# Hygrothermal Durability and Damage Evolution of Bio-Epoxy-Based Composites Reinforced with Different Fibre Types

## TL;DR

This study examines how different fiber types affect the durability of bio-epoxy composites under hygrothermal conditions.

## Contribution

The novelty lies in comparing hygrothermal durability of bio-epoxy composites reinforced with carbon, E-glass, basalt, and flax fibers.

## Key findings

- Flax fibers showed less tensile strength reduction compared to synthetic fibers due to physical rather than chemical damage.
- Flax composites had the highest interfacial shear strength reduction at 10%.
- SEM and EDS analyses revealed distinct failure mechanisms depending on fiber type.

## Abstract

This study investigates hygrothermal durability of bio-epoxy composites reinforced with carbon, E-glass, basalt, and flax fibres. Fibre yarns and bio-composites were exposed for 3000 h at 60 °C and 98% relative humidity. The tensile strength reduction in the fibres and the interfacial shear strength (IFSS) reduction in the composites were assessed after ageing. Chemical deterioration was evaluated using energy-dispersive X-ray spectroscopy (EDS); morphological changes in fibres and composites fracture surfaces were examined using a scanning electron microscope (SEM). Results indicated that the durability was significantly influenced by fibre types. Tensile strength reduction was higher in carbon, glass and basalt compared to flax yarns because of chemical degradation of the sizing layer in synthetic fibres, while only physical damage was observed in flax. The IFSS reduction was highest in flax composites (10%), and lowest in carbon (4%). EDS indicated the hydrolysis and erosion of fibre sizing, with reduced silica content in glass and basalt fibres. SEM revealed matrix-dominated failure in carbon/bio-epoxy, interfacial debonding in glass and basalt composites, fibre slip and pull-out in flax/bio-epoxy. Overall, the results highlighted damage propagation pathways and demonstrated that bio-epoxy composites exhibited reasonable performance under hygrothermal ageing, supporting their potential as a sustainable alternative in durability-critical applications.