Abstract
<title>Abstract</title> <p>Walnut shell (WS) is a lignocellulosic residue with potential for partial substitution of wood particles in particleboard production. This study investigated the effects of WS addition on the properties and stable addition range of wood particleboards. Based on a WS particle size of 20–35 mesh and hot-pressing conditions of 160 °C, 4 MPa, 6 min, and 14% resin content, two-stage experiments were conducted within the 30%–50% WS addition range. The modulus of rupture (MOR), modulus of elasticity (MOE), internal bond strength (IB), and 2 h thickness swelling (2hTS) were evaluated. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) were used to analyze interfacial morphology and structural characteristics. In the first-stage experiment, MOR and MOE generally decreased with increasing WS content, while the 30% group showed better overall mechanical performance and stability. Although the 42% group met the requirements for P2-type particleboard, the MOE values of the 46% and 50% groups were below the standard requirement. In the second-stage experiment, the 42%–50% range showed significant fluctuations in MOE, IB, and 2hTS, and all 2hTS values exceeded 8.0%. Overall, 30% WS addition is recommended as a stable addition ratio under the present processing conditions, whereas 42%–50% represents a critical fluctuation zone for high-ratio WS utilization.</p>