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Thermal decomposition of CNTs and graphene-reinforced glass fibers/epoxy and their kinetics

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Abstract

Currently, and due to their unique properties, carbon nanotubes (CNTs) and graphene (GA) are used extensively as filler materials to improve the performance of glass fiber-reinforced epoxy (GFRE). These additives can act as self-catalysts during treatment of the end-of-life GFRE products thermally and their conversion into energy products. In order to investigate this phenomenon, this research aims to study the effect of CNTs and graphene additives on pyrolysis characteristics of GFRE using thermogravimetry (TGA). The measurements were conducted on two different batches: CNTs/GFRE and GA/GFRE with filler concentration 0.04 wt.% and a batch fabricated using a vacuum-assisted resin transfer method. Also, the chemical compounds formulated during the decomposition process were analyzed using TG-FTIR and GC–MS system. In addition, the pyrolysis kinetics of both batches were simulated using linear isoconversional approaches (KAS, FWO, and Friedman) and nonlinear isoconversional approaches (Vyazovkin and Cai). Finally, the thermogravimetric analysis curves (TGA and DTG) were predicted using the distributed activation energy (DAEM) and the independent parallel reaction (IPR) models with a very small deviation. The ultimate and proximate measurement showed that both batches contained numerous volatile compounds (64%) and carbon element (30%). Meanwhile, TG measurements showed that the main composition zone was located in the range of 300–465 °C with weight loss of 38–40%. Aromatic benzene was the main function group in TG-FTIR result. Meanwhile, phenol, p-isopropenylphenol, phosphine oxide, and boron were the major compounds resulting from the GC–MS measurements. On the other hand, the pyrolysis kinetic analysis showed that the activation energies were estimated at 162–190 kJ/mol (linear isoconversional) and 171–177 kJ/mol (nonlinear isoconversional) with R2 estimated at 98–99%. Based on that, the CNTs and graphene added to GFRE composites act as self-catalysts, hence contributing to improvement in the quantity of the obtained volatile compounds, and their composition affected significantly by the applied heating conditions.

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References

  1. Muneer Ahmed M, Dhakal HN, Zhang ZY, Barouni A, Zahari R (2021) Enhancement of impact toughness and damage behaviour of natural fibre reinforced composites and their hybrids through novel improvement techniques: a critical review. Compos Struct. https://doi.org/10.1016/j.compstruct.2020.113496

    Article  Google Scholar 

  2. Subadra SP, Griskevicius P (2020) Low velocity impact and pseudo-ductile behaviour of carbon/glass/epoxy and carbon/glass/PMMA hybrid composite laminates for aircraft application at service temperature. Polym Testing. https://doi.org/10.1016/j.polymertesting.2020.106711

    Article  Google Scholar 

  3. Subadra SP, Yousef S, Griskevicius P, Makarevicius V (2020) High-performance fiberglass/epoxy reinforced by functionalized CNTs for vehicle applications with less fuel consumption and greenhouse gas emissions. Polym Testing. https://doi.org/10.1016/j.polymertesting.2020.106480

    Article  Google Scholar 

  4. Chen RS, Muhammad YH, Ahmad S (2021) Physical, mechanical and environmental stress cracking characteristics of epoxy/glass fiber composites: effect of matrix/fiber modification and fiber loading. Polym Testing. https://doi.org/10.1016/j.polymertesting.2021.107088

    Article  Google Scholar 

  5. Tatariants M, Bendikiene R, Kriūkienė R, Denafas G (2020) A new industrial technology for closing the loop of full-size waste motherboards using chemical-ultrasonic-mechanical treatment. Process Saf Environ Prot. https://doi.org/10.1016/j.psep.2020.04.002

    Article  Google Scholar 

  6. Tang L, Zhang J, Tang Y, Kong J, Liu T, Gu J (2021) “Polymer matrix wave-transparent composites: a review.” J Mater Sci Technol

  7. Subadra SP, Eimontas J, Striūgas N (2021) “Functionalization of char derived from pyrolysis of metallised food packaging plastics waste and its application as a filler in fiberglass/epoxy composites.” Process Safety and Environmental Protection.

  8. Karuppannan Gopalraj S, Kärki T (2020) A review on the recycling of waste carbon fibre/glass fibre-reinforced composites: fibre recovery, properties and life-cycle analysis. SN Applied Sciences. https://doi.org/10.1007/s42452-020-2195-4

    Article  Google Scholar 

  9. Yousef S (2016) Polymer nanocomposite components: a case study on gears. In Lightweight Composite Structures in Transport: Design, Manufacturing, Analysis and Performance. https://doi.org/10.1016/B978-1-78242-325-6.00016-5

  10. Siddiqui NA, Li EL, Sham ML, Tang BZ, Gao SL, Mäder E, Kim JK (2010) Tensile strength of glass fibres with carbon nanotube-epoxy nanocomposite coating: effects of CNT morphology and dispersion state. Compos A Appl Sci Manuf. https://doi.org/10.1016/j.compositesa.2009.12.011

    Article  Google Scholar 

  11. Anand A, Ghosh SK, Fulmali AO, Prusty RK (2021) Enhanced barrier, mechanical and viscoelastic properties of graphene oxide embedded glass fibre/epoxy composite for marine applications. Constr Build Mater. https://doi.org/10.1016/j.conbuildmat.2020.121784

    Article  Google Scholar 

  12. Zhang Q, Yu Y, Yang K, Zhang B, Zhao K, Xiong G, Zhang X (2017) Mechanically robust and electrically conductive graphene-paper/glass-fibers/epoxy composites for stimuli-responsive sensors and Joule heating deicers. Carbon. https://doi.org/10.1016/j.carbon.2017.09.001

    Article  Google Scholar 

  13. Jena, A., Shubham, Prusty, R. K., & Ray, B. C. (2020). Mechanical and thermal behaviour of multi-layer graphene and nanosilica reinforced glass fiber/epoxy composites. In Materials Today: Proceedings. https://doi.org/10.1016/j.matpr.2020.02.879

  14. Jia Zhao, Junliang Zhang, Lei Wang, Jiakun Li, Tao Feng, Juncheng Fan, Lixin Chen, and Junwei Gu. 2020. “Superior wave-absorbing performances of silicone rubber composites via introducing covalently bonded SnO2@MWCNT absorbent with encapsulation structure.” Composites Communications.

  15. Xutong Yang, Shuguang Fan, Ying Li, Yongqiang Guo, Yunge Li, Kunpeng Ruan, Shengmao Zhang, Junliang Zhang, Jie Kong and Junwei Gu. 2020. Synchronously improved electromagnetic interference shielding and thermal conductivity for epoxy nanocomposites by constructing 3D copper nanowires/thermally annealed graphene aerogel framework. https://doi.org/10.1016/j.compositesa.2019.105670

  16. Mohamed A, Tonkonogovas A, Makarevicius V, Stankevičius A (2022) High performance of PES-GNs MMMs for gas separation and selectivity. Arab J Chem. https://doi.org/10.1016/j.arabjc.2021.103565

    Article  Google Scholar 

  17. Xuetao Shi, Ruihan Zhang, Kunpeng Ruan, Tengbo Ma, Yongqiang Guo, and Junwei Gu. 2021. “Improvement of thermal conductivities and simulation model for glass fabrics reinforced epoxy laminated composites via introducing hetero-structured BNN-30@BNNS fillers.” Journal of Materials Science and Technology.

  18. Xutong Yang, Jiahua Zhu, Dong Yang, Junliang Zhang, Yongqiang Guo, Xiao Zhong, Jie Kong, and Junwei Gu. 2020. “High-efficiency improvement of thermal conductivities for epoxy composites from synthesized liquid crystal epoxy followed by doping BN fillers.” Composites Part B: Engineering.

  19. Naqvi SR, Prabhakara HM, Bramer EA et al (2018) A critical review on recycling of end-of-life carbon fbre/glass fbre reinforced composites waste using pyrolysis towards a circular economy. Resour Conserv Recycl 136:118–129

    Article  Google Scholar 

  20. Tatariants M, Tichonovas M, Bendikiene R, Denafas G (2018) Recycling of bare waste printed circuit boards as received using an organic solvent technique at a low temperature. J Clean Prod. https://doi.org/10.1016/j.jclepro.2018.03.227

    Article  Google Scholar 

  21. Karaer Özmen F, Üreyen ME, Koparal AS (2020) Cleaner production of flame-retardant-glass reinforced epoxy resin composite for aviation and reducing smoke toxicity. J Clean Prod. https://doi.org/10.1016/j.jclepro.2020.124065

    Article  Google Scholar 

  22. Luo H, Zeng Y, Cheng Y, He D, Pan X (2020) Recent advances in municipal landfill leachate: A review focusing on its characteristics, treatment, and toxicity assessment. Sci Total Environ. https://doi.org/10.1016/j.scitotenv.2019.135468

    Article  Google Scholar 

  23. Pegoretti A (2021) Recycling concepts for short-fiber-reinforced and particle-filled thermoplastic composites: a review. Advanced Industrial and Engineering Polymer Research. https://doi.org/10.1016/j.aiepr.2021.03.004

    Article  Google Scholar 

  24. Tatariants M, Bendikiene R, Denafas G (2017) Mechanical and thermal characterizations of non-metallic components recycled from waste printed circuit boards. J Clean Prod. https://doi.org/10.1016/j.jclepro.2017.08.195

    Article  Google Scholar 

  25. Amaechi CV, Agbomerie CO, Orok EO, Ye J (2020) economic aspects of fiber reinforced polymer composite recycling. In Encyclopedia of Renewable and Sustainable Materials. https://doi.org/10.1016/b978-0-12-803581-8.10738-6

    Article  Google Scholar 

  26. Tatariants M, Denafas G, Bendikiene R (2018) Separation and purification of metal and fiberglass extracted from waste printed circuit boards using milling and dissolution techniques. Environ Prog Sustainable Energy. https://doi.org/10.1002/ep.12899

    Article  Google Scholar 

  27. Clark E, Bleszynski M, Valdez F, Kumosa M (2020) Recycling carbon and glass fiber polymer matrix composite waste into cementitious materials. Resour Conserv Recycl. https://doi.org/10.1016/j.resconrec.2019.104659

    Article  Google Scholar 

  28. Regina Kalpokaitė-Dičkuvienė, Arūnas Baltušnikas, Inna Pitak, and Stasė Irena Lukošiūtė. 2021. “A new strategy for functionalization of char derived from pyrolysis of textile waste and its application as hybrid fillers (CNTs/char and graphene/char) in cement industry.” Journal of Cleaner Production.

  29. Yang S, Jiang J, Duan W, Bai S, Wang Q (2020) Production of sustainable wood-plastic composites from the nonmetals in waste printed circuit boards: excellent physical performance achieved by solid-state shear milling. Compos Sci Technol. https://doi.org/10.1016/j.compscitech.2020.108411

    Article  Google Scholar 

  30. Naqvi SR, Prabhakara HM, Bramer EA, Dierkes W, Akkerman R, Brem G (2018) A critical review on recycling of end-of-life carbon fibre/glass fibre reinforced composites waste using pyrolysis towards a circular economy. Resour Conserv Recycl. https://doi.org/10.1016/j.resconrec.2018.04.013

    Article  Google Scholar 

  31. Alessandro Pegoretti, Towards sustainable structural composites: a review on the recycling of continuous-fiber-reinforced thermoplastics, Advanced Industrial and Engineering Polymer Research, 4, 2021, https://doi.org/10.1016/j.aiepr.2021.03.001.

  32. Yun YM, Seo MW, Ra HW, Koo GH, Oh JS, Yoon SJ, …, Kim JH (2015) Pyrolysis characteristics of glass fiber-reinforced plastic (GFRP) under isothermal conditions. J Anal Appl Pyrolysis.https://doi.org/10.1016/j.jaap.2015.04.013

  33. Qiao Y, Das O, Zhao SN, Sun TS, Xu Q, Jiang L (2020) Pyrolysis kinetic study and reaction mechanism of epoxy glass fiber reinforced plastic by thermogravimetric analyzer (Tg) and tg–ftir (fourier-transform infrared) techniques. Polymers. https://doi.org/10.3390/polym12112739

    Article  Google Scholar 

  34. Mohammed Ali Abdelnaby, Justas Eimontas, Nerijus Striūgas. 2022. “Gasification kinetics of char derived from metallised food packaging plastics waste pyrolysis.” Energy.

  35. Justas Eimontas, Nerijus Striūgas, Sharath P. Subadra, and Mohammed Ali Abdelnaby. 2021. “Thermal degradation and pyrolysis kinetic behaviour of glass fibre-reinforced thermoplastic resin by TG-FTIR, Py-GC/MS, linear and nonlinear isoconversional models.” Journal of Materials Research and Technology.

  36. Mohamed A, Eimontas J, Striūgas N (2022) Mohammed Ali Abdelnaby, Pyrolysis kinetic behavior and TG-FTIR-GC–MS analysis of end-life ultrafiltration polymer nanocomposite membranes. Chem Eng J. https://doi.org/10.1016/j.cej.2021.131181

    Article  Google Scholar 

  37. Samy Yousef and Alaa Mohamed. 2016. “Mass production of CNTs using CVD multi-quartz tubes.” Journal of Mechanical Science and Technology.

  38. Yousef S, Mohamed A, Tatariants M (2018) Mass production of graphene nanosheets by multi-roll milling technique. Tribol Int. https://doi.org/10.1016/j.triboint.2018.01.040

    Article  Google Scholar 

  39. Eimontas J, Striūgas N, Praspaliauskas M, Abdelnaby MA (2021) Pyrolysis kinetic behaviour of glass fibre-reinforced epoxy resin composites using linear and nonlinear isoconversional methods. Polymers. https://doi.org/10.3390/polym13101543

    Article  Google Scholar 

  40. Yousef S, Eimontas J, Striūgas N, Abdelnaby MA (2021) Influence of carbon black filler on pyrolysis kinetic behaviour and TG-FTIR-GC–MS analysis of glass fibre reinforced polymer composites. Energy. https://doi.org/10.1016/j.energy.2021.121167

    Article  Google Scholar 

  41. Simona Tuckute, Justas Eimontas, Nerijus Striūgas, Maksym Tatariants, Mohammed Ali Abdelnaby, and Linas Kliucininkas. 2019. “A sustainable bioenergy conversion strategy for textile waste with self-catalysts using mini-pyrolysis plant.” Energy Conversion and Management.

  42. Subadra SP, Griškevičius P, Varnagiris S, Milcius D, Makarevicius V (2020) Superhydrophilic functionalized graphene/fiberglass/epoxy laminates with high mechanical, impact and thermal performance and treated by plasma. Polym Testing. https://doi.org/10.1016/j.polymertesting.2020.106701

    Article  Google Scholar 

  43. Striūgas N, Zakarauskas K, Praspaliauskas M, Abdelnaby MA (2020) Pyrolysis kinetic behavior and TG-FTIR-GC–MS analysis of metallised food packaging plastics. Fuel. https://doi.org/10.1016/j.fuel.2020.118737

    Article  Google Scholar 

  44. Eimontas J, Striūgas N, Mohamed A, Abdelnaby MA (2021) Morphology, compositions, thermal behavior and kinetics of pyrolysis of lint-microfibers generated from clothes dryer. J Anal Appl Pyrol. https://doi.org/10.1016/j.jaap.2021.105037

    Article  Google Scholar 

  45. Ming X, Xu F, Jiang Y, Zong P, Wang B, Li J, …, Tian Y (2020) Thermal degradation of food waste by TG-FTIR and Py-GC/MS: pyrolysis behaviors, products, kinetic and thermodynamic analysis. J Clean Prod.https://doi.org/10.1016/j.jclepro.2019.118713

  46. Icduygu MG, Asilturk M, Yalcinkaya MA, Hamidi YK, Altan MC (2019) Three-dimensional nano-morphology of carbon nanotube/epoxy filled poly(methyl methacrylate) microcapsules. Materials. https://doi.org/10.3390/ma12091387

    Article  Google Scholar 

  47. Abdelnaby MA, Eimontas J, Striūgas N (2021) Pyrolysis kinetic behaviour and TG-FTIR-GC–MS analysis of coronavirus face masks. J Anal Appl Pyrol. https://doi.org/10.1016/j.jaap.2021.105118

    Article  Google Scholar 

  48. Yousef S, Eimontas J, Striugas N, Abdelnaby MA (2020) Modeling of metalized food packaging plastics pyrolysis kinetics using an independent parallel reactions kinetic model. Polymers. https://doi.org/10.3390/polym12081763

    Article  Google Scholar 

  49. Tatariants M, Sidaraviciute R, Denafas G, Bendikiene R (2017) Characterization of waste printed circuit boards recycled using a dissolution approach and ultrasonic treatment at low temperatures. RSC Adv. https://doi.org/10.1039/c7ra07034a

    Article  Google Scholar 

  50. Fredi G et al (2018) Multifunctional epoxy/carbon fiber laminates for thermal energy storage and release. Compos Sci Technol. https://doi.org/10.1016/j.compscitech.2018.02.005

    Article  Google Scholar 

  51. Eimontas J, Striūgas N, Abdelnaby MA (2021) Pyrolysis and gasification kinetic behavior of mango seed shells using TG-FTIR-GC–MS system under N2 and CO2 atmospheres. Renewable Energy. https://doi.org/10.1016/j.renene.2021.04.034

    Article  Google Scholar 

  52. Long, T. R., Knorr, D. B., Masser, K. A., Elder, R. M., Sirk, T. W., Hindenlang, M. D., … Lenhart, J. L. (2017). Ballistic response of polydicyclopentadiene vs. epoxy resins and effects of crosslinking. In Conference Proceedings of the Society for Experimental Mechanics Series. https://doi.org/10.1007/978-3-319-41132-3_37

  53. Sarwar, Zahid, Maksym Tatariants, Edvinas Krugly, Darius Čiužas, Paulius Pavelas Danilovas, Arunas Baltusnikas, and Dainius Martuzevicius. 2019. “Fibrous PEBA-graphene nanocomposite filaments and membranes fabricated by extrusion and additive manufacturing.” European Polymer Journal.

  54. Kim YM, Han TU, Kim S, Jae J, Jeon JK, Jung SC, Park YK (2017) Catalytic co-pyrolysis of epoxy-printed circuit board and plastics over HZSM-5 and HY. J Clean Prod. https://doi.org/10.1016/j.jclepro.2017.08.224

    Article  Google Scholar 

  55. Datsyuk V, Trotsenko S, Trakakis G, Boden A, Vyzas-Asimakopoulos K, Parthenios J, …, Papagelis K (2020) Thermal properties enhancement of epoxy resins by incorporating polybenzimidazole nanofibers filled with graphene and carbon nanotubes as reinforcing material. Polym Testing.https://doi.org/10.1016/j.polymertesting.2019.106317

  56. Ma C, Sánchez-Rodríguez D, Kamo T (2021) A comprehensive study on the oxidative pyrolysis of epoxy resin from fiber/epoxy composites: product characteristics and kinetics. J Hazard Mater. https://doi.org/10.1016/j.jhazmat.2021.125329

    Article  Google Scholar 

  57. Zakarauskas K, Eimontas J, Striūgas N (2021) Microcrystalline paraffin wax, biogas, carbon particles and aluminum recovery from metallised food packaging plastics using pyrolysis, mechanical and chemical treatments. J Clean Prod. https://doi.org/10.1016/j.jclepro.2021.125878

    Article  Google Scholar 

  58. Saidani W, Wahbi A, Sellami B, Helali MA, Khazri A, Mahmoudi E, …, Beyrem H (2021) Toxicity assessment of organophosphorus in Ruditapes decussatus via physiological, chemical and biochemical determination: a case study with the compounds γ-oximo- and γ-amino-phosphonates and phosphine oxides. Mar Pollut Bull.https://doi.org/10.1016/j.marpolbul.2021.112556

  59. Yousef S, Eimontas J, Zakarauskas K, Striūgas N, Mohamed A (2021) A new strategy for using lint-microfibers generated from clothes dryer as a sustainable source of renewable energy. Sci Total Environ. https://doi.org/10.1016/j.scitotenv.2020.143107

    Article  Google Scholar 

  60. Evgeny Trofimov, Nerijus Striūgas, Mohamed Hamdy, and Mohammed Ali Abdelnaby. 2020. “Conversion of end-of-life cotton banknotes into liquid fuel using mini-pyrolysis plant.” Journal of Cleaner Production.

  61. Simona Tuckute, Andrius Tonkonogovas, Arūnas Stankevičius, and Alaa Mohamed. 2021. “Ultra-permeable CNTs/PES membranes with a very low CNTs content and high H2/N2 and CH4/N2 selectivity for clean energy extraction applications.” Journal of Materials Research and Technology.

  62. Justas Šereika, Andrius Tonkonogovas, Tawheed Hashem, and Alaa Mohamed. 2021. “CO2/CH4, CO2/N2 and CO2/H2 selectivity performance of PES membranes under high pressure and temperature for biogas upgrading systems.” Environmental Technology and Innovation.

  63. Abdulkader AF, Hassan QMA, Al-Asadi AS, Bakr H, Sultan HA, Emshary CA (2018) Linear, nonlinear and optical limiting properties of carbon black in epoxy resin. Optik. https://doi.org/10.1016/j.ijleo.2018.01.133

    Article  Google Scholar 

  64. Nerijus Striūgas, Samy Yousef, and Mohammed Ali Abdelnaby. 2021. “Catalytic pyrolysis kinetic behaviour and TG-FTIR-GC–MS analysis of waste fishing nets over ZSM-5 zeolite catalyst for caprolactam recovery.” Renewable Energy.

  65. Cai J, Chen S (2009) A new iterative linear integral isoconversional method for the determination of the activation energy varying with the conversion degree. J Comput Chem. https://doi.org/10.1002/jcc.21195

    Article  Google Scholar 

  66. Vyazovkin S (2001) Modification of the integral isoconversional method to account for variation in the activation energy. J Comput Chem. https://doi.org/10.1002/1096-987x(20010130)22:2<178::aid-jcc5>3.0.co;2-%23

    Article  Google Scholar 

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Funding

This project has received funding from the Research Council of Lithuania (LMTLT), agreement No. S-MIP-20–27.

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Authors and Affiliations

  1. Department of Production Engineering, Faculty of Mechanical Engineering and Design, Kaunas University of Technology, 51424, Kaunas, Lithuania

    Samy Yousef

  2. Laboratory of Combustion Processes, Lithuanian Energy Institute, Breslaujos 3, 44403, Kaunas, Lithuania

    Justas Eimontas & Nerijus Striūgas

  3. Department of Production Engineering and Printing Technology, Akhbar Elyom Academy, 6Th of October, Egypt

    Mohammed Ali Abdelnaby

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  1. Samy Yousef
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  2. Justas Eimontas
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  4. Mohammed Ali Abdelnaby
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Contributions

Samy Yousef: conceptualization, data curation, formal analysis, funding acquisition, investigation, methodology, project administration, resources, software, supervision, writing—original draft, writing—review and editing.

Justas Eimontas: conceptualization, data curation, formal analysis.

Nerijus Striūgas: conceptualization, data curation, formal analysis.

Mohammed Ali Abdelnaby: conceptualization, data curation, formal analysis, software, writing-review and editing.

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Correspondence to Samy Yousef.

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Yousef, S., Eimontas, J., Striūgas, N. et al. Thermal decomposition of CNTs and graphene-reinforced glass fibers/epoxy and their kinetics. Biomass Conv. Bioref. 14, 869–889 (2024). https://doi.org/10.1007/s13399-022-02341-3

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