Published in the journal Collagen and Leather in March 2026, the study reports on the synthesis and application of a copolymer named ATMA-DMAS, which functions as a fatliquor for both chrome-tanned and chrome-free leathers. The primary objective of the research was to address the high chemical oxygen demand (COD) and poor fiber fixation associated with conventional fatliquoring agents, which typically rely on sulfated or sulfonated oils. By engineering a polymer with dual ionic character, the team aimed to create a formulation that could interact effectively with the varying electrostatic properties of collagen in different tanning systems.
The synthesis of the ATMA-DMAS copolymer involved a multi-step chemical process beginning with the quaternization of triethylamine using allyl bromide to produce allyltrimethylammonium bromide (ATMA). This cationic monomer was then copolymerized with dimethylaminoethyl methacrylate (DMAEMA) through free radical copolymerization. To introduce zwitterionic character, the resulting copolymer was subjected to sulfonation using 1,3-propanesultone. The final product, ATMA-DMAS, was characterized using Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), and electrospray ionization mass spectrometry (ESI-MS). These analytical techniques confirmed the successful incorporation of cationic, anionic, and hydrophobic functionalities into the polymer structure, validating the intended chemical design.
A key feature of the ATMA-DMAS copolymer is its pH-responsive ionic behavior, which allows it to adapt to different tanning environments. Zeta potential measurements revealed an isoelectric point at approximately pH 3.5. At acidic pH levels below this point, the copolymer exhibits a positive surface charge, dominated by cationic quaternary ammonium groups. As the pH increases beyond the isoelectric point, the surface charge becomes increasingly negative due to the deprotonation of anionic groups such as sulfonates. This tunable ionic behavior is critical for enhancing compatibility with both chrome-tanned leather, which typically has an anionic collagen surface, and chrome-free alternatives, which may present cationic or neutral surfaces.
The study evaluated the performance of the amphoteric copolymer in both chrome-tanned and chrome-free leather systems. For the experimental trials, re-tanned sheep leather samples were processed through standard post-tanning sequences. The experimental leather was treated with the ATMA-DMAS copolymer blended with jatropha oil in a 1:1 weight ratio, while the control leather received a commercial emulsified fatliquoring product. The fatliquoring process was conducted at 50 degrees Celsius, with subsequent fixation steps involving targeted acidification to promote stable ionic bonding between the copolymer and collagen fibrils. The materials and methods were standardized to ensure uniform operational parameters across both control and experimental trials, allowing for a direct comparison of performance metrics.
In chrome-tanned leather, the amphoteric copolymer demonstrated significantly higher fatliquor uptake compared to conventional systems. The experimental leather achieved a fatliquor uptake of 85.2 percent, whereas the control leather recorded an uptake of 68.7 percent. This increased exhaustion efficiency suggests that the copolymer interacts more effectively with the collagen matrix, leading to deeper penetration and more uniform distribution. The improved uptake is attributed to the dual ionic character of the copolymer, which facilitates electrostatic interactions with both the cationic and anionic sites on the collagen fibers, thereby reducing surface migration and enhancing internal fixation.
Mechanical and thermal properties of the fatliquored leather also showed notable improvements. The shrinkage temperature of the experimental chrome leather increased to 112 degrees Celsius, compared to 103 degrees Celsius for the control. Additionally, the tensile strength of the experimental leather reached 32.25 N/mm², representing a 46.7 percent increase over the control. Softness was also enhanced, with the experimental leather achieving a softness index of 8.3 on a scale where 7 to 10 indicates a very soft nature, compared to 6.1 for the control. These results indicate that the amphoteric copolymer not only improves the physical handle of the leather but also contributes to its structural integrity and thermal stability.
Environmental benefits were also observed in the effluent generated during the leather processing. The chemical oxygen demand (COD) of the effluent decreased from approximately 42,000 mg/L in the conventional system to approximately 32,000 mg/L in the amphoteric system. This reduction of about 24 percent indicates a lower environmental burden, as less chemical waste is discharged into the wastewater. The high exhaustion efficiency of the copolymer minimizes chemical wastage and lowers the residual float load, which directly contributes to the reduced COD. This cleaner production profile aligns with the goals of sustainable leather manufacturing and evolving sustainability regulations such as REACH and ZDHC.
Similar improvements were observed in chrome-free leather, demonstrating the versatility of the copolymer across different tanning systems. The experimental chrome-free leather exhibited enhanced softness and fullness, with a more compact and plump texture compared to the control. The amphoteric copolymer effectively penetrated the collagen matrix, resulting in a more open and well-separated fiber bundle network. This morphological modification was confirmed by scanning electron microscopy (SEM), which showed increased inter-fibrillar spacing in the experimental samples. The improved fiber separation reduces inter-fibrillar friction, leading to greater flexibility and softness in the final leather product.
Surface wettability assessments further corroborated the findings of improved performance. Static water contact angle measurements showed that the amphoteric polymer-treated leather exhibited increased hydrophobicity compared to the control. For chrome leather, the average contact angle increased from 98.29 degrees in the control to 103.15 degrees in the experimental sample. For chrome-free leather, the angle increased from 98.74 degrees to 104.89 degrees. This shift is attributed to the amphiphilic nature of the copolymer, where hydrophobic segments align outward, effectively modulating surface energy. The enhanced hydrophobicity suggests improved moisture barrier properties, which can contribute to better dimensional stability and resistance to microbial growth in the finished leather.
Fourier transform infrared spectroscopy (FTIR) analysis of the fatliquored leather provided evidence of strong molecular interactions between the amphoteric copolymer and the collagen matrix. In the experimental samples, there was a significant enhancement of the amide I and amide II bands, reflecting stronger collagen-copolymer interaction through ionic or hydrogen bonding mechanisms. Additional peaks associated with sulfonate groups and ether functionalities were observed in the experimental leathers, confirming the incorporation of the amphoteric polymer. The presence of these spectral features validates the chemical binding and uniform distribution of the copolymer within the leather matrix, underpinning its role in improving fiber interaction and functional properties.
The study highlights the potential of amphoteric copolymers as a scalable and eco-efficient alternative to conventional fatliquors. The ATMA-DMAS copolymer offers a universally compatible solution that can be applied to both chrome and chrome-free leather processing. Its ability to achieve high exhaustion rates, improve mechanical properties, and reduce effluent COD makes it a technically viable and market-competitive option for the leather industry. The research provides a fundamental advancement in understanding collagen-copolymer interactions, contributing to the development of sustainable leather manufacturing practices that meet the demands of modern environmental regulations and consumer preferences for eco-certified materials.
Despite the promising results, the study notes that chrome-free leathers still exhibit certain limitations compared to chrome-tanned leathers, such as lower thermal and mechanical stability and inferior color fastness. The amphoteric copolymer helps to narrow this performance gap, but it does not completely eliminate the inherent differences between the two tanning systems. Nevertheless, the current findings demonstrate that the strategic use of amphoteric copolymers can significantly enhance the quality and sustainability of leather production, offering a viable path toward cleaner and more efficient manufacturing processes.
Subject of Research: Development and application of an amphoteric copolymer for sustainable leather fatliquoring
Article Title: Sustainable fatliquoring for chrome and chrome-free leather using amphoteric copolymers
Article References: Janani, V., Bhalla, A., & Sahu, B. (2026). Sustainable fatliquoring for chrome and chrome-free leather using amphoteric copolymers. Collagen and Leather, 8(1), Article 13. https://doi.org/10.1186/s42825-026-00238-9
Image Credits: AI Generated
DOI: 10.1186/s42825-026-00238-9
Keywords: leather processing, amphoteric copolymer, fatliquoring, sustainable manufacturing, chrome-free tanning, chemical oxygen demand, collagen interaction, polymer synthesis, Sustainable, chrome, chrome-free, leather
News Source: Denise Maddox. (November 10, 2026). Amphoteric Copolymer Enhances Leather Quality and Reduces Effluent Load. Scienmag.
