Crust Leather Research Articles

Optimizing extraction of collagen from hazardous leather shaving dusts by crude protease enzyme: Chrome recovery and reuse for leather rechroming

This study explores an eco-friendly method to achieve 99.98 % dechroming (reducing Cr from 7700 to 4.71 ppm) of Chrome-tanned leather shaving dust (CSD), through enzymatic hydrolysis using crude protease. The enzyme exhibited strong activity (>40 U mL−1) across a temperature range of 50 °C to 65 °C and a pH range of 5 to 11. The pH of the mixture containing CSD, water, MgO, and enzyme was maintained at 8.9 during hydrolysis. The temperature, hydrolysis time, and enzyme concentration were optimized using response surface methodology (RSM). Under optimal conditions of 17.57 % enzyme concentration, 62.01 °C, and a hydrolysis time of 7 h, the predicted collagen yield was 31.66 %. Laboratory experiments conducted with these predicted parameters resulted in a collagen recovery of 30.9 %, achieving an accuracy of 97.6 % compared to the predictions. In contrast, hydrolysis with MgO alone achieved only 87.01 % dechroming with about 2 % collagen yield, highlighting the enzyme's superior effectiveness. The enzymatic cleavage of peptide bonds in the leather matrix enhanced collagen solubilization. Characterization techniques, including FT-IR, NMR, XRD, DSC, and TGA, confirmed successful extraction and purity, with the collagen being rich in glycine and proline. Cytotoxicity results demonstrated its non-toxic nature, indicating potential applications in biomedical fields, tissue engineering, food, pharmaceuticals, and cosmetics. The recovered chromium sulfate was reused for rechroming goat wet blue leather, with chrome content in crust leather treated with recovered basic chromium sulfate (rBCS) and fresh basic chromium sulfate (BCS) being 3.23 % and 3.35 %, respectively, both meeting industry standards for goat crust leather. SynopsisAn eco-friendly method for dechroming chrome-tanned leather shaving dust (CSD) and extracting collagen was established. The process achieved 99.98 % dechroming and 30.9 % collagen yield using crude protease enzyme. Characterization confirmed the collagen's purity, and recovered chromium sulfate was reused for rechroming goat leather, meeting industry standards.

Magnetic multi-template molecularly imprinted polymers for selective simultaneous extraction of chlorophenols followed by determination using HPLC

Magnetic multi-template molecularly imprinted polymers (M-mt-MIPs) were successfully synthesized by surface imprinting and multi-template imprinting strategy, using polydopamine coated magnetic multi-walled carbon nanotubes as supporting materials, five typical chlorophenols (CPs) as templates, methacrylic acid as functional monomer and ethylene glycol dimethacrylate as cross-linker. Compared to non-imprinted polymers (NIPs), the as-prepared M-mt-MIPs showed high adsorption capacity (32.58‒80.63 mg g−1), rapid mass transfer and specific selectivity for the five targeted CPs, which were applied as magnetic solid-phase extraction (MSPE) adsorbents. Parameters affecting MSPE efficiency were detailed investigated, such as adsorbents dosage, sample pH, extraction time, type and volume of desorption solvent and salt effect. Combined with HPLC-DAD, a simple, rapid and sensitive method was established, showing good linearity (2‒200 μg L−1), low limits of detection (0.32‒0.49 μg L−1), and high enrichment factors (35.2‒108). The developed M-mt-MIPs-MSPE-HPLC method was applied to enrich and determine CPs in tannery wastewater, wet-blue and crust leather, and satisfactory spiking recoveries were attained in the range of 73.95‒109.7% with relative standard deviations (RSDs) of 2.13–8.48%. This study provided a new alternative material and method to rapid simultaneously extract and analyze low concentration of typical CPs in complicated matrices.

Sustainable leather tanning: Enhanced properties and pollution reduction through crude protease enzyme treatment

In this study, proteolytic bacteria, particularly Pseudomonas aeruginosa strain SM4 (OQ349573), were isolated from tannery solid waste dumping yard soil and employed to produce extracellular protease enzymes. The bacteria exhibited optimal growth after 30 h of incubation at 37 °C and pH 7. Under conditions of 55 °C, pH 8, and a substrate concentration of 2 %, the crude enzyme displayed its highest activity at 105 UmL−1. Notably, the produced crude enzyme showed no discernible inhibitory effects on detergents, metal salts, or organic solvents. Application of the crude protease at concentrations of 3 % and 2 % in chrome tanning of goatskins (GS) and cowhides (CH), respectively, yielded significant reductions of 35 % and 30 % in chromium and other post-tanning chemicals compared to conventional processes. Despite the 30 to 35 % reduction in tanning and post-tanning chemicals, the uptake of chrome and associated chemicals by crust leather was higher than observed in conventional processes. Chromium content analysis of the effluent revealed an 81 % reduction during piloting in real industrial operations, accompanied by reductions of about 46 % in BOD and COD pollution loads. The finished leather obtained from the enzymatic process exhibited superior mechanical properties, including higher tensile strengths (210 and 195 kg cm-2), stitch tear (92 and 165 kg cm−1), grain crack load (28 and 32 kg), and distension (73 and 62 mm) for GS and CH, respectively, surpassing or closely aligning with standard values and those obtained in conventional processes.

Development of masked silica tanning system for sustainable leather production.

Amid mounting pressure on the long-term recyclability of chromium in tanned leather and the associated environmental hazards, the quest for an alternative, cleaner tanning system has gained tremendous momentum. In this context, our study explores the remarkable potential of silicates as a versatile platform for skin/hide tanning, circumventing the inherent risks and ecological threats posed by chromium exposure and leaching. We present an alternative approach of using a silica-based tanning system, employing a Taguchi model, to optimize a masked silica (MaSil) tanning product/process for achieving effective collagen stabilization. Our results demonstrate the significant advancements made in hydrothermal denaturation temperature, reaching an impressive 79 °C through precise Taguchi parameters-5% SiO2, masked with 0.3 mole of citrate salt, and a tanning process fixation pH of 4.5. Notably, the mechanical strength analysis reveals compliance with the stringent upper leather recommendation standards, validating the practicality and quality of MaSil crust leather. Moreover, our research highlights the unprecedented environmental benefits of the first reported application of Taguchi's approach to the MaSil tanning system. The developed tanning system remarkably reduces total dissolved solids (TDS), biological oxygen demand (BOD), chemical oxygen demand (COD), and overall water load by 68.4%, 25.4%, 59.5%, and 33.7%, respectively, heralding a promising era of water and environmental sustainability in the leather sector. This study holds the potential to transform leather production, wherein the envisioned future on the use of the Taguchi model and optimized MaSil tanning system could find a place in shaping a cleaner, greener, and more sustainable leather industry.

Solid dicarboxylic acid assisted deliming in beamhouse to reduce nitrogen compounds in tannery wastewater

In leather manufacturing, ammonia salts in deliming operations contribute to the significant addition of ammonia-nitrogen (NH3–N) into wastewater. Wastewater containing NH3–N serious affects aquatic life and the operations of effluent treatment plants. In this study, the strategy of reducing NH3–N released into tannery wastewater, uses non-ammonia deliming agent-solid dicarboxylic acid (malonic acid) to replace the conventional deliming agent (ammonium sulfate). Utilizing a laboratory experiment, a pilot scale test was carried out and found to be almost comparable with the former experimental work. The generated delimed wastewater, delimed pelts, and manufactured crust leathers were subjected to various physicomechanical analyses. Results revealed that the reductions of NH3–N, TKN, and hydroxyproline amounted, respectively, to 98.78%, 88.69%, and 26.9%, compared to conventional deliming agents. The other pollutants, namely TDS, BOD, COD, and EC were significantly reduced. The physicomechanical properties of the crust leathers met the standard requirements. SEM images of delimed pelt and crust leathers revealed a similar fiber structure. The wastewater emitted during deliming with malonic acid is probably an easier way to conduct effluent treatment by reducing nitrogen pollution. This investigation is a novel approach to finding a viable technology that can satisfy the need for modern leather manufacturing being done in environmentally friendly ways.

Effect of Pigment-Acrylic Binder Ratio on the Surface and Physical Properties of Resin Finished Leather

The current study attempts to investigate the surface phenomenon and physical characteristics of leather finished with brown pigment and different types of acrylic binders. Using the contact angle measurements of three different liquids on the above finished leathers and films, the surface energy and work of adhesion were evaluated. The pigment to acrylic binder ratio (PABR) for best adhesion of finish film on the leather surface was optimized using the contact angle goniometer. Different types of acrylic binder films were coated and their surface behaviour was studied. The crust leather was coated with different types of pigment-acrylic binder (Very Soft, Soft and Medium Soft) finish formulations. The contact angle of both the acrylic films and the PABR finished leathers were measured against Water, Dimethyl sulfoxide (DMSO) and Hexadecane (HD). According to the study’s results, the surface properties of finished leather were directly related to the degree of wetting. The PABR was found to be effective at 1:3 for very soft binder, 1:2.5 for soft, 1:2 for medium soft binders due to higher contact angle and lower surface energy values (γsv). At 1:3 and 1:2.5, the contact angle of very soft and soft binder leather was 82.62° and 83.45° and for medium soft binder it was 82.67° at 1:2 ratio. The surface energy values of optimized PABR of very soft binder (1:3) was 28.29 (mN/M), soft binder (1:2.5) was 27.50 (mN/m) and medium soft binder (1:2) was 29.27 (mN/m). The optimized PABR work of adhesion values of very soft binder, soft binder and medium soft binder was 82.15 (mJm-2), 81.11 (mJm-2), 82.09 (mJm-2). In order to correlate the observed surface properties with leather finish properties, finished leathers were tested for finish adhesion, vamp flexing value, water vapour permeability, wet and dry rub fastness. According to the water vapour permeability, soft and medium binder showed good permeation due to the uncovering of nanopores. But the adhesion, grain crack resistance and grain smoothness were higher in the case of the soft binder. Overall leather properties divulges that the pigment to binder ratio and the type of binder plays an important role in surface properties of the finished leather. This study enables us to determine the optimal PABR for effective finish properties to meet the required leather standards for various usage, as well as better utilisation of finishing chemicals.

Application of some Plant Extracts as Biocolorants for Leather During Finishing Process

In this research, chrome-tanned bovine crust leathers were dyed during the finishing process using plant extracts: walnut shell (Juglans regia), oak bark (Quercus cortex), and onion peel (Allium cepa). In this study, the standard recipe applied by the factory was used in the leather finishing process. For this recipe, various plant extracts were used instead of pigments, and groups that did not contain pigment and any dyestuff were formed as the control groups. After these processes, color measurement analyzes were performed on Konica Minolta CM 3600d spectrophotometer. In order to investigate the effects of walnut shell (Juglans regia), oak bark (Quercus cortex), and onion peel (Allium cepa) on the other performance properties of leather, dry and wet rub fastness test according to standard method TS EN ISO 11640 (2001) was performed. The results of the study were statistically evaluated using the NCSS method (Number Cruncher Statistical System). As a result of the study, it was noticed that, depending on the extract, different colors were obtained. It was found that the dry and wet fastness of leathers treated with plant extracts improved.

Side-chain Poly[2]pseudorotaxanes containing β-cyclodextrin for more sustainable tanning process

Sustainability of leather lies in how the hide, a sustainable, naturally renewable, raw material, is processed. Tanning chemistry has been a limiting factor for leather sustainability. In this study, a host-guest synthesis strategy was selected to modify one of the most widely used tanning polymer, MIDA DD, and obtain a new hybrid tanning system containing β-cyclodextrin, and leather drastically less impactful on the earth and people. Poly[2]pseudorotaxane Side-Chain Complexes (PSCCs) have been obtained by threading β-cyclodextrin units onto the side-chains of the commercial MIDA DD. The formation of PSCCs in aqueous solution was investigated by using 1D NMR, ATR-FTIR and TGA experiments. The ability of PSCCs to stabilize the collagen matrix was tested at laboratory and industrial pilot scale by micro-DSC, ATR-FTIR and solid-state NMR techniques. The physical and mechanical performance of the obtained crust leather was determined by standard tests used in tanning industry. Side-chain poly[2]pseudorotaxanes showed better tanning performances than the fossil-based MIDA DD, the most effective supramolecular tannins being obtained by mixing β-CD and MIDA DD in ratios close to 1/1 (w/w). The new tanning mixtures allow for significantly reducing both the amount of fossil-based MIDA-DD polymer in the current tanning processes (by 45%) and the free bisphenol content in leather crust (by more than 80%) due to the presence of bio-based β-CD in the composition of the new supramolecular tanning agents. The findings disclosed here pave the way for the CDs’ employment in improving the sustainability of tanning processes.

Region Wise Surface Level Defect Detection and Ranking of Crust Leather Images Based on Image Processing Techniques

Sorting and aligning of crust leather for grading on position wise defect distribution is one of the methods adopted in the tanning industry. This method is generally carried out manually by a veteran on official sampling position and their input is critical because it is directly linked to sales of the crust leather. The opinion of the experts is believed to be stable and consumes a good amount of time too. Hence, in the current research a robust defect detection method and ranking of crust leather images based on image processing techniques is proposed to give a stable solution in a short span of time. A custom-made dataset of crust leather images consisting of 5640 images were used in this study. The pixel intensity has been extracted on demarcated position of various regions including neck, belly left, belly right, center and butt instead of official sampling position through horizontal and vertical mapping of coordinates with a new method Grading Score on Image Position wise (GSIP) on the actual images. The image processing techniques using Canny Edge Detection and filters such as Laplacian, Median, Prewitt, Roberts, Sobel and Scharr were implemented to get the pixel intensity grouped and classified based on parameters within acceptable range using a Naïve Bayes Classifier. The classifier confirms that the accuracy of Set I - Actual Images and Set II - Defects with implementation of canny edge detection over other image processing techniques at 99.50%. Therefore, the current research confirms that the proposed GSIP method would give an additional tool to inspectors while ranking the crust leather based on region wise surface level defect detection of crust leather images based on image processing techniques.

A green tanning method based on POSS-COONa and zirconium: Achieving cleaner leather production

In this study, a two-step green and clean tanning technology based on the polyhedral oligomeric silsesquioxane sodium carboxylate (POSS-COONa) and zirconium was studied to relieve the environmental pressure and resource strain caused by chrome tanning. Firstly, amino sesquisiloxane was prepared from γ-aminopropyl triethoxy silane by hydrolysis and condensation method, and then was substituted with sodium chloroacetate to form POSS-COONa. The POSS-COONa had crystallinity and maintained cube structure by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Subsequently, POSS-COONa combined with zirconium sulfate was applied in tanning process of goat skin. Compared with untanning, chrome tanning, zirconium tanning crust leather, the shrinkage temperature and thickening rate of combination tanning crust leather were 90.5 °C and 118.3 %, respectively. The tensile strength, tear strength, elongation at break and softness of the combination tanning crust leather were 26.4 MPa, 96.3 N/mm, 105.5 % and 6.5 mm. The scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that combination tanning crust leather collagen fibers were braided more loosely, and POSS-COONa and zirconium sulfate could be uniformly distributed in the collagen fibers. The isoelectric point of the combination tanning crust leather (∼6.7) was similar to that of chrome tanning crust leather (∼7.7). Based on the above results, POSS-COONa combined with zirconium sulfate tanning has a broad prospect in green clean production.

Novel Biomass-Based Polymeric Dyes: Preparation and Performance Assessment in the Dyeing of Biomass-Derived Aldehyde-Tanned Leather.

High-performance chrome-free leather production is currently one of the most concerning needs to warrant the sustainable development of the leather industry due to the serious chrome pollution. Driven by these research challenges, this work explores using biobased polymeric dyes (BPDs) based on dialdehyde starch and reactive small-molecule dye (reactive red 180, RD-180) as novel dyeing agents for leather tanned using a chrome-free, biomass-derived aldehyde tanning agent (BAT). FTIR, 1H NMR, XPS, and UV-visible spectrometry analyses indicated that a Schiff base structure was generated between the aldehyde group of dialdehyde starch (DST) and the amino group of RD-180, resulting in the successful load of RD-180 on DST to produce BPD. The BPD could first penetrate the BAT-tanned leather efficiently and then be deposited on the leather matrix, thus exhibiting a high uptake ratio. Compared with the crust leathers prepared using a conventional anionic dye (CAD), dyeing, and RD-180 dyeing, the BPD-dyed crust leather not only had better coloring uniformity and fastness but it also showed a higher tensile strength, elongation at break, and fullness. These data suggest that BPD has the potential to be used as a novel sustainable polymeric dye for the high-performance dyeing of organically tanned chrome-free leather, which is paramount to ensuring and promoting the sustainable development of the leather industry.

Studies on the Correlation between Surface and Sewability Properties of Crust Leather

The surface properties of leather are critical factors that influence the aesthetic quality of the leather. Commonly, organoleptic properties are evaluated for leathers to ascertain the bulk properties such as compactness, smoothness, softness and general grain appearance. Though these parameters are very subjective, still these properties are essential for leather product manufacture. In the current research, we discuss the correlation between the surface parameters and sewability of the leathers. In our earlier studies, we discussed the influence of syntans and fatliquors on sewability. In aligning to a similar subject, the impact of surface properties has been evaluated through contact angle measurements and correlated with the sewability properties of the leather. From the spread ability measurements, it can be inferred that the sewability properties are better towards the surface of the leather, which is more hydrophilic. This result agrees that the fatliquoringof leathers has enhanced the stitch ability; moreover, the studies provide biophysical parameter importance for qualifying leather sewability.

Hybrid nanoparticles emulsified vegetable oil as an environmentally friendly and sustainable leather fatliquoring agent

Introducing sustainability by a reduction in chemical input has added value to technology innovations, especially in the leather fatliquoring process. Major concern of sustainable leather fatliquoring process lies in factors like usage of natural oil, avoidance of hazardous substances and reduction in organic load to the environment. Due to their special features, such as their ease of preparation and environmental friendliness, Pickering emulsions and their applications have received significant attention in recent years. The present study reports a novel sustainable leather fatliquoring process by usage of hybrid particles (alumina coated with silica) stabilised Pickering emulsions as fatliquor instead of conventional sulphated oil based fatliquor. Eco fatliquoring agent with a particular choice of vegetable oil stabilised by hybrid alumina functionalised with silica (Al-O-SiO2)/ hybrid nanoparticles through Pickering emulsion was reported. During the post tanning process, the uses of this developed fatliquoring agent causes a reduction in the 30% of fatliquoring agent input and 40% reduction in dye input. The presence of alumina nanoparticles resulted in an immediate improvement of the abrasion resistance, softness, and physical properties of the crust leather. Utilizing hybrid particles (Al-O-Si) as a stabiliser readily improves the uptake of other post tanning chemicals. Thus, the prepared fatliquoring agent suitably softened the leather and significantly improved the mechanical properties, light fastness, and fullness with the reduction in the pollution load. To divulge the sustainability of the fatliquoring process, the sustainability analysis for the developed product was analyzed and presented. As compared to the conventional fatliquoring process the E factor of the experimental process was estimated to be lower (at a value of 0.25) which indicates minimum emissions. Based on cost estimation, leather fatliquoring is economically viable when using the prepared fatliquoring agent.

Effect of Calcium in Delimed Hide on Leather Quality

The efficient removal of calcium from delimed hide is essential to leather quality, but few reports have elaborated on how residual calcium in delimed hide affects leather quality. In this study, four delimed hides containing different calcium content were first prepared by using ammonium sulfate and sodium gluconate. Energy dispersive X-ray spectrometry results showed that the atomic percentages of calcium on the grain surfaces of the four delimed hides were 8.17%, 4.82%, 2.34%, and 0.25%, respectively. The bating, chrome tanning, and post-tanning performances of the four delimed hides were then analyzed to evaluate the effect of calcium in delimed hide on leather quality. Results showed that the removal efficiency of non-collagenous protein from hide in enzymatic bating, the evenness of chromium distribution, the shrinkage temperature of wet blue, and the physical properties of crust leather all increased as the calcium content of delimed hide decreased. Furthermore, efficient calcium removal from the grain surface of delimed hide played a key role in the color brightness and uniformity of wet blue and crust leather. The results draw our attention to the importance of considering the effectual removal of calcium from delimed hide for obtaining high-quality leather.

Removal of Proteoglycans in Animal Hides by Glycosidase to Promote Opening-Up of Collagen Fiber Bundles

The degree of proteoglycan removal from animal hides is closely related to the opening-up of collagen fibers and the properties of leather, but conventional leather-making processes are not very effective at removing proteoglycans. By rationally selecting and utilizing glycosidases during the leather-making process, proteoglycans can be efficiently removed without causing collagen damage due to glycosidases specifically hydrolyzing glycosidic bonds. In spite of this, glycosidases are highly specific and come in a wide variety of types. To solve the blindness of optimizing glycosidases and its application in the soaking process, in this study, seven typical commercial glycosidases capable of hydrolyzing β-glycosidic bonds were selected according to the types of major glycosidic bonds in animal hide proteoglycans. The basic properties of the selected glycosidases and its effectiveness in removing proteoglycans from the hide during the soaking process were investigated. Then, the effects of the dosage of the two optimal glycosidases on the dissolution of polysaccharide, total soluble protein and hydroxyproline, as well as the properties of leather during the soaking process were further studied. The results showed that although the optimal pH of the selected glycosidases was between pH 5 - 7, they maintained more than 50% of their activity under weak alkaline conditions and could be applied to the soaking process. The removal of proteoglycan by different glycosidases is closely related to their specificity for glycosidic bonds, and the penetrability of the enzyme proteins, namely the molecular weight and isoelectric point of the enzymes. Among them, β-Mannase-AKT and Xylanase-AKT are more effective in removing proteoglycans. When the dosage of β-Mannase-AKT and Xylanase-AKT reached 47 U/mL, almost all the glycosaminoglycan was removed from the hide, the opening-up of collagen fibers and the softness and physical properties of the crust leather were significantly improved without damage to the structural proteins.

Water Footprint Calculation, Effluent Characteristics and Pollution Impact Assessment of Leather Industry in Bangladesh

Leather processing industries consume high volumes of water and chemicals and release effluents into the environment that pollute the surface water and may cause harm to human health. Leather processing involves different wet processing stages such as soaking, liming, chrome tanning, rechroming, neutralization, fatliqouring and dyeing. The pollution generated from the leather processing stages varies in volume, nature and concentrations. Qualitative and quantitative assessments of effluents generated from different stages of leather processing can be useful to understand the stagewise and overall water pollution of leather wet processing and to design and plan pollution abatement initiatives. Water footprints (WF) can help in understanding the total water consumption and water pollution caused by the leather sector. The objectives of this research are to assess the characteristics of effluents generated from different stages of leather processing, calculate the water footprint (WF) and analyze the pollution load of the Bangladesh leather sector. To perform experimental analyses, effluent samples were collected from the following leather processing stages: soaking, liming, deliming and bating, pickling and tanning, wet back, rechroming, neutralization, retanning, dyeing and fatliqouring from four leather processing factories. The key pollution indicating parameters, such as pH, chemical oxygen demand (COD), biological oxygen demand (BOD), total dissolved solid (TDS) and total suspended solid (TSS) of the effluent samples were analyzed. The experimental study showed that almost 52% effluents generate from beam house and tan yard operations, and about 48% effluents generate from post tanning operations. Due to the presence of high amounts of salt, insecticides and bactericides, the effluent generated from the soaking stage contains high BOD and TDS. On the other hand, effluent generated from liming contains the highest amounts of BOD, COD, TDS, and TSS. The reduction or segregation of soaking and liming effluents will be effective in improving the environmental performance of the wet processing of leather. To assess the total water footprint of the leather sector, the water footprint of feed crops and raw hides were calculated, along with the water footprint of the leather processing stages. The water footprints of bovine and ovine crust leather were found to be 34,000 m3/ton and 17,300 m3/ton, respectively. The blue water footprint is higher in soaking, liming and finishing. The green water footprint of leather is mainly contributed by feed crops of farming animals. The grey water footprint was found higher in the soaking, liming, fatliqouring and dyeing stages. About 97% of the water footprints of tanneries are contributed by the wet processing stages. The grey water footprint is the most significant part of the total water footprint of the leather sector, which indicates the impact of high water pollution by the leather processing stages. This study can help to understand the overall scenario of water consumption and water pollution caused by the leather sector in Bangladesh. This study can also be useful in designing sustainable leather products by reducing the total water footprint per unit of leather goods. The systematic approach of this study could be useful for other countries in leather processing.

Sustainable leather making — An amphoteric organic chrome-free tanning agents based on recycling waste leather

Currently, globally, 90 % of the tannery is still tanned by using chrome, resulting in chromium-containing wastewater and chromium-containing solid waste that will cause serious harm to the environment. Under the pressure of environmental protection, on the one hand, the leather manufacturing industry should to dispose the current problem of chromium pollution, especially chromium-containing solid waste (chromium-containing waste leather (CCWL)), on the other hand, to popularize chrome-free tanning agent. Organic chrome-free tanning agents are the way forward for chrome-free tanning agents. However, organic chrome-free tanning agents exhibit several limitations with respect to their preparation and applications: The preparation process is not eco-friendly, and physicochemical properties of tanned crust leather are poor. More importantly, the leather tanned by an organic chrome-free tanning agent has low absorptivity of traditional anionic wet finishing materials, resulting in high total dissolved solids in tannery wastewater, which increased the difficulty of tannery wastewater treatment, and posed a potential threat to the environment. In this study, collagen polypeptide (CP) was extracted by using in situ dechromization and industrial trypsin from CCWL, followed by modification with ethylene glycol diglycidyl ether (EGDE) to obtain an epoxy-terminated, biomass-based, amphoteric organic, chrome-free tanning agent (CP-EGDE) with a high isoelectric point of 5.16, and an epoxy value of 0.316 mol/100 g. CP-EGDE can be applied in the pickling-free and salt-free tanning processes to prepare wet white leather and the tannery wastewater with good degradability. The shrinkage temperature (Ts = 84.9 °C), grain flatness, fullness, softness, yellowing resistance, mechanical properties, absorptivity of traditional anionic fatliquor (88.4 %) and dyes (95.3 %) of CP-EGDE tanned leather exceeded those of commercial organic chrome-free tanning agents. This research considered both environmental protection and leather quality, especially greatly improving the absorptivity of traditional anionic wet finishing materials. CP-EGDE is expected to replace chrome tanning agents and has good application prospects.

Strategical development of chrome-free tanning agent by integrating layered double hydroxide with starch derivatives

The development of sustainable and eco-friendly leather industry requires green tanning agents because of unbounded chromium (easily converted into hazardous Cr-VI) in chrome tanned leather. In this study, a chrome-free tanning agent (OS-LDHs) was established by integrating layered double hydroxide (magnesium aluminum zirconium hydrotalcite, LDHs) with starch derivatives. A series of oxidized starch (OS) were prepared as masking agents for LDHs tanning process. Among them, the weight-average molecular weight (Mw) of 1685 g/mol could be reached, which will promise the well-distribution of OS. The SEM and EDS analysis confirmed the uniform penetration of OS-LDHs, avoiding accumulation on the surface of crust leather. Notably, leather tanned by OS-LDHs achieved shrinkage temperature of 66.7 °C, porosity of 75.51 % and tear strength of 66.7 N/mm. Not only the hydrogen bond but also the coordination between NH2, COOH in collagen and OS-2-LDHs improved the thermal stability of leather without destroying the collagen triple helix.

A novel synergistic covalence and complexation bridging strategy based on multi-functional biomass-derived aldehydes and Al(III) for engineering high-quality eco-leather

To get rid of the chrome pollution faced by the leather industry, we explored a novel engineering high-quality eco-leather technology based on the synergistic interactions between biomass-based aldehydes and Al(III). Firstly, dialdehyde xanthan gum (DXG) was prepared to covalently crosslink with the collagen fibers (CFs) via Schiff-base linkages under alkaline conditions, endowing the leather with a shrinkage temperature (Ts) of 80 °C and opening channels for the subsequent penetration of Al species (AL). Secondly, and for this latter purpose, the DXG-tanned leather was acidified to release part of the DXG from the leather according to the dynamic nature of the Schiff-base. Containing suitable oxygen-containing groups (OGs) with excellent complexation capabilities, the released DXG served as masking agents for AL, facilitating the penetration of AL into the inner CFs network for further complexation crosslinking. Consequently, a denser crosslinking network was constructed in the leather, and the crust leather exhibited higher Ts (82.2 °C), improved mechanical (tensile strength: 13.4 N/mm2, tear strength: 53.3 N/mm) and organoleptic properties than those of the DXG crust or AL crust leathers. This demonstrates that this synergistic covalence and complexation bridging strategy is a sustainable option to substitute highly restricted chrome tanning agent for eco-leather production.

Effect of Enzymatic Treatment in Leather Manufacture at Different Processing Stage

The use of cleaner leather processing technologies is of great interest today due to the global trends favoring environmentally friendly manufacturing. Modernization and implementation of new technologies, like enzyme-driven catalysis instead of conventional inorganic catalysis, can improve the quality and reduce the cost of leather manufacturing while making the leather more environmentally sustainable. The use of enzymes in pre-tanning operations is a well-known technology. However, a holistic view of the effect of enzymes at various stages of leather processing is limited. We attempt to bridge this gap by studying the influence of enzymes on the characteristics of crust leather at multiple locations of leather processing. Trypsin was used to assess the enzymatic action on delimed pelts, while pepsin was used to evaluate the impact of enzyme treatment on a pickled pelt that was later chrome tanned.
 Similarly, papain was used to study enzymatic activity on neutralized, chrome-tanned leather. The selection of enzymes for three different materials was guided by the optimal activity behavior of the enzymes. It is observed that the physical strength characteristics of the enzyme-treated leathers show minor differences. Hence, this study aims to explore the unconventional application of enzymes at various stages of leather processing.