Environmental Engineering Reference
In-Depth Information
pathway. Epoxidized vegetable oils are obtained through a standard epoxidation
reaction, where the double bonds react with hydrogen peroxide in an acidic envi-
ronment [23]. Epoxidized vegetable oils can be used as plasticizers in polyvinyl
chloride or as toughening agents, and as a platform for further modifications [3].
Reacting epoxidized vegetable oil with acrylic acid produces acrylated epoxi-
dized vegetable oil. Acrylated epoxidized vegetable oils are used for surface coating
and ink applications [24-29]. The properties of cross-linked AESO and styrene
were extensively studied by R. Wool's group [2, 30]; they observed a plasticizing
effect in thermosets of 100% AESO which they contributed to the inherent structure
of the vegetable oil. The storage modulus for the 100% AESO material was similar
to that of a 50/50 mix of AESO and styrene at low temperatures, while at high tem-
peratures the storage modulus was inversely proportional to the styrene content [2].
The behavior at elevated temperatures was explained by the increased cross-linking
density attainable in 100% AESO. However, the tensile properties significantly
increased after incorporation of styrene; the tensile modulus of 100% AESO was
approximately 440 MPa, while for a mix of 60% AESO and 40% styrene the
modulus was 1.6 GPa. Ultimate tensile strengths also increased from approximately
6 MPa for 100% AESO to approximately 21 MPa for the 60/40 AESO/styrene
mix [2]. Replacing the styrene with another biorenewable monomer (acrylated
epoxidized fatty methyl ester) provided a route to increase the renewability of
materials produced from AESO [31]. The fact that the properties of the material can
be tuned by changing the ratio of AESO and monomer (styrene or acrylated
epoxidized fatty methyl ester) illustrates the possibility that these materials may
replace fossil-based polymers for structural applications [2, 32].
Recent work with AESO utilized facile-controlled free-radical polymerization
techniques, such as atom transfer radical polymerization (ATRP) and reversible
addition fragmentation chain transfer (RAFT), to synthesize block copolymers
with triglyceride-based monomers [33]. This work reveals a possible pathway to
replacing the fossil-based thermoplastics by renewable materials.
5.2.4
Polyurethanes from Vegetable Oil
Epoxidized vegetable oils can be reacted to form polyols, commonly by acid-
catalyzed epoxide ring opening by water or by acid-catalyzed alcoholysis with a
mono-alcohol, typically methanol [8]. These vegetable-oil-based polyols can then be
reacted with diisocyanates to form polyurethanes, as shown in Scheme 5.2 [6, 34].
Generally, polyurethanes are used in applications such as coatings, adhesives,
sealants, and elastomers, but the major application is as flexible or rigid foams [6].
When used in flexible foams, polyols typically have a molecular weight ranging
from 3,000 to 6,000 Da with a hydroxyl functionality near 3 [6]. In rigid foams, the
polyols have molecular weights below 1,000 Da and a higher hydroxyl functional-
ity (between 3 and 6) [6]. Because polyols from vegetable oils have functionalities
between 3 and 5, with molecular weights below 1,000 Da, they are suitable for
rigid foam applications [35].
