VARIATION IN ANISOTROPIC SHRINKAGE OF PLANTATION-GROWN PINUS RADIATA WOOD

Eric Wang,Andrew Karalus,Shusheng Pang,Taian Chen

doi:10.4067/s0718-221x2008000300007

Abstract

Anisotropic shrinkage of 27-year old Pinus radiata wood was measured from green to oven-dry condition. The samples were prepared from 21 discs cut from seven trees at different stem heights of 0.1m, 5.2m and 10.3m above ground, respectively. Longitudinal shrinkage was found to vary from 0.02% to 2.34%, with peak values near the pith decreasing towards the bark. The variation was more pronounced at the 0.1m height. The longitudinal shrinkage also showed a trend of decrease with the stem height above the ground. Tangential and radial shrinkage was found to increase with growth ring number from the pith, but the variation along the stem height did not show a clear trend. The results confirmed that the pith-to-bark variation and vertical variation of the anisotropic shrinkage were significant for radiata pine. Large differences were also observed among corewood, transition wood and outerwood. Microfibril angle (MFA) was believed to the main reason for these variations.

Highlights

With more and more wood coming from fast-growing plantation forests, dimensional stability and warp are major concerns in wood processing and utilization
The shrinkage variations along the growth ring number from pith to bark at different stem heights are shown in Fig.2(a) for the 0.1m height, in Fig.2(b) for the 5.2m height and in Fig.2(c) for the 10.3m height
Pith-to-bark and vertical variations of anisotropic shrinkage were found to be significant for radiata pine with most noticeable variation being observed for the longitudinal shrinkage at 0.1m stem height

Summary

Introduction

With more and more wood coming from fast-growing plantation forests, dimensional stability and warp are major concerns in wood processing (drying) and utilization. This problem is believed to be caused by gradients of wood anisotropic shrinkage both in radial and axial directions, as well as spiral grain angle and ring curvature. Transition wood is used to describe the wood at the boundaries between the corewood and the outerwood. These terminologies are widely used for plantation softwoods in the southern hemisphere

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