A comparative study of Dry milling vs Wet milling

What is milling?

A forceful unit action known as milling can help with particle size control for a number of processing, bioavailability, reactivity, and safety-related drivers. This chapter offers some recommendations on how to choose milling machinery and the critical variables that can affect its performance using the data. The physical characteristics of the feed material, such as hardness and brittleness, as well as its beginning size distribution, as well as the mill, all affect the final mean particle size and particle size distribution.
Trial experiments combined with mechanistic methods to characterize particle breakage are typically the most effective way to evaluate the viability of milling. However, effective scale-up of milling is made possible by engineering knowledge of mill operation and important process parameters. As a result, the particle size to be produced at a large scale can be correctly anticipated from well planned gram-scale bench trials.

Wet milling:

Wet milling, sometimes referred to as wet grinding, is a procedure whereby shearing or crushing is used to disperse particles that are suspended in a liquid slurry. These particles can be used right away when milling is finished, or they can be dried and separated to be added to other goods.

Advantages of pharmaceutical wet milling:

1. It Protects compounds that are temperature-sensitive
2. The best method for sensitive materials is wet milling. At the point of contact, milling always generates heat. The liquid that surrounds the particles in the wet mill acts as a heat sink. Lower operating temperatures are achieved by the liquid slurry, which dissipates heat from the mill since it has a far greater heat capacity than the solid.
3. The disadvantages of dry-micronization are avoided by wet-milling.
4. Dry-micronization frequently adds disorder into the milled crystalline API, primarily in the form of amorphous material. This can lead to negative changes in the API’s physicochemical properties, including stability, flow, solubility, dissolution, and other qualities. A change in the polymorphic form could also occur after dry-micronization.
5.  No or Minimal Yield Loss
   The yield loss factor of many milling techniques, including jet mill micronization, can often be 10% or greater. Material losses are minimal since the wet mill is a closed system that is continuously “flushed” with the liquid phase

Types of machines used in wet milling

1. colloid mills
2. media mills
3. toothed rotor stator mills

Dry milling:

Solids are placed in a feed hopper for dry milling, which then continuously feeds a flow through a feeder system and the milling machine. Although the methods of grinding might vary, particles are diminished in size either via particle-particle collisions or collisions with grinding media or walls. The particles are transferred to product collection or a classifier once the dry milling process is finished. The classifier can return bigger molecules to the feed hopper for more dry milling.

Advantages of Dry milling:

As was previously indicated, when APIs crystallize, sometimes the particles are the right size and may be used in formulations without further processing, and other times they need to undergo particle size reduction. A pharmaceutical manufacturer might purposefully develop particles that are larger than the intended PSD(Particle Size Distribution) in an effort to shorten the amount of time that is required for filtration during separation. Wet milling may compromise API purity in certain circumstances, hence dry milling is employed.

Types of machines used in dry milling:

1. hammer mills
2. jet mills
3. pin mills

This picture above shows Senieer’s hammer mill for grinding larger particles into smaller particles.

The difference between wet grinding and dry grinding:

The method of dry grinding is rather straightforward. The raw material is fed into a variety of specialized machines where it moves through a constrained space, colliding with other particles or slamming into machine parts (such wheels) until it is reduced to the required size.

On the other hand, with a wet mill, particles are pushed through a grinding chamber while being dispersed in a liquid solution. The particles are crushed by the rotating blades while floating in the liquid.

Conclusion:

Applying Milling to Reduce Particle Size in Pharmaceutical Manufacturing.
When compared to a technique like precipitation, which builds molecules from a dissolved state, milling is a bottom-up strategy that breaks bigger molecules down into smaller ones.

The size of the particles is decreased as they are ripped or crushed as they are driven through the mill. Many diverse businesses utilize milling for various objectives, but the pharmaceutical sector uses this sort of mechanical size reduction to regulate the size of APIs, chemicals, and excipients to enhance the effectiveness and delivery of medications.
APIs are frequently purified through crystallization, followed by filtration and drying of the particles. When the particle size distribution (PSD) is not optimal, further processing is required, which frequently requires milling the material. In some cases, the isolated particles are suitable for usage in a medication as-is.
Milling improves a solid’s surface area whether it is wet or dry, which speeds up its dissolution and raises its bioavailability. It guarantees consistency in formulations from one batch to the next and can enhance an API’s compatibility with excipients. In addition to being effective, milling is also frequently employed to address low solubility in novel therapeutic compounds since it is less expensive than alternative procedures

Why choosing Senieer?

Senieer, a top supplier and manufacturer of pharmaceutical equipment worldwide, provides ONE STOP SOLUTION. For companies in the pharmaceutical, food, chemical, and cosmetics industries, Senieer is the best global partner. In China, Senieer has spent more than 34 years concentrating mostly on solid dosage forms. Integral process solutions that are trustworthy. We manufacture equipment in accordance with international standards including GMP, cGMP, and US FDA.
Senieer can customize and provide dry and wet milling machines for your business.
The one-stop solution services for complete projects, from advising to design, are improved by members of the Senieer technical team. We completely meet your demands and methods for resolving all of your problems.
We are the best hammer mill manufacturers in China.
For more information you can check our website: www.senieer.com