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PROGRESS %rn& ‘ Progress in Organic Coatings 27 (1996) 45-53 Renewable resources in coatings technology: a review Johannes T.P. Derksen, F. Petrus Cuperus, Peter Kolster Agrotechnological Research Institute (ATO-DLO), PO Box 17, 6700 AA Wageningen, Netherlands Received 17 October 1994; accepted 22 June 1995 Abstract In recent years an increasing interest is observed in the development of more environment friendly paints and coatings. This paper discusses advances in the use of renewable resources in formulations for various types of coatings. In particular, current research on the application of plant proteins and vegetable oils in coatings systems is addressed. In ongoing plant protein re- search at ATO-DLO corn, but particularly wheat gluten, was modified chemically to obtain aqueous protein dispersions that have excellent film-forming characteristics and strong adhesion to various surfaces. In particular, wheat gluten films have very interesting mechanical properties, such as an extensibility over 600%. Gas and moisture permeabilities were found to be easily adjustable by changing the exact formulation of the protein dispersion. Durability and water resistance of the coatings can be tailored by, for example, varying the degree of crosslinking of the protein binder. Based on the observed characteristics of the modified protein binders the development of novel, organic solvent-free paints and coatings appears to be well within reach. Regarding vegetable oil-based binders, research at ATO-DLO and elsewhere includes the application of oils from conventional as well as new oilseed crops. A very interesting new vegetable oil originates from such crops as Euphorbia lagascae and Vernonia galamensis, which have high contents (>60%) of an epoxy fatty acid (9c,12,13 epoxy-octadecenoic acid or vernolic acid) that can be used as a reactive diluent. Another interesting new oil is derived from Calendula officinalis, or ‘ . marigold’ This oil contains >63% of a Cl8 conjugated triene fatty acid (8t,lOt,l2c-octadecatrienoic acid or calendic acid) like that in tung oil. Current research is focused on the film-forming abilities of these oils and of chemical derivatives of these oils, in particular in emulsion systems. Keywords: Renewable resources; Technology 1. Introduction However, in the past few years consumer’ s and industrial interest in environmentally friendlier paints Agricultural raw materials precede petrochemicals and coatings has been growing tremendously. This by millenia in non-food applications. Vegetable oils, for trend has been spurred not only by the realization that instance, have been used for illumination and lubricat- the supply of fossil resources is inherently finite, but ing purposes as well as for coatings and paints for also by a growing concern for environmental issues, many centuries before an abundant and cheap supply such as volatile organic solvent emissions and recycling of mineral oil became available for a wide range of or waste disposal problems at the end of a resin’ s products [l]. This has resulted in a steady decline in the economic lifetime. Furthermore, developments in or- use of renewable resources in paints and coatings indus- ganic chemistry and fundamental knowledge on the tries as well as in other non-food fields. As an illustra- physics and chemistry of paints and coatings enabled tion, the total volume of fats and oils used in drying oil some problems encountered before in vegetable oil- products is now less than a third of the volume in 1950. based products to be solved. This resulted in the devel- Realizing that the total volume of resins in paints has opment of coatings formulations with much improved increased substantially since that time, the reduction in performance that are based on renewable resources. the share of vegetable oil-based products becomes even The above has, on the one hand, led to a further more striking . reduction in the use of organic solvents in paint sys- 0300-9440/96/$15.00 0 1996 Elsevier Science S.A. All rights reserved SSDI 0300-9440(95)00518-J 46 J.T.P. Derksen ef al. 1 Progress Coatings (1996)45-53 in Organic 27 terns, through the development of, for example, new 2.2. Historical overview water-based paint formulations and high-solids sys- tems. On the other hand, it has also led to an in- Development of non-food applications of plant creased interest in the use of renewable resources, i.e. proteins has also been studied. In the thirties, industrial derived from agriculture, in paints and coatings for- non-food applications of soy proteins were developed mulations. in the framework of the ‘ , chemurgic movement’ which The present paper presents an overview of recent aimed at the development of new industrial feedstocks developments and perspectives on the application of from agronomic raw materials . Products such as renewable resources in coatings technology. The use of plastics, fibers, plywood adhesives and paper coatings proteins as biopolymer binders and of vegetable oils as were developed. In several of these non-food binder constituents in coatings formulations is dealt applications, soy proteins were not successful due to the with successively. The paper also discusses some recent competition from petrochemicals. results of our institute on the identification and appli- As a result of the rise of petrochemicals, proteins cation of new seed oils as well as on protein-based and agricultural feedstocks in general as a feedstock for coatings. the non-food sector were replaced by synthetic polymers. There are some exceptions, such as the use of gelatin in photographic emulsions and, to some extent, 2. Protein-based coatings soy proteins in paper coatings and casein in adhesives. It is estimated that in the USA about 25 000-50 000 2.1. Introduction tons of soy proteins are used in paper coatings . An important reason for this substitution of protein by Proteins are polymers of amino acids with a wide petrochemicals has been the lower price of the latter, range of chain lengths, from about 50 amino acids (for but also differences in performance have been instance the hormone insulin) to large complexes of important in this respect. Since World War II, there has more than over 100 000 amino acids (wheat gluten been an enormous increase in the knowledge of the proteins). Two main groups of proteins can be distin- production and adjustment of synthetic polymers. guished: firstly, proteins showing a physiological func- Hence, chemical industry is able to produce tailor-made tion, such as enzymes and hormones and secondly, products that can meet high industrial demands, both structural or storage proteins such as collagen (precur- in terms of performance and, last but not least, stability sor of gelatin) and pea seed proteins. of characteristics over time. Because of the scale on which they are produced, For the following reasons, there are now new only proteins belonging to the latter group are of opportunities for proteins to regain the non-food interest for commodity applications. These proteins market, hence to substitute synthetic polymers in specific may originate from animal products, such as milk applications. Firstly, knowledge of protein technology (casein), hides and connective tissues (gelatin) and and chemistry has increased considerably in the last hen’ eggs (egg-white proteins), and from plant prod- s decades. This includes aspects such as isolation and ucts such as seeds (soy and (corn) gluten proteins). characterization of proteins, elucidation of their These proteins will be referred to hereafter as ‘ indus- structures, structure-function relationships, and trial proteins’ Industrial proteins are traditionally . modifications. Secondly, in many cases the price of used in the feed and food industry. In the food indus- proteins is now comparable or even lower than that of try, industrial proteins are used because of their func- synthetic polymers (with the exception of commodity tional properties. Well known examples of their plastics). In this respect, plant proteins are a more properties are emulsifying (e.g. casein), foaming (e.g. attractive feed stock for non-food applications than egg white), gelling (gelatin), and viscoelastic properties animal proteins because of the differences in price. For (wheat gluten proteins). instance, wheat gluten in a factor of 2 to 3 cheaper than These and other functional properties (e.g. adhe- casein. Thirdly, there is an increasing demand both from sion) of proteins have also been exploited in non-food industries and consumers for the substitution of applications. In most of these applications, animal synthetic polymers by environmentally friendly polymers proteins have been used. The use of proteins such as from renewable resources. This development is sup- blood proteins, casein and gelatin in adhesives goes ported by governments, both in Europe and the USA. back over many centuries . Another example of a well-established non-food application of proteins is the 2.3. Wheat gluten coatings use of gelatin in photographic emulsions, which is based on the unique gelling properties of this protein. In developing non-food applications of proteins, Casein has been used in paper coatings, paints, plas- various proteins such as soy protein, corn gluten, wheat tics and in leather finishes [4-61. gluten and pea proteins are being studied. The research J.T.P. Derksen et al. / Progress in Organic Coatings 27 (1996) 45-53 stress (MPa) strain (%) on the replacement of synthetic polymers will be illus- 6, I trated by the research on wheat gluten proteins. About 300 000 tons of gluten are produced worldwide each year. Based on its unique functional properties, wheat gluten can be distinguished from other industrial proteins. Examples are its insolubility in water, adhe- sive/cohesive properties, viscoelastic behavior, film forming properties and barrier properties for water vapor and gases. These properties have been exploited in the development of edible coatings based on wheat concentration of plasticizer (%) gluten [8,9]. -stress + strain These properties of wheat gluten can also be ex- Fig. 2. The mechanical properties (stress and strain) of gluten coat- ploited in the non-food sector [lo], which is an impor- ings vs. the amount of glycerol. tant aim of our research on wheat gluten. The insolubility and film-forming properties of gluten are The mechanical properties of gluten coating as a for instance important for the development of a gluten- function of the plasticizer concentration are shown in based replacer of synthetic binders. Techniques have Fig. 2 [lo]. At a plasticizer concentration of 30%, the been developed for the production of water-borne extensibility of the gluten coatings is about 600%. A binder dispersions based on wheat gluten. These sus- further increase in the amount of plasticizer does not pensions show good film forming properties and the result in an additional increase in extensibility. An resulting coating has a strong adhesion to various increase in extensibility accompanies a decrease in substrates. Examples will be given of the polymeric strength of the coating. By modifications of the gluten properties of gluten and the adjustment of properties of proteins, such as crosslinking, this reduction in strength the gluten coatings. can be compensated. Wheat gluten shows, like other amorphous poly- In Fig. 3 the effect of hydrophobic additives on the mers, a glass transition temperature (T,). Below the Tg, water vapor permeability of gluten coatings is shown gluten films are brittle. To obtain rubbery gluten coat- [lo]. The permeability decreases proportionally with the ings, the addition of plasticizers is required. In Fig. 1, amount of additive, and can therefore be adjusted the effect of two plasticizers is shown. towards specific requirements for an application. The For biopolymers such as wheat gluten, water is a permeability of the coating with 20% additive is com- powerful plasticizer. An increase in water content of parable to that of commercially applied low density one per cent results in a decrease in Tg of 7.5 “C. The polyethene foil. addition of an additional plasticizer, such as glycerol, As shown, coatings from gluten binders have inter- results in a further decrease in T, of the gluten binder esting barrier and mechanical properties. Furthermore, [lo]. There is a good correlation between the measured the binder and resulting coating is insoluble in water. Tg and the Tg calculated by the Couchman-Karasz By including additives, such as hydrophobic substances, equation [l 11. This equation predicts the T, of mixtures it is possible to adjust the properties of the coatings based on the properties of the pure constituents. Also towards specific requirements. By modifications that are other plasticizers, including plasticizers insoluble in wa- not permitted in food applications, such as crosslinking ter, were shown to be effective. and grafting, it is possible to increase the range of properties of the gluten binder and resulting coating. It has already been shown that by modifications the water Tg (9 loo3 watervapor ‘ permeability (g) -Cl% + 7.5% -a-10% - 12.5% * 15% water content (w/w %) + 20% ??0% glycerol A 10% glycerol Fig. 1. Effect of water and glycerol on the TBof gluten. The symbols time (hrs) represent the measured values. The lines represent the Ts of gluten with 0 or 10% glycerol, calculated from the Couchman-Karasz Fig. 3. The effect of hydrophobic additives on the water vapor equation. permeability of gluten coatings. 48 J.T.P. Derksen et al. /Progress in Organic Coatings 27 (1996) 45-53 and, on the other hand, expand the existing range of FoH a-linolenic acid (Qc,l2c,l5c-octadecatrienoic acid) raw materials available and potentially lead to novel products. Moreover, consumer products made from renewable resources may also carry an appealing envi- ronment-friendly or ‘ green’ label. Below, the current and past use of conventional fats elaeostearic acid (9~1 lt,l3bxtadacatrienoic acid) and oils in the paints and coatings industry as well as the potential use of ‘new’ seed oils in these applications is discussed. -OH catendic acid (8t,lOt,12c-cctadecatrienoic acid) 3.2. Conventional oilseed crops In the past many seed oils have been applied in -T--TOH ricinoleic acid (12hydroxy-Qc-octadecanoic acid) various coatings formulations. In the 1950s the most common plant oil in trade sales paint formulations was linseed oil with a share of 50% . Since then not only the total volume of fats and oils used in drying oil -x---TOH lesquerolic acid (14hydroxy-1 lc-eicosenoic acid) products has declined, also the relative position of linseed oil has slowly declined to less than 30% of the plant oil used. Simultaneously the share of soybean oil increased such that now soybean oil is the predominant -OH dimorphscolic acid (Qhydrory-lM.l2t-octadecadienoic acid) oil used in this area. The use of soybean fatty acids in ‘soybean-modified’ alkyds is obviously a contributing factor to this. OH Table 1 gives an overview of a number of major plant oils that find use in coatings formulations, to- vemolic acid (12,13epoxy-Sxctadienoic acid) gether with some of their characteristics. The origin and Fig. 4. Selected fatty acids for paint applications. characteristics of the oils mentioned will be discussed hereafter. adsorption of gluten binders, which in the past has been 3.2.1. Drying oils an important draw-back of proteins in non-food appli- cations; can be reduced significantly. Furthermore, it 188.8.131.52. Linseed oil has been shown that by acylation of gluten, it is possi- Linseed oil is obtained, typically by mechanical ble to improve the suitability of gluten as a co-binder in expelling, from the seeds of the flax plant (Linum papercoatings [ 121. usitatissimum). This oilseed crop is grown in many parts of the world, including those with a temperate climate. The oil has a high content of a-linolenic acid 3. Vegetable oil-based coatings (Table l), giving rise to a high iodine value (I.V. 175-204, depending on, e.g., cultivar and climatic 3.1. Introduction conditions during the growing season). This high degree of unsaturation renders linseed oil very susceptible to The limited number of available oil crops, with autoxidation and polymerization, resulting in concurrent limited variability in fatty acid composition, crosslinked and tough films upon exposure to air. For has spurred industrial interest in the development of this reason linseed oil has been used for centuries as a new crops, which are optimized for specific applica- chief ingredient in paints and varnishes. tions. These new crops include crops that contain a Crude linseed oil is often treated to increase its higher percentage of a desirable fatty acid and crops suitability as a binder. An important first step is the that contain unique, unusual fatty acids. For non-food refining of the oil, in which process undesirables such as applications, oleochemical as well as fine chemicals gums (sometimes called ‘ ), break’ which consist mainly industries have expressed their interest in new fatty of lecithins, and free fatty acids are removed. This is acids with unusual properties and functionalities, since usually achieved through a combination of physical and current sources contain no more than approximately 10 chemical treatments, such as heating, acid or alkali different types of fatty acid. Such unusual fatty acids addition, water washing, bleaching and vacuum or heat (Fig. 4) could, on the one hand, replace raw materials drying. The exact refining protocol depends on whether from petrochemical origins with renewable resources, the oil will be used for, e.g., varnishes or as a grinding J.T.P. Derksen et al. / Progress in Organic Coatings 27 (1996) 45-53 49 Table 1 Plant oils currently used in coatings industries Plant oil Source Major fatty acids FA content Iodine Specific gravity (% of total) value (I.V.) (g/ml 25 “C) Linseed oil Linum usitatissimum linolenic/linoleic 40/35 175-204 0.931-0.936 Tung oil Aleurites spp. elaeostearic/oleic 19/l 1 155-175 0.939-0.943 Perilla oil Perilla frutescens linolenic/hnoleic 43137 192-208 0.932-0.935 Oiticica oil Licania rigida licanic/elaeostearic 7617 179-218 0.96660.969 Soybean oil Glycine max linoleic/oleic 55128 125-140 0.923-0.929 Safflower oil Carthamus tinctorius linoleic/oleic 59131 140-150 0.925-0.928 Tall oil Pinewood pulping fatty acids/rosin acids 50/40 Castor oil Ricinus communis ricinoleic/linoleic 9014 82-88 0.958-0.969 Dehydrated Castor Ricinus communis conjugated FAs/ricinoleic 80/10 135 medium for pigments. The obtained refined oil may 184.108.40.206. Tung oil then be heat-bodied. In this process the double bonds Tung oil or (Chinese) wood oil is recovered from of the unsaturated fatty acids in the oil are oxidized and the nuts of the tree Aleurites fordii or A. montana (oil to some extent polymerized. This leads to an increase in content approx. 18%). These trees were originally the viscosity of the oil and a decrease in drying time. grown in South-East Asia, but lately crops have also Heat-bodying may be accomplished in several ways, been established in Malawi, Argentina and the USA. each with its specific applications. The oil contains over 70% of the unusual fatty acid Boiled oil is obtained by heating oil in a vessel in the elaeostearic acid (SC, 11t, 13t-octadecatrienoic acid) presence of air and zirconium, manganese or cobalt (Fig. 4). This fatty acid contains three double bonds driers. The oil is kept at a temperature of, typically, that are conjugated rather than methylene-interrupted 137.5 “C until its specific gravity reaches 0.942 at as in linolenic acid. This feature causes the oil to dry 15.6 “C. This process results in an oil with a viscosity of much faster than linseed oil, but also makes the film 80-120 centipoise and a drying time of 12-20 h, more UV-Vis-light sensitive, leading to, for example, whereas raw linseed oil has a viscosity of 40 centipoise more rigid films. Coatings based on tung oil have a and a drying time of 2-4 days. Boiled oil can be added high resistance against water penetration and to both oil-based and alkyd paints to improve flow and saponification. In contrast to linseed oil films, the ease of brushing. air-dried tung oil film has a characteristic ‘ frosted’ Blown oil can be prepared in a similar fashion as appearance. This property can be exploited in boiled oil, except that no metal driers are present. so-called ‘ . wrinkle finishes’ If this effect is not desired Blown oil has a somewhat longer drying time than the oil has to be subjected to heat-bodying, analogous boiled oil (24-36 h) but a higher viscosity (typically to linseed oil. A tung stand oil, for instance, can more than 3 poise). It can be used in highly pigmented be prepared by heating the oil to 280 “C. However, systems to improve flow and leveling properties in the increase in viscosity is much faster than for undercoats and wall paints. linseed oil. This may even result in an irreversible Stand oil is prepared by allowing the oil to thicken at ‘gelling’ of the oil that can be prevented by a careful a relatively high temperature in the absence of metal control of the heat-bodying conditions. It can also be driers. Usually the oil is kept at temperatures around prevented by the addition of other (semi) drying oils 290 “C for 6 h or as long as it takes to reach the desired or rosin acids (from tall oil) during the bodying viscosity. The thickening can proceed under exposure process. to air or, preferably, to an inert gas, which produces a Tung oil is frequently used in combination with paler oil. The viscosity of stand oil can be as high as other compounds such as phenolic resins, coumarone 200 poise. Linseed stand oil can be used in, e.g., resins and ester gums. Applications include air-drying lithographic varnishes, as enamel oils (mixed with tung finishes, marine spar varnishes, in aluminum paints oils) and as a leveling agent in undercoats. and in primers for alkaline surfaces (plasters, A disadvantage of linseed oil and other drying oils as concrete) [13,14]. binders especially in formulations of light-colored coatings is its tendency to yellow with age. This is 220.127.116.11. Castor oil mainly due to their relatively high content of linolenic Castor oil, obtained from the Castor nut (Ricinus acid. This property may be reduced by admixing other, communis) (oil content approx. 50%), is an unusual semi-drying vegetable oils. However, this may also oil in that it contains a very high amount (900/) of negatively affect drying time, so an optimum balance ricinoleic acid: a hydroxy moiety-containing fatty acid must be found. (12-hydroxy-9c-octadecenoic acid) (Fig. 4). It is at 50 J.T.P. Derksen et al. / Progress in Organic Coatings 27 (1996) 45-53 present the only commercially available source of Europe. The oil is extracted with hexane from the natural hydroxylated triglycerides. Although castor oil flaked beans, which contain 15- 18% oil on a dry in itself has no drying properties, it is an interesting oil weight basis. Before further use the crude oil must be for the coating industry. This is to some extent due to refined, in particular to remove the relatively high the fact that its hydroxyl functionality allows the oil to amount of gums (lecithin, or phospholipids). Being a be used, for example, in polyurethane coatings. Also good surfactant, soybean lecithin finds application in the hydroxyl functionality imparts a high viscosity, the coatings industry as pigment-wetting and stability and polar solvent (alcohol) miscibility to this flocculation-control agents. The oil itself contains oil, making it useful as viscosity modifiers, plasticizers predominantly linoleic and oleic acids (I.V. 125-140) and wetting agents in various applications [15- 171. and dries about three times slower than linseed oil The versatility of castor oil can be further enhanced under the same conditions. Since it contains only little by a catalytic, high-temperature conversion of this oil linolenic acid it can be mixed with drying oils such as to dehydrated castor oil. In this process the ricinoleic linseed or tung oil to improve the yellowing acid in castor oil is converted to partially conjugated characteristics. However, a quantitatively more fatty acids, rendering oil drying properties that are important use of soybean oil is the incorporation of its intermediate to linseed and tung oil. Dehydrated castor fatty acids in (‘ soy modified’ or ‘ ) linoleic rich’ alkyd oil yields pale, non-yellowing films with outstanding resins for non-yellowing white paints. color retention properties that are exploited in vehicles for gloss lithographic inks, metal decorating inks as 18.104.22.168. Safflower well as in air-drying and stoving alkyd resins. It is Safflower oil, obtained from the thistle Curthamus seldomly used as an oil in air-drying varnishes or tinctorius, is very similar to soybean oil, although with paints, since after drying it retains a characteristic a higher content of linoleic acid and somewhat less ‘after-tack’ for some time [13,14]. saturated fatty acids. It has, therefore, a slightly higher iodine value than soybean oil (I.V. = 140-150) and is a 22.214.171.124. Other drying oils little faster drying. Just like soybean oil it has excellent A number of minor oilseed crops produce drying oils non-yellowing properties and is for this reason also that have been evaluated in coatings systems. These used to produce light-colored, non-yellowing alkyd include such crops as perilla (Perillu frutescens) and paints. oiticica (Licania riguda). Perilla oil is recovered from the seeds of this crop, 126.96.36.199. Other oils which carry about 38% oil, and has been used in the Tall oil is an atypical oil since it is not obtained from past as a strong drying oil. It has a fatty acid oil-bearing seeds or fruits like other vegetable oils. Tall composition that resembles linseed oil but has a higher oil is a by-product of the paper industry, where it is degree of unsaturation. As its higher iodine value recovered from the ‘ black liquor’ resulting from the (I.V. = 192-208) already suggests, this oil dries faster Kraft (sulfate) pulping of coniferous woods. The than linseed oil under comparable conditions . obtained dark-colored crude tall oil is not composed of Oiticica oil contains a high content of licanic acid pure triglycerides, like other vegetable oils, but is rather (4-keto-9c, 11t, 13t-octadecatrienoic acid) together with a mixture of fatty acids, rosin acids and unsaponifiable some elaeostearic acid. It is extracted from the nuts of matter (e.g., sterols, waxes, hydrocarbons) in a ratio of the brasilian oiticica tree, which contain 55-63% oil on 5 : 4: 1. The fatty acid fraction can be enriched by a dry weight basis. Just like tung oil, oiticica oil fractional distillation to a product that is known as contains a large percentage of conjugated fatty acids. In TOFA (tall oil fatty acids), which contains mainly oleic reactivity and other properties oiticica oil is, therefore, and linoleic acid. It is chiefly used for the production of very similar to tung oil . alkyd resins and dimer acids. The rosin acid-rich Despite their applicability in coatings formulations fraction is converted to drier metal salts (‘ ) tallates’ or both perilla and oiticica oil have been replaced to a incorporated into alkyds [ 13,141’ . large extent by synthetic binders. This is to a large Although not a vegetable oil, fish oil is interesting to degree due to their limited availability and the the paints and coatings industries since it has good uncertain stability of their supply. drying properties. In particular sardine and menhaden oils possess drying properties that can be further 3.2.2. Semi-drying oils enhanced by a segregation, i.e. a solvent separation process, in which the fraction of saturated fatty acids is 188.8.131.52. Soybean decreased. The resulting fraction contains a large Together with protein, soybean oil is the main proportion of unsaturated fatty acids with long chains product of the crop soybean (Glycine max), which is (C20-C22) and a high number of isolated double cultivated on a large scale in, e.g., the USA and bonds (4-6). Fish oil acids can be used in preparing Derksen et al. / Progress in Organic Coatings 27 (1996) 45-53 J.T.P. 51 Table 2 Selected potential oilseed crops (after Refs. [24-261) Oilseed crop Seed yield Oil content Major fatty acid FA content I.V. Specific gravity (tons/ha) (% dry weight) (% of total) (g/ml 25 “C) Crambe abyssinica (crambe) 2.5-3.5 26-39 erucic 55560 112 0.910 Limnanthes alba (meadowfoam) 0.5-1.0 17-29 very long chain 95+ 114 0.905 Dimorphotheca pluvialis (cape marigold) 1.2-1.7 18-26 dimorphecolic 58-65 167 0.905 Lesquerella fendleri (lesquerella) 1.6-2.3 23-29 lesquerolic 51-53 Calendula ojjicinalis (marigold) 1.552.5 19-24 calendic acid 58-63 242 0.940 Euphorbia lagascae (spurge) 1.0-1.5 45-52 vernolic 59965 102 0.955 Vernonia spp. (vernonia) 1.5-2.0 31-42 vernolic 68-75 alkyd and urethane resins. Its sometimes fishy odor is 3.3.2. New hydroxy fatty acid seed oils hard to remove and may in certain cases be Dimorphotheca pluvialis (or cape marigold) seed oil objectionable [ 131. contains more than 60% of a hydroxydiene fatty acid: dimorphecolic acid (A9-hydroxy-lOt,l2t-octa- 3.3. New seed oils decadienoic acid) (Fig. 4). In contrast to the more familiar hydroxy fatty acid ricinoleic acid (A12-hy- Table 2 presents a selection of seven vegetable oil- droxy-9c-octadecenoic acid) from castor oil, or to the bearing plant species that are currently being evaluated newer hydroxy fatty acid lesquerolic acid (A14-hy- as potential oilseed crops in Europe. These oilseed droxy-14c-eicosenoic acid) from Lesquerella spp., di- plants were selected for reasons of agronomic feasibility morphecolic acid contains a conjugated diene moiety, as well as of industrial interest and market opportuni- cc-positioned with respect to the hydroxyl functionality ties and result from a wide range of plant species (see Fig. 4.). This feature renders this fatty acid much screened, both in Europe [18-211 and in the USA more reactive than the two other hydroxy fatty acids [22,23]. The seed oils from the plants selected all have mentioned. This reactivity may be exploited to obtain features that make them ‘ unusual’ when compared to , innovative oleochemicals, but also requires careful seed existing oilseed crops. and oil handling and processing [25,28]. Like castor oil, it was found that lesquerella oil is 3.3.1. Very long chain fatty acid-rich seed oils also non-drying. Despite its two conjugated double Crambe abyssinica and Limnanthes alba (or meadow- bonds dimorphotheca oil also is a non-drying oil. This foam) seed oils contain large amounts of very long is probably due to the fact that the double bonds are chain fatty acids. Crambe abyssinica contains up to 60% positioned in an all-trans configuration. Also the pres- erucic acid (A 13c-docosenoic acid), exclusively posi- ence of an allylic hydroxyl moiety may contribute to tioned on the 1,3-positions of its triglycerides. The this behavior . However, it was found that after a presence of erucic acid makes this crop an alternative prolonged period of time in the presence of cobalt for high erucic acid rapeseed (HEAR), but has the driers dimorphotheca oil did dry to a wrinkled, frosted advantage of a consistently higher erucic acid content. film . This property, similar to tung and oiticica oil, Currently, the major product of erucic acid is eru- suggests that dimorphotheca oil is dehydrated to conju- camide, that is used as a surface-active additive in gated di-and trienes prior to peroxidation and drying. coatings production and as an anti-block or slip agent. However, it is expected that chemical dehydration of Many other applications are foreseen for erucic acid dimorphotheca oil and lesquerella oil produces oils that and its hydrogenated derivative behenic acid, in fields are similar in drying properties to tung oil and linseed such as detergents, lubricants and cosmetics, but also in oil or dehydrated castor oil, respectively. coatings industries. Examples for the latter are found in Apart from producing dehydrated oils, dimor- recently issued patents on their use in hot-melt ink jet photheca oil and lesquerella oil can also be utilized in printing inks and in printing ribbons . Limnanthes coatings system in which the presence of a hydroxyl alba contains over 95% fatty acids of the C20 and C22 group is exploited. An interesting example for such a type, 63% being A5- and Al 1-eicosenoic acids . system is the production of urethane resins based on Limnanthes alba seed oil already finds use as a base oil these new oils plus, e.g., polyols or rosin esters . in cosmetics but also has a large potential market in lubricants. It is a non-drying oil and has therefore 3.3.3. New drying oils limited use as a binder in coatings formulations. How- Calendula oficinalis (or common marigold) contains ever, derivatives from this oil, such as estolides, are fatty acids with conjugated triene functionality (calendic tested in inks and paints as, e.g., viscosity modifiers. acid or A8t, lot, 12c-octadecatrienoic acid) (Fig. 4) very 52 J.T.P. Derksen et al. / Progress in Organic Coatings 27 (1996) 45-53 similar to the elaeostearic acid in tung oil from Aleuritis paints that are exclusively based on renewable re- fordii. This oil presents an alternative source of these sources. fatty acids, and can be utilized in the same applications 3.5. Vegetable oil-based printing inks as tung oil. The film-forming properties and film char- acteristics are expected to be very comparable to those An interesting new development that has come off of tung oil. the ground in recent years is the application of soybean oil in printing inks [37-391. Apart from the replacement 3.3.4. Natural epoxidized seed oils of petroleum based resins by renewable resources, soy- Euphorbia lagascae (or spurge) yields a natural epox- bean oil-based vehicles has considerable advantages in idized oil that contains 60-65% vernolic acid (A12,13- the production of colored inks. The exceptionally light epoxy-9c-octadecenoic acid) (Fig. 4) . This fatty color of the vehicle allows substantially reduced pig- acid also occurs to an even higher extent (72-78%) in ment levels compared to conventional ink formulations Vernonia galamensis and other Vernonia species, which . So far, a large range of formulations, including 75 are currently under investigation in the USA . Ap- black and 25 colored, have been tested . At present, plications for this fatty acid are similar to those for various formulations are already employed by the epoxidized soybean oil, such as in stabilizers and plasti- American Newspaper Publishers Association in com- cizers in polyvinylchloride production, but can also be mercial lithographic and letterpress newsprint applica- found in paints and coatings industries. tions . Other advantages of vegetable oil-based inks Euphorbia lagascae and Vernonia spp. oils are very include the formulation of inks over a broader range of interesting for use in organic coatings. A major reason viscosity, low rub-off characteristics, a reduction in for this is that, in contrast to epoxidized soybean and emission of volatile organic compounds and decreased linseed oils, these oils have a relatively low viscosity health hazards in ‘ ink mist’ inhalation in the working (approx. 101 centipoise at 25 “C ). Its pourability is environment: a problem sometimes encountered around also very good, even below 0 “C [30,31]. A very interest- high speed, rotary letterpress machines . In Europe, ing application for such low viscosity epoxy functional- other vegetable oils, such as rapeseed are also currently ity-containing oils is as reactive diluent in paints. In evaluated for use in, especially, cold-set offset ink for- such an application the oil functions, on the one hand, mulations . as a solvent, making dispersion or solubilization of the Apart from their use as a binder or diluent in formulation with volatile organic solvents superfluous, printing inks, vegetable oils have also been successfully while, on the other hand, the oil reacts with other used as a washing solvent to remove excess printing ink components in the formulation to form an integral part and as a cleaning agent for printing rollers [l]. It was of the dried coating. It has been calculated that a found that, in contrast to organic solvents, vegetable 10 wt.% addition of vernonia oil per gallon of paint oils do not cause swelling of the rubber coatings on the would reduce volatiles by as much as 160 million rollers in the printing machinery. These applications are pounds per year across the USA . Other applica- clearly not only interesting from an environmental, but tions for Euphorbia lagascae and Vernonia spp. oils also from a performance point of view. include coatings relying on the formation of interpene- trating polymer networks [33-351 and flexible baked coatings on metals . The latter coatings show excel- 4. Conclusions and perspectives lent flexibility, adhesion to substrate, chemical resis- tance, cohesive film properties and resistance to Since the advent of alkyd-type paints and of syn- chipping . thetic polymers for latex or vinyl and acrylic resin- based emulsions for surface coatings, the use of linseed 3.4. Vegetable oil-based, water-borne emulsion coatings oil in coating formulations has declined significantly. However, lately a revival of interest in linseed oil-based The major advantage of water-borne emulsion coat- s paints is observed. This is due to the user’ and con- ings is the reduction in volatile organic compounds s sumer’ perception of this type of binder as environ- emission upon drying of the film. In the past, research ment-friendly as well as to the industries interest in has been focused on the emulsification behavior of pure renewable resources as alternatives for petrochemical linseed oil . This has, however, not yet led to feedstocks of an inherently finite supply. marketable products. Recently a joint project between Many new paint and ink formulations appear each our Institute and the University of Technology of End- year. In patent literature one can observe an increasing hoven, Netherlands, has started to investigate the film application of renewable resources. In particular hy- forming properties of emulsion formulations that con- droxyl- or epoxy-functionalized fatty acids are very tain prepolymerized and pre-oxidized vegetable oils. versatile in their applications (for a few examples of This research aims at the development of emulsion recently issued patents see Refs. [40-431). J.T.P. Derksen et al. /Progress in Organic Coatings 27 (1996) 45-53 53 Furthermore, because of the inherent polymer prop-  L.H. Princen, Econ. Bat., 37 (1983) 478.  L.H. Princen and J.A. Rothfus, J. Am. Oil Chem. Sot., 61(1984) erties of proteins, their price, and the possibilities to 281. adjust the technological properties of these biopoly-  Agricultural Commodities as Industrial Raw Materials, Congress mers, there are very good perspectives for the use of of the United States, Office of Technology Assessment OTA-F- proteins in non-food applications. 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