Cured Epoxy Properties

Initial Tensile Modulus (Ey), Fracture Strength (c ), and Fracture Toughness (K,c) as a function curing agent concentration. From Drzal et al.781 

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The actual change in die cured epoxy properties is dependent on the level of LP used. In general, elongation, impact resistance, and tensile strength ineiease with increasing LP level, while brittleness decreases. 

EB processing and rheological properties of EB-cured epoxy adhesives... 

Kamon, T., Furukawa, H. Curing Mechanisms and Mechanical Properties of Cured Epoxy Resins. Vol. 80, pp. 173 — 202. 

Experimental results are presented that show that high doses of electron radiation combined with thermal cycling can significantly change the mechanical and physical properties of graphite fiber-reinforced polymer-matrix composites. Polymeric materials examined have included 121 °C and 177°C cure epoxies, polyimide, amorphous thermoplastic, and semicrystalline thermoplastics. Composite panels fabricated and tested included four-ply unidirectional, four-ply [0,90, 90,0] and eight-ply quasi-isotropic [0/ 45/90]s. Test specimens with fiber orientations of [10] and [45] were cut from the unidirectional panels to determine shear properties. Mechanical and physical property tests were conducted at cold (-157°C), room (24°C) and elevated (121°C) temperatures. 

The corrosion resistance and polymer-bonding compatibilities of the lonizable organophosphonates and the neutral organo-silanes are directly related to their inherent chemical properties. Specifically, NTMP inhibits the hydration of AI2O2 and maintains or Improves bond durability with a nitrile-modified epoxy adhesive which is cured at an elevated temperature. The mercaptopropyl silane, in addition to these properties, is compatible with a room temperature-cured epoxy-polyamide primer and also exhibits resistance to localized environmental corrosion. These results, in conjunction with the adsorbed Inhibitor films and the metal substrate surfaces, are subsequently discussed. 

Thus, the cured epoxy resin is a highly functional material whose final chemical, physical, and electrical properties dictate the ultimate utility of that material. 

As shown in Table 15.5, the epoxy plastics have fair resistance to high temperatures and have good mechanical properties. Cured epoxy resins are resistant to nonoxidizing acids, alkalis, and salts. Because of the presence of polar hydroxyl pendant groups, these polymers have good adhesion to substrates such as wood or metal. 

Superior toughness and mechanical properties The strength of properly formulated epoxy resins usually surpasses other types of casting resins. The cured epoxy resins [Structure (4.35)] are seven times tougher than the cured phenolic resins [Structure (4.36)] as is evident from Figure 4.15. The relative toughness is attributed to the distance between the crosslinking sites and presence of internal aliphatic chains. 

Alteration of this epoxy structure is the result of the fact that the epoxy molecules are both reacting and diffusing at the same time. This process forms a concentration gradient with a high epoxy monomer concentration at the surface which gradually reduces to the bulk concentration away from the surface. The properties of an epoxy with an excess of resin can be quite different from the stoichiometric amount. Figure 2, for example, illustrated the alteration of cured epoxy mechanical properties with epoxy/amine ratio. Excess epoxy or less than the stoichiometric amount of amine produces a brittle material if the mixture is cured in the same manner as the stoichiometric amount (Fig. 2). The stoichiometric sample has the lowest modulus while excess amine produces increased brittleness. The potential for variation in local properties within the epoxy due to the presence of a 200 nm or less layer must be considered. 

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 ... 

Curing Mechanism and Mechanical Properties of Cured Epoxy Resins... 

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