Fine Grinding and Micronization

In the pharmaceutical field, powders consist of a heterogeneous group of solid particles and can be considered the simplest pharmaceutical form as such and/or can be used to produce other formulations such as tablets, capsules, or suspensions.

Generally, the particles are heterogeneous, differing in shape, size, and surface area: hence, powders are a collection of solid, dry, separated particles of regular shape and varying in size from 0.5 to 1000 μm and are the basis for the preparation of granules, tablets, and capsules.

Fine grinding is the mechanical reduction of a coarse solid material into smaller particles.

Depending on the size of the starting material and the type of product obtained we have:

  • Crushing (50-10 mm)
  • Pulverization (or fine grinding) (down to 100 to 50 μm)
  • Micronization (down to 1 μm)

Dedicated special equipment is available for each of these operations.

The reduction of particle size below 100µm, is a key process and requirement in laboratories and in small- and large-scale production. The benefits obtained from this operation are several: bioavailability, dispersion (aerosol) in pharmaceutical applications, dispersion, blending effect, adherence, long-lasting effect and silky touch for cosmetic applications, increased surface area for other applications.

Micronization is the state-of-the-art technique for reducing the particle size of an excipient’s active ingredient. It is used to meet the particle size requirements of APIs and excipients, parameters that are very often critical to the formulation of the finished product and necessary for achieving the desired bioavailability of the product.

Micronization, which reduces particles down to the micrometer or, in some cases, nanometer (1/1000 of a micrometer) size, can be used to improve the bioavailability of poorly soluble APIs by increasing particle surface area and accelerating dissolution rates. Micronization can also be used to improve formulation homogeneity and control particle size. A wide range of drug types, including solid dosage, injectable, ocular, and inhaled products, can benefit from micronization.

Micronization is most often used to describe processes that reduce particle size by using fluid energy, such as a jet mill, rather than by mechanical means.

There are multiple advantages of using a jet mill to grind dry powders over other particle size reduction technologies.

Jet milling offers:

  • High degree of material fineness
  • Low contamination due to absence of media, blades, knives, or screens
  • Internal classifier and good uniformity of size distribution
  • Low maintenance due to an absence of moving parts
  • Rapid disassembly of the system and ease of cleaning
  • Cryogenic application: possibility of working at low temperatures
  • Good productivity given by constant and continuous processing
  • No temperature rise in the mill due to expanding air creating a cooling effect, especially important for temperature sensitive materials, such as cosmetics

Grinding is done by the application of a specific force and technique depending on the material that can deform individual particles until they are broken.

  • Cutting for fibrous, naturally occurring materials
  • Compression for crystalline products
  • Impact (high-speed collisions) for friable materials
  • Friction (pressure-friction)

The adoption of fluid jet mill technology is the “clean” alternative to mechanical milling and has several advantages:

  • involves no moving mechanical parts and no friction,
  • it allows processing of heat-sensitive products,
  • assembly/disassembly is lighter
  • easier and faster cleaning.

The pharmaceutical micronization process uses no mechanical parts, as the reduction of product particles occurs solely by impact between the fragments themselves, which are fed into the grinding chamber through a Venturi injector. The flow of gas (compressed air, nitrogen, argon or steam) is injected into the chamber through nozzles and favors dragging the particles into a vortex, which repeatedly collide with each other and progressively reduce their diameter and mass.

The material particles are dragged by the fluid at very high speed, and as they collide with each other, they undergo changes in speed and direction due to the shape of the chamber. In this way, the reduction of their size to values predefined by process operating conditions takes place.

In order to meet the particle size requirements of the APIs and/or excipients, which are necessary to meet the formulation parameters on the finished product, the selection of the various sizes of the micronized particles takes place through the presence of a “classifier” at the exit of the micronization chamber.

The choice of micronizer type depends on several variables, including:

  • Type of material (hardness, hygroscopicity, particle size, melting point, flammability, elasticity, etc.).
  • Type of operation (desired size, cleanliness, sterility, versatility, space occupied, cost, etc.).
  • Safety level
  • Accessories

Spiral jet mill technology is recommended for target particle size distribution below 30 µm, while QMill technology or pin mill is suitable for PSD in the 30-100 µm range.

FPS offers a full range of equipment that ensures complete and safe micronization of powders of all types of materials. Starting from the early stages of research and customer dialogue to the design and implementation of production facilities and complete after-sales support, FPS ensures the appropriate equipment for any batch size and at every step of development.

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