Development and/or improvement of NIR calibration models to predict important wood properties

NIR detection of tension wood in standing Eucalyptus globulus

Brussels, 06 April 2016

Manuel Touza (GAIN-CIS Madera) Detection of tension wood in standing Eucalyptus globulus

 In the Iberian Peninsula there are more than 1.000.000 ha of Eucalyptus globulus plantations aimed to produce pulp.

 E. globulus timber has a great potential for solid wood uses but it´s utilization remains limited because of tension wood that causes problems as end splitting of the logs or non-recoverable collapse during drying.

 Most promising perspectives aimed to reduce tension wood consider adapting silvicultural sawlogs regimes, but the interactions between tension wood and silviculture are not yet well known. The raw material / Eucalyptus globulus

In Galicia (NW Spain), eucalypts were planted for pulp production (≈ 1,100 stems/ha) and have developed tension wood.

In 2014, from a total harvest close to 4.106 m3, less than 4% of Eucalyptus logs were oriented to sawnwood production.

Typical raw material for sawmills is obtained by selecting the dominat trees from (> 35 years) from overaged pulp plantations or mixed forests.

Existing methods for measuring tension wood

The most employed technique for measuring tension wood is the strain gauge method developed by CIRAD-Forêt

stemwood nails

drilling hole

sensor

0,00mm

bark micrometer

Contradictory conclusions have been induced by trying to extrapolate to the whole life of the tree the results obtained in a punctual moment (measures made at the periphery), thus affecting only to the last growing years.

A new method for detecting tension wood in standing trees would provide significant benefits. An alternative approach for measuring tension wood

Tension wood differs from normal wood in several ways, being the main difference the presence of an extra layer, named the gelatinous layer. Thus one would expect that zones with tension wood should exhibit high cellulose, high wood density and low MFA and, as a consequence, high modulus of elasticity (MOE).

5 µm Normal wood Tension wood Source: B. Clair, 2005

The previous points suggest the potential for using near infrared spectroscopy (NIRS) to detect zones of tension wood in standing trees and boards.

Australian s NIR calibration models for solid wood Eucalyptus globulus provide a cost-effective way of assessing several properties as cellulose content, density, microfibril angle (MFA) and modulus of elasticity (MOE). Material and methods

In Spain there are several companies producing solid wood products from Eucalyptus globulus.

It was initiated an experiment in order to confirm if Australian models may be applied to Spanish plantations and thus the viability of develop a NIR method able to detect tension wood in E. globulus.

25 quarter sawn Eucalyptus globulus boards were sent to Australia. The samples had been planed for avoiding the visual detection of non recoverable collapse (due to tension wood) after drying.

The samples were scanned each 2 mm in both faces (≈ 5000 measurements) looking for a combination of key properties for determining tension wood

Sample 10 Sample 20 65 a. 40 65 b. 40

60 35 60 35

55 30 55 30

50 25 50 25

45 20 45 20 NIR Predicted Cellulsoe (%) Cellulsoe Predicted NIR 40 15 40 15 (GPa) SS_MOE Predicted NIR

Cellulose content MOE Cellulose content MOE 35 10 35 10 0 20 40 60 0 20 40 60 80 Distance (mm) Distance (mm) Detection of tension wood in standing Eucalyptus globulus

Sample 10 Sample 20 65 a. 40 65 b. 40

60 35 60 35

55 30 55 30

50 25 50 25

45 20 45 20 NIR Predicted Cellulsoe (%) Cellulsoe Predicted NIR 40 15 40 15 (GPa) SS_MOE Predicted NIR

Cellulose content MOE Cellulose content MOE 35 10 35 10 0 20 40 60 0 20 40 60 80 Distance (mm) Distance (mm)

It was confirmed that the boards presenting areas with clear non recoverable collapse, had regions where NIR predicted cellulose exceeded 50% and, at the same time, MOE exceeded 25 Gpa. Detection of tension wood in standing Eucalyptus globulus

The results may be applied to detect tension wood in standing trees employing a wood core, thus providing a reliable method for understand the interactions between tension wood and tree growth parameters.

The methodology have been published in October 2014 and is available in internet. Silviculture and tension wood development

Now, NIR provides a reliable method for understanding if current proposals regarding silviculture for solid wood products with eucalypts may contribute to avoid tension wood development. Silviculture and tension wood development

Tasmania (Australia) has 30,000 ha of Eucalyptus plantations (E. nitens and E. globulus) aimed to produce sawnwood.

The silviculture for sawlog is aimed to produce 300 stems/ha, pruned to 6,4 m, with a small end diameter of 40 cm, and rotation periods around 25 years.

In February 2016, some furniture items were made from trees growing under these sawlog regimes (E. globulus and E. nitens aged 22,5 years old).

The same furniture items were produced with regrowth E. obliqua aged 80 years old.

Eucalyptus globulus aimed to produce sawnwood (300 stems/ha,age 16 years) Silviculture and tension wood development

Eucalyptus globulus were 22,5 years old and have been thinned from 1100 to 200 stems/ha at 5 years. These trees represented plantations managed under intensive silviculture (heavy early thinning).

Silviculture and tension wood development

• E. globulus growing under a silvicultural regime aimed to produce sawnwood, could be properly processed and kiln dried.

• The lower density of the trees improves their workability as well as its bonding and bending capabilities when compared with older regrowth eucalypts.

• Sawn timber from E. globulus plantation sawlogs was found to be ideally suited to the manufacture of fine-furniture. European NIR models for Eucalyptus globulus

Twin samples of the boards containing tension wood have been sent to José Rodrigues (IICT/ISA). The samples were scanned each 2 mm in transverse surfaces (> 8000 measurements). NIR models for Eucalyptus globulus New European models (solid wood) have been developed (solid wood / transversal surfaces) for 6 properties; density, total extractives, klason lignin, Property R2 ethanol, syringyl/guaiacyl ratio (S/G) and water extractives. Density 97,3

Klasson lignin 89,9

Ethanol extractives 87,3

Water extractives 87,1

Total extractives 85,3

Syringyl/Guaiacyl Ratio (S/G) 82,6 European NIR models for Eucalyptus globulus

As with Australian models, a combination of two properties is a good indicator of the boards presenting areas with clear non recoverable collapse (tension wood). For example, when density is > 1000 k/m3 and Klason lignin is < 14%. New Headquarter of Norvento, Lugo (Spain)

Eucalyptus globulus timber has a great potential for solid wood applications Thermal modification of Eucalyptus globulus

Timber properties from younger plantations will be different (lower durability, lower density…)

Thermal modification may be used to improve the natural durability and the stability from plantation E. globulus. Natural durability can reach the best classes (1-2) and stability may be improved in around a 40%.

The new European NIR models has been used for providig a better understanding of this technology. Thermal modification of Eucalyptus globulus

With the technology being employed for thermal modification of Eucalyptus globulus, some boards exhibit splits. NIR European models were employed to look for the key property producing these splits.

In all the cases, the splits appear when local density > 1100 k/m3

It is expected that timber from plantations will be thermally modified without this problem as it will have a lower density and a more homogeneous distribution.

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