Changes in viscoelastic vibrational properties between compression and normal wood: roles of microfibril angle and of lignin

This study aims at better understanding the respective influences of specific gravity (gamma), microfibril angle (MFA), and cell wall matrix polymers on viscoelastic vibrational properties of wood in the axial direction. The wide variations of properties between normal wood (NW) and compression wood (CW) are in focus. Three young bent trees (Picea abies, Pinus sylvestris and Pinus pinaster), which recovered verticality, were sampled. Several observed differences between NW and CW were highly significant in terms of anatomical, physical (gamma, shrinkage, CIELab colorimetry), mechanical (compressive strength), and vibrational properties. The specific dynamic modulus of elasticity (E'/gamma) decreases with increasing MFA, and Young's modulus (E') can be satisfactorily explained by gamma and MFA. Apparently, the type of the cell wall polymer matrix is not influential in this regard. The damping coefficient (tan delta) does not depend solely on the MFA of NW and CW. The tan delta-E'/gamma relationship evidences that, at equivalent E'/gamma, the tan delta of CW is approximately 34% lower than that of NW. This observation is ascribed to the more condensed nature of CW lignins, and this is discussed in the context of previous findings in other hygrothermal and time/frequency domains. It is proposed that the lignin structure and the amount and type of extractives, which are both different in various species, are partly responsible for taxonomy-related damping characteristics. Picea abies; Pinus pinaster; Pinus sylvestris; specific dynamic modulus of elasticity; viscoelastic vibrational properties.