Foam Granulation Technology Update and Future Applications

Paul Sheskey of Dow Chemical provides an update on foam granulation technology.
May 01, 2008

Figure 1
Granulation is one of most important unit operations involved in solid dosage form manufacturing and several granulation technologies have been developed. Traditionally, an aqueous solution of a binder is sprayed on the powder during mixing in a granulator. In 2003, The Dow Chemical Company (Midland, MI) introduced foam technology for delivering aqueous binder systems in high-shear and fluid-bed wet granulation applications (1) (see Figure 1). A foam generator can be set up with a binder solution tank and high-sheer granulator to introduce the binder as a foam rather than spraying or pouring in binder onto a moving powder bed. Last year, Pharmaceutical Technology published an article discussing the scale-up of foam granulation technology in a high-shear process (2) (see Figures 2, 3). As a follow-up to that discussion, Paul Sheskey, research and development leader at Dow, provides an update on foam granulation, including process challenges the company has encountered from industry and future applications of the technology.

Q. What was the motivation to develop a new granulation technology versus conventional granulation techniques?

Figure 2
A: We became aware of the granulation needs of the industry through the sale of our functional polymers, whether it was for granulating a matrix controlled-release system using METHOCEL cellulose ethers polymers or immediate-release granulation using our low molecular-weight polymer family. A significant issue experienced throughout the industry, as represented by a large number of research papers published throughout the years, is the uniform distribution of the liquid/binder combination evenly throughout a moving powder bed. It may appear to be uniform when spraying, but it doesn't always happen. We've referenced papers by Litster and Hapgood that showed this is not a very easy thing to accomplish. In their studies they proved it at the very basic level.

Figure 3
Manufacturers of pharmaceutical granulations would call us saying that they were having trouble either during their formulation development work or in a production setting. We determined that a significant proportion of their issues directly related to the even distribution of the granulating liquid. They have hydrophilic polymers in their formulations that tend to preferentially grab the water in the granulating liquid and sometimes this would interfere with its uniform distribution. So we investigated various atomizing techniques when spraying the binder solutions. We did a lot of work to better understand the issues so that we could provide the pharmaceutical formulators specific, hands-on type of advice. However, even that was not doing as good a job as was needed for the pharmaceutical industry. Then we discovered foam technology for granulation applications in our laboratory. My colleague and co-inventor, Colin Keary has a lot of expertise in the area of foams when he was a scientist in the oil well industry. Working in combination, we serendipitously came up with this for pharmaceutical granulating. That satisfied the need of evenly distributing the liquid binder phase much better than a spray could do. That is a recognized need of the industry and that is what foam helps with tremendously.

Q. What are some of the unique challenges and applications of using foam granulation?

A: The pharmaceutical industry is very conservative when it comes to new applications and new technologies. Our job has been to educate people on the use of this technology globally. This has become better, but it always takes time. We've seen that once it gets into a company, they'll also use it for the everyday-type granulations.