The effects of anhydride type and amount on viscosity and film properties of alkyd resin

Progress in Organic Coatings 51 (2004) 273–279

The effects of anhydride type and amount on viscosity and film propertiesof alkyd resin

Serdar Aydin, Huseyin Akcay, EvrenOzkan, F. Seniha Guner∗, A. Tuncer Erciyes

Chemical Engineering Department, Istanbul Technical University, Maslak, 34469 Istanbul, Turkey

Received 19 April 2004; accepted 11 July 2004

Abstract

In this study, a modified method for preparing low viscosity alkyd resin was suggested. For this purpose the preparation of sunfloweroil-based alkyd resins were achieved into two steps. First sunflower oil and glycerol were reacted to form partial glycerides, and then, afterremoving free glycerol, esterification reaction was achieved between partial glycerides and anhydride. Glutaric, maleic, phthalic and succinicanhydride were used. Sunflower oil alkyd resins were also prepared by classical method. The results obtained were compared with each other.B©

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eywords:Alkyd resin; Sunflower oil; Viscosity; Film property

. Introduction

Producing of low solvent amount, high-quality organicoatings for industrial applications are important target inoating industry. Formulation of a low solvent amount coat-ng requires the use of a low molecular weight polymer thatas low viscosity. For this purpose, many investigators sug-ested low molecular weight resins or new methods for prepa-ation of low viscosity resins[1–3].

One of the most widely used types of organic coatingss alkyd resin, which is produced by the reaction of anhy-ride with hydroxyl containing oil derivatives. Alkyd resinas acquired a good reputation because of their economy andase of application. Additionally, they are to a greater ex-

ent biologically degradable polymers because of the oil andlycerol parts. Many researchers are interested in the higher-olids alkyd resins. In this context some of them described aew method for synthesizing polymer; the others used vari-us materials for modifying alkyd resin[2–4].

This paper describes a modified method for preparing lowiscosity alkyd resins. In this method glycerol calculated was

added in one portion to the into a reaction flask and reawas carried out at constant temperature. Before addinanhydride component, free polyol was removed from thaction medium. Since this caused low viscosity polymersolvent amount could be reduced for preparing polymelution. In the study four types of anhydride, glutaric, malphthalic and succinic anhydrides (GA, MA, PA and SA,spectively) were used to determine the effect of compotype on the final product viscosity and film properties. Adtionally, each resin was prepared at four oil/anhydride rato determine the effect of component amount on final proviscosity and film properties. In order to compare the reresins were prepared into from sunflower oil, glycerolphthalic anhydride by classical method.

2. Experimental

2.1. Materials

∗ Corresponding author. Fax.: +90 212 285 29 25.E-mail address:[email protected] (F.S. Guner).

Commercially purchased sunflower oil was used as an oilcomponent.Table 1gives information on the main charac-teristics and fatty acid composition of the oil. Four types of

300-9440/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
oi:10.1016/j.porgcoat.2004.07.009

274 S. Aydin et al. / Progress in Organic Coatings 51 (2004) 273–279

Table 1Some characteristics of the sunflower oils used in the studya

Property Sunflower oil

Refractive index,n20D 1.4750

Acid value 0.8Saponification value 187.9Iodine valueb 123.6Fatty acid composition (%)

C16:0 16.1C18:0 6.3C18:1 22.8C18:2 47.2Other 7.6a Ref. [7].b Ref. [13].

Table 2The chemical structures, molecular weights and acid values of anhydridesused

Component Code Formula Molecularweight

Acid value(mg KOH/g)

Glutaric anhydride GA 114.1 983.4

Maleic anhydride MA 98.06 1144.2

Phthalic anhydride PA 148.12 757.5

Succinic anhydride SA 100.08 1121.1

anhydride components purchased from Fluka were used. Thechemical structures of the anhydride with molecular weightand acid value are shown inTable 2.

2.2. Preparation of alkyd resins by modified method

The first step of the process is the preparation of sunfloweroil partial glycerides (PG) which are formulated at four ratiosof oil/glycerol[5]. In the second step, the resulting ester mix-ture was converted to alkyd resin by reacting with four typesof anhydride components, glutaric anhydride (GA), maleicanhydride (MA), phthalic anhydride (PA) and succinic anhy-dride (SA).

In the first reaction, oil and glycerol were placed intothe reaction flask and heated. When the temperature reached218◦C, CaO was added in the amount of 0.1% of the oilportion as catalyst. The temperature then was at 230◦C andreaction was continued at this temperature for 0.5 h undernitrogen atmosphere. After cooling, the content of the reac-tion flask was dissolved in diethyl ether, washed with water,dried over sodium sulphate, and the solvent was removed.At the last stage of the process, the partial glycerides mix-ture and dry xylene were taken into reaction flask, and anequivalent amount of anhydride component was added. The

temperature was set at 220◦C and maintained. The reactionwas controlled by determination of acid groups.

The samples were represented as PGnumber-abbreviationof anhydride compound.Numberis from 1 to 4. One and 4 areused for polymer having maximum and minimum amount ofoil, respectively.Abbreviations of anhydride compoundsaregiven above.

2.3. Preparation of alkyd resins by the classical method[6]

Conventional sunflower oil alkyd resins were prepared atfour different ratio of oil/anhydride. The oil and first part ofglycerol (in the amount of approximately 86% of glycerolcalculated) were heated to 218◦C in about 2 h, then limewas added in an amount of 1% of the weight of oil, and thetemperature was raised to 232◦C. The temperature was heldconstant when a clear solution of a sample of the product di-luted 1:3 in methyl alcohol was obtained. Phthalic anhydrideand the second part of glycerol were added and the temper-ature maintained at 232◦C for an additional 2 h. Amount ofphthalic anhydride was calculated to be equivalent to the the-oretical hydroxyl value of the mixture of sunflower oil andglycerol. Nitrogen gas was passed through the system whiler

w ethod.

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h -t isp solidc then-a werea andha r theo xibil-i wereu alkalia ndardm

eaction continued.The samples were represented as PGnumber–C.Number

as used as same as alkyd resin prepared by modified m

.4. Characterization

The functional groups of the samples such as hydroxycid values were determined by using analytical method[7].

.5. Determination of viscosities and film properties

The viscosity of alkyd resins was determined by usrookfield RV/DV-II type rotational viscometer at 30◦C. Foretermination of rheological properties power-law model

ested.Film properties such as drying time[8], flexibility [9], ad-

esion[10], hardness[11], water resistance[12], alkali resisance[12], and acid resistance[12] were determined. For thurpose, each sample was thinned with xylene to 40%ontent. 0.5% lead naphthenate and 0.05% cobalt naphte as metal based on solid content were added. Driersdded 24 h before the film application. In drying timeardness determinations, a Bird film applicator with 40�mperture was used for film application on glass plate. Fother tests, a dipping method was employed. For the fle

ty, adhesion, and water resistance tests, tin plate panelssed as a substrate, while glass tubes were used for thend acid resistance tests, as explained in the related staethods.

S. Aydin et al. / Progress in Organic Coatings 51 (2004) 273–279 275

Fig. 1. Preparation of alkyd resins.

3. Results and discussion

3.1. Preparation and characterization

Fig. 1outlines the strategies applied for the production ofalkyd resin.

In Fig. 2 the steps of the preparation of alkyd resin bymodified and classical methods are given. As shown, thefirst step is the preparation of partial glycerides (PG) forboth methods. In the modified method, glycerol in calculatedamount was added in the first step and unreacted glycerolwas removed from the reaction medium at the end of the

Fig. 2. Preparation
of alkyd resins.


Table 3The initial weight ratio of oil/glycerine and final hydroxyl values (mg KOH/g) of partial glycerides (PG)

Code Oil /glycerol Hydroxyl value of PGprepared by modified method

Theoretical hydroxyl value of reaction mixture beforeadding anhydride for classical method

PG1 25.0 65.1 70.4PG2 11.8 109.5 143.3PG3 10.0 145.1 166.3PG4 4.0 154.5 365.9

reaction. On the other hand, in the classical way of prepara-tion glycerol was added twice, one is at the first step and theremaining part was together with anhydride components. Itshould be noted that glycerol removal by washing reactioncontent was not performed in the classical method. The ef-fect of the procedure on the product properties is discussedlater.

In order to determine in effect of the amount of componenton film properties and viscosity of the final products, fourPG with different oil/glycerol ratio were prepared and thesePG’s were reacted with four types of anhydride. The amountof hydroxyl groups of each PG was proportional to the ratiooil/glycerol in the reaction mixture. The ratio oil/glycerol inthe initial mixture for preparation of PG by modified method,and hydroxyl value of the final product are given inTable 3. Asexpected, the hydroxyl value of PG increases with decreasingthe ratio oil/glycerol.

For investigating the effect of anhydride type on theproperties of the final product, PG was reacted with fourkinds of anhydride compounds. These are glutaric anhy-dride (GA), maleic anhydride (MA), phthalic anhydride(PA) and succinic anhydride (SA). During the reaction, acid

Table 4Acid values of the initial reaction mixtures and final products

C

ct

PPPPP

PPPPP

PPPPP

PPPPP

value of the reaction product decreased because the hy-droxyl groups of PG reacted with the anhydride groups.The reaction was controlled by determination of the acidvalue. Acid values of the initial reaction mixture and fi-nal product for each sample are given inTable 4. Asshown, the acid value of the final products fell to con-siderable low values, indicating successful polymerisationreaction.

PG3-MA and PG4-MA gelled during the reaction becauseof the high crosslinking. As comparative samples, conven-tional sunflower oil alkyd resins were prepared by classicalmethod. The ratio oil/glycerol was taken the same as thatof the modified method. Since unreacted glycerol was notremoved from the reaction mixture, the hydroxyl value ofPG was higher than that of PG prepared by the modifiedmethod. InTable 3, theoretical hydroxyl values of reactionmixture before adding anhydride are given. For comper-ative samples this value was calculated as total glyceroladded.

The second step was esterification of PG with anhydride.In this reaction an equivalent amount of anhydride was added.The reaction was controlled by determination of acid value.As shown inTable 4, the acid value of the resins fell to con-siderable low values.

TP

C

PPPPP

P 9P 9P 8P 9P

PP 9P 5P

PPPP

ode Acid value (mg KOH/g) of

Initial reaction mixture Final produ

G1-GA 61.1 6.4G1-MA 61.6 8.5G1-PA 60.0 3.9G1-SA 61.5 8.4G1-C 64.3 3.2

G2-GA 98.5 6.1G2-MA 99.9 6.5G2-PA 95.7 5.7G2-SA 100.1 7.9G2-C 114.7 6.1

G3-GA 126.5 8.9G3-MA 128.8 GelationG3-PA 121.8 10.2G3-SA 128.1 11.6G3-C 139.6 6.8

G4-GA 133.5 9.4G4-MA 136.1 GelationG4-PA 128.3 3.4G4-SA 135.8 9.9G4-C 266.4 10.1

able 5ower-law equation parameters

ode n η0 (Pa s) r2

G1-GA 0.995 0.15 1.0G1-MA 0.993 0.46 1.0G1-PA 0.973 0.15 1.0G1-SA 0.981 0.16 1.0G1-C 0.926 0.13 1.0

G2-GA 0.977 0.20 0.999G2-MA 0.982 3.35 0.999G2-PA 0.994 0.16 0.999G2-SA 0.980 0.18 0.999G2-C 0.994 0.28 1.0

G3-GA 0.978 0.23 1.0G3-PA 0.977 0.33 0.999G3-SA 0.942 0.27 0.999G3-C 0.994 0.36 1.0

G4-GA 0.995 0.30 1.0G4-PA 0.991 0.52 1.0G4-SA 0.992 0.37 1.0G4-C 0.998 2043 1.0


Fig. 3. Drying time of the sample.

3.2. Viscosity

For determinations of rheological properties power-lawmodel was tested

τ = η0γn

whereτ is the shear stress,γ is the shear rate, andη0 isthe apparent viscosity.n is the non-Newtonian power index,which reflects the nature of the rheological behavior.

In order to calculateη0 andn, the values of lnτ are plottedagainst the corresponding values of lnγ. The slope of thestraight line gaven and the intercept of it gave lnη0.

The values of model parameters are given inTable 5. Asshown, the values ofη0 increased with increasing anhydrideamount in the alkyd structure. In the comparison of the sam-ples having same anhydride amount, MA-based samples havethe higher viscosity. This is because of the existence of adouble bond in the anhydride component. During the reac-

esistan

tion thermal polymerization occurs, and viscosity increasesrapidly [9].

For PG1- and PG2-based alkyd resins, the viscositywas found almost the same level when using GA, PA andSA. On the other hand, for PG3- and PG4-based sam-ples, the viscosity of alkyd resin prepared from PA andGA was the highest and the lowest, respectively. This canbe explained by the structure of the anhydride componentused. Benzene ring gives a rigid structure, so the sam-ple prepared from PA is more resist flowing. GA and SAhave aliphatic carbon chain in their structure. This typeof structure causes low viscosity. Since GA has one more

CH2 in its molecule, it causes lower viscosity than thatof SA.

The viscosities of the same anhydride-based products in-creased with decreasing the ratio oil/glycerol of the initialmixture because the amount of hydroxyl groups per weightof PG increased with decreasing the oil/glycerol ratio.

Fig. 4. Water r
ce of the sample.


Fig. 5. Alkali resistance of the sample.

In the comparison of the viscosities of the same PG-basedsamples, polymers prepared by the classical method have thehighest viscosity except PG1-based polymers.

All resins behaved as a Newtonian fluid under test condi-tions, since the value of n was calculated as almost 1.0.

3.3. Film properties

Drying times of the samples are given inFig. 3. As shown,for the same anhydride-based samples while the hydroxylvalue of PG increases, drying time decreases. This is an ex-pected result because drying time depends on the originalpolymer viscosity[5]. While the hydroxyl value of PG in-creases, viscosity of polymer increases. High initial viscositycauses short drying time. Comparing the drying time of thesame PG-based samples, resin prepared from MA had theshortest drying time because of the high viscosity.

In the comparison of water resistance, the worst resultsare obtained for PG4-based resins, because the time requiredfor whitening to disappear is the longest (Fig. 4). This canbe explained by the amount of ester bonds in the polymerstructure, which is sensitive to water and alkali. The increasein amount of anhydride component caused higher amount ofester bond in resin structure. Same PG-based resins preparedby the modified method showed almost the same water resis-t resis-t worstw inedf thant acidc waterm

bada ps.

il-i hib-i ased

Table 6Some film properties of the products

Code Flexibilitya (mm) Adhesionb Hardness Acid resistancec

PG1-GA 2 5B 0 ncPG1-MA 2 5B 1 ncPG1-PA 2 5B 0 ncPG1-SA 2 5B 0 ncPG1-C 2 5B 0 nc

PG2-GA 2 5B 0 ncPG2-MA 2 3B 1 ncPG2-PA 2 5B 0 ncPG2-SA 2 5B 0 ncPG2-C 2 5B 0 nc

PG3-GA 2 5B 0 ncPG3-PA 2 5B 0 ncPG3-SA 2 5B 0 ncPG3-C 2 5B 0 nc

PG4-GA 2 5B 0 ncPG4-PA 2 5B 0 ncPG4-SA 2 5B 0 ncPG4-C 2 5B 9 nc

nc: no change.a The diameter of cylinder which caused no crack on the film[8].b Test method B was applied[9].c The test was carried out at 25◦C with 9% H2SO4 solution[11].

samples developed hardness properties because of the highcontent of aromatic ring coming from PA and of consum-ing of double bonds with formation of cross-linked polymer,respectively.

4. Conclusion

Alkyd resins were prepared by modified and classicalmethods. For the modified method free glycerol was re-moved from reaction medium before adding anhydride com-ponent. The effects of anhydride amount and type on viscosity

ance. However MA-based resins gave the best waterance. Resins prepared by the classical method had theater resistance, due to free glycerol The product obta

rom glycerol and anhydride is more sensitive to waterhe product prepared from PG and anhydride since fattyhains in PG structure defended ester bonds againstolecule.In Fig. 5alkali resistance are shown. All resins gave

lkali resistance, due to saponification of the ester grouAs shown fromTable 6, all samples showed good flexib

ty and acid resistance. All samples, except PG2MA, exted good adhesion properties. Only PG4-C- and MA-b


and film properties of final products were determined.The following conclusion can be drawn from the obtainedresults:

1. Low viscosity resins could be obtained by the modifiedmethod.

2. In the comparison of film properties, the modified methodgave resins with the same or better film properties than theresins from the classical method.

3. Since MA gave Diels–Alder addition, polymer has higherviscosity.

The overall picture is that high solid content alkyd resinscould be prepared with the modified method because of theirlow viscosity and good film properties.

References

[1] R. Buter, Low molecular weight acrylic resins for high solids auto-motive topcoats, J. Coat. Technol. 59 (749) (1987) 37–41.

[2] L.S. Kangas, F.N. Jones, Binders for higher-solids coatings. Part I.Synthesis of model alkyd resins, J. Coat. Technol. 59 (744) (1987)89.

[3] L.S. Kangas, F.N. Jones, Binders for higher-solids coatings. Part II.Properties of model alkyd resins, J. Coat. Technol. 59 (744) (1987)99.

[4] D.S. Chen, F.N. Jones, Binders for higher-solids coatings. Part I.Model alkyd resins modified by liquid crystalline groups, J. Coat.Technol. 60 (756) (1988) 39.

[5] F.S. Guner, A. Gumusel, S. Cakıca, A.T. Erciyes, A study offilm properties of some urethane oils, J. Coat. Technol. 74 (2002)55.

[6] H.F. Payne, Organic Coating Technology, vol. 1, Wiley, New York,1954, p. 289.

[7] L.V. Cocks, C. Rede van, Laboratory Handbook for Oil and FatAnalysts, Academic Press, London, 1966.

[8] ASTM D 1640-83, Annual Book of ASTM Standards, vol. 06.01,1991, pp. 223–226.

[9] DIN 53152, Deutsche Normen, Deutscher Normenausschuss (DNA),October 1959.

[10] ASTM D 3359-90, Annual Book of ASTM Standards, vol. 06.01,Test Method B, 1991, pp. 511–514.



[13] H.P. Kaufmann, Analyse der Fette u. Fettprodukte, vol. 1, SpringerVerlag, Berlin, 1958, pp. 581–582.

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The effects of anhydride type and amount on viscosity and film properties of alkyd resin