Bamboo particleboards bonded with lignin-modified vinyl acetate-ethylene adhesive: physical, mechanical, and thermal properties

The development of sustainable adhesive systems based on renewable resources is essential for advancing environmentally friendly lignocellulosic materials. However, limited information is available on the direct modification of vinyl acetate-ethylene (VAE) adhesives with Kraft lignin for bamboo particleboards, particularly regarding the relationship between adhesive thermal behavior, interfacial morphology, and panel performance. This study evaluated the effect of incorporating Kraft lignin (0, 5, 10, 15, and 20%) into VAE adhesive on the physical, mechanical, morphological, and thermal properties of bamboo particleboards. TGA/DTG and scanning electron microscopy (SEM) were used to investigate adhesive thermal behavior and particle–adhesive interfacial morphology, respectively. Lignin incorporation was associated with improved dimensional stability and mechanical performance. Water absorption decreased from 17.04% to 6.62% after 2 h and from 80.31% to 36.29% after 24 h. At 15% lignin, the modulus of rupture, modulus of elasticity, and internal bond increased from 38.02 to 60.45 MPa, 2219 to 5449 MPa, and 0.31 to 0.68 MPa, respectively. TGA/DTG showed that lignin did not substantially alter the overall degradation profile of VAE but increased carbonaceous residue at high temperatures. SEM revealed improved interfacial cohesion up to 15% lignin, with reduced fiber pull-out, fewer voids, and a more continuous adhesive matrix, whereas 20% lignin promoted agglomeration and microvacuole formation. Thermal conductivity remained stable at 0.13–0.15 W m⁻¹ K⁻¹. Among the formulations evaluated, 10 and 15% Kraft lignin showed the most favorable combination of dimensional stability and mechanical performance, demonstrating the potential of lignin as a renewable modifier for VAE-based bamboo particleboards.