Carbonization of reaction wood from Paulownia tomentosa and Pinus densiflora branch woods

The carbonization characteristics of tension wood (TW) and compression wood (CW) from Paulownia tomentosa and Pinus densiflora branch woods, respectively, were investigated and compared to those of opposite wood (OW) and lateral wood (LW). The carbonization was conducted at 400, 600, and 800 °C. Heating values, pH, char yields, cell wall structures, and combustion characteristics were different in TW and CW, whereas only little differences were found among reaction wood, OW, and LW. The heating values of TW charcoal were lower than those of CW charcoal at 400 and 600 °C, while the pH of TW charcoal was higher than that of CW at all carbonization temperatures. The char yields of CW were the highest among all the samples at all carbonization temperatures. Furthermore, the TW charcoal was more thermally stable than CW charcoal. SEM observations revealed significant differences in the cell wall structures of the woods before and after carbonization. The gelatinous layer in TW disappeared, and the helical cavities and intercellular spaces in CW persisted throughout the carbonization process. The cell wall structures of the wood samples became smooth and amorphous as the carbonization temperature increased.