Views: 0 Author: Site Editor Publish Time: 2025-08-06 Origin: Site
Polyester-based polyurethane adhesives have emerged as a popular choice thanks to their remarkable combination of strength, flexibility, and excellent adhesion to diverse substrates. However, exposure to moisture remains a critical challenge that can compromise their durability and long-term reliability over time. This is where liquid additive polycarbodiimide plays a truly transformative role. By integrating this advanced anti-hydrolysis agent into adhesive formulations, manufacturers can effectively protect vulnerable polymer chains from moisture attack, dramatically enhancing the long-term performance, stability, and overall service life of adhesive bonds across demanding industrial and consumer applications.
Polyester-based polyurethane adhesives are high-performance bonding systems created by reacting polyester polyols with diisocyanates, producing flexible yet strong polymers. Unlike many rigid adhesives, they retain elasticity, making them ideal for bonding materials that experience dynamic stresses.
Polyester polyurethane adhesives are widely used across industries due to their excellent balance of strength and flexibility. Common applications include:
Lamination: For flexible packaging films, furniture panels, and decorative overlays.
Automotive: Bonding interior components, trim parts, and weather seals.
Footwear: Attaching soles and uppers where durability and comfort are critical.
General industrial assembly: Where vibration, movement, or thermal expansion could challenge rigid adhesives.
These adhesives are valued for:
Outstanding flexibility, which allows bonded joints to stretch without breaking.
Excellent adhesion to a wide variety of substrates, including plastics, textiles, and metals.
High mechanical strength, ensuring bonded assemblies can endure impacts, pressure, and wear.
However, despite these strengths, polyester-based polyurethane adhesives face a major challenge: vulnerability to hydrolysis in humid or wet environments.
Hydrolysis is a chemical degradation process where water molecules actively break down polymer chains by attacking the ester bonds present in polyester-based polyurethane adhesives. These ester linkages are particularly vulnerable because they can be cleaved when water penetrates the adhesive layer. Moisture interacts with the ester groups, causing the polymer chains to break apart in a reaction known as chain scission. This breakdown reduces the molecular weight and overall integrity of the adhesive material.
The rate of hydrolysis can increase significantly under certain conditions. Elevated temperatures accelerate the chemical reactions, as do acidic environments that catalyze the breakdown process. Mechanical stresses, such as repeated flexing or impact, can exacerbate the damage by creating micro-cracks where moisture can further penetrate. As a result, polyurethane adhesives used in outdoor applications, tropical climates, or in products subject to frequent wetting and drying cycles are particularly prone to hydrolytic degradation.
When hydrolysis occurs in polyester polyurethane adhesives, the consequences can severely impact product performance and safety:
Reduced bonding strength: As polymer chains break down, the adhesive loses its cohesion and adhesion properties, weakening the bond between substrates. This reduction compromises the structural integrity of the bonded assembly.
Delamination: In laminated materials, hydrolysis can cause layers to peel or bubble apart, leading to visible surface defects and functional failure.
Premature adhesive failure: Under high humidity or immersion in water, the adhesive may fail completely, resulting in joint separation. This can cause leaks in packaging, reduced safety in automotive components, or product recalls due to reliability issues.
Industries such as automotive manufacturing, flexible packaging, and footwear—where products frequently encounter moisture—must therefore prioritize improving hydrolysis resistance to ensure long-term durability and customer satisfaction.
Anti-hydrolysis agents are chemical additives introduced into polyester polyurethane formulations to protect polymer chains against moisture attack. They stabilize vulnerable ester bonds, preventing or significantly slowing down the breakdown process.
Anti-hydrolysis agents work by:
Scavenging water molecules or neutralizing acids that catalyze hydrolysis.
Reacting with carboxylic end groups formed during polymer chain scission, effectively “sealing” them to stop further degradation.
Increasing the intrinsic stability of the polymer network.
In environments exposed to humidity, rain, or water immersion, these agents ensure adhesives:
Maintain peel and shear strength over time.
Resist delamination or blistering.
Deliver long-term performance, reducing warranty issues and improving customer satisfaction.
Polycarbodiimides are a class of stabilizers known for their unique ability to react with carboxylic acid groups — the reactive sites created when ester bonds in polyester polyurethanes start to hydrolyze. By “capping” these groups, polycarbodiimides effectively stop further chain cleavage.
While polycarbodiimides can come in solid, resinous, or paste-like forms, the liquid additive polycarbodiimide offers several key benefits:
Easier dosing and handling: Liquids can be accurately metered and poured, unlike powders that can clump or require specialized feeders.
Better dispersion: They mix evenly throughout the adhesive without the need for high-shear equipment or long mixing times.
No impact on clarity or color streaks, which is essential for transparent laminates and aesthetic applications.
The stabilizing mechanism involves two main actions:
Scavenging carboxylic end groups: When ester bonds break, they form carboxylic acids. Polycarbodiimide reacts with these acids, effectively “tying off” the reactive sites and preventing them from catalyzing more chain scission.
Blocking further hydrolysis: By modifying chain ends, polycarbodiimide reduces the number of vulnerable points in the polymer structure, increasing its resistance to water attack.
This dual action makes liquid polycarbodiimide one of the most effective anti-hydrolysis additives available for polyester-based polyurethane adhesives.
The primary benefit is dramatically improved durability under humid or submerged conditions. Adhesives formulated with liquid polycarbodiimide typically show:
Much higher retained peel and shear strength after exposure to hot water, steam, or accelerated humidity aging tests.
Reduced risk of delamination and adhesive failure, even in tropical or outdoor environments.
Liquid additive polycarbodiimide is designed with low to moderate viscosity, ensuring it does not thicken or otherwise disrupt the flow properties of adhesive formulations. This means:
Easy mixing without needing to increase solvents or adjust processing conditions.
Consistent application thickness and spread on substrates.
Polyurethane adhesives can sometimes hydrolyze slowly even in sealed containers, especially under warm or humid storage. Polycarbodiimide stabilizers extend the shelf life by neutralizing early-stage degradation products, ensuring adhesives stay fresh and effective until used.
Compared to solid carbodiimides, the liquid form ensures more uniform dispersion and avoids dust handling issues.
Unlike hindered amine stabilizers (HALS), which mainly protect against UV, polycarbodiimides directly target hydrolysis.
Compared to organophosphites or other antioxidants, they offer specific and robust hydrolysis resistance tailored to polyester systems.
Liquid polycarbodiimide is typically added to the polyester polyol component or the completed adhesive blend during manufacturing. It integrates seamlessly without requiring additional processing aids.
Typical dosages range from:
0.5% to 2.0% by weight on total solids, depending on the expected exposure conditions. Lower amounts may be sufficient for indoor applications, while higher loadings are advisable for marine, tropical, or prolonged humidity exposure.
Liquid polycarbodiimide is generally compatible with:
Common polyester polyols used in adhesive formulations.
Typical aromatic or aliphatic isocyanates.
Conventional catalysts and solvent systems.
Manufacturers should still conduct compatibility checks, especially if unique pigments, fillers, or reactive plasticizers are also in the formulation.
Polyester-based polyurethane adhesives offer outstanding flexibility, strength, and adhesion, but their performance can be compromised by hydrolysis when exposed to moisture. Incorporating liquid additive polycarbodiimide is a proven way to protect polymer chains, greatly enhancing hydrolysis resistance without altering processing or application. This ensures adhesives maintain strong, durable bonds even in humid, wet, or tropical environments — critical for packaging, automotive, and footwear industries.
To explore advanced liquid polycarbodiimide solutions tailored to your adhesive needs, we recommend contacting Suzhou Ke Sheng Tong New Materials Technology Co., Ltd. Their expertise in polyurethane additives can help you achieve superior long-term performance. Visit their website or reach out directly to learn more.
