Chemistry Reference
In-Depth Information
9.7 Epoxidized Vegetable Oil Paints and Coatings
Due to their versatility, excellent adhesion to a wide range of substrates, and
corrosion and chemical resistance, epoxy resins are widely used in coating
applications.
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EVOs have promise as alternatives or supplements to
petroleum-based epoxies because of a combination of attributes: low viscosity,
low cost, and epoxy functionality. Use of EVOs in coatings not only provides
sustainable chemical content but also offers a way to reduce volatile organic
compounds and, as just discussed, improve the flexibility or toughness of
epoxy coatings.
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However, the challenge for neat EVO polymer coatings is
to improve their mediocre mechanical and thermal performance, especially of
polymer moduli and T
g
values, which, to date, have prevented further market
penetration. Co-polymerization with petroleum-based monomers of rigid
structure and/or an application of inorganic compounds to form blended or
nanocomposite coatings, respectively, are frequently applied strategies to
enhance EVO coating properties.
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Because of their similar reactivity towards cationic polymerization and
stiffer structure, cycloaliphatic epoxies such as 3,4-epoxycyclohexylmethyl
carboxylate are commonly used as co-monomers with EVOs in coating ap-
plications. High-solid, cationically cured coatings based on cycloaliphatic
epoxy resin, ESO and polyols were prepared by Raghavachar et al.
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and had
useful film properties as general-purpose coatings. A blend with 10 wt% ESO
gave a coating with similar performance to the cycloaliphatic epoxy control.
With further increases in the ESO content, the hardness of the coatings
decreased, but this was regulated by the structure of the epoxy and polyol, or
adjustment of the epoxy-to-polyol ratio.
Coatings derived from epoxidized MesuaferreaL.seed oil and DGEBA were
prepared by Das and Karak.
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The results indicated that the EVO not only
reduced the viscosity of the DGEBA but also enhanced the performance of the
polymer. The performance of 50 wt% epoxidized seed oil was further enhanced
by the formation of a nanocomposite using organically modified nanoclay.
Adding 2.5 to 5 wt% clay improved the alkali resistance of the prepared coating.
Ultraviolet-initiated cationic polymerization of EVOs has been the subject
of intensive research due to the convenience of curing at room temperature
and the fast curing rate.
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Bio-based coatings prepared by Thames
and Yu
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exhibited excellent adhesion, impact resistance, UV stability, gloss
retention, and corrosion resistance properties. Vernonia oil or ESO blended
with cycloaliphatic epoxy was used as an epoxy resin and cationically UV
initiated. The incorporation level of EVOs was formulated by their com-
patibility with the other coating ingredients. Although both EVOs were
compatible with cycloaliphatic epoxy at high concentrations, EVO epoxy
blends were only partially compatible and formed hazy formulations with
polyols or UV initiators. The pencil hardness and tensile strength of the
coating films decreased, but the gloss retention increased. Optimum prop-
erties in terms of hardness, gloss and gloss retention were obtained at a
10 wt% of EVO in the coating.
