Advanced thermal characterization of fractionated natural organic matter

• Published in: Journal of environmental quality Vol. 34; no. 3; pp. 842 - 853
• Main Authors: DeLapp, R.C, LeBoeuf, E.J, Chen, J, Gu, B
• Format: Journal Article
• Language: English
• Published: Madison American Society of Agronomy, Crop Science Society of America, Soil Science Society 01.05.2005; Crop Science Society of America; American Society of Agronomy
• Subjects: Agronomy. Soil science and plant productions; Applied sciences; Biological and medical sciences; carbohydrate content; Chemical compounds; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Pollutants; Exact sciences and technology; fulvic acids; Fundamental and applied biological sciences. Psychology; glass transition temperature; humic acids; humin; Organic Chemicals; Pollutants; Pollution; Pollution, environment geology; Sediment transport; soil organic matter; soil temperature; soil transport processes; Thermodynamics; water content; X-Ray Diffraction; Tennessee; Differential scanning calorimetry; Organic matter; Thermal analysis; Thermodynamic properties; Trend analysis
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2004.0241

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 (alpha), 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 degrees C for a terrestrial carbohydrate fraction to 62 degrees 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(g) 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 beta and alpha 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(g).