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Purpose: Data management strategies of pyrolysis results and NMR acquisition modes were examined in humic acids (HAs) from control soils and fire-affected soils. The information supplied by dipolar dephasing (DD) 13C NMR spectroscopy and Curie-point pyrolysis were used to assess chemical structures hardly recognizable and measurable, or of unclear interpretation, when using 13C NMR under standard acquisition pulses (cross-polarization/magic angle spinning, CPMAS).Materials and methods: The HAs were isolated from two forest soils under Pinus halepensis and Pinus sylvestris in control and burned sites affected by medium or severe-intensity wildfires. For NMR analyses, during DD acquisition conditions, a 180° 13C pulse was inserted to minimize phase shifts. Curie-Point pyrolysis was carried out at 510 °C for 5 s, and the pyrolysis fragments were analyzed by GC/MS. The total abundances of the major pyrolysis products were compared by an update of the classical Van Krevelen’s graphical-statistical approach, i.e., as surface density values in the space defined by the compound-specific H/C and O/C atomic ratios.Results and discussion: The DD 13C NMR experiments displayed significant differences in the HA spectral profiles as regards to the standard CPMAS 13C NMR acquisition conditions, mainly in the chemical shift region of alkyl structures as well as for tannin- or carbohydrate-like O-alkyl structures. In fact, the comparison between DD and CPMAS solid-state NMR suggested shortening of alkyl chains and generation of carbohydrate-derived, unsaturated structures—viz. furans—which adds to the aromatic domain. Pyrolytic results showed fire-induced specific changes in HAs chemical structure and its molecular diversity. The changes were evident in the location and sizes of the different clusters of pyrolysis compounds defined by their atomic ratios.Conclusions: The DD 13C NMR provided specific information on the fate of aliphatic structures and the origin of unsaturated HA structures, which could be helpful in differentiating “inherited” from “pyrogenic” aromatic structures. This is further confirmed by the analysis of the molecular assemblages of pyrolytic products, which showed accumulation of condensed polyaromatic domains in the HAs after the high-intensity fire, accompanied by a recalcitrant alkyl hydrocarbon domain. Medium-intensity fire led to aromaticity increase due to a selective accumulation of lignin-derived phenols concomitant to the depletion of aliphatic hydrocarbon constituents. [ABSTRACT FROM AUTHOR]

BACKGROUND Environmental, economic and safety challenges motivate shift towards safer materials for food packaging. New bioactive packaging techniques, i.e. addition of essential plant oils ( EOs), are gaining attention by creating barriers to protect products from spoilage. Analytical pyrolysis gas chromatography-mass spectrometry (Py- GC-MS) was used to fingerprint a bioactive polylactic acid ( PLA) with polybutylene succinate ( PBS) (950 g kg−1:50 g kg−1) film extruded with variable quantities (0, 20, 50 and 100 g kg−1) of Origanum vulgare EO. RESULTS Main PLA: PBS pyrolysis products were lactide enantiomers and monomer units from the major PLA fraction and succinic acid anhydride from the PBS fraction. Oregano EO pyrolysis released cymene, terpinene and thymol/carvacrol peaks as diagnostic peaks for EO. In fact, linear correlation coefficients better than 0.950 R2 value ( P < 0.001) were found between the chromatographic area of the diagnostic peaks and the amount of oregano EO in the bioplastic. CONCLUSION The pyrolytic behaviour of a bio-based active package polymer including EO is studied in detail. Identified diagnostic compounds provide a tool to monitor the quantity of EO incorporated into the PLA:PBS polymeric matrix. Analytical pyrolysis is proposed as a rapid technique for the identification and quantification of additives within bio-based plastic matrices. © 2015 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The relationship between soil organic matter (SOM) content and organic molecular assemblages ( n-alkane/alkenes pairs and n-fatty acids) with soil water repellency (WR) in different sieve fractions (1-2, 0·25-1, 0·05-0·5 and <0·05 mm) was studied in sandy soils from the Doñana National Park (SW Spain) under four vegetation species: Quercus suber (QS), Pteridium aquilinum (PA), Pinus pinea (PP) and Halimium halimifolium (HH). The severity of soil WR [assessed according to the water drop penetration time (WDPT) test] was ordered according to the sequence QS > PA > PP > HH. A positive correlation was found between soil WR from each sieve fraction and SOM content. Most severe soil WR was detected in QS for all sieve fractions, followed by the finer fractions (<0·05 mm) from PA, PP and HH samples. The finer fraction had the highest SOM content, ranging between 20·9% (PP) and 46·9% (QS). Coarser PA, PP and HH soil fractions (1-2 mm) showed the highest long-chain-even C numbered fatty acids in the order PP > PA > HH. A significant correlation was observed between SOM content and the severity of soil WR in QS samples and finer fractions of soil under other vegetation (PA, PP and HH). Coarser fractions (1-2 mm) from PP, PA and HH 1-2 mm sieve fractions showed high severity of WR and relatively low SOM contents that could be explained by a low degree of evolution of the organic residues as seen by analytical pyrolysis, that is, higher alkane/alkene carbon preference index values and the presence of a higher diversity of fatty acid structures. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]