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As adhesives, epoxies bond in three ways: a) Mechanically, because the bonding surfaces are roughened; b) by proximity, because the cured resins are physically so close to the bonding surfaces that they are hard to separate; c) ionically, because the epoxy resins form ionic bonds at an atomic level with the bonding surfaces.
Sand is added to improve compressive strength, hardness and reduce shrinkage. The binding property of clay is also used widely to prepare shaped articles (e.g. pots and vases) or to bind solid pieces (e.g. bricks). In composite materials, epoxy, polyester or phenolic resins are common.
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.
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.
The second most important part of FBE coatings is the curing agent or hardener. Curing agents react either with the epoxy ring or with the hydroxyl groups, along the epoxy molecular chain. Various types of curing agents, used in FBE manufacture, include dicyandiamide, aromatic amines, aliphatic diamines and organic acid anhydrides. [6]
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 ...
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Paper Coating 1) The paper or board 2) The first layer of coating to even out the surface 3) A second layer for an even smoother and whiter surface. Pigments that absorb in the yellow and red part of the visible spectrum can be added. As the dye absorbs light, the brightness of the paper will decrease, unlike the effect of an optical ...