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Removing Moisture in Polyurethane Using Molecular Sieve Powder

Molecular sieve powder provides the complete answer to moisture scavenging problems in a wide various of applications range from polyurethane based plastics, coating, sealants, caulks, adhesive formulations of various types to pigment drying, solvent drying, etc.

polyurethane adhesive

Choose the Right Type of Molecular Sieve Powder

Don't know which type of molecular sieve powder fits your polyurethane system? Read the following details and find the one most suitable for your products.

Why Moisture is a Problem in Polyurethane?

Moisture in polyurethane materials is easy to cause polyurethane bubble, affect viscosity, curing time and pot life of the products, that must be well controlled in your finished products.

1. Ideal Polyurethane Formation Reaction

Polyurethane is formed through an addition reaction between an isocyanate (R-NCO) and a polyol (R'-OH). This reaction can be represented as follows:

 

R1​−NCO + R2​−OH → R1​−NHCOO−R2

 

In this equation, R1 and R2 represent the alkyl or aryl groups of the isocyanate and polyol, respectively, NCO represents the isocyanate group, and OH represents the hydroxyl group.

2. Impact of Moisture on the Reaction

If moisture is present in the system, the hydroxyl groups (-OH) in water can react with isocyanate groups, leading to two main issues:

a. Carbon Dioxide Formation: The hydroxyl group in water reacts with isocyanate groups, leading to the formation of carbon dioxide (CO2), which is released through an elimination reaction. This reaction is represented as:

 

2(R1​−NCO) + H2​O→R1​−NHCONH−R1​+CO2​

 

This reaction consumes two isocyanate groups to produce one molecule of carbon dioxide, which not only reduces the amount of isocyanate available for polyurethane formation but also leads to the formation of bubbles in the polymer mixture due to the release of CO2 gas.

3. Issues caused by moisture

  • Gas Formation and Bubbling: The reaction between water and isocyanate can produce carbon dioxide (CO2) gas, which can become trapped within the curing polyurethane, causing bubbling and defects.

  • Increased Viscosity: The presence of moisture can increase the viscosity of the polyurethane mixture, making it difficult to apply and work with.

  • Premature Curing: Moisture can accelerate the curing process, leading to premature curing and a shorter pot life. This reduces the time available for the application and manipulation of the polyurethane, potentially leading to incomplete or improperly cured products.

  • Physical Property Compromise: The side reactions initiated by moisture can compromise the physical properties of the cured polyurethane, such as its strength, flexibility, and durability.

  • Corrosion Risk: Acidic gases, like CO2, produced from the reaction with moisture can cause corrosion of metal components in contact with the polyurethane.

How to Select the Molecular Sieve Powder

Choose the right molecular sieve powder is essential for your polyurethane product, ensuring the finial products qualified quality and high poformance.

Molecular Sieve Powder 3A

Only adsorb water. All other molecular sieve powder 4A, 5A, 13X have larger pore opening, and can adsorb other molecules such as nitrogen. Such molecules will be desorbed again when water is adsorbed. And hence there is possibility of bubbles being formed in the coating.

Molecular Sieve Powder 4A

Have larger pore opening than molecular sieve powder 3A. There is possibility of bubbles being formed in the coating. Must pay attention if it is workable in your system.

Molecular Sieve Powder 3A LPT

Molecular Sieve Powder 3A LPT is improved molecular sieve powder 3A. Suitable for polyurethane systems that require long pot-life.

Molecular Sieve Powder 4A LPT

Molecular Sieve Powder 4A LPT is improved molecular sieve powder 4A. Suitable for polyurethane systems that require long pot-life.

Molecular Sieve Powder 5A

Have larger pore opening than molecular sieve powder 3A. There is possibility of bubbles being formed in the coating. Must pay attention if it is workable in your system.

Molecular Sieve Powder 13X

Have larger pore opening than molecular sieve powder 3A. There is possibility of bubbles being formed in the coating. Must pay attention if it is workable in your system.

Oxygen Generation

Hydrogen Purification

Air Dryer

Medical Oxygen Concentrator

Flower Drying

Chromatography

Cat Litter

Transformer Breather

Container Drying

Transformer Breather

Polyurethane Moisture Removal

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