Use of Cellulose Fibres from Posidonia oceanica to Obtain Chitosan Biocomposites and Poly(lactic Acid) Laminates
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe study is very interesting. I recommend its publication in the Polysaccharides journal after a minor revision. Below please find my comments:
2.1. Chemicals – please include the purity grade
2.5 Why were the PLA-based films manufactured by lamination instead of solvent casting? Or, on the other hand, the chitosan-based films could also be subjected to compression in 100 C. I mean, it would be better to compare the samples prepared in a similar way. I do not expect you to redo the whole study but an explanation should be included in the paper.
3.1. How was the composition of the fibers established? There is no description of the method.
Author Response
2.1. Chemicals – please include the purity grade
Response: It has been included (line 95).
2.5 Why were the PLA-based films manufactured by lamination instead of solvent casting? Or, on the other hand, the chitosan-based films could also be subjected to compression in 100 C. I mean, it would be better to compare the samples prepared in a similar way. I do not expect you to redo the whole study but an explanation should be included in the paper.
Response:
Thermoplastic processing is the one applied industrially in the plastics industry, using thermoplastic polymers, without the solvent evaporation requirements of the solvent casting method. In the present study, different procedures were applied to obtain PLA and chitosan films due to the different characteristics of the polymers. PLA can be thermoprocessed due to its thermoplastic nature, whereas chitosan is not a thermoplastic polymer and degrades at temperatures below its softening temperature, making thermoprocessing difficult. On the other hand, chitosan, due to its solubility in an acidified aqueous medium, allows films to be obtained without the use of organic solvents and could be obtained by casting and water evaporation. This has been commented on the text. (Lines 150-151, 165-166).
3.1. How was the composition of the fibers established? There is no description of the method.
The method has been described in the revised manuscript (Lines 121-134).
Reviewer 2 Report
Comments and Suggestions for AuthorsThis work primarily discusses the use of cellulose fibers from Posidonia oceanica (PO) as a sustainable material for developing biodegradable composites and PLA laminates. The key focus is on how these fibers, which are obtained using subcritical water extraction and bleaching with hydrogen peroxide or sodium chlorite, are processed and incorporated into various biomaterials including cellulose films, chitosan-cellulose composites, and PLA-cellulose laminates. This work contributed to the field of converting biomass residues into useful and value-added products; however, the manuscript is not in a very good shape, and the general clarity throughout the entire manuscript must be improved.
[1] Abstract: “ The PO fibres were used to obtain cellulose films, chitosan-cellulose composites, and PLA-12 cellulose laminates, which were. characterised as to their optical properties, mechanical performance, oxygen and water vapour permeability, thermal stability, and microstructure.” These are not supposed to be two sentences, being this kind of careless is not acceptable. Also, no need to mention further studies in abstract.
[2] The citation formats for references [5], [24], [25], [27], [28], and [36] are inconsistent with other references. Stay consistent! Please!!
[3] Please explain why Posidonia oceanica cellulose fibers were chosen as the raw material in the Introduction section?
[4] Please briefly introduce Subcritical Water Extraction (SWE) technology in the Introduction, and in Section 2.2, line 98, where the abbreviation "SWE" is used, the full term should be given on its first time appearance.
[5] It is recommended to add a flowchart for the material preparation process to clearly show the steps of the preparation: from PO cellulose fibers preparation to the final film production, as well as the preparation of composite materials and laminated boards.
[6] There are three Section 2.7?
[7] Please provide more in-depth discussion on the advantages of using PO cellulose fibers to obtain chitosan-cellulose biocomposites and cellulose-PLA laminated boards as packaging materials. This should be the key contribution of the current study.
Author Response
[1] Abstract: “ The PO fibres were used to obtain cellulose films, chitosan-cellulose composites, and PLA-12 cellulose laminates, which were. characterised as to their optical properties, mechanical performance, oxygen and water vapour permeability, thermal stability, and microstructure.” These are not supposed to be two sentences, being this kind of careless is not acceptable. Also, no need to mention further studies in abstract.
Response: This mistake has been corrected, and the phrase “Further studies…” has been rewritten in the revised Abstract.
[2] The citation formats for references [5], [24], [25], [27], [28], and [36] are inconsistent with other references. Stay consistent! Please!!
Response: The formats have been corrected.
[3] Please explain why Posidonia oceanica cellulose fibers were chosen as the raw material in the Introduction section?
Response: This has been explained (Lines 44-53).
[4] Please briefly introduce Subcritical Water Extraction (SWE) technology in the Introduction, and in Section 2.2, line 98, where the abbreviation "SWE" is used, the full term should be given on its first time appearance.
Response: It has been included in the revised manuscript (lines 58-63).
[5] It is recommended to add a flowchart for the material preparation process to clearly show the steps of the preparation: from PO cellulose fibers preparation to the final film production, as well as the preparation of composite materials and laminated boards.
Response: The flow chart has been included (now, Figure 1, Lines 115-118).
[6] There are three Section 2.7?
Response: This typing mistake has been corrected.
[7] Please provide more in-depth discussion on the advantages of using PO cellulose fibers to obtain chitosan-cellulose biocomposites and cellulose-PLA laminated boards as packaging materials. This should be the key contribution of the current study.
Response: This has been included in the conclusion (lines 513-516)
Reviewer 3 Report
Comments and Suggestions for AuthorsThis paper deals with the possibility of using the cellulose fibres isolated from Posidonia oceanica for preparation of novel bio-based composites. Composites were produced as neat cellulose films, chitosan-cellulose composites and PLA-cellulose laminates. The intention of the Authors was to determine whether can aforementioned composites be used as materials for packaging. Therefore, selected properties of the composites important for packaging applications were determined.
The manuscript is well prepared and well structured. It deals with interesting topic and is clearly a part of the ongoing research of the same Authors. However, there are few details that need to be addressed prior to manuscript publication. First of all, there is a minor issue with the determination of chemical composition of CC and CP fibres. The Authors cite NREL method being used to determine the lignin, cellulose, hemicelluloses and ash contents, without giving any details on the actual method. As NREL methods are somewhat specific and are not well known as for instance TAPPI, ASTM or ISO standard methods, some details on the method and equipment used must be given. Also, please add information how did you differentiate between cellulose and hemicelluloses, were any corrections made in case of hemicelluloses (due to branching) and are the lignin contents given in Table 1, the combined values of acid-soluble and acid-insoluble lignin fractions. In line 173 please change “stress-Henky strain curves” to Hencky stress-strain curves. Please add subsection 2.8. Determination of microstructural properties, where you should give details on the SEM method and equipment used. Consequently, the subsection Statistical analysis should be subsection 2.9. (not 2.7 as it is now, which is also wrong as there is an error in numbering; subsection 2.7. twice). The TGA and DTG curves given in Figure 2 are smoothed too much (especially DTG ones) that it is rather hard to observe the shoulders of the peaks representing the second stage decomposition. Rather hard but are still noticeable, and those are related to hemicelluloses that are clearly present in the examined celluloses (results given in Table 1). Please add some explanations on this matter, as hemicelluloses can severely influence the materials thermal properties (among some other properties like optical). As for the HRFESEM images, please explain why were different composites cross-sections observed under different magnifications. Also, please add some arrows to (each) images to clearly point to the detail(s) of interest. The same is for the image given in the Figure 4.
Author Response
First of all, there is a minor issue with the determination of chemical composition of CC and CP fibres. The Authors cite NREL method being used to determine the lignin, cellulose, hemicelluloses and ash contents, without giving any details on the actual method. As NREL methods are somewhat specific and are not well known as for instance TAPPI, ASTM or ISO standard methods, some details on the method and equipment used must be given. Also, please add information how did you differentiate between cellulose and hemicelluloses, were any corrections made in case of hemicelluloses (due to branching) and are the lignin contents given in Table 1, the combined values of acid-soluble and acid-insoluble lignin fractions.
Response: The method has been described, and the information required has been specified (Lines 121-133).
In line 173 please change “stress-Henky strain curves” to Hencky stress-strain curves.
Response: This has been corrected (line 203).
Please add subsection 2.8. Determination of microstructural properties, where you should give details on the SEM method and equipment used. Consequently, the subsection Statistical analysis should be subsection 2.9. (not 2.7 as it is now, which is also wrong as there is an error in numbering; subsection 2.7. twice).
Response: It has been corrected (Line 234-240).
The TGA and DTG curves given in Figure 2 are smoothed too much (especially DTG ones) that it is rather hard to observe the shoulders of the peaks representing the second stage decomposition. Rather hard but are still noticeable, and those are related to hemicelluloses that are clearly present in the examined celluloses (results given in Table 1). Please add some explanations on this matter, as hemicelluloses can severely influence the materials thermal properties (among some other properties like optical).
Response: The Figures have been improved (Figure 3 in the revised manuscript, lines 434-436).
As for the HRFESEM images, please explain why were different composites cross-sections observed under different magnifications. Also, please add some arrows to (each) images to clearly point to the detail(s) of interest. The same is for the image given in the Figure 4.
Response: As explained in the manuscript, the different magnifications were selected for highlighting the most relevant structural elements in each case. Arrows are included to mark details of interest and described in the figure captions (Figures 4 and 5 in the revised manuscript, lines 465-466 and 44).
Reviewer 4 Report
Comments and Suggestions for AuthorsThe article is certainly of interest to specialists involved in the development of fully biodegradable composite materials based on natural polymers for the purposes of degradable packaging and medicine. Since polylactide is a thermoplastic material, it was interesting to obtain not only film materials based on polylactide and cellulose fibers, which is discussed in the article, but also some volumetric structures, for example, using modern additive technologies. Perhaps the authors will pay attention to such technologies in the future.
Since chitosan and polylactide films are quite fragile, it would be important to show in the article how filling them with cellulose fibers helped to solve this problem. Unfortunately, the authors of the article failed to do this, since the maximum values ​​of deformation before destruction of the composite films do not exceed 4% (Table 3). In addition, it would be useful to evaluate in the article the transition temperatures of the obtained materials using DMA and DSC methods, and not only the temperatures of the onset of their thermal destruction using the TGA method (Figure 2).
Author Response
The article is certainly of interest to specialists involved in the development of fully biodegradable composite materials based on natural polymers for the purposes of degradable packaging and medicine. Since polylactide is a thermoplastic material, it was interesting to obtain not only film materials based on polylactide and cellulose fibers, which is discussed in the article, but also some volumetric structures, for example, using modern additive technologies. Perhaps the authors will pay attention to such technologies in the future.
Since chitosan and polylactide films are quite fragile, it would be important to show in the article how filling them with cellulose fibers helped to solve this problem. Unfortunately, the authors of the article failed to do this, since the maximum values ​​of deformation before destruction of the composite films do not exceed 4% (Table 3). In addition, it would be useful to evaluate in the article the transition temperatures of the obtained materials using DMA and DSC methods, and not only the temperatures of the onset of their thermal destruction using the TGA method (Figure 2).
Response: The incorporation of cellulose fibres in composites or laminates always means an increase in the stiffness of the material, decreasing its extensibility, due to the stiffness of the fibres. However, it increases the mechanical strength of the material and can also improve the water vapour and oxygen barrier properties, as discussed in the manuscript
DSC and DMA analyses have not been carried out for different reasons. The amorphous PLA used, with better heat-sealability than crystalline PLA, has a known Tg (52-54 oC, Ordoñez et al., 2022) which will not be affected by cellulose lamination as PLA and cellulose are in different phases. On the other hand, DSC studies of chitosan do not provide a clear glass transition or melting endotherm below its degradation temperature. Likewise, DMA analyses also do not reveal such transitions between 25 and 140 oC (Mano, 2008), hence its non-thermoplastic behaviour.
Ordoñez, R., Atarés, L., & Chiralt, A. (2022). Effect of ferulic and cinnamic acids on the functional and antimicrobial properties in thermo-processed PLA films. Food Packaging and Shelf Life, 33, 100882.
Mano, J. F. (2008). Viscoelastic properties of chitosan with different hydration degrees as studied by dynamic mechanical analysis. Macromolecular bioscience, 8(1), 69-76.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsI have no further questions.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Authors,
As all of my comments were addressed, I see no reason why this manuscript can't be accepted in its current form, and published as a scientific paper.
Kind regards
Reviewer
Reviewer 4 Report
Comments and Suggestions for AuthorsThe authors of the article responded to my comments and remarks, and in this form the article can be published in the journal.
