Vinyl chloride formation from the thermal degradation of poly(vinyl chloride)

The volatile products from the thermal degradation of poly(vinyl chloride) (PVC) resins and compounds are shown to contain trace amounts of vinyl chloride. Data presented show the effect of temperature and resin type on the amount of vinyl chloride formed. At the maximum temperatures involved in PVC processing which may reach 210°C, vinyl chloride monomer (VCM) evolution amounts to less than 1 ppm (resin basis). A technique employing a thermogravimetric balance and charcoal adsorption of volatiles is described for studying thermal degradation of PVC. The volatiles are analyzed for vinyl chloride by gas chromatography. Peak identity was confirmed by mass spectrometry.     

Formation of headspace volatiles by thermal decomposition of oxidized fish oilsvs. oxidized vegetable oils

To understand the reasons for differences in oxidative stability among edible oils, the temperature dependence was investigated for the development of volatile lipid oxidation products in fish oils and in vegetable oils. A rapid headspace capillary gas chromatographic method was developed to determine volatile oxidation products of omega-6 (n-6) polyunsaturated fats (pentane and hexanal) and omega-3 (n-3) polyunsaturated fats (propanal) at different decomposition temperatures. Headspace gas chromatographic analyses of partially oxidized menhaden, bonita and sardine oils could be performed at 40°C, whereas soybean, canola, safflower, high-oleic sunflower and high-oleic safflower oils required temperatures greater than 100°C. Volatile formation by thermal decomposition of oxidized oils had lower apparent activation energies in fish oils than in vegetable oils, and significantly higher apparent activation energies in high-oleic oils than in polyunsaturated oils. The activation energy data on headspace volatiles provided another dimension toward a better understanding of the thermal stability of flavor precursors in unsaturated fish and vegetable oils. Presented at the ISF/AOCS joint meeting, Toronto, Canada, May 10–14, 1992.     

Vinyl chloride formation from the thermal degradation of poly(vinyl chloride)

The volatile products from the thermal degradation of poly(vinyl chloride) (PVC) resins and compounds are shown to contain trace amounts of vinyl chloride. Data presented show the effect of temperature and resin type on the amount of vinyl chloride formed. At the maximum temperatures involved in PVC processing which may reach 210°C., vinyl chloride monomer (VCM) evolution amounts to less than 1 ppm (resin basis). A technique employing a thermogravimetric balance and charcoal adsorption of volatiles is described for studying thermal degradation of PVC. The volatiles are analyzed for vinyl chloride by gas chromatography. Peak identity was confirmed by mass spectrometry.     

Dynamic headspace capillary gas chromatographic analysis of soybean oil volatiles

To develop new knowledge on preventing or eliminating the formation of undesirable flavors in soybean oil, we analyzed quantitatively the major volatile products in samples that were oxidized during storage in the dark at ambient conditions. The volatiles formed were recovered and separated by dynamic headspace capillary gas chromatography. The effect of sampling temperatures was investigated by heating the sample, sweeping the volatiles with helium and trapping and desorbing them from a porous polymer Tenax trap. The volatiles were flushed from the trap onto a fused silica capillary column with a bonded mixed dimethyldiphenyl siloxane phase. At peroxide values between 2 and 13, the major volatile products found were acrolein, pentene, pentane, 1-penten-3-ol, pentanal, hexanal, 2-hexenal, 2-heptenal, 2,4-heptadienal, 2-octenal and 2,4-decadienal. The profile of volatiles was significantly affected by the sampling temperature used and by the presence or absence of citric acid in the oils before storage. The relative amounts of volatile thermal decomposition products of linolenate and linoleate hydroperoxides, such as 2,4-heptadienal and 2,4-decadienal, increased significantly when samples were heated above 90 C. Dynamic headspace gas chromatography made it possible to analyze the volatiles in samples heated to 60 and 90 C. These volatiles may be representative of those present in oils at time of tasting.     

Effects of High-Temperature Drying on the Flavor Components in Thai Fragrant Rice

The effects of high-temperature drying on Thai Jasmine rice were investigated. Paddy was first rewetted and then dried using a two-stage drying process, involving a fluidized bed at high temperature, followed by shade drying (ambient air drying). Three high drying temperatures: 100, 125, and 150°C were studied. Volatile compounds were extracted by distillation and extraction in a Likens and Nickerson apparatus, and analyzed by gas chromatography-mass spectrometry. A total of 94 volatile compounds were identified. These included 21 alcohols, 19 aldehydes, 14 ketones, 12 acids, 9 heterocyclic compounds, 8 hydrocarbons, 5 esters, and 6 miscellaneous compounds. 2-Acetyl-1-pyrroline, a major constituent of volatiles in fragrant rice was identified and tended to increase in concentration with increasing drying temperature. The three different drying temperatures used in the fluidized bed dryer were found to have an effect on the volatile components of Thai Jasmine rice. The increase in drying temperature contributed to the formation of new compounds, as well as the loss of other desirable volatiles.     

Behavior of volatile depletion for LaRC™‐PETI‐5 amide acid/N‐methylpyrrolidinone solution

The fabrication of composites from polyimide precursors (polyamide acids) that involve condensation reactions requires the removal of volatiles (solvent and reaction by‐products) prior to consolidation in order to achieve a void‐free laminate. Volatile removal is commonly accomplished with a B‐stage processing step. In this study, a PETAA/NMP (p henyle thynyl t erminated a mide a cid in N‐methylpyrrolidinone) solution and prepreg were characterized using therogravimetric analysis (TGA) and microdielectrometry. A master weight loss profile was constructed by superimposing measurements at various heating rates. The TGA results correlated well with the dielectric ionic conductivities. Under the same thermal conditions, volatiles were depleted at slower rates from the wet prepreg than the neat resin solution. Dielectric properties were more sensitive to the residual volatile contents than the TGA measurements in both the neat resin and wet prepreg. Dielectric sensing technology was demonstrated to be a feasible tool for future volatile management in the fabrication of PETI composites. This study demonstrates that the combination of TGA and dielectrometry provides useful information to develop proper processing conditions for composite fabrication from prepregs containing volatiles. © Published 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1906–1916, 2003     

Phenols and Volatiles of Istarska Bjelica and Leccino Virgin Olive Oils Produced with Talc,NaCl and KCl as Processing Aids

The effect of processing aids (2.5 % of talc, NaCl or KCl) on oil extractability and the profile of phenolic and volatile compounds of Istarska bjelica and Leccino oils was studied. Talc significantly increased extractability in both cultivars, while salts increased extractability in Leccino cv. In the laboratory extracted oils, phenols were determined by a RP‐HPLC–DAD method, whereas volatiles were determined by SPME/GC–MS. Talc addition significantly decreased hydroxytyrosol and increased ligstroside derivatives in produced oils, but did not affect the total phenol content. Among volatile compounds, only Z‐2‐penten‐1‐ol in Leccino and 1‐pentene‐3‐one in Istarska bjelica oils significantly increased by talc addition. Salts improved transfer of most individual phenols into oil, particularly oleuropein derivatives, and increased C6 aldehydes and C5 volatiles in Leccino oils. NaCl exerted a stronger effect in increasing individual phenols and volatiles than KCl.     

Optimizing headspace sampling temperature and time for analysis of volatile oxidation products in fish oil

Headspace-gas chromatography (HS-GC), based on adsorption to Tenax GR®, thermal desorption and GC, has been used for analysis of volatiles in fish oil. To optimize sampling conditions, the effect of heating the fish oil at various temperatures and times was evaluated from anisidine values (AV) and HS-GC. AV indicated sample degradations at 90°C but only small alterations between 60 and 75°C. HS-GC showed increasing response with temperature and time. Purging at 75°C for 45 min was selected as the preferred sampling condition for oxidized fish oil.     

多喷嘴对置式气化炉内颗粒挥发分火焰可视化研究

基于实验室规模多喷嘴对置式水煤浆气化炉及其可视化装置,研究了气化炉喷嘴平面非射流区颗粒挥发分燃烧过程。结合图像处理技术,在气化条件下对粒径小于300 μm颗粒挥发分火焰尾迹形态及变化过程进行分析。研究结果表明,颗粒挥发分火焰非典型包络型火焰,而是形成挥发分火焰尾迹。颗粒挥发分尾迹形态受颗粒脱挥发分所处阶段和颗粒相对于气流的运动状态的影响,随时间不断变化。颗粒挥发分最大火焰尺寸随颗粒粒径增加而增加。气流床气化还原性气氛条件下颗粒挥发分燃烧时间较颗粒在富氧气氛中燃烧时间显著增加。     

Oilseed volatile analysis by supercritical fluid and thermal desorption methods

A knowledge of the volatile components present in an oil sample can provide important information relative to supercritical fluid extraction (SFE) process design, the current oxidative state of the oil, as well as the concentration and presence of important flavor volatiles in the oil. Volatile compounds from supercritical fluid-extracted oils were analyzed by headspace gas chromatography (GC) methods to determine if there were differences in the volatile profiles when two different methods of desorption were used. Canola, corn, soybean and sunflower seeds were extracted with supercritical carbon dioxide at 8000 psi and 50°C. Tenax porous polymer traps, attached at the exhaust port of the SFE apparatus, were utilized to collect the volatile components during the extractions. The volatile compounds on the Tenax trap were desorbed onto a GC column by both thermal and supercritical fluid techniques. Desorption temperature for the thermal method was 150°C, while conditions for the SFE technique were 50°C and 2000 psi. The lower-boiling volatiles from each oilseed were greater when desorbed by thermal means from the Tenax than by SFE; however, SFE desorbed the highermolecular weight compounds that were not removed by the thermal desorption method. Hexanal tended to be desorbed in comparable amounts by both methods. The SFE-based desorption technique provides a unique analysis method for the determination of both volatile and semivolatile compounds, as well as executing desorption under nonoxidative, low-temperature conditions that do not contribute to the degradation of lipid components.     

On the nonlinear behavior of Young's modulus of carbon‐bonded alumina at high temperatures

The origin of the nonlinear behavior of the Young's modulus (E) of carbon‐bonded alumina at high temperatures was addressed, based on the microstructural changes observed during processing and their thermo‐mechanical properties. Impulse excitation technique, thermogravimetric analysis, porosity measurement, and scanning electron microscopy were conducted in order to highlight and explain the E behavior. The finite element model of a virtual microstructure was simulated and the results attained are in good agreement with the experimental data. The tests revealed that the Young's modulus of a cured sample heated from room temperature up to 500°C was governed by the release of volatiles. Above this temperature, the thermal expansion mismatch among alumina, graphite, and the carbon matrix is dominant resulting in an increase in the effective Young's modulus. During cooling, crack networks and gaps between alumina particles and the carbon matrix were developed. The former were induced by volatile release and by the graphite's highly anisotropic thermal expansion. The latter was derived by the thermal expansion mismatch between the alumina and the carbon matrix. The closure of the gaps and cracks governed the expansion behavior during the second heating cycle and a nonlinear effective Young's modulus increase as a function of temperature was observed.     

Effect of α‐, γ‐, and δ‐tocopherol on the distribution of volatile secondary oxidation products in fish oil

The relative ability of α‐, γ‐ and δ‐tocopherol (TOH) to influence the distribution of volatile secondary oxidation products in fish oil was studied, with particular emphasis on oxidation products expected to be important for adverse flavour formation. Purified fish oil samples with 100 ppm or 1000 ppm of the different tocopherols were analysed by dynamic headspace analysis of the volatiles formed after 2, 5 and 8 d of storage at 30 �C. The tocopherol type and concentration affected not only the overall formation of volatile secondary oxidation products, but also the composition of this group of oxidation products. Principal component analysis of the data obtained suggested that high tocopherol hydrogen‐donating power, i.e. a high tocopherol concentration or the use of αTOH as opposed to γTOH or δTOH, directs the formation of hydrocarbons, unsaturated carbonyl compounds of relatively high molecular weight, as well as the formation of cis, trans isomers of unsaturated aldehydes. Although an active inhibitor of overall volatile formation, αTOH at a high concentration thus appears to direct the formation of the more flavour‐potent aldehydes, such as those linking the carbonyl group with ethylenic conjugated unsaturation.     

Comparison of two methods for extraction of volatiles from marine PL emulsions

The dynamic headspace (DHS) thermal desorption principle using Tenax GR tube, as well as the solid phase micro‐extraction (SPME) tool with carboxen/polydimethylsiloxane 50/30 µm CAR/PDMS SPME fiber, both coupled to GC/MS were implemented for the isolation and identification of both lipid and Strecker derived volatiles in marine phospholipids (PL) emulsions. Comparison of volatile extraction efficiency was made between the methods. For marine PL emulsions with a highly complex composition of volatiles headspace, a fiber saturation problem was encountered when using CAR/PDMS‐SPME for volatiles analysis. However, the CAR/PDMS‐SPME technique was efficient for lipid oxidation analysis in emulsions of less complex headspace. The SPME method extracted volatiles of lower molecular weights more efficient than the DHS method. On the other hand, DHS Tenax GR appeared to be more efficient in extracting volatiles of higher molecular weights and it provided a broader volatile spectrum for marine PL emulsion than the CAR/PDMS‐SPME method.     

Volatile Profiles of Rapeseed Oil Flavored with Basil,Oregano, and Thyme as a Function of Flavoring Conditions

The flavoring of oils with herbs gives a specific taste and aroma to the oils and may increase their antimicrobial and antioxidant activity. The volatile aroma compounds in flavored rapeseed oil were studied as a function of flavoring conditions, by means of headspace solid-phase microextraction (SPME) followed by gas chromatography-mass spectrometry (GC-MS) analysis. Rapeseed oils were flavored with dried basil, oregano, and thyme at two different concentrations (3 and 6%) and were heated at different temperatures and for various time intervals, followed by filtration. In the headspace of flavored oils, the main volatiles of the dried herbs were detected. In general, the share of monoterpenes in the headspace of flavored oil was higher than in the original dried herbs, while sesquiterpenes and phenolic compounds were detected to a considerably lower extent in the oil than in the herbs. The concentrations of the volatiles detected in the oil increased with increasing heating time and temperature.     

The kinetics of combustion of coal volatiles

The thermal explosion theory of volatile matter evolved from a coal particle has been adopted to evaluate the activation energy of the combustion of volatiles. The apparent global activation energies calculated from the experimental ignition of three bituminous coal types were in the range 60–70 kJ mol⁻¹. By analogy with rapid coal pyrolysis this suggests that a sequence scheme reaction describing the oxidation of volatiles can be approximated by a global single-step process having a lower activation energy than the combination of any single volatile matter flame component.     

A Versatile Method for On-Line Analysis of Volatile Compounds from Living Samples

A system especially designed for the on-line analysis of volatiles emitted by living aerobic organisms is described. The instrument consists of a modified thermal desorber and utilizes the purge and cold trap (PCT) technique coupled with gas chromatography–mass spectrometry. The system enables the use of a variety of sample vessels especially adapted to individual test organisms. Quantitative analyses of some volatile semiochemicals revealed that when only nanogram amounts of these compounds are evaporated at room temperature for a period of 10 min, they may be trapped and detected by this device. Emission of volatiles from two insect species and a plant species have been studied in detail by using this system.     

Comparison of solvent systems on extraction,quality characteristics,and volatile compounds of palm kernel oil

Hexane (HEX) and dichloromethane (DCM) have been used to extract oils from various sources due to their expansive solubility and low volatility that ease removal at low temperatures. However, environmental and health concerns make them undesirable solvents. The aim of this study was to evaluate the extraction efficiency and physicochemical characteristics of palm kernel oil (PKO) extracted with the addition of acetone in HEX-acetone (1:1, vol/vol) and DCM-acetone (1:1, vol/vol) mixtures as an alternative to DCM and HEX alone. PKO extracted with co-solvent systems had better quality characteristics compared with single solvent extracts. The oil recovered, free fatty acid content, peroxide value and other quality characteristics, and thermal properties were within the range for PKO, and similar oils as stipulated in standards. Monounsaturated fatty acid content in PKO was up to 70% of which lauric acid was the most abundant (48%–52%). A total of 50 volatile compounds were identified by GC–MS in all the extracts including amide (1), alcohol (1), aldehydes (2), ketones (3), acids (6), esters (6) and hydrocarbons (31) with higher numbers of volatiles in the HEX extracts compared to the DCM extracts. Dodecanoic acid, hexanal, and 2-undecanone were the most abundant acid, aldehyde, and ketone, respectively. Principal component analysis (PCA) differentiated the volatiles identified on the polar and non-polar columns with 88.2% and 8.8%, and 67.3% and 19.6% of the variation accounted for by PC1 and PC2, respectively, with several common volatile components forming a cluster from all the solvents used.     

Vinyl ester resin modified with silicone‐based additives: II. Flammability properties

Silicone‐based additives have been used as fire retardants for thermoplastics, presenting the advantages of improving processing and impact resistance of the polymers. In this work we used three different silicone‐based additives as modifiers of a thermoset based on a vinyl ester resin. The additives are fine powders made up of about 50 wt % ultra high molecular weight polydimethylsiloxane and 50 wt % silica. The differences between them are the functional groups inserted on the additives and the size and size distribution of the particles. The additives were dispersed in resin containing 35 wt % of styrene. For curing the mixture a conventional catalyst and initiator were used and the reaction was carried out in two ways, differing in the curing temperature, the post curing temperature, and the time, and in the addition of dimethylaniline (DMA) as a promoter of the polyaddition reaction. The samples were characterized by thermogravimetric analyses and swelling experiments. The fire retardances of the samples were evaluated by the determination of the flash‐ignition, self‐ignition, and pyrolysis temperatures (ASTM D1919–91a), and of the oxygen index (ASTM D‐2863–91). The results obtained showed that the silicone‐based additives and the methods used in the preparation of the modified resin influence the flash‐ignition, self‐ignition, and pyrolysis temperatures, but not the oxygen index. Samples cured by different methods present different network characteristics, which influence their thermal decomposition. The volatile species produced by thermal decomposition may be a combination of inert and active species. The network structure may influence only the inert fraction of the volatiles, not the combustibles. These volatile inert species (smoke‐black, water vapor, carbon dioxide, etc.) probably dilute the combustibles in the solid and in the gaseous phase, increasing the flash‐ignition temperature of the samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 644–649, 2006     

Rapid devolatilization and hydrogasification of bituminous coal

Rapid devolatilization and hydrogasification of a Pittsburgh Seam bituminous coal were studied and an appropriate coal conversion (weight loss) model was developed that accounts for thermal decomposition of the coal, secondary char-forming reactions of volatiles, and homogeneous and heterogeneous reactions involving hydrogen. Approximately monolayer samples of coal particles supported on wire mesh heating elements were electrically heated in hydrogen, helium, and mixtures thereof. Coal weight loss (volatiles yield) was measured as a function of residence time (0–20 s), heating rate (65–10000 °C/s), final temperature (400–1100 °C), total pressure (0.0001–7 MPa), hydrogen partial pressure (0–7 MPa), and particle size (70–1000 μm). Volatiles yield under these conditions increases significantly with decreasing pressure, decreasing particle size, increasing hydrogen partial pressure and increasing final temperature, but only slightly with increasing heating rate. The data support the view that coal conversion under these conditions involves numerous parallel thermal decomposition reactions forming primary volatiles and initiating a sequence of secondary reactions leading to char. Intermediates in this char-forming sequence can escape as tar if residence time in the presence of hot coal surfaces is sufficiently short (e.g. low pressures and small particles well dispersed). Hydrogen at sufficiently high partial pressure can interrupt the char-forming sequence thereby increasing volatile yield. Rate of total product generation is largely controlled by coal pyrolysis while competition between mass transfer, secondary reactions, and rapid hydrogenation affects only the relative proportions of volatile and solid products formed.     

Effect of cultivation area and climatic conditions on volatiles of virgin olive oil

To elucidate the influence of the cultivation area and climatic conditions on volatiles of virgin olive oil from Gemlik cultivar, an investigation was carried out. Five Turkish geographical zones (Bal?kesir, Ayd?n, Manisa, Antalya and Hatay) were chosen. From these areas, fruits were collected at the same maturity stage and processed using a small experimental olive oil mill, applying identical processing conditions for all olive samples. Headspace solid‐phase microextraction (HS‐SPME) technique coupled to GC/MS was used for volatile analysis. Twenty‐seven compounds were identified and characterised, representing 96.40–98.74% of the total GC area. The major volatile representing about 50% was the (E)‐2‐hexenal. This compound was found in higher concentrations on olive oils from Antalya than from Hatay area. Hexanal was the second most abundant volatile compound and varied between 13.89 and 28.96%. Comparing the olive growing areas Hatay and Antalya, the hexanal concentration was about 29 and 14%, respectively. Generally, a significant difference in the composition of volatile compounds between the oils from the same olive cultivar and from different geographic regions was recorded. The results suggest that climatic factors, latitude and longitude affect the formation of volatiles.