Hemicellulose influences on set-recovery and densification

Wood densification is an effective approach to improve the mechanical performance of low-density wood species, but dimensional instability due to set-recovery remains a limitation. While hemicellulose is known to control wood hygroscopicity, their role in elastic strain storage and release during densification is not fully understood. In this study, aspen ( Populus tremula L.) rotary-cut veneer samples, both untreated and treated with hot water extraction, were densified by compression at 100 °C and 6 MPa. Set-recovery, Brinell hardness, density, X-ray scattering-based imaging and morphology were used to evaluate the effects of hemicellulose removal on the behavior of densified wood. Hot water extraction selectively removed primarily hemicellulose and altered the wood matrix before compression. With the most severe treatment resulting in 23% hemicellulose removal, set-recovery after water immersion was significantly decreased from near total recovery to 50%. Treated veneers also compressed more, achieving densities of 1176 kg/m 3 and Brinell hardness of 167 MPa compared to untreated densified samples (1063 kg/m 3 and 80 MPa, respectively). The results indicate that hemicellulose, as the predominantly removed component, contribute to dimensional instability not only through moisture interactions but also by influencing the release of elastic strain energy stored during compression.