Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
PRODUCTION AND ISOCYANATE FUNCTIONALIZATION OF NANO-BOEHMITE
PARTICLES
Gülden EROĞLU 2 , Güngör GÜNDÜZ 1,2 , Üner ÇOLAK 3 , Bora MAVIS 4
1 Middle East Technical University, Polymer Science and Technology Department, 06531, Ankara, Turkey
2 Middle East Technical University, Chemical Engineering Department, 06531, Ankara, Turkey
3 Hacettepe University, Nuclear Engineering Department, 06800, Ankara, Turkey
4 Hacettepe University, Mechanical Engineering Department, 06800, Ankara, Turkey
Abstract— The purpose of this research is production of nano-boehmites to be used in PU-based nanocomposite surface coatings with enhanced physical and
mechanical properties. For this purpose aluminum hydroxide (AH) was transformed to nano-boehmite (NB) particles in a hydrothermal reactor. Crystalline
structure of NBs was examined by XRD and conditions for 100% transformation was determined. 1,6-diisocyanatohexane (HDI) and 4,4'-methylene diphenyl
diisocyanate (MDI) were used as surface grafting agents to react with hydroxyl groups on the surface of the NB particles for the functionalization of NB particles.
The extend of functionalization of NBs was investigated by Fourier Transform Infrared (FTIR) spectroscopy. It was found that the reaction between isocyanates
and hydroxyl groups on the surface of NB was near complete.
The emphasize in the contemporary research and development
of coating materials is on the development of functional materials.
Especially, the development and dissemination of nano-technology
applications influenced the production of nano-particles and their
utilization in diverse areas. In coating applications, siloxanes based
on tetra ethoxy silane (TEOS) are generally used to improve the
scratch resistance of the coatings. However, TEOS’s high cost puts a
burden to its wide use.
The aim of this work is to produce nano-boehmites by using a
low cost starting material like aluminum hydroxide and functionalize
nano-boehmites for the synthesis of scratch resistant coatings.
The work was carried out in two main steps; (i) NB production
by hydrothermal synthesis and (ii) functionalization of NB particles
with two different diisocyanates.
In the first step, NB particles were obtained by using AH, acetic
acid and ammonia. Needle-like, plate-like and cube-like
morphologies are the three different types of NB that were
synthesized. Time, pH, temperature and concentration of the acid and
base in the solution are the main parameters of hydrothermal
synthesis. pH is the most important factor that determines the
structure of NBs. Needle-like NB was produced in acidic pH,
whereas cube and plate-like NB were produced in basic pH. Platelike
structure was used in the functionalization step because of having
high aspect ratio. For producing plate-like NB, firstly, acidic acid was
used to peptize and improve the dispersion of AH. After that,
ammonia was used to adjust the pH of the solution. In hydrothermal
reactor, AH was converted to NB completely. Figure 1 shows the
SEM micrographs of NBs.
Figure 1: SEM micrograps of (a) cubic-like boehmites (b) platelike
nanoboehmites
It is expected that the reaction between isocyanate groups and
hydroxyl groups on the surface of the AH will enhance physical and
mechanical properties of products. Therefore, in the second step,
plate-like NBs were functionalized by using HDI and MDI. Toluene
was used as a solvent and di-butyl tin dilaurate was used as a catalyst.
Functionalization reaction takes place between OH groups on the
surface of NBs and N=C=O groups of the diisocyanates.
Diisocyanates were selected due to having two reactive groups and
while one of the cynate would react with surface OH groups, the
other one would be free. The critical, but undesirable point in the
functionalization process is the reaction of the two cyanates with OH
groups on different surfaces at the same time. In order to avoid this
reaction, excess amount of diiscocyanates were added to the medium.
The amount of catalyst and diisocyanate were optimized.
(a)
(b)
Fiugre 2: FTIR analysis of (a) 1g MDI, 0.05 ml catalyst and 1 g
boehmite, (b) 3 ml HDI, 0.1 ml catalyst and 1 g boehmite
Figure 2 shows FTIR results of the functionalized NBs. Peak at
2270 cm -1 is due to asymetric stretching vibrations of –NCO which
indicates that the cyanates were grafted to the surface of the
boehmites. Peaks at 1540 and 1510 cm -1 are assigned to bending of
the –NH bonds. Absorption peaks at 1600 and 1640 cm -1 are
attributed to stretching of C=O bonds. The peaks at 1230, 1750, 2900
and 2825 cm -1 can be assigned as stretching of C-N (amid groups)
bonds, stretching of ester groups, symmetric and asymmetric
stretching vibrations of methyl groups, respectively.
In future work, functionalized NBs will be used to produce PU
nanocomposites with enhanced mechanical and physical properties. It
is believed that the PU nano-composites will be used in surface
coatings due to their potentially high scratch resistance.
Acknowledgement:This work is supported by TUBİTAK under
Grant No. MAG–108M204.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 280