Abstract
Natural fibres have a high potential as reinforcement of polymer matrices, as they combine a high specific strength and modulus with sustainable production and reasonable prices. Modifying the fibre surface is a common method to increase the adhesion and thereby enhance the mechanical properties of composites. In this study, a novel sustainable surface treatment is presented: the fungal enzyme laccase was utilised with the aim of covalently binding the coupling agent dopamine to flax fibre surfaces. The goal is to improve the interfacial strength towards an epoxy matrix. SEM and AFM micrographs showed that the modification changes the surface morphology, indicating a deposition of dopamine on the surface. Fibre tensile tests, which were performed to check whether the fibre structure was damaged during the treatment, showed that no decrease in tensile strength or modulus occurred. Single fibre pullout tests showed a 30% increase in interfacial shear strength (IFSS) due to the laccase-mediated bonding of the coupling agent dopamine. These results demonstrate that a laccase + dopamine treatment modifies flax fibres sustainably and increases the interfacial strength towards epoxy.
Highlights
Fibre reinforced polymers combine the superior mechanical properties of fibres with the usability of a polymer
The aim of the present study is to transfer this scheme to natural fibres, using the biological reactant dopamine as a bifunctional coupling agent in order to increase interfacial strength and improve the mechanical parameters of the composite
The laccase dopamine treatment improves the interfacial shear strength (IFSS) by 30%
Summary
Fibre reinforced polymers combine the superior mechanical properties of fibres with the usability of a polymer. A fibre-reinforced composite can only be as strong as its interface Conventional reinforcing fibres such as glass, aramid or carbon fibres are usually treated with a sizing or finish in order to improve the adhesion to the polymer matrix [1,2]. They contain bi-functional coupling agents such as silanes, which ideally covalently bond to both fibre and matrix, as well as film formers, which ensure the processability of the fibre and may aid in adhesion. Such sizings need to be optimised with the specific fibre–matrix combination in mind. Surface treatments are seldom used so far, even though they would increase the mechanical properties of the composites [3,4,5,6,7]
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