Wood quality assessment of Pinus radiata (radiata pine) saplings by dynamic mechanical analysis

The use of dynamic mechanical analysis was explored as a possible method of screening for wood quality in breeding programmes. Viscoelastic properties along the grain of wood from 18-month-old Pinus radiata saplings were measured using a humidity-controlled dynamic mechanical analyser. Storage modulus and tan were determined independently for opposite wood (OW) and compression wood (CW) in 25 trees in the temperature range from 10 to 45°C at 5°C intervals at three frequencies (0.1, 1 and 10 Hz) at constant moisture content of 9%. Storage modulus and tan were frequency and temperature dependent. The two wood types did not differ significantly in their storage modulus. But OW exhibited significantly higher tan values than CW. The relationship of viscoelastic properties with physical (acoustic velocity, basic density and longitudinal shrinkage) and chemical wood properties was explored. There was a strong correlation (R=0.76) between storage modulus and dynamic MOE (measured by acoustics). In addition, tan was positively correlated with longitudinal shrinkage. Monosaccharide compositions of the cell-wall polysaccharides and lignin contents were determined and showed significant differences in the relative proportion of major cell-wall components in OW and CW. Correlations between tan and xylose, originating from heteroxylans, and lignin content were found for CW, suggesting that the damping behaviour of cell-walls is controlled by the matrix between cellulose fibril aggregates.