Farm Forestry New ZealandDensification of Eucalyptus nitens and E. fastigata – stability
By Rosie Sargent, Mark Riddell, John Lee, November 2022.
Download SWP-T148 (pdf)
Executive summary
The problem
The objective of this study was to increase the surface density and surface hardness of Eucalyptus nitens and E. fastigata through wood densification. Wood densification is a process of heating wood and compressing it to flatten the wood cells and increase the density and hardness of the wood.
This project
The densification process, and the surface hardness of the densified wood, have been reported previously (Sargent, 2020). In short, the E. nitens samples were able to be compressed to a higher degree than the E. fastigata without sustaining damage, and consequently the increase in surface hardness of the E. nitens boards was significantly higher. Densifying one surface of the E. nitens boards gave a lower density increase than densifying the entire board thickness (bulk densification), but for quarter-sawn boards this difference was not significant. In this report, the dimensional stability (set- recovery), and vertical density profiles of the densified wood are reported on.
Key results
One major result of this study is that the densification process generally resulted in a peak density at, or within 1mm of, the surface of the boards. This is a promising result, as it ensures the maximum increase in surface hardness for a given degree of densification. When soaked in liquid water, or exposed to humid air, densified wood tends to swell irreversibly and regain some of its undensified thickness. For both E. fastigata and E. nitens, the surface densified boards regained most of their original thickness when soaked in water. For the bulk densified E. fastigata boards, some regained most of their original thickness, but some only regained a proportion (40-50%). The bulk densified E. nitens boards regained very little of their original thickness (only 30-40%) when soaked in water. This is a significant improvement over the E. fastigata and is much lower than published figures for other wood species.
Implications of results for the client
Both bulk, and surface densification can be used to increase the surface density and hardness of both E. fastigata and E. nitens. Overall E. nitens was more amenable to densification, as it can be compressed to a greater degree without damage, leading to larger increases in surface density and surface hardness compared to E. fastigata. Additionally, the bulk densified E. nitens swelled very little after contact with liquid water or humid air, which is unusual compared to other species reported in the literature. For an in-service application (e.g. flooring), reducing the tendency of the wood to swell when it gets wet would be a key performance requirement, so this is a positive result.
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