Preparation and Properties of Polyurethane Composite Foams with Silica-Based Fillers

Round 1

Reviewer 1 Report

In this paper, authors have prepared polyurethane composite foams by adding three different types of silica materials as a filler. The structure and performance of the composite foams by different processing method are investigated. Nevertheless, it is an uncomprehensive work. The article lacks of analysis while the data is not convinced. it is insufficient to satisfy the academic level of journal's standard. The main comments are given below:

1.     Page 3, line 148. The authors did not mention the method and condition of the condensation reaction.

2.     Figure 1, (a), (b). The test results only indicate the presence of APTES and PMDI, can’t directly indicate that APTES and PMDI were successfully bonded to the silica surface.

3.     From figure 2, (b), (c), (d). Change in the appearance of the silica aerogel through the modification can’t be observed.

4.     There are no icons such as (a), (b), (c) in the figure 3.

5.     The foam pore sizes measured by Image J program are not accurate enough, and the reasons for change of foam structure must be clearly analyzed.

6.     The whole article only characterized the compressive stress of polyurethane composite foams, which is insufficient for making a fully expression on the mechanical behavior. The article needs more data to make sufficient representation, and the effect of silica materials on foam mechanical properties must be explained.

7.     The article has made delicate comparison between the polyurethane composite foams prepared by silica nanoparticles, silica aerogels and silica produced by sol-gel reaction. However, the polyurethane composite foams, prepared by silica produced by sol-gel reaction, with more defects and lower a compressive stress have shown nothing valuable. It’s meaningless for presenting such a disadvantages prepared method.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The paper reads well and the methodology is clear and well supported. The testing methods provide enough significant information about material mechanical properties. The addition of the filler has limited impact on the morphology of pores and the addition with improving mechanical and insulation properties. It is often in use of nanoparticles in composites that the optimal result is obtained with addition of 3 wt. % of nanoparticles.

I have a serious problem with figures. Figures 3,4 and 5 are simply to small to be able to see something. The letters indicating the numeration of figures are difficult to find and if possible chose other dispositive for figures, like when you present silica particles they are visible and the size is suitable to analyze the image.

Same remark for the mechanical testing, the lines are so small an tiny (figure 7) that and the legend is to small to enable reading.

I have also some questions about the dispersion of fillers in the matrix of the foam. Do you se any problem that the particles could migrate in the environment from the foam during the exploitation of a material? Is it possible to test this possibility?

I see that you present ImageJ results for main pore size of the foam. This is a powerful software and you could analyze more details about the form of pores in the foam and probably to make some more conclusions. In the image with pore size the error bars represent the range of observed pores and not the error of measurement I suppose. Discuss this a little bit more in this section.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

This work is devoted to formation of polyurethane foams for application in insulator. Synergy of silica based aerogels and polyurethanes foams is highly beneficial for this type of application.  Thus, the idea of the research is potentially perspective. However, improvement in introduction and some additional experiments are required. Main questions:

1) please, provide deeper explanation of novelty of this study and difference from recently published papers (https://doi.org/10.1016/j.jnoncrysol.2017.01.037, https://doi.org/10.3390/ma14071790)

2) additional experiments which reveal surface area of obtained foams are required. It could be done by low-temperature adsorbtion-desorbtion, X-ray tomography.  Statistical analysis of SEM images it's not enough

Minor comments

1) p. 2, line 45-46. More clear description of hard and soft segment in polyurethanes (PUs) is required. Please, describe the role of chain extender and typical polyols

2) p. 2, line 85-87. These sentense is too complicated. Please, rewrote is as 2-3 sentences.

3) p. 2, line 92. Please, provide explanation what is LNG

4) add in experimental part description of pore size calculation by Image J

5) p. 2, line 95. Please, specify what polyurethane was used

6) p. 3, line 117. Pleasem specify was NPs in solid form or in disoersion? What was charge of NPs?

7) point 2.2 Please, divide into NPs modification and nanocomposite preparation

8) p. 4, Figure 1. Please, add respective peaks on figure (C=O, NH, C(alkyl) and other which is specific for your PU). Imrove quality of the figure, it's blurry

9) P. 5, figure 2. Imrove quality of the panel a, it's blurry

10) figure 3-5 are repetative. Try to organize them in better way (put some in supplemetary, add a schematic ot other)

11) figure 7 - quality improvement is required, it's blurry

12) figure 8. Please, add error bars on thermal conductivity and provide (in text or in figure) comparison with literature data

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

In this paper, authors have prepared polyurethane composite foams by adding three different types of silica materials as a filler. The structure and performance of the composite foams by different processing method are investigated. The research design is appropriate nd the results are clearly presented.