Abstract
It is important during powder granulation to obtain particles of a homogeneous size especially in critical situations such as pharmaceutical manufacture. To date, homogeneity of particle size distribution has been defined by the use of the d50 combined with the span of the particle size distribution, which has been found ineffective for polymodal particle size distributions. This work focuses on demonstrating the limitations of the span parameter to quantify homogeneity and proposes a novel improved metric based on the transformation of a typical particle size distribution curve into a homogeneity factor which can vary from 0 to 100%. The potential of this method as a characterisation tool has been demonstrated through its application to the production of granules using two different materials. The workspace of an 11mm twin screw granulator was defined for two common excipients (α-lactose monohydrate and microcrystalline cellulose). Homogeneity of the obtained granules varied dramatically from 0 to 95% in the same workspace, allowing identification of critical process parameters (e.g. feed rate, liquid/solid ratio, torque velocities). In addition it defined the operational conditions required to produce the most homogeneous product within the range 5μm–2.2mm from both materials.
Highlights
Wet granulation is a common industrial unit operation in the pharmaceutical industry for particle size enlargement. This operation has been traditionally performed in batch, it could be effectively achieved in a continuous mode using a Twin-Screw Granulator (TSG)
In contrast to batch equipment traditionally used in wet granulation, TSG has been applied by the pharmaceutical industry as a useful continuous operation granulation technique
The method is able to calculate the homogeneity of Particle Size Distributions (PSD) with different shapes allowing easy numerical comparison
Summary
Wet granulation is a common industrial unit operation in the pharmaceutical industry for particle size enlargement. This operation has been traditionally performed in batch, it could be effectively achieved in a continuous mode using a Twin-Screw Granulator (TSG). The understanding of wet granulation has achieved notable advances in the past twenty-five years, since the macroscopic research of granulation was replaced by a microscopic study of the variables ((Ennis and Litster, 1997; Ennis, 1991; Parikh, 2005)). In contrast to batch equipment traditionally used in wet granulation, TSG has been applied by the pharmaceutical industry as a useful continuous operation granulation technique. Mendez Torrecillas et al / International Journal of Pharmaceutics 519 (2017) 230–239
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