Tanning Agent Research Articles

A sustainable and cleaner speedy tanning system based on condensed tannins catalyzed by laccase

Abstract Condensed tannins, a sustainable and environmental-friendly vegetable tanning agent, is confined in the wide application of leather industry owing to its poor shrinkage temperature (Ts). In this work, the tanning effect of condensed tannins was enhanced by the green biocatalyst laccase. Meanwhile, the molecular weight and chemical structure of condensed tannins catalyzed by laccase were observed. Its polydispersity index (PDI) was decreased from 2.88 to 1.77 and the Mw from 6354 to 4041. The changes of relative molecular mass were confirmed by Gel permeation chromatography (GPC) analysis. The UV–visible spectroscopy (UV–vis) and X-ray photoelectron spectroscopy (XPS) spectra provided evidence for the catalyzing change from o-hydroxylation to o-quinones. From the aspects of the thermal stability, tensile strength, breaking elongation, tear strength, thickening percentage and morphological analysis, the leather tanned by catalyzed condensed tannins (BA) was proved to have more excellent physical properties contrast with that of the leather tanned by untreated BA. This indicates that the physical properties of leather tanned by BA were improved significantly, whilst the catalyzed sustainable agent can be independently used as a promising quick tanning agent of sheepskin light leather.

Biogas from anaerobic co-digestion of chrome and vegetable tannery solid waste mixture: Influence of the tanning agent and thermal pretreatment

Abstract Mesophilic anaerobic co-digestion of mixtures of solid wastes from tanneries containing chromium and vegetable tannins was investigated in an orthogonal array. The effect of thermal pretreatment on shavings was evaluated as well. The biogas and methane productivity in terms of VSS was assessed. The treatment efficiency was also evaluated in terms of variation of organic and inorganic load. All assays with chromium-containing sludge showed on average 19.6 ml of biogas/gVSS added, 8.15 ml of methane/gVSS added, 4.8% VSS reduction, 60.4% BOD5 reduction, 55% TOC reduction, 67% IC increase and 54.6% TN increase, showing greater mineralization of the residue when compared to the assays with vegetable tannin sludge, which has proven to be toxic. The origin of shavings was not significant in any parameter due to the small proportion of this residue in assays. The thermal pre-treatment was beneficial only for assays with vegetable tannins, since there was evidence that the heating mechanism degraded part of the phenolic organic matter and consequently reduced its toxicity.

Diffusion and Binding of Laponite Clay Nanoparticles into Collagen Fibers for the Formation of Leather Matrix.

Understanding accessibilityand interactions of clay nanoparticles with collagen fibers is an important fundamental issue for the conversion of collagen to leather matrix. In this study, we have investigated the diffusion and binding of Laponite into the collagen fiber network. Our results indicate that the diffusion behaviors of Laponite into the collagen exhibit the Langmuir adsorption, verifying its affinity for collagen. The introduction of Laponite leads to a shift in the isoelectric point of collagen from ∼6.8 to ∼4.5, indicating the ionic bonding between the positively charged amino groups of the collagen and negatively charged Laponite under the tanning conditions. Fluorescence microscopy, atomic force microscopy, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and wide-angle X-ray diffraction analyses reveal that Laponite nanoparticles can penetrate into collagen microstructure and evenly distributed onto collagen fibrils, not altering native D-periodic banding patterns of collagen fibrils. Attenuated total reflectance-Fourier transform infrared and Raman spectroscopy detections further demonstrate the presence of noncovalent interactions, namely, ionic and hydrogen bonding, between Laponite and collagen. These findings provide a theoretical basis for the use of Laponite as an emerging tanning agent in leather manufacture.

Sustainable Disposal of Cr(VI): Adsorption–Reduction Strategy for Treating Textile Wastewaters with Amino-Functionalized Boehmite Hazardous Solid Wastes

The present work reports a sustainable adsorption–reduction strategy for disposal of Cr(VI)-bearing wastes. By cross-linking between boehmite and chitosan to prepare amino-functionalized boehmite adsorbents, Cr(VI) could be adsorbed from the Cr(VI)-containing solutions by the adsorbents with the maximum adsorption capacity of 120.2 mg/g, which was improved about 3 times compared to that of boehmite. Adsorption mechanism showed that the Cr(VI) was adsorbed by complexing with −NH2 bonds and exchanging with −OH groups of adsorbents. About 31% Cr(VI) was simultaneously reduced to Cr(III) by the reactive −OH and −NH2 electron acceptor of adsorbents. After adsorption, the Cr(VI/III) and boehmite of adsorbents were dissolved in 25% H2SO4 solution, the remaining Cr(VI) was reduced to Cr(III) with 100% reduction yield, and the CrxAl2–x(OH)2y(SO4)8–y·nH2O was prepared as product, while the insoluble chitosan was recycled in a closed loop. In application, column experiments results showed that the γ-AlOOH hazardous wastes could effectively dispose the Cr(VI)-containing textile wastewaters, and aluminum and chromium in the wastes could be comprehensively used to prepare chromium–aluminum tanning agent. The developed “waste-treating-waste” method leads to minimum pollutant emission and avoids the complex post-treatment problems.

Preparation and photocatalytic performance of fibrous Tb3+-doped TiO2 using collagen fiber as template

Fibrous Tb3+-doped TiO2 were prepared using collagen fiber as template. Morphology, crystalline structure, surface area, element content, chemical composition and elemental chemical status, microstructure and element distribution of the prepared samples were characterized by using scanning electron microscopy, X-ray diffraction, specific surface area analysis, inductively coupled plasma atomic emission spectrometer, X-ray photoelectron spectroscopy, transmission electron microscope and element mapping, respectively. The photocatalytic activities were evaluated by following degradation of methyl orange. The results showed that the fiber structure of collagen template was fully preserved when the calcination temperature was 500–800 °C. However, with the increase of calcination temperature, crystallinity and average particle size were increased, and the photocatalytic performance was decreased. For 2% Tb3+–TiO2 calcined at 500 °C, the degradation rate of methyl orange reached 93.87% after 6 h when a high-pressure mercury lamp (150 W) was used as the light source for photocatalytic degradation. Titanium tanning agent performance was excellent, the yield of TiO2 was high, and the fiber structure was presented when 0.2 mol/L citric acid/sodium citrate buffer solution was used.

Nanocomposites cut leather tanning waste

The cost of soft, supple leather shoes and handbags goes beyond the price tag. Chromium tanning agents transform roughly 90% of the world’s animal hides into leather, and a good deal of the chromium ends up in wastewater, where it becomes a hazard. To cut pollution levels, several groups have turned to nanocomposites, which improve chromium uptake into the network of polymerized collagen fibrils that makes up leather. Along those lines, Bin Lyu and Jianzhong Ma of China’s Key Laboratory of Leather Cleaner Production and colleagues now report that pretreating cowhide with vinyl polymer-zinc oxide nanocomposites before tanning improves chromium uptake in the resulting leather. The process also reduces chromium content in wastewater by 50 to 80% (ACS Sustainable Chem. Eng. 2018, DOI:10.1021/acssuschemeng.8b00233). Compared to conventionally tanned samples, the resulting shoe leather has similar durability and softness. Sujay Prabakar of New Zealand’s Leather and Shoe Research Association praised the work

Influence of different tanning agents on bovine leather thermal degradation

The objective of the paper consists in studying the thermal behavior of chrome-free tanned bovine leather (wet-white), using a new product based on titanium and aluminum salts, compared with the same leather tanned by chromium salts (wet-blue). The aim is to find a possibility for replacing the wet-blue leather, containing Cr (III) salts, with the environmentally friendly wet-white leather. The thermal behavior was studied by dynamic thermogravimetry in nitrogen atmosphere, up to 700 °C. Global kinetic thermal decomposition parameters values were obtained with the isoconversional integral method of Flynn–Wall–Ozawa. The kinetic model best describing the thermal degradation process and the kinetic parameters for each individual stage were determined from non-isothermal data by means of a multivariate nonlinear regression method. The evolved gases analysis was conducted on a coupling to a quadrupole mass spectrometer and a Fourier transform infrared spectrophotometer equipped with external modulus for gas analysis. FTIR, microscopic, and elementary composition studies of residues were conducted. There was found that the differences in non-isothermal decomposition kinetics, evolved gases, and residue analyses were dependent on the nature of the two used tanning agents. It was observed that the wet-white leather exhibited lower thermal stability and temperatures of evolved gases. The metal concentrations in the residues and their porous and fibrillar morphologies recommend them as possible candidates for obtaining cost-friendly adsorbents.

Chromium Footprint Reduction: Nanocomposites as Efficient Pretanning Agents for Cowhide Shoe Upper Leather

We report a green chemistry approach to synthesized nanocomposites as pretanning agents in the cowhide shoe upper leather tanning process. Nano ZnO, as-prepared polymer, and polymer/ZnO nanocomposites as pretanning agents were respectively taken for the controls. The amount of chrome tanning agents reduced from 6% (conventional process) to 4% was added in the tanning process as a control process. Chromium footprints in wastewater and chromium distribution in leather samples were mainly analyzed. The results showed that the chromium footprint in the shoe upper leather marking was minimized when using nanocomposites compared with the control process, and the chromium content in leather increased from 13480 to 15039 mg·kg–1. Additionally, thermal properties, mechanical properties, softness, and dyeing fastness of the leather pretreated with nanocomposites were close to those of leather treated with the conventional tanning process. Scanning electron microscopy analysis indicated that leather pretreated with ...

Tanning methodologies using skins of righteye Pleuronectes neatus, Centropomus undecimalis, Oreocchromis niloticus and Chaetodipterus faber

This study aimed to evaluate the determination of tanning processes with fish skin, using vegetable tannins as tanning agent in righteye Pleuronectes neatus and Centropomus undecimalis. The study also performed a leather resistance analysis for young and adult Oreocchromis niloticus and Chaetodipterus faber. The carried out tanning is divided into two steps: Beamhouse operations – tanning (curing, unhairing, scudding, soaking, liming, deliming and pickling) and finishing operations (neutralising, retanning, drum dyeing, fatliquoring and drying). The use of formic acid, with an initial proportion of 1%, suffered 0.5% reduction at the retanning stage for the four species in the experiment. The high acidification in direct contact with the skins adversely affected the tanning process, causing also the decrease from 2% to 1% of soda ash during the liming process, being noticed the rupture of scales insertion coverslips, damaging the final product. The tanning of Centropomus undecimalis and Pleuronectes neatus resulted in hard leather, which does not provide conditions for the mechanical resistance analysis, thus requiring the development of new methodologies to obtain a soft and easy-to-handle final product. The proof-bodies were made for the following tests: tensile strength (N/mm2), elongation and progressive tearing (N/mm) for tilapia and Chaetodipterus faber leathers, using the EMIC® dynamometer at removal speed of 100 ± 20 mm/mm. Regarding the mechanical resistance analysis results, the leather of young and adult Oreocchromis niloticus respectively presented values of 63.3 N/mm2 and 42.58 for tensile strength, 80.9% and 64.3% for elongation and 32.7 N/mm and 41.9 N/mm for progressive tearing, which proves its superiority over the Chaetodipterus faber. This one presented tensile strength of 56.8 N/mm2 and progressive tearing resistance of 20.9 N/mm. Young and adult Oreocchromis niloticus and Centropomus undecimalis, according to ABNT NBR 13525:2015, can be used for fashion leather. Oreocchromis niloticus, exclusively, can also provide leather for automotive purposes and furniture.

Tannery solid waste valorization through composite fabrication: A waste‐to‐wealth approach

The micro‐fined collagenous buffing dust is one of the most airborne pollutants, which contains chromium, tanning agents, synthetic oil, and dyestuffs. Discarding without proper management could cause environmental pollution and ultimately affect human health. In this study, an approach was made to fabricate composite sheet from the buffing dust incorporating various chemicals. The fabrication process was optimized investigating various parameters. The fabricated composite sheet was finished and inspected for physical properties. Composite finished surface was smooth, light in weight, flexible, and elastic in nature. The tensile strength and elongation at break of the finished composite were 6.03 MPa and 23.3%, respectively. The scanning electron microscope analysis shows that buffing dust was uniformly dispersed in the binding material matrix without structural deterioration. The results indicate that the fabricated composite sheet could be used in the footwear and leather products making. © 2018 American Institute of Chemical Engineers Environ Prog, 37: 1722–1726, 2018

The quantitative comparison of wash fastness improvement of acid and direct dyes on wool using full backtan, syntan, and syntan/cation system

ABSTRACTNatural tannin, synthetic tanning agent (syntan), and syntan/cationic agent were applied on wool fabric dyed with different acid and direct dyes to improve the wash fastness of dyes. In this study, a method for quantitative and exact assessment of dye removal after washing from dyed samples was used. Firstly, the optimum operating parameters for application of full backtan and syntan were determined. Then the dyed wool samples were aftertreated, using natural tannin, syntan, and syntan/cationic agent. It was found that all aftertreatments improved the wash fastness. However, aftertreatment with natural tannin improved wash fastness to the greatest extent. In the case of syntan, sequential application of cationic agent on syntaned fabric obtained further improvement in wash fastness.

BEVA® 371-based Synthetic Leather

The use of newly manufactured leather for book repairs has been questioned in recent years as the traceability of tanning and dyeing agents became hazardous. It has also been found that the invasive nature of the repair is often localized on already fragile joints due to extreme paring. In that regard, this method currently in use for leather binding repairs does not always match modern conservation standards and an alternative was found in the use of Japanese tissue as an infill material.Although more adequate in terms of conservation standards, this article shows that consolidating leather with Japanese tissue is less efficient than usually expected. Japanese tissue is compared with BEVA® 371, an acrylate solution originally intended for canvas lining in painting conservation. Over the years, it has been used with great success on leather in ethnological collections. This study investigates how it could be applied to book conservation, and in which ways it can be a superior alternative to leather and Japanese tissue repairs.

Resource addition to leather industry: Adhesive from chrome shaving dust

Leather industry produces a prodigious amount of wastewater and solid wastage containing a significant amount of hazardous chromium. Chrome Shaving Dust (CSD) is tanned collagenous micro-fine solid particulate impregnated with chromium synthetic fat and oil, tanning agents and dye chemicals. Contrariwise, the adhesive is a material which is used for bonding two or more materials together. This study will reflect the way of eliminating the CSD as a pollutant in leather industry rather it will show its lucrative function by making adhesive which is used in various footwear industries. In such way, it not only saves the environment but also aids to gain marginal profit. The process includes treating the shaving dust with distilled water, magnesium oxide and trypsin enzyme followed by force filtration, heating, evaporating, copolymerization with acrylic resin, polyvinyl alcohol, compounding with polyvinyl acetate, glycerol, Busan bactericide, and Busan fungicide. After that produced adhesive was applied in various parts of footwear to assess its function. The study not only tells about the ethical manufacturing and waste management process but also emphasizes on resource management. This considerably shows the waste generation process and also shows its alternate application in another field rather than polluting environment deliberately. Decaying ecology may get its balance with all natural species by controlling the wastes as well as its implication in an alternative way.

Ecofriendly wet–white leather vs. conventional tanned wet–blue leather. A photochemical approach

Abstract Remaining waste disposal after leather tanning has become a cause of worldwide major concern since conventional disposal methods are not practicable when it comes to tanned leather wastes, such as Cr3+ conversion to Cr6+, hydrogen cyanide, nitrogen oxide and ammonia emissions. In order to bring knew knowledge and know–how into the replacing of the hazardous Cr tanned leather (wet–blue) with the eco–friendly Ti Al tanned leather (wet–white), one must first comprehend the photodecomposition mechanism of the differently tanned leathers under environmental accelerated aging conditions. It is theferore that this paper deals with comparing the influence of tanning agents on the artificial accelerated aging of the two tanned leathers. Structural changes during UV exposure were monitored by color modification measurements, fourier transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscope equipped with a EDX for elemental analysis and dynamic water vapour sorption measurements. The different crosslinking patterns with tanning agents and irradiation wavelengths generated differences in photodecomposition behavior, occurring predominantly through collagen triple helix denaturation, at 365 nm, and/or cleavage of intermolecular hydrogen bonds and polypeptide chains, at 254 nm. The proteic structures photochemically decomposed through a photo–oxidative mechanism, assisted by the oxygen from air, with the formation of hydroperoxide entities. The wet–white leather was found to be less stable than the wet–blue leather in the UVA region, because of higher tendencies of polypeptide bonds cleavage occurring together with collagen triple helix denaturation. This aspect was also demonstrated by the more intense color modification registered for wet–white leather. These differences in photodegradation patterns may also further help in finding suitable photostabilizers.

The utilization of sodium lignosulphonate extracted from Egyptian rice straw in leather tanning process

Massive quantities of rice straw are burned annually in Egypt and caused environmental hazards. The present study investigated the utilization of rice straw to produce sodium lignosulphonate (SLS) as a water-soluble derivative of lignin in leather tanning and evaluate its usage as a tanning or re-tanning material as well as its effect on leather quality. The results of testing SLS as a leather tanning agent were unsatisfactory due to its slight effect on shrinkage temperature of leathers, unlike its use as a re-tanning material. Four concentrations of SLS (0%, 5%, 10%, and 20%) were used in re-tanning forty of sheep wet-blues. The results showed that using SLS as a re-tanning agent with concentration till 10% from pelts weight enhances some organoleptic properties, such as fullness and general appearance together with slight improvement in physical properties of leathers. Moreover, the addition of SLS with concentration 20% led to an excessive swelling in the collagen fibers as shown from depicted scanning electron micrographs and decreased trends of physical properties.

Influence of solvent additives on the aqueous extraction of tannins from pine bark: potential extracts for leather tanning

AbstractBACKGROUNDPine bark, which represents approximately 10 to 20% in weight of the tree trunk, is an abundant and low cost agro‐industrial waste. In order to obtain condensed tannin‐rich pine bark extracts (for future application in leather tanning/retanning processes), conventional aqueous extractions were performed, varying the type and amount of the solvent additive: sodium hydroxide (0.5, 1.0 and 1.5%, w/v), formic acid (0.5, 1.0 and 1.5%, v/v) and ethanol (5, 10 and 15%, v/v). Extractions were performed with and without the addition of sodium sulfite (1.0%, w/v).RESULTSThe most favorable solvent additive in terms of total phenolics and condensed tannins was ethanol: extracts achieved 34.8% of gallic acid equivalents and 62.8% of catechin monohydrate equivalents. Moreover, the favorable pH values (∼3.5) of the resultant aqueous solutions and their relatively low viscosities are suitable for subsequent tanning applications.CONCLUSIONSThe results of this study suggest that the high added‐value aqueous extracts of Pinus pinaster bark, which were achieved with small amounts of ethanol, have appropriate characteristics for leather tanning, and therefore they may be used as eco‐friendly tanning agents to partially replace chromium salts, thus reducing some of the environmental impacts typically associated with the leather industry. © 2017 Society of Chemical Industry

Quality properties of leather produced in water and supercritical fluid (SCF) media

Supercritical fluid (SCF) technology is defined as green processing system and used in the industrial applications. This study aims to search the quality properties of leather produced in water and SCF media. Supercritical carbon dioxide (scCO2) was used as SCF. Tanning process was carried out by valonea tannin as natural tanning agent with different process time from 2h to 8h. After tanning in SCF, the skins were processed with conventional methods in water media and finished. Another group of the skins were just conventionally produced. ScCO2 tanned and finished leathers were compared with the leathers which completely processed in conventional ways as control group. Light fastness, tensile strength, tear load and stitch tear resistance analyses for the quality control of the products were carried out. Thermal stability characterization of the leathers were also done by differential scanning calorimetry (DSC) and mechanical shrinkage tests. The results showed that 2h and 4h of SCF-CO2 tanning applications were insufficient in terms of the physical properties expected, but 6h and 8h tanned leathers were in a good quality.

Biogas production for anaerobic co-digestion of tannery solid wastes under presence and absence of the tanning agent

The influence of the presence of the tanning agent in co-digestion of leather shavings mixed with sludge before and after the tanning stage was examined. Chromium and vegetable tannin are the main tanning agents used and the presence of both was evaluated in two orthogonal arrays. The energy efficiency was evaluated through biogas and methane production. The efficiency in waste treatment was evaluated through the variation of TOC, IC, TN and the concentration of the tanning agents. Sludge with chromium proved to be significantly more suitable for AD than sludge without it, producing 27.9mL of biogas/g of VSS with 60% of methane; a reduction of 62.8% of TOC; and a 325.0% increase of IC, showing that the initial 7.6mg/L of chromium in these tests was beneficial. Shavings with chromium also proved to be significantly more suitable for AD, even though with a higher initial 16.4mg/L of chromium, producing 10.7mL of methane/g of VSS and a 55.2% reduction of TOC, confirming that the concentrations of chromium in the residues were not inhibitory. Shavings with vegetable tannins were unfavorable to the mineralization of the wastes through anaerobic digestion, showing significantly poorer results than shavings without it. They produced 4.1mL of methane/g of VSS, confirming the establishment of anaerobic digestion. However, they increased the TOC by 23.7%, showing that the initial hydrolytic activity occurred, but the waste was not mineralized by the other phases of the process due to the high initial concentration of 590mg/L of tannins.

Improvement of Technological Properties of a Vegetal Tanning Agent in Gas Discharge Plasma

The article considers the possibility of modification of the vegetal tanning agent quebracho in the plasma of a radio-frequency induction discharge at low pressure. It is established that plasma treatment leads to a decrease in the size of colloid fractions and a decrease in the molecular weight, while the functionality of the vegetal tanning agent is preserved. Application of the obtained product in the process of leather retanning allows improving its physical, mechanical and consumer properties.

Low-chromium- and low-sulphate emission leather tanning intensified by compressed carbon dioxide

The leather industry transforms raw hides and skins into high-performance leather products. This transformation requires a high usage of chemicals. About 90% of all leather products are tanned by basic chromium sulphate tanning agents. The use of large quantities of tanning agent causes elevated chromium and sulphate concentrations in the wastewater of conventional tanneries. This article focuses on the reduction of tanning agent consumed by the chromium tanning procedure. Compressed carbon dioxide is used to intensify the process. Carbon dioxide-intensified tanning at 60 bar allows the production of high-quality leather by using about 50 wt% less of tanning agent compared to the conventional tanning process. The chromium and sulphate concentrations in the wastewater generated by the tanning process are highly reduced. Results of full skin tanning (bull skin; up to 10 square metre per skin) in a high-pressure reactor with a volume of 1700-L are presented for the first time.