Chemistry Reference
In-Depth Information
co-polymerization of tannin linoleate/acetate mixed esters with tung oil,
resulting in products ranging from soft rubbers to rigid thermosets. It was
found that tannin incorporation into the formulations was essential for the
final product to achieve ample mechanical strength. The film stiffness, T
g
and cross-link density increased with greater tannin linoeate/acetate content
because the tannin component provided rigidity through polyphenolic
aromatic rings and unsaturated chains as cross-linking sites. The films had
ambient modulus values between 0.12 and 1.6 GPa, with T
g
values in the
range 32 to 72 1C.
Huang et al.
128
developed two new monomers from tung oil, and epoxy
resins were prepared accordingly. The new monomers were a 21-carbon
dicarboxylic acid (C21DA) and a 22-carbon tricarboxylic acid (C22TA). They
were converted to triglycidyl esters (DGEC21 and TGEC22, respectively) and
cured with nadic methyl anhydride. Both triglycidyl esters were liquids at
room temperature and had lower viscosity and higher reactivity than the
commercial Bisphenol A (BPA) epoxy resin DER332. The resulting resins ex-
hibited T
g
values in the order DER332 (168 1C)4TGEC22 (131 1C)4DGEC21
(80 1C)4ESO (37 1C). Both cross-link density and molecular rigidity contrib-
uted to this order. Firstly, the cured TGEC22 had a significantly higher cross-
link density than the cured DGEC21, which in turn had a higher cross-link
density than that of the cured ESO, thus TGE22 had a higher T
g
than that
DGE21 and ESO. On the other hand, although the cured DER332 had a lower
cross-link density than the cured TGEC22, the former had a much more rigid
molecular structure than the latter, thus displayed the highest T
g
.
Another new monomer derived from tung oil was described by Liu et al.
129
The monomer was prepared via the alcoholysis of tung oil with pentaery-
thritol (PER) to obtain the corresponding alcoholysis products (TO-PER),
followed by a maleinization reaction to get the maleate half ester (TO-PER-
MA). It was then co-polymerized with 33% styrene and cured subsequently,
to give a polymer matrix with promising mechanical properties: the tensile
strength and modulus were 35.9 and 1.94 GPa, whereas the flexural strength
and modulus were 46.2 and 2.08 GPa.
The chemical modification of tung oil utilizes the conjugated triene in the
fatty acid chains. New functional groups such as hydroxyl groups can be
introduced. Ribeiro da Silva et al.
130
synthesized a tung-oil-based polyol in a
two-step process. Firstly, the hydroxylated tung oil was formed by reaction of
tung oil with hydrogen peroxide and formic acid, and then, this intermediate
was reacted with dry triethanolamine to form the polyol, with an average
hydroxyl number of 450 mg KOH g
1
. This tung-oil-based polyol was then
used for the synthesis of PU foam, which was further reinforced by addition
of rice husk ash (RHA), a residue from the rice processing industry, as a rigid
filler because of its high silica content. The thermal stability of the com-
posite was not affected by the RHA, while a relatively higher thermal con-
ductivity was observed. Wood flour and microcrystalline cellulose can also
be used as reinforcement fillers for tung-oil-based PUs. Mosiewicki et al.
131
found that with 10 wt% wood flour, the tensile modulus and tensile strength
