Content: This paper briefly introduced the process of leather manufacture and the potential pollution sources of soil in tannery sites. Pollutants are mainly derived from the use of a large number of various chemicals and organic matter decomposed by raw skin. The characteristics of typical pollutants in tannery sites soil were summarized, including tannery site soil pH, organic and inorganic compounds, and heavy metals, etc., especially the status of chromium contamination were reviewed. The pH of soil in the tanning workshop (6.65-7.8) is generally lower than tannery sludge dumping site (7.94-8.40). The main organic pollutants contained in the tannery site soil include nitrogen compound, grease, petroleum hydrocarbon. In tannery sludge dumping site soil, the content of nitrogen compound (10cm depth) is 28400 mg/kg, which is similar to tannery sludge. The content of petroleum hydrocarbon is 5-700 mg/kg, which partially exceed the limits of China agricultural land quality standard(<500 mg/kg). In tanning workshop soil, the content of grease is 220-62000 mg/kg. The main inorganic pollutants contained in the tannery site soil include sulfide, high concentration of salt, lime. The high salt content of tannery sludge (99000 mg/kg) leads to high salt content in soil (5500-17500 mg/kg). Total hardness (>450mg/L), total dissolved solids (>1000mg/L), sulfate ions (>250mg/L), nitrite nitrogen (>0.02mg/L) partially exceed the limits of China groundwater quality standard, which are found in groundwater below the tannery site. Heavy metal pollutants in the tannery sites soil have many characteristics and large differences in content, due to the different tanning processes. Among them, chromium (Cr) is the most used heavy metal and the highest content of pollutants. Cr content in tanning process wastewater, dyeing process wastewater and chromiumcontaining sludge are about 2000-3000 mg/L, 30-40 mg/L and 8500-25800 mg/kg, respectively. Total Cr content in the partial tannery sites soil are higher than 800 mg/kg, which exceed the limits of China agricultural land quality standard(<150mg/kg). Surprisingly, Cr(VI) appears in tannery sites soil and the contents are partly higher than 40 mg/kg, which exceed the limits of China development land quality standard(<3.0mg/kg). Furthermore, the more effort needs to be directed toward the chemistry of chromium-organic complex pollutants, and an understanding of the speciation of Cr in highly organics contaminated tannery site soil is essential for the development of suitable remediation strategies for contaminated soil. Take-Away: 1. The pH of soil in the tanning workshop (6.65-7.8) is generally lower than tannery sludge dumping site(7.94-8.40). 2. Total Cr content in the partial tannery sites soil are higher than 800 mg/kg, which exceed the limits of China agricultural land quality standard(<150mg/kg). 3. Cr(VI) appears in tannery sites soil and the contents are partly higher than 40 mg/kg, which exceed the limits of China development land quality standard(<3.0mg/kg).

Content: Microwave is a fast, efficient and energy-saving thermal resource, hence an attempt has been made for applying this technology in the combination tanning using titanium (III) and tannin extracts. In this work, the microwave effects on the complex reaction of Ti (III) with tannin extracts and leather products properties were investigated. The precipitation condition was used to characterize the complexation degree between Ti (III) and tannin extracts. And the shrinkage temperature, tear strength, SEM, DSC, TG, FT-IR, and histological structure were used to characterize the changes in the physical and chemical properties of the combined tanned leather. Take-Away: The results showed that microwave irradiation can accelerate the complex reaction of Ti (III) with tannin extracts. At the room temperature, the mixture of tannin and titanous sulphate kept stable at pH 3-4. In addition, microwave could increase the shrinkage temperature, tear strength, thermal stability, and fibrage of Ti (III)-tannin tanned leather, and it would not change the combination mode of the skins with tanning agents as well as the hierarchical structure of collagen. Therefore, these results inferred that microwave could promote the reaction between Ti (III) and tannins and the combination of tannins with collagen, which may provide a theoretical basis for the application of microwave in Ti (III)-tannin combination tanning technology.

Content: Pre-treatments are widely used during tanning processes as to improve the performance of the main tannage. Synchrotron small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) were used to study four common types of pre-treatments, viz. monodentate complexing agent (sodium formate, SF), chelating agent (disodium phthalate, DSP), covalent cross-linker (glutaraldehyde, GA) and nanoclay (sodium montmorillonite, MMT) about their effects on chromium-collagen cross-linking reaction during tanning. Based on the results, the performance of chromium-collagen cross-linking with and without pre-treatments was presented considering five aspects: cross-linking, the level of hydration, hydrothermal stability, uniformity through leather cross-section and the uptake of chrome. Comparing to the original ThruBlu chrome tanning, at the same chrome offers, leather pre-treated using SF, DSP and MMT showed improved hydrothermal stability, uniformity and the level of hydration, while GA showed decreased hydration. All of the pre-treatments reduce surface fixation by decreasing the reactivity of chromium with collagen. Changes in the reaction performance can influence the properties of the leather products as well as the efficiency of the leather manufacturing processes. Insights into the structural changes of collagen during tanning with varied reaction conditions can guide the design of novel, benign tanning processes to reduce environmental impact. Take-Away: 1. Uniformity of the hydrothermal stability through leather cross-section were improved by all of the studied pre-treatments. 2. Reactivity of chromium to cross-link with collagen was reduced as a result of the complexing, covalent cross-linking, or preferential adsorption. 3. Complexing agents and nanoclay pre-treatments tend to retain collagen bound water, while covalent cross-linker causing decrease in the level of hydration of collagen.

Content: The purpose of this paper is to study the influence of acrylic resins on the properties of the hide when added in the pickling-tanning stage of a wet white process. Among retanning products, acrylic resins are very frequently used because they lend very good properties to the hide on account of their high affinity for chromium. When applied during chrome tanning, these resins provide the hides with high fullness, due to the strong interaction of the carboxylate groups with chromium. Extensive bibliography is available on the application of acrylic resins in wet blue, where it is observed that the properties they provide to the hides depend basically on the type of monomers and molecular weight. However, less information is found when these products are applied in wet white tanning. In this study, 9 resins with different molecular weights and different monomer compositions were selected. Resins were applied to pelt leathers of Spanish origin split at 3.5 mm. Hides were cut along the backbone. A standard process was applied to the left halves and the same process adding the resin was applied to the right halves. The resin was added after adjusting the salt of the bath and before adding the pickling acids. The COD was measured before and after adding formic and sulfuric acid, and the shrinkage temperature and the degree of whiteness of the tanned hide were assessed. Hides were retanned and fatliquored with a standard process, and degree of softness, thickness, color intensity and organoleptic properties (fluffiness, compactness and grain tightness) were assessed. Leather shrinkage under temperature was also assessed, and images of leather sections were obtained by scanning electron microscopy (SEM). While acrylic resins did not increase shrinkage temperature, they did fix and/or deposit themselves in the interfibrillary spaces of the hide; indeed, highly reduced COD values after acidification in the pickling stage were observed. This study shows that homopolymeric acrylic resins provided fuller and fluffier hides, while the rest of resins practically did not improve the physical and organoleptic properties of the hides. Take-Away: Homopolymeric acrylic resins provided full er and fluffier hides, while the rest of resins practically did not improve the physical and organoleptic properties of the hides Wet white tanning improvement

Content: Sustainability is a key factor which control future leather manufacture. Developing several new technologies is one of the primary agenda for sustainability. However, developing countries are facing several challenges which not only limited to best practice technologies but also finding self sustainability in maximizing the available resources. In the present study, an attempt has been made to explore the potential resource of aluminium from kaolin of Pugu hills, Tanzania for combination tanning. Though, extraction of aluminium from several resources are available, there is limited literature pertaining to Tanzania resources. Moreover, the extracted aluminium is basified and studied for its tanning efficiency. Diffraction and vibrational spectroscopic studies were carried out to assess the confirmation of extracted aluminium. Combination tanning has been carried out with vegetable tannins and dialdehyde starch tanning chemicals, which are from natural resources. Leathers tanned with aluminum and wattle resulted with a shrinkage temperature of 118ºC as compared to Al-Dialdehyde starch leathers showed around 90-100ºC. Physical strength characteristics such as tensile, tear and grain crack strength met the standard norms. Grain surface of leathers are found to be smooth which has been confirmed through microscopic studies. The study provides a new insight on accomplishing self sustainability through available resources and manufacture of eco-friendly system. Take-Away: 1. Tanzania is endowed with massive kaolin rich in aluminium, which is potential for application in leather industry for sustainable development of leather industry 2. The combination tanning system using aluminium from Tanzania kaolin with wattle tannins or Dialdehyde starch imparts leather with both physical and organoleptic properties that meet the stipulated norms 3. This new tanning system provides new insight on ecofriendly tanning system for the sustainability of leather industry.

Content: The use of vegetable tanning agents alone for pre-tanning as an alternative to synthetic or chromiumcontaining tanning agents is one way of improving sustainability and ecology in leather production. In recent years, a new group of secondary plant compounds, the iridoids or secoiridoids, has been discovered for use as tanning agents. Due to their molecular structure, these substances probably have a reaction mechanism similar to glutaraldehyde, which means that known disadvantages of conventional vegetable tanning such as long process times or weak interactions can be avoided. Currently, a tanning agent from olive leaves with cross-linking active substances deriving from the secoiridoid Oleuropein is commercially available. In order to extend the product range of alternative vegetable tanning agents with covalent cross-linking mechanism by native raw material, we screened a number of further plants for such crosslinking active substances in a preceding project. Extracts from privet leaves showed a particularly high crosslinking activity. Privet belongs to the Oleacea family and is common in Asia with several species. In Europe, the species Ligustrum vulgare can be found everywhere, especially as a hedge plant. In addition to Oleuropein, the privet extracts contain a high proportion of the secoiridoid Ligustraloside A. The secoiridoids are deglycosylated during extraction and thus converted into an activated state. The analytical determination of the active secoiridoid degradation products is not yet possible, so that the quantitative determination of the tannin content is made more difficult. Here, we aimed to develop a technology for the production of leather that is exclusively pre- tanned with privet tanning agents. The development includes the production, characterization and optimization of the plant extracts, the development of the pre-tanning technology and the adaptation of the wet end for the corresponding application areas. The leathers which have been manufactured show high shrinkage temperature and good mechanical properties. They show an inherent coloring, but seem to be suitable for use in automotive interiors, as a comparison of the test results with the technical delivery conditions of automobile manufacturers shows. Take-Away: With a new tanning agent from a native widespread plant, leather of good quality can be produced.

Content: In order to develop a sustainable and low-cost route for tanning, the stabilization of the collagen fibers of the hides with silica compounds has been investigated for many years. In this context, silica nanoparticles have been studied for application in tanning due to their small size and ability to combine with polymeric substrates. This work investigates the potentialities and limitations of the use of alkoxysilanes in leather tanning, introducing silica nanoparticles in the hides, aim for process and product innovation in leather industry. The synthesis of silica nanoparticles was carried out by a typical sol-gel Stöber process. From the silica precursor tetraethoxysilane (TEOS), ammonium hydroxide as catalyst, ethanol and water, the formation of nanoparticles dispersion takes place. Vegetable tanning process was explored by introducing the silica nanoparticles in this stage starting from pickled cattle hide. Shrinkage temperature, tensile strength, softness and color fastness to light were evaluated in the leather samples. The results achieved show that the tanning experiment with only silica, without other tanning agent, did not reach the minimum shrinkage temperature required to be labeled as tanned leather. Conversely, in the presence of vegetable tannin, the shrinkage temperature reached 80°C. The physical-mechanical properties indicated that the enhanced on the tensile strength of vegetable leathers with nanosilica was about 50% and their softness was not affected by the introduction of silica. A lighter colored leather was generated with silica but less stable to light. The tanning chemistry involving silica nanoparticles and collagen is complex, therefore, more studies are needed to explore the influence of silanes on hide stabilization. Take-Away: The physical-mechanical properties indicated an increase on the tensile strength of vegetable leather. Silica did not affected the softness of the leather. A lighter colored leather was generated with the addition of the silica nanoparticles in vegetable tanning.

Content: The triazine-based coupling reagent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) is a promptly water-soluble white solid commonly used in chemical synthesis, which is proven to act as effective tanning agent. This research work provides an experimental evidence that the tanning ability of DMTMM is associated to an increase of the cross-linking density in the collagen molecule. As a result of the coupling reaction, DMTMM is converted into water-soluble by-products that can be removed by washing. Take-Away: chrome free tanning, reaction mechanism

Content: Leather is a kind of natural biomass composite material which is made of animal skin as material by a series of chemical and physical processing. Its main structure is Collagen fibers of three-dimensional network structure. As we all know sheep leather always exist a common problem with low strength, while the strength of leather depended on the woven degree of collagen fibers. Through the past decades, many methods have been tried to improve the properties of sheep leather. The most commonly used methods are retanning. However, the strength enhancement of sheep leather is extremely limited by retanning, although the fullness and softness may be improved. In this study, a new type of multi-epoxy reinforcement agent (IGE) and IGE with the synergistic effect of polyamine (IGE-PA) were used to enhance the strength of sheep leather in tanning and fatliquoring process. Comparing with chromium tanned leather, it was found that under the optimized conditions (dosage: 10%, pH: 8, Temperature: 35℃ for penetration and 45℃ for fixation, tanning time: 10 h) with IGE as the main tanning agent, the tearing strength was increased 56.8%. While when the polyamine as the synergetic agent for IGE, the tearing strength was significantly increased 87.9%. While IGE and IGE-PA were used in fatliquoring process, it has significant reinforcement effect for tetrakis hydroxymethyl phosphonium (THP) salt tanned leather. It was found that under the optimized conditions (Dosage: 2.5%, pH: 7-8, Temperature: 50℃, Time: 2h) with IGE in fatliquoring process, the tear strength was increased 50.24%, while the IGE-PA was used, the tear strength was increased 64.3%. Furthermore, TGA results showed that decomposition temperatures of IGE and IGE-PA enhanced leather were all higher than traditional chromium tanned leather. In addition, SEM results showed that IGE and IGE-PA enhanced leather obtained better opened-up fiber structure. Take-Away: 1. A new type of multi-epoxy tanning agent (IGE) has reinforcement effect for sheep leather especially in tear strength. 2. IGE with the synergistic effect of polyamine (IGE-PA) were used in tanning process, which has a significant enhancement for the sheep leather. 3. IGE and IGE-PA can be also used in fatliquoring process to enhance the strength of sheep leather.

Das Strukturprotein Kollagen ist der Hautbestandteil von Haut und somit geeignet, die Gerbung auf molekularer Ebene zu studieren. Das schon sehr alte Handwerk des Gerbens hat das Ziel die Kollagenmatrix so zu stabilisieren, dass diese stabil und flexibel bleibt, auch wenn die Feuchtigkeit entweicht und das Leder hohen Temperaturen ausgesetzt ist. Als Größe zur Charakterisierung der Gerbung dient die Schrumpfungstemperatur. Erkenntnisgewinn auf molekularer Ebene ist Ziel der Untersuchungen, da die Mechanismen der Gerbung bis heute nicht vollständig verstanden sind und grundlegend für die Synthese neuer Gerbstoffe sind. Die Kinetik der Assemblierung von Kollagenmonomeren zu Fibrillen wird spektroskopisch studiert. Der Einfluss von Additiven kann somit auf molekularer Ebene evaluiert werden. Ergänzend wird die Morphologie der Assemblate betrachtet. Studien der anschließenden Deassemblierung liefern Informationen über die Festigkeit der Kollagenmatrix. Für die Korrelation der Modellreaktion mit dem Realsystem der Gerbung werden Schrumpfungstemperaturen gemessen und Strukturuntersuchungen durchgeführt. Für diese Untersuchungen wird Hautpulver eingesetzt, um homogene Ergebnisse zu garantieren. Drei praxisrelevante Stoffgruppen, nämlich Chrom, Aldehyde und Polyphenole, wurden untersucht. Der Hauptgerbstoff Chrom zeigt bei den Assemblierungsuntersuchungen nur geringe Auswirkungen auf das Modellsystem. Die Deassemblierung hingegen lässt die gute Gerbeigenschaft klar erkennen. Zur Erklärung des Streifenmusters, das bei chromgegerbten und somit positiv gestainten Fibrillen im TEM zu erkennen ist, wurde ein theoretischer Ansatz unternommen. Glutaraldehyd und Formaldehyd werden zur Gerbung benutzt. Aldehyde vernetzen die Kollagenmatrix kovalent. Die Untersuchung der homologen Reihe der Dialdehyde wurde hinsichtlich einer Tendenz oder einem Optimum in der Moleküllänge untersucht. Die Aldehyde vernetzen die Monomere, sodass in den Assemblierungskinetiken nur verminderte Plateauhöhen erreicht werden. Die Minimierung der Plateauhöhe kann nicht quantitativ mit der Gerbwirkung gleichgesetzt werden. Mit Aldehydzusatz assemblierte Fibrillen haben ein unverändertes Erscheinungsbild. Die Schlussfolgerung ist, dass die Fibrillenstruktur nicht verändert, aber dezimiert ist. Da nur Formaldehyd, Glyoxal und Glutaraldehyd als reine wässrige Lösung vorlagen mussten die andern drei Dialdehyde hergestellt werden. Dabei sind zusätzliche Substanzen in den Lösungen enthalten, die die Ergebnisse stören. Einen Trend, der mit der Moleküllänge einhergeht, konnte nicht beobachtet werden. Dies ist mit der flexiblen Ordnung der Moleküle in Lösung - im Gegensatz zur Kollagenmatrix in der Haut - zu begründen. Eine kombinierte Wirkung von Chrom und Aldehyd konnte bei der Assemblierung nachvollzogen werden und belegt die Annahmen zur Gerbung aus der Literatur, dass die Gerbung über die sauren Seitenketten bzw. über die Aminogruppen geschieht. Die untersuchten Polyphenole haben keine gerbende Wirkung, sind dem Naturgerbstoff Tannin chemisch aber sehr ähnlich, sodass der Unterschied in der räumlichen Struktur liegen muss. Die Kondensate werden bezüglich ihrer Kettenlänge und der Anzahl ihrer funktionellen Gruppen analysiert. Die Störung der Assemblierung ist bei Zusatz von Phenolkondensaten ist stärker als bei den anderen Testsubstanzen, was eine starke Interaktion zeigt. Messungen der Schrumpfungstemperaturen an Hautpulver ergaben, dass die Syntane keinen waschstabilen Effekt haben. Die Anlagerung an das Kollagen ist folglich zu schwach. Parallele TEM-Analysen ergaben, dass der pH-Wert bei der Vernetzung einen Einfluss auf die Intensität der Streifung hat. Mit zunehmendem pH-Wert erscheint die Streifung intensiver, bis hin zu einer erkennbaren Substreifung. Bei verschieden hohen Schrumpfungstemperaturen zeichnen sind zwei Aussagen ab. Zum einen ist mikroskopisch klar zu erkennen, wenn die Probe denaturiert ist, also über ihrer Schrumpfungstemperatur gekommen ist. Zum anderen ist ein leicht verminderter D-Abstand mit zunehmenden Schrumpfungstemperaturen zu verzeichnen. Besitzen Additive eine gerbende Wirkung, so zeigt sich dies nicht analog im Assemblierungsmodell oder in der Morphologie der Fibrillen. Eindeutige Rückschlüsse sind nicht zu ziehen. Bei der Deassemblierung äußert sich die Gerbwirkung aber immer durch eine verminderte Löslichkeit der Matrix. Daher ist dies eine wertvolle Technik für die Grundlagenforschung in der Gerbung.