Kinetics of the enthalpy relaxation process for an epoxy network as determined with a peak shift model

The relaxation kinetics of the epoxy network diglycidyl ether of bisphenol A (n = 0) and m‐xylylenediamine were studied with differential scanning calorimetry experimental data with a shift peak model. Nonlinear parameters were calculated with aging experiments. The nonexponential parameter and the apparent activation energy were found from intrinsic cycles. Adam–Gibbs theory was used to provide a molecular interpretation based on the enthalpy relaxation. Different assumptions of the variation of specific heat capacity (c_p) were used to determine the macroscopic molar configurational entropy of the system. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2003–2008, 2005     

Isothermal and nonisothermal cure kinetics of an epoxy/poly(oxypropylene)diamine/octadecylammonium modified montmorillonite system

The effect of an octadecylammonium‐exchanged montmorillonite on the curing kinetics of a thermoset system based on a bisphenol A epoxy resin and a poly(oxypropylene)diamine curing agent were studied with differential scanning calorimetry (DSC) in isothermal and dynamic (constant‐heating‐rate) conditions. Montmorillonite and the prepared composites were characterized by X‐ray diffraction analysis and simultaneous DSC and thermogravimetric analysis. The analysis of the DSC data indicated that the intercalated octadecylammonium cations catalyzed the epoxy–amine polymerization. A kinetic model, arising from an autocatalyzed reaction mechanism, was applied to the DSC data. Fairly good agreement between the experimental data and the modeling data was obtained. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1765–1771, 2006     

Optimal designs for constant‐heating‐rate differential scanning calorimetry experiments for polymerization kinetics: nth‐order kinetics

Optimal designs have been constructed for differential scanning calorimetry (DSC) experiments conducted under constant‐heating‐rate conditions for materials that are a priori assumed to follow nth‐order kinetics. Two different operating scenarios are considered, including single‐scan and multiscan DSC experiments for eight different kinetic parameter combinations representing a range of typical polymeric curing reactions. The resulting designs are studied to determine which kinetic model parameters are influential in determining the optimal design. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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     

Online near‐infrared measurements of an epoxy cure process compared to mathematical modeling based on differential scanning calorimetry measurements

An epoxy resin containing diglycidyl ether of bisphenol A, dicyandiamide, and an accelerator (diurone) was investigated under different cure cycles. The mathematical prediction of the degree of cure in a thermoset as a function of time and temperature was investigated and compared to measured data. Near‐infrared analysis was used to measure the conversion of epoxy and primary amine and the production of hydroxyl. Modulated differential scanning calorimetry was used to measure the changes in the heat capacity during cure. The measurements revealed differences in the primary amine conversion and hydroxyl production, and close relations to the measurements of heat capacity were found. The measurements of the degree of cure revealed that cure cycles initiated at 80°C produced a lower degree of cure than cure cycles initiated at 90°C, although all cure cycles were postcured at 110°C. These findings were to some degree supported by measurements of the primary amine conversion and hydroxyl production. The characteristics found were attributed to differences in the cure mechanisms. The mathematical model did not incorporate these differences, and this may have led to discrepancies between the predicted and actual values of the degree of cure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cure kinetics of a diglycidyl ether of bisphenol a epoxy network (n = 0) with isophorone diamine

The study of the cure reaction of a diglycidyl ether of bisphenol A epoxy network with isophorone diamine is interesting for evaluating the industrial behavior of this material. The total enthalpy of reaction, the glass‐transition temperature, and the partial enthalpies at different curing temperatures have been determined with differential scanning calorimetry in dynamic and isothermal modes. With these experimental data, the degree of conversion and the reaction rate have been obtained. A kinetic model introduces the mechanisms occurring during an epoxy chemical cure reaction. A modification of the kinetic model accounting for the influence of the diffusion of the reactive groups at high conversions is used. A thermodynamic study has allowed the calculation of the enthalpy, entropy, and Gibbs free energy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Nonisothermal crystallization kinetics of poly(vinylidene fluoride) in a poly(vinylidene fluoride)/dibutyl phthalate/di(2‐ethylhexyl)phthalate system via thermally induced phase separation

The nonisothermal crystallization kinetics of poly(vinylidene fluoride) (PVDF) in PVDF/dibutyl phthalate (DBP)/di(2‐ethylhexyl)phthalate (DEHP) blends via thermally induced phase separation were investigated through differential scanning calorimetry measurements. The Ozawa approach failed to describe the crystallization behavior of PVDF in PVDF/DBP/DEHP blends, whereas the modified Avrami equation successfully described the nonisothermal crystallization process of PVDF. Two stages of crystallization were observed in this analysis, including primary crystallization and secondary crystallization. The influence of the cooling rate and DBP ratio in the diluent mixture on the crystallization mechanism and crystal structure was determined by this method. The Mo approach well explained the kinetics of primary crystallization. An analysis of these two methods indicated that the increase in the DBP ratio in the diluent mixture caused a decrease in the crystallization rate at the primary crystallization stage. The activation energy was determined according to the Kissinger method and also decreased with the DBP ratio in the diluent mixture increasing. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Modeling the chemorheological behavior of epoxy/liquid aromatic diamine for resin transfer molding applications

The analysis of the chemorheological behavior of an epoxy prepolymer based on a diglycidylether of bisphenol‐A (DGEBA) with a liquid aromatic diamine (DETDA 80) as a hardener was performed by combining the data obtained from Differential Scanning Calorimetry (DSC) with rheological measurements. The kinetics of the crosslinking reaction was analyzed at conventional injection temperatures varying from 100 to 150°C as experienced during a Resin Transfer Molding (RTM) process. A phenomenological kinetic model able to describe the cure behavior of the DGEBA/DETDA 80 system during processing is proposed. Rheological properties of this low reactive epoxy system were also measured to follow the cure evolution at the same temperatures as the mold‐filling process. An empirical model correlating the resin viscosity with temperature and the extent of reaction was obtained to carry out later a simulation of the RTM process and to prepare advanced composites. Predictions of the viscosity changes were found to be in good agreement with the experimental data at low extents of cure, i.e., in the period of time required for the mold‐filling stage in RTM process. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4228–4237, 2006     

Isothermal and nonisothermal crystallization kinetics of a semicrystalline copolyterephthalamide based on poly(decamethylene terephthalamide)

The isothermal and nonisothermal crystallization kinetics of a semicrystalline copolyterephthalamide based on poly(decamethylene terephthalamide) (PA‐10T) was studied by differential scanning calorimetry. Several kinetic analyses were used to describe the crystallization process. The commonly used Avrami equation and the one modified by Jeziorny were used, respectively, to describe the primary stage of isothermal and nonisothermal crystallization. The Avrami exponent n was evaluated to be in the range of 2.36–2.67 for isothermal crystallization, and of 3.05–5.34 for nonisothermal crystallization. The Ozawa analysis failed to describe the nonisothermal crystallization behavior, whereas the Mo–Liu equation, a combination equation of Avrami and Ozawa formulas, successfully described the nonisothermal crystallization kinetics. In addition, the value of crystallization rate coefficient under nonisothermal crystallization conditions was calculated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 819–826, 2004     

Nonisothermal crystallization kinetics of nucleated poly(ethylene terephthalate)

Studies of the nonisothermal crystallization kinetics of poly(ethylene terephthalate) nucleated with anhydrous sodium acetate were carried out. The chemical nucleating effect was investigated and confirmed with Fourier transform infrared and intrinsic viscosity measurements. The Avrami, Ozawa, and Liu models were used to describe the crystallization process. The rates of crystallization, which initially increased, decreased at higher loadings of the additive. The activation energy, calculated with Kissinger's method, was lower for nucleated samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Cold‐crystallization kinetics of syndiotactic polystyrene

The kinetics of the isothermal and nonisothermal cold crystallization of syndiotactic polystyrene (s‐PS) were characterized with differential scanning calorimetry. A Johnson–Mehl–Avrami analysis of the isothermal experiments indicated that the cold crystallization of s‐PS at a constant temperature followed a diffusion‐controlled growth mode with a decreasing nucleation rate. Furthermore, the slow nucleation rate was the controlling step of the entire kinetic process. For nonisothermal cold‐crystallization kinetics, we used a simple model based on a combination of the well‐known Avrami and Ozawa models. The analysis revealed that, unlike for melt crystallization, the Avrami and Ozawa exponents were not equal. The activation energies for the isothermal and nonisothermal cold crystallizations of s‐PS were 792.0 and 148.62 kJ mol^?1, respectively, indicating that the smaller motion units in cold crystallization had a weaker temperature dependence than those in melt crystallization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3464–3470, 2003     

Isothermal crystallization kinetics of high‐flow nylon 6 by differential scanning calorimetry

The isothermal crystallization kinetics have been investigated with differential scanning calorimetry for high‐flow nylon 6, which was prepared with the mother salt of polyamidoamine dendrimers and p‐phthalic acid, an end‐capping agent, and ε‐caprolactam by in situ polymerization. The Avrami equation has been adopted to study the crystallization kinetics. In comparison with pure nylon 6, the high‐flow nylon 6 has a lower crystallization rate, which varies with the generation and content of polyamidoamine units in the nylon 6 matrix. The traditional analysis indicates that the values of the Avrami parameters calculated from the half‐time of crystallization might be more in agreement with the actual crystallization mechanism than the parameters determined from the Avrami plots. The Avrami exponents of the high‐flow nylon 6 range from 2.1 to 2.4, and this means that the crystallization of the high‐flow nylon 6 is a two‐dimensional growth process. The activation energies of the high‐flow nylon 6, which were determined by the Arrhenius method, range from ?293 to ?382 kJ/mol. The activation energies decrease with the increase in the generation of polyamidoamine units but increase with the increase in the content of polyamidoamine units in the nylon 6 matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Isothermal crystallization kinetics of polypropylene by differential scanning calorimetry. I. Experimental conditions

Reliable isothermal crystallization kinetic studies can be achieved by differential scanning calorimetric techniques only under restricted conditions. In the case of isotactic polypropylene, our results indicate that those conditions are met in the range of 3°C below the isothermal crystallization temperature T_c. Experimentally, it is only in this range when the complete crystallization peak can be registered by the DSC and depicted in a thermogram. Just around this temperature interval, the Avrami exponent n = 3 for bulk crystallization, whereas for any other test the isothermal temperature T_it, nonisothermal conditions prevail and the Avrami exponent deviates from the expected value. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 970–978, 2004     

Copolymerization kinetics of dental dimethacrylate resins initiated by a benzoyl peroxide/amine redox system

The copolymerization of four dental dimethacrylates initiated by a benzoyl peroxide/4-N,N-dimethylamino phenethyl alcohol redox system at 37°C was studied with differential scanning calorimetry. The studied dimethacrylates were viscous bisphenol A glycidyl dimethacrylate (Bis-GMA), bisphenol A ethoxylated dimethacrylate (Bis-EMA), and urethane dimethacrylate (UDMA), which were characterized as base monomers, and low-viscosity triethylene glycol dimethacrylate (TEGDMA), which was characterized as a diluent. Also, three series of dimethacrylate copolymers were prepared by incremental additions (12.5 wt %) of TEGDMA to a base comonomer (Bis-GMA, UDMA or Bis-EMA). The maximum rate of homopolymerization of the dimethacrylates followed the order of Bis-GMA > UDMA > TEGDMA > Bis-EMA, and the final degree of conversion of the corresponding homopolymers followed the order of TEGDMA > UDMA > Bis-EMA > Bis-GMA. A reaction–diffusion-controlled termination region was clear in all monomers and started earlier in bulky and rigid Bis-GMA and Bis-EMA (followed by the more flexible UDMA and TEGDMA) but lasted longer in the Bis-EMA polymerization. The maximum rate of copolymerization and degree of conversion of copolymers of a base monomer with TEGDMA changed monotonically with an increase in the TEGDMA content in the initial comonomer mixture. A synergistic effect was clear only in the final double-bond conversion of Bis-GMA/TEGDMA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetic study by FTIR,TMA, and DSC of the curing of a mixture of DGEBA resin and γ‐butyrolactone catalyzed by ytterbium triflate

A mixture of diglycidylether of bisphenol A (DGEBA) and γ‐butyrolactone (γ‐BL) was cured in the presence of ytterbium triflate as a catalyst. The kinetics of the various elemental processes that occur in the curing process were studied by means of isothermal curing in the FTIR spectrometer. The kinetics of the contraction during the curing was also evaluated by TMA. In both cases, the kinetics was analyzed by means of isoconversional procedure and the kinetic model was determined with the so‐called compensation effect (isokinetic relationship). The isothermal kinetic analysis was compared with that obtained by dynamic curing in DSC. We found that all the reactive processes and the contraction follow a surface‐controlled reaction type of kinetic mechanism, R₃. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 381–393, 2004     

Crystallization kinetics and melting behavior of nylon 10,10 in nylon 10,10–montmorillonite nanocomposites

The crystallization kinetics and melting behavior of nylon 10,10 in neat nylon 10,10 and in nylon 10,10–montmorillonite (MMT) nanocomposites were systematically investigated by differential scanning calorimetry. The crystallization kinetics results show that the addition of MMT facilitated the crystallization of nylon 10,10 as a heterophase nucleating agent; however, when the content of MMT was high, the physical hindrance of MMT layers to the motion of nylon 10,10 chains retarded the crystallization of nylon 10,10, which was also confirmed by polarized optical microscopy. However, both nylon 10,10 and nylon 10,10–MMT nanocomposites exhibited multiple melting behavior under isothermal and nonisothermal crystallization conditions. The temperature of the lower melting peak (peak I) was independent of MMT content and almost remained constant; however, the temperature of the highest melting peak (peak II) decreased with increasing MMT content due to the physical hindrance of MMT layers to the motion of nylon 10,10 chains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2181–2188, 2003     

Curing behavior of epoxy resins in two‐stage curing process by non‐isothermal differential scanning calorimetry kinetics method

In this research, a new thermal curing system, with two‐stage curing characteristics, has been designed. And the reaction behaviors of two different curing processes have been systematically studied. The non‐isothermal differential scanning calorimetry (DSC) test is used to discuss the curing reaction of two stages curing, and the data obtained from the curves are used to calculate the kinetic parameters. Kissinger‐Akahira‐Sunose (KAS) method is applied to determine activation energy (E_a) and investigate it as the change of conversion (α). Málek method is used to unravel the curing reaction mechanism. The results indicate that the curing behaviors of two different curing stages can be implemented successfully, and curing behavior is accorded with ?esták‐Berggren mode. The non‐isothermal DSC and Fourier transform infrared spectroscopy test results reveal that two different curing stages can be implemented successfully. Furthermore, the double x fitting method is used to determine the pre‐exponential factor (A), reaction order (m, n), and establish the kinetic equation. The fitting results between experiment curves and simulative curves prove that the kinetic equation can commendably describe the two different curing reaction processes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40711.     

Properties and crystallization kinetics of poly(ether ether ketone)‐co‐poly(ether ether ketone ketone) block copolymers

A series of block copolymers composed of poly(ether ether ketone) (PEEK) and poly(ether ether ketone ketone) (PEEKK) components were prepared from their corresponding oligomers via a nucleophlilic aromatic substitution reaction. Various properties of the copolymers were investigated with differential scanning calorimetry (DSC) and a tensile testing machine. The results show that the copolymers exhibited no phase separation and that the relationship between the glass‐transition temperature (T_g) and the compositions of the copolymers approximately followed the formula T_g = T_g1X₁ + T_g2X₂, where T_g1 and T_g2 are the glass‐transition‐temperature values of PEEK and PEEKK, respectively, and X₁ and X₂ are the corresponding molar fractions of the PEEK and PEEKK segments in the copolymers, respectively. These copolymers showed good tensile properties. The crystallization kinetics of the copolymers were studied. The Avrami equation was used to describe the isothermal crystallization process. The nonisothermal crystallization was described by modified Avrami analysis by Jeziorny and by a combination of the Avrami and Ozawa equations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1652–1658, 2005     

Cure kinetics of an epoxy/liquid aromatic diamine modified with poly(ether imide)

The cure kinetics and mechanisms of an epoxy oligomer based on diglycidyl ether of bisphenol A (DGEBA), polymerized with a liquid aromatic diamine based on diethyl toluene diamine (DETDA 80), and its blends with poly(ether imide) (PEI) at concentrations of 0–15 wt % were studied with differential scanning calorimetry under dynamic and isothermal conditions. The kinetic analyses were performed with a phenomenological approach. The reaction mechanism of the blends remained the same as that of the neat epoxy. However, the addition of PEI had a marked effect on the cure kinetics in the DGEBA/DETDA 80 system. The rate of reaction decreased with an increase in the thermoplastic content. Diffusion control was incorporated to describe the cure behavior of the blends in the latter stages. Greater diffusion control was observed as the PEI concentration increased and the cure temperature decreased. Polymer blends based on this epoxy/liquid aromatic diamine had not been previously studied from a kinetic viewpoint. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 660–672, 2005