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Rigid-flexible interface enhances carbon fibre/epoxy performance
A novel “rigid-flexible” interface design combining lignin-based epoxy resin with nano-cerium oxide sol significantly enhances the mechanical performance of carbon fibre/epoxy composites. The approach increased interlaminar shear strength by 55 %, flexural strength by 95 % and tensile strength by 67 %, while using renewable lignin as an eco-friendly alternative to petroleum-based modifiers.
The interface between carbon fibres (CF) and the resin matrix plays a decisive role in the mechanical performance of fibre-reinforced composites. To optimise stress distribution and load transfer efficiency at this critical region, researchers developed a “rigid-flexible hybrid” interface design strategy that combines flexible lignin-based epoxy resin (LBEP) with rigid nano-cerium oxide sol (CeO₂). The synergistic effect of these two components significantly improves both the wettability and surface roughness of the carbon fibres, resulting in enhanced interfacial adhesion with the epoxy matrix.
The rigid CeO₂ particles are uniformly distributed across the interface region, where they enhance mechanical interlocking and load-bearing capacity through physical anchoring and crack deflection mechanisms. The flexible LBEP, in turn, acts as a multifunctional bridging phase. Its abundant reactive functional groups form stable covalent bonds with both the carbon fibre surfaces and the surrounding resin matrix, while mitigating stress concentration through molecular chain conformation adjustment and energy dissipation.
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Significant mechanical improvements and sustainable raw materials
Experimental results demonstrate the effectiveness of the combined approach: carbon fibre/epoxy composites modified with the composite interface showed an increase in interlaminar shear strength (ILSS) of 55 %, in flexural strength of 95 %, and in tensile strength of 67 % compared with unmodified reference systems. The multi-level interfacial structure integrates high strength with high toughness, enabling more efficient stress transfer and energy dissipation under load.
Beyond the mechanical performance gains, the strategy also offers sustainability benefits. By using lignin – a renewable and abundant raw material – as the basis for the flexible epoxy component, the approach provides an eco-friendly alternative to conventional petroleum-based modifiers. Combined with a relatively simple processing route, this makes the method a promising interfacial engineering strategy for the development of high-performance carbon fibre composites in demanding applications.
Source: Wu, S. et al., Construction of a “rigid-flexible” interfacial structure using lignin-based epoxy sizing agent and nano-CeO₂ sol for enhanced mechanical performance of carbon fiber/epoxy composites. Progress in Organic Coatings, 110166 (2026).
