Chemistry Reference
In-Depth Information
hydrogen bonds results in the swelling and collapse of PEUs and this special
property is used to control the delivery of drugs or other active molecules.
5.4 Tung Oil
5.4.1 Use of Tung Oil and its Derivatives for Polymer
Synthesis
Tung oil has the highest average number of double bonds per triglyceride
(7.5).
8
84% of its fatty acid chains are from elaeostearic acid, which contains
a conjugated triene structure. This highly unsaturated property makes it a
drying oil that has been used for more than 1000 years in China.
121
It can be
cationically polymerized with styrene, resulting in a co-polymer with good
mechanical and damping properties as well as shape-memory effects.
122
The
T
g
values are close to room temperature and generally increase with the
content of styrene. The Young's modulus increased from 4.89 to 13.92 MPa
with the increase of styrene from 30 to 70 wt%. Moreover, these hard
elastomers present shape-memory behavior with high recovery and fixity
ratios, opening possibilities for practical applications that require a material
response close to room temperature. Furthermore, a third co-monomer such
as divinylbenzene (DVB) can be used to obtain a co-polymer based on tung
oil with styrene.
123,124
The use of DVB as a co-monomer in the cationic
polymerization of the triglyceride resulted in polymers with high thermal
stability in an ample temperature range and a room-temperature Young's
modulus close to 1 GPa. The co-polymer also displayed shape-memory ef-
fects with the switch temperatures in the range 25 to 40 1C. When the
amount of DVB increased, the T
g
and Young's modulus also increased, this
can be associated with the increase of cross-linking density and the contri-
bution of the rigid aromatic structure of the DVB co-monomer. Das et al.
125
blended an unsaturated polyester resin/styrene mix with tung oil. This novel
material had improved impact strength, creep resistance, Young's modulus,
and hardness. With only 1 wt% of tung oil, the impact strength, Young's
modulus, and hardness increased by 15, 20 and 41%, respectively.
Huang et al.
126
prepared a UV-curable resin based on tung oil. The resin
was synthesized via a Diels-Alder reaction of tung oil with MA, followed by a
non-isocyanate polyurethane (NIPU) reaction and an acrylation modification
with glycidyl methacrylate. The higher concentration of double bonds re-
sulted in a faster curing rate but a lower final conversion of the double
bonds. All the cured films had two T
g
values, which were in the range 8-10 1C
and 46-48 1C, respectively. Excellent thermal stability was observed with
decomposition temperature as high as 350 1C, indicating that they can be
used for UV coatings for substrates with high temperature resistance. Add-
itionally, the introduction of structure by NIPU is helpful for enhancing
adhesion of the cured films to substrates.
Luo et al.
127
synthesized a tung-oil-based thermoset, which was
reinforced by tannin lipid. The polymer films were synthesized by oxidative
