Physical properties of earlywood and latewood of Pinus radiata D. Don: Anisotropic shrinkage, equilibrium moisture content and fibre saturation point

Abstract

Anisotropic shrinkage (tangential and longitudinal), equilibrium moisture content (EMC) and fibre saturation point (FSP) were measured for separated earlywood (EW) and latewood (LW) of a 0.75-m-long log of 20-year old Pinus radiata that was cut at breast height from a selected tree in the forest of Central North Island, New Zealand. The experimental results have shown that at 12% moisture content (MC), tangential shrinkage was 3.23% for EW and 3.90% for LW, with an overall average of 3.56%. Longitudinal shrinkage was 0.23% for EW and 0.21% for LW with an overall average of 0.22%. Shrinkage for the oven dry (OD) state showed similar trends to those at 12% MC in terms of the differences between EW and LW. The tangential and longitudinal shrinkage varied significantly along the radius from pith to bark. The EW tangential shrinkage increased from pith to the seventh growth ring and then remained relatively constant until the last ring adjacent to the bark. The LW tangential shrinkage also increased from the pith outwards until the seventh growth ring, but beyond that was more variable than the EW shrinkage. Both EW and LW showed similar longitudinal shrinkage, with the highest values in the second growth ring, from which the shrinkage decreased exponentially towards the bark. LW had a slightly higher EMC than EW at a relative humidity (RH) below 80%, but the trend was reversed for RH above 80%. The EMC differences between EW and LW were less than 0.6%. The overall average FSP for Pinus radiata was 29.1%, with actual values varying from 25% to 32.8%. The earlywood FSP (28.9%) was slightly lower than that of the latewood (29.4%).

Combining electrical resistance and 3-D X-ray computed tomography for moisture distribution measurements in wood products exposed in dynamic moisture conditions

“…The structure of the wood did not influence their results as specimens were conditioned to equilibrium MC before measuring electrical MC or rather large specimens were used in outdoor conditions. Taking into account these conditions, the MC distribution in the core of the specimens is more or less even and the MC value of high and low density zone is close to each other when the MC is below FSP [25]. Therefore, the electrical MC is in a good agreement with the gravimetrical MC especially when the MC is below 30% [5].…”

Variation of Drying Strains between Tangential and Radial Directions in Asian White Birch

“…Because wood disks are round, the practical shrinkage strain in a tangential direction is closer to the radial strain as one approaches the center of the disk; specifically, the difference in the practical shrinkage strain in the tangential and radial directions is proportional to the radius. Pang and Herritsch noted that tangential shrinkage increased from the pith to the seventh growth ring both in earlywood and latewood [21]. In addition, at each level of moisture content, the practical shrinkage strain in heartwood was higher than in sapwood because of the higher density for heartwood.…”

Combination of neutron imaging (NI) and digital image correlation (DIC) to determine intra-ring moisture variation in Norway spruce

“…Early investigations indicated 0.9% higher MC grav in LW than in EW for Scots pine (Pinus sylvestris) (Boutelje 1962) and fir (Abies alba) (Popper and Bariska 1972). Pang and Herritsch (2005) found a MC grav increase of 0.1% to 0.6% for Radiata pine (Pinus radiata) and attributed this to an increased content in hemicelluloses. Moon et al (2010) found a MC grav increase of 1% for Loblolly pine (Pinus taeda).…”