Thermal and Morphological Effect of Low Tenor Alkali Treatment on Flax and Hemp Fibre Scraps: A Parametric Study

The exploitation in new materials of even the smallest scraps of textiles would contribute to their success in fields, such as the automotive industry. In this work, alkaline treatment with low tenors of sodium hydroxide (NaOH) was applied on flax and hemp fabric textile residues, trying to recover the most suitable process conditions as the function of the quality of treated fibres. Several parameters have been considered, the temperature and the concentration of the alkaline solution, the immersion time in it, and finally the immersion time in distilled water during the neutralization phase. Drying tests were carried out at a controlled temperature to verify the effects of the various treatment parameters. The effect of the various procedures was elucidated by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD) so to measure crystallinity, atomic force microscopy (AFM) to elucidate the variation of roughness, and nitrogen absorption/desorption cycles to how microporosities develop with treatment. It is suggested that only the 1.5 wt./vol.% treatment did produce some worthwhile modification of the fibres to prepare them for their use in composites, more evidently in flax than in hemp, though care needs to be taken about fibre embrittlement and potential permeability to water.