Phenolic resins thermal degradation

Liu, L., Ye, Z. Effects of modified multi-walled carbon nanoUrbes on the curing behavior and thermal stability of boron phenolic resin. Polym. Degrad. Stab. 94, 1972-1978 (2009)... 

When cured with room temperature curing system these resins have similar thermal stability to ordinary bis-phenol A type epoxides. However, when they are cured with high-temperature hardeners such as methyl nadic anhydride both thermal degradation stability and heat deflection temperatures are considerably improved. Chemical resistance is also markedly improved. Perhaps the most serious limitation of these materials is their high viscosity. 

Recently, several reports of the flame-retardant properties of boron-containing bisphenol-A resins have appeared from Gao and Liu.89 The synthesis of a boron-containing bisphenol-A formaldehyde resin (64 and 65) (Fig. 42) from a mixture of bisphenol-A, formaldehyde, and boric acid, in the mole ratio 1 2.4 0.5, has been reported.893 The kinetics of the thermal degradation and thermal stability of the resins were determined by thermal analysis. The analysis revealed that the resin had higher heat resistance and oxidative resistance than most common phenol-formaldehyde resins. 

These polymers may be compared with the more detailed discussion of thermal degradation pathways for phenol-formaldehyde resins described in Section 2.3.3 earlier, which explains the... 

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. 

The structures of the lignins are amenable to conversion to several classes of substituted phenols by thermochemical and thermal degradation methods. The displacement of pyroligneous tars by coal tars eliminated much of the demand that existed for the lignin-based products. Creosote oil or cresylic acid, a mixture of o-, m-, and p-cresols, is now manufactured mainly from coal tars, while only small amounts of cresols are made from wood tars. The use of wood tars and other biomass-derived tars as substitutes for a major portion of the phenol and formaldehyde in phenol-formaldehyde resins could reverse this trend (Himmelblau, 1995). The key to this process seems to be that the... 

Formation of stable free radicals in the hardening and thermal degradation of phenol-formaldehyde resins. Visokomol. Soed. 2, 1167 (1960). 

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. 

Weight Losses during Thermal Oxidative Degradation Showing Dependence on Temperature for Modified and Unmodified Phenolic Resins. Determined by Thermogravimetric Analysis. 

Schutz et al. studied the thermal properties of a phenolic resin nanocomposite containing silsesquioxanes [80]. The thermal oxidative stability of the nanocomposites was improved, as compared to that of the piu e resin. This effect may be a consequence of the formation of a protective layer of SiG2 during silsesquioxanes pyrolysis at the surface of nanocomposites, which retarded the thermal oxidative degradation. The temperatures characteristic to thermal degradation processes were higher in the case of nanocomposites, compared to the pure resin matrix. 

Like phenol resins, epoxy resins can be identified rapidly with the help of a number of relatively simple, yet reliable chemical spot tests, but they serve mostiy only for establishing the class of polymer. More subtle analytical techniques are required to characteri.se technical epoxy resin formulation, especially in the presence of additives, fillers or perhaps even of spurious materials. The decisive breakthrough in the systematic characterisation of epoxy resins came with the introduction of thermal degradation procedures into polymer analysis. The polymer composition can be established beyond doubt from the separated and identified products of thermal degradation. The problems of separation and detection of these products have been solved to practice by GLC - and... 

---