Dynamic mechanical analysis of Scots pine and three tropical hardwoods

Dynamic mechanical analysis (DMA) was used to investigate the viscoelastic behaviour of four species of wood, Scots pine, Gmelina, Obeche and Alstonia. Three frequencies (0.1, 1.0 and 10 Hz) were used over a temperature range of -150 to +150°C. All the wood species showed tan δ peaks corresponding with secondary relaxations in the expected range. The low temperature (γ peak) was seen at 115 to 83°C, differing between species and with frequency. β peaks relating to hemicellulose relaxations in association with water molecules were observed, at two locations for Scots pine and three locations in hardwoods. The α peak for lignin lay outside the temperature range studied. Differences in β peaks are proposed to relate to the composition of hemicellulose, and be influenced by structure and level of heterogeneity in the amorphous polymer domains; differing between the wood species studied, which is in-line with currently proposed cell wall polymer models.