Effects of partial substitution of wood particles with Norway spruce bark on the properties of single-layer particleboards

Spruce bark is generated in large quantities during industrial wood processing, yet its higher-value use in particleboards remains limited. Although bark substitution in particleboards has been studied repeatedly, less is known about how a gradual substitution series influences the broader property profile of single-layer particleboards manufactured under one fixed regime while simultaneously evaluating vertical density profile, screw withdrawal resistance and sound absorption. The objective of this study was to determine how replacing wood particles with 10–50% Norway spruce bark affects the physical and mechanical properties of single-layer particleboards. Up to 20% bark, bending properties, screw withdrawal resistance and sound absorption remained comparable with the reference, while IB increased from 0.44 MPa to 0.50 MPa at 10% bark. At 50% bark, the density profile became U-shaped, MOR reached its lowest mean value of 6.8 MPa, IB decreased to 0.39 MPa and MOE to 1,394 MPa. In contrast, equilibrium moisture content decreased from 9.2% to 6.7%, thickness swelling after 168 h from 65% to 49% and water absorption after 168 h from 153% to 129%, whereas board density remained unchanged. Norway spruce bark can replace wood particles up to 20%; higher substitution levels require optimisation of particle composition, resin dosage and pressing conditions.