The influence of thermo-hygro-mechanical treatment on the micro- and nanoscale architecture of wood cell walls using small- and wide-angle X-ray scattering

Abstract

Tracking the changes of cellulose crystallites upon thermo-hygro-mechanical treatment is essential to understand the response of wood cell walls to steam and compression. In this paper the influence of Compression combined with Steam (CS) treatment on wood cellulose crystallites and pores structure of Chinese fir (Cunninghamia lanceolata) was studied under different steaming temperatures and compression ratios. Small-angle X-ray scattering and wide-angle X-ray scattering were used to investigate the changes of cellulose crystallites dimension, aspect ratio, fibril diameter distribution, non-crystalline fraction, the number of chains in each microfibril, as well as the fractal dimension and size of pores in response to CS treatment conditions. Results indicate that the crystallinity increased due to CS treatment, but did not show alteration with varying CS treatment conditions, i.e. seemed nearly unaffected by higher temperatures or compression ratio, both for earlywood and latewood. The cellulose crystallite diameter depended on processing parameters: it increased with increasing treatment temperature. No considerable differences were found for earlywood and latewood. We interpret our findings as a rearrangement of adjacent cellulose chains towards higher crystalline perfection attributing to the increase in crystallinity. The same effect allows a larger coherence length of crystalline order and therefore features an increasing cross-sectional dimension. In general we can state that the CS treatment leads to higher crystallinity and more perfectly arranged cellulose crystals, while it does not greatly affect the microfibril diameter but rather the amorphous regions of the microfibrils and the surrounding hemicellulose and lignin.

Effects of thermo-hygro-mechanical (THM) treatment on the viscoelasticity of in-situ lignin

“…At the same time, the modulus of the wood increased in accordance with the indentation modulus increment after CS treatment (Guo et al 2015). The modulus increase is probably a result of the densification occurring under the compressive condition as well as a higher cellulose crystallinity and more perfectly arranged cellulose crystals after CS treatment (Navi and Sandberg 2011;Guo et al 2016). The effects of the CS treatments on the T g for all the studied samples are summarized in Figure 3.…”

“…For the further development of THM treatment it is necessary to better understand the mechanisms of the treatment (Inoue et al 1993;Navi and Sandberg 2011;Guo et al 2016). The wood cell wall consisting of cellulose embedded in a matrix composed of lignin and hemicelluloses is complex (Fengel and Wegener 1984;Salmén 2015).…”

“…The behavior of earlywood (EW) and latewood (LW) should be observed in separate DMA experiments because the lignin content of EW is somewhat higher than that of LW mainly due to the higher proportion of middle lamella material in the former (Fergus et al 1969). Compression combined with steam (CS) treatment: CS treatment was conducted in a laboratory-scale autoclave at Kyoto University as reported by Guo et al (2016). Small specimens were treated with a 25% or 50% radial compression (C R ) ratio (the percentage of the decrease in thickness as compared to the initial thickness of the specimen) at 110°C for 6 min was followed by a steaming process at 140°C, 160°C, or 180°C for 30 min, respectively.…”

Effect of Hygrothermal Treatment on the Porous Structure and Nanomechanics of Moso Bamboo

“…Therefore, the average pore size of the samples decreased significantly. In addition, an increasing number of the hydrogen bonds within the celluloses also caused tighter cellulose chain arrangements 50 . Therefore, the total pore volume and average pore size decreased accordingly.…”

“…The increase in crystallinity found in the present study can be explained by the higher reactivity of the cellulose in the amorphous region as compared to that in the crystalline region. The hydroxyls of the amorphous region lost water through condensation and produced ether bonds at certain temperatures, which caused an increase in crystallinity 50,54,55 . On the other hand, the temperature condition exceeded the hemicellulose softening temperature, thus leading to the rearrangement of adjacent cellulose chains in the amorphous region and the formation of hydrogen bonds, which drove the microfibrils towards higher crystalline perfection 52 .…”