Abstract
Abstract The structure of hardwoods representing eight tropical and five temperate species was characterized from the atomistic level up to the cellular level using X-ray scattering, X-ray microtomography and light microscopy. The species were chosen for this study based on their popularity as tonewoods. The ultrastructure of wood cell walls, including crystallite size, orientation and close-range order of cellulose microfibrils were determined by small- and wide-angle X-ray scattering (SAXS, WAXS). The SAXS patterns were interpreted by using an analytical model of cylinders packed in a hexagonal close-range order with paracrystalline distortion. The values for the cylinder diameters given by this model were compared to the average crystallite widths obtained by WAXS using the Scherrer equation. In six out of 26 samples, all of these representing tropical species used especially in fretboard parts of electric guitars, large differences between these two sizes were obtained. The WAXS and microscopy results of these samples corresponded to tension wood structures. These comparisons and interpretations of SAXS results have not been previously presented for any tropical hardwoods, especially related to those containing tension wood tissue. The importance of the ultrastructural characterization was highlighted in this study in the case of tropical hardwood samples.
Highlights
The demand for forest biomass is growing annually, increasing the demand for both temperate and tropical forest resources and resulting in more aggressive logging in all forestry regions
For the samples with an moisture content (MC) value, the crystallite width has been analyzed from the Wide-angle X-ray scattering (WAXS) data measured from wet samples at ESRF and as for the rest of the samples, the crystallite width has been computed from the WAXS data measured at University of Helsinki (UH)
For some specimens representing tropical species, larger cellulose crystallite widths were detected based on the WAXS data, indicating the possible presence of tension wood
Summary
The demand for forest biomass is growing annually, increasing the demand for both temperate and tropical forest resources and resulting in more aggressive logging in all forestry regions. In the Asian market, the need for tropical hardwood timber is increasing (Shearman et al 2012), which has caused some commonly used tree species (e.g. mahogany, ebony, rosewoods) to become vulnerable and even critically endangered (IUCN Red List (IUCN 2018)). The deforestation in tropical regions does concern the biodiversity and has a negative impact on global climate and carbon sinks, strengthening the effect of climate change (Canadell & Raupach 2008; Chow et al 2013). Finding wood species with the same or similar properties matching the currently overharvested tropical species is essential. The structural properties of tropical hardwoods are far less characterized than the temperate zone species.
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