The Effect of Flowagents on the Rheology of a Plastic Powder

Abstract

Flow agents are widely used in industry, such as the plastics and pharmaceutical industry, to promote the flow of cohesive powders. Few studies of the quantitative effects of the flow agents on the flow of the powder have been reported. In this communication the effect of silica flow agents on the flow of a plastic powder is studied by means of avalanching behaviour. The avalanching behaviour of the powder as modified by the silica flow agents is summarized using descriptive parameters based on the calculation of fractal dimensions in data space and phase-space strange attractors. The structure of the strange attractors are shown to be statistically self-similar and effective descriptors of the change of rheology caused by the presence of the flow agents.

Comparative Evaluation of Flow for Pharmaceutical Powders and Granules

“…Cohesion-controlled flow determines whether the large majority of technologically important powders will fluidize, cake, flow out of hoppers and blenders, fill small cavities in compression and encapsulation systems, mix, or segregate. Based on the cohesivity index obtained, flow behavior can be rated as free flowing (<11), easy flowing (11)(12)(13)(14), cohesive (14)(15)(16), very cohesive (16)(17)(18)(19), and extremely cohesive (>19; Texture technologies). A typical forcedisplacement profile for cohesivity test is shown in Fig.…”

“…Shear tests have widespread use in engineering and soil industries, however, is very time consuming and not very reproducible for elastic powders. Another powder flow measurement method includes use of photovoltaic array with patented technology named "AeroFlow" (12). However, it suffers from a major limitation which includes narrowness of the disk which makes significant particlewall friction and is not a true representation of pharmaceutical mixing or filling process.…”

Article

“…These two main steps do not appear with evidence in the Hosokawa methodology. Some of these phenomena have been extensively studied these last few years through avalanching behaviour and the theory of the attractor by Kaye et al [22]. The cooperative behaviour of particles in powders includes both initial potential energy (linked to their density) and the particle interactions.…”

“…The stability of the methodology applied to achieve these measurements is very important, specific to any researcher, and needs to be standardised before general use could occur. Through the avalanche methodology, it is possible to get a fractal representation of each powder, which permits interesting comparisons following the evolution of powder properties in time by an easy comparison of the phase space attractor [22]. In fact, the only machinery developed commercially by TSI is "Aero-flow", an automated powder flowability analyser, which also permits the study of the progress of the powder avalanche.…”

“…It was introduced by the Australian scientist Brian Kaye [22]. The stability of the methodology applied to achieve these measurements is very important, specific to any researcher, and needs to be standardised before general use could occur.…”