Investigation of Castor-oil Foam Adhesion on Aluminium Through Single-lap Tests

Investigation of Castor-oil Foam Adhesion on Aluminium Through Single-lap Tests | 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 Investigation of Castor-oil Foam Adhesion on Aluminium Through Single-lap Tests Luís Felipe Cabral Diogo Nogueira, Júlio Cesar dos Santos, Túlio Hallak Panzera, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5241986/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 15 You are reading this latest preprint version Abstract This work investigates the adhesion of a castor-oil-based polyurethane (PU) biofoam to the surface of 1200 aluminium. The foam is fabricated using water as the blowing agent. The apparent shear strength, joint toughness and adherent strength of single-lap joints are assessed following the ASTM standard D1002. 3D-printed moulds are developed for sample preparation. The study evaluates three different bonding strategies related to polymer curing: (1) Simple Cure, (2) Co-Cure with Adhesive Layer and (3) Direct Bonding. The Simple Curing method is conducted by expanding the PU biofoam in the mould cavity in contact with the aluminium sheets. In the second method, a layer of castor-oil PU resin is previously applied to the internal aluminium surfaces before pouring the water-PU foaming mixture. The foaming process thus occurs inside the mould as in (2), with the additional co-cure of the adhesive PU resin layer on the aluminium sheets. In the direct bonding method (3), a slab of previously cured foam is bonded to the aluminium faces using a layer of castor-oil PU resin previously applied to the internal metallic surfaces, as in (2). This study is motivated by a subsequent study on foam-core sandwich panels, in which the best face-core bonding strategy will be used. Adhesion Castor-oil polyurethane Mechanical Properties Single-Lap Biofoam Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Composite materials play a fundamental role in contemporary engineering, offering an innovative approach to achieving specific properties that are not feasible with traditional materials. Owing to significant advantages such as high strength, high stiffness, reduced weight, reliable performance under fatigue conditions and effective corrosion resistance [ 1 ], the use of composite materials has progressively grown in a wide variety of areas, such as the aeronautic and automotive industries, shipbuilding, railways, civil construction and sports, among others. In this sense, materials scientists and engineers face a significant challenge beyond developing efficient and economical products: promoting technological evolution without jeopardising the availability of resources for future generations. High population growth has resulted in high production and consumption of materials, which has led to waste accumulation and reduced natural resources. As a result, considerable scientific effort has been focused on reducing environmental impact by using alternative materials and renewable natural resources to supply high-quality industrial products [ 2 – 4 ]. Recent studies have focused on using foams as the core of sandwich panels [ 5 – 7 ]. Such structural composites provide improved flexural stiffness at low densities. However, the adhesive strategy used for face-core bonding is essential for their mechanical performance. The single-lap shear test is frequently used to evaluate the mechanical performance of different adhesives. This study is motivated by a subsequent study on foam-core sandwich panels, in which the best face-core bonding strategy will be used. Al-Ostaz et al. [ 8 ] investigated high-performance pressure-sensitive adhesives and VHB™ acrylic foam tapes in 2024 T-4 aluminium joints in single-lap joint (SLJ) configurations. Static load (lap shear) and dynamic impact tests were carried out on the joints to compare the mechanical properties before and after environmental ageing. The results showed that the acrylic tapes provided lower static load resistance compared to the pressure-sensitive adhesives; the impact energy absorption was, however, similar for both materials. Malik et al. [ 9 ] used a single-lap shear strength test to investigate the effect of adding TiO 2 to castor oil-based polyurethane adhesive to improve its mechanical properties. The authors reported a significant increase in shear strength, outperforming commercial wood-bonding adhesives. In a similar study, Santana et al.[ 10 ] evaluated the interlocking effect of silica microparticle or cement inclusions in glass fibre laminate composite single-lap joints. Analysis of variance (ANOVA) was carried out on the results obtained, showing that cement and silica microparticles provide superior resistance, increasing by 31.5% and 25.3%, respectively, compared to single-lap joints without microparticles. Romeu et al. [ 11 ] investigated single-lap joints using castor-oil PU and epoxy composites reinforced with glass fibres. Computer simulations (Finite-Element Method) were used to predict the stresses and strength of the adhesive layer. Experimental analyses were conducted to compare the mechanical performance of epoxy and castor-oil PU, highlighting the potential of castor-oil PU as a viable alternative for eco-friendly composite materials and adhesives. Gouveia et al. [ 12 ] studied polyurethane adhesives containing Kraft lignin. Single-lap shear tests, carried out to assess the strength of wood adhesive joints, reveal that the incorporation of Kraft lignin and hydroxypropylated lignin in polyurethane adhesives resulted in higher apparent strength. To the best of our knowledge, the adhesion of foamed castor-oil polyurethane adhesives has not yet been reported in the literature. The purpose of this work is thus to analyse the core-face adhesion of castor-oil foam on 1200 aluminium through the single-lap test, using three different bonding strategies: (1) simple cure, (2) co-curing with an adhesive layer and (3) direct bonding. The apparent shear strength, joint toughness, and adherent strength for each bonding strategy are measured to identify the best bonding strategy for manufacturing sandwich panels with aluminium faces and castor-oil polyurethane foam core for subsequent studies. The simple-curing method is conducted by expanding the PU biofoam in the mould cavity in contact with the aluminium sheets. In the second method, a layer of castor-oil PU resin is previously applied to the inner aluminium surfaces before pouring the water-PU foaming mixture. The foaming process takes place inside the mould, as in method (1), with the additional co-curing of the PU adhesive layer on the aluminium sheets. In the direct bonding method (3), a slab of previously cured foam is bonded to the aluminium faces using a layer of castor-oil PU resin previously applied to the internal metallic surfaces, as in (2). 2. Methodology 2.1. Materials The AGT 1315 bi-component resin (isocyanate and polyol), manufactured and kindly donated by Imperveg (Brazil), was used to bond the 1200 Aluminium sheets (1 mm thickness). Distilled water is used as a blowing agent, reacting with isocyanate to produce carbon dioxide (CO 2 ) and form the cellular structure of the foam. Poly (lactic acid) filaments, supplied by 3DLab company (Belo Horizonte – Brazil), were used to print 3D moulds to assemble single-lap joints. 2.2. Methods Single-lap joints are manufactured according to ASTM D1002 [ 13 ]. Aluminium sheets are cut to the required dimensions (101.6 x 25.4 mm²) and washed with ordinary detergent. The internal surface of the sheets that will be in contact with the foam is then sanded lengthways with 120-grit sandpaper and subsequently paper-cleaned. Three samples are tested for each bonding strategy. The isocyanate (A) and polyol (B) are mixed according to the manufacturer's recommendations, considering the necessary correction of the isocyanate mass fraction due to the addition of water, used as a blowing agent. Four phr of water are used (per hundred resin, relative to the polyol mass), based on previous work. Therefore, the A/B mass fraction used is 1.2/1.0 to adjust the isocyanate index to 1. The foam expands to approximately three times its liquid volume during curing. An additional 20% volume of material is used to account for losses during the manufacturing process. These values were defined after preliminary manufacturing tests. The study evaluates three different bonding strategies: (1) Simple cure, (2) Co-cure with an adhesive layer and (3) Direct bonding, as already described in the Introduction. Four samples are considered for each bonding strategy. The moulds used to manufacture single-lap joint samples were previously fabricated in PLA on a Creality Ender 3 3D printer. Samples are manufactured and stored for post-curing (15 days) in a controlled environment room at 22°C and 55% relative air humidity. The samples are then bonded to 4-mm-thick, 3D-printed spacer blocks 24 h before testing using epoxy resin (Araldite, TekBond) to provide load alignment. An additional 1 mm-thick aluminium tab is bonded on the blocks as a reinforcement and to balance frictional forces on both sides of the grip faces. The bond line is 10 mm long, and the test-grip area is 25.4 mm long. The foam adhesive bond line is 4 mm thick. Simple-cure samples are fabricated by assembling the aluminium plates on the mould and pouring the foaming mixture into it (Fig. 1 ). The internal surface of the aluminium plates used for samples fabricated with the co-cure strategy receives an additional adhesive layer, applying the PU resin on the internal surface of the aluminium plates. Three strokes of a brush evenly distribute the resin to apply approximately the same amount of material on the surface of the aluminium sheets in contact with the PU foam. The resin is left to stand for 50 minutes (gel time) before pouring the PU foaming mixture. The resin used for the additional adhesive layer is prepared by mixing isocyanate and polyol according to the manufacturer's recommendation (A/B = 1.0/1.2), with no water added. The dimensions of the sample and a specimen ready for testing are illustrated in Figure (2). 3. Results and Discussion The influence of different bonding strategies on the apparent shear strength, joint toughness and adhesive strength of the fabricated samples is assessed through analysis of variance (One-Way ANOVA), carried out at a 5% significance level. ANOVA made it possible to identify whether there were statistically significant differences between the treatments applied. The Anderson-Darling test is performed, with p-values ranging from 0.272 to 0.826. These values indicate that the assumption of normality is satisfied (p > 0.05), validating the use of ANOVA for the analysis. The ANOVA assumption of the equality of variances is also assessed using multiple comparisons and Levene's tests. The p-values for both tests are above 0.05, indicating the equality of variances. Results are shown in Table 1 . The apparent shear stress is calculated considering the 10 x 25.5 mm² bondline area. The ANOVA analyses reveal that the co-cure strategy provides a significantly higher apparent shear strength (1.07 MPa), 84.5% higher relative to direct bonding and 35.4% higher than the value obtained for the simple-cure strategy. In contrast, the joint toughness for simple cure (0.622 J) is 64% higher relative to the co-cure strategy and 167% higher than the value obtained for direct bonding. The joint toughness is the work the applied force exerts to disrupt the adhesive joint, calculated as the area under the force-displacement curve. The adhesive strength is the slope of the initial linear elastic region of the load-displacement curve obtained by linear regression. The ANOVA reveals that the adherent strength is not significantly different among the three strategies investigated (p-value > 0.05). The main effect plot for each mechanical property investigated is presented in Fig. 3 . Tukey's multiple comparison test is applied to determine which means are significantly different from each other. Means with different letters (on the graph) are statistically different; those that share the same letter are statistically equivalent. Table 1 Mechanical performance of tested single-lap joints: mean values. Bonding Strategy Apparent shear strength (MPa) Joint toughness (J) Adherent strength (N/mm) Simple Cure 0.79 ± 0.13 0.622 ± 0.076 222 ± 51 Co-cure with adhesive layer 1.07 ± 0.10 0.38 ± 0.10 335 ± 94 Direct Bonding 0.58 ± 0.08 0.233 ± 0.040 245 ± 62 P-Value* 0.000 0.000 0.112 *P-value ≤ 0.05 for statistical significance The typical load-displacement behaviour of the tested samples is presented in Fig. 4 . A representative sample for each strategy was chosen for plotting. The higher ductility and toughness of simply cured joints are worth noting compared to co-cure with adhesive layer and direct bonding. In fact, the direct bonding method provides the least efficient performance for the properties investigated. Simply cured joints exhibit a cohesive failure type: the fracture occurs at the foam adhesive (Fig. 5 a). Joints fabricated with the co-curing strategy with adhesive layer (Fig. 5 b) also present cohesive fracture. It is worth noting that, in this fabrication method, two adhesive phases are present and co-cured: the PU adhesive layer applied to the metallic faces and the foam mixture poured into the mould. In this case, the cohesive fracture occurs at the foam adhesive phase or at the foam-PU layer interface. Joints manufactured via direct bonding present only the PU adhesive layer, which bonds the aluminium face to the (previously cured) foam. In this case, the fracture is both cohesive (occurring at the foam) or adhesive (occurring at the foam-PU layer interface). Results reveal that, in this case, the adhesion between the PU layer and the foam core is not as efficient as in the co-curing strategy. 4. Conclusions Three different bonding strategies have been evaluated using the single-lap joint test. Results indicate that the co-curing strategy with an adhesive layer provides higher apparent shear strength relative to the simple-cure strategy at the expense of a significantly lower joint toughness. In contrast, the energy required to tear apart simply cured adhesive joint samples is much higher, indicating a ductile failure. The direct bonding method provides the least effective performance regarding apparent shear strength and joint toughness. The adherent strength is statistically equivalent for all curing strategies, even though it tends to be higher for the co-curing strategy with an adhesive layer. These results will be considered to select the most suitable bonding strategy to fabricate sandwich panels with aluminium faces and castor-oil PU foam core. Even though higher loads could, in principle, be achieved by employing the co-cure strategy, catastrophic failure should be avoided in structural composites such as sandwich panels. In view of such findings, the simple-cure strategy seems to be the best bonding strategy. Further investigations are being conducted to corroborate these conclusions and will be reported soon. Declarations Declaration of Competing Interests The authors declare no conflict of interest. Code availability Not applicable. Data availability The raw and processed data required to reproduce these findings cannot be shared at this time as the data is part of an ongoing study. Authors' contributions N.D.C.F.L.: Experimental investigation, data analysis and curation, writing: original draft preparation. J.C.S.: Reviewing, editing. T.H.P.: Supervision, methodology, reviewing. A.L.S.: Experimental investigation. R.T.S.F.: Data analysis and curation, methodology, reviewing and supervision All authors read and accepted the manuscript. Funding N.D.C.F.L.: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior -CAPES, Brazil (Master's degree scholarship); J.C.S.: Post-doc grant 163562/2020-2, Conselho Nacional de Desenvolvimento Científico e Tecnológico -CNPq, Brazil; A.L.S.: CAPES (PhD scholarship); T.H.P.: CNPq (research grant PQ 405506/2023-6). Acknowledgements N.D.C.F.L. and A.L.S. thank CAPES for the scholarship provided. The authors thank Imperveg (Brazil) for donating the castor-oil PU resin for this work. J.C.S. thanks CNPQ for the post-doc grant (163562/2020-2). T.H.P. thanks CNPq for the research grant (PQ 405506/2023-6). References Daniel, I.M. and O. Ishai, Engineering Mechanics of Composite Materials . 2006: Oxford University Press. Ravindran, B., M. Feuchter, and R. Schledjewski Investigation of the Mechanical Properties of Sandwich Composite Panels Made with Recyclates and Flax Fiber/Bio-Based Epoxy Processed by Liquid Composite Molding . Journal of Composites Science, 2023. 7 , 122 DOI: https://doi.org/10.3390/jcs7030122. Mohammadabadi, M., V. Yadama, and J.D. Dolan Evaluation of Wood Composite Sandwich Panels as a Promising Renewable Building Material . Materials, 2021. 14 , 2083 DOI: https://doi.org/10.3390/ma14082083. Abdur Rahman, M., et al. A review of environmental friendly green composites: production methods, current progresses, and challenges . Environmental Science and Pollution Research, 2023. 30 , 16905-16929 DOI: https://doi.org/10.1007/s11356-022-24879-5. Mei, J., J. Liu, and W. Huang Three-point bending behaviors of the foam-filled CFRP X-core sandwich panel: Experimental investigation and analytical modelling . Composite Structures, 2022. 284 , 115206 DOI: https://doi.org/10.1016/j.compstruct.2022.115206. Li, J., Q. Yan, and Z. Cai Mechanical properties and characteristics of structural insulated panels with a novel cellulose nanofibril-based composite foam core . Journal of Sandwich Structures & Materials, 2021. 23 , 1701-1716 DOI: 10.1177/1099636220902051. Junaedi, H., T. Khan, and T.A. Sebaey Characteristics of Carbon-Fiber-Reinforced Polymer Face Sheet and Glass-Fiber-Reinforced Rigid Polyurethane Foam Sandwich Structures under Flexural and Compression Tests . Materials, 2023. 16 , 5101 DOI: https://doi.org/10.3390/ma16145101. Al-Ostaz, A., et al., Evaluation of high-performance pressure-sensitive adhesives and VHB™ acrylic foam tapes bonded aluminum joints subjected to environmental aging. Journal of Adhesion Science and Technology, 2007. 21 (3-4): p. 339-361. Malik, M. and R. Kaur Mechanical and Thermal Properties of Castor Oil–Based Polyurethane Adhesive: Effect of TiO2 Filler . Advances in Polymer Technology, 2018. 37 , 24-30 DOI: https://doi.org/10.1002/adv.21637. Santana, P.R.T., et al. Apparent shear strength of hybrid glass fibre reinforced composite joints . Polymer Testing, 2017. 64 , 307-312 DOI: https://doi.org/10.1016/j.polymertesting.2017.10.022. Da Costa, R.R.C., et al. Experimental and numerical analysis of single lap bonded joints: Epoxy and castor oil PU-glass fibre composites . The Journal of Adhesion, 2017. 93 , 77-94 DOI: 10.1080/00218464.2016.1172212. Gouveia, J., et al. Kraft lignin-containing polyurethane adhesives: the role of hydroxypropylation on thermomechanical properties . The Journal of Adhesion, 2020. 97 , 1-17 DOI: 10.1080/00218464.2020.1784148. ASTM-D1002 Standard Test Method for Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to-Metal) . 2010. DOI: https://doi.org/10.1520/D1002-10R19. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 13 Nov, 2024 Reviews received at journal 13 Nov, 2024 Reviews received at journal 08 Nov, 2024 Reviews received at journal 08 Nov, 2024 Reviews received at journal 06 Nov, 2024 Reviews received at journal 29 Oct, 2024 Reviewers agreed at journal 29 Oct, 2024 Reviewers agreed at journal 27 Oct, 2024 Reviewers agreed at journal 26 Oct, 2024 Reviewers agreed at journal 26 Oct, 2024 Reviewers agreed at journal 26 Oct, 2024 Reviewers invited by journal 26 Oct, 2024 Editor assigned by journal 23 Oct, 2024 Submission checks completed at journal 22 Oct, 2024 First submitted to journal 10 Oct, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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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-5241986","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":377805099,"identity":"47d1beea-9d42-471d-ac42-1e79a2890488","order_by":0,"name":"Luís Felipe Cabral Diogo Nogueira","email":"","orcid":"","institution":"Federal University of São João del-Rei","correspondingAuthor":false,"prefix":"","firstName":"Luís","middleName":"Felipe Cabral Diogo","lastName":"Nogueira","suffix":""},{"id":377805100,"identity":"1d2afb82-4789-4546-8cb4-403906693954","order_by":1,"name":"Júlio Cesar dos Santos","email":"","orcid":"","institution":"Federal University of São João del-Rei","correspondingAuthor":false,"prefix":"","firstName":"Júlio","middleName":"Cesar dos","lastName":"Santos","suffix":""},{"id":377805101,"identity":"c4a00647-4bdc-4ee0-a0b0-5f3b1cd2ab7f","order_by":2,"name":"Túlio Hallak Panzera","email":"","orcid":"","institution":"Federal University of São João del-Rei","correspondingAuthor":false,"prefix":"","firstName":"Túlio","middleName":"Hallak","lastName":"Panzera","suffix":""},{"id":377805102,"identity":"e3bfa74b-05eb-455f-a4f2-7846c76d78b9","order_by":3,"name":"André Luís dos Santos","email":"","orcid":"","institution":"Federal University of São João del-Rei","correspondingAuthor":false,"prefix":"","firstName":"André","middleName":"Luís dos","lastName":"Santos","suffix":""},{"id":377805103,"identity":"9c9535de-c8eb-4580-8f8c-5971526a696b","order_by":4,"name":"Rodrigo Teixeira Santos Freire","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA20lEQVRIie2RsQrCMBCGrwjpos6BVn2Fkw4OFZ/litBOgqODQ6ZMirNv0QdwCBTi4jvYLp1166SmujjVugnmG44/kA/+4wAsll+kowAIYFgHNE8A/klh9FSCOnyhGCLxCi2UiewVeXGYJql28yWswkh427xR8bUbIJXxItVdRDglkfCP2KjwkWScVLZIzxtAR2aR4HFzMc6YW5G6J2iKoXNrpzAgpQg1IDqindIxxebjfb0L6SSQvv6oONdKzUZ97ZZ4WYeDnSeblXcYUj3bC+aM+Te/LRaL5X94AHaPQLJjOB7AAAAAAElFTkSuQmCC","orcid":"","institution":"Federal University of São João del-Rei","correspondingAuthor":true,"prefix":"","firstName":"Rodrigo","middleName":"Teixeira Santos","lastName":"Freire","suffix":""}],"badges":[],"createdAt":"2024-10-10 20:23:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5241986/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5241986/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":72132322,"identity":"94312f81-efc3-498f-9a9c-0d3f986fbacd","added_by":"auto","created_at":"2024-12-23 04:26:52","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":86231,"visible":true,"origin":"","legend":"\u003cp\u003ePLA 3D mould during the manufacture of a sample.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-5241986/v1/4cac9a738f3d6b39ac7fc54b.png"},{"id":72131190,"identity":"0628a546-0763-4571-a5c1-2923a419ae8e","added_by":"auto","created_at":"2024-12-23 04:18:52","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":68085,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Sample dimensions (in mm); (b) specimen ready for testing\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-5241986/v1/caa2f6a9fb4ac7d54add6859.png"},{"id":72131191,"identity":"d2bb71f8-3bb0-4b9a-b1c0-30147878a8aa","added_by":"auto","created_at":"2024-12-23 04:18:52","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":84702,"visible":true,"origin":"","legend":"\u003cp\u003eMain effect plots for the (a) apparent shear strength, (b) joint toughness and (c) adherent strength.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5241986/v1/8ddf6284232713b2075e3aae.png"},{"id":72132323,"identity":"5eb6517d-3549-46a2-ac6a-636d53e4661e","added_by":"auto","created_at":"2024-12-23 04:26:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":32384,"visible":true,"origin":"","legend":"\u003cp\u003eTypical load-displacement behaviour of the manufactured samples in the Single-Lap test for the adhesion strategies investigated.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5241986/v1/63c6dc8a6c771c5cb6181624.png"},{"id":72131193,"identity":"c0b73420-b4a9-4f74-96b1-03354e25c4d9","added_by":"auto","created_at":"2024-12-23 04:18:52","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":968888,"visible":true,"origin":"","legend":"\u003cp\u003eFractured samples according to the adhesive strategy (a) Simple Cure (b) Co-cure with adhesive layer (c) Direct Bonding.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5241986/v1/ca43cccc614c746939db79c1.png"},{"id":72132324,"identity":"405e1abe-1a1e-4f06-94b9-8ec8783ee5a2","added_by":"auto","created_at":"2024-12-23 04:27:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1642070,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5241986/v1/ed816817-8894-4ed4-9ce3-eb9aa8c85ce8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eInvestigation of Castor-oil Foam Adhesion on Aluminium Through Single-lap Tests\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eComposite materials play a fundamental role in contemporary engineering, offering an innovative approach to achieving specific properties that are not feasible with traditional materials. Owing to significant advantages such as high strength, high stiffness, reduced weight, reliable performance under fatigue conditions and effective corrosion resistance [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], the use of composite materials has progressively grown in a wide variety of areas, such as the aeronautic and automotive industries, shipbuilding, railways, civil construction and sports, among others.\u003c/p\u003e \u003cp\u003eIn this sense, materials scientists and engineers face a significant challenge beyond developing efficient and economical products: promoting technological evolution without jeopardising the availability of resources for future generations. High population growth has resulted in high production and consumption of materials, which has led to waste accumulation and reduced natural resources. As a result, considerable scientific effort has been focused on reducing environmental impact by using alternative materials and renewable natural resources to supply high-quality industrial products [\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Recent studies have focused on using foams as the core of sandwich panels [\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Such structural composites provide improved flexural stiffness at low densities. However, the adhesive strategy used for face-core bonding is essential for their mechanical performance. The single-lap shear test is frequently used to evaluate the mechanical performance of different adhesives. This study is motivated by a subsequent study on foam-core sandwich panels, in which the best face-core bonding strategy will be used.\u003c/p\u003e \u003cp\u003eAl-Ostaz et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] investigated high-performance pressure-sensitive adhesives and VHB\u0026trade; acrylic foam tapes in 2024 T-4 aluminium joints in single-lap joint (SLJ) configurations. Static load (lap shear) and dynamic impact tests were carried out on the joints to compare the mechanical properties before and after environmental ageing. The results showed that the acrylic tapes provided lower static load resistance compared to the pressure-sensitive adhesives; the impact energy absorption was, however, similar for both materials.\u003c/p\u003e \u003cp\u003eMalik et al. [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] used a single-lap shear strength test to investigate the effect of adding TiO\u003csub\u003e2\u003c/sub\u003e to castor oil-based polyurethane adhesive to improve its mechanical properties. The authors reported a significant increase in shear strength, outperforming commercial wood-bonding adhesives.\u003c/p\u003e \u003cp\u003eIn a similar study, Santana et al.[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] evaluated the interlocking effect of silica microparticle or cement inclusions in glass fibre laminate composite single-lap joints. Analysis of variance (ANOVA) was carried out on the results obtained, showing that cement and silica microparticles provide superior resistance, increasing by 31.5% and 25.3%, respectively, compared to single-lap joints without microparticles.\u003c/p\u003e \u003cp\u003eRomeu et al. [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] investigated single-lap joints using castor-oil PU and epoxy composites reinforced with glass fibres. Computer simulations (Finite-Element Method) were used to predict the stresses and strength of the adhesive layer. Experimental analyses were conducted to compare the mechanical performance of epoxy and castor-oil PU, highlighting the potential of castor-oil PU as a viable alternative for eco-friendly composite materials and adhesives.\u003c/p\u003e \u003cp\u003eGouveia et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] studied polyurethane adhesives containing Kraft lignin. Single-lap shear tests, carried out to assess the strength of wood adhesive joints, reveal that the incorporation of Kraft lignin and hydroxypropylated lignin in polyurethane adhesives resulted in higher apparent strength.\u003c/p\u003e \u003cp\u003eTo the best of our knowledge, the adhesion of foamed castor-oil polyurethane adhesives has not yet been reported in the literature. The purpose of this work is thus to analyse the core-face adhesion of castor-oil foam on 1200 aluminium through the single-lap test, using three different bonding strategies: (1) simple cure, (2) co-curing with an adhesive layer and (3) direct bonding. The apparent shear strength, joint toughness, and adherent strength for each bonding strategy are measured to identify the best bonding strategy for manufacturing sandwich panels with aluminium faces and castor-oil polyurethane foam core for subsequent studies. The simple-curing method is conducted by expanding the PU biofoam in the mould cavity in contact with the aluminium sheets. In the second method, a layer of castor-oil PU resin is previously applied to the inner aluminium surfaces before pouring the water-PU foaming mixture. The foaming process takes place inside the mould, as in method (1), with the additional co-curing of the PU adhesive layer on the aluminium sheets. In the direct bonding method (3), a slab of previously cured foam is bonded to the aluminium faces using a layer of castor-oil PU resin previously applied to the internal metallic surfaces, as in (2).\u003c/p\u003e"},{"header":"2. Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1. Materials\u003c/h2\u003e\n \u003cp\u003eThe AGT 1315 bi-component resin (isocyanate and polyol), manufactured and kindly donated by Imperveg (Brazil), was used to bond the 1200 Aluminium sheets (1 mm thickness). Distilled water is used as a blowing agent, reacting with isocyanate to produce carbon dioxide (CO\u003csub\u003e2\u003c/sub\u003e) and form the cellular structure of the foam. Poly (lactic acid) filaments, supplied by 3DLab company (Belo Horizonte \u0026ndash; Brazil), were used to print 3D moulds to assemble single-lap joints.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2. Methods\u003c/h2\u003e\n \u003cp\u003eSingle-lap joints are manufactured according to ASTM D1002 [\u003cspan class=\"CitationRef\"\u003e13\u003c/span\u003e]. Aluminium sheets are cut to the required dimensions (101.6 x 25.4 mm\u0026sup2;) and washed with ordinary detergent. The internal surface of the sheets that will be in contact with the foam is then sanded lengthways with 120-grit sandpaper and subsequently paper-cleaned. Three samples are tested for each bonding strategy.\u003c/p\u003e\n \u003cp\u003eThe isocyanate (A) and polyol (B) are mixed according to the manufacturer\u0026apos;s recommendations, considering the necessary correction of the isocyanate mass fraction due to the addition of water, used as a blowing agent. Four phr of water are used (per hundred resin, relative to the polyol mass), based on previous work. Therefore, the A/B mass fraction used is 1.2/1.0 to adjust the isocyanate index to 1. The foam expands to approximately three times its liquid volume during curing. An additional 20% volume of material is used to account for losses during the manufacturing process. These values were defined after preliminary manufacturing tests.\u003c/p\u003e\n \u003cp\u003eThe study evaluates three different bonding strategies: (1) Simple cure, (2) Co-cure with an adhesive layer and (3) Direct bonding, as already described in the Introduction. Four samples are considered for each bonding strategy.\u003c/p\u003e\n \u003cp\u003eThe moulds used to manufacture single-lap joint samples were previously fabricated in PLA on a Creality Ender 3 3D printer. Samples are manufactured and stored for post-curing (15 days) in a controlled environment room at 22\u0026deg;C and 55% relative air humidity. The samples are then bonded to 4-mm-thick, 3D-printed spacer blocks 24 h before testing using epoxy resin (Araldite, TekBond) to provide load alignment. An additional 1 mm-thick aluminium tab is bonded on the blocks as a reinforcement and to balance frictional forces on both sides of the grip faces. The bond line is 10 mm long, and the test-grip area is 25.4 mm long. The foam adhesive bond line is 4 mm thick.\u003c/p\u003e\n \u003cp\u003eSimple-cure samples are fabricated by assembling the aluminium plates on the mould and pouring the foaming mixture into it (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). The internal surface of the aluminium plates used for samples fabricated with the co-cure strategy receives an additional adhesive layer, applying the PU resin on the internal surface of the aluminium plates. Three strokes of a brush evenly distribute the resin to apply approximately the same amount of material on the surface of the aluminium sheets in contact with the PU foam. The resin is left to stand for 50 minutes (gel time) before pouring the PU foaming mixture. The resin used for the additional adhesive layer is prepared by mixing isocyanate and polyol according to the manufacturer\u0026apos;s recommendation (A/B\u0026thinsp;=\u0026thinsp;1.0/1.2), with no water added. The dimensions of the sample and a specimen ready for testing are illustrated in Figure (2).\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003eThe influence of different bonding strategies on the apparent shear strength, joint toughness and adhesive strength of the fabricated samples is assessed through analysis of variance (One-Way ANOVA), carried out at a 5% significance level. ANOVA made it possible to identify whether there were statistically significant differences between the treatments applied. The Anderson-Darling test is performed, with p-values ranging from 0.272 to 0.826. These values indicate that the assumption of normality is satisfied (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05), validating the use of ANOVA for the analysis. The ANOVA assumption of the equality of variances is also assessed using multiple comparisons and Levene\u0026apos;s tests. The p-values for both tests are above 0.05, indicating the equality of variances. Results are shown in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The apparent shear stress is calculated considering the 10 x 25.5 mm\u0026sup2; bondline area. The ANOVA analyses reveal that the co-cure strategy provides a significantly higher apparent shear strength (1.07 MPa), 84.5% higher relative to direct bonding and 35.4% higher than the value obtained for the simple-cure strategy. In contrast, the joint toughness for simple cure (0.622 J) is 64% higher relative to the co-cure strategy and 167% higher than the value obtained for direct bonding. The joint toughness is the work the applied force exerts to disrupt the adhesive joint, calculated as the area under the force-displacement curve. The adhesive strength is the slope of the initial linear elastic region of the load-displacement curve obtained by linear regression. The ANOVA reveals that the adherent strength is not significantly different among the three strategies investigated (p-value\u0026thinsp;\u0026gt;\u0026thinsp;0.05). The main effect plot for each mechanical property investigated is presented in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Tukey\u0026apos;s multiple comparison test is applied to determine which means are significantly different from each other. Means with different letters (on the graph) are statistically different; those that share the same letter are statistically equivalent.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\" style=\"margin-right: calc(43%); width: 57%;\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMechanical performance of tested single-lap joints: mean values.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" style=\"width: 16.8342%;\"\u003e\n \u003cp\u003eBonding Strategy\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" style=\"width: 20.165%;\"\u003e\n \u003cp\u003eApparent shear strength (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" style=\"width: 12.2431%;\"\u003e\n \u003cp\u003eJoint toughness (J)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" style=\"width: 17.1043%;\"\u003e\n \u003cp\u003eAdherent strength (N/mm)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 16.8342%;\"\u003e\n \u003cp\u003eSimple Cure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 20.165%;\"\u003e\n \u003cp\u003e0.79\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 12.2431%;\"\u003e\n \u003cp\u003e0.622\u0026thinsp;\u0026plusmn;\u0026thinsp;0.076\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 17.1043%;\"\u003e\n \u003cp\u003e222\u0026thinsp;\u0026plusmn;\u0026thinsp;51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 16.8342%;\"\u003e\n \u003cp\u003eCo-cure with adhesive layer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 20.165%;\"\u003e\n \u003cp\u003e1.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 12.2431%;\"\u003e\n \u003cp\u003e0.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 17.1043%;\"\u003e\n \u003cp\u003e335\u0026thinsp;\u0026plusmn;\u0026thinsp;94\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 16.8342%;\"\u003e\n \u003cp\u003eDirect Bonding\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 20.165%;\"\u003e\n \u003cp\u003e0.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 12.2431%;\"\u003e\n \u003cp\u003e0.233\u0026thinsp;\u0026plusmn;\u0026thinsp;0.040\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 17.1043%;\"\u003e\n \u003cp\u003e245\u0026thinsp;\u0026plusmn;\u0026thinsp;62\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" style=\"width: 16.8342%;\"\u003e\n \u003cp\u003eP-Value*\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 20.165%;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 12.2431%;\"\u003e\n \u003cp\u003e0.000\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\" style=\"width: 17.1043%;\"\u003e\n \u003cp\u003e0.112\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"4\" style=\"width: 67.0668%;\"\u003e\n \u003cp\u003e\u003cstrong\u003e*P-value\u003c/strong\u003e\u0026thinsp;\u0026le;\u0026thinsp;0.05 for statistical significance\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe typical load-displacement behaviour of the tested samples is presented in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e. A representative sample for each strategy was chosen for plotting. The higher ductility and toughness of simply cured joints are worth noting compared to co-cure with adhesive layer and direct bonding. In fact, the direct bonding method provides the least efficient performance for the properties investigated.\u003c/p\u003e\n\u003cp\u003eSimply cured joints exhibit a cohesive failure type: the fracture occurs at the foam adhesive (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea). Joints fabricated with the co-curing strategy with adhesive layer (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb) also present cohesive fracture. It is worth noting that, in this fabrication method, two adhesive phases are present and co-cured: the PU adhesive layer applied to the metallic faces and the foam mixture poured into the mould. In this case, the cohesive fracture occurs at the foam adhesive phase or at the foam-PU layer interface. Joints manufactured via direct bonding present only the PU adhesive layer, which bonds the aluminium face to the (previously cured) foam. In this case, the fracture is both cohesive (occurring at the foam) or adhesive (occurring at the foam-PU layer interface). Results reveal that, in this case, the adhesion between the PU layer and the foam core is not as efficient as in the co-curing strategy.\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThree different bonding strategies have been evaluated using the single-lap joint test. Results indicate that the co-curing strategy with an adhesive layer provides higher apparent shear strength relative to the simple-cure strategy at the expense of a significantly lower joint toughness. In contrast, the energy required to tear apart simply cured adhesive joint samples is much higher, indicating a ductile failure. The direct bonding method provides the least effective performance regarding apparent shear strength and joint toughness. The adherent strength is statistically equivalent for all curing strategies, even though it tends to be higher for the co-curing strategy with an adhesive layer.\u003c/p\u003e\n\u003cp\u003eThese results will be considered to select the most suitable bonding strategy to fabricate sandwich panels with aluminium faces and castor-oil PU foam core. Even though higher loads could, in principle, be achieved by employing the co-cure strategy, catastrophic failure should be avoided in structural composites such as sandwich panels. In view of such findings, the simple-cure strategy seems to be the best bonding strategy. Further investigations are being conducted to corroborate these conclusions and will be reported soon.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eDeclaration of Competing Interests\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003eCode availability\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003eData availability\u003c/p\u003e\n\u003cp\u003eThe raw and processed data required to reproduce these findings cannot be shared at this time as the data is part of an ongoing study.\u003c/p\u003e\n\u003cp\u003eAuthors\u0026apos; contributions\u003c/p\u003e\n\u003cp\u003eN.D.C.F.L.: Experimental investigation, data analysis and curation, writing: original draft preparation.\u003c/p\u003e\n\u003cp\u003eJ.C.S.: Reviewing, editing.\u003c/p\u003e\n\u003cp\u003eT.H.P.: Supervision, methodology, reviewing.\u003c/p\u003e\n\u003cp\u003eA.L.S.: Experimental investigation.\u003c/p\u003e\n\u003cp\u003eR.T.S.F.: Data analysis and curation, methodology, reviewing and supervision\u003c/p\u003e\n\u003cp\u003eAll authors read and accepted the manuscript.\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eN.D.C.F.L.: \u003cem\u003eCoordena\u0026ccedil;\u0026atilde;o de Aperfei\u0026ccedil;oamento de Pessoal de N\u0026iacute;vel Superior\u003c/em\u003e -CAPES, Brazil (Master\u0026apos;s degree scholarship); J.C.S.: Post-doc grant\u0026nbsp;163562/2020-2, \u003cem\u003eConselho Nacional de Desenvolvimento Cient\u0026iacute;fico e Tecnol\u0026oacute;gico\u003c/em\u003e -CNPq, Brazil; A.L.S.:\u0026nbsp;CAPES (PhD scholarship); T.H.P.:\u0026nbsp;CNPq\u0026nbsp;(research grant PQ 405506/2023-6).\u003c/p\u003e\n\u003cp\u003eAcknowledgements\u003c/p\u003e\n\u003cp\u003eN.D.C.F.L. and A.L.S. thank CAPES for the scholarship provided. The authors thank Imperveg (Brazil) for donating the castor-oil PU resin for this work. J.C.S. thanks CNPQ for the post-doc grant (163562/2020-2). T.H.P. thanks CNPq for the research grant (PQ 405506/2023-6).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eDaniel, I.M. and O. Ishai, \u003cem\u003eEngineering Mechanics of Composite Materials\u003c/em\u003e. 2006: Oxford University Press.\u003c/li\u003e\n \u003cli\u003eRavindran, B., M. Feuchter, and R. Schledjewski \u003cem\u003eInvestigation of the Mechanical Properties of Sandwich Composite Panels Made with Recyclates and Flax Fiber/Bio-Based Epoxy Processed by Liquid Composite Molding\u003c/em\u003e. Journal of Composites Science, 2023. \u003cstrong\u003e7\u003c/strong\u003e, 122 DOI: https://doi.org/10.3390/jcs7030122.\u003c/li\u003e\n \u003cli\u003eMohammadabadi, M., V. Yadama, and J.D. Dolan \u003cem\u003eEvaluation of Wood Composite Sandwich Panels as a Promising Renewable Building Material\u003c/em\u003e. Materials, 2021. \u003cstrong\u003e14\u003c/strong\u003e, 2083 DOI: https://doi.org/10.3390/ma14082083.\u003c/li\u003e\n \u003cli\u003eAbdur Rahman, M., et al. \u003cem\u003eA review of environmental friendly green composites: production methods, current progresses, and challenges\u003c/em\u003e. Environmental Science and Pollution Research, 2023. \u003cstrong\u003e30\u003c/strong\u003e, 16905-16929 DOI: https://doi.org/10.1007/s11356-022-24879-5.\u003c/li\u003e\n \u003cli\u003eMei, J., J. Liu, and W. Huang \u003cem\u003eThree-point bending behaviors of the foam-filled CFRP X-core sandwich panel: Experimental investigation and analytical modelling\u003c/em\u003e. Composite Structures, 2022. \u003cstrong\u003e284\u003c/strong\u003e, 115206 DOI: https://doi.org/10.1016/j.compstruct.2022.115206.\u003c/li\u003e\n \u003cli\u003eLi, J., Q. Yan, and Z. Cai \u003cem\u003eMechanical properties and characteristics of structural insulated panels with a novel cellulose nanofibril-based composite foam core\u003c/em\u003e. Journal of Sandwich Structures \u0026amp; Materials, 2021. \u003cstrong\u003e23\u003c/strong\u003e, 1701-1716 DOI: 10.1177/1099636220902051.\u003c/li\u003e\n \u003cli\u003eJunaedi, H., T. Khan, and T.A. Sebaey \u003cem\u003eCharacteristics of Carbon-Fiber-Reinforced Polymer Face Sheet and Glass-Fiber-Reinforced Rigid Polyurethane Foam Sandwich Structures under Flexural and Compression Tests\u003c/em\u003e. Materials, 2023. \u003cstrong\u003e16\u003c/strong\u003e, 5101 DOI: https://doi.org/10.3390/ma16145101.\u003c/li\u003e\n \u003cli\u003eAl-Ostaz, A., et al., \u003cem\u003eEvaluation of high-performance pressure-sensitive adhesives and VHB\u0026trade; acrylic foam tapes bonded aluminum joints subjected to environmental aging.\u003c/em\u003e Journal of Adhesion Science and Technology, 2007. \u003cstrong\u003e21\u003c/strong\u003e(3-4): p. 339-361.\u003c/li\u003e\n \u003cli\u003eMalik, M. and R. Kaur \u003cem\u003eMechanical and Thermal Properties of Castor Oil\u0026ndash;Based Polyurethane Adhesive: Effect of TiO2 Filler\u003c/em\u003e. Advances in Polymer Technology, 2018. \u003cstrong\u003e37\u003c/strong\u003e, 24-30 DOI: https://doi.org/10.1002/adv.21637.\u003c/li\u003e\n \u003cli\u003eSantana, P.R.T., et al. \u003cem\u003eApparent shear strength of hybrid glass fibre reinforced composite joints\u003c/em\u003e. Polymer Testing, 2017. \u003cstrong\u003e64\u003c/strong\u003e, 307-312 DOI: https://doi.org/10.1016/j.polymertesting.2017.10.022.\u003c/li\u003e\n \u003cli\u003eDa Costa, R.R.C., et al. \u003cem\u003eExperimental and numerical analysis of single lap bonded joints: Epoxy and castor oil PU-glass fibre composites\u003c/em\u003e. The Journal of Adhesion, 2017. \u003cstrong\u003e93\u003c/strong\u003e, 77-94 DOI: 10.1080/00218464.2016.1172212.\u003c/li\u003e\n \u003cli\u003eGouveia, J., et al. \u003cem\u003eKraft lignin-containing polyurethane adhesives: the role of hydroxypropylation on thermomechanical properties\u003c/em\u003e. The Journal of Adhesion, 2020. \u003cstrong\u003e97\u003c/strong\u003e, 1-17 DOI: 10.1080/00218464.2020.1784148.\u003c/li\u003e\n \u003cli\u003eASTM-D1002 \u003cem\u003eStandard Test Method for Apparent Shear Strength of Single-Lap-Joint Adhesively Bonded Metal Specimens by Tension Loading (Metal-to-Metal)\u003c/em\u003e. 2010. DOI: https://doi.org/10.1520/D1002-10R19.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-mechanical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"discmecheng","sideBox":"Learn more about [Discover Mechanical Engineering](https://www.springer.com/journal/44245)","snPcode":"44245","submissionUrl":"https://submission.nature.com/new-submission/44245/3","title":"Discover Mechanical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Adhesion, Castor-oil polyurethane, Mechanical Properties, Single-Lap, Biofoam","lastPublishedDoi":"10.21203/rs.3.rs-5241986/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5241986/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis work investigates the adhesion of a castor-oil-based polyurethane (PU) biofoam to the surface of 1200 aluminium. The foam is fabricated using water as the blowing agent. The apparent shear strength, joint toughness and adherent strength of single-lap joints are assessed following the ASTM standard D1002. 3D-printed moulds are developed for sample preparation. The study evaluates three different bonding strategies related to polymer curing: (1) Simple Cure, (2) Co-Cure with Adhesive Layer and (3) Direct Bonding. The Simple Curing method is conducted by expanding the PU biofoam in the mould cavity in contact with the aluminium sheets. In the second method, a layer of castor-oil PU resin is previously applied to the internal aluminium surfaces before pouring the water-PU foaming mixture. The foaming process thus occurs inside the mould as in (2), with the additional co-cure of the adhesive PU resin layer on the aluminium sheets. In the direct bonding method (3), a slab of previously cured foam is bonded to the aluminium faces using a layer of castor-oil PU resin previously applied to the internal metallic surfaces, as in (2). This study is motivated by a subsequent study on foam-core sandwich panels, in which the best face-core bonding strategy will be used.\u003c/p\u003e","manuscriptTitle":"Investigation of Castor-oil Foam Adhesion on Aluminium Through Single-lap Tests","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-23 04:18:47","doi":"10.21203/rs.3.rs-5241986/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-11-13T17:56:05+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-13T17:49:22+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-08T18:58:19+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-08T07:52:54+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-11-06T13:46:47+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-29T14:55:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"166238254643500189863345696840830153222","date":"2024-10-29T05:13:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"75585365190852535325261741633671070117","date":"2024-10-27T11:00:30+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"231105561275764474331280475600636576309","date":"2024-10-26T18:58:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"202784099948979820640453072263524413358","date":"2024-10-26T17:14:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"268805926452711821602771223271039430532","date":"2024-10-26T09:31:40+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-26T08:22:10+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-23T06:00:17+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-10-22T06:00:30+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Mechanical Engineering","date":"2024-10-10T20:10:27+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-mechanical-engineering","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"discmecheng","sideBox":"Learn more about [Discover Mechanical Engineering](https://www.springer.com/journal/44245)","snPcode":"44245","submissionUrl":"https://submission.nature.com/new-submission/44245/3","title":"Discover Mechanical Engineering","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"3fa7df23-4e42-455d-8747-c16ac97e21de","owner":[],"postedDate":"December 23rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-02-24T16:32:46+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-23 04:18:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5241986","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5241986","identity":"rs-5241986","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}