The effect of different types of carbon blacks on the rheological and thermal properties of acrylonitrile butadiene rubber

The influence of two types of carbon black filler N330 and N990 (primary particle size 46 nm and >230 nm) on elastomeric composites based on acrylonitrile-butadiene rubber (NBR) have been investigated. The activation energy (E _a) were determined from two high temperature rheokinetic curves (T ₁ = 180 °C and T ₂ = 190 °C). For tensile testing, the compounds with different content of carbon black were vulcanized in a hydraulic press at 150 °C. The stress-strain experiments were performed before and after ageing the specimens in an air-circulating oven at 100 °C for 168 h. The thermal degradation and thermal stability of carbon black filled NBR rubber was investigated by thermogravimetric analysis in a flowing nitrogen atmosphere at a heating rate of 10 °C/min.     

Sample temperatures during outdoor and laboratory weathering exposures

Effective exposure temperatures (T_eff) in Arizona were calculated from hourly or 10-min parsed irradiation data along with ambient, black panel, and sample temperatures. The T_eff represents a constant temperature that creates the same amount of photodegradation as the naturally varying temperature and provides a benchmark temperature for making lifetime predictions from accelerated laboratory exposures. The annual ambient and black panel T_eff at a Wittmann, Arizona site were 30 °C and 42 °C, respectively, assuming that the photodegradation has an activation energy (E_a) of 21 kJ/mol (5 kcal/mol). T_eff was only weakly dependent on E_a over the range of 10-40 kJ/mol (3-10 kcal/mol). Samples exposed as van sunroofs were found to have T_eff that were offset from the black panel temperatures by a constant amount for the entire year. Thus, measurements of sample and black panel need to be made for only a few weeks to determine the offset and give the annual sample T_eff if the annual black panel T_eff is known. Light-colored samples probably are better compared with the ambient temperatures. Sample temperatures in xenon arc exposures usually are higher than the outdoor T_eff, so Arrhenius temperature corrections need to be carried out to relate accelerated to outdoor exposures. Temperatures in xenon arc exposure tests often correspond more closely to maximum temperatures that samples might encounter for only a few hours per year.     

Boron increases the transition temperature and enhances thermal stability of heme proteins

Transition temperature and thermal stability of proteins were studied in the presence and absence of boron. The observed midpoint of thermal denaturation (T _m) of cytochrome c (Cyt c) at pH 9.2 was 68.8 °C, which in the presence of boron increased to 71.0 °C. For metmyoglobin, T _m increased from 79.7 °C in the absence of boron to 83.5 °C in the presence of boron. Boron caused an increase of 10% in the reversibility of thermal denaturation of cytochrome c when compared with control. Activity measurements of the heat treated proteins and T _m suggest an increased thermal stability toward inactivation and denaturation of heme proteins in the presence of boron.     

Magnetic superexchange involving the oxygen-sulfur-oxygen pathway of the sulfate ion: A Mössbauer spectroscopy and magnetic susceptibility study of Fe(2,9-di-CH3-phenanthroline) SO4

Zero-field Mössbauer spectra of powder samples of Fe(2,9-di-CH₃-phenanthroline) SO₄ over the range 1.7 to 300°K show a large (～ 3.6 mm/sec) temperature-independent quadrupole splitting corresponding to an orbital singlet ground term. The chemical isomer shift, δ_FE=O, is 1.16 mm/sec (source and absorber at 4.2°K) corresponding to six coordinate high-spin iron (II). Below 4.2°K, the compound exhibits magnetic hyperfine splitting suggesting slow relaxation and the possibility of long-range three-dimensional magnetic ordering with a critical temperature T_c such that 3.5°K < T_c < 4.2°K and an internal hyperfine field H_n = 325 kG at 1.69°K. High-field Mössbauer spectra at 300°K indicate that the principal component of the electric field gradient tensor is positive and axial. Similar spectra at 4.2°K show an absence of nuclear Zeeman splitting for applied fields up to 60 kG, and indicate that at 4.2°K the material is rapidly relaxing but with substantial magnetic polarization and a negative internal hyperfine field. The temperature dependence of the magnetic susceptibility confirms antiferromagnetic interactions with a broad maximum χ′_M at ～ 11.8°K presumably due to low-dimensionality exchange interactions (possibly one) along MOSOM chains. Least-squares fits of χ′_M^?1 versus T for T50°K indicate (Curie-Weiss behavior with C = 3.26 emu/mole, θ = -21.95°K, and μ_eff = 5.11.     

Determination of the glass transition temperature in thin polymeric films used for microelectronic packaging by temperature-dependent spectroscopic ellipsometry

We characterized the glass transition temperature T_g of thin polyimide films by temperature-dependent spectroscopic ellipsometry and compared the results to DSC measurements of the bulk polymer. The effect of the curing temperature on T_g and the thermal expansion α(T) was analyzed. An improved ellipsometric data evaluation was used to get most precise and reliable T_g data. T_g increased with increasing curing temperature, while the bulk T_g was considerably lower than the thin film T_g. Both observations are attributed to the temperature sensitive release of the imidization by-product 2-hydroxyethyl methacrylate (HEMA) and crosslinker components as well as decomposition products from the material. Variation in the curing temperatures of 230–380 °C led to an increase in the T_g of 34 °C.     

Thermogravimetric and FTIR studies of chitosan blends

Results of spectrophotometric and thermogravimetric studies of chitosan (CH) blends with polyvinyl alcohol (PVAL), starch (S) and hydroxypropylcellulose (HPC) obtained by casting from solutions in the form of transparent films containing 0–1.0 weight fraction of CH were discussed. Blends containing S are homogeneous only in the case of low-weight fraction of S (to 0.3).On the basis of results of thermodegradation in dynamic and isothermal conditions, thermal stability of the tested systems was estimated. Thermogravimetric measurements in dynamic conditions were carried out in the temperature range of 100–450 °C at constant heating rate 15 °C/min. From thermogravimetry (TG) and DTG curves the activation energy and characteristic parameters of degradation of the tested blends were determined. The observed growth of activation energy and T_p—temperature of initial weight loss, T_max—temperature of maximal rate and C_e—degree of conversion at the end of the measurement (at temperature 450 °C) along with the increase of polymer fraction (HPC and S) in the CH blend provides an evidence of improved thermal stability of the systems tested.Investigations in isothermal conditions in air at temperature from 100 to 200 °C confirmed appreciable improvement of CH thermal stability in the blends being tested.Infrared spectroscopic analysis of the blends showed a distinct stabilization of the process of chain scission. In the band at 1080 cm⁻¹ associated with absorption in –C–O–C– group during degradation of the blends at temperature 200 °C much smaller decrease due to molecular scission were observed than in the case of pure CH.     

Silica-containing polyetherimide hybrid films based on methyltriethoxysilane as precursor of inorganic network

Polyetherimide hybrid films containing 5–40% silica were prepared through a sol-gel process and thermal imidization by using methyltriethoxysilane as precursor of the inorganic network and a poly(amic acid) resulting from polycondensation reaction of 2,2-bis[4-(4-aminophenoxy)phenyl]propane with 2,2-bis[(3,4-dicarboxyphenoxy)phenyl]propane dianhydride. The properties of these films, morphology, water vapor sorption capacity, free surface energy, mechanical, thermal and electrical characteristics, were studied. The films exhibited good thermal stability, having an initial decomposition temperature above 470 °C and glass transition temperature in the range of 187–200 °C. They showed low dielectric constant and low dielectric loss in a large frequency field. Gas permeation tests using small molecules (He, N₂, O₂ and CO₂) at 6 bar and 30 °C indicated that the hybrid films containing higher silica content showed higher permeability for all the tested gases.     

Modification of poly(propylene carbonate) with chain extender ADR-4368 to improve its thermal,barrier, and mechanical properties

Melt blending with the application of epoxy compound ADR-4368 as a chain extender was used to chemically modify polypropylene carbonate (PPC). ¹H nuclear magnetic resonance spectroscopy (¹H NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tests using a universal material testing machine, a gas permeability tester, a water vapor permeability tester and other instruments were used to assess changes in the chemical structure, thermal and mechanical properties, and barrier efficacy of PPC before and after modification.The epoxy group in ADR-4368 reacted with the terminal hydroxyl group in PPC, considerably enhancing its mechanical properties, thermal stability and barrier efficacy to O₂ and CO₂. With the addition of 1% ADR-4368, the glass transition temperature of PPC was increased from 17 °C to 26.9 °C, while the thermal decomposition temperature (T_−5%) of PPC was increased from 177.3 °C to 240.6 °C. Moreover, the tensile strength of the modified PPC was improved from 3.3 MPa to 20.7 MPa.     

Effective moisture diffusivity and activation energy during convective drying of bread containing clove oil/orange oil

The aim of present study was to investigate the characteristic drying behaviour of bread with the convective drying method for increasing bread shelf life. Effective moisture diffusivity and activation energy were compared in detail. According to the results, bread samples were dried between 0 and 450 min for 40 °C, 0–180 min for 50 °C and 60 °C, respectively. The experimental data with high coefficient of determination (R²) changed between 0.889 and 0.998. The values of D_eff were obtained between 1.21 × 10^?9-1.22 × 10^?8 m²/s. Also, E_a values were found to be in range of 82.47–100.49 kJ/mol for bread samples which had additive-free and additive. When the bread samples without additives and the breads with essential oils were compared, it was found that the activation energy increased with the use of additives. Moisture content values decreased with the increase in time. Drying rate and moisture content relation showed the expected behaviour, thermally and morphologically.     

Homopolyimides containing both benzimidazole and benzoxazole with high Tg and low coefficient of thermal expansion

A pair of isomer diamines containing both benzimidazole and benzoxazole and derived homopolyimides were synthesized for the first time. Due to rich rigid and linear benzoazole units, as well as the strong intermolecular interactions from the hydrogen bonding and the charge transfer complexation (CTC), the obtained polyimides (PIs) exhibited outstanding thermal properties, including high thermal weight loss temperature (T_d5% = 540–561°C), high glass transition temperature (T_g = 392–421°C), and low coefficient of thermal expansion (CTE = 1.3–20.9 ppm/°C). In addition, the obtained PIs also showed ideal mechanical properties (T_S = 189–240 MPa, T_M = 4.1–5.0 GPa and E_B = 2.9%–4.7%). These potential novel PI films with high T_g and low CTE were expected to be applied to next generation of flexible display substrate material.     

Influence of thermal treatment on the glass transition temperature of thermosetting epoxy laminate

The influence of accelerated thermal treatment of thermosetting epoxy laminate on its glass transition temperature was studied. Lamplex^® FR-4 glass fibre-reinforced epoxy laminate (used for printed circuit board manufacturing) was used in these experiments. The composite was exposed to thermal treatments at temperatures ranging from 170 °C to 200 °C for times ranging from 10 to 480 h. The glass transition temperature (T_g) was analysed via dynamic mechanical analysis (DMA). It has been proven that the glass transition temperature rapidly decreases in reaction to thermal stress. The obtained T_g data were used for Arrhenius plots for different critical temperatures (T_g-crit. = 105–120 °C). From their slopes (?E_a/R), the activation energy of the thermal degradation process was calculated as 75.5 kJ/mol. In addition to this main relaxation mechanism, DMA also recorded one smaller relaxation process in the most aged samples. Microscopic analysis of the sample structure showed the presence of pronounced small regions of degradation both on the surface and in the inner structure, which are probably the causes of microscopic delamination and the smaller relaxation process.     

Spectroscopic studies on the effect of field strength upon the curie transition of a VDF/TrFE copolymer

Infrared spectroscopic studies of the effects of field strength upon the ferroelectric phase transition behavior of a VDF/TrFE (75/25) copolymer upon heating and cooling in an electric field have revealed new findings. The paraelectric phase in the absence of an electric field resembles the α phase of PVDF with a trace of short trans sequences distributed randomly along the chain axis. The paraelectric phase in a high electric field is very different from that in the absence of an electric field. The paraelectric phase under an electric field has much longer trans sequences. The Curie transition temperature upon heating is a first-order transition temperature (T^↑_c) and is dramatically elevated from 120 to 135°C under the field of more than 0.4 MV/cm. Upon cooling, the paraelectric phase in an electric field does not show a clear transition. The field-induced phase transition and the loss of dipole switchability observed below a cooling temperature of 120°C, and their dependence on time and filed strength when exposed to a cyclic bipolar electric field are discussed. © 1993 John Wiley & Sons, Inc.     

Effect of the pH value on the thermal stability of alkaline phosphatase

The thermal stability of bovine and chicken intestinal alkaline phosphatase (IAP) was studied at 60°C over a pH range from 6.7 to 9.0. It was shown that the peaks of stability (at pH 7.5) and activity (at pH 9.0) do not coincide. The pH dependence of the elementary rate constants of dissociative thermal inactivation of the IAP dimers was determined: k ₁ (the rate constant of dissociation of active dimer E₂) and k _d (the rate constant of denaturation of the inactive monomers). At pH 7.5, the stability IAP attains its highest level. As the pH increases, k ₁ increases drastically while k _d does so only slightly. A comparison of the rate constants of dissociation k ₁ and association k ₁ showed that the interrelation between these parameters explains why the stability of the active enzyme is lower at acidic and basic pH values. The pH produces a weaker effect on the stability of the inactive monomers. An analysis of the thermal stability of chicken IAP at an optimum pH value and 55–60°C showed that the thermal inactivation is a three-stage process (including dissociation and denaturation) with an induction period. Measuring the induction period makes it possible to determine the minimum number of latent stages preceding the dissociation of E₂: 6, 4, and 3 at 55, 58, and 60°C, respectively.     

Differential scanning calorimetric examination of ruptured lower limb tendons in human

The tendon ruptures are serious injuries of the lover limb in middle age and physically active population. While the Achilles tendon rupture is common, the patellar ligament and quadriceps ligament ruptures are an absolutely rare injury. Usually there is no correlation between the velocity of the trauma and the supervening of the rupture. The aetiology of the degenerative changes in the collagen structures of the tendons and ligaments which could be disposed for the rupture are still not clear. Our hypothesis was that before the injury there are clear pathological abnormalities in the tissues of the tendons, which are predisposed for the rupture, and could be monitored besides the classical histological methods by differential scanning calorimetry. The thermal denaturation 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. DSC scans clearly demonstrated significant differences between the control and ruptured samples (control: T _m = 59.7 °C, T _1/2 = 1.4 °C and ΔH _cal = 8.54 J/g; ruptured Achilles tendon: T _m = 62.75 °C, T _1/2 = 2.6 °C and ΔH _cal = 1.54 J/g, ruptured Quadriceps tendon: T _m = 64.8 °C, T _1/2 = 1.6 °C and ΔH _cal = 1.53 J/g, ruptured Patellar tendon: T _m = 63.9 °C, T _1/2 = 1.41 °C and ΔH _cal = 0.97 J/g). 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 degenerated human tendons and ligaments. We can prove with this method that the degenerative changes of the tissue elements increase the thermal stability of collagen tissues of the tendons which could be disposed for the rupture.     

The thermodynamic dissociation constant of naphazoline by the regression analysis of potentiometric data

The mixed dissociation constant of naphazoline is determined at various ionic strengths I [mol dm⁻³] in the range of 0.01 to 0.26 and at temperatures of 25°C and 37°C using ESAB and HYPERQUAD regression analysis of the potentiometric titration data. A strategy of efficient experimentation is proposed in a protonation constant determination, followed by a computational strategy for the chemical model with a protonation constant determination. Two group parameters, L ₀ and H _T were ill-conditioned in the model and their determination is therefore uncertain. These group parameters, L ₀ and H _T, can significantly influence a systematic error in the estimated common parameter pK_a and they always should be refined together with pK _a. The thermodynamic dissociation constant pK _a^T was estimated by nonlinear regression of {pK _a, I} data at 25°C and 37°C: for naphazoline pK _al^T = 10.41(1) and 10.13(2). Goodness-of-fit tests for various regression diagnostics enabled the reliability of the parameter estimates to be found.      

Kinetic study of crystallization of PHB in presence of hydroxy acids

Poly(3-hydroxybutyrate), PHB, has been structurally modified through reaction with hydroxy acids (HA) such as tartaric acid (TA) and malic acid (MA). The crystallization kinetic of the samples was evaluated by isoconversional method through nonlinear fitting to obtain the estimation for activation energy (E _a ) and pre-exponential (A) values. The thermal behavior of the crystallization temperature, 44.8 and 58.9 °C at 5 °C/min, and results obtained to the average activation energy, 73 ± 9 kJ mol⁻¹ and 63 ± 1 kJ mol⁻¹, to PHB/MA and PHB, respectively, are suggesting that malic acid may be deriving plasticizer units from its own PHB chain. PHB/TA show increase in the medium value of E _a, 119 ± 2 kJ mol⁻¹ and T _c = 48.2 °C (at 5 °C/min), indicating that tartaric acid is probably interacts in different way to the of PHB chain (E _a=73 ± 9 kJ mol⁻¹, T _c = 44.8 °C at 5 °C/min).     

Synthesis,characterization and kinetic computations of fullerene (C60)–CuO on the mechanism decomposition of ammonium perchlorate

CuO, C₆₀–CuO, and Al/C₆₀–CuO nanostructures were synthesized and characterized by scanning electron microscope (SEM)/energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR). differential scanning calorimetry (DSC)/thermogravimetric analysis (TGA) measurements were performed to study the influence of these additives on ammonium percolate (AP) thermal decomposition. From the comparison of DSC and TGA plots, the catalytic effect of CuO and C₆₀–CuO has been clearly noticed in which the lower temperature decomposition of AP was decreased from 331 °C to 315 °C, 310 °C, and 303 °C (in the presence of CuO, C₆₀–CuO, and Al/C₆₀–CuO, respectively) and the HTD was dropped from 430 °C (pure AP) to 352 °C, 335 °C, and 317 °C (for the compounds AP/CuO, AP/C₆₀–CuO, and AP/Al/C₆₀–CuO, respectively). The kinetics of the samples were investigated by isoconversional models and compared with an iterative procedure. The results of pure AP indicated a complex decomposition process involving three decomposition steps with specific reaction mechanism. The nanocatalysts incorporated in the AP have clearly affected its decomposition process in which the reaction mechanism and the number of stages were changed.     

Room temperature processable heat‐resistant epoxy‐oxazolidone‐based syntactic foams

Syntactic foams based on oxazolidone‐modified epoxy resin using glass microballoons as reinforcing filler with varying densities were processed. The influence of various grades of microballoons and their concentration on the mechanical, thermal, thermomechanical, and flammability characteristics were investigated. The effect of temperature on the compressive strength with density was monitored in detail. By incorporating the microballoons, T_g of the syntactic foam increased from 90 °C to 115 °C. Thermal conductivity was found to decrease from (0.064 to 0.056 W/(m·K)) in conjunction with decreasing resin to filler ratio. In the case of composites filled with K25 alone, the creation of large voids due to less effective packing between the microballoons led to lower thermal conductivity. The specific heat of the different composites was in the range of 0.32 to 0.44 cal/g/°C, and the coefficient of thermal expansion was in the range of 13.2 to 17.4 × 10⁻⁶/°C with limiting oxygen index of 28% to 33%.     

Structure and multiferroic properties of Bi<Subscript>5</Subscript>FeTi<Subscript>3</Subscript>O<Subscript>15</Subscript> thin films prepared by the sol–gel method

The Bi₅FeTi₃O₁₅ (BFTO) films of layered structure have been fabricated on Pt/Ti/SiO₂/Si substrates by the sol–gel method. The thermal decomposition behaviors of precursor powder were examined using thermo-gravimetric and differential scanning calorimeters analysis. The optimal heat treatment process for BFTO films were determined to be low-temperature drying at 200 °C for 4 min and high-temperature drying at 350 °C for 5 min followed by annealing at 740 °C for 60 min, which led to the formation of compact films with uniform grains of ~300 nm. The structural, surface topography, ferroelectric and magnetic properties of the films were investigated. The remnant polarization (2P _r) of BFTO thin films under an applied electric field of ~550 kV/cm are determined to be 67.5 μC/cm² . Meanwhile, the weak ferromagnetic properties of the BFTO films were observed at room temperature.     

Influence of imide functionalized organo‐modified Mg‐Al layered double hydroxide on the thermal and mechanical properties of new aliphatic‐aromatic poly (amide‐imide)

A new dicarboxylic acid modified Mg‐Al LDH (DLDH) containing imide groups was prepared and its effects on the thermal and mechanical properties of the new synthesized aliphatic‐aromatic poly (amide‐imide) (PAI) were investigated via preparation of PAI/nanocomposite films by solution casting method. The results of X‐ray diffraction (XRD), field emission‐scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) showed a uniform dispersion for LDH layers into the PAI matrix. For comparison, the effects of polyacrylic acid‐co‐poly‐2‐acrylamido‐ 2‐methylpropanesulfonic acid (PAMPS‐co‐PAA) modified Mg‐Al LDH (ALDH) on the PAI properties were also studied. The thermogravimetric analysis (TGA) results exhibited that the temperature at 5 mass% loss (T₅) increased from 277 °C to 310 °C for nanocomposite containing 2 mass% of DLDH, while T₅ for nanocomposite containing 2 mass% of ALDH increased to 320 °C, along with the more enhancement of char residue compared to the neat PAI. According to the tensile test results, with 5 mass% DLDH loading in the PAI matrix, the tensile strength increased from 51.6 to 70.8 MPa along with an increase in Young's modulus. Also the Young's modulus of PAI nanocomposite containing 5 mass% ALDH reduced from 1.95 to 0.81 GPa.