Headnote
ABSTRACT
Objective: The study aimed to characterize sugarcane bagasse ash (SCBA) regarding its chemical, physicochemical, thermal, structural, crystalline, and morphological properties, in order to evaluate its potential application as a mineral filler in polymer composites.
Theoretical Framework: The literature highlights the relevance of agro-industrial residues as an alternative source of mineral fillers in polymers, mainly due to their availability, low cost, and sustainability aspects. SCBA is recognized for its high silica content, as well as metallic oxides that can influence mechanical and thermal properties (Barrera et al., 2021).
Method: SCBA characterization was conducted using various techniques. Chemical composition was determined by XRF, while thermal stability was assessed by TGA. FTIR was employed to identify functional groups, and XRD determined the crystalline phases and degree of crystallinity of the material. Finally, particle morphology was examined using SEM.
Results and Discussion: The results indicated that SCBA has a chemical composition dominated by SiO2, followed by K2O, Fe2O3, and CaO, with no toxic elements detected. Thermal analysis demonstrated high stability, while FTIR confirmed the predominance of silica. XRD revealed a crystallinity degree of 50.26%. SEM micrographs showed fibrous, rough, and porous particles, with preserved biomass structures, favoring dispersion and interfacial adhesion in polymer matrices. Overall, these results reinforce the feasibility of SCBA as an alternative mineral filler in sustainable composites.
Research Implications: The findings confirm that SCBA exhibits chemical, structural, and morphological characteristics compatible with its use as a polymer filler. Its thermal stability and high silica content underscore its potential for developing sustainable materials with enhanced properties.
Originality/Value: This work contributes to expanding knowledge on the use of SCBA as an alternative mineral filler, integrating different characterization techniques. Its originality lies in demonstrating its technical potential while aligning innovation, cost-effectiveness, and reduction of environmental impacts.
Keywords: Sugarcane Bagasse Ash, Polymer Composites, Characterization, Sustainability.
RESUMO
Objetivo: O estudo teve como objetivo caracterizar a cinza de bagaço de cana-de-açúcar (CBC) quanto às suas propriedades químicas, físico-químicas, térmicas, estruturais, cristalinas e morfológicas, de modo a avaliar seu potencial de aplicação como carga mineral em compósitos poliméricos.
Referencial Teórico: A literatura destaca a relevância de resíduos agroindustriais como fonte alternativa de cargas minerais em polímeros, principalmente pela disponibilidade, baixo custo e viés sustentável. A CBC é reconhecida por apresentar alto teor de sílica, além de óxidos metálicos que podem influenciar propriedades mecânicas e térmicas (Barrera et al., 2021).
Método: A caracterização da CBC foi conduzida por diferentes técnicas. A composição química foi determinada por FRX, enquanto a estabilidade térmica foi avaliada por TGA. A técnica de FTIR permitiu a identificação de grupos funcionais, e determinou por DRX as fases cristalinas e o grau de cristalinidade do material. Por fim, a morfologia das partículas foi examinada por MEV.
Resultados e Discussão: Os resultados indicaram que a CBC possui composição química dominada por SiO2, seguida por K2O, Fe2O3 e CaO, sem a presença de elementos tóxicos. A análise térmica mostrou elevada estabilidade, enquanto a FTIR confirmou a predominância de sílica. O DRX revelou um grau de cristalinidade de 50,26%. As micrografias de MEV evidenciaram partículas fibrosas, rugosas e porosas, com preservação de estruturas da biomassa, o que favorece a dispersão e a adesão interfacial em matrizes poliméricas. Em conjunto, esses resultados reforçam a viabilidade da CBC como carga mineral alternativa em compósitos sustentáveis.
Implicações da Pesquisa: Os resultados confirmam que a CBC apresenta características químicas, estruturais e morfológicas compatíveis com seu uso como carga em polímeros. Sua estabilidade térmica e elevado teor de sílica reforçam o potencial para desenvolvimento de materiais sustentáveis e com propriedades melhoradas.
Originalidade/Valor: O trabalho contribui para ampliar o conhecimento sobre o uso da CBC como carga mineral alternativa, integrando diferentes técnicas de caracterização. Sua originalidade está em evidenciar o potencial técnico, alinhando inovação, economia e redução de impactos ambientais.
Palavras-chave: Cinza de bagaço de cana-de-açúcar, Compósitos Poliméricos, Caracterização, Sustentabilidade.
RESUMEN
Objetivo: El estudio tuvo como objetivo caracterizar la ceniza de bagazo de caña de azúcar (CBC) en cuanto a sus propiedades químicas, fisicoquímicas, térmicas, estructurales, cristalinas y morfológicas, con el fin de evaluar su potencial aplicación como relleno mineral en compósitos poliméricos.
Marco Teórico: La literatura destaca la relevancia de los residuos agroindustriales como fuente alternativa de rellenos minerales en polímeros, principalmente por su disponibilidad, bajo costo y carácter sostenible. La CBC se reconoce por su alto contenido de sílice, así como por óxidos metálicos que pueden influir en las propiedades mecánicas y térmicas (Barrera et al., 2021).
Método: La caracterización de la CBC se realizó mediante diversas técnicas. La composición química se determinó por FRX, mientras que la estabilidad térmica se evaluó mediante TGA. La técnica de FTIR permitió la identificación de grupos funcionales, y por DRX se determinaron las fases cristalinas y el grado de cristalinidad del material. Por último, la morfología de las partículas se examinó mediante SEM.
Resultados y Discusión: Los resultados indicaron que la CBC posee una composición química dominada por SiO2, seguida de K2O, Fe2O3 y CaO, sin presencia de elementos tóxicos. El análisis térmico mostró alta estabilidad, mientras que FTIR confirmó la predominancia de sílice. DRX reveló un grado de cristalinidad del 50,26%. Las micrografías de SEM mostraron partículas fibrosas, rugosas y porosas, con preservación de estructuras de la biomasa, lo que favorece la dispersión y adhesión interfacial en matrices poliméricas. En conjunto, estos resultados refuerzan la viabilidad de la CBC como relleno mineral alternativo en compósitos sostenibles.
Implicaciones de la Investigación: Los resultados confirman que la CBC presenta características químicas, estructurales y morfológicas compatibles con su uso como relleno en polímeros. Su estabilidad térmica y alto contenido de sílice refuerzan el potencial para el desarrollo de materiales sostenibles con propiedades mejoradas.
Originalidad/Valor: Este trabajo contribuye a ampliar el conocimiento sobre el uso de la CBC como relleno mineral alternativo, integrando diferentes técnicas de caracterización. Su originalidad radica en evidenciar su potencial técnico, alineando innovación, economía y reducción de impactos ambientales.
Palabras clave: Ceniza de Bagazo de Caña de Azúcar, Compuestos Poliméricos, Caracterización, Sostenibilidad.
1 INTRODUCTION
Polymeric composites have become established as materials with wide industrial applications across various sectors, due to their versatility, low weight, and the possibility of tailoring specific properties. However, despite technological advances in their processing, these materials still face challenges related to cost-effectiveness and sustainability, especially in light of the growing demand for environmentally responsible alternatives. In this context, the use of agro-industrial residues as fillers in polymer matrices has emerged as a promising strategy, aligned with the principles of the circular economy.
Sugarcane, one of the main agricultural crops in Brazil and worldwide, generates large volumes of solid residues throughout its production chain. Among these, bagasse stands out, frequently used as fuel in cogeneration processes for electricity, whose combustion produces sugarcane bagasse ash (SCBA). This ash is usually generated in large volumes and, in most cases, disposed of in landfills, a practice that has raised increasing environmental concerns (Sales & Lima, 2010).
However, the composition of this material, characterized by a high presence of silicon dioxide and other mineral oxides, gives it potential for use as a filler in polymeric composites, enabling the valorization of an abundant and low-cost by-product (Chuewangkam et al., 2022; Barrera et al., 2021; Cordeiro & Kurtis, 2017).
The central question that arises is: which characteristics of SCBA favor its application as a filler in polymeric composites? Investigating this issue is justified both by the need to reduce the environmental impacts of the sugar-energy sector and by the potential for valorizing a widely available residue, promoting the development of sustainable and technologically competitive materials.
In this context, this study aims to characterize and evaluate SCBA for application as a filler in polymeric composites, considering its composition and its physicochemical, morphological, thermal, and mineralogical properties, as well as to discuss its relevance for composite applications and to correlate the results obtained with its applicability, identifying benefits and limitations.
Thus, the intention is to provide technical and scientific support to enable the valorization of this residue, contributing to the development of more efficient and environmentally sustainable composites.
2 THEORETICAL FRAMEWORK
Over the last three decades, polymeric composites have consolidated themselves as widely used materials, with constant growth in both scale and applications. Despite their recognized efficiency in weight reduction, challenges related to cost-effectiveness and environmental impacts still persist. The industry has resorted to advanced manufacturing technologies, but improvements in processes alone do not guarantee competitiveness against metals, making an integrated approach necessary one that involves design, material selection, and production methods. In this context, interest has been growing in the use of natural fibers and the ashes resulting from these fibers as reinforcing elements, standing out for their sustainability, wide availability, and low cost, which makes them promising alternatives for the development of more efficient and environmentally viable composites (Gangaraju et al., 2024; Asim et al., 2018).
Polymeric composites are materials obtained by combining two or more constituents with the purpose of generating a product with improved properties resulting from the formation of an interfacial region, in addition to the specific properties of each component. In polymeric composites, there are two distinct phases: the matrix, which corresponds to the continuous phase and is represented by the polymeric material, and the dispersed phase (filler), consisting of fibers or particles that function as reinforcing elements (Callister, 2020, p. 865).
Fillers are solid and insoluble additives widely employed as reinforcing agents in resins or binders, such as polymers, concrete, metals, or ceramics. The incorporation of fillers in different composite systems has wide application in diverse industrial sectors, including packaging, agriculture, biomedicine, cosmetics, pharmaceuticals, food, paints, and the automotive industry (Fauzi et al., 2022).
Fillers can be incorporated into different classes of polymers, such as thermoplastics, elastomers, and thermosets (Morreale et al., 2015). The intrinsic characteristics of the filler, such as morphology, particle size distribution, and composition, must be carefully evaluated before incorporation into the matrix, since non-homogeneous dispersion can significantly compromise the performance of the composite. Filler distribution directly affects properties such as mechanical strength, optical transparency, and wear resistance (Praveenkumara et al., 2021; Jagadeesh et al., 2020).
Regarding morphology, fillers may be fibrous or particulate, being selected according to the desired properties. Fibrous fillers, such as glass and natural fibers, provide mechanical reinforcement due to their high aspect ratio, increasing strength and stiffness (Hsissou et al., 2021). Particulate fillers, generally mineral powders, present various shapes, sizes, and geometries, contributing to the improvement of the strength and toughness of polymer matrices (Fauzi et al., 2022).
The particle size of fillers has a significant influence on the final properties of composites. In general, smaller-diameter particles are preferred due to their larger specific surface area, which allows better interaction with the polymer matrix (Hsissou et al., 2021; Praveenkumara et al., 2021; Perthué et al., 2018; Bain et al., 2017; Morreale et al., 2015). Compatibility between the filler and the polymer is another essential factor for obtaining high-performance composites, as differences in polarity between the components may result in heterogeneous structures with inadequate performance (Fauzi et al., 2022).
In this scenario, sugarcane bagasse ash (SCBA) has received considerable attention in applications such as cement production, epoxy resin, rubber, residual oil adsorbent, and improvement of polymeric composites, due to its excellent performance in enhancing material properties (Gangaraju et al., 2024; Barrera et al., 2021; Khalil et al., 2021; Matos et al., 2021).
Sugarcane is widely used in sugar and ethanol production. According to data presented in 2024 by the Foreign Agricultural Service (FAS), world sugar production in the 2023/24 harvest reached 183.8 million tons, with the four largest producers being: Brazil (24.77%); India (18.49%); the European Union (8.10%); and China (5.42%) (USDA, 2024, p. 8).
After the juice extraction stage, bagasse is obtained, representing approximately 50% of the sugarcane mass. This by-product is widely used as fuel in cogeneration systems for the production of steam and electricity. As a residue of this process, SCBA is generated. It is estimated that the combustion of one ton of bagasse produces between 25 and 40 kg of SCBA, a residue that is mostly disposed of in landfills, constituting a significant environmental liability (Sales & Lima, 2010).
In light of this, researchers have been investigating new forms of SCBA utilization, such as in the manufacture of polymeric composites, cements, ceramics, and mesoporous silica-based catalysts. The physical and chemical properties of SCBA vary according to several factors, such as sugarcane variety, growth conditions, temperature and duration of bagasse combustion, bagasse purity, ash collection method, among others (Chuewangkam et al., 2022; Xu et al., 2019).
The color of SCBA ranges from black to white, depending on the combustion temperature, with darker coloration indicating a high carbon content due to incomplete combustion (Katare & Madurwar, 2017; Bahurudeen & Santhanam, 2015). SCBA particles can be classified into four main forms: spherical, prismatic, fibrous, and irregular. Prismatic and irregular particles contain silicon and indicate crystallization, which may reduce the pozzolanic activity of SCBA. Spherical particles are mainly formed by fusion at high temperatures and contain Mg, Ca, P, K, Si, Na, Fe, and other minor elements. Fibrous and unburned particles are generally very rough and have a unique microstructure, with unburned carbon as their main component (Bahurudeen & Santhanam, 2015).
Table 1 presents the chemical composition of SCBA from the work of various authors, showing significant variations among samples, although silica is always present as the main component.
Silica may occur in amorphous and crystalline forms (quartz and cristobalite). Amorphous silica, of biological origin, is absorbed by the plant from groundwater and polymerizes within its cells. Crystalline silica, on the other hand, considered inert, results from high-temperature incineration or from the presence of sand adhered to the sugarcane during harvesting (Cordeiro & Kurtis, 2017).
Silicon dioxide (SiO2) stands out among fillers for its ability to promote significant improvements in the mechanical strength of composites. In the study conducted by Jotiram et al. (2022), the effect of adding SiO2 to polymeric composites reinforced with kenaf fibers was investigated, evaluating four different filler mass fractions: 1%, 2%, 3%, and 4%. The results showed that increasing the SiO2 content gradually improved the mechanical properties of the material up to a concentration of 2%.
Barrero et al. (2021) investigated the morphology of SCBA particles using scanning electron microscopy in order to study the interaction between natural rubber and SCBA. Morphological analysis revealed irregularly shaped particles, with sizes ranging from 44 to 70 µm, in addition to fibers with an average width of 126 µm. The irregularity of the particles favors interaction with the polymer matrix, promoting a reinforcing effect attributed to filler- polymer interfacial interactions.
Supporting these findings, Chuewangkam et al. (2022) investigated SCBA-based geopolymers, studying the morphology of SCBA by SEM and its particle size distribution curve. They observed that the material exhibits an irregular shape, rough surface, and an average particle size of 105.22 µm, structural characteristics that contribute to greater interaction with the polymer matrix, positively influencing the mechanical performance of the composite.
Regarding thermal behavior, SCBA particles showed a mass loss of about 11% in the first degradation stage, attributed to the decomposition of organic matter such as cellulose, hemicellulose, and lignin, while their thermal stability was associated with the inorganic material content, as indicated by TGA (Barrero et al., 2021).
Given these variations, SCBA from different sources must be individually analyzed in terms of physicochemical, morphological, thermal, and mineralogical composition in order to define its most suitable applications.
The methodology of this work reports the description of the characterization methods employed for SCBA.
3 METHODOLOGY
3.1 MATERIALS
Sugarcane bagasse ash (SCBA) supplied by the Petribú Mill, located in the municipality of Lagoa de Itaenga-PE. The SCBA was used after being sieved through a stainless-steel mesh screen, size 5"x2", with an opening of 106 µm (mesh 140), brand: A Bronzinox, in compliance with ISO 3310/1 standard. Subsequently, the ash was dried in an oven with air circulation at 50 °C for 24 hours. The ash density (ρash = 1.983 g/cm3) was experimentally determined by pycnometry.
3.2 METHODS
The composition of the ash was analyzed using an energy-dispersive X-ray fluorescence spectrometer (XRF-EDX-8000, SHIMADZU). For this purpose, a portion of SCBA was transferred to a sample cell, which was covered with a special film for XRF-EDX analysis. The PCEDX Navi software was used to quantitatively obtain the analysis results.
Thermogravimetric analysis (TGA) of the ash was performed using a Mettler Toledo TGA 2 Star System. Approximately 5 mg of the sample was measured using a 70 µL alumina ceramic pan and an STA 6000 thermobalance (Mettler Toledo). The analysis was carried out within a temperature range of 30 °C to 1000 °C, with a heating rate of 10 °C/min, under a nitrogen atmosphere at a flow rate of 50 mL/min.
The spectra of SCBA samples were obtained by Fourier-transform infrared spectroscopy (FTIR) using a Spectrum 400 FTIR/FTNIR spectrometer (Perkin Elmer), equipped with an attenuated total reflectance (ATR) accessory. The spectra were recorded under the following instrument settings: infrared region in the spectral range from 4000 to 650 cm-1 in transmittance mode, averaging 16 scans with a resolution of 4 cm-1. Five averaged spectra corresponding to five SCBA fractions were obtained.
X-ray diffraction (XRD) characterization of SCBA was performed with Cu Kα radiation (λ = 0.1542 nm) and a copper filter. The scanning was conducted in the 2θ range from 5° to 80° at a speed of 0.02° s-1, using a Bruker D2 Phaser diffractometer. The crystallinity was calculated as the ratio between the crystalline area (peaks) and the amorphous area, according to Equation 1.
(ProQuest: ... denotes formula omitted.) (1)
Where:
%C is the crystalline fraction,
Ic is the diffraction peak area,
and Ia is the amorphous halo area. OriginPro 2019 software was used to obtain the amorphous halo and crystalline peak areas, as well as for data analysis.
The morphology of the ash was determined using a scanning electron microscope coupled with energy-dispersive spectroscopy (SEM-EDS, Tescan Mira 3), operated in low vacuum mode at an acceleration voltage of 5.0 kV. The sample was previously mounted on a stub with carbon tape and subsequently coated with a thin chromium layer (average thickness of 10 nm) using a Quorum Q300T TPlus sputter coater.
4 RESULTS AND DISCUSSION
In this chapter, the results obtained from the characterization of SCBA are presented and discussed, describing its chemical composition as well as its physicochemical, thermal, structural, crystalline, and morphological properties.
4.1 CHEMICAL COMPOSITION
The SCBA exhibited a predominantly dark gray color with an opaque appearance, characteristic of materials with a high concentration of residual carbon and the presence of mineral particles (Katare & Madurwar, 2017; Bahurudeen & Santhanam, 2015).
Before sieving, the material showed a heterogeneous appearance, with particles of different sizes and irregular shapes. After sieving, a significant homogenization of particle size distribution was observed, resulting in a finer and more uniform powder, as illustrated in Figure 1. The fraction retained in the sieve consisted of larger and more irregular particles, while the passing fraction was composed of particles with a more controlled granulometry, favoring better dispersion in a polymeric matrix, as reported by Barrera et al. (2021).
The chemical composition analysis of the ash, performed by XRF, identified the main inorganic oxides present in the material, with emphasis on silicon dioxide (SiO2), which showed the highest concentration. This result confirms the high silica content in SCBA reported in the literature, as referenced in Table 1. In addition, significant amounts of potassium oxide (K2O), iron oxide (Fe2O3), and calcium oxide (CaO) were identified. Table 2 presents the percentages of the oxides found in the SCBA evaluated in this study.
The XRF results showed that SCBA has a chemical composition rich in inorganic oxides, with a predominance of SiO2, representing 45.27% of the sample. This high silica content is characteristic of lignocellulosic residues derived from biomass combustion, such as sugarcane bagasse (Khalil et al., 2021; Xu et al., 2019). This composition confers properties that favor the application of SCBA as a mineral filler in polymer matrices, particularly due to its structural rigidity. Moreover, the significant presence of silica can also contribute to improved water vapor barrier properties and enhanced mechanical strength of composites when well dispersed in the matrix (Jotiram et al., 2022; Barrera et al., 2021; Hosseini et al., 2014).
The second most abundant component, K2O at 20.71%, can act as a fluxing agent, influencing the thermal stability of SCBA at elevated temperatures (Abba-Aji et al., 2023). The Fe2O3 content, at 14.20%, may impart a dark color to the material, act as a reinforcing agent, and improve mechanical and thermal properties, depending on its concentration and dispersion within the material (Basit et al., 2024; Najafi et al., 2021). CaO, at 11.70%, also appears as an important component. This oxide is known for its alkalinity and can influence both the filler's pH and its interaction with the polymer matrix. In certain applications, CaO may promote nucleation and increase the crystallinity of semicrystalline polymers, in addition to contributing to thermal stability (Mahmood et al., 2021).
The results also indicated the absence of potentially toxic elements such as cadmium (Cd), mercury (Hg), lead (Pb), and bromine (Br) in the XRF-analyzed sample.
Overall, the results suggest that SCBA presents a composition favorable for use as a filler in polymer composites, both due to its high silica content and the presence of oxides that can act synergistically to enhance the performance of the final material. However, to optimize composite performance, potential treatments or compatibilization strategies should be considered during development and processing to reduce the reactivity of certain oxides, such as K2O and CaO, thereby promoting homogeneous dispersion of SCBA in the matrix.
4.2 THERMOGRAVIMETRIC ANALYSIS
The thermogravimetric characterization (TGA) of the ash was carried out to evaluate its thermal stability and the feasibility of its application as an inorganic filler in polymer composites. The analysis considered both the mass loss curve as a function of temperature and its first derivative (DTG) to identify the main thermal decomposition events (Figure 2).
In the TGA curve, the decomposition range was observed between 438 °C and 590 °C, with the maximum degradation rate occurring around 529 °C, as evidenced by the peak in the DTG curve. This event is related to the combustion of residual organic matter, likely fixed carbon remaining from the incomplete combustion of the bagasse. From 600 °C onward, the TGA curve stabilizes, indicating the presence of a major thermally stable fraction corresponding to compounds such as silica (SiO2) and metal oxides.
The total mass loss was approximately 11%, with a final residue of around 89% of the initial mass, suggesting a high content of thermally stable inorganic phases. This behavior is desirable in polymer composite applications, as the thermal stability of the inorganic filler is essential to ensure structural integrity during the thermal processing of polymers (Jotiram et al., 2022; Barrera et al., 2021).
Therefore, SCBA exhibits suitable characteristics for use as a mineral filler in polymer matrices, contributing to the development of sustainable, lower-cost materials with reduced environmental impact.
4.3 MID-INFRARED SPECTROSCOPY
Spectroscopy was employed to identify the main functional groups present in SCBA and to infer relevant aspects of its chemical composition (Figure 3).
The obtained spectrum revealed the absence of a broad band in the 3400-3500 cm-1 region, which is attributed to O-H stretching vibrations. This region is associated with the presence of free hydroxyl groups and/or physically adsorbed water molecules on the ash surface, and its absence indicates that the material was free of moisture after drying in an air-circulating oven at 50 °C for 24 hours. A weak-intensity band was observed in the 2900-2950 cm-1 range, generally associated with C-H stretching vibrations. The low intensity of this band suggests efficient removal of organic matter during the combustion process and sieving through a 106 µm mesh (mesh 140).
The most intense and relevant band was observed between 1000-1100 cm-1, corresponding to asymmetric stretching vibrations of the Si-O-Si bond. This absorption indicates the presence of silica (SiO2), the main constituent of SCBA. Additionally, a band located between 800-900 cm-1 was attributed to stretching and bending vibrations of the Si-O group, suggesting the existence of silica in an amorphous or partially crystalline form.
In summary, the FTIR results indicate that the ash is primarily composed of silica, with an absence of moisture and low levels of organic matter. The predominance of amorphous silica, evidenced by the characteristic bands, reinforces the potential application of SCBA as a filler in polymeric materials. The conclusions reported by Chuewangkam et al. (2022) and Barrera et al. (2021) are in agreement with these findings.
4.4 X-RAY DIFFRACTION (XRD)
Figure 4 presents the normalized X-ray diffraction pattern of the SCBA sample, which reveals multiple well-defined diffraction peaks, characteristic of a crystalline structure.
The main peaks observed in the diffractogram, located in the 2θ regions around 21.8° and 26.6°, indicate the presence of crystalline silica, predominantly in the form of quartz. The XRD analysis of the SCBA sample revealed crystallographic patterns consistent with those described in ICDD card no. 04-008-8228, corresponding to quartz, and ICDD card no. 04-007- 4908, corresponding to cristobalite.
In addition, the presence of a peak around 29°-30° suggests the formation of wollastonite (CaSiO3), possibly originating from the reaction between CaO and SiO2 during the combustion process. A characteristic peak was also observed in the 34°-35° range, attributed to hematite (Fe2O3).
The identification of these crystalline phases is consistent with the chemical composition of SCBA obtained by XRF, as well as with data from the literature reporting the formation of similar crystalline structures in residues obtained from high-temperature combustion (Chuewangkam et al., 2022; Xu et al., 2019; Cordeiro & Kurtis, 2017; Katare & Madurwar, 2017; Moraes et al., 2016).
Based on the analysis of the SCBA diffraction pattern, a crystallinity degree of 50.26% was determined from Equation 1, highlighting the significant presence of crystalline phases in the sample. These results are in agreement with the data reported by Habte et al. (2025).
4.5 MORPHOLOGICAL ANALYSIS
The morphological characterization of SCBA was carried out with the aim of assessing its potential as an inorganic filler in polymer composites. The obtained micrographs reveal a heterogeneous morphology, composed of fibrous particles with predominantly irregular shapes, rough surfaces, and a high degree of porosity, as illustrated in Figure 5.
The fibrous particles in its microstructure exhibit highly rough surfaces, with the presence of cavities and pores dispersed along the surface (M2, M6 and M8). This complex topography enhances the specific surface area, which may contribute to improved interfacial adhesion with the polymer matrix. A partial preservation of anatomical structures from the original biomass can also be observed, such as cell walls and conductive vessels fossilized by deposition of biogenic silica (M1, M2, M3, M4, M5 and M6), imparting a lamellar or tubular morphology in certain regions of the material. Clemente et al. (2024), Prabhath et al. (2023) and Chusilp et al. (2009) also reported these characteristics. In higher magnification images, it is possible to identify nanopores and microcavities with varying radii (M2, M6, and M8), evidencing a multiscale texture. This feature can positively influence filler dispersion.
The presence of biogenic silica in the composition of SCBA, combined with the observed morphology, reinforces its potential as a filler, with the ability to act as a reinforcing agent and to contribute to the improvement of the thermal and mechanical properties of composites. Therefore, the results obtained indicate that SCBA presents favorable morphological characteristics for application as an alternative mineral filler in polymer matrices, potentially contributing significantly to the performance of sustainable composites, as reported by Chuewangkam et al. (2022) and Barrera et al. (2021).
5 CONCLUSION
The characterization of SCBA revealed a material rich in silica, with a favorable chemical composition, high thermal stability, significant presence of crystalline phases, and a fibrous, irregular, and porous morphology, factors that reinforce its potential as a mineral filler in polymer composites. The absence of toxic elements, combined with the observed structural and morphological properties, confirms the feasibility of SCBA as a sustainable alternative to conventional fillers, with the potential to contribute to the development of lower-cost, higher-performance materials aligned with sustainable practices.
ACKNOWLEDGMENTS
The authors would like to thank the following for their support: the members of the Laboratories of Petrochemistry (LPQ/UFPE), Composite Materials and Structural Integrity (CompoLab/UFPE), Physics Department (DF/UFPE), Fuels (LAC/UFPE) and the Laboratory of Preparation and Characterization of Materials at UFPE. We also acknowledge the Secretariat of Education and Sports of the State of Pernambuco (SEE-PE), the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil) Grant #304657/2025-5 for financial support and the Graduate Program in Chemical Engineering (PPGEQ/UFPE). Their financial and institutional support was essential for the development of this work.
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References
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