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Chemistry of Epoxies / Epoxy Resins,Novolacs,

and Polyurethanes

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PART 1: Chemistry of Epoxiesincluding information on Novolac Epoxies and Epoxy Adducts )

PART 2: Underwater Epoxies

PART 3: Polyurethane Coatingso u r H o s t a n d To u r G u i d e:

au l Oman , MS, MBA - Progress ive Epoxy Po lymers , Inc .

Member : NACE (Na t iona l Assoc . o f Cor ros ion Eng inee r s ), SSPC (Soc . o f P ro tec t ive Coa t ings )

Pro fess iona l s he lp ing Pro fess iona l s"

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Return to Epoxy Index Page

ests of penetrating epoxies - CLICK HERE

Nonyl Phenol as an additive in epoxies - CLICK HERE

Underwater epoxies - Tech Article - CLICK HERE

Knowledge is Power - We like informed consumers!

L e a rn t h e b a s i c s o f e p o x y a t o u r e d u c a t i o n a l E POX Y 1 01 p a g e - Cl i c k H e r e

Fi n a l ly, e m a i l u s b a c k w i t h y o u r q ue s t i o n s o r c o m m e n t s b e f o r e y o u b u y -EMAIL H ERE

Part 1: Epoxies

poxies consist of two components that react with each other forming a hard, inert material. Part A consists of n epoxy resin and Part B is the epoxy curing agent, sometimes called hardener. Let's begin with taking a closerook at the epoxy resin.

poxy resin begins with the reaction of two compounds, bisphenol A - Bis A -(or bisphenol F -Bis F- and/orNovolac ' -( visit our novolac web page ) used for superior temperature and chemical resistance) andpichlorohydrin. Bisphenol A is the chemical product of combining one acetone unit with two phenol groups.henol is a man-made chemical, although it is also found naturally in animal waste and decomposing organic

material. It was originally produced from coal tar and was named carbolic acid. Structurally it contains aenzene ring with an attached hydroxyl (a carbon ring with an attached OH). Acetone is a organic ketone (.i.e.contains a carbonyl C=O group attached to two organic methyl groups) primarily used as a solvent or

hemical intermediate or raw material for many other products.

Nearly 70% of all epichlorohydrin is used in the production of epoxy resin. This colorless liquid with itsritating chloroform like odor finds it way into the production process of various synthetic materials. Leadingroducers are Dow Chemical (Texas) and Shell Chemical (Texas and Louisiana).

he reaction between bisphenol A and epichlorohydrin removes unreacted phenol and acetone and attaches twolycidyl groups to the ends of the bisphenol A, creating a 'diglycidyl ether of bisphenol A (called DGEBA)',

which is standard epoxy resin. The glycidyl group on both ends of the bisphenol A are also referred to as an

Epoxy Curing Ca t a ly s t sDTCS Hycat™ Cure AcceleratorsFree R&D Samples Availaiblewww.Hycat.com

Epox ie s , E t c .Innovative Bonding Solutions.Adhesives & Potting Compounds.www.epoxies.com

Sekis ui PVB S -LEC B/KPVB Resin for Printing & TransferInks, Coatings, Ceramic Binders,etcwww.sekisui.co.jp/cs/eng/index.html

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xirane or ‘epoxy group'. The size of the resulting molecule (and hence its molecular weight) depends upon theatio of epichlorohydrin to bisphenol A.

he ‘amine' curing agent has a molecular structure which typically consists of four hydrogen ‘arms and legs'.hese hydrogens react with the oxirane (epoxy group) ring unit on the ends of the epoxy resin. The result is aew carbon-hydrogen bond, this time using the hydrogen from the curing agent and freeing the epoxy group'sydrogen to unit with the group's oxygen to form an OH (hydroxyl) pendant. This hydroxyl group contributeso the epoxy's outstanding adhesion to may substrates. The aromatic ring unit, which the hydroxyls attach to,elps provide the epoxies positive thermal and corrosion properties.

ecause there are at least four hydrogens on the curing agent they can react with four epoxy resin groups,which causes giant interlocking structures (in a process known as ‘crosslinking').

Epoxy curing agents

he curing agent selection plays the major role in determining many of the properties of the final cured epoxy.hese properties include pot life, dry time, penetration and wetting ability. Curing agents come in manyifferent chemical flavors, generally based upon amines or amides. Some of the more common amines andmides often listed in Material Data Safety Sheets (MSDS) include:

A) Aliphatic (carbon atoms forming open chains) and cycloaliphatic (ring structured aliphatics) amines andolyamines. Amines are basically ammonia with one or more hydrogen atoms replaced by organic groups;

) Amides and polyamides. Amides are basically ammonia with a hydrogen atom replaced by a carbon/oxygennd organic group.

Amine based curing agents are considered to more durable and chemical resistant than amide based curinggents but most have a tendency to ‘blush' in moist conditions. Blushing produces a waxy surface layer on

ctively curing epoxy, the result a reaction with the curing agent and moisture in the air. Other potentially toxichemicals within the curing agent can also be released in the same manner, thus amines are often viewed inght of these potential shortcomings. Amides, on the other hand, are more surface tolerant and less troubled by

moisture. More on Blushing.

ortunately for epoxy end-users involved with underwater applications, there is a small subgroup of non-enzene ring structured amines that maintain all the benefits of amines while removing the toxic leachabilitynd moisture attracting properties of typical amines. These special polyamines form the basis for today's cuttingdge underwater epoxies.

) Cycloaliphatic curing agents. These curatives generally provide better water/moisture resistance,weatherability, low blush and water spotting, and better chemical resistance. Cycloaliphatics there own web

age - CLICK HERE.

ycloaliphatic chemistry explained by "The Chemist" - the hands-down expert on epoxies - in a /18/03 post on the Wooden Boat Forum --

The cycloaliphatic structure refers to a six-member carbon-atom ring in the backbone of the curing gent instead of carbon-carbon linkages between amines in some other curing agents such as West r Sys. 3. The cycloaliphatic curing agents have the amine groups connected to the rings. Both use

Diglycidyl ether of Bisphenol-A as the major component of the epoxide curing agent, and both

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ontain benzyl alcohol, a volatile plasticizer which acts as a molecular lubricant and facilitates curing although systems with cycloaliphatic curing agents contain much more, typically 20-30%, as they imply do not cure more than about half-way at room temperature without it.]

While the cycloaliphatic ring is resistant somewhat to Uv degradation, more that the carbon-carbon nkages between amines in some other types of curing agents, both contain the aromatic ring tructure of diglycidyl ether of Bisphenol-A, which breaks down fairly readily on UV exposure, and oth contain amines; these give both molecular breakdown and yellowing all by themselves.

None of these structures should be considered UV-stable, even though the cycloaliphatic structures re better than the aliphatic amine-structures in that regard."

Amines vs. amides in coal tar epoxies - CLICK HERE

How Epoxies Work

he well known adhesion of epoxies is due to the strong polar bonds it forms with the surfaces it comes in

ontact with. On dry surfaces the bond between the surface and the epoxy displaces the air, which is a fluid. Theame is true underwater. As on dry surfaces, the polar bond attraction is strong enough to displace the fluid, inhis case the water, and produce an strong bond even underwater. Thus, painting underwater is, in theory, noifferent that painting above the water. The crosslinking reaction of epoxies should be independent of theurrounding environment. Still, as mentioned above, many or most curing agents will react with water

molecules rather than the epoxy base, resulting in a waxy layer, also mentioned above, known as amine blush.his makes them unsuitable for underwater application.

At least one modern hydrophobic, underwater epoxy goes one step farther to ensure a strong underwater polarond with the introduction of a proprietary ‘bond enhancer'. This is important because many marine structuresre subjected to active cathodic protection systems. Such systems place an electrical charge on the structure's

urface that will literally and actively repel the epoxy's existing polar bonding surfaces. The enhancer providesdditional polar bond surfaces that are also firmly anchored into the crosslinking epoxy structure.

A more technical third-party article:

y: A. SEN. Consultant, Protective & Functional Coatings Bombay, INDIA.

poxy resins must be crosslinked in order to develop the coating's required characteristics. This crosslinkingrocess is achieved by chemically reacting the resin with a suitable curing agent or hardener. The reactiveroups of molecules in the epoxy resin formulations are the terminal epoxide groups and the hydroxyl groups.

or protective coatings, the principle crosslinking reaction is between the epoxide group and the curing agent.Amine curing agents are the most common type used in epoxy formulations.

rimary amines are organic materials containing a nitrogen atom linked to two hydrogen atoms (-NH2). Inpoxy formulations, the active hydrogen of the amine is what reacts with the epoxide group of the resin. Thetructure of the amine-containing organic compound and the number and type of amine groups in theompound is what determine the rate of crosslinking and the coating's properties.

here are different types of polyamine curing agents: aliphatic, cycloaliphatic, aromatic, polyamine adduct, etc.

he aliphatic amines like EDA, DTA, & TETA contain short, linear chemical chain between amine groups.

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oatings produced with them tend to have highly crosslinked layers with good resistance to heat and chemicals,ncluding solvents. However, they are rather brittle and possess poor flexibility & impact resistance. Because of heir reaction with moisture, they are not suitable for use under damp conditions.

Modified cycloaliphatic amines from IPDA are probably the most used curing agents for epoxy resins today.ecause of their low viscosities, they can be used in low VOC coatings. They produce coatings with a fast cure

ate, short pot life and are also suitable for low temperature cure. They provide very good resistance tohemicals, solvents & water, which makes them suitable for use in portable water tanks.

n the aromatic amines, the amine group is separated by rigid benzene rings rather than flexible chains of molecules as in the aliphatic amines. Coatings produced with them have good physical properties like impactesistance as well as high resistance to heat and chemicals. But being aromatic in nature, they produce darkoatings. They are used to produce chemical & solvent resistant coatings. And particularly when they areormulated with epoxy novolac & phenolic epoxy resins, they produce coatings that can resist highemperatures. Aromatic amines are generally modified for use as curing agents, which although reduces theireat resistance are still good for chemical resistance. They have good resistance to water and hence work well inamp conditions & low temperatures.

One common modification to aliphatic amines is to form a polyamine adduct by reacting the curing agent with amall amount of epoxy resin. This gives high molecular weight polyamines that produce coatings with lowapour pressure, with more practical mixing ratios and less formation of amine bloom than the simple aliphaticmines. Adducting has little effect on other properties. Polyamine adducts can be prepared from either aliphaticr aromatic polyamines.

olyamides are formed by the reaction of aliphatic polyamines and dimer acids of either tall oil fatty acids orrom soya or castor oil. Here again adducting polyamides is common and produce coatings with good lowemperature curing and reduced tendency for amine bloom. Good colour and good chemical resistance can bechieved using these adducted polyamides. They generally produce coatings with excellent adhesion, wateresistance & flexibility. Unmodified polyamides produce coating layers that are much more open in terms of heir chemical structure because of their large distances between amine groups in the chemical chain.onsequently they are more flexible. This open structure of the curing agents results in coatings with low

esistance to chemicals, solvents and acids. However, their resistance to water & corrosion are enhancedecause of their surface wetting and adhesion properties.

When an aliphatic polyamine is reacted with a monofunctional fatty acid rather than a dimer acid, then anmidoamide is formed. These curing agents are less volatile and have less irritation potential than polyamines,nd they have properties that although are similar but inferior to polyamides. For instance, polyamides areetter in water resistance and provide better adhesion than the amidoamides.

n addition to the above types of curing agents there are many other curing agents based on polyamines, andhere are also non-amine based curing agents. Finally, either aromatic or aliphatic isocyanates may also be useds curing agents for epoxy resins. The isocyanates react through the hydroxyl groups of the epoxy resin androvide very good low temperature curing, good flexibility, good impact & abrasion resistance as well as gooddhesion.

trust this brief discussion helps. The "World of Epoxy Curing Agents" is so large and varied that it ismpossible to explain them in a forum of this nature. Over the years, both JPCL & PCE have carried severalrticles and several viewpoints on the different classes of epoxy hardeners. Perhaps a search through them willield lot more. Reference may also be made to "Protective Coatings - Fundamentals of Chemistry &omposition" by Clive H. Hare.

Another more technical third-party article: click here

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Yet another (really good) third-party tech article: click here

Everyone's Guide to Instant Epoxy Knowledge - Click Here

Novolac Epoxies

poxies made with Bis F, a Bis F and novolac mixture, or Novolac resin exhibit greatly improved chemical andeat resistance compared to the much more common Bis A epoxies. Probably 98% of all epoxies are 'regular'is A epoxies. Assume Bis A epoxy unless specifically told otherwise. Novolac epoxies are more expensive than

egular epoxies. They exhibit higher 'heat distortion temperatures', higher 'T sub G temperatures' (both of hese are measures of when the epoxy begins to soften with heat). The values for these measurements vary slight

with the different resins, and by whether the vendor reports conservative values or optimistic numbers.Generally Bis A epoxies will begin to soften in the 120-160 degree F range. Novolac epoxies initially raise this

alue by about 25 degrees F. More important is what happens above this temperature. All epoxies will reharden

when the elevated temperatures fall below this transition temperature. However, Bis Novolac epoxies willontinue to cure when exposed to temperatures of about 150 degrees F for a few hours. After this 'additionaluring' they generally can withstand about 300 degrees F (dry environment) without problems. An exception tohis is our non-hazmat novolac epoxy (FC 2100 N). The non-hazmat curing agents used greatly reduce theemperature resistance (but not the chemical resistance). For 'true' novolac temperature resistance use our

Nova Clear hazmat novolac epoxy.

hemical Resistance: A good quality Bis A epoxy will handle 70% sulfuric acid. A novolac epoxy will handle 97r 98% sulfuric acid.

he bad news: You get good chemical resistance or good heat resistance, generally not both.

A more technical third-party article: click here

We are the supplier of an inexpensive marine and industrial clear novolac epoxy as well as a pigmentedndustrial novolac floor epoxy.

Epoxy Adducts -- example: NSP 120 epoxy, also our NO BLUSH 2 marinpoxy.

Adduct epoxies are two part epoxies but the curing agent actually contains a bit of the epoxy resin. In affect, themixture' has started to cure even before the two parts are mixed. They perform much like other epoxies, butave improved overall physical properties. These include, but are not limited to better color stability and curingt slightly cooler temperatures. Also time (cure time) to 'back in service' can be much faster than with 'regular'poxies.

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Part 2: Specialty Epoxies -

Underwater Epoxy Evolution

n general terms, three generations of apply underwater epoxies have emerged over the years. Each has pushedhe technology window forward. The success of first generation epoxies seems to be in their ability to be appliednd cured underwater. The next generation moved these epoxies into true coating status, albeit with issues of ser friendliness and chemical safety issues still to be addressed. The new third generation epoxies haveddressed those issues successfully.

irst Generation Underwater Epoxy Coatings

Sticky, like ‘Bubble Gum' - similar to a thick putty

Hard to mix and apply - knead the two parts together in hand-sized amounts and literally push on to theurface

Expensive on a ‘cost per square foot' - @ 1/4 thick and $50 gallon = $7.80 per square foot material cost

Potentially difficult to ship and/or store - may require hazmat shipping (Corrosive Liquid - N.O.S.), may havehort shelf life

econd Generation Underwater Epoxy Coatings

Good underwater adhesion - true bonding instead of ‘sticking'

Poor storage stability (heating required) - products tended to crystalize over time

Toxic - MDA and possible solvents (see footnote)

Hazmat shipping required - keep away from foodstuffsProblem with cathodically protected surfaces - interference with the polar bonding

Third and Fourth Generation Underwater Epoxy Coatings

Low cost - $2.50 per sq. ft. for 40 mils, $5.00 per sq. ft. for 80 mils ($100 per gallon)

Stable storage - will not crystalize over time

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mistry of Epoxies / Epoxy Resin, Novolacs, and Polyurethanes

esonant ring upon exposure to UV. The "linear" term simply means a simple saturated line of arbon atoms rather than the alternating unsaturated bonds characteristic of aromatic molecules.

olyester polyurethanes improve upon the excellent properties of linear polyurethanes.

hird party FAQ on Polyurethanes - CLICK HERE

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Painting/Repair - -- - EpoxyProducts Home Page - -- - EpoxyUSAHome Page - -- - Ask Professor E.Poxy - --

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