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TECHNICAL REPORTS

Organic Compounds in the Environment

Advanced Thermal Characterization of Fractionated Natural Organic Matter

^a Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, TN 37325
^b State Agricultural Laboratory, Arizona Department of Agriculture, 2422 West Holly, Phoenix, AZ 85009
^c Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6036

^* Corresponding author (eugene.j.leboeuf{at}vanderbilt.edu)

Received for publication June 23, 2004. This work focuses on an experimental investigation of the thermodynamic properties of natural organic matter (NOM), and whether fractions of NOM possess the same thermodynamic characteristics as the whole NOM from which they are derived. Advanced thermal characterization techniques were employed to quantify thermal expansion coefficients (), constant-pressure specific heat capacities (C_p), and thermal transition temperatures (T_t) of several aquatic- and terrestrial-derived NOM. For the first time, glass transition behavior is reported for a series of NOM fractions derived from the same whole aquatic or terrestrial source, including humic acid–, fulvic acid–, and carbohydrate-based NOM, and a terrestrial humin. Thermal mechanical analysis (TMA), standard differential scanning calorimetry (DSC), and temperature-modulated differential scanning calorimetry (TMDSC) measurements revealed T_t ranging from –87°C for a terrestrial carbohydrate fraction to 62°C for the humin fraction. The NOM generally followed a trend of increasing T_t from carbohydrate to fulvic acid to humic acid to humin, and greater T_t associated with terrestrial fractions relative to aquatic fractions, similar to that expected for macromolecules possessing greater rigidity and larger molecular weight. Many of the NOM samples also possessed evidence of multiple transitions, similar to ß and transitions of synthetic macromolecules. The presence of multiple transitions in fractionated NOM, however, is not necessarily reflected in whole NOM, suggesting other potential influences in the thermal behavior of the whole NOM relative to fractionated NOM. Temperature-scanning X-ray diffraction studies of each NOM fraction confirmed the amorphous character of each sample through T_t.

Abbreviations: DSC, differential scanning calorimetry • GCH, Georgetown carbohydrate • GFA, Georgetown fulvic acid • GHA, Georgetown humic acid • HCH, Harpeth carbohydrate • HFA, Harpeth fulvic acid • HHA, Harpeth humic acid • HHU, Harpeth humin • NMR, nuclear magnetic resonance • NOM, natural organic matter • PMMA, poly(methyl methacrylate) • TMA, thermal mechanical analysis • TMDSC, temperature-modulated differential scanning calorimetry • XRD, X-ray diffraction

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