Cure reaction kinetics

In order to quantify diffiisional effects on curing reactions, kinetic models are proposed in the literature [7,54,88,95,99,127-133]. Special techniques, such as dielectric permittivity, dielectric loss factor, ionic conductivity, and dipole relaxation time, are employed because spectroscopic techniques (e.g., FT i.r. or n.m.r.) are ineffective because of the insolubility of the reaction mixture at high conversions. A simple model, Equation 2.23, is presented by Chem and Poehlein [3], where a diffiisional factor,//, is introduced in the phenomenological equation, Equation 2.1. 

The e-beam pulse frequency is related to the energy absorbed by the material per unit of time, i.e. to the irradiation dose rate therefore it can affect both the cure reaction kinetics and the heat developed during cure. 

Thus, the stated above results have demonstrated that both scaling Eq. (86) of Chapter 1 and fractal Eq. (27) of Chapter 1 (or Eq. (61) of Chapter 2) describe well to an equal extent haloid-containing epoxy polymer 2DPP+HCE/DDM curing reaction kinetics at different curing temperatures. In virtue of this circumstance there exists intercoimection between parameters included into the indicated equations. The fractal Eq. (61) of Chapter 2 introduces in the kinetics problem consideration reaction products structure (in the given case structure of microgels and condensed state after gel formation point), characterized by its fractal dimension D, that makes this conception physically more informative [34]. 

T. Provder, C. M. Neag, G. Carlson, C. Kuo and R. M. Holsworth, "Cure Reaction Kinetics Characterization of Some Model Organic Coatings Systems by FT-IR and Thermal Mechanical Analysis", this volume. 

CURE REACTION KINETICS CHARACTERIZATION OF SOME MODEL ORGANIC COATINGS SYSTEMS BY FT-IR AND THERMAL MECHANICAL ANALYSIS... 

To further understand the effect of the interaction between the nanoparticles and the epoxy resin, the curing reaction kinetics of the composites have been studied. Based on non-isothermal DSC measurements and the Kissinger equation, the activation energy E, the pre-exponential factor A, and the reaction order , of the curing kinetics are obtained (Table 4). Comparison of the kinetic data suggests that the presence of the nanoparticles in epoxy does not change the overall reaction... 

Provder, T, Neag, C.M., Carlson, G.M., Kuo, C and Holsworth, R.M. (1984) Cure reaction kinetics characterization of some model organic coating systems hy FTIR and thermal mechanical analysis, in Arudytical Calorimetry (eds J.F. Johnson and P.S. Gill), Plenum Press, New York. 

Kinetics and mechanism of curing reactions using ylides as a new curing agent. 

The kinetics of resole cure reactions monitored via FTIR suggest that a diffusion mechanism dominates below 140°C. The cure above 140°C exhibits a homogeneous first-order reaction rate. The activation energy of the cure reaction was -"-49.6 kJ/mole.66... 

Future work in this area will involve the extension of these techniques to other temperatures in an effort to better characterize the overall reaction kinetics of these two processes. In addition, degree of cure obtained through isothermal DSC measurements will be compared with the fraction of acetylene consumed as measured by isothermal FTIR experiments for the same temperature and time. Also, the effect of the incorporation of metal fillers on the isomerization and crosslinking reactions will be addressed. 

The temperature reached by a monomer undergoing photopolymerization plays a key role on the reaction kinetics, in particular on the ultimate degree of conversion and therefore on the physico-chemical properties of the UV-cured polymer. It is strongly dependent on the formulation reactivity, the film thickness, as well as on the light intensity. 

Kinetically controlled epoxy curing reactions, 10 423 Kinetic barriers, 11 529 Kinetic friction, 15 224 Kinetic incompatibility, in acrylonitrile copolymerization, 11 203 Kinetic measurements, 14 607-629. See also Very fast kinetics combined methods for unstable reagents, 14 621... 

The curing sequence and kinetics of this adhesive system prevent the NTMP from Inhibiting the reactive amines until the curing reaction Is well under way. In contrast, the epoxypolyamide primer contains free amino groups at room temperature and may be inhibited by the electrophilic NTMP species prior to curing. (Equation 3)... 

The first reactions were carried out at room temperature in devices fabricated from a thiolene resin cured between two glass slides. 2-Hydroxypropyl methacrylate (HPMA) was polymerized by ATRP, and reaction kinetics similar to those obtained in a traditional batch reaction were obtained by adjusting the total flow rate of the fluid through the channel and treating the residence time in the channel as the reaction time (Fig. 21b,c) [102]. 

The techniques to be described here cannot differentiate the multiple reactions that take place during the curing reaction instead, only an overall kinetics is measured [32,142]. The most commonly used techniques will be described briefly. 

A cure kinetics model relates chemical composition with time and temperature dining chemical reaction in the form of a reaction rate expression. Kinetic models may be phenomenological or mechanistic. A phenomenological model captures the main features of the reaction kinetics ignoring the details of how individual species react with each other. Mechanistic models, on the other hand, are obtained from balances of species involved in the reaction hence, they are better for prediction and interpretation of composition. Due to the complexity of thermosetting reactions, however, phenomenological models are the most common. 

Kinetic models determine the minimum time required to cure the resin (i.e., guarantee sufficient physical and mechanical properties). They also determine the heat of reaction of the resin for use by heat transfer models and the degree of crosslinking for use in viscosity submodels. The exothermic cure reaction for the transformation of the epoxy resin to the cured matrix polymer can be expressed as ... 

If the curing reaction occurs at adiabatic or isothermal conditions above the glass transition temperature of the ultimately cured polymer, the reaction kinetics is adequately described by the adopted mechanism 5> 16,l7 69 7i However, at temperatures substantially below the final glass transition temperature, the reaction rate at a certain... 

The second important feature of the reaction mechanism of the epoxy compound curing under the action of amines (primary, secondary and tertiary) and their mixtures consists in formation of various hetero-, auto-, inter- and intramolecular donor-acceptor complexes between the components of the reaction system — the starting substances and reaction products. Consideration of this complex formation can adequately explain the reaction kinetics. 

In Chapter 2 the DSC technique is discussed in terms of instruments, experimental methods, and ways of analysing the kinetic data. Chapter 3 provides a brief summary of epoxy resin curing reactions. Results of studies on the application of DSC to the cure of epoxy resins are reviewed and discussed in Chapter 4. These results are concerned with the use of carboxylic acid anhydrides, primary and secondary amines, dicyanodiamide, and imidazoles as curing agents. 

Although the simple rate expressions, Eqs. (2-6) and (2-9), may serve as first approximations they are inadequate for the complete description of the kinetics of many epoxy resin curing reactions. Complex parallel or sequential reactions requiring more than one rate constant may be involved. For example these reactions are often auto-catalytic in nature and the rate may become diffusion-controlled as the viscosity of the system increases. If processes of differing heat of reaction are involved, then the deconvolution of the DSC data is difficult and may require information from other analytical techniques. Some approaches to the interpretation of data using more complex kinetic models are discussed in Chapter 4. 

In general the amine-epoxy resin curing reactions show complex kinetics typified by an initial acceleration due to autocatalysis, while the later post-gelation stages may exhibit retardation as the mechanism becomes diffusion-controlled. However some workers 72 80) have found that over a limited range of conversion the kinetic data may be described by the simple models of Eq. (2-6) or (2-9). 

The results of the DSC studies on DICY-cured systems are summarised in Table 5. The general comments at the end of Section 4.2, on the complexity of the kinetics apply also to dicyanodiamide cure. In this case the systems are even more complex because the dicyanodiamide is initially present as a dispersion of crystalline particles, so that the onset of the curing reaction is usually coincident with the onset of dissolution of the dicyanodiamide. 

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