The 2019 Wood Solutions Conference in Vancouver featured a presentation by the Norwegian company Voll Arkitekter about the design and construction of Mjøstårnet, the world’s tallest timber building with 18 storeys, completed in March 2019. This building exemplifies the considerable efforts across the world, including British Columbia, to push the limit on utilizing wood in the construction industry. As these initiatives continue to grow and attain establishment, the question about their relevance to our goal of building a circular economy becomes of more importance. While the cascading use of wood, a framework to promote non-fuel applications of wood whenever possible, has a long history, circular economy is bringing new requirements into our perspective for managing wood products.

A renewable resource
Wood is a natural material, abundantly available and easy to produce, thus becoming an excellent material for the circular economy. When it comes to the construction industry, the intensive production energy of some building materials also favors wood as a more sustainable low-energy alternative. In addition, the capacity of wood to capture and store CO2 from the atmosphere helps to mitigate climate change. Despite these benefits, the complications with respect to circular economy and 5R strategy arise when the technological approaches adopted for expanding wood applications are taken into account, as some might hinder circularity and prevent sustainable end-of-life solutions.

Improving durability and strength: are the solutions circular?
Extending the lifespan of wood products, which is also desired by the circular economy principles, entails improving wood resistance against mold and insects, as well as increasing its durability against moisture and sunlight. These requirements have led to the development of many treatment methods that integrate chemicals into wood to enhance its properties. These modifications of wood can impose restrictions on possible pathways for circularity and second life.

Moreover, increasing the load-bearing capacity of wood has led to the development of engineered wood materials, which can potentially complicate the environmental performance of wood in the economy. For example, the fabrication of cross-laminated timber, a key structural material in Mjøstårnet, requires using glues to bond layers of wood lamellae. This multi-material structure can bring about new challenges for recycle and repair which is not present when dealing with unmodified wood.

To ensure long-term sustainability, these innovation efforts need to be accompanied with circular and life cycle thinking at the early stages of product and process development. This will ensure that health and disposal aspects of the chemicals used in the treatment are well understood and the problematic substances are eliminated. In addition, by allowing the design for circularity to guide the development process, the possibilities of next lives for the product and its constituents would be well taken into account.

On the path towards improved circularity, material and manufacturing innovations can play important roles, as well. Bio-based coatings, glues and additives that can be safely disposed to the biological cycle during the recycling process are examples of these innovations. In addition, new technologies are under development that create bonding between wood pieces through mechanical processes, thus eliminating chemicals in the structure.

Design innovations can also facilitate material recovery, repair, and remanufacture for wood products. As an example, the timber construction of the Cradle building in Düsseldorf, Germany, to be completed in 2022, has been designed for easy dismantling of the building façade. Needless to say, these design modifications must be complemented with changes in demolition practices to facilitate the recovery of material.

The efforts to promote circularity and 5R with respect to wood is not limited to the construction sector. The European Union’s Waste Framework Directive requires that 25 percent of wood packaging (e.g., wooden pallets) be recycled in 2025. This can also encourage the repair of these products. The furniture industry is also witnessing the emergence of new circular business models, e.g., Desko in Europe, aiming to promote the remanufacture and refurbishment of office furniture, including the ones made of wood.

Getting the most out of the by-products
The desire in expanding the use of wood as a material resource will also result in an increase in the amount of by-products generated during wood processing operations. Examples of these by-products are bark, the outermost layers of stems, and sawdust whose fate need to be accounted for in a holistic circular framework for wood products. So far, these materials have been mostly burnt into energy; however, more policies and regulations are expected to emerge that encourage other application paths for them.

For example, the antimicrobial and antioxidative compounds found in the wood bark can found applications in pharmaceutical, cosmetic and food industries. Additionally, the high concentration of lignin, the binding agent of wood fibers, in bark can feed the research and commercialization efforts on developing value-added products from lignin, such as carbon fibers and 3d-printing filaments.

Forests: climate change mitigation vs wood production
While the expectations from forests to provide material resources for our future economy is high, they are also playing an important role in capturing carbon dioxide from the atmosphere and thus alleviating climate change. In this regard, proper sourcing of wood becomes critical, and guidance from organizations like PEFC and FSC on sustainably managed forests can help designers and developers make informed decisions regarding their material sourcing. This will ensure a sustainable supply of wood as a renewable material for the emerging circular economy without compromising the benefits trees and forests are offering to our environment.