Modified epoxies

Liquids. Approximately 170,000 railroad tank cars are used in the United States. The interior surfaces of these cars are tailored to carry a wide variety of products and are constmcted of steel which is either unlined or lined with materials to enhance the chemical compatibiUty with a specific product these lining materials include synthetic mbber, phenoHc or modified epoxy resins, or corrosion-resistant materials such as aluminum, nickel-bearing steel, or stainless steel. 

In 1990 the majority of U.S. PCB production resulted from subtractive or print-and-etch processing additive processes were less than 6% of the total multilayer boards accounted for 55.8%. The ratio of rigid to flexible surface areas plated is about 15 1. High performance plastics including polyimide. Teflon, and modified epoxy comprised 6% of the market ( 324 million) flexible circuits were 6.6% ( 360 million) (42). 

Siebeif, A.R., Tolle, L.L. and Drake, R.S., CTBN-modified epoxies work in poor bonding conditions. Adhes. Age, 29, 19 (1986). 

Elastomers, plastics, fabrics, wood and metals can be joined with themselves and with each other using nitrile rubber/epoxy resin blends cured with amines and/or acidic agents. Ethylene-propylene vulcanizates can also be joined using blends of carboxylated nitrile rubber, epoxy resin and a reactive metal filler (copper, nickel, cobalt). However, one of the largest areas of use of nitrile rubber modified epoxy systems is in the printed circuit board area [12]. 

During the temperature ramp period, pressure is applied. How much pressure is applied depends on the adhesive and the type of assembly. Honeycomb assemblies are limited by the compression strength of the honeycomb core, so cure pressure is typically limited to 50 psi for aluminum core of standard density. Metal to metal assemblies can withstand higher pressures and usually have fewer bondline voids when cured at higher pressures. Metal-to-metal assemblies bonded with standard modified epoxies are cured at 90 psi. 

W. A. Romanchick, J. E. Sohn, and J. F. Geibel Synthesis, Morphology, and Thermal Stability of Elastomer-Modified Epoxy Resin, in ACS Symposium Series 221 — Epoxy Resin Chemistry II, R. S. Bauer (ed.), American Chemical Society, Washington DC, 1982, pp. 85-118. 

S02-cured epoxy resin. Modified epoxy/acrylic resins (1.2 to 1.4% of sand weight) are mixed with organic peroxide (26 to 60% of resin weight), the mixture is blown into the core box and a hardening mechanism similar to the S02 process takes place. 

Elastomer impression materials, 8 327 Elastomer-modified epoxy resins, 10 436 Elastomer-modified epoxies, 10 375-376 Elastomer production, tetrahydrofurfuryl alcohol in, 12 279... 

To assess the effect of elastomer degradation on composite performance, additional composites were fabricated with the same 121°C cure epoxy without any addition of the elastomer (211. The expansion behavior of the modified epoxy composite was similar to the toughened material. For electron doses less than 10 rads the CTE of the toughened and untoughened composites were essentially the same which suggests that the epoxy matrix and not the elastomeric component controls the thermal expansion behavior. 

Chain Extendable Urethane Modified Epoxy Oligomer. The chain extendable urethane modified oligomers were prepared by combining equimolar amounts of epoxy-diol adduct and half-blocked diisocyanates, and heating the resulting mixture at 80°C for 4-6 hours until the isocyanate Infrared band disappeared. 

Figures la and lb show the OH and NH infrared bands of the oligomer as a function of temperature in uncatalyzed and catalyzed formulations. The uncatalyzed urethane modified epoxy oligomer shows only small changes in the OH/NH absorbance ratio at temperatures below 165°C only about a 60% conversion of the blocked isocyanate was observed. In contrast, sample of the oligomer catalyzed with 0.5% dlbutyl tin dilaurate shows nearly complete chain extension at temperatures as low as 130°C.

Phase Separation Mechanism in Hexane-Epoxy Systems. . Influence of Reaction Parameters on the Morphology of Cyclohexane-Modified Epoxy Networks Prepared via CIPS... 

Fig. 12. Free energy curves for 2,6-dimethyl-4-heptanone modified epoxies calculated with the solubility parameter approach at a constant temperature (315 K) as a function of conversion...

Fig. 13. Phase diagram for the 2,6-dimethyl-4-heptanone modified epoxy system derived graphically from Fig. 12...

Fig. 16. Free energy curves for hexane-, octane-, and decane-modified epoxies at a constant temperature (T=315 K) and conversion (q=0)...

A further increase in the amount of solvent leads to the development of a bi-modal pore size distribution, as observed with SEM on samples prepared with concentrations of 10-15 wt % hexane (Fig. 18c,d). Similar bimodal distributions have also been reported with the octane and decane based systems [88,89] as well as in in rubber-modified epoxies prepared via phase separation [67,95-98]. 

In comparison to the results obtained for the samples prepared with hexane, it can be concluded that the mean pore size and volume fraction do not depend on the initial concentration of the solvent, ( )o, but mainly on the difference between ( )o and (Fig. 25). Similar qualitative results are also reported for rubber-modified epoxies prepared via reaction induced phase separation [103]. 

Fig. 29. Weight loss of cyclohexane modified epoxies by holding at T=200 °C...

While the surface modification is not effective to suppress cavitation, Yee and coworkers performed an experiment to suppress the cavitation mechanically in a rubber-modified epoxy network. They applied hydrostatic pressure during mechanical testing of rubber toughened epoxies [160]. At pressures above BOSS MPa the rubber particles are unable to cavitate and consequently no massive shear yielding is observed, resulting in poor mechanical properties just like with the unmodified matrix. These experiments proved that cavitation is a necessary condition for effective toughening. 

Fig. 45. Glass transition temperature of solvent-modified epoxy networks used for SENB testing and prepared via CIPS with various amounts of cyclohexane...

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