Thermal and Mechanical Behavior of Elastomers Incorporated with Thermoregulating Microcapsules

Round 1

Reviewer 1 Report

This is a well described study about incorporation of phase change materials into elastomers. I would like to complement the authors on a well written manuscript.

I would note to the authors that the latent heats reported herein are very modest compared to those examples outlined in the introduction. I was also left wondering what the onset temperatures are for the phase changes described in Table 3. Are they different from the parent phase-change material, and is there any hysteresis observed?

Author Response

Firstly, many thanks to the reviewer 1 for the effort in the revision of this paper and for the valuable comments.

This is a well described study about incorporation of phase change materials into elastomers. I would like to complement the authors on a well written manuscript.

Thank you very much for your positive comment.

I would note to the authors that the latent heats reported herein are very modest compared to those examples outlined in the introduction. I was also left wondering what the onset temperatures are for the phase changes described in Table 3. Are they different from the parent phase-change material, and is there any hysteresis observed?

In this work, the incorporated microencapsulated content has been up to the double of some relevant works such as the one of Juarez at al. [15] in which not only the thermal properties but also the mechanical ones were studied. On the works mentioned in the introduction section exhibiting high PCM contents, the main attention was the development elastomer materials having large thermal properties, without any special relevance to the mechanical ones which are the most important characteristics for being considered as an elastomer. In this way, this work can be considered as the first approach to improve the thermal properties of polyurethane elastomers while trying to keep the mechanical response. Future work can be done to increase the PCM content in order to reach higher latent heats.

In order to observe the influence of the elastomer matrix on the phase transition of the PCM, the peak melting and crystallization temperatures have been included in Table 3. In this way, the following sentence was added in the text:  

“As can be seen, there are a slight increase in the melting point for all composites as result of the porosity and density diminution with the microcapsule content, causing a reduction of the global thermal conductivity of these form-stable materials. On the other hand, the crystallization temperature is practically equal to the melting point for microcapsules content lower than 15 wt%, indicating that this form stable materials do not exhibit any hysteresis. Nevertheless, for microcapsules content within 15-20 wt% the crystallization temperature tends to the original microcapsules indicating that they work as the key thermal material instead of the matrix elastomer.”

 

Author Response File: Author Response.docx

Reviewer 2 Report

This is a case study where thermal and mechanical performances of polyurethane elastomers are evaluated as a function of isocyanate/polyol proportion and microcapsules content dispersed in the polymer matrix.   Results have been presented quite well and the take-home message is straightforward. For these reasons I recommend the present work for publication only after addressing a few questions/suggestions:  

1. The title should contains the word "mechanical" in addition to "thermal" since Authors show both thermal and mechanical properties of their materials and this is also present in the selected key words;
2. The full name of the acronym EVA is missing in the main text (first mention in Line 105);
3. I am totally not sure what is the specific theory behind the weight loss prediction reported in Figure 7. Non Reference is given. Please explain;
4. In Figure 7 a few straight lines are plotted against experimental data points. What do they represent? There is no mention in the figure caption. Although, I would suggest to remove them especially for the black and white version;
5. Authors claim that every experimental measurement has been repeated three times. In general I always promote showing standard error bars (especially in Figure 7 and 8 in this case). However, if the values are too small to be seen in the graph, it is recommended to mention that in the main text or in Figure captions;
6. In Figure 6 the data point of the pure paraffin RT27 are barely noticeable in the black/white version. Please change data line set up;

  Minor comments:   Typos at: Line 105 - 10 m, Line 224 - an structure, Line 249 - lineal, and Line 365 - 9a)

Author Response

Firstly, many thanks to the reviewer 2 for the effort in the revision of this paper and for the valuable comments.

This is a case study where thermal and mechanical performances of polyurethane elastomers are evaluated as a function of isocyanate/polyol proportion and microcapsules content dispersed in the polymer matrix. Results have been presented quite well and the take-home message is straightforward. For these reasons I recommend the present work far publication only after addressing a few questions/suggestions:

1. The title should contains the word "mechanical" in addition to "thermal" since Authors show both thermal and mechanical properties of their materials and this is also present in the selected key words;

We agree and the word mechanical was added to the title.

2. The full name of the acronym EVA is missing in the main text (first mention in Line 105);

The full name has been included.

3. I am totally not sure what is the specific theory behind the weight loss prediction reported in Figure 7. Non Reference ­given. Please explain

 

The following sentence has been added to the text, in order to increase the understandability of the figure: “The theoretical values are estimated from the mass content of microcapsules, their composition and the mass of polyurethane components added in the elastomers synthesis recipe”. We think that it is clear and it means:

e.g, for an elastomer with a microcapsules content of 20wt%, the shell weight loss should be of a 11.3 wt% since the shell constitutes about the 56wt% of the microcapsule. In the same way, the SS theoretical weight loss in E-1.05-20 is calculated considering the amount of PTMG employed in the recipe, which represents in this case 58.89 wt%, being the amount of SS in the real TGA 53.95 wt%. Same explication can be taken out for HS but considering in this case, the theoretical amount of MDI and 1,4-butanediol.

4. In Figure 7 a few straight lines are plotted against experimental data points. What do they represent? There is no mention in the figure caption. Although, I would suggest to remove them especially for the black and white version;

Straight lines were plotted to indicate the weight loss tendencies. In order to clarify it, it has been indicated in the figure caption.

5. Authors claim that every experimental measurement has been repeated three times. In general I always promote showing standard error bars (especially in Figure 7 and 8 in this case). However, if the values are too small to be seen in the graph, it is recommended to mention that in the main text or in Figure captions;

The standard errors bars have been included in the figures 8 and 9.

6. In Figure 6 the data point of the pure paraffin RT27 are barely noticeable in the black/white version. Please change data line set up;

The data points of the pure paraffin have been changed.

Minor comments: Typos at: Line 105 - 10 m, Line 224 - an structure, Line 249 - lineal, and Line 365 - 9a)

Thanks for the careful revision. The minor mistakes have been corrected.

All the changes in the manuscript text have been highlighted in yellow colour.

 

Author Response File: Author Response.docx