Travail de fin d'études en chimie et bio-industries : Chemical Pretreatment-Assisted Refining of Textile Waste Fibres for Construction Applications.

Abstract

This study investigated the effects of alkaline NaOH/urea (5/12 wt%) and concentrated acetic acid (50 wt%) pretreatments on recycled cotton, polyethylene terephthalate (PET), and 50/50 polycotton fibres. The fibres were studied both before and after mechanical refining to evaluate their suitability for lightweight fibre-based construction foams. Fibres were characterised by water retention value (WRV), ATR-FTIR spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In addition polycotton suspensions were further evaluated by oscillatory rheometry, Turbiscan optical stability analysis, and gravimetric foam characterisation. NaOH/urea pretreatment increased the WRV of cotton by 12.1% and, after refining, led to extensive longitudinal fibril delamination. The surface O/C ratio also increased from 0.57 to 0.62, together with near-complete removal of nitrogen-containing sizing agents, indicating improved surface purification and greater cellulose exposure. A weak carbonyl band at 1710 cm⁻¹ was observed in all cotton samples, but it was noticeably stronger in the NaOH/urea-treated sample (Cot-NaU), which may be linked to mild alkaline oxidation or partial carbamate formation. In contrast, acetic acid pretreatment reduced the WRV of cotton by 9.4%, suggesting inter-fibrillar consolidation and selective hydrolysis of amorphous cellulose. This was supported by a slight increase in crystallinity index (70.26% compared to 68.65% for Cot-Ctrl). PET fibres remained chemically unaffected under both pretreatment conditions. In polycotton, the effects of both pretreatments were noticeably weaker compared to pure cotton across all characterisation methods. This is likely due to physical and capillary constraints introduced by the PET component. PC-NaU formed a much stronger viscoelastic gel (G′₀ = 2,970 Pa) than PC-AcA (G′₀ = 454 Pa). It also showed better sedimentation stability over 60 minutes and produced foams with a denser fibrillar structure and lower bulk porosity (60.07% compared to 67.56% for PC-Ctrl). These results demonstrate that the type of chemical pretreatment strongly influences fibrillation behaviour and network-forming capacity of recycled textile 9 fibres. Among the two pretreatments, NaOH/urea proved to be more effective in generating stable, processable fibre suspensions for construction applications.