Effect of Binder Coatings on the Fracture Behavior of Polymer–Crystal Composite Particles Using the Discrete Element Method
Round 1
Reviewer 1 Report
Dear Authors,
Thank you for your manuscript.
I think your manuscript is very well written and I personally found it quite interesting. I only have few comments and they are mentioned in the pdf attached along with review. Please find the attachment.
Thank you.
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 1 Comments
Comments and Suggestions for Authors:
I think your manuscript is very well written and I personally found it quite interesting. I only have few comments and they are mentioned in the pdf attached along with review. Please find the attachment.
Response: The authors thank the reviewer for the positive assessment and valuable comments on our manuscript, which are very helpful to the improvement of our paper. Please note that all of the changes were marked red in the revised manuscript. Our response to each comment is presented below.
Point 1: change ‘formed by coating crystals’ to ‘coated’.
Response 1: ‘formed by coating crystals with binders’ was revised as ‘formed by crystals coated with binders’
Point 2: change ‘was’ to ‘were’ in line 73.
Response 2: Corrected.
Point 3: What are four these classes? Please highlight here.
Response 3: The name of the four classes of morphological characteristics were added in line 113 of the manuscript.
Point 4: Could you please insert a scale in figure?
Response 4: The scale bars were inserted in Fig. 3 and Fig. 4 (b)
Point 5: What are we seeing in the inset?
Response 5: In Fig.7 (a) and Fig.8 (a), except force-displacement, spatial distribution of different micro-cracks was added, and the classification was described in lines 219-223. And “spatial distribution of different microcracks” was added in caption of Fig.7 (a) and Fig.8 (a).
Point 6: Does uniformity increase as the load increases?
Response 6: In the plastic stage, with the loading process, the microcracks spread from the middle of the particle to the whole particle. And this sentence described the stage about the first peak to the failure, so the distribution of microcracks became more uniform.
Point 7: What kind of particle was used for this test? Short rod or spherical? What is the vertical axis?
Response 7: Shot particles were used, as illustrated in Fig. 8. The vertical axis was parallel to the Z axis and located in center of particle. To avoid misunderstanding, the particle shape was added in captions of Fig. 8 and Fig. 9.
Point 8: How would the adhesion affect the nature of tensile and shear microcracks? ls there a way to incorporate that either in this or another manuscript?
Response 8: This is a very interesting topic, but difficult to quantify by experiments. We would like to design a more refined test to explore this issue in the future.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The subject of the paper is interesting; generally the fracture behaviour of polymer-crystal composite particles is an important topic. The applied methods are up-to-date methods; the experimental work and the modelling and numerical simulation complement each other. The aims of the research work and manuscript have been drawn exactly. However, the presentation of the research work and the results is overall not unambiguous, important elements and details have not been described. Consequently, the manuscript should be amended.
Please,
- separate the references in one sentence (e.g. “the Brazil split test, the indentation test, the double cantilever beam test, and the four-point bend test [14-17]” (rows 37-38));
- summarize the relevant results of your previous study [49] under the section 1 (“Introduction”);
- add the details to the figure caption of Fig. 1 belonging to (a), (b) and (c);
- add the name of four classes of morphological characteristics to the text (rows 106-107) and Fig. 2;
- add the designation of the two groups to the text (row 108);
- explain the differences of the Force-Displacement curves in Fig. 4, Fig. 7 and Fig. 8, separately, and explain their connections with the characteristics of the particles, too;
- separate the parameters belonging to the six elements in Table 1 correctly;
- use the same terminology in Table 1: “Friction coefficient” and “Coefficient of friction”;
- add the nomenclatures to Fig. 9 (b) belong to “a”, “b”, “c” and “d”;
- add the binder content in the whole manuscript if relevant (e.g. Figs. 7-10);
- add the experimental results to Fig. 13 belonging to 10% and 15% binder contents and explain the differences if necessary;
- add the type of the used equipment in the whole manuscript.
Author Response
Response to Reviewer 2 Comments
Comments and Suggestions for Authors:
The subject of the paper is interesting; generally, the fracture behaviour of polymer-crystal composite particles is an important topic. The applied methods are up-to-date methods; the experimental work and the modelling and numerical simulation complement each other. The aims of the research work and manuscript have been drawn exactly. However, the presentation of the research work and the results is overall not unambiguous, important elements and details have not been described. Consequently, the manuscript should be amended.
Response: The authors thank the reviewer for the valuable and constructive comments on our manuscript, which we have found very helpful to the improvement of our paper. Please note that all of the changes were marked red in the revised manuscript. Our response to each comment is presented below.
Point 1: Separate the references in one sentence (e.g. “the Brazil split test, the indentation test, the double cantilever beam test, and the four-point bend test [14-17]” (rows 37-38)). 

Response 1: According to the suggestion, the references were separated in lines 36-38, 46-48.
Point 2: Summarize the relevant results of your previous study [49] under the section 1 (“Introduction”).
Response 2: According to the suggestion, the relevant results of our previous study were summarized into the section 1 (“Introduction”) in lines 66-68.
Point 3: Add the details to the figure caption of Fig. 1 belonging to (a), (b) and (c).
Response 3: The details were added to the figure caption of Fig. 1 in lines 97-99.
Point 4: Add the name of four classes of morphological characteristics to the text (rows 106-107) and Fig. 2.
Response 4: The name of four classes of morphological characteristics were added in line 113 of the manuscript.
Point 5: Add the designation of the two groups to the text (row 108).
Response 5: The designation of the two groups was added in lines 115-116 of the manuscript.
Point 6: Explain the differences of the Force-Displacement curves in Fig. 4, Fig. 7 and Fig. 8, separately, and explain their connections with the characteristics of the particles, too.
Response 6: The differences and connections of the Force-Displacement curves in Fig. 4, Fig. 7 and Fig. 8, separately were described and explained in lines 223-230, 246-252, 255-257.
Point 7: Separate the parameters belonging to the six elements in Table 1 correctly.
Response 7: The parameters belonging to the six elements were separated by horizontal lines in Table 1
Point 8: Use the same terminology in Table 1: “Friction coefficient” and “Coefficient of friction”.
Response 8: According to the suggestion, the terminology was unified as “Friction coefficient” in Table 1.
Point 9: Add the nomenclatures to Fig. 9 (b) belong to “a”, “b”, “c” and “d”.
Response 9: The nomenclatures to Fig. 9 (b) belong to “a”, “b”, “c” and “d” were added lines 288-289
Point 10: Add the binder content in the whole manuscript if relevant (e.g. Figs. 7-10).
Response 10: In this paper, coating effect of composited particle included not only the binder content, but also mechanical behavior, so it is critical to reveal the failure mechanism of composited particle. As viscoelastic material, the morphology has an important influence on the mechanical behavior of composited particle, shown in Fig. 7 and Fig. 8. The propagation of microcracks was further investigated by Fig. 9 and Fig. 10.
Point 11: Add the experimental results to Fig. 13 belonging to 10% and 15% binder contents and explain the differences if necessary.
Response 11: The experimental result of 20% binder content was mainly used for the validation of the DEM parameters adopted in this study. The samples with 10% and 15% binder contents were not prepared. The investigation on the effect of binder content on the crushing behaviours of polymer-crystal composite particles mainly relied on the DEM simulations.
Point 12: Add the type of the used equipment in the whole manuscript.
Response 12: The type of the used equipment was added in lines 84-85, 89, 93-94.
Author Response File: Author Response.docx
Reviewer 3 Report
The submitted manuscript presents the results describing the effect of binder coatings on the behavior of polymer-crystalline composite particles. The subject and object of the study are fully consistent with the aims and scopes of the journal. Thus, the work can be published in the journal "Coatings". However, there are several issues that need to be addressed by the authors before publication.
The abbreviation µCT for X-ray micro-computed tomography was provided in the Abstract section. I recommend repeating it in the Introduction when it first appears (line 52) for benefit of readers.
Section 2.1. The authors point out the growth procedure, referring [46]. However, it is not clear whether the polymer-crystalline composite particles were obtained by the authors using the technique described in [46], or whether the authors used samples prepared earlier for studies Ref. [46]. I recommend providing more information on composite particle synthesis.
Please, specify equipment used for CT imaging and SEM.
Figure 2 has insets showing SEM images of composite particles and the corresponding CT scans. The CT images are quite small, and it is impossible to assess the distribution of crystals and binders.
Section 2.3. Fig. 4 shows the force-displacement series, and the "typical" curve is described in more detail. How many particles were analyzed using the crush test?
Lines 198-200 seem to be instructions to the authors.
Author Response
Response to Reviewer 3 Comments
Comments and Suggestions for Authors:
The submitted manuscript presents the results describing the effect of binder coatings on the behavior of polymer-crystalline composite particles. The subject and object of the study are fully consistent with the aims and scopes of the journal. Thus, the work can be published in the journal "Coatings". However, there are several issues that need to be addressed by the authors before publication.
Response: The authors thank the reviewer for the valuable and constructive comments on our manuscript, which we have found very helpful to the improvement of our paper. Please note that all of the changes were marked red in the revised manuscript. Our response to each comment is presented below.
Point 1: The abbreviation µCT for X-ray micro-computed tomography was provided in the Abstract section. I recommend repeating it in the Introduction when it first appears (line 52) for benefit of readers. 

Response 1: According to the suggestion, X-ray micro-computed tomography repeating µCT in the Introduction when it first appears (lines 52-53).
Point 2: Section 2.1. The authors point out the growth procedure, referring [46]. However, it is not clear whether the polymer-crystalline composite particles were obtained by the authors using the technique described in [46], or whether the authors used samples prepared earlier for studies Ref. [46]. I recommend providing more information on composite particle synthesis.
Response 2: The author Guo is our collaborator. Yes, the samples were the same as used in the authors’ previous study [46]. More detailed information of the kneading granulation method was given in lines 82-83.
Point 3: Please, specify equipment used for CT imaging and SEM.
Response 3: The type of the used equipment was added in lines 84-85, 89, 93-94.
Point 4: Figure 2 has insets showing SEM images of composite particles and the corresponding CT scans. The CT images are quite small, and it is impossible to assess the distribution of crystals and binders.
Response 4: In Fig. 2(b), we just choose one slice of the CT images. Due to similar density of crystal and binders, it is a big challenge to assess the distribution of crystals and binders. So, we just qualitatively described the distribution of the crystals and binders by brightness.
Point 5: Fig. 4 shows the force-displacement series, and the "typical" curve is described in more detail. How many particles were analyzed using the crush test?
Response 5: A statistical method was used to explore survival probability distribution and Weibull distribution of composite particles, and 30 particles were chosen to analyze in the crushing test. The number of particles was added in line 143.
Point 6: Lines 198-200 seem to be instructions to the authors.
Response 6: The instructions to the authors were removed from the manuscript
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Thanks the Authors for the valuable amendments, the added information and the corrections of more details. The modifications were precisely highlighted in the manuscript and were explained in the cover letter (Response to Reviewer 2 Comments).
Authors have elaborated my suggestions attentively and answered correctly. I can accept their responses in full (inclusive “The samples with 10% and 15% binder contents were not prepared”, too).
Reviewer 3 Report
The authors responded to the comments made, improving and supplementing the manuscript according to suggestions. Thus, the manuscript can be published in the journal.
