What is the difference between Amine, Amide, Cycloaliphatic, and Amine Adduct Epoxy?
Starting with the basics, Epoxy resins consist of two components that react with each other forming a hard, inert material. Part A consists of an epoxy resin and Part B is the epoxy curing agent, sometimes called hardener. In order to discuss the more specific classifications of epoxy resins we must dive into some technical info.
Epoxy resin begins with the reaction of two compounds a part A and Part B. The part A usually consist of Bisphenol A (Bis A) or Bisphenol F (Bis F) Bis A is a cost-effective, general-purpose resin which demonstrates excellent alkali resistance, good acid resistance and fair-to-good solvent resistance. BISPHENOL F epoxy resin is a low-viscosity material which provides excellent alkali resistance and offers improved acid and solvent resistance compared to BISPHENOL A.
When someone refers to a polyamine epoxy he is referring to the curing agent. There are hundreds of curing agents available. Industrial epoxy coating catalysts usually fall into one of these four categories, aliphatic and cycloalishatic amines and polyamine, amides and polyamides, cycloaliphatic, and amine adducts.
The curing agent selection plays the major role in determining many of the properties of the final cured epoxy. These properties include pot life, dry time, penetration and wetting ability. Curing agents come in many different chemical flavors, generally based upon amines or amides. Some of the more common amines and amides often listed in Material Data Safety Sheets (MSDS) include:
Aliphatic (carbon atoms forming open chains) and cycloaliphatic (ring structured aliphatics) amines and polyamines are basically ammonia with one or more hydrogen atoms replaced by organic groups. Amides and polyamides are basically ammonia with a hydrogen atom replaced by a carbon/oxygen and organic group.
From a practical standpoint, amine based curing agents are considered to more durable and chemical resistant than amide based curing agents but most have a tendency to ‘blush' in moist conditions. Blushing produces a waxy surface layer on actively curing epoxy, the result a reaction with the curing agent and moisture in the air. Other potentially toxic chemicals within the curing agent can also be released in the same manner, thus amines are often viewed in light of these potential shortcomings. Amides, on the other hand, are more surface tolerant and less troubled by moisture.
Cycloaliphatic curing agents generally provide better water/moisture resistance, weatherability, low blush and water spotting, and better chemical resistance.
The ring structure (the 'cyclo' part) also provides (in many cases) a bit more structural 'stretch' than the traditional straight chain curing agent. This provides for better 'impact' resistance (note: 'hard' epoxies, on the other hand, offer better abrasion resistance).
Most or all of the top grade, exterior quality, high performance epoxies use a Part B curing agent blend consisting partially of cycloaliphatics. Thus, checking the MSDS of the Part B side of an epoxy product for mention of cycloaliphtics is a good way to judge the quality and performance of the epoxy.
Amine Adduct epoxies are two part epoxies but the curing agent actually contains a bit of the epoxy resin. In effect, the 'mixture' has started to cure even before the two parts are mixed. They perform much like other epoxies, but have improved overall physical properties. These include, but are not limited to better color stability and curing at slightly cooler temperatures. Cure time can be much faster than with 'regular' epoxies.