The comparative solid state 13C CPMAS NMR spectra
of cornstarch, mimosa tannin, UF, cornstarch–UF
(10:90 w/w) and cornstarch–mimosa tannin–UF
(10:4:86 w/w) resins are shown in Fig. 5. The spectral
feature of cornstarch–mimosa tannin–UF (10:4:86 w/w)
resin are quite similar to those of cornstarch, mimosa
tannin and UF. With the present result, it is not possible
to ascertain if there interactions between mimosa tannin
and UFresin. Used method would be not definite enough to
identify chemical reactions between mimosa tannin and
UF resin. When small amounts of mimosa tannin are
added to a cornstarch–UF (10:90 w/w) resin, a reaction
takes place immediately, at ambient temperature, giving a
soft mass easily dissolved by fast stirring and the addition
of small amounts of water. Using MS, Pizzi [12] showed
that the –CH2OH groups of the UF resin react with resorcinolic A-rings of the flavonoid units while forming a methylene bridges (Fig. 6).