Epoxy Resins

Abstract

Epoxy resins are an important class of polymeric materials, characterized by the presence of more than one three-membered ring known as the epoxy, epoxide, oxirane, or ethoxyline group.The word "epoxy" is derived from the Greek prefix "ep," which means over and between, and "oxy," the combining form of oxygen (1). By strict definition, epoxy resins refer only to uncross-linked monomers or oligomers containing epoxy groups. However, in practice, the term epoxy resins is loosely used to include cured epoxy systems. It should be noted that very high molecular weight epoxy resins and cured epoxy resins contain very little or no epoxide groups. The vast majority of industrially important epoxy resins are bi-or multifunctional epoxides. The monofunctional epoxides are primarily used as reactive diluents, viscosity modifiers, or adhesion promoters, but they are included here because of their relevance in the field of epoxy polymers.Epoxies are one of the most versatile classes of polymers with diverse applications such as metal can coatings, automotive primer, printed circuit boards, semiconductor encapsulants, adhesives, and aerospace composites. Most cured epoxy resins provide amorphous thermosets with excellent mechanical strength and toughness; outstanding chemical, moisture, and corrosion resistance; good thermal, adhesive, and electrical properties; no volatiles emission and low shrinkage upon cure; and dimensional stability-a unique combination of properties generally not found in any other plastic material. These superior performance characteristics, coupled with outstanding formulating versatility and reasonable costs, have gained epoxy resins wide acceptance as materials of choice for a multitude of bonding, structural, and protective coatings applications.Commercial epoxy resins contain aliphatic, cycloaliphatic, or aromatic backbones and are available in a wide range of molecular weights from several hundreds to tens of thousands. The most widely used epoxies are the glycidyl ether derivatives of bisphenol A (>75% of resin sales volume). The capability of the highly strained epoxy ring to react with a wide variety of curing agents under diverse conditions and temperatures imparts additional versatility to the epoxies. The major industrial utility of epoxy resins is in thermosetting applications. Treatment with curing agents gives insoluble and intractable thermoset polymers. In order to facilitate processing and to modify cured resin properties, other constituents may be included in the compositions: fillers, solvents, diluents, plasticizers, catalysts, accelerators, and tougheners.Epoxy resins were first offered commercially in the late 1940s and are now used in a number of industries, often in demanding applications where their performance attributes are needed and their modestly high prices are justified. However, aromatic epoxies find limited uses in exterior applications because of their

Bio-based epoxy resin toughening with cashew nut shell liquid-derived resin

“…3 In this study, the cross-linker reactivity is kept constant while the EEW and the viscosity are varied. The high viscosity and low epoxide equivalent weight resin DGEDP-Me was the most reactive with gel times at 52 and 25 min at 60 and 80°C, respectively.…”

“…However, these thermosets may possess low impact resistance and brittle fracture. 3 Bisphenol A (BPA) and, subsequently, the diglycidyl ether of bisphenol A (DGEBA), is currently used for the preparation of a versatile family of high-performance cured epoxy resins.…”

“…3 Consequently, important work has been performed to toughen cured epoxy resins. 18 Rubber toughening, also known as phase separation toughening, involves incorporation of a rubbery phase within cured epoxy resins.…”

“…where ρ is density (densities determined by ASTM D792-13 were all 1 g/cm 3 ), R is the universal gas constant, G N is the shear modulus and T is the temperature at the peak of the tan δ + 50°C in Kelvin. 37 The shear modulus was determined from oscillatory rheology by averaging frequency-independent G′ values as shown in supporting information 4 in the online supplementary data.…”

Cura de compósitos de sistemas epóxi via irradiação de micro-ondas.

“…Outros fatores, como a presença de bolhas ou trincas também podem ocorrer como consequência do calor de reação excessivo. Neste sentido, foram realizados experimentos buscando-se prolongar o tempo de ensaio, considerando-se as recomendações do fabricante quanto à temperatura de cura do sistema epóxi em teste (a base de DGEBA) [48,54].…”