From Static to Dynamic: How to Improve the Fluidity of Powders

From Static to Dynamic: How to Improve the Fluidity of Powders

With the rapid development of nanotechnology, the fluidity of powder has become an emerging research hotspot, as a very complex physical phenomenon, it occupies a pivotal position in many fields such as food, chemical, pharmaceuticals, etc. For example, the production of drugs often involves the precise proportioning and homogeneous mixing of a variety of ingredients, and if the drug powder has a good mobility, it will be able to ensure that the consistency and stability of the ingredients of each batch of drugs during the mixing process, and reduce the quality of drugs due to uneven composition. If the drug powder has good fluidity, it can ensure the consistency and stability of each batch of drugs during the mixing process, which reduces the quality problems of drugs caused by uneven composition; in the production of plastic pellets, good fluidity can guarantee the smooth progress of injection or extrusion molding process, preventing the products from uneven wall thickness, surface defects and other quality problems. Next, I will introduce the fluidity of the powder, the factors affecting it and the ways to deal with it.

• What is powder fluidity?

Powder fluidity refers to the characteristics of powder particles flowing under different conditions. Powder as a special class of materials, at the same time with the solid and liquid two kinds of characteristics, solid characteristics so that it can carry a certain amount of shear stress, in a stationary state to maintain a fixed form. When the shear stress reaches a certain critical value, the powder can flow like a liquid. As an important parameter in industrial production, powder fluidity not only affects the production efficiency and quality of products, but also relates to the design of structural parameters of powder processing equipment and the selection of process parameters.

• Influencing factors

There are many factors affecting the fluidity of powders, including the type of particles, average particle size, particle size distribution, moisture content, particle shape, specific surface area, density, storage time and inter-particle interactions. Here are just a few items for you to understand and recognize.

1. Particle size and size distribution

Powder size is the linear dimension occupied by a particle size in a spatial range. Particle size distribution is the amount of particles within a certain range of a number of sizes sequentially arranged as a percentage of the total population of particles is generally given in the form of a simple table, graph or function. When the particle size is large, the voids between the particles are larger, making the interaction force between the particles smaller and the powder easier to flow. When the particle size is small, the surface area of the particles is larger, and the interaction forces between the particles such as van der Waals force and electrostatic force will be enhanced as a result, making the particles less mobile and prone to form agglomerates, increasing the flow resistance.

JLAmoros et al. with different particle size distribution of monodisperse quartz sand as a material, through the shear test to study the relationship between the cohesion between the particles and particle size and bed tightness, the results show that cohesion with the tightness of the increase and increase, with the decrease in particle size and increase. The coefficient of friction of the bed increases with the increase of bed compactness, and the relationship depends on the particle size.

2. Powder moisture content

Powder water content refers to the amount of water in the powder. When the water content of powder is very low, water is adsorbed on its surface, and this adsorbed water has little effect on the fluidity of powder, with the increase of water, film water is formed around the adsorbed water, at this time, the relative movement between particles is not easy to occur, which restricts the flow of the particles as a whole, and the fluidity of the powder deteriorates or even loses when the water is increased to more than the maximum molecular binding water.

Xie Xiaoxu et al. modulated three kinds of coal samples, Yanzhou coal, mixed coal and Datong coal, into different water content for testing. They analyzed the effects of water content changes on the flow function, cohesion and angle of internal friction of coal powder, and concluded that: with the increase of water content of coal powder, the flow function of coal powder decreases, and the fluidity becomes worse; the cohesion between coal powder particles becomes larger, and it is easier to be agglomerated; and the coefficient of internal friction of coal powder decreases, which may be due to the fact that after the increase of water between the particles of coal powder, the water will be present in the craters of the particle surfaces or between particles, and the lubrication effect will be produced, so that the particles will not flow well. produce lubrication, so that the friction between the particles becomes smaller.

3. Particle morphology

When the particles have a regular shape, they can slide or roll more easily, less resistance, mobility is usually better; when the shape of the particles are irregular, they are easy to cross each other, resulting in flow path blockage, making the mobility worse. For example, the specific surface area of spherical particles is small, the contact points between particles are fewer, the interaction force is weaker, and the agglomeration of powder is not strong; while non-spherical particles generally have a larger specific surface area, the number of points of contact between the powder particles is larger, and the van der Waals force, electrostatic force and other forces between the particles are increased dramatically, which makes the fluidity of powder worse.

Lac Haifeng studied six kinds of coal and other powder particles (glass beads, FCC, yellow sand, asphalt powder, ammonium sulfate crystal particles, etc.) in the Plexiglas hopper under the material and Jenike shear experiments of mobility, found that the glass beads and particles with the morphology of the regularity of the higher degree of sphericity, the surface of the particles is also smoother, and coal particles angular, the edge of the particles, the tooth-like bumps are obvious, the shape of the rules of the degree is low. Therefore the coal dust particles with more points of contact with each other are more cohesive.

• Improvement of powder flowability

Methods for improving powder flowability can be broadly categorized into two groups: by increasing particle size or by surface modification of the particles.

1. Flow additives

Flow additives can significantly improve the fluidity of powders, avoiding the phenomenon of agglomeration or hardening, and their main function is to reduce the adhesion between particles. By adding flow additives, the contact distance between particles can be increased, thus reducing the van der Waals forces between particles. Nanoparticles, surfactants, and polymers can be added as flow additives to improve the flowability of powders, of which nanoparticles have been used for a longer period of time. During use, nanoparticles need to be dispersed into the system in order to cover the surface of the powder particles uniformly, and the strong affinity of the nanoparticles for the powder particles allows them to bind tightly to each other. The adhesion of these small binders on the particle surface can have the effect of improving the flowability of the particles.

2. Increase particle size

Increasing the particle size of powder particles is mainly done by increasing the gravity of the particles, thereby overcoming forces such as inter-particle friction, in order to improve the flowability of the powder. Both agglomeration and granulation are used to describe the process of combining many individual small particles together to form large particles without any change in the properties of the small particles. This process results in the large particles having a much larger particle size than the original small particles, which can have the effect of improving the flowability of the powder. In the case of dairy powders, for example, the agglomeration process usually occurs in a spray drying chamber or in an external fluidized bed after spray drying. In the spray drying chamber, the surfactant and particles are agglomerated together to form large clusters by primary agglomeration of wet particles or collision of secondary agglomeration of wet and dry particles.

3. Optimization of the crystallization process

It is widely believed that the flowability of powders can be improved by increasing the size of the particles, and in the case of crystalline particles, it is actually possible to change the shape and size of the crystals by means of crystallization in order to achieve an improvement in flowability. This method can combine crystallization and granulation in a single unit and is simple to operate. In addition, this method has many advantages, such as the entire process can be operated in a sterile environment, no additional excipients need to be added, and it can be applied to GMP production.

In the plastics industry, the addition of flame retardants is a key step in improving material safety. By improving the flowability of flame retardant powders, production efficiency and product quality can be significantly improved.

Highly flowable flame retardant powders, such as YINSU Flame Retardant's Antimony Replacement T3, ensure fast and uniform dispersion into the plastic substrate during the mixing process. This ensures the 100% replacement of antimony trioxide in equal quantities while at the same time efficiently reducing costs. This not only helps to reduce energy consumption and time in the production process, but also avoids material property degradation due to uneven distribution. In addition, good flowability reduces adhesion and clogging in production equipment, extending equipment life and reducing maintenance costs.

In conclusion, by optimizing the flowability of flame retardant powders, YINSU Flame Retardant Company's products improve the flame retardant properties of plastic materials and at the same time ensure the high efficiency and economy of the production process, providing a double guarantee for the quality and safety of plastic products.