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<p>Epoxy networks, despite outstanding properties, cannot be reprocessed and reused; thus, disposing of them usually involves landfilling or incineration, causing adverse environmental consequences. This study introduces a bio-based vanillin-derived hardener containing thermally reversible imine bond for epoxy resin curing in the presence or absence of polyethylene glycol (PEG) as a modifying agent to create vitrimers that support environmental sustainability and circular economy. This research deals with investigation of the curing process, examination of the physical-chemical, mechanical, and thermal properties of cured matrix and carbon fiber reinforced polymer (CFRP) composite, assessment of their self-healability, recyclability, weldability, and reprocessability, besides performance experiments as reversible structural adhesives. The vitrimer matrix retained over 86.0% of lap shear strength after multiple rebonding cycles, while recycled carbon fibers maintained 92.0% of tensile strength, and microwave-assisted welding restored 94.5% of tensile strength within 4&#xa0;min. PEG enhanced thermostability as high as 45&#xa0;°C (TGA, T<sub>d1%</sub>), and the onset curing temperature occurred earlier between 3 and 10&#xa0;°C. Stress relaxation analysis indicated lower activation energy for bond exchange in PEG-modified vitrimers (40.4 vs. 46.5&#xa0;kJ/mol). Additionally, DFT verified the coexistence of dual dynamic mechanisms, i.e., covalent imine bond and supramolecular H-bonding, and it correlated PEG-induced H-bonding (average 42.1&#xa0;kJ/mol) with mechanical and thermal properties. A simplified life-cycle assessment (GREEN-MOTION™ analysis) further confirmed a favorable balance between material performance and environmental impact. These combined results highlight a distinctive molecular design strategy offering high-performance, recyclable, and eco-efficient epoxy networks.</p>

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Epoxy CFRP Composites and Structural Adhesives from a Bio-Derived Dynamic Hardener: Preparation, Recyclability, Reprocessability, Healability, Weldability, Greenness and DFT Evaluation

  • 期刊论文

  • 发表日期：

    2026年2月9日

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  • Mohammad Reza Zamani,
  • Mohammad Jalal Zohuriaan-Mehr,
  • Mehdi Ghambarian,
  • Kourosh Kabiri,
  • Omid Zabihi

摘要

Epoxy networks, despite outstanding properties, cannot be reprocessed and reused; thus, disposing of them usually involves landfilling or incineration, causing adverse environmental consequences. This study introduces a bio-based vanillin-derived hardener containing thermally reversible imine bond for epoxy resin curing in the presence or absence of polyethylene glycol (PEG) as a modifying agent to create vitrimers that support environmental sustainability and circular economy. This research deals with investigation of the curing process, examination of the physical-chemical, mechanical, and thermal properties of cured matrix and carbon fiber reinforced polymer (CFRP) composite, assessment of their self-healability, recyclability, weldability, and reprocessability, besides performance experiments as reversible structural adhesives. The vitrimer matrix retained over 86.0% of lap shear strength after multiple rebonding cycles, while recycled carbon fibers maintained 92.0% of tensile strength, and microwave-assisted welding restored 94.5% of tensile strength within 4 min. PEG enhanced thermostability as high as 45 °C (TGA, Td1%), and the onset curing temperature occurred earlier between 3 and 10 °C. Stress relaxation analysis indicated lower activation energy for bond exchange in PEG-modified vitrimers (40.4 vs. 46.5 kJ/mol). Additionally, DFT verified the coexistence of dual dynamic mechanisms, i.e., covalent imine bond and supramolecular H-bonding, and it correlated PEG-induced H-bonding (average 42.1 kJ/mol) with mechanical and thermal properties. A simplified life-cycle assessment (GREEN-MOTION™ analysis) further confirmed a favorable balance between material performance and environmental impact. These combined results highlight a distinctive molecular design strategy offering high-performance, recyclable, and eco-efficient epoxy networks.