Variation of surface and bonding properties among four wood species induced by a high voltage electrostatic field (HVEF)

A high voltage electrostatic field (HVEF) was applied to enhance the bonding performance of wood composites prepared with phenol-formaldehyde (PF) adhesive and different wood species and radial cut combinations. Four wood species including Masson pine (Pinus massoniana), Chinese fir (Cunninghamia lanceolata), poplar (Populus tomentosa) and ayous (Triplochiton scleroxylon) were studied. The results of HVEF-treatment turn out to be species-dependent, and are related to the anatomical and chemical properties of wood. It was demonstrated by a statistical approach that the lignin content is the most significant parameter with a good correlation coefficient (R-2 >0.8). High lignin content leads to high free radical concentration at the wood surface and the HVEF enhanced the adhesive penetration depth, the maximal density and the bonding strength (Bst) at the interphase. On the contrary, high extract contents and large lumina diameters negatively impacted the surface modification by HVEF. The magnitude of the effects was in the following order: ayous < poplar < Masson pine < Chinese fir.