Fabrication and investigation of Mechanical and Moisture‑Resistant Hybrid Composites from Chitosan, Nano‑Silica, Biochar, and Rice Bran

Fabrication and investigation of Mechanical and Moisture‑Resistant Hybrid Composites from Chitosan, Nano‑Silica, Biochar, and Rice Bran | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Fabrication and investigation of Mechanical and Moisture‑Resistant Hybrid Composites from Chitosan, Nano‑Silica, Biochar, and Rice Bran Sambhrant Srivastava, SAVENDRA PRATAP SINGH, AKRITI DUTT This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8945576/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 12 You are reading this latest preprint version Abstract Epoxy composites are gaining attention in industries because they are lightweight, strong, and customizable. However, many epoxy composites still struggle with moisture resistance. This study explores epoxy-based composites reinforced with chitosan, nano-silica, biochar, and rice bran to develop stronger and more water-resistant material. Among the fabricated five formulations (H1–H5), H1 and H4 show the best results, with tensile and flexural strengths reaching 17.7 MPa and 173.8 MPa for H1, and 16.9 MPa and 168.2 MPa for H4. H4 also displays the lowest water absorption (2.21%) due to its dense microstructure and uniform filler dispersion. By exploring how different filler combinations and dispersions affect the polymer matrix, this work aims to enable the design of strong, durable, and sustainable composite materials. Chitosan Nano‑silica Biochar Rice bran Mechanical properties Water resistance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 1. Introduction Epoxy composites are vital in modern materials, valued for their high strength, thermal resistance, and chemical stability. They are widely used in aerospace, automotive, construction, and energy sectors[1]. Natural fibre composites have emerged as eco-friendly alternatives due to their low weight, strength, and sustainability benefits[2].Epoxy resin and hardener form the primary matrix in these composites, providing strong adhesion and structural integrity[3]. However hydrophilic nature of the fibers can cause water absorption, leading to swelling, loss of strength, cracking, and long-term degradation[4].To improve water resistance, researchers focus on surface treatments, better fiber–matrix bonding, selecting low-absorption matrices, adding protective coatings, and using fillers[5]. However, incorporating hybrid composite can lead to improvement in water resistant properties[6].Like, Biochar, a fine (2–3 µm) filler, reduces cost and weight while enhancing thermal and mechanical characteristics[7]. Biochar, a thermally stable, porous material, improves the mechanical, thermal, and electrical properties of epoxy composites, making it a promising, eco-friendly filler[8]. Biochar’s surface functional groups bond well with the epoxy matrix, enhancing stress transfer and tensile strength[9], [10]. However, at higher loadings, biochar can form agglomerates that create voids, reducing strength, impact resistance, and moisture resistance[11], [12].Rice bran, rich in cellulose and lignin, contributes to the composite’s tensile behavior and water absorption characteristics[13]. Meanwhile, natural fibres such as hemp, bamboo, and coir (1.3–1.5 g/cm³) add strength, reduce environmental impact, and boost flexural properties[14]. Rice bran fiber can enhance the strength and, when properly treated, the water resistance of composites, with its effectiveness largely influenced by the choice of matrix, fiber content, and surface treatments[15], [16]. While it improves tensile and flexural strength, its hydrophilic nature can increase water absorption unless mitigated by treatments and water-resistant polymers[17].Nano bio-silica (~ 20 nm) improves surface characteristics, thermal resistance, and filler-matrix bonding, making these composites a sustainable and high-performance material choice[8]. Nano bio-silica improves water resistance in composite material by filling the spaces within it, making it denser and harder for water to penetrate[3]. Thus, incorporating nano bio silica in composite which not only resist the also increases the mechanical strength[4]. Chitosan, derived from shellfish waste, acts as a natural biopolymer that improves surface properties and compatibility[18].Chitosan is a versatile, biodegradable biopolymer that can be combined with natural fibers, nanoparticles, or other polymers to create eco-friendly composites with improved strength and stability[3], [19], [20]. Its film-forming, antimicrobial, and water-absorbent properties make it ideal for applications in biomedical scaffolds, wastewater treatment, food packaging, textiles, and cosmetics[21], [22].Chitosan–hemp fiber composites combine strength and water resistance for sustainable applications[23]. Hemp fibers boost tensile strength (e.g., ~ 30% with 20 wt%), while chitosan acts as a binding matrix that can be cross-linked (e.g., with glutaraldehyde) to increase water resistance[23]–[25].Biochar as a filler in hemp fiber composites were tested the best results — tensile, impact, and hardness increased by ~ 94%, ~ 38%, and ~ 7%, respectively, compared to the biochar-free composite[26]. Combining nano-silica, biochar, and chitosan creates a strong and versatile material with improved surface area, strength, and adsorption abilities[27]. The present work introduces a unique hybrid composite formulation by combining biochar, chitosan, and natural fibre with nano-reinforcements, a blend that has been scarcely explored in literature. This approach aims to optimize mechanical strength and water resistance simultaneously, making the material suitable for a diverse range of applications from aerospace to biomedical engineering. 2. Material and methods 2.1 Materials The epoxy resin and corresponding hardener used in this study were procured from Pidilite Industries Ltd., Mumbai, India. Biochar with an average particle size of 2–3 µm and a density of 2.0 g/cm³ was supplied by Greenfield Eco-Solution. Chitosan, with a bulk density of 0.38 g/mL and a particle size range of 2–3 mm, was used as a natural biopolymer additive. Rice bran, having a bulk density of 0.35 g/cm³, served as an agricultural filler in selected composite formulations. Natural fibres including hemp is utilized, each possessing a density in the range of 1.3–1.5 g/cm³, providing reinforcement and mechanical strength to the composites. Additionally, nano bio-silica with a particle size of approximately 20 nm and a density of 2.7 g/cm³ was incorporated to enhance interfacial bonding within the matrix. 2.2 Methodology All composites’ samples are fabricated using the hand lay-up method. The epoxy and hardener were mixed in a stoichiometric ratio and stirred mechanically for 5 minutes. Separately, the chitosan was dissolved in a 1:100 acetic acid solution and stirred at 430 rpm for 10 minutes[28]. The chitosan solution was blended with the epoxy-resin matrix in a 1:5 ratio and sonicated for 20 minutes[29]. For samples containing nano bio-silica, the silica was added to the resin mixture at 1–5% by weight and ultrasonicated to ensure uniform dispersion. Dried fillers (biochar, rice bran, hemp) were then added into the matrix according to designated sample ratios as shown in Fig. 1 .. The prepared slurry was cast into a silicon rubber mold of 30 × 30 × 3.5 cm dimensions, which had been pre-coated with mold release wax. Reinforcement fibers (where applicable) were layered within the mold(Fig. 2 ). A compression pressure of 5 bar was applied for 1 hour using a hydraulic press at room temperature. Following layup and compaction, the composites were cured for 12 hours at room temperature and post-cured for 2 hours at 120°C. Cured composites were machined into standard specimen geometries using Abrasive Jet Machining (AJM) in compliance with ASTM testing standards abrasive flow rate was controlled at 0.42 g/s[30], [31]. Specimens for tensile testing were prepared according to ASTM D638(Fig. 3 ), flexural specimens followed ASTM D790(Fig. 4 ), and water absorption samples adhered to ASTM D570 [32], [33]. Five composite samples are formulated as H1, H2, H3, H4 and H5 as shown in Table 1 . Table 1 Composition details of hybrid epoxy composites (H1–H5) with varying weight percentages of chitosan, biochar, rice bran, natural fibres, and nano bio-silica. Sample Epoxy (%) Chitosan (%) Biochar (%) Rice Bran (%) Natural Fibers (%) Nano-Silica (%) H1 85 10 5 0 0 0 H2 80 5 10 5 0 0 H3 70 10 5 0 15 (hemp) 0 H4 65 10 5 0 15 (hemp) 5 H5 75 0 15 10 0 0 3. Results 3.1 Mechanical Properties As per the standard tensile, flexural test is conducted and observed with three specimens from each sample and is shown in Table 2 as (Mean ± SD). The graph of tensile strength, Tensile modulus, Flexural strength and flexural modulus is shown in Fig. 5 . Table 2 Mechanical properties of epoxy–chitosan composites with varying biochar, rice bran, hemp, and nano-silica contents. Sample Tensile Strength (MPa) Tensile Modulus (MPa) Flexural Strength (MPa) Flexural Modulus (MPa) H1 17.7 ± 0.9 8046 ± 194 173.8 ± 6.3 4933 ± 89 H2 15.1 ± 0.75 6005 ± 110 138.8 ± 2.5 3796 ± 43 H3 16.2 ± 1.2 7650 ± 150 162.4 ± 4.1 4280 ± 65 H4 16.9 ± 1.1 7810 ± 142 168.2 ± 3.6 4512 ± 73 H5 10.8 ± 0.65 4375 ± 524 98.6 ± 6.4 832 ± 49 3.2 Water Absorption and porosity The test measures sample weight before and after 24 h of water immersion as per the ASTM D570[33]. Porosity is then calculated using Eq. ( 1 ) and shown in Table 3 . $$\:Porosity=\frac{Water\:absorbed\:in\:specimens}{Intial\:Dry\:weight\:of\:specimens}x100$$ 1 Table 3 Water absorption (%) and porosity (%) of epoxy-based composite samples (H1–H5). Sample Water Absorption (%) Porosity (%) H1 2.32 0.13 H2 4.69 0.27 H3 3.65 0.19 H4 2.21 0.11 H5 9.04 0.55 3.3 Surface morphology by SEM The surface morphology of the tensile‑fractured samples H1–H5 was examined using SEM, and the resulting images for all five samples are presented in Fig. 6 . 4. Discussion The mechanical, moisture resistance, and microstructural properties of five sample composite are thoroughly analyzed. As evidenced in Fig. 5 , H1 demonstrated the best mechanical performance, achieving a tensile strength of 17.7 MPa, tensile modulus of 8,046 MPa, flexural strength of 173.8 MPa, and flexural modulus of 4,933 MPa. This superior performance is attributed to the uniform dispersion of biochar and chitosan within the epoxy matrix, yielding strong interfacial bonding is shown in Fig. 6 . From H1 to H2 as the percentage of biochar increases the strength decreases due to biochar’s porous structure and high surface area reduces the porosity thus water absorption also increased[34]. While chitosan percentage decrement from 10% to 5% also supports the decrease in strength and water resistant[35]–[38]. However chitosan inclusion doesn’t always supports the increase in strength or water resistance[38]. In H2 Rice bran hydrophilic nature also plays a major role in increasing the moisture absorption characteristics[39].Comparable results are evidenced from H4 sample composites with tensile and flexural strengths of 16.9 MPa and 168.2 MPa, and tensile and flexural moduli of 7,810 MPa and 4,512 MPa, respectively as shown in Fig. 5 . These results are well supported from SEM with dense structure but some micro cracks were observed. From Table 3 , H4 is observed with low water absorption (2.21%) and porosity (0.11%), indicating an effective barrier effect from the nano-silica. Removing the nano silica in H3 sample and incorporating Hemp fiber evidenced with moderate mechanical performance (tensile strength: 16.2 MPa, tensile modulus: 7,650 MPa, flexural strength: 162.4 MPa, flexural modulus: 4,280 MPa). From Fig. 6 of H3 sample some fibers pull out but well embedded fibers. However, from Table 3 , it is observed that water absorption of H3 sample is 3.65% which is due to hemp moisture affinity[40], in the end, H2 and H5 are two certain samples which observed with lowest strength and water resistance properties. H2 shows a tensile strength of 15.1 MPa which is highest among both. These results are well supported SEM examination of H2 samples, the presence of microcracks and moderate voids, indicating weaker interfacial adhesion of rice bran[41]. In similar way a high percentage of rice bran and absence of nano silica and chitosan makes H5 weak in strength and low water-resistant composite. The chitosan impact in strength can be clearly evidence in H3 composite where the strength and moisture resistance are very close to H1. The strength of H4 is found to be greater than H2 due to blend of nano silica, due to filling of pores by nano silica and removing voids, it becomes denser and stronger and thus water resistant property is increased[42], [43]. 5. Conclusion The study highlights the mechanical properties of polymer composite filler compositions and their influence on water resistance. Among five sample composites (H1–H5) with hybrid fillers, H1 and H4 emerge with the highest tensile and flexural strength and the best water resistance. H1 achieves the highest tensile (17.7 MPa) and flexural (173.8 MPa) strengths, while H4 offers comparable tensile (16.9 MPa) and flexural (168.2 MPa) properties combined with the best water resistance (2.21%), owing to the densification and uniform filler dispersion facilitated by nano-silica. In contrast, the sample blended with biochar and rice bran exhibits the weakest performance due to void generation when combined with the epoxy matrix. These results signify that a balanced combination of fillers ensures strong structural integrity, and that chitosan, nano-silica, and hemp fiber form a promising filler combination for water-resistant composite materials. These insights guide the design of high-performance, sustainable composites for automotive, construction, and biomedical applications. Declarations Funding Declaration This research received no external funding. Competing Interests Declaration The authors declare that they have no competing interests. Conflict of Interest Authors declare that there is no conflict of interest in terms of research, authorship and publication in this research paper. Funding Authors declare that no known financial sources available for this research work. Author Contribution Sambhrant Srivastava & Savendra Pratap Singh: Conceptualization; experimental work; wrote paper **Akriti Dutt:** proofread; wrote paper Acknowledgement Authors are very thankful to REC, Azamgarh for providing laboratory for research work. Data Availability All used data are included in the research paper. References L. Bartosova, M. Kohutiar, M. Krbata, J. Escherova, M. Eckert, and M. Jus, “The Influence of Accelerated Electron Irradiation on the Change of Tribological Behavior of Polymeric Materials PET, PTFE & PE2000C,” Manuf. Technol. , vol. 23, no. 5, pp. 589–596, 2023. S. Srivastava, S. K. Sarangi, and S. P. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8945576","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":636734570,"identity":"f0323f3a-7c05-4b01-9342-5ef84315a9d4","order_by":0,"name":"Sambhrant Srivastava","email":"","orcid":"","institution":"Rajkiya Engineering College Azamgarh","correspondingAuthor":false,"prefix":"","firstName":"Sambhrant","middleName":"","lastName":"Srivastava","suffix":""},{"id":636734571,"identity":"e41a24db-b8c5-4f14-b5a1-3ffb06f9d54d","order_by":1,"name":"SAVENDRA PRATAP SINGH","email":"data:image/png;base64,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","orcid":"","institution":"Rajkiya Engineering College Azamgarh","correspondingAuthor":true,"prefix":"","firstName":"SAVENDRA","middleName":"PRATAP","lastName":"SINGH","suffix":""},{"id":636734572,"identity":"f2f79eb2-209e-440e-8244-2567e218abad","order_by":2,"name":"AKRITI DUTT","email":"","orcid":"","institution":"Narendra Dev University of Agriculture and Technology","correspondingAuthor":false,"prefix":"","firstName":"AKRITI","middleName":"","lastName":"DUTT","suffix":""}],"badges":[],"createdAt":"2026-02-23 09:54:11","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8945576/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8945576/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":109014022,"identity":"8c0ac6d1-cbda-47cf-97a5-834d1612df6d","added_by":"auto","created_at":"2026-05-11 17:12:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":128056,"visible":true,"origin":"","legend":"\u003cp\u003eFabrication of composites by mixing epoxy, chitosan, nano‑silica, and dried fillers.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8945576/v1/274d5a9dd539b1c0180b4788.png"},{"id":109014030,"identity":"4afcdd14-521b-4cc9-9095-ae805431c0c5","added_by":"auto","created_at":"2026-05-11 17:12:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":312154,"visible":true,"origin":"","legend":"\u003cp\u003eBlending of biochar-chitosan-hemp-rice bran using hand layup technique.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8945576/v1/5056c27ecb4d873c86a89c0a.png"},{"id":109014034,"identity":"4f93f4e8-854c-4f0d-a2d7-0e0fa06f101f","added_by":"auto","created_at":"2026-05-11 17:12:18","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":636745,"visible":true,"origin":"","legend":"\u003cp\u003eFive samples H1, H2,H3,H4 and H5 as per ASTM standard for Tensile Strength.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8945576/v1/130e9104c0a83b13526b5e8b.jpeg"},{"id":109014047,"identity":"eb4ad2cc-689e-4868-b1fa-00ba2bda7d81","added_by":"auto","created_at":"2026-05-11 17:12:24","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":484591,"visible":true,"origin":"","legend":"\u003cp\u003eFive samples H1, H2, H3, H4 and H5 as per ASTM standard for Flexural Strength.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8945576/v1/cf010ea2d70b285605dace6d.png"},{"id":109014025,"identity":"efd44a1e-75a9-4f74-a407-e4b4e00f4247","added_by":"auto","created_at":"2026-05-11 17:12:16","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":119905,"visible":true,"origin":"","legend":"\u003cp\u003eGraphical representation of mechanical properties of epoxy-based composite samples (H1–H5). (Top Left) Tensile Strength (MPa), (Top Right) Tensile Modulus (MPa), (Bottom Left) Flexural Strength (MPa), and (Bottom Right) Flexural Modulus (MPa).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8945576/v1/d9fb56fcc5693d2e9cfb80a5.png"},{"id":109014049,"identity":"b0774955-4beb-4296-9a32-8fa19dcb2f82","added_by":"auto","created_at":"2026-05-11 17:12:25","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":604686,"visible":true,"origin":"","legend":"\u003cp\u003eScanning Electron Microscopy (SEM) micrographs of composite samples H1 to H5 showing surface morphology and filler dispersion characteristics\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8945576/v1/c9baf9690f7547cac3d80e55.png"},{"id":109205856,"identity":"8d427f24-e5e0-4b43-b4e6-bbe7181ac5c8","added_by":"auto","created_at":"2026-05-13 15:08:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2694967,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8945576/v1/db00935a-3f96-4fc0-bbc8-c2b87a8fad8b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Fabrication and investigation of Mechanical and Moisture‑Resistant Hybrid Composites from Chitosan, Nano‑Silica, Biochar, and Rice Bran","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eEpoxy composites are vital in modern materials, valued for their high strength, thermal resistance, and chemical stability. They are widely used in aerospace, automotive, construction, and energy sectors[1]. Natural fibre composites have emerged as eco-friendly alternatives due to their low weight, strength, and sustainability benefits[2].Epoxy resin and hardener form the primary matrix in these composites, providing strong adhesion and structural integrity[3]. However hydrophilic nature of the fibers can cause water absorption, leading to swelling, loss of strength, cracking, and long-term degradation[4].To improve water resistance, researchers focus on surface treatments, better fiber\u0026ndash;matrix bonding, selecting low-absorption matrices, adding protective coatings, and using fillers[5]. However, incorporating hybrid composite can lead to improvement in water resistant properties[6].Like, Biochar, a fine (2\u0026ndash;3 \u0026micro;m) filler, reduces cost and weight while enhancing thermal and mechanical characteristics[7]. Biochar, a thermally stable, porous material, improves the mechanical, thermal, and electrical properties of epoxy composites, making it a promising, eco-friendly filler[8]. Biochar\u0026rsquo;s surface functional groups bond well with the epoxy matrix, enhancing stress transfer and tensile strength[9], [10]. However, at higher loadings, biochar can form agglomerates that create voids, reducing strength, impact resistance, and moisture resistance[11], [12].Rice bran, rich in cellulose and lignin, contributes to the composite\u0026rsquo;s tensile behavior and water absorption characteristics[13]. Meanwhile, natural fibres such as hemp, bamboo, and coir (1.3\u0026ndash;1.5 g/cm\u0026sup3;) add strength, reduce environmental impact, and boost flexural properties[14]. Rice bran fiber can enhance the strength and, when properly treated, the water resistance of composites, with its effectiveness largely influenced by the choice of matrix, fiber content, and surface treatments[15], [16]. While it improves tensile and flexural strength, its hydrophilic nature can increase water absorption unless mitigated by treatments and water-resistant polymers[17].Nano bio-silica (~\u0026thinsp;20 nm) improves surface characteristics, thermal resistance, and filler-matrix bonding, making these composites a sustainable and high-performance material choice[8]. Nano bio-silica improves water resistance in composite material by filling the spaces within it, making it denser and harder for water to penetrate[3]. Thus, incorporating nano bio silica in composite which not only resist the also increases the mechanical strength[4]. Chitosan, derived from shellfish waste, acts as a natural biopolymer that improves surface properties and compatibility[18].Chitosan is a versatile, biodegradable biopolymer that can be combined with natural fibers, nanoparticles, or other polymers to create eco-friendly composites with improved strength and stability[3], [19], [20]. Its film-forming, antimicrobial, and water-absorbent properties make it ideal for applications in biomedical scaffolds, wastewater treatment, food packaging, textiles, and cosmetics[21], [22].Chitosan\u0026ndash;hemp fiber composites combine strength and water resistance for sustainable applications[23]. Hemp fibers boost tensile strength (e.g., ~\u0026thinsp;30% with 20 wt%), while chitosan acts as a binding matrix that can be cross-linked (e.g., with glutaraldehyde) to increase water resistance[23]\u0026ndash;[25].Biochar as a filler in hemp fiber composites were tested the best results \u0026mdash; tensile, impact, and hardness increased by ~\u0026thinsp;94%, ~\u0026thinsp;38%, and ~\u0026thinsp;7%, respectively, compared to the biochar-free composite[26]. Combining nano-silica, biochar, and chitosan creates a strong and versatile material with improved surface area, strength, and adsorption abilities[27].\u003c/p\u003e \u003cp\u003eThe present work introduces a unique hybrid composite formulation by combining biochar, chitosan, and natural fibre with nano-reinforcements, a blend that has been scarcely explored in literature. This approach aims to optimize mechanical strength and water resistance simultaneously, making the material suitable for a diverse range of applications from aerospace to biomedical engineering.\u003c/p\u003e"},{"header":"2. Material and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe epoxy resin and corresponding hardener used in this study were procured from Pidilite Industries Ltd., Mumbai, India. Biochar with an average particle size of 2\u0026ndash;3 \u0026micro;m and a density of 2.0 g/cm\u0026sup3; was supplied by Greenfield Eco-Solution. Chitosan, with a bulk density of 0.38 g/mL and a particle size range of 2\u0026ndash;3 mm, was used as a natural biopolymer additive. Rice bran, having a bulk density of 0.35 g/cm\u0026sup3;, served as an agricultural filler in selected composite formulations. Natural fibres including hemp is utilized, each possessing a density in the range of 1.3\u0026ndash;1.5 g/cm\u0026sup3;, providing reinforcement and mechanical strength to the composites. Additionally, nano bio-silica with a particle size of approximately 20 nm and a density of 2.7 g/cm\u0026sup3; was incorporated to enhance interfacial bonding within the matrix.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Methodology\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eAll composites\u0026rsquo; samples are fabricated using the hand lay-up method. The epoxy and hardener were mixed in a stoichiometric ratio and stirred mechanically for 5 minutes. Separately, the chitosan was dissolved in a 1:100 acetic acid solution and stirred at 430 rpm for 10 minutes[28]. The chitosan solution was blended with the epoxy-resin matrix in a 1:5 ratio and sonicated for 20 minutes[29]. For samples containing nano bio-silica, the silica was added to the resin mixture at 1\u0026ndash;5% by weight and ultrasonicated to ensure uniform dispersion. Dried fillers (biochar, rice bran, hemp) were then added into the matrix according to designated sample ratios as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.. The prepared slurry was cast into a silicon rubber mold of 30 \u0026times; 30 \u0026times; 3.5 cm dimensions, which had been pre-coated with mold release wax. Reinforcement fibers (where applicable) were layered within the mold(Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). A compression pressure of 5 bar was applied for 1 hour using a hydraulic press at room temperature. Following layup and compaction, the composites were cured for 12 hours at room temperature and post-cured for 2 hours at 120\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eCured composites were machined into standard specimen geometries using Abrasive Jet Machining (AJM) in compliance with ASTM testing standards abrasive flow rate was controlled at 0.42 g/s[30], [31]. Specimens for tensile testing were prepared according to ASTM D638(Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), flexural specimens followed ASTM D790(Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), and water absorption samples adhered to ASTM D570 [32], [33]. Five composite samples are formulated as H1, H2, H3, H4 and H5 as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComposition details of hybrid epoxy composites (H1\u0026ndash;H5) with varying weight percentages of chitosan, biochar, rice bran, natural fibres, and nano bio-silica.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEpoxy (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eChitosan (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBiochar (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRice Bran (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNatural Fibers (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eNano-Silica (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e85\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e15 (hemp)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e15 (hemp)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Mechanical Properties\u003c/h2\u003e \u003cp\u003eAs per the standard tensile, flexural test is conducted and observed with three specimens from each sample and is shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e as (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD). The graph of tensile strength, Tensile modulus, Flexural strength and flexural modulus is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMechanical properties of epoxy\u0026ndash;chitosan composites with varying biochar, rice bran, hemp, and nano-silica contents.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026plusmn;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTensile Strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTensile Modulus (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFlexural Strength (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFlexural Modulus (MPa)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e17.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e8046\u0026thinsp;\u0026plusmn;\u0026thinsp;194\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e173.8\u0026thinsp;\u0026plusmn;\u0026thinsp;6.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e4933\u0026thinsp;\u0026plusmn;\u0026thinsp;89\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e15.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e6005\u0026thinsp;\u0026plusmn;\u0026thinsp;110\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e138.8\u0026thinsp;\u0026plusmn;\u0026thinsp;2.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e3796\u0026thinsp;\u0026plusmn;\u0026thinsp;43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e16.2\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7650\u0026thinsp;\u0026plusmn;\u0026thinsp;150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e162.4\u0026thinsp;\u0026plusmn;\u0026thinsp;4.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e4280\u0026thinsp;\u0026plusmn;\u0026thinsp;65\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e16.9\u0026thinsp;\u0026plusmn;\u0026thinsp;1.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e7810\u0026thinsp;\u0026plusmn;\u0026thinsp;142\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e168.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e4512\u0026thinsp;\u0026plusmn;\u0026thinsp;73\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c2\"\u003e \u003cp\u003e10.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c3\"\u003e \u003cp\u003e4375\u0026thinsp;\u0026plusmn;\u0026thinsp;524\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c4\"\u003e \u003cp\u003e98.6\u0026thinsp;\u0026plusmn;\u0026thinsp;6.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026plusmn;\" colname=\"c5\"\u003e \u003cp\u003e832\u0026thinsp;\u0026plusmn;\u0026thinsp;49\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Water Absorption and porosity\u003c/h2\u003e \u003cp\u003eThe test measures sample weight before and after 24 h of water immersion as per the ASTM D570[33]. Porosity is then calculated using Eq.\u0026nbsp;(\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:Porosity=\\frac{Water\\:absorbed\\:in\\:specimens}{Intial\\:Dry\\:weight\\:of\\:specimens}x100$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eWater absorption (%) and porosity (%) of epoxy-based composite samples (H1\u0026ndash;H5).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWater Absorption (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePorosity (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.13\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e3.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.19\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eH5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e9.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Surface morphology by SEM\u003c/h2\u003e \u003cp\u003eThe surface morphology of the tensile‑fractured samples H1\u0026ndash;H5 was examined using SEM, and the resulting images for all five samples are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eThe mechanical, moisture resistance, and microstructural properties of five sample composite are thoroughly analyzed. As evidenced in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, H1 demonstrated the best mechanical performance, achieving a tensile strength of 17.7 MPa, tensile modulus of 8,046 MPa, flexural strength of 173.8 MPa, and flexural modulus of 4,933 MPa. This superior performance is attributed to the uniform dispersion of biochar and chitosan within the epoxy matrix, yielding strong interfacial bonding is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. From H1 to H2 as the percentage of biochar increases the strength decreases due to biochar\u0026rsquo;s porous structure and high surface area reduces the porosity thus water absorption also increased[34]. While chitosan percentage decrement from 10% to 5% also supports the decrease in strength and water resistant[35]\u0026ndash;[38]. However chitosan inclusion doesn\u0026rsquo;t always supports the increase in strength or water resistance[38]. In H2 Rice bran hydrophilic nature also plays a major role in increasing the moisture absorption characteristics[39].Comparable results are evidenced from H4 sample composites with tensile and flexural strengths of 16.9 MPa and 168.2 MPa, and tensile and flexural moduli of 7,810 MPa and 4,512 MPa, respectively as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. These results are well supported from SEM with dense structure but some micro cracks were observed. From Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, H4 is observed with low water absorption (2.21%) and porosity (0.11%), indicating an effective barrier effect from the nano-silica. Removing the nano silica in H3 sample and incorporating Hemp fiber evidenced with moderate mechanical performance (tensile strength: 16.2 MPa, tensile modulus: 7,650 MPa, flexural strength: 162.4 MPa, flexural modulus: 4,280 MPa). From Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e of H3 sample some fibers pull out but well embedded fibers. However, from Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, it is observed that water absorption of H3 sample is 3.65% which is due to hemp moisture affinity[40], in the end, H2 and H5 are two certain samples which observed with lowest strength and water resistance properties. H2 shows a tensile strength of 15.1 MPa which is highest among both. These results are well supported SEM examination of H2 samples, the presence of microcracks and moderate voids, indicating weaker interfacial adhesion of rice bran[41]. In similar way a high percentage of rice bran and absence of nano silica and chitosan makes H5 weak in strength and low water-resistant composite.\u003c/p\u003e \u003cp\u003eThe chitosan impact in strength can be clearly evidence in H3 composite where the strength and moisture resistance are very close to H1. The strength of H4 is found to be greater than H2 due to blend of nano silica, due to filling of pores by nano silica and removing voids, it becomes denser and stronger and thus water resistant property is increased[42], [43].\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eThe study highlights the mechanical properties of polymer composite filler compositions and their influence on water resistance. Among five sample composites (H1\u0026ndash;H5) with hybrid fillers, H1 and H4 emerge with the highest tensile and flexural strength and the best water resistance. H1 achieves the highest tensile (17.7 MPa) and flexural (173.8 MPa) strengths, while H4 offers comparable tensile (16.9 MPa) and flexural (168.2 MPa) properties combined with the best water resistance (2.21%), owing to the densification and uniform filler dispersion facilitated by nano-silica. In contrast, the sample blended with biochar and rice bran exhibits the weakest performance due to void generation when combined with the epoxy matrix. These results signify that a balanced combination of fillers ensures strong structural integrity, and that chitosan, nano-silica, and hemp fiber form a promising filler combination for water-resistant composite materials. These insights guide the design of high-performance, sustainable composites for automotive, construction, and biomedical applications.\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eFunding Declaration\u003c/strong\u003e \u003cp\u003eThis research received no external funding.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCompeting Interests Declaration\u003c/strong\u003e \u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003eConflict of Interest\u003c/h2\u003e \u003cp\u003eAuthors declare that there is no conflict of interest in terms of research, authorship and publication in this research paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eAuthors declare that no known financial sources available for this research work.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eSambhrant Srivastava \u0026amp;amp; Savendra Pratap Singh: Conceptualization; experimental work; wrote paper **Akriti Dutt:** proofread; wrote paper\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eAuthors are very thankful to REC, Azamgarh for providing laboratory for research work.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e \u003cp\u003eAll used data are included in the research paper.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eL. Bartosova, M. Kohutiar, M. Krbata, J. Escherova, M. Eckert, and M. Jus, \u0026ldquo;The Influence of Accelerated Electron Irradiation on the Change of Tribological Behavior of Polymeric Materials PET, PTFE \u0026amp; PE2000C,\u0026rdquo; \u003cem\u003eManuf. Technol.\u003c/em\u003e, vol. 23, no. 5, pp. 589\u0026ndash;596, 2023.\u003c/li\u003e\n\u003cli\u003eS. Srivastava, S. K. Sarangi, and S. P. Singh, \u0026ldquo;An FEA Analysis of Nano-Silica Reinforced Chitosan Based Dental Implant Under Dynamic Loading,\u0026rdquo; \u003cem\u003eSilicon\u003c/em\u003e, vol. 16, no. 17, pp. 6055\u0026ndash;6072, Nov. 2024, doi: 10.1007/s12633-024-03133-2.\u003c/li\u003e\n\u003cli\u003eS. Srivastava, S. K. Sarangi, and S. P. Singh, \u0026ldquo;Water Absorptivity and Porosity Investigation of Nano Bio-silica, Hemp, and Bamboo Fibre-reinforced Chitosan Bio-composite Material,\u0026rdquo; \u003cem\u003eSilicon\u003c/em\u003e, vol. 16, no. 11, pp. 4723\u0026ndash;4728, Jul. 2024, doi: 10.1007/s12633-024-03027-3.\u003c/li\u003e\n\u003cli\u003eM. A. E.-S. Arab, A. S. Mohamed, M. K. Taha, and A. Nasr, \u0026ldquo;Microstructure, durability and mechanical properties of high strength geopolymer concrete containing calcinated nano-silica fume/nano-alumina blend,\u0026rdquo; \u003cem\u003eConstr. Build. Mater.\u003c/em\u003e, vol. 472, p. 140903, 2025, doi: https://doi.org/10.1016/j.conbuildmat.2025.140903.\u003c/li\u003e\n\u003cli\u003eE. Woldesenbet, N. Gupta, and J. R. Vinson, \u0026ldquo;Determination of moisture effects on impact properties of composite materials,\u0026rdquo; \u003cem\u003eJ. Mater. 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Reddy, \u0026ldquo;18 - Role of nanomaterials in protecting building materials from degradation and deterioration,\u0026rdquo; in \u003cem\u003eBiodegradation and Biodeterioration At the Nanoscale\u003c/em\u003e, H. M. N. Iqbal, M. Bilal, T. A. Nguyen, and G. Yasin, Eds., in Micro and Nano Technologies. Elsevier, 2022, pp. 405\u0026ndash;475. doi: https://doi.org/10.1016/B978-0-12-823970-4.00024-5.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"silicon","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scon","sideBox":"Learn more about [Silicon](https://www.springer.com/journal/12633)","snPcode":"12633","submissionUrl":"https://submission.nature.com/new-submission/12633/3","title":"Silicon","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Chitosan, Nano‑silica, Biochar, Rice bran, Mechanical properties, Water resistance","lastPublishedDoi":"10.21203/rs.3.rs-8945576/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8945576/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEpoxy composites are gaining attention in industries because they are lightweight, strong, and customizable. However, many epoxy composites still struggle with moisture resistance. This study explores epoxy-based composites reinforced with chitosan, nano-silica, biochar, and rice bran to develop stronger and more water-resistant material. Among the fabricated five formulations (H1\u0026ndash;H5), H1 and H4 show the best results, with tensile and flexural strengths reaching 17.7 MPa and 173.8 MPa for H1, and 16.9 MPa and 168.2 MPa for H4. H4 also displays the lowest water absorption (2.21%) due to its dense microstructure and uniform filler dispersion. By exploring how different filler combinations and dispersions affect the polymer matrix, this work aims to enable the design of strong, durable, and sustainable composite materials.\u003c/p\u003e","manuscriptTitle":"Fabrication and investigation of Mechanical and Moisture‑Resistant Hybrid Composites from Chitosan, Nano‑Silica, Biochar, and Rice Bran","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-11 17:12:11","doi":"10.21203/rs.3.rs-8945576/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-15T06:16:07+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-08T08:52:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"153727642933626986055112063315558680868","date":"2026-05-02T19:22:03+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-02T11:12:49+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"148785677125247373547408046056582692892","date":"2026-05-02T10:36:41+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"63564672167971246450727049426732245994","date":"2026-05-02T08:31:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"62767748705005605848623933144605878150","date":"2026-05-02T05:56:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"214261356619309565743017881685175457133","date":"2026-05-02T00:56:08+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-05-01T16:48:21+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-26T22:58:48+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-26T22:58:03+00:00","index":"","fulltext":""},{"type":"submitted","content":"Silicon","date":"2026-02-23T09:43:26+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"silicon","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scon","sideBox":"Learn more about [Silicon](https://www.springer.com/journal/12633)","snPcode":"12633","submissionUrl":"https://submission.nature.com/new-submission/12633/3","title":"Silicon","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"3c6df7d1-ac23-4221-acaa-1c6516d311d9","owner":[],"postedDate":"May 11th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-15T06:16:07+00:00","index":19,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-08T08:52:38+00:00","index":18,"fulltext":""},{"type":"reviewerAgreed","content":"153727642933626986055112063315558680868","date":"2026-05-02T19:22:03+00:00","index":16,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-05-02T11:12:49+00:00","index":15,"fulltext":""},{"type":"reviewerAgreed","content":"148785677125247373547408046056582692892","date":"2026-05-02T10:36:41+00:00","index":14,"fulltext":""},{"type":"reviewerAgreed","content":"63564672167971246450727049426732245994","date":"2026-05-02T08:31:00+00:00","index":13,"fulltext":""},{"type":"reviewerAgreed","content":"62767748705005605848623933144605878150","date":"2026-05-02T05:56:45+00:00","index":12,"fulltext":""},{"type":"reviewerAgreed","content":"214261356619309565743017881685175457133","date":"2026-05-02T00:56:08+00:00","index":11,"fulltext":""},{"type":"reviewersInvited","content":"7","date":"2026-05-01T16:48:21+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-11T17:12:11+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-11 17:12:11","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8945576","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8945576","identity":"rs-8945576","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}