(T1430-08-54) Determining the Effect of Blade Fouling on the Approach to Steady State and Final Residence Mass within a Continuous Blender

Purpose: The purpose is to determine how both the approach to steady state and the residence mass of the continuous blender change when the blender blade is clean (freshly washed, unused) or dirty (already coated with powder, previously used). Approach to steady state is key in determining the startup fraction of blended material. Blender residence mass is proportional to the mean residence time of material in the continuous blender which determines the robustness of a blending process. Robustness is determined by the sensitivity of the blending process to high frequency perturbations from feeding powder through a loss in weight (LIW) feeder.

Methods: Excipients Avicel PH 102 and Lactose FF 316 were individually fed using a loss-in-weight (LIW) feeder and continuously blended using a linear blender. Starting with an empty linear blender, powder was fed into the inlet of the blender until the mass flow rate out of the blender, determined by a catch scale, was equal to the mass flow rate into the blender. After the system reached steady state, the feeding and blender were stopped simultaneously and the residence mass was determined by emptying the blender and weighing the contents. The amount of powder on the blender blade was captured using handheld microscope photos and quantified using a greyscale analysis in Matlab.

Results: The difference in time to steady state for clean versus dirty blender blades is considerable with the time to steady state of a clean blade being up to 8 x longer than the average of the dirty blade set. The steady state residence mass within the blender is not greatly affected by blade dirtiness as both the residence mass and blade image whiteness (%) plateau early in a run set and remain consistent for subsequent runs.

Conclusion: The time to reach steady state is greatly affected by blender blade dirtiness while steady state residence mass is not. Both factors should be considered for at scale continuous manufacturing.

Table 1. Time to Steady State

Figure 1. Residence Mass per Run Set

Figure 2. Image Analysis of Blade Foul