Improvement of thermo-oxidative stability of electrically insulating polymeric materials by organic-inorganic hybrid coating

The thermo-oxidative stability of poly(ethylene terephthalate) (PET) and low-density polyethylene (LDPE) films, coated with organic-inorganic hybrid coatings of various compositions, has been investigated after accelerated ageing tests, in order to ascertain a possible beneficial effect of these coatings on the electrical performances of these insulating materials. The results have shown that the coating affects degradation mechanisms for both LDPE and PET.Thermo-oxidation is slow in LDPE, leading to significantly better insulating characteristics after ageing: a strong reduction of the embrittlement time was also observed.The strong increase of crystallinity upon ageing, observed for both coated and uncoated PET samples, probably dominates the effect of ageing on the electrical properties. As a consequence, only slight beneficial effects on PET electrical performances have been observed (both on conductivity and electrical strength). On the other hand, the coating has a strong effect on molecular weight changes leading to a significant increase of molecular weight for coated PET, while uncoated PET undergoes a significant decrease. This suggests that coated PET should present significantly better properties upon very long times of ageing.     

Effect of acid treated multi-walled carbon nanotubes on the mechanical, permeability, thermal properties and thermo-oxidative stability of isotactic polypropylene

The effect of acid treatment of multi-walled carbon nanotubes (MWCNTs) on the mechanical, thermal and mainly thermo-oxidative stability of isotactic polypropylene (iPP) was evaluated. From the acid treatment surface carboxylic groups were mainly formed, while the nanotubes' length was gradually reduced by increasing the treatment time. Young's modulus, tensile strength and storage modulus of the iPP/MWCNT nanocomposites were increased by increasing the treatment time of the MWCNTs, due to finer dispersion inside the polymer matrix, as revealed by TEM and micro-Raman spectroscopy. Furthermore, the nanotubes acted as nucleating agents, an effect more pronounced with finer filler dispersion. Thermal stability in an inert atmosphere also increased. Thermo-oxidative stability tests in air and O₂ revealed that oxidative degradation took place in two stages. In the first stage, corresponding to temperatures up to 230 °C, the MWCNTs accelerated the oxidation of iPP, while at higher than 300 °C temperatures the trend was reversed. Incubation studies proved that, at the first stages, oxidation was due to random chain scission of iPP and oxygen uptake. This behaviour was accelerated by the MWCNTs' surface carboxylic groups and, as found by O₂ permeability studies, was mainly a surface process. In the second stage, due to the shielding effect of MWCNTs, the removal of the gases produced during decomposition was hindered. At this stage the presence of MWCNTs resulted in more thermo-oxidatively stable nanocomposites.     

HRGC/FID/NPD and HRGGC/MSD study of Colombian ylang-ylang (Cananga odorata) oils obtained by different extraction techniques

Steam distillation (SD), simultaneous distillation-solvent extraction (SDE), and supercritical (CO₂) extraction (SFE) were used to isolate volatile secondary metabolites from fresh, totally mature flowers of Colombian ylang-ylang (Cananga odorata). The various extracts were analyzed by capillary chromatography (DB-1, DBWAX, 60 m columns) using FID, NPD or MSD (EI, 70 eV). Kováts indexes, mass spectra, or standard substances were employed for compound identification. 51, 70, and 73 compounds at concentrations above 100 ppb were detected in the SD, SDE, and SFE extracts, respectively. The main constituents of these extracts were linalool (20.7, 28.0, and 16.5%), germacrene-D (10.1, 3.1, and 20.3%) benzyl benzoate (14.1, 2.9, and 3.9%), benzyl acetate (9.6, 17.0, and 6.2%), caryophyllene (3.1, 2.9, and 3.9%), and p-methylanisole (6.8, 6.1, and 2.7%). 85% of the composition of SDE extracts was represented by oxygenated compounds. Heavy hydrocarbons (C_n >20) and fatty acids were found only in the SFE extracts, which also had a higher content of nitrogenated compounds (phenylacetonitrile, 4-methylbenzaldoxime, indole, 2-phenyl-nitroethane, and methyl anthranilate) and sesquiterpenes (43% vs 19.5% in SD and 8.1% in SDE) and 1.5 – 2 times lower concentration of monoterpenes and light oxygenated compounds than the SD (49.7%) and SDE (64.5%) extracts.     

Simultaneous determination of five common additives in insulating mineral oils by high‐performance liquid chromatography with ultraviolet and coulometric detection

Dielectric mineral oils are used to impregnate power transformers and large electrical apparatus, acting as both liquid insulation and heat dissipation media. Antioxidants and passivators are frequently added to mineral oils to enhance oxidation stability and reduce the electrostatic charging tendency, respectively. Since existing standard test methods only allow analysis of individual additives, new approaches are needed for the detection of mixtures. For the first time we investigate and discuss the performance of analytical methods, which require or do not require extraction as sample pretreatment, for the simultaneous reversed‐phase high‐performance liquid chromatography determination of passivators (benzotriazole, Irgamet^® 39) and antioxidants (N‐phenyl‐1‐naphtylamine, 2,6‐di‐tert‐butylphenol, 2,6‐di‐tert‐butyl‐p‐cresol), chosen for their presence in marketed oils. Quick easy, cheap, effective, rugged and safe and solid phase extractions were evaluated as sample pretreatments. Direct sample‐injection was also studied. Ultraviolet spectrophotometry and direct‐current coulometry detection were explored. As less prone to additive concentrations variability, the direct‐injection high‐performance liquid chromatography with ultraviolet and coulometric detection method was validated through comparison with Standard Method IEC 60666 and through an ASTM interlaboratory proficiency test. Obtained detection limits are (mg kg^?1): benzotriazole (2.8), Irgamet^® 39 (13.8), N‐phenyl‐1‐naphtylamine (11.9), 2,6‐di‐tert‐butylphenol (13.1), 2,6‐di‐tert‐butyl‐p‐cresol (10.2). Simultaneous determination of selected additives was possible both in unused and used oils, with good precision and accuracy.     

Effect of structure on properties of polyols and polyurethanes based on different vegetable oils

We synthesized six polyurethane networks from 4,4′‐diphenylmethane diisocyanate and polyols based on midoleic sunflower, canola, soybean, sunflower, corn, and linseed oils. The differences in network structures reflected differences in the composition of fatty acids and number of functional groups in vegetable oils and resulting polyols. The number average molecular weights of polyols were between 1120 and 1300 and the functionality varied from 3.0 for the midoleic sunflower polyol to 5.2 for the linseed polyol. The functionality of the other four polyols was around 3.5. Canola, corn, soybean, and sunflower oils gave polyurethane resins of similar crosslinking density and similar glass transitions and mechanical properties despite somewhat different distribution of fatty acids. Linseed oil–based polyurethane had higher crosslinking density and higher mechanical properties, whereas midoleic sunflower oil gave softer polyurethanes characterized by lower T_g and lower strength but higher elongation at break. It appears that the differences in properties of polyurethane networks resulted primarily from different crosslinking densities and less from the position of reactive sites in the fatty acids. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 809–819, 2004     

The antioxidant reactivity of sorbitylfurfural towards potential harmful radicals,studied by radiation chemistry techniques

Ionising radiations, employed in a broad range of dose-rate, together with a complex non-linear computation of reaction mechanisms, allow the determination of boundary values of rate constants concerning sorbitylfurfural (SF) reactivity towards a wide series of oxidant and/or virtually harmful radicals. SF reacts with some radicals (H, SO₄^-˙, CO₃^-˙, Br₂^-˙, CH₃˙), produced with both pulse and stationary radiolysis in neutral aqueous solution, having electrophilic and/or oxidative behaviour. The rate constants range from diffusional (k = (7-9) × 10⁹ M^-1 s^-1) to relatively low values (k = 2 × 10⁵ M^-1 s^-1). The possibility to observe these reactions, by means of radiolytical techniques, is heavily influenced by dose-rate. A relation between the radical E⁰_NHE and their reactivity with SF is hinted.     

Evaluation of peroxide value of olive oil and antioxidant activity by luminol chemiluminescence

Three procedures are developed and investigated for the simple and fast determination of peroxide value of olive oil by luminol chemiluminescence. The procedure using hemin as catalyst in carbonate alkaline solution allows the determination of hydrogen peroxide within the range 0.014-50 μM. The method can be used for the determination of peroxide value within the range 2.00-30.0 mequiv. O₂/kg oil and results correlate very well (r² = 0.99) with those of the official method. All reagents are aqueous solutions and olive oil is dissolved in acetone:ethanol mixed solution and, hence, the method is using minimal amounts of organic solvents and can be successfully applied to field analysis. Antioxidant activity of five common compounds found in natural products was determined by using luminol CL with Co(II) as EDTA complex as catalyst at pH 9.00.     

Evaluation of antioxidant activity of hydrophilic and lipophilic compounds in edible oils by a novel fluorimetric method

A novel fluorimetric method is described for the evaluation of the antioxidant activity of hydrophilic and lipophilic compounds and complex natural products such as edible oils. The method is based on the measurement of fluorescence emission intensity of N-methylacridone produced during the reaction of lucigenin with hydrogen peroxide. The presence of antioxidants in the sample inhibits the concentration of N-methylacridone and reduces the fluorescence intensity. The method was fully validated and applied to a variety of hydrophilic and lipophilic compounds as well as to various types of edible oils and their corresponding hydrophilic and lipophilic extracts. Results were compared to those derived from a lucigenin based chemiluminescent method and the Folin-Ciocalteau method for total phenols. The differences in total antioxidant activity of edible oils of various origins and the effect of heating on total antioxidant activity was further studied and discussed.     

Combustion characteristics of lignite and oil shale samples by thermal analysis techniques

In this research thermal analysis and kinetics of ten lignite's and two oil shale samples of different origin were performed using a TA 2960 thermal analysis system with thermogravimetry (TG/DTG) and differential al analysis (DTA) modules. Experiments were performed with a sample size of ~10 mg, heating rate of 10°C min^-1. Flow rate was kept constant (10 L h^-1) in the temperature range of 20-900°C. Mainly three different reaction regions were observed in most of the samples studied. The first region was due to the evaporation of moisture in the sample. The second region was due to the release of volatile matter and burning of carbon and called as primary reaction region. Third region was due to the decomposition of mineral matter in samples studied. In kinetic calculations, oxidation of lignite and oil shale is described by first-order kinetics. Depending on the characteristics of the samples, the activation energy values are varied and the results are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Investigation and optimization of the recovery of coal fines using oil agglomeration process: Use of waste oils from different sectors

The high cost of the bridging liquid subdues the implementation and commercialization of oil agglomeration process. To overcome this problem, waste oils from different sectors were used in this present study. The performance of the process was assessed based on the responses like ash rejection and organic matter recovery. The aim of the present study was to investigate the usage of waste oils from different sectors and to optimize and analyze the behavioral pattern showcased by different variables (pulp density, oil dosage, agglomeration time and oil type) using response surface methodology (Box-Behnken design). Experimental investigation shows that the optimum pulp density, oil dosage, agglomeration time and oil type condition obtained as 3%, 15%, 15?min and waste engine oil, respectively. At optimum condition, the % ash rejection and % organic matter recovery obtained as 63.94% and 81.8%, respectively.     

Effect of modified nano-silica/EVA on flow behavior and wax crystallization of model oils with different wax contents

The nano-hybrid pour-point depressant (PPD) was prepared with organically modified nano-silica covering in EVA. The effects of modified nano-silica/EVA on the flow behavior and wax crystallization of model oils with different wax contents were evaluated. Compared with pure EVA and nano-silica/EVA, modified nano-silica/EVA exhibited a better effect, when doped with 500?ppm, the pour point of the model oil containing 20?wt% wax was reduced from 33°C to 0°C. However, it is noteworthy that pour point cannot accurately reflect the effect of YSiO2/EVA as cold flow improver for a high wax content. The crystal morphology and crystallization behavior of the model oils at low temperature were also observed using polarizing optical microscopy (POM). The results indicated that modified nano-silica/EVA can reduce the size of the wax crystals and disperse the wax crystals by heterogeneous nucleation.     

Analysis of the thermal decomposition of commercial vegetable oils in air by simultaneous TG/DTA

This work presents a study of the thermal decomposition of commercial vegetable oils and of some of their thermal properties by termogravimetry (TG), derivative termogravimetry (DTG) and by differential thermal analysis (DTA). Canola, sunflower, corn, olive and soybean oils were studied. A simultaneous SDT 2960 TG/DTA from TA Instruments was used, with a heating rate of 10 K min^-1 from 30 to 700°C. A flow of 100 mL min^-1 of air as the purge gas was used in order to burnout the oils during analysis to estimate their heat of combustion. From the extrapolated decomposition onset temperatures obtained from TG curves, it can be seen that corn oil presents the highest thermal stability (306°C), followed by the sunflower one (304°C). Olive oil presents the lowest one (288°C). The heat of combustion of each oil was estimated from DTA curves, showing the highest value for the olive oil. Except for corn oil, which presents a significantly different thermal decomposition behavior than the other oils, a perfect linear correlation is observed, with negative slope, between the heat of combustion of an oil and its respective extrapolated onset temperature of decomposition in air. This revised version was published online in August 2006 with corrections to the Cover Date.     

Evaluation of Water-in-Crude-Oil Emulsion Stability Using Critical Electric Field: Effect of Emulsion Preparation Procedure and Crude Oil Properties

The critical electrical field has been used as a tool to probe water in crude emulsion stability to electrical fields in many previous studies. Given the increasing importance of this metric, this study investigates factors that are important to the reproducibility of the measurement and the effect of emulsion preparation variables on the critical electric field. It was observed that the emulsion preparation procedure has a strong effect on the measured critical electric field due to droplet size effects. Furthermore, the effect of crude oil properties on the critical electric field was investigated using emulsions from different oils but with the same average droplet diameter, where it was found that the measurement was dominated by crude oil viscosity.     

Preparation and characterization of bioactive oils nanoemulsions: Effect of oil unsaturation degree,emulsifier type and concentration

The effect of formulation parameters namely oil type, emulsifier type and concentration was assessed on various properties of the nanoemulsions. All nanoemulsions yielded droplets with a desirable size ranged from 38.5 to 127.9?nm. The findings showed that emulsifier type had significant effects on the physicochemical properties of emulsions. Emulsifier concentration had a negative correlation with droplet diameter, turbidity and positive correlation with polydispersity index, viscosity and creaming stability. Nanoemulsions prepared from pomegranate seed oil were different from that of two other oils in droplet size, viscosity, creaming and turbidity because of its higher intrinsic viscosity and degree of unsaturation.     

Comprehensive two-dimensional gas chromatography for fingerprint pattern recognition in olive oils produced by two different techniques in Portuguese olive varieties Galega Vulgar, Cobrançosa e Carrasquenha

For olive oil production a metal hammer-decanter olive processing line was compared to a traditional metal hammer-press line, a discontinuous method which, if properly used, yields high-quality virgin olive oils. Galega, Carrasquenha and Cobrançosa olives (traditional Portuguese varieties) were studied. The analysis of the aroma compounds was performed after headspace-solid phase micro extraction. The analytical results obtained after comprehensive gas chromatography in tandem with time of flight mass spectrometry (GC × GC/ToFMS) for these three different olive oil varieties, from a single year harvest and processed with two different extraction technologies, were compared using statistical image treatment, by means of ImageJ software, for fingerprint recognitions and compared with principal component analysis when the area data of each chromatographic spot of the contour plots were considered. The differences used to classify the olive oils studied under different groups after principal component analysis were observed independently of the treatment used (peak areas or the sum of the pixels counts). When the individual peak areas were considered, more then 75.7% of the total variance is explained by the first two principal components while in the case where the data were subjected to image treatment 84.0% of the total variance is explained by the first two principal components. In both cases the first and second principal components present eigenvalues higher then 1.0. Fingerprint image monitoring of the aroma compounds of the olive oil allowed a rapid differentiation of the three varieties studied as well as the extraction methods used. The volatile compounds responsible for their characterization were tentatively identified in a bi-dimensional polar/non-polar column set in the GC × GC/Tof-MS apparatus. This methodology allowed the reduction of the number of compounds needed for matrices characterization, preserving the efficiency of the discrimination, when compared with the traditional methods where the identification of all peaks is needed.     

1H-NMR评价不同重油缓和热转化过程中的相对供氢能力

以蒽为化学夺氢探针,采用 ¹H-NMR为检测手段测定了三种典型重质渣油及其亚组分在380℃、临氮初压4MPa、反应8 min条件下的可供氢含量,并分析了产物的甲苯不溶物、液体馏程分布以及气体组成。结果表明,本实验条件下的热反应较为缓和,渣油及组分反应前后结构变化不明显,样品体系内部主要发生渣油及组分向夺氢体(蒽)的氢转移反应。¹H-NMR中化学位移在1.4~2.0的H_cβ和2.5~4.7的H_cα含量的变化值与化学探针法测定的实际可供氢量有较好的线性关联,可利用此两段化学位移内的氢含量评价不同重质油品在缓和热改质过程中的相对供氢能力。     

Estimation of kinetic rate constants by turbidity and nephelometry techniques in a homocoagulation process with different model colloids

 In this work turbidimetric and nephelometric techniques have been used to study the homocoagulation of aqueous dispersions of uniform spherical particles of surfactant-free latexes. Cationic and anionic latexes of similar particle sizes (361 and 370 nm) and different surface charge densities (+16.4 and −3.6 μC/cm²) were used throughout. The kinetic constants which control the aggregation processes when the electrical repulsion disappears were estimated by both techniques at different particle concentration and wavelength in order to establish the experimental conditions which provided reliable and similar values for the coagulation rate constant. Both experimental techniques (turbidity and nephelometry) and two ways of fitting the data have been used with both latexes. For the first method, the initial slope of turbidity or total scattered intensity versus time curves were used to calculate the kinetic constants. In the second method, the whole turbidity or total scattered intensity versus time curves were fitted and the kinetic constants calculated. An unambiguous experimental value for the doublet rate constant in diffusion conditions is obtained by turbidity and nephelometry techniques. By nephelometry both data treatments have permitted a distinction between the doublet rate constant and the global rate constant in diffusion conditions. Received: 2 June 1997 Accepted: 14 August 1997     

Analysis of essential oils from Voacanga africana seeds at different hydrodistillation extraction stages: chemical composition,antioxidant activity and antimicrobial activity

In this study, essential oils from Voacanga africana seeds at different extraction stages were investigated. In the chemical composition analysis, 27 compounds representing 86.69–95.03% of the total essential oils were identified and quantified. The main constituents in essential oils were terpenoids, alcohols and fatty acids accounting for 15.03–24.36%, 21.57–34.43% and 33.06–57.37%, respectively. Moreover, the analysis also revealed that essential oils from different extraction stages possessed different chemical compositions. In the antioxidant evaluation, all analysed oils showed similar antioxidant behaviours, and the concentrations of essential oils providing 50% inhibition of DPPH-scavenging activity (IC₅₀) were about 25 mg/mL. In the antimicrobial experiments, essential oils from different extraction stages exhibited different antimicrobial activities. The antimicrobial activity of oils was affected by extraction stages. By controlling extraction stages, it is promising to obtain essential oils with desired antimicrobial activities.     

抗氧剂对植物油氧化稳定性影响的高压差示扫描量热法评价

利用高压差示扫描量热法（ＰＤＳＣ）研究了二烷基二硫代氨基甲酸锌（ＶＡＺ）、２,２′－亚甲基双（４－甲基－６特丁基苯酚）（２２４６）、苯江三唑（ＢＴＺ）和二烷基对苯二胺（ＤＢＡ）４种抗氧添加剂对菜子油氧化稳定性的影响,得到了它们抗氧化作用的大小顺序。别外,根据队仑尼乌斯公式计算了不同油样氧化反应的活化能,证明了ＰＤＳＣ是一种快速简便评价基础油氧化稳定性的方法,适用于抗氧添加剂配方的设计工作。