A Study of the Microscopic Characteristics of Fracture Surface of MDI-Bonded Wood Fiber/Recycled Tire Rubber Composites Using Scanning Electron Microscopy
Scanning electron microscopy (SEM) was utilized to observe the microstructure and fracture surfaces of tensile, bending, and internal bonding specimens of diphenylmethane diisocyanate (MDI) bonded wood fiber/recycled tire rubber composites. Microscopic characteristics of the composites, such as interface bonding between fibers and between fiber and rubber, geometry changes of wood fibers and rubber crumbs, and density profile along the thickness direction of composites, were examined. Four fracture types were classified by the observation of micrographs of various samples: fiber pull-out, fiber breakage, fiber partial pull-out and then breakage, and fiber split. The effects of two important factors, fiber to rubber ratio and MDI level, on bonding quality and fracture type were studied. The results illustrated that excellent bonding was formed between fibers, and good bonding was also observed between fiber and rubber in the micrographs. The degree of wood fiber densification varies along the thickness direction of the composites, forming a density profile. Fiber-slippage and density profile formed during the hot-press process give the composite a layerlike structure. Fiber breakage often occurs in high-densified layers or the layers with high resin content. Fiber pull-out often occurs in low-densified layers or the layers with low resin content
