Leather Manufacturing Process Research Articles

Assessment and Characterization of Leather Solid Waste from Sheba Leather Industry PLC, Wukro, Ethiopia

Leather manufacturing processes raw hides and skins into various finished leather products, generating huge amounts of untanned and untanned leather solid wastes (LSWs). The present study investigates the LSWs generation, characterization, and management practices of the Sheba leather industry in Ethiopia. Results revealed that LSWs are categorized as non-chrome solid waste, including de-dusted salt, raw trimming, hairs, fleshing waste, pickle trimming, and splitting wastes. Chrome-based wastes include chrome shaving waste, crust leather trimming waste, buffing dust waste, finished leather trimming waste, etc. Further, solid wastes were characterized for the physico-chemical parameters viz. moisture (31.5%), ash content (7.3%), pH (5.7), carbon content (14.7%), nitrogen content (0.3%), chromium content (2%), calorific value (20,107 kJ.kg-1), VOCs (75.1%) and carbon to nitrogen ratio (52:1). Results obtained suggested various sustainable technological options for the effective LSWs management to preserve environment.

Experimental and Computational Fluid Dynamics Investigation on Tanning Process in a Rotating Drum

Mass transfer of chemicals greatly affects leather production efficiency and product quality. Leather shows different motions in a rotating drum during processing, which is strongly associated with chemicals’ mass transfer. However, how leather motions affect mass transfer remains unclear, which disfavors highly efficient leather manufacturing process. Here, different leather motion states were obtained by adjusting the drum rotation speed. Experimental results showed that the duration of leather rolling motion greatly increased by 41% when the rotation speed increased from 5 r/min to 20 r/min, and the uptake of the tanning agent was consequently improved, which indicated that the rolling motion is beneficial to mass transfer. Computational fluid dynamics simulation results showed that the mass transfer rate under rolling motion was higher than those under slipping, elevating and hanging motions, because the flow velocity and concentration gradient near the leather surface were higher under rolling motion. Accordingly, increasing the rolling motion enhanced the mass transfer in leather processing. This work identifies the leather motion beneficial for mass transfer and provides guidance on operating condition optimization and drum design for high-efficiency leather production.

Acrylic Finished Leather Upgraded with Thermoplastic Polyurethane Filament using 3D Printing – A New Generation Hybrid Leather of Synthetic and Natural Polymer

Leather manufacturing process involves a lot of waste disposal which pollutes environment, some of the processes are inevitable. In the present investigation, 3D printing technology was used to reduce the wastage and to cover defective regions in leather. The present study focuses on synthesis of acrylic binder using emulsion polymerization technique. These binders were analysed for solid content for better optimisation of the amount of binder to be utilised for finishing operation. The experimental binder was prepared with 26% solids. Particle size and thermogravimetric analyses were carried out to understand the size and shape of the particles and their thermal resistance. These binders were used for leather finishing and the performance of leather was studied. Surface morphology changes of leathers were studied using Scanning Electron Microscopy (SEM). Wet and dry rub fastness, finish film adhesion, light fastness and organoleptic properties were studied and found to be superior compared with control leathers. The acrylic finished leather with minor defects was taken for 3D printing and designed using Thermoplastic Polyurethane (TPU) as filament. The acrylic finished leather shows good adhesion for TPU and it results in numerous designs in short duration. The new additive was added to leather using 3D printing technology to produce a tailor-made valuable design without any waste disposal and chemical discharge. This invention may convert the rejected waste leather into valuable material and lead to the new generation hybrid leather for use.

Tannery effluent treatment and its environmental impact: a review of current practices and emerging technologies

Abstract The tannery industry plays a significant role in the economy but poses a severe environmental threat due to its high water and chemical usage, leading to wastewater generation with a high concentration of pollutants. This wastewater contains a range of contaminants created throughout the leather manufacturing process, making effluent disposal a significant challenge for the industry. The tanning process also contributes significantly to the pH, biological oxygen demand (BOD), total suspended solids (TSS), chemical oxygen demand (COD), total dissolved solids (TDS), and concentrations of T Cr, Cr(III), Cr(VI), Cl−, sulfate, sulfide, and inorganic constituents in the wastewater. This review paper provides a concise overview of the origins and characteristics of post-tanning effluent, different treatment techniques, and applications of treated wastewater. Comparing the prominent tannery effluent technologies, adsorption and advanced oxidation processes (AOPs) effectively improved wastewater biodegradability before biological treatment. AOPs, enzymatic, adsorption, and coagulation treatment effectively upgraded the effluent to desired levels for disposal. Additionally, membrane separation processes have shown high pertinency in cases where the treated effluent is intended for reuse, whereas hybrid technologies can be the answer for better and cost-effective results.

Subtilisin Carlsberg immobilization and its application for eco-friendly leather processing

Conventional dehairing based on application of huge amount of chemicals is the most polluting process of all leather manufacturing processes. In this study, Subtilisin Carlsberg (SC) was immobilized on magnetic chitosan (mCTS) using two different crosslinkers: 2% glutaraldehyde (GA) and 0.5% genipin (GE). The reaction medium for SC immobilization consisted of 500 mg carrier and 5 ml (1 mg/ml) enzyme solution. Also, the immobilization conditions were pH 8, 25 °C and 2 h incubation period. The hydrolysis activity of immobilized SC has been extensively investigated. The structure and surface morphology of the prepared carriers were characterized by Scanning Electron Microscop (SEM), Thermogravimetric Analyzis (TGA) and Energy Dispersive X-Ray Spectroscopy (EDX). Optimum temperature and pH values of SC activity were found to be 50 °C and pH 8.0, respectively for free and immobilized SC. Higher activity of SC at around pH 8 and 50 °C makes it suitable for industrial applications. Thermal stability of immobilized SC was found greater than free SC. At the end of 4 h of exposure to high temperature, while the immobilized enzyme can maintain its activity around 50%, the free enzyme can maintain around 20%. Enzymatic hair removal from leather skin with SC was carried out as an alternative eco-benign deharing process. In enzymatic hair removal, a softer and smoother skin surface was obtained compared to the chemical method. Leather skins was characterized by SEM images.

An integrated pickling-bating technology for reducing ammonia-nitrogen and chloride pollution in leather manufacturing

Currently, ammonia-nitrogen (NH3–N), chloride (Cl−) and chromium (Cr) pollution from leather manufacturing processes attracts much attention and limited the sustainable development of the leather industry. In this paper, conventional trypsin bating and high-salt pickling procedures were substituted by a salt-free pickling-bating system, using acidic protease L80A and salt-free pickling agent naphthalene sulfonic acid (NSA); a novel integrated technology comprising non-ammonia bating, salt-free pickling and high-exhausting chrome-tanning methods was established to reduce NH3–N, Cl− and Cr pollution. The results indicated that the properties of the leather produced by the established method were better than the conventional method. Furthermore, the established integrated salt-free pickling-bating technology resulted in the almost elimination of NH3–N and chloride pollution from waste effluent. The total Cr utilization ratio was increased to 95% from 80%, the total Cr discharge was reduced by 74%. Scale-up experiments further verified the acceptability of this novel technology in terms of physical and organoleptic properties of the resultant leather. It can be easy to predict that the effluent liquors with a little amount of NH3–N, chloride and chromium can be disposed of conveniently. We suppose that the established novel technology is an environment-friendly technology and a way forward in the development of the modern sustainable leather industry.

Optimization of Enzymatic Degreasing of Sheep Leather for an Efficient Approach and Leather Quality Improvement Using Fractional Experimental Design.

Leather industry is making significant contributions to economic development. However, it is notably leading to a serious environmental pollution. Recently, the enzyme technology developments offer new opportunities for enzymatic application in leather making. In the present investigation, microbial lipases were studied and used in degreasing process of sheep leathers. In order to optimize degreasing efficiency, a fractional experimental design with four parameters (enzyme source, processing stage, lipase amount, and degreasing duration) was used. Lipases A from Aspergillus niger, F from Rhizopus oryzae, R from Penicillium roqueforti, and AY from Candida rugosa were selected for leather degreasing. Enzymatic treatment of sheep skin was carried out during two stages of beamhouse operations: deliming-bating and pickling. Obtained results showed that enzymatic degreasing efficiency is higher than those obtained with the conventional process. Lipase F from Rhizopus oryzae demonstrated the most interesting hydrolysis with yields of 58.3% and 37.2% for delimed and pickled skins, respectively. An enzymatic degreasing process on pickled leather using 0.125% (w/v) of lipase F during 3.5h is the most promising for an industrial application with a 76.03 of degreasing efficiency. Results of the physico-mechanical tests of leathers having undergone enzymatic treatment complied with industry requirement. The enzymatic treatment may be carried out in the same conditions as employed in leather manufacturing process. Results suggested that the enzymatic degreasing improves the leather quality and reduces the use of chemical compounds and surfactant.

Optimization of Collagen Extraction from Sheep Raw Trimming Wastes Using Acid Hydrolysis

Although leather industry plays a significant role in the global economy, it has been categorized as one of highly polluting industries due to its generation of huge amount liquid and solid wastes. Large amount of solid and liquid wastes is generated from tanning industries during leather manufacturing process. These wastes bring about various problems to the environment and human health. Tannery wastes contain significant amount of raw skin wastes that are produced in hide/leather trimming process. The recycling and use of these raw skin/hide wastes (trimming wastes) is very important from environmental as well as economic point of views. The aim of this work was to investigate production of collagen from sheep skin trimming waste. The trimming waste was first pre-treated and then acetic acid hydrolysed to extract collagen. The extracted collagen was characterized using Fourier Transform Infrared (FTIR), UV-spectrometer and Scanning Electron Microscope (SEM). Response Surface Methodology (RSM) was used to optimize collagen extraction parameters (acetic acid, mixing ratio and extraction time). A three-factor, three-level Box-Behnken Design (BBD) based RSM was applied to determine the optimal conditions to obtain maximum collagen yield. A maximum collagen yield of 25.75% was obtained at optimum conditions (acetic acid concentration of 0.54 M, skin to acetic acid ratio of 0.03 g/ml and extraction time 3.33 day) using the RSM. Under these optimum conditions, experimental determined collagen yield of acid-soluble collagen was 25.85% which is in good agreement with the predicted value.

Effective utilization of tannery hair waste to develop a high-performing re-tanning agent for cleaner leather manufacturing

Accumulation of hair waste is a major burden to the leather industry, causing a negative impact on the industry's sustainable development. The industry is already bogged down by the usage of synthetic re-tanning agents that are not only extremely challenging for biodegradation but also release free-form of formaldehyde in the final leather stage. This research work focuses on developing a formaldehyde-free bio-based re-tanning agent from hair waste. In order to do so, hair waste is subjected to alkali hydrolysis and subsequently graft-copolymerized with methacrylic acid (MAA). These treatments were optimal using 20 % (w/w) sodium hydroxide and thermal activity at 90 °C. This resulted in effective hydrolysis of red sheep hair, which was the ideal candidate in this study. The hydrolysate was subjected to monomer in situ polymerization (using MAA) with potassium per sulfate/sodium meta-bisulphite redox system, leading to the development of keratin hydrolysate-g-methacrylic acid (KH-g-MA) copolymer (this was noted both at a laboratory level and pilot scale). The obtained KH-g-MA copolymer exhibited ideal characteristics such as increased protein content (78.3 ± 1.2), appropriate particle size (1516 nm), suitable pH (5) and required viscosity of 512 cP. The developed KH-g-MA copolymer was then applied as a re-tanning agent in the leather manufacturing process. Significant improvement in leather's mechanical strength characteristics was observed. In addition, the organoleptic properties of leather such as fullness, softness and grain tightness showed much improvement. Scanning electron microscopy (SEM) showed an enhanced surface smoothness and filling of the voids in experimental leather in comparison to the control leather. This recycle and reuse strategy of hair waste not only helps resolve issues with handling of hair solid waste but also results in producing an eco-friendly re-tanning agent in leather manufacturing, thereby paving the way for cyclic economic utilization and cleaner environment.

Metal-Free Combination Tanning with Replenishable Polyphenols and Marine Oil

In line with the resurgence of natural products in the global manufacturing industry, the leather industry is also relooking the increased use of organic materials. To exploit the benefits of the vegetable tanning materials and to couple with suitable organic material for overcoming the inherent shortcomings of vegetable tanning materials, studies were undertaken. Tanning materials like raw fish oil have advantageous properties to impart on leather such as softness, lightweight, and washability characteristics. Hence studies were undertaken on polyphenol-fish oil combination tannages.
 The quantities of wattle and fish oil and process conditions were standardized. The study indicated that the oxidation of fish oil could take place in the presence of vegetable tannins. The leathers tanned by this combination tanning system could be converted into garment leathers of rich shades and possessed good strength and physical properties. Propelled by encouraging results, investigations were also made on the nature of interaction between vegetable tannins and fish oil with collagen. It was also observed that the vegetable tannins probably do not hinder the oxidation of oil. To sum up, the study leads to the development of a viable, versatile organic tanning system to gain eco-acceptability for the leather manufacturing process.

Nanotechnology for cleaner leather production: a review

The leather industry holds a significant place in the global economy, yet the scarcity of raw hides and skins, growing ethical concern, competitive leather substitutes and regulation of manufacturing processes with adverse environmental effects restrict the expansion of the leather industry. These issues may be partly solved by nanotechnology to add innovative products and to treat tannery effluents. This article reviews research gaps of conventional leather manufacturing processes including curing, tanning, and effluent treatment using nanotannage, photocatalysts and filtration. Nanomaterials have been applied at various stages of leather manufacturing to achieve better performances.

Impact of Leather Toxicity on People and Places: A Review

The production of the most luxurious form of textile, i.e. Leather, has always been associated with environmental toxicity. The royal texture and firm durability of leather demands animal as well as environmental sacrifices. The process of leather production not only introduces chemicals in the environment but also causes undeniable animal abuse. The leather manufacturing process involves beam house operations and tanning procedures involving toxic chemicals rich in heavy metals and carcinogens. The effluents from the leather tanneries expose these toxins into the environment, posing a threat to different life forms. The increased toxin load from tannery effluents has percolated the food chain, thus inducing toxicity in human beings. The effect of lather manufacturing has been mostly observed in occupational regions displaying evidence of severe respiratory diseases, gastrointestinal tract infections, skin infections, chromium toxicity in biological fluids and high risk of morbidity. Different studies have been performed on regions receiving tannery discharge indicating toxin exposure affecting agricultural land, water systems, plants and aquatic life forms. The present study reviews sources of toxicity in the leather manufacturing process and describes bioassays that can be utilized to study the effect of leather toxicity on the ecosystem. The study mentions examples of sustainable alternatives and waste management for tanneries that can be explored to provide an insight for better future of leather industries.

Impact of Leather Toxicity on People and Places: A Review

The production of the most luxurious form of textile, i.e. Leather, has always been associated with environmental toxicity. The royal texture and firm durability of leather demands animal as well as environmental sacrifices. The process of leather production not only introduces chemicals in the environment but also causes undeniable animal abuse. The leather manufacturing process involves beam house operations and tanning procedures involving toxic chemicals rich in heavy metals and carcinogens. The effluents from the leather tanneries expose these toxins into the environment, posing a threat to different life forms. The increased toxin load from tannery effluents has percolated the food chain, thus inducing toxicity in human beings. The effect of lather manufacturing has been mostly observed in occupational regions displaying evidence of severe respiratory diseases, gastrointestinal tract infections, skin infections, chromium toxicity in biological fluids and high risk of morbidity. Different studies have been performed on regions receiving tannery discharge indicating toxin exposure affecting agricultural land, water systems, plants and aquatic life forms. The present study reviews sources of toxicity in the leather manufacturing process and describes bioassays that can be utilized to study the effect of leather toxicity on the ecosystem. The study mentions examples of sustainable alternatives and waste management for tanneries that can be explored to provide an insight for better future of leather industries.

A new approach for quantitative characterization of hydrolytic action of proteases to elastin in leather manufacturing.

Leather biotechnology based on enzyme is one of the main directions toward clean technology in the leather manufacturing process. Proteins such as collagen, elastin, and keratin are important components in animal hides or skins, and proteases are most frequently used in the leather manufacturing process for the removal of interfibrillar substance and opening-up of collagen fiber instead of toxic chemicals. Elastin is an important and highly elastic structural protein in the animal hides or skins and significantly affects the properties of the final leather product. For improving the quality of leather product, thorough understanding of the mechanism of action of proteases on elastin is necessary. The action of proteases on elastin has been mostly studied either qualitatively by histological analysis or quantitatively based on substrate casein or stained substrates, such as congo red-elastin and Remazol Brilliant Blue R-elastin; however, the resulting products have not been accurately characterized and thus these methods are not up to the standard. Besides, controlling the hydrolytic action of proteases to elastin has been very difficult, and excessive hydrolytic action of protease damages the elastin, restricting the wide application of proteases in the leather manufacturing process. In order to quantitatively evaluate the hydrolytic action of proteases on elastin in a more accurate manner, in this study, a new method was established by determining the unique amino acid desmosine based on the covalently bonded elastin-desmosine conjugate. Quantitative analysis of desmosine was performed in liquor based on cowhides substrate, and qualitative characterization was accomplished by histological analysis of elastic fiber in hides using an optical microscope. The results of this study indicated that the newly developed method is sensitive, accurate, and reproducible. In addition, the unhairing trials also demonstrated the suitability of newly established method in the leather manufacturing process to evaluate the action of proteases on the elastin in animal hides or skins.

Research on recycling of waste leather produced in leather manufacturing process based on supply chain management

Research on recycling of waste leather produced in leather manufacturing process based on supply chain management

REMOVAL OF ORGANIC MATERIALS FROM TANNERY WASTEWATER CONTAINING AMMONIA FOR REUSE USING ELECTRO-OXIDATION

Leather manufacturing process generates significant volume of wastewater. Deliming is one of the unit processes, in which about 4.5 L of wastewater is generated per one Kg of pelt. Reuse of wastewater from the unit processes, where significant volume of wastewater is generated is much important to address pollution mineralization and water conservation. Presence of significant level of organic pollutants is the primary factor that deters reuse of waste streams. In this paper, the Electro-Oxidation (EO) of deliming waste streams was carried out. It was found that EO was found to be effective in removing organic pollutants. The effect of process parameters such as pH, current density and duration on removal of organic pollutants was studied. Treatment efficiency was evaluated in terms of Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), Total Kjehldahl Nitrogen (TKN). Results indicate that the pollution reduction was better during electro-oxidation at current density 0.015 A/cm2 and pH 8.0 for 90 min. The kinetics of pollutants removed by electro-oxidation was found to obey pseudo-first order with an R2 value of 0.9963. The reduction in BOD, COD, TKN, chloride and TDS was 87.37%; 81.95%; 82.67%; 5.75% and 6.56% respectively. The possibility of reuse of treated wastewater was also assessed. Treated deliming wastewater was reused for soaking did not show any impairment in quality of pelt and leather. It is concluded that EO was very effective in treating the deliming waste streams rendering the same suitable for reusing for soaking.

Fabrication of silver nanoparticle sponge leather with durable antibacterial property

Leather product with durable antibacterial property is of great interest both from industry and consumer’s point of view. To fabricate such functional leather, gallic acid modified silver nanoparticles (GA@AgNPs) were first in situ synthesized with a core–shell structure and an average size of 15.3nm. Due to its hydrophilic gallic acid surface, the GA@AgNPs possessed excellent stability and dispersibility in wide pH range from 3 to 12 and also showed effective antibacterial activity with a minimum inhibitory concentration (MIC) of around 10μgmL−1. Then, such GA@AgNPs were used as retanning agent to be successfully filled into leather matrix during the leather manufacturing process. Moreover, taking the advantage of its high surface density of carboxyl groups, these GA@AgNPs could be further chemically cross-linked onto collagen fibers by chrome tanning agent. After retanning, the resultant leather was given a “AgNPs sponge” feature with high payload of silver nanoparticles against laundry, exhibiting high and durable antibacterial activity.

Materials and energy flow in the life cycle of leather: a case study of Bangladesh

This article presents the results of the materials and energy flow analysis for leather produced in Bangladesh and establishes an inventory for the life cycle assessment. Also, a comparison is made with the material and energy flow of the Indian leather. A cradle to gate analysis is performed for full-chrome leather (FCL), a representative leather article from an export-oriented industry in Bangladesh, taking into consideration the main processes associated with leather production and the corresponding materials and energy input. Data was collected on annual wet-salted rawhide consumption, water, and steam consumption, chemicals requirement, tannery solid waste generation, electricity, fuel oil use for the generator and steam boiler. Moreover, an analysis of the physical and chemical properties of wastewater emissions of the different leather unit processes was performed. The input and output profiles of the FCL were compared to those of an Indian leather. It was seen that FCL consumed water 2 times higher than the Indian leather while the electricity consumption of Indian leather was almost 2 times higher than its Bangladeshi counterpart. The Indian leather had significantly higher carbon footprint (in terms of CO2 equivalent emission) mainly because of the consumption of grid electricity that comes from coal-based power generation. Wastewater parameters such as chloride, Total Dissolved Solids (TDS) and Total Solids (TS) for the Indian leather are more than 4.5, 3 and 3 times higher respectively than that of corresponding emissions for the Bangladeshi FCL, which can be attributed to the higher use of inorganic salts in the process. Despite similar input of chromium compounds for both the leathers, the emission of total chromium was slightly higher in the case of Indian leather probably due to lower uptake of chromium by the substrate. Bangladeshi FCL used twice in the amount of (NH4 )2 SO4 than India, which may be responsible for the higher BOD load in the wastewater. It can also be seen that a significant amount of rawhide input is not converted into the usable leather as demonstrated by the high proportion of solid waste generation (70% and 55% for Bangladeshi FCL and Indian leather respectively). This study highlights that wide variations exist in the materials and energy flows from different tanneries. Understanding these variations is essential to pinpoint areas where resources can be used more efficiently and optimally in the leather manufacturing process.

Innovative method for traceability of hides throughout the leather manufacturing process

In this work, a novel technological solution for the traceability of hides throughout the leather manufacturing process is addressed. The proposed solution relies on marking the raw hide with a permanent sub-surface tattoo, made with specific substances used as identification markers. In practical applications, the markers can be embedded so as to form a pre-established pattern, thus creating a unique identification code. To experimentally demonstrate the feasibility of the proposed solution, in this work, different types of markers were injected in a raw hide (i.e., prior to its tanning). After the tanning process, the persistence of the markers and of their pattern was verified by comparatively inspecting the hide with two different sensing technologies: microwave reflectometry and X-ray imaging. The obtained results demonstrated that the proposed traceability system is a promising solution to circumvent the age-old problem related to counterfeiting and fraudulent substitutions of raw materials in the leather manufacturing industry.

Parameters Optimization of PID Controllers for Leather Manufacturing Process by Using Genetic Algorithms

Parameters Optimization of PID Controllers for Leather Manufacturing Process by Using Genetic Algorithms