Autocatalytic Model Research Articles

An analytical model of through-thickness photopolymerisation of composites: Ultraviolet light transmission and curing kinetics

In this paper, a kinetic model able to predict the evolution of the through-thickness degree of cure of ultraviolet (UV) cured composites has been developed and validated. The kinetic model, which is based on the autocatalytic model, depends on the temperature of the composite and the absorbed intensity by the photoinitiators. This intensity is calculated by an optical model divided into discrete values of wavelength. As a result, the kinetic model considers the main factors of UV curing: the resin, reinforcement and thickness of the composite; the incident UV light spectrum; the absorbance range of photoinitiators and its consumption during the photopolymerisation. The main values of the model can be obtained by spectrometry and measuring the electric resistance of the composite during the whole UV curing process.

Decomposition of HMX in solid and liquid states under nanoconfinement

The thermal properties of bulk and nanoconfined HMX were studied using differential scanning calorimetry in dynamic scanning mode at rates ranging from 0.3 to 100 °C/min. At the slowest heating rates, decomposition occurs in the solid phase; at intermediate heating rates, it starts in the solid phase, melts, and finishes with a faster rate of reaction in the liquid state; and at the highest heating rates, the decomposition is entirely in the liquid phase. The activation energy decreases with conversion and is highest for 12 nm-diameter pores. The decomposition reaction is accelerated for nanoconfined HMX compared to the bulk with the onset of decomposition decreased by 1–5 °C in 50 nm-diameter pores and by 4–11 °C in 12 nm-diameter pores. The kinetics of decomposition is well described by a first-order autocatalytic reaction model with the reaction rate constants increasing with nanoconfinement. In addition, the reaction rate constant is one order of magnitude higher in the melt state than in the solid state.

Effect of Cu(II) on Mn(II) Oxidation by Free Chlorine To Form Mn Oxides at Drinking Water Conditions.

The chemical oxidation of dissolved Mn(II) to Mn(III/IV) oxides (MnOx) can lead to the accumulation of Mn deposits in drinking water distribution systems. However, Mn(II) oxidation by free chlorine is quite slow under mild conditions (e.g., pH 7.7 and 1.0 mg/L Cl2). This study found a significant role for Cu(II) in Mn(II) oxidation under conditions relevant to the supply of chlorinated drinking water. At pH 7.7, dissolved Cu(II) accelerated Mn(II) oxidation more than 10 times with a dose of 20 μg/L. Solid characterization revealed that during Mn(II) oxidation, Cu(II) adsorbed to freshly formed MnOx and produced Mn-Cu mixtures (denoted as MnOx-Cu(II)). An autocatalytic model for the reaction kinetics suggested that the freshly formed MnOx-Cu(II) had a much higher catalytic activity than that of pure MnOx. Solid CuO also catalyzed Mn(II) oxidation, and kinetic modeling indicated that after an initial oxidation of Mn(II) facilitated by the CuO surface, the freshly formed MnOx-Cu(II) on CuO surface played the dominant role in accelerating further Mn(II) oxidation. This study indicates a high potential for the formation of Mn oxides at locations in a drinking water distribution system or in premise plumbing where both Mn(II) and Cu(II) are available. It provides insights into the co-occurrence of other metals with Mn deposits that is frequently observed in distribution systems.

Oxidation Kinetics of Biodiesel by Non-Isothermal Pressurized-Differential Scanning Calorimetry

<b>Highlights</b> <list list-type=bullet><list-item> A non-isothermal PDSC method was developed to calculate oxidative stability and shelf-life of biodiesel. </list-item><list-item> First order and autocatalytic kinetic models were developed for biodiesel oxidation reactions. </list-item><list-item> Non-isothermal PDSC results showed good correlation with induction period data from Rancimat instrument. </list-item><list-item> Shelf-life data inferred from PDSC results were more consistent than extrapolation of induction period data. </list-item></list> <b>Abstract.</b><sc> </sc>Biodiesel is a renewable fuel that can be made from transesterification of plant oils, waste greases, animal fats, or microalgal oils with methanol. During long-term storage, autoxidation can adversely affect the viscosity and ignition quality of biodiesel. The objective of this work was to investigate the kinetics of oxidation of fatty acid methyl esters (FAME) made from canola, palm, and soybean oils (CaME, PME, and SME) plus methyl oleate and stearate (MeC18:1 and MeC18:2). The FAME were analyzed by non-isothermal pressurized-differential scanning calorimetry (PDSC) in dynamic mode (positive airflow) at heating scan rates (β) of 2, 5, 10, 15, and 20 °C min^-1. Results were analyzed to infer oxidation rate constants (k_T). First order and two autocatalytic kinetic models were applied to calculate isothermal oxidation induction times (Δt) for each FAME. While Δt values varied between the models, ranking the FAME in descending order of Δt was the same for each model regardless of temperature. In contrast, ranking the FAME by the oxidation induction period (IP_R) obtained from a Rancimat instrument depended greatly on temperature. Shelf-life data for each FAME were calculated by extrapolating IP_R measured at high temperatures to 25°C (SL1). Ranking the FAME by SL1 yielded trends that were unpredictable based on the IP_R data. On the other hand, Δt values calculated at 25°C (SL2) from the PDSC results were more consistent. These findings suggest that estimating the shelf-life of biodiesel from dynamic mode non-isothermal PDSC data yielded more reliable results than extrapolation of IP_R data measured at high temperatures.

Carbon dioxide activation of the plane tree seeds derived bio-char: Kinetic properties and application

Goal of this work is to establish technical feasibility and fundamentals of producing activated carbon from plane tree seeds biomass for porous materials derivation. Bio-chars produced via carbonization from plane tree seeds precursor were activated in CO2 at 750 and 850?C, during various residence times. Their surface area and porosity were characterized by N2 adsorption at 77 K. Surface areas of activated carbons can be correlated with kinetics mechanism and activation energy magnitudes of oxidation reaction by CO2, which are closely related to applied activation temperature. Result showed that high temperature activated carbon had higher gas adsorption as compared to activated carbon obtained from lower temperature during two-hour residence time. Breakthrough behavior was detected at 850?C where surface reactions dominate, and it is characterized by autocatalytic kinetic model under designed conditions. Both, temperature and CO2 concentration in vicinity of solid surface effect on breakthrough time of adsorbent. Derived bio-chars are converted into high quality activated carbons, with surface area of 776.55 m2/g, where micro-pores with pore diameters less than 2 nm prevail. Produced activated carbons have properties comparable with commercially available activated carbons, which can be successfully used for removal of harmful gaseous pollutants toward air purification.

Autocatalytic Models for the Origin of Biological Homochirality.

Autocatalytic models for the emergence of homochirality have been of interest for more than half a century. The sole experimental example of such an amplifying autocatalytic reaction is the Soai reaction. In this review, we trace the history of the theoretical models and the experimental work that led up to the discovery of the remarkable, singular Soai reaction. The experimental and computational studies that have helped to delineate the mechanism of this reaction are discussed in detail. Studies of both the concept of chiral symmetry breaking as well as the subsequent chiral amplification process are discussed. Particular attention is paid to flaws in some of the published models, and suggestions are offered for how such issues might be avoided in future work. The outlook in the search for a prebiotically plausible version of such an amplifying autocatalytic system is presented.

Amino-Functionalized Lead Phthalocyanine-Modified Benzoxazine Resin: Curing Kinetics, Thermal, and Mechanical Properties.

Phenol-diaminodiphenylmethane-based benzoxazine (P-ddm)/phthalocyanine copolymer was prepared by using P-ddm resin as matrix and 3,10,17,24-tetra-aminoethoxy lead phthalocyanine (APbPc) as additive. Fourier-transform infrared (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA) were used to investigate the curing behavior, curing kinetics, dynamic mechanical properties, thermal stability, and impact strength of the prepared copolymers. The kinetic parameters for the P-ddm/APbPc blend curing processes were examined by utilizing the iso-conversional, Flynn–Wall–Ozawa, and Málek methods. The P-ddm/APbPc blends exhibit two typical curing processes, and DSC results confirmed that the blending of APbPc monomer can effectively reduce the curing temperature of P-ddm resin. The autocatalytic models also described the non-isothermal curing reaction rate well, and the appropriate kinetic parameters of the curing process were obtained. The DMA and impact strength experiments proved that the blending of APbPc monomer can significantly improve the toughness and stiffness of P-ddm resin, the highest enhancements were observed on 25 wt.% addition of APbPc, the recorded values for the storage modulus and impact strength were 1003 MPa and 3.60 kJ/m2 higher, respectively, while a decline of 24.6 °C was observed in the glass transition temperature values. TGA curves indicated that the cured copolymers also exhibit excellent thermal stabilities.

Thermal hazardous evaluation of autocatalytic reaction of cumene hydroperoxide alone and mixed with products under isothermal and non-isothermal conditions

Severe fire and explosions are frequent phenomena during handling of organic peroxides that are promoted supremely by conditions such as chemical impurities and thermal instability. As an initiator in the polymerization process, cumene hydroperoxide (CHP) has wide usage in the chemical process industry. This violently reactive chemical is studied here experimentally using differential scanning calorimeter (DSC), an isothermal mode of operation that can access the thermal hazards in the decomposition of CHP alone and later mixed with products following an autocatalytic reaction scheme. Importantly, DSC-evaluated thermokinetic parameters such as reaction enthalpy (ΔHd), time to maximum rate (TMRiso), and maximum heat flow (Qmax) were estimated to ascertain the degree of thermal hazard under various transportation and storage temperatures. The Heat-Wait-Search mode of accelerating rate calorimeter has been used to investigate decomposition kinetics parameters data under an adiabatic condition. Data such as initial exothermic temperature (T0), self-heating rate (dT/dt), pressure rise rate (dP/dt) and pressure–temperature profiles help to gauge the runaway reaction hazard of CHP alone and then mixed with its products to support the autocatalytic model of exothermic decomposition. The curve fitting data indicated that activation energy had reduced from 245.4 to 236.7 and 242.3 kJ mol−1, when CHP was mixed with acetone or dicumyl peroxide, respectively. The decrease in activation energy for autocatalytic material thermal decomposition reaction is depicted here with various experimental findings and mathematical analysis.

Curing kinetic of self-promoted alicyclic-based bisphthalonitrile monomer

Self-promoted alicyclic-based phthalonitrile possesses outstanding properties, which would be determined by the special free radical curing mechanism and curing process. Thus, the curing kinetic of alicyclic-based phthalonitrile was studied and the curing kinetic parameters were determined by DSC at various heating rates. Double fit peaks were used to analyze the reaction processes. The autocatalytic model based on Šesták–Berggren model of DAIM-PN was confirmed. Moreover, the predicated models of DAIM-PN could fit well with the experimental values.

Study of the curing kinetics of melamine/phthalonitrile resin system

The exploration of curing process is important for the application of phthalonitrile resins in advanced materials. In this study, the curing behaviors of 1,3-bis (3,4-dicyanophenoxy) benzene (3BOCN) and melamine (MI) system was studied by differential scanning calorimetry (DSC) at different heating rates. An autocatalytic model could describe the curing reaction of 3BOCN-MI. The curing parameters including apparent activation energy, reaction orders and pre-exponential factor were calculated. The average activation energies for the three different proportions of 3BOCN-MI (8:1, 8:2, 8:3) system were 93, 98 and 96 kJ/mol, respectively. Besides, the predicted models for the reaction of 3BOCN-MI curing fitted well with the experimental data.

FLOW CURVATURE APPLIED TO MODELLING OF CRITICAL PHENOMENA

Modeling of critical phenomena is a very important problem, which has direct applied application in many branches of science and technology. In this paper we regard a modification of the low curvature method applied to construction of invariant manifolds of autonomous fast-slow dynamic systems. We compared a new method with original ones via finding duck-trajectories and their multidimensional analogues surfaces with variable stability. Comparison was used a three-dimensional autocatalytic reaction model and a model of the burning problem.

Oxidative stability, thermal hazard analysis, and decomposition kinetics of 1-methylimidazolium nitrate via DSC, TGA, and GC/MS

Imidazolium-based ionic liquids are green solvents used as separation and electrolyte media in liquid–liquid extraction processes and electrochemical devices. However, they are volatile and flammable once they reach their thermal decomposition temperatures. In the present study, the oxidative stability, decomposition, and combustion reaction of 1-methylimidazolium nitrate [Mim][NO3] were investigated via thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). TG analysis revealed a single-stage mass loss between 117.6 and 230.2 °C with oxidative onset temperatures in the range of 126.6–163.2 °C with the increase in heating rate (1.0, 2.0, 4.0, and 8.0 °C min−1). DSC results indicated the degradation as exothermic with the average enthalpy of decomposition as 1610.4 J g−1. The estimated average value of apparent activation energy using isoconversional methods such as Kissinger, FWO, and Friedman was in the range of 106.1–114.2 kJ mol−1, and the reaction function (autocatalytic model) is expressed as: f(α) = (1 − α)1.42 (0.017 + α0.62) using multivariate nonlinear regression. The GC/MS analysis revealed the formation of methane isocyanate indicating the hazardous, toxic, corrosive, and carcinogenic nature of the decomposed gases. This research was aimed to develop a predictive model for oxidative degradation behavior and to provide the necessary basis for the design of precise safety systems.

Curing characteristics and cellular morphology of natural rubber/silica composite foams

The curing behavior and microstructure of natural rubber/silica foams were studied. Error function-based and autocatalytic models were correlated with the curing characteristics data of samples. The incorporation of silica into natural rubber caused an increase in the foam density and decrease in the cell size. Moreover, by increasing the curing temperature, cell size became larger and cell size distribution became non-uniform. It was thought that the higher temperature of foaming limited the bubble growth due to faster curing reaction. Lower viscosity and lower strength of rubber at high temperature increased the cell coalescence resulting in larger cell size and non-uniform cell distribution.

Numerical analysis of auto-catalytic glycolysis model

The main purpose of this paper is to investigate the solution of general reaction–diffusion glycolysis system numerically. Glycolysis model demonstrates the positive solution as the unknown variables show concentration of chemical substances. Three numerical methods are used to solve glycolysis model. Two methods are well-known finite difference (FD) schemes and one is proposed FD scheme. The proposed scheme is explicit in nature. The main feature of the proposed FD scheme is to preserve the property of positivity retained by the glycolysis model. Results are compared with forward Euler explicit scheme and Crank Nicolson implicit scheme. All the attributes are verified by simulations.

Isothermal Curing Kinetics of Epoxidized Fatty Acid Methyl Esters and Triacylglycerols

AbstractPlant oil triacylglycerols are attractive renewable resources for biobased epoxy resins. We investigated the curing kinetics of three model epoxidized fatty acid methyl esters and representative epoxidized triacylglycerols with varied epoxide functionalities and distributions in the presence of a latent cationic initiator. Isothermal differential scanning calorimetry (DSC) was used to analyze the curing kinetics of the epoxy systems, and kinetic parameters (i.e., rate constants, reaction orders) were determined. Both epoxidized fatty esters and triacylglycerols followed the autocatalytic curing mechanism, and the DSC data were analyzed according to the Kamal autocatalytic model. Epoxidized methyl linoleate (EMLO) had the highest maximum curing rate, followed by epoxidized methyl linolenate (EMLON), and epoxidized methyl oleate (EMO) had the lowest maximum curing rate. We conclude that EMLO with two epoxide groups has the highest reactivity in this curing system, while the EMO with one epoxide group has the lowest reactivity. For epoxidized triacylglycerols, epoxidized camelina oil had the highest curing reactivity at higher temperatures, followed by epoxidized linseed oil and soybean oil.

A Lagrangian Particle Algorithm (SPH) for an Autocatalytic Reaction Model with Multicomponent Reactants

For the numerical simulation of convection-dominated reacting flow problems governed by convection-reaction equations, grids-based Eulerian methods may cause different degrees of either numerical dissipation or unphysical oscillations. In this paper, a Lagrangian particle algorithm based on the smoothed particle hydrodynamics (SPH) method is proposed for convection-reaction equations and is applied to an autocatalytic reaction model with multicomponent reactants. Four typical Eulerian methods are also presented for comparison, including the high-resolution technique with the Superbee flux limiter, which has been considered to be the most appropriate technique for solving convection-reaction equations. Numerical results demonstrated that when comparing with traditional first- and second-order schemes and the high-resolution technique, the present Lagrangian particle algorithm has better numerical accuracy. It can correctly track the moving steep fronts without suffering from numerical diffusion and spurious oscillations.

Curing Kinetics and Mechanism Research of E44/T31 Insulation Paint

Epoxy resin insulation paint was prepared with epoxy resin (E44) as binder and with proper inorganic fillers and curing agent (T31) as additives. The isothermal curing reaction process of paint was studied by the differential scanning calorimetry method (DSC), and the curves of curing reaction rate versus time of paint were obtained. The curing reaction kinetics was investigated by using the phenomenological method, and the corresponding parameters of the n-order model, autocatalytic model and Kamal model were determined by fitting the experimental data, respectively. According to the values of R2 and the sum of square due to error (SSE), a suitable curing reaction kinetic model was determined. The curing reaction mechanism of paint was ascertained by the dynamic temperature DSC method and IR spectroscopy (FTIR) method. The results show that the Kamal model can be used to describe the curing kinetics of epoxy resin paint, and the total reaction orders increase from 1.30 to 2.14. The two rate constants increase with the increase of the curing temperature. The activation energy is 90.5832 kJ/mol and 68.3733 kJ/mol respectively, and the pre-exponential factors are 6.521 × 1015 s-1 and 6.3807 × 109 s-1. The curing reaction of paint consists of two steps: the first step is the addition reaction of epoxy group and primary amine or secondary amine; the second step is the etherification reaction of epoxy group and phenolic hydroxyl or alcoholic hydroxyl.&#x0D; Epoxy resin insulation paint was prepared with epoxy resin (E44) as binders and with proper inorganic fillers and curing agent (T31) as additives. The isothermal curing reaction process of paint was studied by differential scanning calorimetry method (DSC), and the curves of curing reaction rate versus time of paint were obtained. The curing reaction kinetics was studied by using the phenomenological method, the corresponding parameters of the n-order model, autocatalytic model and Kamal model were determined by fitting the experimental data, respectively. According to the values of R2 and the sum of square due to error (SSE), a suitable curing reaction kinetic model was determind. The curing reaction mechanism of paint was ascertained by dynamic temperature DSC method and IR spectrogram (FTIR) method. The results show that the kamal model can be used to describe the curing kinetics of epoxy resin paint, the total reaction orders increase from 1.30 to 2.14. The results also show that the two rate constants increase with increasing curing temperature, The activation energies are 90.5832 kJ/mol and 68.3733 kJ/mol, and the pre-exponential factor are 6.521×1015 s-1 and 6.3807×109 s-1. The curing reaction of paint in two steps, the first step is the addition reaction of epoxy group and primary amine or secondary amine. The second step is the etherification reaction of epoxy group and phenolic hydroxyl or alcoholic hydroxyl.

Condensation By-Products in Wet Peroxide Oxidation: Fouling or Catalytic Promotion? Part I. Evidences of an Autocatalytic Process

The present work is aimed at the understanding of the condensation by-products role in wet peroxide oxidation processes. This study has been carried out in absence of catalyst to isolate the (positive or negative) effect of the condensation by-products on the kinetics of the process, and in presence of oxygen, to enhance the oxidation performance. This process was denoted as oxygen-assisted wet peroxide oxidation (WPO-O2) and was applied to the treatment of phenol. First, the influence of the reaction operating conditions (i.e., temperature, pH0, initial phenol concentration, H2O2 dose and O2 pressure) was evaluated. The initial phenol concentration and, overall, the H2O2 dose, were identified as the most critical variables for the formation of condensation by-products and thus, for the oxidation performance. Afterwards, a flow reactor packed with inert quartz beads was used to facilitate the deposition of such species and thus, to evaluate their impact on the kinetics of the process. It was found that as the quartz beads were covered by condensation by-products along reaction, the disappearance rates of phenol, total organic carbon (TOC) and H2O2 were increased. Consequently, an autocatalytic kinetic model, accounting for the catalytic role of the condensation by products, provides a well description of wet peroxide oxidation performance.

A novel multifunctional glycidylamine epoxy resin containing phthalide cardo structure: Synthesis, curing kinetics and dynamic mechanical analysis

A novel glycidylamine epoxy resin containing phthalide cardo structure (TGMP) was designed and synthesized based on o-cresolphthalein using a three-step procedure. Its curing systems were prepared using methyl-nadilic anhydride (MNA) and 2-ethyl-4-methylimidazole (EMI-24) as the curing agent and accelerating agent, respectively. The chemical structures of synthetic intermediate, epoxy resin and its curing systems were characterized by Fourier transform infrared (FTIR) spectra and nuclear magnetic resonance (NMR) spectra. The curing behavior and kinetics were investigated by differential scanning calorimetry (DSC) and the activation energies were calculated according to the Kissinger equation and Flynn-Wall-Ozawa (FWO) equation. The TGMP/MNA/EMI-24 system is of more reactivity more that of pure TGMP. The Friedman method was used to describe the progress of the curing reaction of the TGMP/MNA/EMI-24 system, finding it follows the autocatalytic reaction model and nth-order reaction mechanism is predominant. The thermal-mechanical properties of the TGMP/MNA/EMI-24 composites were studied by dynamic mechanical analysis (DMA). The tan δ curves show double peaks and the maximum glass transition temperature is up to 345 °C.

Effect of surface area of nanosilica particles on the cure kinetics parameters of an epoxy resin system

ABSTRACTKnowing of thermoset curing kinetics is essential for process development, quality control, and achieving desirable products. Hence, in this article, cure kinetics of an EPON 828 epoxy resin/dicyandiamide curing agent/diuron accelerator system is investigated. This resin system is usually used for the production of epoxy/glass fiber prepregs used in wind turbine blades. For this, differential scanning calorimetry analysis is used and the effect of temperature, weight percentage, and size of nanosilica is studied by conducting isothermal tests at several temperatures for samples with and without nanoparticles. An autocatalytic curing model is applied to describe the cure kinetic of system and then the variations in model parameters calculated by curve fitting using the MATLAB software. The results show that the increase in temperature, weight percentage of nanosilica from 0 to 6%, and surface area of nanosilica particles lead to the increase in curing rate, whereas the increase in the percentage and surface area of nanosilica particles significantly decreases total heat of reaction. At the end, the relation between each of model parameters and the total surface area of nanosilica particles, calculated by mathematical equations, is obtained. The allowable maximum surface area of nanosilica used in the mathematical equations is 12 m2 g−1. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47958.