Three main determinations were made on the representative
samples of each different tannin sources: SEM, BET surface and
porosimetry studies (histogram of pore size).The bulk density of
these tanningels are quite similar among them all, with a mean
value of 1.43 g cm3 inside the range of 1.35–1.58. As a matter of
fact, just comparative studies can be made in order to explain the
slow kinetics and the high adsorbent q capacity. First, a graphical
approach to the nature of the rigid gels was carried out with the
SEM images that are shown in Fig. 3. As can be appreciated, signifi-
cant differences are presented in each case. The four tanningels are
quite similar in their macroscopic structure and appearence (rigid
and non-porous aspect). However, PFC seemed to be rather different
in its mechanical properties; it is more brittle. This means the
polymerization was carried out in a different way with P. pinaster
and in the rest of the tannin resins, surely due to the polyphenolic
nature of the tannin extracts.