Analytical Pyrolysis Techniques Research Articles

Plastics in Heritage Science: Analytical Pyrolysis Techniques Applied to Objects of Design.

The first synthetic polymers were introduced as constituents of everyday life, design objects, and artworks at the end of the 19th century. Since then, the history of design has been strictly connected with the 20th century evolution of plastic materials. Objects of design from the 20th century are today a precious part of the cultural heritage. They raise specific conservation issues due to the degradation processes affecting synthetic polymer-based plastics. Museums and collections dealing with the conservation of design objects and modern materials need to base their conservation strategies on compositional data that reveal the formulations of historical plastics and their decay processes. Specific and specifically optimized analytical tools are thus needed. We employed flash analytical pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS) and evolved gas analysis coupled with mass spectrometry (EGA-MS) to characterize “historic polymeric materials” (HIPOMS) and heritage plastics at the molecular level with high chemical detail. This approach complements non-invasive spectroscopic diagnosis whenever it fails to obtain significant or complete information on the nature and the state of preservation of the materials under study. We determined the composition of several 20th century design objects (1954–1994) from the Triennale Design Museum of Milan (Triennale Milano - Museo del Design Italiano), which for different morphological, chemical, or physical reasons were unsuitable for characterization by non-invasive spectroscopy. EGA-MS proved capable for the study of the different fractions constituting heterogeneous micro-samples and for gaining an insight into their degradation processes from the contextual interpretation of thermal and mass-spectrometric data.

Use of the Nitrogen/Carbon Ratio (N/C) and Two End-Member Sources Mixing Model to Identify the Origins of Dissolved Organic Matter from Soils in the Water-Level Fluctuation Zones of the Three Gorges Reservoir

Soil dissolved organic matter (soil DOM) plays a crucial role in the environmental fate of pollutants because of its exceptional biogeochemical reactivity. Therefore, tracing the sources and understanding the properties of DOM through chemical characterization is important for clarifying the "structure-reactivity" of DOM in the environment. In this study, traditional elementary analysis methods including nitrogen/carbon ratio (N/C) determinations and derived two end-member source-loads mixing models were applied to soil DOM extracted from the water-level fluctuation zones of the Three Gorges Reservoir (TGR) area. The results were further compared to other characterization techniques that operate on the molecular scale (e. g., FTIR and analytical pyrolysis techniques). The ultimate objective was to assess the performance of N/C ratio and two end-member modeling for identifying the DOM sources. Additionally, a photo-bleaching kinetic experiment was conducted to test the correlation between DOM reactivity and its source-loadings. Results showed, based on the N/C ratio and mixing modeling, all soil DOM samples in the TGR area share "dual-source" characteristics, namely, allochthonousness (e. g., terrestrial) and autochthonousness (e. g., internal) attributes, which is in agreement with other advanced characterization tools. The traditional method results were comprehensible in light of the data from molecular techniques, but the information revealed only reflects certain aspects of DOM compositional characteristics. It can be concluded that the N/C ratio and mixing modeling can validate general sources of soil DOM, but not information about specific components. Meanwhile, the significant correlation between the photo-bleaching kinetic constant and N/C and source-loadings indicated that these two parameters can be used as rapid indicators to estimate soil DOM reactivity in photochemical processes. However, it should be emphasized that it remains essential to employ multiple characterization methods to investigate the biogeochemistry of soil DOM, so as to increase the characterization resolution with regard to the heterogeneity of DOM.

Combined direct analysis in real-time mass spectrometry (DART-MS) with analytical pyrolysis for characterization of Chinese crude propolis

A combination of direct analysis in real-time mass spectrometry (DART-MS) with analytical pyrolysis comprising evolved gas analysis-mass spectrometry (EGA-MS) and heart-cut EGA-gas chromatography (GC)/MS was used for characterization of Chinese crude propolis samples. DART-MS allowed us to profile general whole chemical components in propolis including terpenoids, phenolic acids and esters, flavonoid aglycones, flavonoid glycosides, phenolic glycerides and hydrocarbons with their molecular weights in the range of 100 – 800. EGA-MS was used to investigate the thermal behaviors of main components observed by DART-MS. The results revealed three temperature zones for the releasing behaviors of main constituents: (1) vaporization of terpenoids within 120–160 °C, (2) vaporization of phenolic acids and flavonoid aglycones, and pyrolysis of some flavonoid glycosides and beeswax within 160–300 °C, (3) pyrolysis of some flavonoid glycosides, phenolic glycerides and beeswax within 300–550 °C. Based on extracted ion thermograms of flavonoids, it is clear that chrysin and tectochrysin existed only as aglycones, while pinocembrin, galangin, 2′, 6′-dihydroxy-4′-methoxychalcone and naringenin existed as both aglycones and glycosides. According to temperature zones, heart-cut EGA GC/MS data clearly indicated that 43 components were identified for 3 crude propolis samples collected from different origins, and grouped into 7 classes: alcohols/phenols, aldehydes/ketones, terpenoids, phenolic acids and esters, flavonoids, hydrocarbons and others. Among them, terpenoids, phenolic acids and esters, and flavonoids were main bioactive classes. Terpenoids accounted for 43.5–82.1 % in zone A, and flavonoids accounted for 3.7–23.9 % in zone B and 5.2–46.5 % in zone C, showing their different origins. In addition, flavonoid aglycones and their glycosides also could be semiquantitatively analyzed separately by analytical pyrolysis techniques used. Flavonoid aglycones accounted for a majority of total flavonoids with its proportions more than 52.6–66.7 % in propolis samples. All the obtained results demonstrate that the combination of these methods is effective for profiling all main components in Chinese crude propolis.

Structure\u2212property relationships of polypropylene-based nanocomposites obtained by dispersing mesoporous silica into hydroxyl-functionalized polypropylene. Part 2: Matrix\u2212filler interactions and pore filling of mesoporous silica characterized by evolved gas analysis

Nanocomposites containing mesoporous silica (MPS) materials with various pore structures (SBA-15 and MCM-41 types) melt mixed into polypropylene (PP) or PP functionalized with hydroxyl groups (PPOH) were characterized by analytical pyrolysis techniques, such as evolved gas analysis (EGA)-mass spectrometry (MS) and heart-cut EGA-gas chromatography (GC)/MS, to evaluate the interactions between the polymer matrix and MPS and the pore filling of the MPS in the nanocomposite. The EGA-MS measurements revealed that nanocomposites with MPSs evolve specific degradation products, which can be attributed to strong interactions between the polymer molecules and the internal pores. The amount of these specific products increased upon increasing the pore size of the MPS and the hydroxyl content in the polymer matrix. Sufficiently large pores of MPS and high hydroxyl contents in the matrix appear to provide strong interactions because the MPS pores are well-filled with polymer molecules, which contributes to the improved physical properties of the nanocomposites.

Non-isothermal pyrolysis properties of Laminaria japonica

The pyrolysis of Laminaria (L.) japonica was examined using non-isothermal analytical pyrolysis techniques, such as thermogravimetric (TG) and multi-shot pyrolyzer (Py)-gas chromatography/mass spectrometry (GC/MS) analysis. TG, derivative TG curves, and the apparent activation energy suggested that the decomposition of L. japonica has three thermal decomposition stages. The average mass spectra and multi-shot Py-GC/MS chromatograms obtained at each thermal decomposition stage confirmed the main decomposition reaction at each thermal zone. At the first stage, the decomposition of lipids and carbohydrates was initiated. The main decomposition of carbohydrates occurred at the second stage. At the final stage, proteins were decomposed and char intermediates were stabilized by supplying a higher temperature. A low activation energy at the second stage and the presence of metals in L. japonica suggests that during the non-isothermal pyrolysis of L. japonica, the catalytic effect is enhanced and involves the decomposition of carbohydrates.

Analytical pyrolysis of proteins in samples from artistic and archaeological objects

The paper presents a study of proteins found in artistic and archaeological objects based on analytical pyrolysis. Proteins (mainly egg yolk and/or egg white, casein, animal glue and collagen) have been extensively used as paint binders, adhesives and varnishes in mural and easel paintings, and they can be found in archaeological findings, such as bones and skin tissues. In order to overcome limitations of wet chemical methods arising from the reduced solubility of aged proteins in samples of cultural heritage, a combination of analytical pyrolysis techniques was used to characterise reference materials, paint reconstructions and samples from different historical periods (2nd century BC-20th century AD) and geographical origins, which were collected from paintings and archaeological findings. In particular evolved gas analysis mass spectrometry (EGA/MS), pyrolysis coupled with gas chromatography/mass spectrometry (Py/GC/MS) and double shot pyrolysis/gas chromatography/mass spectrometry (DSP/GC/MS) were used. This analytical approach allowed us to characterise and differentiate the proteinaceous media, investigate their thermal behaviour and evidence changes occurring with ageing. Data clearly indicate that egg, casein and animal glue can be identified and distinguished in a sample of unknown composition using each of the analytical pyrolysis techniques used. With time though differences tend to disappear to the extent that extremely degraded samples present pyrolytic profiles extremely similar to each other, irrespective of the nature of the proteins present. The data also indicate that proteins tend to become more thermally stable with ageing, suggesting that extensive intramolecular and intermolecular aggregation, and/or covalent cross-linking occur with time.

Structural elucidation of inhomogeneous lignins from bamboo

A better understanding of the inhomogeneous molecular structure of lignin from bamboo is a prerequisite for promoting the “biorefinery” technologies of the bamboo feedstock. A mild and successive method for fractionating native lignin from bamboo species was proposed in the present study. The molecular structure and structural inhomogeneity of the isolated lignin polymers were comprehensively investigated by elemental analysis, carbohydrate analysis, state-of-the-art NMR and analytical pyrolysis techniques (quantitative 13C NMR, 13C-DEPT 135 NMR, 2D-HSQC NMR, 31P NMR, and pyrolysis–GC–MS). The results showed that the proposed method is effective for extracting lignin from bamboo. NMR results showed that syringyl (S) was the predominant unit in bamboo lignin over guaiacyl (G) and p-hydroxyphenyl (H) units. In addition, the lignin was associated with p-coumarates and ferulates via ester and ether bonds, respectively. Moreover, various substructures, such as β-O-4, β-β, β-5, β-1, and α,β-diaryl ether linkages, were identified and quantified by NMR techniques. Based on the results obtained, a proposed schematic diagram of structural heterogeneity of the lignin polymers extracted from the bamboo is presented. In short, well-defined inhomogeneous structures of native lignin from bamboo will facilitate further applications of bamboo in current biorefineries.

Carbon nanotube-reinforced crosslinked polyethylene pipes for geothermal applications: From synthesis to decomposition using analytical pyrolysis–GC/MS and thermogravimetric analysis

Abstract Carbon nanotube reinforced crosslinked high density polyethylene (PEX) nanocomposites were synthesized for geothermal applications requiring higher polymer thermal conductivity and a comprehensive thermal decomposition study was performed. The prepared nanocomposites were investigated by laser flash analysis and temperature modulated differential scanning calorimetry revealing a great enhancement on the specific heat capacity along with a further enhancement on the thermal diffusivity, resulting in some cases in an overall thermal conductivity increase of more than 200%. For the thermal decomposition or recycling process of the produced nanocomposites, a thorough examination of the decomposition process and its kinetics was performed by using thermogravimetry and analytical pyrolysis–gas chromatography–mass spectroscopy. From this systematic study, two possible decomposition mechanisms for PEX were proposed for the first time in literature and the decomposition kinetics results, which were conducted using isoconversional and model-fitting methods, were in agreement with the proposed mechanisms. From the complementary use of analytical pyrolysis and thermal analysis techniques study it was revealed that the presence of carbon nanotubes hinders the diffusion of the primary scission products of PEX and enhances its thermal stability.

Diminishing hazardous air pollutant emissions from pyrolysis of furan no-bake binders using methanesulfonic acid as the binder catalyst

The formation of hazardous air pollutants (HAPs) in thermal decomposition of furan no-bake foundry binders was investigated using analytical pyrolysis techniques. Two furan binders cured with p-xylenesulfonic acid (conventional acid catalyst used in foundries) and methanesulfonic acid (alternative catalyst proposed for diminishing HAPs) were flash pyrolyzed in a Curie-point pyrolyzer at 920 °C and slowly pyrolyzed in a thermogravimetric analyzer from 50 to 800 °C with a heating rate of 20 °C min−1. Similar HAPs (mainly benzene, toluene, and xylenes) were identified in the emissions of the two binders. However, the HAP yields were much higher for the binder cured with p-xylenesulfonic acid than for the binder cured with methanesulfonic acid (3.74 and 1.24 mg HAPs/g binder pyrolyzed, respectively). By analyzing the HAP formation pathways, it was concluded that for the binder cured with p-xylenesulfonic acid, the aromatic HAPs were originated mainly from the acid catalyst. In addition, some HAPs (predominantly benzene) could be formed from the recombination of furan-derived fragments (e.g., C2–C4 radicals generated from ring-opening of furans). The results suggest that by replacing the conventionally used catalysts (arylsulfonic acids) with methanesulfonic acid, the HAP emissions from furan no-bake molds can be decreased significantly in metal casting processes.

Hydrothermal Treatment (HTT) of Microalgae: Detailed Molecular Characterization of HTT Oil in View of HTT Mechanism Elucidation

The understanding of the chemical nature of the oil is important for both the optimization of the process and the design of upgrading strategies for further use as an energy carrier or toward transportation fuels. Hydrothermal treatment (HTT) oil is a complex matrix, whose composition is strongly affected by the feedstock type and by the HTT experimental conditions. In the present work, HTT oil from Desmodesmus sp. was subjected to a detailed chemical analysis. Various characterization techniques (silica gel chromatography, methanolysis, size exclusion chromatography, analytical pyrolysis, elemental analysis, and thermogravimetric techniques) were coupled to gather clearer information on the chemical nature of HTT oil obtained at different reaction times, temperatures, and slurry concentrations. Special attention was paid to the fate of N in the HTT process and the nature of the N-containing species in the oil. By cross-checking results from the chemical characterization of the oil with process data, it was finally possible to identify some different competitive reactions involved in the formation of HTT oil at different conditions. Results show that main compounds obtained at low temperature are still classifiable as lipids, which are extractable without the HTT, together with some short chain algaenan and some hydrophobic protein fragments that end up in the organic solvent phase. At higher temperature (300–375 °C), proteins and cellulose started to break down, giving cyclic dipeptides and amino acids side chains (by pyrolysis-like reactions), carbohydrates derivatives (e.g., furans) and products from the cross reaction of proteins and carbohydrates (e.g., formation of alkyl-pyrrolidinones, pyrazines, pyrroles and melanoidin-like materials). This phenomenon is responsible for the observed increase in oil mass yield with increasing processing temperature, as well as the increase in nitrogen content of the oil. Optimization of the production of fuels and fuel precursors by HTT should be done in conjunction with evaluation of downstream processing options and/or the possibility to recycle unconverted material to the algae cultivation.

Development of a Simple Vent-free Interface for Capillary Gas Chromatography-Mass Spectrometry

A novel and simple interface for capillary gas chromatography-mass spectrometry (GC-MS) was developed using a piece of deactivated stainless-steel tubing. This interface eliminated the need to vent the MS ion source when changing columns. Various chromatographic performance indicators, such as inertness, and thermal and chemical stability, were confirmed to be unaffected by using this interface at an elevated temperature of around 300°C. The new interface should facilitate the characterization of polymeric materials using analytical pyrolysis techniques in which frequent switching is required in the measuring mode, such as evolved gas analysis-MS and flash pyrolysis-GC-MS.

Characterization of Hydrocarbon Emissions from Green Sand Foundry Core Binders by Analytical Pyrolysis

Analytical pyrolysis was conducted to study a relative comparison of the hydrocarbon and greenhouse gas emissions of three foundry sand binders as follows: (a) conventional phenolic urethane resin, (b) biodiesel phenolic urethane resin, and (c) collagen-based binder. These binders are used in the metal casting industry for making cores that are used to create internal cavities within castings. In this study, the core samples were flash pyrolyzed in a Curie-point pyrolyzer at 920 degrees C with a heating rate of about 3000 degrees C/sec. This simulated some key features of the fast heating conditions that the core binders would experience at the metal-core interface when molten metal is poured into green sand molds. The core samples were also pyrolyzed in a thermogravimetric analyzer (TGA) from ambient temperature to 1000 degrees C with a heating rate of 30 degrees C/min, and this simulated key features of the slow heating conditions that the core binders would experience at distances that are further away from the metal-core interface during casting cooling. Hydrocarbon emissions from flash pyrolysis were analyzed with a gas chromatography-flame ionization detector, while hydrocarbon and greenhouse gas (CO and CO2) emissions from TGA pyrolysis were monitored with mass spectrometry. The prominent hazardous air pollutant emissions during pyrolysis of the three binders were phenol, cresols, benzene, and toluene for the conventional phenolic urethane resin and biodiesel resin, and they were benzene and toluene for the collagen-based binder. It was also found that volatile organic compound and polycyclic aromatic hydrocarbon emissions considerably decreased in order from conventional phenolic urethane resin to biodiesel resin to collagen-based binder. These results have shown some similarity with those for stack emission testing conducted at demonstration scale and/or full-scale foundries, and the similar trends in the two sets of results offered promise that bench-scale analytical pyrolysis techniques could be a useful screening tool for the foundries to compare the relative emissions of alternative core binders and to choose proper materials in order to comply with air-emission regulations.

Organic Matter in Volcanic Ash Soils under Forest and Páramo along an Ecuadorian Altitudinal Transect

The volcanic ash soils along an altitudinal transect in Guandera Biological Station in northern Ecuador have been developed under varying vegetation around the upper forest line. Generally, the soils currently covered by forest are composed of Fulvic Andosols (melanic index >1.7) while those under páramo (tropical alpine grasslands) have developed into Melanic Andosols. This vegetation effect on soil formation is believed to be associated with differences in organic matter composition. In this study, we examined whether Fulvic Andosols differed from Melanic Andosols in organic matter composition. Using analytical pyrolysis techniques, we found hardly any differences in the organic matter characteristics related to vegetation cover, not even between soils that supposedly have been covered by forest and páramo for millennia. Small differences were found within the lipid compounds, while the polysaccharides and lignin were virtually absent from the (deeper) mineral soil horizons. The low abundance of polysaccharides in soils that have undergone severe organic matter decomposition is not unusual for most soils, but is uncommon in other Andosols studied with the same pyrolysis techniques.

Flame retardant mechanism of polydimethylsiloxane material containing platinum compound studied by analytical pyrolysis techniques and alkaline hydrolysis gas chromatography

The flame retardant mechanism for silicone rubber induced by adding ppm order of a platinum compound, platinum (0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex was studied by analytical pyrolysis techniques and alkaline hydrolysis gas chromatography. The thermal degradation measurement of the flame retardant silicone rubber sample (FR-SR) indicated that a considerable amount of methane was evolved from the FR-SR sample at around 400–800 °C while formations of cyclic siloxanes were fairly suppressed in comparison with that from the control SR sample. On the other hand, on the gas chromatogram of the hydrolysis products from the FR-SR residue samples thermally treated over 400 °C, significant amounts of characteristic products reflecting the cross-linking structures generating from methylene-bridge and trifunctional siloxane structures in the polymer chains were observed. These results suggest that the thermal decomposition of the FR-SR material is strongly suppressed by the formation of the cross-linking structures induced by the platinum compound during combustion, which leads to its flame retardancy.

Preferential accumulation of selectively preserved biomacromolecules in the humus fractions from a peat deposit as seen by analytical pyrolysis and spectroscopic techniques

A series of structural features of the three main humic fractions (humic acid, fulvic acid and humin) from different depths of a peat bog deposit in Mazagón (Huelva, Southern Spain) were isolated and analysed by flash pyrolysis–gas chromatography–mass spectrometry, solid-state 13C-nuclear magnetic resonance and Fourier transformed infrared spectroscopy. Such techniques demonstrate that the various humic fractions were very different not only in terms of molecular weight but also in their composition and structural characteristics, showing well differentiated patterns in the relative distribution of alkyl, O-alkyl and aromatic moieties in each humic fraction. To a large extent, selectively preserved lignin accumulates in the humic acid (HA) fraction, whereas the fulvic acid (FA) consists of a colloidal carbohydrate with a substantial peptidic moiety and the humin includes the noteworthy concentration of insoluble, macromolecular polyalkyl structures. A diagnostic lignin signature in the resolution-enhanced infrared spectra of the HA points to processes of selective preservation of macromolecular substances derived from vascular plants. In general, the humic fractions were not extensive sources of chemotaxonomic descriptors of previously documented biodiversity changes along the period of the peat deposit formation. This is in harmony with a substantial homogenising effect of diagenetic transformations throughout the whole sedimentary record with peat stratigraphy recording mostly the authigenic processes of bog formation and development. Anthropogenic perturbations may be also responsible for the loss of information in the humic proxy resulting in the lack of an apparent relationship between any particular input and the composition of the humic fractions from the peat bog.

Flame retarding mechanism of polycarbonate containing trifunctional phenylsilicone additive studied by analytical pyrolysis techniques

The flame retarding mechanism for polycarbonate (PC) by a trifunctional phenyl-rich silicone additive was studied by analytical pyrolysis techniques. In order to clarify the actions of the silicone-based flame retardant for PC substrate during combustion, the change in the chemical structure of the flame retarded PC with the silicone additive (FR-PC) after thermal treatment at 380 °C was investigated by pyrolysis-gas chromatography (Py-GC) in the presence of organic alkali. On the pyrogram of the thermally treated FR-PC, which exhibited highly insoluble nature, the peaks reflecting the abnormal structures, formed through the reaction between a silyl radical originating from the additive and an ether like oxygen atom in the carbonate linkage of the PC chain accompanied by decarboxylation or Fries rearrangement, were clearly observed in much larger intensity than those on the pyrogram of the thermally treated PC. On the basis of the observed results for the thermally treated FR-PC, it was suggested that the formation of a char barrier on the surface of the FR-PC material was promoted during combustion to reduce the radiant heat of flame and to restrict the diffusion of flammable degradation products into the combustion zone. Thus formed cross-linking structure might surpress the thermal decomposition and confine the movements of the degradation products.

Thermal Decomposition of Polymer Mixtures Containing Poly(vinyl chloride)

Thermal decomposition of a series of 1 : 1 mixtures of typical polymer waste materials [polyethylene (PE), poly(propylene) (PP), polystyrene (PS), polyacrylonitrile (PAN), polyisoprene, poly(methyl methacrylate) (PMMA), polyamide-6 (PA-6), polyamide-12 (PA-12), polyamide-6,6 (PA-6,6), and poly(1,4-phenylene terephthalamide) (Kevlar)] with poly(vinyl chloride) (PVC) was examined using thermal analysis and analytical pyrolysis techniques. It was found that the presence of polyamides and PAN promotes the dehydrochlorination of PVC, but PVC has no effect on the main decomposition temperature of polyamides. The hydrogen chloride evolution from PVC is not altered when other vinyl polymers or polyolefins are present. The thermal degradation of PAN is retarded significantly, whereas that of the other vinyl polymers is shifted to a slightly higher temperature in the presence of PVC. Among the pyrolysis products of PAN-PVC mixture methyl chloride was found in comparable amount to the other gaseous products at 500°C pyrolysis temperature.

Characterisation of a unique ‘asphalt’ sample from the early 19th century Hafkenscheid painting materials collection by analytical pyrolysis MS and GC/MS

Asphalt has been used since antiquity for various purposes and by painters since the 17th century. Asphalt as a pigment material with a known pre-19th century provenance is extremely rare. The analytical pyrolysis techniques of direct temperature-resolved mass spectrometry (DTMS) and pyrolysis gas liquid chromatography coupled with mass spectrometry (Py-GC/MS) were applied to characterise a unique ‘asphalt’ sample from a painting materials collection dating from the early 19th century. The provenance of this sample was investigated by comparison with a sample from a present day floating asphalt from the Dead Sea. DTMS demonstrated a complex envelope of ions from hydrocarbons ranging past m/z 1000 in both samples. Both samples showed evaporating sets of compounds as well as pyrolysing materials evolving from asphaltenes. Asphaltene network polymers were marked by aliphatic cross-links releasing alkenes and alkanes, and aromatic centres releasing alkylbenzenes, alkylnaphthalenes, alkylanthracenes, alkylphenanthrenes, and alkylbenzothiophenes. Hopanoid hydrocarbons and C-ring monoaromatic steroid hydrocarbons were among the biomarker compounds identified. Particularly striking were homologous series of alkylbenzothiophenes and alkyldibenzothiophenes with long hydrocarbon chains that could be traced with DTMS and confirmed by DTMS/MS. The results indicate that the early 19th century ‘asphalt’ sample from the Hafkenscheid collection is indeed a true asphalt that shows many similarities to the Dead Sea asphalt sample, which is therefore proposed as the possible region of provenance.

Factors limiting oxygen delignification of kraft pulp

Softwood kraft pulp was subjected to a laboratory one- and three-stage oxygen delignification process. Pulp and liquor samples were collected at different stages of the process with particular attention being paid to the early and late stages. A novel residual lignin isolation method extracted about 65% of the oxidized residual lignins at a purity exceeding 90%. Using this methodology coupled to quantitative31P NMR,13C NMR, 2D heteronuclear (HMQC) NMR spectroscopic and analytical pyrolysis techniques allowed a thorough characterization of the residual and solubilized lignin fractions at the various stages of the process. Our conclusions do not point to a single factor as being responsible for the limits confronting oxygen delignification. Amongst the major factors impeding the effectiveness of oxygen delignification are: (i) the accumulation of relatively inert 5,5' biphenyl structures originally present in kraft lignin from dibenzodioxocin ring opening reactions; and (ii) the accumulation of considerably less reactive p-hydroxyphenyl structures. Detailed quantitative information was obtained and discussed in relation to the presence and role of these unreactive phenolic fractions on the residual oxidized lignins. As such we arrived at important conclusions as to why and how these structures remain and accumulate on the fiber. In addition, issues related to the profiles of the total phenolic hydroxyl content of the residual lignins and the remaining arylglycerol β-O-4 structures are discussed.Key words: analytical pyrolysis, biphenyl structures, HMQC, NMR, oxidation mechanism, oxygen delignification, p-hydroxyphenyl moieties, quantitative13C NMR, quantitative31P NMR, residual lignin, solubilized lignin, total phenolic hydroxyls.

Characterization of functional polymers by temperature-programmed analytical pyrolysis techniques

Characterization of functional polymers by temperature-programmed analytical pyrolysis techniques