Flax fibre sizings for fibre-reinforced thermosets - investigating the influences of different sizing agents on the composite properties

The functionalisation of the fibre surface offers high potential to improve the fabric properties and fibre-matrix adhesion. For this purpose, the application of sizings is promising. Sizings are conventionally used to maintain fibre quality during the weaving process and are not specifically designed as a coupling agent between fibre and matrix for structural composites. The present work provides a comparative study of flax fibre reinforced composites (FRCs) containing 2, 6 and 12 % sizing volume fraction relative to the fibre volume using oxidised starch, polyvinyl acetate (PVAc) and cellulose acetate (CA) as sizing agents. The composite porosity was one of the main aspects influenced by the sizing. PVAc and low amounts of CA sizing improved the Young’s modulus of the composite up to 13 % without lowering the tensile strength. The performance of the composites containing PVAc sizings was almost independent of the sizing volume fraction.