Degradation epoxy resin

The products of the chemical degradation of PETP with triethylene tetramine and triethaneolamine can be used as epoxy resin hardeners, it is demonstrated. Products of PETP aminolysis with triethylene tetramine and aminoglycolysis with triethanolamine, were characterised using NMR and rheometric measurements. Characteristics of the crosslinking process for the system epoxy resin/ PETP/amine degradation product, and epoxy resin/TETA for comparison were investigated by DSC. Three classes of liquid epoxy resins based on bisphenol A, bisphenol F and epoxy novolak resins were used in the experiments. 16 refs. 

Thermosets consist of a network of interconnected chains whose positions are fixed relative to their neighbors. Such polymers do not flow when heated. Instead, when exposed to high temperatures, thermosets degrade into char. Examples of thermosets include some polyurethanes and epoxy resins. 

Different behaviors and mechanisms were clearly recognized between these resins. Epoxy resin cured with amine showed no degradation during immersion because of its stable crosslinks. Epoxy resin cured with anhydride showed the uniform corrosion with the softening and dissolution of the surface and also behaved similar to the oxidation corrosion of the metal at high temperature obeying linear law. 

The epoxy resin formed by tetraglycidyl 4,4 -diamino diphenyl methane and 4,4 -diamino diphenyl sulfone was characterized by dynamic mechanical analysis. Epoxy specimens were exposed to varying dose levels of ionizing radiation (0.5 MeV electrons) up to 10,000 Hrads to assess their endurance in long-term space applications. Ionizing radiation has a limited effect on the mechanical properties of the epoxy. The most notable difference was a decrease of approximately 40°C in Tg after an absorbed dose of 10,000 Mrads. Sorption/desorption studies revealed that plasticization by degradation products was responsible for a portion of the decrease in Tg. 

The most noticeable property change is a decrease in the glass transition temperature of the epoxy resin as a function of absorbed dose. The decrease in Tg is due to plasticization by degradation products and free chain ends from chain scission. 

Table 2. Application of Fourier Transform IR to Dehydration Studies of Epoxy Systems. Tentative Infrared Absorption Assignments for the Three Cured Epoxy Resins and the Absorption Variations During Degradation 18)... 

R Original IR spectrum of epoxy resin. b TD Theynal degradation. 

J. Kim, K. Lee, K. Lee, J. Bae, J. Yang, and S. Hong, Studies on the thermal stabilization enhancement of ABS synergistic effect of triphenyl phosphate nanocomposite, epoxy resin, and silane coupling agent mixtures, Polym. Degrad. Stab., 79(2) 201-207, 2003. 

Tpo maximize the utility of crosslinked cycloaliphatic epoxy resins in some of the more critical application areas, improved toughness is required. Such improvements can often be made through modification with various flexibilizing agents, but as a rule this improvement is accompanied by a severe degradation of the strength and heat distortion temperature of the cured 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. 

Levchik, S. V., Camino, G., Luda, M. P., Costa, L., Muller, G., and Costes, B., Epoxy resins cured with aminophenymethylphosphine oxide Mechanism of thermal decomposition, Polym. Degrad. Stab., 1998, 60, 169-183. 

Ren, H., Sun, J., Wu, B., and Zhou, Q., Synthesis and properties of a phosphorus-containing flame retardant epoxy resin based on bisphenoxy(3-hydroxy) phenyl phosphine oxide, Polym. Degrad. Stab., 2007, 92, 956-961. 

Toldy, A., Anna, P., Csontos, I., Szabo, A., and Marosi, Gy. 2007. Intrinsically flame retardant epoxy resin—Fire performance and background—Part I. Polymer Degradation and Stability 92(12) 2223-2230. 

Epoxy resin can have varying amounts of inorganic material remaining in the product after its synthesis. One of these is sodium chloride, which is formed by the reaction of sodium hydroxide with epichlorohydrin molecules, as described in Chap. 2. This is important in electrical applications because the sodium salt can be hydrolyzed and can degrade electrical properties. Some epoxy resin manufacturers will offer special ultrapure electrical grades or low-chlorine grades of epoxy resins for application where this is an important factor. 

Epoxy resins and curing agents must have a relatively low viscosity so that formulation compounding can be accomplished easily and without a great deal of energy or degradation of the components. Viscosity is defined as the resistance of a liquid material to flow. It is usually measured in fundamental units of poise (P) or centipoise (cP). Table 3.2 shows a relationship between various common fluids and their viscosity as measured in centipoise. 

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