Abstract People in north-east Brazil mostly rely on fuelwood and charcoal for domestic energy consumption. Traditionally, four local wood taxa (Mimosa tenuiflora, Mimosa ophthalmocentra, Croton sonderianus and Cenostigma pyramidale) from the caatinga have been selected for this purpose. As the final quality of charcoal is directly related to the charring conditions, as well as the chemical composition of the raw materials and the behaviour of the lignocellulosic matrix during the charring process, the aim of this study was to investigate how far differences in these parameters exert a major control on the charcoal formation, in order to give a molecular insight as to why these particular wood species might be preferred for high-quality charcoal in the perspective of sustainable management and harvesting regimes. Pyrolysis gas chromatography mass spectrometry (Py-GC-MS) and scanning electron microscopy (SEM) were used to study the chemical composition and anatomical changes of the wood samples before and after charring experiments were carried out at 400 and 600 °C. The charring conditions were also reproduced in the controlled environment of the pyrolysis chamber and evolved gas analysis mass spectrometry (EGA-MS) was used for the first time to monitor the evolution of the thermal degradation products. The thermal behaviour of the wood components was different compared to other wood taxa for which comparable data are available. These differences were partially related to the particular nature of the carbohydrate-lignin interactions, to a relatively low level of lignin condensation, and to the substantial presence of gums or resins, which formed charred deposits. These characteristics, often neglected in charcoal analysis, imply that the wood components (especially cellulose) are released more slowly during the charring process, and this translates into the ability of these wood species to retain the main features of their anatomical structure even when exposed to high temperature for a relatively long time. The anatomical alterations observed, such as the loss of the middle lamella, the disappearance of the pit membranes, and the homogenisation of cell walls are ultimately in agreement with the formation of a particularly recalcitrant carbonaceous matrix upon charring at relatively low temperature (400 °C for 2 hours). This study presents the first molecular characterisation of these wood species and some methodological advancement on the use of EGA analysis using isothermal conditions is provided. The role of carbohydrate-lignin interactions and non-lignocellulosic wood components in charcoal production is discussed and the importance of combining chemical data and anatomical observations in wood research is underlined.

中文翻译：

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使用分析热解和扫描电子显微镜评估巴西东北部卡廷加四种木材类群的木炭形成

摘要 巴西东北部的居民主要依靠薪材和木炭作为家庭能源消费。传统上，为此目的选择了来自卡廷加的四种当地木材分类群（含羞草、眼含羞草、巴豆和 Cenostigma pyramidale）。由于木炭的最终质量与炭化条件、原料的化学成分和炭化过程中木质纤维素基质的行为直接相关，因此本研究的目的是调查这些参数的差异程度对木炭的形成进行主要控制，以便从分子角度了解为什么从可持续管理和采伐制度的角度来看，为什么这些特定的木材物种可能更适合高品质木炭。采用热解气相色谱质谱(Py-GC-MS)和扫描电子显微镜(SEM)研究了木材样品在400℃和600℃炭化实验前后的化学成分和解剖学变化。炭化条件也在热解室的受控环境中重现，并且首次使用逸出气体分析质谱 (EGA-MS) 来监测热降解产物的演变。与可获得可比数据的其他木材类群相比，木材成分的热行为是不同的。这些差异部分与碳水化合物-木质素相互作用的特殊性质、相对低水平的木质素缩合以及大量存在的树胶或树脂有关，形成烧焦的沉积物。这些特性在木炭分析中经常被忽略，这意味着木材成分（尤其是纤维素）在炭化过程中释放得更慢，这意味着这些木材种类即使暴露在空气中也能保持其解剖结构的主要特征。高温时间相对较长。观察到的解剖学改变，例如中层的丢失、凹坑膜的消失和细胞壁的同质化，最终与在相对较低的温度（400°C）下炭化时形成特别顽固的碳质基质一致。持续2个小时）。本研究首次介绍了这些木材种类的分子特征，并提供了在等温条件下使用 EGA 分析的一些方法学进步。讨论了碳水化合物-木质素相互作用和非木质纤维素木材成分在木炭生产中的作用，并强调了在木材研究中结合化学数据和解剖观察的重要性。