Intenzitet toplinske modifikacije topolovine. Dio 1: Karakterizacija i predikcija površinskog sloja

Wood heat treatment is an environmentally friendly method, and the heat-treated wood properties are closely related to thermal modification intensity. This study focuses on the 0-3 mm surface layer (SL) of poplar wood heat treated at 160~220 °C. The modification intensity, including surface color, hardness, chemical component and morphological changes of the SL, was evaluated. The findings of this research showed that the color difference of the poplar wood before and after heat treatment (ΔE*1) increased; the color difference between up-surface and down-surface of the SL (ΔE*2) also increased with the treatment temperature. Consequently, the surface hardness (HR) decreased with the increase of treatment intensity. When the treatment temperature was higher than 160 °C, the up-surface and down-surface of the SL were statistically different in color. Chemical component analysis revealed that the heat treatment degrades wood components, especially the hemicellulose, and correlation analysis showed a significant correlation between the change rate of hemicellulose and the ΔE*1 or HR value; the prediction functions have been established at a high confidence level of 0.99. Overall, the thermal modification intensity of the heat-treated surface layer (SL) of poplar wood varies, and the HR and ΔE*1 value could be used to characterize and predict the modification intensity and degree of thermal degradation of the surface layer of heat-treated poplar wood.Toplinska obrada drva ekološki je prihvatljiva metoda, a svojstva toplinski modificiranog drva usko su povezana s intenzitetom toplinske modifikacije. Ovo je istraživanje usredotočeno na površinski sloj (SL) od 0 – 3 mm toplinski modificirane topolovine pri 160 – 220 °C. Istražen je utjecaj intenziteta modifikacije na boju površine, tvrdoću, kemijski sastav i morfološke promjene površinskog sloja. Rezultati su pokazali da se s povećanjem temperature modifikacije povećala razlika u boji topolovine prije i nakon modifikacije (ΔE*1) te razlika u boji između gornje i donje površine površinskog sloja (ΔE*2). Posljedično se tvrdoća površine (HR) smanjila s povećanjem intenziteta modifikacije. Pri temperaturi modifikacije višoj od 160 °C razlika u boji između gornje i donje površine površinskog sloja statistički je značajna. Analiza kemijskog sastava otkrila je da toplinska modifikacija razgrađuje komponente drva, posebice hemicelulozu, a korelacijskom je analizom utvrđena značajna međusobna ovisnost između stupnja promjene hemiceluloze i vrijednosti ΔE*1 i HR. Utvrđene su funkcije predviđanja s visokom razinom pouzdanosti od 0,99. Sve u svemu, intenzitet toplinske modifikacije topolovine u površinskom sloju varira, a vrijednosti HR i ΔE*1 mogu se iskoristiti za karakterizaciju i predviđanje intenziteta modifikacije i stupnja toplinske razgradnje površinskog sloja toplinski modificirane topolovine

Thermal Modification Intensity of Heat-treated Poplar Wood. Part 2: Characterization and Predication from Outside to Core Layers

Based on the previous study of the heat-treated wood at 0-3 mm surface layer, this study focuses on the transition of thermal modification intensity on 160-220 °C heat-treated poplar from surface to core layers. The color change was evaluated by CIELAB, and surface hardness was detected via Shore D (HD) and pressing ball method (HR); furthermore, the FT-IR was applied to detect the thermal degradation of wood components. The results show that the degradation of cell wall components in the surface layer of heat-treated poplar wood is greater than that in the core layers, and the thermal degradation intensity of the surface layer of the heat-treated poplar wood is greater than that of the other inner layers. Surface color and hardness properties of the heat-treated wood between S0 and S1-S5 test surfaces were significantly different under the same heat treatment conditions; the surface hardness showed an increasing trend, and the HR value of the H220-2 core layer was 105.71 % higher than that of the surface layer. Heat treatment temperature is the main factor affecting the property of wood surface, while the effect of duration is smaller. The hemicellulose content change was mainly related to the degradation intensity on heattreated wood at different locations. An accurate prediction model of surface color, hardness, and other properties of the heat-treated wood at different locations was established by Table Curve 3D software