Using Cellulose Nanofibril from Sugarcane Bagasse as an Eco-Friendly Ductile Reinforcement in Starch Films for Packaging

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study focuses on the use of nanofibrillated cellulose (CNF) extracted from sugarcane bagasse to reinforce starch-based films. 

• What are the advantages and limitations of biodegradable materials over traditional plastics in the context of food packaging?
• How do the structure and properties of cellulose nanofibrils influence the mechanical properties and moisture resistance of biodegradable films?
• Why is nanofibrillated cellulose (NFC) from sugarcane bagasse an interesting choice for the production of biodegradable films, and how does its extraction affect the quality of the final product?
• How does bagasse pulp bleaching affect the mechanical and hydrophobic properties of CNF-based films?
• What are the implications of adding different concentrations of nanofibrillated cellulose (CNF) to the water vapor permeability of biodegradable films?
• What is the impact of residual lignin in films made from unbleached CNF, and how does this influence their performance for food packaging?
• How does the presence of lignin in unbleached cellulose nanofibrils (UB-CNF) influence the fibrillation process and suspension stability?
• Why do unbleached cellulose nanofibril suspensions exhibit higher turbidity and instability than bleached ones, despite the role of lignin in complicating fibrillation?
• What other factors, in addition to lignin content, contribute to the fibrillation process?

Author Response

Dear Reviewer #1

Please find below your comments and the respective responses. The authors thank all the contributions. Modifications to the manuscript have been marked in red.

This study focuses on the use of nanofibrillated cellulose (CNF) extracted from sugarcane bagasse to reinforce starch-based films.

 

1.What are the advantages and limitations of biodegradable materials over traditional plastics in the context of food packaging?

Response: The reviewer raised a good question. Today, we had a considerable discussion on this topic. Research conducted in all institutions focuses on replacing traditional materials, which generally come from petroleum, which does not classify them as biodegradable since they take centuries to decompose. As advantages, we can mention the good availability of lignocellulosic material in terms of quantity and throughout the year, coming from the forestry and agricultural chains, which are very strong in Brazil. Lignocellulosic material is also attractive to microorganisms that can accelerate decomposition because they are composed of organic material, alleviating the environment. Unfortunately, the food packaging industry still prefers to use plastic packaging, which is cheap but not environmentally friendly. These parts were added in the Introduction of the work, as they are part of the problematization issue of the study.

 

2.How do the structure and properties of cellulose nanofibrils influence the mechanical properties and moisture resistance of biodegradable films?

Response: The properties of CNF influence all the characteristics of the films, as long as it serves as the raw material. Appropriate pre-treatments will affect energy consumption and the difficulty of fibrillation. Pre-treatments should eliminate as much lignin and hemicellulose as possible. Authors state that low levels of lignin and hemicellulose may not impact the properties of the films; in some cases, they may even enhance the properties (this is mentioned in the discussions). Efficient fibrillation may indicate better quality CNF for generating films with superior mechanical properties since the bonds between the fibrils are stronger. In the manuscript, we only evaluated tensile strength, which is the most common metric in academic works; however, puncture resistance can also excel if there is good fibrillation. Moisture resistance can also be higher in films with improved fibrillation quality. The hydrogen bonds between the fibrils are stronger in these cases, leaving fewer areas available for bonding with water hydroxyls. The presence of lignin may lead to a film with greater moisture resistance since lignin is a hydrophobic component, potentially hindering moisture absorption and enhancing water vapor barrier properties (this is discussed in the manuscript, in the results).

 

3.Why is nanofibrillated cellulose (NFC) from sugarcane bagasse an interesting choice for the production of biodegradable films, and how does its extraction affect the quality of the final product?

Response: All studies involving nanocellulose have a common goal, which is to try to find options that can replace materials derived from petroleum, such as plastics. Bagasse is a very common waste product in Brazil, as the country is very rich in sugarcane fields for the production of ethanol and sugar. Using bagasse allows for the valuable allocation of residue, which could benefit the wood-based nanocellulose sector. Furthermore, the properties of nanocellulose from sugarcane bagasse are viable for application in packaging and coatings. There is still no industrial extraction of nanocellulose from sugarcane bagasse. Extraction is still limited to traditional species, such as eucalyptus in Brazil. When extraction is carried out with adequate parameters, both in terms of pre-treatment and regulation of the fibrillator mill and fiber concentration, the CNF will have good quality, and consequently the packaging generated can be applied. This information has been added at the end of the results and discussion, as have the Sustainable Development Goals (SDGs) with which the study aligns.

 

4.How does bagasse pulp bleaching affect the mechanical and hydrophobic properties of CNF-based films?

Response: Bleaching is extremely important for the application of CNF. This process makes the cellulose purer and more crystalline. The almost total removal of lignin makes the fibrils more capable of forming hydrogen bonds. With more solid and well-formed hydrogen bonds, mechanical properties may be superior, although the literature assumes that low amounts of lignin do not affect the properties negatively. Stronger bonds can also affect the characteristics of the relationship with water, as they generate more cohesive surfaces between the fibrils, making it difficult for water to penetrate the film. However, it is important to highlight that bleaching alone does not necessarily indicate that all properties will be satisfactory; many factors must be evaluated for the films to be suitable for use in packaging.

 

5.What are the implications of adding different concentrations of nanofibrillated cellulose (CNF) to the water vapor permeability of biodegradable films?

Response: A higher concentration of CNF in a starch matrix can result in a greater barrier to water vapor. This occurs due to the strong hydrogen bonds established between the fibrils. Starch is considered highly hydrophilic. In the study, it is noted that higher percentages of CNF presented lower WVP values. Lower concentrations of CNF in starch matrices can indicate higher permeability values. However, WVP also depends on other factors, such as raw material composition, CNF drying, and degree of fibrillation, so the CNF concentration cannot be evaluated in isolation. These discussions are highlighted in the barrier properties section of the manuscript.

 

 

6.What is the impact of residual lignin in films made from unbleached CNF, and how does this influence their performance for food packaging?

Response: Regarding unbleached CNF, the lignin content was 1.27%, which is considered low. Low lignin contents may not impair, or even improve some properties, such as mechanical and barrier properties, since it is a hydrophobic component. High lignin contents can harm the properties of the films, as they can cause agglomeration of lignin granules, which are released after fibrillation. Therefore, pre-treatments must be well executed to leave the fibers with lower lignin contents. It is highly recommended to bleach the fibers before fibrillation.

 

7.How does the presence of lignin in unbleached cellulose nanofibrils (UB-CNF) influence the fibrillation process and suspension stability?

Response: In fibrillation, lignin exerts a negative influence, as it increases the energy consumption of fibrillation. Lignin is responsible for the rigidity of the cell wall, therefore, it represents an obstacle to the process, requiring the application of previous treatments. This information was added to Table 2, which shows the results of the chemical analysis.

Regarding the suspension stability, we have explained the follow: “The lignin can act as an antioxidant, which prevents the reconnection of covalent bonds that had already been broken, according to Solala et al. (2019). However, the greater stability of unbleached CNF is better explained given the percentage of hemicelluloses (15.23%) present in this sample, and its structural properties, such as amorphous character, macromolecular branching, and high hydrophilicity. Hemicellulose may have acted as a physical barrier to keep the cellulose nanofibrils away from each other, thus preventing their aggregation (Chaker et al., 2013).”

 

8.Why do unbleached cellulose nanofibril suspensions exhibit higher turbidity and instability than bleached ones, despite the role of lignin in complicating fibrillation?

Response: The explanations in the manuscript were confusing and contradictory in the previous version. Our study obtained an unexpected result. The authors went deep to find the explanations. In the revised version, we added more effective explanations such as the following: “Regarding B-CNF, fibrillation may have been influenced by the reduction in pulp tenacity with the bleaching treatment. Treatments on sugarcane bagasse fibers may have caused very accelerated passes of suspensions through the discs of a mechanical mill, leaving many fibrils suspended, resulting in greater turbidity of the suspension, as shown in a study from Mendonça et al. (2022). The behavior of UB-CNF in the stability test may have been caused by the antioxidant action of lignin, which prevented the reconnection of covalent bonds that had already been broken (Solala et al., 2019)—or given the percentage of hemicelluloses (15.23%) present in this sample, and its structural properties, such as amorphous character, macromolecular branching, and high hydrophilicity. Hemicellulose may have acted as a physical barrier to keep the cellulose nanofibrils away from each other, thus preventing their aggregation (Chaker et al., 2013).”

 

9.What other factors, in addition to lignin content, contribute to the fibrillation process?

Response: In addition to the lignin content, several factors can interfere with fibrillation. Regarding the raw material, we can mention that the thickness of the cell wall of the biomass to be fibrillated, hemicellulose content, mineral content, and water retention are the main ones to be remembered. About treatments, the type of pre-treatment to which the biomass was subjected can be mentioned, for example, treatments with high pressure, strong acids, mercerization treatments with high alkali contents. Regarding the fibrillation process, we can mention the distance between the discs, the source material of the discs, the number of passes through the fibrillator mill, and the concentration of the suspension. These factors were not evaluated in the manuscript, so the authors chose not to cite them.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Please see the attached file.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Please see the attached file.

Author Response

Dear Reviewer #2

Please find below your comments and the respective responses. The authors thank all the contributions. Modifications to the manuscript have been marked in red.

 

1. Lack of logic in the sentence in L62. Why are “reuse” “recycling” “recovery” related to biodegradability? You used this word “Thus” after this sentence, which is confusing.

 Response: We understand that reusing, recycling, and recovering are all part of the concept of sustainability. The relationship of these three verbs with biodegradability only emphasises the need to choose to use materials that can bring environmental relief. This is what our study proposes, since nanocellulose packaging can be reused, recycled, recovered and is also biodegradable. We are not saying the concepts are the same; they are only interconnected. The sentence was reformulated to clarify the inconsistency pointed out.

 

2. Logic is not accurate in L67-70. Ss starch an agricultural “by-product”? Also, a lot of lignocellulosic materials are agricultural “by-product” like corn stover and sugar bagasse. You should not use the word “another”.

Response: We can indeed consider starch as an agricultural by-product, because it comes from cassava. The sentence was reformulated to remove the inconsistency pointed out. The new sentence is the follows: “In this context, lignocellulosic biomass emerges as a material option with great potential for formulating biodegradable films”.

 

3. You need to clearly clarify the importance of this study. Why did you propose bleached and unbleached ones are different?

Response: That's precisely it. Unbleached and bleached pulps are different. Bleached pulps undergo one more chemical treatment than unbleached pulps. Comparing the two types of pulps can help us determine ​​which is more efficient in packaging development. If unbleached pulp is more successful, preparing the raw material would require one less treatment. This information has been added to the discussions, as suggested by the reviewer.

 

4. To produce CNF, it requires high energy consumption and your treatment requires additional chemicals, how to justify this point?

Response: The transition of the pulp from the micro scale to the nanoscale requires energy. The energy required for the process comes precisely from the deconstruction of the cell wall by the action of the microfibrillator mill. Without this process, we will not be able to obtain nanocellulose films, which have superior characteristics to those of existing papers. In addition to packaging, nanocellulose has several other applications, such as adhesives, electronic equipment, fabrics for controlled drug release, and the automotive and aviation industries. Therefore, to achieve these objectives, high energy consumption is justified. Chemical treatments work by reducing the fibrillation energy of the mill. Nowadays these treatments are done with chlorine-free chemicals, which are more environmentally friendly. This information has been added to the manuscript in the end of the Results and Discussion.

 

5. Break down the introduction into multiple focused paragraphs instead of one lengthy paragraph for enhanced clarity and readability.

Response: The Introduction was broken into multiple focused paragraphs instead of one lengthy paragraph as suggested by the reviewer.

 

6. Extend explanations for off-trend data points observed in the WVP, water contact angle, and mechanical tests. Clarify anomalies or unexpected results clearly.

Response: The explanations have been extended as suggested by the reviewer. Explaining contradictions is always challenging, as it involves raising assumptions and hypotheses. In the new version, the discussions of WVP, mechanical tests and contact angle have been expanded. In the Results and Discussion section, explanations have been added.

 

7. One useful reference can be considered to cite to enhance the discussion of the effect of lignin. https://doi.org/10.1016/j.cej.2024.156142. It described that small amounts of lignin may enhance the mechanical strength of materials. However, when the lignin content is too much, mechanical strength will decrease (decrease of flexibility as well). Also, lignin changed the WVP and water contact angle of materials in this study.

Response: The authors are grateful for the article indicated. It contains fertile and necessary discussions. Furthermore, it is a current article and adds a lot to the discussions that have taken place.

 

8. Please indicate how many samples you measured for all the results to improve the repeatability and reliability of your data.

Response: In the Materials and Methods section, we added the number of samples evaluated for each test. For water vapor permeability, contact angle and wettability, the tests were performed on an average of five samples. For mechanical properties, ten samples were evaluated per treatment.

 

9. You said the starch was obtained from local family. Did you consider testing the properties of starch? Given your mention that starch rigidity results from amylose-amylose or amylose-amylopectin interactions (L453-L454), knowing the exact starch composition is critical.

Response: Starch characteristics have been added. “Crystallinity index (CI) of around 45% and amylopectin content of 85%”.

 

10. If starch was not characterized, consider adding comparisons with established literature data on similar starch-based films were made to ensure reliability and comparability.

Response: Starch characteristics have been added. Some comparisons with established literature data on similar starch-based films were made in this version. We used the article as a basis for comparisons “Starch/PVA-based nanocomposites reinforced with bamboo nanofibrils” http://dx.doi.org/10.1016/j.indcrop.2015.03.014

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This study explores the use of cellulose nanofibrils (CNF) derived from sugarcane bagasse as reinforcement agents in cassava starch-based films for eco-friendly packaging applications. This work is relatively underexplored. However, there are still cases that require attention before publication.

1. The CNFs were not characterized in terms of fiber dimensions, crystallinity index, or surface charge (zeta potential). These parameters are vital for correlating structure–property relationships.
2. SEM images are interpreted mostly qualitatively. There is no quantitative surface roughness analysis (e.g., via AFM), which limits the conclusions on the effects of surface heterogeneity on barrier or mechanical performance.
3. There is no direct comparison to commercial packaging films, which limits understanding of where these biocomposites stand in terms of real-world applicability.

 Therefore, I suggest a major revision for publication.

Author Response

Dear Reviewer #3

Please find below your comments and the respective responses. The authors thank all the contributions. Modifications to the manuscript have been marked in red.

 

1. The CNFs were not characterized in terms of fiber dimensions, crystallinity index, or surface charge (zeta potential). These parameters are vital for correlating structure–property relationships.

Response: The authors agree that these analyses are fundamental in the characterization of CNFs and that they could result in important information. However, specifically in this work, the focus is on using CNF as a ductile reinforcement material in starch films for potential packaging, so much so that we include this in the title. Adding all these characterizations could make the manuscript overly long and would change the focus of the intended discussions. In any case, we added information on how crystallinity can change after alkaline treatment and bleaching, and how this can affect the film characteristics, mainly in mechanical and barrier properties. The effect of these treatments on the crystallinity and chemical composition of the fibers is already a consensus in the literature when referring to lignocellulosic biomass.

 

2. SEM images are interpreted mostly qualitatively. There is no quantitative surface roughness analysis (e.g., via AFM), which limits the conclusions on the effects of surface heterogeneity on barrier or mechanical performance.

Response: The SEM discussions were improved to provide better details of the film surface. Unfortunately, our laboratory does not have AFM for quantitative surface studies, but the images provided provide satisfactory visibility to obtain the conclusions required for the main focus of the study.

 

3. There is no direct comparison to commercial packaging films, which limits understanding of where these biocomposites stand in terms of real-world applicability.

Response: The authors added comparisons with commercial polymers in terms of mechanical strength, which is the focus of this study. “Commercial polymers frequently used in the production of flexible packaging for the food and agricultural sectors were previously studied in Auras et al. (2004) and Tanpichai et al. (2019) and found values of 37 MPa for linear low-density polyethylene, and 35 MPa for polypropylene, which were superior compared to those presented in this study. On the other hand, the abovementioned authors obtained 6.9-16 MPa for low-density polyethylene, 17 MPa for polyesteramide, and 8.5-10.5 MPa for highly branched low-density polyethylene, which makes the films in the present study interesting for this application”

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Sustainability

Manuscript Draft

Manuscript Number: sustainability-3587737

 

Full Title: Cellulose nanofibril from sugarcane bagasse as an eco-friendly ductile reinforcement in starch films for potential packaging

 

Major Revision

 

Title suitable     N

The summary    Y

The units and symbols N

Figures and Table text  N

Table and graphs duplicate N

All the references Y

 

 

Comments:

The manuscript entitled "Cellulose nanofibril from sugarcane bagasse as an eco-friendly ductile reinforcement in starch films for potential packaging" presents experimental research about starch films reinforced with cellulose from sugarcane bagasse.

 

1. The English grammar of the manuscript needs additional review.
2. The abstract should be improved by the contribution of the manuscript and the conclusion of the work performed.
3. The authors can rethink the title of the manuscript to be more appropriate to the manuscript content.
4. The quality of Figure 1 should be improved.
5. Authors must provide all the parameters regarding the characterization analysis by microscopy.
6. It is necessary to insert characterization techniques (SEM, DLS, Zeta Potential) to validate the cellulose fibrils at the nanoscale.
7. A thermoanalytical characterization (TG/DTG, DTA) should be performed to collaborate with the thermal stability study.
8. The original curves ( tensile vs deformation) would enrich the manuscript instead of figures 6,7, and 8 presented in the manuscript. The legend of the Figures is out of place.
9. Authors need to suggest at the conclusion which sample was most suitable, considering all the results obtained, for the application intended.

Comments on the Quality of English Language

The English grammar of the manuscript needs additional review.

Author Response

Dear reviewer #4

Please find below your comments and the respective responses. The authors thank all the contributions. Modifications to the manuscript have been marked in red.

 

1. The English grammar of the manuscript needs additional review.

Response: The English and grammar were reviewed with specific grammar software and provided an English version in which the information is understandable to the reader;

 

2. The abstract should be improved by the contribution of the manuscript and the conclusion of the work performed.

Response: The authors improved the abstract with information on how the study can contribute to the environment and society. In the new version, the authors added this information to the abstract section: “Treatments with 50% CNF of sugarcane bagasse (unbleached or bleached) should be highlighted among the properties evaluated”. This sentence highlights the most suitable samples for the intended application. The same information was added to the conclusion.

 

 

3. The authors can rethink the title of the manuscript to be more appropriate to the manuscript content.

Response: The authors believe that the title illustrates well the objective of the study, which is precisely to add CNF to the starch matrix to provide more ductile films, so much so that the results section on mechanical properties is the longest in the manuscript. The authors even thought of other possibilities, but we preferred a relatively short and attractive title. We could mention the issue of unbleached and bleached pulps, but the title would be too long. Anyway, at the moment we think that the title may be appropriate for the study focus of the manuscript, without straying from the essence of the objective.

 

4. The quality of Figure 1 should be improved.

Response: In the new version, Figure 1 has been improved, as suggested by the reviewer. The authors preferred to add real images of the experiments.

 

5. Authors must provide all the parameters regarding the characterization analysis by microscopy.

Response: The suggested scanning electron microscopy (SEM) parameters were added. In addition, a morphological analysis by transmission electron microscopy (TEM) was added so that the reader could validate the nanoscale dimensions of the CNF from sugarcane bagasse (new Figure 3).

 

6. It is necessary to insert characterization techniques (SEM, DLS, Zeta Potential) to validate the cellulose fibrils at the nanoscale.

Response: The authors added characterization of the bleached and unbleached CNF by Transmission Electron Microscopy (TEM) to show the nanoscale dimension (Figure 3). These images can be even more effective than SEM analysis, DLS or Zeta Potential.

 

7. A thermoanalytical characterization (TG/DTG, DTA) should be performed to collaborate with the thermal stability study.

Response: The authors agree that these analyses are fundamental in the characterization of CNF and films and that they could result in important information. However, specifically in this work, the focus is on using CNF as a ductile reinforcement material in starch films for potential packaging, so much so that we include this in the title. Adding all these characterizations could make the manuscript overly long and would change the focus of the intended discussions. In any case, we added information on how crystallinity can change after alkaline treatment and bleaching, and how this can affect the film characteristics, mainly in mechanical and barrier properties. The effect of these treatments on the crystallinity and chemical composition of the fibers is already a consensus in the literature when referring to lignocellulosic biomass.

 

 

8. The original curves (tensile vs deformation) would enrich the manuscript instead of figures 6,7, and 8 presented in the manuscript. The legend of the Figures is out of place.

Response: The authors improved the discussions of mechanical properties in terms of comparisons with commercial polymers such as LDPE and PP, which allow a better understanding of the viability of CNF. The authors would like to add tensile vs deformation graphs to the manuscript, but the mentioned curves had problems when registering. The authors only have the values ​​for the calculations of the properties presented in the manuscript. Nonetheless, we think that the lack of these curves does not affect the quality of the manuscript information.

 

9. Authors need to suggest at the conclusion which sample was most suitable, considering all the results obtained, for the application intended.

Response: In the new version, the authors added this information to the conclusion section: “Treatments with 50% CNF of sugarcane bagasse (unbleached or bleached) should be highlighted among the properties evaluated”. This sentence highlights the most suitable samples for the intended application. The same information was added to the abstract.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

it's a good work

Reviewer 2 Report

Comments and Suggestions for Authors

The authors addressed all my comments.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript has been well-revised, and I suggest it to be accepted.

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript is accepted in the present form after the modifications performed by the authors.