DGEBA resin

Liquid crystal thermoplastics, 10 8 Liquid dessicants, 8 365-366 Liquid DGEBA resins, 10 460 Liquid diffusion, 9 109, 110-112 Liquid discharge treatment, ion-exchange, 14 422... 

This paper rerports an investigation of the yield behavior of several amine and anhydride cured DGEBA resin systems. The Argon theory is used to assess the controlling molecular parameters from the experimental results. Such parameters are then compared with the known chemical structures of the resins. The mechanisms of plastic flow in thermoset polymers such as epoxies is demonstrated. 

It is evident that relaxation studies in the solid state can look at the motions which are responsible for the mechanical properties of the cured epoxy systems 43). Therefore, Garroway, Moniz and Resing continued to do relaxation studies 61). Garroway, et al. looked at four epoxy polymers based on the DGEBA resin. Two of the epoxy resins were cured with amines and the other two were cured with anhydrides. Proton enhanced spectra of the epoxy systems were generated. The solid state spectra were compared to the solution spectra of the unreacted epoxy. The< epoxy resin of interest was again DGEBA which was reacted with ... 

The typical effect of rate on the measured value of K,c and the associated type of crack growth can clearly be seen in Fig. 4 for an epoxy polymer based upon a DGEBA resin and cured with various amounts of TETA. The values of K ci and K ca are those for crack initiation and arrest (Fig. 2b) respectively and the difference between them characterises the amount of crack jumping which has taken place. When the difference... 

The interaction between these films and bulk epoxy resin was assessed by immersing an aluminum mirror coated with an air-dried primer film in a Petri dish filled with the epoxy resin, heating the dish in an oven at 100°C for 1 h, allowing the dish to cool overnight, and then extracting any unreacted material from the surface of the mirror by MEK extraction. Figure 6A is the reflection spectrum of a relatively thick film (ca. 3 / n) of neat DGEBA resin (cast onto polished aluminum from a 3% solution in toluene), and Fig. 6B shows the RAIR spectrum obtained from the mirror that was primed, heated in resin, and extracted. The... 

Figure 25 (a) Emission spectra at 293 K of/ac-ClRe(CO)3(4.7-Ph2-phcn) in the mixed epoxy system of bisphenol-A/novalac and DGEBA resin (0.05-mm thin film) containing a triarylsulfonium hexafluoroantimonate photoinitiator as a function of UV-irradiation time (A) 0 s, (B) 15 s, (C) 30 s, and (D) 60 s. The emission spectra are uncorrected for photomultiplier response and vertically displaced for clarity. Excitation wavelength is 420 nm in each case, (b) Plot of emission intensity at the MLCT band maximum of /ac-ClRe(CO)3(4,7-Ph2-phen) as a function of UV-irradiation time. (From Ref. 100.)... 

Solid, higher-MW epoxy resins are often used for adhesive formulations that are applied as solids (e.g., film and powder) or a solvent solution. The higher-MW DGEBA resins are also used where improved toughness, flexibility, and adhesion are required. These resins have a greater number of hydroxyl groups along the chain and, thus, can provide better adhesion and additional reaction mechanisms. 

Bisphenol F-based epoxy resins (Fig. 2.7) are analogous to DGEB A-based epoxy resins in most respects. They use the same curing agents and reaction mechanisms. Bisphenol F epoxies are often used in blends with DGEBA resins to lower the viscosity or to modify certain properties. 

The cycloaliphatic epoxy resins are characterized by the saturated ring in their chemical structure. They are almost water-white, very low-viscosity liquids. They provide excellent electrical properties such as low dissipation factor and good arc-track resistance, good weathering, and high heat distortion temperature. They are also free of hydrolyzable chlorine, sometimes present in DGEBA resins, which adversely affects certain electronic applications. 

The resins based on glycerol and pentaerythritol are water-soluble and have low viscosity. They can have greater functionality and reactivity than conventional DGEBA resins. Resins based on polytaerythritol are claimed to have excellent adhesive properties including the ability to adhere to wet surfaces. They cure between 2 and 8 times faster than DGEBA epoxy resins and reduce the viscosity of DGEBA by 50 percent when used in concentration of 20 pph. 

Other products that may be epoxidized in this way include dihydric and trihydric phenols, aliphatic polyols such as glycerol, and simple alcohols such as butanol or alyl alcohol. These products, especially the monofunctional glycidyl ethers, are used at relatively low percentages to reduce the viscosity of formulations containing DGEBA resins. In this way, they act as reactive diluents. 

These resins are most often characterized by their epoxy equivalent weight (EEW), molecular weight (number of repeating units ri), and viscosity. Table 4.2 shows the relationship between EEW and viscosity. These DGEBA epoxy resins can be used alone or in blends with other DGEBA resins, other epoxy resins, or even other types of polymeric resins. Very often commercial epoxy resin products are actually blends of resins having a broad molecular weight distribution. 

A majority of the world s epoxy resin market consists of the DGEBA type. The liquid DGEBA resins are typically used where low viscosity, high reactivity, and high crosslink density are required. The low viscosity allows them to be conveniently and easily compounded with fdlers and other additives. The relatively high functionality allows them to... 

The lower-viscosity grades have an EEW of about 175 and are virtually pure diglycidyl ethers of bisphenol A. They are so pure, however, that they will crystallize on storage. The crystals melt on warming above 40°C, and heating can be used to restore a crystallized resin to its previous form. Special crystallization-free resins systems have been formed by blending low-viscosity DGEBA resins with more conventional bisphenol A-based epoxy resins. 

These low-viscosity DGEBA resins provide all the general properties of the higher-MW epoxies with the following additional advantages ... 

TABLE 4.4 Properties of an Epoxy Resin Formulation Based on a Blend of Polyglycol Diepoxy Flexibilized Resin and Standard DGEBA Resin, Cured with Methylene Dianiline5... 

In adhesive formulations, aliphatic amines are most commonly used to cure the DGEBA type of epoxy resin. Aliphatic amines are not widely used with the non-glycidyl ether resins, since the amine-epoxy reaction is slow at low temperatures. The reaction usually requires heat and accelerators for an acceptable rate of cure. Aliphatic amines are primarily used with lower-viscosity DGEBA resins because of the difficulty in mixing such low-viscosity curing agents with the more viscous epoxy resins. 

Glycidyl Adducts of Aliphatic Amines. An aliphatic amine such as diethylenetriamine can be partially reacted with an epoxy, such as a DGEBA resin, to produce a low-volatility adduct. In a typical reaction, the epoxy is added slowly to a large excess of DETA. The reaction is maintained at 75°C by cooling. The reaction products are continuously agitated effectively to provide for good contact and uniform concentration effects. At the end of the reaction, excess DETA is vacuum-distilled away from the adduct. 

DADS melts at 135°C and is employed stoichiometrically with DGEBA at 33.5 pph. Fortunately, it is relatively unreactive so it can be mixed with epoxy resin at elevated temperatures. It can also be used in epoxy solutions to provide an adhesive formulation for manufacturing supported or unsupported film with long shelf life. Because of the low reactivity of the system, DADS is generally employed at a concentration that is about 10 percent greater than stoichiometry, or an accelerator, such as BF3-MEA, is employed at about 0.5 to 2 pph. When DADS is mixed with liquid DGEBA resin, it provides a pot life of 3 h at 100°C and requires a rather extended high-temperature cure to achieve optimal physical properties. 

True solvents are considered to be those solvents that provide resin solutions which can be diluted to infinity without resin precipitation. True solvents for epoxies include MEK, diacetone alcohol, methylcyclohexanone, and most glycol ethers and their acetates. Acetone, not a true solvent, can be used to prepare 40% solutions of high-MW DGEBA epoxy resin, but not a 20% solution. Aromatic solvents such as toluene and xylene, as well as simple alcohols, such as isopropyl and n-butyl alcohol, are not active solvents for DGEBA resins however, they can be used in combination with other solvents to improve solubility. 

Dicyandiamide has an activation temperature of about 177°C. However, this can be reduced to about 120°C by the use of accelerators. When mixed into liquid DGEBA resins, dicyandiamide has very good shelf life due to its latency. The shelf life of unaccelerated systems is about 6 months at room temperature or longer if refrigerated. The shelf life is reduced significantly with the addition of accelerators. 

Resolution Performance Products) DGEBA resin (EPON 828) 25 75 ... 

DER 542 305-355 Semisolid Generally blended with other DGEBA resins Dow... 

Fig. 21. Plot of permittivity and loss factor versus time during the cure of a low molecular weight DGEBA resin (EPON 825) with DDS at 137 °C. (Reprinted from Ref.47) with permission of the Society for the Advancement of Material and Process Engineering)...

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