Characteristics and Kinetics of Thermal Degradation of Fluoroether Rubber

An advanced, heat-resistant fluoroether rubber (FM-20) was subjected to dynamic thermogravimetric analysis (TGA) in the air atmosphere. The results suggested that its thermal degradation process can be divided into two parts. As the heating rate increased, the initial decomposition temperature and degradation temperature would move to higher ranges. The apparent activation energy of thermal decomposition, calculated by the Kissinger, Friedman and Flynn-Wall-Ozawa methods were 209, 240, and 211kJ/mol, respectively. Furthermore, the probable thermal degradation mechanism was also analyzed by the Coats-Redfern method. As a result, the most reasonable thermal degradation mechanism of FM-20 was g (α) = α^3/2     

Thermal Degradation Behavior and Flame Retardancy of Polycarbonate Containing Poly[(phenylsilsesquioxane)-co-(dimethylsiloxane)] and Potassium Diphenyl Sulfonate

The synergistic effect of poly[(phenylsilsesquioxane)-co-(dimethylsiloxane)] (PPSQDS) and potassium diphenyl sulfonate (KSS) on the thermal degradation and flame retardancy of polycarbonate (PC) was studied. The flame retardancy of PC was improved by the combination of PPSQDS and KSS, and a V-0 rating for 1.6 mm thickness sample was successfully obtained. The thermal degradation of the flame retarded PC was characterized by thermogravimetric analysis (TGA) and the degradation activation energy (E _a) was calculated according to the Kissinger and Flynn-Wall-Ozawa (F-W-O) methods. The E _a value of PC was decreased by the combination of PPSQDS and KSS, indicating that the synergistic effect of PPSQDS and KSS facilitates the thermal degradation of PC and accelerates char formation.     

A thermal and electrochemical properties research on gel polymer electrolyte membrane of lithium ion battery

N-methyl-N-propyl-piperidin-bis(trifluoromethylsulfonyl)imide/bis(trifluoromethylsulfonyl) imide lithium base/polymethyl methacrylate(PP₁₃TFSI/LiTFSI/PMMA) gel polymer electrolyte (GPE) membrane was prepared by in situ polymerization. The physical and chemical properties were comprehensively discussed. The decomposition characteristics were emphasized by thermogravimetric (TG-DTG) method in the nitrogen atmosphere at the different heating rates of 5, 10, 15 and 20 °C min⁻¹, respectively. The activation energy was calculated with the iso-conversional methods of Ozawa and Kissinger, Friedman, respectively, and the Coats-Redfern methods were adopted to employ the detailed mechanism of the electrolyte membrane. The equation f(α)=3/2[(1−α)^1/3−1] was quite an appropriate kinetic mechanisms to describe the thermal decomposition process with an activation energy (E_α) of 184 kJ/mol and a pre-exponential factor (A) of 1.894×10¹¹ were obtained.     

The Peculiar Temperature Response of Dynamic Rheological Behaviors of Poly (Vinyl Chloride)/trioctyl Trimellitate (100/70) System

The dynamic rheological behavior, application of time-temperature superposition (TTS) and the failure mechanism of TTS are studied for the poly(vinyl chloride) (PVC)/trioctyl trimellitate (TOTM) (100/70) system. The Arrhenius equation, Williams–Landel—Ferry (WLF) equation, mathematical non-linear fitting and manual shift are applied to TTS fitting. For the PVC/TOTM (100/70) system, none of those methods can give well-superimposed master curves with either single horizontal shift or two-dimensional (horizontal and vertical) shift. The failure reason is attributed to the thermorheological complexity of the PVC/TOTM (100/70) system. Curves of the storage modulus versus the frequency can be well fitted with an empirical equation (G′=G′₀+Kω ⁿ ) usually used to describe filled polymer systems, indicating the multilevel flowing unit characteristic in this system. With the increase of test temperature, the structure of the PVC/TOTM (100/70) system changes and an apparent transition appears in the rheological behavior. Differential scanning calorimetry (DSC) results reveal that for the PVC/TOTM (100/70) system there are microcrystallites present below 220°C, but above the rheological transition temperature (190°C) the bulk of the microcrystallites melted, which corresponds to the appearance of viscous flow participating in the rheological behavior. It verifies the fact that the gel networks crosslinked by microcrystallites dominate the rheological behavior below the transition temperature in the PVC/TOTM (100/70) system. The quantity of microcrystallites remaining in the melt determines the perfection of the physical gel networks. With the increase of test temperature, the microcrystallites melted gradually and the gel networks are broken up.     

Model fitted and model free approaches for crystallization kinetics in Se85Te15-xBix glasses

In this research work, we have described the model-fitted and model free approaches for the study of crystallization kinetics in Se₈₅Te_15-xBi_x chalcogenide glasses. Se₈₅Te_15-xBi_x bulk alloys were synthesized by melt quenching technique. High Resolution X- Ray diffraction (HRXRD) was used to confirm the amorphous nature of prepared alloys. Non-isothermal Differential Scanning Calorimetry (DSC) measurements were done at heating rates of 5, 10, 15, 20 and 25 K/min for crystallization kinetics studies in Se₈₅Te_15-xBi_x glasses. The various characteristic temperatures, such as glass transition (T_g), on-set crystallization (T_c) temperature, peak crystallization temperature (T_p) and melting temperatures (T_m) have been obtained from various DSC thermograms. The activation energies of glass transition (ΔE_t) were calculated by using Kissinger and Moynihan approaches and found to be minimum for Se₈₅Te₁₂Bi₃ chalcogenide glass which indicates that this alloy has maximum probability to jump into a less configurational energy state and has larger stability. The model-free approaches; Kissinger–Akahira–Sunose (KAS), Flynn-Wall-Ozawa (FWO), Tang and Straink (TS) reveal that the activation energy of crystallization varies with crystallization degree and temperature both. This variation shows that amorphous to crystalline phase transformation in Se₈₅Te_15-xBi_x chalcogenide glasses is a complex process with various nucleation and growth mechanisms.     

Effect of different plasticizers on the secondary relaxation of poly(vinyl chloride)

Samples of poly(vinyl chloride) plasticized with variable amounts of either dibutyl phthalate (DPB) or dicyclohexyl phthalate (DCHP) were investigated by dynamic-mechanical measurements in the β relaxation temperature range. In this range of temperature, a superposition of the relaxation due to the cyclohexyl group with the PVC β peak was found for the samples plasticized with DCHP. By studying the dependence of the activation energy and of the peak broadness on the DCHP concentration it was possible to show that the PVC β relaxation is reduced to zero at the critical plasticizer weight fraction W₁ = 0.2. For the PVC-DBP series the β peak disappears at the same plasticizer content. These results strengthen the hypothesis that the β peak of PVC is due to a kind of cooperative motion since 1 mole of plasticizer for every 20 repeating units of the polymer is sufficient to suppress the PVC β relaxation.     

Kinetic regularities and mechanism of polymerization of perfluoromethylvinyl ether at high pressures

The kinetics of the thermal polymerization of perfluoromethylvinyl ether (PFMVE) is studied at pressures of 3–13 kbar (300–1300 MPa) and temperatures of 80–260°C. The activation energy (E _act = (76 ± 3) kJ/mol) and activation volume (ΔV₀^⪼ = −(27 ± 2) cm³/mol) for the overall polymerization rate are determined. The inhibition method is used to estimate the activation energy of thermal initiation (E _in = (79.9 ± 3) kJ/mol). The quantity E _p − (1/2)E _t was calculated to be 36.6 ± 3 kJ/mol. The limiting polymerization temperature was evaluated: T _lim = (180 ± 3)°C. A mechanism of PFMVE polymerization is proposed on the assumption that the reaction is bimolecular.     

Thermal and Thermo-Oxidative Degradation of Biodegradable Poly(Ester Urethane) Containing Poly(L-Lactic Acid) and Poly(Butylene Succinate) Blocks

A novel biodegradable poly(ester urethane; PEU) was synthesized by chain extension reaction of dihydroxylated poly(L-lactic acid; PLLA) and poly(butylene succinate; PBS) using diisocyanate as a chain extender. The kinetics of thermal and thermo-oxidative degradation of PEU containing PLLA and PBS blocks were studied by thermogravimetric analysis (TGA). TGA results indicated that PEU was more stable in air than in nitrogen and went through a two-stage degradation process irrespective of the experimental atmosphere. Activation energy of each stage was calculated by means of Kissinger, Kim-Park, Friedman, Flynn-Wall-Ozawa, and Kissinger-Akahira-Sunose methods. For the first stage, the activation energy value obtained in air was slightly higher than the corresponding value obtained in nitrogen; and for the second stage, the activation energy showed a much higher value in air than in nitrogen. The Coats-Redfern method was employed to study the degradation mechanism of each stage. The results indicated that the degradation of the first stage follows the P3/4 mechanism irrespective of the experimental atmosphere; the degradation of the second stage of PEU obeys the P1 mechanism in nitrogen while P3/2 in air.     

新型GeSe2-In2Se3-AgI玻璃性能研究

采用传统熔融-淬冷法制备了一系列新型(100-x) (4GeSe₂-In₂Se₃) -xAgI(x=20,30,40 mol%)硫系玻璃样品.利用X射线衍射分析、差热分析、可见-近红外吸收光谱、红外透过光谱、喇曼分析等技术手段研究了该玻璃系统的组成、结构、热稳定性和光学特性等.利用Tauc方程计算出了样品的间接带隙;测试了部分样品在不同升温速率下的差示扫描量热曲线,并采用Kissinger法计算了玻璃样品的析晶活化能.X射线衍射数据表明,该玻璃体系在较宽的组分范围内有良好的非晶特性,成玻范围较宽;差热分析和析晶动力学研究表明,玻璃样品70(4GeSe₂-In₂Se₃)-30AgI具有较好的热稳定性(ΔT=114℃)和较高的活化能(E_a=320.4 kJ/mol).随着AgI含量的增加,玻璃的短波吸收限蓝移,并且光学带隙有增大的趋势.此外,红外透过光谱分析表明该玻璃体系具有良好的红外透过性能,其红外截止波长不会随着AgI含量的增加而发生明显变化,皆为16μm左右.     

Blending Optimization of Non-Dioctyl Phthalate Plasticized Poly (vinyl chloride) Formulations

The use of non-ortho-phthalate plasticizers in poly (vinyl chloride) (PVC) packaging materials and medical devices has been in increasing demand due to worldwide regulatory trends to minimize or eliminate phthalate plasticizers (particularly di(2-ethylhexyl)phthalate (DEHP) or dioctyl phthalate (DOP)) in the PVC industry. This study evaluates the dry-blending cycle time of a suspension grade PVC formulated with various non-DOP plasticizers, di-(2-ethylhexyl) terephthalate (DEHT or DOTP), tris (2-ethylhexyl) trimellitate (TEHTM or TOTM) and alkyl sulphonic phenyl ester (ASE), and compares them with the DOP standard. A design of experiments was also conducted to study the critical dry-blending parameters for optimization of PVC formulated with only DEHT. Effects of PVC temperature (measured during plasticizer addition to the blender), plasticizer pre-heat temperature, plasticizer and lubricant concentrations and the method of plasticizer addition on the dry-blending cycle time and peak amperage of the blender were studied. The blending cycle time is shown to be related to the resultant plasticizer efficiency and the peak amperage is related to the power consumption (the energy required to mix the PVC).     

Thermal stability and crystallization kinetics of Ge13In8Se79 chalcogenide glass

Ge-In-Se system, similar to many other chalcogenide glasses, has attracted much attention due to its interesting physical properties and applications. This article reports thermal analysis and estimation of activation energies of the glass transition and amorphous-crystallization transformation of Ge₁₃In₈Se₇₉ chalcogenide glass. The kinetic parameters were investigated under a non-isothermal condition at different heating rates (7–40?K/min) using differential scanning calorimetric (DSC) technique. The amorphous nature of the samples was confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The activation energy was calculated from DSC data using five isoconversional methods: Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Tang, Starink, and Vyazovkin. The results confirm that the activation energy of crystallization varies and depends on the degree of crystallization as well as temperature. It was also observed that the transformation from amorphous to the crystalline structure is complex involving different mechanisms of nucleation, diffusion, and growth.     

Kinetics,mechanism and thermodynamics of reactions of CH3NHNH2 with OOH

Reactions between CH₃NHNH₂ and OOH radical were studied using computational methods. The activation energies (E_a) and Gibbs free energies of activation (ΔG^#) were calculated at the MP2 and B3LYP levels of theory. The calculated activation energies of the hydrogen abstraction reactions were less than 100 kJ/mol and those for the substitution reactions were about 150–250 kJ/mol. The calculated activation energies for the intra-molecular hydrogen transfer reactions in CH₃NHNH, CH₂NNH₂ and CH₃NN molecules were 210–250 kJ/mol. Catalytic effect of the water molecule on the intra-molecular hydrogen transfer reactions was studied. It was found that the water molecule decreases the activation energies by about 70–100 kJ/mol. Rate constants of the reactions were calculated using transition state theory in the temperature range of 298–2000 K. Consecutive hydrogen abstraction reactions from CH₃NHNH₂ led to the formation of CH₂NN, which was a very stable molecule.     

Ionic transport, thermal, XRD, and phase morphological studies on LiCF3SO3-based PVC–PVdF gel electrolytes

The plasticized polymer electrolyte composed of polyvinylchloride (PVC) and polyvinylidene fluoride (PVdF) as host polymer, the mixture of ethylene carbonate and propylene carbonate as plasticizer, and LiCF₃SO₃ as a salt was studied. The effect of the PVC-to-PVdF blend ratio with the fixed plasticizer and salt content on the ionic conduction was investigated. The electrolyte films reveal a phase-separated morphology due to immiscibility of the PVC with plasticizer. Among the three blend ratios studied, 3:7 PVC–PVdF blend ratio has shown enhanced ionic conductivity of 1.47 × 10⁻⁵ S cm⁻¹ at ambient temperature, i.e., the ionic conductivity decreased with increasing PVC-to-PVdF ratio and increased with increasing temperature. A temperature dependency on ionic conductivity obeys the Arrhenius behavior. The melting endotherms corresponding to vinylidene (VdF) crystalline phases are observed in thermal analysis. Thermal study reveals the different levels of uptake of plasticizer by VdF crystallites. The decrease in amorphousity with increase in PVC in X-ray diffraction studies and larger pore size appearance for higher content of PVC in scanning electron microscopy images support the ionic conductivity variations with increase in blend ratios.     

Ionic conductivity, thermal stability and FT-IR studies on plasticized PVC / PMMA blend polymer electrolytes complexed with LiAsF6 and LiPF6

The lithium salt (x) (x=LiAsF₆, LiPF₆) was complexed with a blend of poly(vinyl chloride) (PVC) / poly(methyl methacrylate)(PMMA) and plasticized with a combination of ethylene carbonate(EC) and propylene carbonate(PC). The electrolyte films were prepared using doctor blade method and subjected to ionic conductivity measurements at nine different temperatures viz.,-30, -15, 0, 15, 30, 40, 50, 60 and 70 °C. The films were also subjected to TG - DTA and FT-IR analysis. The effect of salt on ionic conductivity is discussed. A 75:25 PMMA/PVC blend at 60 % plasticizer content has been found to possess optimal properties in terms of ionic conductivity, thermal and electrochemical stability.     

Thermodynamics and heat treatment of B-enriched nanocomposite NdFeB alloys containing Dy

The thermodynamics of B-enriched NdFeB alloys (Nd_1-xDy_x)_4.5Fe₇₇B_18.5 (x=0.00.4) is investigated by the Kissinger method, with the aim of obtaining an optimized microstructure for these nanocomposite NdFeB alloys. The appearance activation energy (E_a) of the first two stages, calculated by the Kissinger method, increases with increasing Dy content. The crystallization procedure and microstructural evolution are characterized by differential scanning calorimetry (DSC), in-situ X-ray diffraction (XRD), and transmission electron microscopy (TEM). A step-annealing (SA) method is employed, and an optimal microstructure with a narrow distribution of grain sizes is obtained in the samples annealed by this method. Accordingly, the maximum remanence, remanence ratio, coercivity, and energy product of the samples annealed by the SA method are increased, from their values in conventionally annealed samples of the same compositions, to 1.30 T, 0.82, 261 kA/m, and 134 kJ/m³, respectively. PACS 65.80.+n; 61.10.-i; 07.20.Dt; 07.55.Db; 75.30.Et     

Influences of Bis-(2,6-Diisopropylphenyl) Carbodiimide on the Thermal Stability and Crystallization of Poly(P-Dioxanone)

The influences on the thermal degradation and crystallization behaviors of poly(p-dioxanone) (PPDO) were initially investigated by adding bis-(2,6-diisopropylphenyl) carbodiimide (labeled as St). It was found that the addition of St could significantly enhance the thermal stability and crystallizability of PPDO. The thermal decomposition temperature of PPDO increased with the increase of the amount of St added. The thermal decomposition activation energies of PPDO increased from 94.2 to 130.8 kJ mol^?1 in the case of 5 wt% St. The addition of St did not change the crystal structure of PPDO, while it increased the number of nucleation sites and improved the crystallizability of PPDO. The crystallization activation energies, calculated by the Kissinger method, for PPDO and PPDO/5 wt% St were ?111.4 and ?141.5 kJ mol^?1, respectively, confirming the crystallizability of PPDO was enhanced after the addition of St.     

Nonisothermal Degradation Kinetics and Life Prediction of the Pendent Phenyl-Containing Polyarylate

The nonisothermal degradation kinetics of a pendent phenyl-containing polyarylate (PAR-P)were studied using different kinetic models, including the Kissinger method, Flynn–Wall–Ozawa (FWO) method, and Coats–Redfern (CR) method. The “three kinetic factors” of degradation, namely, activation energy (E), pre-exponential factor (A), and the reaction mechanism function (f(α)) were determined by these methods. Moreover, the lifetime equations of PAR-P were deduced, and its lifetime was predicted. The Kissinger method could be used to describe the nonisothermal degradation of PAR-P, and the results indicated that PAR-P could be degraded more easily in air than in nitrogen. The FWO method was expected to give more reliable values of the activation energy (209.71 kJ·mol^?1 in nitrogen and 176.22 kJ·mol^?1 in air) due to not having to introduce the reaction mechanism function during the calculation. According to the results of the CR method, the thermal degradation reaction mechanism was probably the R1 model in nitrogen, while it was likely to be the F2 model in air. The long-term and short-term use temperatures of PAR-P in air were 260°C and 300°C, respectively. The lifetime of PAR-P in nitrogen was much longer than that in air at low temperature, but had little difference when the use temperature exceeded 260°C. Although the lifetime of PAR-P obtained from the present work was unrealistic due to probable contributions from other unconsidered factors and being determined by a single factor method, it still could play a guiding role for designing the structure and determining the use conditions of the material.     

Nonisothermal Crystallization Kinetics of Miscible Blends of Polycaprolactone and Crosslinked Carboxylated Polyester Resin

The nonisothermal crystallization process of polycaprolactone (PCL)/crosslinked carboxylated polyester resin (CPER) blends has been investigated for different blend concentrations by differential scanning calorimetry (DSC). The DSC measurements were carried out under different cooling rates namely: 1, 3, 5, 10, and 20°C/min. Thermally induced crosslinking of CPER in the blends was accomplished using triglycidyl isocyanurate as a crosslinking agent at 200°C for 10 min. The cured PCL/CPER blends were transparent above the melting temperature of PCL and only one glass transition temperature, T_g, located in the temperature range between the two T_gs of the pure polymer components, was observed, indicating that PCL and crosslinked CPER are miscible over the entire range of concentration. The nonisothermal crystallization kinetics was analyzed based on different theoretical approaches, including modified Avrami, Ozawa, and combined Avrami–Ozawa methods. All of the different theoretical approaches successfully described the kinetic behavior of the nonisothermal crystallization process of PCL in the blends. In addition, the spherulitic growth rate was evaluated nonisothermally from the spherulitic morphologies at different temperatures using polarized optical microscope during cooling the molten sample. Only one master curve of temperature dependence of crystal growth rate could be constructed for PCL/CPER blends, regardless of different blend concentrations. Furthermore, the activation energy of nonisothermal crystallization process (ΔE_a) was calculated as a function of blend concentration based on the Kissinger equation. The value of ΔE_a was found to be concentration dependent, i.e., increasing from 83 kJ/mol for pure PCL to 115 and 119 kJ/mol for 75 and 50 wt% PCL, respectively. This finding suggested that CPER could significantly restrict the dynamics of the PCL chain segments, thereby inhibit the crystallization process and consequently elevate the ΔE_a.     

Investigation of temperature dependence of dielectric processes in thermally aged PVC insulation

The temperature dependence of dielectric processes was investigated of PVC cable insulation. For the investigation voltage response measurement was used, since this method ensures the independent investigation of conductive and polarisation processes. From the results of the measurement activation energies have been calculated to conductivity and polarisation conductivity of the material, the results are in 105.4 kJ/mol…133.8 kJ/mol and 32.1 kJ/mol…51.8 kJ/mol ranges, respectively.These results suggest that different charge carrier distribution mechanisms act main role in dc conductivity and slow polarisation processes in PVC cable insulating material.