Molecular Dynamics Investigation of the Effect of Shear during Extrusion on the Permeation Behavior of CH4 in High-Density Polyethylene
Round 1
Reviewer 1 Report
Good job on investigating the barrier properties of HDPE casing using the state of the art molecular dynamics simulation. An integrated approach to combining the coefficients of adsorption and diffusion of gases is understandable. In my opinion, the work can be published after certain improvements.
Questions below:
1. What model was used in the calculations? Justify your choice of model.
2. Was a "model calculation mesh" created in the calculations? What shape is the mesh and how many cells? Justify, please, the choice of mesh form.
3. How correct is it to take a degree of 200 from HDPE, and not 200 thousand? The Average molecular weight (Mw) of HDPE is usually 100-300 thousand. And what are the general characteristics of HDPE - Density, MFR, rheological viscosity, monomodal or bimodal type?
4. Fig.8b and 11b. What is the difference between your given solubility and diffusion coefficients and other researchers [32,33]? Why do the curves in Figures 8b and 11b go through a maximum?
5. The amorphism of PE after extrusion can be estimated from the crystallinity.? Were model experiments carried out on an extruder? Was polyethylene analyzed before and after extrusion for MFR, Mw and Crystallinity?
6. Have real tests of PE been carried out to study the barrier properties to methane.
7. Conclusions point 2. “The solubility coefficients exhibit a pattern of initially increasing and subsequently decreasing with increasing shear rate. Compared with the isosteric heat, the phenomenon can be more effectively explained by considering the Langmuir-type sites, which are influenced by the microstructure of the material”. I believe that a more serious justification is required here, especially since the data of the authors differ from other authors (see question 4). In addition, there are no real data on the microstructure of PE (granules before extrusion and particle of pipes after extrusion).
8. In the introduction, it is necessary to add a description about the types of PE (bimodal HDPE) and the characteristics of PE (MFR, wide MWD (short and long macromolecules), crystallinity) that are used for coating pipes used for the transportation of oil and gas + references to literature on this topic of work.
Author Response
Thank you for your advice.
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
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Comments for author File: Comments.pdf
Author Response
Thank you for your advice.
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Explanations and corrections accepted.
The manuscript is recommended for publication
