Ultrasound and Eco-Detergents for Sustainable Cleaning

Round 1

Reviewer 1 Report

The work can not be accepted in the present form. English language must be improved; the state of the art should be extended; there several typographical errors; cross references must be included (there are several "Error! Reference source not found.");  SI measuremet units must be explained in the text next to the equations ; Plan of the experiments must be clarified

Extensive editing in english language is required. There are several errors

Author Response

Manuscript Number: processes-2413915
Ultrasound and ecodetergents for sustainable cleaning

The authors would like to thank the reviewers for their evaluation. Each comment has been individually responded and referenced. The reviewers will also find the revised text with numbered lines and all the mayor changes highlighted in yellow. Both mayor and minor changes have been tracked. The authors hope to ease in this way the re-evaluation of the paper.

The work can not be accepted in the present form. English language must be improved; there several typographical errors;

-The whole document has been revised and corrected by a native speaker with change tracking

 

 

The state of the art should be extended.

-Following reviewer #2 and #1 suggestions the state of the art has been extended (lines 89 to 113)

 

cross references must be included (there are several "Error! Reference source not found."); 

-With due respect, this problem is related to the pdf conversion of the MDPI server. With the aim of easing the work to the editorial, both references have been overwritten.  

 

SI measurement units must be explained in the text next to the equations;

-SI units explained next to each variable (lines 65 to 68)

 

 Plan of the experiments must be clarified.

-The description the experimental plan has been extended and clarified (lines 130 to 141)

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The manuscript (MS) reports on the simultaneous use of ultrasound and surfactants to remove stains and shows that the use of ultrasound is beneficial to increase the removal of dirt from glass surfaces. It also shows that ultrasound and detergents have different actions on stain removal. The manuscript uses a very interesting approach by fixing a glass plate on the side on the sonotrode of an ultrasound equipment.

The influence of surfactants or detergents and ultrasound separated and in combination on wettability enhancement and silicone and hydrocarbon grease removal as well as the effect of ultrasound on sliding mechanism, visual appearance of droplets of detergents was evaluated.

As a general outcome the authors report that ecological detergents combined with ultrasound might substitute toxic synthetic detergents. Ultrasound alone can remove grease by physical action, but detergents are needed to avoid reimpregnation of the dirt on the surface.

Although interesting, the MS lacks experimental details and statistical treatment. Most evaluations seem to have been made qualitatively and even when data are presented, information about repeats and standard deviations are missing (table 3, table 4, table 2, which is out of order, another table 3, figure 10, figure 13)

To my understanding, the authors also overstress the term toxic or harmful throughout the manuscript. Toxicity depends on concentration, exposure time and to whom toxicity applies, amongst other parameters.

It should be better explained how the ultrasonic system with the blade sonotrode works. It seems that it is not dipped into any liquid.

More information on the detergents or surfactants should be given. Are they anionic, nonionic, etc. ?

Although CMC are mentioned and discussed in the text, data are not presented!

How authors measured the critical angle of inclination (see table 4)

How exactly the sliding mechanism (figure 7) was investigated? What was the exact procedure?

The text should be revised with respect to typing errors, tables and figures should be improved and put in correct order.

Although discussion in general is good, comparison to other results with other detergents and cleaning systems should be included.

What is different in this work to other previous investigations? Authors should make clear what is new and different in their work in comparison to previous studies.

The text should be revised with respect to typing errors, tables and figures should be improved and put in correct order.

Author Response

Manuscript Number: processes-2413915
Ultrasound and ecodetergents for sustainable cleaning

The authors would like to thank the reviewers for their evaluation. Each comment has been individually responded and referenced. The reviewers will also find the revised text with numbered lines and all the mayor changes highlighted in yellow. Both mayor and minor changes have been tracked. The authors hope to ease in this way the re-evaluation of the paper.

 

Although interesting, the MS lacks experimental details and statistical treatment. Most evaluations seem to have been made qualitatively and even when data are presented, information about repeats and standard deviations are missing (table 3, table 4, table 2, which is out of order, another table 3, figure 10, figure 13)

-Repetitions, average values, standard deviations, and measurement errors have been included in the experiments. Further discussion about the statistical behavior of some results has been extended and highlighted in yellow.  (lines 197 to 199, 203 to 210 and 269 to 272)

 

To my understanding, the authors also overstress the term toxic or harmful throughout the manuscript. Toxicity depends on concentration, exposure time and to whom toxicity applies, amongst other parameters.

-The authors agree absolutely with the suggestion.  The word “toxic” has been removed and substituted by “synthetic”. 

 

It should be better explained how the ultrasonic system with the blade sonotrode works. It seems that it is not dipped into any liquid.

-Further explanations of the blade horn have been included. (Lines 149 to 152)

 

More information on the detergents or surfactants should be given. Are they anionic, nonionic, etc. ?

-The content of each detergent has been included in table 1

 

Although CMC are mentioned and discussed in the text, data are not presented!

-Table 3 shows de surface tension values. CMC of each detergent was highlighted in bold, but perhaps it was not visible enough. Each CMC has been underlined instead and commented in the table capture.

 

How authors measured the critical angle of inclination (see table 4). How exactly the sliding mechanism (figure 7) was investigated? What was the exact procedure?

-Description of the tilting and measurement system included (lines 155 to 159)

 

The text should be revised with respect to typing errors, tables and figures should be improved and put in correct order.

-Revised and numbers updated

 

Although discussion in general is good, comparison to other results with other detergents and cleaning systems should be included. What is different in this work to other previous investigations? Authors should make clear what is new and different in their work in comparison to previous studies.

-Originally the work was very focused on the sustainability aspects, but following the recommendation of the reviewer, a stronger emphasis on the novelty of the work has been done. The wetting and rinsing phenomena have been highlighted as main difference with other works during the abstract and the introduction (lines 89 o 113)

 

Author Response File: Author Response.pdf

Reviewer 3 Report

1) The abstract is too vague. "The problem is not the chemical composition, but the property sought itself" does not sufficiently explain the background to this work. Tangible, quantitative results are also missing.

2) Line 63/265: A reference is missing (an error message shows).

3) Line 68: 'n' should be 'In'.

4) Fig. 1: I can't tell what is happening in the images. Can you elaborate the caption with an explanation of the left and right images.

5) Line 85: In this final paragraph of the introduction, it would be helpful to specify this is aimed at industrial cleaning (e.g. of tempered glass). If you think it is a technology that could also be adopted by commercial/professional cleaners then please say so.

6) Line 163: "3" is missing. There are several formatting issues that need to be fix.

7) Table 3/Fig 5 & Table 2 (number is out of order)/Fig 10 & Table 3 (the 2nd one!)/Fig 13: The duplication of data is unnecessary. The tabulated data is nice to have, so maybe move that to a supplementary material?

8) Fig. 6: The photo editing ("The pictures were contrasted at 50% in black and white scale") needs to be repeated in the caption for clarity.

9) Line 193: A reference is needed for "As demonstrated by same authors, ..."

10) Table 4: Please rephrase the caption.

The abstract is too whimsical, minor improvements to reduce the ambiguity of the remaining text would also be appreciated.

Author Response

Manuscript Number: processes-2413915

Ultrasound and ecodetergents for sustainable cleaning

The authors would like to thank the reviewers for their evaluation. Each comment has been individually responded and referenced. The reviewers will also find the revised text with numbered lines and all the mayor changes highlighted in yellow. Both mayor and minor changes have been tracked. The authors hope to ease in this way the re-evaluation of the paper.

1) The abstract is too vague. "The problem is not the chemical composition, but the property sought itself" does not sufficiently explain the background to this work. Tangible, quantitative results are also missing.

-Both reviewers coincide on the lack of explanation of the background. Following their recommendations, the authors have rewritten the abstract and have enlarged the introduction (lines 89 o 113).

 

2) Line 63/265: A reference is missing (an error message shows).

-with due respect, this problem is related to the pdf conversion of the MDPI server. With the aim of easing the work to the editorial, both references have been overwritten and tested in pdf.

 

3) Line 68: 'n' should be 'In'.

-corrected, now in line 70

 

4) Fig. 1: I can't tell what is happening in the images. Can you elaborate the caption with an explanation of the left and right images.

-further explanations have been included in the caption

 

5) Line 85: In this final paragraph of the introduction, it would be helpful to specify this is aimed at industrial cleaning (e.g. of tempered glass). If you think it is a technology that could also be adopted by commercial/professional cleaners then please say so.

-Following the recommendation of the reviewer, the authors have included mentions to the industrial cleaning of solar plants.

 

6) Line 163: "3" is missing. There are several formatting issues that need to be fix.

-The authors do not see any 3 missing in line 163. It might be that during the pdf conversion, the reference to table 3 has been lost. The authors have checked the pdf proper transformation to pdf format.

 

7) Table 3/Fig 5 & Table 2 (number is out of order)/Fig 10 & Table 3 (the 2nd one!)/Fig 13: The duplication of data is unnecessary. The tabulated data is nice to have, so maybe move that to a supplementary material?

- With due respect, the statement contradicts reviewer N#1, who is asking for explicit numerical data.

 

8) Fig. 6: The photo editing ("The pictures were contrasted at 50% in black and white scale") needs to be repeated in the caption for clarity.

-Caption explained with suggested clarification

 

9) Line 193: A reference is needed for "As demonstrated by same authors, ..."

-reference included (line 232)

 

10) Table 4: Please rephrase the caption.

-The caption has been rewritten and clarified.

 

 

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The editing suggestions seem to be satisfied. Accept in present form

The editing suggestions seem to be satisfied. Accept in present form

Author Response

According to the reviwer, suggestions seem to be satisfied. 

The authors would like to thank the work of the reviewer. 

Reviewer 2 Report

The authors responded satisfactorily to some of my queries, however the changes they made in the introduction are not convincing. Arguments are superficial and for the reader it is still not able to see what of this work is different from previous investigations or common knowledge. It is obvious that without rinsing the cleaning process is incomplete. Some of the newly introduced information is simply wrong, such as that glass has a positive zeta potential (except under certain conditions or if charged positively). Some essential data of the detergents used in this study are still missing, such as detailed information on composition, some physical chemical data, e.g., viscosity. The authors should also include some literature on critical sliding angle. Although some of the results seem quite interesting some things remain unclear.

The selection of the studied detergents is not clear to me and does not seem to make much sense. Ecodetergents containing enzymes are useful for textiles or dishwashing, but the selected greases are not potential substrates for the common biocatalysts (not informed) used in detergents.

The discussion and conclusion part were not improved at all.

To my understanding the manuscript still must be improved significantly before considering for publication.

 

Detailed comments:

Abstract: lethal dose is quite dramatic and does not sound very scientific; not all surfactants are toxic!

Critical slinging angle = critical sliding angle?

Page 3, line 91: there seems no relation between the affirmation in the text of the manuscript and the cited reference 24

Line 95: same problem for ref 26 and 27 as reported for ref 24 in line 91

Line 97, 98: the authors cite a reference saying that glass is positively charged, however, see reference 26: , the zeta potential of the silica surfaces was −90 mV

Line 116 ff and table 1:

 what is the problem of a surfactant containing KOH? Toxicity is concentration related and KOH is an additive of some detergents to provide alkaline conditions, however other substances may be added to provide alkaline pH, as are the alkaline salts used in the so called “ecologic detergents”.

The detergents listed in table 1 are still badly defined, the reader should know which components are contained. What is the amount of each type of surfactant? What are the enzymes for? Hydrocarbon grease and silicon grease are most probably not degraded by any of the enzymes in these formulations, so the main contribution of the detergents for dissolution or removal is due to the formation of micelles of surfactants and additional changes in surface charge due to adsorption of other ingredients of the detergents.

Line 155: Where is figure 3?

Line 158: what is meant by “increasing the whole system” ?

Figure 13, table 2, table 3 and the surrounding text, and of the whole manuscript: instead of cleaned surface rate, it should be probably cleaned surface ratio or surface cleaning efficiency, as rate refers to velocity. In addition: how was this value calculated? By the image area? This should be better described in the materials and method section.

Legend of table 3 should be corrected: it should be: detergent concentration in % (v/v)?

Etc.

no comments

Author Response

Manuscript Number: processes-2413915
Ultrasound and ecodetergents for sustainable cleaning

The authors would like to thank the reviewers for their evaluation. Each comment has been individually responded and referenced. The reviewers will also find the revised text with numbered lines and all the mayor changes highlighted in yellow. Both mayor and minor changes have been tracked. The authors hope to ease in this way the re-evaluation of the paper.

 

The authors responded satisfactorily to some of my queries, however the changes they made in the introduction are not convincing. Arguments are superficial and for the reader it is still not able to see what of this work is different from previous investigations or common knowledge. It is obvious that without rinsing the cleaning process is incomplete. Some of the newly introduced information is simply wrong, such as that glass has a positive zeta potential (except under certain conditions or if charged positively).

-Corrected. Glass (silicon dioxide) carries negative charge naturally. After each experiment, its surface has been perfectly cleaned by rubbing with tissues (this is the reason why it charges positively). However, the authors agree that for a generic case in the introduction, negative charges should be considered, not positive ones. 

 

Some essential data of the detergents used in this study are still missing, such as detailed information on composition, some physical chemical data, e.g., viscosity. Although some of the results seem quite interesting some things remain unclear. The selection of the studied detergents is not clear to me and does not seem to make much sense. Ecodetergents containing enzymes are useful for textiles or dishwashing, but the selected greases are not potential substrates for the common biocatalysts (not informed) used in detergents.

-Table 1 has been extended with further data about the properties of each detergent. However, the authors must clarify that the selected detergents are commercial products, whose complete formulation is confidential and part of the company know-how.

The authors should also include some literature on critical sliding angle.

-Thank you for the suggestion, references have been included.

The discussion and conclusion part were not improved at all.

To my understanding the manuscript still must be improved significantly before considering for publication.

-Following Reviewer’s indication Discussion and conclusions have been improved by introducing the aspects commented in previous comments: properties of the different detergent solutions, critical sliding angles and non-returning mechanism.

 Detailed comments:

Abstract: lethal dose is quite dramatic and does not sound very scientific; not all surfactants are toxic!

-removed

Critical slinging angle = critical sliding angle?

-corrected

 

Page 3, line 91: there seems no relation between the affirmation in the text of the manuscript and the cited reference 24. Line 95: same problem for ref 26 and 27 as reported for ref 24 in line 91 Line 97, 98: the authors cite a reference saying that glass is positively charged, however, see reference 26: , the zeta potential of the silica surfaces was −90 mV. 

Thank you for notice our mistake, the references have been checked and improved, and additionally the text has been also improved.

Line 116 ff and table 1: what is the problem of a surfactant containing KOH? Toxicity is concentration related and KOH is an additive of some detergents to provide alkaline conditions, however other substances may be added to provide alkaline pH, as are the alkaline salts used in the so called “ecologic detergents”.

-With due respect, the surfactant containing KOH causes skin irritation (H 315) and serious eye damage (H318). Without knowing the precise formulation the detergents (it is confidential) the authors conclude that the problem is the excessive concentration of KOH.

 

The detergents listed in table 1 are still badly defined, the reader should know which components are contained. What is the amount of each type of surfactant? What are the enzymes for? Hydrocarbon grease and silicon grease are most probably not degraded by any of the enzymes in these formulations, so the main contribution of the detergents for dissolution or removal is due to the formation of micelles of surfactants and additional changes in surface charge due to adsorption of other ingredients of the detergents.

The information about the detergents has been improve as much as it is possible considering that are patented. We believe that these description describe enough information for researchers and industrial user that what to use this technology.

Line 158: what is meant by “increasing the whole system” ?

-increasing the inclination of the whole system. Corrected

 

Line 155: Where is figure 3?

-there was a desynchronizing between captions and figures and tables during the text formatting. It has been solved in the whole document

Figure 13, table 2, table 3 and the surrounding text, and of the whole manuscript: instead of cleaned surface rate, it should be probably cleaned surface ratio or surface cleaning efficiency, as rate refers to velocity. In addition: how was this value calculated? By the image area? This should be better described in the materials and method section.

-the word ratio has been changed by ratio. The method has been described in detail in materials and methods section.  

Legend of table 3 should be corrected: it should be: detergent concentration in % (v/v)?

-corrected

Round 3

Reviewer 2 Report

The manuscript was improved, however some important aspects are possibly difficult to resolve, as data for detergents according to the authors, are insufficient to create a sound scientific explanation. My suggestion for further works is to prepare their own surfactants or work with better defined surfactants, as outcomes are difficult to explain, especially if some points are needed to be explained by fundamental surface and surfactant science while information on the used products is superficial.

Unfortunately, I am still not convinced that the presented results and discussions are meaningful.

I would like to comment on the following author responses:

1. -Corrected. Glass (silicon dioxide) carries negative charge naturally. After each experiment, its surface has been perfectly cleaned by rubbing with tissues (this is the reason why it charges positively). However, the authors agree that for a generic case in the introduction, negative charges should be considered, not positive ones. 

If authors consider the rubbing of the surface with a tissue that results in charge separation and adsorption of positive charges on the glass surface, they should write and explain this in the manuscript, so that the reader is able to understand the reasons behind the arguments. However, if it is questionable if this charge remains in an aqueous media and this has to be proven by measurements of surface charge.

2. Line 116 ff and table 1: what is the problem of a surfactant containing KOH? Toxicity is concentration related and KOH is an additive of some detergents to provide alkaline conditions, however other substances may be added to provide alkaline pH, as are the alkaline salts used in the so called “ecologic detergents”.

-With due respect, the surfactant containing KOH causes skin irritation (H 315) and serious eye damage (H318). Without knowing the precise formulation the detergents (it is confidential) the authors conclude that the problem is the excessive concentration of KOH

Despite of the commented Hazard Statement Codes H315 and H318 for KOH, its use in detergents might be essential to obtain specific cleaning results or properties such as texture in detergents or soaps. What I wanted to say is that authors must be more specific, and arguments must be better justified. Authors should be careful with certain affirmations, as it is not enough to conclude from imprecise information or believes.

Detailed Comments:

In figures 8 and 9 the authors should include in the legend that black (for silicon grease) means unsoiled and white (in the case of hydrocarbon) means unsoiled, this would facilitate the understanding of the pictures.

Author Response

Manuscript Number: processes-2413915
Ultrasound and ecodetergents for sustainable cleaning

The authors would like to thank the reviewers for their evaluation. Each comment has been individually responded and referenced. The reviewers will also find the revised text with numbered lines and all the mayor changes highlighted in yellow. Both mayor and minor changes have been tracked. The authors hope to ease in this way the re-evaluation of the paper.

 

The manuscript was improved, however some important aspects are possibly difficult to resolve, as data for detergents according to the authors, are insufficient to create a sound scientific explanation. My suggestion for further works is to prepare their own surfactants or work with better defined surfactants, as outcomes are difficult to explain, especially if some points are needed to be explained by fundamental surface and surfactant science while information on the used products is superficial.

The authors would like to thank the reviewer for the comment. Indeed, we are considering stablishing a new collaboration on this area. However, this work is part of an R&D project with a private company, so there was no option to analyze self-prepared formulations and we were more focus in the process. Further work will consider seriously this aspect.

Unfortunately, I am still not convinced that the presented results and discussions are meaningful.

I would like to comment on the following author responses:

1. -Corrected. Glass (silicon dioxide) carries negative charge naturally. After each experiment, its surface has been perfectly cleaned by rubbing with tissues (this is the reason why it charges positively). However, the authors agree that for a generic case in the introduction, negative charges should be considered, not positive ones. 

If authors consider the rubbing of the surface with a tissue that results in charge separation and adsorption of positive charges on the glass surface, they should write and explain this in the manuscript, so that the reader is able to understand the reasons behind the arguments. However, if it is questionable if this charge remains in an aqueous media and this has to be proven by measurements of surface charge.

-with the aim of understanding the electric behavior of the glass, the authors have performed measurements under three different conditions: initial, after rubbing and after pouring water. None of the cases show any measurable charge, concluding that the sample is not electrically charged (table 7)

2. Line 116 ff and table 1: what is the problem of a surfactant containing KOH? Toxicity is concentration related and KOH is an additive of some detergents to provide alkaline conditions, however other substances may be added to provide alkaline pH, as are the alkaline salts used in the so called “ecologic detergents”.

-With due respect, the surfactant containing KOH causes skin irritation (H 315) and serious eye damage (H318). Without knowing the precise formulation the detergents (it is confidential) the authors conclude that the problem is the excessive concentration of KOH

Despite of the commented Hazard Statement Codes H315 and H318 for KOH, its use in detergents might be essential to obtain specific cleaning results or properties such as texture in detergents or soaps. What I wanted to say is that authors must be more specific, and arguments must be better justified. Authors should be careful with certain affirmations, as it is not enough to conclude from imprecise information or believes.

-Taking in consideration reviewer’s suggestion the text referring to KOH have been re-written. Lines 130 to 135.

Detailed Comments:

In figures 8 and 9 the authors should include in the legend that black (for silicon grease) means unsoiled and white (in the case of hydrocarbon) means unsoiled, this would facilitate the understanding of the pictures.

-Comments included in captions of figure 8 and 9. The same this applies to figures 11 and 12.

 

Author Response File: Author Response.pdf