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Preparation and evaluation of linseed oil based alkyd paints
Progress in Organic Coatings 77 (2014) 81–86
Contents lists available at ScienceDirect
Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat
Preparation and evaluation of linseed oil based alkyd paints Döndü I˙ s¸eri-C¸a˘glar, Emre Bas¸türk, Burcu Oktay, M. Vezir Kahraman ∗ Department of Chemistry, Faculty of Art & Science, Marmara University, 34722 Göztepe-Istanbul, Turkey
a r t i c l e
i n f o
Article history: Received 12 June 2013 Received in revised form 16 August 2013 Accepted 21 August 2013 Available online 17 September 2013 Keywords: Alkyd resins Linseed Oil Renewable resources Aerosil R972 Huntite
a b s t r a c t Alkyd resins are produced with reaction of oil or fatty oil, polyol and polyacid. Alkyd resins are commonly used in coating and paint industry due to ease of application in changing environmental conditions. Linseed oil based paints executed all requirements of technical properties, drying time, storage properties, simplicity in maintenance, appearance, economy, etc. In this study, linseed oil based alkyd resins having different oil contents were synthesized Paint formulations were prepared by mixing alkyd resin and various additives such as huntite, Aerosil R972, talc, titanium dioxide, dryer, wetting agent and anti-skinning agent. All formulations were applied on paper test plates and were dried at 30 ◦ C. The obtained coatings were characterized by pencil hardness test, pendulum hardness test, chemical resistance test, cross-cut test, contact angle and gloss measurement. Also thermal and morphological properties were investigated by thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) respectively. The thermal stability of the paint materials are improved with by increasing the amount of huntite and Aerosil R972 in the paint compositions. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The utilization of fossil fuels for the manufacture of plastics accounts for about 7% of the worldwide use of oil and gas, which will arguably be depleted within the next 100 years [1]. The peak in global oil production is estimated to occur within the next few decades. In this age of increasing oil prices, global warming, and other environmental concerns (i.e. waste), a change from fossil feed stocks to renewable resources is important for sustainable development into the future [2]. The utilization of renewable resources can consistently provide raw materials for everyday products, effectively avoiding further contribution to greenhouse effects, because of the minimization of CO2 emissions [3]. Therefore, academic and industrial researchers are devoted to increase attention and put on their efforts to the possible utilization of renewable resources as raw materials for the production of both chemicals and polymeric materials. The most widely used renewable raw materials are; polysaccharides (mainly cellulose and starch), proteins, sugar, natural rubber, and plant oils [4,5]. Vegetable oils and modified vegetable oils have become attractive sustainable alternatives to petroleum-based materials for industrial applications such as soaps, lubricants, coatings, paints, and, more recently, bio-plastics and composites due to their biodegradability, low toxicity, non-content of volatile organic chemicals, easy availability, and relatively low price [6]. In the past few years, consumers and
∗ Corresponding author. Fax: +90 2163478783. E-mail address: [email protected] (M.V. Kahraman). 0300-9440/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.porgcoat.2013.08.005
individual interests in environmentally friendly paints and coating have been growing tremendously [7]. Common household oil paint, the oldest form of modern paints, uses a binder that is derived from vegetable oils, which is obtained from linseed or soya bean. Alkyd paints are based on alkyd resins (vegetable-derived drying oils), which contain a variety of polyunsaturated fatty-acid chains, commonly linoleic and linoleic acid and their triglycerides [8], which undergo free-radical-mediated autoxidation during the curing/drying process [9,10] Alkyd resins are branched polyesters that are obtained by reacting dicarboxylic acids or anhydrides and polyols such as glycerol or pentaerythritol, and long-chain unsaturated monocarboxylic fatty acids derived from natural oils (e.g., linseed oil, soybean oil or dehydrated castor oil) [11]. Alkyd resins are susceptible to oxidative processes in the presence of catalytic systems such as light, heat, enzymes, metals, metallo proteins, and micro-organisms. Alkyd resins may undergo autoxidation, photo-oxidation, thermal oxidation, and enzymatic oxidation under different conditions, most of which involve some type of free radical or oxygen species. Then chemical drying (also called oxidative drying) occurs, a lipid autoxidation process, which means that the paint dries by oxidation of the binder compound with molecular oxygen from the air. The curing of alkyd resin is the result of autoxidation, the addition of oxygen to an organic compound and the subsequent crosslinking. This process begins with an oxygen molecule (O2 ) in the air inserting into carbon hydrogen (C H) bonds adjacent to one of the double bonds within the unsaturated fatty acid. The resulting hydroperoxides are susceptible to crosslinking reactions. Bonds form between neighboring fatty acid
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chains, resulting in a polymer network, often visible by formation of a skin-like film on samples. [12]. Today alkyds are known as the most important and widely used resins in the coating field. They are outstanding in terms of their versatility of formulations and applications, low prices and durability. Alkyd resins are therefore can well be suited to the field of applications such as air-drying varnishes, architectural paints, and marine coatings typically in solvent-based formulations [13]. In some of the paint formulations, inorganic fillers are dispersed in a polymer matrix resulting in tremendous improvement in performance of the polymer. Mineral fillers are inert substances added to reduce the resin cost and/or improve its physical properties, hardness, stiffness, optical properties, flame resistance, thermal properties and impact strength [14]. Commonly used mineral fillers are calcium carbonate, hydrated alumina, clay, fly ash/mica hybrid and huntite [15]. Huntite (Mg3 Ca(CO3 )4 ) is categorized in the group of salt-type carbonate minerals. The commercially used reserves of huntite are located in Greece and Turkey [16]. The attractive properties of huntite minerals are from noncorrosive to processing equipment, low smoke generation, no acid gas emission, halogen free, environmentally safe, recyclable, no combustion gas corrosion, no limitation in coloring and low combustion [17]. Also, huntite is one of the most important flame retardant additives, when it is used together with hydro-magnesite. [18] This type of flame retardant materials has been in the market since the late 1980s [19]. There have been many studies done on using huntite as flame retardant filler [20]. In this study, we investigated the utilization of linseed oil in order to obtain alkyd resin, by changing the oil content. It was synthesized from medium oil resins (48%) and long oil resins (60%). In the first step of the resin synthesis, alcoholysis, linseed oil and trimethylolpropane were reacted using calcium carbonate as a catalyst. In the next step, polyesterification, the monoglyceride was reacted with phthalic anhydride. The reaction was controled by the acid number (AN), which should be under 15 mg KOH/g of resin in the end of the reaction. The obtained resins were characterized by ATR-FTIR and 1 H NMR techniques. Then, linseedbased alkyd resins were used in paint formulations. In addition, huntite, Aerosil R972, talc, titanium dioxide, dryer, wetting agent and anti-skinning agent were used in the paint formulations. The paint materials were characterized with the analysis of various properties such as hardness, gloss, cross-cut adhesion, chemical resistance test, contact angle measurement. Thermal and morphological characteristics of the paint materials were determined by using thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM).
Table 1 Formulation of different linseed oil based alkyd resins.
Linseed oils (g) Phthalic anhydride (g) Trimethylolpropane (g) Calcium carbonate (g) Xylene (g)
AKD 1 (48% oil content)
AKD 2 (60% oil content)
50 30.11 23.16 0.4 10.82
80 30.11 23.16 0.64 13.32
2.2. Characterization FT-IR spectrum was measured on Perkin–Elmer Spectrum100 ATR-FTIR spectrophotometer. 1 H NMR spectrum was recorded by using a Varian model T-60 NMR spectrometer operated at 500 MHz. Other coating properties were also measured in accordance with the corresponding standard test methods as indicated. Cross cut (DIN 53151), pencil hardness (ASTM D-3363), pendulum hardness (DIN 53157), and gloss (ASTM D-523-80) were performed to determine the physical properties of the coatings. MEK rub test (ASTM D-5402) was performed to check for the thorough curing of the coatings; the surface was inspected for visual changes in appearance. The wettability characteristics of free films were performed on a Kruss (Easy Drop DSA-2) tensiometer. The contact angles (Â) were measured by means of sessile drop test method in which drops were created by using a syringe. Measurements were made using 3–5 l drops of distilled water. The viscosity of the paint formulations were measured by using a Krebs Unit Viscometer Model KU-2 viscometer. The measurements were done under atmospheric pressure and at 23 ◦ C temperature. Thermogravimetric analyses (TGA) were performed using a Perkin–Elmer Thermogravimetric analyzer Pyris 1 TGA model. Samples were heated from 30 to 750 ◦ C with heating rate of 10 ◦ C/min under air atmosphere. SEM imaging of the films were performed on Philips XL30 ESEM-FEG/EDAX. The specimens were prepared for SEM by freeze-fracturing in liquid nitrogen and applying a gold coating. 2.3. Synthesis of linseed oil based alkyd resin Linseed oil based alkyd resin was synthesized in two stages. Linseed oil was charged into three-necked round bottom flask equipped with a thermometer, mechanical stirrer, condenser, Dean-Stark trap and a nitrogen inlet. The oil was heated to 200 ◦ C. The formulations of alkyd resins having different quantities of oil content are given in Table 1. The trimethylolpropane as a reactant and calcium carbonate (catalyst, oil 0.8% up) were added. After the addition linseed oil was heated to 240 ◦ C. Small samples were taken and diluted in anhydrous methanol. If the resulting solution
2. Materials and methods 2.1. Materials Linseed oils were supplied by Arifo˘glu Chemical. Trimethylolpropane was provided by Sigma Aldrich. Calcium carbonate (CaCO3 ) was recieved from Merck. Phthalic anhydride, talc, Titanium dioxide (TiO2 ), Cobalt(II) naphthenate, Zirconium naphthenate and Calcium naphthenate (drying agents), Antiterra 204 (wetting agent), methyl ethyl ketoxime (MEKO) and anti-skinning agent were supplied from Kayalar Chemical A.S¸. SiO2 (Aerosil R972) was purchased from Evonik Industries and used as received. Huntite (Mg3 Ca(CO3 )4 ) was obtained from Denizli, Turkey. Common solvents such as methanol, xylene, toluene, ısopropyl alcohol, dietylether, hexane and methyl ethyl ketone (MEK) were used as received.
Fig. 1. The acid number versus the reaction time for different alkyd resins.
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Table 2 The composition of linseed oil based alkyd paint materials. Paint formulations
Resin (g)
Talc (g)
White sprite (g)
TiO2 (g)
Huntite (g)
SiO2 Aerosil R972 (g)
Drying Agents (g)
Wetting Agent (g)
Methyl ethyl ketoxime (g)
P1 P2 P3 P4 P5 P6
60AKD 2 60AKD 2 60AKD 2 60AKD 1 60AKD 1 60AKD 1
25 25 25 25 25 25
– – 23 – – 23
10 5 5 10 5 5
– 5 – 5 – –
– – 5 – – 5
3.16 3.16 3.16 3.16 3.16 3.16
1.38 1.38 1.38 1.38 1.38 1.38
0.46 0.46 0.46 0.46 0.46 0.46
was clear in methanol, it was concluded that alcoholysis step has completed. In second stage the mixture was cooled to 140 ◦ C and 30.11 g (0.2 mol) of phthalic anhydride with xylene was added. The reaction
Fig. 2. (a) FT-IR spectrum of linseed oil based alkyd (% 48 oil content).
mixture was heated to 240 ◦ C and reaction was persued until acid number is decreased to 15 mg KOH/g. Fig. 1. shows acid value in time for two resins containing different amount of linseed oil resin formulations.
(b) FT-IR spectrum of linseed oil based alkyd (60% oil content).
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2.4. Preparation of alkyd paint formulations The alkyd paint formulations were prepared by mixing the linseed oil alkyd resin, talc, white spirit, huntite, TiO2 , Aerosil R972, drying, wetting and anti-skinning agent and methyl ethyl ketoxime.The mixture was homogenized by stirring it with disperser. The alkyd paint formulations were casted on to paper species and dried at 30 ◦ C. Then all the formulations were characterized by various tests. The composition of the all formulations is given in Table 2. 3. Results and discussion For this study, the alkyds paints were prepared by using the natural linseed oil that contains triglycerides consisting of a mixture of linolenic (57%), oleic (19%), linoleic (15%), palmitic (5%), and stearic (4%) fatty acids. Alkyd resin was synthesized by the reaction of linseed oil with trimethylolpropane and phthalic anhydride at 200–250 ◦ C for 12 h. 3.1. Structural analysis The functional groups of linseed based alkyd resin were confirmed by its ATR-FTIR, and 1 H NMR spectra. Fig. 2a and b shows the FTIR spectra of different oil content alkyd resin. After the esterification step, the characteristic ester band at 1726 cm−1 , aliphatic and aromatic C C band at 1599–1580 cm−1 and the CH band (linseed oil) around 3010 cm−1 , aliphatic C H band at 2925–2854 cm−1 and 1257–1120–1070 cm−1 C O C band were observed [21]. The 1 H NMR spectrums of different oil content alkyd resins are given in Fig. 3a and 3b. In the 1 H NMR (500 MHz, CDCI3 ) spectrum of alkyd resin, the signal at 0.9 ppm is characteristic for CH3
Fig. 3. (a) H NMR spectrum of linseed oil based alkyd (% 48 oil content). (b) H NMR spectrum of linseed oil based alkyd (% 60 oil content).
Table 3 Linseed oil based alkyd paint formulations viscosity. (ku: Krebs unit). Paint formulations
Viscosity (ku)
P1 P2 P3 P4 P5 P6
98 98 71 135 136 96
in fatty acids hydrogen’s and 1.2, 1.3 and 1.5 ppm are CH2 of fatty acids group hydrogen’s. The signals at 4.0 and 4.1 ppm correspond to the diastereotopic protons of the glycerin methylene units (CH2 O C O). The degree of unsaturation can be calculated from the area of the signal at 5.4–5.2 ppm. 3.2. Viscosity measurement The viscosity of a paint formulation governs the film formation and surface characteristics. The P3 and P6 paint formulations have high viscosity at room temperature and when the white sprite is added, it acts as a paint thinner, which results in reduced viscosity. The results of paint formulations viscosity measurements are reported in Table 3. The paint formulations generally have a viscosity value between 96 and 140 ku (krebs unit) prepared and applied. Paint formulations, which were prepared alkyd 1, have higher viscosity than prepared alkyd 2. The viscosity of the formulations increased with decreasing of linseed oil content in the alkyd resin. 3.3. Coatings’ properties Some physical properties of the alkyd based paint, such as gloss, pencil hardness, pendulum hardness, cross-cut adhesion, drying time were measured and their results were given in Table 4. The drying time of paint formulations are listed in Table 4. The drying time increases continuously with the increase of oil content in alkyd resins. P1, P2 and P3 formulations show the higher drying time (213, 203 and 193 min.) in comparison to P4, P5, P6 formulations (155, 150, 145 min). The low extent of polymerization in the case of alkyd resins having high oil content may be the reason for having higher drying time. The neat alkyd resin and pigmented formulations have exhibited the drying performance as similar to the results reported elsewhere [22]. It can be noticed that, the drying time was shorter the ones containing Aerosil R972 and huntite formulations as compared to other formulations. The hardness of the paint is the most important variable since it is affected by the chain flexibility and crosslinking degree of the network. Besides that, the type of substrate, adhesion to the substrate, and heterogeneity within the coating can influence the hardness measurements. In this study, the effects of silica, huntite, and linseed oil content on the hardness of the paint formulation. As can be seen in Table 4, for all the dyes pencil hardness ranges from 1H to 3H. Moreover, pencil and pendulum hardness increases slightly with silica and huntite content. After 4 weeks, the paints’ pencil and pendulum hardness have increased. And then, pendulum hardness increased continuously with the decrease of oil content in alkyd resins. The crosscut adhesion experiments showed that 100% adhesion was reached for all paints formulations are determined. The gloss of the paints’ materials is a complex phenomenon, which results from the interaction between light and surface of the paint. As shown in Table 4, the gloss measurements were given at 60◦ and 85◦ for all types of the paint samples. It is an important property of coating when the esthetic or decorative appearance of a coating is of prime importance. The gloss of the coating decreased with the increase of Aerosil R972 and huntite content in the formulation. After 4
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Table 4 Physical characterizations of linseed oil based alkyd paint materials. Sample
P1 P2 P3 P4 P5 P6
Drying Time (min)
213 203 193 155 150 145
Pendulum hardness
Pencil hardness
1 week
4 week
1 week
4 week
9 11 24 11 12 18
19 21 32 30 27 34
1H 1H 2H 1H 1H 2H
2H 2H 3H 2H 2H 3H
Cross-cut
0 0 0 0 0 0
MEK rubbing test
200 300 300+ 200 300 300+
Gloss 1 week 60◦
4 week 85◦
1week 60◦
4 week 85◦
47.8 35.6 9.6 50.6 53.2 11.6
68.4 53.4 16.3 76.0 63.7 16.9
43.5 33.2 7.1 48.6 44.6 13.2
55.2 56.3 13.0 77.7 71.5 22.8
Table 5 TGA analysis of linseed oil based alkyd paints. Sample
T5% (◦ C)
Max. weight loss (◦ C)
Char yield (%)
P1 P2 P3 P4 P5 P6
235 268 246 282 282 276
401 414 404 401 405 392
40.1 36.9 43.2 41.7 41.7 42.1
Fig. 5. SEM micrograph of P6.
Fig. 4. Contact angle values of linseed oil based alkyd paint with water.
weeks, the paints gloss decreased. And then, paints gloss increases continuously with the decrease of oil content in alkyd resins. The solvent resistance of the paints was investigated by performing the MEK rubbing test. All samples showed excellent resistance performance, exceeding from 150 to 300+ MEK rubs. It can be noticed that, the MEK rubbing test results are considered well for containing Aerosil R972 and huntite formulations
as compared to other formulations. The chemical resistance of all the paints was also investigated by immersing samples in various reagents for 24 h time period. Although all samples were affected from %10 NaOH, the general physical appearance of samples was perfect and no breaks were observed. The results of chemicals resistance are listed in Table 5. The contact angle is the angle at which a liquid interface meets a solid surface. There was a slight enhancement in the contact angle as the Aerosil R972 content of the paint increased orderly. This was expected because we assumed that pendent Aerosil R972 will make the surface more hydrophobic. Contact angle photos are given in Fig. 4.
Fig. 6. TGA thermograms of all samples.
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3.4. Morphologic analysis The morphologies of the paints were investigated by SEM. The SEM images of the flocculated surface of the paint film are shown in Fig. 5. In Fig. 5 it can be observed that silica nanoparticles are homogenously dispersed through the organic matrix. 3.5. Thermal stability Thermogravimetric analysis (TGA) was used to evaluate the thermal stability of these paint materials as a function of the huntite content. Table 5 collects the TGA data determined under air atmosphere, and Fig. 6 shows the TGA curves for all samples under air atmosphere at 10 ◦ C/min. For the huntite-containing paint materials, the char yields at 750 ◦ C slightly decreased with the huntite content. A second step in the weight loss rate appears at higher temperature, between 405 ◦ C and 414 ◦ C, corresponding to the thermo-oxidative degradation. It is also observed that the thermal stability of the paint materials increased with addition of huntite and AKD 2 content in the paint formulations. 4. Conclusion An investigation has been made on the utilization of linseed oil for the preparation of alkyd resins. Linseed oil based alkyd resin was added into the paint formulations. The physical and mechanical properties of paint materials such as pencil hardness, pendulum hardness, MEK rubbing test, adhesion, gloss and contact angle were investigated. The thermal stability of the coating is improved by increasing the amount of huntite and Aerosil R972 in the paint compositions. SEM studies of the paint materials depicted
that silica particles were homogeneously dispersed through the organic matrix. References [1] Y. Lu, R.C. Larock, Chem. Sus. Chem 2 (2009) 136–147. [2] G. Lligadas, J.C. Ronda, M. Galia, V. Cadiz, Biomacromolecules 7 (2006) 3521–3526. [3] L. Hojabri, X. Kong, S.S. Narine, Biomacromolecules 10 (2009) 884–891. [4] S.B. David, K. Sathiyalekshmi, G.A.G. Raj, J. Mater. Sci. Mater. Med. 20 (2009) 61–70. [5] D.D. Andjelkovic, R.C. Larock, Biomacromolecules 7 (2006) 927–936. [6] M. Sacristan, J.C. Ronda, M. Galia, V. Cadiz, Biomacromolecules 10 (2009) 2678–2685. [7] M.D. Soucek, A.H. Johnson, J.M. Wegner, Prog. Org. Coat 51 (2004) 300–311. [8] R. Ploeger, D. Scalarone, O. Chiantore, Polym. Degrad. Stabil. 94 (2009) 2036–2041. [9] M. Boruah, P. Gogoi, B. Adhikari, S.K. Dolui, Prog. Org. Coat 74 (2012) 596–602. [10] I.E. Ezeh, S.A. Umoren, E.E. Essien, A.P. Udoh, Ind. Crop. Prod 36 (2012) 94–99. [11] A.I. Aigbodion, C.K. Pillai, J. Appl. Polym. Sci 79 (2001) 2431–2438. [12] D.T.C. Ang, S.N. Gan, Prog. Org. Coat. 73 (2012) 409–414. [13] T.E. Odetoyea, D.S. Ogunniyia, G.A. Olatunjib, Prog. Org. Coat. 73 (2012) 374–381. [14] G. Bayramo˘glu, M.V. Kahraman, N. Apohan, A. Güngör, Prog. Org. Coat. 57 (2006) 50–55. [15] N.M. Ahmed, H.T.M.A. Fatah, E.A. Youssef, Prog. Org. Coat. 73 (2012) 76–87. [16] Y. Seki, K. Sever, M. Sarikanat, A. Sakarya, E. Elik, Composites: Part B. 45 (2013) 1534–1540. [17] O. Kangal, A. Güney, Miner. Eng. 19 (2006) 376–378. [18] L.A. Hollingbery, T.R. Hull, Thermochim. Acta 509 (2010) 1–11. [19] M.V. Kahraman, N. Apohan, N. Arsu, A. Güngör, Prog. Org. Coat. 51 (2004) 213–219. [20] L.A. Hollingbery, T.R. Hull, Polym. Degrad. Stabil. 97 (2012) 504–512. [21] R. Ploeger, D. Scalarone, O. Chiantore, J. Cult. Herit. 9 (2008) 412–419. [22] M.N.S. Kumar, Z. Yaakob, S. Maimunah, S.R.S. Abdullah, J. Polym. Environ. 18 (4) (2010) 539–544.
Contents lists available at ScienceDirect
Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat
Preparation and evaluation of linseed oil based alkyd paints Döndü I˙ s¸eri-C¸a˘glar, Emre Bas¸türk, Burcu Oktay, M. Vezir Kahraman ∗ Department of Chemistry, Faculty of Art & Science, Marmara University, 34722 Göztepe-Istanbul, Turkey
a r t i c l e
i n f o
Article history: Received 12 June 2013 Received in revised form 16 August 2013 Accepted 21 August 2013 Available online 17 September 2013 Keywords: Alkyd resins Linseed Oil Renewable resources Aerosil R972 Huntite
a b s t r a c t Alkyd resins are produced with reaction of oil or fatty oil, polyol and polyacid. Alkyd resins are commonly used in coating and paint industry due to ease of application in changing environmental conditions. Linseed oil based paints executed all requirements of technical properties, drying time, storage properties, simplicity in maintenance, appearance, economy, etc. In this study, linseed oil based alkyd resins having different oil contents were synthesized Paint formulations were prepared by mixing alkyd resin and various additives such as huntite, Aerosil R972, talc, titanium dioxide, dryer, wetting agent and anti-skinning agent. All formulations were applied on paper test plates and were dried at 30 ◦ C. The obtained coatings were characterized by pencil hardness test, pendulum hardness test, chemical resistance test, cross-cut test, contact angle and gloss measurement. Also thermal and morphological properties were investigated by thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM) respectively. The thermal stability of the paint materials are improved with by increasing the amount of huntite and Aerosil R972 in the paint compositions. © 2013 Elsevier B.V. All rights reserved.
1. Introduction The utilization of fossil fuels for the manufacture of plastics accounts for about 7% of the worldwide use of oil and gas, which will arguably be depleted within the next 100 years [1]. The peak in global oil production is estimated to occur within the next few decades. In this age of increasing oil prices, global warming, and other environmental concerns (i.e. waste), a change from fossil feed stocks to renewable resources is important for sustainable development into the future [2]. The utilization of renewable resources can consistently provide raw materials for everyday products, effectively avoiding further contribution to greenhouse effects, because of the minimization of CO2 emissions [3]. Therefore, academic and industrial researchers are devoted to increase attention and put on their efforts to the possible utilization of renewable resources as raw materials for the production of both chemicals and polymeric materials. The most widely used renewable raw materials are; polysaccharides (mainly cellulose and starch), proteins, sugar, natural rubber, and plant oils [4,5]. Vegetable oils and modified vegetable oils have become attractive sustainable alternatives to petroleum-based materials for industrial applications such as soaps, lubricants, coatings, paints, and, more recently, bio-plastics and composites due to their biodegradability, low toxicity, non-content of volatile organic chemicals, easy availability, and relatively low price [6]. In the past few years, consumers and
∗ Corresponding author. Fax: +90 2163478783. E-mail address: [email protected] (M.V. Kahraman). 0300-9440/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.porgcoat.2013.08.005
individual interests in environmentally friendly paints and coating have been growing tremendously [7]. Common household oil paint, the oldest form of modern paints, uses a binder that is derived from vegetable oils, which is obtained from linseed or soya bean. Alkyd paints are based on alkyd resins (vegetable-derived drying oils), which contain a variety of polyunsaturated fatty-acid chains, commonly linoleic and linoleic acid and their triglycerides [8], which undergo free-radical-mediated autoxidation during the curing/drying process [9,10] Alkyd resins are branched polyesters that are obtained by reacting dicarboxylic acids or anhydrides and polyols such as glycerol or pentaerythritol, and long-chain unsaturated monocarboxylic fatty acids derived from natural oils (e.g., linseed oil, soybean oil or dehydrated castor oil) [11]. Alkyd resins are susceptible to oxidative processes in the presence of catalytic systems such as light, heat, enzymes, metals, metallo proteins, and micro-organisms. Alkyd resins may undergo autoxidation, photo-oxidation, thermal oxidation, and enzymatic oxidation under different conditions, most of which involve some type of free radical or oxygen species. Then chemical drying (also called oxidative drying) occurs, a lipid autoxidation process, which means that the paint dries by oxidation of the binder compound with molecular oxygen from the air. The curing of alkyd resin is the result of autoxidation, the addition of oxygen to an organic compound and the subsequent crosslinking. This process begins with an oxygen molecule (O2 ) in the air inserting into carbon hydrogen (C H) bonds adjacent to one of the double bonds within the unsaturated fatty acid. The resulting hydroperoxides are susceptible to crosslinking reactions. Bonds form between neighboring fatty acid
82
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chains, resulting in a polymer network, often visible by formation of a skin-like film on samples. [12]. Today alkyds are known as the most important and widely used resins in the coating field. They are outstanding in terms of their versatility of formulations and applications, low prices and durability. Alkyd resins are therefore can well be suited to the field of applications such as air-drying varnishes, architectural paints, and marine coatings typically in solvent-based formulations [13]. In some of the paint formulations, inorganic fillers are dispersed in a polymer matrix resulting in tremendous improvement in performance of the polymer. Mineral fillers are inert substances added to reduce the resin cost and/or improve its physical properties, hardness, stiffness, optical properties, flame resistance, thermal properties and impact strength [14]. Commonly used mineral fillers are calcium carbonate, hydrated alumina, clay, fly ash/mica hybrid and huntite [15]. Huntite (Mg3 Ca(CO3 )4 ) is categorized in the group of salt-type carbonate minerals. The commercially used reserves of huntite are located in Greece and Turkey [16]. The attractive properties of huntite minerals are from noncorrosive to processing equipment, low smoke generation, no acid gas emission, halogen free, environmentally safe, recyclable, no combustion gas corrosion, no limitation in coloring and low combustion [17]. Also, huntite is one of the most important flame retardant additives, when it is used together with hydro-magnesite. [18] This type of flame retardant materials has been in the market since the late 1980s [19]. There have been many studies done on using huntite as flame retardant filler [20]. In this study, we investigated the utilization of linseed oil in order to obtain alkyd resin, by changing the oil content. It was synthesized from medium oil resins (48%) and long oil resins (60%). In the first step of the resin synthesis, alcoholysis, linseed oil and trimethylolpropane were reacted using calcium carbonate as a catalyst. In the next step, polyesterification, the monoglyceride was reacted with phthalic anhydride. The reaction was controled by the acid number (AN), which should be under 15 mg KOH/g of resin in the end of the reaction. The obtained resins were characterized by ATR-FTIR and 1 H NMR techniques. Then, linseedbased alkyd resins were used in paint formulations. In addition, huntite, Aerosil R972, talc, titanium dioxide, dryer, wetting agent and anti-skinning agent were used in the paint formulations. The paint materials were characterized with the analysis of various properties such as hardness, gloss, cross-cut adhesion, chemical resistance test, contact angle measurement. Thermal and morphological characteristics of the paint materials were determined by using thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM).
Table 1 Formulation of different linseed oil based alkyd resins.
Linseed oils (g) Phthalic anhydride (g) Trimethylolpropane (g) Calcium carbonate (g) Xylene (g)
AKD 1 (48% oil content)
AKD 2 (60% oil content)
50 30.11 23.16 0.4 10.82
80 30.11 23.16 0.64 13.32
2.2. Characterization FT-IR spectrum was measured on Perkin–Elmer Spectrum100 ATR-FTIR spectrophotometer. 1 H NMR spectrum was recorded by using a Varian model T-60 NMR spectrometer operated at 500 MHz. Other coating properties were also measured in accordance with the corresponding standard test methods as indicated. Cross cut (DIN 53151), pencil hardness (ASTM D-3363), pendulum hardness (DIN 53157), and gloss (ASTM D-523-80) were performed to determine the physical properties of the coatings. MEK rub test (ASTM D-5402) was performed to check for the thorough curing of the coatings; the surface was inspected for visual changes in appearance. The wettability characteristics of free films were performed on a Kruss (Easy Drop DSA-2) tensiometer. The contact angles (Â) were measured by means of sessile drop test method in which drops were created by using a syringe. Measurements were made using 3–5 l drops of distilled water. The viscosity of the paint formulations were measured by using a Krebs Unit Viscometer Model KU-2 viscometer. The measurements were done under atmospheric pressure and at 23 ◦ C temperature. Thermogravimetric analyses (TGA) were performed using a Perkin–Elmer Thermogravimetric analyzer Pyris 1 TGA model. Samples were heated from 30 to 750 ◦ C with heating rate of 10 ◦ C/min under air atmosphere. SEM imaging of the films were performed on Philips XL30 ESEM-FEG/EDAX. The specimens were prepared for SEM by freeze-fracturing in liquid nitrogen and applying a gold coating. 2.3. Synthesis of linseed oil based alkyd resin Linseed oil based alkyd resin was synthesized in two stages. Linseed oil was charged into three-necked round bottom flask equipped with a thermometer, mechanical stirrer, condenser, Dean-Stark trap and a nitrogen inlet. The oil was heated to 200 ◦ C. The formulations of alkyd resins having different quantities of oil content are given in Table 1. The trimethylolpropane as a reactant and calcium carbonate (catalyst, oil 0.8% up) were added. After the addition linseed oil was heated to 240 ◦ C. Small samples were taken and diluted in anhydrous methanol. If the resulting solution
2. Materials and methods 2.1. Materials Linseed oils were supplied by Arifo˘glu Chemical. Trimethylolpropane was provided by Sigma Aldrich. Calcium carbonate (CaCO3 ) was recieved from Merck. Phthalic anhydride, talc, Titanium dioxide (TiO2 ), Cobalt(II) naphthenate, Zirconium naphthenate and Calcium naphthenate (drying agents), Antiterra 204 (wetting agent), methyl ethyl ketoxime (MEKO) and anti-skinning agent were supplied from Kayalar Chemical A.S¸. SiO2 (Aerosil R972) was purchased from Evonik Industries and used as received. Huntite (Mg3 Ca(CO3 )4 ) was obtained from Denizli, Turkey. Common solvents such as methanol, xylene, toluene, ısopropyl alcohol, dietylether, hexane and methyl ethyl ketone (MEK) were used as received.
Fig. 1. The acid number versus the reaction time for different alkyd resins.
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Table 2 The composition of linseed oil based alkyd paint materials. Paint formulations
Resin (g)
Talc (g)
White sprite (g)
TiO2 (g)
Huntite (g)
SiO2 Aerosil R972 (g)
Drying Agents (g)
Wetting Agent (g)
Methyl ethyl ketoxime (g)
P1 P2 P3 P4 P5 P6
60AKD 2 60AKD 2 60AKD 2 60AKD 1 60AKD 1 60AKD 1
25 25 25 25 25 25
– – 23 – – 23
10 5 5 10 5 5
– 5 – 5 – –
– – 5 – – 5
3.16 3.16 3.16 3.16 3.16 3.16
1.38 1.38 1.38 1.38 1.38 1.38
0.46 0.46 0.46 0.46 0.46 0.46
was clear in methanol, it was concluded that alcoholysis step has completed. In second stage the mixture was cooled to 140 ◦ C and 30.11 g (0.2 mol) of phthalic anhydride with xylene was added. The reaction
Fig. 2. (a) FT-IR spectrum of linseed oil based alkyd (% 48 oil content).
mixture was heated to 240 ◦ C and reaction was persued until acid number is decreased to 15 mg KOH/g. Fig. 1. shows acid value in time for two resins containing different amount of linseed oil resin formulations.
(b) FT-IR spectrum of linseed oil based alkyd (60% oil content).
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2.4. Preparation of alkyd paint formulations The alkyd paint formulations were prepared by mixing the linseed oil alkyd resin, talc, white spirit, huntite, TiO2 , Aerosil R972, drying, wetting and anti-skinning agent and methyl ethyl ketoxime.The mixture was homogenized by stirring it with disperser. The alkyd paint formulations were casted on to paper species and dried at 30 ◦ C. Then all the formulations were characterized by various tests. The composition of the all formulations is given in Table 2. 3. Results and discussion For this study, the alkyds paints were prepared by using the natural linseed oil that contains triglycerides consisting of a mixture of linolenic (57%), oleic (19%), linoleic (15%), palmitic (5%), and stearic (4%) fatty acids. Alkyd resin was synthesized by the reaction of linseed oil with trimethylolpropane and phthalic anhydride at 200–250 ◦ C for 12 h. 3.1. Structural analysis The functional groups of linseed based alkyd resin were confirmed by its ATR-FTIR, and 1 H NMR spectra. Fig. 2a and b shows the FTIR spectra of different oil content alkyd resin. After the esterification step, the characteristic ester band at 1726 cm−1 , aliphatic and aromatic C C band at 1599–1580 cm−1 and the CH band (linseed oil) around 3010 cm−1 , aliphatic C H band at 2925–2854 cm−1 and 1257–1120–1070 cm−1 C O C band were observed [21]. The 1 H NMR spectrums of different oil content alkyd resins are given in Fig. 3a and 3b. In the 1 H NMR (500 MHz, CDCI3 ) spectrum of alkyd resin, the signal at 0.9 ppm is characteristic for CH3
Fig. 3. (a) H NMR spectrum of linseed oil based alkyd (% 48 oil content). (b) H NMR spectrum of linseed oil based alkyd (% 60 oil content).
Table 3 Linseed oil based alkyd paint formulations viscosity. (ku: Krebs unit). Paint formulations
Viscosity (ku)
P1 P2 P3 P4 P5 P6
98 98 71 135 136 96
in fatty acids hydrogen’s and 1.2, 1.3 and 1.5 ppm are CH2 of fatty acids group hydrogen’s. The signals at 4.0 and 4.1 ppm correspond to the diastereotopic protons of the glycerin methylene units (CH2 O C O). The degree of unsaturation can be calculated from the area of the signal at 5.4–5.2 ppm. 3.2. Viscosity measurement The viscosity of a paint formulation governs the film formation and surface characteristics. The P3 and P6 paint formulations have high viscosity at room temperature and when the white sprite is added, it acts as a paint thinner, which results in reduced viscosity. The results of paint formulations viscosity measurements are reported in Table 3. The paint formulations generally have a viscosity value between 96 and 140 ku (krebs unit) prepared and applied. Paint formulations, which were prepared alkyd 1, have higher viscosity than prepared alkyd 2. The viscosity of the formulations increased with decreasing of linseed oil content in the alkyd resin. 3.3. Coatings’ properties Some physical properties of the alkyd based paint, such as gloss, pencil hardness, pendulum hardness, cross-cut adhesion, drying time were measured and their results were given in Table 4. The drying time of paint formulations are listed in Table 4. The drying time increases continuously with the increase of oil content in alkyd resins. P1, P2 and P3 formulations show the higher drying time (213, 203 and 193 min.) in comparison to P4, P5, P6 formulations (155, 150, 145 min). The low extent of polymerization in the case of alkyd resins having high oil content may be the reason for having higher drying time. The neat alkyd resin and pigmented formulations have exhibited the drying performance as similar to the results reported elsewhere [22]. It can be noticed that, the drying time was shorter the ones containing Aerosil R972 and huntite formulations as compared to other formulations. The hardness of the paint is the most important variable since it is affected by the chain flexibility and crosslinking degree of the network. Besides that, the type of substrate, adhesion to the substrate, and heterogeneity within the coating can influence the hardness measurements. In this study, the effects of silica, huntite, and linseed oil content on the hardness of the paint formulation. As can be seen in Table 4, for all the dyes pencil hardness ranges from 1H to 3H. Moreover, pencil and pendulum hardness increases slightly with silica and huntite content. After 4 weeks, the paints’ pencil and pendulum hardness have increased. And then, pendulum hardness increased continuously with the decrease of oil content in alkyd resins. The crosscut adhesion experiments showed that 100% adhesion was reached for all paints formulations are determined. The gloss of the paints’ materials is a complex phenomenon, which results from the interaction between light and surface of the paint. As shown in Table 4, the gloss measurements were given at 60◦ and 85◦ for all types of the paint samples. It is an important property of coating when the esthetic or decorative appearance of a coating is of prime importance. The gloss of the coating decreased with the increase of Aerosil R972 and huntite content in the formulation. After 4
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Table 4 Physical characterizations of linseed oil based alkyd paint materials. Sample
P1 P2 P3 P4 P5 P6
Drying Time (min)
213 203 193 155 150 145
Pendulum hardness
Pencil hardness
1 week
4 week
1 week
4 week
9 11 24 11 12 18
19 21 32 30 27 34
1H 1H 2H 1H 1H 2H
2H 2H 3H 2H 2H 3H
Cross-cut
0 0 0 0 0 0
MEK rubbing test
200 300 300+ 200 300 300+
Gloss 1 week 60◦
4 week 85◦
1week 60◦
4 week 85◦
47.8 35.6 9.6 50.6 53.2 11.6
68.4 53.4 16.3 76.0 63.7 16.9
43.5 33.2 7.1 48.6 44.6 13.2
55.2 56.3 13.0 77.7 71.5 22.8
Table 5 TGA analysis of linseed oil based alkyd paints. Sample
T5% (◦ C)
Max. weight loss (◦ C)
Char yield (%)
P1 P2 P3 P4 P5 P6
235 268 246 282 282 276
401 414 404 401 405 392
40.1 36.9 43.2 41.7 41.7 42.1
Fig. 5. SEM micrograph of P6.
Fig. 4. Contact angle values of linseed oil based alkyd paint with water.
weeks, the paints gloss decreased. And then, paints gloss increases continuously with the decrease of oil content in alkyd resins. The solvent resistance of the paints was investigated by performing the MEK rubbing test. All samples showed excellent resistance performance, exceeding from 150 to 300+ MEK rubs. It can be noticed that, the MEK rubbing test results are considered well for containing Aerosil R972 and huntite formulations
as compared to other formulations. The chemical resistance of all the paints was also investigated by immersing samples in various reagents for 24 h time period. Although all samples were affected from %10 NaOH, the general physical appearance of samples was perfect and no breaks were observed. The results of chemicals resistance are listed in Table 5. The contact angle is the angle at which a liquid interface meets a solid surface. There was a slight enhancement in the contact angle as the Aerosil R972 content of the paint increased orderly. This was expected because we assumed that pendent Aerosil R972 will make the surface more hydrophobic. Contact angle photos are given in Fig. 4.
Fig. 6. TGA thermograms of all samples.
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3.4. Morphologic analysis The morphologies of the paints were investigated by SEM. The SEM images of the flocculated surface of the paint film are shown in Fig. 5. In Fig. 5 it can be observed that silica nanoparticles are homogenously dispersed through the organic matrix. 3.5. Thermal stability Thermogravimetric analysis (TGA) was used to evaluate the thermal stability of these paint materials as a function of the huntite content. Table 5 collects the TGA data determined under air atmosphere, and Fig. 6 shows the TGA curves for all samples under air atmosphere at 10 ◦ C/min. For the huntite-containing paint materials, the char yields at 750 ◦ C slightly decreased with the huntite content. A second step in the weight loss rate appears at higher temperature, between 405 ◦ C and 414 ◦ C, corresponding to the thermo-oxidative degradation. It is also observed that the thermal stability of the paint materials increased with addition of huntite and AKD 2 content in the paint formulations. 4. Conclusion An investigation has been made on the utilization of linseed oil for the preparation of alkyd resins. Linseed oil based alkyd resin was added into the paint formulations. The physical and mechanical properties of paint materials such as pencil hardness, pendulum hardness, MEK rubbing test, adhesion, gloss and contact angle were investigated. The thermal stability of the coating is improved by increasing the amount of huntite and Aerosil R972 in the paint compositions. SEM studies of the paint materials depicted
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