Measuring the Flow Functions of Pharmaceutical Powders Using the Brookfield Powder Flow Tester and Freeman FT4

Round 1

Reviewer 1 Report

Dear Authors,

you have written a good paper on an exciting topic. Despite the fact that I am not an expert on powders, I was able to understand the procedure and the results well. However, I did notice some inconsistencies. However, I suggest that you change a few small things before the paper is accepted (see my notes in the attached file).

Comments for author File: Comments.pdf

Author Response

1. The situation with Ta is clarified. In the initial discussion it is a force which accounted for by interparticle forces apart form friction. Later in the paper the concept of cohesion, interparticle force per unit area is used and that is now tau1. This is measured by both machines when obtaining the data.
2. Figure 1 is now labelled correctly
3. The issue with phi is now dealt with.
4. Fig 3 and 4 issues are now dealt with.
5. Line 120 has been modified.
6. Fig 6 and 7 now have better scales.
7. The flow functions are using a logarithmic scale to obtain the key functions and identify "dog-legs". Therefore the negative numbers indicate loads less than 1kPa and are OK.
8. Formatting issues with the equations have now been dealt with.

Reviewer 2 Report

1. The author can add at least two more paragraphs regarding the importance of flow testers in the industries. Please include literature and studies where these powder testers have been used and how they helped that particular study.
2. In Figure 1, does the red arrow represent the shear force, S_f? If so, please label it accordingly.
3. In Figure 3, it would be better if the author can add a schematic to better illustrate the movement of the pistons.
4. In line 120, the author did not provide the reference for the work.
5. Can the author elaborate more on Figures 6 and 7? How does the morphology create challenges?
6. For all the graphs in section 4, especially Figure 8-12, the author is urged to elaborate and infer on. The results obtained. In the current manuscript, the author has only stated the results but not discussed it.

Author Response

Modifications are indicated in red on the script.

1. The author can add at least two more paragraphs regarding the importance of flow testers in the industries. Please include literature and studies where these powder testers have been used and how they helped that particular study. This extra material has been added.
2. In Figure 1, does the red arrow represent the shear force, S_f? If so, please label it accordingly. This has been done.
3. In Figure 3, it would be better if the author can add a schematic to better illustrate the movement of the pistons. Basically the piston moves down at a controlled rate. It is designed to let the trapped air out of the powder without spillage.
4. In line 120, the author did not provide the reference for the work. This has been added.
5. Can the author elaborate more on Figures 6 and 7? How does the morphology create challenges? This section has been expanded.
6. For all the graphs in section 4, especially Figure 8-12, the author is urged to elaborate and infer on. The results obtained. In the current manuscript, the author has only stated the results but not discussed it.

This section has been expanded, using Figures 6 and 7 to further explain the results.

Reviewer 3 Report

This is an interesting study on determination of the flow function characteristics of pharmaceutical powders. Two different powder flow testers have been compared in the measurement of the flow function of powders over different compaction loads. Some concerns/suggestions are:

1. Line 12, “method of Wang et al.” is not clear. It is better to include more detailed information on the method or rephrase the relevant sentence.
2. Line 120, in “in previous work []”, specific references should be provided.
3. Lines 132-139, figures 6 and 7, it should be indicated which material each photo/figure represents.
4. Line 147, “Figure 8. compares…” should be “Figure 8 compares…”.
5. Lines 155 and 156, it was stated that “The plot shows that the effect of the test equipment is not significant.” It is better to provide more detailed explanation on the results in the figure to demonstrate the statement.
6. Line 160, the results in Figures 9-12 need to be discussed.
7. Line 172, the coefficient and index of the functions obtained using the two different testers are different for the same test material. This can cause a big difference between the two testers in terms of the value of sigma_c under the same sigma_1. Please add a brief discussion on this.
8. On the line with equation (2), delete “(1)”.
9. In equation (2), does “I” represent the initial compaction? This should be clearly indicated.
10. Line 196, check the position of equation (3).
11. Line 201, change “Plot of ffc vs. 1/C*…” from bold to normal.
12. Lines 219-255, check the numbers of the references. Both the first and second references have the same number “1”. Check the text to see if the references have been correctly cited.

Author Response

Modifications to all reviewers are indicated in red on the manuscript.

1. Line 12, “method of Wang et al.” is not clear. It is better to include more detailed information on the method or rephrase the relevant sentence. This has been expanded.
2. Line 120, in “in previous work []”, specific references should be provided. This has been added.
3. Lines 132-139, figures 6 and 7, it should be indicated which material each photo/figure represents. This has been done
4. Line 147, “Figure 8. compares…” should be “Figure 8 compares…”. This has been corrected.
5. Lines 155 and 156, it was stated that “The plot shows that the effect of the test equipment is not significant.” It is better to provide more detailed explanation on the results in the figure to demonstrate the statement. This has been expanded.
6. Line 160, the results in Figures 9-12 need to be discussed. This section has been expanded, using the Figures 6 and 7 further explain the results.
7. Line 172, the coefficient and index of the functions obtained using the two different testers are different for the same test material. This can cause a big difference between the two testers in terms of the value of sigma_c under the same sigma_1. Please add a brief discussion on this. This has been added.
8. On the line with equation (2), delete “(1)”. This has been deleted
9. In equation (2), does “I” represent the initial compaction? This should be clearly indicated. This has been done
10. Line 196, check the position of equation (3). This has been done.
11. Line 201, change “Plot of ffc vs. 1/C*…” from bold to normal. This has been done.
12. Lines 219-255, check the numbers of the references. Both the first and second references have the same number “1”. Check the text to see if the references have been correctly cited. The formatting error has been connected.

Round 2

Reviewer 2 Report

1. In Figure 6 and 7, the author should add the scale in the image with the length of the scale.
2. Line 114-130 should be in the introduction part. It is not suitable to be in the methods and materials because these lines explain on the background of the methods. Please reorganize these sections.  

Author Response

Lines 114-130 about the Freeman FT4 have now been placed in the introduction section, along with the previous literature involving the Brookfield PFT. Figures 6 and 7 have a completed scale.

Author Response File: Author Response.pdf