Effect of natural weathering on water absorption and pore size distribution in thermally modified wood determined by nuclear magnetic resonance

Abstract

Thermally modified wood (TMW) is widely used in outdoor applications due to its advanced properties towards weathering stresses. Although the structure changes of TMW from weather factors have been reported, investigation of the quantitative analysis of water states and cell wall structure of TMW after weathering is limited. In this work, the amount of bound water, fiber saturation point (FSP), cell wall pores, and free water distribution of thermally modified Scots pine, Norway spruce, and European ash were measured before and after a 2-year natural weathering via NMR relaxometry, cryoporometry, and magnetic resonance imaging. The results show that weathering increased T 2 relaxation time of lumens, indicating the degradation of tracheids and vessels, especially in TMW compared to unmodified wood. The amounts of bound water, FSP value, and cell wall pores were increased after weathering; however, an increase in thermal modification intensity resulted in lower FSP and limited the increase in number of pores. In summary, TMW showed better performance than unmodified wood after weathering. Keywords Bound water Á Free water Á Fiber saturation point (FSP) Á Cell wall pores Á Nuclear magnetic resonance (NMR) Á Thermally modified wood

Enhanced water uptake in the longitudinal direction by shiitake mycelium in shiitake cultivation logs: increase in effective diffusion coefficient based on mass of liquid water uptake

“…Water molecules existing in wood that is adequately supplied with liquid water are roughly classified into two types: "bound water" and "free water" (Brownstein 1980;Gezici-Koç et al 2017;Cai et al 2020;Hiltunen et al 2020). Since bound water is tightly bound to molecules in the cell walls and fibers composed of mainly cellulose, hemicellulose and lignin, the T 2 relaxation time constant of the hydrogen atoms in the bound water is shorter than 1 ms (Müller et al 2001;Gezici-Koç et al 2017;Cai et al 2020;Hiltunen et al 2020). On the other hand, since free water existing in the voids such as cell lumens and vessels can move relatively freely, the T 2 relaxation time constant of free water is longer than 1 ms.…”

“…The origin of the NMR signal that reconstructs the MR image is the hydrogen atoms in water molecules. The NMR signal emitted from the hydrogen atoms contained in the many water molecules constituting wood tissue such as cellulose or hemicellulose cannot be measured under the MRI measurement condition of echo time TE = 12 ms since the T 2 relaxation time constant of the hydrogen atoms is much shorter than 1 ms (Müller et al 2001;Gezici-Koç et al 2017;Cai et al 2020;Hiltunen et al 2020). However, if wood contains liquid water, the water inside the wood can be visualized by MRI (Hall and Rajanayagam 1986;Chang et al 1989;Wang and Joseph 1989;Bucur 2003;Kuroda et al 2006;Hameury and Sterley 2006;Zhou et.…”

Thermal modification of wood—a review: chemical changes and hygroscopicity

“…Hygroscopicity Thermal modification reduces the amount of bound water in the wood cell wall [139,140]. However, the behaviour of HT dry and HT wet wood is different.…”

Leachability and Decay Resistance of Wood Polyesterified with Sorbitol and Citric Acid

“…The water-saturated samples were characterised with LFNMR and showed four peaks in the T 2 relaxation spectrum. For unmodified wood samples, typically only three peaks are determined which arise from water within the wood structure-one peak with the shortest relaxation time attributed to bound water within the cell wall, another smaller peak attributed to free water in small voids of the wood anatomy (e.g., bordered bits and ray lumina) and a large peak for free water in tracheid lumina [50][51][52]70]. The small fourth peak determined for control samples in the current study (peak 1.5, Figure 5a, Table 3) may be due to the 18 h 140 • C thermal treatment that these samples received, since thermal treatment can cause microcracking within the cell wall [72,73].…”

“…In porous media, the relaxation time of water molecules depends on both the size of the pores containing the water and the chemical interaction between the water and the pore wall [46]. In a Carr-Purcell Meiboom-Gill (CPMG) experiment, T 2 relaxation time is measured and water saturated wood samples exhibit 3-4 water populations with distinct T 2 values [47][48][49][50][51][52]. One population is attributed to water within the cell wall and the 2-3 other populations arise from free water within the wood void structure.…”