Epoxy resin cure kinetics

Size Exclusion Chromatography Analysis of Epoxy Resin Cure Kinetics... 

Cure Kinetics. The cure kinetics of the mixed system to the B-stage were determined by the method outlined by Senich, MacKnight and Schneider (7) for two epoxy resins cured with dicyandianide by dynamic spring analysis (DSA). Senich et al. (7) used the elapsed time to the loss peak maximum of tan delta as a measure of the rate of the reaction at each temperature and for each frequency. The slope of an Arrhenius plot of In (tmax) vs. 1/T was then used to determine the activation energy. 

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). 

It is beyond the scope of this review to discuss in detail viscoelastic properties at and after gelation. The gel point is one of the important characteristics in the epoxy resin curing process from both kinetic and rheological aspects. The gelation transition has been widely studied for epoxy resin systems [39,44,133-138] and already discussed in some of this series, such as by Malkin and Kulichikhin [28], Williams et al. [139], and Winter and Mours [140]. Rheological techniques for the determination of the gel point have been summarized for thermosetting resins by Halley et al. [29,141]. 

In a fundamental study of the factors affecting the growth of the rubber domains in a CTBN-toughened DGEBA epoxy resin cured by piperidine (Manzione and GilUiam, 1981) the kinetics of phase separation were linked to the diffusivity, Uab, of the rabber (A) dissolved in the epoxy resin (B). The relevant dependence on the molar volume of the rubber (proportional to the radius of the rubber molecules when dissolved in the epoxy resin) at the viscosity for the temperature T of reaction is given by the Stokes-Einstein equation ... 

Thermoplastic-modified epoxy resins cured with different functionalities amine mixtures. Kinetics and miscibility study. Journal of Thermal Analysis and Calorimetry, Vol.97, No.3, (June 2009), pp. 969-978, ISSN 1388-6150. 

Buist, G., Hamerton, L, and Barton, J. M., Comparative kinetic analyses for epoxy resins cured with imidazole-metal complexes,/ Mater. Chem., 4, 1793, 1994. 

Because of all these minor components (e.g., catalysts and inhibitors, added to major ones) the cure of vinyl ester resins is very complex, involving many competitive reactions. There are some new variables to account for, such as the inhibitor and initiator concentrations and induction time. Several papers [81,96,200,201] use the mechanistic approach, claiming that the phenomenological models do not explicitly include these facts, resulting in a new parameter characterization after each change in resin formulation [96]. Despite these arguments, the phenomenological approach is the most widely used and is based on an autocatalytic model which has been successfully applied to epoxy resins. Many authors [30,34,74,199,202,203] proposed the Equation 2.30 to describe the cure kinetic of unsaturated polyesters ... 

Several researchers have modeled the cure kinetics of thermosetting resins in the past, including an unsaturated polyester resin [8], epoxies [9-11], and bismaleimide [5], As an example, a graphite/BMI material, IM6/3100, was modeled in [5] using... 

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