Surface Engineering of Regenerated Cellulose Nanocomposite Films with High Strength, Ultraviolet Resistance, and a Hydrophobic Surface
Round 1
Reviewer 1 Report
In this manuscript, the authors described the preparation of regenerated cellulose films with silica nanoparticles and further hydrophobized by OTS. The resulting films showed excellent properties for broad applications. The topic is interesting and a minor revision is highly recommended. The following concerns can be addressed before its publication.
1. Please add a suitable statement to highlight the novelty in the introduction.
2. The authors can discuss the potential mechanisms behind these results, such as the formation process of hydrophobic films.
3. Please explain why the films show good oxygen permeability.
4. The results of 13C-NMR of RC6 and HRC2 films should be explained in details.
Author Response
Response to Reviewer 1 Comments
Point 1: Please add a suitable statement to highlight the novelty in the introduction.
Response 1: Thank you very much for your suggestion. We agree with your comment and revise the introduction in the revised manuscript. The research purpose and motivation of this paper are highlighted in lines 84 to 91 of the manuscript. The motivation of this paper is the preparation of hydrophobic nanocomposite films, which have more superior multifunctional integration of tensile strength, strain-at-break, hydrophobicity, UV resistance, and oxygen barrier property than previously reported regenerated cellulose films in packaging materials. Moreover, the modified regenerated cellulose films biodegrade entirely in soil. Such films can help replace some of the petroleum-based plastics as waterproof packaging material, effectively alleviate the environmental pollution of petrochemical plastics.
Point 2: The authors can discuss the potential mechanisms behind these results, such as the formation process of hydrophobic films.
Response 2: Thank you for your suggestion. The potential mechanisms of hydrophobic films are highlighted in lines 181 to 187 of the manuscript. The reason for the increased hydrophobicity is twofold: firstly, the addition of nano-SiO2 makes the surface roughness of the RC films higher than that of the RC0 films, and a water-impermeable barrier was formed by the strong hydrogen bonding between the nano-SiO2 and cellulose. Secondly, OTS crystals were evenly distributed onto the surface of the cellulose films after solvent-vaporized crystallization, resulting in a micro-nano binary structure and interstitial spaces between the microplates, affecting the hydrophobicity and self-cleaning properties of the RC films.
Point 3: Please explain why the films show good oxygen permeability.
Response 3: Thank you for your suggestion. The reasons for the good oxygen permeability of the films are highlighted in lines 414 to 430 of the manuscript. The inorganic nanoparticles filled the matrix's holes and reduced the porosity of the polymer, yet hindering the vertical penetration of oxygen. Thus, the penetration path was convoluted in a manner that the oxygen migration rate was lowered, hence increasing the polymer's barrier properties. OTS was introduced into the regenerated cellulose matrix for surface silanization graft modification to improve oxygen barrier performance, mainly for two reasons. First, the surface layered structure can block the diffusion of oxygen from all directions and increase the diffusion path of oxygen, because oxygen molecules cannot directly pass through the surface of the composite film. Second, OTS has a large specific surface area. When molecular oxygen diffuses, it is adsorbed onto the surface of the OTS sheet. At this time, the oxygen molecule fills the space between the OTS and regenerated cellulose gaps, resulting in the HRC film's low oxygen permeability.
Point 4: The results of 13C-NMR of RC6 and HRC2 films should be explained in details.
Response 4: Thank you for your suggestion. The 13C-NMR results for the RC6 and HRC2 films are described in additional detail in lines 243 to 258 of the manuscript. The chemical shifts of cellulose were 105.1 ppm for C1, 88.6 ppm for C4, 74.6 ppm, 72.4 ppm for C2, 3,5, and 65.1 ppm for C6. C4 and C6 had strong and sharp signal peaks at 88.6 ppm and 64.9 ppm, broad and relatively. The signal peaks at 83.0 ppm and 61.9 ppm were broad and relatively weak, showing the crystalline and amorphous regions of cellulose, respectively. The chemical shifts of the RC film were 104.7 ppm, 83.1 ppm, 74.8 ppm, and 62.7 ppm for C1, C4, C2, 3, 5, and C6, respectively. Compared with cellulose, C4 of the RC film showed almost no signal at 88 ppm and an enhanced signal peak at 83 ppm, indicating that the hydrogen bonding network was broken during the dissolution process, the cellulose crystalline region was reduced and the amorphous region increased; C6 shifted from cellulose 64.9 ppm to 62.7 ppm and changed from a duplex peak to a single peak, indicating that the hydrogen bonding network of the sample was broken and the hydroxyl group conformation at the C6 position changed from cellulose I to regenerated cellulose II. The NMR signal peak near the chemical shift value of 33.2 ppm in the HRC film carbon nucleogram was C–Cl, which indicated the successful grafting of OTS with cellulose.
Reviewer 2 Report
Please read and “fully” address the comments listed below:
1. The ABSTRACT is not written in a logical order. Start with an overview of the topic and a rationale for your paper. Describe the methodology you used and the general outline of the manuscript. Also, in the end, state the result in more detail (i.e., provide some numbers).
2. The novelty of your work is still unclear to the reader, which should be further detailed both in the Abstract and Introduction. In other words, the purpose of the research is missing, which must be clearly presented.
3. Scale bars are missing from many figures.
4. Detail on the exact procedure used for TGA analysis. One example I can give you is:
"sample mass loss during the heating process was recorded using XXXX (e.g., NETZSCH STA 409 DTA/DTG) machine. A XXX ֯C (e.g., 1600֯C) furnace and a XXX (Westinodel 2050 programmable) temperature controller were designed to increase the temperature from XXX to YYY (e.g., 30 to 800֯C) with a constant heating rate of XXX ֯C/min( e.g., 20֯C/ min). Differential thermal analysis (DTA) was also used to determine the enthalpy change of powder as a function of temperature."
5. Provide more explanation for this sentence: Page 14, Line 372: " However, the contact angle of the RC films increased gradually with increasing nano-SiO2 content; the contact angle of the RC8 film was 62.7° ± 0.5° (Figure 7a)”.
6. For Fig. 7b determine when the contact angles were measured (was it immediately after drop placement?) and how the contact angles value changes with time on RC and HRC films.
7. Similarly, this sentence needs to be better explained: Page 1, Line 39: “However, using RC films to meet market demand is difficult because of the films’ low strength, water resistance, and gas barrier at high humidities”.
8. On page 4 the authors mentioned that a commercial contact angle goniometer (JGW-360a, HAKE, China) was used to test the contact angle of the film surface at 25°C. Commercial goniometers are expensive; hence, many research labs may not have access (or afford to use) this expensive equipment. Therefore, in your manuscript, please write a few sentences introducing inexpensive contact angle goniometers that perfectly work with either smartphones phones or USB microscopy cameras (coupled with machine learning) which can "alternatively" but accurately characterize the surface wettability of solids (and reference the papers listed below).
Smartphone-Based Goniometery:
· Crowe, C. D., Hendrickson-Stives, A. K., Kuhn, S. L., Jackson, J. B., & Keating, C. D. (2021). Designing and 3D Printing an Improved Method of Measuring Contact Angle in the Middle School Classroom. Journal of Chemical Education, 98(6), 1997-2004.
Machine Learning-Enabled Camera Goniometery:
· Kabir, H., & Garg, N. (2023). Machine learning enabled orthogonal camera goniometry for accurate and robust contact angle measurements. Scientific Reports, 13(1), 1497.
9. Conclusion: Can authors highlight future research directions and recommendations? Also, highlight the assumptions and limitations (e.g., shortcomings of the present study). Besides, recheck your manuscript and polish it for grammatical mistakes (you can use “Grammarly” or similar software to quickly edit your document).
Author Response
Response to Reviewer 2 Comments
Point 1: The ABSTRACT is not written in a logical order. Start with an overview of the topic and a rationale for your paper. Describe the methodology you used and the general outline of the manuscript. Also, in the end, state the result in more detail (i.e., provide some numbers).
Response 1: Thank you very much for your suggestion. The Abstract has been revised according to your suggestions.
Abstract: Regenerated cellulose packaging materials with good barrier properties can replace traditional plastics and other chemicals, alleviating the environmental pollution and carbon emissions. Herein, using an environmentally friendly solvent at room temperature, a straightforward procedure for synthesizing regenerated cellulose (RC) films doped with nano-SiO2 is presented. After the surface silanization modification, the obtained nanocomposite films exhibited a hydrophobic surface (HRC), in which the nano-SiO2 provides high mechanical strength, whereas Octadecyltrichlorosilane (OTS) provides hydrophobic long-chain alkanes. The contents of nano-SiO2 and concentrations of OTS/n-hexane in regenerated cellulose composite films are crucial as they define the morphological structure, tensile strength, UV-shielding ability, as well as the other performance of composite films. When the nano-SiO2 content was 6%, the tensile stress of the composite film (RC6) increased by 41.2%, the maximum tensile stress was 77.22 MPa and strain-at-break was 14%. Meanwhile, the HRC films had more superior multifunctional integration of tensile strength (73.91 MPa), hydrophobicity (HRC WCA = 143.8°), UV resistance (>95%), and oxygen barrier property (5.41×10−11 mL·cm/m2·s·Pa) than previously reported regenerated cellulose films in packaging materials. Moreover, the modified regenerated cellulose films could biodegrade entirely in soil. These results provide an experimental basis for preparing regenerated-cellulose-based nanocomposite films that exhibit high performance in packaging applications.
Point 2: The novelty of your work is still unclear to the reader, which should be further detailed both in the Abstract and Introduction. In other words, the purpose of the research is missing, which must be clearly presented.
Response 2: Thank you very much for your suggestion. We agree with your comment and revise the Introduction in the revised manuscript. The research purpose and motivation of this paper are highlighted in lines 84 to 91 of the manuscript. The motivation of this paper is the preparation of hydrophobic nanocomposite films, which have more superior multifunctional integration of tensile strength, strain-at-break, hydrophobicity, UV resistance, and oxygen barrier property than previously reported regenerated cellulose films in packaging materials. Moreover, the modified regenerated cellulose films biodegrade entirely in soil. Such films can help replace some of the petroleum-based plastics as waterproof packaging material, effectively alleviate the environmental pollution of petrochemical plastics.
Point 3: Scale bars are missing from many figures.
Response 3: Thank you for pointing out the error, the scale bars have been added to the figures. (Figure 2. Rheological properties of composite film liquids with various quantities of added nano-SiO2.)
Point 4: Detail on the exact procedure used for TGA analysis. One example I can give you is: "sample mass loss during the heating process was recorded using XXXX (e.g., NETZSCH STA 409 DTA/DTG) machine. A XXX ֯C (e.g., 1600֯C) furnace and a XXX (Westinodel 2050 programmable) temperature controller were designed to increase the temperature from XXX to YYY (e.g., 30 to 800֯C) with a constant heating rate of XXX ֯C/min( e.g., 20֯C/ min). Differential thermal analysis (DTA) was also used to determine the enthalpy change of powder as a function of temperature."
Response 4: Thank you for your suggestion, the corrections have been made as your request. The decomposition behaviors of the composite films were analyzed by TGA (TGA-600, Shimadzu, Japan) machine; over a temperature range of 30–800°C, under a nitrogen atmosphere, at a constant heating rate of 20°C/min. Differential thermal analysis (DTA) was also used to determine the enthalpy change of films as the function of temperature.
Point 5: Provide more explanation for this sentence: Page 14, Line 372: " However, the contact angle of the RC films increased gradually with increasing nano-SiO2 content; the contact angle of the RC8 film was 62.7° ± 0.5° (Figure 7a)”.
Response 5: Thank you very much for your suggestion. The explanation of this statement is highlighted in lines 373-378 of the manuscript. The surface roughness of the RC films increases with increasing nano-SiO2 content and the strong hydrogen bonding between the nano-SiO2 and cellulose form a water impermeable barrier.
Point 6: For Fig. 7b determine when the contact angles were measured (was it immediately after drop placement?) and how the contact angles value changes with time on RC and HRC films.
Response 6: Thank you very much for your advice. The contact angle is the average value obtained from five points on the same film at a certain time interval, and the experiments have shown that the contact angle of HRC film is not significantly affected by time, as added in lines 155-157 of the manuscript.
Point 7: Similarly, this sentence needs to be better explained: Page 1, Line 39: “However, using RC films to meet market demand is difficult because of the films’ low strength, water resistance, and gas barrier at high humidities”.
Response 7: Thank you very much for your suggestion, I have made modifications in the article. RC films have serious limitations, as RC films are rich in hydroxyl groups, which are hydrophilic groups, making them less water resistant and lacking in water vapour barrier properties, while RC films do not have UV blocking properties as they do not have photosensitive groups, making it difficult to use RC films to meet market demand.
Point 8: On page 4 the authors mentioned that a commercial contact angle goniometer (JGW-360a, HAKE, China) was used to test the contact angle of the film surface at 25°C. Commercial goniometers are expensive; hence, many research labs may not have access (or afford to use) this expensive equipment. Therefore, in your manuscript, please write a few sentences introducing inexpensive contact angle goniometers that perfectly work with either smartphones phones or USB microscopy cameras (coupled with machine learning) which can "alternatively" but accurately characterize the surface wettability of solids (and reference the papers listed below).
Smartphone-Based Goniometery:
- Crowe, C. D., Hendrickson-Stives, A. K., Kuhn, S. L., Jackson, J. B., & Keating, C. D. (2021). Designing and 3D Printing an Improved Method of Measuring Contact Angle in the Middle School Classroom. Journal of Chemical Education, 98(6), 1997-2004.
Machine Learning-Enabled Camera Goniometery:
- Kabir, H., & Garg, N. (2023). Machine learning enabled orthogonal camera goniometry for accurate and robust contact angle measurements. Scientific Reports, 13(1), 1497.
Response 8: Thanks for your advice, we have also carefully read the references you provided. The contact angle goniometer used in the laboratory (JGW-360a, HAKE, China) does not use martphones phones or USB microscopy cameras (coupled with machine learning).
Point 9: Conclusion: Can authors highlight future research directions and recommendations? Also, highlight the assumptions and limitations (e.g., shortcomings of the present study). Besides, recheck your manuscript and polish it for grammatical mistakes (you can use “Grammarly” or similar software to quickly edit your document).
Response 9: Thanks for your kind suggestion. The directions and recommendations for future research in this study are highlighted in lines 446-449 of the manuscript. An environmentally friendly preparation technology of fully biodegradable materials was developed to manufacture high-strength, UV-resistant, gas-barrier, biodegradable RC films; which have potential applications in packaging and functional materials. Further exploration can be made in the future in the modification of filler particles. I have also rechecked the manuscript using 'Grammarly' and made corrections for grammatical errors.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 2 Report
The authors failed to fully address my comments. Therefore, I cannot the paper unless the authors properly revise the manuscript by addressing the comments listed below:
1- The Abstract is still not systematic because:
· There is a sharp transition between the first and second sentences. The first sentence discusses how regenerated cellulose materials can replace traditional plastics and chemicals to reduce environmental pollution and carbon emissions. However, the second sentence abruptly introduces a specific process for synthesizing cellulose films doped with nano-SiO2. A transitional sentence is needed to link the two topics and provide context for the reader.
· Use active voice instead of passive voice to make the writing more engaging and easier to follow.
2- Scale bars are still missing from many figures. For example, in Fig. 7, add scale bars (ruler) to the droplet images. It is very important for the reader to understand the size of the real drop (by correct visualizations) because:
· For large drops, gravity can also have an impact on the contact angle. As the droplet becomes larger, the weight of the liquid can cause the contact line to move downward, resulting in a larger apparent contact angle. This effect is more pronounced for liquids with high surface tension and for surfaces with low energy.
· Also, for small drops, evaporation can also influence the contact angle over time. As the droplet evaporates, the contact line may retreat towards the center of the droplet, causing the apparent contact angle to increase. This effect is more significant for liquids with low boiling points or high vapor pressure, and for surfaces with high energy. Overall, the impact of droplet size on contact angle is influenced by a variety of factors, including surface properties, liquid properties, droplet shape, gravity, and evaporation.
3- The goniometer used by the authors (JGW-360a, HAKE, China) is expensive; hence, many research labs may not have access to (or afford to use) this pricey equipment. Therefore, in your manuscript, please write a few sentences introducing inexpensive contact angle goniometers that perfectly work with either smartphones or USB microscopy cameras (coupled with machine learning) which can "alternatively" but accurately characterize the surface wettability of solids (and cite/ reference the papers that I listed in my previous comments).
Author Response
对审核者2意见的回复
Point 1: The Abstract is still not systematic because:
- There is a sharp transition between the first and second sentences. The first sentence discusses how regenerated cellulose materials can replace traditional plastics and chemicals to reduce environmental pollution and carbon emissions. However, the second sentence abruptly introduces a specific process for synthesizing cellulose films doped with nano-SiO2. A transitional sentence is needed to link the two topics and provide context for the reader.
- Use active voice instead of passive voice to make the writing more engaging and easier to follow.
Response 1: Thank you very much for your suggestion. The Abstract has been revised according to your suggestions.
Abstract:
Regenerated cellulose packaging materials can alleviate the environmental pollution and carbon emissions caused by conventional plastics and other chemicals. It requires regenerated cellulose films with good barrier properties, such as strong water resistance. Herein, using an environmentally friendly solvent at room temperature, a straightforward procedure for synthesizing regenerated cellulose (RC) films with excellent barrier properties of doped with nano-SiO2 is presented. After the surface silanization modification, the obtained nanocomposite films exhibited a hydrophobic surface (HRC), in which the nano-SiO2 provides high mechanical strength, whereas Octadecyltrichlorosilane (OTS) provides hydrophobic long-chain alkanes. The contents of nano-SiO2 and concentrations of OTS/n-hexane in regenerated cellulose composite films are crucial as they define the morphological structure, tensile strength, UV-shielding ability, as well as the other performance of composite films. When the nano-SiO2 content was 6%, the tensile stress of the composite film (RC6) increased by 41.2%, the maximum tensile stress was 77.22 MPa and strain-at-break was 14%. Meanwhile, the HRC films had more superior multifunctional integration of tensile strength (73.91 MPa), hydrophobicity (HRC WCA = 143.8°), UV resistance (>95%), and oxygen barrier property (5.41×10−11 mL·cm/m2·s·Pa) than previously reported regenerated cellulose films in packaging materials. Moreover, the modified regenerated cellulose films could biodegrade entirely in soil. These results provide an experimental basis for preparing regenerated-cellulose-based nanocomposite films that exhibit high performance in packaging applications.
Point 2: Scale bars are still missing from many figures. For example, in Fig. 7, add scale bars (ruler) to the droplet images. It is very important for the reader to understand the size of the real drop (by correct visualizations) because:
- For large drops, gravity can also have an impact on the contact angle. As the droplet becomes larger, the weight of the liquid can cause the contact line to move downward, resulting in a larger apparent contact angle. This effect is more pronounced for liquids with high surface tension and for surfaces with low energy.
- Also, for small drops, evaporation can also influence the contact angle over time. As the droplet evaporates, the contact line may retreat towards the center of the droplet, causing the apparent contact angle to increase. This effect is more significant for liquids with low boiling points or high vapor pressure, and for surfaces with high energy. Overall, the impact of droplet size on contact angle is influenced by a variety of factors, including surface properties, liquid properties, droplet shape, gravity, and evaporation.
Response 2: Thank you very much for your advice. The contact angle is the average value obtained from five points on the same film at a certain time interval, and the experiments have shown that the contact angle of HRC film is not significantly affected by time, as added in lines 158-164 of the manuscript.
A contact angle goniometer (JGW-360a, HAKE, China) was used to test the contact angle of the film surface at room temperature. The static contact angle of the samples was measured using water as the measurement droplet in a volume of 10 μL. Five different locations were selected on each sample to measure the water contact angle and the average of the five contact angles was taken as the final measurement result to guarantee data accuracy and reproducibility. The equilibrium state was determined when the droplet size and contact angle did not change within 10 min; the sampling error was ±1.5%.
Point 3: The goniometer used by the authors (JGW-360a, HAKE, China) is expensive; hence, many research labs may not have access to (or afford to use) this pricey equipment. Therefore, in your manuscript, please write a few sentences introducing inexpensive contact angle goniometers that perfectly work with either smartphones or USB microscopy cameras (coupled with machine learning) which can "alternatively" but accurately characterize the surface wettability of solids (and cite/ reference the papers that I listed in my previous comments).
Response 3: Thanks for your effort in reading our manuscript and providing us with useful comments. We have elaborated on the water contact angle test, in lines 158 to 164 of the manuscript. We have also carefully read the references you provided and have improved the article on the basis of them, citing the references you mentioned.
A contact angle goniometer (JGW-360a, HAKE, China) was used to test the contact angle of the film surface at room temperature. The static contact angle of the samples was measured using water as the measurement droplet in a volume of 10 μL. Five different locations were selected on each sample to measure the water contact angle and the average of the five contact angles was taken as the final measurement result to guarantee data accuracy and reproducibility. Using the smart device as the imaging base provides better image quality and a better data acquisition experience when measuring contact angles.The equilibrium state was determined when the droplet size and contact angle did not change within 10 min; the sampling error was ±1.5%.
However the manuscript Polymers-2246997 used for the revisions cannot have references added directly due to the formatting settings. So I have made changes to the references in the original manuscript and I would appreciate it if you could revise them.
Round 3
Reviewer 2 Report
Comments are addressed.
