Glass transition and crystallite melting in natural organic matter

The presence Of (CH2)(n) crystalline components in lipid extracts from soil and peat was detected by solid-state NMR and X-ray diffraction. The lipid fractions were extracted from geosorbents including the IHSS Pahokee peat and leonardite, a second peat and its humic acid. The existence of two peaks in the 30-33 ppm NMR shift region demonstrates the presence of semicrystalline carbon in the lipid fraction, presumably in long aliphatic chains. X-ray diffraction patterns of the lipid fractions are similar to polyethylene, with the strongest reflections at 4.13 and 3.72 angstrom. The melting temperatures of the lipid fractions vary among the geosorbents and are in the same temperature interval with the glass transition reported in the literature for the IHSS peat and leonardite. After removing the fraction containing the crystalline components, the leonardite and Guanella Pass peat humic acid do not show any thermal events in their respective DSC thermograms. This finding suggests that, at least for the systems studied, the reported glass transition was actually the melting of the crystallites present in the lipid fraction. (c) 2005 Elsevier Ltd. All rights reserved.