Alkyd resin synthesis by enzymatic alcoholysis

Iranian Polymer Journal https://doi.org/10.1007/s13726-019-00738-y ORIGINAL RESEARCH Alkyd resin synthesis by enzymatic alcoholysis Renata Kobal Campos de Carvalho1 · Fernando dos Santos Ortega2 · Andreia de Araújo Morandim‑Giannetti1 Received: 13 February 2019 / Revised: 28 May 2019 / Accepted: 21 July 2019 © Iran Polymer and Petrochemical Institute 2019 Abstract The synthesis of an alkyd resin through an enzymatic alcoholysis provided by Novozym 435 was analyzed in this study. The alcoholyses were performed in different enzyme concentrations (2.63, 4.00, 6.00, 8.00, and 9.36%, based on oil’s mass), oil/glycerin ratios (1.68, 2.50, 3.50, 4.50, and 5.18 oil mol/glycerin mol), at temperatures (33.18, 40.00, 50.00, 60.00, and 66.82 °C) to determine the best reaction conditions for obtaining the highest percentage of monoacylglycerides and diacylglycerides [glycerin/vegetal oil ratio of 1:3.5 (mol/mol), at temperature of 56.73 °C, and 9.36% enzyme concentration based on oil’s mass (w/w)]. It was verified that 2 h was the ideal reaction time. Under the best alcoholysis condition, the alkyd resin was produced using phthalic anhydride and the product presented similar characteristics as the current resin produced by a chemical catalyst in the industrial process (final viscosity = Y2, solid content = 44.00%, and IA ≤ 12). 1H NMR and FTIR analyses confirmed the formation of an alkyd resin as they showed the presence of characteristic signals of the final product. The re-usability of the enzyme was investigated, and significant results were observed in the reaction after five cycles (by activity reduction of 6%) showing the viability of applying enzymatic steps in industrial procedures to produce resins in the future, once the application of enzymes also reduced the level of toxicity in the processes. Keywords Design of experiments · Alkyd resin · Enzymatic alcoholysis · Enzymatic catalysis · Novozym 435 Introduction The application of polymer materials has grown substantially in this century with a depletion of resources derived from petroleum [1, 2]. This has led to an advance in the research related to the substitution of synthetic raw materials by natural and renewable non-petrochemical resources, such as the production of alkyd resins, considered an eco-friendly compound [3–5]. Alkyd resins consist of a special polyester family which have been used for approximately 100 years [4, 6, 7], of great industrial importance with a high application to produce several types of paints [8] (representing 50% of the utilized resins), adhesive tapes, lacquer, and resins [9–11]. In this context, many studies on innovation related to this class of alkyd resin have been developed, such as the * Andreia de Araújo Morandim-Giannetti [email protected] 1 Department of Chemical Engineering, Centro Universitário FEI, São Bernardo do Campo, São Paulo, Brazil 2 Department of Materials Engineering, Centro Universitário FEI, São Bernardo do Campo, São Paulo, Brazil preparation stages, which involve condensation reactions of polyalcohols, fatty acids, vegetable oils (Chinese wood oil, tall oil fatty acid, soybean oil, yellow oleander, seed oil, Parinari polyandra Benth seed oil, castor oil, sunflower oil, and coconut oil), or polyacids [4, 8, 12]. It is also possible to mention studies involving new ways to obtain intermediates, mainly related to alcoholysis reaction [8, 12, 13]. These reactions are frequently used due to difficulties in adding fatty acids and glycerin directly to the production of alkyd resins. Different polyalcohols can be mentioned in this process, such as pentaerythritol, ethylene glycol, trimethylolpropane, neopentyl glycol, and glycerol. In this context, different intermediates can be obtained, which would be used in the final esterification with different polyacids, such as phthalic anhydride, trimellitic anhydride, maleic anhydride, and fumaric acid, leading to the final resin with specific characteristics [6]. Therefore, due to several possibilities to modify reagents and combine them with other resins, such as phenolic, acrylic, vinyl, epoxy, and silicone, the use of these compounds allows the attainment of products with different properties [1–3]. Among these characteristics, it is possible 13 Vol.:(0123456789) Iranian Polymer Journal to highlight their resistance to alkaline media, thermal stability, corrosion resistance, fast drying [6, 7, 13], better properties related to superficial tension, adhesion, excellent luster and adherence, easy leveling during the application, and compatibility with other resins, which have fostered their application ever intensified in the chemical industry [14–16]. In this context, this work focuses on the development of an environmentally friendly enzymatic transesterification intermediate stage, particularly when it uses Novozym 435 (lipase B from Candida antarctica) as catalyst, the most common immobilized lipases used in processes [17, 18]. This procedure aims at replacing the ongoing chemical process and reducing the generation of toxic waste originated from the current chemical catalyst. It also corroborates with new research that has been of increasing importance as a new trend in biotechnological processes, thus contributing to the green polymer chemistry [19]. Experimental Materials To carry out the characterizations of the reagents and enzymatic alcoholyses, Novozym 435 was purchased from Novozymes Latin America (Araucária, Brazil). The glycerin (≤ 100%), tetrahydrofuran (THF) (≥ 99.9%), tert-butanol (≥ 99.5%), acetone (≥ 99.9%), analytical grade, and acetonitrile (≥ 99.9%) HPLC grade were purchased from Sigma-Aldrich (St. Louis, MO, USA). Phthalic anhydride (99.5%) was purchased from Petrom (Mogi das Cruzes, Brazil), xylene (98.5%) was purchased from Merck (Darmstadt, Germany), and mineral turpentine was purchased from Petrobrás Distribuidora (Rio de Janeiro, Brazil), which was provided by BASF SA (São Bernardo do Campo, Brazil). Optimization of enzymatic alcoholysis Before beginning the alcoholysis stage, the characterization of soybean oil was carried out, determining the acidic index according to the AOCS Cd 3d-63 and the saponification index according to the AOCS Cd 3b-76 [15]. With these data, it was possible to determine the oil’s average molar mass using Eq. (1): ̄ oil = M 3 × MKOH (IS −IA ) 1000 , (1) where MKOH is the molar mass of KOH; IS represents the saponification index; IA is the acidic index; and Moil is the oil’s average molar mass. 13 The composition of the oil used and the best solvent to be applied during the alcoholysis were also determined, as well as the enzymatic activity of Novozym 435 in the presence of hexane, t-butanol, tetrahydrofuran, and water [16], in order to verify the best reaction solvent. The enzymatic activity of Novozym 435 was determined for each of the solvents applied using Eq. (2): ( ) − VkOH2 ] [V U = KOH1 × 1000 × c, Activity (2) g txm where activity (Ug−1) represents the necessary quantity of enzymes to consume 1 µmol of oleic acid per minute (U) under reaction conditions; VKOH1 represents the volume spent during the titration without adding the enzyme (mL); VKOH2 represents the volume used during the titration including the enzyme (mL); c is the solution’s concentration (g mL−1); t is the time; and m is the sample’s mass (g). After this stage, experiments on enzymatic alcoholyses (Fig. 1) were carried out to determine the best reaction condition to obtain an elevated percentage of monoglycerides and diglycerides. These experiments were conducted by varying the enzyme concentrations (2.63, 4.00, 6.00, 8.00, and 9.36%, related to the oil’s mass), the oil/glycerin ratios (1.68, 2.50, 3.50, 4.50, and 5.18 oil/glycerin at mol/mol), and the reaction temperatures (33.18, 40.00, 50.00, 60.00, and 66.82 °C) (Table 1). The procedures were carried out in duplicate in a Shaker Innova 43 incubator, Eppendorf International (Hamburg, Germany) at 300 rpm and during 40 min. The products of the reactions were analyzed using a Shimadzu HPLC system (Kyoto, Japan) made by LC-20AD pumps, RID-10A refraction index detector, UV SPD-20A detector, CTO-20A column oven and CBM-20A controller, Shim-pack CLC-ODS (C18) 4.6 mm × 150 mm column with CLC-ODS pre-column, determining the percentages of monoglycerides, diglycerides, and triglycerides. The mobile stage consisted of an isocratic gradient (60% acetone and 40% acetonitrile). The detector used was the refraction index with a flux of 0.6 mL/min. The data obtained were analyzed using the Statistica 12.0 software (Stat Soft, 2014, Oklahoma, USA) with a confidence level of 95% to define the best reaction conditions. To this end, a rotational central composite design statistical planning (RCCD) was used and the results were evaluated by response surfaces [20]. The variables which mostly influenced the process were also evaluated. By using the desirability function (Eq. 3), through the use of restrictions, it was possible to determine the condition which allowed the highest conversion from oil to monoglycerides and diglycerides: √ D = m d1 d2 … d m , (3) Iranian Polymer Journal Fig. 1 The proposed mechanism involved in enzymatic alcoholysis where d describes the individual desirability and m describes the number of parameters analyzed. The most important parameters that affect a material achieved with the desired characteristics were verified by analyzing the Pareto charts with a 95% confidence interval for the selection of significant variables. The standardized effects were determined for each input variable (enzyme concentration, the oil/glycerin ratio, and the reaction’s temperature) and the interaction among these variables was determined by Eq. (4): tcal = 𝜃 , EP(𝜃) (4) where tcal represents the standardized effects; θ is the value of the effect; and EP(θ) shows the standard error for each effect. Besides the time factor, the oil/glycerin ratio, and the catalyst percentage, a study was also conducted to determine the optimal reaction time. This way, experiments were carried out in duplicate using the best parameters obtained after the analysis of the data acquired through statistical planning, varying the times in 1, 2, 4, 6, 8, 12, and 24 h. The samples were also evaluated by HPLC. The tests were performed aiming at recovering the catalyst and making the process more viable with less environmental impact, as “rejects” would not be generated for the catalyst to dispose. In this context, enzyme recovery was evaluated for five cycles and the data analyzed by HPLC. After determining the best conditions to carry out the alcoholysis and posterior attainment of the alkyd resin, the product of this stage was evaluated through the solubility test in methanol [21]. Attainment of the alkyd resin The product obtained after the optimization in enzymatic alcoholysis conditions was submitted to the resin attainment process in an Inox Reactor with agitation and capacity of 3 L, provided with electrical heating/cooling and digital temperature control, reflux condenser and N2 atmosphere. 13 Iranian Polymer Journal Table 1 Variables in optimization of alcoholysis stage Table 2 Composition of soybean oil Temperature (°C) Compound Percentage (%) Myristic acid Palmitic acid Palmitoleic acid Stearic acid Oleic acid Linoleic acid Linolenic acid Other components 0.12 11.40 0.16 4.14 23.47 53.46 6.64 0.57 50.00 (0) 50.00 (0) 50.00 (0) 50.00 (0) 50.00 (0) 50.00 (0) 60.00 (+ 1) 60.00 (+ 1) 60.00 (+ 1) 60.00 (+ 1) 40.00 (− 1) 40.00 (− 1) 40.00 (− 1) 40.00 (− 1) 66.82 (+ 1.68) 33.18 (− 1.68) Oil/glycerin ratio (oil mol/glycerin mol) 3.50 (0) 5.18 (+ 1.68) 1.82 (− 1.68) 3.50 (0) 3.50 (0) 3.50 (0) 2.50 (− 1) 4.50 (+ 1) 4.50 (+ 1) 2.50 (− 1) 4.50 (+ 1) 2.50 (− 1) 2.50 (− 1) 4.50 (+ 1) 3.50 (0) 3.50 (0) Catalyst (%) (based on oil’s mass) 2.63 (− 1.68) 6.00 (0) 6.00 (0) 6.00 (0) 9.36 (+ 1.68) 6.00 (0) 8.00 (+ 1) 8.00 (+ 1) 4.00 (− 1) 4.00 (− 1) 4.00 (− 1) 4.00 (− 1) 8.00 (+ 1) 8.00 (+ 1) 6.00 (0) 6.00 (0) For this process, an m/m ratio of 34.02% of soybean oil, 7.08% of glycerin, 10.72% of THF, 1.29% of Novozym 435, 10.53% of phthalic anhydride, 0.72% of xylene, and 33.00% of turpentine were used. The reaction was conducted until the desired acidity and viscosity were obtained (lower than 12 and between Z and Z2, respectively). The resin was characterized through the Gardner viscosity and color scales, acidity index, and determination of rheological parameters. The Gardner viscosity scale, the acidity index, and the Gardner color were determined by the ASTM D1545, D1639, and D1544 methods, respectively [22]. The alkyd resin was also characterized through nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR), and rheological analysis. The 1H NMR and 13C NMR spectra were obtained using Chloroform-d (CDCl3) with a Bruker Avance III 600 HD spectrometer (Germany) operating at 600 MHz for protons and 150 MHz for carbon. Chemical shifts (δ, ppm) were reported relative to tetramethylsilane (TMS). The infrared spectroscopy analysis was performed using a Thermo Scientific Nicolet 6700 FTIR Spectrophotometer (USA). The attenuated total reflectance spectrum was collected in the range of 4,000–500 cm−1 with a resolution of 4 cm−1 and 256 scans per sample. The rheological characteristics of the oil, alcoholysis product, and alkyd resin were investigated using a rotational viscometer model DV-II + Pro with an SC4-25 spindle (Brookfield, USA) for alkyd resin and an SC4-18 spindle (Brookfield, USA) for oil and alcoholysis products. The samples (10 mL) were placed into a cylindrical sample 13 chamber equipped with a temperature probe (SC4-13RP, accuracy of ± 0.1 °C) and attached to a water jacket assembly. The temperature was maintained at 36.8 °C (± 0.1 °C) using a temperature-controlled stirred water bath (Brookfield EX-200, USA). In order to reduce heat loss during the experiment, the sample chamber was covered with an insulation cap. The analysis consisted of measuring the shear stress as the shear rate gradually increased, in 8 steps, from 5 to 35 s−1 and then returned to 5 s−1, following the same path. An equilibration time of 10 s was held on each shear rate before the shear stress was measured. The data were analyzed using Eqs. (5) and (6) 𝜏 = K ⋅ 𝛾̇ n , (5) 𝜂ap = 𝜏∕𝛾, ̇ (6) where τ is the shear stress; K is the consistency index; 𝛾̇ is the shear rate (s−1); n is the dimensionless power law index; and ηap (mPa s) is the apparent viscosity. Results and discussion Physicochemical properties of the oil During the process to determine the best enzymatic alcoholysis conditions to obtain alkyd resins, soybean oil was initially characterized. An acidity index of (1.00 ± 0.12 mg KOH g−1), a saponification index of 182.27 ± 11.16 mg KOH g−1, an average molar mass of 927.30 gmol−1, and the composition (Table 2) were determined. Optimization of enzymatic alcohololysis After characterizing the soybean oil, the alcoholysis stage was optimized. To this end, a study on the influence of applying different solvents in the process was carried out. This analysis was needed because the viscosity proved to be an important factor during the enzymatic processes, as Iranian Polymer Journal the high viscosity hinders the miscibility among the oil, glycerin and enzyme. Regarding the enzymatic activity, it was possible to verify an activity of 15.00, 51.50, 36.50, and 33.00 U/g using hexane, t-butanol, tetrahydrofuran (THF), and water, respectively [15]. Therefore, t-butanol, a low-cost non-toxic solvent, was chosen to carry out all alcoholysis reactions. The results of monoglyceride, diglyceride, and triglyceride percentages are shown in Table 3 [18]. Analyzing the data on monoglycerides, diglycerides, and triglycerides regarding each of the alcoholyses, a reduction of triglyceride percentage and a significant increase in monoglyceride and diglyceride percentages can be verified. Through the analysis of the Pareto diagram (Fig. 2) and considering p equal to 0.05 with a confidence level of 95.00%, it was possible to evaluate the variables which mostly influenced the process and the interactions among them. Therefore, analyzing the effects related to the production of monoglycerides, it was possible to verify that the temperature (linear and quadratic terms) and the catalyst percentage (linear) were the variables which mostly influenced their attainment. This can be explained possibly by the inactivation of the enzyme when the temperature is increased due to the denaturation, and the increased probability of ruptures of the same molecule by the increase in catalyst’s concentration. Regarding the conversion of diglycerides, only the linear and quadratic terms related to the temperature influenced the process. Table 3 Monoglyceride, diglyceride, and triglyceride percentages obtained in each reaction The terms “linear” and “quadratic” concerning the temperature influenced on the consumption of triglycerides, as well as the enzyme’s concentration. Once the enzyme’s denaturation happens, its inactivity increases, thus reducing the reaction’s yield. The lower the enzyme’s concentration, the higher would be the probability of preserving the triglycerides. It is also possible to verify that the variables which mostly influenced the process to form monoglycerides were the temperature and the enzyme’s concentration (Fig. 2a). This analysis confirms the hypothesis of a possible inactivity of the enzyme due to the denaturation when the temperature is greatly increased. This leads to the need for higher enzymatic concentrations for larger numbers of breaks in the triglycerides’ structure, thus obtaining a higher concentration of monoglycerides. The temperature was the variable which mostly influenced the formation of diglycerides, as well as monoglycerides. However, in this case, the catalyst’s concentration did not have a significant influence, as the smaller concentrations performed fewer breaks, allowing the formation of diglycerides, as previously mentioned (Fig. 2b). Concerning triglycerides (Fig. 2c), the percentage was affected by the temperature and the enzyme’s concentration. In this case, the elevated temperature led to the denaturation of the enzyme, minimizing the formation of monoglycerides and diglycerides. The enzyme’s low concentrations hindered the occurrence of a reaction. Analyzing the contour surfaces (Fig. 3), it was possible to verify that very low or very high temperatures impair the formation of mono and diglycerides. The higher the Independent variable Dependent variable Temperature (°C) Oil/glycerin ratio Catalyst (%) Monoglycerides (%) Diglycerides (%) Triglycerides (%) 0.0 50.0 50.0 50.0 50.0 50.0 50.0 60.0 60.0 60.0 60.0 40.0 40.0 40.0 40.0 66.8 33.2 0.00 3.50 5.18 1.82 3.50 3.50 3.50 2.50 4.50 4.50 2.50 4.50 2.50 2.50 4.50 3.50 3.50 0.00 2.64 6.00 6.00 6.00 9.36 6.00 8.00 8.00 4.00 4.00 4.00 4.00 8.00 8.00 6.00 6.00 3.59 ± 0.02 59.38 ± 5.75 68.47 ± 1.49 64.92 ± 2.35 63.26 ± 2.13 63.11 ± 1.76 51.83 ± 2.17 57.20 ± 8.72 68.12 ± 6.27 37.32 ± 4.31 43.58 ± 17.55 9.78 ± 0.39 17.44 ± 0.83 48.44 ± 4.58 25.65 ± 3.61 62.77 ± 3.01 9.00 ± 3.63 3.00 ± 0.06 36.85 ± 6.33 31.53 ± 1.49 33.35 ± 1.87 20.18 ± 1.35 28.69 ± 4.23 23.33 ± 3.77 38.91 ± 8.25 23.31 ± 6.83 29.99 ± 4.82 33.55 ± 11.95 5.35 ± 0.70 6.07 ± 0.03 19.79 ± 1.17 7.90 ± 0.53 21.84 ± 2.70 4.14 ± 1.38 93.41 ± 0.04 3.77 ± 0.58 0.00 ± 0.00 1.73 ± 0.47 16.56 ± 0.78 8.20 ± 2.47 24.84 ± 5.95 3.88 ± 0.47 8.57 ± 0.56 32.69 ± 0.51 22.87 ± 5.60 84.87 ± 1.09 76.49 ± 0.80 31.76 ± 5.75 66.45 ± 3.09 15.40 ± 0.31 86.86 ± 5.01 13 Iranian Polymer Journal In Table 4, the regression coefficients obtained during the analysis of the enzymatic alcoholysis data show the effects of the variables studied (temperature, oil/glycerin ratio, or catalyst’s percentage) in the production of monoacylglycerides, diacylglycerides and consumption of triacylglycerides. Besides the data analysis and the verification of the influence of each parameter, the condition which led to the attainment of the largest quantity of monoacylglycerides and diacylglycerides was determined using the desirability function (Fig. 4) (temperature at 56.70 °C, molar ratio at 1:3.5, catalyst’s percentage = 9.36%) with a confidence level above 95%. After the analysis on the influence of temperature, oil/ glycerin ratio, and enzyme’s concentration, studies on the optimal reaction time were carried out. It was verified that 2 h was the ideal time to convert and obtain the contents of monoacylglycerides and diacylglycerides needed in producing the alkyd resin (approximately 95% conversion) (Fig. 5). It is also important to highlight that the standard deviations obtained during the analyses are justified by the fact that the enzyme is a non-specific catalyst to form mono or diglycerides, thus deviations above 1% are normally acceptable. The optimal alcoholysis obtained with the parameters established above (56.70 °C, glycerin/oil molar ratio of 1:3.5 m/m, and a catalyst’s percentage of 9.36%) was submitted to the esterification with phthalic anhydride. The solvent was added to control the desirable viscosity and acidity in the process, and after the specified values obtained, the final resin was diluted. Attainment and characterization of the alkyd resin Fig. 2 Standardized main effect through the Pareto charts: the variables which mostly influence the production of monoacylglycerides (a), diacylglycerides (b), and the conservation of triacylglycerides (c) enzyme’s concentration, the higher the production of monoacylglycerides and diacylglycerides, as the oil/glycerin ratio did not provide a significant influence on the process. 13 A resin was produced with the same viscosity and acidity as shown in Table 5. The first result of viscosity was obtained with 6 h of esterification. The final viscosity attained was Y2, and the content of solids was 44.00%. It is important to highlight that, during the esterification of an alkyd resin, the viscosity values obtained are only referential, as the acidity level is the main control variable in the development. Therefore, the control of the advancement is carried out until a lower level of acidity or similar to the specified is attained (IA ≤ 12). The final viscosity level is extremely important for the final application. It defines the quantity of solvent that is used in the formulation of the resin during the process and final stages of the production of coatings and paintings, for example, along with the content of the solids of the resin. The viscosities of the soybean oil, alcoholysis product, and resin showed that the materials exhibit Newtonian behavior, including shear-dependent viscosity and yield stress (Table 6). These characteristics could be investigated Iranian Polymer Journal Fig. 3 Contour surface during the alcoholysis process’s optimization Table 4 Equations of the curve for monoglycerides and diglycerides Polynomial equation: a0 + a1X1 + a2X2 + a3X3 + a4X1X2 + a5X1X3 + a6X2X3 + a7X12 + a8X22 + a9X32 R2 Mono Di Tri 0.747 0.774 0.814 Linear parameter Quadratic parameter a0 a1 a2 a3 a4 a5 a6 a7 a8 a9 − 266.200 − 147.202 513.402 11.369 6.230 − 17.600 − 20.740 − 6.876 27.616 11.140 2.935 − 14.074 0.439 0.082 − 0.357 − 0.015 − 0.110 0.125 0.127 − 1.450 1.323 − 0.114 − 0.044 0.158 − 0.489 2.446 − 1.956 − 0.604 0.640 − 0.036 X1 = temperature, X2 = oil/glycerin ratio, and X3 = enzyme’s concentration through the tests that measure the shear stress as a function of a shear rate applied to the fluid. It was also found that the viscosity increases significantly at the end of the resin formation process when compared to the oil viscosity of the product of alcoholysis, to indicate the occurrence of polymerization. By analyzing the obtained 1H NMR spectrum (Figs. 6, 7) for the alkyd resin produced, there are signals with chemical shifts of 0.883–0.896 ppm relative to the hydrogens of the methyl group peaks of the fatty acid chain. It is also possible to observe the presence of signals at 1.249–1.592 ppm and 2.038–2.766 ppm relative to the –CH2 aliphatic chain group of the fatty acid of soybean oil and allylic hydrogens, respectively. The presence of glycerin can be confirmed by the signals at 4.127 ppm and 4.304 ppm. The other signals at 7.507, 7.693, and 5.329 ppm could be attributed to hydrogens of phthalic anhydride and the presence of unsaturations in the main fatty acids of soybean oil. By analyzing the spectra obtained for the soybean oil and for the alcoholysis product, it was possible to observe the presence of fatty acid protons, as well as glycerin protons, and the absence of signals related to aromatic protons. These data corroborate with the results obtained by Patil et al. and Poorabdollah et al., confirming the attainment of the resin through enzymatic alcoholysis [9, 23, 24]. 13 Iranian Polymer Journal Fig. 4 Optimal reaction conditions using the desirability function Table 5 Results of viscosity and acidity obtained during the production of the resin Fig. 5 Content of acyl glycerides obtained after alcoholysis in accordance with the conversion time 13 Esterification time (h) Process viscosity (Gardner) Acidity 6 7 8 9 10 11 12 13 13.5 N–O S– U+ V+ X+ Y– Y–Z Z Z2 29.70 22.80 19.30 17.40 15.20 13.80 13.10 12.60 12.1 The data obtained through FTIR analysis for the soybean oil, alcoholysis product, and resin (Fig. 8) indicated the presence of bands at approximately 1500 and 750 cm−1, which can be attributed to the –C–H bending and rocking vibrations, respectively. Iranian Polymer Journal Table 6 Rheological parameters obtained from the power law model for alkyd resin Parameter Soybean oil Alcoholysis product Alkyd resin K (mPa sn) n R2 ηapp (mPa s) 34.55 0.99 0.99 32.43–33.59 41.88 0.99 0.99 39.91–41.24 3154.28 0.99 0.99 3121.29–3080.94 The presence of bands was also verified in the region of 1,150 and 1750 cm−1 assigned to the C–O–C stretching vibration of the ester group and C=O stretching vibration of the carbonyl group, respectively, as well as bands at 2950, 2850, and 3200–3500 cm−1 referring to the –C–H symmetric and asymmetric-stretching vibration and the hydroxyl group. The band at 3010 cm−1 assigned to the unsaturation (=C–H) and the aromatic C=C stretching frequency at 1580–1590 cm−1 confirmed the formation of the alkyd resin and corroborate with the results obtained by Patil et al. [9, 24]. Fig. 6 Representation of the reaction to obtain the alkyd resin from the enzymatic alcoholysis product Fig. 7 1H NMR spectra for the soybean oil, enzymatic alcoholysis product, and alkyd resin 13 Iranian Polymer Journal Conclusion Fig. 8 FTIR-ATR spectra for soybean oil, alcoholysis product and alkyd resin The enzymatic esterification reactions in a heterogeneous medium with Novozym 435 were effective to produce alkyd resins, presenting the same performance obtained in the process currently used by the industry through chemical catalysis. In the enzymatic alcoholysis reactions of soybean oil, the contents of monoglycerides and diglycerides obtained, when compared to the chemical alcoholysis, presented rather similar values and times, enabling the process to be carried out by enzymatic reaction. The best conversion into monoglycerides and diglycerides was acquired at temperature of 56.73 °C, molar ratio of 1:3.5 (glycerin/oil m/m), catalyst percentage of 9.36%, and 2 h duration. The use of an enzymatic catalyst has presented sustainable benefits, as it is perfectly possible to recover the enzyme to be reused in the production process. Acknowledgements The authors would like to thank BASF SA for allowing the use of its laboratories and facilities for the development of part of the work, Fundação Educacional Inaciana Padre Sabóia de Medeiros (Centro Universitário FEI) for supporting this research, and Dr. Nivaldo Boralle for the NMR measurements. 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