Nanofiltration of Cork Wastewaters and Their Possible Use in Leather Industry as Tanning Agents

Cork processing wastewater is a very complex mixture of vegetal extracts and has, among other natural compounds, a very high content of phenolic/tannic colloidal matter that is responsible for severe environmental problems. In the present work, the concentration of this wastewater by nanofiltration was investigated with the aim of producing a cork tannin concentrate to be utilized in tanning. Permeation results showed that the permeate fluxes are controlled by both osmotic pressure and fouling/gel layer phenomena, leading to a rapid decrease of permeate fluxes with the concentration factor. The rejection coefficients to organic matter were higher than 95%, indicating that nanofiltration has a very good ability to concentrate the tannins and produce a permeate stream depleted from organic matter. The cork tannin concentrate obtained by nanofiltration and evaporation had total solids concentration of 34.8 g/l. The skins tanned by this concentrate were effectively converted to leather with a shrinking temperature of 7 degrees C

Current trends in leather science

Abstract In preparing the second edition of ‘Tanning Chemistry. The Science of Leather.’, the literature was updated and the content was revised and reviewed. Here, the new findings are presented and discussed. Notable developments include the necessary rethinking of the mechanism of sulfide unhairing because of new understanding of the aqueous chemistry of sulfide species. Revision upwards of the value of the second pKa for sulfide species ionisation means that S2− cannot exist in an aqueous medium, so the unhairing species in hair burn reactions is HS−. Although the technology remains the same, this means the mechanisms of associated reactions such as immunisation must be revised. Rawstock preservation has benefitted from studies of the potential role of materials from plants which accumulate salt, but which also contribute terpene compounds. There is also further discussion on the continuing issue of chromium (VI) in the leather industry. The application to processing of new solvents, ionic liquids and deep eutectics, is the coming technology, which offers transforming options for new chemistries and products. Renewed interest in vegetable tanning and methods of wet white processing are current trends. Also, within the topic of reagent delivery is processing in a solid medium of plastic beads. Graphical abstrac

Processing of leather using deep eutectic solvents

Processing of leather has an historical reputation as a chemically and energetically intensive process that produces large volumes of aqueous waste. Saline pollution combined with heavy-metal, dyes and acid and base streams make leather production an ecologically sensitive industry. The current study shows that a variety of deep eutectic solvents (DESs) may be used for the tanning, fatliquoring and dyeing of animal hides, being particularly useful for mineral (chromium) and vegetable tanning processes. The tanning agents are able to penetrate rapidly into the hide, driven by lyotropic swelling due to their high ionic strength. The samples are shown to have similar tanning agent content to the currently used aqueous chromium(III) sulfate solution; however, the waste metal content is shown to be significantly reduced. Incorporation of the DES Ethaline into the leather significantly alters the swelling properties of the leather increasing the flexibility and ductility of the material, therefore acting in the same manner as a fatliquor that lubricates or plasticizes the fibrous structure of the collagen. Ethaline was also used to transport a lysochromic dye throughout the cross section of the leather, and the hydrophobicity of the dye prevents leaching into the aqueous wash solution. Physical measurements show that leather processed using DESs have similar mechanical properties to that processed using conventional aqueous systems

Lightfastness properties of leathers tanned with various vegetable tannins

The color changes of bovine leathers, tanned with commonly used hydrolysable and condensed vegetable tannins, were measured colorimetrically as a function of prolonged irradiation with Xenon test light. The results showed that hydrolysable and condensed tannins exhibited differences in their light fastnesses. The color change of hydrolysable tannins under the effect of light was considerably low when compared to the condensed tannins. Gambier and quebracho tannins, among the condensed tannins, exhibited a rapid color change in the direction of red and yellow, while mimosa showed a slower color shift. Tara, among the hydrolysable tannins, exhibited a slower color shift than the others. At the end of 24 hours, the color changes, observed as darkening in all the tannin groups reached a maximum point after which color lightening was observed with extended time

Usage of starch in leather making

6th International Conference on Advanced Materials and Systems, ICAMS 2016 -- 20 October 2016 through 22 October 2016 -- 139798In recent years, various industries begin to head towards cleaner production due to increasingly restrictive regulations. Therefore, production from natural and renewable sources has become more important. Starch is a remarkable raw material because it is abundant, inexpensive and biodegradable natural polymer. The use of natural starch has remained limited, to be usually for food purposes, until recent decades. However, the usage of starch has increased significantly over the last few decades; via modification some of the properties of the starch and it has found wide range of applications in many industries such as plastics, agriculture, pharmaceutics, adhesive, textile, paper and food. In recent years, several studies have taken part in literature on possible use of modified starches also in leather industry - especially in tanning and retanning processes to ensure cleaner production. And it seems that starch products that modified with various methods in accordance their field of use will find more interest and use in leather making. For this reason in the present paper it is aimed to make an overview on the structure of starch as a renewable and natural resource and its potential applications in leather making. © 2016 Certex, INCDTP-ICPI

Ultrasound extraction of valonea tannin and its effects on extraction yield

Ultrasound extraction of valonea tannin from the acorn cups of the Quercus species was investigated and compared to the conventional extraction method. Effects of ultrasonic power, time and temperature on extraction were examined. Considering the highest extraction yields and tannin contents of two extraction methods, it was found out that ultrasound extraction result in 17.16% increase in extraction yield and 6.61% in tannin amount. Additionally, apart from the temperature study, the sound effect on extraction yields that occurred during ultrasound extractions was also determined. The results were evaluated statistically by using One-Way ANOVA and Duncan tests with the SPSS 15 statistic program. The results showed that ultrasonic extraction method can be used as an alternative to conventional method for extraction of tannin (valonea) from acorn cups

Possible use of corn starch as tanning agent in leather industry: Controlled (gradual) degradation by H 2 O 2

PubMed ID: 30404028High 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 H 2 O 2 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 ( 1 H 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 H 2 O 2 in a controlled manner and oxidized starch can be utilized as a tanning/retanning agent in leather making. © 2018 Elsevier B.V.14MUH029The authors would like to thank the Ege University Faculty of Engineering Scientific Research Projects Commission, which supported our study financially (Project No: 14MUH029 ). -

Determination of antioxidant properties of commonly used vegetable tannins and their effects on prevention of Cr(VI) formation

Even though Cr(VI) is not used in any step of leather making, the presence of Cr(VI) in leather has become a concern in the leather industry. Free radicals usually play an important role in the formation of Cr(VI) in leather. The effectiveness of antioxidant materials in preventing free radical formation is well known. Tannins as phenolic materials are also known to have antioxidant properties. However, the antioxidant effectiveness shows variations regarding to the type and structure of tannins. In the present study, the vegetable tannins which are commonly used in the leather industry (mimosa, quebracho, sumac, tara, valonea and chestnut) were selected and their antioxidant powers were determined by FRAP (The Ferric Reducing Ability of Plasma) and TEAC/ABTS (Trolox-Equivalent Antioxidant Capacity/2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid)) methods. Furthermore, these vegetable tannins were used in leather processing and their effect on prevention of Cr(VI) formation was examined. The results show that gallotannins within the hydrolysable tannins have taken the first places in ranking with superior antioxidant activities and, compatible with their antioxidant powers they were found to be the most effective tannin types at preventing Cr(VI) formation

A novelway to avoid Cr(VI) formation in leather: Copper mordanting

In recent decades many studies have been conducted in order to understand the exact origin of Cr(VI) in leather and find remedies for this problem and it seems that most tanners have resolved this issue in industry. However, in the present study a novel way to avoid Cr(VI) formation in leather by copper mordanting (CuSO4.5H2O) was investigated. 0.5 and 1.0% (w/w) of CuSO4.5H2O were used both standalone and also in combination with vegetable tannins which are commonly used in leather industry. From the results it was seen that both, in standalone, and in combination usage with vegetable tannins, copper seems to be a solution against formation of Cr(VI) in leather and keeping the Cr(VI) values below the permissible limits.Spectrum Pharmaceuticals 109M383During researches on natural extracts as additives for the leather industry with an aim to manufacturing ecological items within a bilateral project supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Grant (number 109M383), we have used valonea and henna as natural colouring materials and, in order to expand shades used mordants.1As is well known, mordanting generally improves dye performance and helps the dyer to achieve a broad spectrum of colours on a wide range of natural as well as synthetic fibres with expanded shade ranges and better fastness properties2 and for this purpose most commonly used mordants in natural dyeing are aluminium potassium sulphate, potassium dichromate, stannous chloride, ferrous sulphate and copper sulphate.3 -