8 Oleochemistry Products
237
characterized by two or more units of unsaturation separated by no more than one
methylene group. Typical sources for drying oils include soybean, linseed, sunflower
and dehydrated castor oil [220]. Eventual trace contaminants present in the oils can
influence their acceptability in a given market, i.e. phenolic contaminants can modify
the colour of the resin as it oxidizes in air.
VO find application in the formulation of different kinds of paint and coating.
Natural VO are triacylglycerols of fatty acids. They contain several functionalities
in their backbone that can undergo a huge number of chemical reactions useful to
modify their chemical structure.
In general, VO can be directly used, without any further modification, as corrosion
inhibitors and to produce drying-oil coatings. The main features of these two classes
of products are reported as follows.
Corrosion inhibitors: VO and plant extracts have been used as natural corrosion
inhibitors against alkaline and acid media as well as chloride ions [49, 119]. The
anticorrosion activity is attributed to the presence of heterocyclic constituents such
as alkaloids, cellulose, flavonoids and tannins.
True drying-oil coatings: VO have the tendency to dry forming films in their
virgin forms. Drying is a characteristic of the VO, depending on the unsaturated
portion, i.e. the number of carbon–carbon double bonds (iodine value or drying
index). VO characterized by with high drying index are used, meaning the sum of
the percentage of linoleic acid plus two times the linolenic acid content of the oil.
VO with a value greater than 70 are considered drying oils. Drying or semi-drying
VO are used in surface coatings. Non-drying VO can be used, instead, to incorporate
suitable chemicals (e.g. hydroxyls) or modifiers (vinyls, acrylics, acrylic copolymers)
in VO backbone, through chemical reactions. This fact has the aim to transform them
into film formers. Drying VO can react with atmospheric oxygen to form polymeric
materials with crosslinked structures [140].
VO in their virgin forms require longer drying times, and the related films do not
meet the desirable physico-mechanical and corrosion resistance performance. Thus,
several chemical reactions can be carried out at the functional groups present in the
virgin VO, i.e. hydrogenation, transesterification, epoxidation, acrylation. The main
products that can be synthesized starting from VO are listed below and summarized
in Fig. 8.9.
Alkyds: oil-modified polyesters, consisting of a multi-functional acid (phthalic
acid or trimellitic acid), a polyol (i.e. glycerol, trimethalolpropane or pentaerythritol)
and an unsaturated fatty acid formed by a polycondensation reaction. There are three
normal alkyd classes, based on the amount of unsaturated oil used in producing the
alkyd resin [86]:
• Long oil alkyds: used for architectural paints. They contain more than 60% oil,
characterized by slow drying speed and softness.
• Medium oil alkyds: used for architectural paints and as a co-resin in coatings,
containing a VO amount of 40–60%, characterized by slow drying velocity but
are slightly harder and are faster to dry than long oil alkyds.
237
characterized by two or more units of unsaturation separated by no more than one
methylene group. Typical sources for drying oils include soybean, linseed, sunflower
and dehydrated castor oil [220]. Eventual trace contaminants present in the oils can
influence their acceptability in a given market, i.e. phenolic contaminants can modify
the colour of the resin as it oxidizes in air.
VO find application in the formulation of different kinds of paint and coating.
Natural VO are triacylglycerols of fatty acids. They contain several functionalities
in their backbone that can undergo a huge number of chemical reactions useful to
modify their chemical structure.
In general, VO can be directly used, without any further modification, as corrosion
inhibitors and to produce drying-oil coatings. The main features of these two classes
of products are reported as follows.
Corrosion inhibitors: VO and plant extracts have been used as natural corrosion
inhibitors against alkaline and acid media as well as chloride ions [49, 119]. The
anticorrosion activity is attributed to the presence of heterocyclic constituents such
as alkaloids, cellulose, flavonoids and tannins.
True drying-oil coatings: VO have the tendency to dry forming films in their
virgin forms. Drying is a characteristic of the VO, depending on the unsaturated
portion, i.e. the number of carbon–carbon double bonds (iodine value or drying
index). VO characterized by with high drying index are used, meaning the sum of
the percentage of linoleic acid plus two times the linolenic acid content of the oil.
VO with a value greater than 70 are considered drying oils. Drying or semi-drying
VO are used in surface coatings. Non-drying VO can be used, instead, to incorporate
suitable chemicals (e.g. hydroxyls) or modifiers (vinyls, acrylics, acrylic copolymers)
in VO backbone, through chemical reactions. This fact has the aim to transform them
into film formers. Drying VO can react with atmospheric oxygen to form polymeric
materials with crosslinked structures [140].
VO in their virgin forms require longer drying times, and the related films do not
meet the desirable physico-mechanical and corrosion resistance performance. Thus,
several chemical reactions can be carried out at the functional groups present in the
virgin VO, i.e. hydrogenation, transesterification, epoxidation, acrylation. The main
products that can be synthesized starting from VO are listed below and summarized
in Fig. 8.9.
Alkyds: oil-modified polyesters, consisting of a multi-functional acid (phthalic
acid or trimellitic acid), a polyol (i.e. glycerol, trimethalolpropane or pentaerythritol)
and an unsaturated fatty acid formed by a polycondensation reaction. There are three
normal alkyd classes, based on the amount of unsaturated oil used in producing the
alkyd resin [86]:
• Long oil alkyds: used for architectural paints. They contain more than 60% oil,
characterized by slow drying speed and softness.
• Medium oil alkyds: used for architectural paints and as a co-resin in coatings,
containing a VO amount of 40–60%, characterized by slow drying velocity but
are slightly harder and are faster to dry than long oil alkyds.