Evaluation of the Dimensional Stability of Black Poplar Wood Modified Thermally in Nitrogen Atmosphere

Abstract

Black poplar (Populus nigra L.) was thermally modified in nitrogen atmosphere. The effects of the modification process on poplar wood were evaluated for temperatures: 160 °C, 190 °C, and 220 °C applied for 2 h; and 160 °C and 190 °C for 6 h. The percentual impact of temperature and time of modification on the properties of modified wood was analysed. The study permitted the identification correlations between the chemical composition and selected physical properties of thermally modified poplar wood. The dimensional stability of poplar wood was improved after thermal modification in nitrogen. The higher the temperature of modification, the lower the equilibrium moisture content (EMC) of black poplar. At the temperature of 220 °C, EMC was two times lower than the EMC of non-modified black poplar. It is also possible to reduce the dimensional changes of wood two-fold (at the modification temperature of 220 °C), both in radial and tangential directions, independently of the acclimatization conditions (from 34% to 98% relative humidity, RH). Similar correlations have been found for wood that has been soaked in water. Higher modification temperatures and longer processing times contributed to a lower swelling anisotropy (SA).

Effects of Heat Treatment on Interfacial Properties of Pinus Massoniana Wood

“…With the increase of temperature, the hemicelluloses content decreased linearly and were 11.3% and 8.8%, respectively, at 160 and 180 • C, with those at 200 and 220 • C 4.5% and 1.0%, respectively. This showed that the hemicelluloses structure, which was quite unstable, was prone to degradation during the heat treatment, and the degradation was the most acute within 200-220 • C. This was because hemicelluloses were heterogenous glycan consisting of different types of monosaccharide unit, with many branch structures; the bonding force between different monosaccharide units was weak, so they could be easily degraded in the heat treatment process; and the degradation products were mainly acids [16,19]. Seen from Figure 3 and Table 1, lignin content was gradually elevated with increased treatment temperature, the content was increased not obviously within 160-180 • C, but quite obviously within 200-220 • C. Hemicelluloses were the first to degrade and could most easily experience pyrolysis during the heat treatment; the cellulose would undergo pyrolysis to a certain extent, too, but the lignin would not.…”

“…Hemicelluloses are degraded first during heat treatment, and the degradation products are mainly water, acetic acid, formic acid, methanol and furfural. With the increase of treatment temperature and time, the concentration of formic acid and acetic acid increased [16,17]. The thermal stability of cellulose was very high, but hemicelluloses degradation in acidic condition also had a certain influence on the stability of cellulose due to the intertwining of cellulose and hemicelluloses.…”

Temperature, Time, and Interactions between Them in Relation to Colour Parameters of Black Poplar (Populus nigra L.) Thermally Modified in Nitrogen Atmosphere

“…Chemical compositions of non-modified and selected variants of thermally modified black poplar were determined according to the procedure presented in the Bytner et al study [12]. Black poplar wood was subjected to chemical tests after modification at temperatures of 160 • C and 190 • C for 2 h and 6 h; and at 220 • C for 2 h.…”

“…Results published in the literature indicate that nitrogen modification is less destructive compared to modification in water vapour. The mass loss of black poplar modified in superheated steam for 2 h at the temperature of 160 • C, 190 • C, and 220 • C amounted to 3%, 4%, and 12%, correspondingly, while for nitrogen modification these values amounted to 1%, 1%, and 7%, respectively [11,12].…”

“…Poplar, mainly the cultivar "Hybrid 275", from plantation crops, is used for energy purposes or as a source of raw material for the wood-based panels sector. Black poplar wood is used mainly as a resource for the cellulose industry and as a fuel material [12]. Poplar is one of the fastest growing trees in the world.…”