The Mechanical Properties of PVC Nanofiber Mats Obtained by Electrospinning

Round 1

Reviewer 1 Report

For confirmation of normal Gaussian distribution, the skew of distribution (coefficient of asymmetry A) need be calculate. In other case, the standard deviations cannot be used for nanofibers distribution characterization. Only if /A/<0.5, a standard deviation can be used (see GAV Leaf “Practical Statistics for the Textile Industry”, Manchester, 1984).

How many SEM images of the same material were used for nanofibers diameter calculation?

How many tests were done for average values calculations of each property?

The standard deviation of thickness need be presented also (as is done for other properties).

What the reason of fineness fibres at higher speed? Less stacked fibres on the surface as it were suggested in papers DOI: 10.1155/2013/416961 and DOI: 10.2478/aut-2014-0023? Do authors have some other suggestions?

Author Response

For confirmation of normal Gaussian distribution, the skew of distribution (coefficient of asymmetry A) need be calculate. In other case, the standard deviations cannot be used for nanofibers distribution characterization. Only if /A/<0.5, a standard deviation can be used (see GAV Leaf “Practical Statistics for the Textile Industry”, Manchester, 1984).

Response: Thank you very much for the reminder. The results of skew of distribution (|A|) for the nanofibers, which obtained at 0, 500, 1000, 1500, 2000, 2500 rpm were 0.38, 0.22, 0.24, 0.1, 0.17, 0.23, respectively. We have added the value report | A | in the manuscript (lines 153-155).

How many SEM images of the same material were used for nanofibers diameter calculation?

Response: Thank you very much for your question. We have used 3 SEM image of the same material for nanofibers diameter calculation. The total of nanofibers used to measure the diameter were more than 200 nanofibers. We have added a description to the manuscript (line 106)

How many tests were done for average values calculations of each property?

Response: Thank you very much for the question. For the nanofiber diameter calculation, we measured 200 different nanofiber diameters of 3 SEM images of the same material, because each of our SEM images contains a lot of nanofibers. When we analyzed orientation of nanofiber mat, we repeated the steps outlined in the article 3 times. When determining the thickness of the sample we measured the thickness in three different positions. At least 5 measurements were performed to determine tensile properties. We have added the description to the manuscript (lines 106, 124-125, 128-131)

The standard deviation of thickness need be presented also (as is done for other properties).

Response: Thank you very much for the reminder. We have made revisions accordingly (line 180).

What the reason of fineness fibres at higher speed? Less stacked fibres on the surface as it
were suggested in papers DOI: 10.1155/2013/416961 and DOI: 10.2478/aut-2014-0023?
Do authors have some other suggestions?

Response: Thank you very much for the question. We think the fineness of the fiber is highly dependent on the type of polymer, type solvent and the condition of the electrospinning process. When the conditions are optimal, the fibers will be smooth and have less defects. In this work, we have used PVC with a molecular mass of 40000 and electrospinning conditions are voltage – 20 kV, feed rate of solution – 0.5 mL/h and the distance between the needle tip and the collector – 15 cm. In addition, when using rotating drum collector, the nanofiber is pulled by the collector's movement, thereby reducing the chance of fabricating beads defects, moreover the pull force caused by the rotating drum collector, has a direct effect on the thickness of the electrospun nanofibers.

Reviewer 2 Report

Dear Editor,

The manuscript, "The mechanical properties of PVC nanofiber mats obtained by electrospinning" by Quoc Pham Le et al., reports the relation between the mechanical property and alignment of e-spinning nanofibers. There have been various reports on the mechanical property and alignment of e-spinning nanofibers, so I think the originality of this manuscript was not enough high. However, as there are not many researches on the e-spinning nanofiber comprising PVC, it may be an interesting contribution to Fibers. From my point of view, there are points that must be addressed.

- Generally, with increasing Young’s modulus, the stress at break increases and the strain at break decreases in using the same polymer with different morphology or density. In the manuscript (Table 2), although the mat became stiff (increasing Young’s modulus and the stress at break), the elongation at break maintained at the almost same value. I want to know the mechanism that does not become brittle even if it becomes hard.

- In line 187, authors wrote as “Nanofibers-based studies have shown that as the fiber diameter decreases to a critical value, the mechanical properties increase exponentially”, and in line 196, “In the process of electrospinning under the action of electromagnetic forces, the polymer molecules are pulled out creating an orientation in the polymer molecule”. From these description, It is assumed that a shear induced crystallization has occurred. If so, the crystallinity of nanofibers should be changed at this critical value. I think it needs XRD measurement.

- In Figure 7, despite the thickness of nanofibers on the horizontal axis, the change of tensile strength and Young’s modulus were ascribed by the orientation of nanofibers. It needed the index for representing the orientation of nanofibers. I recommend authors to use the degree of orientation calculated from the FFT image of SEM by ImageJ (see RSC Adv., 2020, 10, 38045).

Author Response

The manuscript, "The mechanical properties of PVC nanofiber mats obtained by electrospinning" by Quoc Pham Le et al., reports the relation between the mechanical property and alignment of e-spinning nanofibers. There have been various reports on the mechanical property and alignment of e-spinning nanofibers, so I think the originality of this manuscript was not enough high. However, as there are not many researches on the e-spinning nanofiber comprising PVC, it may be an interesting contribution to Fibers. From my point of view, there are points that must be addressed.

- Generally, with increasing Young’s modulus, the stress at break increases and the strain at break decreases in using the same polymer with different morphology or density. In the manuscript (Table 2), although the mat became stiff (increasing Young’s modulus and the stress at break), the elongation at break maintained at the almost same value. I want to know the mechanism that does not become brittle even if it becomes hard.

Response: Thank you very much for the kind reminder and question. First, we fully agree with what you have stated "while increasing Young's modulus, the stress at break increases and the strain at break decrease", which, it is true for solid materials. However, when talking about fibers, the increase in Young's modulus and the stress at break is due to increasing of fibers orientation. We think that due to nanofibers entanglement in the mat, the value of the elongation at break, is very small, which make it almost unchangeable. We have added this to the manuscript (lines 189-190).

- In line 187, authors wrote as “Nanofibers-based studies have shown that as the fiber diameter decreases to a critical value, the mechanical properties increase exponentially”, and in line 196, “In the process of electrospinning under the action of electromagnetic forces, the polymer molecules are pulled out creating an orientation in the polymer molecule”. From these description, It is assumed that a shear induced crystallization has occurred. If so, the crystallinity of nanofibers should be changed at this critical value. I think it needs XRD measurement.

Response: Thank you very much for the kind suggestion. We will thoroughly study this issue in the future. However, PVC is an amorphous material, its crystalline ratio is very low.

- In Figure 7, despite the thickness of nanofibers on the horizontal axis, the change of tensile strength and Young’s modulus were ascribed by the orientation of nanofibers. It needed the index for representing the orientation of nanofibers. I recommend authors to use the degree of orientation calculated from the FFT image of SEM by ImageJ (see RSC Adv., 2020, 10, 38045).

Response: Thank you very much for the reminder and suggestion. We have made revisions in Figure 7.

Reviewer 3 Report

The manuscript by Le et al. describes the study of the mechanical properties of polymer (PVC) mats produced by electrospinning. Despite the topic is not new and well-studied, this research presents some interesting and valuable results that could be accepted after careful revisions.

• I would suggest authors to improve the introduction stressing the application aspect (e.g. tissue engineering, scaffolds, biosensors etc.) of electro spun nanofibers. More recent articles should be included (e.g. DOI:10.1016/j.msec.2020.111401, 10.1021/acsami.7b13199)
• please provide the full title for acronyms: PVC, SEM, EDX etc.
• the novelty of the presented research should be underlined in the introduction.
• fig2a. main elements of the electro spinning machine should be indicated.
• the values of mechanical parameters (young's modulus etc.) should be compared and analysed with previously obtained ones. 
• fig7. future captions are too small. captions should have the same size for all figures.
• authors claimed that the mechanical properties of polymer mats depends on the morphology. what is about the chemistry of the produced nanofibers?
• why authors have used PVC?

 

Author Response

The manuscript by Le et al. describes the study of the mechanical properties of polymer (PVC) mats produced by electrospinning. Despite the topic is not new and well-studied, this research presents some interesting and valuable results that could be accepted after careful revisions.

I would suggest authors to improve the introduction stressing the application aspect (e.g. tissue engineering, scaffolds, biosensors etc.) of electro spun nanofibers. More recent articles should be included (e.g. DOI:10.1016/j.msec.2020.111401, 10.1021/acsami.7b13199)

Response: Thanks for the suggestions. We have made revisions accordingly (lines 38-39).

please provide the full title for acronyms: PVC, SEM, EDX etc.

Response: Thank you very much for the reminder. We have made revisions accordingly (lines 10, 70, 80,81, 94-95, 108, 136, 139).

the novelty of the presented research should be underlined in the introduction.

Response: Thank you very much for the kind reminder. PVC is the cheapest polymer that can be found in the market, has many advantages, such as, high resistance to acids, alkalis, and corrosion. PVC nanofibers had the potential to be used for water filtration, air filtration, and as anti-corrosion materials. However, research on strengthening PVC nanofibers, by using rotating drum collector is lacking in literature. We have added and expanded more on the study novelty in introduction (lines 63-67).

fig2a. main elements of the electro spinning machine should be indicated.

Response: Thank you very much for the reminder. We have made revisions accordingly (Figure 2a and lines 143, 144).

the values of mechanical parameters (young's modulus etc.) should be compared and analysed with previously obtained ones. 

Response: Thank you very much for the reminder. We have made revisions accordingly (lines 190-192).

fig7. future captions are too small. captions should have the same size for all figures.

Response: Thanks for your kind reminders. We have made revisions accordingly (Figure 7).

authors claimed that the mechanical properties of polymer mats depends on the morphology. what is about the chemistry of the produced nanofibers?

Response: Thank you very much for your question. We reported in the manuscript that PVC is an amorphous polymer, therefore the random distribution of molecules in the polymer chain strongly affects the mechanical properties of the nanofiber. In the process of electrospinning under the action of an electric force, the molecules are arranged in an oriented way and enhance the mechanical properties of the nanofiber.

why authors have used PVC?

Response: Thank you very much for your question. We used PVC for our research because it is an inexpensive polymer. In addition, PVC is stable in acids and bases, therefore PVC nanofiber is suitable for applications like air filtration, water filtration, and water-oil separation.

Round 2

Reviewer 2 Report

The author's response well explains the some of the queries, so I recommend accepting this manuscript.

Reviewer 3 Report

Authors addressed all my comment. The manuscript can be accepted.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

The rotation speed of had been deeply studied for that I didn't find any originality (novelty) in this research.

Reviewer 2 Report

Title: The mechanical properties of PVC nanofiber mats obtained by electrospinning

 

In this work the Authors report how the speed of a rotating collector affects the morphology and mechanical properties of electrospun PVC mats. The PVC fibers were obtained starting from a 50:50 vol:vol THF:DMF solution, while the speed of the rotating drum collector ranged from 0 rpm to 2500 rpm.

 

The Authors should consider extending the introduction since it does not give a complete overview.

 

The high number of typing, punctuation and grammar errors makes the manuscript not clear, hard to read and understand. An extensive revision of the English is recommended.

 

Line: 18, 19, 20, 140, 153, 163, 165, 173, 236, 237. All the morphological and mechanical test values present in the text should be reported as mean value with standard deviation.

 

Line: 49, 50. Incorrect use of citation.

 

Table3: There is no mention in the materials and methods section of different orientations during the deposition.

Reviewer 3 Report

This study shortly and clearly shows the effect of the alignment in electrospun PVC nanofibers. Both fiber production and analyzation methods were well described. The correct standards were also followed. The conclusions and assumptions are reasonable.

Unfortunately, this paper needs support in terms of English. There is no major problem with scientific sound but grammar support is certainly needed. 

After editing in terms of English, it can be published.

Reviewer 4 Report

This is a solid work about investigation of the properties of oriented PVC nanofibers mats obtained by electrospinning. The science is solid and the characterization is complete. However, I have some concerns before I can recommend it for publication.

(1) Some images are of low resolution, which need to be corrected. For example, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7, Figure 8.

 

(2) The SEM images do not have scale bars. (Figure 3&4) The authors need to add scale bars.

 

(3) The error analysis of this work is not properly handled – the standard deviations have too many significant figures. For example, in table 2& table 3, "53.24±13.98" should be ""53±14".

 

(4) In the introduction section, the authors gives a brief overview of applications of electrospun nanofibers. However, I think the authors have missed some important emerging applications, such as air filtration (ACS Applied Materials & Interfaces, 2019, 11, 12880-12889; Carbohydrate Polymers, 2019, 205, 55–62), antibacterial (ACS Applied Materials & Interfaces, 2020, 12, 31, 34999–35010), oil/water separation (Separation and Purification Technology, 2020, 250, 117116; Journal of Hazardous Materials, 2020, 383, 121152) and drug delivery (Journal of Materials Chemistry B 2019, 7, 709–729; Carbohydrate Polymers, 2016,151,1240–1244). The authors need to include those new emerging development in the introduction section to have a more complete overview.

 

Based on the above concerns, I suggest a minor revision.

Reviewer 5 Report

line 32, the sentence of ''One of the potential methods for producing nanofibers is electrospinning method’’ needs to be more accurate as nowadays nanofibers through electrospinning are produced in large/industrial scale.  

please make sure that all sentences that is not your work have appropriate references, e.g.,line 37.

The one-dimensional nature of the linear polymer chain in fibres makes it possible to obtain strongly anisotropic properties. The anisotropy arises when molecules are aligned along a common direction. this property is for linear polymers such as nylon6 which increase the mechanical strength and not nessesirilly for all polymeric systems; hence I strongly recommend to rewrite lines 37 to 42 and use more appropriate references. 

line 42 needs some references. please read the following link: https://www.sciencedirect.com/science/article/abs/pii/S1751616118301541

Please report fibre size and size distribution of Figure 3. and mention how statistical significance of the data of your tests have been evaluated.

Figure 3 and for could be merged somehow deleting the repeated SEM images.

In figure 5, why the stress Zero points of samples are settles in different strain points? when the strain points is counted in calculations this differences in pre-elongation of samples may make potential readers to doubt table 2.

According to introduction, since the factor of finer alignment has been hypothesised as reinforcing factor for nanofibers, I recommend to also show the impact of directionality of fibres for each diagram in Figures 6.