- Email: [email protected]
Bio-based multifunctional fatty acid methyl esters as reactive diluents in coil coatings
Progress in Organic Coatings 136 (2019) 105277
Contents lists available at ScienceDirect
Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat
Bio-based multifunctional fatty acid methyl esters as reactive diluents in coil coatings
T
Sameer Nameera, Tomas Deltinb, Per-Erik Sundellc, Mats Johanssona,1,⁎ a
KTH Royal Institute of Technology, School of Engineering Sciences in Chemistry, Biotechnology and Health, Department of Fibre and Polymer Technology, Division of Coating Technology, SE-100 44 Stockholm, Sweden b PTE Coatings AB, SE-594 31, Gamleby, Sweden c SSAB EMEA, SE-781 84, Borlänge, Sweden
ARTICLE INFO
ABSTRACT
Keywords: Coil-coatings Vegetable oil Epoxidized fatty acid methyl esters Protective coatings Renewable resources
The increased environmental awareness has driven academia and industry to utilize environmentally benign sources. An industrially available process that is effective in the coatings industry is the coil-coating process where sheet steel can be pre-coated. During this process volatile organic compounds (VOCs) are generated and incinerated for energy recovery. One way to minimize VOCs is to use a reactive diluent i.e. a molecule that acts both as a solvent as well as chemically react into the final coating upon curing. Fatty acid methyl esters obtained from renewable resources such as vegetable oils are suitable candidates as reactive diluents. In this paper epoxidized fatty acid methyl esters (e-FAMEs) obtained from epoxidized linseed oil where compared with fatty acid methyl esters (FAMEs) obtained from rapeseed oil as reactive diluents in coil-coating formulations. Coilcoating formulations were followed by real-time Fourier transform infrared spectroscopy (RT-FTIR) in order to evaluate the e-FAMEs or the FAMEs reactivity in the coating system. In addition, coil-coating formulation containing e-FAME or FAME where cured in a pilot scale simulated coil-coating process. Moreover, thermal properties of the final coatings were evaluated by differential scanning calorimetry (DSC).
1. Introduction In the past few decades there has been an increasing interest of utilizing renewable and sustainable resources due to concerns regarding environment, waste disposal and fossil fuel depletion [1]. Renewable resources are considered as a potential platform to provide new building blocks for the chemical and materials industry [2]. Furthermore, not only the industry is shifting to more sustainable alternatives the final consumers and society in general are more aware of what they buy and demand sustainable alternatives [3]. One interesting renewable resource used in polymeric materials is vegetable oils due to their low cost, natural abundance, and variability [4,5]. Vegetable oils have for a long time been used in the production many different types of product groups e.g. coatings [6], paints [7], adhesives [8,9], composites and hybrid materials [10] just to mention a few. Another sustainability aspect is not only to use renewable resources but also to employ production processes that are efficient with a minimal negative fossil carbon footprint as well as a minimum of emissions from the process.
One of these processes that address some of these aspects in the field of organic coatings is pre-coated sheet steel i.e. coil coatings. The coil-coating process is a continuous industrial coating process used to efficiently coat sheet metal with an organic coating to form coated steel coils. The coated metal coil can subsequently be used for numerous applications such as roofing, water management systems, etc [11–13]. Compared to traditional on-site painting of exterior built steel constructions this is advantageous both from a cost perspective and from an environmental aspects since direct emissions of VOC is avoided [14]. Traditionally the coating formulation is a solvent-borne liquid coating that dries through evaporation and chemical crosslinking in a convection oven. A typical coil coating process utilizes high temperature convection ovens to reach a peak metal temperature (PMT) of 230–240 °C to allow for a full cure to be obtained in less than a minute. However, during curing a vast amount of volatile organic compounds (VOCs) are generated which is incinerated for energy recovery and used to aid the energy balance of the oven [11]. The main emission is thus CO2 rather than VOC but it is still desirable to find other alternatives or ways to reduce these CO2 emissions [15,16]. Several
Corresponding author. E-mail address: [email protected] (M. Johansson). 1 The corresponding author Professor Mats Johansson is the Editor-in-Chief of this journal but he had no role in the assessment of this work. The initial assessment, peer review process and the assessment of the revision was managed independently by Dr Marcel Piens who serves as an Editor on this journal. ⁎
https://doi.org/10.1016/j.porgcoat.2019.105277 Received 20 June 2019; Received in revised form 30 July 2019; Accepted 12 August 2019 Available online 20 August 2019 0300-9440/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
technologies have been considered as alternative to solvent-borne thermally curing of sheet metals e.g. UV-curable systems [17–19], water-borne coating formulations [20,21], powder coatings [22,23]. However, most of these methods have some drawbacks e.g. clean-up difficulties due to color change and high cost of modifying the production facilities. Another way to exclude VOCs (or subsequent fossil-based CO2 formation) in coating formulations is to increase the solid content by e.g. adding a reactive diluent [24–26]. A reactive diluent is a molecule that can both act as a diluting solvent as well as chemically react into the final coating during curing thus becoming a part of the final coating. In order to fulfill these demands the reactive diluent should have low viscosity, be compatible with the other components and have reactive functional groups suitable for the specific crosslinking chemistry used [24]. Previous studies on coilcoating systems [6,27] have shown that a suitable candidate for this is fatty acid methyl esters (FAMEs) that can be utilized as renewable and sustainable reactive diluents in polyester/melamine based coil coatings. FAMEs provides a decrease in viscosity when mixed into the formulation thus reducing the need for conventional organic solvents. The acyl group of the methyl ester furthermore allow for a transesterification between the FAME and the polyester to occur leading to an incorporation of the FAME into the dry film [11,12]. An important conclusion for this system was also that the FAME under typical coil coating curing conditions either reacted into the film or evaporated but it did not remain as a non-reacted plasticizer in the film hence a good long term performance could be obtained. The epoxy functional group have a central role in resin formulations for coatings application due to its ring-strain making it suitable for reaction in both acidic and basic conditions [28]. Epoxides have high reactivity to numerous functional groups including anhydrides [29,30], amines [31,32] and carboxylic acids [9]. Naturally formed epoxides can be found as building-blocks in renewable resources. One such example are epoxidized fatty acids which can be found in natural sources such as suberin and cutin [1,33,34] or Euphorbia lagascae and Vernonia galamensis [26,35–37]. Epoxidized fatty acids have previously been applied in resin formulations for coatings e.g. as sucrose based epoxy fatty acids [29] or as photo-cured resin systems [38–40]. Although significant steps towards more sustainable coil coating systems have been demonstrated there are still challenges to address such as increasing overall non-fossil content of the system, less energy consumption and increased life time of the final product. The present paper describes one way to address these challenges by an introduction of additional functionalities in the FAME that further improve the performance of these diluents in coil coatings. Epoxidized fatty acid methyl esters (eFAMEs) are demonstrated to introduce additional positive features such as higher degree of incorporation into the final films and an enhanced curing performance. Epoxidized vegetable oils are readily available on the market and easy to transform into methyl esters in the same way as vegetable oil based biodiesel is made. It is moreover notable that this type of fatty acid epoxide structures is abundant in nature [1], although at present not retrieved commercially to any significant extent. Epoxy functional omegahydroxyl fatty acids can for example be found in large amount in suberin from Birch tree bark [41,42] and in the cutin tissue [34,43].
(EMLO) and Epoxy methyl linolenate (EMLEN) were retrieved from ELO as described below. Hot dip galvanized (HDG) steel substrates were provided by SSAB EMEA (SE-781 84 Borlänge, Sweden). All materials where used as received In order for the reader to follow the text easier the coil-coating formulations were referred to as follows: Coil-coating formulation that contains 10 wt% FAME is referred to as “FAME10” while coil-coating formulation with no FAME is referred to as “PE/Melamine”. 3. Methods 3.1. Synthetic procedures 3.1.1. Synthesis of epoxidized fatty acid methyl esters (e-FAMEs) The epoxy fatty methyl esters (e-FAME)s were retrieved from epoxidized linseed oil (ELO) by methanolysis as previously reported [44]. ELO (20 g) was dissolved in 250 mL of 0.02 M NaOH in methanol and set at reflux condition for 1 h. The obtained e-FAME were extracted in 4 x 100 mL n-heptane. The n-heptane phase was then dried over MgSO4 (s) and filtered. Solvent was then removed by rotary evaporator to give e-FAME with a yield of 75% (15 g). Automated column chromatography with gradient elution of n-heptane/ethyl acetate as mobile phase was used in order to purify the epoxy fatty methyl esters: epoxy methyl oleate (EMO), epoxy methyl linoleate (EMLO) and epoxy methyl linolenate (EMLEN) from e-FAME. Pure fractions of EMO, EMLO and EMLEN were used for the model studies. Where the original e-FAME mixture containing, methyl stearate, EMO, EMLO and EMLEN were used for coil-coating formulations. 3.1.2. Model reactions In order to determine occurrence and rate of the different reactions between e-FAME and non-FAME were model reactions performed by mixing LOH in a 1:1 M ratio with respective pure epoxy fatty methyl ester (EMO or EMLO or EMLEN). DDBSA was weighed to approximately 3 wt% of the total reactants amount and then added as a catalyst. The reactions of respective mixture was then monitored by in situ real-time FTIR measurements at 130 °C, 150 °C and 170 °C. 3.1.3. Curing of formulated clear coats Formulations with increasing amount of e-FAME mixed with PE/ Melamine were prepared (Table 1). The different formulations were Table 1 Samples of resin formulations and their respective physical properties obtained. Viscosity is measured on the resin formulations. The Tg, Pendulum test and Contact angle are obtained from cured coatings in laboratory scale at 170 °C. Sample name
Amount eFAME [wt.%]
Viscosity resin [Pa s]
Tg [°C]
Pendulum test [min]f
Contact Angle [°]d
a
0 0 5 10 15 20
3.5 1.9c 2.1 1.4 0.9 0.7
32 ± 2 28 ± s 26 ± 0 15 ± 1 −1 ± 1 0±2
2.88 2.60 2.61 2.21 1.23 0.19
88 ± 4 89 ± 2 90 ± 2 93 ± 2 99 ± 1 99 ± 1
FAME10 coilcoate e-FAME5 coilcoate e-FAME10 coilcoate
0b
N/A
26 ± 5
N/A
N/A
5
N/A
26 ± 2
N/A
N/A
10
N/A
20 ± 3
N/A
N/A
PE/Melamine FAME10 b e-FAME5 e-FAME10 e-FAME15 e-FAME20
2. Experimental 2.1. Materials Epoxidized linseed oil (ELO), fatty methyl esters (FAMEs) from rapeseed oil, two model coil-coating polyester/melamine (hexahydroxymethyl melamine (HMMM)) formulations were provided by PTE Coatings AB (SE-59431, Gamleby, Sweden). One formulation contains 10 wt% FAME and the second did not contain FAME. The polyester in the coil-coating formulations was hydroxyl functional with a hydroxyl value of 120.9 mg KOH/g resin, and acid value of 8 mg KOH/resin, and a molecular weight (Mw) of 4000 ± 500 g/mol. Lauryl alcohol (LOH) and p-dodecylbenzenesulfonic acid (DDBSA) were purchased from Sigma-Aldrich. Epoxy methyl oleate (EMO), Epoxy methyl linoleate
a
Coil-coating formulation without fatty methyl esters (FAMEs), b Coil-coating formulation with 10 wt% fatty methyl esters (FAMEs), c From ref [11], d On steel substrate; steel substrate without coating had contact angle 54 ± 2, e Samples from simulated coil-coating curing. These samples where cured on steel substrate at 220–240 °C peak metal temperature, f Performed on glass substrates with coatings thickness of approx. 150 μm. 2
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
spread on both glass and steel substrates using 60 μm or 150 μm applicators and then put in oven at 130 °C or 170 °C for 30 min. The curing of the resin formulations were also followed spectroscopically by in situ real-time FTIR measurements at 170 °C in the same way as for the model studies. The glass substrate samples with coating thickness of 150 μm and cured at 170 °C were used for pendulum hardness evaluation.
steady state constant viscosity i.e. low shear and frequency. 3.2.6. Simulated coil-coating curing The resins e-FAME5, e-FAME10 and FAME10 were cured on steel substrates for 30 s in a simulated coil-coating curing environment at peak metal temperature (PMT) of 220–240 °C. The curing occurred at PTE Coatings AB (SE-59431, Gamleby, Sweden) resembling pilot scale coil-coating curing.
3.2. Analytical methods and instruments 3.2.1. Fourier transform infrared spectroscopy (FTIR) and real-time FTIR For FTIR and real-time FTIR analysis a Perkin-Elmer spectrum 100 instrument was used equipped with an ATR accessory unit (Golden Gate) from Graseby Specac LTD (Kent, England). The Golden Gate unit was equipped with a temperature control (Specac, Heated Golden Gate Controller). The analysis occurred in a single reflection (attenuated total reflection (ATR) setup and the spectra were based on 8 scans averaged at 4.0 cm−1 resolution range of 600 – 4000 cm−1. The data was processed in Spectrum 10 software from Perkin-Elmer. For realtime FTIR measurements was the ATR crystal first pre-heated to set temperature and then a background spectra was recorded. A homogenous formulated sample was then placed directly on the ATR crystal as the real-time data acquisition started simultaneously. The temperature was kept constant during the measurement. The data were collected at an optimized rate of 1 scan per 5.4 s with a resolution of 4.0 cm−1 using TimeBase® software from Perkin-Elmer.
4. Results & discussion 4.1. Retrieval of the e-FAMEs from ELO Methanolysis of triglycerides utilizing Candida antarctica lipase B (CALB) has previously been studied and proved to be difficult due to e.g. glycerol inhibition [45] hence, leading to the choice of methanolysis of ELO in alkaline condition for this study. The alkaline condition provided means for breaking the ester bonds between the fatty chains and glycerol backbone. The glycerol and fatty methyl esters were then separated by extraction in n-heptane while glycerol retained in the methanol phase. Constituents from methanol phase was not used for this study it should however be noted that this phase contains large amount of glycerol. This implies that glycerol can be purified from the methanol phase and used in different applications such as cosmetics or pharmaceuticals. The yield of free epoxidized fatty acid methyl esters (e-FAME) after methanolysis was 75%. The crude mixture proved to be a mixture of 4 different products by TLC and after purification shown to be methyl stearate, epoxy methyl oleate (EMO), epoxy methyl linoleate (EMLO) and epoxy methyl linolenate (EMLEN) analyzed by NMR and FTIR (Fig. 1). NMR and FTIR of the pristine oils, ELO and e-FAME crude mixture, can be found in ESI (Figure S1 and S2).
3.2.2. Nuclear magnetic resonance (NMR) In order to obtain 1H NMR and 13C NMR spectra of the different compounds a Bruker spectrometer (400 MHz) was used. The data were recorded using 32 scans and a relaxation time of 1 s for 1H NMR and 256 scans and relaxation time of 5 s for 13C NMR. Deuterated chloroform (CDCl3) containing tetramethylsilane (TMS) was used to dilute the samples and the residual solvent peak of CDCl3 was used as reference (singlet at 7.26 ppm for 1H NMR and central line of triplet 77.16 ppm for 13C NMR). The obtained spectra were analyzed with MestReNova v9.0.0–12821 (Mestrelab Research S.L. 2013).
4.2. Model studies Model studies of EMO, EMLO and EMLEN respectively reacting with LOH were evaluated in 130 °C, 150 °C and 170 °C by in situ real-time FTIR. The different reactions were followed by observing the alcohol region (approximately 3500 cm−1), the carbonyl region (1750 – 1720 cm−1), the linear ether region (1100 – 1050 cm−1) and the epoxide ring-vibration (860 – 790 cm−1). To better visualize how the reactions occurred, time profiles were generated from the area under the curves over time for the respective region as seen in Fig. 2. The realtime FTIR data obtained showed that a higher temperature resulted in faster reaction rate in all systems. In addition, during the reactions at 150 °C and 170 °C it was observed that a transesterification reaction occurred first followed by ring-opening of an epoxide in all cases under set conditions. Reactions occurring at 130 °C resulted only in a transesterification reaction. In all reactions, transesterification was confirmed by the increase and shift in carbonyl region while a decrease in OH region occurred simultaneously indicating a reaction between the methyl ester of EMO/EMLO/EMLEN with the hydroxyl group on LOH. A ring-opening reaction of an epoxide in the reaction mixture could occur by either another epoxide or OH group acting as a nucleophile. Both these reactions result in formation of linear ether and secondary alcohol. This was observed by an increase in linear ether while a simultaneous decrease in epoxide region. As mentioned earlier, the OH profiles decreases at first followed by an increase. This behavior further confirms that at first the transesterification due to reaction with methyl ester occurs followed by epoxide ring-opening reaction i.e. formation of secondary alcohol groups. In addition, it was possible to qualitatively assess that by increasing the number of epoxides i.e. EMO < EMLO < EMLEN resulted in a decrease in transesterification rate.
3.2.3. Differential scanning calorimetry (DSC) DSC analysis were performed in order to obtain thermal properties of the coatings using a Mettler Toledo DSC-1 equipped with Gas Controller GC100. To analyze the cured coatings approximately 5–10 mg of each sample was measured into 100 μl aluminum crucibles. The data were collected using a heating/cooling rate of 10 °C min−1 from -50 to 200 °C with 5 min isotherms. All analyses were carried out in nitrogen gas of 20 mL min−1. Stare Excellence Software was used to evaluate the collected data. The glass transition (Tg) was acquired from the second heating scan and reported as the midpoint of the heat capacity change. 3.2.4. Pendulum test (ASTM standard D4366-16) Pendulum damping test (ASTM D4366-16) was followed in order to evaluate the hardness of the coatings. Glass substrates were coated and used for the evaluation. The thicknesses of the coatings were approximately 150 μm. 3.2.5. Rheometry Viscosity measurements were obtained from rheology measurements on a TA Instrument (New Castle, DE, USA) DHR-2 (Discovery Hybrid 2) equipped with a Peltier plate for temperature control. The temperature for the analysis was set to 30 °C. Approximately 0.5–1 mL of sample was placed on the Peltier plate and the parallel- plate geometry (60 mm) was used in all experiments while the gap was set to 0.5 mm. Sample trimming was made on samples exceeding parallelplate size. The viscosity was evaluated on flow sweep mode of scouting mission of torque 0–1000 μNm. The viscosity was reported from the 3
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
Fig. 1. 1H NMR and FTIR of the pure epoxidized fatty acid methyl esters, (A) EMO, (B) EMLO and (C) EMLEN.
4.3. Physical properties of the resin formulations
different resins, viscosity of the resin formulations where characterized by rheometry. Table 1 shows with increasing amount of e-FAME in the resin formulation a decrease in viscosity was obtained. The result shows that approximately 5 wt% e-FAME is needed to obtain similar flow properties to FAME10.
One of the properties desired for a good resin for coating applications is the ability to flow easily and form a uniform film when applied on a substrate. In addition, a reactive diluent should act both as a solvent and a reactant. In order to understand the flowing properties of the
Fig. 2. Real-time FTIR from model reactions at 130 °C (black), 150 °C (red) and 170 °C (blue). (A) shows EMO:LOH reaction, (B) shows EMLO:LOH reaction and (C) shows EMLEN:LOH reaction. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). 4
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
Fig. 3. FTIR analysis showing before and after reaction of lab cured sample e-FAME10.
4.4. Incorporation of reactive diluent e-FAME using laboratory oven and coil-coating simulation Model reactions of EMO, EMLO and EMLEN reacting with LOH proved that both transesterification and epoxide ring-opening reaction can occur at set temperatures of 150 °C and 170 °C. Furthermore, the reaction rates were increased by increasing the temperatures. During reactions under set temperature of 130 °C it was proved that only transesterification occurred. The curing performance of e-FAME mixed with polyester/melamine system where evaluated to understand if eFAME could be incorporated. The curing performance in laboratory scale was evaluated on both glass and steel substrate using a preheated oven. The temperatures evaluated were 130 °C and 170 °C for 30 min. All resin formulations had well spreading on both glass and steel and uniform films were obtained. However, tack-free clear coatings were only obtained from curing at 170 °C. Samples for FTIR were taken before and after curing (see Fig. 3). As previously mentioned model reactions predicted, the reaction was confirmed by the decrease in alcohols 3500 cm−1 while an increase and shift in carbonyl region (1750 – 1720 cm−1) indicating that a transesterification has occurred. In addition, the epoxides (860 – 790 cm−1) disappeared after the reaction while an increase in linear ether region (1100 – 1050 cm−1) was observed. For 130 °C the resins were left to cure for about 1 h, however tack-free coatings were not obtained. The curing performance of e-FAME5, e-FAME10 and FAME10 were evaluated on steel substrates in a simulated coil-coating curing at approximately 220–240 °C peak metal temperature for 30 s to give dry clear coats. FTIR analysis from before and after reaction can be found in ESI (Figure S3 – S5). The analysis revealed that the coil-coating simulated coatings were fully cured resembling FTIR results obtained from lab cured coatings and from model reactions. This was evidenced by the decrease in in alcohols 3500 cm−1 while a shift in carbonyl region (1750 – 1720 cm−1) indicating that a transesterification has occurred for all samples. In addition, for e-FAME5 and e-FAME10 a decrease in epoxide region were observed indicating that the epoxides react. Fig. 4 shows the thermal properties of fully cured coatings at 170 °C and from simulated coil-coating simulation. The DSC analysis of lab cured coatings proved that by increasing the amount of e-FAME a decreases in Tg was observed. Increasing the amount of e-FAME provides more aliphatic chains in the final structure hence, the decrease in Tg.
Fig. 4. DSC thermograms of cured samples from lab cured coatings at 170 °C and coil-coating simulation cured coatings at PMT 220–240 °C.
Interestingly, e-FAME5 and FAME10 had similar Tg’s, both from lab cured samples and from coil-coating simulations. These results implies that the e-FAME was more readily incorporated into the final cured coating compared to a FAME-diluent. The e-FAME is also less prone to oxidative degradation since the unsaturations are no longer present. 5. Conclusion The study showed that it was possible to utilize epoxidized fatty acid methyl esters (e-FAMEs) in coil-coating applications. Model experiments on RT-FTIR revealed that both a transesterification and epoxide ring-opening reaction occur during catalysis by DDBSA. The eFAMEs provided a diluting effect when they were added to the resin formulation. Resin formulation containing 5 wt% e-FAME showed most 5
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
promising results both as resin and coating i.e. resembling application and thermal properties as FAME10. The results from DSC suggested that e-FAME was more effective in the incorporation into the final coating compared to FAME-diluent.
10.1016/0300-9440(95)00533-1. [21] S. Creutz, R. Jerome, G.M.P. Kaptijn, A.W. Van Der Werf, J.M. Akkerman, Design of polymeric dispersants for waterborne coatings, J. Coat. Technol. 70 (1998) 41–46, https://doi.org/10.1007/BF02720518. [22] T.A. Misev, R. Van Der Linde, Powder coatings technology : new developments at the turn of the century, J. Coat. Technol. 34 (1998) 160–168. [23] P. Sundell, C. Miller, C. Hasselgren, S. Jönsson, Photoinitiator-Free, UV-Curable Powder Coatings for Coil Coating, Radnews, 1998. [24] G. Das, N. Karak, Epoxidized Mesua ferrea L. seed oil-based reactive diluent for BPA epoxy resin and their green nanocomposites, Prog. Org. Coat. 66 (2009) 59–64, https://doi.org/10.1016/j.porgcoat.2009.06.001. [25] Y. Xia, R.C. Larock, Vegetable oil-based polymeric materials: synthesis, properties, and applications, Green Chem. 12 (2010) 1893–1909, https://doi.org/10.1039/ c0gc00264j. [26] P. Muturi, D. Wang, S. Dirlikov, Epoxidized vegetable oils as reactive diluents I. Comparison of vernonia, epoxidized soybean and epoxidized linseed oils, Prog. Org. Coat. 25 (1994) 85–94, https://doi.org/10.1016/0300-9440(94)00504-4. [27] K. Johansson, M. Johansson, Fatty acid methyl ester as reactive diluent in thermally cured solvent-borne coil-coatings-The effect of fatty acid pattern on the curing performance and final properties, Prog. Org. Coat. 63 (2008) 155–159, https://doi. org/10.1016/j.porgcoat.2008.05.003. [28] W.R. Ashcroft, W.J. Cantwell, X.M. Chen, B. Ellis, G.P. Johari, F.R. Jones, H.H. Kausch, S.J. Shaw, Chemistry and Technology of Epoxy Resins, First, Springer Science & Business Media, 1993, https://doi.org/10.1007/978-94-011-2932-9. [29] X. Pan, P. Sengupta, D.C. Webster, High biobased content epoxy-anhydride thermosets from epoxidized sucrose esters of fatty acids, Biomacromolecules 12 (2011) 2416–2428, https://doi.org/10.1021/bm200549c. [30] S. Ma, X. Liu, Y. Jiang, Z. Tang, C. Zhang, J. Zhu, Bio-based epoxy resin from itaconic acid and its thermosets cured with anhydride and comonomers, Green Chem. 15 (2013) 245–254, https://doi.org/10.1039/c2gc36715g. [31] G.R. Palmese, R.L. McCullough, Effect of epoxy–amine stoichiometry on cured resin material properties, J. Appl. Polym. Sci. 46 (1992) 1863–1873, https://doi.org/10. 1002/app.1992.070461018. [32] S. Vyazovkin, N. Sbirrazzuoli, Mechanism and kinetics of epoxy-amine cure studied by differential scanning calorimetry, Macromolecules 29 (1996) 1867–1873, https://doi.org/10.1021/ma951162w. [33] P.E. Kolattukudy, K. Kronman, A.J. Poulose, Determination of structure and composition of suberin from the roots of carrot, parsnip, rutabaga, turnip, red beet, and sweet potato by combined gas-liquid chromatography and mass spectrometry, Plant Physiol. 55 (1974) 567–573, https://doi.org/10.1104/pp.55.3.567. [34] P.J. Holloway, A.H. Brown Deas, Epoxyoctadecanoic acids in plant cutins and suberins, Phytochemistry 12 (1973) 1721–1735, https://doi.org/10.1016/00319422(73)80393-0. [35] J. Samuelsson, M. Johansson, A study of fatty acid methyl esters with epoxy or alkyne functionalities, JAOCS J. Am. Oil Chem. Soc. 78 (2001) 1191–1196, https:// doi.org/10.1007/s11745-001-0412-y. [36] R.E. Perdue, K.D. Carlson, M.G. Gilbert, Vernonia galamensis, Potential new crop source of epoxy acid, Econ. Bot. 40 (1986) 54–68, https://doi.org/10.1007/ BF02858947. [37] T. Baye, H.C. Becker, S.V. Witzke-Ehbrecht, Vernonia galamensis, a natural source of epoxy oil: variation in fatty acid composition of seed and leaf lipids, Ind. Crops Prod. 21 (2005) 257–261, https://doi.org/10.1016/j.indcrop.2004.04.003. [38] J.V. Crivello, R. Narayan, Epoxidized triglycerides as renewable monomers in photoinitiated cationic polymerization, Chem. Mater. 4 (1992) 692–699, https:// doi.org/10.1021/cm00021a036. [39] S. Torron, S. Semlitsch, M. Martinelle, M. Johansson, Polymer thermosets from multifunctional polyester resins based on renewable monomers, Macromol. Chem. Phys. 215 (2014) 2198–2206, https://doi.org/10.1002/macp.201400192. [40] S. Torron, M. Johansson, Oxetane-terminated telechelic epoxy-functional polyesters as cationically polymerizable thermoset resins: tuning the reactivity with structural design, J. Polym. Sci. Part A: Polym. Chem. 53 (2015) 2258–2266, https://doi.org/ 10.1002/pola.27673. [41] B.R. Ekman, The Suberin Monomers and Triterpenoids from the Outer Bark of Betula verrucosa Ehrh. 37 (1983), pp. 205–211. [42] A. Gandini, C.P. Neto, A.J.D. Silvestre, Suberin : a promising renewable resource for novel macromolecular materials, Prog. Polym. Sci. 31 (2006) 878–892, https://doi. org/10.1016/j.progpolymsci.2006.07.004. [43] P.E. Kolattukudy, Polyesters in higher plants, Adv. Biochem. Eng. Biotechnol. 71 (2007) 1–49, https://doi.org/10.1007/3-540-40021-4_1. [44] S. Nameer, M. Johansson, Fully bio-based aliphatic thermoset polyesters via selfcatalyzed self-condensation of multifunctional epoxy monomers directly extracted from natural sources, J. Coat. Technol. Res. 14 (2017) 757–765, https://doi.org/10. 1007/s11998-017-9920-y. [45] S.N. Fedosov, J. Brask, A.K. Pedersen, M. Nordblad, J.M. Woodley, X. Xu, Kinetic model of biodiesel production using immobilized lipase Candida antarctica lipase B, J. Mol. Catal. B Enzym. 85–86 (2013) 156–168, https://doi.org/10.1016/j.molcatb. 2012.09.011.
Acknowledgements The authors wish to thank the Swedish research council, FORMAS (Grand number 211-2013-70) and SSAB EMEA for the support. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.porgcoat.2019. 105277. References [1] M.N. Belgacem, A. Gandini, Monomers, Polymers and Composites From Renewable Resources, Elsevier, Oxford, 2008http://www.polymerexpert.biz/ PolymersandComposites.html. [2] T. Werpy, G. Petersen, Top value added chemicals from biomass volume I — results of screening for potential candidates from sugars and synthesis gas top value added chemicals from biomass volume I : results of screening for potential candidates, U.S. Dep. Energy. 1 (2004), https://doi.org/10.2172/15008859. [3] A. Biswas, M. Roy, Green products: an exploratory study on the consumer behaviour in emerging economies of the East, J. Clean. Prod. 87 (2015) 463–468, https://doi. org/10.1016/J.JCLEPRO.2014.09.075. [4] M.A.R. Meier, J.O. Metzger, U.S. Schubert, Plant oil renewable resources as green alternatives in polymer science, Chem. Soc. Rev. 36 (2007) 1788, https://doi.org/ 10.1039/b703294c. [5] G. Lligadas, J.C. Ronda, M. Galià, V. Cádiz, Renewable polymeric materials from vegetable oils: a perspective, Mater. Today 16 (2013) 337–343, https://doi.org/10. 1016/J.MATTOD.2013.08.016. [6] K. Johansson, M. Johansson, A model study on fatty acid methyl esters as reactive diluents in thermally cured coil coating systems, Prog. Org. Coat. 55 (2006) 382–387, https://doi.org/10.1016/j.porgcoat.2006.02.002. [7] J.T.P. Derksen, F.P. Cuperus, P. Kolster, Paints and coatings from renewable resources, Ind. Crops Prod. 3 (1995) 225–236, https://doi.org/10.1016/09266690(94)00039-2. [8] B.K. Ahn, S. Kraft, D. Wang, X.S. Sun, Thermally stable, transparent, pressuresensitive adhesives from Epoxidized and dihydroxyl soybean oil, Biomacromolecules 12 (2011) 1839–1843, https://doi.org/10.1021/bm200188u. [9] S. Torron, D. Hult, T. Pettersson, M. Johansson, Tailoring Soft polymer networks based on sugars and fatty acids toward pressure sensitive adhesive applications, ACS Sustain. Chem. Eng. 5 (2017) 2632–2638, https://doi.org/10.1021/ acssuschemeng.6b02978. [10] M.A. Mosiewicki, M.I. Aranguren, A short review on novel biocomposites based on plant oil precursors, Eur. Polym. J. 49 (2013) 1243–1256, https://doi.org/10.1016/ J.EURPOLYMJ.2013.02.034. [11] K. Johansson, Thermally Cured Coil-Coatings Utilizing Novel Resins and Fatty Acid Methyl Esters As Reactive Diluents, Doctoral Thesis, Stockholm, Sweden, (2008). [12] M. Johansson, M. Svensson, P.-E. Sundell, Method for Production of Thermally Cured Coatings, US7799386B2 (2004). [13] R. Moyle, J. Soltwedel, Coating Composition and Metal Coil Coating Process Employing Same, EP0551727A1 (1992). [14] Z.W.J. Wicks, F.N. Jones, P.S. Pappas, D.A. Wicks, Organic Coatings Science and Technology, 3rd ed., John Wiley & Sons, INC, 2007. [15] M. De Meijer, Review on the durability of exterior wood coatings with reduced VOC-content, Prog. Org. Coat. 43 (2001) 217–225. [16] J. Lindeboom, Air-drying high solids alkyd pants for decorative coatings, Prog. Org. Coat. 34 (1997) 147–151, https://doi.org/10.1016/S0300-9440(98)00034-4. [17] S.P. Pappas, Radiation Curing: Science and Technology, Springer Science & Business Media, 2013. [18] H. Fagerholm, A. Ranta-Eskola, M. Hautala, C. Filhaut, P.-E. Sundell, M. Ferreira, Multilayer coatings with improved performance for construction applications, Eur. Comm. Tech. Steel Res. (2002) 1–145. [19] B.-J. Skrifvars, P.-E. Sundell, M. Schatzl, K. Ahvonen, M. Heylen, P. Keil, Space Efficient Curing Methods and Simulation-aided Coating Engineering for Extending Lifetime of Aesthetic Coil Coatings, Eur. Comm. Tech. Steel Res. (2019) n.d.. [20] T. Nabuurs, R.A. Baijards, A.L. German, Alkyd-acrylic hybrid systems for use as binders in waterborne paints, Prog. Org. Coat. 27 (1996) 163–172, https://doi.org/
6
Contents lists available at ScienceDirect
Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat
Bio-based multifunctional fatty acid methyl esters as reactive diluents in coil coatings
T
Sameer Nameera, Tomas Deltinb, Per-Erik Sundellc, Mats Johanssona,1,⁎ a
KTH Royal Institute of Technology, School of Engineering Sciences in Chemistry, Biotechnology and Health, Department of Fibre and Polymer Technology, Division of Coating Technology, SE-100 44 Stockholm, Sweden b PTE Coatings AB, SE-594 31, Gamleby, Sweden c SSAB EMEA, SE-781 84, Borlänge, Sweden
ARTICLE INFO
ABSTRACT
Keywords: Coil-coatings Vegetable oil Epoxidized fatty acid methyl esters Protective coatings Renewable resources
The increased environmental awareness has driven academia and industry to utilize environmentally benign sources. An industrially available process that is effective in the coatings industry is the coil-coating process where sheet steel can be pre-coated. During this process volatile organic compounds (VOCs) are generated and incinerated for energy recovery. One way to minimize VOCs is to use a reactive diluent i.e. a molecule that acts both as a solvent as well as chemically react into the final coating upon curing. Fatty acid methyl esters obtained from renewable resources such as vegetable oils are suitable candidates as reactive diluents. In this paper epoxidized fatty acid methyl esters (e-FAMEs) obtained from epoxidized linseed oil where compared with fatty acid methyl esters (FAMEs) obtained from rapeseed oil as reactive diluents in coil-coating formulations. Coilcoating formulations were followed by real-time Fourier transform infrared spectroscopy (RT-FTIR) in order to evaluate the e-FAMEs or the FAMEs reactivity in the coating system. In addition, coil-coating formulation containing e-FAME or FAME where cured in a pilot scale simulated coil-coating process. Moreover, thermal properties of the final coatings were evaluated by differential scanning calorimetry (DSC).
1. Introduction In the past few decades there has been an increasing interest of utilizing renewable and sustainable resources due to concerns regarding environment, waste disposal and fossil fuel depletion [1]. Renewable resources are considered as a potential platform to provide new building blocks for the chemical and materials industry [2]. Furthermore, not only the industry is shifting to more sustainable alternatives the final consumers and society in general are more aware of what they buy and demand sustainable alternatives [3]. One interesting renewable resource used in polymeric materials is vegetable oils due to their low cost, natural abundance, and variability [4,5]. Vegetable oils have for a long time been used in the production many different types of product groups e.g. coatings [6], paints [7], adhesives [8,9], composites and hybrid materials [10] just to mention a few. Another sustainability aspect is not only to use renewable resources but also to employ production processes that are efficient with a minimal negative fossil carbon footprint as well as a minimum of emissions from the process.
One of these processes that address some of these aspects in the field of organic coatings is pre-coated sheet steel i.e. coil coatings. The coil-coating process is a continuous industrial coating process used to efficiently coat sheet metal with an organic coating to form coated steel coils. The coated metal coil can subsequently be used for numerous applications such as roofing, water management systems, etc [11–13]. Compared to traditional on-site painting of exterior built steel constructions this is advantageous both from a cost perspective and from an environmental aspects since direct emissions of VOC is avoided [14]. Traditionally the coating formulation is a solvent-borne liquid coating that dries through evaporation and chemical crosslinking in a convection oven. A typical coil coating process utilizes high temperature convection ovens to reach a peak metal temperature (PMT) of 230–240 °C to allow for a full cure to be obtained in less than a minute. However, during curing a vast amount of volatile organic compounds (VOCs) are generated which is incinerated for energy recovery and used to aid the energy balance of the oven [11]. The main emission is thus CO2 rather than VOC but it is still desirable to find other alternatives or ways to reduce these CO2 emissions [15,16]. Several
Corresponding author. E-mail address: [email protected] (M. Johansson). 1 The corresponding author Professor Mats Johansson is the Editor-in-Chief of this journal but he had no role in the assessment of this work. The initial assessment, peer review process and the assessment of the revision was managed independently by Dr Marcel Piens who serves as an Editor on this journal. ⁎
https://doi.org/10.1016/j.porgcoat.2019.105277 Received 20 June 2019; Received in revised form 30 July 2019; Accepted 12 August 2019 Available online 20 August 2019 0300-9440/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
technologies have been considered as alternative to solvent-borne thermally curing of sheet metals e.g. UV-curable systems [17–19], water-borne coating formulations [20,21], powder coatings [22,23]. However, most of these methods have some drawbacks e.g. clean-up difficulties due to color change and high cost of modifying the production facilities. Another way to exclude VOCs (or subsequent fossil-based CO2 formation) in coating formulations is to increase the solid content by e.g. adding a reactive diluent [24–26]. A reactive diluent is a molecule that can both act as a diluting solvent as well as chemically react into the final coating during curing thus becoming a part of the final coating. In order to fulfill these demands the reactive diluent should have low viscosity, be compatible with the other components and have reactive functional groups suitable for the specific crosslinking chemistry used [24]. Previous studies on coilcoating systems [6,27] have shown that a suitable candidate for this is fatty acid methyl esters (FAMEs) that can be utilized as renewable and sustainable reactive diluents in polyester/melamine based coil coatings. FAMEs provides a decrease in viscosity when mixed into the formulation thus reducing the need for conventional organic solvents. The acyl group of the methyl ester furthermore allow for a transesterification between the FAME and the polyester to occur leading to an incorporation of the FAME into the dry film [11,12]. An important conclusion for this system was also that the FAME under typical coil coating curing conditions either reacted into the film or evaporated but it did not remain as a non-reacted plasticizer in the film hence a good long term performance could be obtained. The epoxy functional group have a central role in resin formulations for coatings application due to its ring-strain making it suitable for reaction in both acidic and basic conditions [28]. Epoxides have high reactivity to numerous functional groups including anhydrides [29,30], amines [31,32] and carboxylic acids [9]. Naturally formed epoxides can be found as building-blocks in renewable resources. One such example are epoxidized fatty acids which can be found in natural sources such as suberin and cutin [1,33,34] or Euphorbia lagascae and Vernonia galamensis [26,35–37]. Epoxidized fatty acids have previously been applied in resin formulations for coatings e.g. as sucrose based epoxy fatty acids [29] or as photo-cured resin systems [38–40]. Although significant steps towards more sustainable coil coating systems have been demonstrated there are still challenges to address such as increasing overall non-fossil content of the system, less energy consumption and increased life time of the final product. The present paper describes one way to address these challenges by an introduction of additional functionalities in the FAME that further improve the performance of these diluents in coil coatings. Epoxidized fatty acid methyl esters (eFAMEs) are demonstrated to introduce additional positive features such as higher degree of incorporation into the final films and an enhanced curing performance. Epoxidized vegetable oils are readily available on the market and easy to transform into methyl esters in the same way as vegetable oil based biodiesel is made. It is moreover notable that this type of fatty acid epoxide structures is abundant in nature [1], although at present not retrieved commercially to any significant extent. Epoxy functional omegahydroxyl fatty acids can for example be found in large amount in suberin from Birch tree bark [41,42] and in the cutin tissue [34,43].
(EMLO) and Epoxy methyl linolenate (EMLEN) were retrieved from ELO as described below. Hot dip galvanized (HDG) steel substrates were provided by SSAB EMEA (SE-781 84 Borlänge, Sweden). All materials where used as received In order for the reader to follow the text easier the coil-coating formulations were referred to as follows: Coil-coating formulation that contains 10 wt% FAME is referred to as “FAME10” while coil-coating formulation with no FAME is referred to as “PE/Melamine”. 3. Methods 3.1. Synthetic procedures 3.1.1. Synthesis of epoxidized fatty acid methyl esters (e-FAMEs) The epoxy fatty methyl esters (e-FAME)s were retrieved from epoxidized linseed oil (ELO) by methanolysis as previously reported [44]. ELO (20 g) was dissolved in 250 mL of 0.02 M NaOH in methanol and set at reflux condition for 1 h. The obtained e-FAME were extracted in 4 x 100 mL n-heptane. The n-heptane phase was then dried over MgSO4 (s) and filtered. Solvent was then removed by rotary evaporator to give e-FAME with a yield of 75% (15 g). Automated column chromatography with gradient elution of n-heptane/ethyl acetate as mobile phase was used in order to purify the epoxy fatty methyl esters: epoxy methyl oleate (EMO), epoxy methyl linoleate (EMLO) and epoxy methyl linolenate (EMLEN) from e-FAME. Pure fractions of EMO, EMLO and EMLEN were used for the model studies. Where the original e-FAME mixture containing, methyl stearate, EMO, EMLO and EMLEN were used for coil-coating formulations. 3.1.2. Model reactions In order to determine occurrence and rate of the different reactions between e-FAME and non-FAME were model reactions performed by mixing LOH in a 1:1 M ratio with respective pure epoxy fatty methyl ester (EMO or EMLO or EMLEN). DDBSA was weighed to approximately 3 wt% of the total reactants amount and then added as a catalyst. The reactions of respective mixture was then monitored by in situ real-time FTIR measurements at 130 °C, 150 °C and 170 °C. 3.1.3. Curing of formulated clear coats Formulations with increasing amount of e-FAME mixed with PE/ Melamine were prepared (Table 1). The different formulations were Table 1 Samples of resin formulations and their respective physical properties obtained. Viscosity is measured on the resin formulations. The Tg, Pendulum test and Contact angle are obtained from cured coatings in laboratory scale at 170 °C. Sample name
Amount eFAME [wt.%]
Viscosity resin [Pa s]
Tg [°C]
Pendulum test [min]f
Contact Angle [°]d
a
0 0 5 10 15 20
3.5 1.9c 2.1 1.4 0.9 0.7
32 ± 2 28 ± s 26 ± 0 15 ± 1 −1 ± 1 0±2
2.88 2.60 2.61 2.21 1.23 0.19
88 ± 4 89 ± 2 90 ± 2 93 ± 2 99 ± 1 99 ± 1
FAME10 coilcoate e-FAME5 coilcoate e-FAME10 coilcoate
0b
N/A
26 ± 5
N/A
N/A
5
N/A
26 ± 2
N/A
N/A
10
N/A
20 ± 3
N/A
N/A
PE/Melamine FAME10 b e-FAME5 e-FAME10 e-FAME15 e-FAME20
2. Experimental 2.1. Materials Epoxidized linseed oil (ELO), fatty methyl esters (FAMEs) from rapeseed oil, two model coil-coating polyester/melamine (hexahydroxymethyl melamine (HMMM)) formulations were provided by PTE Coatings AB (SE-59431, Gamleby, Sweden). One formulation contains 10 wt% FAME and the second did not contain FAME. The polyester in the coil-coating formulations was hydroxyl functional with a hydroxyl value of 120.9 mg KOH/g resin, and acid value of 8 mg KOH/resin, and a molecular weight (Mw) of 4000 ± 500 g/mol. Lauryl alcohol (LOH) and p-dodecylbenzenesulfonic acid (DDBSA) were purchased from Sigma-Aldrich. Epoxy methyl oleate (EMO), Epoxy methyl linoleate
a
Coil-coating formulation without fatty methyl esters (FAMEs), b Coil-coating formulation with 10 wt% fatty methyl esters (FAMEs), c From ref [11], d On steel substrate; steel substrate without coating had contact angle 54 ± 2, e Samples from simulated coil-coating curing. These samples where cured on steel substrate at 220–240 °C peak metal temperature, f Performed on glass substrates with coatings thickness of approx. 150 μm. 2
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
spread on both glass and steel substrates using 60 μm or 150 μm applicators and then put in oven at 130 °C or 170 °C for 30 min. The curing of the resin formulations were also followed spectroscopically by in situ real-time FTIR measurements at 170 °C in the same way as for the model studies. The glass substrate samples with coating thickness of 150 μm and cured at 170 °C were used for pendulum hardness evaluation.
steady state constant viscosity i.e. low shear and frequency. 3.2.6. Simulated coil-coating curing The resins e-FAME5, e-FAME10 and FAME10 were cured on steel substrates for 30 s in a simulated coil-coating curing environment at peak metal temperature (PMT) of 220–240 °C. The curing occurred at PTE Coatings AB (SE-59431, Gamleby, Sweden) resembling pilot scale coil-coating curing.
3.2. Analytical methods and instruments 3.2.1. Fourier transform infrared spectroscopy (FTIR) and real-time FTIR For FTIR and real-time FTIR analysis a Perkin-Elmer spectrum 100 instrument was used equipped with an ATR accessory unit (Golden Gate) from Graseby Specac LTD (Kent, England). The Golden Gate unit was equipped with a temperature control (Specac, Heated Golden Gate Controller). The analysis occurred in a single reflection (attenuated total reflection (ATR) setup and the spectra were based on 8 scans averaged at 4.0 cm−1 resolution range of 600 – 4000 cm−1. The data was processed in Spectrum 10 software from Perkin-Elmer. For realtime FTIR measurements was the ATR crystal first pre-heated to set temperature and then a background spectra was recorded. A homogenous formulated sample was then placed directly on the ATR crystal as the real-time data acquisition started simultaneously. The temperature was kept constant during the measurement. The data were collected at an optimized rate of 1 scan per 5.4 s with a resolution of 4.0 cm−1 using TimeBase® software from Perkin-Elmer.
4. Results & discussion 4.1. Retrieval of the e-FAMEs from ELO Methanolysis of triglycerides utilizing Candida antarctica lipase B (CALB) has previously been studied and proved to be difficult due to e.g. glycerol inhibition [45] hence, leading to the choice of methanolysis of ELO in alkaline condition for this study. The alkaline condition provided means for breaking the ester bonds between the fatty chains and glycerol backbone. The glycerol and fatty methyl esters were then separated by extraction in n-heptane while glycerol retained in the methanol phase. Constituents from methanol phase was not used for this study it should however be noted that this phase contains large amount of glycerol. This implies that glycerol can be purified from the methanol phase and used in different applications such as cosmetics or pharmaceuticals. The yield of free epoxidized fatty acid methyl esters (e-FAME) after methanolysis was 75%. The crude mixture proved to be a mixture of 4 different products by TLC and after purification shown to be methyl stearate, epoxy methyl oleate (EMO), epoxy methyl linoleate (EMLO) and epoxy methyl linolenate (EMLEN) analyzed by NMR and FTIR (Fig. 1). NMR and FTIR of the pristine oils, ELO and e-FAME crude mixture, can be found in ESI (Figure S1 and S2).
3.2.2. Nuclear magnetic resonance (NMR) In order to obtain 1H NMR and 13C NMR spectra of the different compounds a Bruker spectrometer (400 MHz) was used. The data were recorded using 32 scans and a relaxation time of 1 s for 1H NMR and 256 scans and relaxation time of 5 s for 13C NMR. Deuterated chloroform (CDCl3) containing tetramethylsilane (TMS) was used to dilute the samples and the residual solvent peak of CDCl3 was used as reference (singlet at 7.26 ppm for 1H NMR and central line of triplet 77.16 ppm for 13C NMR). The obtained spectra were analyzed with MestReNova v9.0.0–12821 (Mestrelab Research S.L. 2013).
4.2. Model studies Model studies of EMO, EMLO and EMLEN respectively reacting with LOH were evaluated in 130 °C, 150 °C and 170 °C by in situ real-time FTIR. The different reactions were followed by observing the alcohol region (approximately 3500 cm−1), the carbonyl region (1750 – 1720 cm−1), the linear ether region (1100 – 1050 cm−1) and the epoxide ring-vibration (860 – 790 cm−1). To better visualize how the reactions occurred, time profiles were generated from the area under the curves over time for the respective region as seen in Fig. 2. The realtime FTIR data obtained showed that a higher temperature resulted in faster reaction rate in all systems. In addition, during the reactions at 150 °C and 170 °C it was observed that a transesterification reaction occurred first followed by ring-opening of an epoxide in all cases under set conditions. Reactions occurring at 130 °C resulted only in a transesterification reaction. In all reactions, transesterification was confirmed by the increase and shift in carbonyl region while a decrease in OH region occurred simultaneously indicating a reaction between the methyl ester of EMO/EMLO/EMLEN with the hydroxyl group on LOH. A ring-opening reaction of an epoxide in the reaction mixture could occur by either another epoxide or OH group acting as a nucleophile. Both these reactions result in formation of linear ether and secondary alcohol. This was observed by an increase in linear ether while a simultaneous decrease in epoxide region. As mentioned earlier, the OH profiles decreases at first followed by an increase. This behavior further confirms that at first the transesterification due to reaction with methyl ester occurs followed by epoxide ring-opening reaction i.e. formation of secondary alcohol groups. In addition, it was possible to qualitatively assess that by increasing the number of epoxides i.e. EMO < EMLO < EMLEN resulted in a decrease in transesterification rate.
3.2.3. Differential scanning calorimetry (DSC) DSC analysis were performed in order to obtain thermal properties of the coatings using a Mettler Toledo DSC-1 equipped with Gas Controller GC100. To analyze the cured coatings approximately 5–10 mg of each sample was measured into 100 μl aluminum crucibles. The data were collected using a heating/cooling rate of 10 °C min−1 from -50 to 200 °C with 5 min isotherms. All analyses were carried out in nitrogen gas of 20 mL min−1. Stare Excellence Software was used to evaluate the collected data. The glass transition (Tg) was acquired from the second heating scan and reported as the midpoint of the heat capacity change. 3.2.4. Pendulum test (ASTM standard D4366-16) Pendulum damping test (ASTM D4366-16) was followed in order to evaluate the hardness of the coatings. Glass substrates were coated and used for the evaluation. The thicknesses of the coatings were approximately 150 μm. 3.2.5. Rheometry Viscosity measurements were obtained from rheology measurements on a TA Instrument (New Castle, DE, USA) DHR-2 (Discovery Hybrid 2) equipped with a Peltier plate for temperature control. The temperature for the analysis was set to 30 °C. Approximately 0.5–1 mL of sample was placed on the Peltier plate and the parallel- plate geometry (60 mm) was used in all experiments while the gap was set to 0.5 mm. Sample trimming was made on samples exceeding parallelplate size. The viscosity was evaluated on flow sweep mode of scouting mission of torque 0–1000 μNm. The viscosity was reported from the 3
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
Fig. 1. 1H NMR and FTIR of the pure epoxidized fatty acid methyl esters, (A) EMO, (B) EMLO and (C) EMLEN.
4.3. Physical properties of the resin formulations
different resins, viscosity of the resin formulations where characterized by rheometry. Table 1 shows with increasing amount of e-FAME in the resin formulation a decrease in viscosity was obtained. The result shows that approximately 5 wt% e-FAME is needed to obtain similar flow properties to FAME10.
One of the properties desired for a good resin for coating applications is the ability to flow easily and form a uniform film when applied on a substrate. In addition, a reactive diluent should act both as a solvent and a reactant. In order to understand the flowing properties of the
Fig. 2. Real-time FTIR from model reactions at 130 °C (black), 150 °C (red) and 170 °C (blue). (A) shows EMO:LOH reaction, (B) shows EMLO:LOH reaction and (C) shows EMLEN:LOH reaction. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article). 4
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
Fig. 3. FTIR analysis showing before and after reaction of lab cured sample e-FAME10.
4.4. Incorporation of reactive diluent e-FAME using laboratory oven and coil-coating simulation Model reactions of EMO, EMLO and EMLEN reacting with LOH proved that both transesterification and epoxide ring-opening reaction can occur at set temperatures of 150 °C and 170 °C. Furthermore, the reaction rates were increased by increasing the temperatures. During reactions under set temperature of 130 °C it was proved that only transesterification occurred. The curing performance of e-FAME mixed with polyester/melamine system where evaluated to understand if eFAME could be incorporated. The curing performance in laboratory scale was evaluated on both glass and steel substrate using a preheated oven. The temperatures evaluated were 130 °C and 170 °C for 30 min. All resin formulations had well spreading on both glass and steel and uniform films were obtained. However, tack-free clear coatings were only obtained from curing at 170 °C. Samples for FTIR were taken before and after curing (see Fig. 3). As previously mentioned model reactions predicted, the reaction was confirmed by the decrease in alcohols 3500 cm−1 while an increase and shift in carbonyl region (1750 – 1720 cm−1) indicating that a transesterification has occurred. In addition, the epoxides (860 – 790 cm−1) disappeared after the reaction while an increase in linear ether region (1100 – 1050 cm−1) was observed. For 130 °C the resins were left to cure for about 1 h, however tack-free coatings were not obtained. The curing performance of e-FAME5, e-FAME10 and FAME10 were evaluated on steel substrates in a simulated coil-coating curing at approximately 220–240 °C peak metal temperature for 30 s to give dry clear coats. FTIR analysis from before and after reaction can be found in ESI (Figure S3 – S5). The analysis revealed that the coil-coating simulated coatings were fully cured resembling FTIR results obtained from lab cured coatings and from model reactions. This was evidenced by the decrease in in alcohols 3500 cm−1 while a shift in carbonyl region (1750 – 1720 cm−1) indicating that a transesterification has occurred for all samples. In addition, for e-FAME5 and e-FAME10 a decrease in epoxide region were observed indicating that the epoxides react. Fig. 4 shows the thermal properties of fully cured coatings at 170 °C and from simulated coil-coating simulation. The DSC analysis of lab cured coatings proved that by increasing the amount of e-FAME a decreases in Tg was observed. Increasing the amount of e-FAME provides more aliphatic chains in the final structure hence, the decrease in Tg.
Fig. 4. DSC thermograms of cured samples from lab cured coatings at 170 °C and coil-coating simulation cured coatings at PMT 220–240 °C.
Interestingly, e-FAME5 and FAME10 had similar Tg’s, both from lab cured samples and from coil-coating simulations. These results implies that the e-FAME was more readily incorporated into the final cured coating compared to a FAME-diluent. The e-FAME is also less prone to oxidative degradation since the unsaturations are no longer present. 5. Conclusion The study showed that it was possible to utilize epoxidized fatty acid methyl esters (e-FAMEs) in coil-coating applications. Model experiments on RT-FTIR revealed that both a transesterification and epoxide ring-opening reaction occur during catalysis by DDBSA. The eFAMEs provided a diluting effect when they were added to the resin formulation. Resin formulation containing 5 wt% e-FAME showed most 5
Progress in Organic Coatings 136 (2019) 105277
S. Nameer, et al.
promising results both as resin and coating i.e. resembling application and thermal properties as FAME10. The results from DSC suggested that e-FAME was more effective in the incorporation into the final coating compared to FAME-diluent.
10.1016/0300-9440(95)00533-1. [21] S. Creutz, R. Jerome, G.M.P. Kaptijn, A.W. Van Der Werf, J.M. Akkerman, Design of polymeric dispersants for waterborne coatings, J. Coat. Technol. 70 (1998) 41–46, https://doi.org/10.1007/BF02720518. [22] T.A. Misev, R. Van Der Linde, Powder coatings technology : new developments at the turn of the century, J. Coat. Technol. 34 (1998) 160–168. [23] P. Sundell, C. Miller, C. Hasselgren, S. Jönsson, Photoinitiator-Free, UV-Curable Powder Coatings for Coil Coating, Radnews, 1998. [24] G. Das, N. Karak, Epoxidized Mesua ferrea L. seed oil-based reactive diluent for BPA epoxy resin and their green nanocomposites, Prog. Org. Coat. 66 (2009) 59–64, https://doi.org/10.1016/j.porgcoat.2009.06.001. [25] Y. Xia, R.C. Larock, Vegetable oil-based polymeric materials: synthesis, properties, and applications, Green Chem. 12 (2010) 1893–1909, https://doi.org/10.1039/ c0gc00264j. [26] P. Muturi, D. Wang, S. Dirlikov, Epoxidized vegetable oils as reactive diluents I. Comparison of vernonia, epoxidized soybean and epoxidized linseed oils, Prog. Org. Coat. 25 (1994) 85–94, https://doi.org/10.1016/0300-9440(94)00504-4. [27] K. Johansson, M. Johansson, Fatty acid methyl ester as reactive diluent in thermally cured solvent-borne coil-coatings-The effect of fatty acid pattern on the curing performance and final properties, Prog. Org. Coat. 63 (2008) 155–159, https://doi. org/10.1016/j.porgcoat.2008.05.003. [28] W.R. Ashcroft, W.J. Cantwell, X.M. Chen, B. Ellis, G.P. Johari, F.R. Jones, H.H. Kausch, S.J. Shaw, Chemistry and Technology of Epoxy Resins, First, Springer Science & Business Media, 1993, https://doi.org/10.1007/978-94-011-2932-9. [29] X. Pan, P. Sengupta, D.C. Webster, High biobased content epoxy-anhydride thermosets from epoxidized sucrose esters of fatty acids, Biomacromolecules 12 (2011) 2416–2428, https://doi.org/10.1021/bm200549c. [30] S. Ma, X. Liu, Y. Jiang, Z. Tang, C. Zhang, J. Zhu, Bio-based epoxy resin from itaconic acid and its thermosets cured with anhydride and comonomers, Green Chem. 15 (2013) 245–254, https://doi.org/10.1039/c2gc36715g. [31] G.R. Palmese, R.L. McCullough, Effect of epoxy–amine stoichiometry on cured resin material properties, J. Appl. Polym. Sci. 46 (1992) 1863–1873, https://doi.org/10. 1002/app.1992.070461018. [32] S. Vyazovkin, N. Sbirrazzuoli, Mechanism and kinetics of epoxy-amine cure studied by differential scanning calorimetry, Macromolecules 29 (1996) 1867–1873, https://doi.org/10.1021/ma951162w. [33] P.E. Kolattukudy, K. Kronman, A.J. Poulose, Determination of structure and composition of suberin from the roots of carrot, parsnip, rutabaga, turnip, red beet, and sweet potato by combined gas-liquid chromatography and mass spectrometry, Plant Physiol. 55 (1974) 567–573, https://doi.org/10.1104/pp.55.3.567. [34] P.J. Holloway, A.H. Brown Deas, Epoxyoctadecanoic acids in plant cutins and suberins, Phytochemistry 12 (1973) 1721–1735, https://doi.org/10.1016/00319422(73)80393-0. [35] J. Samuelsson, M. Johansson, A study of fatty acid methyl esters with epoxy or alkyne functionalities, JAOCS J. Am. Oil Chem. Soc. 78 (2001) 1191–1196, https:// doi.org/10.1007/s11745-001-0412-y. [36] R.E. Perdue, K.D. Carlson, M.G. Gilbert, Vernonia galamensis, Potential new crop source of epoxy acid, Econ. Bot. 40 (1986) 54–68, https://doi.org/10.1007/ BF02858947. [37] T. Baye, H.C. Becker, S.V. Witzke-Ehbrecht, Vernonia galamensis, a natural source of epoxy oil: variation in fatty acid composition of seed and leaf lipids, Ind. Crops Prod. 21 (2005) 257–261, https://doi.org/10.1016/j.indcrop.2004.04.003. [38] J.V. Crivello, R. Narayan, Epoxidized triglycerides as renewable monomers in photoinitiated cationic polymerization, Chem. Mater. 4 (1992) 692–699, https:// doi.org/10.1021/cm00021a036. [39] S. Torron, S. Semlitsch, M. Martinelle, M. Johansson, Polymer thermosets from multifunctional polyester resins based on renewable monomers, Macromol. Chem. Phys. 215 (2014) 2198–2206, https://doi.org/10.1002/macp.201400192. [40] S. Torron, M. Johansson, Oxetane-terminated telechelic epoxy-functional polyesters as cationically polymerizable thermoset resins: tuning the reactivity with structural design, J. Polym. Sci. Part A: Polym. Chem. 53 (2015) 2258–2266, https://doi.org/ 10.1002/pola.27673. [41] B.R. Ekman, The Suberin Monomers and Triterpenoids from the Outer Bark of Betula verrucosa Ehrh. 37 (1983), pp. 205–211. [42] A. Gandini, C.P. Neto, A.J.D. Silvestre, Suberin : a promising renewable resource for novel macromolecular materials, Prog. Polym. Sci. 31 (2006) 878–892, https://doi. org/10.1016/j.progpolymsci.2006.07.004. [43] P.E. Kolattukudy, Polyesters in higher plants, Adv. Biochem. Eng. Biotechnol. 71 (2007) 1–49, https://doi.org/10.1007/3-540-40021-4_1. [44] S. Nameer, M. Johansson, Fully bio-based aliphatic thermoset polyesters via selfcatalyzed self-condensation of multifunctional epoxy monomers directly extracted from natural sources, J. Coat. Technol. Res. 14 (2017) 757–765, https://doi.org/10. 1007/s11998-017-9920-y. [45] S.N. Fedosov, J. Brask, A.K. Pedersen, M. Nordblad, J.M. Woodley, X. Xu, Kinetic model of biodiesel production using immobilized lipase Candida antarctica lipase B, J. Mol. Catal. B Enzym. 85–86 (2013) 156–168, https://doi.org/10.1016/j.molcatb. 2012.09.011.
Acknowledgements The authors wish to thank the Swedish research council, FORMAS (Grand number 211-2013-70) and SSAB EMEA for the support. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.porgcoat.2019. 105277. References [1] M.N. Belgacem, A. Gandini, Monomers, Polymers and Composites From Renewable Resources, Elsevier, Oxford, 2008http://www.polymerexpert.biz/ PolymersandComposites.html. [2] T. Werpy, G. Petersen, Top value added chemicals from biomass volume I — results of screening for potential candidates from sugars and synthesis gas top value added chemicals from biomass volume I : results of screening for potential candidates, U.S. Dep. Energy. 1 (2004), https://doi.org/10.2172/15008859. [3] A. Biswas, M. Roy, Green products: an exploratory study on the consumer behaviour in emerging economies of the East, J. Clean. Prod. 87 (2015) 463–468, https://doi. org/10.1016/J.JCLEPRO.2014.09.075. [4] M.A.R. Meier, J.O. Metzger, U.S. Schubert, Plant oil renewable resources as green alternatives in polymer science, Chem. Soc. Rev. 36 (2007) 1788, https://doi.org/ 10.1039/b703294c. [5] G. Lligadas, J.C. Ronda, M. Galià, V. Cádiz, Renewable polymeric materials from vegetable oils: a perspective, Mater. Today 16 (2013) 337–343, https://doi.org/10. 1016/J.MATTOD.2013.08.016. [6] K. Johansson, M. Johansson, A model study on fatty acid methyl esters as reactive diluents in thermally cured coil coating systems, Prog. Org. Coat. 55 (2006) 382–387, https://doi.org/10.1016/j.porgcoat.2006.02.002. [7] J.T.P. Derksen, F.P. Cuperus, P. Kolster, Paints and coatings from renewable resources, Ind. Crops Prod. 3 (1995) 225–236, https://doi.org/10.1016/09266690(94)00039-2. [8] B.K. Ahn, S. Kraft, D. Wang, X.S. Sun, Thermally stable, transparent, pressuresensitive adhesives from Epoxidized and dihydroxyl soybean oil, Biomacromolecules 12 (2011) 1839–1843, https://doi.org/10.1021/bm200188u. [9] S. Torron, D. Hult, T. Pettersson, M. Johansson, Tailoring Soft polymer networks based on sugars and fatty acids toward pressure sensitive adhesive applications, ACS Sustain. Chem. Eng. 5 (2017) 2632–2638, https://doi.org/10.1021/ acssuschemeng.6b02978. [10] M.A. Mosiewicki, M.I. Aranguren, A short review on novel biocomposites based on plant oil precursors, Eur. Polym. J. 49 (2013) 1243–1256, https://doi.org/10.1016/ J.EURPOLYMJ.2013.02.034. [11] K. Johansson, Thermally Cured Coil-Coatings Utilizing Novel Resins and Fatty Acid Methyl Esters As Reactive Diluents, Doctoral Thesis, Stockholm, Sweden, (2008). [12] M. Johansson, M. Svensson, P.-E. Sundell, Method for Production of Thermally Cured Coatings, US7799386B2 (2004). [13] R. Moyle, J. Soltwedel, Coating Composition and Metal Coil Coating Process Employing Same, EP0551727A1 (1992). [14] Z.W.J. Wicks, F.N. Jones, P.S. Pappas, D.A. Wicks, Organic Coatings Science and Technology, 3rd ed., John Wiley & Sons, INC, 2007. [15] M. De Meijer, Review on the durability of exterior wood coatings with reduced VOC-content, Prog. Org. Coat. 43 (2001) 217–225. [16] J. Lindeboom, Air-drying high solids alkyd pants for decorative coatings, Prog. Org. Coat. 34 (1997) 147–151, https://doi.org/10.1016/S0300-9440(98)00034-4. [17] S.P. Pappas, Radiation Curing: Science and Technology, Springer Science & Business Media, 2013. [18] H. Fagerholm, A. Ranta-Eskola, M. Hautala, C. Filhaut, P.-E. Sundell, M. Ferreira, Multilayer coatings with improved performance for construction applications, Eur. Comm. Tech. Steel Res. (2002) 1–145. [19] B.-J. Skrifvars, P.-E. Sundell, M. Schatzl, K. Ahvonen, M. Heylen, P. Keil, Space Efficient Curing Methods and Simulation-aided Coating Engineering for Extending Lifetime of Aesthetic Coil Coatings, Eur. Comm. Tech. Steel Res. (2019) n.d.. [20] T. Nabuurs, R.A. Baijards, A.L. German, Alkyd-acrylic hybrid systems for use as binders in waterborne paints, Prog. Org. Coat. 27 (1996) 163–172, https://doi.org/
6