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Densification of E. fastigata and E. nitens for improved surface hardness - Results of Scion’s SSIF funded work

By Rosie Sargent, July 2020.

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Executive summary

Densification is a method of increasing wood density and hardness using compression and heat to deform and flatten the wood cells. It has been applied experimentally to a number of temperate softwood species worldwide, as well as a few hardwood species. Here the technique is applied to two New Zealand grown eucalypt species (Eucalyptus fastigata and E. nitens).

Two densification techniques were used, one to compress the entire thickness of the board (bulk densification) and one to just deform and compress one surface (surface densification). Surface densification is intended to give a hard surface, similar to that of bulk densification, but without increasing the overall board density, and without reducing the board thickness as much as the bulk densification.

The E. nitens boards were able to be compressed to a greater extent than the E. fastigata boards without being damaged (E. fastigata was only able to compressed by 20% of its thickness for bulk densification, compared to 50% for E. nitens). All densified boards had significant increases in density and surface hardness, with the surface densified boards not having a significantly different hardness to the bulk densified boards.

When soaked in water, the surface densified boards recovered more than 80% of the thickness lost during densification, whereas the bulk densified boards only recovered 40-50% of their original thickness, with the E. nitens boards swelling significantly less than the E. fastigata boards.

Overall, the E. nitens boards densified more successfully, with increased levels of densification possible, and reduced swelling when soaked in water compared to the E. fastigata boards.

For both species the surface densifications had the desired effect of increasing the surface hardness without increasing the overall board density, but further work is required to prevent the boards from swelling back to their original dimensions when soaked in water.

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