Glass Transition Behavior in a Peat Humic Acid and an Aquatic Fulvic Acid

Abstract

This paper presents the results of a thermal investigation of the physical and chemical properties constituting the macromolecular structure of natural organic matter (NOM). It presents new evidence of glass transition phenomena in a peat humic acid and a stream-derived fulvic acid as identified through use of temperature-modulated differential scanning calorimetry (TMDSC) and thermal mechanical analysis (TMA). Identification of glass transition temperatures (Tgs) in both soil- and stream-derived humic materials suggests a general macromolecular structure for humic and fulvic materials in NOM. Quantified Tgs are found to be related to their elemental and chemical functional group composition, where a more aromatic peat humic acid possesses higher glass transition temperatures than Suwannee River fulvic acid. Theory of glass transition behavior is used as a backdrop to explore the potential use of thermal analysis techniques for quantifying other thermodynamic parameters of NOM, including specific heat capacity, compressibility, and thermal expansion coefficient. Use of this information is then discussed in terms of its application to developing and verifying molecular simulation modeling of NOM structures.