dual-purpose derivatives three amines (4-6).€¦ · using both dimer acid and dimer diamine in one...

Quelle/Publication: European Coatings Journal

Ausgabe/Issue: 05/2009

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Dual-purpose derivatives

Fatty acid dimers are well established as naturally-derived ingredients in polyamides, polyesters,epoxy resins and amine curatives. Amine-functionaltypes have recently been introduced which offernew formulation options. Tests formulations showperformance advantages in polyamide hot-meltadhesives, in epoxies as curing agents and in polyureacoatings.

Amine functionality extends scope for formulating with fattyacid dimersAngela Smits*Erwin HoncoopRemco van TrietTanja van Bergen-BrenkmanDimerised fatty acids have been used for many years inpolyamides, polyesters, epoxy resins and amine curatives.The benefits that these C36 diacids provide in coatingsand adhesives are mainly related to their low Tg andhydrophobic nature.For several years, Croda has offered dimer fatty diolsand a range of polyester polyol derivatives of dimerisedfatty acids. Now new bio-based, amine-functional buildingblocks have been developed, extending the range of acid-and hydroxy-functional fatty dimers and derived polyesters.This new technology brings benefits in many applications.The new materials broaden the scope of application, withenvironmental benefits due to their renewable nature, lowvolatility and durability.In polyamide hot-melts, the use of dimer diamine extendsfreedom in formulating, allowing wider melting pointadjustment, while improving hydrophobicity. In epoxycoatings, a higher functionality dimer diamine serves asa low-volatility, low-viscosity curative, creating high-solidsformulations with good flexibility, hydrophobicity, pigmentwetting and excellent durability.In polyurea coatings, both dimer diamines can be used aschain extenders, forming smoother coatings with enhancedimpact resistance and outdoor stability, extending bothhydrolytic and thermo-oxidative stability.The impact of amine-functional dimerised fatty acids onkey properties of polyamide hot-melt adhesives, epoxy andpolyurea coatings were examined and results are presentedbelow.

Dimers are derived from natural oilsNatural oils and fats have for years provided the polymerchemist with a variety of building blocks such as glycerinand castor fatty acids. Although they have been used formany years, the so-called dimerised fatty acids are perhapsless well-known derivatives for polymer chemistry.Conversion of unsaturated fatty acids (from natural sourcessuch as soybean oil or tall oil) via a combination of pressure,temperature and catalysis generates a mixture of products,the most important being dimerised fatty acid. Figure 1 givesan overview of the dimerisation process, which is normallyfollowed by purification.Starting from the C18 fatty acids that

nature typically provides, the dimer acid is a molecule with36 carbon atoms, making it by far the longest dioic acidavailable. This hydrocarbon nature and non-crystallinityprovides flexibility, even at very low temperatures, lubricity,extreme hydrophobicity and enhanced substrate wettingproperties.

Applications in polyamide hot-melt adhesivesPolyamide adhesives are used in a wide range ofapplications, such as footwear, electronics fixing andsealing, textile, furniture assembly and packaging. Theamine component brings intermolecular bonding andcohesive strength, high melting point, green strength andadhesion to polar substrates. Dimer fatty acids enhanceflexibility and stress absorption, flow and wetting, andadhesion to low energy substrates. Other dioic acids in thecarboxylic acid component are used to raise the meltingpoint.The ability to incorporate dimer within the amine componentof the polymer gives wider control of the melting point.Using both dimer acid and dimer diamine in one formulationwill enhance moisture resistance, which is of interestin electronics and packaging applications, and flexibility,which can be interesting in several application areas.

Hot-melt adhesives synthesised and testedPolyamide hot-melt adhesives were synthesised by heatingthe acid component and subsequently adding the aminecomponent for reaction. After the (variable) foaming stage,temperature was gradually increased to 230°C (or higherwhen viscosity required it). Reactions were continueduntil an acid value of 9 mg KOH/g had been reached,representing a molecular weight of 12500 g/mol. Theresulting hot-melts are shown in Table 1. Comparisonsmade are no dimer, dimer acid and dimer diamine (1-3) andthree amines (4-6).Thermogravimetric Analysis (TGA) of the aminecomponents revealed differences in volatility and thermalstability (Figure 2). It is clear that dimer diamine (DDA)has excellent stability and performs well in low-volatilityapplications, with no volatiles released below 270°C.The commercial amines tested in comparison give muchinferior results. The low molecular weight ethylene diamine(EDA) and hexamethylene diamine (HMDA) are clearlyvolatile. In the polyether amines, "Jeffamine D400" and"D230" the ether makes them more sensitive to thermaldegradation.The prepared hot-melt adhesives were analysed byDifferential Scanning Calorimetry (DSC) for the glasstransition (Tg) and melting (Tm) temperatures. Shore Dhardness was also measured, this property being linked tothe Tg of the materials (see Table 2).The data from the first three samples show, asexpected, that the C36 dimer structure drasticallyreduces both the melting point and the glass transitiontemperature, enhancing flexibility. The difference betweenthe formulations containing dimer acid and dimer diamine



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can be explained by the variation in total dimer content(83% vs. 78%), caused by formulating with a carboxylic acidexcess. Dimer diamine thus extends freedom in formulating,allowing wider melting point adjustment. By altering theacid component in the formulation, the melting point can befurther adjusted.The next three samples have similar melting points. Sample4 has a lower total soft monomer content (89% vs. 93%),resulting in the highest Tg and a harder polyamide. Thepolyether amine appears to have a larger impact in reducingthe Tg than the dimer diamine does, whereas the hardnessis similar for both.The Tg transition in DSC is the same for both dimer diamineand polyether amine but is sharper with the latter. Differentrelaxation behaviour may shift the Tg midpoint withoutsignificantly affecting flexibility.

Dimer diamine enhances flow and moisture resistanceTo quantify the flow properties of the diamines, meltviscosities were determined using a Brookfield analyser(Table 2). Dimer diamine gives a lower viscosity thanHMDA; polyether amine, however, decreases the viscosityfurther. Viscosity build-up was examined by retainingsamples at 190°C for 8 hours. For all three samples, only aminor increase was found, implying that dimer diamine doesnot reduce stability.Adhesive layers were stored in open cups at 190°C, and thelevel of surface skin formation was examined. The samplecontaining dimer diamine (sample 6) shows reducedskinning behaviour, due to better oxidative stability.Moistureuptake was tested by allowing adhesive samples to absorbmoisture by exposure in water at 25°C for 1 week, andanalysing the weight increase. Sample 4 absorbs 0.15%water and sample 6 absorbs 0.12%, whereas sample5 absorbs 0.26%. As expected, polyether amine has agreater affinity for moisture. The combination of dimer acidand dimer diamine reduces water absorption because ofadditional hydrophobicity.

Dimer diamine maintains or improves adhesionAdhesion properties were analysed by measuring lap-shear adhesion strength (DIN EN 1465) of the varioushot-melts on beech wood, polypropylene, ABS and PA6(nylon). Samples were melted, applied at 500µm thickness,attached to a second substrate, and allowed to cool downwhile being held together by a weight.For better differentiation, samples 4-6 were adjusted toformulations with an amine-excess, and 0.5% stearic acidwas used as chain stopper. Aditionally, a sample wasprepared using aminoethylpiperazine, which is known toimprove adhesion properties. Samples were made at anamine value of 7 mg KOH/g, representing a molecularweight of 16000 g/mol.Results in Figure 3 show that increasing the level of softcomponents has a positive effect on adhesion properties.Lap shear adhesion to wood resulted in no break (at 3.2MPa) for all four samples.On the plastic substrates PA6 and ABS in particular,the soft diamines and piperazine significantly raise theadhesive strength. On PA6, the sample containing dimerdiamine clearly performs better than the other diamines.On the low-energy substrate PP, due to the hydrophobicnature of dimer diamine, it clearly improves the adhesivestrength.Samples 2 and 3 were also examined, but as

expected the use of dimer diamine instead of dimeracid does not clearly affect adhesive strength. Lap shearadhesion on ABS was 0.7 MPa and on PA6 was 0.3 MPafor both samples, whereas lap shear adhesion on wood andaluminium resulted in no break.

Low viscosity obtained in epoxy coatingsEpoxy resins possess high mechanical strength, goodadhesion, and resistance to solvents, acids, alkali, andcorrosion. Epoxy coatings are therefore widely used inindustrial and protective applications, for example on metaland concrete structures. However, they usually do notweather well, low MW diamines are often volatile, andhigher MW polyamides have high viscosities.Dimer diamine can be used as low-volatility, low-viscositycurative, while providing high-solids formulations with goodflexibility, hydrophobicity, pigment wetting, and especiallyexcellent weatherability.Epoxy coatings were prepared by diluting "Epikote 1001",a bisphenol-A type epoxy resin (53wt%), with solvent (27%xylene plus 20% methyl isobutyl ketone) then mixing withstoichiometric amounts of curatives.A dimer diamine with higher functionality (f >2) thanthat used in the adhesives was tested against twopolyaminoamide curatives, "Versamid 115" and "125". Thefirst was diluted at 70% in xylene. Viscosities of the resin- curative mixtures were adjusted to 40-50 mPas at 23°C,by adding the required amount of a blend of a 50/50 (v/v) n-butanol/xylene, resulting in a clear appearance. Theformulations are presented in Table 3.The formulation containing higher functionality DDA clearlyrequires no solvent to reach the same viscosity; its use thusallows for higher solid content coatings, and so is beneficialto the environment. The pot life is also extended, whichallows more freedom when applying these materials.

Thermal and physical properties improvedVolatility and thermal stability were examined by TGA ona range of amine curatives (Figure 4) used in the testedcoating formulations, plus some conventional curativesanalysed for comparison. The higher functionality dimerdiamine has excellent stability, which is desirable for low-volatility applications.The first volatiles are released only above 270°C with higherlevels above 350°C. An initial fraction is released by thephenolic alkamine "Cardolite NC-541LV" and by "Versamid125" at much lower temperature, while the triethylenetetramine (TETA) and "Epikure 3072" curatives show muchhigher volatility.The epoxy coating formulations were coated onto glassand metal by Meyer bar then dried overnight at 23°C and50% relative humidity before testing (Table 3). Gloss wasdetermined at 20° and 60° on 150µm coatings on glass(DIN EN ISO 2813). The use of the higher functionalitydimer diamine clearly results in a higher gloss than with thepolyaminoamide curatives, though the coating viscositiesare similar.König hardness was determined on 150µm coatings onboth glass and metal (DIN EN ISO 1522). Dimer diamineimproved the coating hardness. However, this improvedhardness did not cause failure on the indirect (reverse)impact test.Drying time was determined on 75µm coatings on glassusing a drying recorder (Byk-Gardner). The following stages



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in the drying process were observed: levelling of the coating(stage 0), basic trace (1), film building phase (2), surfacetrace (3) and finally the dry stage (4).As can be seen from the results in Table 3, the dimerdiamine formulation clearly gives faster drying. This is notsurprising, given its lower solvent content. Despite this, thepot life is longer (Table 3), a combination which offers bothapplication benefits and faster handling of coated parts.

Both types evaluated in polyurea coatingsPolyurea coatings are commonly applied over concreteand steel for corrosion protection and abrasion resistance.They are used for waterproofing, decoration and structuralenhancement, as they offer good chemical resistance (tovarious solvents, caustics and mild acids) and weatherresistance. They are applied as spray, hand-mix and caulk-grade materials, and can be cured and applied over a widerange of temperatures (from -30° to over 150°C) and inhumid environments. Polyurea is particularly known for itsrapid setting.Polyurea coatings were prepared by reacting the MDIprepolymer "Suprasec 2067" with stoichiometric amountsof four chain extenders. The polyether materials "JeffamineD-2000" and "T-403" were tested alongside both types ofdimer diamine. To control viscosity and curing speed, thechain extenders were mixed with propylene carbonate as areactive solvent.The polyurea coatings were applied at 100µm thicknesson a range of substrates for evaluation of mechanical andchemical properties. Subjectively, the coatings containingthe amine-functional dimers showed enhanced flow with asmooth appearance.

Physical and chemical resistance enhancedDirect impact tests were performed according to DIN ENISO 6272 at 25°C. This test is a means of predicting energystorage and loss as a function of temperature. For goodresults, a coating polymer must offer strong intermolecularentanglements and flow, combined with energy dissipationcapability.Coatings with higher functionality chain extenders havea higher crosslink density, normally reducing their impactstrength. However, both the difunctional and higherfunctionality dimer diamines along with the difunctional"Jeffamine D-2000" passed the 200 kg.cm test. "JeffamineT-403", which has similar crosslink density to the higherfunctionality dimer diamine, gave very poor results of lessthan 50 kg.cm.The test polyurea coatings were exposed to a range ofchemicals and coating damage was evaluated (Table 4).Damage is rated from 0 to 5, where 0 implies no damageand 5 implies severe damage.Both dimer diamines equalled or outperformed thepolyether types. The most striking result is the waterresistance, where the polyethers show severe damage tothe surface.With these results in mind, the water absorption of thefilms was tested (Figure 5). The benefits of the hydrophobiccharacter of the two dimer diamines are clear. The filmscontaining polyether based chain extenders absorb up to12% of water versus a mere 3-4% for the dimer diaminetypes. This reduction allows for improved water resistance,which may be expected to improve corrosion resistance.

Environmental gains, performance advantages

These results confirm that amine-functional dimerised fattyacid technology can be used to good effect in coatingsand adhesives, broadening the scope of applications in,for example, polyamide, epoxy and polyurea systems.These new bio-based based building blocks bring severalperformance as well as environmental benefits in theseapplications, through their renewable nature, reduction involatility and good thermal and oxidative stability.Overall, this novel amine functional dimer technologyoffers new application options, helping to enhance coatingand adhesive properties while bringing benefits for theenvironment. ?

* Corresponding Author:Dr. Angela SmitsCroda Polymers and CoatingsTel. +31 182 542 [email protected]

Results at a glance»› Amine-functional dimerised fatty acids offer newformulation options in polyamide, epoxy and polyureabased adhesives and coating. These new bio-basedbuilding blocks provide low volatility, low viscosity and goodthermal and oxidative stability to enhance durability.»› Inpolyamide hot-melt adhesives, the use of dimer diamineextends freedom in formulating, with test formulationsshowing improved adhesion.»› In epoxy coatings, dimerdiamine serves as a low-volatility, low-viscosity curative,allowing high-solids formulations to be created. Testcoatings exhibited good hardness, impact strength, highgloss and longer pot life combined with faster cure.»›Amine-functional dimers used as chain extenders inpolyurea coatings gave excellent gloss, impact resistanceand chemical resistance when compared with conventionalpolyether amines, and water absorption was extremely low.



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Ref Acidcomponent

Type Content(% wt)

Aminecomponent

Type Content(% wt)

1 Adipic acid C6 56% HMDA C6 44%

2 Dimer acid C36 83% HMDA C6 17%

3 Adipic acid C6 22% dimerdiamine

C36 78%

4 Dimer acid C36 89% EDA/HMDA20:80 mol

C2/C6 7%/4%

5 Dimer acid C36 82% EDA/JeffamineD40020:80

C2/ether 7%/11%

6 Dimer acid C36 81% EDA/dimerdiamine20:80

C2/C36 7%/12%



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Ref/test 1 2 3 4 5 6

Melting ptTm, °C

(250)* 79.0 104.4 93.5 93.0 92.3

Glasstransitionpt Tg, °C

60 -6 -9 -10 -23 -14

HardnessShore D

86 47 57 48 41 40

ViscosityPas@190°C

-- -- -- 11.3 5.1 10.0

Skinning2h

-- -- -- 100% 100% 70%

Skinning4h

-- -- -- 100% 100% 100%

( *not analysed; literature data)



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Curative/test Versamid 115polyamide(70% in xylene)

Versamid 125polyamide

Higherfunctionalitydimer diamine

Parts per 100 partsE1001

44 54 42

Parts by weightsolvent

50 37.5 --

Viscosity @23°C,mPas

45 50 42

Solids 37 46 53

Pot life (days) 3 3 >3

König hardness (s)on glass

89 74 99

König hardness (s)on metal

96 145 160

Gloss 20º/60º onglass

123/124 78/100 168/145

Impact (indirect) onmetal

>200 >200 >200

Drying recorder (hours)

Stage 0 ½ ¾ - 1 ½

Stage 1 3½ - 4 4 1 – 2

Stage 2 5 - 6 6 - 7 2½ - 3

Stage 3 7 -8 8½ - 9 5

Stage 4 >12 >12 10 - 11

* 150 µm wet film thickness applied ** 76µm wet film thickness applied



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Extender type/test liquid

JeffamineD-2000

Dimer diamine Dimer diamine(f>2)

JeffamineT-403

Ammonia 10%(2 min)

0 0 0 0

Acetic acid (1h) 3 1-2 1-2 4

Ethanol 50%(1h)

1 0 0 0

NaCl 5% (5h) 4 2-3 2-3 2

Water (16 h) 4-5 0-1 1 4-5

0 = No damage to coating to 5 = Severe damage to coating



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Figure 3: Lap shear adhesion of polyamide hot-melt adhesives: formulationscontain dimer acid and 0.5% stearic acid with 7% EDA and HMDA (7),Jeffamine D400 (8), aminoethylpiperazine (9) or dimer diamine (10); NB = nobreak; SF = substrate failure; all other samples show adhesive failure



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Figure 4: TGA curves of a range ofamine curative compounds



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Figure 5: Water absorption of polyureacoatings with a range of chainextenders



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Figure 1: Reactions in dimerisation offatty acids



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Figure 2: TGA curves of a range ofdiamine compounds

dual-purpose derivatives three amines (4-6).€¦ · using both dimer acid and dimer diamine in one...

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