Magnetic Biofoams Based on Polyurethane Applied in Oil Spill Cleanup Processes - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 261

table 4. Main results obtained from SAXS analysis.

Peak Center (nm -1 ) FWHM (nm -1 ) ds (nm) Lc (nm)

1 0.27 0.21 23.3±0.2 59.8±0.6

2 0.42 0.33 15.0±0.1 38.1±0.4

maGNetiC ForCe oF maGNetiC BioFoams
The magnetic force of composite material was measured by weighting in two distinct
moments: in the absence of the magnetic field and in the presence of the magnetic
field. In both cases it is used a known distance between the magnet and the sample.
There is an exponential increase in the magnetic force when the magnet gets close to
the maghemite and magnetic biofoam samples. The empiric model to describe this
behavior is

da

MF = F + a e .

Eq.1

2

¥ 1

In the Eq. 1, MF is the magnetic force; F ∞ is the force exercised by the mag-
neto over the sample with the distance tending to infinite; a 1 is the amplitude, a 2
is the decay constant and finally d is the distance between the magneto center and
the sample.
Using this model is possible to determinate the previously mentioned parameters
and the correlation between the experimental data and the model, shown in Table 5.
This model allows extrapolating the magnetic force to obtain its value when the dis-
tance between the magneto and the samples is zero, this value is named initial mag-
netic force or MF 0 , which corresponds to the sum of F ∞ and a 1 . The values found to
MF 0 for the magnetic biofoam and the maghemite are equal to (2.0 ± 0.4) × 10 -2 and
(9 ± 8) × 10 -3 N, respectively. It indicates that the maghemite nanoparticles, dispersed
into the polymer matrix, are attracted by magneto with a force around 110% higher, in
comparison with the pure maghemite nanoparticles, shown in Figure 10. It is possibly
due to high dispersion degree that nanoparticles own in the polymer matrix, which
allows the increasing of the attraction capability. These results are in agreement with
the SAXS ones.

table 5. Parameter values and correlations of the model.

Parameter PU-5 Maghemite

F ∞ (3.4 ±0.4) x 10 -5 (3 ± 2) x 10 -6

a 1 (2.0 ± 0.4) x 10 -2 (9 ± 8) x 10 -3

a 2 (7.6 ± 0.3) x 10 -1 (1.2 ± 0.3) x 10 0

R 2

0.9997 0.9959