Round 1

Reviewer 1 Report

line 18: COF, should be coefficient of friction (COF)

Optional: If the authors can  provide examples of thermplastic polymer Tribological applications to the beneficial.  

Author Response

Comments and Suggestions for Authors

line 18: COF, should be coefficient of friction (COF)

Optional: If the authors can  provide examples of thermplastic polymer Tribological applications to the beneficial.  

Response to reviewer:

Thank you for the kind proposition: Line 18 was rewritten and the following sentence was included in the conclusion:

Possible applications are at drivetrain technology, for bearings and seals

Reviewer 2 Report

However, there are several points that I would like to address.

Minor comments:

Introduction

1.     In many places the authors wrote: in the previous paper, previous study  - please write the references.

2.     Lines 90,98: Table 1 is the table with lubricants, not equations.

3.     There is missed title of the first table in the manuscript.

4.     Please explain what mean: g11 and g33.

5.     First table in the manuscript: titles of parameters are given by capital and small letters-it should be homogenized. Why there is numeration of equations in order: 1,3,5,7,8,etc?

Materials

6.     On what basis have the liquid mediums been chosen for research?

7.     What temperatures were used for testing: friction, rheology, contact angle?

8.     Rheological studies: does only dynamic viscosity was measured? What about viscoelastic properties?

Results

9.     Line 230: Fr, Fn – please explain abbreviations in text.

10.  Line 233: s, f– please explain abbreviations in text.

11.  Figures: there are illegible descriptions in some places in the figures. The quality of some figures should be improved – the description letters are not clear/readable.

12.  Titles of figures: I propose to put abbreviations used in figures in titles next to appropriate parameter (in brackets).

13.  Numerations of pages is incorrect.

14.  In my opinion  in results section the general comparison of the obtained test results will be interested.

15.  The last figure in paper: no title, no cited in the manuscript.

16.  There is no homogeneity in References – used different styles, sometimes paper titles or  journal titles are missed. It should be uniform.

17. Please check other comments in the attached manuscript.

Comments for author File: Comments.pdf

Author Response

Comments and Suggestions for Authors

Author focused on tribology of PEEK/PA46 –steel tribosystems in the static and boundary friction regime. The problem of the effect of the lubricants on the static and the dynamic friction is important. There are a lot of science works which try to discuss the idea of lubrication in such types of friction. But there is no directly response and clear mechanism of these processes. The results of the work show that the adhesion threshold of PA46 with the non-spreading lubricants water, 19 glycerine, a water-glycerine mixture, ethylene glycol and poly-1-decene decreased with increasing 20 solving tendency of the lubricants.  The manuscript is interesting and well written.

However, there are several points that I would like to address.

Minor comments:

Response to reviewer:

Thank you for the kind suggestion of useful corrections. We have corrected lists, numerations, references, page numbers and we have added further explanations. Please find revised aspects point to point below.

Introduction

1.     In many places the authors wrote: in the previous paper, previous study  - please write the references.

We have added the references.

2.     Lines 90,98: Table 1 is the table with lubricants, not equations.  

Table 1 (of equations) and Table 2 (of lubricants) were separated and referenced.

3.     There is missed title of the first table in the manuscript.

Table 1 (of equations) and Table 2 (of lubricants) were separated and referenced.

4.     Please explain what mean: g11 and g33.

G11 is the free surface energy of polymer and g33 is the cohesive energy of liquid. We have added this to the manuscript.

5.     First table in the manuscript: titles of parameters are given by capital and small letters-it should be homogenized. Why there is numeration of equations in order: 1,3,5,7,8,etc?

We have chosen small letters for a homogeneous format of these titles and renumbered the equations from 1-8.

Materials

6.     On what basis have the liquid mediums been chosen for research?

We have added the following sentence to the material section:

By doing so, two groups of liquids with comparable viscosity were obtained. One group is representing industrial base oils and the other group widely used obtainable chemicals being none or highly polar.

7.     What temperatures were used for testing: friction, rheology, contact angle?

We have added the following sentence to the material section:

If not stated all data were taken for 25°C and experiments were done at 25°C.

8.     Rheological studies: does only dynamic viscosity was measured? What about viscoelastic properties?

The viscoelastic properties of the altered polymer surface would be interesting but were not investigated during this study. A deviation of linear viscosity was presumed to be negligible for the chosen liquids and tribological test with a soft to hard surface contact.

Results

9.     Line 230: Fr, Fn – please explain abbreviations in text.

We have added the ratio of Friction Force and Normal Force for explanation.

10.  Line 233: s, f– please explain abbreviations in text.

We have added the following explanation (s: amplitude of ball surface displacement, f: frequency of oszillation was 1 Hz)

11.  Figures: there are illegible descriptions in some places in the figures. The quality of some figures should be improved – the description letters are not clear/readable.

The figures in the document have a lower quality than the ones that were uploaded to the journal and the online version. The smallest text in the figures was resized to increase the quality of the figures. The tables with the small description letters just give the energy values and parameter of table that are helpful to qickly access the necessary data. We think they are helpful to the online presentation of graphics and less disctracting to the printed paper. We hope you will find our arguments adequate.

12.  Titles of figures: I propose to put abbreviations used in figures in titles next to appropriate parameter (in brackets).

We have followed your suggestions: e.g. PEEs (red, pentaerythrite ester)

13.  Numerations of pages is incorrect.

We assume that you refer to a numeration as 10 of 4. We corrected the overall number of pages to be 15.

14.  In my opinion  in results section the general comparison of the obtained test results will be interested.

We have structured the tests and hypotheses according to their regimes and discussed them with respect to their nature being solving or spreading. The most condensed presentation you may find at an intensive investigation of the graphical abstract.

15.  The last figure in paper: no title, no cited in the manuscript.

The last figure is the graphical abstract that will appear separately. We forgot, that the reviewers will find them lost on the manuscript. We have taken the figure from the manuscript.

16.  There is no homogeneity in References – used different styles, sometimes paper titles or  journal titles are missed. It should be uniform.

There was a hidden problem in our reference software. We have corrected the references to the necessary uniform type.

17. Please check other comments in the attached manuscript

Thank you.

Reviewer 3 Report

I think this is an interesting job, continuation of a previous, studying the effect of the spreading or non-spreading character of lubricants in polymer-steel contatcs. The authors reach interesting conclusions, relating the behavior of lubricants with work-of-spreading.

The main question that arises, after reading the work, is the way in which the measurements have been carried out, that is, in the Materials and Methods section it is not explained if the values shown in Table 1 or in the different graphs are obtained from a single experiment, or if those values are the average of several measurements. In any case, values of uncertainty are not indicated anywhere.

On the other hand, I have a couple of minor (formal) comments:

1) Figure 6 caption can not be on a different page than the figure.

2) On page 8, line 307, "the" seems to be repeated 

Author Response

Comments and Suggestions for Authors

I think this is an interesting job, continuation of a previous, studying the effect of the spreading or non-spreading character of lubricants in polymer-steel contatcs. The authors reach interesting conclusions, relating the behavior of lubricants with work-of-spreading.

The main question that arises, after reading the work, is the way in which the measurements have been carried out, that is, in the Materials and Methods section it is not explained if the values shown in Table 1 or in the different graphs are obtained from a single experiment, or if those values are the average of several measurements. In any case, values of uncertainty are not indicated anywhere.

On the other hand, I have a couple of minor (formal) comments:

1) Figure 6 caption can not be on a different page than the figure.

2) On page 8, line 307, "the" seems to be repeated 

Response to reviewer

Thank you for the kind corrections. We have revised the manuscript according to the suggestions 1 and 2. In the experimental section we have added a description to the deviations of this method: To achieve stable and reproducible conditions a testing sequence was applied to form a run-in situation. Each diagram is a representative graph that was chosen for a minimum of 10 repetitions, to identify a run-in state by similarity to the others. Differences can only be found for the first runs.

Round 2

Reviewer 2 Report

Dear Authors,

Thank you for your reply.