Retanning Agent Research Articles

Influence of Retanning Agents on Physical Characteristics of Snow-White Glove Leather from Goat Skin

The quality of leather is subject to various elements, such as the specific raw material used, and the processing techniques implemented throughout the production process. Goatskin, renowned for its exceptional softness and durability, is frequently employed in the production of gloves owing to its desired attributes, notably its capacity to produce snow-white gloves. Retanning is an essential step in the leather manufacturing process as it significantly improves the characteristics of the leather. Through an investigation into the impacts of distinct retanning agents on goatskin leather gloves, this research endeavor seeks to offer significant knowledge regarding the most effective retanning procedures that can augment the tactile attributes of snow- white leather gloves. In this study, formaldehyde, alum, chromium, and chromium alum were employed as retanning agents. The retanned leathers were assessed by physical parameters, Principal Component Analysis (PCA), and Fourier Transform Infrared spectroscopy (FTIR), then compared to a commercially available snow-white leather glove. The physical characteristics of chrome alum retanned leather showed a high degree of softness (6.60±0.02 mm), good tear strength (1.530±117 N/cm), and tensile strength (1.500±100 N/cm 2 ). The principal component analysis (PCA) also supported that the properties of chrome alum retanned snow-white glove leather closely resemble commercial leather and the result from this study suggested that all factors notably impact the skin's physical quality, except for thickness. Additionally, the FTIR analysis reveals similar functional groups from the different retanned leathers indicated by comparable peaks and stretching patterns. Therefore, chrome-alum could be a well alternative retanning agent for the production of snow-white glove leather.

New materials-based on gelatin coordinated with zirconium or aluminum for ecological retanning

Ecological retanning agent is an effective way to solve the pollution source of leather manufacturing industry. In this study, the gelatin from chrome-containing leather shavings in the leather industry was used to realize sustainable leather post-tanning. The gelatin hydrolysate (GH) coordinated with Zr4+ or Al3+ to prepare eco-friendly retanning agents GH-Zr and GH-Al. The successful coordination between GH and metal ions was characterized by FTIR and XPS. The retanning agents were characterized by FTIR curve-fitting and circular dichroism spectroscopy. The results showed that the conformation of the secondary structure of the polypeptide became ordered and stable after coordinating with the metal ions. The particle size and weight average molecular weight of the retanning agents were ~1700 nm and ~2100, respectively, measured by nanoparticle size analyzer and gel permeation chromatography (GPC). The retanning agents were applied to retanning of chrome tanned leather and glutaraldehyde tanned leather. The abundant free amino from retanning agents can consume the free formaldehyde. Meanwhile, retanning agents can effectively improve the multiple binding sites, resulting in favorable thickening rate (>110 %) and excellent dye and fatliquor absorption rate with ~99.91 % and ~93.18 %. Thus, this strategy can provide a viable choice for solid leather waste and sustainable development of the leather industry.

Cationic amphiphilic acrylic copolymer retanning agent for metal-free eco-leather production

Producing metal-free leather is an effective approach to eliminate Cr pollution and achieve sustainable development of the leather industry. However, the high water sorption of the metal-free leather and the mismatching of the charge properties between the metal-free tanned leather and anionic post-tanning chemicals result in the unsatisfactory properties of the leather products, thereby restricting the industrial application of metal-free tanning technologies. Herein, a series of cationic amphiphilic acrylic copolymers (PSD) with different molar ratios of hydrophobic monomer to cationic hydrophilic monomer were synthesized and applied in the retanning of a metal-free tanned leather. PSD can effectively penetrate to the hierarchy of collagen fibril of leather and firmly bind to collagen carboxyls to form a thin hydrophobic coating on the fibril surface due to their small particle size (< 70 nm), excellent surface activity and cationic amine groups (3–27 μmol/g). Molecular dynamics (MD) simulations confirm that the primary driving force between PSD and collagen is electrostatic interaction. MD simulations and water resistance tests demonstrate that the amphiphilic PSD provides the metal-free leather with moderate hydrophobicity, which indicates the upgrade of the comprehensive properties of leather. PSD retanning enhances the uptake rate of anionic dyes and fatliquors (> 90 %) and endows the metal-free leather with excellent filling effect and bright color. The molar ratio of hydrophilic monomer and hydrophobic monomer plays an important role in the performance of PSD. The hydrophobic segments contribute to the hydrophobicity enhancement of leather, and the cationic hydrophilic segments in PSD contribute to the charge regulation of leather and robust binding of post-tanning chemicals. Hence, the multifunctional PSD retanning agents can fulfill the demands for versatile metal-free leather types and promise to boost the sustainable development of the leather industry.

Effect of Different Retanning Agents on Shrinkage Temperature of Leathers

Retanning of tanned leathers played an important role to raise the shrinkage temperature characteristic and quantum of retanning agents, where crosslinks are formed with the polypeptide chain of the collagen or other reactive available sites of the collagen. This study is useful for the tanners to determine the percentage of shrinkage by using different retannages. The results revealed that the maximum thermal stability (increase in shrinkage temperature 21-25%) has been found in the basic chromium sulphate retanned leather without destruction of physical properties. Beside this, other types of retannages i-e, mineral retanning, phenolic based retanning, formalin based syntan have been showed thermal stability upto different levels (increase in shrinkage temperature 4-6%,12-15%, 10- 14% respectively) in addition to the development of physical properties such as tensile strength (N/ mm2 ), tear strength (N/mm), fullness , etc. to suit different needs.

The Effect of Amphoteric Polymers on Dyestuff Consumption

In recent years, the importance and use of wet-white tanning technology have increased due to the increase in environmental and health concerns. On the other hand, this technology still has problems related with fixation of dyestuff and fatliquoring agents during wet-end processes. In this study, the effect of the use of different commercial amphoteric retanning agents in different ratios on dyestuff consumption was investigated. For this purpose, amphoteric polymers were used at the beginning of dyeing process of syntan tanned leathers and the concentrations of remaining dyestuff after the process have been measured using UV-Vis Spectrophotometer for each trial. From the results it was concluded that the use of amphoteric polymers in retanning of wet-white tanned leathers significantly decreased the remaining dyestuff in the floats. Also, the physical and mechanical properties of the final leather were not adversely affected up to the use of 6 wt% the amphoteric polymer.

Utilization of Collagen Wastes as Bioretanning Agent and Effects on the Mechanical Properties of Leather

A bioretanning agent was developed as an alternative to conventional synthetic retanning agents to pave the way for sustainability in the leather industry. Tanned solid waste shavings obtained from leather processing was utilized to produce a proteinic sub-structure for constitution building block of the bioretanning agent's backbone. The protein hydrolyzates were acquired with different molecular weights and the hybrid biopolymers were obtained by grafting the hydrolyzates with acrylic acids (AAc) and acrylamides (AAm). To evaluate the properties imparted by the designed bioretanning agent, it was incorporated into the leather in the retanning processes and compared to the control samples fabricated with conventional procedures. Penetration of hybrid biopolymer into the matrix for retanning was achieved easily, and using low and high molecular weight biopolymers have been recorded by 20% and 23% of improvement on the mechanical performance of the leather samples, respectively. The ratio of the hydrolyzate and AAm/AAc was found to be fitted at 1:2 for both. Furthermore, as per the evaluation of the leathers retanned by novel biopolymer, the results were promising in terms of technical viability and revealed that the biopolymer usage could enhance the mechanical performance of the leather while benefiting from the waste-to-wealth approach.

Preparation and application of novel amphoteric acrylic retanning agents to improve dye absorption

Amphoteric acrylic polymers are some of the commonly used leather retanning agents, and possess assistant-dyeing function in contrast to traditional anionic acrylic retanning agents.

Leather wastes into high-value chemicals: Keratin-based retanning agents via UV-initiated polymerization

Eco-friendly keratin-based retanning agents have aroused widespread interest in leather manufacturing, because they recycle the biomass wastes for sustainable industry. However, the poor filling effect and binding strength of hydrolyzed keratin from bovine hair wastes limit its application for leather retanning. Here we reported a series of polyacrylate-modified keratin (PMK) retanning agents synthesized from vinyl monomers and bovine hairs via a surfactant-free and UV-initiated polymerization. The obtained spherical PMK retanning agents exhibited ideal characteristics, such as appropriate molecular weight (13–22 kDa) and particle size (86–110 nm), and good colloidal stability in the tanning bath (pH 5.5). We further validated these agents for retanning bovine shoe upper leather. Compared with FB (i.e., a commercial retanning agent), leather retanned with PMK75 showed increased thickness (∼50%) and reduced Δb* (∼80%), suggesting excellent filling properties and yellowing resistance. Moreover, the retanning agent afforded the products improved physical properties (e.g., tensile strength ∼17.3 N/mm2, tear strength ∼72.7 N/mm and elongation at break ∼75.4%) and sensory properties (e.g., compression thickness ∼0.25 mm and resilience thickness ∼0.21 mm). This work not only offered a robust method for preparing low-cost retanning agents in sustainable industry, but also provided more opportunities for recycling biomass-based wastes aiming to closed-loop economy.

Nonionic Short Fluorocarbon Chain Surfactants for Improving Application Properties of Acrylic Resin in the Retanning of Wet-blue Leather

Acrylic resin (AR) is one of the most commonly used leather retanning agents owing to its excellent selective filling property and low cost. However, there are some defects affecting the quality of wet-blue leather in the practical application of AR, such as “excessive convergence”, “detanning”, and “fading”. Herein, the nonionic short fluorocarbon chain surfactants (F6-m) combined with AR for retanning wet-blue goat leather to further improve the application properties of AR. In a series of comparative experiments, the grain surface state and mechanical properties of leather retanned with 4 wt% AR and 2wt% F6-400 are preferred. Moreover, after dyeing, the dye adsorption rate and a* (red-greenness) value of AR/F6-400 retanned leather are higher than that of leather retanned with AR alone. The above issues reveal that F6-400 can improve application properties of AR in the retanning of wet-blue leather to a certain extent, benefiting to further upgrade the quality of leather.

Functional nanocomposite based on waterborne polyurethane and layered double hydroxide as a flame retardant for leather

Incorporation of multifunctional nanomaterials into collagen fibers is considered as a promising approach to fabrication of multifunctional leather. In this study, an effective approach for improving the flame retardancy of leather and promoting absorption of anionic dyes and fatliquoring agents on leather through introduction of layered double hydroxide (LDH) into waterborne polyurethane (WPU) by physical blending method to prepare WPU/LDH nanocomposite as leather retanning agent has been reported. The results indicate that the original form and intercalated form of LDH both coexist in the WPU/LDH composites, and the LDH is evenly dispersed in WPU. Moreover, hydrogen bond and electrostatic interaction exist between LDH and WPU. The penetration and dispersion of LDH in collagen fibers improves the thickening rate, dye uptake, softness and mechanical properties of leather. Moreover, the introduction of LDH also improves the flame retardancy of the resulting leather. Compared to the leather treated with WPU, the ignition time, the length of charring, and the mass loss rate of the leather treated with WPU/LDH-8% are reduced by 74.2%, 58.6% and 46.2%, respectively, and the limiting oxygen index (LOI) value increases from 23.6% to 26.0%. The peak heat release rate (PHRR) and total heat release (THR) of the leather treated with WPU/LDH-8% decreased by 34.4% and 28.7% compared to that of the leather treated with WPU. The excellent flame retardancy of leather can attributed to the barrier effect of highly reinforced carbonaceous char, retarding the escaping of flammable volatiles in the leather and shielding the further damage of the leather by external heat irradiation. The high performance nanocomposites are promising for applications in the manufacture of flame-retardant leather. In addition, the reduction of BOD and COD of the WPU/LDH post-tanning systems is beneficial to reduce the impact of retanning agents on the environment, which is of great significance to “cleaner production”.

Melamine Ethoxylates as Novel Formaldehyde Free Replacements of Resin Re-Tanning Agents

Melamine urea formaldehyde condensates or resin re-tanning agents are commonly used in the leather industry. They give riseto homogeneous filling, are easily and widely applicable, but generally contribute to free formaldehyde, measurable in emissionor extraction methods. Many projects to resolve this issue have been carried out. The weakness of the resin re-tanning is the reversibility of the bond formation between formaldehyde and two amino groups. The formaldehyde forms a methylene group after condensation with two amino groups and releases water. This methylene group can be hydrolyzed under acidic conditions to release formaldehyde again, reversing the synthesis.&#x0D; Melamine ethoxylates were found to be a formaldehyde free, stable, and easily applicable alternative. Besides the fact that they are made without formaldehyde, it proved to be possible to incorporate renewable components into their synthesis, giving rise to an even more sustainable product. Another sustainable aspect of this chemistry is the delivery of the potential product as a concentrated liquid versus most resin re-tanning agents being placed into the market as spray dried powders, consuming significant amounts of energy in the process.&#x0D; Melamine ethoxylates show advantages in application on leather in comparison with classical resin re-tanning agents. An insightinto the scope of application will be given, showing that melamine ethoxylates can be considered a formaldehyde free replacement for resin re-tanning agents

Synthesis of a Waterborne Melamine Resin and its Retanning Behaviors Investigation

Recently, the application of waterborne melamine resin (WMR) is greatly increasing in the leather industry because of its convenient operation, but it often suffers from poor storage stability. Here, two waterborne melamine resin retanning agents (WMRs) with high storage stability were prepared using melamine, glutaraldehyde and collagen hydrolysates (CHs) as raw materials at different mole ratios. FTIR, 13C-NMR and XPS were used to characterize the chemical structure of synthesized resins, and their retanning behaviors for wet blue and wet white leather were fully investigated. The particle sizes of WMR1 and WMR2 were 28.73 nm and 8.78 nm, and their zeta potentials were 4.0 and 4.5, respectively. The introduction of CHs provided not only good water solubility but also amphoteric properties to synthesized resins, thereby resulting in high absorption of retanning and fatliquoring agents. Moreover, the retanning application investigation of WMRs manifested good storage stability and excellent overall performance, which are comparable with commercial retanning agents. This work showed that glutaraldehyde and CH could be used as starting materials in the synthesis of environmentally friendly WMR.

Polyurethane-based retanning agents with antimicrobial properties

Abstract Polyurethane-based retanning agents with antimicrobial properties were synthesized by the chemical incorporation of ciprofloxacin (CPFX) units into polyurethane chains. The chemical structures were characterized by Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). Then, the retanning agents were applied in the leather retanning process. Owing to the conjugation of CPFX into polyurethane chains, the molecular weight increases, further leading to the decrease in hydroxyl value and increase in particle size. The shrinkage temperature was improved after retanning. Owing to the filling of retanning agents in the gap of collagen fibers, the average thickness of leather increased by 65.8%. The mechanical properties of leather were visibly improved because of the large number of –COOH coordinate with Cr3+ and more hydrogen crosslinking with carboxyl group, amino group, and hydroxyl group of leather collagen. Furthermore, leather retanned by these polyurethane-based retanning agents presented good antimicrobial properties. The antibacterial activity could be conserved above 89% even after rinsing for ten times.

Utilization of Acacia seyal(Talih) bark powder Extract for Manufacture of Upper leather as Alternative Retanning Agent

This study was conducted at Alfula area which located at longitude 20-28 south and latitude 11-43 north the over all objective of this study were to fill the looser and softer parts of leather in order to produce leathers of more uniform physical properties. This is to investigate that the process will allow for the production of unlined footwear, to improve on the chemical stability of the leather, prompt rapid finishing and delivery to the customer. The plant has been evaluated and reported for application in the retanning of the leather. The process involves extracting the barks of Acacia seyal (Talih) for 1 hour with distilled water (1:10 w/v) at temperature above 80˚C. The Talih extract once was applied during prepared the retanning of wet blue leathers. To determine The efficacy of the pontency and effectiveness of the Acacia seyal (Talih) and extract during the retanning of wet blue leathers when the control and experimental retannage methodologies was applied was determined. The result of Acacia seyal (Talih) retanned compared to Acacia pycnantha(Wattle) retanned leathers. Acacia seyal (Talih) showed good grain tightness and retanned leathers were found to be better than Acacia pycnantha(Wattle) retanned. Further analysis of physical characteristic tests indicated that it can be used as an alternative retanning material.

Effect of cationic monomer structure on the aggregation behavior of amphoteric acrylic polymer around isoelectric point

Amphoteric polymer can be used as retanning agent in leather manufacture. It is particularly useful in chrome-free tanning systems since it can regulate the charge properties of chrome-free leather and enhance the fixation of anionic post-tanning chemicals in leather. However, the aggregation and precipitation of amphoteric polymer retanning agents around the isoelectric point (pI) hinder their wide application. Herein, we synthesized five amphoteric acrylic polymers (AAPs) by free radical copolymerization with acrylic acid and five different cationic acrylic monomers. The effect of cationic monomer structure on the aggregation behavior of AAPs was investigated. The aggregation of AAPs in aqueous solution showed pH and concentration dependence. Light scattering analysis showed that Poly (AA-co-MAPTAC) and Poly (AA-co-DMAPMA) were in the shape of coiled linear flexible chains with small particle size (Rg 7.6 nm and 14.8 nm, respectively) near the pI. However, Poly (AA-co-DAC), Poly (AA-co-DMC) and Poly (AA-co-DMAEMA) were in the shape of hollow spheres and exhibited serious aggregation. Quantum chemical calculations suggested that the amide groups in the cationic monomers MAPTAC and DMAPMA enhanced the nucleophilicity of AAPs. Thus the corresponding AAPs could carry a large number of cationic charges to slow their aggregation when the pH just climbed over the pI. The results are expected to provide theoretical reference for the synthesis and widespread application of AAPs.

Effective utilization of tannery hair waste to develop a high-performing re-tanning agent for cleaner leather manufacturing

Accumulation of hair waste is a major burden to the leather industry, causing a negative impact on the industry's sustainable development. The industry is already bogged down by the usage of synthetic re-tanning agents that are not only extremely challenging for biodegradation but also release free-form of formaldehyde in the final leather stage. This research work focuses on developing a formaldehyde-free bio-based re-tanning agent from hair waste. In order to do so, hair waste is subjected to alkali hydrolysis and subsequently graft-copolymerized with methacrylic acid (MAA). These treatments were optimal using 20 % (w/w) sodium hydroxide and thermal activity at 90 °C. This resulted in effective hydrolysis of red sheep hair, which was the ideal candidate in this study. The hydrolysate was subjected to monomer in situ polymerization (using MAA) with potassium per sulfate/sodium meta-bisulphite redox system, leading to the development of keratin hydrolysate-g-methacrylic acid (KH-g-MA) copolymer (this was noted both at a laboratory level and pilot scale). The obtained KH-g-MA copolymer exhibited ideal characteristics such as increased protein content (78.3 ± 1.2), appropriate particle size (1516 nm), suitable pH (5) and required viscosity of 512 cP. The developed KH-g-MA copolymer was then applied as a re-tanning agent in the leather manufacturing process. Significant improvement in leather's mechanical strength characteristics was observed. In addition, the organoleptic properties of leather such as fullness, softness and grain tightness showed much improvement. Scanning electron microscopy (SEM) showed an enhanced surface smoothness and filling of the voids in experimental leather in comparison to the control leather. This recycle and reuse strategy of hair waste not only helps resolve issues with handling of hair solid waste but also results in producing an eco-friendly re-tanning agent in leather manufacturing, thereby paving the way for cyclic economic utilization and cleaner environment.

Preparation and assistant-dyeing of formaldehyde-free amphoteric acrylic retanning agent

With the enhancement of environmental protection consciousness, concerns have been raised about non-toxic and biodegradable leather retanning agents. According to the European standard 2002/231/EC, the free formaldehyde content of leather products should be less than 150 mg/kg. As one of the retanning agents in the market, the content of free formaldehyde in the Multifunctional retanning agent (MTA) is 372.22 mg/kg and higher than the limit value. In this work, glutaraldehyde as an alternative of formaldehyde was used to modify acrylic polymer and an amphoteric acrylic retanning agent was prepared. Then it was used in retanning process, and its retanning and assistant-dyeing properties were investigated. The results showed that the free formaldehyde content of amphoteric acrylic retanning agent modified with glutaraldehyde was only 4.17 mg/kg. Meanwhile, the presence of amino groups in the amphoteric acrylic retanning agent improved the dyeing properties of leather by electrostatic attraction. Compared with the leather treated with anionic acrylic retanning agent, the residual dye concentration of the dyeing effluent of the retanned leather with amphoteric acrylic retanning agent decreased from 17.4 mg/L to 10.0 mg/L, and the dyed leather had better resistances to friction and water-washing. In addition, the BOD5/COD value of the wastewater after Mannich base polymer retanning was only 0.32, indicating that the retanning agent was biodegradable. Moreover, the leather retanned with amphoteric acrylic retanning agent had good thermal stability, fullness and physical and mechanical properties.Graphical abstract

ИССЛЕДОВАНИЕ БИОЦИДНОЙ ОБРАБОТКИ КОЖИ СРЕДНЕВЕКОВЫХ КНИЖНЫХ ПЕРЕПЛЕТОВ МЕТОДОМ ДОДУБЛИВАНИЯ АЛЮМИНИЕВЫМ КОМПЛЕКСОМ, СТАБИЛИЗИРОВАННЫМ ТРИМЕТИЛОЛМЕЛЕМОМ

It was shown in the past that different re-tanning agents were used as a repellent to enhance the antifungal properties of the hydrothermal stability of the skins of ancient book covers, including the aluminum sulphate-stabilized complex aluminum salt (Al-ЭDA). Although the skin treatment with this re-tanning agent improves the properties of the skin, the collagen structure cannot be considered very safe, i.e., it was relatively low. An additional biocidal substance, catamine AB, was used to ensure the antifungal properties of the treated leather. That is why, a new aluminum complex material has been synthesized for the skin re-tanning of the covers. As a stabilizer of aluminum sulphate, trimethylmeleme was used, for the production of which the meleme material was taken and reacted with formaldehyde. The resulting trimethylolmeleme, having three methylol groups, can form a complex salt when it interacts with aluminum sulphate. The mentioned complex material was filtered and the water part was removed from the crystals formed from the purified liquid by evaporation. The resulting complex salt is soluble, and the crystals left on the filter are insoluble. Both were tested as re-tanning agent samples on the cover leather samples. Treatment with crystals separated from the filtered liquid completely increases the welding point of the skin treated with the tannin extract of ancient leather up to 1000C and more, and up to 75-770C during re-tanning with the complex salt removed from the filter. The research of antifungal properties of the complexes has identified an expressive activity of the difficulty of dissolving complex II in comparison to the compound used earlier. High hydrothermal stability gives strength, less elasticity and other high-performance properties to the leather

Recent Advances in Functional Polyurethane and Its Application in Leather Manufacture: A Review.

Over last few years, polyurethane (PU) has been applied in a number of areas because of its remarkable features, such as excellent mechanical strength, good abrasion resistance, toughness, low temperature flexibility, etc. More specifically, PU can be easily “tailor made” to meet specific demands. This structure–property relationship endows great potential for use in wider applications. With the improvement of living standards, ordinary polyurethane products cannot meet people’s growing needs for comfort, quality, and novelty. This has recently drawn enormous commercial and academic attention to the development of functional polyurethane. Among the major applications, PU is one of the prominent retanning agents and coating materials in leather manufacturing. This review gives a summary of academic study in the field of functional PU as well as its recent application in leather manufacture.

Preparation and Characteristics of Graphene-based Polymeric Leather Fatliquor

Although the research of leather chemicals has experienced considerable advances, it remains imperative and challenging to develop functional ones; especially functionalized fatliquors or re-tanning agents. In consideration with the unique structure and properties, graphene oxide (GO) has been reported as a potential alternative to ameliorate the performance of leather. However, one of the intractable handicaps is how to make graphene penetrate evenly and react with collagen fibers. Here, we demonstrate a method for preparing graphene-based polymeric fatliquor (PFGO) via an amidation reaction between amino-groups of aminated graphene (AGO) and anhydride bonds of maleic anhydride-rapeseed oil copolymer (MRO), which was synthesized by free radical copolymerization. The results show that the as-prepared fatliquor has good emulsion stability and can penetrate into the collagen fibers uniformly. Compared with the control sample without graphene, the antibacterial, electromagnetic shielding, flame retardant and UV resistance characteristics of the PFGO-treated leather were significantly improved. Overall, this e?ective yet promising paradigm may provide an achievable solution toward developing graphene-based polymer composites simultaneously with high physical property and high functional performance.