Young Eucalyptus Wood Unveils Innovative Construction Applications at University of São Paulo
Brazil is the world’s largest producer of eucalyptus from renewable forests, but the resource is not exploited to its full potential. In the country, it is used almost exclusively for the production of cellulose paper, bioenergy and reconstituted panels. But young eucalyptus wood, aged seven years, could have new purposes in the civil construction sector, in the manufacture of structural class engineered products, such as beams and columns, which are obtained through the industrial processing of raw short-cycle eucalyptus wood. . The proposal comes from research at the Luiz de Queiroz College of Agriculture (Esalq) at USP in partnership with the University of Stellenbosch, in South Africa. With appropriate techniques, knots and warping, characteristics that make short-cycle eucalyptus a weak and low-quality wood are practically eliminated, which gives it high added value.
According to the research author, Bruno Balboni, “young eucalyptus wood can be quite resistant and, sometimes, even superior to Pinus (pine) wood, the planted tree most used in Brazil for structural products, but which takes around 20 years to reach harvesting age and be used industrially.”
According to the forestry engineer, knots weaken the resistance of the wood and warping makes it difficult to use, directly affecting its value, especially when the end use is building structures, where resistance is fundamental. In search of solutions to take advantage of this abundant resource in Brazil, the forestry engineer began by selecting some eucalyptus clones (varieties), among the numerous planted for bioenergy generation, to check whether some of them would have appropriate characteristics for the use of structural wood.
At the same time, he sought to understand the mechanical behavior of young eucalyptus wood and its weak points, so that, by applying a technique called Glued Laminated Timber (GLA), the negative effects of knots and warping could be eliminated.
MLC is an industrial processing of wood for the manufacture of engineered products. Using this technique, “the eucalyptus lamellas (boards) are pressed and glued together with highly resistant adhesives, so that the fibers of the lamellas are parallel to each other. At the end of the entire process, a solid block of wood is produced, giving rise to structural pieces with varying dimensions and in accordance with the needs of the consumer market”, says the researcher.
Selection of eucalyptus clones
Clonal eucalyptus trees are genetic copies of a selected plant containing several positive characteristics, which, when planted, tend to maintain the properties of the original plant.
Among the dozens of eucalyptus species that were already destined for the bioenergy industry, Balboni selected six varieties and analyzed the density and mechanical properties of the wood. The aim was to assess its suitability for the manufacture of structural products. After harvesting, the logs went to Esalq for processing and mechanical tests.
According to the researcher, eucalyptus clonal forestry in Brazil is among the most advanced in the world and finding already developed clones that are suitable for the wood industry would be a big step towards obtaining sustainable wood for various sectors, such as civil construction and the furniture industry.
The clones evaluated at this stage of the research showed great differences in density and mechanical properties (some were denser, others lighter, some more resistant), which in the researcher’s opinion was a positive aspect, as the more diversity, the greater the possibilities of uses and applications (engineered products, civil construction, furniture, etc.).
Another important finding of the experiment was that of the six clones evaluated, two stood out. One had light and resistant wood, characteristics considered perfect for the manufacture of engineered products, and the other had denser and proportionally resistant wood, suitable for use as structural solid wood.
Neutralization of knots and warping
Once the most appropriate clones were identified, the engineer sought to find out whether the negative characteristics that potentially made young eucalyptus a low-quality wood could be neutralized or minimized with the “Glued Laminated Timber (MLC) technique. This time, the researcher used wood from trees planted by seeds, because they have a high variability of defects. This was necessary to evaluate the effects of knots and warping on the final product.
According to the forestry engineer, the beams manufactured from this industrial processing were extremely resistant and of good quality, with smaller knots when compared to other types of wood. And the low adhesion when gluing the boards, something that is common to knotted wood, was also neutralized by using an optimization in the arrangement of the lamellas: the most resistant were positioned in the outermost layers of the beams, in the lower and upper portions.
As for bending (one of the many types of warping), the researcher said that it was a beneficial factor for the beams extracted from glulam, because when the wood was pressed and glued straight, the bending generated internal stresses in the beams. The more curved the lamellas, the greater the internal tensions and, consequently, the stronger the beams. “This even allowed the use of wood that would be classified as waste due to its high rates of bending, for the manufacture of products with high added value”, reports the researcher.
According to Balboni, the negative impact of the knots on the strength of the beams was observed in only one of the 18 tested. “This partially negative result, however, was extremely useful for understanding the maximum size recommended for nodes in glued beams of young eucalyptus trees,” he says.
USP Highlight Thesis Award
Bruno Balboni’s research resulted in the thesis Investigating the use of wood containing defects from young eucalyptus plantations for the manufacture of engineering products , supervised by professor José Nivaldo Garcia (Esalq), which was awarded the honorable mention of the USP Highlight Thesis Award in 2023, in the broad area “Sustainability”.
According to Professor José Nivaldo, the main advantages of using young eucalyptus for engineered products are that this tree grows quickly, is highly adaptable to different climatic conditions and can be planted close to the consumer market.
“The results of the thesis help to demystify several issues related to the use of wood from young eucalyptus trees for structural purposes.
By unlocking the potential of this resource, Brazil will have a sustainable source of wood at a reduced cost, contributing to civil construction with a lower environmental impact and reducing pressure on the Amazon forest for wood, in addition to promoting the creation of jobs in the industry and increased income for rural producers.
Asked about the problems of environmental degradation associated with eucalyptus plantation, such as soil impoverishment and excessive absorption of water from the soil, Balboni says that current cultivation techniques seek to reduce any possible environmental impact, and the way to deal with these issues is up to daily life of the forestry engineering course. He emphasizes that eucalyptus trees are very efficient in absorbing carbon dioxide (CO2), and thus contribute to reducing the greenhouse effect.