SYNTHESIS OF POLYPYRROLE/TIO NANOPARTICLES IN WATER BY CHEMICAL OXIDATIVE POLYMERIZATION - Biomaterial Applications: Macro to Nanoscales - page 87

4.4.3 TGA ANALYSIS
The TGA diagrams for pure PPy and the PPy/TiO 2 composite are shown
in Fig. 4.10. The comparison of pure PPy and PPy/TiO 2 composite shows
that the mass loss of PPy is more than the composite up to 450ºC. The bet-
ter stability in this range of temperature (from room temperature to 450ºC)
is due to the presence of TiO 2 nanoparticles. It should be noted that our
composite has only 2.5% (mass) TiO 2 .
The degradation of PPy shows a three-stage decomposition pattern as
three major slope changes are observed. At T < 100ºC, the mass loss is
caused by the presence of residual water in the sample. The next stage of
the mass loss is by degradation that lasts until 225ºC, and is attributed to
the loss of dopant ions that are weakly (electrostatically) bound, from the
interchain sites of the polymer [37]. When the temperature increases, the
more obvious degradation begins. This mass loss is due to degradation and
decomposition of the polymer backbone. Unlike pure PPy, the degradation
process of PPy/TiO 2 composites shows two stages, and the mass loss is
less at T < 450ºC. TiO 2 particles have a positive effect on the degradation
in this temperature range which means binding of PPy to TiO 2 makes the
PPy chemical bonds stronger.
In Curve b, the mass loss of the PPy/TiO 2 composite observed at T <
125ºC is because of the evaporation of residual water in the sample. The
binding of PPy to TiO 2 is most probably from the C-NH side (see the dis-
cussion of IR spectra in Section 4.4.1) and therefore less NH is available to
absorb water (via hydrogen bonding). Another potential cause is the steric
effect that could happen due to possible crosslinking of PPy chains on the
surface of TiO 2 nanoparticles. Therefore there is less mass loss in the PPy/
TiO 2 composite at T < 125ºC. In the second stage from 125ºC to 750ºC
weight loss is because of the degradation and decomposition of the PPy
backbone. This decomposition is slower up to 450ºC in the PPy/TiO 2 com-
posite compared to pure PPy. When the temperature approaches 800ºC,
the mass loss of PPy/TiO 2 is about 90%, while the pure PPy is completely
degraded. This is due to the TiO 2 content (2.5%) and the residues bound
to TiO 2 which are stabilized by TiO 2 nanoparticles. The conclusion that
emerges from comparison of the TGA data of PPy/TiO 2 and PPy as well as
DSC data that will be discussed later is the following: PPy is more like a
linear polymer but when the polymer is grown on the surface of rutile TiO 2
nanoparticles a large degree of crosslinking happens. This causes the shift