The Role of Multiwalled Carbon Nanotubes in the Mechanical, Thermal, Rheological, and Electrical Properties of PP/PLA/MWCNTs Nanocomposites
Round 1
Reviewer 1 Report
The article is about the different properties of modified PP/PLA40/MWCNT composites. It is worth to be published after some modification. In my opinion, the authors should add some information:
How can authors explain the increase in tensile modulus and at the same time decreasing in elongation in break according to higher PLA%?
Could the authors relate the measurement results to the microscopic images from Figure 1?
Fig 8a and Fig. 9 - the plots for PP/PLA40/MWCNT2% differ from other plots in a significant way. How do the authors explain it?
Author Response
Response to Reviewer 1 Comments
Point 1: How can authors explain the increase in tensile modulus and at the same time decreasing in elongation in break according to higher PLA%?
Response 1: Thank you for your comment, as mentioned in the manuscript “ thanks to the higher tensile modulus of the PLA, compared to the PP matrix” the increase in the tensile modulus of the PP/PLA blend is attributed to the higher tensile modulus of any part of the blend including the PLA part. However, due to the intrinsically low elongation at break of the PLA, the overall elongation at break of the PP/PLA blend decreased.
Point 2: Could the authors relate the measurement results to the microscopic images from Figure 1?
Response 2: The relationship between the mechanical properties and the morphology of the polymer blend has been addressed and added to the text as:
“Also, the addition of higher PLA content (20, 30 and 40 wt%) in PP/PLA blend were resulted in the formation of a co-continous phase of PLA (see Figure 1d-1f). Thus, as observed, the mechanical properties of polymer blends were strongly intensified with greater intrinsic properties of PLA”
Point 3: Fig 8a and Fig. 9 - the plots for PP/PLA40/MWCNT2% differ from other plots in a significant way. How do the authors explain it?
Response 3: As explained in the rheology part: the change from the non-terminal to the terminal behaviour in composite materials at low frequencies is linked to the entanglement of MWCNTs which restricted polymer chains mobility. Therefore, at 2 wt% of the additive, a percolation threshold was found. In addition, a remarkable increase in electrical conductivity of the composite is expected at percolation threshold that we can see clearly in Figure 9b.
Reviewer 2 Report
In this manuscript is described an approach to develop new blends of PP/PLA loaded with MWCNTs. The role of the nanomaterial to improve the mechanical properties of the blends is relevant. However, as the Authors can be seen below, I suggest more studies in the section of biodegradability needs before make some conclusions.
Please consider the follow recommendations:
Line 54 – The role of compatibilizer, perhaps, should be developed since is crucial to the stabilization of the blend.
Line 56 - This part of the text should be changed. Here are two concepts that cannot be mixed, what happens at the moment. I propose to the authors to subdivide into two well-defined parts, one explaining the action of plasticizers and the other the role and state-of-the-art of nanoparticles being used to increase mechanical properties.
Line 176 – Instead “…formed nea w linkage” perhaps “…formed new linkage”
In the subsection “4.3. Thermal properties”, it would be interesting to calculate crystallinity degree and compare the values with those present in the paper S.P. Bao, S.C. Tjong / Materials Science and Engineering A 485 (2008) 508–516, where the formula of crystallinity degree can be found.
Line 286 – Please, rewrite the sentence that begins here.
Line 287 – In this sentence, the verb is missing.
In section “5. Conclusions”, in my opinion, the sentence
about biodegradability is not correct. As was proven by the results, only the
PLA part of the blend is biodegradable, as was expected. Moreover, the
composites with MWCNTs were not tested and the toxicity of these nanomaterials
remains without any conclusion. I suggest that the composites PP/PLA/MWCNTs be tested
in biodegradability studies.
Author Response
Response to Reviewer 2 Comments
Point 1: Line 54 – The role of compatibilizer, perhaps, should be developed since is crucial to the stabilization of the blend.
Response 1: “Maleic anhydride as a compatibilizer can make a strong bond between the phase components in styrene-ethylene butylene-styrene (SEBS)/propylene (PP) blend and their composites with glass fiber additive, and consequently is resulted in a significant increase of the impact strength of the SEBS/PP composites [35]. In addition, the interfacial adhesion between the high-density polyethylene and polystyrene blend was improved using SEBS as a compatibilizer, and the ductility of the polymer blend was increased remarkably [36]”
Point 2: Line 56 - This part of the text should be changed. Here are two concepts that cannot be mixed, what happens at the moment. I propose to the authors to subdivide into two well-defined parts, one explaining the action of plasticizers and the other the role and state-of-the-art of nanoparticles being used to increase mechanical properties.
Response 2: This part rephrased and divided as requested.
Point 3: Line 176 – Instead “…formed nea w linkage” perhaps “…formed new linkage”
Response 3: It has been corrected.
Point 4: In the subsection “4.3. Thermal properties”, it would be interesting to calculate crystallinity degree and compare the values with those present in the paper S.P. Bao, S.C. Tjong / Materials Science and Engineering A 485 (2008) 508–516, where the formula of crystallinity degree can be found.
Response 4: Thank you for your comment, the degree of the crystallinity has been calculated according to the equation mentioned in the text and listed in Table II.
Point 5: Line 286 – Please, rewrite the sentence that begins here.
Response 5: This part revised. Thank you.
Point 6: Line 287 – In this sentence, the verb is missing.
Response 6: This part has been revised.
Point 7: In section “5. Conclusions”, in my opinion, the sentence about biodegradability is not correct. As was proven by the results, only the PLA part of the blend is biodegradable, as was expected. Moreover, the composites with MWCNTs were not tested and the toxicity of these nanomaterials remains without any conclusion. I suggest that the composites PP/PLA/MWCNTs be tested in biodegradability studies.
Response 7: The sentence related to the biodegradability has been revised now. The biodegradability of the PP/PLA/MWCNTs composite was not in our research plan due to the toxicity concern of the nano additive.
Round 2
Reviewer 2 Report
The Authors modified the manuscript according to the suggestions.
