In industries such as cosmetics, pharmaceuticals, nutraceuticals, additive metals and plastics, the precise mixing and drying of powders can be critical to the color, consistency, performance, safety and cost effectiveness of a wide range of products.
Casey Muench Bickhardt, president of GEMCO—a Middlesex, NJ-based manufacturer of tumble blending and vacuum tumble drying equipment—offers formulators and process engineers the following expert advice in this niche area.
Consider the Process
"Powder size, shape, density, chemistry, static charge and moisture content can determine successful formulation. Because these variables can change during the supply chain, it is essential for manufacturers to ... look at the entire process to help optimize product quality and the production process." This could mean consulting a third-party powder specialist, Bickhardt adds.
"Failing to do so can lead to sub-par product, potential failure in the field and an array of inefficient efforts during production that attempt to correct deficiencies but do not address the root causes," Bickhardt notes. For example, if a manufacturer does not know which factors must be within specification, or what the specs should be, an operator can spend hours or days reworking the batch, trying to get it right.
“If a manufacturer using powdered materials does not take the time to look at the raw ingredients to ensure that they are properly prepared for a mix, an operator often may just try blending the ingredients longer, faster or with greater force,” says Bickhardt. “More or less liquid may be added. More processing equipment may be added to the process train. All this guesswork and experimentation adds cost and complexity to production...”
Powder mixing/drying of raw ingredients and chemicals requires a strategy and knowledge of powder chemistry and physics to ensure the same desired results every time.
Factors in Powder/Product Quality
Cost effectively mixing powders to achieve a quality product requires understanding factors such as powder size, shape, density, chemistry and moisture content.
powder mixing/drying of raw ingredients and chemicals requires a strategy and knowledge of powder chemistry and physics
Powder Size, Shape and Density
When powders with different particle sizes are mixed, the larger particles will leave a space or gap where smaller particles may “fall out,” making the blend difficult to keep together. Alternatively, powder particles can come in various irregular shapes that can lead to particles interlocking or clumping, which must be broken up to achieve uniformity. Dissimilar powder density is also an issue that must be resolved in order for different powders to blend homogenously.
To help mix and balance particles with dissimilar size, shape or density, Bickhardt recommends using a combination of macro and micro blending to produce a better distribution. Macro mixing is achieved by rotating the shaped vessel, allowing the material bed to fall away from the vessel’s walls. The blender moves at a precise speed, with the vessel wall at a precise angle, so that the material cascades over itself.
As this occurs, if needed, micro mixing can be carried out simultaneously via agitator blades located in the mixing zone center of the vessel, where fine processing in the material transpires. Together, the macro and micro mixing evenly expose each particle to six times more active blending per revolution than traditional mixers.
Another critical factor manufacturers must understand to achieve quality blends and products is powder chemistry. “For different powder particles, it is critical to understand the chemical characteristics of the particles,” says Bickhardt. “You could be looking at how they form chemical bonds, if they are polar or non-polar, etc. It is essential to pay attention to the science to get the powders fundamentally prepared to be blended.”
According to Bickhardt, understanding the chemistry of raw powder ingredients to be mixed is crucial for any time-release technologies; enrobing, i.e., enabling a powder coating to accumulate as it contacts other particles in a controlled process; and hydrophilic or hydrophobic coatings.
To help mix and balance particles with dissimilar size, shape or density, Bickhardt recommends using a combination of macro and micro blending.
Determining whether powder particles may be affected by a static electrical charge is also essential and must be addressed in the blending units, according to Bickhardt.
“If you have powder particles that will be polarized by static electricity or any charge, then you literally have forces working inside the mixer that will compete against a good mix,” says Bickhardt. “In such cases, it is important to equip the unit with static electricity arresters.”
Powder mixing and drying, in particular, will be affected by the presence of moisture in raw ingredients, which must be monitored and controlled to optimize the purchase price, processing and end product.
“If moisture levels are too high in a raw ingredient, the manufacturer is overpaying for excess water that must be removed by extended drying,” says Bickhardt, who adds that manufacturers want to deal with excess external moisture in raw powder materials before it becomes inbound moisture. “Once water is trapped inside a powder particle, you need exponentially more vacuum and heat directed inward to remove inbound moisture than with surface moisture,” Bickhardt explains.
On the other hand, if the moisture level is too low in a raw material powder input, it could negatively affect blending and end product performance, which can be critical particularly for regulated products like pharmaceuticals. “So, it is really important to measure both moisture content and loss on drying,” says Bickhardt.
Raw Material Input Consistency
Finally, in addition to the science of mixing, there is the question of the raw material input itself. As noted, raw materials can have variations in size, shape, density, etc. This can cause clumping and granulation that results in improper mixing and drying. Left unaddressed, this can lead to end product quality problems including diminished performance, aesthetics, durability and safety in industries such as cosmetics, pharmaceuticals and automotive paints.
“Controlling all stages of the supply chain and production is critical to achieve a quality end product reliably and consistently,” concludes Bickhardt. “But that starts with having the raw ingredient evaluated to see if it meets all necessary requirements and specifications." Again, this could mean involving expert consultation with powder specialists.
For more information, visit the GEMCO website.