Adhesive Through-Reinforcement Improves the Fracture Toughness of a Laminated Birch Wood Composite

Figure 10

Fracture surfaces of a laminated birch wood composite bonded with unmodified single component polyurethane adhesive; (a) adhesive on fractured wood surface showing pull-out and microfracture of adhesive that partially covers the wood surface (arrowed left; scale bar = 100 μm); (b) fractured wood surface showing a multiseriate ray (centre) and pull-out of adhesive from the lumens of individual ray cells (arrowed centre; scale bar = 20 μm); (c, d) higher magnification photographs showing the pillars of adhesive that pulled out of ray cells shown in (b). Note the fractured ends of the pillars and the intact and fractured side-arms (branches) (arrowed left and centre; scale bars = 10 μm (c) and 1 μm (d)); (e) fractured column of adhesive that provided through-reinforcement to the composite (arrowed centre) and residual adhesive on the fractured wood surface (scale bar = 200 μm); (f) higher magnification photograph of the adhesive column shown in (e). Note the fracture and distortion of the adhesive column and the distortion of the adjacent wood (arrowed; scale bar = 200 μm).

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