Qualitative and quantitative assessment of water sorption in natural fibres using ATR-FTIR spectroscopy

•Effect of moisture sorption on plant fibres was investigated by FTIR spectroscopy.•Hydroxyl and carboxyl moieties are specific sites for water sorption.•Partial least squares regression quantified the water content of natural fibres.•Models fitted the sorption isotherms and diffusion kinetics. In the field of composite materials, natural fibres appear to be a viable replacement for glass fibres. However, in humid conditions, strong hydrophilic behaviour of such materials can lead to their structural modification. Then, understanding moisture sorption mechanisms in these materials is an important issue for their efficient use. In this work, the water sorption on three natural fibres (flax, hemp and sisal) was studied using Fourier transformed infrared spectroscopy. The spectral information allowed both qualitative and quantitative analyses of the moisture absorption mechanisms. The main chemical functions involved in the water sorption phenomenon were identified. The absolute water content of the fibres was also determined by using a partial least square regression (PLS-R) approach. Moreover, typical sorption isotherm curves described by Park model were fitted as well as water diffusion kinetics. These last applications confirmed the validity of the FTIR spectra based predictive models.