(657a) Resonant Acoustic (Vibratory) Powder Mixing Performance
Powder mixing is one of the most important operations during food, chemical and pharmaceutical processing. Blending performance of various blender designs, including V-blenders, double-cone blenders, tote-blenders and rotary-drum blenders, have been previously studied in depth. The efficiency of the powder mixing process is measured as the speed at which the desired uniformity of a blend is achieved. The blending performance has been found to be dependant on blender type, material properties and even environmental conditions. In these studies, the performance of a new laboratory-scale ResonantAcoustic® Mixer (RAM) is studied. The RAM uses acoustic energy to provide both bulk and micro mixing. Resonant acoustic mixing is known to significantly reduce mixing time making it a good candidate for improving the efficiency of powder mixing processes.
The blend uniformity of lactose and acetaminophen powders blended using the RAM is compared to mixing results obtained using a double-cone tumble blender. Uniformity is determined by the variance in acetaminophen concentration (as measured by near infrared spectroscopy (NIR)) obtained from numerous small samples collected over the duration of mixing. The optimal RAM operating parameters resulted in relative standard deviation (RSD) values for acetaminophen concentration of 0.4 as opposed to 0.8 for the double cone blender. The RAM achieved these minimal RSD results in 30 seconds as opposed to 240 seconds for the double cone blender. In the second part, a fractional factorial design of experiments is performed to characterize and optimize the mixing performance of the RAM. Variations in fill level, mixing time, and mixing intensity were used. Combinations of binary mixtures were used in order to understand the effects of mixing parameters and material properties. Three fill levels (25%, 50%, and 75%), three mixing times (1 min, 2 min, and 4 min), three mixing intensities (25 Gs, 50 Gs, and 75 Gs) were used as mixing parameters. The binary mixtures used were composed of three API grades (micronized and granulated APAP, and caffeine), three API concentrations (3%, 10%, and 30%), and two grades of MCC (Avicel PH102 and Avicel PH200). After each experimental combination, numerous samples were extracted from the 273-ml vessel in order to determine the mixing performance determined by the variance in the acetaminophen concentration (as measured by near infrared spectroscopy). The results indicated that the RSD decreased with increasing acceleration. For the materials and parameters used, the time of mixing was not significant, although higher acceleration results in better mixing. Temperature increased with increasing fill level, time and acceleration.