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The other production route for epoxy resins is the conversion of aliphatic or cycloaliphatic alkenes with peracids: [13] [14] In contrast to glycidyl-based epoxy resins, this production of such epoxy monomers does not require an acidic hydrogen atom but an aliphatic double bond. The epoxide group is also sometimes referred to as an oxirane group.
Epoxy resins can be categorized into three distinct types based on the chemical structure of their resin backbone: aliphatic, cycloaliphatic, and aromatic epoxy resins. [4] An increase in the molecular length between reactive epoxy groups results in a reduction of crosslink density and resin modulus, while simultaneously enhancing the failure ...
Araldite adhesive sets by the interaction of an epoxy resin with a hardener. Mixing an epoxy resin and hardener together starts a chemical reaction that produces heat – an exothermic reaction. [2] It is claimed that after curing the bond is impervious to boiling water and to all common organic solvents.
It is a precursor in the production of epoxy resins. [19] Halohydrins react with base to give epoxides. [20] The reaction is spontaneous because the energetic cost of introducing the ring strain (13 kcal/mol) is offset by the larger bond enthalpy of the newly introduced C-O bond (when compared to that of the cleaved C-halogen bond).
After evaporation of the solvent, a solid compound is formed. Chemical bonds are also important in certain adhesive / substrate combinations, for example when bonding glass using silicone adhesives, wood using polyurethane adhesives and aluminium using epoxy adhesives. Chemical bonding leads to significantly higher adhesion than physical bonding.
In composite materials, epoxy, polyester or phenolic resins are common. In reinforced carbon–carbon, plastic or pitch resin is used as a source of carbon released through pyrolysis. Transite, hypertufa, papercrete and petecrete used cement as a binder.
An epoxy may be used for mounting, but can lead to failure in the epoxy/polymer interface instead of in the bonded joint. [2] The most common method for testing solvent bonds is the tensile shear test using a lap joint configuration. Specimens are tested in shear to failure at a given overlap cross section via tensile loading.
Cationic polymerization is used in the curing of epoxy resins in the presence of UV in the industry. [16] Light energy from UV breaks apart photoinitiaters, forming an acidic solution which then donates a proton to the polymer. The monomers then attach themselves to the polymer, forming longer and longer chains leading to a cross-linked network.