Chromium-free and waterless vegetable-aluminium tanning system for sustainable leather manufacture

The development of chrome free chestnut and Tetrakis Hydroxymethyl Phosphonium Sulfate based Eco-benign combination tanning system

The replacement of the conventional chromium tanning system with an eco-benign tanning systems has received great attention owing to stringent environmental regulations. In this specific study, a chrome-free combination tanning system based on chestnut and tetrakis (hydroxymethyl) phosphonium sulfate (THPS) was developed and presented as an effective alternative cleaner tanning technology. Processing of the tanning trials were carried out varying the percentages of chestnut as a tannage, followed by THPS as a re-tannage for process optimization. The leathers obtained were characterized for their thermal stability, grain surface properties using a scanning electron microscope, physical strength characteristics, comfort, and organoleptic properties. Finally, the environmental impact of the tanning systems was assessed through the comparative analysis of their spent liquors. The chestnut-THPS combination system tanned leathers using 20 % chestnut followed by 2 % THPS resulted in maximum shrinkage temperature of 95OC. The hydrothermal stability of the leathers tanned using this combination tanning system were found to be better than those tanned using chestnut and THPS tanning systems alone, respectively. The strength and comfort properties of the leathers produced using the developed combination tanning system were found to be on par with or better than those of conventionally tanned leathers, and the scanning electron microscopic study depicted that the grain surface of the leathers produced were observed to be free of surface deposition. The environmental impact assessment showed that the combination tanning system used resulted in a significant reduction in TS, TDS, TSS, and BOD in the wastewater. This research article has attempted and established the use of chestnut-THPS-based combination tanning systems as an effective, eco-friendly alternative tanning process technology.

Synthesis and crosslinking of collagen using 4-3,4,5-tris(oxiran-2-ylmethoxy)benzamido)benzenesulfonic acid for the development of robust metal-free leather

The leather manufacturing sector is actively pursuing organic alternatives to replace the utilization of inorganic tanning chemicals such as chromium, zirconium, and aluminum due to concerns over their environmental impact. Although glutaraldehyde has been considered a feasible alternative, it still falls short in providing the leather with greater tensile properties and is also considered to be toxic. In this study, we report the synthesis of a sulfonated gallic acid-based epoxide (GSE) and evaluate its performance as a metal-free tanning compound. The synthesized compound was subjected to comprehensive characterization using FTIR (functional group), ESI-MS (molecular weight), and NMR (chemical environment) spectroscopy. Furthermore, the leather treated with GSE demonstrated organoleptic and physical properties that were comparable to those achieved with glutaraldehyde tanning systems. SEM analysis of the GSE-tanned leather exhibited a homogeneous distribution pattern, confirming the stability of the collagen. In addition, the hydrothermal stability temperature of leather crosslinked with epoxide was found to be 83 ± 2 °C. The wastewater generated from the GSE tanning process exhibited a BOD to COD ratio of 0.35 ± 0.04, indicating its high treatability. The results showed that the GSE tanning system provided better tanning efficiency and improved crosslinking and thermal stability without the use of metal salts. Furthermore, the use of GSE as a tanning agent offers several advantages, such as easy availability, biodegradability, and low toxicity, making it a sustainable and environment-friendly option for the leather industry.

Efficient removal of Cr (VI) from aqueous solution by using tannery by-product (Buffing Dust)

The current study is focused on using tannery waste called buffing dust to remove hexavalent chromium from an aqueous solution. The buffing dust was characterised by using different technique like FTIR, SEM, and BET analysis. The adsorption experiment was conducted in batch mode. The different operating factors including contact time, dose and initial Cr (VI) concentration were investigated. The optimum adsorption capacity was observed at contact time of 240 min and dose of 1g/100 mL. The adsorption isotherm such as Langmuir, Freundlich and Temkin were investigated at different initial concentration. It was observed that Langmuir isotherm model was best fitted for present study with maximum adsorption efficiency of 11.33 mg/g. The kinetic study was performed for pseudo first order and pseudo second order and it was found that pseudo second order model was provided the best match with regression coefficient (R²) of 0.9991.

Characterization and Strength Quality of the Oryctolagus cuniculus Leather Compared to Oreochromis niloticus Leather

This study aimed to compare the resistance of the Oryctolagus cuniculus L. (rabbit) and Oreochromis niloticus L. (Nile tilapia) skins, as well as to observe the design of the flower of these skins and the morphology of the dermis. Tilapia and rabbit skins were placed inside the same equipment (tannery machine) for the chromium salt tanning process. The flower design of the fish leather distinguishes it from the rabbit leather, the latter being constituted by the opening of the hair follicles and pores, while the fish leather is constituted by the presence of protective lamellae and insertion of the scales. The dermis of rabbit skin consists of thick bundles of collagen fibers arranged in all directions, which differs from the morphology observed in the dermis of fish skin. However, in the Nile tilapia skin dermis, overlapping and parallel layers of longitudinal collagen fiber bundles are observed, these layers are interspersed with fiber bundles crossing the sking surface (transversely), tying the fibers together and providing greater strength, which can be proven by the strength test. The fish leathers, despite having less thickness (1.0 mm), demonstrated significantly greater tensile strength (13.52 ± 1.86 N mm^-2) and tear strength (53.85 ± 6.66 N mm^-2) than rabbit leathers, that is, (8.98 ± 2.67 N mm^-2) and (24.25 ± 4.34 N mm^-2). However, rabbit leather demonstrated higher elasticity (109.97 ± 13.52%) compared to Nile tilapia leather (78.97 ± 8.40%). It can be concluded that although the rabbit leather is thicker due to the histological architecture of the dermis (thick bundles of collagen fibers arranged in all directions with no pattern of organization of collagen fibers), it shows less resistance than Nile tilapia leather, which demonstrates an organization of overlapping and parallel layers and intercalating collagen fiber bundles transversally to the surface, functioning as tendons for the swimming process. It is recommended to use a piece of fabric (lining) together with the fleshy side of the rabbit leather, to increase resistance when used in clothing and footwear, as these products require greater tensile strength. Thus, it minimizes this restriction for the use of rabbit leather in the aforementioned purposes.

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.

Review of Soil Quality Improvement Using Biopolymers from Leather Waste

This paper reviews the advantages and disadvantages of the use of fertilizers obtained from leather waste, to ameliorate the agricultural soil quality. The use of leather waste (hides and skins) as raw materials to obtain biopolymer-based fertilizers is an excellent example of a circular economy. This allows the recovery of a large quantity of the tanning agent in the case of tanned wastes, as well as the valorization of significant quantities of waste that would be otherwise disposed of by landfilling. The composition of organic biopolymers obtained from leather waste is a rich source of macronutrients (nitrogen, calcium, magnesium, sodium, potassium), and micronutrients (boron, chloride, copper, iron, manganese, molybdenum, nickel and zinc), necessary to improve the composition of agricultural soils, and to remediate the degraded soils. This enhances plant growth ensuring better crops. The nutrient release tests have demonstrated that, by using the biofertilizers with collagen or with collagen cross-linked with synthetic polymers, the nutrient release can be controlled and slowed. In this case, the loss of nutrients by leaching into the inferior layers of the soil and ground water is minimized, avoiding groundwater contamination, especially with nitrate.

Composite Polymers from Leather Waste to Produce Smart Fertilizers

The leather industry is facing important environmental issues related to waste disposal. The waste generated during the tanning process is an important resource of protein (mainly collagen) which can be extracted and reused in different applications (e.g., medical, agricultural, leather industry). On the other side, the utilization of chemical fertilizers must be decreased because of the negative effects associated to an extensive use of conventional chemical fertilizers. This review presents current research trends, challenges and future perspectives with respect to the use of hide waste to produce composite polymers that are further transformed in smart fertilizers. Hide waste contains mostly protein (collagen that is a natural polymer), that is extracted to be used in the cross-linking with water soluble copolymers to obtain the hydrogels which are further valorised as smart fertilizers. Smart fertilizers are a new class of fertilizers which allow the controlled release of the nutrients in synchronization with the plant's demands. Characteristics of hide and leather wastes are pointed out. The fabrication methods of smart fertilizers and the mechanisms for the nutrients release are extensively discussed. This novel method is in agreement with the circular economy concepts and solves, on one side, the problem of hide waste disposal, and on the other side produces smart fertilizers that can successfully replace conventional chemical fertilizers.