Avaliação química da qualidade de couros e efluentes de curtume

Abstract

For the transformation of animal skin into leather, a stable and not putrescible material, various chemicals are used to produce a material with good quality and appearance. Because it presents low cost and generates high strength product, Cr(III) is the main tanning agent used in leather processing. However, it is toxic, mainly in the oxidized form (Cr(VI)). The environmentally friendly alternative is the use of tannins (synthetic or vegetable), replacing Cr(III). Regardless of the tanning process, it is important to evaluate the quality of the leather produced and the generated waste, whose characteristics must be known for treatment or reuse. Thus, this thesis aims to evaluate the quality and thermal stability of sheep hides of different genotypes tanned with Cr(III) or tannin; the proposition of models for assessing the quality of bovine hides by combining near-infrared spectroscopy (NIRS) with physic-mechanical data; and the development of procedures to determine the inorganic constituents in the final product (leather) and in the effluents generated during the tanning process. The influence of the genotype and the type of tanning, chromium or tannins, on the physical-mechanical properties and thermal stability of sheep hides, was evaluated with the aid of Principal Component Analysis (PCA). The results indicated a more significant influence on the type of tanning than those related to the genotype of the animals. Chromium-tanned leather is more stable thermally when compared to tanned leather, but this difference occurs only at temperatures above 250 °C. Differences were also observed in the direction that the physical-mechanical test was performed, longitudinal or transverse to the cephalous-caudal axis caused as a function of the way in which the collagen fibers are elongated during the physical-mechanical test. The combination of NIRS associated with chemometric tools was used in the construction of classification models to predict the quality of bovine hides from physical-mechanical data, such as tensile strength, elongation, and resistance to tear and tear two legs. The mean accuracy obtained with different models (kNN, SIMCA, and PLS-DA) was 88%. For the determination of chromium present in hides, the preparation of samples using acid digestion and alkaline solubilization with tetramethylammonium hydroxide (TMAH) were developed. The analyses were made by microwave-induced plasma optical emission spectrometry (MIP OES). Samples of bovine, sheep, and goat hides were analyzed after digestion, according to the best conditions previously defined by experimental design, and the results were not statistically different (t-test) in both procedures used. Strategies for the preparation of samples of tannery effluents to determine the elements foreseen in the legislation (CONAMA 430/2011) were evaluated in a system of UV and H2O2 radiation and determination by MIP OES. Different analytical techniques were applied to evaluate the quality of leather and effluents of the tannery and are adequate, both from product quality and for the evaluation and proposal of treatment of the generated waste.