Critical review on the use of extractives of naturally durable woods as natural wood protectants

Authors: KIRKER, GRANT - Forest Products Laboratory; HASSAN, BABAR - University Of Sunshine Coast; MANKOWSKI, MARK - Forest Products Laboratory; Eller, Fred

Submitted to: Insects
Publication Type: Review Article
Publication Acceptance Date: 1/11/2024
Publication Date: 1/18/2024
Citation: Kirker, G.T., Hassan, B., Mankowski, M.E., Eller, F.J. 2024. Critical review on the use of extractives of naturally durable woods as natural wood protectants. Insects. https://doi.org/10.3390/insects15010069.
DOI: https://doi.org/10.3390/insects15010069

Interpretive Summary: Extractives, being the non-structural component of wood biomass, are frequently targeted for their biocidal potential due to their evolutionary success in deterring pests in both standing trees and downed woody debris. Effective extractive utilization also offers an alternative product stream where extractives are removed from woody biomass that can further be used as feedstock for downstream processes (i.e., pulping, nanocellulose production, biochar) once extractives are removed. The goal of this review is to provide details on prior studies using wood extractives as wood protectants, highlight limitations to this approach, and discuss research opportunities.

Technical Abstract: Naturally durable wood pre-dates preservative treated wood and has been demonstrated to offer suitable service life for certain applications where preservative treated wood is not feasible. Heartwood extractives have been demonstrated to impart biodeteriorative resistance to naturally durable wood species. These extractives are typically found in the heartwood of the living tree and are produced either by the death of parenchyma cells or as the result of external stimuli. Mechanisms of natural durability are not well understood as heartwood extractives can be extremely variable in their distribution, composition and efficacy in both living and harvested trees. The underlying complexity of heartwood extractives has hindered their standardization in residential building codes for use as wood preservatives. Ultimately, the use of naturally durable lumber is not always feasible as woods with highly durable heartwood do not typically yield lumber with acceptable machining properties. A potential approach to overcome the inherent difficulty in establishing guidelines for the appropriate use of naturally durable wood is to focus solely on the extractives as a source of bioactive protectants that could theoretically include bio-based wood protectants based on strategies used in living and dead wood to repel agents of biodeterioration. The goal of this critical review is to summarize relevant literature on naturally durable wood, their extractives and their potential use as bioinspired wood protectants. Additional discussion will be aimed at underscoring past difficulties in the adoption of this approach and how to overcome future hurdles.