(1) Commercially available tannin extracts, such as Acacia mearnsii
de Wild (Weibull black) and S. balansae (Quebracho colorado)
were supplied by TANAC (Brazil). They were products involved
in the leather treatment and they are presented as powder.
(2) Lab-extracted tannins, such as P. pinaster (Pine) and C. sempervivens
(Cypress). They are extracted according to the following
procedure [35]: 100 g of bark were milled in a cutting mill
(RETSCH, SM 2000 model) and they were put in 600 mL of
tap water. Then 5 g of NaOH (PANREAC) were added and the
mixture was stirred in magnetic stirrer at 90 ◦C for 1 h. Solids
were separated by filtration and liquid fraction was dried in
oven (65 ◦C) overnight. The resultant was considered the tannin
extract.