Context: The negative impact of magnesium stearate on the hardness of tablets is a well-known phenomenon, but the influence of paddle movement in the forced feeder on the lubricant effect during tablet compression is often neglected.

Objective: The purpose of this research was to investigate the influence of paddle speed in the forced feeder on tablet tensile strength.

Materials and methods: Mixtures of microcrystalline cellulose and magnesium stearate (0.5%) were blended using different methods (low & high shear). After blending, the formulations were compressed into tablets. All parameters of the tableting cycle were kept constant except the speed of the paddles in the forced feeder.

Results and discussion: The blending technique affected the sensitivity of the formulation to the paddle speed. The tensile strength of pure microcrystalline cellulose tablets didn’t change in function of paddle speed, while tablets prepared by low shear mixing became softer at higher paddle speed. The tensile strength of tablets manufactured using the high-shear mixed blend was low and didn’t vary in function of paddle speed, suggesting that overlubrication already occurred during the initial blending step. Furthermore, analysis of the machine parameters allowed evaluation of the influence of the paddles on the flowability, initial packing and compactability of the powder mixtures.

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