Epoxy composites reinforced with deacetylated Phormium tenax leaf fibres

Leaf fibres from Phormium tenax (harakeke, New Zealand flax) were treated with 1 wt.% aqueous NaOH at 30 °C to remove all of the acetyl groups, accounting for most of a 7% mass loss. Increasing the treatment time to 4 h showed no detectable increase in mass loss, but increasing the NaOH concentration to 5% doubled the mass loss by removing some of the xylans. Changes in fibre morphology were interpreted in terms of swelling of cell walls into lumens, followed by shrinkage on drying without reopening the lumens. Deacetylation retarded the rate of water uptake in unidirectional epoxy composites, but showed no detectable influence on the equilibrium moisture content, flexural modulus or strength. The results suggest that high levels of natural acetylation are not a useful feature of leaf fibres, at least in the context of reinforcement for epoxy composites.