Mechanism of High Chrome Uptake of Tanning Pickled Pelt by Carboxyl‐Terminated Hyper‐Branched Polymer Combination Chrome Tanning

Tuning a green carboxymethyl cellulose-based pre-tanning agent via peroxide oxidation for high chrome exhaustion in leather industry

The low chrome uptake by collagen in the conventional tanning process leads to the pollution of the wastewater. Due to environmental concerns, leather scientists are already searching for innovative ways to produce pre-tanning agents as a high exhaustion chrome tanning auxiliary. Herein, a novel kind of pre-tanning agent is engineered by converting carboxymethyl cellulose (CMC) to oxidized carboxymethyl cellulose (OCMC) via the hydrogen peroxide process. FT-IR and carboxyl content analysis demonstrated the increase in carboxyl content after oxidation. After that, the obtained OCMC was utilized as a pre-tanning agent, resulting in a high exhaustion of chrome (92.76 %) which is 27.76 % more than conventional chrome tanning (65 %), and the amount of chrome in wastewater reduced to 7.24 %. The hydrothermal stability of wet-blue increased by increasing the uptake of chrome (Ts = 118 °C). The obtained crust leather represented excellent mechanical properties (Tensile strength: 305.68 kg/cm2; tear strength: 50 kg/cm) and desirable organoleptic properties. The environmental analysis signifies a significant step towards a cleaner and sustainable tanning process (COD = 1600, BOD5 = 560 mg/L) compared to the conventional chrome tanning process. Consequently, the obtained results offer a green pre-tanning agent to meet the requirements of the sustainable development of the leather industry.

A new-fangled horizon in leather process to sidestep toxic chrome and formaldehyde using hyperbranched polymer

A novel chrome-free tanning and formaldehyde-free post tanning process with PEG-melamine base hyperbranched polymer by complexing aluminum (Al³⁺) present in aluminum sulfate for eco-friendly tanning applications. The hyperbranched polymers PEGM-400-C-Al and PEGM-600-C-Al were synthesized and characterized by FT-IR, NMR, UV, and XRD. The molecular weight of polymers was assessed by GPC and subjected to the leather process. The processed crust leathers were analyzed for physical characteristics by tensile strength, tear strength, elongation, and quality assessments by hand evaluation by experts. FE-SEM analyzed collagen fibers and fiber splitting of goat skin, and COD, BOD, and total solid in spent liquor were analyzed and compared. The highlighting feature of hyperbranched polymers is (a) Improved shrinkage temperature (Ts) (85 ± 1 °C), (b) Improved physical-mechanical properties (c) Better BOD, COD, and total solids over the aluminum sulfate tanning process. This study confirmed that hyperbranched polymer is effective for tanning and post-tanning leather, which obviates the need to use toxic chromium and formaldehyde for tanning leathers.

Zero Liquid Discharge System for the Tannery Industry—An Overview of Sustainable Approaches

The tannery industry is characterized by the consumption of a large quantity of water, around 30–40 m3 for processing 1000 kg of hide or skin. This amount becomes wastewater, containing about 300 kg of different chemicals, mainly refractory organic compounds, with high chemical oxygen demand (COD), total dissolved salts (TDS), chromium, and evolution of toxic gases, such as ammonia and sulfides, etc. The remaining tanning chemicals are released as effluent having high resistance against biological degradation, becoming a serious environmental issue. Usually, end-of-pipe treatment is not sufficient to meet the concerns of environmental issues. In terms of cleaner production options, the redesigning of the existing effluent treatment procedures with alternate or additional treatment techniques, which “supports resource recovery with no added chemicals”, is expected to give a sustainable solution for the management of toxic effluent. The Zero Liquid Discharge (ZLD) system serves to ensure zero water emission, as well as treatment facilities by recycling, recovery, and reuse of the treated wastewater using advanced cleanup technology. The international scenario shows the implementation of ZLD thanks to pressure from regulatory agencies. The ZLD system consists of a pre-treatment system with conventional physicochemical treatment, tertiary treatment, softening of the treated effluent, reverse osmosis (RO) treatment for desalination, and thermal evaporation of the saline reject from RO to separate the salts. By adopting this system, water consumption is reduced. Moreover, ZLD also becomes effective in disaster mitigation in areas where the tannery industry is a strong economic actor. With this review, we aim to give an outlook of the current framework.

Immobilizing chromium in tannery sludge via adding collagen protein waste: an in-depth study on mechanism

Owing to containing high fraction of organic matter, the tannery sludge seemed to be fit for composting. Actually, it was intensively harmful to the environment, due to containing chromium (Cr). So it might undergo a long time of storage until finding a proper way to dispose it. In the storage period, it would expose the surrounding environment a risk via releasing Cr. In this study, an approach was proposed to minimize the amount of released Cr, and reveal the mechanism on immobilizing Cr. Collagen protein waste (CPW) was adopted to immobilize Cr, and it was evaluated via leaching experiment. The lowest leaching concentration of Cr was 12 mg/L, meeting the limits of related standard in China (GB 5085.3-2007, Tcr < 15 mg/L). Moreover, the compositions and functional groups of the optimum sample (12 mg/L) were also characterized, confirming that the dominant functional groups cross-linking with Cr were hydroxyl (-OH), carboxyl (-COOH), and epoxy (-COC). Importantly, density functional theory (DFT) calculation was also employed, suggesting that Cr was restrained by accepting electrons from O atoms donating by functional groups.

Interactions between Collagen and Alternative Leather Tannages to Chromium Salts by Comparative Thermal Analysis Methods

This study aims to investigate the interactions between collagen and tanning process performed by Ecoltan®, phosphonium, EasyWhite Tan®, glutaraldehyde, formaldehyde-free replacement syntan, condensed (mimosa) and hydrolyzed (tara) vegetable tanning agents as alternative tannages to conventional basic chromium sulphate widely used in leather industry. Collagen stabilization with tanning agents was determined by comparative thermal analysis methods; differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and conventional shrinkage temperature measurement. Analysis techniques and tanning agents were compared and bonding characteristics were commented by thermal stabilization they provided. Chromium tanning agent was also examined to be comparable of novel tannages for leather industry. The results were interesting as a different perspective than the conventional view to provide a better understanding of the relationship between tanning and thermal stability of leather materials.