Environmental Engineering Reference
In-Depth Information
because of their low cost and versatility, but for high performance/chal-
lenging areas, they are not suitable [1].
6.1.2 Urethanes
Urethanes and polyurethanes are essentially polymeric esters of carbamic
acid or derivatives of carbamic acid with general formula R-NH-COOR [2].
h ey are prepared by reaction of diisocyanate with polyfunctional com-
pound containing active hydrogen atoms such as water, alcohols, amines,
etc. h e main advantage of the coatings based on urethanes are their high
chemical and abrasion resistance, low temperature cure, and wide range
of l exibility coupled with toughness. However, toxicity and yellowing ten-
dency in outdoor applications limit their use as binders. Urethane paints
are toxic and should be used with caution. Because they contain iscocy-
anantes, airborne compounds that enter the lungs or skin, investigating
proper precautions and aerating techniques is important when working
with urethane.
6.1.3 Epoxies
Epoxy resins are polyether resins containing more than one epoxy group
capable of being converted into the thermoset form. h ese resins, on cur-
ing, do not create volatile products in spite of the presence of a volatile
solvent. h e large groups of polyepoxides or epoxide resins [3] which are
commonly used in surface coatings are based upon the reaction products
of epichlorohydrin and bisphenol A. Because of high chemical and cor-
rosion resistance, excellent adhesion, low shrinkage, toughness, and good
abrasion resistance properties, epoxy resins i nd ample application in the
industrial maintenance i eld.
h e coatings industry is the biggest consumer of epoxy resins. h ese
resins are used mostly as chemical and special purpose coatings. Epoxy
resins provide thin-layer durable coatings having mechanical strength and
good adhesion to a variety of substrates. h ey are resistant to chemicals,
corrosion, and solutions. h ey i nd applications in washing machines and
appliances, ships and bridges, pipelines and chemical plants, automobiles,
farm implements, containers, and l oor coatings. Epoxy coating formu-
lations are available as liquid resins, solid resins, high molecular weight
thermoplastic resins, multifunctional resins, radiation curable resins, and
special purpose resins. Epoxy baking i nishes are obtained by high molecu-
lar weight epoxy resins crosslinked by phenolic or amino resins. h ese res-
ins are used as lining for tanks, cars, drums, pails, pipes, downhole oili eld
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