Runaway reaction on <Emphasis Type="Italic">tert</Emphasis>-butyl peroxybenzoate by DSC tests

Tert-butyl peroxybenzoate (TBPB) is one of the sensitive and hazardous chemicals which have been popularly employed in petrifaction industries in the past. This study attempted to elucidate its unsafe characteristics and thermally sensitive structure so as to help prevent runaway reactions, fires or explosions in the process environment. We employed differential scanning calorimetry (DSC) to assess the kinetic parameters (such as exothermic onset temperature (T ₀), heat of reaction (ΔH), frequency factor (A)), and the other safety parameters using four different scanning rates (1, 2, 4 and 10°C min⁻¹) combined with curve-fitting method. The results indicated that TBPB becomes very dangerous during decomposition reactions; the onset temperature and reaction heat were about 100°C and 1300 J g⁻¹, respectively. Through this study, TBPB accidents could be reduced to an accepted level with safety parameters under control. According to the findings in the study and the concept of inherent safety, TBPB runaway reactions could be thoroughly prevented in the relevant plants.     

Differential scanning calorimetric examination of the degenerated human palmar aponeurosis in dupuytren disease

The Dupuytren contracture - degenerative shortening of the palmar aponeurosis - is a common disease of the hand in Europe. The aetiology of the degenerative changes in the collagen structures is still not clear. To describe the clinical manifestation of the disease we use an international classification according to Iselin. Our hypothesis was that in Dupuytren disease there is a clear pathological abnormality in the tissue elements building up the palmar aponeurosis, which is responsible for the disease, and could be monitored besides the classical histological methods by differential scanning calorimetry. The thermal denaturation of different parts of human samples was monitored by a SETARAM Micro DSC-II calorimeter. All the experiments were performed between 0 and 100°C. The heating rate was 0.3 K min⁻¹. DSC scans clearly demonstrated significant differences between the different types and conditions of samples (control: T _m=63°C and ΔH _cal=4.1 J g⁻¹, stage I.: T _m= 63°C and ΔH _cal=5.1 J g⁻¹, stage II.: T _m=64°C and ΔH _cal=5.2 J g⁻¹, stage III.: T _m=60°C and ΔH _cal=5.2 J g⁻¹, stage IV.: T _m=60.2°C and ΔH _cal=5.3 J g⁻¹). The heat capacity change between native and denatured states of aponeurosis samples increased with the degree of structural alterations indicating significant water loosing. These observations could be explained with the structural alterations caused by the biochemical processes. With our investigations we could demonstrate that DSC is a useful and well applicable method for the investigation of collagen tissue of the human aponeurosis. Our results may be of clinical relevance in the future i.e. in the choice of the optimal time of surgical therapy of different clinical level Dupuytren contractures.     

DSC analysis of human fat tissue in steroid induced osteonecrosis

Osteonecrosis (ON) of the femoral frequently occurs after steroid medication. One of the final pathways leading to steroid induced ON is thought to be pathologic fat metabolism. The pathobiological mechanism underlying the induction of fat metabolism outslides by steroids leading to ON has not been fully elucidated. The purpose of this study was to examine the intraoperative obtained gluteal fat tissue from ON patients with histology, gas chromatography (GC) and differential scanning calorimetry (DSC) and to compare them with otherwise healthy patient’s samples. The histological sections showed no significant differences compared with the control group. GC revealed that fraction of saturated fatty acids decreased in ON samples from mean values of controls of 24% to 21, the polyunsaturated fraction from 20 to 14%. The monounsaturated acids showed an increase from mean rate of 52% of the controls to 65% of steroid treated samples. DSC curves correlate with chromatographic analysis of the tissue fatty acids (Steroid treated, heating between 0–100°C: T _m=5.7°C, ΔH= −15.8J/g⁻¹; heating between −20–100°C: Tm= −9.96 and 5.85°C, ΔH= −59.17 and −16.2 J g⁻¹. Non-necrotic, heating between 0–100°C: two separable transition with Tm=5.7 and 9.9°C, total ΔH= −20.8 J g⁻¹; heating between −20–100°C: Tm= −10.9 and 4.95°C, total ΔH= −75.8 J g⁻¹.) Our preliminary findings are rather tendentious. Further investigations are needed with higher sample rate and under other anamnestic circumstances too.     

Glass transition temperature and thermal decomposition of cellulose powder

Cellulose powder and cellulose pellets obtained by pressing the microcrystalline powder were studied using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermal gravimetry (TG). The TG method enabled the assessment of water content in the investigated samples. The glass phase transition in cellulose was studied using the DSC method, both in heating and cooling runs, in a wide temperature range from −100 to 180 °C. It is shown that the DSC cooling runs are more suitable for the glass phase transition visualisation than the heating runs. The discrepancy between glass phase transition temperature T _g found using DSC and predictions by Kaelbe’s approach are observed for “dry” (7 and 5.3% water content) cellulose. This could be explained by strong interactions between cellulose chains appearing when the water concentration decreases. The T _g measurements vs. moisture content may be used for cellulose crystallinity index determination.     

Glass transition and crystallization study of chalcogenide Se<Subscript>70</Subscript>Te<Subscript>15</Subscript>In<Subscript>15</Subscript> glass

Differential scanning calorimetry data at different heating rates (5, 10, 15 and 20 °C min⁻¹) of Se₇₀Te₁₅In₁₅ chalcogenide glass is reported and discussed. The crystallization mechanism is explained in terms of recent analyses developed for use under non-isothermal conditions. The value of Avrami exponent (n) indicates that the glassy Se₇₀Te₁₅In₁₅ alloy has three-dimensional growth. The average values of the activation energy for glass transition, E _g, and crystallization process, E _c, are (154.16 ± 4.1) kJ mol⁻¹ and (98.81 ± 18.1) kJ mol⁻¹, respectively. The ease of glass formation has also been studied. The reduced glass transition temperature (T _rg), Hruby’ parameter (K _gl) and fragility index (F _i) indicate that the prepared glass is obtained from a strong glass forming liquid.     

Synthesis of Diblock Copolymers With Cellulose Derivatives. 2. Characterization and Thermal Properties of Cellulose Triacetate-Block-Oligoamide-15

Well-defined A-block-B type cellulose derivatives consisting of cellulose triacetate (CTA) and oligoamide-15 were synthesized. Chemical structures of the diblock copolymers were characterized by MALDI-TOF MS, ¹H-NMR, and GPC. Influence of length of CTA and oligoamide-15 segments on their thermal properties was investigated by means of differential scanning calorimetry (DSC). All diblock copolymers displayed T _g, T _c, and T _m transition temperatures. Their T _g and T _m values increased with the increase of molecular weight of CTA segment. The crystallinity of diblock copolymers increased after isothermal crystallization at 200 °C. Its X-ray analysis revealed that the diblock copolymer had CTA II crystal structure. Thermal analysis supported microphase separation between CTA and oligoamide-15 segments at room temperature, because T _g and T _m values of polyamide-15 are −7 °C and 170–180 °C, respectively.     

Cure kinetics of thermosetting bisphenol E cyanate ester

Resin injection repair is a common method to repair delamination damage in polymer matrix composites (PMCs). To repair high-temperature PMCs, the resin should have a very low viscosity, yet cure into a compatible adhesive with high temperature stability. Normally, thermosetting polymers with high glass transition temperatures (T _g) are made from monomers with high room temperature viscosities. Among the high temperature resins, bisphenol E cyanate ester (BECy, 1,1’-bis(4-cyanatophenyl)ethane), is unique because it has an extremely low viscosity of 0.09–0.12 Pa s at room temperature yet polymerizes as a cross-linked thermoset with a high T _g of 274°C. BECy monomer is cured via a trimerization reaction, without volatile products, to form the high T _g amorphous network. In this study, the cure kinetics of BECy is investigated by differential scanning calorimetry (DSC). Both dynamic and isothermal experiments were carried out to obtain the kinetic parameters. An autocatalytic model was successfully used to model isothermal curing. The activation energy from the autocatalytic model is 60.3 kJ mol⁻¹ and the total reaction order is about 2.4. The empirical DiBenedetto equation was used to evaluate the relationship between T _g and conversion. The activation energy of BECy from the dynamic experiments is 66.7 kJ mol⁻¹ based on Kissinger’s method, while isoconversional analysis shows the activation energy changes as the reaction progresses.     

Studying Cu2–xSe phase transformation through DSC examination

The thermal effect accompanying the transition of Cu_2–xSe into a superionic conduction state was studied by non-isothermal measurements, at different heating and cooling rates (β=1, 2.5, 5, 10 and 20°C min^–1). During heating the peak temperature (T_p) remains almost stable for all values of β, (136.8±0.4°C for Cu₂Se and 133.0±0.3°C for Cu_1.99Se). A gradual shift of the initiation of the transformation towards lower temperatures is observed, as the heating rate increases. During cooling there is a significant shift in the position of the peak maximum (T_p) towards lower temperatures with the increase of the cooling rate. A small hysteresis is observed, which increases with the increase of the cooling rate, β. The mean value of transformation enthalpy was found to be 30.3±0.8 J g^–1 for Cu₂Se and 28.9±0.9 J g^–1 for Cu_1.99Se. The transformation can be described kinetically by the model f(ǯ)=(1–ǯ)^n(1+kcatX), with activation energy E=175 kJ mol^–1, exponent value n equal to 0.2, logA=20 and log(k_cat)= 0.5.     

Research of thermal decomposition kinetic characteristic of emulsion explosive base containing Fe and Mn elements

The kinetic characteristic of thermal decomposition of the Emulsion Explosive Base Containing Fe and Mn elements (EEBCFM) which was used to prepare nano-MnFe₂O₄ particles via detonation method was investigated by means of non-isothermal DSC and TG methods at various heating rates of 2.5, 5 and 7.5°C min⁻¹respectively under the atmosphere of dynamic air from room temperature to 400°C. The results indicated that the EEBCFM was sensitive to temperature, especially to heating rate and could decompose at the temperature up to 60°C. The maximum speed of decomposition (dα/dT)_m at the heating rate of 5 and 7.5°C min⁻¹ was more than 10 times of that at 2.5°C min⁻¹ and nearly 10 times of that of the second-category coal mine permitted commercial emulsion explosive (SCPCEE). The plenty of metal ions could seriously reduce the thermal stability of emulsion explosive, and the decomposition reaction in the conversion degree range of 0.0∼0.6 was most probably controlled by nucleation and growth mechanism and the mechanism function could be described with Avrami-Erofeev equation with n=2. When the fractional extent of reaction α>0.6, the combustion of oil phase primarily controlled the decomposition reaction.     

Thermal stability and degradation of Co(II), Cd(II), and Zn(II) complexes with <Emphasis Type="Italic">N</Emphasis>-benzyloxycarbonylglycinato ligand

Thermal behavior of Co(II), Cd(II), and Zn(II) complexes with N-benzyloxycarbonylglycinato ligand was investigated using the results of TG, DSC and DTG analysis obtained at different heating rates (2.5 to 30 °C min⁻¹), from room temperature to about 900 °C. Mechanisms of complex degradation, as well as enthalpies of the degradation processes were determined. It is shown that thermal stability of investigated complexes correlates with their crystal structures, especially with the presence of crystallization and coordinated water molecules. The values of dehydration enthalpies are discussed and correlated with composition of the complexes. Kissinger’s, Ozawa’s, and Friedman’s isoconversion methods were used for the determination of kinetic parameters: the pre-exponential factor A and the apparent activation energy E _a. For all three complexes and all steps of degradation, the values of kinetics parameters obtained by Kissinger’s and Ozawa’s methods are in good agreement. The results obtained by Friedman’s method showed that some decomposition steps are simple and some others are complex ones.     

Saturated Vapor Pressure of Iridium(III) Acetylacetonate

The temperature dependency of the saturated vapor pressure of Ir(acac)₃ has been measured by the method of calibrated volume (MCV), the Knudsen method, the flow transpiration method, and the membrane method. The thermodynamic parameters of phase transition of a crystal to gas were calculated using each of these methods, and the following values of ΔH _T ⁰ (kJ mol⁻¹) and ΔS _T ⁰ (J mol⁻¹K⁻¹), respectively, were obtained: MCV: 101.59, 156.70; Knudsen: 130.54, 224.40; Flow transpiration: 129.34, 212.23; Membrane: 95.45, 149.44 Coprocessing of obtaining data (MCV, flow transportation method and Knudsen method) at temperature ranges 110−200°C as also conducted:ΔH _T ⁰ =127.9±2.1 (kJ mol⁻¹ ); ΔS _T ⁰ =215.2±5.0 (J mol⁻¹ K⁻¹ ). This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal properties of lignin-and molasses-based polyurethane foams

Lignin-and molasses-based polyurethane (PU) foams with various lignin/molasses mixing ratios were prepared. The hydroxyl group in molasses and lignin is used as the reaction site and PU foams with various isocyanate (NCO)/the hydroxyl group (OH) ratios were obtained. Thermal properties of PU foams were investigated by differential scanning calorimetry (DSC), thermogravimetry (TG) and thermal conductivity measurement. Glass transition temperature (T _g) was observed depending on NCO/OH ratio in a temperature range from ca. 80 to 120°C and thermal decomposition temperature (T _d) from ca. 280 to 295°C. Mixing ratio of molasses and lignin polyol scarcely affected the T _g and T _d. Thermal conductivity of PU foams was in a range from 0.030 to 0.040 Wm⁻¹ K⁻¹ depending on mixing ratio of lignin and molasses.     

Cross-linking epoxide resins with hydrolysates of chrome-tanned leather waste

Differential scanning calorimetry was employed to investigate the reaction of diglycidyl ethers of bisphenol A (DGEBA) of mean molecular mass 348–480 Da, with collagen hydrolysate of chrome-tanned leather waste in a solvent-free environment. The reaction leads to biodegradable polymers that might facilitate recycling of plastic parts in products of the automotive and/or aeronautics industry provided with protective films on this basis. The reaction proceeds in a temperature interval of 205–220°C, at temperatures approx. 30–40°C below temperature of thermal degradation of collagen hydrolysate. The found value of reaction enthalpy, 519.19 J g⁻¹ (= 101.24 kJ mol⁻¹ of epoxide groups) corresponds with currently found enthalpy values of the reaction of oxirane ring with amino groups. Reaction heat depends on the composition of reaction mixture (or on mass fraction of diglycidyl ethers in the reaction mixture); proving the dependence of kinetic parameters of the reaction (Arrhenius pre-exponential factor A (min⁻¹) and activation energy E _a (kJ mol⁻¹)) did not succeed. Obtained values of kinetic parameters are on a level corresponding to the assumption that reaction kinetics is determined by diffusion.     

Investigation of thermal behavior of nicotinic acid

The thermal behavior of nicotinic acid under inert conditions was investigated by TG, FTIR and TG/DSC-FTIR. The results of TG/DSC-FTIR and FTIR indicated that the thermal behavior of nicotinic acid can be divided into four stages: a solid-solid phase transition (176–198°C), the process of sublimation (198–232°C), melting (232–263°C) and evaporation (263–325°C) when experiment was performed at the heating rate of 20 K min⁻¹. The thermal analysis kinetic calculation of the second stage (sublimation) and the fourth stage (evaporation) were carried out respectively. Heating rates of 1, 1.5, 2 and 3 K min⁻¹ were used to determine the sublimation kinetics. The apparent activation energy, pre-exponential factor and the most probable model function were obtained by using the master plots method. The results indicated that sublimation process can be described by one-dimensional phase boundary reaction, g(α)=α. And the ‘kinetic triplet’ of evaporation process was also given at higher heating rates of 15, 20, 25, 30 and 35 K min⁻¹. Evaporation process can be described by model of nucleation and nucleus growing, .     

Kinetics of non-isothermal oxidation of anhydrous milk fat rich in conjugated linoleic acid using differential scanning calorimetry

Anhydrous milk fat (AMF) with low, medium, and high content of conjugated linoleic acid (L-, M-, and H-CLA) was oxidized using differential scanning calorimetry (DSC) at five different heating rates (3, 6, 9, 12, and 15 °C min⁻¹) in a temperature range of 100–350 °C. For the first time, kinetic oxidation parameters of AMF rich in CLA are reported. DSC spectra were analyzed to locate the start temperature (T _s), onset temperature (T _on), and maximum heat flow temperature (T _p). These reference points were further used to calculate the effective activation energy (E) and pre-exponential factor (z) using the Ozawa-Flynn-Wall method. The T _s shifts to lower values as the CLA content increases, while the T _on and T _p were less affected by the CLA content. The calculated kinetic parameters not only depend on the ratio between unsaturated to saturated fatty acids but also on the selected reference points. For the L-CLA sample, the E values calculated from T _s, T _on, and T _p were 146.51, 114.11, and 121.31 kJ mol⁻¹, respectively. For the M-CLA sample, the E values calculated were 112.42, 104.06, and 87.41 kJ mol⁻¹, respectively. For the H-CLA sample, the E values calculated were 87.60, 82.42, and 73.64 kJ mol⁻¹, respectively. These variations in E values do not have any physical background according to the compensation effect. In non-isothermal oxidation of AMF, several reactions with different kinetic parameters simultaneously take place and DSC only detects those reactions that have the highest exothermal effect. The T _s is the most consistent reference point to calculate E and z values.     

Adsorption properties of BEA zeolites and their aluminum phosphate extrudates for purification of isomaltose

The disaccharide isomaltose is produced via an enzymatic reaction and is adsorbed to BEA zeolite. This reaction integrated adsorption can be achieved as fluidized bed as well as fixed bed. We investigated isotherms, adsorption enthalpies and sorption kinetics of BEA zeolite and extrudates with a novel aluminum phosphate sintermatrix. These extrudates contain 50% (w/w) of BEA 150 zeolites (Si/Al = 75) as primary crystals. BET-surface for extrudates is 245 m²⋅g⁻¹ and 487 m²⋅g⁻¹ for zeolite. Extrudates show a monomodal macropore structure with a maximum at 90 nm. All isotherms show a type I shape. For lower equilibrium concentrations, which occur during the enzymatic reaction, Henry’s law is applied and compared to a Langmuir model. Adsorption equilibrium constant K _i,L calculated from Langmuir for extrudates at 4 °C is 64.7 mL⋅g⁻¹ and more than twice as high as obtained from Henry’s law with K _i is 26.8 mL⋅g⁻¹. Adsorption on extrudates at 4 °C is much stronger than on zeolite crystals where the Henry coefficient K _i is 17.1 mL⋅g⁻¹. Adsorption enthalpy Δh _Ad calculated from van’t Hoff plot with the Henry equation is −44.3 kJ⋅mol⁻¹ for extrudates and −29.6 kJ⋅mol⁻¹ for zeolite crystals. Finally, the kinetics for ad- and desorption were calculated from the initial slope. The diffusion rate for ad- and desorption on extrudates were in the same range while adsorption on zeolites is three orders of magnitudes faster than desorption.     

Water sorption and glass transition of freeze-dried camu-camu (myrciaria dubia (H.B.K.) Mc Vaugh) pulp

Differential scanning calorimetry (DSC) was used to determine phase transitions of freeze-dried camu-camu pulp in a wide range of moisture content. Samples were equilibrated at 25°C over saturated salt solutions in order to obtain water activities (a_w) between 0.11–0.90. Samples with a_w>0.90 were obtained by direct water addition. At the low and intermediate moisture content range, Gordon–Taylor model was able to predict the plasticizing effect of water. In samples, with a_w>0.90, the glass transition curve exhibited a discontinuity and T^’_g was practically constant (–58.8°C), representing the glass transition temperature of the maximally concentrated phase(T_g ).     

Preparation and ionic conductivity of poly(ethylene oxide) oligomers having thiolate groups on the chain ends

Poly(ethylene oxide) (PEO) oligomers having alkali metal thiolate groups on the chain ends (PEO _m -S⁻M⁺) were prepared as an ion conductive matrix. The molecular weight of the PEO part (m) and the content of the thiolate groups in the molecule were changed to analyze the effect of carrier ion concentration in the bulk. In a series of potassium salt derivatives, PEO₃₅₀-SK showed the highest ionic conductivity of 6.42 × 10⁻⁵ S/cm at 50 °C. In spite of a poor degree of dissociation which was derived from the acidity of the thiolate groups, PEO _m -SM showed quite high ionic conductivity among other PEO/salt hybrids. PEO _m -SM had glass transition temperatures (T _g) 20 °C lower than other PEO/salt hybrids. Lowering the T _g was concluded to be effective in providing higher ionic conductivity for PEO-based polymer electrolytes. Received: 30 April 1999 / Accepted: 20 June 1999     

Thermal Analysis of the Poly(Siloxane)–Poly(Tetrafluoroethylene) Coating System

Thermal properties of poly(siloxane)–poly(tetrafluoroethylene) (SIL–PTFE) system were investigated, using Perkin Elmer DSC-7 differential scanning calorimeter and TGA-7 thermogravimetric analyzer. For SIL–PTFE compositions, one glass transition temperature T _g has been found, in accordance with the reciprocal rule up to about 40 mass% of PTFE. However, for higher PTFE contents, T _g values about –118 to –112°C were observed that can be ascribed to motions of cross-linked SIL structures. Endo- and exothermic transitions, found in the range from 70 to 290°C, not observed for pure SIL and PTFE components, are considered as specific ones for the SIL–PTFE semi-IPN structures. The SIL–PTFE system, as well as its components, is thermally stable, if degradation reactions are considered; the temperatures of decomposition at the maximum decomposition rate were above 530°C. It has been found that the thermal stability of the SIL–PTFE system is increasing with the increase of the PTFE content. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of soluble,thermosetting polymides derived from 1,4-phenylenebis(phenylmaleic anhydride) and aromatic diamines

The dianhydride monomer 1,4-phenylenebis(phenylmaleic anhydride) was polymerized with various aromatic diamines in a one-step solution polymerization to afford high molecular weight, soluble polyimides containing backbone phenylmaleimide structures. The polymides were soluble in amide solvents, chlorinated hydrocarbons, and tetrahydrofuran at 25°C at a concentration of 15% (w/v), displayed molecular weight distributions (M_w/M_n) of 2.0–2.2 as determined by absolute GPC and showed T_g values of 240°C and above as measured by differential scanning calorimetry. In addition, polyimide thermosets were prepared from these materials by thermal cure at 350–360°C. The crosslinked polyimides displayed T_gs 20–25°C higher than their soluble precursors, and chloroform extraction indicated gel fractions ranging from 74–100% after cure. © 1994 John Wiley & Sons, Inc.