Effect of additive on flour flowability using Granupack

Effect of additive on flour flowability using

Principle

In this study, the effect of the addition of small particles to a flour has been studied.
The physical behavior of the powder before and after the addition of the charge has been analyzed by using the GranuPack instrument.

Sample analysis

Figure 1 shows the evolution of the density as a function of the tap number for the two samples.

figure with tap density versus stress (taps) : flow curves for the different samples analysed

table with the samples results (powder A and powder A + charge)

Figure 1 clearly shows that the addition of small particles strongly modifies the behavior of the powder.
These two powders can be distinguished by using the GranuPack instrument.

Indeed, the powder without small particles is characterized by the lowest density variation during the measurment.

Moreover, this behavior is confirmed in table 1 which gives the parameters extracted from the curves (density values, flowability index and n1/2) for each powder.

By considering the flowability index and n1/2, we can conclude that the powder without small particules is characterized by the best flowability.
By considering ESEM analysis (see figures 2 and 3), we are able to demonstrate that the particles of the powder without the charge show a very low surface rugosity by comparison to the powder with the charge.

Indeed, the small particles are adsorbed on the spherical larger particles (see figure 3).

Thus, the surface of the particles with and without the charge is very different.

The difference of flowability of the two powders can be related this difference of surface rugosity.

figure 2 : micrographs of powder 1 without charges

figure 3 : micrographs of powder A with chargesIn order to analyse the compaction dynamics in more details, the curves could be rescaled.
Figure 4 and 5 show respectively the evolution of the Hausner ratio value (d/d0) and the kinetic of compaction according to the stress applied to the powders.

The difference observed concerning the initial density for powder without and with the charge can be explained by the larger particle size distribution by adding the charge.

The small particles of the charge can take place in the small holes between the larger particles.

Therefore, the initial density is increased (see table 1 and figure 1).

Under stress, the small particles move through the pile.
The sample with the charge shows a higher haunsner ratio curve (figure 4) than the sample without the charge due to a higher rate of compaction.

It is also important to note that the first taps seem to be the most important in the mecanisme of compaction.

So, the maximum variation of density takes place at the beginning of the compaction process.
The compaction kinetic is very fast at the beginning of the measurement and a plateau of relative density is rapidly reached (figure 4 and 5).

However, sample without the charge is more sensitive to the first taps than sample with the charge.

So, for sample without the charge, less taps are requiered to reach the plateau of maximum density.
This behaviour is due to the absence of small particles which can percolate through the pile of coarse particles.

figure 4 : Hausner ratio curves for sample with and without charges figure 5 : kinetic of compaction curves for sample with and without charges