Renewable resources in coatings technology review by mikesanye

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									                                                                                                                         PROGRESS
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                                             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 [2].                                                        reduction   in the use of organic solvents in paint sys-

0300-9440/96/$15.00 0 1996 Elsevier Science S.A. All rights reserved
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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 [7]. 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 [7]. 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 [3]. 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% [2]. 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
                                                                                                3.2.1.1. 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                                    3.2.1.2. 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                                 3.2.1.3. 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                        3.2.2.2. 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
    3.2.1.4. 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,                    3.2.2.3. 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 [14].                      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 [14].                                          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
     3.2.2.1.   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 [29]. 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 [29]. 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 [27]. 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 [25].                         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 [29].
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) [25]. 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
                                                                       [37]. So far, a large range of formulations, including 75
are currently under investigation in the USA [30]. Ap-
                                                                       black and 25 colored, have been tested [38]. 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 [39]. 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 [25]). 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 [39]. 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 [39].
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 [32]. 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 [31]. 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 [30].                                                         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 [36]. 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


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