Thermal Behavior and Flammability of Epoxy Composites Based on Multi-Walled Carbon Nanotubes and Expanded Graphite: A Comparative Study
, Evgeny A. Maksimovskii 3, Maxim V. Popov 1,4 and Irina S. Berdyugina 1Round 1
Reviewer 1 Report
The authors report an interesting investigation on the thermal behavior of epoxy nanocomposites based on carbon nanotubes and expanded graphite. The work reports useful results investigated which are could be published in the journal of Applied Sciences however some corrections/modifications are recommended.
1) Page 2, line 63: for the reference 28 cited in this line, it would be considered as a good gesture if you report the first author as [first author] et al.
2) Page 2, line 63/64: the authors should explain what study was made by the reference 28. For the readers, hence it becomes clears how this submitted work differs from the references mentioned in the introduction of this paper.
3) Page 2, lines 80-83: the procedure of expansion of graphite is mentioned in a complicated way. Kindly improve it for easier understanding for the reader.
4) Page 2, line 90: Replace 'There' with 'It'.
5) Page 3, line 96: For the SEM analysis, were the specimens coated with a conductive layer? or were they as produced used for analysis.
6) Page 3, line 100: Kindly improve the wording "Thermal behavior at the heating of the prepared epoxy composites". Also at what temperature the test was started?
7) Page 3, lines 110-114: Test description of flammability is very complicated for the reader to understand.
8) Page 4, Figure 1a-c: scale bars can be more prominent and clear.
9) Page 4, Figure 1d: x axis is very small and completely unreadable. It can be improved.
10) Page 6, line 172: my sincere suggestion would be to not represent the typical curves rather than a good comparison of all the TG and DSC curves. Since the shape of the curves would be different by changing the amount of the filler in epoxy.
11) Page 9, line 268: change 'act' by 'acts'
12) Page 9, line 269: change 'increase' by 'increases'.
Author Response
Authors would thank the reviewers for their useful comments, which help to make the quality of this paper better.
1) Page 2, line 63: for the reference 28 cited in this line, it would be considered as a good gesture if you report the first author as [first author] et al.
Answer:
Thank you for comment. The changes have been made.
“Asante et al. [28] studied thermal degradation of the epoxy/expandable graphite composites.”
2) Page 2, line 63/64: the authors should explain what study was made by the reference 28. For the readers, hence it becomes clears how this submitted work differs from the references mentioned in the introduction of this paper.
Answer:
Thank you for comment. The changes have been made.
“The weight percentage of EG in the studied epoxy composites was 1, 3 and 5 wt. %. It was found that the time-to-ignition, the critical heat flux, the ignition temperature, the thermal inertia, the smoke yield, and the peak heat release rate decreased with increasing the EG content in the epoxy composites.“
3) Page 2, lines 80-83: the procedure of expansion of graphite is mentioned in a complicated way. Kindly improve it for easier understanding for the reader.
Answer:
Thank you for comment. The changes have been made.
The reference was added.
“Thermally expanded graphite was produced from commercial intercalated graphite (EG-350-50 brand, “Khimicheskie systemy” Co., Russia) using the method of programmable heating [Steksova, Y.P., Berdyugina, I.S., Shibaev, A.A. et al. Effect of synthesis parameters on characteristics of expanded graphite. Russ J Appl Chem 89, 1588–1595 (2016). https://doi.org/10.1134/S1070427216100049]. According to this method, expanded graphite was obtained from intercalated graphite at the heating it at a rate of 20 °C/min to temperature of 500 °C.”
4) Page 2, line 90: Replace 'There' with 'It'.
Answer:
Thank you for comment. ‘There’ was changed by ‘It’.
5) Page 3, line 96: For the SEM analysis, were the specimens coated with a conductive layer? or were they as produced used for analysis.
Answer:
The samples were not coated by a conductive layer. They were studied as they are.
“Morphology of the surface of samples obtained was investigated by S–3400N (Hitachi) scanning electron microscope (SEM) without sputtering. “
6) Page 3, line 100: Kindly improve the wording "Thermal behavior at the heating of the prepared epoxy composites". Also at what temperature the test was started?
Answer:
Thank you for comment. The changes have been made.
“…from 20 °C….”
7) Page 3, lines 110-114: Test description of flammability is very complicated for the reader to understand.
Answer:
Thank you for comment. The description of the test was shortened.
“The flammability of the prepared epoxy composites was studied using the standard method of experimental determination of the ignition temperature of solid substances and materials according to GOST 12.1.044-89 (ISO 4589-84) “Occupational safety standards system. Fire and explosion hazard of substances and materials. Nomenclature of indices and methods of their determination”. The sample of a cylindrical shape with a diameter of 31.4 mm and the weight of 6 ± 0.1 g was placed inside a furnace chamber and gradually heated from ambient temperature to the ignition temperature. The ignition temperature was determined at a point when flame ignites on application of a pilot flame. Six tests for each sample were conducted.”
8) Page 4, Figure 1a-c: scale bars can be more prominent and clear.
Answer:
The scale bars were modified.
9) Page 4, Figure 1d: x axis is very small and completely unreadable. It can be improved.
Answer:
The figure was changed to the one with a better quality.
10) Page 6, line 172: my sincere suggestion would be to not represent the typical curves rather than a good comparison of all the TG and DSC curves. Since the shape of the curves would be different by changing the amount of the filler in epoxy.
Answer:
Thank you for comment.
In real, it is hard to compare all the curves in one Figure since, they are overlapped a bit at large temperature scale. Therefore, to quantitatively the real change of temperatures at various mass loss, the data were presented in the form of Table 2 which is more convenient and precise, than an analysis of ten curves shown in one graph.
In order to complement the data, Figure 4 was used in the article for showing the typical shape of the curves.
11) Page 9, line 268: change 'act' by 'acts'
Answer:
Thank you for comment. ‘Act’ was changed by ‘acts’
12) Page 9, line 269: change 'increase' by 'increases'.
Answer:
Thank you for comment. ‘Increase’ was changed by increases’.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Overall the paper is interesting but more detail needs to be provided for the experimental details so other scientists can reproduce the data, in particular the characterisation
- Calibration of instruments – How was the TEM, SEM and Raman spectrometer calibrated?
What were the typical operational parameters for the SEM and TEM measurements?
- Raman measurements - What was the power level for the laser in the Raman measurements? What was the grating used?
What was the integration time? How many spectra were acquired per sample?
What is the error on the I(D)/I(G) ratio for the samples studied using Raman?
- Why are multiwalled nanotubes used instead of single walled nanotubes? Is there a performance difference?
- In the introduction please emphasize more what is novel about the approach used in this work
- What other type of nanotubes or nanomaterials could be used to reduce flammability and improve thermal stability of polymers during heating? Focus on the new generation of 1D and 2D materials
Author Response
Authors would thank the reviewers for their useful comments, which help to make the quality of this paper better.
- Calibration of instruments – How was the TEM, SEM and Raman spectrometer calibrated?
What were the typical operational parameters for the SEM and TEM measurements?
Answer:
Thank you for remark. Typical parameters of SEM measurements are presented in Figure 2, where the acceleration voltage (5 kV and 20 kV), working distance (8.1 mm and 10.2 mm), magnification have been shown.
TEM and SEM were calibrated using the standard procedures recommended by the producers, JEOL Co. (for TEM) and Hitachi Co. (for SEM). The details of Raman spectroscopy are presented below. The calibration of EDX was done using the standards MAC (Micro-Analysis Consultants Ltd.).
- Raman measurements - What was the power level for the laser in the Raman measurements? What was the grating used?
What was the integration time? How many spectra were acquired per sample?
What is the error on the I(D)/I(G) ratio for the samples studied using Raman?
Answer:
Thank you for remark. The necessary information was added to the text.
ï‚· Calibration of instruments .
“Each time, before recording the spectra from the samples, a test spectrum from monocrystalline silicon was recorded. This made it possible to calibrate the device both in the position of the frequencies (the frequency of the long-wavelength optical phonon in silicon is well known and equal to 520.6 reciprocal centimeters) and in the intensity of signals. The spectrometer T64000 and argon laser are highly stable and reproducible.”
ï‚· Raman measurements.
The monochromator used standard gratings for the visible range - 1200 lines per millimeter. All Raman spectra were excited with a 514.5 nm Ar+ laser line in the back-scattering geometry. Triple spectrometer T64000 Horiba Jobin Yvon with micro-Raman setup and CCD multi-channel detector cooled by liquid nitrogen was used. To avoid local overheating of the samples the laser beam was slightly unfocused (diameter of spot was about 10 micrometers, the laser power reaching the sample was about 1 mW). All spectra were measured at room temperature. The spectral resolution was not worse than 1.5 cm-1.
ï‚· What was the integration time? How many spectra were acquired per sample?
Integration time was 10 second, 6 signal accumulations were made at each point.
The error of determination of the I(D)/I(G) ratio was 2.1% for CNTs and 0.5% for EG.
- Why are multiwalled nanotubes used instead of single walled nanotubes? Is there a performance difference?
Answer:
MWCNTs have a lower cost compared SWCNTs that make them more attractive for polymer composite applications, especially taking into account that a scale-up of production of composites need higher amounts of filler which can be achieved only for MWCNTs. Moreover, the method of production of SWCNTs is more complex and should include the purification and separation techniques. The synthesis method of the latter material led to the formation of low yield of single-walled carbon nanotubes with a large amount of amorphous carbon and catalyst, which must be removed. Whereas the method of MWCNT production has higher yield with considerably lower amounts of catalyst and amorphous carbon (sometimes they are free of amorphous carbon) in the composition of as-received material.
- In the introduction please emphasize more what is novel about the approach used in this work.
Answer:
Thank you for comment. The following information was added to Introduction section.
“Asante et al. [28] studied the thermal degradation of epoxy/expandable graphite composites. The weight percentage of EG in the studied epoxy composites was 1, 3 and 5 wt. %. It was found that the time-to-ignition, the critical heat flux, the ignition temperature, the thermal inertia, the smoke yield, and the peak heat release rate decreased with increasing the EG content in the epoxy composites. Despite the presence of a lot of publications devoted to epoxy resin based on multi-walled carbon nanotubes and expanded graphite, there are no enough data on filler concentration effect at the low filler content on thermal behavior and flammability.”
Therefore, the thermal behavior of epoxy composites at low filler content is of interest.
- What other type of nanotubes or nanomaterials could be used to reduce flammability and improve thermal stability of polymers during heating? Focus on the new generation of 1D and 2D materials
Answer:
Thank you for comment. This article is devoted to application of carbon materials for reduction of flammability of epoxy composites. Other types of carbon nanomaterials for reduction of flammability were added to Introduction.
“Owing to unique physical properties carbon nanomaterials such as carbon nanotubes [16] and nanofibers [17], graphene [18–20], graphene nanoplatelets [21], reduced graphene oxide [22], graphene oxide [23,24], expanded graphite [25] have attracted a great attention in recent years, particularly, for the improvement of flame retardancy of epoxy composites [26–34]. ”
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Paper can be accepted
