Andiroba Oil (Carapa guianensis Aubletet) as a Functionalizing Agent for Titica Vine (Heteropsis flexuosa) Nanofibril Films: Biodegradable Products from Species Native to the Amazon Region

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

General comments

 

The submitted manuscript creprotd the production and characterisation of functionalization of 32 Heteropsis flexuosa derived cellulose micro/nanofibrils (MFC/NFC) films, loaded with andiroba oil for food packaging applications.

The paper is interesting and its topic worthy of investigation. Some revisions have to be applied, particularly for the Introduction and Experimental sections.

Furthermore, an English grammar and language revision is strongly recommended.

Some comments are provided below point by point.

Asbtract

The conclusion “More studies should be carried out on the pretreatment of waste fibers to reduce energy consumption and improve their mechanical properties.” does not sound appropriate for an Abstract section, but more suitable for a Conclusions one. Please, remove or move it.

Keywords

The chosen keywords (i.e. biopolymers; mechanical fibrillation; essential oils; lignocellulosic waste.) do not completely cover the manuscript content. Please, add further ones.

 

 

I. Introduction

- The incipit “Materials from renewable and biodegradable sources have gained attention from the scientific and industrial communities.” needs appropriate references, including “Bio-nanocomposites as food packaging materials; the main production techniques and analytical parameters. Advances in Colloid and Interface Science, 310 (2022), 102806.”.

- For the statement “Conventional petroleum-based polymeric products are being replaced due to immense ecological disruption, such as global warming and plastic pollution [1].” the reference is too old (2017). Please, replace it with more recent ones, including “An overview of the packaging industry: State of the art, opportunities, challenges, criticisms, and solutions. Nanostructured Materials for Food Packaging Applications, 2024: 1-30.”.

- The following sentence “many species still need to have their potential evaluated, especially in nanotechnology.” is not clear. Please, rewrite it.

- The following statement “The literature strongly presents the potential of different essential oils in nanocellulose matrix, which offer antimicrobial properties in food packaging, as many researchers have been committed to studying this function [10]” neds a more recent and appropriate reference, such as “Recent advances in qualitative and quantitative characterization of nanocellulose-reinforced nanocomposites: A review. Advances in Colloid and Interface Science 318 (2023) 102961.”

- It is strongly suggested to add a brief list of the used characterisation techniques at the end of the Introduction section.

 

 

2.3. Characterization of the fibers

Please, add more details, even if reported elsewhere.

 

2.10. Physical and morphological properties of the films

- More details have to be added about all the performed characterisations.

- For example, the number of samples analysed for every characterisation has to be specified, in order to provide an average value and the related standard deviation.

- For the SEM observation, the used instrument has to be specified.

- Please correctly rewrite the dimension. Replace “5 × 5 mm” with “5 mm * 5 mm” or “5*5 mm^2”.

2.12. X-ray diffraction (XRD)

- The reported equations have to be supported with proper references.

 

2.13. Light transmission and transparency of the films

- Please correctly rewrite the dimension. Replace “30 × 20 mm” with “30 mm * 20 mm” or “30 x 20 mm^2”.

- The reported equation has to be supported with proper references.

 

2.16. Degradation in water of the films

- Please correctly rewrite the dimension. Replace “30 × 30 mm” with “30 mm * 30 mm” or “30 x 30 mm^2”.

- The reported equation has to be supported with proper references.

 

2.17. Barrier to water vapor and grease

- The reported equation has to be supported with proper references.

- Please correctly rewrite the dimension. Replace “216 × 279 mm” with “216 mm * 279 mm” or “216 x 279 mm^2”.

2.18. Contact angle and wettability of the films

- The reported equation has to be supported with proper references.

- Please correctly rewrite the dimension. Replace “10 × 50 mm” with “10 mm * 50 mm” or “10 x 50 mm^2”.

 

2.19. Mechanical properties of the films

- Please correctly rewrite the dimension. Replace “100 × 100 mm” with “100 mm * 100 mm” or “100 x 100 mm^2”.

2.21. Biodegradation of films

- Please correctly rewrite the dimension. Replace “2 × 2 cm” with “2 cm *2 cm” or “2 x 2 cm^2”.

 

 

 

Comments on the Quality of English Language

It is good

Author Response

REVIEWER #1

General comments

 

The submitted manuscript creprotd the production and characterisation of functionalization of  Heteropsis flexuosa derived cellulose micro/nanofibrils (MFC/NFC) films, loaded with andiroba oil for food packaging applications.

 

The paper is interesting and its topic worthy of investigation. Some revisions have to be applied, particularly for the Introduction and Experimental sections.

 

Furthermore, an English grammar and language revision is strongly recommended.

 

Some comments are provided below point by point.

 

 

 

 

 

Asbtract

 

The conclusion “More studies should be carried out on the pretreatment of waste fibers to reduce energy consumption and improve their mechanical properties.” does not sound appropriate for an Abstract section, but more suitable for a Conclusions one. Please, remove or move it.

Response: Adjusted. Removed from the text.

 

Keywords

 

The chosen keywords (i.e. biopolymers; mechanical fibrillation; essential oils; lignocellulosic waste.) do not completely cover the manuscript content. Please, add further ones.

Response: Keywords were added as suggested by the reviewer.

 

1. Introduction

 

- The incipit “Materials from renewable and biodegradable sources have gained attention from the scientific and industrial communities.” needs appropriate references, including “Bio-nanocomposites as food packaging materials; the main production techniques and analytical parameters. Advances in Colloid and Interface Science, 310 (2022), 102806.”.

Response: Included related references in the text

 

- For the statement “Conventional petroleum-based polymeric products are being replaced due to immense ecological disruption, such as global warming and plastic pollution [1].” the reference is too old (2017). Please, replace it with more recent ones, including “An overview of the packaging industry: State of the art, opportunities, challenges, criticisms, and solutions. Nanostructured Materials for Food Packaging Applications, 2024: 1-30.”

Response: Included related references in the text

 

- The following sentence “many species still need to have their potential evaluated, especially in nanotechnology.” is not clear. Please, rewrite it.

Response: Sentence corrected in the text.

 

- The following statement “The literature strongly presents the potential of different essential oils in nanocellulose matrix, which offer antimicrobial properties in food packaging, as many researchers have been committed to studying this function [10]” neds a more recent and appropriate reference, such as “Recent advances in qualitative and quantitative characterization of nanocellulose-reinforced nanocomposites: A review. Advances in Colloid and Interface Science 318 (2023) 102961.”

Response: Included recent reference suggested by the reviewer.

 

- It is strongly suggested to add a brief list of the used characterisation techniques at the end of the Introduction section.

Response: The authors thank you for the suggestion. A paragraph has been added about the characterization techniques.

 

2.3. Characterization of the fibers

 

Please, add more details, even if reported elsewhere.

Response: The characterization of the fibers was written in more detail in the text.

 

2.10. Physical and morphological properties of the films

 

- More details have to be added about all the performed characterisations.

- For example, the number of samples analysed for every characterisation has to be specified, in order to provide an average value and the related standard deviation.

- For the SEM observation, the used instrument has to be specified.

- Please correctly rewrite the dimension. Replace “5 × 5 mm” with “5 mm * 5 mm” or “5*5 mm^2”.

Response: Modifications and changes to the text were made.

 

2.12. X-ray diffraction (XRD)

 

- The reported equation has to be supported with proper references.

 

Response: The proper reference was provided to support the reported equations.

 

 

2.13. Light transmission and transparency of the films

 

- Please correctly rewrite the dimension. Replace “30 × 20 mm” with “30 mm * 20 mm” or “30 x 20 mm^2”. The reported equation has to be supported with proper references.

 

Response: Corrected in the text. The proper reference was provided to support the reported equations.

 

 

2.16. Degradation in water of the films

 

- Please correctly rewrite the dimension. Replace “30 × 30 mm” with “30 mm * 30 mm” or “30 x 30 mm^2”. The reported equation has to be supported with proper references.

 

Response: Corrected in the text. The proper reference was provided to support the reported equations.

 

 

2.17. Barrier to water vapor and grease

 

- The reported equation has to be supported with proper references.

 

- Please correctly rewrite the dimension. Replace “216 × 279 mm” with “216 mm * 279 mm” or “216 x 279 mm^2”.

Response: Corrected in the text. The proper reference was provided to support the reported equations.

 

 

 

2.18. Contact angle and wettability of the films

 

- The reported equation has to be supported with proper references.

- Please correctly rewrite the dimension. Replace “10 × 50 mm” with “10 mm * 50 mm” or “10 x 50 mm^2”.

Response: Corrected in the text. The proper reference was provided to support the reported equations.

 

2.19. Mechanical properties of the films

 

- Please correctly rewrite the dimension. Replace “100 × 100 mm” with “100 mm * 100 mm” or “100 x 100 mm^2”.

Response: Corrected in the text.

 

 

2.21. Biodegradation of films

 

- Please correctly rewrite the dimension. Replace “2 × 2 cm” with “2 cm *2 cm” or “2 x 2 cm^2”.

Response: Corrected in the text.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Minor editing is recommended.

Author Response

REVIEWER #2

Review of Andiroba oil as functionalizing agent for titica vine nanofibril films: biodegradable products from species native to the Amazon region’

 

In their work the authors discuss about combining Andiroba oil in the concentration range from 1-5% in fibrillated titica vine cellulose for film formation by the casting method. Besides the description of the production method, several characterisations of the films were conducted, including microscopy, SEM, XRD and wetting angle determination among others. There is comprehensive data of the films and the topic as the findings are of interest for readers of Sustainability.

Besides extensive data presentation, the manuscript lacks a clear classification of the produced films. It does not seem clear what properties are desired. Besides, the addition of andiroba oil does seem to alter the properties of the films only very gradually. The difference between the formulations seem minor. As with the different characterisation, they somehow do not fit to one big picture, but at times seem contraindicatory. E.g. no tentative argumentation for decreasing contact angles with increasing andiroba oil contents is given. Simultaneously, structural parameters of the different andiroba oil seem minute.

The manuscript would benefit from clearing such differences in obtained properties to used materials. Besides, there is multitude of cellulose-oil films, but few references are drawn concerning obtained and desired properties. It would help to grasp a more thorough picture of the obtained films. It is not clear why these compounds were chosen, apart from coming from the Amazon.

 

Major Issues

The introduction is not focused, very short and does not introduce the reasons for the study. It would furthermore benefit from a hypothesis or desired film properties, that would be aspired.

Introduction: There is several studies about the barrier properties of cellulose-oil films. Could you include them to get a better comparison?

Response: The introduction has been improved according to reviewers.

 

2.16: It does not seem to be degradation. Is it elution or water-extractable? If it is degradation, what happens after 48h or after 5h? And what do you want to show with water-extractables? Please also refer to section 3.12.

Response: Some articles present the test as degradation in water, disintegration in water (cited below) or solubility. In short, they are the same thing, they evaluate how the material behaves when immersed in water. The time interval may vary, but generally, within 24 hours, we have a result with good precision, since, if there is degradation, it will largely occur within this time interval. The literature is accurate in saying cellulose is practically insoluble. Therefore, after 48 h or more, the values would not differ much from the 24 h values. The reviewer questions the term water-extractable. Well, we do not use this term throughout the manuscript. Still, we can deduce that they are structures that can be extracted using water, like some extractives present in lignocellulosic materials. However, when preparing nanocellulose, the lignocellulosic material undergoes treatments that eliminate or almost wholly reduce the extractives, making it impossible to remove them later in a film.

 

Bio-based films/nanopapers from lignocellulosic wastes for production of added-value micro-/nanomaterials. Environmental Science and Pollution Research https://doi.org/10.1007/s11356-021-16203-4

 

3.4: L 464 states that it is 9% sedimentation, however in your plot it is 1%. And Figure 6b also suggest rather 10% than 1%. Maybe magnify the 24h vials.

Response: The reviewer's recommendation was timely, as there was an error in plotting the graph. In the new version, the authors corrected the inconsistency and Figure 6b is now consistent with Figure 6a

 

FTIR: Maybe the differences in the peaks derive from different measurement intensities. Would it make sense to background correct the signals and normalize these?

Response: The samples were taken together in the equipment, so the differences between the results probably come from differences between the compositions of the films and structures modified in their formation. No abnormalities were observed in the test.

 

3.9: The films seem non transparent. Only 20% of the light in a share of the visible light region passes.

Response: The text was modified as suggested by the reviewer. We really cannot say that 26% is high transparency. In the current version, we have also added images from the films to give you an idea of their transparency.

 

L 600: How well are the differences in the degradation onset resolvable. Can we really conclude that AN3 has a lower initial onset of degradation. And do we expect that? The cellulose degrades relatively similar in all samples.

Response: In reality, the Tonset degradations were very close, as mentioned by the reviewer. However, we can see that the An3 film has a small increase in temperature compared to the other treatments. Therefore, the authors wanted to mention this fact for due accuracy of the information in the manuscript, even if a few ºC in advance.

 

Based on the contact angle measurements: Did you check surface roughness as an indicator for structuring?

Response: In this work, we did not evaluate roughness as a specific parameter, as the focus is on indicating the film for functionalized packaging. The surface granularity can be seen in the SEM figures (Figure 7) and even in the figure showing biodegradation (Figure 16). This granularity can affect the contact angle and wettability, and this discussion has been added to the text.

 

The conclusion fails to set a perspective to complementary studies. What other films perform equally or different? What, and how, could be improved about the films, their production as their constituents?

Response: The reviewer's suggestions improved the conclusion. Future work was proposed, previous studies with other lignocellulosic residues were mentioned, and some points were indicated for improvements in the production process.

 

Minor Issues

2.1. why were these filters chosen? Why not bigger/smaller sieves?

m/m: mass/mass or mol/mol?

Response: The parameters and material selection were made according to the study by Scatolino et al. (2017) (reference below).

 

Scatolino, M.V.; Bufalino, L.; Mendes, L.M.; Guimaraes Junior, M.; Tonoli, G.H.D. Impact of nanofibrillation degree of eucalyptus and Amazonian hardwood sawdust on physical properties of cellulose nanofibril films. Wood Sci. Technol. 2017, 51, 1095-1115. https://doi.org/10.1007/s00226-017-0927-4

 

 

The sentence “Passed through the 35 mesh (0.500 mm) sieve and was retained in the 60 mesh (0.250 mm) sieve.” was corrected in the text.

 

211. 149: 90 pm? It seems the whole FEG section is repeated at line 211. There it is 90 pA.

Why did you add cupric ethylendiamine? Could the solutions not be characterised directly after production?

Response: The same equipment was used for microstructural analysis of the suspension and films. Tescan-Clara (Kohutovice, Czech Republic) ultra-high resolution (UHR) FEG scanning electron microscope under 10 KeV, ''90 pA'' conditions. Cupric ethylendiamine is the necessary reagent to analyze the viscosity of the suspension. In this work, the authors preferred to carry out this viscosity analysis closer to the time of producing the films. This information have been added to the text.

 

Figure 1: Maybe add HPMC + Surfactant in sketch?

Response: HPMC + Surfactant have been added to the Figure 1.

 

Equation 7 seems odd. Does it really need the Log() as Tr usually is between 0 and 1?

Response: The equation has been modified according to the adapted by Dias et al. (2023), referenced below. The previous equation presented an inconsistency.

 

Mandacaru cactus as a source of nanofibrillated cellulose for nanopaper production.  International Journal of Biological Macromolecules. https://doi.org/10.1016/j.ijbiomac.2023.123850

 

 

L 271: DrTGA was not introduced yet.

Response: DrTGA means derived from thermogravimetric analysis curves. The information has now been added to the text.

 

L 327: p/S5?

Response: The term inconsistent has been removed

 

L 383-385: so with lignin it does or does not fibrillate easier?

Response: The presence of lignin in the fiber structures can make it difficult to deconstruct the cell wall, making the nanofibrillation process less expensive. Corrected in text.

 

Figure 3: What is a gel appearance. Did you perform any viscosity or rheometry measurements?

Response: Gel appearance means viscous, gelatinous and slightly transparent consistency. When fibrils begin to form, the solution begins to have a greater viscosity due to the interaction of hydrogen bonds. Some articles bring the name gel appearance, others bring gel consistency, others bring a gelatinous appearance, this is very variable. Images 1 and 3 show the appearance well and we can get an idea of the term gel. The viscosities were made and presented in Figure 7.

 

L 462: Would we not expect the particles to settle, even though lignin and hemicellulose are high-molecular weight? The trend seems quite linear

Response: Tha explanation has been improved “The sedimentation after 3 h can be attributed to the presence of non-fibrillated matter in suspensions. During mechanical fibrillation, some fibers may cling to the equipment's stone discs, being detached at the end of the process without necessarily being fibrillated. This fact can also explain by the large proportion of MFC over NFC in suspensions. This sedimentation reached a final proportion of approximately 9% after 24 h. A high-molecular-weight constituent as the lignin can also contribute to the precipitation of material at the bottom of the tube.”

 

From the error bars in Figure 7, I am surprised the viscosity values are significantly different.

Response: The authors got confused when plotting the letters and the error was corrected in the new version, new Figure 7. The text has been modified accordingly.

 

L 495-499: Would we not expect a similar share of cell wall fragments in all samples? Is this artefacts?

Response: It may be influenced by the addition of oil and the polarity relationships between the oil and the lignocellulosic nanostructures. This information has been added to the text.

 

L 530: If there is a reduction in intensity, how high roughly? Would we not expect the cellulose crystalline regions to be of same magnitude as the reference. l – 545: with crystallinity increase would we not expect increased signal intensities?

Response: In this work, crystallinity was calculated in the form of Crystal Fraction, not crystallinity index. The Crystalline Fraction takes into account the crystalline area under the curve, eliminating the amorphous halo. Therefore, even at higher intensities, the crystalline area can be smaller. In this case, the Crystalline Fraction of the An3 film was higher, as the amorphous halo generated in the deconvolution of the curves was probably smaller. The other films, control, An1 and An5, obtained high intensities, but the crystalline areas were smaller due to the amorphous halo being larger.

 

Table 3: Could you add a level of uncertainty?

Response: The data presented in Table 3 correspond to the crystalline fraction and crystallite size that are calculated from the area under the curve of the x-ray pattern (Figure 9). Therefore, these are unique measurements that did not present repetition, they are only the result of a single calculation, showing no standard deviation.

 

Table 3 and Figure 10 don’t match. At higher crystalline fraction would we not expect lower transmittance? And would the highest transmittance not correspond to the lowest opacity (Table 4)?

Response: This fact must have occurred due to confusion on the part of the authors when putting together the table. The values had been displayed incorrectly. In the new version, the authors corrected this detail.

 

L 584: what are acceptable limits?

Response: Acceptable limits are imprecise. The authors think it is better to change to “It's worth noting that despite the increase in opacity after the addition of andiroba oil, these values remain so that it does not compromise the visibility of the product to be packaged”.

 

L 632: what are significant parameters? Which are these?

Response: Most significant values (bulk density, thickness and grammage).

Corrected in text.

 

Figure 13b: wettability in %s or in mN/m.

Response: ''º/s'' Corrected in the text.

 

Why 90° contact angle differentiation. What would be desired? What does that mean in terms of application?

Response: A contact angle smaller than 90° characterizes a hydrophilic surface, that is, a surface can be wetted by the liquid; on the other hand, when the contact angle is greater than 90°, there is a hydrophobic surface, showing almost no contact between the droplet and the surface.

Packaging produced with materials of a hydrophilic nature may cause some difficulties in storing certain types of products, especially food and perishables.

 

L 675: From Figure 14 it seems An3 has a lower E-modulus?

Response: The Young's Modulus of An3 was the largest, not significantly different from An1, but it presented a lower modulus until rupture, that is, lower tensile strength.

 

Figure 15: Readers might not remember FRAP as a Unit.

Response: The meaning FRAP (Ferric Reducing Antioxidant Power) was inserted in the text before Figure 15.

 

L 708: Micropores are mentioned, which I did not find mentioning before.

Response: In fact, the authors do not mention micropores, but rather mention the porous microstructure of the film. In the current version, the authors removed the term “micro” and left only the porous structure to make it clearer.

 

Figure 16: The biodegradation of An3 seems unexpected. Again, any ideas why it would behave so different? As in puncture stress and Young’s modulus.

Response: Two distinct analyses can be established: mass loss analysis and visual analysis of the samples. An0 (control) and An3 treatments showed more pronounced degradation, especially after 14 days of testing, with 44.7 and 43.1%, respectively, of final mass. On the other hand, films An1 and An5 showed lower percentages of degradation. When visually analysing the samples, we noticed that the An1 films had a better appearance, or a more preserved appearance after biodegradation, suggesting that higher concentrations of andiroba oil treatments did not avoid the microbial activity over the films. This discussion has been added to the text.

 

Figure 3: Interesting perspective, but as I don’t know, or have a hard time estimating the energy consumption of similar films, I cannot elaborate on it. Again, it would benefit from a perspective.

Response: These perspectives would be great to obtain. Future work could take this data and estimate the amount of energy spent on the fibrillation of other materials, based on the viscosity or density of the plant fiber, for example, or the water retention index. However, for now, we must measure consumption after the material has fibrillated, and cannot lower anything before that.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the revision. There still is no clear picture why An3 behaves better in biodegradation and transmittance, comparing with a better biodegradation.

Besides, the results could further be set in reference to similar studies, including transmittance, structural and behavioural properties. The findings stills seem alone-standing and readers might have a hard time placing the properties. Better inter-comparison also might lead to more citations, as a better understanding of the films' uniquenesses, for authors and readers.

Comments on the Quality of English Language

Minor spell checking seems possible. Becker<->beaker etc.

Author Response

REVIEWER #2

Thank you for the revision. There still is no clear picture why An3 behaves better in biodegradation and transmittance, comparing with a better biodegradation.

Response: In fact, An3 and control showed greater biodegradation compared to the others, this is clear in Figure 16 (green and red curves). Figure 1 6 has been improved to clearly show the state of destruction that sample An3 remained after biodegradation. Some references have been added to support the discussion, such as Guimarães et al. (2022) and Bardi and Rosa (2007).

 

Besides, the results could further be set in reference to similar studies, including transmittance, structural and behavioural properties. The findings stills seem alone-standing and readers might have a hard time placing the properties. Better inter-comparison also might lead to more citations, as a better understanding of the films' uniquenesses, for authors and readers.

Response: Guimarães et al. (2022) and Dias et al. (2023) carried out interesting studies on the biodegradation and transmittance properties of films with banana pseudostem waste and mandacaru cactus, respectively. The authors added comparisons against these tests in this version of the manuscript to better support the discussions.

 

Minor spell checking seems possible. Becker<->beaker etc.

Response: The word has been corrected

Author Response File: Author Response.docx