Magnetic Biofoams Based on Polyurethane Applied in Oil Spill Cleanup Processes - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 257

addition of concentrated ammonium hydroxide into the beaker under continuous agitation.
After 30 min, the medium was filtrated and the obtained particles were washed several
times with water and finally dried at 60°C in an oven. Magnetite was converted into
maghemite through annealing at 200ºC along one hour. The maghemite nanoparticles
are shown in Figure 5. These maghemite nanoparticles were chosen because they pres-
ent a good magnetic behavior. It means that, after removing the applied magnetic field,
these maghemite nanoparticles have residual magnetization close to zero. It is possible
to notice that in presence of the magnetic field the nanoparticles were aligned (Figure
5a) and after removing the applied magnetic field, they lose their alignment.
Figure 5. (a) Maghemite nanoparticles in the presence and (b) absence of the magnetic field.
magnetic Biofoam Production and Characterization
The opened porous volumes of the prepared resins are presented in Table 2. Generally
speaking, it can be seen that the increase of water amount cause a weakening of the
walls, evidenced by porosity decrease from PU-1 to PU-4. This is due to fewer avail-
able diisocyanate to react with the hydroxyl groups of castor oil. It caused the collapse
of several cells, leading to the decrease of the internal volume. Among the prepared
bioresins, the values presented in Table 2 show that PU-1 was the most porous mate-
rial (2.6 ± 0,2 cm 3 of opened pores volume). It means that this material has the thinnest
walls, been perfect to prepare particulated material useful to the environmental recov-
ered processes. So, the PU-1 foam was chosen to prepare the composite containing
the maghemite nanoparticules, sample PU-5. This magnetic biofoam was prepared
through fusion and mixture of polyurethane resin and maghemite nanoparticles, gen-
erating a material containing 5wt% of the maghemite, shown in Figure 6. It can be
noticed that PU-5 sample presented pores smaller than the ones presented by the PU-1
one. The nanoparticules presence generated a decrease in the open porous volume. It
is related to an increase of the thickness of the walls. However, the reddish composite
remains easily processable.