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

Abstract

This study aims at better understanding the respective influences of specific gravity (1), microfibril angle (MFA), and cell-wall matrix polymers on viscoelastic vibrational properties of wood in 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) that recovered verticality were sampled. Several observed differences between NW and CW were highly significant in terms of anatomical, physical (1, shrinkage, CIELab colorimetry), mechanical (compressive strength), and vibrational properties. Specific dynamic modulus of elasticity (E'/1) decreases with increasing MFA, and Young's modulus (E') can be satisfactorily explained by 1 and MFA. Apparently, the type of the cell wall polymer matrix is not influential in this regard. The damping coefficient (tan2) does not depend solely on MFA of NW and CW. The tan2 -E'/1 relationship evidences that, at equivalent E'/1, the tan2 of CW is approx. 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.

Modelling the effects of wood cambial age on the effective modulus of elasticity of poplar laminated veneer lumber

“…The difference can rely on the relationship between the specific modulus and MFA (Fig. 3) based on Bremaud et al (2013). These experimental results show a significant dispersion in the 10°to 20°range.…”

“…According to Bremaud et al (2013), there exists a strong relationship between the dynamic specific modulus of elasticity and the MFA (Fig. 3).…”

“…This study is based on poplar wood properties in general, but principally on the measurements of Rahayu et al (2014), who studied several poplar cultivars: A4A, Alcinde, Brenta, Dvina, I-214, Koster, Lambro, Lena, Mella, Polargo, Soligo, Taro, Trichobel, Triplo. The model developed is also based on numerous measured properties from the literature (Bao et al 2001;Fang et al 2006;Bjurhager et al 2008;Bremaud et al 2013;Hein et al 2013).…”

Relationships between anatomical and vibrational properties of wavy sycamore maple

“…(Table 5 and 6), which is higher than the individual effects of MFA or of grain angle on these properties. It needs to be noted, though, that such statistical analysis is not sufficient as it is based on linear relations, while it is known that the dependence of mechanical properties on MFA or on grain angle is not of a linear form (Obataya et al 2000;Brémaud et al 2011Brémaud et al , 2013. Further, although w and MFA show significant correlations with the vibrational properties in the L direction; in contrast, in the R direction, the correlation between w and MFA with E' R /ρ or tanδ R is low (Table 4).…”

“…It is also determined that the tanδ L in more wavy wood is higher than the standard relationship (Ono & Norimoto 1983) which is followed by the less wavy specimens. It is suggested to conduct more research comparing the vibrational properties between wavy-figured wood with various kinds of anatomical features (either by extending the sampling on sycamore maple, or by including other species to allow more variations in the different types of cells), and maybe also to observe in parallel possible chemical variations as affecting factors (Longui et al 2012;Brémaud et al 2013). …”