Review Reports

Round 1

Reviewer 1 Report

The article proposes a good series of experimental data aimed at characterizing the aging due to environmental and/or chemical factors of two HDPE geomembrane samples. However, some relevant aspects need to be revised to improve the quality of the paper.

In general, the article would be much more interesting if the experimental data obtained could be compared with those predicted/expected for the virgin geomembrane.

1) from a methodological point of view, a serious shortcoming is given by the total lack of information on the original characteristics of the two materials: was it not possible to obtain any information on/from the producer of the geomembranes?

2) similarly there is a total lack of information on the chemical characteristics of the sewage/leachate with which the geomebranes have been in contact

3) If this information is not available, this aspect should be highlighted, starting from the abstract; in any case, a systematic comparison with typical data should be proposed.

4) In how much space of the geomembrane were the specimens taken for the different tests? Could there be a non-homogeneity of the aging of the material? Please add a comment.

5) by reading the paragraphs 3.1, 3.2 and 3.3 it is not possible to say anything more than whether the material can still be considered with acceptable characteristics or not. However, there is no evidence that any deficiencies are due to aging instead of to initial defects of virgin materials. Similarly, some characteristics of the material could have decayed but, if still adequate, they do not highlight the aging process.

6) referring to paragraphs 3.4 and 3.5, the behavior of the two geomebranes should be discussed not so much with respect to each other, but with respect to virgin material. If there is a typical behavior of the HDPE, please report the curves for comparison purposes. Furthermore, no mention is made of the fact that the interaction and the aging may be different, not only in relationship to the different fluids, but also in relationship to the different thickness of the geomembranes and to the different periods of time elapsed (2.75 and 5.17 years).

7) in the light of the above, please review and improve the conclusions

8) pay attention to describe, at least once in the text, the meaning of all the abbreviations used (check for example DSC...)

9) avoid using the symbol / to separate the unit of measurement in the axes of the figures; I suggest to put the unit of measure in brackets

 

Other specific suggestions:

row 22: the sentence is not clear for me (the comparison of... shows ?)

rows 180-182: by considering Fig. 8 and 9, a greater number of heating-cooling cycles seems to have been done; please clarify this aspect

row 190: please check the sentence and related references

row 198: please indicate the minimum reference values of tensile and tear resistance

Fig. 3 and 4: the different curves are not easy to distinguish; evaluate the use of different colors or symbols. Moreover, the values of 5-10-20-30 °C should be expressed in °C/min

row 257-258: this sentence may appear questionable given that no information is provided regarding the behavior of the virgin geomembrane

Table 1: in the table caption please remove the dot in the unit of measure: (°C min-1) instead of (°C.min-1). Moreover, it is not easy to understand how the temperature ranges were selected; please explain and, if possible, make the presentation homogeneous (alway 3 or 4 intervals)

row 333: "The HDPE kinetics parameters.. " please improve the form of the sentence, for example adding "For comparison purposes.." and summarizing the parameters indicated in the cited study

Fig. 8 and 9: understanding of figures is not immediate. I suggest to insert some notes indicating sequentially the various phases of heating-cooling (phase 1, phase 2 .... phase 6) and to move here the explanation of the cycles previously reported in the paragraph 2.5

row 433: review the sentence "at the peak temperature of tan-δ (32 °C).. "; probably it should be "at the temperature of 32°C a peak of tan-δ.."

row 439-440:"Tan-δ decreases with increasing 439 stiffness, that is, if the material is rigid, tan-δ will be constant (will have a zero value) [44, 45]"  I suggest to anticipate this sentence in order to make more easy the comprehension of text; moreover it would be good not to confuse the term "rigid" with "constant stiffness"

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper is of the interesting topic and good to be published. However, the  author needs to give feedback to the below comments:

1- As for section of Materials and Methods:

please provide the flow chart of the methodology, and please describe the reason to select the referrer no. [28] and [29] to perform the mechanical properties. Why do you think it is the best to select 50 mm-51mm a speed, as you mentioned in lines 139-142.

2- As for Results and Discussion:

please for lines 420-425, please can you give deep details to support the arguments about HDPE "elastic potential" and attribution to "molecular interaction" , and please provide any current new previous studies to support the results you found. 

3- As for conclusions;

lines 473-475, please try to give extra details to support the conclusion of the both samples. And please give recommendation for the future studies. 

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

I suggest to remove the period at the end of the various notations °C/min in figures 4-5-6 Moreove, I strongly reccommend to review the English form of the last sentences (rows 492-495). Regarding the methodology, I repeat again that I would consider it correct to specify in the abstract that the comparison of the data is with average values of literature, since the original characteristics of the materials studied are not available.