Kinetics of the curing reaction of unsaturated polyester resins catalyzed with new initiators and a promoter

In this article, the curing of unsaturated polyester resins catalyzed with a promoter [cobalt(II) octoate] and free‐radical initiators is presented. The new initiators were formed by the oxidation process of ethyl methyl ketone or cyclohexanone with hydrogen peroxide and the mixture of solvents containing hydroxyl groups. As a reference, a typical curing system containing ethyl methyl ketone hydroperoxide (Luperox) and the promoter was used. The differential scanning calorimetry runs were performed at different heating rates. The experimental data were fitted with the empirical kinetic model. First, the kinetic parameters (activation energy, frequency factor, and reaction order) were obtained with a single reactive process and with the nth‐order reaction f(α), the nth‐order reaction f(α) with autocatalysis, and the first‐order reaction f(α) with autocatalysis. Second, two or three different reactive processes with the nth‐order reaction f(α) for each step were used. The obtained values of the activation energies for the curing of the unsaturated polyester resins with the free radical initiator–cobalt(II) salt catalytic system were in the range 40–60 kJ/mol for the polymerization initiated by the redox decomposition of the initiators and 80–90 kJ/mol for the polymerization initiated by the thermal decomposition of the initiators at high temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1870–1876, 2006     

Cure kinetics and thermal properties of tetramethylbiphenyl epoxy resin/phthalazinone‐containing diamine/hexa(phenoxy)cyclotriphophazene system

Inherently flame retardant epoxy resin is a kind of halogen‐free material for making high‐performance electronic materials. This work describes an inherently flame retardant epoxy system composed of 4,4′‐diglycidyl (3,3′,5,5′‐tetramethylbiphenyl) epoxy resin (TMBP), 1,2‐dihydro‐2‐(4‐aminophenyl)‐4‐(4‐(4‐aminophenoxy) phenyl) (2H) phthalazin‐1‐one (DAP), and hexa(phenoxy) cyclotriphophazene (HPCTP). The cure kinetics of TMBP/DAP in the presence or absence of HPCTP were investigated using isoconversional method by means of nonisothermal differential scanning calorimeter (DSC). Kinetic analysis results indicated that the effective activation energy (E_α) decreased with increasing the extent of conversion (α) for TMBP/DAP system because diffusion‐controlled reaction dominated the curing reaction gradually in the later cure stage. TMBP/DAP/HPCTP(10 wt %) system had higher E_α values than those of TMBP/DAP system in the early cure stage (α < 0.35), and an increase phenomenon of E_α ～ α dependence in the later cure stage (α ≥ 0.60) due to kinetic‐controlled reaction in the later cure stage. Such complex E_α ～ α dependence of TMBP/DAP/HPCTP(10 wt %) system might be associated with the change of the physical state (mainly viscosity) of the curing system due to the introduction of HPCTP. These cured epoxy resins had very high glass transition temperatures (202–235°C), excellent thermal stability with high 5 wt % decomposition temperatures (>340°C) and high char yields (>25.6 wt %). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermal degradation studies on rigid polyurethane foams blown with pentane

The effect of sodium dihydrogenphosphate, trisodium pyrophosphate, and sodium aluminocarbonate on the thermal decomposition of rigid polyurethane (PUR) foams, based on diphenylmethane‐4,4‐diisocyanate, diphenyl‐2,2‐propane‐4,4‐dioxyoligo(ethylene oxide), and oxyalkylenated toluene‐2,6‐diamine, blown with pentane, was studied. Thermogravimetric (TG) data have shown that there is a stabilization effect of additives in the initial stage of degradation, both in nitrogen and air atmosphere, and the decomposition proceeded in two steps up to 600°C. Results of the kinetic analysis by the isoconversional methods of Ozawa–Flynn–Wall and Friedman yielded values of (apparent) activation energy (E_a) and preexponential factor (A). For phosphate‐stabilized PUR samples, E_a remained stable over a broad area of the degree of conversion, while for carbonate‐containing sample two regions of E_a were observed. Further advanced kinetic analysis by a nonlinear regression method revealed the form of kinetic function that was the best approximation for experimental data—for a two‐stage consecutive reaction the first step was the Avrami–Erofeev nucleation‐dependent model, and the second step was a chemical reaction (1st or nth order) model. The integrated thermogravimetric (TG)/Fourier transform infrared (FTIR) technique probed the thermal degradation of modified PURs by analyzing the evolved gases. The solid residue remaining at different temperatures was identified by diffuse reflection FTIR (Kubelka–Munk format). The complex thermal behavior was discussed on the basis of the obtained results—it can be shown that the global stabilization effect is a multistage process whose initial conditions are of critical importance in governing the nature of the entire process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2319–2330, 2003     

The effect of CTBN concentrations on the kinetic parameters of decomposition of blends of cardanol‐based epoxidized novolac resin modified with carboxyl‐terminated liquid copolymer

Cardanol‐based novolac resins were separately prepared with different mole ratios of cardanol‐to‐formaldehyde with different acid catalysts. These resins were epoxidized with epichlorohydrin, in basic medium, at 120°C. The resins were, separately, blended with different weight percentages of carboxyl‐terminated butadiene acrylonotrile copolymer and cured with polyamine. Structural changes during blending were studied by FTIR spectroscopic analysis. Coats–Redfern equation was utilized to calculate the kinetic parameters, viz., order of decomposition reaction (n), activation energy (E), pre‐exponential factor (Z), and rate decomposition constant (k), for the decomposition of the samples. It was found that the degradation of the epoxies and their blend samples proceeded in two steps. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Flame‐retardant properties of magnesium hydroxystannate and strontium hydroxystannate coated calcium carbonate on soft poly(vinyl chloride)

The flame‐retardant and smoke‐suppressant properties of soft poly(vinyl chloride) (PVC) treated with zinc hydroxystannate (ZHS), calcium carbonate (CaCO₃), magnesium hydroxystannate [MgSn(OH)₆], strontium hydroxystannate [SrSn(OH)₆], ZHS–MgSn(OH)₆, ZHS–SrSn(OH)₆, MgSn(OH)₆‐coated CaCO₃, SrSn(OH)₆‐coated CaCO₃, ZHS–MgSn(OH)₆‐coated CaCO₃, and ZHS–SrSn(OH)₆‐coated CaCO₃ were studied with the limited oxygen index, char yield, and smoke density rating methods; the mechanical properties were also studied. The results showed that, with the equivalent addition of the corresponding hydroxystannate, the soft PVC treated with hydroxystannate‐coated CaCO₃ had a higher limited oxygen index than the corresponding hydroxystannate, and the soft PVC treated with the agents containing magnesium had a higher limited oxygen index than the soft PVC treated with the agents containing strontium, except for ZHS–MgSn(OH)₆‐coated CaCO₃. The improvement in the char formation of the hydroxystannate‐coated CaCO₃ was better than that of the corresponding hydroxystannate in most cases, and the aforementioned agents reduced the smoke density rating, decreased the tensile strength, and increased the elongation and impact strength basically. Thermal analysis showed that the additives promoted the evolution of hydrogen chloride, early crosslinking, and rapid charring through the strong catalyzing effect of Lewis acids. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A kinetic study of the effect of three catalytic systems on the curing of an unsaturated polyester resin

We studied by differential scanning calorimetry (DSC) the influence of three tertiary amines used as promoters on the curing kinetics of unsaturated polyester resins catalyzed with an organic peroxide. The kinetic study was made by means of the analysis of isothermal experiments and we used a kinetic model that does not presuppose knowledge of the experimental rate equation f(α), which relates the reaction rate dα/dt at constant temperature with the degree of conversion α through a rate constant k according to dα/dt = kf(α). It is thus possible to predict the time, temperature, and degree of curing without needing to know f(α). This model makes a linear relation between the logarithm of time needed to reach a given degree of conversion with the inverse of the inverse of the curing temperature according to the expression ln t = A+E/RT for a constant α, where A is a constant, R is the universal gas constant, and E the activation energy. The proposed model has been used to calculate the activation energies for each degree of conversion according to the type and amount of promoter used. From the relation between the time and the curing temperature for a given conversion, it is possible to predict values of curing time for different temperatures. We thus simulated curing kinetics by using the proposed model and compared them with those obtained experimentally by DSC. © 1994 John Wiley & Sons, Inc.     

Model‐free kinetics: Curing behavior of phenol formaldehyde resins by differential scanning calorimetry

Isoconversional analysis was used to treat nonisothermal DSC data and yield the dependence of activation energy on conversion during the curing process of PF resins. The shape of the dependence revealed that the curing process of PF resins displayed a change in the reaction mechanism from a kinetic to a diffusion regime. In the kinetic regime a comparative DSC experimental analysis between monomer mixtures and PF resins showed that the addition reactions between phenol and formaldehyde had been mostly completed during the synthesis of PF resins and that the main kinetic reactions contained parallel condensations in the curing process. For the diffusion regime a modified equation for the diffusion rate constant, k_D = D₀ exp(?E_D /RT + K₁α + K₂α²), is proposed. This equation is in good agreement with the experimental dependence of E_α on α in the diffusion regime, which shows the effect of both temperature and conversion on diffusion. A prediction of the conversion advancement with the reaction time under isothermal condition for PF resin has been made. This prediction can be useful in practical applications for evaluating isothermal behavior of thermosetting systems from nonisothermal experimental data. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 433–440, 2003     

Novel amine preaccelerators for polyester resins

The reactions between N,N‐dimethyl‐p‐phenylenediamine and ethylene or propylene oxide were carried out to obtain 3‐[p‐(N,N‐dimethylamino)phenyl]‐3‐azapentane‐1,5‐diol and 4‐[p‐(N,N‐dimethylamino)phenyl]‐4‐azaheptane‐2,6‐diol, respectively. The structures of the products were determined using elemental analysis, ¹H‐NMR and IR spectroscopy techniques. The diols were incorporated into unsaturated polyester resins. The time of gelation and stability of the resins was observed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2973–2976, 2003     

Effects of different ionizable groups on the thermal properties of waterborne polyurethanes used in bulletproof composites

The thermal stability of the resin matrix is an important factor affecting the safety performance of fiber‐reinforced bulletproof composites (FRBCs) during their service period. In this study, two kinds of waterborne polyurethanes based on polyester diol (PEDL218) and isophorone diisocyanate were synthesized; these were used as the matrix of para‐aramid FRBCs. Their thermal stability and thermal decomposition behaviors in a nitrogen atmosphere were studied by dynamic thermogravimetric analysis techniques. The kinetic parameters, including the activation energy (E) and pre‐exponential factor (A), were calculated by the Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, Kissinger, and ?atava–?esták methods. The results show that the cationic waterborne polyurethane with quaternary ammonium groups has better thermal stability than the anionic waterborne polyurethane with carboxylate groups. Their nonisothermal decomposition mechanisms were studied, and the kinetic parameters were also calculated; this will offer theoretical reference for the manufacturing and application of FRBCs based on waterborne polyurethane. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42374.     

Advanced isoconversional cure kinetic analysis of epoxy/poly(furfuryl alcohol) bio‐resin system

Furfuryl alcohol as a biomass‐derived monomer was used for synthesizing poly(furfuryl alcohol). A diglycidyl ether of bisphenol A (DGEBA) epoxy resin along with 3% and 15% by weight of the poly(furfuryl alcohol) was cured using an aliphatic amine hardener. The cure kinetics of the DGEBA/poly(furfuryl alcohol)/amine systems were investigated by nonisothermal differential scanning calorimetry. The kinetic triplets [E_α, A_α, and f(α)] were computed by using an integral isoconversional method. Based on the E_α‐dependency results a single‐step autocatalytic model was suggested for the reactions mechanism, however, the A_α‐dependency and f(α) analysis did not confirm the suggested model. Detailed kinetics analysis revealed that the cure reaction mechanism of the DGEBA did not change due to the presence of the poly(furfuryl alcohol) in the degree of conversion range < 0.75, nevertheless, it dramatically changed in the degree of conversion range > 0.75 due to the presence of 15 wt % poly(furfuryl alcohol). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45432.     

Mathematical model for the pultrusion of blocked PU–UP matrix composites

The thermokinetic behavior of blocked polyurethane (PU)–unsaturated polyester (UP)–based composites during the pultrusion of glass‐fiber‐reinforced composites was investigated utilizing a mathematical model that accounted for the heat transfer and heat generation during curing. The equations of continuity and energy balance, coupled with a kinetic expression for the curing system, were solved using a finite difference method to calculate the temperature profiles and conversion profiles in the thickness direction in a rectangular pultrusion die. A kinetic model, dP/dt = A exp(?E/RT)P^m(1 ? P)ⁿ, was proposed to describe the curing behavior of a blocked PU–UP resin. Kinetic parameters for the model were obtained from dynamic differential scanning calorimetry scans using a multiple regression technique, which was able to predict the effects of processing parameters on the pultrusion. The effects of processing parameters including pulling speed, die wall temperature, and die thickness on the performance of the pultrusion also were evaluated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1996–2002, 2003     

Thermal behavior and flame retardancy of flexible poly(vinyl chloride) treated with zinc hydroxystannate and zinc stannate

The flame‐retardant and smoke‐suppressant properties of inorganic tin compounds such as zinc hydroxystannate (ZHS) and zinc stannate (ZS) were studied in comparison with those of alumina trihydrate and magnesium hydroxide through the limiting oxygen index test and a smoke density test. The thermal degradation in air of flexible poly(vinyl chloride) (PVC) treated with the above compounds was studied by thermal analysis from ambient temperature to 800°C. The activation energy was calculated by using the Vyazovkin model‐free kinetic method and the Kissinger method. The results showed that tin compounds such as ZHS and ZS could be used as highly effective flame retardants for flexible PVC; these flame retardants enhanced the stability and the activation energy of the oxidation of the char. J. VINYL ADDIT. TECHNOL, 2008. © 2008 Society of Plastics Engineers     

Zinc hydroxystannate and zinc stannate as flame‐retardant agents for flexible poly(vinyl chloride)

The flame‐retardant and smoke‐suppressant properties of inorganic tin compounds such as zinc hydroxystannate (ZHS) and zinc stannate (ZS) were investigated in a comparison with alumina trihydrate, magnesium hydroxide, and Sb₂O₃ through the limiting oxygen index test and smoke density test. The flame‐retardant mechanisms were studied through the char yield test, SEM, quantitative analysis, thermogravimetry and differential thermal analysis. The thermal degradation in air of flexible PVC treated with the above compounds was studied by thermal analysis from ambient temperature to 800°C. The results showed that tin compounds such as ZHS and ZS could be used as a highly effective flame retardant for flexible PVC, and it appears that the tin compound may exert its action in both the condensed and vapor phases, but mainly in condensed phases as a Lewis acid. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1469–1475, 2005     

Investigation of the Thermal Decomposition Kinetics of Chalcopyrite Ore Concentrate usıng Thermogravimetric Data

The kinetics of the thermal decomposition of chalcopyrite concentrate was investigated by means of thermal analysis techniques, Thermogravimetry/Derivative thermogravimetry (TG/DTG) under ambient air conditions in the temperature range of 0–900°C with heating rates of 2, 5, 10, 15, and 20°C min^?1. TG and DTG measurements showed that the thermal behavior of chalcopyrite concentrate shows a two-step decomposition. The decomposition mechanism was confirmed using X-ray diffraction (XRD), Scanning Electron Microscope (SEM)/energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR) analyses. Kinetic parameters were determined from the TG and DTG curves for steps I and II by using two model-free (isoconversional) methods—Flyn–Wall–Ozowa (FWO) and Kissinger–Akahira–Sunose (KAS). The kinetic parameters consisting of E_a, A, and g(α) models of the materials were determined. The average activation energies (E_a) obtained from both models for the decomposition of chalcopyrite concentrate were 72.55 and 300.77 kJ mol^?1 and the pre-exponential factors (A) were 15.07 and 29.39 for steps I and II, respectively. The most probable kinetic model for the decomposition of chalcopyrite concentrate is an first-order mechanism, i.e., chemical reaction [g(α) = (?ln(1?α))], and an Avrami–Eroeyev equation mechanism, i.e., nucleation and growth for n = 2 [g(α) = (?ln(1?α)^1/2)], for steps I and II, respectively.     

Comparison of model‐fitting kinetics for predicting the cure behavior of commercial phenol–formaldehyde resins

Phenol–formaldehyde (PF) resins have been the subject of many model‐fitting cure kinetic studies, yet the best model for predicting PF dynamic and isothermal cure has not been established. The objective of this research is to compare and contrast several commonly used kinetic models for predicting degree of cure and cure rate of PF resins. Toward this objective, the nth‐order Borchardt–Daniels (nth‐BD), ASTM E698 (E698), autocatalytic Borchardt–Daniels (Auto‐BD), and modified autocatalytic methods (M‐Auto) are evaluated on two commercial PF resins containing different molecular weight distributions and thus cure behaviors. The nth‐BD, E698, and M‐Auto methods all produce comparable values of activation energies, while Auto‐BD method yields aberrant values. For dynamic cure prediction, all models fail to predict reaction rate, while degree of cure is reasonably well predicted with all three methods. As a whole, the nth‐BD method best predicts degree of cure for both resins as assessed by mean squared error of prediction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Reactivity,chemical structure,and molecular mobility of urea–formaldehyde adhesives synthesized under different conditions using FTIR and solid‐state 13C CP/MAS NMR spectroscopy

This study was conducted to investigate the effects of reaction pH condition and hardener type on the reactivity, chemical structure, and molecular mobility of urea–formaldehyde (UF) resins. Three different reaction pH conditions, such as alkaline (7.5), weak acid (4.5), and strong acid (1.0), were used to synthesize UF resins, which were cured by adding four different hardeners (ammonium chloride, ammonium sulfate, ammonium citrate, and zinc nitrate) to measure gel time as the reactivity. FTIR and ¹³C‐NMR spectroscopies were used to study the chemical structure of the resin prepared under three different reaction pH conditions. The gel time of UF resins decreased with an increase in the amount of ammonium chloride, ammonium sulfate, and ammonium citrate added in the resins, whereas the gel time increased when zinc nitrate was added. Both FTIR and ¹³C‐NMR spectroscopies showed that the strong reaction pH condition produced uronic structures in UF resin, whereas both alkaline and weak‐acid conditions produced quite similar chemical species in the resins. The proton rotating‐frame spin–lattice relaxation time (T_1ρH) decreased with a decrease in the reaction pH of UF resin. This result indicates that the molecular mobility of UF resin increases with a decrease in the reaction pH used during its synthesis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2677–2687, 2003     

Halogeno‐modified polystyrene: monomer reactivity ratios,thermal behaviour and flammability

Chemical modification based on incorporation of flame retardants into polymer backbones was used in order to reduce flammability of polystyrene (PSt). The halogeno‐substituted styrenes: 4‐chlorostyrene (ClSt), 4‐bromostyrene (BrSt) and 2,3,4,5,6‐pentafluorostyrene (5FSt) were applied as reactive flame retardants. Homo‐ and copolymers of these halogeno‐substituted styrenes and styrene (St) were synthesized with various feed ratios using free radical bulk polymerization with azobisisobutyronitrile as a initiator. This yielded series of (co)polymers with various amounts of included ClSt, BrSt and 5FSt (5–50 mol% of modified St). Copolymer compositions were determined using ¹H NMR spectroscopy. The relative reactivity ratios of the used comonomers were determined by applying conventional linearization methods. The Jaacks (J) method was used for systems including BrSt and ClSt monomers whereas the Fineman–Ross method was additionally used to confirm the values of reactivity ratios of St–5FSt. The reactivity ratios of comonomer pairs obtained from J plots were 0.75 and 0.38 (St–ClSt), 1.65 and 0.46 (St–BrSt), 0.44 and 0.42 (St–5FSt). Glass transition temperature and thermal stability of obtained (co)polymers were determined using differential scanning calorimetry and thermogravimetric analysis (TGA), respectively. The thermal degradation kinetic of PSt, PClSt, PBrSt and P5FSt was studied applying TGA. Kinetic parameters such as thermal decomposition activation energy (E) and frequency factor (A) were estimated using Ozawa and Kissinger models. The resulting activation energies estimated using these two methods were quite close. The values of activation energy (kJ mol^?1) increased in the following order: PClSt (E(O) = 216.1) < PSt (E(O) = 219.9) < PBrSt (E(O) = 224.7) < P5FSt (E(O) = 330.9). A pyrolysis combustion flow calorimeter was applied as a tool for assessing the flammability of the synthesized (co)polymers. © 2014 Society of Chemical Industry     

Thermal Degradation Behavior and Kinetics of 3D Porous Polycarbonate Monoliths

The thermal degradation behavior and kinetics are important to understand the nature of polymers. In this work, the thermal degradation behavior and kinetics of polycarbonate (PC) monoliths with a three dimension (3D) continuous interconnected porous structure is investigated. Thermogravimetric analysis reveals that the thermal stability of the PC monoliths shows a significant reduction compared to pristine PC due to its 3D porous structure, which drastically increases the heating surface area during the thermal degradation process. An interesting second degradation stage at 480–550 °C is observed for PC monoliths from the barrier effect formed by the collapse and coalescence of the porous structure at high temperature, which is further confirmed by volatile and solid char analyses. The kinetic analysis suggests that the PC monolith shows a low degradation activation energy (E_α ) at the first degradation stage, which increases rapidly and goes beyond the E_α of pristine PC at the second degradation stage.     

Zinc‐based compounds as smoke suppressant agents for an aerospace epoxy matrix

Smoke is considered to be the main hazard of fires involving epoxy resins but its production depends on many variables, principally the chemical character and the burning rate of the polymer plus the availability of oxygen. The work reported aimed to study the smoke suppressant effect and flammability performance of zinc‐based compounds (FR system) in epoxy matrix composites used in the aerospace and aeronautical industry. The flammability performance of neat and FR‐loaded systems was screened using microcombustion calorimetry, while smoke generation, in terms of carbon monoxide (CO) and carbon dioxide (CO₂) production, was analysed under dynamic conditions using cone calorimetry. Final results indicate that the dispersion of zinc borate and zinc hydroxystannate (ZHS) into epoxy matrices leads to a significant variation in flame retardant properties reducing both total heat release by about 25 and 30%, respectively, and heat release capacity by about 30 and 50%, respectively. The system containing ZHS shows an enhancement in all smoke suppressant properties; both tin compounds (zinc stannate (ZS) and ZHS) give a reduction of CO₂/CO ratio from 41 to 25 for ZS and from 41 to 36 for ZHS compared to neat matrix. Copyright © 2010 Society of Chemical Industry