Effects of modification with glutaraldehyde on the mechanical properties of wood

Scots pine (Pinus sylvestris L.) sapwood was treated with glutaraldehyde (GA) and magnesium chloride (MgCl2) as a catalyst. The effects of treating conditions on the mechanical properties were examined. The weight percent gain (WPG) of thin veneer strips after leaching was highest at pH 4.0-4.5 and tensile strength measured in zero-span strength and finite-span strength decreased with decreasing pH in a range of 3.5-5.5. Sole treatment with MgCl2 also gradually decreased the tensile strength up to 25% with decreasing pH. At a fixed GA concentration (1.2 M), increasing MgCl2 concentration linearly diminished tensile strength. Conversely, increasing GA at a fixed MgCl2 concentration (1.5%) displayed the same effect, whereas in both cases zero-span strength loss was higher than finite span-strength loss. GA treatment of Scots pine sapwood stakes did not affect the modulus of rupture and the modulus of elasticity, but significantly reduced work to maximum load in bending and impact bending strength indicating embrittlement of wood. At the same time, compression strength increased with increasing WPG of GA. It is assumed that embrittlement caused by hydrolysis and crosslinking of cell wall polymers is compensated by enhanced compression strength thereby resulting in unchanged bending strength.