Life-Cycle Assessment Of Thermally-Modified Southern Pine Decking

Abstract

Thermally-modified wood is currently used for solid wood flooring, external cladding, and decking products, as it imparts advantageous properties, including attractive darker color, reduced equilibrium moisture content, reduction of mass, degradation of water-binding hemicelluloses, and elimination of many volatile organic compounds The result is a high-value, high-performing solid wood product with increased moisture resistance, decreased swelling and shrinkage due to weathering and atmospheric moisture changes, and increased resistance to degradation from rot-inducing fungi. Thermal modification can also reduce environmental impacts of wood products because it is an alternative to chemical preservatives, such as creosote, chromated copper arsenate (CCA), and acid copper chromate. While substantial life-cycle assessment (LCA)-developed environmental impact data exists for a wide range of wood products, there is little published data on the environmental impacts of thermally-modified wood. Thus, unsubstantiated claims on the performance of these products still exist. This study fills this knowledge gap by completing a comparative LCA of thermally-modified softwood exterior decking and ACQ-treated softwood exterior decking following International Organization for Standardization (ISO) 14040 and 14044 guidelines. This study reveals that the environmental impacts of thermally-modified wood decking, whether landfilled or incinerated at end-of-life, are very similar. The thermally-modified wood decking also has lower human health, resource use, and climate change impacts than landfilled ACQ-treated wood decking, but has lower water use impacts. The thermally-modified wood decking also has lower stratospheric ozone depletion, fine particulate matter formation, terrestrial acidification, terrestrial ecotoxicity, freshwater ecotoxicity, marine ecotoxicity, and mineral resource scarcity potential. This study also reveals that the production of softwood boards accounts for the largest portion of total impact in each impact category for both decking types. Manufacture of the ACQ preservative itself is the next largest contributor to the total impacts in each impact category for the ACQ-treated wood decking, while combustion of fuel oil for heating the thermal-modification equipment is the next largest contributor to the total impacts for the thermally-modified wood decking. This – and future – research helps thermally-modified wood manufacturers more effectively identify possible ways to improve the environmental profile of their manufacturing processes, which may allow retailers and distributors to more effectively market the products against competing alternatives.