Durability of Thermally Modified Western Hemlock Lumber Against Wood Decay Fungi

Gerald Presley,Jed Cappellazzi,Ivan Eastin

doi:10.3389/ffgc.2022.813080

Gerald Presley, Jed Cappellazzi + Show 1 more

Open Access

https://doi.org/10.3389/ffgc.2022.813080

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Abstract

The chemical modification of wood is gaining popularity as a treatment to increase wood durability, particularly in jurisdictions where restrictions on the use of chemical impregnation are increasing. This work measures the impact of thermal modification of western hemlock lumber durability against decay fungi. Western hemlock lumber was thermally modified using a cycle with temperatures ranging from 80 to 170°C and was cut into standard 19 mm blocks for testing according to AWPA method E10. Performance of thermally modified wood was measured against two brown rot fungi, Rhodonia placenta and Gloeophyllum trabeum and one white rot fungus, Trametes versicolor over an 8, 12, and 16-week incubation period. Unmodified western hemlock wood, untreated southern pine and copper azole-treated southern pine were included for comparison. Thermal modification resulted in a slight improvement in durability against Gloeophyllum trabeum, but not Rhodonia placenta compared to untreated western hemlock which caused 50.3 and 52.2% mass loss in thermally modified western hemlock after 16 weeks, respectively. T. versicolor caused a 21.2% mass loss after 16 weeks, but this value was not statistically different than untreated western hemlock (p = 0.46). For comparison, copper azole-treated southern pine showed only an average of 0 and 15% mass loss when exposed to G. trabeum or R. placenta for 16 weeks, respectively. Together, these data indicate that while there may be some protective effect of thermally modifying western hemlock, further development of treatment processes are needed to improve the durability of thermally modified western hemlock.

Highlights

Most wood preservation methods include the application of a chemical biocide to the wood in a pressure or non-pressure process
This study describes durability testing of thermally modified, Tsuga heterophylla wood using an American Wood Protection Association (AWPA) E10 soil bottle test (American Wood Protection Association [AWPA], 2020)
The white rot fungus caused relatively less mass loss over this period, averaging 44.2 and 29.2% for southern pine and western hemlock, respectively. These values were well within a normal range for untreated wood and indicate the fungal strains used in this test exhibited sufficient vigor. These data indicate that western hemlock is not resistant to attack by brown rot fungi but shows a moderate level of resistance to attack by a white rot fungus

Summary

Introduction

Most wood preservation methods include the application of a chemical biocide to the wood in a pressure or non-pressure process. Wood preservation technologies that directly modify the wood rather than impregnate it with biocides are gaining greater interest in areas where chemical treatments are heavily restricted. To date these methods have proven successful in a relatively limited range of wood species. Thermal modification of wood is done by heating wood in a low-oxygen environment to facilitate chemical and structural alteration (Sandberg et al, 2017). Chemical modifications such as covalent crosslinking in lignin and partial polysaccharide decomposition reduce hygroscopicity and increase the resistance of wood to fungal decay (Tjeerdsma et al, 1998; Alen et al, 2002; Kamden et al, 2002; Marcon et al, 2021). Process conditions can be modified to alter the characteristics of the final product

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