What Is the Mechanism of Barium Sulfate Density in the Foaming Process of Flexible PU Foam?

Barium sulfate (also known as barite) is a common industrial filler, and its physical property—density—has a significant impact on the foaming process of flexible PU foam. This article systematically analyzes the density characteristics of barium sulfate powder, its mixing process, and its key role in flexible PU foam production.

1. Physical Properties and Performance Correlation of Barium Sulfate Powder

The natural density of barium sulfate ore is usually around 4.5 g/cm³, but the powder density can be precisely adjusted through raw material ratio and processing methods. This means that powders of different fineness, such as 400 mesh and 600 mesh, may have the same density. In materials science, this is referred to as bulk density and particle density.

High-density barium sulfate powder occupies less volume per unit mass, which is crucial in flexible PU foam formulations, as it increases the filler rate without raising overall volume, thereby enhancing the final foam’s mechanical properties.

However, high density is not always advantageous. Such powders tend to settle easily in liquid phases, and if mixing is not well controlled, stratification may occur. To address this, optimized stirring processes or dispersants are required to improve suspension stability. Moreover, during mixing with polyether, high-density powder may cause flow resistance when passing through nozzles due to sedimentation and viscosity changes. Nevertheless, foams made with high-density powder often show better physical performance, especially tensile strength, showing that powder properties not only affect mixing but are directly linked to final foam quality.

2. Process Optimization: From Equipment to Workflow

Mixing tanks for powders typically range from 2 to 4 cubic meters and can be classified as high-position or low-position tanks. High-position tanks facilitate downstream feeding but require lifting devices for input; low-position tanks make feeding easier but complicate discharge.

To ensure uniform blending, it is recommended to extend the pre-mixing time of barium sulfate with polyether, especially when the formulation includes other difficult-to-disperse components. During feeding, powders should be added gradually after stirring begins, to prevent clumping or overloading that could damage the mixing system.

In multi-story factory layouts, long-distance and high-lift material transfer is a common challenge. Intermediate buffer tanks can optimize pumping efficiency: splitting the transfer into two stages with relay pumps reduces strain on each pump and extends service life.

In actual PU foaming, different additives have widely varying rheological properties. For example, mixing barium sulfate powder with flame retardants in one container may cause viscosity spikes that overload mixers. A wiser approach is to design independent pre-mixing systems for different components, ensuring uniform dispersion and avoiding production risks in flexible PU foam manufacturing.

In summary, the use of barium sulfate powder requires precise control. From selecting the right powder and configuring equipment to following strict operating procedures, each step directly affects the final foam’s quality and production efficiency.

How do you think we should balance the pros and cons of high-density barium sulfate? We look forward to your insights!