Research advances the viability of SA's fast-growing plantation species for engineered wood products
Research advances the viability of SA's fast-growing plantation species for engineered wood products
Adding value to stressed timber
In the era of heightened concern for sustainability and conserving our planet's resources, timber stands out as one of the few renewable construction materials, possessing the unique ability to store carbon and return to nature harmlessly upon disposal.
W ith the rising demand for timber, plantations are expanding rapidly and being harvested earlier. Since these trees are commonly destined for reconstituted products like paper and MDF, inherent defects do not compromise the final product quality while keeping their high productivity.
Short Rotations
How can we take advantage of the high productivity of these short-rotation forests and use them to produce timber for the construction industry?
Thinking about that, our research team at Stellenbosch University focused on identifying the bottlenecks of converting these young trees into sawn wood and proposing solutions for them. Simultaneously, by applying the same strategy, we aimed to maximise the timber's use from the existing sources.
Eucalyptus, one of the most widely planted trees globally with exceptional productivity, is primarily used in paper or charcoal production. Our initial investigation focused on reducing these defects, such as splitting and warping.
Splitting
Adjusting primary processing parameters proved effective. However, the breakthrough came with longitudinally glueing short boards with finger joints before the wood dried, minimising split propagation and warping during the drying process.
This innovative and economically viable solution improved log processing recovery and is sold commercially in South Africa. The technology involves glueing 'green' wood using fast-curing polyurethane that utilises wood moisture for curing.
The same idea was applied to edge- glued panels.
Restraining the wood movement during drying by glueing boards together minimised their deformation and significantly increased the yield on secondary processing.
Warping
But what can we do when the timber is already presenting warping? With adequate methodology, young Eucalyptus timber with 80% warping rejection produced straight glulam beams with high mechanical performance.
Surprisingly, knots, a common defect in timber from young trees, did not adversely affect mechanical performance or wood adhesion, reducing the need for defect removal and finger jointing.
Using waney-edge boards in CLT manufacture shows the potential to increase yield from young plantation resources
Waney Boards
Another defect under scrutiny was wane, where boards retain portions of the round shape from logs. Preliminary results indicated a low impact on the mechanical properties of cross-laminated timber (CLT) panels. This prompted further investigation into potential yield gains by surpassing standard allowances for wane in boards. It resulted in a 25% increase in the efficiency of primary processing for pine logs from mature plantations.
While Eucalyptus is often associated with short rotations, trials of a pine species from Mexico, Pinus maximinoi, indicate high potential to provide structural-grade timber at only nine years old.
In addition to identifying the best species or varieties of trees available in South Africa, our team is currently focused on:
- Fine-tuning the processing parameters for green-glueing wood.
- Adjusting CLT technical standards to suit the local reality.
- Developing novel methods to reduce the costs of CLT manufacturing.
Beyonf Sustainability
Upon achieving these objectives, the global trend of building with wood will be further reinforced and stimulated in South Africa. The advantages of wood buildings extend beyond sustainability. It energises an entire production chain, providing employment opportunities and potentially becoming a lucrative export activity that positively impacts the country's economy.
Dr Bruno Balboni
By: Drs Bruno Balboni and Brand Wessels, Stellenbosch University