The Impact of Primary Sludge on the Physical Features of High-Density Polyethylene (HDPE) Composites
Round 1
Reviewer 1 Report
The paper “The impact of primary sludge on the physical features of high-density polyethylene (HDPE) composites” presents an interesting study and deserves to be considered for publication.
Before publication, please consider following comments that may enhance the manuscript:
L67-L77: In the literature search consider also other kinds of alternative raw materials, e.g. husks:
Hýsek, Š.; Podlena, M.; Bartsch, H.; Wenderdel, C.; Böhm, M. Effect of wheat husk surface pre-treatment on the properties of husk-based composite materials. Ind. Crops Prod. 2018, 125, 105–113.
Last paragraph in the Introduction part: Please define your hypothesis.
L139-L141: The methodology of the elemental analysis has to be described more deeply. From the methodology it is not clear how the results in the Table 2 were obtained.
Author Response
Dear Editor and Reviewer1
Thank you for your insightful and constructive comments about our text. I’m pleased to send you our re-revised manuscript. The comments helped us to improve this manuscript significantly. We considered your comments, suggestion and questions very carefully, and according to those, we have made changes in the manuscript. The corrections and addendums are highlighted by red colored font in the manuscript.
The detailed corrections and responses to the comments are listed as follows:
(Example: - Location: “Your (editor or reviewer) comment” --> Our response
Introduction: “Reviewer1: L67-L77: In the literature search consider also other kinds of alternative raw materials, e.g. husks: Hýsek, Š.; Podlena, M.; Bartsch, H.; Wenderdel, C.; Böhm, M. Effect of wheat husk surface pre-treatment on the properties of husk-based composite materials. Ind. Crops Prod 2018, 125, 105-113” --> Other raw materials have been also considered, and for example, this reference is added. New reference numbers henceforth. The end of introduction: “Reviewer1: ”Last paragraph in the Introduction part. Please define your hypothesis.” --> The hypothesis is defined. Material and Methods: “Reviewer1: L139-L141: The methodology of the elemental has to be described more deeply. From the methodology it is not clear how the results in the Table 2 were obtained.” --> The methodology is described more deeply.Thank you for your considering this paper. We hope that the amendments please you.
Yours faithfully,
Kati Mustonen, the corresponding author
Reviewer 2 Report
Dear authors,
Your manuscript work is interesting from experimental point of view.
The novelty consists in the analysis of the effects of the admixture of the primary sludge on the physical features of the composites based on high-density polyethylene (HDPE).
The manuscript provides important contributions to the research concerning to the replacing of spruce wood flour with primary sludge in HDPE composite materials in order to improve some physical properties: water absorption, swelling and impact strength after cyclic freeze-thawing test. This subject of research matches with the topic of Resources journal since the primary-sludge might use as valuable raw material in manufacturing of HDPE composites. The conclusions are adequately supported by the data presented in order I recommend the publication of this paper after some major improvements.
In order to improve this interesting manuscript, I recommend some minor changes and improvements as it is shown below.
Section “2. Materials and Methods”:
-The section “2. Materials and Methods” may be divided in: “2.1. Materials” and “2.2. Work methods”.
-The section “2.2.Work methods” may be divided in the following sub-sections: “Water absorption”, “Impact test after freeze-thawing cycles”, “SEM analyses”. Each sub-section must contain: a brief description of the test methods, number of the sample replicates, shape and dimensions of the samples, equipment used, loading schemes.
-In impact test, the authors should clarify that impact test by Charpy method was used. The authors should add information about shape and dimensions corresponding to the impact samples, clarify if samples are with or without notch according with EN ISO 179-1.
-What standard was used for water absorption test?
-Equation (2) and line 134: lowercase letter t should be used to denote sample thickness because T usually denotes temperature.
- Standards EN ISO 179-1 and EN 15534-1:2014 + A1:2017 should be added to References list.
-Authors should show by a chart or describe the freeze-thaw cyclic treatment of the samples applied before impact test (cooling temperature, storage time). What kind of equipment what used for freeze-thaw cyclic treatment?
Section “Moisture properties”:
-Line 175-176: What was the average value of standard deviation recorded for WA and TS in case of the both Pr-Sl/HDPE and reference composites?
-Do the curves of water absorption fit on Fick’s law which characterizes the polymeric composites? In order to compute the parameters of the Fick’s law for the both absorption curves, the authors could use the following references:
1.Springer, G. S. (1988). Chapter: “Environmental effects” in: Environmental Effects on Composite Materials, Vol. 3, Edited by Springer, G. S., Technomic Publishing Company, Lancaster, PA.
2.Cerbu, C.; Cosereanu, C. Moisture effects on the mechanical behavior of fir wood flour/glass reinforced epoxy composite. BioResources 2016, vol. 11, no.4, pp. 8364-8385.
3.Naceri A. An analysis of moisture diffusion according to Fick’s law and the tensile mechanical behavior of a glass-fabric-reinforced composite. Mechanics of Composite Materials 2009, 45(3), 331-336.
Section “Freeze-thawing durability of materials”:
Please, add additional comments concerning to the effects of cyclic treatment on the structure of the both composites analyzed (lines 190-191). The authors should explain what are the main remarks regarding the changing of the structures that lead to the decreasing or increasing of the impact strength in case of Pr-Sl/HDPE and reference composites, respectively.
Section “Discussion”:
Lines 227: You should clarify the mechanism of degradation of the interfacial bonding between fibers and matrix: “…swelling causes residual stresses on the interfacial bonding of WPC’s components, which lead to developing of micro-cracks at this area and finally, lead to weakening of the strength.” The second reference (2) indicated in the above list might be referred to support this phenomenon.
Author Response
Dear Editor and Reviewer2
Thank you for your insightful and constructive comments about our text. I’m pleased to send you our re-revised manuscript. The comments helped us to improve this manuscript significantly. We considered your comments, suggestion and questions very carefully, and according to those, we have made changes in the manuscript. The corrections and addendums are highlighted by red colored font in the manuscript.
The detailed corrections and responses to the comments are listed as follows:
(Example: - Location: “Your (editor or reviewer) comment” --> Our response
Section 2. Materials and Methods: “Reviewer2: The section “2. Materials and Methods” may be divided in: “2.1. Materials” and “2.2. Work methods”.” --> The section is divided according to your proposal.
Section 2. Materials and Methods: “Reviewer2: The section “2.2.Work methods” may be divided in the following sub-sections: “Water absorption”, “Impact test after freeze-thawing cycles”, “SEM analyses”. Each sub-section must contain: a brief description of the test methods, number of the sample replicates, shape and dimensions of the samples, equipment used, loading schemes.” --> The section is divided sub-sections according to your proposal and the description of the test methods etc are added. A name of first sub-section is clarified a little bit more detailed (Instead of “water absorption”, we have used terminology of “moisture properties” that includes all of tests).
Section 2. Materials and Methods: “Reviewer2: ” In impact test, the authors should clarify that impact test by Charpy method was used. The authors should add information about shape and dimensions corresponding to the impact samples, clarify if samples are with or without notch according with EN ISO 179-1.” --> The method is clarified.
Section 2. Materials and Methods: “Reviewer2: ” What standard was used for water absorption test?” --> Water absorption based on the standard EN 15534-1:2014 + A1:2017, and this is added on the section “2.2. Work methods”. All used standards are selected from recommendation of standard EN 15534-1 “Composites made from cellulose-based materials and thermoplastics (usually called wood-polymer composites (WPC) or natural fibre composites (NFC)). Part 1: Test methods for characterisation of compounds and products”
Equation (2): “Reviewer2: lowercase letter t should be used to denote sample thickness because T usually denotes temperature." --> The letter were changed. It is now marked by small letter that is congruent with another (WA) equation.
Material and Methods: “Reviewer2: Standards EN ISO 179-1 and EN 15534-1:2014 + A1:2017 should be added to References list.” --> The standards are added to reference list, as well standard EN 317.
Material and Methods: “Reviewer2: Authors should show by a chart or describe the freeze-thaw cyclic treatment of the samples applied before impact test (cooling temperature, storage time). What kind of equipment what used for freeze-thaw cyclic treatment?” --> The equipment and procedure is shortly described. More exactly description is available in the standard that is presented as a reference. See: EN 15534-1:2014 + A1:2017 [18], topic: “8.3.2 Moisture resistance under cyclic conditions”.
3.2 Moisture properties: “Reviewer2: Line 175-176: What was the average value of standard deviation recorded for WA and TS in case of the both Pr-Sl/HDPE and reference composites?.” --> The average values are presented in Figure 3 as an error bars. More exactly, standard deviations values are presented in next table, for your information.
Standard deviation of water absorption
|
|
24 h |
48 h |
96 h |
168 h |
336 h |
672 h |
|
Reference |
0.79 |
1.71 |
6.13 |
3.66 |
4.65 |
4.71 |
|
Pr-Sl/HDPE |
0.20 |
0.24 |
0.23 |
0.30 |
0.31 |
0.22 |
Standard deviation of thickness swelling
|
|
24 h |
48 h |
96 h |
168 h |
336 h |
672 h |
|
Reference |
1.92 |
1.69 |
2.19 |
2.03 |
2.39 |
1.88 |
|
Pr-Sl/HDPE |
0.22 |
0.34 |
0.30 |
0.33 |
0.36 |
0.31 |
--> We thank reviewer for the comment but the mathematical models are not included in this work. We believe that the measuring of Fick’s law does not increase the value of this study remarkable. According to the rough approximation of Klyosov (2007, “Wood-Plastic Composites” p. 397), Fick’s law predicts that the mass of water absorbed increases linearly with time and then gradually slows until it reaches equilibrium plateau. Based on the Figure 3a, we have not any suspicions to suspect this opinion. In addition, Fick’s law based on the idea “only one-directional description of the mass transfer” so it would need actions where some sides of sample should be treated for a hydrophobic form. Especially, when we taken account on the fact of relative high content of fiber amount (44%), in which the saturation point is 30%, approximately.
3. Freeze-thawing durability of materials: “Reviewer2: Section “Freeze-thawing durability of materials”:Please, add additional comments concerning to the effects of cyclic treatment on the structure of the both composites analyzed (lines 190-191). The authors should explain what are the main remarks regarding the changing of the structures that lead to the decreasing or increasing of the impact strength in case of Pr-Sl/HDPE and reference composites, respectively.” --> Acknowledged. The phenomenon is explained.
Discussion: “Reviewer2: “Section “Discussion”:Lines 227: You should clarify the mechanism of degradation of the interfacial bonding between fibers and matrix: “…swelling causes residual stresses on the interfacial bonding of WPC’s components, which lead to developing of micro-cracks at this area and finally, lead to weakening of the strength.” The second reference (2) indicated in the above list might be referred to support this phenomenon.” --> Acknowledged. The phenomenon is explained based on the study of Cerbu and Cosereanu.
Review Report From: ”English language and style are fine/minor spell check required” --> The manuscript was checked by a professional grammatical expert (MDPI English Editing, editing ID: English-13839) at 10th of November, so it should meet the standards of journal.
Thank you for your considering this paper. We hope that the amendments please you.
Yours faithfully,
Kati Mustonen, the corresponding author
Round 2
Reviewer 1 Report
After carefully performed rvisions the manuscript can be accepted for publication.
