Life cycle assessment of a novel tannin-boron association for wood protection

Abstract

In these studies of fix boron compounds, associations between tannins and boron (TB) in the form of boric acid appear to be of interest. These TB associations allow the use of boron at very low levels (in compliance with EU restrictions, 2008/58/EC) and limit boron leaching which maintains biological resistance and fire retardant properties. As a consequence, TB wooden products present an extended service life compared to boron compounds alone and were designed to be environmentally-friendly wood protection systems. A follow-up of tannin‑boron use identified the environmental impacts using a life cycle assessment (LCA). This LCA was performed on tannin‑boron preservative products as well as several industrial preservative-treated timbers and concrete used in the landscape. Cr-containing inorganic salt and an alkaline copper quaternary preservative formulation, as well as concrete, have been used as referential materials to compare the environmental footprint with the tannin‑boron treated system. A model was created with life cycle stages used to calculate inputs and outputs during raw material extraction, supplier transportation, manufacturing process, distribution, disposal transportation and processing. Tannin production data were based on Vieira et al. in the field of condensed tannin extraction. However, the extracted tannin in the extraction yield, the inorganic salt, and the process applied are not perfectly comparable with the extraction conditions industrially applied for the Mimosa (Acacia mearnsii) extract which is the major constituent of the TB formulations. The latter is counter-current water extracted without any chemicals or with a limited amount of NaHSO3 or Na2SO3 (at 0.5 % to 1 %) — at a temperature of 70–90 °C. Unfortunately these parameters cannot be elaborated by the LCA program because there is no data available for the production of Na bisulphite or Na bicarbonate in the LCI data used. Other input data were sourced from the ecoinvent v3.8 database. The ReCiPe midpoint method was used to assess the environmental footprint and the CED method was chosen to analyze a general view of the energy-related environmental impacts in the life cycle. Overall, the results demonstrated that tannin‑boron preservatives can be regarded as a low-environmental impact formulation. Additionally, an economic analysis of the development of a commercially-viable tannin‑boron preservative would now be timely.