Effect of biological delignification with Phanerochaete chrysosporium on the densification and mechanical properties of poplar wood

Biological pretreatment with Phanerochaete chrysosporium was evaluated as a route to facilitate thermo-mechanical densification of poplar. Twenty-four specimens were incubated for 16 weeks either with vermiculite (enhanced decay) or without, then hot-pressed radially from 25 mm to 8 mm, while maintaining a temperature of 120 °C. Vermiculite-assisted samples showed a much higher mean mass loss (29.0% vs. 5.9%) but a lower mean densification degree (74.4% vs. 115.8%) compared to non-vermiculite samples. Set recovery after 72 h at high relative humidity remained approximately 40% for both variants. Mechanical testing revealed that vermiculite-assisted specimens suffered significant longitudinal strength loss (L 10.1 ± 5.6 N·mm⁻²). In contrast, the non-vermiculite samples showed significant gains in radial strength (R 31.4 ± 10.7 N·mm⁻²) compared to undensified poplar controls. The applied fungal pretreatment did not result in selective delignification sufficient to improve dimensional stability after densification.