Discoloration and Surface Changes in Spruce Wood after Accelerated Aging

Area of Science:

• Materials Science
• Wood Science
• Surface Chemistry

Background:

• Spruce wood is a common material for outdoor applications.
• Susceptibility to sunlight and moisture causes degradation, limiting its lifespan.
• Understanding aging mechanisms is crucial for improving wood durability.

Purpose of the Study:

• To investigate the effects of accelerated aging on spruce wood's surface chemistry, microstructure, geometry, and color.
• To compare aging impacts under dry (rainless) and wet (rain) outdoor conditions.
• To elucidate the relationship between structural changes and surface property alterations.

Main Methods:

• Accelerated aging tests were conducted in two distinct outdoor modes: dry and wet.
• Fourier-transform infrared (FTIR) spectroscopy was used to analyze chemical changes, particularly lignin and carbonyl group degradation.
• Surface morphology and roughness were assessed using micro- and macrostructural analysis.
• Discoloration was quantified to correlate with chemical and structural modifications.

Main Results:

• Significant discoloration occurred in both aging modes, with dry conditions leading to a dark brown color.
• FTIR analysis revealed primary lignin degradation, especially in early stages, linearly correlating with color change.
• Carbonyl groups increased in dry mode (influenced by extractives) but leached out in wet mode.
• Cellulose crystallinity decreased, and hydrophilicity increased due to lignin degradation and structural changes.
• Surface roughness increased in both modes, with distinct changes observed perpendicular to the grain in wet conditions.

Conclusions:

• Accelerated aging profoundly impacts spruce wood, altering its chemistry, microstructure, and surface properties.
• Lignin degradation is a primary driver of aging-induced discoloration and increased hydrophilicity.
• The distinct effects of dry and wet aging modes highlight the importance of moisture in wood degradation.
• Understanding these mechanisms provides a basis for developing strategies to enhance spruce wood's resistance to environmental factors.