Physico-mechanical characterization of fiberboards made from African locust bean pod fiber using two ecological tannic binders

 Corresponding author: Kokouvi Happy N’TSOUAGLO Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution License 4.0. Physico-mechanical characterization of fiberboards made from African locust bean pod fiber using two ecological tannic binders Soviwadan DROVOU 1, 2, 3, 5, Kokouvi Happy N’TSOUAGLO 1, 2, *, Sinko BANAKINAO 1, 3, Komlan Assogba KASSEGNE 1, 2, Antony PIZZI 5, 6, Komla SANDA 3, 4 and André DL BATAKO 7 1 Polytechnical School of Lomé in University of Lomé (EPL – UL), 01Po. Box 1515 Lomé 01, Togo. 2 Laboratory of Structure and mechanic of materials (LaS2M), (EPL – UL), 01Po. Box 1515 Lomé 01, Togo. 3 Laboratory of Recherche on Agricultural resources and Environmental Health (LARASE), University of Lomé, 01Po. Box 20131 Lomé 01, Togo. 4 University of Kara, Kara, Togo. 5 Laboratory of Study and Recherche on Wood Materials, University of Lorraine (LERMAB – UL), Épinal, 88000, France 6 Department of Physics, King Abdulaziz University, Jeddah, Saudi Arabia. 7 Liverpool John Moores University, Byrom Street, Liverpool, L3 3AF, UK. World Journal of Advanced Research and Reviews, 2025, 28(03), 478-491 Publication history: Received 18 October 2025; revised on 01 December 2025; accepted on 04 December 2025 Article DOI: https://doi.org/10.30574/wjarr.2025.28.3.4025 Abstract This study explores the valorization of agricultural residues, specifically African locust bean pod fibers and tannic powders extracted from their husks and Indian tamarind peels, for the development of eco-friendly fiberboards. Two fiber size ranges (0.8–1.6 mm and 1.6–2 mm) were used to produce panels with different binder types and tannin contents. The physical properties (density, thickness swelling and water absorption) and mechanical properties (modulus of elasticity, modulus of rupture and tensile strength) of the fiberboards were evaluated. Results revealed that the fiberboards can be classified as Medium Density Fiberboards (MDF) according to the ANSI A208.1–2022 standard. While the water resistance did not meet the standard requirements, the mechanical performance significantly exceeded the thresholds, particularly in terms of stiffness and strength. These findings highlight the potential of underutilized agricultural residues and natural tannin-based binders in the development of sustainable bio-based panels for future material applications. Keywords: African locust bean pod; Indian tamarind peels; Fiber size; Fiberboards; Tannin-based binders; Physical and mechanical properties 1. Introduction The construction, industrial, and furniture manufacturing sectors are facing increasing pressure to transition toward sustainable and environmentally friendly materials in response to the challenges of climate change and the depletion of natural resources. These sectors contribute significantly to global CO₂ emissions; for instance, construction activities and building operations alone account for approximately 40% of total emissions, with around 15% specifically linked to the manufacture of building materials [1]. To reduce the environmental impact of these activities and preserve nonrenewable resources, the development and use of alternative materials have become essential. The integration of agricultural biomass and waste into panel production represents a viable solution to this challenge, while also aligning with key principles of the circular economy [2], [3]. As a result, innovative alternatives to conventional materials such as plywood, fiberboards, and particleboards are emerging [4], [5], [6], [7]. World Journal of Advanced Research and Reviews, 2025, 28(03), 478-491 479 Among these bio-based solutions, materials derived from agricultural residues, including rice straw [8], coconut shells [9], hemp fibers [10], [11], and other crops, have attracted growing attention [12], [13], [14], [15]. Numerous studies have demonstrated that these bio-composites exhibit favorable physical and mechanical properties, providing significant potential for a wide range of applications [16], [17], [18]. These findings provide a foundation for continued innovation in the field of sustainable materials. With this perspective, the exploration of new bio-based raw materials is a promising avenue. The husks of African locust bean (Parkia Biglobosa), an abundant by-product in West Africa [19], [20], have interesting properties for the manufacture of composite fiberboards [21]. This renewable resource offers a dual opportunity: to provide an environmentally-friendly alternative to traditional materials, and to valorise an often-under-utilized agricultural waste product. The aim of the present study is to investigate the physical and mechanical properties of fiberboards made from African locust bean husks, using natural tannic binders extracted from Parkia Biglobosa husk and Pithecellobium Dulce bark. 2. Materials and methods 2.1. Raw materials The materials used for the production of fiberboards from African locust bean husks were locally sourced in Togo. The African locust bean husks were collected in the Sokodé region (Figure 1). Two types of tannin-based binders were selected to evaluate their influence on the properties of the produced fiberboards. These include tannins extracted from Parkia Biglobosa (African locust bean) and Pithecellobium Dulce (Indian tamarind). Figure 1 Tannic based elements, (a) African locust bean pods; (b) Indian tamarind peel 2.2. The preparation of tannic powders The pod of African locust bean was dried in an oven at a temperature of 72°C for three days to eliminate all moisture. Then, it is transformed into powder in the RETSCH knife mill with a 2 mm diameter sieve. The material resulting from the grinding is sieved successively with a sieve of 1.6 mm and 0.8 mm. Thus, two fibers are obtained; the first with a diameter between 1.6 and 2 mm (G1) and the second with a diameter between 0.8 and 1.6 mm (G2) to separate the fiber from the husk. The material that has passed through the 0.8 mm sieve is again sieved with a 0.125 mm sieve to obtain the tannic powder. The peels of Indian tamarind were also dried in an oven of MEMMENT type, from the LARASE (Laboratory of Research on Agro resources and Environmental Health) at the University of Lomé. The drying temperature is 72◦C and the drying time is three days. These peels are then cut into small pieces and crushed. The grinder has knives and is of RETSCH SK 1000 type. It is equipped with a sieve with the diameter of the mesh of 0.125 mm to obtain tannic powder. The powders obtained from African locust bean pods and Indian tamarind peels were then mixed with the African locust bean pod fibers at different proportions. The chemical composition of these two ecological tannic binders, previously characterized by Nénonéné [22], is presented in Table 1. World Journal of Advanced Research and Reviews, 2025, 28(03), 478-491 480 Table 1 Chemical composition (%) of African locust bean pods and Indian tamarind peel Parameter (%) African locust bean pods Indian tamarind peel Moisture Content 8.32 5.88 Ash content 2.9 4.97 Crude fat 0.9 0.99 Crude protein 4.69 15.50 Cellulose 49.76 44.61 Hemicellulose 2.52 20.96 Lignin 32.95 13.30 2.3. Fibreboards preparation The granulometries G1 (1.6 < g ≤ 2 mm) and G2 (0.8 < g ≤ 1.6 mm) are mixed with the both tannic powders (African locust bean (AL) and Indian tamarind (IT) in the proportion shown in Table 2. Water was added at 20% of the total mixture weight (i.e., 80 g for 400 g). The mixture is kneaded for five (5) minutes. In Table 2, the binder content (%) refers to the weight percentage of binder relative to the total dry weight (binder + fiber). For instance, a 5% binder content means 20 g of binder and 380 g of fiber, totaling 400 g, with the binder making up 5% of the dry mixture. Table 2 Binder and fiber proportions in fiberboard production Binder content (%) Binder weight (g) Fibre weight (g) 5.0 20 380 7.5 30 370 10.0 40 360 12.5 50 350 15.0 60 340 2.4. Fibreboards thermal pressing The homogenized mixture is poured into a square mould with dimensions of 36 cm x 36 cm x 12 cm preheated to the required thermal pressing temperature of 160 °C. The mold is sealed with a top plate (31cm x 31 cm x 10 cm) and placed between the heated plates of a Carver hydraulic thermal pressing, with the lower plate being movable and the upper plate fixed. Figure 2 Thermal pressing process: a) Fibers in the mould before thermal pressing, b) the mould out of the pressing machine and c) Demolded fiberboard. World Journal of Advanced Research and Reviews, 2025, 28(03), 478-491 481 The thermal pressing process is carried out at a temperature of 160 °C under a pressure of 11 bars. After the temperature stabilizes, the fiberboards are demolded and allowed to cool at ambient air temperature. The thermal pressing time is about 15 minutes. Once cooled, the materials are ready for characterization. 2.5. Physical properties determination The physical properties are performed according to the ANSI A208.1-2022 standard on the samples of dimensions 50 cm x 50 cm. 2.5.1. Density The density of the materials was determined by calculating the ratio of the weight of each sample to its volume, following the method described in [23]. It is determined according to ANSI A208.1-2022 on 10 specimens of each of the six fibreboards produced. The density is calculated using the following Equation 1: ρ = M V (1) Where ρ is the density of the material (kg/m³), M is the mass of the specimen (kg), and V is its volume (m³). The weight was measured using a high – precision digital scale, while the volume was determined by measuring the dimensions of the sample after pressing. 2.5.2. Determination of water absorption and thickness swelling Water absorption and thickness swelling tests are essential for evaluating the ability of materials to absorb water and undergo dimensional changes when exposed to humid environments [24], [25], [26]. The water absorption test measures the amount of water absorbed by a material after immersion for a defined period, while the thickness swelling test quantifies the variation in the sample's thickness after immersion for a specific duration. In this study, the tests were conducted in accordance with the ANSI A208.1-2022 Standard. Twelve (12) specimens with dimensions of 50 mm x 50 mm were used. Before immersion, the initial weight and thickness of each sample were carefully measured. The specimens were then immersed in water, and the weights and thicknesses of six specimens were recorded after 2 hours and other six after 24 hours of immersion. It should be noted that after immersion, the specimens were left at room temperature for 15 to 20 minutes to allow excess surface water to drain before final weighing and thickness measurement. These measurements enabled the calculation of water absorption and thickness swelling, providing key indicators of the materials performance in humid conditions. The thickness swelling (TS) is determined using Equation 2: TS (%) = ti− t0 t0 ×100 (2) Where: TS: is the thickness swelling (%), t0: is the thickness before immersion in water (mm), ti: is the thickness after immersion in water (mm) 2 or 24 hours. The water absorption (WA) was calculated using Equation 3: WA (%) = Wi−W0 W0×100 (3) Where: WA: is the water absorption (%), World Journal of Advanced Research and Reviews, 2025, 28(03), 478-491 482 W0: is the weight before immersion in water (gr), Wi: is the weight after immersion in water (gr) 2 or 24 hours. 2.6. Mechanical properties determination The mechanical properties of the samples were determined using a mechanical testing bench equipped with accessories specifically designed for three-points bending and tensile tests. The tests were conducted under controlled conditions, maintaining a relative humidity of 65% and a temperature of 20± 3 °C. 2.6.1. Three point bending test The samples dimensions were 150 mm x 100 mm for bending test. The mechanical tests were performed according to the standards EN 312-2 2004 and EN 310 [27], [28]. The standards NF B51-124:1993 and NBN EN 310:999 [29], [30] were used to calculate the mechanical properties such as elasticity modulus (MOE), the modulus of rupture in bending (MOR). The values of MOE and MOR were giving by the following expressions: MOE =F. l3 4be3y (4) With 𝐹 = (F2− F1) and 𝑦 = (y2− y1), leading to the expression: MOE =(F2− F1). l3 4be3(y2− y1) (5) The modulus of rupture (MOR) was calculated using Equation 6: MOR =3Fl 2be2 (6) In these equations, l is the distance between supports, e is the thickness of the specimen, and b is the width of the specimen. F represents the strength at break, while F1 and F2 correspond to 10% and 40% of F , respectively. y1 and y1 are the deflections corresponding to F1 and F2. 2.6.2. Tensile test The tensile test was performed on specimens with dimensions of 150 mm × 20 mm. The Young’s modulus (E) and the tensile modulus of rupture (MOT) of the fiberboards are determined using the Equations 7: 𝐄 = 𝛔 𝛆= 𝐅 𝐒𝟎 ∆𝐥 𝐋𝟎 = 𝐅×𝐋𝟎 ∆𝐥×𝐒𝟎 (7) The modulus of tensile rupture (MOT) was determined using Equation 8: 𝐌𝐎𝐓 = 𝐅𝐦 𝐛 × 𝐞 (8) In these equations, F represents the elastic limit load, 𝐅𝐦 is the maximum tensile load applied to the specimen, and l0 is the initial length of the specimen. ∆l denotes the elongation during the test, while 𝐒𝟎 is the initial cross-sectional area of the specimen. The parameters 𝐛 and 𝐞 correspond to the width and thickness of the specimen, respectively. 3. Results and discussion 3.1. Density The density results of the different materials, based on binder content and fiber size, are presented in Figure 3. AL G1: Fiberboards made from African locust bean fibers, with a fiber size of 1.6–2 mm, bonded using tannin extracted from African locust bean pod husks. Densities range from 788 kg/m³ (at 5% binder content) to 798 kg/m³ (at 15% binder content). World Journal of Advanced Research and Reviews, 2025, 28(03), 478-491 483 AL G2: Similar fiberboards using smaller fibers (0.8–1.6 mm) show densities ranging from 793 kg/m³ (5% binder) to 800 kg/m³ (15% binder). IT G1: Fiberboards using African locust bean fibers (1.6–2 mm) and tannin derived from Indian tamarind bark. Densities range from 770 kg/m³ (5% binder) to 788 kg/m³ (15% binder). IT G2: The same formulation with smaller fibers (0.8–1.6 mm) results in densities between 781 kg/m³ (5% binder) and 794 kg/m³ (15% binder). It is also important to note that density variation is more pronounced at lower binder contents. For instance, the standard deviation reaches ±8 kg/m³ at 5% binder content, compared to only ±5 kg/m³ at 20%. All fiberboards have a density between 640 and 800 kg/m³, classifying them as medium-density fiberboard according to ANSI A208.1-2022. These results align with those of Kadja [31], who developed cotton and Kenaf tree fiber fiberboards using pearls bone glue, and Drovou et al. [32], who used tannic powders from Parkia biglobosa pod husk and Pithecellobium dulce peels to bind Antiaris Africana sawdust, creating formaldehyde-free environmental fiberboards. The granulometry significantly impacts fiberboard density; finer fibers are denser . Given the same weight, finer fibers occupy less volume, pack more efficiently, and reduce porosity, leading to thinner, more compact fiberboards [32], [33]. In general, the density increases with the binder content in the fiberboard, as higher binder ratios enhance fiber adhesion and reduce void spaces, which is consistent with some results presented in the literature [9], [32]. Additionally, African locust bean husk tannin-based fiberboards systematically exhibit higher densities compared to Indian tamarind bark tannin-based fiberboards, suggesting a stronger binding effect. This effect has already been demonstrated in the literature, where fiberboards made with tannic powder from African locust bean pod husks are denser than those manufactured with other binders [7]. AL: African locust bean pods, IT: Indian Tamarind, G1: 1.6  g ≤ 2, G2: 0.8  g ≤ 1.6 Figure 3 Variation of density according to granulometry and binder 3.2. Thickness Swelling Figure 4 shows the thickness swelling of the fiberboards after 2 hours and 24 hours immersion in water. After 2 hours of immersion, all tested fiberboards exceed the 20% threshold defined for floor fiberboards. Surprisingly, fiberboards with smaller fiber sizes exhibit particularly high swelling rates, reaching up to 68% when using the tannin binder from Indian tamarind bark. Conversely, fiberboards with larger fiber sizes show more moderate and consistent swelling rates, regardless of the type of binder used. After 24 hours of immersion, there is no significant variation in the swelling rate of fiberboards with larger fibers compared to the swelling observed after 2 hours. This suggests that absorption is very high at the beginning but World Journal of Advanced Research and Reviews, 2025, 28(03), 478-491 484 stabilizes over time. On the other hand, for fiberboards with smaller fibers, swelling remains significant, reaching up to 100% when using the tannin binder derived from African locust bean at 5%. In contrast to the results observed after 2 hours, where the tannin binder from Indian Tamarind bark led to a higher swelling rate, it is now the fiberboards made with the tannin binder derived from African locust bean that show the highest swelling rate after 24 hours. Overall, it is also observed that the swelling rate decreases with the binder content. AL: African locust bean pods, IT: Indian Tamarind, G1: 1.6  g ≤ 2, G2: 0.8  g ≤ 1.6 Figure 4 Thickness swelling variation according to the granulometry and binder after 2and 24-hours immersion It is important to note that, according to the ANSI A208.1 – 2022 standard, the acceptable thresholds for thickness swelling are defined as follows: 20% for flooring fiberboards, 8% for roofing fiberboards after 2 hours of immersion, and 50% for general applications after 24 hours. However, the swelling values recorded in this study remain significantly higher than those prescribed by the more stringent EN 317 standard [34]. 3.3. Water absorption The water absorption test revealed significant variations depending on fiber size and immersion duration. Figure 5 shows the evolution of water absorption under different configurations. After 2 hours of immersion, all fiberboards absorbed more than 50% of their weight in water. The values ranged from 55.0% (IT G1, 15% binder content) to 135.3% (IT G2, 5% binder content). It was observed that fiberboards with smaller fiber sizes exhibited the highest water absorption. Similar to the swelling trends, the difference between water absorption at 2 and 24 hours is not substantial, as one might have expected. After 24 hours, water absorption ranged from 89.2% (IT G1, 15% binder content) to 176.7% (IT G2, 5% binder content). This suggests that water absorption is very high during the initial phase but tends to stabilize over time as the internal pores become saturated. The water absorption values obtained in this study are comparable to those reported by Diop et al. [35], who found absorption ranging from 120% to 160% in fiberboards made from thermomechanical pulp and lignocellulosic nanofibrils. In contrast, our results differ markedly from the findings of Rodríguez et al. [36] and Boran and Torun [37], who evaluated fiberboards made from medium-density fiberboard residues and from microcrystalline cellulose combined with antimony trioxide, respectively. In Rodríguez et al.’s work, water absorption ranged from 18% to 60% after 24 hours, while Boran and Torun reported values between 20% and 25% over the same duration. Overall, it was also observed that the water absorption decreased as the binder content increased. World Journal of Advanced Research and Reviews, 2025, 28(03), 478-491 485 AL: African locust bean pods, IT: Indian Tamarind, G1: 1.6  g ≤ 2, G2: 0.8  g ≤ 1.6 Figure 5 Water absorption (WA) variation according to fiber size and binder after 2 and 24 hours immersion 3.4. Three-point bending test properties This section presents the results related to the moduli of elasticity (MOE) and rupture (MOR) of the fiberboards. 3.4.1. Moduli of elasticity (MOE) Figure 6 shows the evolution of the MOE as a function of binder. The results show that fiberboards manufactured with tannin extracted from Indian Tamarind bark (IT) exhibit MOE values ranging from 1825.0 MPa to 2462.2 MPa. Similarly, fiberboards produced with tannin extracted from African locust bean husk (AL) display MOE values between 1726.4 MPa and 2303.1 MPa. It is also noteworthy that fiberboards made with smaller fiber particles exhibit higher MOE values than those made with larger particles. This trend is consistent with previous studies, which have shown that finer particles contribute to improved mechanical strength due to better compaction and reduced porosity. Moreover, MOE values increase with higher binder content, confirming findings reported in the literature [32], [38]. All tested fiberboards meet or exceed the minimum requirements defined by the ANSI A208.1 – 2022 standard. The MOE values obtained in this study are comparable to those reported by Rodríguez et al. [36] and Jazayeri et al. [39], who developed fiberboards incorporating modified graphene as an additive in urea-formaldehyde (UF) adhesive. Their results showed a progressive increase in MOE with higher additive content. Although not strictly equivalent in terms of formulation, a comparison was made with Sellers [40] and Xu et al. [41], who studied fiberboards manufactured without any binder. This comparison was included to highlight the significant improvement in mechanical performance achieved through the use of tannin-based binders in our study. The MOE values observed in our boards are considerably higher than those without binder, underscoring the effectiveness of tannin adhesives in enhancing the stiffness and reliability of fiberboards. World Journal of Advanced Research and Reviews, 2025, 28(03), 478-491 486 AL: African locust bean pods, IT: Indian Tamarind, G1: 1.6  g ≤ 2, G2: 0.8  g ≤ 1.6 Figure 6 Variation of modulus of Elasticity (MOE) according to binder content and fiber size 3.4.2. Moduli of rupture (MOR) Figure 7 shows how the modulus of rupture (MOR) of the fiberboards varies depending on the type and amount of binder used. Fiberboards made with tannin from Indian Tamarind peels (IT) have MOR values ranging from 36.1 MPa to 67.2 MPa. Those made with tannin from African locust bean husk (AL) show MOR values between 22.4 MPa and 74.4 MPa. In general, as observed for MOE, fiberboards made with smaller particles have higher MOR values than those made with larger particles. However, in the case of tannin from IT, an opposite trend is observed: fiberboards with smaller particles have lower MOR values than those with larger particles. As concluded in the previous subsection for the MOE, all MOR values obtained in this study meet or exceed the minimum requirements specified by the ANSI A208.1–2022 standard. Furthermore, these values are significantly higher than those reported by other authors in the literature who also developed natural fiberboards [40], [41], [42]. These results confirm the mechanical strength and reliability of the manufactured fiberboards, regardless of the binder type or fiber particle size used. AL: African locust bean pods, IT: Indian Tamarind, G1: 1.6  g ≤ 2, G2: 0.8  g ≤ 1.6 Figure 7 Variation of modulus rupture (MOR) according to binder content and fiber size