COMPARATIVE ANALYSIS OF PHYSICAL-CHEMICAL PROPERTIES OF LARCH AND PINE BARK: THERMAL ANALYSIS AND ANALYTICAL PYROLYSIS

The study focuses on the thermal analysis and flash pyrolysis of bark of Siberian larch ( Larix sibirica Ledeb.) and Scots pine ( Pinus sylvestris L.). Using thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC), a number of patterns of thermal decomposition of bark were established. The fourth derivatives of the DTG contours revealed differences in the “fractionality” of mass loss during heating of the bark samples. The thermal decomposition kinetics of bark was investigated using the Ozawa - Flynn - Wall isoconversion method. The obtained dependence of the activation energy ( E _a) on the conversion degree was used to calculate the thermodynamic parameters (Δ H , Δ G and Δ S ) of thermal decomposition. The mean values of E _a, Δ H , Δ G and Δ S were 206.7, 201.1, 248.7 kJ/mol and -78.0 J/(mol×K) for larch bark (LB) and 235.3, 229.7, 310.6 kJ/mol and -129.4 J/(mol×K) for pine bark (PB). The composition of mono-, sesqui-, diterpenes and oxygen-containing hydrocarbons of bark was determined by headspace GC/MS analysis. 37 and 41 volatile organic compounds were identified for LB and PB, respectively. The thermal stability of LB and PB was characterized using recalcitrant indices calculated from TG and DSC data. Integral values of exothermic effects of thermo-oxidative degradation were 15.1 kJ/g for LB and 15.9 kJ/g for PB. 55 flash pyrolysis products were identified, which accounted for 77.6 % of the total peak area for LB and 89.7 % for PB.