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

Figure 11

Fracture surfaces of a laminated birch wood composite bonded with a single component polyurethane adhesive containing 5.5% w/w milled (60 mesh) glass-fibre: (a) fractured wood surface showing pull-out and fracture of glass-fibre (arrowed left) and wood cells; pull-out of adhesive from ray cells; and adhesive that partially covers the wood surface (scale bar = 100 μm); (b-c) higher magnification photographs [from (a)] showing fracture of wood cells and pull-out of adhesive from the lumens of individual ray cells (scale bars are 10 μm (b) and 1 μm (c)); (d) fractured wood surface showing residual adhesive, pull-out of bundles of fibres (arrowed left and centre) and presence of numerous glass-fibre strands (right) (scale bar = 100 μm); (e-f) fractured column of adhesive containing embedded glass-fibre that provided through-reinforcement to the composite (arrowed top right of centre in (e), and centre and right in (f)). Note the fracture and distortion of the adhesive column and the distortion of the adjacent wood (scale bars are 100 μm (e) and 20 μm (f)).

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