RESISTANCE OF PIRARUCU Arapaima gigas SKIN TANNED IN DIFFERENT PLANT TANNIN  CONCENTRATIONS  

Arapaima gigas, known as Giant of the Amazon, since it reaches up to 300 kg in body weight, is the second most cultivated species in Rondônia, Brazil. This state produces 9 thousand tons/year of this fish slaughtered at the average commercial weight of 12 kg, with approximately 14% of scaly leather. The use of plant tannins as a replacement for chromium in pirarucu leather tanning seeks to aggregate the use of regional products in tanning costs and reduce environmental impacts. The aim of this study was to evaluate the physical-mechanical resistance of Pirarucu skin tanned at different plant tannin concentrations.

The study was carried out at the Texturas da Amazônia tannery industry, Rondônia, in January 2017. Twenty pirarucu fishs were used, presenting 14 ± 1.2 kg body weight from a certified excavated nursery. The hides were tanned at 5%, 10%, 15% and 20% plant tannin concentrations, and, after reaching 18% humidity, lengthwise and crosswise bodies of evidence from the dorsal region of the fish were removed and submitted to physical-mechanical analyses according to ABNT standards, by the MK chemistry of Brazil Laboratory. The mean of the Pirarucu dermis thickness ranged from 2.0 to 4.7 mm. The increase in tannin concentrations reduced tensile strength and increased the progressive tearing of Pirarucu leather, although they did not influence elasticity (resistance to elongation until rupture). At 15% tannin the tanning did not influence lengthwise leather tensile strength (P < 0.05), of 15.99 N/mm2, while the other concentrations presented lower crosswise resistance (table 1). The tear rate was significantly higher, of 10.8 N/mm, in the crosswise direction of the leather at 5% tannin. At 15% tannin greater leather physical-chemical stability for the preparation of garments and artifacts from the leather of Pirarucu was observed.