DGEBA epoxy

We then compare the measured linewidth to that implied by the "lifetime broadening" of at an rf field of 66 kHz and static field of 15 MHz for the piperidine cured DGEBA epoxy at 33°C. 

Yamani and Young (5) applied the theory to explain the plastic deformation of a diglycidyl ether of bisphenol A (DGEBA) epoxy resin cured with various amount of triethylene tetramine (TETA). They found that the theory gave a reasonable description for the resins below the glass transition temperatures T. ... 

Materials Description. Three CIBA-GEIGY epoxy/hardener systems were studied Araldite 6010/906, Araldite 6010/HY 917 and Araldite 6010/972 with stoichiometries 100/80, 100/80 and 100/27, respectively. Araldite 6010 was a DGEBA epoxy resin. The hardeners 906, HY 917 and 972 were, respectively, methyl nadic anhydride (MNA), methyltetrahydro phthalic anhydride (MTPHA) and methylene dianiline (MDA). These systems were investigated previously for the matrix controlled fracture in composites (6-8). The curing cycles used can be found in (6). The ideal chemical structures of the systems are shown in Table I. Neat resins were thoroughly degassed and cast into 1.27 cm thick plates for preparation of test specimens. 

The phase separation behavior during curing of polyetherimide (PEI) modified diglycidyl ether of bisphenol A (DGEBA) epoxy and PEI modified bisphenol A dicyanate (BPACY) were studied using SEM, light scattering, and dynamic mechanical analyzer. 

Diglycidyl ether of bisphenol-A (DGEBA), epoxy resin (YD 128, Kuk Do Chem., Mn = 378), and bisphenol-A dicyanate (BPACY, Arocy B-10, Ciba-Geigy) were used as the thermoset resin. 4,4 -diaminodiphenyl sulfone (DDS, Aldrich Chem. Co.) was used as a curing agent for epoxy. Polyetherimide (PEI, Ultem 1000, General Electric Co., M = 18,000) and 2-methyl imidazole (2MZ, Aldrich Chem. Co.) were used as the thermoplastic modifier and catalyst. 

It was noted that more refinement in spectral resolution was still needed. The combination of proton enhanced C-13 spectra combined with magic angle spinning made possible the identification of functional groups in the four DGEBA epoxy systems. A peak between 70-73 ppm were evidenced in all four systems indicative of the carboxyl-methine ether carbon of the reacted epoxide groups and adjacent methylene groups. 

Fig. 12. C- 13 spectrum of the piperidine (PIP) cured DGEBA epoxy polymer at room temperature. The assignments have been discussed and the structure indicates a possible polymerization mechanism 2 ...

Fig. 17. The C-13 spectra over a 200 K temperature range for DGEBA epoxy cured with piperidine. The chemical structure on the left shows one half of the (symmetrical) monomer (top half) and a possible curing structure with piperidine (bottom half). In the spectra the methyl resonance broadens and then disappears at low temperature the remaining peak at about 25 x 10 6 is assigned to the piperidine. The low-temperature splittings of peaks c and d.collapse at higher temperature, indicating reorientation of the phenyl group with respect to the backbone 641...

The amine-cured DGEBA epoxies utilized as matrices for filament wound composites generally form exclusively from epoxide-amine addition reactions (1). 

Table 1. Gk values measured at room temperature for Diglycidyl ether of bisphenol A (DGEBA) epoxy resins cured with various hardeners 11...

Fig. 4. Variation of K,c with crosshead speed, y, for a DGEBA epoxy polymer cured with different stated phr of TETA and tested at 20 °C 1,1 Brittle stable (type C) propagation O Kfa,...

Recently, alternative theoretical expressions have been developed by using classical thermodynamic treatments to describe the compositional dependence of the glass transition temperature in miscible blends and further extended also to the epoxywater systems 2S,27). The studies carried out on DGEBA epoxy resins of relatively low glass transition have shown that the plasticization induced by water sorption can be described by theoretical predictions given by ... 

A molecularly interlocked IPN of epoxy and polyimide was developed by Gaw et al. to form molecular composites of ODA-PMDA polyimide and DGEBA epoxy [73]. In this system the epoxy monomers were homogeneously mixed with a fully polymerized precursor to the polyimide, polyamic acid, that contained reactive groups that could react with the epoxy forming the three dimensional network. This system overcame many of the problems of previous systems by the use of a novel solvent system. 

FIGURE 2.4 Synthesis of DGEBA epoxy resin from bisphenol A and epichlorohydrin/... 

TABLE 2.2 Typical Properties of DGEBA Epoxy Resins8... 

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. 

Brominated Epoxy Resins. The conventional DGEBA epoxy resins are flammable when cured. In an adhesive, flammability is generally not considered critically important because the mass of adhesive in any one area is relatively small. However, in certain applications (printed-circuit manufacture, aircraft interiors, furniture, etc.) nonflammability is an important criterion. Flame-retardant additives and chlorinated curing agents have been used to impart nonflammability to epoxy resins. 

For example, using an amine of structure NF12-CF[2-CF[2-NF[-CF[2-CF[2-NF[2 (D.E.F1. 20 from Dow Epoxy Resins) and DGEBA epoxy resin having an EEW of 189 (D.E.R. 331 from Dow Epoxy Resins). 

The viscosity of an epoxy resin is dependent primarily on its molecular weight (MW). Low-MW resins typically have a viscosity in excess of 6000 cP, and conventional DGEBA epoxy resins (EEW = 190) have a viscosity around 12,000 cP. Therefore, for applications requiring relatively low viscosity, it is necessary to include other types of epoxy resin or to use diluents to achieve the desired properties. 

Another possible preassembly reaction mechanism has been noted with regard to amine cured epoxy resins.10 A variability and reduction in the rate of conversion of epoxy groups in DGEBA epoxy resin cured at room temperature with diethylene triamine (DETA) was noticed. This is due to a side reaction of the amine with air, resulting in bicarbonate formation. As a result, the adhesive strength decreased drastically when the uncured epoxy amine was exposed to ambient air for a significant period of time. 

FIGURE 3.13 Idealized molecular structure of a diglycidyl ether of biphenol A (DGEBA) epoxy resin. 

Properties of several commercially available DGEBA epoxy resins from various suppliers are listed in App. C. Generally they can be divided into the following classifications ... 

Figure 4.1 shows a comparison of the physical and curing properties for liquid and solid DGEBA epoxy resins. 

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. 

FIGURE 4.1 Comparative physical and curing properties for DGEBA epoxy resins.1... 

The highest-MW DGEBA epoxy resins are termed phenoxy resins. They are highly linear molecules that are used primarily as thermoplastic coating resins. However, they can be blended with lower-MW epoxy resins for the improvement of specific properties such as flexibility, impact and fatigue resistance, and thermal cycling. Phenoxy resins are sometimes used alone as a thermoplastic hot melt adhesive generally in film form. 

The synthesis of brominated epoxy resins was discussed in Chap. 2. The resulting resins are available primarily as semisolids or solids in solvent solutions. They have properties similar to those of other DGEBA epoxies except that the high bromine content (18 to 21 percent) in the finished resins provides outstanding flame ignition resistance. Tetrabromo diphenylolpropane (Fig. 4.2) is an example of a commercially brominated epoxy resin. 

Bisphenol F resins are often mixed with conventional DGEBA epoxy resins because of the relatively high cost of the bisphenol F product. When mixed with bisphenol A resins, the two form crystallization-free resins of moderate viscosity. 

Temperature, °C Aging time, h DGEBA epoxy 2.5 Functional epoxy novolac 4.0 Functional epoxy novolac... 

Diglycidyl ether of resorcinol-based epoxy resins provide the highest functionality in an aromatic diepoxide. It is one of the most fluid of epoxy resins, with a viscosity of 300 to 500 cP at 25°C. Because of its high functionality, it is a very reactive resin and cures more rapidly than DGEBA epoxies with most conventional curing agents. 

Five hundred grams per batch with a DGEBA epoxy with an EEW of 180 to 200. Highly dependent on curing agent concentration. 

TABLE 5.3 Effect of Curing Temperature on Bond Strength of DGEBA Epoxy Resin Cured with Two Different Aliphatic Polyamines6... 

Diethylenetriamine and Triethylenetetramine. Diethylenetriamine (DETA) and trieth-ylenetetramine (TETA) are very reactive, low-viscosity liquids that are widely used with DGEBA epoxy resins. The application characteristics and cured properties of adhesive formulations prepared with these two curing agents are very similar. The lower vapor pressure of TETA generally favors its use. 

With liquid DGEBA epoxy resins, DETA is normally used at the stoichiometric concentration of 10 to 11 parts per hundred (pph), and TETA is used at a concentration of 14 pph. However, both curing agents can be used at mix ratios as low as 70 to 75 percent of stoichiometry for greater toughness and increased pot life at the sacrifice of heat and chemical resistance. The effect of the mix ratio of DETA and TETA on the heat deflection temperature of castings is shown in Fig. 5.3. 

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