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This paper presents a thermal characterization of hardwoods of Hungarian origin. The study covers the wood of the following tree species: sessile oak (Quercus petraea), beech (Fagus sylvatica), hornbeam (Carpinus betulus), black locust (Robinia pseudoacacia), lime (Tilia platyphyllos), ash (Fraxinus ornus), maple (Acer campestre), alder (Alnus glutinosa), and aspen (Populus tremula). Wood samples were subjected to differential scanning calorimetry and thermogravimetry in an air atmosphere at different heating rates of 10, 20, and 40 °C·min−1. The activation energy was calculated using the Flynn–Wall–Ozawa method. Thermogravimetric analysis revealed that tree species differed considerably in the mass loss and the temperature of the maximum mass loss rate related to the thermal degradation of the main wood components and the oxidation of char mainly derived from lignin. Beech, hornbeam and ash were characterized by a high mass loss attributed to decomposition of hemicelluloses. The mass loss assigned to the thermal degradation of cellulose varied from 35.41% (ash wood) to 53.65% (alder wood). Sessile oak wood showed the greatest mass loss and the highest temperature of thermoxidation of residual lignin and char. Calorimetrically measured values of the exothermic effect of the wood thermal degradation were in the range 7.93–9.65 kJ g−1. The average values of activation energy for the thermal degradation of carbohydrates and the thermoxidation of residual lignin and char were found to be 176.0 ÷ 197.3 kJ mol−1and 196.4 ÷ 319.5 kJ mol−1, respectively.

The thermal decomposition of tree rings (separately, latewood and earlywood) of Larix gmelinii (Rupr.) Rupr.) during the period from 1988 to 1998 was studied using thermogravimetric analysis (TG / DTG) and differential scanning calorimetry (DSC). Thermal analysis was performed in oxidizing (air) condition. The stages of thermal decomposition of wood were analyzed by heating the sample from 30 to700 °C at the heating rates of 10, 20, 40 °C/min for TG / DTG and from 30 to590 °C at the heating rates of 10, 40 °C/min for DSC. The temperature ranges, mass loss, mass loss rate, temperature DTG / DSC peaks, thermal evaporation effects of moisture and the processes of thermal decomposition for each annual layer were studied. The result of thermogravimetry measurements were carried out using the Broido and Ozawa – Flynn – Wall methods. Tree rings of larch wood on the basis of the analysis of the activation energy values of the individual stages of thermal decomposition and activation energy dependency on the degree of conversion of wood material different tree rings; and based on the comparison of the mass loss for corresponding stages of thermal destruction, thermal effects, and other parameters of TG / DSC and DTG were characterized. The material presented in the study would, in our view, to study the impact of growing conditions on wood physical properties and chemical composition of wood, which are the basis for determining the direction of ways to use it, as well as indicators of the reaction of wood plants on endogenous and exogenous conditions.