Vegetable tannin composition and its association with the leather tanning effect

Abstract

The increasing environmentally friendly approach of using renewable materials has led to vegetable tannins having an important role as tanning agents in the leather industry. Tannins are complex phenolic structures, and the literature shows that a considerable amount of chemical parameters measured through analytical techniques can be associated with their tanning ability. In the present study, five types of vegetable tannins highly used in the tanning industry were chosen for the evaluation of some of their relevant chemical parameters and the correlation with their cross-sectional penetration in the hide. Black wattle (Acacia mearnsii), quebracho (Schinopsis lorentzii), chestnut (Castanea sativa), tara (Caesalpinia spinosa), and myrobalan (Terminalia chebula) were tested. The chemical properties of the total tannin polyphenols, non-tannin polyphenols, insoluble solids, soluble solids, total solids, total phenols, non-tannin polyphenols:total phenols ratio, and residual tanning float concentration were measured and associated with the leather cross-sectional penetration results. The statistical Mann–Whitney-U test showed that the insoluble solids, non-tannin polyphenols, soluble solids, and total tannin polyphenol percentages distinguished the groups of tannins that crossed the hide from those that did not well. Hence, since the analysis of insoluble solids is the simplest and the most direct among them, it would be recommended to use this parameter to define a cutoff to distinguish the performance of tannins for leather application.     

Tuning the Mechanical Properties of BIEE‐Crosslinked Semi‐Interpenetrating,Double‐Hydrophilic Hydrogels

Double‐hydrophilic, semi‐interpenetrating (semi‐IPN) hydrogels are synthesized by encapsulating hydrophilic polyvinylpyrrolidone (PVP) linear chains in structure‐defined 1,2‐bis‐(2‐iodoethoxy)ethane (BIEE)‐crosslinked (poly(2‐(dimethylamino)ethyl methacrylate) (pDMAEMA) hydrogels. A series of semi‐IPN double‐hydrophilic hydrogels are prepared in which the pDMAEMA/BIEE content is kept the same and only the PVP content is varied, from 0 up to 33 wt%. The mechanical properties of the water‐swollen hydrogels are experimentally evaluated under unconfined compressive loading conditions, while a nonlinear hyperelastic constitutive equation is used to predict their mechanical response. No significant difference is found in the mechanical response of the semi‐IPN PVP/pDMAEMA/BIEE hydrogel containing 5 wt% PVP compared to the pDMAEMA/BIEE analog, however, for greater loading percentages (15 and 33 wt% of PVP), the semi‐IPN hydrogels exhibit less stiffness/higher ductility. Furthermore, in vitro biocompatibility studies are carried out for the pDMAEMA/BIEE and the semi‐IPN PVP/pDMAEMA/BIEE, indicating that both the formulations exhibit no toxicity in cultured cells.     

Optimization of the Biotechnological Process for Hide Unhairing in Substitution of Toxic Sulfides

Screening and isolation of a new Bacillus subtilis strain and production of its proteases for leather unhairing are described. B. subtilis strain BLBc 11 was isolated from the aerobic sludge of a tannery. Optimization of enzyme production by this bacterium was carried out using the Plackett‐Burman and central composite design. Unhairing and inter‐fibrillary removal capabilities were evaluated by scanning electron microscopy and determination of proteoglycans and glycosaminoglycans. Crude enzymatic extracts of B. subtilis BLBc 11 cultures were applied for the unhairing process of hides with excellent results, suggesting that this safe enzymatic preparation can replace the toxic chemicals commonly used in this process.     

Treatment of Leather Dyeing Wastewater with Associated Process of Coagulation-Flocculation/Adsorption/Ozonation

This study is based on the investigation of performance of associated wastewater treatments of coagulation-flocculation/adsorption (CF-ADS) and coagulation-flocculation/ozonation (CF-OZ) for the removal of pollutants from tannery wastewater. The chemical dosage was optimized and the use of waste from the tannery process was tested as a low-cost alternative adsorbent for wastewater treatment plants. For the CF-ADS the removal of TOC, COD, Na⁺ and color were 50.04%, 53.13%, 17.05% and 61.13%, respectively, and for the CF-OZ the removal were 46.50%, 56.25%, 11.10% and 85.34%. Also, BOD/COD and COD/TOC ratios were studied to verify the oxidation efficiency of the wastewater.