Influence of particle size and surface treatment on agro-industrial food waste composite boards

Abstract Agro-industrial residues offer sustainable lignocellulosic feedstock for particleboards, yet their high extractive contents limit their bonding quality. This study investigated the combined effects of waste type, particle fraction (medium, 0.425–2 mm; coarse, 2–4 mm), and surface treatment on physical, mechanical, and microstructural properties of boards manufactured from macadamia nutshells (MC), coffee parchment (CF), mango seed coat (MN), and avocado seed residue (AV). Waste particles were bonded with urea-formaldehyde to produce panels with a target density of ~ 850 kg/m 3 . Water absorption (WA), thickness swelling (TS), internal bond strength (IB), modulus of rupture (MOR), modulus of elasticity (MOE), and compressive strength (CS) were evaluated according to EN and ASTM standards. X-ray computed tomography, scanning electron microscopy, and statistical analyses related processing variables to board performance. Waste type exerted the strongest influence, while effects of particle fraction and surface treatment were linked to packing density and porosity. Coarse MC and AV enhanced MOE and CS through improved stress transfer and mechanical interlocking, whereas fibrous MN improved MOR but, together with CF, reduced IB through void formation. Surface treatment generally enhanced mechanical properties but increased WA and TS due to induced microporosity and fibre fibrillation. Water-treated coarse MC exhibited the best overall performance (TS 3.4%, MOR 10.4 MPa, MOE 5855 MPa, IB 5.40 MPa, and CS 22.9 MPa), while water-treated MN achieved the highest MOR (12.8 MPa). Several board configurations satisfied EN 312 P1 and P2 requirements, demonstrating the effectiveness of particle engineering and surface modification for underutilised agro-industrial food residues.