Nanostructural deformation of high-stiffness spruce wood under tension

Abstract

Conifer wood is an exceptionally stiff and strong material when its cellulose microfibrils are well aligned. However, it is not well understood how the polymer components cellulose, hemicelluloses and lignin co-operate to resist tensile stress in wood. From X-ray scattering, neutron scattering and spectroscopic data, collected under tension and processed by novel methods, the ordered, disordered and hemicellulose-coated cellulose components comprising each microfibril were shown to stretch together and demonstrated concerted, viscous stress relaxation facilitated by water. Different cellulose microfibrils did not all stretch to the same degree. Attempts were made to distinguish between microfibrils showing large and small elongation but these domains were shown to be similar with respect to orientation, crystalline disorder, hydration and the presence of bound xylan. These observations are consistent with a major stress transfer process between microfibrils being shear at interfaces in direct, hydrogen-bonded contact, as demonstrated by small-angle neutron scattering. If stress were transmitted between microfibrils by bridging hemicelluloses these might have been expected to show divergent stretching and relaxation behaviour, which was not observed. However lignin and hemicellulosic glucomannans may contribute to stress transfer on a larger length scale between microfibril bundles (macrofibrils).

Effect of the Longitudinal Tensile Creep on the Stiffness of Radiata Pine (Pinus radiata D. Don)

“…Similar behavior has been found in other herbaceous fibers subjected to different load cycles [60][61][62]. On the other hand, the tensile mechanical behavior of wood sheets (thickness in microns) has also been studied [57,[63][64][65], as well as the influence of the microfibril angle [66] and the moisture content in very thin wood tissues subjected to longitudinal tensile creep [67]. Kamiyama et al investigated the effect of tensile loading on the angle of microfibrils in compression wood tissues, finding that they tend to align [68] and decrease the microfibril angle in the axial direction to the cell axis and load [69].…”

“…In addition, this variability is also reflected in the variation in the microfibril angles [92], which is the main factor determining the mechanical properties [93]. Investigations using advanced spectroscopy techniques have reported that for wood having high microfibril angles subjected to tensile stress, the deformations are produced by polymer reorientation and sliding, while for wood with low microfibril angles, stretching of the disordered polymers is generated [65]. This implies that depending on the wood cell wall microfibril angles, the mechanical response, at the macroscopic level, will be greater or less depending on the case.…”

Carbohydrate-aromatic interface and molecular architecture of lignocellulose

“…1a ) 11 . Elementary microfibrils frequently coalesce, forming large fibrils that often span across tens of nanometers 12 , 13 . Hemicelluloses, such as xylan, glucuronoxylan, arabinoxylan, and glucomannan, are highly variable in their monosaccharide composition and linkage pattern.…”

Micro- and Nano-Scales Three-Dimensional Characterisation of Softwood

“…Previous studies have found that µCt could be used to determine differences between earlywood and latewood shrinking and swelling in Picea abies wood samples [9,10]. More recently, a combination of X-ray scattering, neutron scattering and spectroscopic data was used to explore how the constituent polymers of wood cell wall interact to resist tension [12]. Dimensional change occurs due to a change in MC.…”