Characteristics of alkaline-modified coconut fibre via microwave-assisted extraction in cementitious composites

Coconut fibre, a lignocellulosic by-product of Cocos nucifera L, is recognised as a sustainable strength-enhancing material in cementitious composites. Untreated fibres, however, exhibit poor interfacial bonding due to surface impurities and limited reactivity. This study examines the effects of NaOH treatment at concentrations of 2, 3.5, and 5 per cent on the microstructural, elemental composition, and functional groups of coconut fibre. SEM analysis revealed progressive morphological refinement as the NaOH concentration increased. SEM observations revealed that untreated coconut fibres possessed rough surfaces covered with non-cellulosic components, which can hinder effective fibrematrix bonding. Progressive surface modification was observed as NaOH concentration increased, with NaOH-treated fibres exhibiting enhanced surface roughness and porosity, and the removal of surface impurities. EDX confirmed carbon (C) and oxygen (O) as dominant elements. The C-O ratio increased after treatment due to the removal of hydrophobic impurities and greater exposure of cellulose hydroxyl groups. FTIR spectra revealed a broad O-H stretching band around 3400 cm⁻¹, indicating hydroxyl groups associated with cellulose and the partial removal of hemicellulose, lignin, and surface impurities after treatment. Among the conditions examined, coconut fibre treated with 5% NaOH displayed the most favourable surface characteristics, suggesting a strong potential to improve the fibre-matrix interaction within cementitious composites. These results indicate that alkalinetreated coconut fibre can serve as an effective reinforcement material for the development of sustainable fibre-reinforced concrete.