant fibers are formed by the union of several fiber cells, bound by lignin, which make up the fiber bundles (ff), along with the other cells of the mesophyll. In all genotypes, the presence of glandular trichomes on the adaxial (ed) and abaxial (be) surfaces, aerenchyma (ae) in the chlorophyll parenchyma (pc), stomata on the abaxial surface, a unistratified epidermis covered by a thick cuticle layer, and vascular bundles (fv) distributed in both parenchyma types were observed. In Figure 4, it is also possible to identify other structures of the pineapple leaf: fl = phloem; lu = lumen; pa = aquiferous parenchyma; pl = lignified cell wall of the fiber; xi = xylem.
The fibers have two main functions: (i) the fibers located in the chlorophyll parenchyma (pc), as seen in Figure 4A, have an approximately circular shape and are arranged triangularly, primarily in the region closest to the abaxial epidermis, and their purpose is to maintain the leaf’s resistance against its own weight or external agents; and (ii) the fibers surrounding the phloem and xylem (Figure 4C), in turn, serve to protect the vascular system, surrounding it with a fiber bundle in the shape of an arch to prevent the disruption of sap flow due to leaf folding.
The anatomical characteristics of the leaf, associated with the presence of fibers, are presented in Table 3. The greatest leaf thickness was observed in the ‘BRS Potyra’ and ‘Smooth Cayenne’ genotypes, while the thinnest was observed in ‘BRS Potyra’ and ‘BRS Boyrá’. The number of fiber bundles (NFS) per cm2 of leaf, observed in cross-sections, ranged from 694 in ‘BRS Potyra’ to 196 in ‘Smooth Cayenne’. It can be noted that there is no direct correlation between leaf thickness and the quantity of fibers present in the genotypes.
The productivity of pineapple fiber for commercial use was evaluated based on the proportion of fibers, air-dried, extracted from the leaves after decortication. The fiber yield (Table 3) ranged from 1.6% to 5.8% of the weight of fresh leaves. The highest yields were obtained from fibers extracted from the leaves of the ornamental genotypes.
Using mechanical extraction, Patrick [33] obtained a fiber yield of 6.64% to 7.70%, while Kengkhetkit [34], using different extraction methods, including scraping, retting, ball-milling, and milling, obtained a yield ranging from 1.8% to 3%. Hazarika [35] achieved a yield ranging from 1.5% to 3%, depending on the immersion time in the water of the pineapple leaves prior to mechanical decortication. This fiber yield of PALF is comparable to that of sisal fiber, which ranges from 3% to 5% [36].
Table 3 indicates that, after extraction, pineapple fibers have a length ranging from 426 to 929 mm, allowing them to be used as long continuous reinforcement in the form of yarns or fabrics. Additionally, the fibers can be cut and used as short, discontinuous reinforcement dispersed in cement-based matrices. In comparison, other natural fibers are extracted with varying lengths, such as sisal fiber, which has an average length of 1500 mm, or coconut fiber, which is extracted and used with a maximum length of 300 mm.
The length of pineapple fibers after decortication ranged from 426 to 929 mm (Table 3), while sisal fibers have an average length of 1500 mm. However, this does not limit the industrial application of pineapple fiber, since coconut fibers are used with a maximum length of 300 mm.
In the representative micrograph of the pineapple fiber cross-section (Figure 5a), a structure similar to other plant fibers is observed, consisting of numerous fiber cells held together by the middle lamella. Similar features were observed in the pineapple genotypes regarding the shape of the cross-section, with fibers having a circular or arc-like shape near the vascular bundles. The lateral surface (Figure 5b) appeared rough, which is a positive aspect for use as reinforcement in composites, as it enhances adhesion with cementitious matrices [37]. The detail of the cross-section (Figure 5c) shows the fibrocytes with the lumens and cell walls.
In the mechanical decortication process, leaves are crushed and beaten by a rotating wheel set with blunt knives, leaving only fibers behind. In this study, a decortication machine designed for sisal fiber was used, which has a larger cross-section and greater rigidity than pineapple fibers. As a result, some fibers were damaged, with the emergence of internal microcracks (Figure 6a), loss of cross-sectional shape (Figure 6b), and separation of fiber cells (Figure 6c). The inefficiency of the decortication process is further demonstrated by the presence of plant pulp around the fiber, indicating the need for specialized equipment for pineapple leaf decortication, as proposed by [38].

3.1.2. Water Absorption and Dimensional Variation of Fibers

Figure 7 illustrates the water absorption and dimensional variation of pineapple fibers. The ‘BRS Imperial’ and ‘Pérola’ varieties exhibited the highest water absorption, reaching values of 175% and 187%, respectively.
One of the key characteristics of plant fibers is their high water absorption capacity. This behavior is attributed to their hydrophilic nature, resulting from the presence of pendant hydroxyl and polar groups in various constituents [39], as well as the presence of lumens, as shown in Figure 4C, which makes the fiber porous. These lumens act as natural conduits that facilitate water movement. According to [40], this high absorption occurs because the internal structure of the fibers is porous, allowing water to accumulate within the pores. In a study conducted by the same author, sisal fiber was also found to exhibit high water absorption, exceeding 150% of its initial weight. This value is close to some of the analyzed fibers, such as the ‘BRS Potyra’ and ‘Curauá’ varieties, which exhibited the lowest water absorption, with values of 149% and 153%, respectively.
One of the main consequences of the high water absorption in fibers is the increase in their cross-sectional area (swelling). Figure 7 presents the dimensional variation of the fibers. Despite their high absorption capacity, the maximum dimensional variation observed ranged from 26% to 37%, with the ‘Curauá’ and ‘BRS Boyrá’ varieties exhibiting the least variation. It is observed that there is no direct relationship between water absorption capacity and fiber swelling, indicating that water fills the free pores of the fibers without causing significant internal pressure. Ferreira [41] observed that sisal fibers, which exhibit a water absorption capacity of approximately 200%, undergo a dimensional variation of 27% when exposed to changes in humidity between dry and saturated states.
In polymeric composites, fiber expansion generates internal stress at the fiber–matrix interface, which can lead to interface failure. In cementitious composites, after the curing process, moisture loss occurs gradually until equilibrium with the external environment is reached. This process causes a significant reduction in fiber diameter, which is much greater than the shrinkage of the cement paste and may result in interface cracking and rupture of the fiber–matrix transition layer. The extent of this interface failure is proportional to the fiber’s dimensional variation. Consequently, excessive dimensional variation due to natural wet–dry cycles leads to cracking at the fiber–matrix interface, resulting in a loss of load-bearing capacity in the composites over time. Therefore, using fibers with greater dimensional stability is crucial. To address this issue, various fiber treatments are proposed in the literature to reduce water absorption [42].

3.1.3. X-Ray Diffraction (XRD)

The X-ray diffraction (XRD) patterns of pineapple fibers shown in Figure 8 exhibit similarities with spectra obtained for Curauá fibers [43]. These patterns feature three peaks corresponding to crystallographic planes at 2θ values of θc1, θc2, and θc3, along with an amorphous region (θa) between them.
The primary crystalline plane (θc2) corresponds to an enhanced alignment of the glycosidic rings within the plane [36] and is therefore associated with the fiber’s crystallinity index. The peaks at θc1 and θc2 represent planes oriented perpendicular to the cellulose fiber axis, while the peak at θc3 represents a plane oriented parallel to the cellulose fiber axis [44].
The Crystallinity Index—CI(%)—for each studied pineapple fiber is presented in Table 4 and was obtained using the following Equation (1) [45]:
C I ( % ) = 100   I c 2 − I a I a  
where I c 2 is the intensity (peak height) of the crystalline peak at the maximum value (2θ between 22° and 23°) and Ia is the intensity at the minimum value (2θ between 18° and 19°).
The crystallinity index (CI) indicates the proportion of cellulose in a crystalline state and is one of the key factors influencing the mechanical behavior of lignocellulosic materials. The CI values obtained for the fruit genotypes range from 63.82% to 64.25%, which are similar to those observed for the hybrid ornamental genotypes, varying between 63.08% and 64.50%. The Curauá fiber exhibited the highest CI value, reaching 67.53%. According to [46], Curauá fiber has a total cellulose content (cellulose + hemicellulose) exceeding 91%, whereas fruit pineapple leaf fibers contain cellulose levels between 80% and 83%.
Compared to other plant fibers, the crystallinity index of pineapple fibers is slightly lower. For instance, sisal fiber has a CI ranging from 81% to 91% [36,47], while hemp and kenaf fibers exhibit CI values ranging from 69% to 83% and 61% to 69%, respectively [48].

3.1.4. Mechanical Behavior of Fiber

The typical stress–strain diagrams for each genotype, with a length of 30 mm, are presented in Figure 9. A linear behavior with brittle failure is observed, which is common in hard plant fibers extracted from leaves, such as sisal.
Table 5 presents the average values of the diameter of fiber and mechanical properties obtained from the direct tensile strength test, along with the coefficient of variation (%) in parentheses.
The highest tensile strength obtained for Curauá fiber, used as a control, was approximately 480 MPa, which aligns with values reported in the literature, ranging from 212 to 691 MPa [47,49,50]. For fibers from the cultivated genotypes, tensile strength values ranged from 51% to 79% of that of Curauá fiber, while for hybrid genotypes, strength varied from 30% to 89%. The variation in strength among genotypes may be associated with different cellulose contents (see Figure 10), as indicated by the crystallinity index shown in Table 4, as well as the morphology of each fiber, given that cell wall thickness and lumen dimensions directly affect the strength of plant fibers [49].
A comparison with other fibers shows that pineapple fibers have tensile strength and elastic modulus similar to those of sisal and superior to some fibers used as reinforcement in composites [51,52]. The tensile strength of plant fibers varied with sample length, which is expected since larger samples have a higher probability of defects. In fact, localized damage to the fibers due to the decortication process was observed in some of the analyzed fibers, indicating that a more suitable fiber extraction process needs to be implemented.
The determination of the elastic modulus of materials is performed by measuring axial deformations during the tensile test. This measurement is usually performed using sensors called clip gauges, which are directly attached to the sample. However, the flexibility of natural fibers prevents the attachment of these sensors. As a result, the deformation reading is obtained from the testing machine, but this value is greater than the actual deformation of the fiber. Because of this, it is necessary to correct the elastic modulus obtained from the deformations measured by the testing machine using a procedure suggested by [53], which considers the effect of the testing machine’s compliance (C) on the elastic modulus. The corrected fiber modulus (E*) can be calculated using Equation (2) [53]:
1 E * = 1 E + C A L o
where A is the fiber cross-section, E is the elastic modulus obtained from the test, Lo is the initial fiber length, and C is the testing machine’s compliance.
The fiber modulus can be determined using Equation (2), which involves plotting the experimental inverse modulus (1/E) against the fiber cross-sectional area divided by the gauge length (A/Lo) and finding the intercept of the resulting straight line. Figure 11 shows the data for the measured pineapple fiber modulus, plotted according to Equation (2). The actual fiber elastic modulus values were obtained from the intercepts of the least-squares fitted lines and are presented in Table 2. These values align well with the accepted range for these fibers [47,49,50].

3.2. Flexural Behavior of PALF Reinforced Cement-Based Composites

Figure 12 shows the bending response of the PALF-reinforced cement composite for each type of fiber and its crack spacing measurements. The stress–displacement curves were divided into four phases, each identified by Roman numerals, which are associated with the cracking process of the composites, as shown in Figure 13.
Phase I corresponds to the displacement range in which the composite behavior is governed by both the matrix and the fibers. This phase ends with the appearance of cracks in the matrix, although the fibers do not yet contribute significantly to the composite’s load-bearing capacity.
In Phase II, after the first crack, the fibers begin to play a significant role in transferring stresses within the cracked matrix. As the load increases, the fibers bridging the crack allow the internal stresses in the matrix to once again reach its tensile strength, leading to the formation of a new crack. As the load increases, stresses continue to rise, leading to the formation of additional cracks until the matrix is divided into multiple segments separated by cracks. This phase, known as multiple cracking, is characterized by the emergence and propagation of numerous cracks across the entire width of the sample (Figure 13).
Figure 12 shows the variation in crack spacing along the displacement of the composites. After a displacement of about 10 mm, the crack spacing reaches a constant value, Scr, which varies according to the type of fiber used.
In Phase III, no new cracks open, but existing cracks propagate and widen. Phase IV marks the onset of fiber–matrix debonding. During this phase, the composite’s load-bearing capacity is primarily influenced by the fibers.
The effect of pineapple fiber on the behavior of cement-based composites under direct tension was evaluated by [54], who identified a multiple cracking process for composites reinforced with 1.5% (by volume) of fibers. This phenomenon occurs due to the transfer of internal loads to the fiber, which continues to resist internal stresses until it is pulled out of the matrix. The flexural behavior observed in this study was also similar to the results observed with the use of sisal fibers in cementitious composites [32,55].
The mechanical results of the first-cracking flexural strength (σcr), the maximum post-cracking flexural strength (σmax), and the displacement corresponding to the first crack (δ) are presented in Table 6.
As observed in Table 6, for the composites reinforced with long fibers, the post-peak stress increased, ranging from 6.25 to 12.64 MPa. The ‘BRS Boyrá’ exhibited the highest peak stress. However, ‘BRS Potyra’ (12.64 MPa) and ‘Curauá’ (10.89 MPa) had the highest post-peak stresses, indicating an improvement in the composite due to the use of plant fibers, which influenced the composite’s behavior, making it more resistant and leading to multiple cracks.
The average crack spacing values, shown in Table 6, varied according to the type of fiber used, indicating differences in fiber–matrix adhesion among the different genotypes. According to Aveston [56], for composites reinforced with continuous and aligned fibers, the mechanical behavior before failure is governed by fiber pullout through a frictional shear stress transfer mechanism. Based on this hypothesis, it is believed that a constant frictional shear transfer with stress τfu develops at the fiber–matrix interface, which can be calculated using Equation (3) [57]:
τ f u = V m V f σ c r r 2 S c r
where Scr is the cracking spacing, Vm and Vf are the matrix volume and fiber volume at composite, σcr is the cracking stress, and r is the fiber radio (assuming fibers of circular cross-section).
The stress values τfu obtained for the composites studied are presented in Table 6. It is observed that fibers from ornamental genotypes exhibited higher adhesion stress, ranging from 0.55 to 0.92 MPa, while the other fibers showed values between 0.41 and 0.63 MPa. The fiber–matrix adhesion has been determined through pull-out tests, which reported a τfu value of approximately 0.34 MPa for Curauá fiber [47].
The force–displacement curves were used to determine the flexural toughness parameters of composites according to the ASTM C1018 method [31]. In this method, the toughness is calculated as the area under the curve at specific deflections, namely δ, 3 δ, 5.5 δ, and 10.5 δ, where δ represents the deflection at the formation of the first crack (see Table 6). The I5 index corresponds to the area under the curve until deflection of 3 δ (AOACD), divided by area until deflection δ (AOAB), as shown in Figure 14. Indexes I10 and I20 correspond to areas until deflection of 5.5 δ (AOACEF) and 10.5 δ (AOACEGH), respectively, divided by the area until deflection δ (AOAB). Figure 15 shows the toughness indexes obtained for all composites.
Pineapple fiber leads to an increase in the flexural toughness indices of the composites, with the Smooth–Cayenne and ‘BRS Potyra’ fibers showing the best results. Composites reinforced with the ‘Perola’ genotype exhibited the lowest toughness values. The I5 index varied from 7.85 to 12.79, while the I10 index ranged from 18.52 to 33.51, and the I20 index varied from 45.52 to 79.83.
An increase in the toughness of composites subjected to bending and reinforced with 1.5% pineapple fibers of 30 mm in length was also observed by [54]. The authors obtained I5 and I10 index values of 4.45 and 8.31, respectively. These values are lower than those observed in the present study, which used longer fibers, resulting in better anchorage and greater load transfer capacity.

4. Conclusions

This study investigated the physical and mechanical properties of pineapple leaf fibers obtained from different plants, including ornamental and fruit genotypes. Six cementitious composites reinforced with long pineapple fibers were then produced and evaluated for their mechanical behavior under bending. The main findings of this study can be summarized as follows:
  • Fibers produced from fruit genotypes exhibited physical and mechanical properties suitable for use as reinforcement in cement-based matrices. Their dimensional variation due to humidity variations was around 30%, their tensile strength exceeded 250 MPa, and their elastic modulus was approximately 20 GPa. The high mechanical strength is directly associated with the cellulose content of the fibers, with a crystallinity index above 63%.
  • When used as reinforcement in cement-based composites, pineapple fibers from fruit genotypes demonstrated a fiber–matrix adhesion greater than 0.4 MPa, which was sufficient to transfer stresses within the cracked matrix, allowing for multiple cracking of the composites and a deflection–hardening behavior, thereby increasing the flexural strength and toughness of the composites.
  • Considering that pineapple plants become agricultural waste after fruit harvesting and that fiber production from the leaves yields up to 2.1%, it is believed that fiber extraction from these genotypes is economically viable. This process adds value to an agricultural byproduct and promotes the development of a circular economy, integrating the pineapple agroindustry with the construction sector.

Author Contributions

Conceptualization, P.R.L.L.; methodology, J.M.d.S., A.B.d.A.F. and P.R.L.L.; validation, J.M.d.S., A.B.d.A.F. and P.R.L.L.; formal analysis, J.M.d.S., A.B.d.A.F., L.d.N.F. and P.R.L.L.; investigation, J.M.d.S., A.B.d.A.F. and E.H.d.S.; resources, F.V.D.S.; data curation, P.R.L.L.; writing—original draft preparation, L.d.N.F. and P.R.L.L.; writing—review and editing, L.d.N.F., E.H.d.S., C.F.F. and P.R.L.L.; supervision, P.R.L.L. and C.F.F.; project administration, P.R.L.L. and F.V.D.S.; funding acquisition, F.V.D.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Fundação de Amparo à Pesquisa do Estado da Bahia (FAPESB—grant number TSC 0013/2014).

Data Availability Statement

Data are contained within the article.

Acknowledgments

The authors would like to thank Coordenação de Aperfeiçoamento de Pessoal de Nível Superior for the scholarships (CAPES). P.R.L.L. and F.V.D.S. thanks Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for the for a productivity grant (304631/2022-1 and 307128/2021-0, respectively).

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Pineapple genotypes: (a) ‘Pérola’; (b) ‘Smooth Cayene’; (c) ‘BRS Imperial’; (d) ‘Curauá’; (e) ‘BRS Boyrá’; and (f) BRS Potyra.
Figure 1. Pineapple genotypes: (a) ‘Pérola’; (b) ‘Smooth Cayene’; (c) ‘BRS Imperial’; (d) ‘Curauá’; (e) ‘BRS Boyrá’; and (f) BRS Potyra.
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Figure 2. Fiber preparation: (a) Extraction; (b) Exposure to the sun for drying.
Figure 2. Fiber preparation: (a) Extraction; (b) Exposure to the sun for drying.
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Figure 3. Composite molding procedure: (a) placement of the first layer of matrix; (b) placement of the fibers; (c) immersion of the fibers with a plastic roller; (d) placement of the second layer of matrix.
Figure 3. Composite molding procedure: (a) placement of the first layer of matrix; (b) placement of the fibers; (c) immersion of the fibers with a plastic roller; (d) placement of the second layer of matrix.
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Figure 4. Leaf anatomy of pineapple genotypes [Ananas comosus (L.) Merr.]. (A) Cross-sections of leaves; (B) fibrous clusters (ff) on chlorophyll parenchyma; (C) vascular bundles surrounded by fibrous clusters. Scale: (A) = 1 mm; (B) = 50 µm; (C) = 100 µm.
Figure 4. Leaf anatomy of pineapple genotypes [Ananas comosus (L.) Merr.]. (A) Cross-sections of leaves; (B) fibrous clusters (ff) on chlorophyll parenchyma; (C) vascular bundles surrounded by fibrous clusters. Scale: (A) = 1 mm; (B) = 50 µm; (C) = 100 µm.
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Figure 5. Micrograph of pineapple fibers: (a) cross-section; (b) lateral surface; (c) internal microstructure.
Figure 5. Micrograph of pineapple fibers: (a) cross-section; (b) lateral surface; (c) internal microstructure.
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Figure 6. Pineapple fibers after decortication: (a) internal microcracks; (b) damaged fiber; (c) separation of fiber-cells; (d) leaf residue due inefficient decortification.
Figure 6. Pineapple fibers after decortication: (a) internal microcracks; (b) damaged fiber; (c) separation of fiber-cells; (d) leaf residue due inefficient decortification.
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Figure 7. Dimensional variation and water absorption of pineapple leaf fibers.
Figure 7. Dimensional variation and water absorption of pineapple leaf fibers.
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Figure 8. X-ray diffraction of pineapple plant fibers.
Figure 8. X-ray diffraction of pineapple plant fibers.
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Figure 9. Stress–strain diagrams of pineapple fibers under direct tension: (a) fruit genotypes; (b) ornamental genotypes.
Figure 9. Stress–strain diagrams of pineapple fibers under direct tension: (a) fruit genotypes; (b) ornamental genotypes.
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Figure 10. Correlation between tensile strength and Crystallinity Index.
Figure 10. Correlation between tensile strength and Crystallinity Index.
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Figure 11. Estimation of actual fiber modulus from gauge length experiments: (a) Curaua; (b) ‘BRS Imperial’; (c) ‘BRS Boyrá’; (d) BRS Potyra; (e) ‘Smooth Cayene’ and (f) ‘Pérola’.
Figure 11. Estimation of actual fiber modulus from gauge length experiments: (a) Curaua; (b) ‘BRS Imperial’; (c) ‘BRS Boyrá’; (d) BRS Potyra; (e) ‘Smooth Cayene’ and (f) ‘Pérola’.
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Figure 12. Flexural response of the pineapple fiber reinforced composite system indicating the flexural stress (black line) and crack spacing (gray triangle).
Figure 12. Flexural response of the pineapple fiber reinforced composite system indicating the flexural stress (black line) and crack spacing (gray triangle).
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Figure 13. Cracking map of the composite under bending.
Figure 13. Cracking map of the composite under bending.
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Figure 14. Determination of toughness indices according to ASTM C1018 [31].
Figure 14. Determination of toughness indices according to ASTM C1018 [31].
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Figure 15. Toughness indices of cement-based composite.
Figure 15. Toughness indices of cement-based composite.
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Table 1. Pineapple genotypes used in the study.
Table 1. Pineapple genotypes used in the study.
GenotypeScientific Nomenclature
Fruit
Genotypes		‘BRS Imperial’Ananas comosus (L.) Merr.
‘Pérola’A. comosus
‘Smooth Cayenne’A. comosus
Ornamental
Genotypes 		‘BRS Potyra’A. comosus var. erectifolius (L.B.Sm.) Coppens and F.Leal × A. comosus var. bracteatus (Lindl.) Coppens and F.Leal
‘BRS Boyrá’A. comosus var. bracteatus × A. comosus var. erectifolius
‘Curauá’Ananas comosus (L.) Merr. var. erectifolius (L.B.Sm.) Coppens and F.Leal
Table 2. Binder constituents.
Table 2. Binder constituents.
CharacteristicsCementFly Ash (FA)Silica Fume (SF)
Major chemical component (%)CaO69.772.060.17
SiO215.8953.3395.3
SO34.761.51not identified
Al2O34.3533.230.04
K2O1.073.441.33
Fe2O33.664.960.35
Specific gravity (g/cm3)3.062.012.65
Table 3. Anatomical characteristics of pineapple leaves.
Table 3. Anatomical characteristics of pineapple leaves.
GenotypesLeaf Thickness (mm)Fiber/cm2Fiber Yield (%)Fiber Length (mm)
‘BRS Imperial’38.29 3421.70426
‘Pérola’114.83 4491.60525
‘Smooth Cayenne’27.31 1962.10473
‘BRS Potyra’233.12 6944.90611
‘BRS Boyrá’141.87 3735.80585
‘Curauá’122.47 3514.80929
Table 4. X-ray diffraction results of pineapple plant fibers.
Table 4. X-ray diffraction results of pineapple plant fibers.
GenotypeCharacteristic Angles (2θ) IntensityCI (%)
θc1θc2θc3θaImax
(2θ = θc2)		Imin
(2θ = θa)
‘BRS Imperial’15.7922.4318.7134.4013,962505263.82
‘Pérola’15.8122.7118.7034.4915,277546264.25
‘Smooth Cayenne’15.4722.4518.9034.0913,969503163.98
‘BRS Potyra’15.8922.5618.8934.8115,458548864.50
‘BRS Boyrá’15.9722.6618.8134.4814,698542663.08
‘Curauá’15.7922.5218.8134.4017,637572767.53
Table 5. Experimental results of the direct tensile test.
Table 5. Experimental results of the direct tensile test.
GenotypesDiameter (mm)Tensile Strength (MPa)Corrected Elastic Modulus (GPa)
30 mm50 mm70 mm
‘BRS Imperial’0.11 (34)321.47 (48)289.77 (46) 276.33 (32) 19.34
‘Pérola’0.15 (25)257.48 (26)255.64 (46) 260.77 (36) 20.12
‘Smooth Cayenne’0.11 (43)396.12 (35)391.62 (39) 387.65 (36) 21.28
‘BRS Potyra’0.19 (11)336.70 (24)301.88 (30) 312.96 (16) 20.16
‘BRS Boyrá’0.13 (25)272.95 (30)242.86 (44) 228.77 (44) 25.19
‘Curauá’0.12 (36)480.23 (43)447.22 (41) 436.08 (43) 28.01
Table 6. Experimental results of the composite bending test.
Table 6. Experimental results of the composite bending test.
Fiberσcr (MPa)δ (mm)σmax (MPa)Scr
(mm)		τfu
(MPa)
‘BRS Imperial’2.88 (19)0.50 (56)7.59 (22)6.250.41
‘Pérola’3.82 (17)0.75 (57)6.25 (13)7.690.63
‘Smooth Cayenne’3.69 (25)0.75 (56)7.28 (23)6.000.56
‘BRS Potyra’3.41 (21)0.25 (56)12.64 (24)5.660.92
‘BRS Boyrá’4.06 (17)1.25 (59)7.43 (21)7.690.55
‘Curauá’3.74 (29)0.75 (57)10.89 (31)6.250.60
σcr = first-cracking flexural strength; δ = displacement corresponding to first crack; σmax = maximum post-cracking flexural strength; Scr = cracking spacing; τfu = frictional shear transfer with stress.
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da Silva, J.M.; de Arruda Filho, A.B.; Farias, L.d.N.; de Souza, E.H.; Souza, F.V.D.; Ferreira, C.F.; Lima, P.R.L. Characterization and Application of Different Types of Pineapple Leaf Fibers (PALF) in Cement-Based Composites. Fibers 2025, 13, 51. https://doi.org/10.3390/fib13050051

AMA Style

da Silva JM, de Arruda Filho AB, Farias LdN, de Souza EH, Souza FVD, Ferreira CF, Lima PRL. Characterization and Application of Different Types of Pineapple Leaf Fibers (PALF) in Cement-Based Composites. Fibers. 2025; 13(5):51. https://doi.org/10.3390/fib13050051

Chicago/Turabian Style

da Silva, Julianna M., Adilson Brito de Arruda Filho, Lidianne do N. Farias, Everton Hilo de Souza, Fernanda V. D. Souza, Cláudia F. Ferreira, and Paulo R. L. Lima. 2025. "Characterization and Application of Different Types of Pineapple Leaf Fibers (PALF) in Cement-Based Composites" Fibers 13, no. 5: 51. https://doi.org/10.3390/fib13050051

APA Style

da Silva, J. M., de Arruda Filho, A. B., Farias, L. d. N., de Souza, E. H., Souza, F. V. D., Ferreira, C. F., & Lima, P. R. L. (2025). Characterization and Application of Different Types of Pineapple Leaf Fibers (PALF) in Cement-Based Composites. Fibers, 13(5), 51. https://doi.org/10.3390/fib13050051

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