L DOW IQUID EPOXY RESINS - Science Engineering

Table1ResinD.E.R. 317D.E.R. 330D.E.R. 331D.E.R. 332D.E.R. 337D.E.R. 362D.E.R. 364D.E.R. 383Typical Properties† of DOW Liquid Epoxy ResinsEpoxideEquiv. 10176-183ViscosityRange(cps @ 25 0400-800 14,500-6,5004,000-7,0009,000-10,500Color, Max(Gardner)5125 3125 375 3312125 3FlashPoint,( F) 2485485485485485480480485SpecificGravity,25/25 C1.161.161.161.161.161.141.161.16Weight(Lbs/Gal)@ 25 C9.79.79.79.79.79.59.79.7170% non-volatile in DOWANOL* DB solvent.2Pensky-Martens, ASTM D-93.3APHA Color — ASTM method 1209.†Typical properties; not to be construed as specifications.Table2ResinD.E.R. 324D.E.R. 325Typical Properties† of DOW Liquid Epoxy ResinsContaining a Reactive DiluentEpoxideEquiv. Wt.197-206185-206ViscosityRange(cps @ 25 C)600-800850-2,800Color, Max(Gardner)32FlashPoint,( F)1350375Specific WeightGravity, (Lbs/Gal)25/25 C @ 25 C1.119.31.149.51Pensky-Martens, ASTM D-93.†Typical properties; not to be construed as specifications.Table3ResinD.E.R. 732D.E.R. 736Typical Properties† of DOW Liquid Epoxy ResinsBased On Polyglycol Di-epoxidesEpoxideEquiv. Wt.305-335175-205ViscosityRange(cps @ 25 C)55-10030-60Color, Max(APHA)125125FlashPoint,( F)1310320Specific WeightGravity, (Lbs/Gal)25/25 C @ 25 C1.068.91.149.51Pensky-Martens Closed Cup†Typical properties; not to be construed as specifications.4

RESINSTRUCTUREEpoxy resins contain a reactive oxirane structureO— CH — CH2which is commonly referred to as an “epoxy” functionality. Liquid epoxyresins are converted through these reactive epoxy sites into tough,insoluble, and infusible solids.The simplest possible epoxy resin derived from the reaction of bisphenolA and epichlorohydrin is (2,2-bis[4-(2'3' epoxy propoxy) phenyl]propane), commonly called the diglycidyl ether of bisphenol A (DGEBA).OCH2— CH— CH2— O—CH3— C—O— O— CH2— CH— CH2CH3The higher molecular weight homologs are represented by thefollowing theoretical structure:OCH2— CH— CH2—— O—CH3— C—OH— O— CH2— CH—CH2——CH3—O—CH3— C—nO— O— CH2— CH— CH2CH3Generic Bisphenol A Based Epoxy Resin Chemical StructureWith increasing molecular weight, another reactive site — the OH group— is introduced. This group can react at higher temperatures with anhydrides, organic acids, amino resins, and phenolic resins, or with epoxidegroups (when catalyzed) to give additional cross-linking.Typical value of “n” is about 0.15 for D.E.R. 331 epoxy resin (epoxy equivalent weight range of 182-192 and viscosity of 11,000-14,000 cps at 25 C).The low melting point solid resins begin at an “n” of about 2.5.In high melting point solid resins, “n” may be as high as 18.ORR O—————————————CH2 CH CH2 OCH2 CH OCH2 CH O CH2 CH— CH2nGeneric Aliphatic Polyglycol Diepoxide StructureD.E.R. 736 resin has a lower value of “n,” and hence a shorter chainlength than D.E.R. 732.5

CURINGAGENTSMany commercial materials are suitableas reactive cross-linking agents for liquid epoxy resins. The most commontypes of curing agents are: primary and secondary polyaminesand their adducts anhydridesThe amines react with the epoxygroup through the active aminehydrogen. Each primary aminegroup is theoretically capable of reactingwith two epoxide groups, and each secondary amine group is capable of reacting with one epoxide group. The reaction of a primary amine with an epoxy isseen as follows:The presence of hydroxyls, however,has an important function becausethey assist in opening the epoxidering. Alcoholic or phenolic hydroxylsaccelerate the primary and secondaryamine cures and thus provide for themore rapid gel time of the amineadducts and the higher molecularweight resins.ORNH2 CH2— CHHRN— CH2— CH polyamidesOH catalytic typesPrimary And SecondaryPolyfunctional AminesTypical of this class of curing agents arealiphatic amine compounds, such asD.E.H. 20 epoxy hardener (diethylenetriamine), D.E.H. 24 epoxy hardener(triethylene tetramine), and D.E.H. 26epoxy hardener (tetraethylene pentamine). Also used are adducts of theabove amines with epoxy resins, diluents, or other amine-reactive compounds. Room temperature cures areusually employed.Aromatic amines, such as metaphenylenediamine and diamino diphenyl sulfone,are also widely used to achieve higherheat distortion temperatures. Elevatedtemperature cures are usually employed.The secondary amine thus formedreacts further:HORN— CH2— CH CH2—CHOHOHRNCH2—CHCH2—CHOHTheoretically, the hydroxyls formedshould be capable of reacting with epoxygroups to form an ether linage:CHO CH2— CHOHCHOCH2—CHOHThis reaction is often catalyzed bytertiary amines. However, the tertiaryamine formed by the epoxy-secondaryamine reaction is apparently too immobile and sterically hindered to act as acatalyst.6

Aliphatic PolyaminesThe liquid aliphatic polyamines and theiradducts are convenient to handle, giveexcellent cured resin physical characteristics, including chemical and solventresistance, and cure at ambient or moderately elevated temperatures. Goodlong-term retention of properties is possible at temperatures up to 100 C.Short-term exposure at higher temperatures can be tolerated. Pot life is shortand exotherm is high in thick sectionsand large masses. See Table 4.follows, using D.E.H. 20 (NH2 — CH2 —CH2 — NH — CH2 — CH2 — NH2)as an example:1. To calculate the Amine H equivalentweight, use the following equation:Cured systems give excellent performance up to about 150 C (302 F). Theyare used in adhesives, wet lay-up laminates, tooling, small pottings, and coatings. Shrinkage of aromatic polyaminecured resins, particularly with the highmolecular-weight resins, is quite low —a useful feature for encapsulation andpotting.Calculation of Stoichiometric RatiosTo obtain optimum properties with polyfunctional epoxide-reactive curingagents (particularly the amines), it isdesirable to react the resin and the curing agent at approximately stoichiometricquantities. To determine the ratiorequired, calculations can be made as7EEW of mix Total WtWt aWt bWt c EEWa EEWb EEWcTotal weight includes all materials,both reactive and nonreactive.Equation (1):MW of amineno. of active hydrogenAmine H eq wt a,b,c, etc., are only the materialsreactive with the curing agent, andare characterized by an epoxy ring.Example:Amine H eq wt D.E.H. 20 Aromatic PolyaminesMost aromatic polyamines are solidsand are usually incorporated in the resinby melting at elevated temperatures.Pot life is considerably longer than withaliphatic polyamines, and elevated temperature cures are required to developoptimum properties. See Table 5.Equation (3):103.2 20.652. To calculate the stoichiometric ratio ofDEH 20 to use with D.E.R. 331 epoxyresin having an epoxide equivalentweight of 189:Equation (2):phr† of amine Amine H eq wt 100Epoxide eq wt of resinExample:Example:100 parts D.E.R. 331Avg EEW 189100 parts D.E.R. 337Avg EEW 24030 parts BGE (diluent)Avg EEW 130230 parts Filler—460 TotalEEW of mix 460100 100 30189240130 460 3911.1766By equation (2):Amount D.E.H. 20 20.6 100 5.27 parts per391hundred partsfilled formulationphr D.E.H. 20 to be used with D.E.R. 331.phr 20.6 100 10.91893. Frequently, epoxy resins are blended,filled, or modified with reactive andnonreactive components. It is thennecessary to adjust the concentrationof the curing agent to cure only theportion of the mix that is reactive;e.g., the resins and any reactive diluent present. This may be simply doneby calculating the epoxide equivalentweight (EEW) of the total mix andthen applying equation (2) to determine the amount of curing agent toadd to 100 parts of formulation.†Parts by wt per 100 parts resin

Table4Aliphatic Polyamines and Adducts†Wt. PerActiveHPHRD.E.R.331D.E.H. 20(diethylenetriamine, DETA)20.610.9D.E.H. 24(triethylenetetramine, TETA)24.4D.E.H. 26(tetraethylenepentamine, TEPA)Curing AgentSuggested CureScheduleSourceCommentsGel at RT plus several days at RTor 1-2 hrs at 100 C for full cure.The DowChemicalCompanyGeneral purpose RT curing agent. High exotherm inlarge mass. May blush under humid conditions.12.9Gel at RT plus several days at RTor 1-2 hrs at 100 C for full cure.DowGeneral purpose RT curing agent. High exotherm inlarge mass. Lower vapor pressure than D.E.H. 20.May blush under humid conditions.27.114.3Gel at RT plus several days at RTor 1-2 hrs at 100 C for full cure.DowRT curing agent often used in 2 package protectivecoating systems. May blush under humid conditions.D.E.H. 29(amine mix)28.815.2Gel at RT plus several days at RTor 1-2 hrs at 100 C for full cure.DowAmine curing agent with low vapor pressure for saferhandling. Similar in properties to D.E.H. 24 but curedsamples have less tendency to blush when cured underhumid conditions.D.E.H. 39(amino ethylpiperazine, AEP)4322.8Gel at RT plus several days at RTor 1-2 hrs at 100 C for full cure.DowTrifunctional amine with short pot life. Imparts moderatedegree of flexibility and gives improved impact.D.E.H. 52(amine-epoxy resinadduct)5328.0Gel at RT plus several days at RTor 1-2 hrs at 100 C for full cure.DowAmine adduct with D.E.R. 331. Fast cure time. Viscosity6,000-8,000 cps. Lower vapor pressure and less criticalratios offer improved handling characteristics.D.E.H. 58(acceleratedaliphatic amine)3015.9Gel at RT plus several days at RTor 1-2 hrs at 100 C for full cure.DowAmine containing an accelerator for fast reactingambient cure systems.XUS 19036.00(polyethylenepolyamine)3418.0Gel at RT plus several days at RTor 1-2 hrs at 100 C for full cure.DowAmine curing agent with low-odor, non-corrosive andexcellent chemical-resistant properties, especially forsecondary containment applications with reduced blushtendency under humid cure conditions.RT Room Temperature†Typical properties; not to be construed as specifications.8

Table5Aromatic Polyamines†Wt. PerActiveHPHRD.E.R.331Metaphenylenediamine (MPDA)2714.3Gel at 55 C 2 hrs at 125 C 2hrs at 175 C.Aromatic diamine with a melting point of approx. 60 C.Can be used to make eutectic mix. Good elevated temp.performance. Used in laminates, castings, andfilament winding.Diamino diphenylsulfone (DDS orDADS)5730.21 hr at 150 C3 hrs at 220 C.Aromatic polyamine with a melting point of approx.175 C. Used in laminates. Has good B-stage shelf life.Cure may be accelerated with BF3 MEA oraliphatic amines.Diethyltoluenediamine44.623.62 hrs at 100 C4 hrs at 175 C.Low viscosity liquid aromatic diamine. Gives longer potlife than other aromatic amines. Low exotherm.Curing AgentSuggested CureScheduleComments†Typical formulations and cure schedules only; not to be construed as specifications.AnhydridesLiquid and solid anhydrides areextensively used to cure epoxy resins.Products typical of this class are shownin Table 6.1. The opening of the anhydride ringwith an alcoholic hydroxyl to formthe monoester:OO— C— C— O— CH—C—CO HO— CHThe reactivity rate of some anhydrideswith epoxies is slow. An accelerator, usually a tertiary amine, is often used (0.5% to3%) to speed gel time and cure. The optimum amount is usually critical, dependingupon the anhydride and resin used andcure schedules. Amounts above or belowthe “correct” amount reduce high temperature performance. The “best” concentration should be determined experimentally.Eutectic mixtures to depress resin melting points may be prepared.—C—C—C— C—OHOO2. Subsequent to (1), the nascent carboxylic groups react with the epoxideto give an ester linkage:O— C— C— O— CHO CH2— CH—C— C—OHOO— C— C— O— CH— C— C— O— CH2— CHOThe reaction of anhydrides with epoxygroups is complex, with several competing reactions capable of taking place.The three most important are:OH3. The epoxide groups react with nascentor existing hydroxyl groups, catalyzedby the acid, producing an ether linkage:OHC— OH CH2— CHHC— O— CH2— CHOH9At low elevated temperature cures, theether and ester reactions take place atabout the same rate. At higher temperatures, the ester linkage occurs morefrequently, and this probably accounts forthe reduced elevated temperature performance of systems gelled at initially hightemperatures. Since reaction (3) can takeplace independently in the acid medium,the ratio of anhydride to epoxy is lesscritical than with an amine. It can varyfrom 0.5 to 0.9 equivalents of anhydrideper equivalent of epoxy and should bedetermined experimentally to achievedesired properties.Pot life of the mix is usually long;exotherm is low. Elevated temperaturecures are necessary and long post curesare required to develop ultimate properties. Electrical and physical strengthproperties are good over a wide temperature range. Chemical resistance to somereagents is less than with amine-cured systems, but is better against aqueous acids.

TableAnhydrides†6PHRD.E.R.331Curing AgentSuggested CureScheduleCommentsNadic methylanhydride (NMA)60-9012 hrs at 90 C 4 hrs at 165 C 16 hrs at 200 CLiquid anhydride having long pot life at room temp.Excellent elevated temp. properties.Hexahydrophthalicanhydride (HHPA)60-7512 hrs at 100 C 2-6 hrs at 150 CLow melting point solid, approx. 35 C, soluble in liquidresin at room temp. Used in potting, filament windings, andclear castings.Trimellitic anhydride(TMA)60-90124 hrs at 150-180 CGood electrical properties, good high temperatureproperties. Reacts rapidly at high temperatures.Dodecenyl succinicanhydride (DDSA)95-13012 hrs at 100 C 4-6 hrs at 150 CLiquid anhydride. Imparts flexibility to cured composition.Phthalicanhydride (PA)40-6524 hrs at 120 C or 8 hrs at 150 CSolid anhydride with melting point 128 C. Low exothermand long pot life. Used in large encapsulations.Methylhexahydrophthalicanhydride (MHHPA)60-7513 hrs at 100 C 6 hrs at 140 CExcellent light stability, fast gel time.Tetrahydrophthalicanhydride (THPA)60-75124 hrs at 120 C or 8 hrs at 150 CSolid anhydride with melting point of 100 C. Similar tohexahydrophthalic anhydride in cured resin properties.Used in pottings and encapsulations.Methyltetrahydrophthalicanhydride (MTHPA)70-9012 hrs at 90 C 4 hrs at 150 CLiquid anhydride with higher reactivity than NMA butsimilar cured physical properties.1Plus suitable accelerator.†Typical formulations and cure schedules only; not to be construed as specifications.PolyamidesThis class of compounds can be considered as modified polyfunctional aliphaticamines, since the polyamides mostwidely used are the condensationproducts of dimerized fatty acids and adifunctional amine such as ethylenediamine. Their theorized structure isrepresented as follows:OOOH—— C—R— C—NH—CH2— CH2—NH—— Hn 5 to 15nThe reactivity of polyamides withepoxies is similar to that of the aliphaticamines. Since the polyamides arerelatively large polymers, the ratio ofpolyamide to epoxy is less critical thanwith the low-molecular-weight amines. Itis varied quite broadly to obtain properties from hard to semi-flexible. In thissense, the polyamides can be consideredresin modifiers as well as curing agents.Polyamide-cured formulations havelonger pot life than formulations curedwith aliphatic polyamines and theiradducts. They cure at room temperaturewithout blushing and show outstandingadhesion. Formulations are high in viscosity and are sometimes incompatiblewith the resin until reaction has beeninitiated. They are usually dark in color.Polyamide systems lose structuralstrength and insulation value rapidlywith increasing temperatures, and areusually restricted to applications under65 C (149 F). Similar products from twopolyamide curing agent producers areshown in Table 7.10

Table7Polyamides†PHRD.E.R.331Suggested CureScheduleVersamid 1 100Ancamide 2 10070-110RT several days to full cure.Semi-solid polyamide resin used primarily as a solvent cut solutionto cure intermediate-molecular-weight epoxy resins in coatingapplications. Also available in solutions. Can be used to cure resinson wet substrates.Versamid 115Ancamide 22060-100RT gel several days to full cureor 1-2 hrs at 100 C.High-viscosity fluid polyamide. Can be used at 100% solids bywarming to reduce viscosity. Used in laminates, adhesives, potting,sealants, and coatings. Also available in solution.Versamid 125Ancamide 260A50-100RT gel several days to full cureor 1-2 hrs at 100 C.Intermediate-viscosity fluid polyamide. Can be blended at RT orwarmed slightly to reduce viscosity. Used in wet lay-ups, adhesives, potting, sealants, coatings, epoxy mortars, and tooling.Versamid 140Ancamide 350A30-70RT gel several days to full cureor 1-2 hrs at 100 C.Low-viscosity polyamide having higher heat distortion, excellentadhesion, and low shrinkage. Used in 100% solids spray applications, wet lay-ups, epoxy mortars, casting, tooling, and adhesives.Curing AgentRT Room Temperature†Typical properties; not to be construed as specifications.CommentsTrademark of HenkelTrademark of Air Products and Chemicals, Inc.12Catalytic Curing AgentsCatalytic curing agents are those compounds that promote epoxy-to-epoxy orepoxy-to-hydroxyl reactions and do notthemselves serve as direct cross-linkingagents. Tertiary amines, amine salts,boron trifluoride complexes, and amineborates are in this class.The mechanism of epoxy-to-epoxypolymerization using a tertiary aminecatalyst (or other catalytic curing agent)theoretically takes place as follows:1. Opening of the epoxy group:OR3N CH2— CHR3N — CH2— CHO 2. The ion thus formed is capable ofopening another epoxy group:11CH2— CHO CH2— CHO CH2— CHOCH2— CHO This continues until a dense cross-linkedstructure containing the stable etherlinkages is formed.This oversimplified explanation doesnot consider the hydroxyl groups eitherpresent in the higher weight resinhomologs or introduced by resin modifiers and curing agents. While the stepsof the epoxy-hydroxyl reaction differ, theend structure is very similar to thatpostulated for the epoxy-epoxy reaction.Pot life is moderate (2 to 24 hours) fortertiary amine and amine salts, and isvery long, up to several months, for thelatent catalysts, such as BF3 · MEA(boron trifluoride monoethylamine)complex or dic

D.E.R. 331 Epoxy Resin A general purpose, widely used liquid resin. It is recognized as a standard from which variations have been developed. D.E.R. 332 Epoxy Resin The uniqueness of D.E.R. 332 epoxy resin is reflected in its maximum epox-ide equivalent weight of 178 (chemically pure