Thermal properties of fats extracted from powdered baby formulas

The aim of this research was to analyse composition, fatty acids distribution and oxidative stability of fats extracted from four samples of baby formulas. The fats were oxidized in a differential scanning calorimeter (DSC) under polythermal (dynamic) conditions and at normal pressure. The DSC experiments were carried out in an oxygen flow atmosphere using different, linearly programmed, heating rates in the range of 4?C12.5?°C/min. The extrapolated onset temperatures were determined using DSC exotherms and used for the assessment of the thermal oxidative stabilities of the samples. Activation energies (E _a), pre-exponential factors (Z) and reaction rate constants (k) for oil oxidation under DSC conditions were calculated using the Ozawa?CFlynn?CWall method and the Arrhenius equation. The melting characteristics of the studied fats were obtained. The fats extracted from the agglomerated samples with higher onset temperatures were more stable than the fats extracted from the initial samples of baby formulas.     

Measurement and modeling of peroxides half-life: A thermo-kinetic approach

Half-life values of organic peroxides at elevated temperature conditions are important in characterizing the reactivity and are often available in literature or through vendors. However, there is often lack of details/accuracy on methods used to obtain these values, as well as differences in methods across vendors and publications, thus resulting in discrepant reactivity profile. To address this, a method involving calorimetric experiment and thermo-kinetic modeling was developed. The current approach was applied on five peroxides samples to obtain kinetic parameters and estimate their half-life in the temperature range of interest. The measurements were performed by DSC under non-isothermal conditions on the dilute peroxide solutions (∼0.12 M in mineral oil) and the data were kinetically treated according to three model-based and one model-free kinetic equations. A very good agreement was found between the half-life calculated by all kinetic methods, but significant differences were noticed with the kinetic parameters reported in literature. Additionally, the obtained half-life results, based on non-isothermal measurements developed kinetic models, were validated through isothermal calorimetric testing. Given the accuracy and robustness of our results, the current method can be applied to estimate half-life of organic peroxides at elevated temperature conditions.     

Thermal runaway hazards of <Emphasis Type="Italic">tert</Emphasis>-butyl hydroperoxide by calorimetric studies

Thermal runaway reactions associated with exothermic behaviors of tert-butyl hydroperoxide (TBHP) solutions and TBHP reacting with alkaline contaminants were studied. A differential scanning calorimetry (DSC) was used to characterize these inherent behaviors of TBHP solutions with KOH, NaOH, LiOH and NH₄OH. The exothermic peak in thermal curves of TBHP solutions with different alkali were detected by DSC thermal analysis. By thermal analysis, we compared various heats of decomposition of TBHP solutions with alkaline impurities, and determined the incompatible hazards of various TBHP solutions with alkaline contaminants. Comparing with TBHP in various diluents, the adiabatic runaway reaction via vent sizing package 2 (VSP2) indicated that aqueous TBHP intrinsically possesses the phenomena of thermal explosion with dramatic self-reactive rate and pressure rise under adiabatic conditions. Many commercial organic peroxides may have different hazard behaviors. Therefore, using thermal method to classify the hazards is an important subject.     

The effect of tetrahydrofuran as solvent on matrix-assisted laser desorption/ionization and electrospray ionization mass spectra of functional polystyrenes

It is demonstrated that tetrahydrofuran (THF) should be used with caution as a solvent in polymer sample preparation for matrix-assisted laser desorption/ionization (MALDI) analyses. The presence of peroxides in THF may cause the oxidation of chemically active groups. This effect is illustrated in the case of S-containing polystyrene derivatives. The oxidation of the trithiocarbonate group resulted in the formation of poly(styrene)sulfonic acids, R(CH(2)CHPh)(n)SO(3)H, which was detected in negative mode by MALDI and electrospray ionization (ESI) methods after the samples remained in THF for several hours.     

Autooxidation of Unsaturated Fatty Acids and Their Esters

The shape of DSC curves of non-isothermal oxidation of fats was explained. Two main exothermic effects overlapped partially are caused by hydroperoxide formation (first peak) and by further oxidation of peroxides (second peak). The oxidation of oils and lipid analogues of various peroxide concentration showed that only the start of the oxidation process is affected by initial concentration of peroxides, other temperatures determined from DSC curves are not connected with this parameter. The computer simulations gave the best agreement of theoretical and experimental data for kinetic scheme of a two-step consecutive reaction with autocatalytic start. The comparison of activation energies calculated for isothermal and non-isothermal autooxidation of unsaturated fatty acids and their esters also confirmed this interpretation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Radiation grafting of NIPAAm and acryloxysuccinimide onto PP films and sequent crosslinking with polylysine

N-isopropylacrylamide (NIPAAm) and N-acryloxysuccinimide (NAS) were grafted from their binary mixtures in tetrahydrofurane (THF) and toluene solutions onto polypropylene (PP) films by the pre-irradiation oxidative method in air. Effects of pre-irradiation dose, dose rate, and monomer concentrations (NAS/NIPAAm) were studied. The grafted copolymers exhibited the lower critical solution temperature (LCST) at around 31 °C. Based on its thermo-reversible behavior, this system has been used for immunoassay, drug delivery, separation processes and immobilization of enzymes. N-acryloxysuccinimide (NAS) has been used as an active ester to bind proteins through amide bond formation with lysine, and because of this property, the grafted copolymer has been crosslinked with polylysine. Techniques used to characterize the films included differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), infrared (FTIR-ATR) and elemental analysis. Results on thermo-sensitivity are presented. This new system could find applications in vesicle immobilizations.     

Thermal decomposition of organic peroxide with metals using calorimeters

In this study, we evaluated the reactivity of organic peroxides with metals. The effect of the metals on the decomposition of organic peroxides was measured using a differential scanning calorimeter (DSC). Results of DSC measurements showed that some organic peroxides have high reactivity with a gold plated cell. Especially, hydroperoxides were decomposed at lower temperature using the gold plated cell when compared to other type of cells. In order to evaluate the effect of metals on the hydroperoxides, the decomposition characteristics of cumenhydroperoxide (CHP) with metal powders were studied using a C80 calorimeter and the products were analyzed by a gas chromatograph. These results indicated that the radical reaction of CHP was catalyzed by the gold and the autocatalytic reaction of CHP was catalyzed by stainless steel (SUS) and hastelloy c (HC).     

The detection of tetrahydrofuran hydrate formation and saturation using magnetic resonance imaging technique

Tetrahydrofuran (THF) hydrate was formed in bulk as well as in glass beads pack with a mean diameter of 3.0 mm by controlling the temperature under ambient pressure. Images of THF hydrate formation procedure were obtained using the magnetic resonance imaging (MRI) technique. The experiment results showed that MRI is an effective method for the detection of hydrate formation. Saturation of hydrate formed both in bulk and glass beads can be confirmed by intensity integration of MRI images.     

A rapid separation method for gel content determination in pressure sensitive adhesive dispersions and acrylic-based latices for an industrial setting

A rapid method has been developed for determining gel content in industrial samples such as water-borne pressure sensitive adhesives (PSAs) and acrylic-based latices. The method is based on thermal field-flow fractionation (ThFFF) and evaporative light scattering detection (ELSD). Results are compared to those obtained using a centrifugation-based gravimetric method.Sample preparation was an important aspect of the developed analysis. Although the latices and PSA are similar in chemistry, they required different handling and sample preparation procedures. The PSA sample, with its sub-ambient glass transition temperature (T_g), formed visible macro-gels, if it was added directly to tetrahydrofuran (THF). No macro-gels were formed, if the PSA was pre-diluted in water and then suspended in THF. By using this new sample preparation procedure and ThFFF total analysis time was reduced from days to a few hours. The gel content in water-borne pressure sensitive adhesives and acrylic-based latices varied from 5 to 51% with an average relative standard deviation (RSD) of 11%.     

Breath figure patterns prepared by spin coating in a dry environment

We introduce a novel method for fabricating breath figure patterns on a homopolymer film by spin coating of polymer solutions with various solvents. The homopolymers employed in this study were cellulose acetate butyrate, monocarboxylated end-functional polystyrene, and poly(methyl methacrylate). Breath figure patterns were generated even when a water-miscible solvent such as tetrahydrofuran (THF) was used as a solvent. We even succeeded in generating breath figure patterns by spin coating even under a dry environment (relative humidity less than 30%), when water was directly added into THF solution. With the combination of the spin coating method, pores with a few hundred nanometers to several micrometers have been generated. We found that the pore size becomes larger with increasing water content in THF solution and decreasing rotating speed. This is equivalent to increasing humidity and decreasing evaporation speed, respectively, in the conventional method, which is direct solvent evaporation under a humid environment. Thus, compared with the conventional method for making breath figure patterns, this method would be very convenient for fabricating large-scale films with various pore sizes.     

Evaluation of adiabatic runaway reaction and vent sizing for emergency relief from DSC

Analytical equations related adiabatic runaway reactions to programmed scanning thermal curves from differential scanning calorimetry (DSC) were proposed. Thermal or pressure hazards can be assessed from the adiabatic trajectories expressed in the analytical equations. These industrially energetic materials include polymerizable monomers, unstable organic peroxides and nitro-compounds. Various emergency relief behaviors, such as tempered vapor, gassy, and hybrid were re-evaluated for calculating vent sizing or mass flow rates from DSC thermal curves and the related physical properties.     

一种简便渗透压法测定高聚物分子量

本工作采用一种改进的一膜两室渗透计和简便动态渗透压法测定了一系列聚合物的数均分子量,该法操作方便、快速、可靠,测定分子量相对误差在±5％以内。     

碳前驱体CH3ArCH2NH2的热解性能及动力学研究

通过密闭压力容器法、常压DSC、高压DSC及紫外分光光度定量分析法等实验手段,对液相沉积法制碳／碳复合材料用碳前驱体CH3ArCH2NH2的热裂解行为进行了研究,获得不同温度、不同压力下该碳前驱体的热分解温度和残碳率,用等温动力学和非等温动力学方法获得了热裂解反应的表观活化能,实验结果表明,常压热裂解温度大约为530．15－556．55K,1－3MPa的高压范围内的热裂解温度大约在618．34－675．49K,密闭压力容器中的残碳率为56．23％,常压下的残碳率为28．96％－36．47％,而高压下残碳率可达59．11％,根据基辛格等方法获得了等温条件下和非等温条件下热裂解反应的表观活化能Ea分别为206．78kJ/mol和183．93kJ/mol, 反应级数N~1.     

DSC by the TGA/SDTA851e Considering Mass Changes

DSC measurements in open pans are often disturbed by mass losses such as sublimation during melting or release of water during chemical reactions. By simultaneous DSC and TG measurements the DSC signal can be corrected. For this purpose, a temperature dependent calibration function has to be determined by which the SDTA signal from the TGA/SDTA851^e measuring cell can be converted into a heat flow curve (DSC). By this procedure, accurate heat of melting can be determined despite ongoing sublimation in open pans. This method is illustrated with reference of the melting of anthracene. Additionally, condensation reactions were investigated and analyzed by DSC/TG even under ambient pressure, knowing the heat of evaporation. Using phenol formaldehyde resins the influence of the presence or the release of volatile reaction products on the reaction rate and kinetic parameters were studied. In general, the method can be used to correct DSC curves for thermal effects related to mass change. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tetrahydrofuran hydrate decomposition characteristics in porous media

Many tetrahydrofuran (THF) hydrate properties are similar to those of gas hydrates. In the present work THF hydrate dissociation in four types of porous media is studied. THF solution was cooled to 275.15 K with formation of the hydrate under ambient pressure, and then it dissociated under ambient conditions. THF hydrate dissociation experiments in each porous medium were conducted three times. Magnetic resonance imaging (MRI) was used to obtain images. Decomposition time, THF hydrate saturation and MRI mean intensity (MI) were measured and analyzed. The experimental results showed that the hydrate decomposition time in BZ-4 and BZ-3 was similar and longer than that in BZ-02. In each dissociation process, the hydrate decomposition time of the second and third cycles was shorter than that of the first cycle in BZ-4, BZ-3, and BZ-02. The relationship between THF hydrate saturation and time is almost linear.     

The reactions of flavin analogues and other heterocycles as models for bacterial bioluminescence

The reactions of 10a-peroxyflavins have been examined to increase understanding of the oxidative and chemiluminescent reactions catalysed by the flavin co-enzymes. A remarkable series of structural requirements in the peroxides used has been uncovered, and in addition to serving as models for the mechanism of bacterial luciferase, they constitute a set of new chemiluminescent reactions.     

Vapour pressure of DSC calibration substances

For a large number of DSC calibration substances the vapour pressure at room temperature or at transition temperature (whichever is the highest) is given. It is important to know the vapour pressure of substances, because a DSC measurement on a substance with a high vapour pressure requires encapsulation of the substance in a hermetically sealed crucible to prevent evaporation. Because the calibration procedure must be performed using the same type of sample pan as will be used during the actual measurements, the presented information allows one to decide which calibration substances and/or what type of sample pan should be used for calibration.This revised version was published online in November 2005 with corrections to the Cover Date.     

Photocrosslinking of poly(2,3-epithiopropyl methacrylate) by the oxidation of pendant episulfide groups

In the photocrosslinking of poly(2,3-epithiopropyl methacrylate) (PETMA) films the effect of the pendant episulfide group's oxidation on the crosslinking of PETMA was investigated. Thermal crosslinking of PETMA is promoted by peroxides such as benzoyl peroxide and hydrogen peroxide. IR spectrum of the crosslinked PETMA showed that the reaction proceeded through the oxidation of episulfide groups by the peroxides. The anthracene (An) sensitized photocrosslinking of PETMA films also proceeded via the oxidation of episulfide groups by singlet oxygen. It was found that residual tetrahydrofuran (THF) in the films remarkably increased the rate of the photocrosslinking and/or reduced the induction period. From the further investigation concerning casting solvents it was found that residual CS₂, CCl₄, and CHCl₃ in films increased the rate of the photocrosslinking and/or reduced the induction period of the photocrosslinking. The disappearance rate of An in the films was also increased by the presence of residual CS₂, CCl₄, and CHCl₃, differring from the result of THF. These results were explained by a difference in lifetime of singlet oxygen in the films. From the results were explained by a difference in lifetime of singlet oxygen in the films. From the results concerning the effects of hydroperoxides such as THF hydroperoxide and t-butyl hydroperoxide on the photocrosslinking of PETMA films the acceleration effect of the residual THF was deduced to be due to the promotion of singlet oxygen-oxidation of sulfide groups by protic compounds such as THF hydroperoxide and H₂O in the THF.     

The way to measure quantitatively full dissolution and crystallization of polyamides in water up to 200 °C and above by DSC

The way to measure quantitatively full dissolution and crystallization of polyamides in water up to 200 °C and above by DSC is described. Stainless-steel high-pressure pans enable research on fully dissolving polyamides in water under vapor pressure. The results show clearly that polyamide 6 (PA6) is soluble in water under vapor pressure in the whole concentration range and that water acts as a crystallization and melting point suppressor. The maximum temperature depression is approximately 60 °C. This depression of the transitions is independent of concentration over a large range (10-70 mass% PA6 in water). When PA6 dissolves in water during heating, the polymer often sets to the sides of the DSC sample pan. Because of this the contact between the sample and the bottom of the pan reduces during measurement and therefore DSC heating curves are frequently curved. Adding steel wool to these stainless-steel high-pressure pans improves the measurements by increasing the thermal conductivity between the sample and pan bottom, and as a result the DSC curves become less curved. The interpretation of the measurements improves and the possibility of reproducible peak area calculations also in heating comes in sight.     

Chemical thermodynamics

The curing of composition containing epoxy bond is complicated chemical and technological process where under temperature and pressure conditions a change of its structure occurs. The structure changes are possible to know by thermal methods as DSC, DTA, etc. and also by measurement of dielectrical response under the low frequency electrical field.