Epoxy-Anhydride System

Typical epoxy—anhydride systems are described in Table 7. 

Table 7. Epoxy—Anhydride System Handling and Performance...

Epoxy—amino resin weight ratios, 10 445 Epoxy—anhydride systems, properties of, 10 403-404... 

Figure 4.6 DSC thermograms of an epoxy-anhydride system cured at 80°C (a) and 130°C (b), for different times, tc (h). (Montserrat, 1992 - Copyright 2001 - Reprinted by permission of John Wiley Sons, Inc.)...

Accelerators are often used to increase the reactivity of epoxy-anhydride systems. The proper amount of cure accelerator is empirically determined and varies according to the material being used as the accelerator, the anhydride and epoxy resin used, and the desired cure speed and end properties. 

In contrast to epoxy-amines, water really participates in the cure chemistry of the epoxy-anhydride system and alters the living polymerisation mechanism because of interfering termination reactions [34]. A less dense network structure with altered properties results [35]. 

Figure 2.2c shows the corrected heat flow phase for the epoxy-anhydride system cured at 100°C the heat flow phase measured quasi-isothermally at 100° C for the fully cured resin was used as a reference point. The evolutions will be discussed in detail in the following section. In this paragraph, the magnitude of the signal is considered. 

Figures 2.7 and 2.8 show the influence of the heating rate on the vitrification-devitrification behaviour of the anhydride and amine-cured epoxies, respectively. For the epoxy-anhydride system, no vitrification is observed...

Figure 2.18. Diffusion factor for the quasi-isothermal cure of an epoxy-anhydride system at 120°C (), 100°C (O), 85°C (A), 70°C (x), 60°C (> ) Data points from MTDSC (DF ) and...

Figure 2.20. Reaction rate for the quasi-isothermal cure of an epoxy-anhydride system.

The epoxy-amine system is obviously more difficult to treat than the epoxy-anhydride system. The experimental conditions are more stringent (temperature interval of more than 200°C) and the empirical kinetic rate equation is probably not accurate enough. However, the proposed approach allows the model to be refined without too much difficulty. 

Figure 2.26. Glass transition temperature as a function of cure conversion for an epoxy-anhydride system. Experimental points were measured in a heating subsequent to a partial cure. T — x and T — x curves [see Eq. (27)] are simulations by means of the optimised model for diffusion-controlled cure.

Figure 2.27. Progress of the glass transition in the heat capacity signal during cure of an epoxy-anhydride system. Reference lines are indicated (see text).

Figure 2.28. Heat capacity change at the glass transition (ACp) and its width (A7g) as a function of cure conversion for an epoxy-anhydride system.

MTDSC quasi-iso thermal cure of the epoxy-anhydrid system... 

The variations of this ratio correlate to the differences in final isothermal cure state. Since the rate of conversion at vitrification is non-zero, conversion and Eg further increase in the (partially) glassy state with a rate dependent on the relative rate at vitrification. A relatively lower (dx/d/) )f .o.5 or ratio r results in a smaller increase in conversion and Eg after vitrification. For example, Eg at the end of the isothermal cure at 70°C for the epoxy-anhydride system amoxmts to 85°C, whereas a value of 103°C is determined for the amine system under similar isothermal cure conditions. 

Various accelerators can be used with epoxy/anhydride systems to promote cure. Some accelerators in use are ... 

The application of microwave irradiation to cure isocyanate/epoxy resins in the presence of N-(2-hydroxyalkyl)trialkylammonium halides was claimed to impart accelerations to both curing and post-curing kinetics with respect to conventional hot-air heating [122]. More recently, Parodi et al. presented further development of new class of catalysts that endow aromatic isocyanate/epoxy and aliphatic or cycloaliphatic epoxy/anhydride systems with a particular efficiency for microwave processability [123]. The catalysts belong to the family of N-(cyano-alkoxy-alkyl)trialkylammonium halides, of the general formula ... 

Cured epoxy-anhydride systems exhibit excellent thermal, mechanical, and electrical properties, and are used in filament-wound epoxy pipe, PCB laminates, mineral-filled composites, and electrical casting and encapsidation applications. Anhydride-cin-ed epoxies also have better aqueous acid resistance than similar amine-cured systems. Anhydrides are the principal curing agents for cycloaliphatic and epoxidized olefin resins in electrical casting and potting. Some... 

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