Preparation of composite particleboard based on Camellia oleifera shell core layer: Effect of surface-to-core layer ratio on properties

This study developed a three-layer composite particleboard using Camellia oleifera shell (COS) as the core material and pine particles as surface layers, bonded with a foaming polyurethane (PU) adhesive, to decrease dependence on wood resources in conventional particleboard manufacturing and upgrade the utilisation value of agricultural and forestry residues. A layered configuration utilizing a three-stage hot-pressing process was implemented, while the PressMAN monitoring system recorded real-time temperature and gas pressure evolution within the mat during pressing. The influence of the surface-to-core mass ratio (1:1, 1:2, and 1:3) on panel performance was evaluated, with single-layer pine particleboards serving as controls. Experimental results confirmed that the 1:1 ratio configuration provided the most balanced overall performance. It exhibited higher modulus of rupture (38.9 MPa), modulus of elasticity ( 5090 MPa), and internal bond strength (0.97 MPa) than the single-layer pine particleboard, together with a low 2 h thickness swelling of 3.8%. Thermogravimetric analysis verified the complete curing of the adhesive in the 1:1 panel, thereby contributing to its improved properties. Scanning electron microscopy (SEM) revealed a densely bonded interface that improved panel structural stability, while fourier transform infrared spectroscopy (FTIR) confirmed the formation of chemical cross-links between polyurethane and COS via carbamate bonds, thus supporting the rationale of the structural design and its enhanced performance. Through the synergistic optimization of the layered structure and hot-pressing parameters, this study offers important guidance for the resource utilization of COS and for producing high-performance particleboards derived from agricultural and forestry residues.