Formation of α-Tocopherolquinone and α-Tocopherolquinone Epoxides in Plant Oil

The antioxidative activity of α-tocopherol in oil is necessary for the inhibition of lipid peroxidation. If no regeneration of antioxidants is possible in foods, oxidation products are formed to a measurable extent. The aim of this study was to investigate oxidation products of α-tocopherol in plant oil. The oxidation of α-tocopherol in plant oil leads to α-tocopherolquinone and to two epoxides (α-tocopherolquinone-2,3-epoxide, α-tocopherolquinone-5,6-epoxide). These three reaction products were identified and quantified in plant oil. The 2,3-epoxide is formed at lower temperatures (90°C) whereas at high temperatures (180–220°C) only the 5,6-epoxide appears. The kinetics show that the 5,6-epoxide is produced as long as α-tocopherol is present. With longer reaction times the concentration of the 5,6-epoxide starts to decrease. α-Tocopherolquinone is found at substantially lower concentrations.     

Thermal oxidation of polypropylene in the temperature range of 120–280°c

Thermal oxidation of isotactic polypropylene films at 120–280°C in air was studied. Separation and identification of the volatiles formed was carried out by gas chromatography–mass spectrometry. Sixteen products were tentatively identified for the first time. Altogether, 50 compounds representing hydrocarbons, ethers, alcohols, aldehydes, ketones, and acids are reported. Oxygen deficiency is manifested in diffusion-limited products of olefines, dienes, and aromatic compounds. The relative amounts of acetaldehyde and acetone are almost temperature independent in the range of 120–280°C. This indicates a similarity of oxidative degradation of the polymer in a broad temperature range. Addition of an antioxidant to the polymer depresses the evolution of the main volatiles by 9–10 times at 280°C. The relative amounts of the volatiles formed are, nevertheless, the same as for the polymer without an antioxidant. The mechanism of formation of the degradation products is discussed.     

Thermal degradation of polypropylene in a capillary rheometer

Melt viscosity of a polypropylene (PP) resin was measured in a capillary rheometer between 220 and 260°C. The melt viscosity showed a power law behavior with strong shear rate dependence. The effects of temperature and shear rate on the degradation were studied in the rheometer by heating at 260 and 280°C, and extruding at shear rates up to 10000 sec ?1 . Melt flow index (MFI) of samples after shearing and heating treatment was measured to characterize the molecular weight change. An increase in MFI was found for PP sheared at high temperature. Heating for longer time also increased MFI. Increase of shear rate had a small effect on increasing MFI at 260°C but produced a larger effect at 280°C. A constant increment in MFI was observed in PP subjected to high temperature processing and was attributed to degradation due to oxygenated products.     

Lipid Oxidation and Degradation Products in Raw Materials: Low‐Fat Topical Skin‐Care Formulations

Topical skin formulations with a lipid content below 15% were stored for 6 months at 5, 20, or 40 °C or for 2 weeks at 50 °C in darkness or at 20 °C with exposure to light for 6 months. The volatile lipid‐oxidation compounds formed during this storage period were compared to those formed in the raw materials during 3 months of accelerated stability storage at 40 °C. The volatile compounds were collected by dynamic headspace and analyzed using gas chromatography–mass spectrometry. It was possible to link eight out of nine volatile compounds detected during storage of topical skin formulations to the raw materials. In addition, a possible link between the appearance of butane nitrile and the decomposition of an initiator used for polyacrylate crosspolymer‐6 production was observed. The polymer may originate from texture modifiers added to the topical skin formulation or from plastics used for packaging of topical skin formulations. Furthermore, six well‐known lipid‐oxidation and nonenzymatic browning products were suggested to originate from the two raw materials, tricaprylin/tricaprin and coconut oil.     

Thermal degradation of EVA and EBA—A comparison. I. Volatile decomposition products

This is the first in a series of papers in which structural changes during thermal degradation of ethylene-vinyl acetate (EVA) and ethylene-butyl acrylate (EBA) copolymers are compared. EVA, containing 11.4 mol% vinyl acetate (VA) and EBA, containing 5.4 mol% butyl acrylate (BA), were pyrolyzed at 280°C in nitrogen for 30 min. In another series of pyrolysis, EVA containing 1.2, 2.2, and 11.4 mol% VA were treated at 150–190°C for 3 h. The volatile decomposition products were collected in cooled traps respectively gas bags and then analysed with GC-MS and ion-chromatography. EVA is rather labile. The main volatile decomposition product is acetic acid. A linear decomposition rate was found already at the lowest investigated pyrolysis temperature, 150°C. After 30 min at 280°C every 15th of the acetate side groups had been eliminated. EBA is much more stable to pyrolysis. Thirty minutes at 280°C resulted in a decomposition of one out of 1500 BA groups. Butene is the main volatile decomposition product. Ester pyrolysis is supposed to account for the degradation of both types of polymers. The big difference in reactivity is presumably due to conformational differences. The ester pyrolysis mechanism will result in random unsaturations in EVA and carboxylic groups in EBA. To a minor extent acetaldehyde is formed when EVA is degraded. According to the mechanisms suggested, carbonyl groups remain in the main chain. Contrary to what is reported for poly(butyl acrylate), no alcohol was formed when pyrolysing EBA. This indicates that adjacent acrylate groups are needed for alcohol formation. For both types of polymer, scissions of the main chain results in hydrocarbon fragments mainly. In addition, acrylate containing fragments are observed when EBA is degraded. EVA, however, does not give any acetate-containing fragments.     

Thermal oxidative degradation of poly(4-methyl-1-pentene). I. Identification of products and mechanisms

Isotactic and atactic poly(4-methyl-1-pentene) powders were degraded in the presence of pure oxygen at temperatures of 145° and 175°C. The functional groups present in the nonvolatile products were identified using infrared spectroscopy. The volatile products that formed were identified by means of a relativly new technique which combines gas chromatography and mass spectroscopy. In this study, seventeen volatile products were detected and identified and their relative abundance estimated. The results obtained could readily be reproduced. Various oxidation mechanisms for these products are postulated.     

Temperature‐dependent pyrolytic product evolution profile for polypropylene

The composition of the pyrolysis products of plastics depends on disintegration of the macromolecule into variety of hydrocarbon fractions. In this work, a detailed gas chromatographic study of pyrolysis products of polypropylene (PP) between 200 and 600°C was carried out. The pyrograms have been analyzed in terms of amount of different products evolved at various pyrolysis temperatures. At low pyrolysis temperatures (200–300°C), the yield of lighter hydrocarbons (C5‐C10) is low; it gradually increases until maximum decomposition temperature (446°C) and decreases thereafter. The following reaction types were considered to explain the decomposition mechanism of PP: (a) main chain cleavage to form chain‐ terminus radicals; (b) intramolecular hydrogen transfer to generate internal radicals; (c) intermolecular hydrogen transfer to form both volatile products and radicals; and (d) β‐scission to form both volatiles and terminally unsaturated polymer chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermal oxidation of poly(1-pentene): 1. Indentification of products and mechanisms

Isotactic poly(1-pentene) was degraded in the presence of pure oxygen at 115°C. The functional groups present in the non-volatile products were identified using infra-red spectroscopy. The volatile products formed were identified by means of a relatively new technique which combines thermal and mass chromatography. In this study, fourteen volatile products were detected and identified and their relative abundance estimated. The results obtained could readily be reproduced. Various oxidation mechanisms for these products are postulated.     

The catalytic decomposition of 4-phenyl-1,3-dioxan on copper-based catalysts

Transformations of 4-phenyl-1,3-dioxan on copper-based catalysts were investigated in an integral flow reactor in the gas phase in the temperature range 220–280°C. The main products of splitting were 3-phenylpropanal, 3-phenylpropan-1-ol and allylbenzene, and in some cases, styrene. Suitable reaction conditions were sought for the preparation of 3-phenylpropanal and allylbenzene from 4-phenyl-1,3-dioxan.     

Thermal degradation of long‐chain polyunsaturated fatty acids during deodorization of fish oil

Long‐chain polyunsaturated fatty acids (LC‐PUFA) of the n‐3 series, particularly eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid, have specific activities especially in the functionality of the central nervous system. Due to the occurrence of numerous methylene‐interrupted ethylenic double bonds, these fatty acids are very sensitive to air (oxygen) and temperature. Non‐volatile degradation products, which include polymers, cyclic fatty acid monomers (CFAM) and geometrical isomers of EPA and DHA, were evaluated in fish oil samples obtained by deodorization under vacuum of semi‐refined fish oil at 180, 220 and 250 °C. Polymers are the major degradation products generated at high deodorization temperatures, with 19.5% oligomers being formed in oil deodorized at 250 °C. A significant amount of CFAM was produced during deodorization at temperatures above or equal to 220 °C. In fact, 23.9 and 66.3 mg/g of C20 and C22 CFAM were found in samples deodorized at 220 and 250 °C, respectively. Only minor changes were observed in the EPA and DHA trans isomer content and composition after deodorization at 180 °C. At this temperature, the formation of polar compounds and CFAM was also low. However, the oil deodorized at 220 and 250 °C contained 4.2% and 7.6% geometrical isomers, respectively. Even after a deodorization at 250 °C, the majority of geometrical isomers were mono‐ and di‐trans. These results indicate that deodorization of fish oils should be conducted at a maximal temperature of 180 °C. This temperature seems to be lower than the activation energy required for polymerization (intra and inter) and geometrical isomerization.     

Volatile compounds extracted from polypropylene sheets by hot water: Influence of the temperature of sheets injection

The influence of the formulation of polypropylene (PP) on the organoleptic properties of the foodstuff in contact is of great importance for the quality of the product. A study was made on PP pellets degraded and not degraded and pointed out the presence and olfactive importance of volatile components extracted from PP pellets by hot water. Plastic packaging materials correspond to a further step of manufacturing: the injection step, and this is often conducted at high temperature. PP (not degraded) and PP-CR (degraded) were transformed into sheets at several temperatures; Lickens–Nickerson extracts were made and allowed the quantification of volatile compounds already identified. A statistical analysis showed that temperature was a very significant parameter. An increasing injection temperature (275 or 300°C) creates increasing quantities of volatiles. This was well correlated with the sensory analysis made on the organic extracts of the sheets and also directly on molded cups. © 1993 John Wiley & Sons, Inc.     

Kinetics of vapour phase oxidation of furfural on vanadium catalyst

Vapour phase oxidation of furfural over vanadium pentoxide catalyst was studied using an isothermal flow reactor in the temperature range of 220–280°C. Maleic anhydride and carbon dioxide are found to be formed from furfural by a parallel reaction scheme. The following rate equation based on the two-stage redox mechanism—the substance to be oxidized reduces the catalyst which in turn is reoxidized by oxygen from the feed—is found to explain the data satisfactorily.

The reoxidation of the reduced catalyst was found to be the rate controlling step.     

Oxidation of polypropylene in a solution of monochlorobenzene

The oxidation of polypropylene (PP) was performed in a solution of monochlorobenzene using tetrabutyl ammonium permanganate either in the presence or absence of purified air and dodecanol‐1. The experiments were conducted under atmospheric pressure at 128–130°C. The oxidized PP was found to contain polar groups such as carboxylates, carboxylic acids, ketones, esters, etc. as determined by Fourier transform infrared, ultraviolet, nuclear magnetic resonance, and electron spectroscopy for chemical analysis. The presence of the MnO₂ formed upon the decomposition of tetrabutyl ammonium permanganate was determined by electron spectroscopy for chemical analysis. The dodecanol‐1 was used as an accelerator for the oxidation reaction of PP in presence of air. Solubility trials of oxidized PP in toluene and methyl ethyl ketone were performed. A reaction mechanism is proposed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3417–3424, 1999     

Oxidation behavior of 3D SiCf/SiBCN composites at 800–1200 °C

3D SiC_f/BN–SiC/SiBCN composites were fabricated via precursor impregnation and polymer infiltration pyrolysis (PIP). Oxidation behavior of the composites heated in air at 800 °C, 1000 °C and 1200 °C for 50 h was investigated. Following the oxidation treatment, it was found that the bending strength of the composites at different oxidation temperatures was degraded. The weight loss of the composites decreased gradually over the range of oxidation times of 1–50 h. In order to clarify the oxidation mechanism of the composites, reconstructed images, microstructures, phase compositions, the oxide layer formed on the composites and main chemical reactions were all analyzed. It was revealed that the degradation in the fracture strength of the composites was closely related to the oxidation of SiBCN matrix and BN-SiC interphase, whereas there was no signs of oxidation products about SiC fiber, which indicated that SiC fiber could be protected from oxygen by SiBCN matrix at 800?1200 °C in air.     

Products Formed During Thermo-oxidative Degradation of Phytosterols

Oxidative degradation of cholesterol has been extensively researched, however, not all products formed have been established. When a phytosterols standard was heated at 60, 120 and 180 °C for different period of time the following groups of components were detected: oxidized phytosterols, fragmented phytosterol molecules, volatile compounds and oligomers. Taking into account all the components formed, we were able to balance the amounts of disappearing sterols with components formed. We established that the amount and type of products formed during thermo-oxidative degradation is affected by temperature and time. The amount of intact phytosterols decreased when temperature and time increase. The amount of oxidized phytosterols was at the highest level when a temperature of 120 °C was applied, whereas the lowest amounts were observed when a temperature of 60 °C was used. At a temperature of 180 °C the amount of oxidized sterols was lower than at 120 °C and it decreased when the heating time was increased. This indicates that oxidized sterols were the main precursors involved in the formation of other components during thermo-oxidative degradation. The amount and type of volatile compounds formed increased when time and temperature increased. We observed diversified groups of volatile compounds formed and most of them are defined as off-flavor compounds for rancid oils.     

海藻酸钠的热分解研究

用热重法 ( TG)和差示扫描量热法 ( DSC)并结合 IR详细研究了海藻酸钠的热分解过程。研究表明 ,海藻酸钠的热分解共分四步 :60～ 170°C之间海藻酸钠脱去内部结合水 ;2 2 0～ 2 80°C之间海藻酸钠裂解为中间产物 ;3 0 0～ 3 70°C之间中间产物进一步裂解并部分碳化 ;5 60°C左右最终氧化生成 Na2 O。并用三步判别法对人们较感兴趣的第二步反应的机理和动力学进行了研究。     

Formation and decomposition of stigmasterol hydroperoxides and secondary oxidation products during thermo‐oxidation

The oxidation mechanisms of stigmasterol at 100 and 180 °C were investigated by using the HPLC‐UV‐FL method. An overall picture of the oxidation status was achieved with a single HPLC analysis, enabling us to monitor the formation and decomposition of both primary and secondary oxidation products. The oxidation behavior of stigmasterol was different at the two temperatures. At 180 °C, the amounts of hydroperoxides increased sharply during the first 10 min and then began to decrease. At 100 °C, the amounts of hydroperoxides increased over the entire experimental period. At 180 °C, all major secondary oxidation products, except 7‐ketostigmasterol, reached a plateau after 40 min of oxidation, while at 100 °C their amounts increased constantly. The same oxidation products were formed at both temperatures, but their distribution differed. At 180 °C, the formation of free radicals at position 7 was more favorable than formation of radicals at position 25. The situation was the opposite at 100 °C; radicals formed more easily at the tertiary position 25. At 180 °C, 7‐ketostigmasterol was dominant after 40 min of oxidation, whereas at 100 °C it was the main oxidation product over the entire experiment.     

Effect of maleic anhydride‐grafted polypropylene on polypropylene/recycled acrylonitrile butadiene rubber/empty fruit bunch composite

The effect of maleic anhydride‐grafted polypropylene (PP‐g‐MAH) as a compatibilizer on the properties of polypropylene (PP)/recycled acrylonitrile butadiene rubber (NBRr)/empty fruit bunch (EFB) composites were studied. The composites were melt mixed using a heated two roll mill at 180°C and a speed of 15 rpm with six different compositions (100/0/10, 80/20/10, 70/30/10, 60/40/10, 50/50/10, 40/60/10 phr). The effects of PP‐g‐MAH on mechanical, morphological and chemical properties of the PP/NBRr/EFB composites were examined. The PP‐g‐MAH compatibilized composites have higher tensile values compare to uncompatibilized composites. Scanning electron microscopy showed better adhesion between EFB and PP/NBRr matrices in the presence of PP‐g‐MAH. Better interaction was formed between EFB and PP/NBRr matrices via C‐O‐C ester bonds as indicated by FTIR analysis. J. VINYL ADDIT. TECHNOL., 24:275–280, 2018. © 2016 Society of Plastics Engineers     

Temperature-reversible oxidation of carbon monoxide by new and weathered whetlerite

The oxidation of CO in mixtures with purified air passing into whetlerite was followed by online measurements of CO and CO₂ in the effluent between 20–200°C. The CO concentrations attained a steady-state at each temperature and these were found to be temperature reversible. Two molecules of CO were required to form one CO₂ up to 100°C, and above 100°C, the ratio was less than two for new whetlerites and greater than two for weathered whetlerites. An oxygen balance was indicated but a sink for the carbon other than carbon-on-carbon deposition was not evident. While whetlerite in air flows formed mainly CO₂, the activated carbon support alone formed both CO and CO₂. The whetlerite impregnation (copper II, chromium VI, and silver I) had little influence on the magnitude of the total carbon gasified up to 200°C, but the ratio of CO₂/CO was many fold greater for the whetlerite. The spontaneous ignition temperature (SIT) of the coal-base charcoal support (490°C) was lowered in whetlerite (270–280°C).