Mechanical Behavior of Cellulose Microfibrils in Tension Wood, in Relation with Maturation Stress Generation

Abstract

A change in cellulose lattice spacing can be detected during the release of wood maturation stress by synchrotron x-ray diffraction experiment. The lattice strain was found to be the same order of magnitude as the macroscopic strain. The fiber repeat distance, 1.033 nm evaluated for tension wood after the release of maturation stress was equal to the conventional wood values, whereas the value before stress release was larger, corresponding to a fiber repeat of 1.035 nm, nearly equal to that of cotton and ramie. Interestingly, the fiber repeat varied from 1.033 nm for wood to 1.040 nm for algal cellulose, with an increasing order of lateral size of cellulose microfibrils so far reported. These lines of experiments demonstrate that, before the stress release, the cellulose was in a state of tension, which is, to our knowledge, the first experimental evidence supporting the assumption that tension is induced in cellulose microfibrils.

Maturation Stress Generation in Poplar Tension Wood Studied by Synchrotron Radiation Microdiffraction

“…Two effects can produce a change in d 004 : either a mechanical strain in the crystal, as was previously demonstrated in several studies (Ishikawa et al, 1997;Nakai et al, 2005;Clair et al, 2006a;Peura et al, 2007), or a change in equilibrium lattice spacing, for example due to a change in crystal size (Davidson et al, 2004). Indeed, several studies reported differences in apparent cellulose crystal size measured from the broadening of the 200 peak and the application of the Sherrer equation (Washusen and Evans, 2001;Mü ller et al, 2002Mü ller et al, , 2006Washusen et al, 2005;Ruelle et al, 2007), but this method is criticized since broadening is not affected only by crystal size but also by other factors such as crystal disorder (Kennedy et al, 2007;Nishiyama, 2009; for more details, see Supplemental Material S3).…”

“…Sample preparation was designed to prevent the release of mechanical stress within the segment in order to keep the sample as close as possible to its in planta mechanical state (Clair et al, 2006a). On each tree, a 40-cm-long stem segment (approximately 3 cm in diameter) was taken from the curved basal part of the stem.…”

“…X-ray diffraction can be used to investigate the orientation of microfibrils (Cave, 1966(Cave, , 1997a(Cave, , 1997bPeura et al, 2007Peura et al, , 2008aPeura et al, , 2008b and the lattice spacing of crystalline cellulose. The axial lattice spacing d 004 is the distance between successive monomers along a cellulose microfibril and reflects its state of mechanical stress (Clair et al, 2006a;Peura et al, 2007). If cellulose microfibrils indeed support a tensile stress, they should be found in an extended state of deformation.…”

“…1). The experiment was designed to make this measurement in planta, in order to minimize sources of mechanical disturbance and be as close as possible to the native mechanical state (Clair et al, 2006a). The 200 and 004 diffraction patterns of cellulose were analyzed to investigate the process of maturation stress generation in tension wood.…”

Tree growth stress and related problems

“…The scale are 10 lm creation of free surface results in stress redistribution in its vicinity, which accounts for both the apparent deformation and easy detachment of the G-layer from the lignified wall after the action of sectioning initiated the crack propagation. Based on their findings, we can consider that the characteristic behavior of G-fiber can be, indeed, attributed to the intrinsic property of G-layer [42,44,46,48,[51][52][53][54][55][56].…”