Epoxy thermal degradation

Peltonen K, et ah Determination of the presence of Bisphenol A and the absence of diglycidyl ether of Bisphenol A in the thermal degradation products of epoxy power paint. Am Ind Hyg Assoc J 47 399, 1986... 

The Isometric ion plots of Figures A and 5 indicate that evolution of benzene from the silicone-epoxy samples occurs in two distinct stages, with the low temperature peak attributable to residual solvent species. Above 200°C, thermal degradation processes involving scission of the Si-phenyl bond occur and account for the increased formation rate of benzene. The other high temperature volatile products are similar to those observed for the novolac epoxy samples, and are attributed to decomposition of the epoxy fraction of samples D and E. 

Electrical/Electronic Grade Epoxy. TGA and DSC analyses revealed no difference in thermal degradation below 200°C due to the presence of FR. DSC and EGA measurements showed that the FR breaks down above 350°C, in the range where it can perform its designated function. However, the EGA analysis did detect a small quantity of bromine-containing fractions below 200°C, and aqueous extraction revealed a fairly high Br concentration of 160 ppm. 

Crosslinking has no specific direct effect on thermal degradation crosslinks can be either weak points (e.g., tertiary carbons in polyester or anhydride-cured epoxies) or thermostable structural units (e.g., trisubstituted aromatic rings in phenolics, certain epoxies, or certain thermostable polymers). Indirect effects can be observed essentially above Tg crosslinking reduces free volume and thus decreases 02 diffusivity. It also prevents melting, which can be favorable in burning contexts. 

The isopropanol segment -CH2-CH(OII) CH2 can always be considered as the weakest point of amine-crosslinked epoxies, both in oxidation and in thermal degradation. 

Sequential Processes. In many cases (anhydride cured-epoxies, amine-cured epoxies, etc.), thermal degradation curves, for instance gravimetric ones, exhibit two distinct stages (Lehuy et al., 1991). The first one corresponds to a relatively fast, pseudo-first-order process, whereas the sec-... 

Among the other reported volatile TDP of B-carotene include B-cyclo-cltral, 5,6-epoxy-B-ionone and dihydroactinidiolide (25). These compounds were also found by Isoe et al. (30, 31), Wahlberg et al. (32) and Kawakami and Yamanishi (33) as photo-oxygenation products of B-carotene. Volatile thermal degradation of carotenoids has been extensively studied, mainly in nonfood systems. Hence, the objective of this study was to identify the volatile components of the TDP of B-carotene formed in a food model system. 

D.P. Bishop and D.A. Smith, Combined pyrolysis and radiochemical gas chromatography for studying the thermal degradation of epoxy resins and polyimides. I. The degradation of epoxy resins in nitrogen between 400° and 700°C. J. Appl. Polym. Sci., 14, 205 (1970). 

Phenolic resins have a low flammability by themselves due to the high aromatic content which leads to a high char formation on thermal degradation. However, end-capped brominated epoxy resins are used when necessary. Decabromodiphenyl ether in combination with antimony oxide is also used. 

Since epoxy formulations are generally good thermal insulators, the exotherm will depend on the mass of the system. A high rate of exotherm is needed with some epoxy adhesive systems to achieve practical curing rates. However, excessively high exothermic temperatures can result in bubble formation, thermal degradation, and even a potentially hazardous situation. Control of the exotherm is, therefore, a very important factor in formulating epoxy adhesives. 

In this Section, an experimental approach for constructing isothermal TTT cure diagrams has been described, TTT diagrams of representative epoxy systems including high Tg and rubber-modified epoxy resins have been discussed, and perturbations to the TTT cure diagram due to thermal degradation and rubber modification have been illustrated. 

For high temperature and rubber-modified epoxy resins, thermal degradation events and the cloud point curve are included on the diagrams, respectively. Two degradation events have been assigned devitrification, or a glass-to-rubber event and revitrification, which is associated with char formation. The cloud points and depressions of Tg for different rubber-modified epoxies can be compared and related to volume fractions of the second phase and to the mechanical properties of the cured materials. 

Comparison of several techniques (namely Fourier transform infrared spectroscopy (FTIR), simultaneous thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) and ultrasonic spectroscopy) for assessing the residual physical and mechanical characteristics of polymer matrix composites (PMCs) exposed to excessive thermal loads showed the measured power spectra of ultrasonic energy to correlate with performance of graphite fibre epoxy matrix composites exposed to thermal degradation, and also that analyses with the three techniques all pointed to the same critical temperature at which thermally induced damage increased sharply [58],... 

Participation of radical products of thermal degradation of PMBs in the epoxy resin curing process at high temperatures. 

A comprehensive study of the thermal degradation of epoxy resins has been reported by Lee [239]. Their stability was found to be lower than that of polycarbonate, polyphenylene sulphide and teflon (Fig. 64). 

As in polyester resins, reactive halogens containing fire-retardant chemicals are most often used in epoxy materials. Tetrabromobisphenol A is perhaps the most widely used component for flame-retarding epoxy resins. Nara and Matsuyama (24) and Nara et al. (25) described the thermal degradation and flame retardance of tetrabrominated bisphenol A diglycidyl ether compared to the nonbrorainated structure. Their results indicate that bromine acts by vapor-phase as well as condensed-phase mechanisms of flame inhibition. 

The reaction mechanism of epoxy groups with dicyanediamide is complex [14]. We therefore confine ourselves to say that GEPN and dicyanediamide are forming a solid resin matrix during an exothermic reaction. The reaction heat can cause thermal breakdown of the matrix material just built-up. Earlier performed experiments pointed at the release of ammonia and possibly some pyridine-like components during this thermal degradation process. But the release of water and a phenolic-OH residue can also be expected, see Figure 6.24. 

This will generally occur by boosting mold and/or resin temperature to decrease cure time while remaining subject to temperature requirements. For epoxy + AEP in 0.A76 cm cavity, a mold temperature of 125°C and a resin temperature of 70 C will provide a demold time of about 45 sec and a peak temperature of 262°C. In a 0.635 cm cavity the same material will process best on the basis of minimum demold time and avoidance of thermal degradation with a mold temperature of 115°C and a resin temperature of 55°C. 

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