Seed oils rich in linolenic acid as renewable feedstock for environment-friendly crosslinkers in powder coatings
Introduction
Powder coatings have been widely accepted in the industrial coating market. The main advantage of this type of coatings is that they are 100% solvent-free and practically without volatile organic emissions. Besides their environment-friendly character, powder coatings have excellent mechanical and physical properties.
Powder-coating formulations usually contain a resin, a crosslinker, pigment and several additives. Triglycidyl isocyanurate (TGIC), depicted in Fig. 1, is a widely applied crosslinker in powder coatings (Bodnar, 1997), but environmental and health risks of toxic and mutagenic TGIC called for the development of a more friendly substitute. Generally, epoxy crosslinkers used for powder coatings form networks with acid-functionalized resins during the heat induced curing process. Crosslinkers based on epoxidized fatty acids seem to offer a good alternative for TGIC (Molhoek, 1997). In a recent patent (EP 600 546), DSM Resins BV has claimed the use of aliphatic oxiranes based on vegetable oils as crosslinkers in commercial powder-coating formulations (Fawer, 1996). For this purpose, the unsaturations in the vegetable oils are epoxidized and the epoxides introduced are used for the crosslink-reaction with acid-functional resins. However, these aliphatic oxiranes give rise to disadvantages when compared to conventional TGIC systems. In contrast to the other ingredients of the coating formulation, aliphatic oxiranes are fluids or have melting points close to room temperature. It is known that nonfunctional fatty acids and vegetable oils act as plasticizer and cause a decrease in the glass transition temperature (Tg) of the powder formulation. As a consequence, the reduced Tg can have a negative effect on the stability of the powder-coating formulation. Especially when the powders are transported or stored at ambient temperatures (i.e. close to the glass transition temperature), network formation leading to clustered regions (clots) can be initiated. Another disadvantage of vegetable oil based epoxides refers to the final coating performance. The degree of yellowing of the coating is relatively high when aliphatic oxiranes, synthesized from unsaturated fatty acids are applied as crosslinkers in powder-coating formulations. It is expected that these drawbacks can be reduced by employing unsaturated fatty acids with high iodine values. After epoxidation, the higher percentage oxirane oxygen justifies the addition of less aliphatic oxirane to the powder formulation. As a direct result of the reduced amount of added crosslinker, the mentioned drawbacks are expected to be reduced.
An example of a commercially available vegetable oil with high iodine value is linseed oil. Linseed oil is a well known rich source of linolenic acid (Prentice and Hildebrand, 1991, Salunkhe et al., 1992). Because unsaturated fatty acids are susceptible to autoxidation and polymerization, linolenic acid containing oils are widely used in oil-modified alkyd resins and alkyd-emulsion paints and varnishes (Derksen et al., 1995, Knörr et al., 1995). Other applications are printing inks, cloth oil, soaps, automobile brake linings, linoleum and binding agents (Prentice and Hildebrand, 1991, Salunkhe et al., 1992, Lühs and Friedt, 1994).
Very interesting is the isolated oil of the oilseed crop Lallemantia iberica (Fisch et Mey), better known as Iberian dragonhead, showing a very high content of linolenic acid (67–74%) (Hondelmann and Radatz, 1984, van Soest et al., 1987, Hondelmann and Dambroth, 1990) exceeding that of linseed oil (55%). Originally, L. iberica has been found in Asia (Syria, Israel, Iran, Iraq) and the Caucasus, but now the crop also appears in Central and Southern Europe. Unsuccessful attempts were made to introduce the plant species in Germany, Austria and Canada; seed productions were found to be low and unstable, possibly due to relatively wet climate conditions (van van Soest et al., 1987). However, with sufficient interest from industry, the crop might have potential.
The unsaturated double bonds of seed oils rich in linolenic acid may be used to introduce functional groups like epoxides. Fig. 2 shows an example of a typical epoxidation product of linseed oil. Epoxidized oils offer a wide range of industrial applications, like lubricants, solvent-free paints and crosslinkers (Muturi-Mwangi et al., 1994, Sperling and Manson, 1983, Barrett et al., 1993).
In the work described here, the fatty acid composition of the oil from the potentially interesting crop L. iberica was studied and compared to the compositions of commercially available linseed oil (Linum usitatissimum) and Canadian linseed oil. Due to the influence of climate conditions during oilseed production, Canadian linseed oil is relatively rich in linolenic acid if compared to refined linseed oil. Linseed oil, Canadian linseed oil and the oil of L. iberica seeds were epoxidized, yielding products with increasing percentages of oxirane oxygen according to their increasing iodine values. The epoxidized oils were applied as environment-friendly aliphatic crosslinkers in powder-coating formulations. The characteristics of the powders and the final coatings obtained were determined.
Section snippets
Materials
L. iberica seeds grown in the Netherlands were obtained from the Center for Plant Breeding and Reproduction Research (CPRO-DLO, Wageningen, the Netherlands). Canadian linseeds were obtained from the Grain Research Laboratory (Winnipeg, Canada). Refined linseed oil was purchased from the Vereenigde oliefabrieken (Dodewaard, the Netherlands).
All solvents were of high purity (98%) and were used without further purification. The solvents were purchased from Biosolve Ltd. (Valkenswaard, the
Oil recovery
The oil obtained from L. iberica seeds is a clear green/yellowish oil. The oil content (%w/w) of the seeds was determined at 22%. In literature, oil contents between 20 and 38% were found (Hondelmann and Radatz, 1984, van Soest et al., 1987, Hondelmann and Dambroth, 1990). Canadian linseeds contained 37% of a clear orange/yellowish oil.
Fatty acid composition
Linseed oil contained 54.1% of linolenic acid (Table 1). Compared to this oil, the percentage of linolenic acid in the Canadian variant is significantly higher,
Conclusion
Seed oils rich in linolenic acid have been successfully applied as renewable feedstock for the synthesis of epoxidized aliphatic oxiranes. In our studies we used commercially available linseed oil, Canadian linseed oil and the oil of L. iberica containing 54.1, 60.2 and 68.0% of linolenic acid, respectively. The chemical epoxidation of these oils proceeds very well, resulting in high overall yields (>90%) and complete conversions of unsaturation.
Epoxidized vegetable oils were applied as
Acknowledgements
The authors thank the Vereenigde oliefabrieken (Dodewaard, The Netherlands) for the refined linseed oil. The Grain Research Laboratory (D. DeClercq, Winnipeg, Canada) is acknowledged for providing the Canadian linseeds.
References (29)
- et al.
Paints and coatings from renewable resources
Ind. Crops Prod.
(1995) - et al.
Enzymatic peroxycarboxylic acid formation in a hollow-fibre membrane reactor: kinetics and mass transfer
Catalysis Today
(1994) - et al.
The effect of temperature on oil quality and yield parameters of high and low erucic acid Cruciferae seeds (rape and mustard)
Ind. Crops Prod.
(1995) - et al.
Naturally functionalized triglyceride oils in interpenetrating polymer networks
J. Am. Oil Chem. Soc.
(1993) Powder coatings on the road to the 21st century
Eur. Coating J.
(1997)- et al.
Epoxidation of Lesquerella and Limnanthes (Meadowfoam) oils
J. Am. Oil Chem. Soc.
(1994) - et al.
Epoxidation of fatty acid methyl esters with organic hydroperoxides and molybdenum oxide
Fat Sci. Technol.
(1993) - et al.
Catalytic epoxidation of methyl linoleate-cyclisation products of the epoxyacid esters
Fat Sci. Technol.
(1995) - Fawer, B., 1996. Powder coatings; New developments, new trends and moves that are boosting sales volume. Coatings...
The study of natural epoxy oils and epoxidized vegetable oils by 13C nuclear magnetic resonance spectroscopy
J. Am. Oil Chem. Soc.
(1993)
Identification and evaluation of oilseed-bearing wild species of forbs as potential crops for the extraction of industrial raw materials
Plant-Res. Develop.
Zur evaluierung ölsamentragender wildarten
Landbauforschung Völkenrode
Development of new fields of application for linseed oil
Fat Sci. Technol.
Non-food uses of vegetable oils and fatty acids
Cited by (40)
Developing two new types of nanostructured vehicles to improve biological activity and functionality of curcumin
2021, Food BioscienceCitation Excerpt :Lallemantia iberica plant is used as a stimulant and expectorant for curing a common cold, nervous diseases, and high blood pressure in traditional medicine (Al-Snafi, 2019; Khosravi, Gohari, Sadat, Naghdi, & Amanzadeh, 2016). Lallemantia iberica seed oil is broadly employed in the food and cosmetic systems because it has a high amount of linolenic acid (67–74%) (Mozaffarian, 2003; Overeem et al., 1999). Linoleic acids have been shown to have anti-carcinogenic, anti-obesity, anti-atherogenic and immunomodulatory functions (Azain, 2003).
Extraction, characterization and rheological study of the purified polysaccharide from Lallemantia ibrica seeds
2018, International Journal of Biological MacromoleculesBio-based thermosetting epoxy foam: Tannic acid valorization toward dye-decontaminating and thermo-protecting applications
2018, Journal of Hazardous MaterialsCitation Excerpt :Disappointingly, epoxy resins are produced from not sustainable with fluctuating price petro-resources. In recent decade, researchers tried to replace bisphenol A as the main precursor of the epoxy resins with natural resources such as lignin [2–4], tannin [5], plant oils (e.g., soybean oil [6,7] and linseed oil [8]), simple polyols [9–11], rosin [12] and liquefied biomass [13,14] to produce thermosetting epoxy foam. These thermosetting foams are being used in different applications namely wastewater remediation, removal of organic and heavy metal pollutants from the environment, and thermal insulation [15,16].