Cellulose Crystallite Width Research Articles

Combined X-ray diffraction tomography imaging of tension and opposite wood tissues in young hybrid aspen saplings

Combining spatially localized X-ray diffraction (XRD) with X-ray microtomography (XMT) enables the mapping of the micro- and nanoscale structures simultaneously. The combination of these methods results in a powerful tool when considering the structural studies of hierarchical materials, allowing one to couple the relationships and connections of the structures at various scales. In this study, XMT was used to map the anatomy and cellular structures in 3D in tension and opposite wood with 1.5 µm resolution, while XRD was used to determine the cellulose crystallite widths and microfibril orientations with 100 µm spatial resolution within the same tissues. Tension wood (TW) has an important biological function with clearly distinct properties to opposite (OW) and normal wood, e.g. differing cellular structures with a higher cellulose content. This is the first study of very young hybrid aspen saplings (1-month-old) using the combined diffraction tomography method. The TW tissues could be identified from the OW tissues based on both the XMT and XRD results: TW had a higher average size of the cellulose crystallites and smaller mean microfibril angles (mMFA) than those in OW. With the XRD data, we were able to reconstruct the images of the cross sections of the saplings using the structural parameters (cellulose crystallite width and mMFA) as contrast mechanisms. As far as the authors know, there are no previous studies with images on any TW samples using the XRD-based contrast. Home laboratory bench-top set-up offers its advantages for these studies, considering the number of samples characterized, time-dependent studies and larger field of views.

Cellulose structure and lignin distribution in normal and compression wood of the Maidenhair tree (Ginkgo biloba L.).

We studied in detail the mean microfibril angle and the width of cellulose crystals from the pith to the bark of a 15-year-old Maidenhair tree (Ginkgo biloba L.). The orientation of cellulose microfibrils with respect to the cell axis and the width and length of cellulose crystallites were determined using X-ray diffraction. Raman microscopy was used to compare the lignin distribution in the cell wall of normal/opposite and compression wood, which was found near the pith. Ginkgo biloba showed a relatively large mean microfibril angle, varying between 19° and 39° in the S2 layer, and the average width of cellulose crystallites was 3.1-3.2 nm. Mild compression wood without any intercellular spaces or helical cavities was observed near the pith. Slit-like bordered pit openings and a heavily lignified S2L layer confirmed the presence of compression wood. Ginkgo biloba showed typical features present in the juvenile wood of conifers. The microfibril angle remained large over the 14 annual rings. The entire stem disc, with a diameter of 18 cm, was considered to consist of juvenile wood. The properties of juvenile and compression wood as well as the cellulose orientation and crystalline width indicate that the wood formation of G. biloba is similar to that of modern conifers.

Effects of pressurized hot water extraction on the nanoscale structure of birch sawdust

Pressurized hot water extraction with a flow-through system was used to extract hemicelluloses and lignin from birch sawdust. The structure of the extraction residue was studied on various levels. Molecular mass distributions were determined with gel permeation chromatography and the crystal structure of cellulose was characterized using wide-angle X-ray scattering (WAXS). Information on the short-range order of cellulose microfibrils and on the nanoscale pore structure was obtained with small-angle X-ray scattering (SAXS), and the micrometre scale cellular morphology was imaged with X-ray microtomography. The pressurized hot water treatment was observed to increase the lateral width of cellulose crystallites, determined with WAXS, whereas a possible small decrease in the crystallinity of cellulose compared to native wood was detected. The molecular mass of cellulose remained at a relatively high level. According to the SAXS results, a tighter lateral association of cellulose microfibrils was observed in the extracted samples, which possibly led to opening of pores between bundles of microfibrils, as indicated by an increased specific surface area. A reduction in the thickness of the fibre cell walls was evidenced by X-ray microtomography.

Structure of oak wood from the Swedish warship Vasa revealed by X-ray scattering and microtomography

Abstract The degradation of oak wood of the historical warship Vasa was studied, focusing on cellular structure by X-ray microtomography (μCT) and on the nanostructure of the cell wall by wide- and small-angle X-ray scattering (WAXS, SAXS). Solid samples [polyethylene glycol (PEG)-, impregnated and PEG-extracted] were submitted to X-ray analysis and the results compared to those of recent oak. The cellular structure of the Vasa oak was surprisingly well preserved at the micrometer level, according to the μCT images. As revealed by WAXS, the fraction of crystalline cellulose was lower in the Vasa samples compared with recent oak, but the average length and width of cellulose crystallites (25±2 nm and 3.0±0.1 nm, respectively), and the mean microfibril angles (4–9°), showed no significant differences. Accordingly, the crystalline parts of cellulose microfibrils are well preserved in the Vasa oak. The SAXS results indicated a declined short-range order between the cellulose microfibrils and a higher porosity of the Vasa oak compared with recent oak, which may be explained by modification of the hemicellulose-lignin matrix.

Evolution of cellulose crystals during prehydrolysis and soda delignification of sugarcane lignocellulose

This work investigates the evolution of cellulose crystals from sugarcane lignocellulose (bagasse and leaves) submitted to prehydrolysis (hydrothermal, dilute acid, or steam explosion) and soda delignifications. Raw and treated materials are characterized by X-ray diffraction with modeling of area-detector patterns. Three treatment effects are correlated: increase in cellulose content, quantified by strong acid hydrolysis; increase in average cellulose crystallite width, inferred from sharper 200 diffraction peaks; and decrease in crystallite distortion, evidenced by d 200-spacing approaching reference values. Crystal contents measured according to recent developments (in Driemeier and Calligaris, J Appl Cryst 44:184–192, 2011) are compared to cellulose contents. Limitations for this comparison are discussed. Results are consistent with minimum non-crystalline cellulose in raw lignocellulose, and with partial cellulose decrystallization or more defective crystallites in treated materials.

Investigation of potential sawlog quality indicators – A case study with 32-year-old plantation Eucalyptus globulus Labill.

Thirty dominant or co-dominant, straight trees were selected from a 32-year-old thinned plantation of Eucalyptus globulus Labill. Growth strain at breast height was estimated using the longitudinal displacement which was measured with a CIRAD-foret method. One 12-mm diametrical increment core was collected from each tree at breast height and a SilviScan specimen prepared from each core. Density, cellulose microfibril angle (MFA), cellulose crystallite width (Wcryst) and Young’s modulus along the grain (EL) were determined using the SilviScan-2 technology. Weighted means and other characteristics of these four wood properties were determined and used as sawlog quality candidate indicators. Relationship between each sawlog quality candidate indicator and each of several arbitrarily defined sawlog quality descriptors were examined. Growth strain appeared to be the only useful indicator for log-end split severity and may also be a useful indicator for spring in dried boards. The radial variation of MFA (percentage of MFA values smaller than 12 degrees) appeared to be the most useful indicator of spring in dried boards. The radial variation of EL (EL slope) appeared to be more useful in predicting distortion in green slabs and possibly flitch during sawing. Density and cellulose crystallite width, either as tree means or in other expressions, showed no significant correlation with any sawlog quality descriptors.

Evaluating growth strain of Eucalyptus globulus Labill. from SilviScan measurements

Abstract Longitudinal surface strain was measured or estimated using three different methods along the stems of nine trees of 10-year-old Eucalyptus globulus Labill. Wood samples were collected close to the location where the strain was measured or estimated. Microfibril angle (MFA), cellulose crystallite width (Wcryst), microdensity and Young's modulus along the grain (EL) were determined using the SilviScan-2 technology at high spatial resolution. Relationships of measured strain and estimated strain to wood properties were established. The quality of the relationships depends on a particular wood property. Strain was more closely related to mean Wcryst than to any other wood properties. Its relationship with MFA was the next closest. Based on the results of regression analysis, we propose that Wcryst may be suitable for the prediction of surface strain at a moderate level of reliability. Adding measurement of MFA, microdensity and EL does not significantly improve the prediction quality. The strain measurement method also affects the results. The best relationships were obtained with longitudinal displacement measured by the CIRAD method. Strain measured by the strain gauge method gave weak relationships, possibly owing to variation in the cambium age of the specimens.

Effect of thinning and fertilizer on the cellulose crystallite width of Eucalyptus globulus

An analysis of cellulose crystallite width, microfibril angle and wood density after the time of thinning (at 8 years) in straight vertical trees was undertaken in a 13-year-old E. globulus trial designed to assess the effect of thinning on tension wood formation. The most important effect was on cellulose crystallite width, which increased with thinning intensity and this was mitigated where fertilizer was applied at the time of thinning. Given the relationship between high crystallite width and tension wood occurrence the results demonstrate that heavy thinning of E. globulus at this age can contribute to tension wood formation. However, tension wood production may be significantly reduced where fertilizer is applied. This is possibly because increased diameter growth as a response to fertilizer application stabilises the stems and this is the mechanism by which trees cope with internal stresses that are generated from wind in destabilsed stands following thinning. In contrast, trees that respond poorly to thinning produce tension wood.

A Study of Eucalyptus Grandis and Eucalyptus Globulus Branch wood Microstructure

Experimental measurements of cellulose crystallite width and microfibril angle (MFA) by X-ray diffractometry on SilviScan-2 and by conventional microtechniques revealed that the branch wood of the two species exhibited very similar trends in cellulose crystallite width and MFA. Cellulose crystallite width was greater on the upper side of the branches. Tension wood, as defined by the occurrence of gelatinous fibres, was found where cellulose crystallite width was greater than 3.0 nm and 3.1 nm in Eucalyptus grandis and E. globulus respectively. In the tension wood zones, MFA was lower than in the rest of the samples and so could be used to differentiate tension wood. On the lower side of the branches MFA determined from X-ray diffractometry unexpectedly exceeded 40° and fibres were often buckled in both the tangential and radial directions in both species. This local variation in the direction of the fibre axes contributed only slightly to the magnitude of the MFA determined by SilviScan-2. Even given this misalignment, the additional evidence gained from pit angles and cracks in fibre walls suggested that the MFA was indeed around 40° in the lower radius of the branches. This MFA is considerably larger than would be expected for eucalypt stem wood and it is suggested that opposite wood in eucalypt branches may provide a complimentary structural role to that of the tension wood. Experimental measurements of crystallite width produced by SilviScan-2 may be used to accurately locate tension wood zones in both species.

An unusual formation of tension wood in a natural forest Acacia sp.

Abstract The determination of microfibril angle (MFA), cellulose crystallite width and microdensity by SilviScan-2 at CSIRO confirmed that several dark bands in the heartwood of an Acacia species were associated with tension wood (TW) fibres. The straight log was taken from a tree of about 30 years of age that had been apparently growing vertically as there were no signs of the usual stimuli for TW formation. The continuous dark bands of about 5 mm width extended radially from the inner heartwood in a spiral pattern and were separated by continuous normal wood bands of similar width. The TW bands continued in the sapwood from the heartwood boundary to the cambium but were not coloured. The dark colour of the TW was probably caused by extractives being polymerised at the heartwood boundary by enzymes in the TW fibres in the sapwood. The MFA and cellulose crystallite width indicated the TW in a band was of similar intensity throughout its length, indicating similar microstructural characteristics at different cambial ages. The initiation of spiral grain formation occurs before that of tension wood in the Acacia samples studied.

Identifying check-prone trees of Eucalyptus globulus Labill. using collapse and shrinkage measurements

Summary Fifty-nine trees were sampled from three provenances of 10-y- old Eucalyptus globulus Labill. plantations grown at two sites in South Australia. The butt logs were backsawn and 176 boards (40 mm × 100 mm × 3600 mm) from the centre cant (two to four boards per cant) were dried. A 10-mm-thick cross-section was removed 400 mm from the end of each board (corresponding to the smaller end of the log) and inspected for the presence of internal checks. The samples were ranked using the mean values of several wood properties, including tangential collapse, total tangential shrinkage, density, growth strain, microfibril angle (MFA) and cellulose crystallite width (Wcryst). The rank positions of the check-prone trees were inspected in each ranking. Tangential collapse showed good potential for identifying the check-prone trees, while total tangential shrinkage and total cross-sectional shrinkage were slightly less sensitive. Density, growth strain, MFA, Wcryst and other shrinkage properties were not as useful. It is recommended that tree breeders should use total tangential shrinkage as an indicator to identify check-prone trees, because this property is not only reliable but can be easily measured on trimmed increment cores at low cost.

Tension wood occurrence in Eucalyptus globulus Labill. I. The spatial distribution of tension wood in one 11-year-old tree

Summary In preliminary work for a project to develop methods for rapid detection of tension wood in standing trees, the spatial distribution of tension wood was assessed in one 11-y-old tree of Eucalyptus globulus Labill, from East Gippsland, Victoria, Australia. Tangential shrinkage was assessed at about 500 locations within the tree by drying small wood samples to 12% moisture content after reconditioning, and high tangential shrinkage was used to indicate tension wood. A shrinkage differential was calculated as the difference between the tangential shrinkage at the site of maximum shrinkage and the minimum normal shrinkage in tissue of similar cambial age at the same height in the stem. In earlier studies regression analysis indicated that cellulose crystallite width (which is a good indicator of the presence and severity of tension wood) and microdensity (measured on SilviScan-2; a system developed at CSIRO for rapid assessment of wood microstructure) were significant predictors of the shrinkage differential. In addition, at a shrinkage differential of 3.0% or greater, tension wood was easily identified histochemically in thin transverse microscope sections. Hence the shrinkage differential could be used to map tension wood occurrence. Tension wood was located predominantly below 30% of tree height and increased in extent and severity toward the base. The spatial distribution suggests that sample cores from low in the stem could be used to detect tension wood in standing trees, and the results warrant expansion of the work to more trees in order to further develop detection methods.

Prediction of wood tangential shrinkage from cellulose crystallite width and density in one 11-year-old tree of Eucalyptus globulus Labill

Summary The relationship between variation in wood shrinkage and cellulose crystallite width determined by X-ray diffraction was assessed using SilviScan-2 (a system developed at CSIRO for rapid assessment of wood microstructure). Cellulose crystallite width, density and microfibril angle were determined for 600μm wide zones on small wood samples with known tangential shrinkage. The tangential shrinkage measurements included shrinkage to 12% moisture content after reconditioning (MC AR); and a shrinkage differential calculated from tangential shrinkage to 12% MC AR recorded for each zone; and the minimum shrinkage recorded in adjacent wood of similar cambial age. Spearman correlations and forward stepwise regressions showed that the cellulose crystallite width was a good predictor of the shrinkage measures and that density was a minor predictor. Together, cellulose crystallite width and density could explain 75% of the variation in tangential shrinkage for randomly selected locations throughout the tree, and 87% of the variation in tangential shrinkage in samples selected from the lower 5% of tree height. The results suggest that SilviScan-2 can be used to predict tangential shrinkage during drying in increment cores, and may therefore be useful in developing nondestructive sampling strategies in tree improvement programs for E. globulus.

THE ASSOCIATION BETWEEN CELLULOSE CRYSTALLITE WIDTH AND TENSION WOOD OCCURRENCE IN EUCALYPTUS GLOBULUS

The association between cellulose crystallite width and the occurrence of tension wood was assessed for Eucalyptus globulus Labill., a commercially important plantation hardwood species. Crystallite width (uncorrected for instrumental broadening) was determined from X-ray diffraction patterns collected on SilviScan-2, an instrument developed for the rapid assessment of wood microstructure. Comparisons of crystallite widths were made using 66 samples of tension wood and normal wood selected randomly from one tree known to have abundant tension wood. Tension wood was found to have significantly wider crystallites than normal wood. The mean crystallite widths were 3.6 nm for tension wood and 3.2 nm for normal wood. The normal wood crystallite widths were consistent with those reported in previous studies, allowing for an experimental broadening equivalent to about 0.5 nm in this work. This study demonstrates that SilviScan-2 is useful for the detection of tension wood in solid wood samples such as increment cores.