Investigation of Impregnation Approach of Zinc Oxide Nano-Dispersions for Potential UV Stabilization in Abies alba and Fagus sylvatica

Round 1

Reviewer 1 Report

The study of Sommerauer et al. evaluates ZnO nano-dispersions based on propylene glycol, its uptake by means of impregnation technology and the effect of the nano-dispersions on the stability of the optical appearance to UV exposure.

The work presents little novelty as other similar, if not almost identical,  manuscripts on this topic are already present [1-3], some are even cited in the present manuscript as correlations(i.e. Nair et al., 2018) , therefore I am sorry to state that the novelty is low. A clear novel element should be brought in to make a distinction, especially due to the high EU specialization regarding wood processing of the organizations that have released the proposed manuscript.

Introduction

Line 46: "UV radiation has the effect of splitting lignin into smaller units due to the high radiation energy" please elaborate

Line 52: "damage that negatively affects the visual appearance in particular." what are the particular structural damages in these cases?

Line 63: "For example, ZnO nanoparticles are already used in sunscreens as UV blockers" TiO NP are as well used in the mentioned case, perhaps even more often than ZnO [4].

Line 67: "ZnO impregnation reduced water uptake [ 14]."correct reference format.

Lines 83, 99: "weight was constant" state weights

Line 25; 2.4.Scanning Electron Microscopy; Line 60-61; Line 74; Line 251

It is unclear how the "deep into the cell of the wood", "full cell impregnation" as well as "whole-cell impregnation" is present.

Also, state the interaction of PEG and wood cells [5]

2.5. Leaching

From where was this protocol taken? Cite methodology.

2.6. UV-Treatment and CIELab colour measurement

"2 h UV-radiation" what UV wavelenghts were used? Was only UVA used, if so, please state the reason why.

Line 148: "Bio Rad KnowItAll software" as KnowItAll is a paid software, please state license identification rights.

3. Results

Line 153: state "sample weight"

Line 155: "Propylene glycol seems to be suitable as an impregnating agent for softwoods, but for hardwoods the uptake is unexpectedly low despite larger pores." this has already been reported in literature. State the interactions between PEG ligning and cellulose

References

1.          Nair, S.; Nagarajappa, G.B.; Pandey, K.K. UV Stabilization of Wood by Nano Metal Oxides Dispersed in Propylene Glycol. J Photochem Photobiol B 2018, 183, 1–10, doi:10.1016/J.JPHOTOBIOL.2018.04.007.

2.          Wood Protection Using Nano Metal Oxides in Propylene Glycol Available online: https://www.irg-wp.com/irgdocs/details.php?983074b5-d980-2cc5-6e5e-2a85067e30fa (accessed on 14 January 2023).

3.          Faure, B.; Salazar-Alvarez, G.; Ahniyaz, A.; Villaluenga, I.; Berriozabal, G.; de Miguel, Y.R.; Bergström, L. Dispersion and Surface Functionalization of Oxide Nanoparticles for Transparent Photocatalytic and UV-Protecting Coatings and Sunscreens. http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=tsta20#.VmBmuzZFCUk 2013, 14, 23, doi:10.1088/1468-6996/14/2/023001.

4.         Smijs TG, Pavel S. Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness. Nanotechnol Sci Appl. 2011 Oct 13;4:95-112. doi: 10.2147/NSA.S19419. PMID: 24198489; PMCID: PMC3781714.

5.          Jeremic, Dragica, Cooper, Paul and Brodersen, Peter. "Penetration of poly(ethylene glycol) into wood cell walls of red pine" , vol. 61, no. 3, 2007, pp. 272-278. https://doi.org/10.1515/HF.2007.068

Author Response

Thank you very much for your review and apologizes for my late reply – I was on a sabbatical and therefore not available for further work on this. We hope the updated version is approved for publication now or if there are more points to address, thank you for your further review.

• The study of Sommerauer et al. evaluates ZnO nano-dispersions based on propylene glycol, its uptake by means of impregnation technology and the effect of the nano-dispersions on the stability of the optical appearance to UV exposure.
  The work presents little novelty as other similar, if not almost identical, manuscripts on this topic are already present [1-3], some are even cited in the present manuscript as correlations (i.e. Nair et al., 2018), therefore I am sorry to state that the novelty is low. A clear novel element should be brought in to make a distinction, especially due to the high EU specialization regarding wood processing of the organizations that have released the proposed manuscript.

Thank you for your assessment. The combination of whole-cell treatment and elaboration the treatment on its UV Stability, especially the penetration behavior and leaching with the carrier medium of propylene glycol is new to literature. In addition, the treatment is so far not applied on European wood species Fagus sylvatica or Abies alba.

• Line 46: "UV radiation has the effect of splitting lignin into smaller units due to the high radiation energy" please elaborate

“The UV radiation produces radicals which leads to partial energetic imbalances within the lignin molecule and changes of its polymeric structure due to free radical reactions, liberation of phenolics and condensation of lignin compounds (10.1016/j.polymdegradstab.2008.08.013, 10.6084/m9.figshare.6143234). “

• Line 52: "damage that negatively affects the visual appearance in particular." what are the particular structural damages in these cases?

“[…] outdoors and indoors, these changes negatively affect the visual appearance in particular because it is less preferred in visible applications though the structural integrity is not significantly reduced.”

• Line 63: "For example, ZnO nanoparticles are already used in sunscreens as UV blockers" TiO NP are as well used in the mentioned case, perhaps even more often than ZnO [4].

As we partial agree there are several advantages of ZnO over TiO, which is now stated clearer in the manuscript. “As mentioned, there are other nanoparticles besides ZnO, such as CuO and TiO, which are suitable for use as UV protection, but ZnO, for example, shows higher dispersion stability than CuO [25]. Also, Titanium dioxide can be used as a very effect agent to prevent photoprotection in paints but in applications of wood it can lead to increased degradation of wood polymers due its UV-induced photoactivity. Zinc oxide nanoparticles are more preferrable in the regard that it has an equal UV-filtering effect as titanium dioxide at lower concentrations and a lower whitening on the surface color [26].”

• Line 67: "ZnO impregnation reduced water uptake [ 14]."correct reference format.

We corrected that point.

• Lines 83, 99: "weight was constant" state weights

Due the reason we work with relative uptake the origin sample weight is not as relevant. But we added the range of weight constancy which was ±0,3 mg.

• Line 25; 2.4.Scanning Electron Microscopy; Line 60-61; Line 74; Line 251 It is unclear how the "deep into the cell of the wood", "full cell impregnation" as well as "whole-cell impregnation" is present.

Whole cell impregnation is more the term for a pre applied vacuum and pressure technique in applying a preservative – the results on penetration behavior in combination with the SEM shows that the UV protecting agent is present in layers in 2-3mm depth of the wood sample. Blocking of pores lead to partial penetration of the cells.

• Also, state the interaction of PEG and wood cells [5]

Thank you for that comment. As we work with 1,2-propandiol or Propylene glycol (PG) as carrier medium for ZnO there is no PEG present

• From where was this protocol taken? Cite methodology.

We based our methodology on our previous publications. (10.1515/hf-2018-0130)

• "2 h UV-radiation" what UV wavelenghts were used? Was only UVA used, if so, please state the reason why.

Deeper penetration on substrate then UVB (10.1149/2.0171614jes) seemed more suitable for an in-depth application of UV protecting agent.

• Line 148: "Bio Rad KnowItAll software" as KnowItAll is a paid software, please state license identification rights.

It was a student license. Several sources report just the program and not the license rights so we didn’t report it. We are available for requests.

• Line 153: state "sample weight".

Due the reason we work with relative uptake of 70%the origin sample weight is not as relevant.

• Line 155: "Propylene glycol seems to be suitable as an impregnating agent for softwoods, but for hardwoods the uptake is unexpectedly low despite larger pores." this has already been reported in literature.

Listed literature refers to PEG. We worked with Propylene glycol (PG) and therefore we cannot reply to that comment. If there is still literature about PG and wood interaction, we will take your advice into account.

• State the interactions between PEG ligning and cellulose

Thank you for the comment. PEG is not present in this application.

Reviewer 2 Report

The manuscript is really interesting and provides new knowledge. However, there are several points to be improved in the text.

In the abstract, the scientific names of the species should be completed. In the abstract, please explain in the text or in a parenthesis what is meant by "1% ZnO" (solution, uptake?). In lines 32-33, the meaning is not very clear concerning saturation. I would rather add more key words in the manuscript in order to increase its visibility/readability. In line 47, please check again the phrase "within and below". In line 64, correct the "food". In lines 66-67, please provide more information about the uptake etc. of the referred research attempts. In line 67, in which ZnO proportion used? The basic state-of-the-art description on the topic lies in the part of 64-70 lines, which is very short, not providing details on the conditions applied and there are several relevant research works missing from such a description. In the end of introduction, the description of objectives is as well too brief, leaving behind the referance of characterization of these impregnated specimens. The reason why you investigate the specific one (ZnO) is not clear in the text.

In materials-methods, the raw materials are not properly described. The forest species should be analytically referred in the start of the manuscript text. You did not refer to the age of the trunks, the number of the trunks, where the samples were obtained from (which height etc.). Which are the details on the stirrer machine and sonication process? Correct please the "and the and the " in line 100. The " used for investigated" should be improved. The "leaching resistance equation" should be clear,  explained to the reader. Line 142: correct the "trough" and explain what the "Frontier" means. Did you apply any statistical analysis?since this is not explained in the text. The colour parameters should be presented in italics in text/tables etc.. In 206 line, why Lignin is in capital? In 211 line, probably a "to" is missing. In 2016 a dot is missing. The abstract and conclusions chapter present high similarity -common phrases - and should be improved in this direction. The number of 26 references in the list seems to be quite low and this is the result of the lack of a high-quality state-of-the-art analysis in the introduction chapter. 

Author Response

Thank you very much for your review and apologizes for my late reply – I was on a sabbatical and therefore not available for further work on this. We hope the updated version is approved for publication now or if there are more points to address, thank you for your further review.

The manuscript is really interesting and provides new knowledge. However, there are several points to be improved in the text.

• In the abstract, the scientific names of the species should be completed.

Thank you for your comment. We already listed the full species name.

• In the abstract, please explain in the text or in a parenthesis what is meant by "1% ZnO" (solution, uptake?).

It is stated clearer now as “% w/v of dispersion”.

• In lines 32-33, the meaning is not very clear concerning saturation. I would rather add more key words in the manuscript in order to increase its visibility/readability.

Applied.

• In line 47, please check again the phrase "within and below".

Applied.

• In line 64, correct the "food".

Applied.

• In lines 66-67, please provide more information about the uptake etc. of the referred research attempts.

Applied.

• In line 67, in which ZnO proportion used?

Applied.

• The basic state-of-the-art description on the topic lies in the part of 64-70 lines, which is very short, not providing details on the conditions applied and there are several relevant research works missing from such a description.

Updated and extended.

• In the end of introduction, the description of objectives is as well too brief, leaving behind the referance of characterization of these impregnated specimens.

We hope we made it clearer now.

• The reason why you investigate the specific one (ZnO) is not clear in the text.

Applied.
[…] besides ZnO, such as CuO and TiO, which are suitable for use as UV protection, but ZnO, for example, shows higher dispersion stability than CuO [25]. Also, Titanium di-oxide can be used as a very effect agent to prevent photoprotection in paints but in ap-plications of wood it can lead to increased degradation of wood polymers due its UV-induced photoactivity. Zinc oxide nanoparticles are more preferrable in the regard that it has an equal UV-filtering effect as titanium dioxide at lower concentrations and a lower whitening on the surface color [26].

• In materials-methods, the raw materials are not properly described. The forest species should be analytically referred in the start of the manuscript text. You did not refer to the age of the trunks, the number of the trunks, where the samples were obtained from (which height etc.).

The material was an already cut board supplied by a local wood panel dealer. The origin, height and age of the wood could therefore not be determined.

• Which are the details on the stirrer machine and sonication process?

Updated.

• Correct please the "and the and the " in line 100.

Applied.

• The " used for investigated" should be improved.

Applied.

• The "leaching resistance equation" should be clear,  explained to the reader.

Applied.

• Line 142: correct the "trough" and explain what the "Frontier" means.

Applied.

• Did you apply any statistical analysis?since this is not explained in the text.

Improved.

• The colour parameters should be presented in italics in text/tables etc..

Applied.

• In 206 line, why Lignin is in capital?

Applied.

• In 211 line, probably a "to" is missing.

Applied.

• In 2016 a dot is missing.

Applied.

• The abstract and conclusions chapter present high similarity -common phrases - and should be improved in this direction.

We improved on this point.

• The number of 26 references in the list seems to be quite low and this is the result of the lack of a high-quality state-of-the-art analysis in the introduction chapter. 

Updated.

Reviewer 3 Report

I would very much suggest more detailed explanantion of CIELab colour measurements.  Otherwise the paper is sufficiently interesting and well-prepared to justify publication. Some sentences are a bit difficult to follow due to linguistic reasons - some level of English correction is required.  

Author Response

Thank you very much for your review and apologizes for my late reply – I was on a sabbatical and therefore not available for further work on this. We hope the updated version is approved for publication now or if there are more points to address, thank you for your further review.

• I would very much suggest more detailed explanantion of CIELab colour measurements.  Otherwise the paper is sufficiently interesting and well-prepared to justify publication. Some sentences are a bit difficult to follow due to linguistic reasons - some level of English correction is required.

The CIELab color measurements were updated and described more in detail now. Also, an English correction was done.

Round 2

Reviewer 1 Report

The authors have made a proper revision and I know find the manuscript, in its current form, acceptable for publication.

Reviewer 2 Report

As I have checked the authors have implemented the proposed changes in the revised verion of manuscript towards the improvement of their work. Almost all the changes have been implemented and in my opinion, the manuscript is well-prepared and organized enough to be accepted for publication in this journal. I remain at your disposal for any clarification.