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1.
The ability to understand and model the mechanism of cure kinetics accurately is crucial for the production of thermosetting resin‐based nanocomposites. This article reports on work performed to elucidate an accurate model of cure kinetics for the formation of polybenzoxazine–montorillonite nanocomposites through the use of differential scanning calorimetry with nonisothermal methods, including single‐heating and multiple‐heating methods. The results indicated that both the Kissinger and Ozawa methods for calculating the activation energy gave fairly close results of 115 and 120 kJ/mol, respectively. The reaction order was about 1.31, calculated from the single‐heating method based on the autocatalytic method, and a comparison was made of the dynamic curing behaviors in the syntheses of polybenzoxazine and polybenzoxazine–montorillonite nanocomposites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 194–200, 2003 相似文献
2.
The different transitions and reactions involved in the thermal processing of ternary ethylene vinyl acetate (EVA)–polyethylene (PE)–azodicarbonamide (ADC) mixtures with different concentrations of PE and ADC, which was used as a foaming agent, were studied by means of differential scanning calorimetry. The effect of the concentration of PE in the ternary samples was practically linear, which showed an increase in the fusion heat of the PE and the PE domains of the EVA. On the contrary, the mechanism of the thermal decomposition of ADC that the ternary mixtures contained was strongly dependent on its concentration in the sample, which showed clear deviations from linearity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
3.
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 相似文献
4.
Cyclomatrix phosphazene–triazine network polymers were synthesized by co‐curing a blend of tris(2‐allylphenoxy), triphenoxy cyclotriphosphazene (TAP), and tris(2‐allylphenoxy) s‐triazine (TAT) with bis(4‐maleimido phenyl) methane (BMM). The co‐curing of the three‐component resin was investigated by dynamic mechanical analysis using rheometry. The cure kinetics of the Diels–Alder step was studied by examining the evolution of the rheological parameters, such as storage modulus (G′), loss modulus (G″), and complex viscosity (η*), for resins of varying compositions at different temperatures. The curing conformed to an overall second‐order phenomenological equation, taking into account a self‐acceleration effect. The kinetic parameters were evaluated by multiple‐regression analysis. The absence of a definite trend in the cure process with blend composition ratio was attributed to the occurrence of a multitude of competitive reactions whose relative rates depend on the reactant ratio and the concentration of the products formed from the initial phase of reaction. The cure was accelerated by temperature for a given composition, whereas the self‐acceleration became less prominent at higher temperature. Gelation was accelerated by temperature. The gel conversion decreased with increase in maleimide concentration and, for a given composition, it was independent of the cure temperature. The activation energy for the initial reaction and the crosslinking process were estimated for a composition with a maleimide‐to‐allyl ratio of 2 : 1. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 908–914, 2003 相似文献
5.
The effect of shearing in a corotating twin‐screw extruder on the apparent kinetic rate of model reactions was studied. Oxazoline‐terminated oligomers with different molar masses were prepared and used in condensation reactions with carboxylic acid terminated oligomers. A miscibility study of these oligomers allowed the choice of miscible and nonmiscible reactive systems. Reactions were first conducted in a glass reactor and then in the kneading‐disc area of a corotating twin‐screw extruder modified to neutralize the transport along the screws. For nonmiscible reactive systems, reactions were slower than equivalent reactions with miscible reactants. A shear increase for these nonmiscible reactants resulted in an increase in the apparent kinetic rate, which was in all cases lower than the rate obtained for miscible reactants. For very high shear rates, mechanical degradation was observed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2357–2362, 2004 相似文献
6.
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 相似文献
7.
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 相似文献
8.
The free‐radical terpolymerization of a monocyclic terpene, namely, limonene (Lim), with styrene (Sty) and methyl methacrylate (MMA) in xylene at 80 ± 0.1°C for 2 h, with benzoyl peroxide (BPO) as an initiator under an inert atmosphere of nitrogen was extensively studied. The kinetic expression was Rpα[BPO]0.5[Sty]1.0[MMA]1.0[Lim]?1.0, where Rp is the rate of polymerization. The overall energy of activation was calculated as 26 kJ/mol. Rp decreased as [Lim] increased. This was due to a penultimate unit effect. The Fourier transform infrared spectra of the terpolymer showed bands at 3025–3082, 1728, and 2851–2984 cm?1 due to C? H stretching of phenyl (? C6H5) protons of Sty, ? OCH3 of MMA, and trisubstituted olefinic protons of Lim, respectively. The 1H‐NMR spectra showed peaks at 7.3–8.1, 3.9–4.4, and 5.0–5.5 δ due to the phenyl, methoxy, and trisubstituted olefinic protons of Sty, MMA and Lim, respectively. The values of the reactivity ratios r1 (MMA; 0.33) and r2 (Sty + Lim; 0.06) were calculated with the Kelen–T?udos method. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2343–2347, 2004 相似文献
9.
During the cure of thermosetting polymer composites, the presence of reinforcing fibers significantly alters the resin composition in the vicinity of the fiber surface via several microscale processes, forming an interphase region with different chemical and physical properties from the bulk resin. The interphase composition is an important parameter that determines the micromechanical properties of the composite. Interphase development during processing is a result of the mass‐transport processes of adsorption, desorption, and diffusion near the fiber surface, which are accompanied by simultaneous cure reactions between the resin components. Due to complexities of the molecular‐level mechanisms near the fiber surface, few studies have been carried out on the prediction of the interphase evolution as function of the process parameters. To address this void, a kinetics model was developed in this study to describe the coupled mass‐transfer and reaction processes leading to interphase formation. The parameters of the model were determined for an aluminum fiber/diglycidyl ether of bisphenol‐A/bis(p‐aminocyclohexyl)methane resin system from available experimental data in the literature. Parametric studies are presented to show the effects of different governing mechanisms on the formation of the interphase region for a general fiber–resin system. The interphase structure obtained from the model may be used as input data for the prediction of the overall composite properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3220–3236, 2003 相似文献
10.
Ana L. Daniel‐da‐Silva João C. Moura Bordado José M. Martín‐Martínez 《应用聚合物科学杂志》2007,104(2):1049-1057
The curing of an isocyanate (NCO)‐ended quasi‐prepolymer by reaction with water in stoichiometric ratio was monitored by using differential scanning calorimetry both under isothermal and non‐isothermal conditions. A quasi‐prepolymer containing 16 wt % free NCO prepared by reacting trifunctional polypropylene glycol (PPG) with polymeric MDI was used in this study. The variation of the effective activation energy with the extent of the curing reaction was calculated by means of model‐free differential and integral isoconversional methods. Both isoconversional methods provided similar results showingthat the activation energy depends on the extent of thereaction of the quasi‐prepolymer with water. The dependence of the effective activation energy proved to be different under isothermal and non‐isothermal curing conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1049–1057, 2007 相似文献
11.
A simple numerical model for the interpretation of the reaction kinetics in ethylene–propylene–diene monomer (EPDM) vulcanized with accelerated sulfur is presented. The model is based on the assumption that during vulcanization, a number of partial reactions occurs, both in series and in parallel, which determine the formation of intermediate compounds, including activated and matured polymers. Once written a standard first‐order differential equation (DIFF‐EQ) for each partial reaction, an ordinary DIFF‐EQ system (ODEs), was obtained and solved through Runge–Kutta algorithms. Alternatively and more efficiently, a single second‐order nonhomogenous DIFF‐EQ with constant coefficients was deduced, for which a closed‐form solution was derived, provided that the nonhomogenous term was approximated with an exponential function. Kinetic constants were evaluated through experimental data fitting on standard rheometer tests. To assess model predictions, an experimental campaign at different temperatures on two EPDM compounds was performed. They exhibited moderate reversion at intermediate and high curing temperatures. A nonlinear least‐squares fitting was performed to evaluate unknown constants entering into the DIFF‐EQ model proposed. Scaled rheometer curves fit rather well, also in the presence of reversion. In addition, partial reaction kinetic constants were provided: this gave an interesting insight into the different reticulation processes occurring during vulcanization. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
12.
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 相似文献
13.
Microcapsules containing a curing agent, 2‐phenyl imidazole (2PZ), for a diglycidyl ether of bisphenol A (DGEBA) epoxy resin were prepared by a solid‐in‐oil‐in‐water emulsion solvent evaporation technique with poly(methyl methacrylate) (PMMA) as a polymeric wall. The mean particle size of the microcapsules and the concentration of 2PZ were about 10 μm and nearly 10 wt %, respectively. The onset cure temperature and peak temperature of the DGEBA/2PZ–PMMA microcapsule system appeared to increase by nearly 30 and 10°C, respectively, versus those of the DGEBA/2PZ system because of the increased reaction energy of curing. The former could take more than 3 months at room temperature, whereas the latter was cured after only a week. The values of the reaction order (a curing kinetic parameter) for DGEBA/2PZ and DGEBA/2PZ–PMMA microcapsules were quite close, and this showed that the curing reactions of the two samples proceeded conformably. The curing mechanism was investigated, and a two‐step initiation mechanism was considered: the first was assigned to adduct formation, whereas the second was due to alkoxide‐initiated polymerization. The glass‐transition temperature of DGEBA/2PZ was 165.2°C, nearly 20°C higher than the glass‐transition temperatures of DGEBA/2PZ–PMMA microcapsules and DGEBA/2PZ/PMMA microspheres, as determined by differential scanning calorimetry measurements. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
14.
The nonisothermal and isothermal crystallizations of low‐density polyethylene (LDPE) and polypropylene (PP) in phosphate glass (Pglass)–polymer hybrid blends were studied through differential scanning calorimetry (DSC). As the Pglass volume fraction was increased, the percentage crystallinity decreased. The half‐time for crystallization decreased as the propagation rate constant rose, for both of the polymer matrices, with increasing Pglass concentrations. The Pglass was observed to be a nucleating agent for formation of two‐ or three‐dimensional spherulites in the hybrids. Tensile modulus improved for both of the Pglass–polymer hybrids up to 40% Pglass, but the energy to break decreased. Tensile strength changed slightly with the addition of Pglass to the LDPE matrix, exhibiting a larger value than that of pure LDPE at 30%. The tensile strength decreased as more Pglass was added to the PP matrix. The observed differences between tensile properties of the Pglass–PP and Pglass–LDPE hybrids at identical Pglass volume concentration were found to be consistent with that of the crystallization behavior of the hybrids. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3445–3456, 2003 相似文献
15.
The most common commercial processes for manufacturing prepregs for electronic applications use solvent‐based resin systems. Solvents are not environmentally friendly and contribute to voids in prepregs and laminates. The resin impregnation process is performed in an open resin bath. This low‐pressure impregnation is conducive to voids in prepregs. Voids cause product variability, which is a major source of scrap in board shops. To eliminate these drawbacks, a solventless process, based on the concept of injection pultrusion, has been developed. The impregnation is performed in a die under pressure to minimize voids. In previous work, chemorheological and kinetic measurements were used to identify a potential epoxy‐based resin system. In addition, flow visualization with model fluids was used to establish the basic flow mechanism. Here we use the previous results to develop a mathematical model for the B‐staging process. A prototype B‐staging die has been built and used to verify the mathematical model. The results show that the model agrees well with the experimental data for low pulling speeds and slightly underpredicts the runs at high pulling speeds. The properties of the prepregs, the dielectric constant (DK) and dielectric loss (DF), have also been measured in this research. The measurements show that the solventless prepregs have acceptable DK and DF values according to the Institute for Printed Circuits FR‐4 designation (a permittivity and tangent loss standard). A microscope has been used to observe the void contents of the prepregs. The solventless prepregs have been compared against standard FR‐4 prepregs and shown qualitatively to have fewer voids. Based on the mathematical model, two potential process alternatives for the manufacture of solventless prepregs have been developed and analyzed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1136–1146, 2004 相似文献
16.
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 相似文献
17.
The matrix polymer of reactive hot‐melt adhesive (RHMA) is an isocyanate‐terminated urethane prepolymer based on oligoester or oligoether diols and diisocyanates. In this study, we explored wet cure kinetics with both isothermal and nonisothermal differential scanning calorimetry methods. Second‐order autocatalytic models were successfully used to evaluate the cure process of both oligoester‐ and oligoether‐based RHMAs. The autocatalyzation effect did not to depend on the structure of diols but on the reaction nature of the end isocyanates. The apparent energy of the overall cure reaction was 86.54 and 84.46 kJ/mol, respectively, which was based on nonisothermal DSC results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2708–2713, 2003 相似文献
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19.
This article describes the curing and thermal behavior of diglycidyl ether of bisphenol A with phthalic anhydride (PA)/pyromellitic anhydride/diaminodiphenyl sulfone (DDS) or a mixture of anhydrides and amines in varying ratios as curing agents. The kinetics of the curing behavior was investigated with a multiple‐rate method. The activation energy of the curing reaction as determined in accordance with Ozawa's method was found dependent on the structure of the anhydride and on the ratio of amines to anhydrides. The activation energy was highest with sample DP3 (0.25 : 0.75) and DM3 (0.25 : 0.75). We evaluated the thermal stability of epoxy resin, cured isothermally, by recording thermogravimetric traces in a nitrogen atmosphere. The char yield was highest for resins cured with a mixture of DDS and PA (0.5 : 0.5) and a mixture of DDS and pyromellitic dianhydride (0.25 : 0.75). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3919–3925, 2006 相似文献
20.
The curing kinetics of styrene (30 wt %) and cardanyl acrylate (70 wt %), which was synthesized from cardanol and acryloyl chloride, was investigated by differential scanning calorimetry under isothermal condition. The method allows determination of the most suitable kinetic model and corresponding parameters. All kinetic parameters including the reaction order, activation energy Ea and kinetic rate constant were evaluated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2034–2039, 2002 相似文献