Cottonised flax fibres vs. cotton fibres: structural, textural and adsorption characteristics

Abstract

Structural (crystallinity), textural (pore volume, V_p, specific surface area, S_BET, pore size distribution, PSD) and adsorption characteristics of bleached flax fibres and cotton fibres have been determined using equilibrium adsorption of nitrogen, water, chlorhexidine diacetate (CHX) and methylene blue (MB), adsorption–desorption kinetics of MB and CHX, X-ray diffraction, infrared spectroscopy, thermogravimetry, differential scanning calorimetry (DSC) and DSC cryoporometry. Air-dry, degassed, wetted (RH ≈ 95%), swollen (24 h in water) and air-dried and heated (120 °C for 1 h) fibres were studied. Flax fibres have higher crystallinity, adsorption capacity (MB, CHX, water), and smaller MB desorption than cotton fibres. Cotton fibres have larger V_p value (nitrogen adsorption) and the S_BET,N2 similar to that of flax. Water vapour adsorption is higher on flax since the adsorbed water volume is V_p,w = 0.19 and 0.14 cm³ g⁻¹ for flax and cotton, respectively, at RH ≈ 95%. Wetted fibres are characterised by V_p,w larger by an order of magnitude than V_p,N2 for degassed samples because of swelling effect. However, nanopores at radius R < 1 nm are practically absent in all samples studied regardless of the characterisation technique. The adsorption of MB and CHX on flax fibres is much larger than that for cotton fibres. The specific surface area determined from MB adsorption is 51 m² g⁻¹ (close to S_BET,w estimated from water adsorption but larger than S_BET,N2) and 8 m² g⁻¹ (much smaller than S_BET,N2 and S_BET,w) for flax and cotton fibres, respectively.