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, significant
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.