Molecular sieves play a key role in solving the problem of bubbles in polyurethane adhesives, and their core mechanisms and comprehensive solutions can be summarized as follows:

1. The principle of water removal and defoaming of molecular sieves

1) Selective adsorption of moisture

Molecular sieve is a crystalline aluminosilicate material with a regular microporous structure, with uniform pore size (such as 3A type molecular sieve with a pore size of about 0.3nm). Only molecules with a diameter smaller than the pore size (such as water molecules with a diameter of 0.27-0.32nm) are allowed to enter and be adsorbed, while molecules larger than the pore size (such as CO ₂ and organic solvents) are excluded. This characteristic enables it to efficiently adsorb trace amounts of water in polyurethane systems, blocking the pathway of water reacting with isocyanates (NCO) to generate CO ₂ bubbles, and eliminating chemical bubbles from the source.

2) Dynamic balance control

Molecular sieves absorb moisture rapidly in the early stages of the reaction, and maintain system viscosity stability through desorption in the middle and later stages to avoid gas expansion caused by local overheating. For example, under the conditions of 10 ℃ and relative humidity of 40%, adding 3% molecular sieve to polyurethane prepolymer can stably maintain a bubble free state.

3) Physical filling and interface optimization

Micro sized molecular sieve particles (particle size 1-5 μ m) form physical cross-linking points in the matrix, enhancing the interfacial bonding between the adhesive and the adhered material through adsorption and filling, and reducing residual bubbles caused by pores or stress concentration.

2. The core advantage of molecular sieves in solving bubble problems

1) Efficient water removal and improved stability

The static water adsorption capacity of molecular sieves can reach over 23%, and they can still stably adsorb in high temperature and high humidity environments, avoiding the problems of high water consumption and possible damage to the molecular structure of adhesives caused by traditional high-temperature distillation dehydration.

By removing moisture, molecular sieves significantly improve the storage stability of polyurethane adhesive, extend shelf life, and ensure unchanged performance after long-term storage.

2) Strong process compatibility and easy operation

Molecular sieves can be directly added in proportion during the raw material mixing stage (recommended dosage of 0.5-2%), and uniformly dispersed through high-speed shear dispersion (2000-3000rpm) or ultrasonic assisted dispersion, without the need for complex equipment modification.

When used in combination with defoamers, the amount of defoamer can be reduced by 30% while maintaining a porosity of<1%, balancing cost and effectiveness.

3) Multi functional synergy effect

Adjusting the curing speed: Molecular sieves adsorb some of the curing reactants, delaying the reaction rate and providing sufficient operating time for construction, while ensuring that the required strength is quickly achieved after curing.

Enhanced mechanical properties: Molecular sieve particles absorb energy through the "Pull out effect", increasing tensile strength by 20-30%, elongation at break by 10-15%, and improving toughness and durability.

Improving heat resistance: In high-temperature application scenarios, molecular sieves help maintain the adhesive strength and stability of the adhesive.

3. Conclusion

Molecular sieves have become an all-around player in solving the problem of polyurethane adhesive bubbles through multidimensional mechanisms such as selective adsorption of moisture, dynamic equilibrium control, physical filling, and interface optimization. Its advantages of efficient water removal, strong process compatibility, and multifunctional collaboration make it outstanding in high-end application fields such as automotive, electronics, and wind power. By precisely controlling the dosage and dispersion process, molecular sieves can significantly enhance the comprehensive performance of polyurethane adhesives, providing low-cost and high-efficiency bubble solutions for the industry.