Carr’s compressibility

Tablet properties inputs) Dose (mg) Solubility Particle size (gm) Minimum bulk density (g mU ) Tapped bulk density (g mU ) Carr s compressibility (%) Formulation 50.0 Insoluble 5.0 0.4 0.7 42.857 ...

The Carr s compressibility percentages have been effectively correlated to measure ... 

Description of flow Angle of repose (degree) Carr s compressibility (%) Hausner ratio (—)... 

The compressibility of resin and other materials is also used to determine factors such as flowability and the proper designing of hoppers, blowers, and vacuum systems. Two formulas used for this are the Hausner ratio and Carr s Compressibility Index [2]. These formulas use both the aerated and tapped bulk densities in order to provide an estimation on the compressibility, which then leads to flowability, but these formulas do not account for the variation that occurs between those two points. They are also used on a smaller scale basis, and do not provide results that eould accurately predict the bulk density or weight in a silo at a given point. 

The classification system introduced by Carr [29,30] was used to evaluate the flow properties of the sorbitol powders. In Carr s system, a flowable powder is defined as free flowing and will tend to flow steadily and consistently. This is to be contrasted with a floodable powder, which will exhibit an unstable, discontinuous, and gushing type of flow. The parameters in Carr s system include the angle of repose, angle of spatula, compressibility, cohesion, and dispersibility. Based on these parameters, flowability and floodability indices are calculated to determine the handling properties of bulk solids. 

It would be desirable to have simple tests capable of characterising the fluidisation behaviour or flowability of particulate materials on the basis of their bulk properties. To this end, Carr19 developed a system to characterise bulk solids with respect to flowability. Table 6 summarises the properties which are determined. In Carr s method a numerical value is assigned to the results of each of these tests, and is summed to produce a relative flowability index for that particular bulk material. Given the extensive use of these empirical techniques in academia and industry, a brief review on the subject is reported here. Nevertheless, it should be emphasised that these techniques allow measurements of the flow-ability or cohesion of materials solely in their stationary or compressed status and at ambient conditions. A direct relationship between these... 

Given that the bulk volume associated with the particle mass is a mixture of air and solid material, the bulk density value is highly dependent on sample history prior to measurement. Calculation of the tapped density can then be achieved by tapping the bulk powder a specified number of times (to overcome cohesive forces and remove entrapped air) to determine the tapped volume of the powder. The tapped and bulk density values can be used to define the flowability and compressibility of a powder using Carr s index and the Hausner ratio. 

The powder s flow properties are also important because they control the physical processes that are used to manipulate the material. Carrs s index, which is a measure of powder bulk density and angle of repose, provides information on flow properties, which are important when production utilises high-speed tableting machines. Compression properties are important in determining the ability of the compound to form tablets wdth or without the presence of excipients. 

Another, this time indirect, method of assessing flowability was proposed by Carr36. This was based on measuring four properties of the powder (angles of repose and spatula, compressibility and uniformity coefficient, all as defined by Carr36) and, by awarding points (out of 25) for each, the sum total was then a measure of flowability and called Carr s Index . A commercial piece of equipment is available (Hosokawa Powder Characteristics Tester) for measuring the properties necessary for Carr s Index. 

Carr s percentage compressibility from bulk densities... 

Flowability 10.8-11.7g/s for corn starch 30% for corn starch (Carr compressibility index). Corn starch is cohesive and has poor flow characteristics. 

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