Leather is flexible, breathable, and durable, but its material structure is not naturally hydrophobic. Leather consists primarily of collagen fibers. These fibers contain polar groups such as hydroxyl, amino, and carboxyl groups, which readily interact with water molecules. Meanwhile, the interior of leather is composed of interwoven collagen fiber bundles, creating a naturally hierarchical porous structure.
When water comes into contact with the leather surface, it may not only be adsorbed by hydrophilic groups on the collagen fibers, but also gradually penetrate into the material through interfiber gaps and pores.
01.
Leather Hydrolysis: From Surface Wetting to Internal Penetration
When leather comes into contact with rainwater, perspiration, a damp cloth, or water-based stains, the moisture may undergo the following three processes:
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01 Surface Wetting Water first spreads across and remains on the leather surface |
02 Pore Penetration Water migrates into the material through pores between the collagen fibers |
03 Fiber Adsorption Hydrophilic groups in the collagen fibers further interact with water molecules |
Water ingress may cause water marks and changes in color and hand feel. Under service conditions involving repeated exposure to moisture, drying, or abrasion, it may also affect the integrity and adhesion stability of the leather surface finish.
Improving the water resistance of leather depends not only on the substrate itself, but also on the ability of the surface coating to form a stable, continuous protective barrier.
As environmental requirements continue to increase, materials such as waterborne polyurethane and waterborne acrylic have become widely used in leather finishing and surface treatment.
Waterborne resins use water as the dispersion medium, offering clear advantages in environmental performance and application safety. However, to enable stable dispersion in water, hydrophilic groups such as carboxyl groups are generally introduced into waterborne systems. Even after film formation, these groups may still interact with moisture.
If the degree of crosslinking within the coating film is insufficient, the polymer chains remain relatively loosely bound. Water may gradually penetrate through hydrophilic sites and free volume within the film, causing water absorption, swelling, or softening, and consequently affecting water resistance, chemical resistance, and adhesion.
The key to improving water resistance is to increase the crosslink density and structural stability of the coating film, thereby reducing pathways for water ingress and diffusion.
To address this need, Langyi Advanced Materials has introduced the HyMax® CA eco-friendly waterborne carbodiimide crosslinker, providing an efficient and environmentally friendly crosslinking solution for carboxyl-containing waterborne resin systems.
HyMax® CA is a series of environmentally friendly waterborne crosslinkers containing carbodiimide functional groups.
HyMax® CA contains carbodiimide groups (-N=C=N-) that can crosslink with carboxyl groups (-COOH) in polymer chains, linking previously separate polymer chains to form a more stable three-dimensional crosslinked network within the coating film.
As the crosslinked structure gradually develops, the coating film becomes denser and more stable, thereby improving its water resistance, chemical resistance, abrasion resistance, and adhesion to the substrate surface.
HyMax® CA can react with carboxyl groups at room temperature. Increasing the temperature and lowering the system pH help accelerate curing; the recommended drying temperature is above 80°C.
1｜Improved Coating Film Water Resistance
HyMax® CA crosslinks with carboxyl groups in waterborne resins, strengthening the connections between polymer chains and reducing pathways for water to enter the coating film, thereby improving its water resistance.
2｜Enhanced Chemical Resistance
Product application evaluations show that HyMax® CA significantly improves the alcohol resistance of waterborne polyurethane coating films and enhances the alkali resistance of waterborne acrylic coating films, providing more comprehensive protection for leather surfaces.
3｜Enhanced Coating Film Adhesion
A stable crosslinked network helps increase the cohesive strength of the coating film and improve its adhesion to the substrate surface, helping maintain the integrity and stability of the surface treatment layer.
4｜Improved Abrasion Resistance and Coating Film Hardness
The three-dimensional crosslinked structure formed by HyMax® CA further improves the abrasion resistance of the coating film and increases the hardness of waterborne polyurethane films, helping leather surfaces withstand everyday friction and scratching.
5｜Balanced Pot Life and Production Workability
HyMax® CA offers a long pot life in certain waterborne resin systems and is insensitive to moisture, providing greater operational flexibility in the production and application of leather finishing formulations.
Improvement in Hydrolysis Resistance and Adhesion with HyMax® CA
HyMax® CA is suitable for carboxyl-containing waterborne resin systems, including waterborne polyurethane, waterborne acrylic, and other carboxyl-containing waterborne polymer systems.
In addition to leather surface treatment, HyMax® CA can be used for the surface treatment of textiles, metals and coil materials, plastic films, and other materials, as well as in adhesives, inks, and coatings.
The HyMax® CA series includes aqueous solution types, emulsion types, high-solids universal products for waterborne and solvent-based systems, and 100% solids products. The appropriate grade can be selected according to the resin system, processing conditions, and target performance.
Leather's natural collagen fiber structure gives it flexibility and breathability, while also making it susceptible to interaction with moisture. Under real-world conditions involving rainwater, perspiration, damp cloths, and cleaning media, leather surface coatings must provide stable and lasting protection.
With its non-toxic, zero-VOC, moisture-insensitive, long-pot-life, easy-to-add, and easy-to-disperse characteristics, HyMax® CA provides a new solution that helps leather surface treatment systems balance environmental requirements, production workability, and overall performance.
