Significant influence of lignin on axial elastic modulus of poplar wood at low microfibril angles under wet conditions

Abstract

Wood is extensively used as a construction material. Despite increasing knowledge of its mechanical properties, the contribution of the cell-wall matrix polymers to wood mechanics is still not well understood. Previous studies have shown that axial stiffness correlates with lignin content only for cellulose microfibril angles larger than around 20°, while no influence is found for smaller angles. Here, by analysing the wood of poplar with reduced lignin content due to down-regulation of CAFFEOYL SHIKIMATE ESTERASE, we show that lignin content also influences axial stiffness at smaller angles. Micro-tensile tests of the xylem revealed that axial stiffness was strongly reduced in the low-lignin transgenic lines. Strikingly, microfibril angles were around 15° for both wild-type and transgenic poplars, suggesting that cellulose orientation is not responsible for the observed changes in mechanical behavior. Multiple linear regression analysis showed that the decrease in stiffness was almost completely related to the variation in both density and lignin content. We suggest that the influence of lignin content on axial stiffness may gradually increase as a function of the microfibril angle. Our results may help in building up comprehensive models of the cell wall that can unravel the individual roles of the matrix polymers.

Comparative studies on wood structure and microtensile properties between compression and opposite wood fibers of Chinese fir plantation

“…In general, it is difficult to study the role of lignin during tensile loading, because changes in lignin content typically occur together with changes in MFA. Recently, Özparpucu et al [20] found on genetically modified poplar slices with similar MFAs but different lignin contents, that lignin contributed to the axial stiffness by increasing the shear stiffness of the cell wall matrix; and the influence of lignin content on axial stiffness may gradually increase as a function of the MFA. In addition to these studies, effects of chemical treatments on plant fiber mechanics were studied experimentally [10,21].…”

Twist and lock: nutshell structures for high strength and energy absorption

“…Lignin is known to play a role in the mechanical properties of plant CWs, e.g. in poplar wood axial stiffness was higher in wild-types than in mutants with reduced lignification [ 33 ]. On the other hand, less lignin gives a weak interface, which facilitates high-energy absorption (toughness) [ 34 ], as observed in pistachio ( figure 4 c ).…”

Numerical Simulation of the Deformation Behavior of Softwood Tracheids for the Calculation of the Mechanical Properties of Wood–Polymer Composites

“…Subsequently, the material parameters of the unidirectional layers were exported as a material data sheet and used to construct the cell wall of EW and LW tracheids in Ansys Composite PrepPost. The temperature-and moisture-dependent modification of the mechanical properties of cellulose, hemicellulose and lignin has not yet been represented in the RVE model and is to be implemented as part of further research work by using the relevant findings known from research [31][32][33][34][35] or determined by experiments. Then, the built models were used to simulate the deformation behavior of 0.1 mm long representative cutouts of EW and LW tracheids during compression perpendicular to their longitudinal axis (radially as well as tangentially) to determine the level of compression pressure at which the EW tracheids fail and the LW tracheids deform purely elastically.…”