Kinetics of non‐isothermal decomposition of basic cobalt carbonate

The kinetics of the thermal decomposition of basic cobalt carbonate was investigated under non‐isothermal heating in air media using thermogravimetric analysis (TGA). TG‐DTG curves showed that the decomposition proceeded through two well‐fined steps in air. Weight loss of the thermal decomposition of basic cobalt carbonate was in good agreement with the theoretical weight loss. The isoconversional method has been applied to the data in order to evaluate a dependence of the effective activation energy on the extent of conversion, and the possible conversion functions have been estimated through the multiple linear regression method. The average apparent activation energies of the second steps (0.4 ≤ α ≤0.9) were 96.607–144.537 kJ/mol.     

亚麻纤维热解动力学的“model free”法和Coats-Redfern模型拟合法研究

亚麻纤维是一种潜在的气化原料,本文对亚麻纤维的热解行为进行了热重分析研究。10 mg粒径为0.60～0.85 mm的亚麻纤维颗粒在高纯氮气的保护下分别以10、20、30、50 K·min^-1的升温速率线性升温到550℃。使用“model free”方法和Coats-Redfern模型拟合方法分析亚麻纤维的热解过程,并估算出热解反应的表观活化能。本文中“model free”方法包括Friedman、Flynn-wall-Ozawa、Vyazovkin and Wight三种等转化率方法及Kissinger法。三种等转化率方法均得到活化能随着转化率的升高而升高的规律。四种“model free”方法显示亚麻纤维的活化能主要在155～175 kJ·mol^-1之间,使用模型拟合方法所获得亚麻纤维热解反应的活化能值在175 kJ·mol^-1左右,使用模型拟合方法和“model free”方法所得的活化能值接近。这些活化能值可以为亚麻纤维高效的热化学利用提供基础数据。     

Isoconversional kinetic analysis of DSC data on nonisothermal crystallization: Estimation of Hoffman-Lauritzen parameters and thermal transitions in PET/MMT nanocomposites

The differential isoconversional method of Friedman is applied to non-isothermal melt crystallization DSC data to obtain effective activation energy ΔE. In comparison to neat PET, ΔE of intercalated 93A MMT clay nanocomposites (PCNs) decreased and highly dependent on the clay content. Hoffman-Lauritzen (H–L) secondary nucleation theory parameters, K_g and U* were evaluated using isoconversional approach of Vyazovkin and Sbirrazzuoli. Crystallization regime transition from regime III is observed at 190°C for neat PET, which shifted to higher temperature range 200°C–208 °C for PCNs. The K_g parameters for both regimes for PET are consistent with our isothermal experiments and reported in literature. However, the K_g values of nanocomposites are highly sensitive to the temperature dependent nucleation activity and ΔE of PET chain motion in melt and are not very much comparable with our isothermal results. Nevertheless, the observed results clearly indicate that the 93AMMT clay layers predominantly act as heterogeneous nucleating sites.     

Iterative method to improve calculation of the pre-exponential factor for dynamic thermogravimetric analysis measurements

The conventional isoconversional plot of ln(β/T²) versus 1/T usually has a large error of about −10% in calculation of the pre-exponential factor as a consequence of assuming h(x)=1. Iterative calculation using the plot of ln(β/hT²) versus 1/T is thus suggested. It is illustrated that the iterative method can greatly improve calculation for the pre-exponential factor. Success in calculation for the pre-exponential factor is accompanied by an enhanced accuracy in value of activation energy given by the iterative method in comparison with the conventional isoconversional plot of ln(β/T²) versus 1/T. One explanation is due to the compensation effect of the Arrhenius parameters. The iterative method has been applied to thermal degradation reactions of poly(methyl methacrylate) (PMMA) and polyethylene.     

Some remarks on the use of isothermal thermogravimetric data for the evaluation of kinetic parameters. Applications for degradation of polymeric materials

A critical analysis of the isoconversional methods for evaluating kinetic parameters of decomposition of solids from isothermal thermogravimetric data is presented. An isoconversional integral method to evaluate the activation energy is suggested. This method allows removing the errors due the correction of the degradation time by subtracting the induction period to onset of the main reaction (also including the time required to heat the sample to the temperature at which the isotherm is recorded). This procedure was used to study the degradation of two series of polymeric materials, (a) poly(vinyl chloride)/acrilonitrile–butadiene–styrene (PVC/ABS) blends and (b) poly(vinyl chloride)/chlorinated poly(ethylene) (PVC/CPE) blends. The values obtained for the activation energy are in fairly good agreement with those obtained from the Prout–Tompkins model in case (a) and from nonisothermal data in case (b). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 355–360, 2003     

腰果酚缩醛胺与环氧树脂的固化反应动力学的研究

在不同升温速率下,用差示扫描量热分析(DSC)研究了腰果酚缩醛胺固化剂(PCD)与环氧树脂的固化反应动力学。通过Kissinger、Crane方程和等转化率的方法求得了其表观活化能E=39.89kJ/mol,固化反应级数n=0.906。     

Synthesis and curing of liquid crystalline epoxy resin based on asymmetric mesogen

A novel liquid crystalline epoxy resin (LCER) derived from asymmetric mesogen unit was synthesized. Its structure and liquid crystalline behavior were characterized by hydrogen nuclear magnetic resonance (H‐NMR), differential scanning calorimetry (DSC), polarized optical microscopy (POM). The results indicated that the LCER converted to a nematic phase at 85°C during heating and finally became isotropic at 145°C. The curing behavior and phase behavior of the LCER with 4,4′‐diaminodiphenyl methane and methyl hexahydrophthalic anhydride were also studied by DSC and POM, respectively. Their apparent activation energy (E_a) was evaluated according to the Ozawa's isoconversional method. The results suggested that autocatalytic reaction had occurred in these two systems. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Thermal Stabilities and the Thermal Degradation Kinetics of Poly(ε-Caprolactone)

The thermal degradation behavior of poly(ε-caprolactone) (PCL) in nitrogen atmosphere was investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) techniques and Fourier Transform Infrared (FTIR) spectroscopy. TGA/DTG/DSC curves display only one main degradation step. TGA/FTIR results indicate PCL decomposes into CO₂ and hexanoic acid before 500°C. The activation energies were estimated by iterative isoconversional procedure. Friedman plot indicates a change in degradation mechanism. The differential method and integral method were used to confirm the exact kinetic mechanism. The best models are Dn (n = 1, 2, 3, and 4) when 0.08≤a≤0.2 and R2 when 0.25≤a≤0.8.     

Study of mullite formation in porcelain stoneware applying isoconversional and IKP methods

The growth process of mullite in a porcelain stoneware body has been studied under isoconversional, isokinetic relationship and invariant kinetic parameters. Activation energy for mullite crystallisation of over 589–628 kJ mol⁻¹ and a Ln A over 50–59 min⁻¹ was obtained. The model was Johnson–Melh–Avrami with n = 1.5. The model chosen implies quick nucleation and subsequent one or three-dimensional growth. Isoconversional methods show an independent activation energy variation in mid range conversion degrees. Lower and higher conversion degrees show different reactions in mullite formation. Results obtained with the methods employed here are in agreement with a previous paper where the Kissinger non-isothermal method and Ligero et al. approximation were applied.     

Nonisothermal crystallization kinetics study of LDPE/MWCNT nanocomposites: Effect of aspect ratio and surface modification

In this article, the effect of aspect ratio and chemical modification of multiwall carbon nanotubes (MWCNT) on the nonisothermal crystallization kinetics of LDPE/MWCNT nanocomposites was studied. Nine different samples were prepared using different MWCNT to study both effects. The cooling rate (R) was varied in the range 2–10°C/min. In this article, the effect of CNT loading, surface modification, and aspect ratio were studied. For the same MWCNT concentration, aspect ratio and  COOH modification had weak influence on both the peak crystallization temperature and the crystallization onset temperature. However, the crystallization onset temperature was significantly affected by the amount of MWCNT. The rate parameters in the modified Avrami method and Mo method [F(T)] of analyses show a very good fit of data. The Vyazovkin and Sbirrazzuoli method of analysis, which is based on Hoffman–Lauritzen theory for secondary crystallization, was also used. Temperature dependency of activation energy was obtained for 30–75% relative crystallinity of the produced nanocomposites. Activation energy based on calculations of Hoffman‐Lauritzen theory showed a decrease with the increase in the concentration of MWCNT and crystallization temperature. A proposed model of the form E = a exp (‐bXT) which relates the activation energy, E, to relative crystallinity, X, and crystallization temperature, T, was able to fit the whole set of data. Incorporation of MWCNT in nanocomposites lowers the activation energy; hence enhances the initial crystallization process as suggested by the different methods of data analyses. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Role of the alkyl moiety and counter ions on the thermal stability of chitosan derivatives

The thermal stability of alkyl chitosan derivatives (RChi) and N,N,N‐trimethyl chitosan bearing different counter ions (TMCX) was assessed by means of TG analyses. Multistep TG curves were observed for TMCX regardless of the counter ion. They exhibited lower DTG peak temperatures (TMCCl/238.2°C, TMCBr/224.5°C, TMCI/222.6°C, and TMC‐SO₄/237.0°C) as compared to the parent chitosan (306.4°C) while, in contrast, the RChi showed higher DTG temperatures (ButChi/311.7°C, OctChi/327.8°C, and DodecChi/306.3°C). The apparent activation energy values determined by using the isoconversional method revealed that the RChi derivatives have low activation energy (OctChi/111.6 ± 5 kJ/mol), whereas quaternary salts have high activation energy (TMCI/155.5 ± 10 kJ/mol). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

聚砜/酚醛树脂共混体系的固化反应动力学研究

采用非等温DSC方法研究了不同升温速率下聚砜(PSF/)酚醛树脂(PF)共混体系的固化动力学,运用Kissinger方法和Crane方程计算PSF/PF共混体系的活化能(Ea)及固化反应级数,并利用KAS等转化率法分析热塑性PF的固化机理及PSF对PF固化反应动力学的影响。结果表明:PSF的加入降低了PSF/PF共混体系固化反应的Ea值,当PSF含量为10%时,共混体系的Ea值最小;热塑性PF的固化过程比较复杂,Ea值随着转化率变化而改变;PSF的加入加剧了低转化率下PSF/PF共混体系Ea值的下降趋势,并使得其在高转化率下的固化机理与纯PF不同。     

Comparative study of the cure kinetics of an unsaturated polyester resin using different procedures

The cure kinetics of an unsaturated polyester resin were studied by differential scanning calorimetry (DSC), and different dynamic and isothermal procedures were compared. It was established that the isothermal kinetic analysis through the isoconversional adjustment lnt = A + E/RT is the method that offers the most accurate results for unsaturated polyester resin cure kinetics. From this comparative study it was noted that the activation energy not only varies according to the degree of conversion but also according to the method used to evaluate the kinetic parameters. Furthermore, it was shown that the activation energy cannot be separated from the other adjustment parameters, so the different kinetic procedures used are not generally comparable. Different methods of evaluating the degrees of conversion α and the reaction rates dα/dt according to the experimental reaction heat were also studied. It was found that the method used has a strong influence on the values of α and dα/dt, but only a slight one on the kinetic parameters.     

Methods to determine solubility parameters of polymers using inverse gas chromatography

Experimental values of the Flory–Huggins parameter, χ, between polymers and solvents, are frequently used to determine the solubility parameters of the polymers. A method using nonlinear curve fitting of RTχ/V was compared to the linear regression method commonly used. It was found that the formulas for the solubility parameter were the same, but the linear method produced a slightly different entropy term. The nonlinear method gave a lower correlation coefficient and wider confidence intervals and was more effective at distinguishing systems than the linear model. The effect of the deviation of probes in the solubility parameter model is discussed. Using probes with low solubility parameters to measure the polymer solubility parameter gave wider confidence intervals. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2894–2902, 2004     

Effect of bundling on the π plasmon energy in sub-nanometer single wall carbon nanotubes

Due to their unusual electronic and vibrational properties, single walled carbon nanotubes (SWCNTs) with sub-nanometer diameters d ∼ 0.5–0.9 nm have recently gained interest in the carbon community. Using UV–Vis–NIR spectroscopy and ultra-centrifugation, we have conducted a detailed study of the π plasmon energy (present at∼5–7 eV) in sub-nm SWCNTs as a function of the size of the bundle. We find that the energy of the π plasmon peak E varies with the bundle diameter D_h as E = (-0.023 eV)^∗ln(D_h/d_o) + 5.37 eV, where d_o = 0.5 nm and corresponds to the smallest tube diameter.¹ This is compared with the same data for HiPCo and Carbolex SWCNTs of larger diameter (1–1.4 nm) confirming a clear dependence of E on the bundle size, which is present in addition to the previously reported dependence of E on SWCNT diameter d.     

以温度为函数的硝仿系炸药的爆发分解反应动力学参数

用爆发点试验装置测定了6种硝仿系炸药:2,2,2-三硝基乙基-N-硝基-甲胺(TNMA)、二(2,2,2-三硝基乙基-N-硝基)乙二胺(BTNEDA)、4,4,4-三硝基丁酸-2,2,2-三硝基乙酯(TNETB)、二(2,2,2-三硝基乙醇)缩甲醛(BTNF)、1,1,1,3-四硝基丙烷(TETNP)和二(2,2,2-三硝基乙基)硝胺(BTNNA)在不同温度下的爆发延滞期.依据谢苗诺夫方程lnt_(lag,i)=E_α/RT_i-lnA_α,由lnt_(lag,i)对1/T_i的关系,用作图法和最小二乘法计算了爆发分解反应的表观活化能(E_α)、指前因子(A_α)和5 s爆发点.用非线性等转化率积分法所得的表观活化能(E_α)校验了由lnt_(lag,i)～1/_Ti关系得到的Eα值.借助热力学关系式,计算了爆发分解反应的活化热力学参数[活化自由能(ΔG≠),活化焓(ΔH≠)和活化熵(ΔS≠)].结果表明: (1) E_α和作图法所得E_α间的相对误差在±5%以内; (2) E_α与最小二乘法所得E_α相等的事实佐证了不同温度下爆发分解反应延滞期内的分解深度是相等的,所得E_α和A_α值是可接受的,谢苗诺夫方程推导过程中采用A_α>>G(α)的假设是合理的; (3) 以5 s爆发点和ΔG~#为判据,6种硝仿系炸药对热抵抗能力的次序为:TNETB＞BTNF＞BTNEDA＞TETNP＞TNMA＞BTNNA.     

Thermal decomposition kinetics of dynamically vulcanized polyamide 6–acrylonitrile butadiene rubber–halloysite nanotube nanocomposites

Thermally stable thermoplastic elastomer nanocomposites based on polyamide 6 (PA6), acrylonitrile butadiene rubber (NBR), and halloysite nanotubes (HNTs) were dynamically vulcanized, and their nonisothermal decomposition kinetics were examined. The Friedman, Kissinger–Akahira–Sunose (KAS), Ozawa–Wall–Flynn (FWO), and modified Coats–Redfern (m-CR) isoconversional models were used to obtain information about the kinetics of the thermal decomposition of PA6–NBR–HNTs in terms of the activation energy per partial mass loss monitored through thermogravimetric analyses performed at different heating rates. An erratic trend was due to the Friedman model, especially for systems having higher HNT loadings, whereas the KAS, FWO, and m-CR models revealed very similar meaningful thermal decomposition kinetics. A relatively high activation energy corroborating a reliable thermal stability was obtained by the addition of HNTs to PA6–NBR, and the resistance against decomposition was higher for systems containing more HNT. This signified the role of the HNTs as thermal stability modifiers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47483.     

Thermal degradation of urea‐formaldehyde cellulose composites filled with aluminum particles: Kinetic approach to mechanisms

This article reports a study on structural characterization and thermal degradation kinetics of insulating/conducting urea‐formaldehyde cellulose (UFC) composites filled with aluminum particles. Structural characterization of UFC/Al composites carried out by SEM, XRD, and FTIR analyses reveals that composites are fairly homogenous, and the interactions between UFC and aluminum in UFC/Al composites are more probably physical in nature. Measurements of inherent thermal stabilities, probing reaction complexity, and thermal degradation kinetics of UFC and UFC/Al composites have been undertaken by thermogravimetric (TG)/differential thermogravimetric (DTG) analyses under nonisothermal conditions. The integral procedure decompositions temperature (IPDT) elucidates significant thermal stability of UFC, and higher aluminum contents in composites are capable of enhancing the thermal stability of UFC resin. TG/DTG analyses suggest highly complicated thermal degradation profiles of UFC and UFC/Al composites, which consist of various parallel/consecutive reactions. Generalized linear integral isoconversional method has been employed to determine the activation energies of thermal degradation processes. Substantial variations in activation energies of UFC and UFC/Al composites with the advancement of reaction verify their multi‐step reaction pathways. Advanced reaction model determination methodology with the help of a novel kinetic function F(α,T) reveals that the multi‐step thermal degradation of UFC goes to completion by principally following intricate nucleation/growth mechanisms. It is also found that aluminum more likely participates in the thermal degradation of resin and tends to alter its reaction mechanism. Detailed interpretations of the obtained kinetic parameters are given, and their probable physical significances are discussed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44826.     

Lifetime predictions for the epoxy system BADGE n=0/m‐XDA using kinetic analysis of thermogravimetry curves

Lifetime of the epoxy system diglycidil ether of Bisphenol A (BADGE n=0)/ m‐xylylenediamine (m‐XDA) was calculated by thermogravimetric analysis. The Flynn‐Wall‐Ozawa method is used to determine the activation energy of the reaction. Experimental lifetimes in the range of 60–300°C vary from 1.41 10⁹ (2682 years) to 3.35 10^?4 min. This isoconversional method is not appropiate to calculate lifetime prediction because of high errors. Scaling factors were determined using the ratio of two reaction rates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1692–1696, 2002     

Diglycidyl ether of bisphenol A/chitosan‐graft‐polyaniline composites with electromagnetic interference shielding properties: Synthesis,characterization, and curing kinetics

Conducting filler based on chitosan and grafted polyaniline (Ch‐g‐PANI) was prepared with different grafting ratios and used as fillers for polyester powder coating system. Differential scanning calorimetry is applied to study the effect of Ch‐g‐PANI on the curing of the polyester powder coating. The activation energy calculated by isoconversional Kissinger method was increased by either increasing the Ch‐g‐PANI content or the content of polyaniline in the filler, suggesting the contribution of the filler in the curing reactions. The cured samples were characterized using FTIR and TG analyses. Thermogravimetric analysis showed that the total thermal stability was enhanced upon the filler addition as detected from the values of integral procedural decomposition temperature. Furthermore, a dielectric study showed that the dielectric constant and loss were increased upon increasing of the filler. Vogel–Fulcher–Tammann equation was well‐fitted when used to examine the dependence of α‐relaxation on the temperature and the dielectrically calculated T_g values were comparable to that measured by DSC. The shielding effectiveness toward microwaves was enhanced by increasing the filler content. POLYM. ENG. SCI., 59:372–381, 2019. © 2018 Society of Plastics Engineers