Structural biocomposites from flax - Part II: The use of PEG and PVA as interfacial compatibilising agents

Flax fibre, pre-treated in a 2-step process with a chelating agent for calcium followed by a commercial pectinolytic enzyme preparation, was modified with either PVA (poly(vinyl acetate)) or PEG (poly(ethylene glycol)). After treatment the fibres were found to have undergone surface and bulk chemical changes, identified through near infra-red spectroscopy (NIR) and differential thermo gravimetry (DTG). Changes to the linear density of the fibre were also found to have occurred. Modification with PVA and PEG did not result in any change in the fibre Young's modulus, but did result in a loss in tensile strength of about 15%, accompanied by an increase in the coefficient of variation from around 10% to 25%, indicating structural change to the fibre. When used as reinforcement in an epoxy matrix composite, an increase in the composite's Young's modulus from ≈4.5 GPa to 5.5 GPa was observed, accompanied by a reduction in tensile strength, strain to failure and work-of-fracture. It is believed that the PVA and PEG modify the interfacial behaviour in these systems, improving fibre and matrix adhesion.