Views: 0 Author: Site Editor Publish Time: 2025-08-08 Origin: Site
Polyester-based hot-cast polyurethanes are valued for their exceptional toughness, load-bearing capacity, and abrasion resistance. Yet prolonged exposure to moisture can trigger hydrolysis, severely weakening these materials and leading to early failures and costly downtime. Low viscosity anti-hydrolysis agents offer a powerful solution by protecting ester bonds, ensuring polyurethanes maintain their strength, flexibility, and visual quality even in humid or wet environments.
Polyurethane is an incredibly versatile polymer that can be tailored for a wide range of applications. Among its many forms, polyester-based hot-cast polyurethane is widely used because of its exceptional mechanical properties, toughness, and abrasion resistance.
Polyester-based hot-cast polyurethane is a type of elastomer made by reacting polyester polyols with diisocyanates, typically processed in a heated, liquid state (the “hot-cast” method). This results in a thermoset polymer that combines elasticity with strength.
Thanks to its balance of properties, polyester-based hot-cast polyurethane is commonly found in:
Wheels and rollers: For material handling equipment, conveyor systems, and forklifts.
Mining screens: Where excellent abrasion resistance is crucial.
Industrial parts: Such as seals, linings, and protective coatings that require resilience under load and impact.
Despite their benefits, polyester-based polyurethanes have a well-known drawback: they are susceptible to hydrolysis, especially in humid or water-rich environments. Over time, exposure to moisture can break down the polymer chains, leading to significant performance loss.
This vulnerability makes it critical to find ways to protect polyester-based hot-cast polyurethane from premature degradation — which is where low viscosity anti-hydrolysis agents play a vital role.
Hydrolysis is a chemical process in which water molecules break the ester bonds within the polymer backbone. Polyester polyols contain ester linkages, which are sensitive to attack by water, especially at elevated temperatures.
When water penetrates the polymer structure, it can cleave these bonds, effectively cutting the long chains into shorter segments. This molecular breakdown translates into a loss of physical integrity.
When polyester-based polyurethanes undergo hydrolysis, you may observe:
Loss of mechanical strength: The material becomes noticeably weaker, less able to bear loads or withstand impacts.
Cracking or surface degradation: Visible cracks, chalking, or soft spots often appear.
Reduced service life: Parts that were intended to last years might fail prematurely when exposed to water or humidity.
For applications in damp environments — such as outdoor equipment, marine applications, or industrial machinery subject to wash-down — hydrolysis resistance is crucial. Failure to protect against moisture attack can lead to:
More frequent replacements and higher maintenance costs.
Unexpected breakdowns, causing operational downtime.
Safety risks if critical components fail under load.
That’s why selecting the right additives, such as low viscosity anti-hydrolysis agents, is an essential strategy for ensuring long-term durability.
Anti-hydrolysis agents are specialized chemical additives designed to enhance a polymer’s resistance to degradation by moisture. They work by protecting the susceptible ester bonds in polyester-based polyurethane systems, either by stabilizing them chemically or by physically hindering water’s ability to penetrate and react.
Anti-hydrolysis agents typically function in one or more of the following ways:
Chemical stabilization: Reacting with or blocking the sites that water would otherwise attack, slowing or preventing chain scission.
Scavenging acids or catalysts: Some hydrolysis reactions are accelerated by acidic conditions. Anti-hydrolysis agents can neutralize acids formed during polymer degradation.
Forming hydrophobic barriers: Certain agents create water-repellent zones within the polymer, making it harder for water to reach sensitive ester bonds.
Common anti-hydrolysis agents used in polyester-based polyurethane systems include:
Carbodiimides: React with carboxylic acid end groups to prevent hydrolytic chain cleavage.
Hindered amine stabilizers (HALS): While primarily used for UV resistance, they can also offer auxiliary benefits.
Low molecular weight additives: Designed to migrate slightly within the polymer, providing broader protection.
Each type has strengths and weaknesses, but increasingly, formulators turn to low viscosity anti-hydrolysis agents for ease of use and superior processing benefits.
The viscosity of an anti-hydrolysis agent plays a surprisingly important role in both processing and final performance. Here’s why low viscosity anti-hydrolysis agents are often preferred.
Polyurethane formulations, especially hot-cast systems, require precise mixing to ensure uniform properties. Low viscosity anti-hydrolysis agents blend more easily into polyol components, resulting in:
More uniform distribution of the protective agent throughout the polymer.
Reduced risk of local under-protected regions, which could become failure points.
In contrast, high viscosity additives may resist mixing, leading to streaks or agglomerates.
Because they are less viscous, these agents can more effectively migrate and integrate into the polymer matrix, reaching ester bonds more completely. This enhances the overall protection against water attack.
Highly viscous or solid additives can change the rheology (flow behavior) of polyurethane systems, affecting how they fill molds or cure. Low viscosity agents typically:
Maintain flow characteristics, ensuring clean mold filling and good surface finish.
Preserve important mechanical properties like hardness, elasticity, and tensile strength.
While high viscosity or polymeric stabilizers can be effective, they often come with drawbacks such as:
Difficult dosing and uneven mixing.
Potential interference with curing, leading to longer demolding times or incomplete crosslinking.
Low viscosity anti-hydrolysis agents avoid these issues, making them a smarter choice for many manufacturers.
In hot-cast polyurethane production, low viscosity anti-hydrolysis agents are generally added directly to the polyol component before reacting it with isocyanate. This ensures the agent is thoroughly mixed into the resin.
Typical process steps include:
Preheating the polyol blend (which may include plasticizers, colorants, and the anti-hydrolysis agent) to the target processing temperature.
Mixing under vacuum or with mechanical agitation to remove air and ensure uniform distribution.
Reacting with the isocyanate component and pouring into molds.
Dosages vary by product, but common levels range from 0.5% to 2% by weight of the total formulation. Too little may not provide sufficient protection, while too much could impact curing or cost.
Compatibility is also important:
The anti-hydrolysis agent must be chemically compatible with the polyurethane system (it should not react undesirably with isocyanates or catalysts).
It should not promote phase separation or migration over time.
Consider a manufacturer producing mining screens from polyester-based hot-cast polyurethane. By incorporating a low viscosity anti-hydrolysis agent at 1.2% by weight:
The screens exhibited 60% higher retained tensile strength after 2 weeks in hot water aging compared to unprotected samples.
The overall service life in high humidity conditions nearly doubled, reducing replacement frequency and maintenance costs.
When selecting a low viscosity anti-hydrolysis agent for polyester-based polyurethane, formulators should consider several critical performance parameters.
Lower molecular weight typically correlates with lower viscosity, enabling:
Better mixing and wetting of the polymer chains.
More even distribution, ensuring consistent hydrolysis protection.
However, it must still be large enough to remain in the polymer matrix and not easily volatilize.
Look for data such as:
Retained tensile strength after hot water aging (eg: >80% after 14 days at 70°C immersion).
Elongation retention, showing that flexibility is maintained alongside strength.
Color stability: Some anti-hydrolysis agents can yellow over time, so choose stabilized versions if aesthetics matter.
Influence on curing speed: Ideally, the agent should not slow down the reaction between polyol and isocyanate or require additional catalyst adjustments.
Thermal stability: It should withstand the processing temperatures of hot-cast polyurethane (typically 80-120°C) without degrading.
Polyester-based hot-cast polyurethanes are renowned for their excellent mechanical properties, yet they remain prone to hydrolysis, which can lead to premature failure in humid or water-exposed conditions. Incorporating low viscosity anti-hydrolysis agents is a proven way to overcome this challenge. These additives are easy to integrate, disperse uniformly without disrupting processing, and significantly extend the service life of polyurethane products. They also maintain crucial mechanical strength and visual quality, making them ideal for demanding applications such as wheels, mining screens, and marine components.
To explore advanced low viscosity anti-hydrolysis solutions, we recommend contacting Suzhou Ke Sheng Tong New Materials Technology Co., Ltd. Their expertise and tailored additives can help you achieve superior, long-lasting polyurethane performance. Learn more or get in touch to discuss your specific needs.
