Polyurethane (PU) is usually prepared by the reaction of isocyanate or terminal NCO prepolymer with polyol or polyamine. Among them, polyol is the main raw material in polyurethane chemistry. According to different monomers, synthesis processes and molecular structures, polyols can also be divided into two major categories: polyether and polyester.
What is polyol?
Polyol, also known as polyhydric alcohol, is a chemical compound that contains multiple hydroxyl (-OH) groups. Polyols are widely used in various industries due to their unique properties.
Types of polyol
1. Polyether polyols
– These are made by the reaction of epoxides (such as propylene oxide or ethylene oxide) with a starter molecule like water, alcohols, or amines.
– Polyether polyols are known for their good flexibility, low viscosity, and excellent hydrolytic stability. They are commonly used in the production of flexible polyurethane foams, coatings, adhesives, and sealants.
2. Polyester polyols
– Synthesized by the condensation reaction of polybasic acids (such as adipic acid, phthalic acid) and polyhydric alcohols (such as ethylene glycol, propylene glycol).
– Polyester polyols offer good mechanical properties, high heat resistance, and good adhesion. They are mainly used in the production of rigid polyurethane foams, thermoplastic polyurethanes, and polyester resins.
3. Bio-based polyols
– Derived from renewable resources such as vegetable oils, sugars, and lignin.
– These polyols are environmentally friendly and have gained increasing attention in recent years. Examples include soy-based polyols, castor oil-based polyols, and sugarcane-based polyols. They can be used in various polyurethane applications similar to traditional polyols.
4. Specialty polyols
– Include fluorinated polyols, silicone polyols, and hyperbranched polyols.
– Fluorinated polyols provide enhanced chemical resistance and low surface energy. Silicone polyols offer improved hydrophobicity and thermal stability. Hyperbranched polyols have a highly branched structure, resulting in unique properties such as low viscosity and high reactivity.
The relationship between polyester polyols and polyurethanes and their importance
Polyester polyols are one of the key raw materials for synthesizing polyurethanes. Polyurethanes, with their excellent physical properties such as high elasticity, wear resistance, and oil resistance, are widely used in many fields such as coatings, adhesives, foam plastics, and elastomers. The structure and properties of polyester polyols directly determine the quality of polyurethanes, so their importance in the polyurethane industry is self-evident.
The impact of hydrolysis on polyurethane performance and the significance of adding anti-hydrolysis agents to polyester polyols
Under specific circumstances, polyester polyurethanes are easily affected by factors such as moisture, temperature, and acids and bases and undergo hydrolysis. Hydrolysis will cause the molecular chain of polyurethane to break, the molecular weight to decrease, and then significantly reduce the performance of polyurethane. Specific manifestations include weakened mechanical properties, changed viscosity, and deteriorated water resistance. Adding anti-hydrolysis agents to polyester polyols can inhibit the hydrolysis of polyester polyols from the source, thereby improving the hydrolysis resistance of polyurethanes and prolonging their service life.
The mechanism of action of anti-hydrolysis agents
In polyester polyols and polyurethanes, the ester bonds undergo hydrolysis and breakage, which leads to a decline in the performance of the materials. The hydrolysis of ester bonds reduces the molecular weight and integrity of the polymers, resulting in decreased mechanical properties such as tensile strength and elongation at break, as well as deteriorated chemical resistance and thermal stability. This degradation ultimately affects the usability and lifespan of the materials in various applications.
The addition of anti-hydrolysis agents can repair the broken ester bonds, inhibit further hydrolysis reactions, and prevent the decline of material properties. These agents can react with the hydrolysis products or interact with the polymer chains to stabilize the molecular structure. By doing so, they effectively maintain the overall performance of the materials, ensuring their long-term usability and reliability in different applications.
see more about anti-hydrolysis agents
Application methods of anti-hydrolysis agents in polyester polyols and Polyurethanes
Anti-hydrolysis agents can be added to both polyester polyols and polyurethanes. In general, the process involves heating, mixing, and stirring to ensure uniform distribution. In many cases, adding the anti-hydrolysis agent to the polyester polyol yields better results. When added to polyester polyols, it can prevent hydrolysis from the source as polyester polyols are used in the synthesis of polyurethanes. This early intervention helps in maintaining the integrity of the ester bonds and overall performance of the final polyurethane product. However, when added directly to polyurethanes, it can also act on the existing ester bonds to inhibit further hydrolysis.
Evaluation of the application effect of anti-hydrolysis agents
To evaluate the application effect of anti-hydrolysis agents in polyurethane, the aging tests can be conducted. Aging tests can simulate the environmental conditions of polyurethanes in actual use, such as high temperature, high humidity, and light irradiation, and test the performance changes of polyurethanes. By comparing the performance changes of polyurethanes with and without anti-hydrolysis agents in aging tests, the anti-hydrolysis effect of anti-hydrolysis agents can be evaluated.
see the effect of anti-hydrolysis in PU/TPU
Conclusion
Adding anti-hydrolysis agents to polyester polyols is of crucial significance for improving the hydrolysis resistance of polyurethanes and prolonging their service life. By selecting appropriate anti-hydrolysis agents, determining the optimal addition amount and addition method, and conducting effective application effect evaluations, the role of anti-hydrolysis agents can be fully exerted, and the quality and reliability of polyester polyols and polyurethanes can be improved. With the continuous progress of technology, the performance of anti-hydrolysis agents will continue to improve, and their application prospects in polyester polyols will be even broader.
