Hydrothermal treatment of beech wood in buffered mediums was carried out to study the effect of different mediums of heat treatment on crystallinity index of treated specimens due to degradation of carbohydrates. Different mediums (water, buffer5, 7 and 8) and temperatures (160 and 180 °C) were used. ATR spectra focusing on indexes of carbohydrates degradation obtained and analyzed. Results showed that crystallinity index of cellulose in specimens treated in water and buffer 5 were increased in both temperatures; whereas it didn’t changed in specimens treated in buffer 7, 8 in 160°C but increased slightly in 180°C. The ratio (T1740/1506) was decreased in treated specimens in water and buffer 5, whereas it did not change in treated specimens in buffer 7, 8 in 160°C and slightly decreased in 180°C. The intensity of carbonyl peak (1740 cm-1) was higher in specimens treated in buffer 5, water, and buffer 7, 8, respectively. It seems that because of higher amount of acids released in higher temperature (180°C), the ability of buffers to buffer the medium decreased. Thus, deacetylation and degradation of carbohydrates increased, consequently. Buffering the medium of hydrothermal treatment in neutral level prevents the strength loss and extends the usage of heat-treated wood in load-bearing applications.

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