Finding the Additives Incorporation Moment in Hybrid Natural Pigments Synthesis to Improve Bioresin Properties
, Jorge Jordán 2, Esther Perales 1, Francisco Miguel Martínez-Verdú 1 and Francisco Cases 3Round 1
Reviewer 1 Report
Manuscript number: 403680
Title: Finding the additives incorporation moment in hybrid natural pigments synthesis to improve bioresin properties
One of the authors’ objective was “to know the best additive combination for laminar nanoclays with different anion exchange capacities to achieve hybrid nanopigments with distinct natural dye structures.” But this subject was studied by authors in “A combination of three surface modifiers for the optimal generation and application of natural hybrid nanopigments in a biodegradable resin” (DOI 10.1007/s10853-016-0384-8, J Mater Sci (2017) 52:889–898). Other research objectives have also been previously studied by authors in the published article.
So, the manuscript seems like a part of a larger study, another part being previously published. The first article was not cited and no reference has been made to previous results.
The authors must cite the published study, to avoid the duplication of information, and must correlate the results. They need to reestablish the aims for this study, because they are quite similar with the first one, and are supposed to have been resolved in the first article.
I have also few recommendations:
1. Line 186 – “the pic shift” must be corrected.
2. In Line 133-134 – “the degradation temperature of the composite materials (Td)”. The degradation temperature was denoted Td (as a temperature), but further it was noted dT (as a derivative) – Line 306 – “Degradation temperature (dT)” and Line 309, 310, 314, 319, 377. The authors must correct and change “dt” with “Td”.
3. Line 133 - TGA/SDTA 851 (Mettler-Toledo Inc) equipment is a thermogravimetric analyzer. Please change the name.
4. The TG, DTG and DTA curves must be provided. Is it another discussion about the same experiments which were previously published? In this case, it must be clearly specified.
Author Response
One of the authors’ objective was “to know the best additive combination for laminar nanoclays with different anion exchange capacities to achieve hybrid nanopigments with distinct natural dye structures.” But this subject was studied by authors in “A combination of three surface modifiers for the optimal generation and application of natural hybrid nanopigments in a biodegradable resin” (DOI 10.1007/s10853-016-0384-8, J Mater Sci (2017) 52:889–898). Other research objectives have also been previously studied by authors in the published article.
The reviewer is right, this is study is a continuation of the work that has been done and summarized in the paper “A combination of three surface modifiers for the optimal generation and application of natural hybrid nanopigments in a biodegradable resin”. However, several improvements have been done to optimize the synthesis with both kinds of nanoclays. First we add the calcination process in the hydrotalcite and add the calcined nanoclay as third factor in the synthesis process. Due to the factor selection in this study we need to study three levels for each factor, instead of two levels like in the previous work. For this reason, we selected a Taguchy L9 Design. In previous work we modified the pH level using HCl-, in this work we decided fix the pH at [4-5] due to our previous work results. Also in this study we add characterization technics as X-Ray diffraction and FTIR, in order to describe the nanoclays and additives interactions, as the new bonds between all the components of the hybrid pigments, and the position of the intercalated additives, nanoclay surface or basal space. For the final biocomposite the characterization was deeper to, and apart from checking the thermal and colour fastness using acceleration UV-VIS test, we add the color fastness to rubbing. With this last test we have proved the dye migration prevention with both nanoclays.
However, the most important difference is in the title “Finding the additives incorporation moment”. In this work we try to go far away of the incorporation and combination of different surface modifiers into the nanoclay. We want to optimize also the incorporation moment of this additives, because the initial hypothesis is that there should be a preference intercalation depending of the previous nanoclay modification. If all the additives are incorporated into the basal space previous to the dye incorporation, it is going to be affected the adsorption capacity with the natural dyes? That’s why we use the incorporation moment with three factors (without, after or before the dye addition), to answer this question. We have found a significant influence of the addition moment of the modifiers in the thermal properties of the composite material, that should be taken into account as the combination of the three of them.
So, the manuscript seems like a part of a larger study, another part being previously published. The first article was not cited and no reference has been made to previous results.
To clarify the main objective and differentiate this study from the previously published by our group, we add comments highlighted in red type in the paper.
The authors must cite the published study, to avoid the duplication of information, and must correlate the results. They need to reestablish the aims for this study, because they are quite similar with the first one, and are supposed to have been resolved in the first article.
That’s right and we add the previous work reference in the introduction and in the results sections. We add the discussion of the same test that we have done in both studies and we highlighted the new funding’s in this study.
I have also few recommendations:
1. Line 186 – “the pic shift” must be corrected.
We have corrected and highlighted in red as the other changes in the new version.
2. In Line 133-134 – “the degradation temperature of the composite materials (Td)”. The degradation temperature was denoted Td (as a temperature), but further it was noted dT (as a derivative) – Line 306 – “Degradation temperature (dT)” and L. 309, 310, 314, 319, 377. The authors must correct and change “dt” with “Td”.
We have corrected and highlighted in red as the other changes in the new version.
3. Line 133 - TGA/SDTA 851 (Mettler-Toledo Inc) equipment is a thermogravimetric analyzer. Please change the name.
Do it and highlighted in red in the new version.
4. The TG, DTG and DTA curves must be provided. Is it another discussion about the same experiments which were previously published? In this case, it must be clearly specified.
Ins not a discussion of previous results because we have make the analysis with the new hybrid pigments synthesized using the L9 conditions, and also we duplicate the hybrid pigments load in the composites. We have selected a representative curve to show the example of the thermal changes (new Figure 8), which are due to the conditions as it can be seen in the design analysis (now Figure 9).
Author Response File: 
Author Response.docx
Reviewer 2 Report
This paper focuses on the stability enhancement of naturally occurring dyes by combining some clays having a layered structure. Three natural dyes, each of which has a different nature, were employed in this study. In addition, the effect of the combination of three additives on the stability was also investigated. The complexation with clays enhanced the color stability of the natural dyes. The leaching of the dye to the polymer resin matrice was also suppressed by the complexation with the clays. Since this is a positive results, the reviewer thinks that this work is worth for publication. Before acceptance, the point addressed below should be modified.
---The authors insist that the modification of the clays with surfactants had a positive effect on the stabilization of the dye. However, in the XRD data the interlayer distance of the surfactant-modified clay were almost the same as that without the surfactants. In FTIR analysis, no significnt differences were found between the intensities of the C-H stretching band of clays between with and without surfactants. Those two data suggest that the interlayer space of the clays are not modified by the surfactants. It is recommended that the authors show their idea about the adsorption of the dye molecules on the organo-modified clay resulting in the stabilization.
When preparing the next manuscript in the future, please consider the following points. These modifications are not essential for this manuscript, but if the authors will revise this manuscript according to the following comment, it would be better.
---Please improve the way to show the data. Because the raw numerical data are given in this manuscript as a large table, I think it is difficult for readers to judge what kind of conclusion the authors get from what data. It would be better if data are shown more systematically, as well as more visually.
---In the present study, the differences of the stabilization effect cannot be find between each clays. The additives neither showed differences in the stabilization effect. Therefore, we can get no information about what is the most effective parameters for the stability enhancement. The suggestion about the best preparation method is not shown in this paper, either. If the authors do not change plural parameters but control them individually, the effect of each parametrs can be individually evaluated. I guess that most of the readers will be interested in the optimized preparation method of the stable dye-clay hybrid materials.
Author Response
Rev2
This paper focuses on the stability enhancement of naturally occurring dyes by combining some clays having a layered structure. Three natural dyes, each of which has a different nature, were employed in this study. In addition, the effect of the combination of three additives on the stability was also investigated. The complexation with clays enhanced the color stability of the natural dyes. The leaching of the dye to the polymer resin matrice was also suppressed by the complexation with the clays. Since this is a positive results, the reviewer thinks that this work is worth for publication. Before acceptance, the point addressed below should be modified.
---The authors insist that the modification of the clays with surfactants had a positive effect on the stabilization of the dye. However, in the XRD data the interlayer distance of the surfactant-modified clay were almost the same as that without the surfactants.
The reviewer is right and we agree with the non-evident influence of the surfactant in Montmorillonite hybrid pigments, like it can be observed in Figure 4 (see attached document).
Figure 4. The XRD diffraction patterns of the original montmorillonite (M) and the hybrid pigments with M and the chlorophyll natural dye [L9G1-L9G3]
However, in previously calcined Hydrotalcite samples [L9G7-9] there is a peak shift of the samples depending of the addition moment of the surfactant (SDS). As it can be observed in Figure 3 (see attached document), samples with SDS added after the dye load, show a left peak shift (blue plot), which corresponds to high basal space. Less pronounced left shift is shown in the samples with the surfactant added before the dye adsorption, and no differences can be observed when there is no surfactant modification. The same pattern can be observed with non-calcined Hydrotalcite samples [L9G4-G6], but is more difficult to see because of the mordant effect in L9G4 and L9G6 samples, with the peak shoulder that appears as a result of higher structural changes in the hydrotalcite clay. We add this comments highlighted in blue in the new paper version, to reinforce our hypothesis of the surfactant effect.
Figure 3. The XRD diffraction patterns of the original hydrotalcite (H), the calcined hydrotalcite (HC), the hybrid pigments with H and the chlorophyll natural dye [L9G4-L9G6] and with HC [L9G7-L9G9]
In FTIR analysis, no significnt differences were found between the intensities of the C-H stretching band of clays between with and without surfactants. Those two data suggest that the interlayer space of the clays are not modified by the surfactants. It is recommended that the authors show their idea about the adsorption of the dye molecules on the organo-modified clay resulting in the stabilization.
Again we agree in with the reviewer comments with montmorillonite clay. Montmorillonite nanoclay swelling effect is huge, and despite the anion charge of the natural dyes, the nanoclay adsorption capacity is enough to increase the basal space and load 70-100 of the three natural dyes, and this not depends of the surfactant, mordant or silane modifiers. However, as we have already commented we detected and influence in the basal space modification depending of the addition moment with hydrotalcite nanoclay. When the surfactant is added before the natural dye all the carbonates anions were replaced by the additives as we highlighted in the paper “The intensity of the band at 34000px-1, which corresponded to the carbonate vibration, reduced in most hybrid samples, or completely disappeared when silane was not used, the surfactant was added before, and when the mordant was employed after NG.” paying attention in the C-H stretching bands in the hydrotalcite nanoclay modified before with SDS [L9G4], both peaks intensity is higher than with samples modified after [L9G5] or without SDS [L9G6]. Using previous calcination, this stretching bands only appears in the samples modified with the SDS [L9G7-L9G8], and disappears when we didn’t use SDS, and use the Silane before the dye adsorption and the mordant salt before. The structural HC changes again are more significant with the mordant salt presence. We add some of this discussion in the FTIR analysis highlighted in blue to reinforce our hypothesis of the surfactant effect in the nanoclay modification and the dye adsorption.
When preparing the next manuscript in the future, please consider the following points. These modifications are not essential for this manuscript, but if the authors will revise this manuscript according to the following comment, it would be better.
---Please improve the way to show the data. Because the raw numerical data are given in this manuscript as a large table, I think it is difficult for readers to judge what kind of conclusion the authors get from what data. It would be better if data are shown more systematically, as well as more visually.
The reviewer is right. We deleted the rows with less remarkable results trying to let the just the bands that are mentioned and highlighted in the text in order to make easy to the readers to understand the point of the analysis. Thanks for the suggestion.
---In the present study, the differences of the stabilization effect cannot be find between each clays. The additives neither showed differences in the stabilization effect. Therefore, we can get no information about what is the most effective parameters for the stability enhancement. The suggestion about the best preparation method is not shown in this paper, either. If the authors do not change plural parameters but control them individually, the effect of each parametrs can be individually evaluated. I guess that most of the readers will be interested in the optimized preparation method of the stable dye-clay hybrid materials.
As reviewer says most improvements and optimizations will be find increasing the experimentation in this way. In this work we can say that depending of the hybrid pigment or biocomposite properties measured, there were significant differences between the selected parameters. For example, to increase the adsorption capacity hydrotalcite nanoclay (calcined or not) must be used. This parameter is important to get deeper colours and not lose dye in the synthesis process. Thermal properties of the bioresin and natural dyes were improved. The best thermal stability was obtained using again Hydrotalcite and the mordant salt before the dye adsorption. We couldn’t find say that the differences between the addition moment of the silane or surfactant were significant, but we agree with the reviewer, and increasing the experiments we should find that is better using the surfactant after the dye addition, ant the silane after or before. For future works and applications, we are going to work with the modifiers concentrations using response surface designs and D-Optimal tools.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors responded to the suggestions.
Reviewer 2 Report
Generally, the expansion of the clay interlayer space by the modification with surfactants corresponds to the alkyl chain length of the surfactant molecule, i.e., the expansion reaches about 1 to 2 nm. In the present study, the expansion caused by the surfactant was far smaller than those value. Therefore, I guess that the modification of the interlayer space with the surfactant molecule was not yet sufficient. Nevertheless, just as the authors still argue, now I have understood that the interlayer space is modified with the surfactants, and that the modification has the positive effect on the adsorption and the stabilization of each dye molecules. I do not object to their idea. The manuscript is well revised to show the authors' standpoint more clearly.
As for the additional two comments, I have understood the authors' insistence. The authors made adequate modification on their manuscript.
Therefore, I recommend this paper for publication.
