Abstract
With the intensification of fish farming, the amount of residues also increased. One of the by-products generated is leather. However, several factors influence its quality, among them, the types of tanning used. Paiche (Arapaima gigas) is the largest freshwater fish in the world, and therefore has great potential in the use of leather, in addition to being one of the most cultivated fish in the Rondônia state. The aimed was to evaluate the physicomechanical resistance, histological and morphological aspects in different directions of the fibers of the paiche to evaluate the tanning with chromium oxide and vegetable tannin. Paiches with an average weight of 12.0 kg were used, skins were made and tanned using chromium and vegetable tannin as techniques. After tanning, 20 specimens were removed in longitudinal, transverse and diagonal directions to the fish body, to determine resistance in dynamometer and leather for histological analysis, scanning electron microscopy and physical-chemical analysis. The average thickness of the specimens of the leathers ranged 1.79mm to 2.82mm, in addition, there was no interaction between the type of tanning agent and the directions obtained for strength, traction and elongation. Regarding the progressive tearing test, there was also no interaction effect. However, the defined factors had relevant differences for the maximum and average amount applied, and the leathers tanned with vegetable tannin expanded to larger dimensions 110.19 and 85.52 N. According to the images obtained by histology and scanning microscopy, they presented that in the longitudinal and transverse direction the collagen fibers are presented in layers parallel to the leather surface and in the diagonal direction the interlacing is more intense, that is, in addition to the overlapping layers intercalated thinner, close to the surface, fiber bundles can also be seen crossing each other. It is concluded that leathers tanned with vegetable tannin have less resistance than leathers tanned with chromium salts for traction to rupture and greater resistance to tear.
Highlights
The demand to increase the production of food for human consumption has made efforts to make viable alternatives in quantity and quality, and in this sense, aquaculture has been shown to be adequate for this purpose [1, 2]
With the unfolding of this interaction, it can be inferred that the leathers with vegetable tannin were thicker (P
Comparing the results reported with those obtained in this experiment with the paiche (A. gigas) leather, it can be inferred that in addition to the types of tanning agents applied in the tanning process, the species is essential in the evaluation of strength, as it presents an architecture in the arrangement and orientation of collagen fibers that determines a greater or lesser resistance to the leather after processing
Summary
The demand to increase the production of food for human consumption has made efforts to make viable alternatives in quantity and quality, and in this sense, aquaculture has been shown to be adequate for this purpose [1, 2]. The development of fish farming in Brazil is due to factors such as investments in the production and processing sector, the increase in research, together with the vast available water resources [3]. To carry out the tanning of fish skins, whatever the species, several types of tanning agents can be used, including chromium salts, vegetable or synthetic tannin, aluminum, as well as for dyeing, the use of special chemical dyes for leather or natural fabrics from different origins [7]. The use of tanning agents of mineral origin has been neglected, as is the case with chromium, as they can be harmful to the environment, leading many countries to give commercial preference to leathers that used vegetable tannins [8]
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