Chemical changes of hardwoods at thermal loading by radiant heating
2016
Čabalová Iveta | Kačík František | Zachar Martin | Dúbravský Rastislav
This paper describes the chemical changes of three hardwood species, white willow(Salix alba L.) , alder (Alnus glutinosa(L.) Gaertn.), and poplar (Populus tremula L.) with dimensions 50 ×50 ×1000 mm after thermal loadingby radiant heating for 30 minutes. We determined the amounts of extractives, cellulose and lignin in degraded and sound wood by wet chemistry methods. The influence of thermal loading on carbohydrates changes was investigated by high-performance liquid chromatography (HPLC). After thermal loading the increase of cellulose content (approx. 2–19%), lignin (approx. 26–61%) and also extractives (approx. 83–125%) except for alder sample, where the decrease of extractives content for approx. 20% was observed. Increase of cellulose content is probably due to changes in its structure (carbonization and crosslinking). The lignin content increase due to its greater thermal stability compared to carbohydrates, as well as a result of its condensation. Increased extractives content is due to the creation of new extractive components by thermal decomposition of hemicelluloses. Hemicelluloses were degraded to the greatest extent in the case of poplar (42.91%), less in the willow wood (29.20%) and the most resistant was in the alder wood (loss of hemicelluloses were only 17.60%). The least thermally stable monosaccharide was galactose, which was completely removed in all three investigated samples. Resistance other carbohydrates depends on the species -in alder were more labile pentosans, contrary to poplar and willow wood.
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