Synthesis and characterization of alkyd resins based

Progress in Organic Coatings 101 (2016) 553–568

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Synthesis and characterization of alkyd resins based on Camelina sativa oil, glycerol and selected epoxidized vegetable oils as functional modifiers Hanna Nosal ∗ , Janusz Nowicki, Marek Warzała, Izabela Semeniuk, Ewa Sabura Institute of Heavy Organic Synthesis “Blachownia”, Energetyków 9, PL 47-225 K˛edzierzyn-Ko´zle, Poland

a r t i c l e

i n f o

Article history: Received 16 July 2016 Received in revised form 28 September 2016 Accepted 3 October 2016 Keywords: Alkyd resins Camelina sativa oil Glycerol Epoxidized vegetable oil

a b s t r a c t Novel alkyd resins based on the Camelina sativa oil as a new renewable raw material and glycerol as a polyol component were synthesized. Selected epoxidized vegetable oils (linseed oil and camelina oil) as new functional modifiers were used in the alcoholysis reaction with purified camelina oil. The influence of the added epoxidized linseed oil and epoxidized camelina oil on the course of alkyd resin synthesis and the properties of the final products were investigated. The glycerol-based alkyd resins with improved properties were produced. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Alkyd resins are considered as one of the important class of synthetic polymers, which have been long known and produced in large commercial scale. Alkyd resins are widely used in the manufacture of paints and varnishes. The production volume in Europe currently amounts to about 450 thousand tons per year [1,2]. Plant oils, like soybean oil and linseed oil, and synthetic pentaerythritol and phthalic or maleic anhydrides make the commonly used raw materials for the production of alkyd resins [3]. One of the key challenges for modern chemistry is to develop new varieties of polymeric materials using renewable raw materials to replace depleting resources of fossil fuels and at the same time to reduce emissions of greenhouse gases which significantly impact the climate change. Glycerol can be considered as a potentially valuable renewable component for the synthesis of alkyd resins. It is a cheap and easily available raw material. The main source of glycerol in the European market is the biodiesel industry, where it is a main by-product (about 10 wt% of raw material) [4]. The use of glycerol for the synthesis of alkyd resins would make it possible to utilize the abundant volumes of glycerol, which are available in the market (about 900,000 t/y). Unfortunately, alkyd resins obtained from polyols with three or less hydroxyl groups (like glycerol) give

∗ Corresponding author. E-mail address: [email protected] (H. Nosal). http://dx.doi.org/10.1016/j.porgcoat.2016.10.003 0300-9440/© 2016 Elsevier B.V. All rights reserved.

coatings with poor performance properties, especially as regards their ability to cure. This property results from the presence of unsaturated bonds in the fatty acid chains, but which is equally important is the number of hydroxyl groups in polyols. For example, the resins obtained from pentaerythritol (four hydroxyl groups), offer significantly better coating properties than those obtained from glycerol. They dry out faster and they are harder and more resistant to moisture [5,6]. In our previous paper we described the possibility of using the glycerol oligomerization products as alternative raw materials for the synthesis of alkyd resins. This change led to glycerol-based alkyd resins with improved properties [7]. In this paper we propose a different solution for this issue, i.e. the use of selected epoxidized vegetable oils as modifiers in the resin synthesis. Due to high reactivity of their epoxide rings, epoxidized vegetable oils can form additional branches in the structure of the resin. A vegetable oil with higher functionality in the reaction system should allow to obtain resins with more branched structures. Various vegetable oils, mainly soybean oil and linseed oil, are used as fatty raw materials for the synthesis of alkyd resins. The authors of this study suggest replacing these traditional fatty raw materials with the plant oil extracted from Camelina sativa seeds. Camelina sativa seems an attractive alternative raw material because of its resistance to adverse soil and climatic conditions and its high resistance to such diseases as Alteraria brassicae [8,9] and to pests [10]. This makes it possible to use low-grade soil for cultivation of Camelina sativa, which are unsuitable for other crops

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H. Nosal et al. / Progress in Organic Coatings 101 (2016) 553–568

[11]. Most importantly, the camelina oil is characterized by a high degree of unsaturation, so that it can be an excellent raw material for the synthesis of alkyd resins. The application of modified vegetable oils like epoxidized vegetable oils and polyol oils (obtained by epoxidation of selected unsaturated vegetable oils and then by addition of water, or alcohol to the formed oxirane ring) in the synthesis of polyurethanes, epoxide resins and polyesters have been widely described in literature [12–16]. Epoxidized vegetable oils are also used as plasticizers and stabilizers for polyvinyl chloride (PVC) [17–19]. Epoxidized natural rubber was incorporated into the alkyd chain in order to improve the crosslink density of alkyd resins [20]. Muturi et al. reported the use of vernonia oil (a naturally occurring epoxidized vegetable oil) as an attractive reactive diluent for low-volatility organic compound [21]. They are also known some modified alkyd resins contain epoxidized vegetable oils as one of compounds (as adduct). The first example was achieved by heating epoxidized vegetable oil (e.g. epoxidized soybean oil), unsaturated fatty acid and organic sulfur compounds (e.g. 2-benzothiazolylthiosuccinic acid tertiary amine salt) until the acid number is lower than 25 mg KOH/g. The modified alkyd resins was obtained by mixing known amounts adduct with alkyd resin or adding known amount the adducts during manufacture of the resins [22]. An another example modified alkyd resin with improved properties was achieved by heating alkyd resins with epoxidized and unepoxidized vegetable oils and a metal drier at 30–120 ◦ C or by heating epoxidized and unepoxidized vegetable oils with the drier at 150–180 ◦ C before adding the alkyd resin [23]. However there are no reports on the use of epoxidized vegetable oils directly in the synthesis of alkyd resins. Epoxidized vegetable oils, due to high reactivity of the epoxide rings, can significantly affect the properties of the obtained polymers. Depending on the iodine number of vegetable oil, epoxidized oils with different contents of oxirane rings can be obtained. Epoxidation of two vegetable oils (camelina oil and linseed oil) with varying degrees of unsaturation was conducted within the present study. The epoxidation of unsaturated fatty raw materials are widely used in the industry. The most commonly method is based on oxidation with hydrogen peroxide as oxygen donor and carboxylic acid as oxygen carrier via peroxy carboxylic acid formed in situ in the reaction of a carboxylic acid (formic acid, acetic acid) with the aqueous solution of hydrogen peroxide [24–27]. In this paper this method (hydrogen peroxide and formic acid) was used to obtain epoxidized vegetable oils. This paper describes the synthesis of alkyd resins based on camelina oil as an oil component, glycerol as polyol, and with the addition of selected epoxidized vegetable oils as functional modifiers. The type of epoxidized plant oil used for the production of alkyds can have a significant impact on the properties of the final alkyd resins. Epoxidized camelina oil and linseed oil, which are significantly different in terms of their contents of oxirane rings were used as modifiers in alkyd resins.

2. Materials and methods 2.1. Materials Camelina oil was obtained from Industrial Institute of Agricultural Engineering, Poznan´ (Poland), and linseed oil was obtained from Eurolen (Poland). Commercial grade citric acid monohydrate 99.5% (Stanlab) and bleaching earth Rafinol 910 – acid-activated bentonite (Brenntag) were used to purify the camelina oil samples. Commercial grade 85.0 aq. wt% formic acid (Chempur) and 30.0 aq. wt% hydrogen peroxide (Chempur) were used for epoxidation of vegetable oil. Commercial grade di-sodium hydrogen phosphate dodecahydrate (Chempur) was used in purification of

epoxidized vegetable oil. Commercial grade glycerol 99.5% (Brenntag), phthalic anhydride 99.0% (Alfa Aesar), maleic anhydride ≥98.0% (Alfa Aesar), xylene ≥98.5% (POCh), and lithium hydroxide 98.0% anhydrous (Alfa Aesar) were used in this study to synthesize alkyd resins. White spirit ∼17.0 wt% aromatics basis (Sigma Aldrich) and anhydrous methanol 99.9% (POCh) were used as solvents. The siccative (Standard) containing: C7 -C12 hydrocarbons, Ca salts of C6 -C19 fatty acids, cobalt 2-ethylhexanoate, zirconium 2-(2-butoxyethoxy)ethanol (Co = 1.15–1.25%, Zr = 5.9–6.1%, Ca = 2.9–3.1%) was used as a drier. All raw materials, except camelina oil and linseed oil, were used without any further purification. 2.2. Analytical methods 2.2.1. Infrared Fourier Transformation (ATR-FTIR) analysis The infrared spectra were recorded on a THERMO Scientific FTIR Nicolet Model 6700 spectrophotometer. The tests applied the reflection technique with (ATR), SMART ARK, using ZnSe crystals, the number of reflections = 7, and the sample penetration depth by the IR beam = 1.11 ␮m. 2.2.2. Gas chromatography The GC/MS analysis was performed on a Hewlett Packard Model 7890 chromatograph equipped with a 7000 GC/MS Triple Quad MS detector. The GC analysis used a capillary column HT-5 (l = 30 m, diameter = 0.25 mm, grain size of stationary phase = 0.25 ␮m) and it followed the temperature-programmed mode from 70 to 380 ◦ C. Helium was used as a carrier gas, at the flow rate of 2 ml/min. The reaction mixture components were identified qualitatively by detailed interpretation of the mass spectra and – whenever possible – by looking for matching spectra provided in the reference library NIST MS Search 2.0. The concentrations of particular groups of compounds (i.e. quantitative analysis) were established by internal standardization of the chromatographic peak areas, assuming that the correction factors were equal to 1.0. These analyzes were performed on a Hewlett-Packard series II5890 chromatograph with the capillary column HT-5, flame ionization detector (FID), sample injector and sample splitter. 2.2.3. Thermogravimetric analysis (TGA) The thermo-oxidative stability of alkyd resins was investigated by thermogravimetric analysis (TGA). A Mettler Toledo TGA/SDTA851e Thermobalance was used for the TG measurements. The samples were heated up in an open platinum crucible (Pt 70 ␮l without lid), in the temperature range 25–600 ◦ C with the heating rate ␤ = 12 ◦ C/min, in the dynamic (100 ml/min) air atmosphere. The thermographs were analyzed with the use of the STARe Thermal Analysis Software (version 9.20) furnished with the instrument. 2.2.4. Gel permeation chromatography The gel permeation chromatography method (GPC) was used to determination the molecular masses of alkyd resin samples. The analyses were performed on a GPC system with a L-7100 pump (Merck Hitachi), VISCOTEK VE3580 refractive index detector, and operated under the GRAMS/386 software for the chromatography data system. The instrument was equipped with a guard column (PLgel 50 × 4.6 mm) and two columns (PLgel MiniMix E 3 ␮m 250 × 4.6 mm). Liquid chromatography grade THF was used as the eluent. The column temperature, the flow rate and the detector temperature were 22 ◦ C, 0.3 ml/min and 30 ◦ C, respectively. Low polydispersity linear polystyrene standards were used to construct a calibration curve based on the universal GPC calibration procedure.


2.2.5. Physicochemical characteristics The iodine value of camelina oil was determined according to the Polish Standard PN-87/C-04281. In this method, a fatty raw material is dissolved in the Kaufmann solution, it is left for a known length of time in the dark, than potassium iodide is added and the liberated free iodine is titrated with thiosulphate. The acid values of camelina oil and alkyd resins were found according to PN-EN 14104. The phosphorus contents in the samples of crude and purified camelina oil were analyzed by the UV/vis method, according to PN-ISO 10540-1:2005, using a UV/VIS HP 8452 Diode Array Spectrophotometer. The water content in camelina oil was determined according to the Polish Standard PN-ISO 760. These measurements were performed on a 870 KF Titrino Plus titration assembly (Metrohm). The hydroxyl values of fatty raw materials and alkyd resins were analyzed according to DIN 53240. Oxirane value was determined according to the Polish Standard PN-C-89085-13:1987. In this method, the sample is dissolved in hydrogen chloride solution in dioxane and is left for half an hour in a sealed flask, than cresol red is added and it is titrated with potassium hydroxide solution (0.1 M KOH in ethanol). The Gardner color specifications of camelina oil and alkyd resins were determined on a Lange Lico 4000 spectrophotometer. The viscosity of alkyd resins samples (55 wt% solutions in white spirit) were evaluated in the course of the synthesis (expressed in sec.; measured as the flow time from the Ford cup #4) according to PN-EN ISO 2431. A Brookfield viscometer was used to measure the dynamic viscosity values of the alkyd resin samples (55 wt% solutions in white spirit) at 22 ◦ C. The viscometer was equipped with the spindle № 28. The content of volatile compounds was estimated as the weight loss of the sample in the range of 25–150 ◦ C. The residue is the non-volatile compound. In this study, a Mettler Toledo TGA/SDTA-851 thermobalance was used.

2.3. Synthesis procedures 2.3.1. Purification of camelina oil and linseed oil The feed oil was refined by adding 35 wt% aqueous solution of citric acid (1 wt% on oil) at 30 ◦ C. The resulting mixture was first stirred vigorously for 10 min and then stirring was very slow for additional 4 h. The aqueous and oil phases were separated by centrifugation. The oil phase was mixed with 15 wt% aqueous solution of KOH (3 wt% on oil) at 50 ◦ C for 15 min. The aqueous phase was separated by centrifugation and the oil phase was dried by purging it with nitrogen at 105 ◦ C. The purified oil was heated up to 100 ◦ C and bleaching earth (Rafinol 910, 1 wt%) was added to it. The suspension was stirred for 30 min at 100 ◦ C and bleaching earth was separated by filtration.

2.3.2. Epoxidation of vegetable oils The vegetable oils epoxidation process was carried out in a 2500 ml laboratory glass reactor equipped with a mechanical stirrer. Formic acid (44.8 g) was added to linseed oil or camelina oil (300.0 g). The mixture was then vigorously stirred and heated up to 40 ◦ C. When the temperature reached about 40 ◦ C, 441.3 g of hydrogen peroxide (35 wt% aqueous solution) was added drop by drop for about one hour. Then the temperature was raised to 60 ◦ C and the reaction was continued for another 7 h. The reaction mixture was sampled after 1, 2, 4, 6 and 8 h. Each sample (also the postreaction mixture) was dissolved in ethyl acetate. The aqueous layer was removed and the organic phase was washed sequentially with 0.1 M Na2 HPO4 and with distilled water (with the amount corresponding to the sample volume) until pH of epoxidized vegetable oil reached close to 7. The purified samples and the product were dried under vacuum.

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Table 1 The percentage compositions of fatty raw materials in alkyd resins formulations. Component [wt%]

Epoxidized linseed oil Epoxidized camelina oil Camelina oil

Alkyd resins AR1

AR2

AR3

AR4

AR5

– – 100

10 – 90

20 – 80

– 10 90

– 20 80

2.4. Preparation and characterization of alkyd resins Five different alkyd resin samples were prepared. Four of them were based on glycerol as the polyol component and camelina oil as the fatty raw material with epoxidized linseed oil or epoxidized camelina oil as an additive. One resin sample, adopted as reference sample, was synthesized from glycerol as the polyol component and from camelina oil as the fatty raw material, and no modifier was added. The reactions were carried out in a 500 ml four-necked glass reactor equipped with a variable speed stirrer, thermometer, nitrogen inlet tube and condenser. The alkyd resins were synthesized in two stages. At the first stage, purified camelina oil was subjected to alcoholysis with glycerol at 220 ◦ C with lithium hydroxide (0.07 g) as a catalyst, and optionally epoxidized linseed oil or epoxidized camelina oil was added. The percentage compositions of fatty raw materials (173.5 g in total) in alkyd resins formulations were presented in Table 1. The alcoholysis reaction was monitored by sampling the reaction mixture every 30 min. Solubility of the samples in anhydrous methanol was verified at the 1:2 vol ratio (methanol test). The alcoholysis process was terminated when the methanol test was positive (one volume of the reaction mixture was fully soluble in two volumes of methanol). The test is based on the fact that diglycerides are poorly soluble in methanol, and triglycerides are not soluble in methanol, unlike monoglycerides. After the reaction was stopped, the reaction mixture was cooled down to 120 ◦ C. At the second stage, phthalic anhydride (54.7 g), maleic anhydride (1.3 g) and xylene (8.1 g) were added to the reaction mixture. The temperature was quickly raised to about 230 ◦ C and the intermediate product from the first stage was subjected to esterification with selected anhydrides to produce monoesters of dicarboxylic acids. After increasing the temperature to 230–250 ◦ C, the polycondensation process was initiated leading to an increase the molecular weight of the resins. Water formed in the condensation reaction was removed from the reaction mixture azeotropically with the use of xylene. The water/xylene azeotropic mixture was distilled out, condensed and collected in Dean-Stark trap. After phase separation the water phase was removed and the xylene phase was returned into reactor. The acid values of reaction mixtures and viscosity measurements (Ford cup #4, 55 wt% solution in white spirit, 20 ◦ C) were adopted to control the progress of the condensation process. The alkyd resin samples were finally characterized by FT-IR spectrophotometry. 2.4.1. Formulation of clear varnish and determination of its drying time The alkyd resins samples were diluted with white spirit (55 wt% solution) and mixed with a siccative (1 wt%) to produce clear varnishes. The varnish films were obtained by applying 5 ml volumes of clear varnishes on smooth and clean surfaces (10 × 10 cm glass plates) with the use of an applicator to form 0.06 mm films. The plates were then dried at room temperature (22 ◦ C). The surface of the varnish film was checked periodically until the film was dry (tack drying test). The test was performed according to PN-79/C81519, which defines two levels of drying. The first level of drying was carried out as follows: the test plate was exposed to 0.5 g of glass beads falling down from 30 ÷ 50 mm. After 1 min, the beads

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were removed with a soft brush to check whether the coat was damaged or not. The varnish films were found to have achieved the drying level 1 when the beads caused no damage to the film. The second level of the drying test was carried out as follows: the test plate was covered with a piece of filter paper and a 20 g weight was placed on the paper, with a rubber disk between the paper and the weight to distribute the pressure equally. The weight and the paper were removed after 1 min to check whether the coat was tack-free. 2.4.2. Bending resistance Determination of varnish films bending resistance was performed according to PN-EN ISO 1519:2002. Metal plates coated with varnish films after conditioning (18 days) were fastened and bent over a conical mandrel. The result of this method is expressed as the diameter of the first mandrel over which the coating cracks.

Table 2 Physicochemical properties of purified camelina oil and linseed oil. Properties

Camelina oil

Linseed oil

Color (Gardner scale) Monoglyceride (wt%) Diglyceride (wt%) Triglyceride (wt%) Free fatty acids (wt%) Acid value (mg KOH/g) Iodine value (g I2 /100 g) Saponification value (mg KOH/g) Water content (wt%) Phosphorus content (ppm)

1.0 0.48 2.09 96.81 0.55 0.35 144.0 191 0.03 7.2

4.0 0.03 2.46 96.42 0.42 0.10 170.0 190 0.02 8.5

Table 3 Chemical compositions of camelina oil and linseed oil. Fatty acid

2.4.3. Persoz pendulum hardness Determination of varnish films hardness applied onto glass panels was measured with a Persoz pendulum hardness tester according to PN-EN ISO 1522. The films of varnishes before tests were dried at atmospheric pressure at room temperature. The measurements were made after 7 and 10 days. The Persoz hardness gives the time in seconds for the swing amplitude of the Persoz pendulum to decrease from 12◦ to 4◦ . This method is based on the principle, that the hardness of a film is related to its capacity to dampen oscillations. The less attenuated the oscillations, the harder the film is. 3. Results and discussion 3.1. Purification and properties of camelina oil and linseed oil The physical and chemical properties of purified camelina oil and purified linseed oil (for comparison) were presented in Table 2. After purification, the content of free fatty acids (0.55 wt%), the acid value (0.35 mg KOH/g) and the content of phosphorus (7.2 ppm) were found sufficiently low in camelina oil, and thus the oil could be used as a raw material for the synthesis of alkyd resins. Similarly, purified linseed oil is characterized by a low content of free fatty acids (0.42 wt%), a low acid value (0.10 mg KOH/g) and a low content of phosphorus (8.5 ppm). Vegetable oils are characterized by various degrees of unsaturation and various lengths of hydrocarbon chains. It was particularly important to determine the iodine number (Table 2) and the fatty acid profile for camelina oil (Table 3) and to compare them with

Acids C22

Composition (wt%) Camelina oil

Linseed oil

5.48 2.59 18.45 15.42 34.04 1.52 17.96 4.49

5.88 4.39 17.57 11.15 60.19 0.44 0.23 0.12

equivalents for linseed oil since the changes in that profile change the crosslinking ability of resins. Linseed oil is characterized by a higher iodine number (170.0 g I2 /100 g) and higher degree of unsaturation. The content of highly unsaturated linolenic acid is 60.19 wt% and the amount of oleic acid and gadoleic acid (only one unsaturated bond in the fatty acid chain) is 17.57 wt% and 0.23 wt% respectively. Camelina oil has a lower iodine value (144 g I2 /100 g) than linseed oil. The total content of linolenic acid in camelina oil is 34.04 wt%, while the amount of oleic acid and gadoleic acid is 18.45 wt% and 17.96 wt% respectively. Higher concentrations of highly unsaturated fatty acids in alkyd resins result in faster drying of the coats. Both above mentioned vegetable oils are considered as highly unsaturated products. Camelina oil was used as a fatty raw material in the synthesis of alkyd resins as well as a vegetable oil in the epoxidation process. On the other hand, linseed oil was used only as a fatty raw material in the production of epoxidized vegetable oil.

Fig. 1. Scheme for formation of epoxy triglyceride of camelina and linseed oil.

H. Nosal et al. / Progress in Organic Coatings 101 (2016) 553–568 Table 4 Physicochemical properties of epoxidized camelina oil and linseed oil. Properties

Camelina oil

Linseed oil

Color (Gardner scale) Acid value (mg KOH/g) Oxirane value (mol/100 g) Hydroxyl value (mg KOH/g) Iodine value (g I2 /100 g)

0.3 1.13 0.45 22.6 8.8

1.2 1.47 0.52 48.6 8.9

3.2. Epoxidation of vegetable oils The aim of this work was the synthesis of epoxidized camelina oil and epoxidized linseed oil with the possibly highest content of oxirane rings (proportional to the degree of vegetable oil unsaturation). This reaction scheme is shown in Fig. 1. The epoxidation process was controlled with the use of the oxirane value and hydroxyl value in the reaction mixture. For each of the plant oil, a high epoxide ring content was achieved after 4 h, i.e. 0.44 mol/100 g for camelina oil and 0.51 mol/100 g for linseed oil. Longer epoxidation times yielded a small increase in the oxirane value only. Table 4 shows some parameters of the final epoxidation products for different vegetable oils. The data presented in Table 4 show that a small number of oxirane rings in camelina oil was hydrolyzed to hydroxyl groups under the epoxidation conditions. The hydroxyl value of camelina oil was 22.6 mg KOH/g after eight hours. For linseed oil, a higher number of oxirane rings was opened to hydroxyl groups. After 8 h, the hydroxyl value of linseed oil was 48.6 mg KOH/g. When epoxidized vegetable oils are used as alkyd resin functional additives, the presence of both oxirane rings and hydroxyl groups in the molecule is desirable. This is because both the oxirane rings and the hydroxyl groups contained in the hydrocarbon chains of vegetable oils increase the functionality of the reaction system of alkyd resins, and it can lead to the formation of additional branches in the polymer structures. The structure of epoxidized oil was confirmed by infrared spectroscopy (FT-IR). The FT-IR spectra of camelina oil and linseed oil versus corresponding FT-IR spectra of epoxidized camelina oil and epoxidized linseed oil were shown in Fig. 2. For reaction products also oxirane value were measured. However, for each sample zero oxirane value were obtained. The FT-IR spectra of both camelina and linseed oils have absorption bands at 3010 cm−1 which correspond to C H stretching and deformation vibrations in HC CH unsaturated bond, and at 1654 cm−1 , which correspond to C C stretching vibrations. The presence of these bands clearly indicates the presence of unsaturated C C bonds in the chemical structure of camelina oil and linseed oil. The formation of epoxy groups in epoxidized camelina oil and in epoxidized linseed oil is indicated by disappearance of absorption bands at 3010 cm−1 and at 1654 cm−1 and by the presence of the characteristic absorption band at 822 cm−1 (epoxidized camelina oil, Fig. 2b) and at 821 cm−1 (epoxidized linseed oil, Fig. 2a) corresponding to C O stretching vibrations of the epoxide ring. The epoxidized camelina and linseed oils were then used as oil raw materials in the alkyd resin synthesis according to the formulation as presented in Table 1. 3.3. Synthesis of alkyd resins 3.3.1. First stage of synthesis (alcoholysis) Five different types of alkyd resins were prepared from camelina oil (Table 1). In the alcoholysis step, triglycerides from camelina oil were reacted with glycerol and with epoxidized camelina oil or epoxidized linseed oil (epoxidized oil was not used as an additive

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Table 5 Compositions (wt%) of the first stage products in the alkyd resins synthesis (positive result of methanol test) by GC/MS and GC/FID. Alkyd resin sample

AR1

AR2

AR3

AR4

AR5

Glycerol Diglycerol Fatty acids Glycerol monoesters Diglycerol monoesters Glycerol diesters Glycerol triesters Other

4.85 0.16 1.10 53.16 1.73 32.80 6.06 0.15

7.43 0.26 1.07 57.29 1.44 28.88 3.62 0.00

7.04 0.30 1.40 54.99 1.61 30.32 4.35 0.00

3.82 0.16 1.45 48.20 1.51 34.96 9.87 0.04

3.73 0.07 1.40 51.55 0.96 34.33 7.70 0.26

only in AR1 sample). The first stage of the synthesis (alcoholysis) is expected to yield glycerol monoesters which, unlike glycerol diesters, are bifunctional compounds and hence they are capable of reacting in polycondensation processes. Whether the alcoholysis reaction was run to completion, it was verified by the methanol tests. The post-reaction mixtures, after successful methanol tests, were also analyzed by GC/MS and GC/FID. Table 5 shows the chemical compositions of the analyzed alcoholysis products. Based on the data presented in Table 5 it can be concluded that the positive result of the methanol test is representative for a product, in which the content of glycerol monoesters is higher than 48 wt% and the content of glycerol triesters is below 10 wt%. The presence of diglycerol and diglycerol monoesters was also identified within the products of this reaction step. The presence of these types of compounds is not very surprising. The conditions of alcoholysis (220 ◦ C, lithium hydroxide as a catalyst) allow for side reactions (e.g. glycerol oligomerization). There are widely known, that the common method of diglycerol production is high temperature glycerol condensation with the use of basic homogeneous catalysts (also LiOH) [28]. The presence of diglycerol and diglycerol monoesters in the alcoholysis products is not disadvantageous. These compounds are more than bifunctional and hence they – like glycerol monoesters – are capable of reacting in polycondensation processes. The structures of alcoholysis products were confirmed by FT-IR spectroscopy. The example of FT-IR spectra for alcoholysis products, for camelina oil, for epoxidized camelina oil (EpCamOL) and for epoxidized linseed oil (EpLinOL) was shown in Figs. 3 and 4. The IR spectra were presented both for the initial components and for the final alcoholysis products. As it was already mentioned, specific bands were observed in the FT-IR spectra of epoxidized oils: at 821 cm−1 – for epoxidized linseed oil, and at 822 cm−1 – for epoxidized camelina oil, corresponding to the C- O stretching vibrations of the epoxide rings. However, this band is not observed in the FT-IR spectra of alcoholysis products where the epoxidized vegetable oils were used as reagents (samples AR2-AR5). This may indicate that not only the transesterification reaction (Fig. 5) but also the oxirane ring opening reaction occur in the alcoholysis process. On the other hand, there is a strong band at 1047 cm−1 corresponding to the O C- O ether group stretching vibrations in the FT-IR spectra of alcoholysis products. The presence of this band confirms the presence of the diglycerol molecule in the reaction mixture but it may be also indicative for the oxirane ring opening products. Glycerol, used a raw material for the synthesis of alkyd resins, may also react with the epoxide rings to form corresponding hydroxyethers (Fig. 6) at the temperature about 220 ◦ C and in the presence of alkaline catalysts. Opening of the oxirane rings in epoxidized vegetable oils as shown in Fig. 6 during the alcoholysis reaction can lead to mono-, di- and triglycerides with more branched structures. Epoxidized vegetable oils were added in small quantities only (see Table 1) in tested variants. Up to 20 wt% of vegetable oil (camelina oil) was replaced with epoxidized vegetable oil. However, the

558


70

1654

3471

75

65 60 55

45

1100

30

1242

3010

1459

35

822

%T 40

724

1386

1019

50

2854

25 20

5

4000

3500

1158

- camelina oil - epoxidized camelina oil

2924

10

1742

15

3000

2500

2000

1500

1000

500

Wave numbers (cm-1)

a) 80 75

65

1654

3469

70

60 55 50 45 723

%T 40

25

1240

1463

3010

30

821

35

0 4000

- linseed oil - epoxidized linseed oil 3500

1164

5

1747

10

2854

15

2925

20

3000

2500

2000

1500

1000

500

Wave numbers (cm-1)

b) Fig. 2. FT-IR spectra of camelina oil and epoxidized camelina oil (a); linseed oil and epoxidized linseed oil (b).

resulting glyceride structures can be more branched than the structures of glycerides from non-epoxidized oil, so even small quantities may affect the structure of the whole resin and conse-

quently can also affect its properties. In this way, the increase of alkyd resin branching is obtained by introducing a poly-functional substrate, i.e. epoxidized vegetable oil.


559

100 95 90 85 3009

80 75

1243

1463

55 50

40

Camelina oil 25 20 4000

722 1045

1173

AR1 without additive

1739

30

AR3 20% EpLinOL 2924

35

1113

2854

45

927

60

821

65 %T

1378

3370

70

Epoxidized linseed oil 3500

3000

2500 2000 Wave numbers (cm-1)

1500

1000

500

Fig. 3. FT-IR spectra of alcoholysis products – variants differ in the content of epoxidized linseed oil 20 wt% EpLinOL (AR3) in comparison to the FT-IR spectra of the variant with no additive (AR1), camelina oil and epoxidized linseed oil.

95 1655

90 85 80 75

55

1463

50

927

821

3009

60

1242

%T 65

1378.

3370

70

3500

3000

2000

2500

1500

721 1047

Epoxidized camelina oil

1173

30

1739

Camelina oil

2925

AR1 without additive

35

4000

2854

AR5 20% EpCamOL 40

1113

45

1000

500

Wave numbers (cm-1) Fig. 4. FT-IR spectra of alcoholysis products – variants differ in the content of epoxidized camelina oil 20 wt% EpCamOL (AR5) in comparison to the FT-IR spectra of the variant with no additive (AR1), camelina oil and epoxidized camelina oil.

3.3.2. Second stage of synthesis (polycondensation) At the second stage of the synthesis, the intermediate product from the alcoholysis stage was subjected to esterification with phthalic anhydride and maleic anhydride. The viscosity and acid value measurements were used to monitor the progress of

polycondensation. The acid value represents the amount of unreacted carboxylic groups and viscosity stands for the progress of the polycondensation reaction as that process gradually increases the molecular weight of the product.

560


Fig. 5. Transesterification of epoxidized vegetable oils with glycerol.

Fig. 6. The plausible scheme of the epoxide ring opening reaction during alcoholysis.

Figs. 7 and 8 show the changes in the acid value and viscosity (flow time) during the reaction time for various resins samples synthesized from camelina oil and glycerol, with epoxidized camelina oil (EpCamOL) or epoxidized linseed oil (EpLinOL) added, or without any additive. Viscosity of the reaction mixture increases in the course of the condensation process, in line with the increasing molecular weight of the reaction product, and the acid value decreases due to higher and higher conversion of the acidic substrate (Figs. 7 and 8). During condensation of the AR1 sample, where epoxidized oil was not used as an additive, viscosity of the reaction mixture increased very slowly and the maximum value (24 s) was obtained after 300 min despite the fact, that the acid component was almost completely converted, as it was shown by the acid value which was very low (1.6 mg KOH/g). During condensation of alkyd resins with the addition of epoxidized linseed oil as a functional additive, viscosity of the reaction mixture increased faster and final value for the resulting resin was higher than in the case of AR1. Viscosity of reaction mixture after 120 min for AR2 (10 wt% of epoxidized linseed oil was used) was 42 s and for AR3 (20 wt% of epoxidized linseed oil was used) was 96 s. Further continuation of the synthesis resulted in an increase of the reaction mixture viscosity. After 180 min viscosity for AR2 was 51 s and for AR3–120 s. It was clearly shown,

Fig. 7. Viscosity of reaction mixtures during the polycondensation process, variants differ in the content of epoxidized linseed oil – EpLinOL (a) and epoxidized camelina oil – EpCamOL (b).


561

containing lower amounts of epoxidized oil (epoxidized linseed oil as well as epoxidized camelina oil) are characterized by lower acid values, than the variants in which higher amounts of epoxidized oil were used. This phenomena could be explain by higher functionality of epoxidized oils leading to more branched structure. This causes the esterification reaction proceeds more difficulty and consequently the acid value decreases more slowly. The molecules of epoxidized linseed oil and epoxidized camelina oil evaluated in this study have different chemical structures and different numbers of epoxide groups, and – as can be seen from the presented results – affects the course of the polycondensation process and consequently the properties of the final products. A higher number of reactive groups in the molecules used in the synthesis results in the faster growth of viscosity of the reaction mixture during condensation. Epoxidized linseed oil is characterized by a higher oxirane value and hydroxyl value than epoxidized camelina oil. Therefore viscosity of AR2-3 samples (with the addition of epoxidized linseed oil) was increased faster than for AR4-5 (with the addition of epoxidized camelina oil). Hence, the lowest viscosity was observed in AR1, where only glycerol was used. The structures of polycondensation products were also analyzed by infrared spectroscopy (FT-IR). The FT-IR spectra of polycondensation products (variants differ in the content of epoxidized vegetable oils) were shown in Fig. 9. The FT-IR spectra of all obtained alkyd resins (variants AR1–AR5) are very similar. The stretching vibrations: OH at 3508 cm−1 (Fig. 9b) and 3503 cm−1 (Fig. 9a), corresponding to groups C H of alkene at 3009 cm−1 , C O of ester groups at 1730 cm−1 (Fig. 9b) and 1731 cm−1 (Fig. 9a) and C C bond in the benzene ring at 1599 cm−1 and 1580 cm−1 are observed in FT-IR spectra for all synthesized alkyd resins. It may therefore be assumed, that the use of epoxidized vegetable oil as modifier does not lead to the formation of new type functional groups in the alkyd resin structure, which are not present in the structure of a standard resin (AR1). The modification of the resin is based on differences in the structure of the connections and in improved branching. Fig. 8. Acid value of reaction mixtures during the polycondensation process, variants differ in the content of epoxidized linseed oil – EpLinOL (a) and epoxidized camelina oil – EpCamOL (b).

that viscosity of the reaction mixture increased faster, when higher amounts of epoxidized linseed oil were used. The viscosity plots for the alkyd resins, which contain additions of epoxidized camelina oil, follow similar patterns. After 120 min, viscosity for AR4 (10 wt% of epoxidized camelina oil) was 39 s and for AR5 (20 wt% of epoxidized camelina oil) it was 66 s. Longer synthesis times resulted in a further increase of the reaction mixture viscosity. After 180 min, viscosity for AR4 was 51 s and for AR5–87 s. During condensation of AR4-5 viscosity of the reaction mixture increased faster and its final value for the resulting resin was higher, than in the case of AR1, but it was slightly lower than in the case of AR2-3. For each resin samples, the acid value profile was found to be more steep in the first 60 min of the condensation process but then the acid value was not decreasing so quickly (Fig. 8). The resins

3.3.3. Physiochemical properties of resins The alkyd resins were characterized be determination of the volatile compounds, color, acid value and hydroxyl value. These properties are presented in Table 6. The contents of hydroxyl and carboxyl groups is an important parameters. For air drying alkyd resins the concentration of both groups affects their drying properties. The hydroxyl groups are responsible for the cross-linking reaction while the carboxyl groups being acidic act as a catalyst. However, the too high acid value has a negative impact on the resins cross-linking ability. AR1 is characterized by the lowest acid value. For AR 2 the acid value is 5.1 mg KOH/g and is lower than 10 mg KOH/g, and for AR 3 the acid value is slightly higher (12.7 mg KOH/g). This means that a significant amount of the carboxyl groups remains unreacted in AR3. This is important because the resins characterized by higher acid values (higher concentrations of carboxyl groups) are not able to form coatings. With regard to the samples AR4 and AR5, the condensation products reached the acid values below 10 mg KOH/g.

Table 6 Physicochemical properties of alkyd resins. Parameters

Alkyd resins

Modifier

AR1 –

Acid value (mg KOH/g) Hydroxyl value (mg KOH/g) Volatile compounds (wt%)

1.6 40.2 1.2

AR2 epoxidized linseed oil

AR3

AR4 epoxidized camelina oil

AR5

10 wt%

20 wt%

10 wt%

20 wt%

5.1 56.5 0.9

12.7 81.4 3.0

2.3 57.0 0.3

6.3 67.0 2.0

562


95

80 75

1580

85

3009

3503

90

1599

70 65

2854

50

25

AR 3

15

1116

1731

20

10 3500

3000

2500

2000

742

AR 2

1070

30

706

AR 1 1266

35

2925

40

1041

45

986

55

1456

%T

1377

60

1500

1000

Wave numbers (cm-1)

a)

100

3508

95

80

1580

3009

85

1599

860

75 70

50

AR 4

30

AR 5

742

35

1267

AR 1 2925

40

1456

45

1730

25 20 15 4000

1041

2854

1417

55

987

60

3500

3000

2500

2000

Wave numbers (cm-1)

1500

1125 1065

%T

1377.

65

706

90

1000 500

b) Fig. 9. FT-IR spectra of alcoholysis products – variants differ in the content of epoxidized linseed oil – EpLinOL (a) and epoxidized camelina oil – EpCamOL (b).

As regards the hydroxyl groups, AR1 (without additive) was characterized by the lowest hydroxyl value – 40.2 mg KOH/g, AR2 and AR4 were characterized by higher hydroxyl values, 56.5 and

57.0 mg KOH/g. AR3 and AR5 samples were characterized by the highest values 67.0 mg KOH/g and 81.4 mg KOH/g respectively. A higher amount of epoxidized vegetable oil in alkyd formulation


563

Table 7 Molecular parameters of alkyd resins. Parameters

Alkyd resins

Modifier

AR1 –

Mn Mw Mw /Mn

2.12 × 103 0.86 × 104 4.06

AR2 epoxidized linseed oil

AR3

AR4 epoxidized camelina oil

AR5

10 wt%

20 wt%

10 wt%

20 wt%

3.18 × 103 2.38 × 104 7.48

3.10 × 103 2.12 × 104 6.86

3.15 × 103 1.73 × 104 5.49

2.95 × 103 1.68 × 104 5.69

Table 8 Temperatures required for reaching certain weight losses (wt%). Alkyd resin

T5% (◦ C)

T10% (◦ C)

T90% (◦ C)

AR1 AR2 AR3 AR4 AR5

282.5 286.9 209.9 307.1 249.0

319.3 322.8 295.6 332.4 307.9

461.3 463.9 453.4 456.9 453.6

results in the higher hydroxyl value of the resin. This may be due to by opening of the oxirane rings in epoxidized vegetable oils in the first step of synthesis as shown in Fig. 6. A high concentration of hydroxyl and carboxyl functional groups in combination with a steric accessibility results in strong intermolecular forces and thus in a high viscosity. This is because hydroxyl groups function as hydrogen bond donors, while ester and carboxyl groups are acceptors. On the other hand for air-drying alkyds the concentration of hydroxyl groups determines good drying properties and pigment wetting properties. Analyzing the content of volatile compounds it may be noted that AR2 (contains 10 wt% of epoxidized linseed oil) and AR4 (contains 10 wt% of epoxidized camelina oil) have lower contents of volatile compounds than all other resins samples. The content of those compounds is especially low in AR4 (0.3 wt%). However, greater amounts of epoxidized oil added to the resin synthesis caused higher amounts of volatile compounds present in the product. The average molar masses and molar mass distributions of the synthesized alkyd resins were also investigated. The GPC chromatograms of all resin samples are presented in Fig. 10. The GPC analysis was performed to compare molecular weights of the synthesized alkyd resins. The GPC chromatograms of the alkyd resin samples are indicative for the formation of broaddispersed polymers. It was established, that the fractions with higher molecular masses were formed mainly in the alkyds which contained epoxidized vegetable oils as modifiers (a sharp peak at a retention time of about 11.5 min corresponds to a higher molecular weight compound). The GPC chromatogram of the alkyd resin without any additive (AR1) contained only a small amount of the fractions with higher molecular masses (a small peak at a retention time of about 11.5 min corresponds to a higher molecular weight compound). The fractions of higher molecular weight have a positive effect on the crosslinking process, but also increase the viscosity of the polymer, while large amounts of oligomers of low molecular weight will decrease the viscosity, but adversely affect the crosslinking process (this correlation is confirmed by the data presented in Table 8). Basic molecular parameters of the resins were given in Table 7. The molecular weight values for the AR1 sample are found to be lower than those for AR2-AR5 samples. The Mw of the AR1 sample is 0.86 × 104 while those of the AR2 and AR3 samples (they have various contents of epoxidized linseed oil) fall between 2.12 × 104 and 2.38 × 104 , and those for the AR4 and AR5 samples (with various contents of epoxidized camelina oil) are between 1.68 × 104 and

1.73 × 104 . In the variants, where epoxidized linseed oil was used (characterized by higher oxirane value – 0.52 mol/100 g), the resins with higher molecular weight values were obtained than in the variants where the epoxidized camelina oil was used (with a little lower oxirane value – 0.45 mol/100 g). The Mw /Mn is in general high, which is expected for this kind of uncontrolled reactions and the ability to create molecules of different weights and structures. For the AR1 sample, the Mw /Mn is 4.06, and for AR2–AR5 samples it is higher – between 5.49 and 7.48. This might be due to the presence of epoxidized vegetable oils used in the synthesis of AR2-AR5 samples, which increases functionality of the reaction mixture. Thus, the effect of steric hindrances is higher, which leads to a broader molecular weight distribution in the resins AR2–AR5. One of the significant factors which determine the functional properties of alkyd resins is their thermo-oxidative stability. The TGA analysis were conducted to determine the effect of epoxidized vegetable oil on the thermo-oxidative stability of the obtained resins. The thermo-oxidative degradation of the received resins was investigated by TGA in air (oxidative atmosphere), at the heating rate of 12 ◦ C/min. The TG and DTG curves were shown in Figs. 11 and 12 respectively. The TG curves of all synthesized alkyd resins show similar thermal degradation behaviors (AR1–AR5). However it was found that the AR2 sample (which contains 10 wt% of epoxidized linseed oil) and AR4 (10 wt% of epoxidized camelina oil) had a little higher thermal stability than other resins (increase of T5% and T10% parameters). It can be assumed that the addition of 10 wt% of vegetable oil can somewhat improve thermooxidative stability of alkyd resins, but the addition of more than 10 wt% of epoxidized vegetable oil to the alkyd resin synthesis is associated with the decrease of these properties in comparison to the standard resin (AR1). The temperatures required for reaching certain weight losses (wt%) are given in Table 8. The DTG curves (Fig. 12) shows a multiple-step decomposition of AR 1–5 samples. The presence of epoxidized vegetable oils in AR 2–4 samples shifted the position of derivative thermograms (DTG) the first three peaks to slightly higher temperatures compared to the DTG peaks of alkyd resin without any additive – AR1. From TGA results can be concluded, that modification of the alkyd resin with epoxidized vegetable oils slightly improve the thermooxidative stability of the alkyd resin, but the course of the degradation process remained unchanged. Borugadda and Goud [29] reported, that compounds (esters) with epoxidized unsaturated bonds are thermally and oxidatively more stable than esters with high polyunsaturation content. In our work total content of unsaturated bond in AR2–AR5 resins is lower than in AR1. Some part of the vegetable oil in the formulation of the AR2–AR5 resins were replaced with epoxidized vegetable oils. This may explain better thermal stability of alkyd resins synthesized with addition of epoxidized vegetable oils as modifiers. Additionally our study shows, that under the adopted reaction conditions epoxide ring opening reaction of epoxide groups present in alkyd resin samples was observed. As the result the ether linkages and

564


AR 1 without additive AR 2 10 wt% EpLinOL AR 3 20 wt% EpLinOL

25

MilliVolts

20

15

10

5

0

10

12

14

16

18

20

Eluon me [min]

a)

AR1 without additive AR4 10 wt% EpCamOL 15

MilliVolts

AR5 20 wt% EpCamOL

10

5

0

10

12

14

16

18

20

Eluon me [min]

b) Fig. 10. GPC chromatograms of alkyd resins, variants differ in the content of epoxidized linseed oil – EpLinOL (a) and epoxidized camelina oil – EpCamOL (b).

hydroxyl groups (able to esterification reaction) are formed. In this way, the increase of alkyd resin branching is obtained and more stable bonds then unsaturated bonds and epoxy groups are formed. It also may be a factor affecting the alkyd resins thermal stability. 3.3.4. Varnish properties The drying properties of the alkyd resins are the most critical parameters for their application as binders in air-drying coatings. One of the objectives of this research was therefore to determine the ability of the alkyd resin to undergo cross-linking when new raw materials like epoxidized vegetable oils are used. All the

synthesized resins were tested in the form of varnishes (55 wt% solution in white spirit and mixed with a siccative). The drying time, Persoz pendulum hardness and other performance properties of the studied alkyd resin samples are presented in Table 9. As can be seen, the characteristics of varnishes obtained from the resins synthesized with the addition of epoxidized vegetable oils as modifiers and standard resins (without any modifier) are very diversified. The film of varnish obtained from AR1 (without any modifier) remained tacky after a long exposure to atmospheric air. The drying level 1 was achieved after 8.0 h while the drying level 2 – after 26.0 h. On the other hand, the films based on


565

TGA (air, 12°C/min)

%

Weight (%)

100 90

AR-1

80

AR-2

70

AR-3

60 50 40 30 20 10 0 50

100

150

200

250

300

350

400

450

500

550

600 °C

7HPSHUDWXUH°&

a)

TGA (air, 12°C/min)

% 100

Weight (%)

90

AR-1

80

AR-4

70

AR-5

60 50 40 30 20 10 0 50

100

150

200

250

300

350

400

450

500

550

600 °C

Temperature (°C)

b) Fig. 11. The TG curves of alkyd resins, variants differ in the content of epoxidized linseed oil – EpLinOL (a) and epoxidized camelina oil – EpCamOL (b).

AR2-AR5 resins are characterized by significantly shorter drying times (level 2 between 7.0 h and 9.5 h). In those cases, the presence of compounds with highly reactive epoxide rings in the alkyd resin formulations generates additional branching in the polymer structure and it was possible to obtain resins, which gave crosslinked structure in shorter times. Regards the resin, for which only glycerol as a polyol was used without any modifier (AR1), the structure of the resin is characterized by less branched structure and resulting in longer drying time. The varnishes formulated from AR2 and AR3 (containing 10 and 20 wt% of epoxidized linseed oil,

respectively) are characterized by shorter drying times compared to the varnishes formulated from AR4 ad AR5 (containing 10 and 20 wt% of epoxidized camelina oil, respectively). In the AR2 and AR3 formulations, epoxidized linseed oil with higher functionalities than for AR4 and AR5 (containing epoxidized camelina oil as a modifier) was used and it was possible to obtain resins, which gave higher molecular mass and higher numbers of more branched network connections in shorter times. From the results presented in Table 9 cannot be declared that there is a simple dependency between the amount of the modifier

566


%/°C

DTG (air, 12 °C/min)

0,000 -0,002

AR-1 AR-2

-0,004

AR-3

-0,006 -0,008 -0,010 -0,012 -0,014

50

100

150

200

250

300

350

400

450

500

550

600

500

550

600

Temperature (°C)

a) DTG (air, 12 °C/min)

%/°C 0,000

AR-1 -0,002

AR-4 AR-5

-0,004

-0,006

-0,008

-0,010

-0,012 50

100

150

200

250

300

350

400

450

Temperature (°C)

b) Fig. 12. The DTG curves of alkyd resins, variants differ in the content of epoxidized linseed oil – EpLinOL (a) and epoxidized camelina oil – EpCamOL (b).

introduced to alkyd resins and the drying time of the varnishes. However, the use of smaller amounts of functional modifiers is more preferable because of slightly shorter drying times the varnish films obtained based on the resins with smaller amounts of epoxidized oils. Hardness of a varnish film is also its important property. The research showed that the hardness of varnish films obtained from the resins synthesized with the addition of epoxidized vegetable oils was higher compared to hardness of standard resins (without any modifier). Good hardness properties of film is related to the resin cross-linking [30]. The films with higher crosslinkings are generally harder and tougher [31]. Epoxy groups from epoxidized vegetable oils during alkyd resins synthesis can form

additional branches in the fatty acids hydrocarbon chain. Whereby the crosslinking density of the resin is increased in comparison to the neat resin without modifier addition. It is resulting in improved hardness properties of the modified alkyd resins films. The varnish films formulated from AR2–AR4 were characterized by a similar hardness levels (35.0–38.5 s). The varnish film formulated from AR5 (containing 20 wt% of epoxidized camelina oil) was characterized by the highest hardness level (42 s). However, these differences in hardness levels are rather small and actually it can be noted that the hardness levels of varnish films formulated from all tested resins are similar. As regards other parameters, the varnishes formulated from AR1 – based on glycerol, without any modifier – exhibit


567

Table 9 Physicochemical properties of varnishes formulated from AR1-AR5. Varnish were formulated from the following resins: Alkyd resin Modifier amount

AR1 –

AR2 AR3 epoxidized linseed oil

AR4 AR5 epoxidized camelina oil

10 wt%

20 wt%

10 wt%

20 wt%

Parameters of the obtained varnishes: Viscosity (mPa s) Color (Gardner)

86.7 8.5

257.5 8.3

580.0 8.6

250.0 8.9

505.0 9.8

Parameters of the varnish films (coatings) Bend test (mm) after 7 days Persoz pendulum after 10 days hardness (s) Drying time (level 1) (h) Drying time (level 2) (h)

2 25.0 28.0 8.0 26.0

2 38.5 38.5 4.0 7.0

2 33.0 35.0 3.5 7.5

2 34.0 38.0 4.0 9.0

2 35.0 42.0 5.0 9.0

significantly lower viscosity compared to varnishes formulated from AR2-AR5. The higher viscosity of modified resins results, among others with higher molecular weights of formed polymers. The use of larger amounts of epoxidized oils in the alkyd resin synthesis gives respectively higher viscosities of the varnishes formulated from that resins. The color of all resins is quite similar. However, some small differences were observed. The color of AR4 and AR5 (contains respectively 10 and 20 wt% epoxidized linseed oil) is a little darker compared to other resins with the addition of epoxidized linseed oil (AR2 and AR3). All the varnishes formulated from the synthesized resins showed the same great flexibility and they were comparable with the reference sample. 4. Conclusions The results of this study indicate, that epoxidized vegetable oils are promising raw materials for the production of alkyd resins. There is a real possibility to synthesize alkyd resins based on Camelina sativa oil, glycerol and epoxidized vegetable oils as functional modifiers with improved properties in comparison to standard resins synthesized only from Camelina sativa oil and glycerol without any modifiers. The use of oil obtained from easy-to-grow Camelina sativa plants, in place of more expensive linseed oil, allows us to obtain coatings with comparable properties. It is particularly important that the addition of new functional modifiers shortens the resin crosslinking time, improve Persoz pendulum hardness and reduces the content of volatile compounds. The drying times of coatings based on camelina oil and epoxidized linseed oil were slightly shorter than the drying times of coatings based on camelina oil and epoxidized camelina oil. The linseed oil has a higher content of unsaturated bonds so it was possible to obtain resins, with more branched network and it results in shorter drying times of coatings. Epoxidized vegetable oils may be used as alkyd resin modifiers, but their amounts must be chosen carefully. The use of too high amounts of epoxidized vegetable oil in the alkyd resin synthesis may give a product with poorer properties than for standard resins synthesized without any modifiers. Acknowledgements Ms Hanna Nosal received a Ph.D. scholarship under a project funded by the European Social Fund. The research was conducted with financial support from the Ministry of Science and Higher Education for the statutory research. References [1] Alkyd Resins: European Union Market Outlook 2011 and Forecast till 2016” Merchant Research and Consulting Ltd., November 2011.

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