Characteristics of secondary fibres derived from recycling processes of fibreboard manufacturing residues and post-consumer wood waste

Recycling of post-consumer fibreboards has gained significant traction in both academic research and industrial applications. The quality of secondary fibres plays a crucial role when reusing them in fibreboard production. This study presents a comprehensive analysis of recycled (hereafter referred as secondary) fibres recovered through modified thermo-mechanical pulping and steam treatment methods, in comparison to virgin fibres. The fibres were systematically characterized in terms of their physical, chemical, and morphological properties, supplemented by microscopic analysis. Results showed that the average fibre length of steam-treated secondary fibres derived from post-consumer fibreboards and fibreboard production (processing) residues was comparable to that of virgin fibres, whereas secondary fibres from solid wood waste were 18 % shorter due to identified presence of hardwood species. All secondary fibre types exhibited higher fines content, increased surface roughness, and elevated formaldehyde emissions relative to virgin fibres. FTIR spectroscopy and elemental nitrogen analysis, confirmed the presence of residual resin, which contributes to a higher pH and increased alkaline buffering capacity in secondary fibres. Dynamic vapour sorption (DVS) analysis revealed reduced water uptake and increased hysteresis in secondary fibres from steam treatment. Scanning electron microscopy (SEM) and inductively coupled plasma (ICP) analysis identified inorganiccontaminants and elevated concentrations of elements-specifically sodium, aluminium, and lead, particularly in fibres from post-consumer fibreboard fractions. Finally, Fibre blends containing 15 % or 25 % (w/w) secondary fibres from fibreboard processing residues exhibited comparable properties to virgin fibre benchmarks. This study establishes a fundamental property baseline for secondary fibres, providing a framework for the formulation and optimization of future sustainable composites.