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Synthesis and characterization of sacha inchi (Plukenetia volubilis L.) oil-based alkyd resin
Progress in Organic Coatings 136 (2019) 105289
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Synthesis and characterization of sacha inchi (Plukenetia volubilis L.) oilbased alkyd resin
T
Santiago Flores , Artemio Flores, Carlos Calderón, Daniel Obregón ⁎
Pontificia Universidad Católica del Perú, Av. Universitaria 1801, L-32, Lima, Peru
ARTICLE INFO
ABSTRACT
Keywords: Sacha inchi oil Plukenetia volubilis oil Renewability Alcoholysis-polyesterification Alkyd resin
Sacha Inchi (Plukenetia volubilis L.) is a wild oleaginous plant of the Euphorbiaceae family that grows in the Peruvian rainforest. The oil obtained from the seeds, which can reach 92% polyunsaturated fatty acid content, has been used as a raw material for the synthesis of alkyd resins. Short oil and medium oil alkyd resins in sacha inchi and linseed oil (control) were synthesized by a two-step alcoholysis-esterification process, reacting the oil with glycerol and phthalic and maleic anhydride in different proportions. The resins were structurally characterized using Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopic techniques. The physicochemical properties of the resins in the liquid state, such as the acid value, colour, viscosity and density, were evaluated. The coating performance of the cured resins was studied by measuring the touch dry and hard dry times, hardness, chemical resistance, and thermal stability and by accelerated corrosion tests. We concluded that sacha inchi oil can be used as a raw material alternative to linseed oil in the synthesis of alkyd resins for industrial applications.
1. Introduction Economic and population growth depends on sufficient quantities of raw materials for industrial production. Currently, the main source of organic industrial chemical input is petroleum, a limited, environmentally unfriendly nonrenewable raw material. For this reason, the use of plantbased materials for polymer synthesis is receiving global attention due to the renewability, biodegradability and low cost of these materials [1]. Vegetable oils are one of the most important biosources for producing different types of polymeric materials, such as polyurethanes, polyesters, polyethers and polyolefins [2]. Alkyd resins are branched polyesters that are obtained by the reaction of dicarboxylic acids or anhydrides, polyols, and unsaturated chains of fatty acids derived from vegetable oils [3]. Among the vegetable oils most used in the surface coating industry for the synthesis of alkyd resins, linseed oil, soybean oil, rapeseed oil, castor oil, sunflower oil, Tung oil, tall oil and crude fish oil are the most prominent [4]. However, new sources of raw materials are being explored, such as Karanja oil [5], palm oil [6], yellow oleander oil [1], Jatropha curcas oil [7], palm stearin [8], modified tobacco seed oil [9,10] Camelina sativa oil [11], locust bean seed oil [12], Karawila seed oil [13], Hura crepitans seed oil [14] and nahar seed oil [15]. Sacha inchi (Plukenetia volubilis L.), also called Inca inchi, is a wild oleaginous plant of the Euphorbiaceae family that grows in the
rainforests of the Americas at altitudes between 200 and 1500 m. This plant is also known as maní inca (Inca peanut), maní silvestre (wild peanut) or montaña maní (mountain peanut). The lenticular-shaped seeds of this plant are rich in oil and protein, and representations of the plant and its fruits have been found in vessels in Incan tombs, implying that sacha inchi was cultivated by the preIncans and the Incans [16]. The first compositional analysis of sacha inchi is attributed to Hamaker et al. [17]. The seeds have a high oil content (35–60%) [18] rich in linoleic and linolenic acids, which is why oil has had potential uses in the food and pharmaceutical industries [18]. Guillén et al. [16] studied sacha inchi seed oil using Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopies, showing a high content of monounsaturated (5.0–9.6%) and polyunsaturated (82.0–87.0%) acyl groups. Fanali et al. [19] applied liquid chromatography in combination with a photodiode array (PDA), fluorescence (RF) and mass spectrometry (MS) and found 92% unsaturated fatty acids (18:1, 18:2 and 18:3) in sacha inchi oil obtained from a Peruvian supplier. Gutierrez [18] analysed the content of polyunsaturated fatty acids in sacha inchi oil extracted with hexane using the Soxhlet apparatus. The oil was rich in α-linolenic (50.8%) and linoleic (33.4%) acids, with low levels of oleic (9.1%), palmitic (4.4%) and stearic (2.4%) acids [18]. A similar content of polyunsaturated fatty acids, αlinolenic (50.73%), linoleic (33.67%) and oleic (8.77%) acid was
Corresponding author. E-mail addresses: [email protected] (S. Flores), [email protected] (A. Flores), [email protected] (C. Calderón), [email protected] (D. Obregón). ⁎
https://doi.org/10.1016/j.porgcoat.2019.105289 Received 24 May 2019; Received in revised form 29 July 2019; Accepted 19 August 2019 Available online 02 September 2019 0300-9440/ © 2019 Elsevier B.V. All rights reserved.
Progress in Organic Coatings 136 (2019) 105289
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reaching an acid value close to 10. The acidic value of the reaction mixture was determined following the ASTM D 1639-90 standard. The method consists of dissolving the aliquot taken in a neutral solution and titrating with 0.1 M KOH solution using phenolphthalein as an acidbase indicator. The nomenclature assigned to the eight resins synthesized was as follows: S = sacha inchi oil and L = linseed oil, followed by the type of alkyd resin, S = short oil alkyd resin and M = medium oil alkyd resin, followed by the percentage (w/w) of maleic anhydride with respect to phthalic anhydride, 0%, 2% or 4%. The starting compositions for the synthesis of the eight alkyd resins are presented in Table 3.
Table 1 Physical-chemical analysis of sacha inchi oil. Property
Sacha inchi oil
Acid value (expressed as oleic acid) Peroxide value (meq O2/Kg) Refractive index at 20 °C Density at 20 °C (g/cm3) Iodine value (g I2/100 g oil) Saponification value (mg KOH/g oil)
0.10% 2.77 1.4816 0.9255 189.16 189.60
reported by Bondioli [20]. Drying oils with high contents of polyunsaturated fatty acids produces alkyd resins that can reach a high degree of crosslinking after curing, with good protection properties (e.g., hardness). Due to its high content of α-linolenic, linoleic and oleic acids, sacha inchi could be studied as a source of oil for the synthesis of high performance alkyd resins. The present study aims to investigate the synthesis and characterization of the alkyd resins based sacha inchi oil.
2.3. Characterization of the alkyd resins 2.3.1. Physical characterization The short and medium oil liquid resins were characterized in terms of their physical properties, including colour (ASTM D1544-04), density (ASTM D1475-13) and viscosity (ASTM D 15454-04). The viscosity of the alkyd resins was determined by a comparative method using a Gardner Bubble Tube from Z1 to Z10 in a hand-held tube holder. For this purpose, the resins of each group (short or medium) were diluted in the same proportion with a mixture of white spirit/xylene solvents (3:1 v/v) until the viscosity range of commercial resins was reached. Likewise, the resins synthesized were cured with a mixture of cobalt-based drying agents (0.27% w/w resin, without solvent) and zirconium (0.63% w/w resin, without solvent). The resins containing the drying agent mixture were applied to glass plates using a 30 mm Erichsen manual applicator and allowed to cure at room temperature for 7 days. The touch dry and hard dry times were determined according to the procedure described in ASTM D 1640-14. The hardness of the cured resins applied on glass plates was determined according to ASTM D 3363-05 at room temperature using pencil leads from 7B to 7H, softest to hardest with a Gardco pencil hardness gauge (model H 501).
2. Materials and methods 2.1. Materials The sacha inchi vegetable oil was provided by the Amazon Health Products S.A. factory (Lima, Peru), and the linseed vegetable oil was obtained from a commercial brand on the market. The physicochemical properties of the sacha inchi oil are shown in Table 1. Table 2 shows the monounsaturated and polyunsaturated fatty acid content of both oils. Analytical grade glycerol (Merck, Germany), phthalic anhydride (Merck, Germany) maleic anhydride (Merck, Germany), xylene (Mallinckrodt Chemicals, USA), and lithium carbonate (LC) were used in the synthesis of the alkyd resins. The dryers (cobalt octoate, zirconium octoate and calcium octoate) and methyl ethyl ketoxime in the present study were provided by Arc Chemicals Private Limited, India.
2.3.2. FTIR analysis The alkyd resins were analysed by FTIR spectroscopy using a Perkin Elmer Spectrum Two FTIR spectrometer using a KBr pellet at wavelengths between 4000 and 450 cm−1.
2.2. Synthesis of alkyd resins The short oil alkyd resins (less than 40% w/w oil content) and medium oil (between 40 and 60% w/w oil content) were synthesized following a two-step method of alcoholysis-esterification. The compositions of the two linseed oil-based resins and six sacha inchi oil-based resins are presented in Table 3. In the first synthesis stage, the monoglyceride was preheated by heating the mixture of oil, glycerol and catalyst (Li2CO3) in a threenecked round-bottomed flask equipped with a mechanical stirrer (Caframo, Canada), a thermometer and a nitrogen gas inlet. The mixture was held at 200 °C under continuous stirring at a speed of 300 rpm for 5 h until the monoglyceride was formed. The formation of the monoglyceride was verified by the methanol solubility test. For the second stage, the phthalic anhydride or phthalic/maleic anhydride mixture was added to the reaction balloon. The temperature was raised to approximately 230–250 °C. The progress of the reaction was monitored by taking aliquots at different time intervals and titrating until
2.3.3. H-NMR analysis The 1H NMR spectra of the resins were obtained using a 500 MHz Ascend NMR (Bruker, USA) with deuterated chloroform solvent. 2.3.4. Thermogravimetric analysis The thermal stability of the alkyd resin was investigated by thermogravimetric analysis (TGA) in an inert nitrogen atmosphere at a heating rate of 10°/min from 25 °C to 600 °C using a Netzsch Jupiter STA 449 thermal analyzer. 2.3.5. Immersion testing The chemical resistance of the cured films of the eight resins was evaluated in different media: 1% (w/v) NaOH, 10% (v/v) HCl, 10% (w/ v) NaCl, ethanol and distilled water. The coated glass plates (4.5 × 10 cm) were immersed in 250 mL vessels containing 150 mL of different chemical media for 3 days at 20 °C.
Table 2 Monounsaturated and polyunsaturated fatty acid content of sacha inchi oil and linseed oil. Fatty acid content
a
Oleic acid Linoleic acid Linolenic acid
9.65 % 35.71 % 47.87 %
a b
Sacha inchi oil
b
2.4. Paint manufacture and application
Linseed oil
Alkyd paints were prepared in the laboratory using the medium oil resins synthesized as a binder. The general formulation of the alkyd paints is presented in Table 4. The paint samples were prepared using a VMA-Getzmann BMGH Dispermat TU laboratory disperser. Steel specimens (JIS G3141, SPCC grade; C: 0.15%, Mn: 0.60%, S: 0.05% and P: 0.10%) sized 10 x 15 cm were sandblasted to a white
19.94 % 19.20 % 49.47 %
Values from Quality Certificate provided by Amazon Health Products. Values from the product´s nutritional information. 2
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Table 3 Starting compositions and designations of the eight alkyd resins synthesized with oil. Composition
Short
Sacha inchi oil, g Linseed oil, g Glycerol, g Phthalic anhydride, g Maleic anhydride, g Lithium carbonate, g
Medium
SS-0%
LS-0%
SS-2%
SS-4%
SM-0%
LM-0%
SM-2%
SM-4%
63.11 – 35.32 67.57 – 0.06
– 63.11 35.32 67.57 – 0.06
63.13 – 35.68 65.85 1.34 0.06
63.13 – 35.67 64.50 2.69 0.06
86.03 – 25.06 54.91 – 0.09
– 86.03 25.06 54.91 – 0.09
86.03 – 25.05 53.81 1.10 0.09
86.04 – 25.21 52.56 2.19 0.09
dioxide tests. Gloss measurements were performed at 60° using a BYKGardner GmbH Micro-TRI-gloss meter on the exposed surface of the alkyd primers during the accelerated ageing test.
Table 4 Composition of alkyd primers (wt.%). Component
wt.%
Component
wt.%
White spirit Toluene Alkyd resin* Modified bentonite Dispersing additive Antifoaming agent
9.75 3.09 33.34 1.10 0.10 0.44
Titanium dioxide Talc Zirconium octoate Cobalt octoate Calcium octoate Methyl ethyl ketone
41.61 8.93 0.77 0.44 0.06 0.37
3. Results and discussion 3.1. Alkyd resin characterization 3.1.1. Physical characterization The esterification step continued until an acid value close to or less than 10 mg KOH/g was reached. For the short oil resins, the values reached ranged from 9.9 to 11.7 mg KOH/g. The medium oil resins reached values ranging from 8.3 to 9.6 mg KOH/g, indicating a slightly higher degree of polymerization than that of the short oil alkyd resins. Before determining the viscosity, colour and density, the proportion of the resin/solvent mixture was adjusted to reach the Gardner viscosity values in the commercial ranges of Z3-Z5 for short oil and Z7-Z10 for medium oil alkyd resins. The short oil resins, showing greater viscosity after the esterification step, needed to be diluted 45% by weight of solvent. On the other hand, the medium oil resins were diluted 10% by weight of solvent. Table 6 summarizes the viscosity, colour and density of each of the synthesized alkyd resins. The densities of the short oil resins were in the range of 0.98–1.03 g/cm3, while the densities of the medium oil resins were in the range of 1.03–1.06 g/cm3. The medium oil alkyd resins were lighter in colour (Gardner colour 3) than the medium oil linseed resins (Gardner colour 10). On the other hand, as shown in Table 6, the colour of the alkyd resins became lighter with increasing maleic anhydride. This behaviour could be related to the higher thermal stability that maleic anhydride provides to the alkyd polymer, as shown in Table 6, which is discussed in Section 3.1.4. The short oil alkyd resins, at 55% solids by weight, presented viscosities between Z4 and Z5, while the medium oil alkyd resins, diluted to 90% solids by weight, presented viscosities between Z9 and Z10. Thus, the short oil alkyd resins presented higher viscosities than the medium oil resins. Singh [21], synthesizing alkyd resins from deodourizer distillate, found that the short oil resin (37% oil length) had a higher viscosity than the long oil alkyd resin (49% oil length), which was attributed to the low functionality and lower molecular
* Resin: Dissolved in 20% mixture of white spirit/xylene solvents (3:1 v/v).
metal surface with abrasive sand that meets the requirements of ASTM D 4940-15. The sandblasted specimens were cleaned with dry compressed air and degreased with technical grade acetone. A layer of alkyd paint manufactured in the laboratory was applied by hand with a 1.5" 100% nylon brush. The painted specimens were allowed to cure in the laboratory for 7 days at room temperature before the application of a second coat with commercial alkyd finishing paint. The painted specimens were allowed to cure in the laboratory for at least 10 days at room temperature before carrying out the accelerated corrosion tests. The dry film thickness of the primers prepared with the sacha inchi and linseed medium oil resins and the thickness of the complete systems was determined with a DeFelsko Positector 6000. Table 5 shows the mean dry film thickness of the primers and complete systems. 2.5. Accelerated testing on painted panels The steel plates coated with the sacha inchi oil- and linseed oilbased alkyd primers and those protected with the complete systems were evaluated in accelerated corrosion tests. Neutral salt spray testing was performed in a Q-Lab CCT 600 accelerated corrosion chamber according to ASTM B 117-18. Sulphur dioxide testing based on ASTM G 87-02 was performed in a VLM GmbH CON 300-FL AIR chamber, generating a volume of 1 L of SO2 per cycle. Finally, accelerated ageing testing (ASTM G 53-96) of the alkyd primers was performed in a Q-Lab QUV-Spray chamber. The degree of blistering (ASTM D 714-02) and degree of oxidation (ASTM D 610-08) were determined during the salt spray and sulphur Table 5 Average dry film thicknesses of alkyd paints applied on mild steel specimens used in accelerated corrosion tests. Paint
Paint
Average dry film thickness (μm)
type
designation
Salt spray test
SO2 test
Weathering test
Primer
P-LM-0% P-SM-0% P-SM-2% P-SM-4% S-LM-0% S-SM-0% S-SM-2% S-SM-4%
47.70 51.57 53.73 62.36 96.47 83.33 90.07 97.20
48.17 54.47 54.60 64.60 99.97 90.87 107.67 103.67
46.73 48.90 50.43 60.17 86.00 76.27 77.07 84.53
System
Table 6 Physical properties of synthesized alkyd resins. Alkyd resins
Viscosity (Gardner)
Colour (Gardner)
Density (g/cm3)
LS-0% SS-0% SS-2% SS-4% LM-0% SM-0% SM-2% SM-4%
Z5 Z4 Z5 Z4 Z10 Z10 Z10 Z9
12 13 7 7 10 3 3 3
1.03 0.98 1.00 1.01 1.06 1.03 1.04 1.05
Short alkyd resins: 55% solidsMedium alkyd resins: 90% solids. 3
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It is relevant to note that, unlike what other researchers have studied, small amounts of maleic anhydride (2–4%) in replacement of the phthalic anhydride have been shown to have an effect on increasing the drying time and reducing the hardness of the resin.
Table 7 Dry-to-touch time, dry-hard time and pencil hardness of synthesized alkyd resins. Alkyd resins
Dry-to-touch time (min)
Dry-hard time (min)
Pencil hardness
LS-0% SS-0% SS-2% SS-4% LM-0% SM-0% SM-2% SM-4%
140 120 90 40 190 180 130 80
160 150 130 120 240 230 180 160
4H 4H 2H 2H 2H 2H HB HB
3.1.2. FTIR analysis The polyesterification reaction and the presence of ester functional groups and olefinic double bonds were confirmed by FTIR spectroscopy. All the resins synthesized presented the characteristic peak of the stretching vibration of the C]O carbonyl group at 1738 cm−1 [1,5,7] (Fig. 1). The FTIR-ATR bands attributed to the eOH groups at 3492 cm−1 (rounded broad band) and CeH aliphatic stretching vibrations at 2853-2928 cm−1 from the oil are seen in Fig. 1 [1,5,7]. The aromatic rings present in the polyester chain were identified from the double peak of aromatic stretching at 1600 and 1582 cm−1 [27,28]. The peak observed at 1453 cm−1 corresponds to the vibration of the CeH bond [1,5,7,25,27,28]. In the 1272-1070 cm-1 range, bands related to the stretching of the CeOeC bonds bound to aliphatic and aromatic entities could be distinguished [25]. The unsaturated aromatics in plane deformation correspond to the peaks observed at 744 and 705 cm−1 [27,28].
weight of the short oil resin. On the other hand, certain researchers [22,23] have reported that the reactivity of maleic anhydride during the synthesis reaction increases the viscosity of the resin obtained relative to a 100% [23] or to a 25–50% [22] phthalic anhydride replacement. However, the replacement rates of maleic anhydride in the present study were apparently not high enough to show this effect. Alkyd resins form a film through a complex process of radical polymerization [24]. Regarding the drying time, the values shown in Table 7 indicate that the resins based on sacha inchi oil had shorter drying times than the resins based on linseed oil. Likewise, as the amount of maleic anhydride in the sacha inchi oil alkyd resins increased, the touch dry and hard dry times of the applied films decreased. Boruah et al. [7] attributed this behaviour to that when the content of maleic anhydride increases, the degree of unsaturation of the resin increases, which decreases the curing time in a process of crosslinking by a free radical mechanism. The hardnesses of the cured film of the alkyd resins synthesized with sacha inchi and linseed oil were equivalent, confirming that sacha inchi oil can be used to obtain an alkyd resin with a high degree of crosslinking. However, as the amount of maleic anhydride in the short and medium oil alkyd resins in sacha inchi oil increased, the hardness of the cured films decreased. The presence of rigid aromatic rings in the structure of the resin improved the hardness [25,26], which is why the hardness of the cured film decreased when the content of phthalic anhydride decreased by 2–4% wt.%.
3.1.3. H-NMR analysis The 1H-NMR spectra of the four alkyd resins (SS-0%, SS-4%, SM-0% and SM-4%) are presented in Fig. 2. The integrated area of each proton displacement located at δ = 1.04-0.94 ppm and δ = 0.94–0.82 ppm (a) corresponds to the terminal methyl groups of the fatty acid chains, and the peaks located at δ = 1.55–1.18 ppm (b) correspond to all the internal protons of the -CH2- groups present in the fatty acid chains [1,5,7,25]. The peaks located at δ = 1.72–1.50 ppm (c) correspond to the -CH2- group bound to the terminal methyl group [1,5,7,25]. However, other authors such as Assanvo et al. [23] and Ibrahim et al. [29] claim that the peaks at δ = 1.53–1.60 ppm correspond to protons in CH2 beta position of the ester group. The peaks located at δ = 2.16–1.87 ppm (d) correspond to allylic protons of -CH2, and those located at δ = 2.70–2.57 ppm (f) correspond to the double allylic protons of -CH2. [1,5,7,25]. The peaks observed at δ = 2.44–2.16 ppm (e) may be due to the α-protons of the ester group. The protons of -CH2from the glycerol moiety presented peaks at δ = 4.24–4.14 ppm and 4.53–4.32 ppm (g). The peaks related to the protons of the unsaturated
Fig. 1. FTIR spectra of the synthesized alkyd resins. 4
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Fig. 2. 1H NMR spectra of the sacha inchi oil alkyd resins SS-0%, SS-4%, SM-0% and SM-4%.
Fig. 3. TGA thermogram of sacha inchi and linseed oil alkyd resins SS-0%, LS-0%, SM-0% and LM-0%.
carbons appeared at δ = 5.54–5.29 ppm (h). The phthalic anhydride present in the resin presented aromatic protons at δ = 7.81–7.64 ppm and δ = 7.62–7.45 ppm (i) [1,5,7,25]. Assanvo et al. [22] synthesized alkyd resins based on R. heudelotii oil with different molar amounts of phthalic and maleic anhydride. The 1H-NMR analysis confirmed the incorporation of the maleic anhydride moiety in the resin structure, with peaks at δ =6.90 ppm attributed to the resonance of the -OOCCH=CH-COO- protons. However, the H-NMR spectra of the alkyd
resins synthesized based on sacha inchi oil (Fig. 2) did not present defined peaks around δ =7.00 ppm, probably due to the lower molar concentrations or weights of maleic anhydride compared with the resins synthesized by Assanvo et al. [22]. 3.1.4. Thermogravimetric analysis The TGA of the short and medium oil alkyd resins in the sacha inchi and linseed oils is presented in Figs. 3 and 4. 5
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Fig. 4. TGA thermogram of sacha inchi oil alkyd resins SM-0%, SM-2% and SM-4%.
The decomposition profiles of the short oil resins of the linseed and sacha inchi were similar, with a mass loss of 20% at approximately 300 °C (Fig. 3). For the medium oil resins, the linseed oil-based resin was slightly more stable than the sacha inchi oil-based resin (Fig. 3). Table 8 shows the thermal degradation data for the short and medium oil resins in the sacha inchi oil. For both the short and medium oil resins, an increase in maleic anhydride content gave the resin greater thermal stability (Fig. 4). According to Boruah et al. [7] this behaviour is due to maleic anhydride causing an increase in the density of the crosslinking in the resin, resulting in improvement in the thermal stability of the resin.
Table 8 Thermal degradation data for sacha inchi alkyd resins. Alkyd resin
Thermal degradation
SS-0% SS-2% SS-4% SM-0% SM-2% SM-4%
Td.10% (°C)
Td.50% (°C)
Td.90% (°C)
220 247 250 276 296 305
341 341 342 357 360 370
402 404 410 421 441 448
3.1.5. Chemical resistance In general terms, the medium oil alkyd resins in the linseed and sacha inchi oils showed better chemical resistance than the short oil resins in the different media tested. The medium oil resins were resistant to diluted HCl, NaCl solution and distilled water [1,5,7]. All the alkyd resins showed poor resistance to the alkaline medium due to the presence of hydrolysable alkali ester groups, as has been reported by various researchers [1,5,7,30] (Table 9).
Table 9 Chemical resistance of alkyd resins. Alkyd resins
10% HCl (aq)
1% NaOH (aq)
10% NaCl (aq)
Distilled water
Ethanol
LS-0% SS-0% SS-2% SS-4% LM-0% SM-0% SM-2% SM-4%
Excellent Excellent Poor Good Good Good Good Excellent
Poor Poor Poor Poor Poor Poor Poor Poor
Good Good Poor Good Excellent Good Excellent Good
Good Poor Poor Good Good Good Good Good
Poor Poor Poor Poor Poor Poor Poor Poor
3.2. Accelerated tests on painted panels 3.2.1. Salt spray testing The results obtained after 720 h of salt spray testing are presented in Table 10. The alkyd primers formulated with medium oil linseed and sacha inchi resins showed identical degrees of oxidation and blistering as a function of testing time. On the other hand, as shown in Fig. 5, an increase in the content of maleic anhydride in the alkyd resin appeared to slightly improve the resistance of the resin to oxidation. The paint systems with linseed oil- and sacha inchi oil-based alkyd primers showed similar behaviour in terms of resistance to corrosion and blistering in the salt spray test.
Table 10 Salt spray test: Rusting and blistering degrees, 720 h. Sample
P-LM-0% P-SM-0% P-SM-2% P-SM-4% S-LM-0% S-SM-0% S-SM-2% S-SM-4%
Degree of Rusting
Degree of Blistering
24h
48h
96h
168h
720h
24h
48h
96h
168h
720h
9 8 9 9 10 10 10 10
6 6 8 7 9 10 9 9
4 4 6 5 9 8 8 9
2 2 5 4 8 7 8 7
0 0 0 0 4 3 3 4
10 10 10 10 10 10 10 10
10 10 10 10 10 10 10 10
10 10 10 8M 10 10 10 10
8M 8M 8F 8M 10 8F 8F 10
4M 4MD 2MD 4MD 2F 2M 4M 6M
3.2.2. Sulphur dioxide testing As shown in Table 11 and Fig. 6, the sacha inchi oil-based primers showed better resistance to oxidation than the linseed oil-based primer. Regarding the degree of blistering, the test pieces protected with linseed oil-based paints had slightly better performances towards the end 6
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Fig. 5. Rusting degree as a function of the time of the alkyd primers after 720 h of salt spray test.
of the tests in both the primer and complete systems.
Table 11 Sulphur dioxide test: Rusting and blistering degrees, 456 h. Sample
P-LM-0% P-SM-0% P-SM-2% P-SM-4% S-LM-0% S-SM-0% S-SM-2% S-SM-4%
Degree of Rusting
Degree of Blistering
24h
48h
96h
168h
456h
24h
48h
96h
168h
456h
10 10 10 10 10 10 10 10
9 9 9 9 10 10 10 10
9 8 9 9 10 10 10 10
7 7 8 8 10 10 10 10
1 2 3 3 8 7 9 7
10 10 10 10 10 10 10 10
10 10 10 10 10 10 10 10
10 10 8F 10 10 8F 10 10
8F 8F 8M 8F 10 8F 8F 8F
8MD 6MD 6MD 6M 8M 6M 6M 6M
3.2.3. Accelerated weathering testing Fig. 7 shows the evolution of the gloss of the specimens measured at 60° in an accelerated weathering chamber for 504 h. At the beginning of the test, the specimens protected with sacha inchi oil-based primers showed better gloss retention than the linseed oil-based alkyd primer. On the other hand, towards the end of the testing, all the painted specimens presented the same degradation in terms of gloss. Likewise, the initial gloss of the sacha inchi oil increased with increasing content of maleic anhydride in the alkyd resin.
Fig. 6. Visual appearance of the specimens painted with alkyd primers after the 456 h of accelerated test in sulfur dioxide chamber. 7
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Fig. 7. Evolution of gloss at 60° of linseed and sacha inchi oil alkyd primers after 504 h of accelerated weathering test.
4. Conclusion
[4] L.N. Tuck, Waterborne and Solvent Based surface coating resins and Their Applications: Waterborne and Solvent Based Alkyds and Their End User Applications – Volume VI Volume 6 John Wiley & Sons Ltd., London, 2000. [5] M.M. Bora, R. Deka, N. Ahmed, D.K. Kakati, Karanja (Millettia pinnata (L.) Panigrahi) seed oil as a renewable raw material for the synthesis of alkyd resin, Ind. Crops Prod. 61 (2014) 106–114, https://doi.org/10.1016/j.indcrop.2014.06.048. [6] C.F. Uzoh, O.D. Onukwuli, R.S. Odera, S. Ofochebe, Optimization of polyesterification process for production of palm oil modified alkyd resin using response surface methodology, J. Environ. Chem. Eng. 1 (2013) 777–785, https://doi.org/ 10.1016/j.jece.2013.07.021. [7] M. Boruah, P. Gogoi, B. Adhikari, S.K. Dolui, Preparation and characterization of Jatropha Curcas oil based alkyd resin suitable for surface coating, Prog. Org. Coat. 74 (2012) 596–602, https://doi.org/10.1016/j.porgcoat.2012.02.007. [8] A.A. Nanvaee, R. Yahya, S.N. Gan, Cleaner production through using by-product palm stearin to synthesis alkyd resin for coating applications, J. Clean. Prod. 54 (2013) 307–314, https://doi.org/10.1016/j.jclepro.2013.04.027. [9] D.S. Ogunniyi, T.E. Odetoye, Preparation and evaluation of tobacco seed oil-modified alkyd resins, Bioresour. Technol. 99 (2008) 1300–1304, https://doi.org/10. 1016/j.biortech.2007.02.044. [10] A. Mukhtar, H. Ullah, H. Mukhtar, Fatty acid composition of tobacco seed oil and synthesis of alkyd resin, Chin. J. Chem. 25 (2007) 705–708, https://doi.org/10. 1002/cjoc.200790132. [11] H. Nosal, J. Nowicki, M. Warzała, E. Nowakowska-Bogdan, M. Zarębska, Synthesis and characterization of alkyd resins based on Camelina sativa oil and polyglycerol, Prog. Org. Coat. 86 (2015) 59–70, https://doi.org/10.1016/j.porgcoat.2015.04. 009. [12] A.I. Aigbodion, F.E. Okieimen, An investigation of the utilisation of African locustbean seed oil in the preparation of alkyd resins, Ind. Crops Prod. 13 (2001) 29–34, https://doi.org/10.1016/S0926-6690(00)00050-9. [13] S.H.U.I. De Silva, A.D.U.S. Amarasinghe, B.A.J.K. Premachandra, M.A.B. Prashantha, Effect of karawila (Momordica charantia) seed oil on synthesizing the alkyd resins based on soya bean (Glycine max) oil, Prog. Org. Coat. 74 (2012) 228–232, https://doi.org/10.1016/j.porgcoat.2011.12.013. [14] I.E. Ezeh, S.A. Umoren, E.E. Essien, A.P. Udoh, Studies on the utilization of Hura crepitans L. seed oil in the preparation of alkyd resins, Ind. Crops Prod. 36 (2012) 94–99, https://doi.org/10.1016/j.indcrop.2011.08.013. [15] N. Dutta, N. Karak, S.K. Dolui, Synthesis and characterization of polyester resins based on Nahar seed oil, Prog. Org. Coat. 49 (2004) 146–152, https://doi.org/10. 1016/j.porgcoat.2003.09.005. [16] M.D. Guillén, A. Ruiz, N. Cabo, R. Chirinos, G. Pascual, Characterization of sacha inchi (Plukenetia volubilis L.) Oil by FTIR spectroscopy and1H NMR. Comparison with linseed oil, JAOCS, J. Am. Oil Chem. Soc. 80 (2003) 755–762, https://doi.org/ 10.1007/s11746-003-0768-z. [17] B.R. Hamaker, C. Valles, R. Gilman, R.M. Hardmeier, D. Clark, H.H. Garcia, A.E. Gonzales, I. Kohlstad, M. Castro, R. Valdivida, T. Rodriguez, M. Lescano, Amino Acid and Fatty Acid profiles of the inca peanut (Plukenetia volubilis), Cereal Chem. 69 (1992) 461–563 (Accessed 23 May 2019), https://www.aaccnet.org/ publications/cc/backissues/1992/Documents/69_461.pdf. [18] L.F. Gutiérrez, L.M. Rosada, Á. Jiménez, Chemical composition of Sacha Inchi (Plukenetia volubilisi L.) seeds and characteristics of their lipid fraction, Grasas y Aceites 62 (2011) 76–83, https://doi.org/10.3989/gya044510.
Short and medium oil alkyd resins based on sacha inchi oil and its variations in different proportions of phthalic and maleic anhydride were successfully synthesized. The resin structures were confirmed by FTIR and 1H NMR analyses. The resins had comparable viscosity and density; however, the sacha inchi oil-based resins presented lighter Gardner colours than the linseed oil-based alkyd resin. Maleic anhydride improved the thermal properties and decreased the drying time of the resins. In addition, the cured resins had hardness and chemical resistance properties that make the resins suitable for use in surface coatings. The paints formulated with sacha inchi-based medium oil resins showed similar behaviour and, in certain cases, better properties than that of the linseed oil in the corrosion and accelerated ageing tests. This study revealed that sacha inchi oil can be used as a raw material alternative to linseed oil in the synthesis of alkyd resins for industrial applications. Acknowledgements This research was funded by the National Fund for Scientific and Technological Development and Technological Innovation (FONDECYT-Perú) and the PUCP agreement (Pontificia Universidad Católica del Perú / FONDECYT) [grant 166- 2015-FONDECYT-DE]. The authors thank the Nuclear Magnetic Resonance Laboratory (Chemical Unit - PUCP) for the 1H NMR analysis and the Materials Laboratory (Mechanical Engineering Unit - PUCP) for the thermogravimetric analysis. References [1] M.M. Bora, P. Gogoi, D.C. Deka, D.K. Kakati, Synthesis and characterization of yellow oleander (Thevetia peruviana) seed oil-based alkyd resin, Ind. Crops Prod. 52 (2014) 721–728, https://doi.org/10.1016/j.indcrop.2013.11.012. [2] S. Miao, P. Wang, Z. Su, S. Zhang, Vegetable-oil-based polymers as future polymeric biomaterials, Acta Biomater. 10 (2014) 1692–1704, https://doi.org/10.1016/j. actbio.2013.08.040. [3] A.I. Aigbodion, C.K.S. Pillai, Synthesis and molecular weight characterization of rubber seed oil-modified alkyd resins, J. Appl. Polym. Sci. 79 (2001) 2431–2438, https://doi.org/10.1002/1097-4628(20010328)79:13<2431::AID-APP1050>3.0. CO;2-A.
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S. Flores, et al. [19] C. Fanali, L. Dugo, F. Cacciola, M. Beccaria, S. Grasso, M. Dachà, P. Dugo, L. Mondello, Chemical characterization of Sacha inchi (Plukenetia volubilis L.) oil, J. Agric. Food Chem. 59 (2011) 13043–13049, https://doi.org/10.1021/jf203184y. [20] P. Bondioli, L. Della Bella, P. Rettke, Alpha linolenic acid rich oil. Composition of Plukenetia volubilis (Sacha Inchi) oil from Peru, La Rivista Italiana Delle Sostanze Grasse 83 (2006) 120–123 (Accessed 23 May 2019), https://scholar.google.com. pe/scholar?hl=es&as_sdt=0%2C5&q=Alpha+linolenic+acid+rich+oils %3A+Composition+of+Plukenetia+volubilis+%28Sacha+Inchi%29+oil +from+Peru&btnG=. [21] S. Singh, Preparation and analysis of alkyd resin from deodourizer distillate, J. Sci. Ind. Res. (India) 68 (2009) 807–811 (Accessed 29 July 2019), https://scholar. google.com.pe/scholar?hl=es&as_sdt=0%2C5&q=S.+Singh%2C+Preparation +and+analysis+of+alkyd+resin+from+deodourizer+distillate%2C+J.+Sci. +Ind.+Res.+%28India%29.+68+%282009%29+807%E2%80%93811.+& btnG=. [22] E.F. Assanvo, P. Gogoi, S.K. Dolui, S.D. Baruah, Synthesis, characterization, and performance characteristics of alkyd resins based on Ricinodendron heudelotii oil and their blending with epoxy resins, Ind. Crops Prod. 65 (2015) 293–302, https:// doi.org/10.1016/j.indcrop.2014.11.049. [23] S. Aydin, H. Akcay, E. Ozkan, F.S. Guner, A.T. Erciyes, The effects of anhydride type and amount on viscosity and film properties of alkyd resin, Prog. Org. Coat. 51 (2004) 273–279, https://doi.org/10.1016/j.porgcoat.2004.07.009. [24] S.T. Warzeska, M. Zonneveld, R. Van Gorkum, W.J. Muizebelt, E. Bouwman,
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J. Reedijk, The influence of bipyridine on the drying of alkyd paints: a model study, Prog. Org. Coat. 44 (2002) 243–248, https://doi.org/10.1016/S0300-9440(02) 00057-7. P.P. Chiplunkar, A.P. Pratap, Utilization of sunflower acid oil for synthesis of alkyd resin, Prog. Org. Coat. 93 (2016) 61–67, https://doi.org/10.1016/j.porgcoat.2016. 01.002. V. Atimuttigul, S. Damrongsakkul, W. Tanthapanichakoon, Effects of oil type on the properties of short oil alkyd coating materials, Korean J. Chem. Eng. 23 (2006) 672–677, https://doi.org/10.1007/BF02706813. R. Ploeger, D. Scalarone, O. Chiantore, The characterization of commercial artists’ alkyd paints, J. Cult. Herit. 9 (2008) 412–419, https://doi.org/10.1016/j.culher. 2008.01.007. R. Ploeger, O. Chiantore, Characterization and stability issues of artists’ alkyd paints, smithson, Contrib. Museum Conserv. 3 (2012) 89–95 (Accessed 23 May 2019), https://repository.si.edu/bitstream/handle/10088/20494/16.Ploeger. SCMC3.Mecklenburg.Web.pdf?sequence=1. K.A. Ibrahim, K.A. Abu-sbeih, I. Al-Trawneh, L. Bourghli, Preparation and characterization of alkyd resins of Jordan Valley tomato oil, J. Polym. Environ. 22 (2014) 553–558, https://doi.org/10.1007/s10924-014-0664-9. S.S. Mahapatra, N. Karak, Synthesis and characterization of polyesteramide resins from Nahar seed oil for surface coating applications, Prog. Org. Coat. 51 (2004) 103–108, https://doi.org/10.1016/j.porgcoat.2004.07.003.
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Synthesis and characterization of sacha inchi (Plukenetia volubilis L.) oilbased alkyd resin
T
Santiago Flores , Artemio Flores, Carlos Calderón, Daniel Obregón ⁎
Pontificia Universidad Católica del Perú, Av. Universitaria 1801, L-32, Lima, Peru
ARTICLE INFO
ABSTRACT
Keywords: Sacha inchi oil Plukenetia volubilis oil Renewability Alcoholysis-polyesterification Alkyd resin
Sacha Inchi (Plukenetia volubilis L.) is a wild oleaginous plant of the Euphorbiaceae family that grows in the Peruvian rainforest. The oil obtained from the seeds, which can reach 92% polyunsaturated fatty acid content, has been used as a raw material for the synthesis of alkyd resins. Short oil and medium oil alkyd resins in sacha inchi and linseed oil (control) were synthesized by a two-step alcoholysis-esterification process, reacting the oil with glycerol and phthalic and maleic anhydride in different proportions. The resins were structurally characterized using Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopic techniques. The physicochemical properties of the resins in the liquid state, such as the acid value, colour, viscosity and density, were evaluated. The coating performance of the cured resins was studied by measuring the touch dry and hard dry times, hardness, chemical resistance, and thermal stability and by accelerated corrosion tests. We concluded that sacha inchi oil can be used as a raw material alternative to linseed oil in the synthesis of alkyd resins for industrial applications.
1. Introduction Economic and population growth depends on sufficient quantities of raw materials for industrial production. Currently, the main source of organic industrial chemical input is petroleum, a limited, environmentally unfriendly nonrenewable raw material. For this reason, the use of plantbased materials for polymer synthesis is receiving global attention due to the renewability, biodegradability and low cost of these materials [1]. Vegetable oils are one of the most important biosources for producing different types of polymeric materials, such as polyurethanes, polyesters, polyethers and polyolefins [2]. Alkyd resins are branched polyesters that are obtained by the reaction of dicarboxylic acids or anhydrides, polyols, and unsaturated chains of fatty acids derived from vegetable oils [3]. Among the vegetable oils most used in the surface coating industry for the synthesis of alkyd resins, linseed oil, soybean oil, rapeseed oil, castor oil, sunflower oil, Tung oil, tall oil and crude fish oil are the most prominent [4]. However, new sources of raw materials are being explored, such as Karanja oil [5], palm oil [6], yellow oleander oil [1], Jatropha curcas oil [7], palm stearin [8], modified tobacco seed oil [9,10] Camelina sativa oil [11], locust bean seed oil [12], Karawila seed oil [13], Hura crepitans seed oil [14] and nahar seed oil [15]. Sacha inchi (Plukenetia volubilis L.), also called Inca inchi, is a wild oleaginous plant of the Euphorbiaceae family that grows in the
rainforests of the Americas at altitudes between 200 and 1500 m. This plant is also known as maní inca (Inca peanut), maní silvestre (wild peanut) or montaña maní (mountain peanut). The lenticular-shaped seeds of this plant are rich in oil and protein, and representations of the plant and its fruits have been found in vessels in Incan tombs, implying that sacha inchi was cultivated by the preIncans and the Incans [16]. The first compositional analysis of sacha inchi is attributed to Hamaker et al. [17]. The seeds have a high oil content (35–60%) [18] rich in linoleic and linolenic acids, which is why oil has had potential uses in the food and pharmaceutical industries [18]. Guillén et al. [16] studied sacha inchi seed oil using Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR) spectroscopies, showing a high content of monounsaturated (5.0–9.6%) and polyunsaturated (82.0–87.0%) acyl groups. Fanali et al. [19] applied liquid chromatography in combination with a photodiode array (PDA), fluorescence (RF) and mass spectrometry (MS) and found 92% unsaturated fatty acids (18:1, 18:2 and 18:3) in sacha inchi oil obtained from a Peruvian supplier. Gutierrez [18] analysed the content of polyunsaturated fatty acids in sacha inchi oil extracted with hexane using the Soxhlet apparatus. The oil was rich in α-linolenic (50.8%) and linoleic (33.4%) acids, with low levels of oleic (9.1%), palmitic (4.4%) and stearic (2.4%) acids [18]. A similar content of polyunsaturated fatty acids, αlinolenic (50.73%), linoleic (33.67%) and oleic (8.77%) acid was
Corresponding author. E-mail addresses: [email protected] (S. Flores), [email protected] (A. Flores), [email protected] (C. Calderón), [email protected] (D. Obregón). ⁎
https://doi.org/10.1016/j.porgcoat.2019.105289 Received 24 May 2019; Received in revised form 29 July 2019; Accepted 19 August 2019 Available online 02 September 2019 0300-9440/ © 2019 Elsevier B.V. All rights reserved.
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reaching an acid value close to 10. The acidic value of the reaction mixture was determined following the ASTM D 1639-90 standard. The method consists of dissolving the aliquot taken in a neutral solution and titrating with 0.1 M KOH solution using phenolphthalein as an acidbase indicator. The nomenclature assigned to the eight resins synthesized was as follows: S = sacha inchi oil and L = linseed oil, followed by the type of alkyd resin, S = short oil alkyd resin and M = medium oil alkyd resin, followed by the percentage (w/w) of maleic anhydride with respect to phthalic anhydride, 0%, 2% or 4%. The starting compositions for the synthesis of the eight alkyd resins are presented in Table 3.
Table 1 Physical-chemical analysis of sacha inchi oil. Property
Sacha inchi oil
Acid value (expressed as oleic acid) Peroxide value (meq O2/Kg) Refractive index at 20 °C Density at 20 °C (g/cm3) Iodine value (g I2/100 g oil) Saponification value (mg KOH/g oil)
0.10% 2.77 1.4816 0.9255 189.16 189.60
reported by Bondioli [20]. Drying oils with high contents of polyunsaturated fatty acids produces alkyd resins that can reach a high degree of crosslinking after curing, with good protection properties (e.g., hardness). Due to its high content of α-linolenic, linoleic and oleic acids, sacha inchi could be studied as a source of oil for the synthesis of high performance alkyd resins. The present study aims to investigate the synthesis and characterization of the alkyd resins based sacha inchi oil.
2.3. Characterization of the alkyd resins 2.3.1. Physical characterization The short and medium oil liquid resins were characterized in terms of their physical properties, including colour (ASTM D1544-04), density (ASTM D1475-13) and viscosity (ASTM D 15454-04). The viscosity of the alkyd resins was determined by a comparative method using a Gardner Bubble Tube from Z1 to Z10 in a hand-held tube holder. For this purpose, the resins of each group (short or medium) were diluted in the same proportion with a mixture of white spirit/xylene solvents (3:1 v/v) until the viscosity range of commercial resins was reached. Likewise, the resins synthesized were cured with a mixture of cobalt-based drying agents (0.27% w/w resin, without solvent) and zirconium (0.63% w/w resin, without solvent). The resins containing the drying agent mixture were applied to glass plates using a 30 mm Erichsen manual applicator and allowed to cure at room temperature for 7 days. The touch dry and hard dry times were determined according to the procedure described in ASTM D 1640-14. The hardness of the cured resins applied on glass plates was determined according to ASTM D 3363-05 at room temperature using pencil leads from 7B to 7H, softest to hardest with a Gardco pencil hardness gauge (model H 501).
2. Materials and methods 2.1. Materials The sacha inchi vegetable oil was provided by the Amazon Health Products S.A. factory (Lima, Peru), and the linseed vegetable oil was obtained from a commercial brand on the market. The physicochemical properties of the sacha inchi oil are shown in Table 1. Table 2 shows the monounsaturated and polyunsaturated fatty acid content of both oils. Analytical grade glycerol (Merck, Germany), phthalic anhydride (Merck, Germany) maleic anhydride (Merck, Germany), xylene (Mallinckrodt Chemicals, USA), and lithium carbonate (LC) were used in the synthesis of the alkyd resins. The dryers (cobalt octoate, zirconium octoate and calcium octoate) and methyl ethyl ketoxime in the present study were provided by Arc Chemicals Private Limited, India.
2.3.2. FTIR analysis The alkyd resins were analysed by FTIR spectroscopy using a Perkin Elmer Spectrum Two FTIR spectrometer using a KBr pellet at wavelengths between 4000 and 450 cm−1.
2.2. Synthesis of alkyd resins The short oil alkyd resins (less than 40% w/w oil content) and medium oil (between 40 and 60% w/w oil content) were synthesized following a two-step method of alcoholysis-esterification. The compositions of the two linseed oil-based resins and six sacha inchi oil-based resins are presented in Table 3. In the first synthesis stage, the monoglyceride was preheated by heating the mixture of oil, glycerol and catalyst (Li2CO3) in a threenecked round-bottomed flask equipped with a mechanical stirrer (Caframo, Canada), a thermometer and a nitrogen gas inlet. The mixture was held at 200 °C under continuous stirring at a speed of 300 rpm for 5 h until the monoglyceride was formed. The formation of the monoglyceride was verified by the methanol solubility test. For the second stage, the phthalic anhydride or phthalic/maleic anhydride mixture was added to the reaction balloon. The temperature was raised to approximately 230–250 °C. The progress of the reaction was monitored by taking aliquots at different time intervals and titrating until
2.3.3. H-NMR analysis The 1H NMR spectra of the resins were obtained using a 500 MHz Ascend NMR (Bruker, USA) with deuterated chloroform solvent. 2.3.4. Thermogravimetric analysis The thermal stability of the alkyd resin was investigated by thermogravimetric analysis (TGA) in an inert nitrogen atmosphere at a heating rate of 10°/min from 25 °C to 600 °C using a Netzsch Jupiter STA 449 thermal analyzer. 2.3.5. Immersion testing The chemical resistance of the cured films of the eight resins was evaluated in different media: 1% (w/v) NaOH, 10% (v/v) HCl, 10% (w/ v) NaCl, ethanol and distilled water. The coated glass plates (4.5 × 10 cm) were immersed in 250 mL vessels containing 150 mL of different chemical media for 3 days at 20 °C.
Table 2 Monounsaturated and polyunsaturated fatty acid content of sacha inchi oil and linseed oil. Fatty acid content
a
Oleic acid Linoleic acid Linolenic acid
9.65 % 35.71 % 47.87 %
a b
Sacha inchi oil
b
2.4. Paint manufacture and application
Linseed oil
Alkyd paints were prepared in the laboratory using the medium oil resins synthesized as a binder. The general formulation of the alkyd paints is presented in Table 4. The paint samples were prepared using a VMA-Getzmann BMGH Dispermat TU laboratory disperser. Steel specimens (JIS G3141, SPCC grade; C: 0.15%, Mn: 0.60%, S: 0.05% and P: 0.10%) sized 10 x 15 cm were sandblasted to a white
19.94 % 19.20 % 49.47 %
Values from Quality Certificate provided by Amazon Health Products. Values from the product´s nutritional information. 2
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Table 3 Starting compositions and designations of the eight alkyd resins synthesized with oil. Composition
Short
Sacha inchi oil, g Linseed oil, g Glycerol, g Phthalic anhydride, g Maleic anhydride, g Lithium carbonate, g
Medium
SS-0%
LS-0%
SS-2%
SS-4%
SM-0%
LM-0%
SM-2%
SM-4%
63.11 – 35.32 67.57 – 0.06
– 63.11 35.32 67.57 – 0.06
63.13 – 35.68 65.85 1.34 0.06
63.13 – 35.67 64.50 2.69 0.06
86.03 – 25.06 54.91 – 0.09
– 86.03 25.06 54.91 – 0.09
86.03 – 25.05 53.81 1.10 0.09
86.04 – 25.21 52.56 2.19 0.09
dioxide tests. Gloss measurements were performed at 60° using a BYKGardner GmbH Micro-TRI-gloss meter on the exposed surface of the alkyd primers during the accelerated ageing test.
Table 4 Composition of alkyd primers (wt.%). Component
wt.%
Component
wt.%
White spirit Toluene Alkyd resin* Modified bentonite Dispersing additive Antifoaming agent
9.75 3.09 33.34 1.10 0.10 0.44
Titanium dioxide Talc Zirconium octoate Cobalt octoate Calcium octoate Methyl ethyl ketone
41.61 8.93 0.77 0.44 0.06 0.37
3. Results and discussion 3.1. Alkyd resin characterization 3.1.1. Physical characterization The esterification step continued until an acid value close to or less than 10 mg KOH/g was reached. For the short oil resins, the values reached ranged from 9.9 to 11.7 mg KOH/g. The medium oil resins reached values ranging from 8.3 to 9.6 mg KOH/g, indicating a slightly higher degree of polymerization than that of the short oil alkyd resins. Before determining the viscosity, colour and density, the proportion of the resin/solvent mixture was adjusted to reach the Gardner viscosity values in the commercial ranges of Z3-Z5 for short oil and Z7-Z10 for medium oil alkyd resins. The short oil resins, showing greater viscosity after the esterification step, needed to be diluted 45% by weight of solvent. On the other hand, the medium oil resins were diluted 10% by weight of solvent. Table 6 summarizes the viscosity, colour and density of each of the synthesized alkyd resins. The densities of the short oil resins were in the range of 0.98–1.03 g/cm3, while the densities of the medium oil resins were in the range of 1.03–1.06 g/cm3. The medium oil alkyd resins were lighter in colour (Gardner colour 3) than the medium oil linseed resins (Gardner colour 10). On the other hand, as shown in Table 6, the colour of the alkyd resins became lighter with increasing maleic anhydride. This behaviour could be related to the higher thermal stability that maleic anhydride provides to the alkyd polymer, as shown in Table 6, which is discussed in Section 3.1.4. The short oil alkyd resins, at 55% solids by weight, presented viscosities between Z4 and Z5, while the medium oil alkyd resins, diluted to 90% solids by weight, presented viscosities between Z9 and Z10. Thus, the short oil alkyd resins presented higher viscosities than the medium oil resins. Singh [21], synthesizing alkyd resins from deodourizer distillate, found that the short oil resin (37% oil length) had a higher viscosity than the long oil alkyd resin (49% oil length), which was attributed to the low functionality and lower molecular
* Resin: Dissolved in 20% mixture of white spirit/xylene solvents (3:1 v/v).
metal surface with abrasive sand that meets the requirements of ASTM D 4940-15. The sandblasted specimens were cleaned with dry compressed air and degreased with technical grade acetone. A layer of alkyd paint manufactured in the laboratory was applied by hand with a 1.5" 100% nylon brush. The painted specimens were allowed to cure in the laboratory for 7 days at room temperature before the application of a second coat with commercial alkyd finishing paint. The painted specimens were allowed to cure in the laboratory for at least 10 days at room temperature before carrying out the accelerated corrosion tests. The dry film thickness of the primers prepared with the sacha inchi and linseed medium oil resins and the thickness of the complete systems was determined with a DeFelsko Positector 6000. Table 5 shows the mean dry film thickness of the primers and complete systems. 2.5. Accelerated testing on painted panels The steel plates coated with the sacha inchi oil- and linseed oilbased alkyd primers and those protected with the complete systems were evaluated in accelerated corrosion tests. Neutral salt spray testing was performed in a Q-Lab CCT 600 accelerated corrosion chamber according to ASTM B 117-18. Sulphur dioxide testing based on ASTM G 87-02 was performed in a VLM GmbH CON 300-FL AIR chamber, generating a volume of 1 L of SO2 per cycle. Finally, accelerated ageing testing (ASTM G 53-96) of the alkyd primers was performed in a Q-Lab QUV-Spray chamber. The degree of blistering (ASTM D 714-02) and degree of oxidation (ASTM D 610-08) were determined during the salt spray and sulphur Table 5 Average dry film thicknesses of alkyd paints applied on mild steel specimens used in accelerated corrosion tests. Paint
Paint
Average dry film thickness (μm)
type
designation
Salt spray test
SO2 test
Weathering test
Primer
P-LM-0% P-SM-0% P-SM-2% P-SM-4% S-LM-0% S-SM-0% S-SM-2% S-SM-4%
47.70 51.57 53.73 62.36 96.47 83.33 90.07 97.20
48.17 54.47 54.60 64.60 99.97 90.87 107.67 103.67
46.73 48.90 50.43 60.17 86.00 76.27 77.07 84.53
System
Table 6 Physical properties of synthesized alkyd resins. Alkyd resins
Viscosity (Gardner)
Colour (Gardner)
Density (g/cm3)
LS-0% SS-0% SS-2% SS-4% LM-0% SM-0% SM-2% SM-4%
Z5 Z4 Z5 Z4 Z10 Z10 Z10 Z9
12 13 7 7 10 3 3 3
1.03 0.98 1.00 1.01 1.06 1.03 1.04 1.05
Short alkyd resins: 55% solidsMedium alkyd resins: 90% solids. 3
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It is relevant to note that, unlike what other researchers have studied, small amounts of maleic anhydride (2–4%) in replacement of the phthalic anhydride have been shown to have an effect on increasing the drying time and reducing the hardness of the resin.
Table 7 Dry-to-touch time, dry-hard time and pencil hardness of synthesized alkyd resins. Alkyd resins
Dry-to-touch time (min)
Dry-hard time (min)
Pencil hardness
LS-0% SS-0% SS-2% SS-4% LM-0% SM-0% SM-2% SM-4%
140 120 90 40 190 180 130 80
160 150 130 120 240 230 180 160
4H 4H 2H 2H 2H 2H HB HB
3.1.2. FTIR analysis The polyesterification reaction and the presence of ester functional groups and olefinic double bonds were confirmed by FTIR spectroscopy. All the resins synthesized presented the characteristic peak of the stretching vibration of the C]O carbonyl group at 1738 cm−1 [1,5,7] (Fig. 1). The FTIR-ATR bands attributed to the eOH groups at 3492 cm−1 (rounded broad band) and CeH aliphatic stretching vibrations at 2853-2928 cm−1 from the oil are seen in Fig. 1 [1,5,7]. The aromatic rings present in the polyester chain were identified from the double peak of aromatic stretching at 1600 and 1582 cm−1 [27,28]. The peak observed at 1453 cm−1 corresponds to the vibration of the CeH bond [1,5,7,25,27,28]. In the 1272-1070 cm-1 range, bands related to the stretching of the CeOeC bonds bound to aliphatic and aromatic entities could be distinguished [25]. The unsaturated aromatics in plane deformation correspond to the peaks observed at 744 and 705 cm−1 [27,28].
weight of the short oil resin. On the other hand, certain researchers [22,23] have reported that the reactivity of maleic anhydride during the synthesis reaction increases the viscosity of the resin obtained relative to a 100% [23] or to a 25–50% [22] phthalic anhydride replacement. However, the replacement rates of maleic anhydride in the present study were apparently not high enough to show this effect. Alkyd resins form a film through a complex process of radical polymerization [24]. Regarding the drying time, the values shown in Table 7 indicate that the resins based on sacha inchi oil had shorter drying times than the resins based on linseed oil. Likewise, as the amount of maleic anhydride in the sacha inchi oil alkyd resins increased, the touch dry and hard dry times of the applied films decreased. Boruah et al. [7] attributed this behaviour to that when the content of maleic anhydride increases, the degree of unsaturation of the resin increases, which decreases the curing time in a process of crosslinking by a free radical mechanism. The hardnesses of the cured film of the alkyd resins synthesized with sacha inchi and linseed oil were equivalent, confirming that sacha inchi oil can be used to obtain an alkyd resin with a high degree of crosslinking. However, as the amount of maleic anhydride in the short and medium oil alkyd resins in sacha inchi oil increased, the hardness of the cured films decreased. The presence of rigid aromatic rings in the structure of the resin improved the hardness [25,26], which is why the hardness of the cured film decreased when the content of phthalic anhydride decreased by 2–4% wt.%.
3.1.3. H-NMR analysis The 1H-NMR spectra of the four alkyd resins (SS-0%, SS-4%, SM-0% and SM-4%) are presented in Fig. 2. The integrated area of each proton displacement located at δ = 1.04-0.94 ppm and δ = 0.94–0.82 ppm (a) corresponds to the terminal methyl groups of the fatty acid chains, and the peaks located at δ = 1.55–1.18 ppm (b) correspond to all the internal protons of the -CH2- groups present in the fatty acid chains [1,5,7,25]. The peaks located at δ = 1.72–1.50 ppm (c) correspond to the -CH2- group bound to the terminal methyl group [1,5,7,25]. However, other authors such as Assanvo et al. [23] and Ibrahim et al. [29] claim that the peaks at δ = 1.53–1.60 ppm correspond to protons in CH2 beta position of the ester group. The peaks located at δ = 2.16–1.87 ppm (d) correspond to allylic protons of -CH2, and those located at δ = 2.70–2.57 ppm (f) correspond to the double allylic protons of -CH2. [1,5,7,25]. The peaks observed at δ = 2.44–2.16 ppm (e) may be due to the α-protons of the ester group. The protons of -CH2from the glycerol moiety presented peaks at δ = 4.24–4.14 ppm and 4.53–4.32 ppm (g). The peaks related to the protons of the unsaturated
Fig. 1. FTIR spectra of the synthesized alkyd resins. 4
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Fig. 2. 1H NMR spectra of the sacha inchi oil alkyd resins SS-0%, SS-4%, SM-0% and SM-4%.
Fig. 3. TGA thermogram of sacha inchi and linseed oil alkyd resins SS-0%, LS-0%, SM-0% and LM-0%.
carbons appeared at δ = 5.54–5.29 ppm (h). The phthalic anhydride present in the resin presented aromatic protons at δ = 7.81–7.64 ppm and δ = 7.62–7.45 ppm (i) [1,5,7,25]. Assanvo et al. [22] synthesized alkyd resins based on R. heudelotii oil with different molar amounts of phthalic and maleic anhydride. The 1H-NMR analysis confirmed the incorporation of the maleic anhydride moiety in the resin structure, with peaks at δ =6.90 ppm attributed to the resonance of the -OOCCH=CH-COO- protons. However, the H-NMR spectra of the alkyd
resins synthesized based on sacha inchi oil (Fig. 2) did not present defined peaks around δ =7.00 ppm, probably due to the lower molar concentrations or weights of maleic anhydride compared with the resins synthesized by Assanvo et al. [22]. 3.1.4. Thermogravimetric analysis The TGA of the short and medium oil alkyd resins in the sacha inchi and linseed oils is presented in Figs. 3 and 4. 5
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Fig. 4. TGA thermogram of sacha inchi oil alkyd resins SM-0%, SM-2% and SM-4%.
The decomposition profiles of the short oil resins of the linseed and sacha inchi were similar, with a mass loss of 20% at approximately 300 °C (Fig. 3). For the medium oil resins, the linseed oil-based resin was slightly more stable than the sacha inchi oil-based resin (Fig. 3). Table 8 shows the thermal degradation data for the short and medium oil resins in the sacha inchi oil. For both the short and medium oil resins, an increase in maleic anhydride content gave the resin greater thermal stability (Fig. 4). According to Boruah et al. [7] this behaviour is due to maleic anhydride causing an increase in the density of the crosslinking in the resin, resulting in improvement in the thermal stability of the resin.
Table 8 Thermal degradation data for sacha inchi alkyd resins. Alkyd resin
Thermal degradation
SS-0% SS-2% SS-4% SM-0% SM-2% SM-4%
Td.10% (°C)
Td.50% (°C)
Td.90% (°C)
220 247 250 276 296 305
341 341 342 357 360 370
402 404 410 421 441 448
3.1.5. Chemical resistance In general terms, the medium oil alkyd resins in the linseed and sacha inchi oils showed better chemical resistance than the short oil resins in the different media tested. The medium oil resins were resistant to diluted HCl, NaCl solution and distilled water [1,5,7]. All the alkyd resins showed poor resistance to the alkaline medium due to the presence of hydrolysable alkali ester groups, as has been reported by various researchers [1,5,7,30] (Table 9).
Table 9 Chemical resistance of alkyd resins. Alkyd resins
10% HCl (aq)
1% NaOH (aq)
10% NaCl (aq)
Distilled water
Ethanol
LS-0% SS-0% SS-2% SS-4% LM-0% SM-0% SM-2% SM-4%
Excellent Excellent Poor Good Good Good Good Excellent
Poor Poor Poor Poor Poor Poor Poor Poor
Good Good Poor Good Excellent Good Excellent Good
Good Poor Poor Good Good Good Good Good
Poor Poor Poor Poor Poor Poor Poor Poor
3.2. Accelerated tests on painted panels 3.2.1. Salt spray testing The results obtained after 720 h of salt spray testing are presented in Table 10. The alkyd primers formulated with medium oil linseed and sacha inchi resins showed identical degrees of oxidation and blistering as a function of testing time. On the other hand, as shown in Fig. 5, an increase in the content of maleic anhydride in the alkyd resin appeared to slightly improve the resistance of the resin to oxidation. The paint systems with linseed oil- and sacha inchi oil-based alkyd primers showed similar behaviour in terms of resistance to corrosion and blistering in the salt spray test.
Table 10 Salt spray test: Rusting and blistering degrees, 720 h. Sample
P-LM-0% P-SM-0% P-SM-2% P-SM-4% S-LM-0% S-SM-0% S-SM-2% S-SM-4%
Degree of Rusting
Degree of Blistering
24h
48h
96h
168h
720h
24h
48h
96h
168h
720h
9 8 9 9 10 10 10 10
6 6 8 7 9 10 9 9
4 4 6 5 9 8 8 9
2 2 5 4 8 7 8 7
0 0 0 0 4 3 3 4
10 10 10 10 10 10 10 10
10 10 10 10 10 10 10 10
10 10 10 8M 10 10 10 10
8M 8M 8F 8M 10 8F 8F 10
4M 4MD 2MD 4MD 2F 2M 4M 6M
3.2.2. Sulphur dioxide testing As shown in Table 11 and Fig. 6, the sacha inchi oil-based primers showed better resistance to oxidation than the linseed oil-based primer. Regarding the degree of blistering, the test pieces protected with linseed oil-based paints had slightly better performances towards the end 6
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Fig. 5. Rusting degree as a function of the time of the alkyd primers after 720 h of salt spray test.
of the tests in both the primer and complete systems.
Table 11 Sulphur dioxide test: Rusting and blistering degrees, 456 h. Sample
P-LM-0% P-SM-0% P-SM-2% P-SM-4% S-LM-0% S-SM-0% S-SM-2% S-SM-4%
Degree of Rusting
Degree of Blistering
24h
48h
96h
168h
456h
24h
48h
96h
168h
456h
10 10 10 10 10 10 10 10
9 9 9 9 10 10 10 10
9 8 9 9 10 10 10 10
7 7 8 8 10 10 10 10
1 2 3 3 8 7 9 7
10 10 10 10 10 10 10 10
10 10 10 10 10 10 10 10
10 10 8F 10 10 8F 10 10
8F 8F 8M 8F 10 8F 8F 8F
8MD 6MD 6MD 6M 8M 6M 6M 6M
3.2.3. Accelerated weathering testing Fig. 7 shows the evolution of the gloss of the specimens measured at 60° in an accelerated weathering chamber for 504 h. At the beginning of the test, the specimens protected with sacha inchi oil-based primers showed better gloss retention than the linseed oil-based alkyd primer. On the other hand, towards the end of the testing, all the painted specimens presented the same degradation in terms of gloss. Likewise, the initial gloss of the sacha inchi oil increased with increasing content of maleic anhydride in the alkyd resin.
Fig. 6. Visual appearance of the specimens painted with alkyd primers after the 456 h of accelerated test in sulfur dioxide chamber. 7
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Fig. 7. Evolution of gloss at 60° of linseed and sacha inchi oil alkyd primers after 504 h of accelerated weathering test.
4. Conclusion
[4] L.N. Tuck, Waterborne and Solvent Based surface coating resins and Their Applications: Waterborne and Solvent Based Alkyds and Their End User Applications – Volume VI Volume 6 John Wiley & Sons Ltd., London, 2000. [5] M.M. Bora, R. Deka, N. Ahmed, D.K. Kakati, Karanja (Millettia pinnata (L.) Panigrahi) seed oil as a renewable raw material for the synthesis of alkyd resin, Ind. Crops Prod. 61 (2014) 106–114, https://doi.org/10.1016/j.indcrop.2014.06.048. [6] C.F. Uzoh, O.D. Onukwuli, R.S. Odera, S. Ofochebe, Optimization of polyesterification process for production of palm oil modified alkyd resin using response surface methodology, J. Environ. Chem. Eng. 1 (2013) 777–785, https://doi.org/ 10.1016/j.jece.2013.07.021. [7] M. Boruah, P. Gogoi, B. Adhikari, S.K. Dolui, Preparation and characterization of Jatropha Curcas oil based alkyd resin suitable for surface coating, Prog. Org. Coat. 74 (2012) 596–602, https://doi.org/10.1016/j.porgcoat.2012.02.007. [8] A.A. Nanvaee, R. Yahya, S.N. Gan, Cleaner production through using by-product palm stearin to synthesis alkyd resin for coating applications, J. Clean. Prod. 54 (2013) 307–314, https://doi.org/10.1016/j.jclepro.2013.04.027. [9] D.S. Ogunniyi, T.E. Odetoye, Preparation and evaluation of tobacco seed oil-modified alkyd resins, Bioresour. Technol. 99 (2008) 1300–1304, https://doi.org/10. 1016/j.biortech.2007.02.044. [10] A. Mukhtar, H. Ullah, H. Mukhtar, Fatty acid composition of tobacco seed oil and synthesis of alkyd resin, Chin. J. Chem. 25 (2007) 705–708, https://doi.org/10. 1002/cjoc.200790132. [11] H. Nosal, J. Nowicki, M. Warzała, E. Nowakowska-Bogdan, M. Zarębska, Synthesis and characterization of alkyd resins based on Camelina sativa oil and polyglycerol, Prog. Org. Coat. 86 (2015) 59–70, https://doi.org/10.1016/j.porgcoat.2015.04. 009. [12] A.I. Aigbodion, F.E. Okieimen, An investigation of the utilisation of African locustbean seed oil in the preparation of alkyd resins, Ind. Crops Prod. 13 (2001) 29–34, https://doi.org/10.1016/S0926-6690(00)00050-9. [13] S.H.U.I. De Silva, A.D.U.S. Amarasinghe, B.A.J.K. Premachandra, M.A.B. Prashantha, Effect of karawila (Momordica charantia) seed oil on synthesizing the alkyd resins based on soya bean (Glycine max) oil, Prog. Org. Coat. 74 (2012) 228–232, https://doi.org/10.1016/j.porgcoat.2011.12.013. [14] I.E. Ezeh, S.A. Umoren, E.E. Essien, A.P. Udoh, Studies on the utilization of Hura crepitans L. seed oil in the preparation of alkyd resins, Ind. Crops Prod. 36 (2012) 94–99, https://doi.org/10.1016/j.indcrop.2011.08.013. [15] N. Dutta, N. Karak, S.K. Dolui, Synthesis and characterization of polyester resins based on Nahar seed oil, Prog. Org. Coat. 49 (2004) 146–152, https://doi.org/10. 1016/j.porgcoat.2003.09.005. [16] M.D. Guillén, A. Ruiz, N. Cabo, R. Chirinos, G. Pascual, Characterization of sacha inchi (Plukenetia volubilis L.) Oil by FTIR spectroscopy and1H NMR. Comparison with linseed oil, JAOCS, J. Am. Oil Chem. Soc. 80 (2003) 755–762, https://doi.org/ 10.1007/s11746-003-0768-z. [17] B.R. Hamaker, C. Valles, R. Gilman, R.M. Hardmeier, D. Clark, H.H. Garcia, A.E. Gonzales, I. Kohlstad, M. Castro, R. Valdivida, T. Rodriguez, M. Lescano, Amino Acid and Fatty Acid profiles of the inca peanut (Plukenetia volubilis), Cereal Chem. 69 (1992) 461–563 (Accessed 23 May 2019), https://www.aaccnet.org/ publications/cc/backissues/1992/Documents/69_461.pdf. [18] L.F. Gutiérrez, L.M. Rosada, Á. Jiménez, Chemical composition of Sacha Inchi (Plukenetia volubilisi L.) seeds and characteristics of their lipid fraction, Grasas y Aceites 62 (2011) 76–83, https://doi.org/10.3989/gya044510.
Short and medium oil alkyd resins based on sacha inchi oil and its variations in different proportions of phthalic and maleic anhydride were successfully synthesized. The resin structures were confirmed by FTIR and 1H NMR analyses. The resins had comparable viscosity and density; however, the sacha inchi oil-based resins presented lighter Gardner colours than the linseed oil-based alkyd resin. Maleic anhydride improved the thermal properties and decreased the drying time of the resins. In addition, the cured resins had hardness and chemical resistance properties that make the resins suitable for use in surface coatings. The paints formulated with sacha inchi-based medium oil resins showed similar behaviour and, in certain cases, better properties than that of the linseed oil in the corrosion and accelerated ageing tests. This study revealed that sacha inchi oil can be used as a raw material alternative to linseed oil in the synthesis of alkyd resins for industrial applications. Acknowledgements This research was funded by the National Fund for Scientific and Technological Development and Technological Innovation (FONDECYT-Perú) and the PUCP agreement (Pontificia Universidad Católica del Perú / FONDECYT) [grant 166- 2015-FONDECYT-DE]. The authors thank the Nuclear Magnetic Resonance Laboratory (Chemical Unit - PUCP) for the 1H NMR analysis and the Materials Laboratory (Mechanical Engineering Unit - PUCP) for the thermogravimetric analysis. References [1] M.M. Bora, P. Gogoi, D.C. Deka, D.K. Kakati, Synthesis and characterization of yellow oleander (Thevetia peruviana) seed oil-based alkyd resin, Ind. Crops Prod. 52 (2014) 721–728, https://doi.org/10.1016/j.indcrop.2013.11.012. [2] S. Miao, P. Wang, Z. Su, S. Zhang, Vegetable-oil-based polymers as future polymeric biomaterials, Acta Biomater. 10 (2014) 1692–1704, https://doi.org/10.1016/j. actbio.2013.08.040. [3] A.I. Aigbodion, C.K.S. Pillai, Synthesis and molecular weight characterization of rubber seed oil-modified alkyd resins, J. Appl. Polym. Sci. 79 (2001) 2431–2438, https://doi.org/10.1002/1097-4628(20010328)79:13<2431::AID-APP1050>3.0. CO;2-A.
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