Effects of Heat Treatment on the Mechanical Properties of Loblolly Pine, Sweetgum, and Red Oak

Abstract

Heat treatment has been assessed as an eco-friendly means to reduce wood's dimensional instability and biodeterioration under varying ambient conditions. However, irreversible losses in mechanical properties have been reported to occur when wood is subjected to elevated temperatures as a result of the autocatalytic breakdown of the cell-wall constituents. The reduced strength of heat-treated wood is a disincentive for its extensive use in structural applications where high-strength quality is important. Thus, improved durability must be balanced with the preservation of the mechanical properties of heat-treated wood. The strength properties of heat-treated loblolly pine (Pinus taeda), sweetgum (Liquidambar styraciflua), and water oak (Quercus nigra) were assessed to quantify the effects of varying temperature levels, up to 204°C, and duration, up to 8 hours, on flexural strengths, compression strengths, shear strength, and hardness. Two-factor analysis of variance (ANOVA) and 1-factor ANOVA (where there is temperature–duration interaction) of results coupled with Tukey's pairwise comparison (α = 0.05) indicated effects ranging from indicative differences in modulus of elasticity to significant increment and decrement in other strength parameters. Generally, strength properties for the three species were optimally preserved, or peaked and dominantly improved in specimens treated at 149°C for 8 hours. This study provides a knowledge base for process optimization in heat treatment industries and for the use of heat-treated wood in structural applications.