What is the thickening mechanism of polyurethane thickeners in suspensions?

As a supplier of polyurethane thickeners, I often encounter inquiries from customers regarding the thickening mechanism of these remarkable products in suspensions. Understanding this mechanism is crucial for formulators and end - users alike, as it allows for the optimization of product performance in a wide range of applications. In this blog post, I will delve into the science behind the thickening action of polyurethane thickeners in suspensions.

The Basics of Polyurethane Thickeners

Polyurethane thickeners are a class of associative thickeners that have gained significant popularity in various industries, including coatings, adhesives, and personal care products. These thickeners are typically composed of a hydrophobic backbone with hydrophilic groups at the ends. The unique molecular structure of polyurethane thickeners enables them to interact with other components in a suspension, leading to an increase in viscosity.

Association and Network Formation

The primary thickening mechanism of polyurethane thickeners in suspensions is based on association and network formation. When a polyurethane thickener is added to a suspension, the hydrophobic segments of the thickener molecules tend to associate with each other or with other hydrophobic particles in the system. At the same time, the hydrophilic groups interact with the continuous phase, usually water in aqueous suspensions.

This association process leads to the formation of a three - dimensional network structure throughout the suspension. As the network is formed, it restricts the movement of the liquid phase and the suspended particles, resulting in an increase in viscosity. The strength and density of the network depend on several factors, such as the concentration of the thickener, the molecular weight of the thickener, and the nature of the suspension components.

Hydrophobic Interactions

Hydrophobic interactions play a vital role in the thickening mechanism. The hydrophobic segments of the polyurethane thickener are attracted to other hydrophobic entities in the suspension. For example, in a paint formulation, the hydrophobic parts of the thickener may associate with the pigment particles or the polymer droplets. This association not only helps in thickening the system but also improves the stability of the suspension by preventing the aggregation of the particles.

Hydrogen Bonding and Electrostatic Interactions

In addition to hydrophobic interactions, hydrogen bonding and electrostatic interactions also contribute to the thickening process. The hydrophilic groups on the polyurethane thickener can form hydrogen bonds with water molecules or other polar groups in the suspension. Electrostatic interactions can occur between charged groups on the thickener and the suspended particles or the ions in the solution. These interactions further strengthen the network structure and enhance the thickening effect.

Influence of Shear Rate

The thickening behavior of polyurethane thickeners in suspensions is also influenced by the shear rate. At low shear rates, the three - dimensional network formed by the thickener remains relatively intact, resulting in a high viscosity. As the shear rate increases, the network is gradually broken down, and the viscosity decreases. This phenomenon is known as shear - thinning behavior, which is desirable in many applications.

For example, in a coating application, a high viscosity at low shear rates helps to prevent sagging during application, while a low viscosity at high shear rates allows for easy spreading and leveling. Our Low Shear Polyurethane Thicknener is specifically designed to provide excellent thickening performance at low shear rates, making it ideal for applications where sag resistance is critical.

Compatibility with Other Components

Another important aspect of the thickening mechanism is the compatibility of polyurethane thickeners with other components in the suspension. Polyurethane thickeners need to be compatible with the polymers, pigments, solvents, and additives used in the formulation. Incompatibility can lead to phase separation, flocculation, or a decrease in thickening efficiency.

We have developed a range of polyurethane thickeners that offer excellent compatibility with various components. Our Elementis Rheolate 299 Alternative Associative Thickener is a great example. It is designed to be compatible with a wide range of polymers and additives, providing consistent thickening performance in different formulations.

Thixotropic Behavior

Some polyurethane thickeners exhibit thixotropic behavior, which means that the viscosity of the suspension decreases over time under a constant shear stress and then gradually recovers when the shear stress is removed. Thixotropy is beneficial in applications where the material needs to be easily pumped or applied but then maintain its shape after application.

Our Thixotropic Associated Thickener Heur is formulated to provide thixotropic properties. The thixotropic behavior is due to the reversible nature of the network structure formed by the thickener. When shear is applied, the network is broken down, reducing the viscosity. Once the shear is removed, the network gradually reforms, and the viscosity increases again.

Applications in Different Industries

The unique thickening mechanism of polyurethane thickeners makes them suitable for a wide range of applications in different industries.

Coatings Industry

In the coatings industry, polyurethane thickeners are used to control the viscosity, sag resistance, and leveling properties of paints and coatings. They help to improve the appearance and performance of the coatings by preventing pigment settling, improving film formation, and enhancing the overall stability of the formulation.

Adhesives Industry

In adhesives, polyurethane thickeners are used to adjust the viscosity of the adhesive formulation. A proper viscosity is essential for good wetting, bonding strength, and application properties. The thickeners also help to prevent the adhesive from flowing or dripping during application.

Personal Care Industry

In the personal care industry, polyurethane thickeners are used in products such as shampoos, conditioners, and lotions. They provide the desired viscosity and texture to the products, improving the sensory experience for the consumers.

Conclusion

The thickening mechanism of polyurethane thickeners in suspensions is based on association and network formation through hydrophobic interactions, hydrogen bonding, and electrostatic interactions. The shear - thinning and thixotropic behaviors of these thickeners make them highly versatile and suitable for a wide range of applications.

As a supplier of polyurethane thickeners, we are committed to providing high - quality products with excellent thickening performance. Our products are designed to meet the specific needs of different industries and applications. If you are interested in learning more about our polyurethane thickeners or have any questions regarding their application, please feel free to contact us for a procurement discussion. We look forward to working with you to find the best thickening solutions for your products.

References

1. Morrison, I. D., & Ross, S. (2002). Colloidal Dispersions: Suspensions, Emulsions and Foams. John Wiley & Sons.
2. Landfester, K. (Ed.). (2009). Polymer Dispersions and Their Industrial Applications. Wiley - VCH.
3. Asua, J. M. (Ed.). (2002). Polymer Dispersions and Their Applications. Kluwer Academic Publishers.