Thermal Degradation of Condensed Tannins from Radiata Pine Bark

ISSN： 0277-3813

Source： Journal of Wood Chemistry and Technology, Vol.29, Iss.4, 2009-10, pp. : 305-321

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Abstract

In order to understand the influence of the inherent chemistry on the relative thermal stability of condensed tannins, the thermal degradation behaviors of various radiata pine bark extracts have been investigated using thermogravimetric analysis (TGA). Generally, results suggest pine bark extract fractions may be readily processed at temperatures below 200°C if co-extracted polysaccharides contents are minimized. Those extracts possessing greater carbohydrate content and lower tannin purity tend to have decreased thermal stability. The initial onset temperature for degradation of relatively crude extracts with high proportions of carbohydrate contents were relatively low (ca. 150°C), whereas extract purification to < 5%="" carbohydrate="" content="" gave="" increases="" in="" thermal="" stability="" of="" at="" least="" 50°c.="" the="" complicity="" of="" the="" carbohydrate="" content="" in="" the="" degradation="" of="" the="" tannin="" samples="" was="" also="" supported="" by="" calculated="" ozawa="" activation="" energies="" and="" modulated="" tga="" experiments.="" while="" no="" increase="" in="" the="" thermal="" stability="" was="" gained="" by="" acetylating="" the="" pendant="" hydroxyl="" groups="" of="" the="" pine="" bark="" tannin="" extract,="" chemical="" variations="" such="" as="" sulfonation="" have="" a="" large="" effect="" on="" thermal="" degradation,="" promoting="" lower="" degradation="" temperatures.="">