Tanning Agent Research Articles

Electroplating for chromium removal from tannery wastewater

The performance of electroplating in the removal of chromium ions from crude tannery wastewater and from a synthetic wastewater solution was investigated. Brazil is a major producer of leather, and such industries generate large environmental impacts. A novel batch reactor setup was developed for tannery wastewater treatment, employing graphite and aluminum as anode and cathode, respectively. Crude wastewater from a tannery was characterized and presented an acidic pH, elevated biochemical oxygen demand and chemical oxygen demand, and a total chromium concentration of 544 mg/L, a value that is one thousand times higher than permitted by local legislation. Electroplating was able to remove 90.0% of chromium content from a synthetic trivalent chromium solution. Moreover, 96.5% of total chromium content was removed when electroplating was applied in untreated tannery wastewater. Additionally, antifoam addition inhibited foam generation during the electroplating process without interfering in chromium removal. The results showed that the electroplating technique is a viable wastewater treatment alternative and/or a complement for tannery industries that use chromium as a tanning agent.

Clay/polymer nanocomposites as filler materials for leather

Abstract In the present study organoclay based acrylic polymer nanocomposites were prepared via emulsion polymerization and used as filling agent for leather. The main objective of the study is to use inexpensive clay for preparation of synthetic tanning agent (syntan) for leather processing. Prepared clay/polymer nanocomposites consisting of different weight ratios of organoclay were characterized for morphological and mechanical strength properties. The results showed that surface roughness and mechanical strength of the films increased with increasing concentration of organoclay. The particle size and zeta potential analysis reveal that the clay/polymer nanocomposites (CPNs) were electrostatically stable with particle size varying between 62 and 295 nm. The leathers treated with experimental clay-polymer nanocomposite incorporated with 5 wt% clay exhibited smooth fibrillar arrangement suggesting excellent dispersion and filling properties, thus opening new avenues for efficient leather processing. The experimental leathers also exhibited better tensile strength of 28 ± 0.5 compared to control 26 ± 0.5 N/mm2 and organoleptic properties such as fullness, belly filling and softness were also improved. Thus, the preparation and application of the syntan paves a way to the sustainable approach for making leather filling agent, which is cost-effective, abundantly available and eco-friendly.

Vegetable tannin composition and its association with the leather tanning effect

The increasing environmentally friendly approach of using renewable materials has led to vegetable tannins having an important role as tanning agents in the leather industry. Tannins are complex phenolic structures, and the literature shows that a considerable amount of chemical parameters measured through analytical techniques can be associated with their tanning ability. In the present study, five types of vegetable tannins highly used in the tanning industry were chosen for the evaluation of some of their relevant chemical parameters and the correlation with their cross-sectional penetration in the hide. Black wattle (Acacia mearnsii), quebracho (Schinopsis lorentzii), chestnut (Castanea sativa), tara (Caesalpinia spinosa), and myrobalan (Terminalia chebula) were tested. The chemical properties of the total tannin polyphenols, non-tannin polyphenols, insoluble solids, soluble solids, total solids, total phenols, non-tannin polyphenols:total phenols ratio, and residual tanning float concentration were measured and associated with the leather cross-sectional penetration results. The statistical Mann–Whitney-U test showed that the insoluble solids, non-tannin polyphenols, soluble solids, and total tannin polyphenol percentages distinguished the groups of tannins that crossed the hide from those that did not well. Hence, since the analysis of insoluble solids is the simplest and the most direct among them, it would be recommended to use this parameter to define a cutoff to distinguish the performance of tannins for leather application.

A green chemistry approach to leather tanning process: Cage-like octa(aminosilsesquioxane) combined with Tetrakis(hydroxymethyl)phosphonium sulfate

The octa(aminopropylsilsesquioxane) (POSS–NH2) was synthesized by hydrolytic and condensation of γ-aminopropyltriethoxysilane in isopropyl alcohol solvent with tetraethylammonium hydroxide as catalyst. The structure and morphology of products was characterized by Nuclear magnetic resonance (1H, 13C-NMR), fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). A novel chrome-free tanning process based on combination tanning with cage-like octa(aminosilsesquioxane) and tetrakis(hydroxymethyl) phosphonium sulfate (THPS) has been proposed. Hygrothermal stability test showed that the shrinkage temperature (Ts) of THPS tanned leather was obviously increased with the introduction of POSS-NH2, implying that THPS and POSS nanoparticles had synergistic effect in the combination tanning process. The tanning process is optimized as 6.0% POSS-NH2 combination with 2.5% THPS, endowing the leather with Ts above 83.0 °C and thickness rate 44.6%. FT-IR analysis showed that hydrogen bond were formed between amino groups of POSS and hydroxyl groups of collagen during tanning process. The results of scanning electron microscope and energy dispersive X-ray spectroscopy (SEM-EDX) results reveal that POSS and THPS tanning agents could penetrate and bind evenly in the leather matrix, thus promoting the weaving of collagen fibers into a tight network structure.

PH-Sensitive and Chromium-Loaded Mineralized Nanoparticles as a Tanning Agent for Cleaner Leather Production

In this work, pH-sensitive and chromium-loaded mineralized nanoparticles (Cr-PPA NPs) were developed by self-assembly of poly (poly(ethylene glycol) methyl ether acrylate-co-acrylic acid) (poly(PEG-co-AA)) copolymers templated Cr(OH)3 mineralization. The Cr-PPA NPs exhibit excellent colloidal stability in water with high salt concentration, protein, and pH above 3.0. As a novel chrome tanning agent, such Cr-PPA NPs could effectively protect and deliver chromium into pickled pelt without reacting with collagen fibers during the penetration process, due to its antifouling PEG surface and nanosize. When the interior pH of the pickled pelt was lower than 2.5, the dissolution of the mineralized Cr(OH)3 core would cause disassembly of Cr-PPA NPs and rapid release of Cr3+ ions, leading to uniform chromium distribution in leather. After basifying, the released Cr3+ ions would cross-link the carboxyl groups both on collagen fibers and poly(PEG-co-AA) copolymers, resulting in chromium adsorption efficiency in leath...

The Utilization of Chitosan as Natural Antibacterial for Vegetable Tanned Leather

Leathers, which are made from natural fibers, can serve as media for microorganisms to grow. The currently used antimicrobial agents or biocides in the leather industry are harmful to human health and the environment. Therefore, the use of antimicrobial agents should be restricted. This study aims at developing eco-friendly biocides that could substitute for toxic chemicals as it will be tested on vegetable-tanned leather. Due to their large surface area and ability to retain moisture, the vegetable tanned leather has a higher possibility of biodeterioration than other types of leathers tanned by mineral tanning agents. In this work, the natural biopolymer of chitosan was chosen for its ability to inhibit the bacterial growth. The results showed that chitosan coating by impregnation method in drum using chitosan/leather ratio of 1% in formic acid for 2 hours is successfully achieved the bacterial growth inhibition.

Sustainable use of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride as metal free tanning agent

Leather manufacturing is water, energy and waste intensive and requires integrated prevention and control of pollution. Tannery effluents, if not properly treated, may cause significant damage to soil and water bodies thus, tanners are looking for more environmentally sustainable technologies. In this concern, a process has been designed employing a new tanning agent allowing to produce totally metal-, formaldehyde- and phenol-free non-toxic leather. The agent tested is 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM), which appears to be a very efficient tanning agent producing hides with shrinkage temperatures as high as Ts = 87 °C. Environmental and economic benefits arising from the use of DMTMM are discussed.

The penetration and accumulation of hydroxyapatite and the hydrothermal stability of collagen matrix material

Abstract Hydroxyapatite (HAP) has been extensively used in the clinic, for example, for bone tissue repair, because of its outstanding performance. However, whether HAP can be utilized in other fields, such as leather manufacturing, remains unknown. The process of making leather from hide involves a hydrothermal treatment. Thus, in the present work, HAP was synthesized using a hydrothermal method with diammonium hydrogen phosphate and calcium nitrate as phosphorus and calcium precursors, respectively. The condition optimization test results indicated that high-purity HAP can be obtained when the reaction is carried out at 80 °C and pH 11, with surfactant added. To study the effect of HAP on cowhide and to determine whether it can be used as a tanning agent, tests of in vitro and in vivo HAP addition into cowhide were conducted. The cowhide was first subjected to a wet-end leather making process and then cut into samples. Samples were treated using different HAP addition methods, and experimental results obtained under different conditions were compared. Fourier-transform infrared spectroscopy analysis indicated that HAP added by both methods can react with cowhide. Physicochemical properties of cowhide were improved after reaction with HAP, specifically, the thermal stability was enhanced when HAP was synthesized in the skin. The thermal shrinkage temperature of the treated hide was 78 °C, which was higher than 54 °C for the control group samples. The hide tear strength was greatly enhanced because HAP synthesized on hide collagen caused the formation of a rigid module. Therefore, HAP has the potential to be used as a chrome-free tanning agent. This study demonstrated that the modification of cowhide by HAP was feasible and HAP tanning or HAP combination tanning was of practical significance.

Potential of phyto-constituents as a skin tanning agents

Potential of phyto-constituents as a skin tanning agents

Thermal degradation study of vegetable tannins and vegetable tanned leathers

In this study, hydrolyzable tannins (commercial chestnut, valonea and tara extracts), condensed tannins (commercial quebracho and mimosa extracts) as well as calf leathers produced using these vegetable tanning agents were characterized by thermal decomposition methods using slow and high heating rates. Calf gelatin obtained by heating calf pelt in water at 70 °C was chosen as a reference material. Thermogravimetry/mass spectrometry (TG/MS) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments were performed on the tannin and leather samples. The evolution profiles of the decomposition products as well as the thermal stability of tannins and leathers were studied by TG/MS. A net difference was observed in the thermal behavior of hydrolyzable and condensed tannins. The condensed tannins produced the highest char yield, while the hydrolyzable tara extract released the most volatile products. The tannins of higher reactivity produced more stable leathers as it results from their higher decomposition temperature. The composition of both vegetable tanned leathers and vegetable tanning agents was characterized by the pyrolysis product distribution measured by Py-GC/MS method. Resorcinol and its methylated derivative (orcinol) were found to be a characteristic decomposition product for both condensed tannins, i.e. mimosa and quebracho. They were identified among the pyrolysis products of the mimosa and quebracho tanned leathers, as well.

Preparation of a Highly Effective Organic Tanning Agent with Wide Molecular Weight Distribution from Bio‐Renewable Sodium Alginate

AbstractDialdehyde sodium alginate (DSA) with wide molecular weight distribution was prepared by periodate oxidation without alcohol‐precipitation. Its tanning properties in fur processing were investigated. It was found that this DSA could endow fur with high shrinkage temperature (Ts, 89 °C) and area yield (107%), showing better tanning properties than conventional dialdehyde sodium alginate product that was prepared by repeated alcohol‐precipitation process and thus had narrow molecular weight distribution. Low molecular weight components in DSA mainly contributed to crosslinkage and dispersion of the collagen fiber network, viz. tanning effect, while high molecular weight DSA components contributed to filling performance. SEM analysis illustrated that satisfactory dispersion of skin matrix and intact scale layer of wool were achieved by DSA tanning. The DSA tanned fur exhibited reasonable resistance to oxidation bleaching and presented a better performance in physical properties compared with traditional chrome tanned fur after fatliquoring. Besides, the DSA tanning system led to a better treatability of tanning and post‐tanning wastewaters in view of chrome‐free and higher biodegradability. The DSA with wide molecular weight distribution is a potential sustainable tanning agent in terms of both preparation and tanning processes.

Possible use of corn starch as tanning agent in leather industry: Controlled (gradual) degradation by H2O2

High molecular weight/size and poor solubility of native starch seems to be preliminary drawbacks in its possible use in leather processing as a tanning/retanning agent. For this purpose, firstly the native starch which has too large molecular size to penetrate between skin fiber matrix was oxidized with H2O2 in different molar ratios for disintegrating into appropriate molecular size that can be used in tanning process. Then, the product yields, water solubilities and degree of substitutions of oxidized starches were determined. Also, the oxidized starch samples were characterized by Fourier Transforms Infrared (FT-IR) Spectroscopy, Gel Permeation Chromatography (GPC) and Proton Nuclear Magnetic Resonance (1H NMR) Spectroscopy. According to the GPC results, the oxidized starch samples which their molecular weights were reduced for penetrating into skin fibers were selected and they were used in tanning process of goat skins. The tanning effects of selected oxidized starches were evaluated according to shrinkage temperatures, filling coefficients and Scanning Electron Microscopy (SEM) analysis. From the results, it was revealed that the native corn starch can be oxidized with H2O2 in a controlled manner and oxidized starch can be utilized as a tanning/retanning agent in leather making.

Thermal stability of shoe upper leather: Comparison of chestnut and quebracho as vegetable tanning agent

Thermal stability is one of the most important factors in the leather tanning process and mainly affected by the tannin type used to tan the hides. Vegetable-tanned leather for shoe upper is a material that could be used and preserved for a long time. However, it makes leather easily degraded because of temperature and time. Additionally, one of the stages in shoe making process is the heating process to stick the upper leather into midsole material. Therefore, this study aims to compare the effect of different tanning agents, chestnut and quebracho, on the thermal stability of shoe upper leather. Measured were degree of tannage and thermal stability, using shrinkage temperature, thermogravimetric analysis and differential scanning microscopy. The morphology of leathers tanned with chestnut and quebracho in different concentration were also observed. The shrinkage temperature of leather tanned with chestnut was lower than that of quebracho-tanned leathers. Leathers tanned with 20 and 25% of chestnut showed higher degree of tannage than the ones tanned with quebracho. Thermogravimetric analysis (heating rate of 10 °C min−1; gas flow of 60 ml min−1) showed that the maximum weight loss rate decreased with the increase in the concentration of chestnut or quebracho. The differential scanning calorimetry results showed that quebracho-tanned leather had a higher heat resistance than chestnut-tanned one. The presence of vegetable tanning agent improved the thermal stability of leather. Furthermore, it was shown that leather tanned with 20% and 25% of chestnut resulted in almost equal thermal stability. Quebracho calf leather was more resistant against heat than chestnut calf leather.

Mechanical Blending Preparation of Hydrophilic Spherical Nano-SiO2/Acrylic Resin Nanocomposite for Tanning Leather

In this study, the spherical silica nanoparticles (denoted as PASP-K-SiO2) were firstly prepared with 3-aminopropyltriethoxy silane (KH550) and polyaspartic acid (PASP) as surface-modifiers by sol–gel method. The PASP-K-SiO2 nanoparticles were well dispersed in water and combined with waterborne acrylic resin matrix (denoted as PAA) for preparing novel nanocomposite tanning agents (denoted as PASP-K-SiO2/PAA) successfully through a strong mechanical blending. The nanocomposite tanning agents were used to tan pickling white-wet sheepskin and the tanned leather was characterized by rheological measurements, revealing an increase in the storage modulus and relaxation time of the leather compared to the leather tanned with bare nano-SiO2 and neat PAA. The leather tanned with PASP-K-SiO2 nanoparticles also exhibits excellent mechanical properties, high thermal stability and chromium absorption rate. Moreover, the shrinkage temperature of the leather tanned with PASP-K-SiO2/PAA and just 0.2% chromium powder based on the sheepskin weight can reach above 80 C, which is potentially advantageous in completely or partially replacing toxic chromium tanning agents used in traditional leather industry. Compared with the chromium tanning process, the tanning method with the nanocomposites would be regarded as eco-friendly, thus contributing to the reduction of environmental impact.

Chromium bioavailability in aquatic systems impacted by tannery wastewaters. Part 2: New insights from laboratory and in situ testing with Chironomus riparius Meigen (Diptera, Chironomidae)

Chromium is widely used as a tanning agent and can become a contaminant of concern in aquatic ecosystems receiving discharges from industrial or artisanal tanning activities. In a companion study, we showed that Cr discharged by tanneries was bioavailable to indigenous chironomids with accumulation via sediment ingestion likely to represent the predominant exposure route. However, Cr accumulation by chironomids did not directly reflect the degree of sediment contamination and the potential adverse effects of Cr accumulation on chironomids were not evaluated. In the present study, chironomids were exposed to homogenised, field-collected sediments in the laboratory and to intact sediments in situ using a customized caging system. Chromium concentrations were assessed in sediments, exposed larvae of laboratory-reared Chironomus riparius and overlying waters of in situ cages. Experimental results of Cr bioaccumulation were compared with expected Cr body burden in chironomids calculated using biodynamic modelling. Our data provided strong support to the hypothesis that Cr bioaccumulation in the field is specifically controlled by the deposition of contaminated suspended particulate matter (SPM) containing a pool of Cr readily bioavailable to surface deposit feeders. Considering freshly deposited SPM as an additional route of exposure for surface deposit feeders leads to a good agreement between the modelling and experimental results. Additionally, a Cr body burden of about 77 μg g−1 d.w. was identified as a tentative threshold above which effects on the growth of C. riparius may appear. While both laboratory and in situ experiments provide evidence for the availability of Cr in aquatic system impacted by tannery wastewaters, standard laboratory exposure conditions may miss additional exposure routes in the field and underestimate possible adverse effects on benthic organisms.

Effects of tanning on the stable isotopic compositions of hair

We investigated the effect of tanning on the stable isotopic compositions (CNHOS) of hair keratin. Samples of hair from polar bear (Ursus maritimus) hides were collected before and after the tanning process from a commercial tannery. With the exception of sulphur isotopes, tanning did not alter the stable isotopic compositions of hair. δ34S values were slightly more positive (1 per mil) in hair that had gone through the tanning process, likely as a result of the tanning agent, alum (Al2(SO4)3) or exposure to sulphuric acid (H2SO4). This indicates that, with the exception of sulphur isotopes, hair keratin is resistant to subsequent isotopic alteration by the techniques used in tanning of animal hides and thus the original stable isotopic information is likely to be preserved in archived samples, such as taxidermic mounts and museum specimens. This is an important consideration when dealing with ecological and forensic applications to wildlife, such as evaluating provenance or migratory reconstructions, and so will assist in conservation efforts and investigations of trafficking and poaching.

A star-shaped POSS-containing polymer for cleaner leather processing.

A water-based silsesquioxane (POSS)-containing polymer, POSS-PAA, was synthesized by using octavinyl-POSS (V-POSS) and acrylic acid (AA) via interfacial polymerization. The TEM of POSS-PAA showed that the polymer formed a core-shell structure in aqueous solution and was well-dispersed. The star-shaped POSS-PAA and linear PAA were both tanned with 3.5% chromium tanning agent, and leather hide was tanned with 3.5% chromium tanning agent as a control. The results showed that the shrinkage temperature of wet-blue leather treated by POSS-PAA was increased by 3.5 °C than that of the control. The thickening rate of the POSS-PAA treated wet-blue leather samples was increased by 21% and 96% than the linear PAA-treated leather and the control leather, respectively. The EDS results suggested that the POSS-PAA pre-treated leather had a higher chromium content than the others, and the chromium distribution from the leather flesh side to the grain side was uniform. Moreover, the Cr2O3 content in both the POSS-PAA and the PAA pre-treated tanning waste water was reduced by about 50%, compared to the control waste. The COD and BOD of the POSS-PAA pre-tanning waste were decreased compared to the others. Therefore, POSS-PAA appeared to be promising for promoting the development of cleaner leather production.

Effect of structure features of polysaccharides on properties of dialdehyde polysaccharide tanning agent

Sodium alginate (SA), tara gum (TG), starch (ST) and cyclodextrin (CD) were oxidized to dialdehyde polysaccharides (DAPs) using equivalent sodium periodate. The effects of polysaccharide structure features on aldehyde group content, molecular size and tanning performance of DAPs were investigated. Each DAP had abundant aldehyde groups (>7 mmol/g) for fur tanning in the experimental conditions, and DAP with higher aldehyde group content was obtained when polysaccharide with lower molecular weight and linear chain was used. Lower crystallinity and β-(1→4) glycosidic linkage of polysaccharide benefited its degradation. Compared with dialdehyde ST (Mw>150,000) and dialdehyde CD (Mw<500), DAPs prepared from β-(1→4)-linked amorphous SA and TG had moderate molecular sizes (Mw 15,000–30,000) and exhibited satisfactory penetrability and crosslinking reactivity in collagen fiber network, and thus performed more favorable tanning properties in terms of higher shrinkage temperature and whiteness of fur. This suggests the suitability of β-(1→4)-linked amorphous polysaccharides for preparing dialdehyde tanning agents.

A novel chrome-free tanning approach based on sulfonated tetraphenyl Calix[4]resorcinarene: Preparation and application

Chrome tannage is the main tanning method because of its excellent hydrothermal stability and physical performances. However, the chromium absorption is limited, so the emissions of solid wastes can bring many environmental issues and human health risks. Therefore, a novel chrome-free tanning agent based on a water-soluble calixarene has been attempted. Water-soluble calixarene is a chemical with a unique molecular structure, thermal stability and high chemical stability, it contains a lot of more active coordination of phenolic hydroxyl. In this work, tetraphenyl calix [4]resorcinarene (TC4R) was synthesized with one-step process, and then was sulfonated by concentrated sulfuric acid, which obtained the sulfonated tetraphenyl calix [4]resorcinarene (STC4R). The chemical structure of the TC4R and STC4R were detected by IR and H-NMR. Then STC4R was added to the tanning process as an experimental process and 6% conventional chrome tannage was added to tanning as control. The result shows that the Ts of tanned leather is 77.2 °C using 10% STC4R at final pH 4.0. SEM analyses show that collagen fibers have been dispersed, STC4R makes the fiber loosen and the fullness is increased. FT-IR shows that the hydrogen bond is formed between phenol hydroxyl of sulfonated calixarenes and amino of collagen in the tanning process. At the same time, STC4R does not enter the micro fibrils within the collagen, so three helix structures are not damaged and consistent with AFM.

Use of the Phenol-Degrading Pseudomonas aeruginosa Strain 21SG for Industrial Wastewater Decontamination

The features of a phenol-degrading Pseudomonas aeruginosa strain 21SG isolated from the soil at the territory of Russia’s largest manufacturing facility for synthetic tanning agents (city of Ufa, Bashkortostan Republic) are reported. The strain identification was based on cultural, morphological, physiological, biochemical, and morphometric features and on the results of comparative analysis of 16S rRNA gene sequences. The growth of P. aeruginosa 21SG was assessed in batch culture, and a decrease of phenol content in the culture liquid by 84% of the control level after 4 days was observed. The possibility of using P. aeruginosa 21SG for the destruction of phenol present in wastewater from the petrochemical industry and tanning extract production facilities was detected.