Effect of Sodium Hydroxide, Succinic Acid and Their Combination on Densified Wood Properties
Round 1
Reviewer 1 Report
This study reports the alkali and acid pretreatment for wood densification. The topic is not new but the discussion and interpretation of the results in general makes sense. I think This manuscript can become much better for other researchers.
1) Recently, some research on alkali and acid solution as a pretreatment in wood densification have been published. For instance, Properties of densified poplar wood through partial delignification with alkali and acid pretreatment. https://doi.org/10.1007/s10853-020-05034-2; Characterization of Microstructure, Chemical, and Physical Properties of Delignified and Densified Poplar Wood. https://doi.org/10.3390/ma14195709; Fabrication of densified wood via synergy of chemical pretreatment, hot‑pressing and post mechanical fixation https://doi.org/10.1186/s10086-020-1853-x.
The innovation of this work should be emphasized more in the Introduction.
2) There are too many experimental details in the Abstract. Please provide the innovation, importance and more results.
3) Table 2. Please check the ANOVA result. Are the specific gravity values of wood before treatment not involved in the ANOVA analysis? Why is there no character ‘a’ for the column of Pisang putih and the column of Nyatoh?
4) Figure 8. It is the transmission spectra, not the absorbance spectra. What is the meaning of three arrows? It is not clear about the peak ranged from 1720-1726 cm-1 in the spectra of acid pretreated wood and combination-pretreated wood.
5) More discussion of FTIR results should be paid attention on. What happens about the IR bands peaked at 1510 cm-1, 1424 cm-1, 1330 cm-1, 1315 cm-1, 1264 cm-1, 890 cm-1 and 864 cm-1? More chemical changes of wood cell wall components after pretreatment could be clarified.
It could help us understand the change of wood property after treatment more.
Author Response
Reviewer 01
Comments and Suggestions for Authors:
This study reports the alkali and acid pretreatment for wood densification. The topic is not new but the discussion and interpretation of the results in general makes sense. I think This manuscript can become much better for other researchers.
1) Suggestion: Recently, some research on alkali and acid solution as a pretreatment in wood densification have been published. For instance, Properties of densified poplar wood through partial delignification with alkali and acid pretreatment. https://doi.org/10.1007/s10853-020-05034-2; Characterization of Microstructure, Chemical, and Physical Properties of Delignified and Densified Poplar Wood. https://doi.org/10.3390/ma14195709; Fabrication of densified wood via synergy of chemical pretreatment, hot‑pressing and post mechanical fixation https://doi.org/10.1186/s10086-020-1853-x.
The innovation of this work should be emphasized more in the Introduction.
Answer: Thank you for your comment. Actually, those references that you mentioned above already citated in this manuscript. You can check it on References part.
In this study, no delignification was done separately. However, the results of this study indicated that NaOH could be softening the wood cells and increased their compressibility, because it was able to make cellulose, hemicellulose and lignin swells. It was proven by stress-strain curve of NaOH-pretreated wood during compression. In the other hand, the effect of succinic acid on wood structure or even densified wood is rarely investigated. Acid-pretreatment can be partially degraded hemicellulose and low molecular weight of lignin, which broke down the wood ultrastructure. The utilization of succinic acid as pretreatment in this research was proven to be able to prevent the recovery-set. Therefore, densified wood through combination of NaOH and succinic acid improves the hydrogen bonding of the cellulosic materials, thus results in a decrease of spring-back value, as well.
2) Suggestion: There are too many experimental details in the Abstract. Please provide the innovation, importance and more results.
Answer: Thank you for your suggestion. I intentionally put those experimental detail on abstract to make sure the reader knew about scope of study of this research.
3) Question: Table 2. Please check the ANOVA result. Are the specific gravity values of wood before treatment not involved in the ANOVA analysis? Why is there no character ‘a’ for the column of Pisang putih and the column of Nyatoh?
Answer: Specific gravity values of wood before treatment were involved in the ANOVA analysis. These are indicated by the difference in the range with the untreated samples.
4) Question: Figure 8. It is the transmission spectra, not the absorbance spectra. What is the meaning of three arrows? It is not clear about the peak ranged from 1720-1726 cm-1 in the spectra of acid pretreated wood and combination-pretreated wood.
Answer: Thank you for your correction. Yes, it is transmittance spectra because in this study I’m using FTIR-UATR. The arrows and vertical lines showed distinguish changes for the treatment compared to untreated wood. Actually, the arrows pointed on distinguish peak but when I saw it in the manuscript, the distinguish peak value was disappeared and needed to shift the box a little to show the value. About the peak ranged from 1720-1726 cm-1, It can be seen on Figure 8, the peak more visible in acid pretreated wood and combination-pretreated wood than untreated and HD treatment, while that peak doesn’t exist in alkali pre-treated wood.
5) Question: More discussion of FTIR results should be paid attention on. What happens about the IR bands peaked at 1510 cm-1, 1424 cm-1, 1330 cm-1, 1315 cm-1, 1264 cm-1, 890 cm-1 and 864 cm-1? More chemical changes of wood cell wall components after pretreatment could be clarified.
Answer: Thank you for your suggestion. Those peak that you mentioned doesn’t have a visible change in all of treatment. The visible changes occurred in alkali pretreated wood just because the spectra shifted. According to Pandey (1999), band peak at 1510 cm-1 related to aromatic skeletal vibration; band peak at 1424 cm-1 related to C-H in-plane deformation with aromatic ring stretching; band peak at 1315 cm-1 related to C-O of syringyl ring; band peak at 1264 cm-1 related to C-O of guaiacyl ring; peak ranged from 664-890 cm-1 related to C-H out of plane.
It could help us understand the change of wood property after treatment more.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The review of an article “Effect of Sodium Hydroxide, Succinic Acid and Their Combination on Densified Wood Properties” submitted by Augustina et al. to Forests Journal.
The subject of the paper is very interesting and up-to-date considering the high intensity of work on the thermomechanical modification of wood. Moreover, it applies to species that have not been studied in this respect so far, which is additionally advantageous. In my opinion, the article is written correctly (from the language perspective) and contains the references from high-profile scientific journals.
Both the title and abstract of the paper are informative. The abstract contains basic information about the conducted research. In my opinion it could focus more on the results and less on methodology but this is just a general suggestion, not a mistake.
The introduction part is well thought out. It introduces the reader to all the issues covered by the article in a non-chaotic way.
Line 38: “Various processes have been attempted and shown to improve physical and mechanical properties of densified wood” – it would be interesting to develop this subject. Authors using that many references to support this statement should, in my opinion, add a brief comment on which ways were actually studied.
Line 61: This part is a little confusing as the result of fast change of subject. It should be explained what matrix Authors had in mind.
In general, I think the presentation of previous results in case of NaOH application is beneficial. Moreover, it is also great that Authors emphasize the novelty while describing both the application of succinic acid and the treatment with the combination of alkali and acid. As a general suggestion from the reader perspective I would recommend to add some information about the species involved in this study since it can be a material unknown to some readers (basic information: maybe a range of density, which way of applications are recommended for this species etc.).
Materials and Methods are presented clearly, the methods seem to be correctly selected.
Line 105: The boards were air-dried in laboratory room having a specific conditions?
Table 1: What is the reason for slightly different dimensions of samples from the “C” variant?
2.2.: The subsection name should be extended since it shows also the details about the pre-treatment.
Line 116: The accuracy of weighting process should be included.
Line 122: The word “similar” indicates some slight differences. Was the pressing conditions the same?
2.3-2.6: The number of replications is missing.
Line 180: The accuracy “around 5 mg” is not enough in case of instrumental methods as FTIR.
2.8: The wood sample preparation is missing. At this point the information about testing only one species should be included.
Results are presented clearly and the discussion is well presented. In most cases, Authors provide explanations of observed effects referring to the scientific literature.
3.1. The name of subsection should be extended.
Line 196: The significance level for statistical analysis should be included in the Methodology. This information is repeated in many fragments of texts which in my opinion is unnecessary. The way of presenting significance level is confusing and rarely seen.
Line 205: Is the statement “Combination between alkali and acid (…) resulted in a higher SG (…)” fully supported by statistical analysis in case of all the species which were tested?
Table 2: Maybe it would be more clear to present just a change in given average values. The information in the note under the table about 3 replicates could be included in methodology, similarly as significance level.
Figure 1 should be enlarged to be more clear.
Line 230: The placement of Figure 4 is a little confusing. In my opinion it should be placed where the Table 3 is placed.
Line 235: Since the percentage of early- and latewood is important maybe it would be interesting to perform the measurements and present it. It doesn’t require any complicated equipment.
Table 3: In my opinion the ANOVA should be presented at the end of subsection since it refers to all the properties described in this part of the text.
Line 255: More comment on Nur et al. [35] studies would be beneficial.
Line 268: Can you please provide more explanation for “softening of the wood cells”.
Line 356: The first sentence with introduction is unnecessary.
Line 372, 399: The “p-value” should not be capitalized.
Line 386: What hydrothermal Authors mean?
Figure 8: It is a little unclear what the arrows and vertical lines means. Some of the spectra are additionally marked with a rectangle, however I didn’t see it being mentioned within the text. I would suggest to shorten the spectra and only show the areas where there are actual changes. In addition, labeling individual spectra with letters or the name of the variant would make reading easier. Taking into account the number of presented variants, it is difficult to distinguish the shades of black from each other, especially on the printout.
Line 437: The word absorbance may be replaced with the peak.
The conclusions are informative and well written, however, the comment on FTIR analysis is missing.
Suggestions presented above are mostly the general suggestions or just a thoughts from reader perspective. Overall, I think this paper is well written, correctly planned and interesting. In my opinion it would be a valuable reference for scientists working on thermomechanical modification of wood.
Author Response
Reviewer 02
Comments and Suggestions for Authors:
Overview
The review of an article “Effect of Sodium Hydroxide, Succinic Acid and Their Combination on Densified Wood Properties” submitted by Augustina et al. to Forests Journal.
The subject of the paper is very interesting and up-to-date considering the high intensity of work on the thermomechanical modification of wood. Moreover, it applies to species that have not been studied in this respect so far, which is additionally advantageous. In my opinion, the article is written correctly (from the language perspective) and contains the references from high-profile scientific journals.
Both the title and abstract of the paper are informative. The abstract contains basic information about the conducted research. In my opinion it could focus more on the results and less on methodology but this is just a general suggestion, not a mistake.
The introduction part is well thought out. It introduces the reader to all the issues covered by the article in a non-chaotic way.
1. Suggestion: Line 38: “Various processes have been attempted and shown to improve physical and mechanical properties of densified wood” – it would be interesting to develop this subject. Authors using that many references to support this statement should, in my opinion, add a brief comment on which ways were actually studied.
Answer: Line 38-39: author added “The density can significantly increase as well as Brinell hardness, MOE and MOR [5, 8]”.
2. Suggestion: Line 61: This part is a little confusing as the result of fast change of subject. It should be explained what matrix Authors had in mind.
Answer: Line 61-63 correction: “Thus, it results in sufficient surface area and load transfer to strengthen the mechanical bonding (superior adhesion) between bamboo fiber and matrix (hemicellulose and lignin) in the cell wall.
3. Suggestion: In general, I think the presentation of previous results in case of NaOH application is beneficial. Moreover, it is also great that Authors emphasize the novelty while describing both the application of succinic acid and the treatment with the combination of alkali and acid. As a general suggestion from the reader perspective I would recommend to add some information about the species involved in this study since it can be a material unknown to some readers (basic information: maybe a range of density, which way of applications are recommended for this species etc.).
Answer: Thank you for your suggestion. Actually, I have referred it in the manuscript (Introduction part), especially in Line 43-45 “This finding is consistent with Rautkari et al. [10] for beech- and spruce-densified wood as well as Augustina [11] and Augustina et al. [12] for nyatoh-, sepetir- and pisang putih-densified wood, where their initial specific gravity range is around 0.35 to 0.52”. Maybe the reader can find the information related to the basic properties of wood species in that references.
4. Suggestion: Materials and Methods are presented clearly, the methods seem to be correctly selected.
Answer: Thank you for your comment.
5. Question: Line 105: The boards were air-dried in laboratory room having a specific condition?
Answer: Yes, the boards were air-dried using fan for 2 weeks in the room temperature condition.
6. Question: Table 1: What is the reason for slightly different dimensions of samples from the “C” variant?
Answer: The “C” sample is untreated wood. The size of samples for untreated wood is similar for the final size of densified wood (2x2x2 cm). So, untreated wood can be used as comparison for each parameter and treatment applied in this study. The initial radial direction of the densified wood sample is 2.8 cm. The sample was then compressed with 40% compression ratio to 2 cm to make it uniform with the size of untreated (uncompressed) wood.
7. Suggestion: 2.2.: The subsection name should be extended since it shows also the details about the pre-treatment.
Answer: Line 116 correction: “2.2. Densification process through alkali, acid and their combination as pre-treatments”
8. Suggestion: Line 116: The accuracy of weighting process should be included.
Answer: Thank you for your suggestion. Weighting process used is simple and common procedure. There is no special treatment to be done.
9. Question: Line 122: The word “similar” indicates some slight differences. Was the pressing conditions the same?
Answer: Yes, the pressing condition was the same for all of densification treatment.
10. Suggestion: 2.3-2.6: The number of replications is missing.
Answer: Thank you for your suggestion. I already mentioned it in Line 111 “The number of samples for all treatments was 81 pieces (3 replications x 3 species x 9 categories)”. It was implied to all of parameter tested.
11. Suggestion: Line 180: The accuracy “around 5 mg” is not enough in case of instrumental methods as FTIR.
Answer: Thank you for your correction. Actually, we used 2 mg of wood powder (30-40 mesh) for FTIR test. I already changed it in the manuscript.
12. Suggestion: 2.8: The wood sample preparation is missing. At this point the information about testing only one species should be included.
Answer: Thank you for your suggestion. I was added some word in Line 182-184 “Around 5 mg of samples in powder shape (30-40 mess) was scanned from 400 to 4000 cm-1 with a resolution of 4 cm-1, 3 scans per treatment at 24 °C room temperature”.
13. Suggestion: Results are presented clearly and the discussion is well presented. In most cases, Authors provide explanations of observed effects referring to the scientific literature.
Answer: Thank you for your comment.
14. Suggestion: 3.1. The name of subsection should be extended.
Answer: Thank you for your suggestion. I was added some words in Line 197 “3.1. Specific gravity improvement of densified wood under several treatment categories”.
15. Suggestion: Line 196: The significance level for statistical analysis should be included in the Methodology. This information is repeated in many fragments of texts which in my opinion is unnecessary. The way of presenting significance level is confusing and rarely seen.
Answer: Thank you for your suggestion. I already added some words in statistical analysis part (Line 193-195) “Analysis of variance (ANOVA) was performed to evaluate the effect of each factor on several properties of densified wood. If there were significant differences (p<0.05), it will be followed by Duncan’s multi-range test”.
16. Suggestion: Line 205: Is the statement “Combination between alkali and acid (…) resulted in a higher SG (…)” fully supported by statistical analysis in case of all the species which were tested?
Answer: Yes, this phenomenon is clearly showed on Figure 1 (related to Increasing SG under various treatment categories compared to untreated wood). Statistical analysis shows only significant differences in each factor, namely wood species (JK), type of pretreatment applied (PT), and immersion time within NaOH (DP).
17. Suggestion: Table 2: Maybe it would be clearer to present just a change in given average values. The information in the note under the table about 3 replicates could be included in methodology, similarly as significance level.
Answer: About Table 2, actually the changes in given average values already mentioned on Figure 1. About the replication, I already mentioned it in Line 111 “The number of samples for all treatments was 81 pieces (3 replications x 3 species x 9 categories)”. It was implied to all of parameter tested.
18. Suggestion: Figure 1 should be enlarged to be more clear.
Answer: Thank you for your suggestion. In my opinion, Figure 1 is clear enough to be seen and read. Enlarging the size of Figure 1 would require a lot of space and added more pages to the entire document.
19. Suggestion: Line 230: The placement of Figure 4 is a little confusing. In my opinion it should be placed where the Table 3 is placed.
Answer: Thank you for your suggestion. I already made some correction about this in the manuscript.
20. Suggestion: Line 235: Since the percentage of early- and latewood is important maybe it would be interesting to perform the measurements and present it. It doesn’t require any complicated equipment.
Answer: Thank you for your suggestion. In our wood species case, there are no visible early and latewood portion.
21. Suggestion: Table 3: In my opinion the ANOVA should be presented at the end of subsection since it refers to all the properties described in this part of the text.
Answer: Thank you for your suggestion. In my opinion, it is easier to read and detect ANOVA results if I put it at the beginning of subsection rather than at the end of subsection.
22. Suggestion: Line 255: More comment on Nur et al. [35] studies would be beneficial.
Answer: Thank you for your suggestion. I was added some words in Line 258-259 “This phenomenon also agreed by Nur et al. [35], which stated the positive correlation be-tween WPG and SG”.
23. Question: Line 268: Can you please provide more explanation for “softening of the wood cells”.
Answer: In general, wood densification consists of four stages i.e. plasticization or cell wall softening, compression in the softened state, setting in the deformed state, and fixing the deformed state (Morsing and Hoffmeyer, 2000). Among them, cell wall softening is very important stage and related to glass transition temperature of lignin (Gašparik and Barcik, 2014). But in this study, softening of the wood cells mostly related to degradation of hemicellulose and lignin due to application alkali and acid solution.
24. Suggestion: Line 356: The first sentence with introduction is unnecessary.
Answer: Thank you for your suggestion.
25. Suggestion: Line 372, 399: The “p-value” should not be capitalized.
Answer: Thank you for your suggestion. I already changed it in the manuscript.
26. Suggestion: Line 386: What hydrothermal Authors mean?
Answer: Actually, the sentence in Line 391 is used as supporting sentence for the similar phenomenon occurred in this study. In case you want to know, according to Wang et al. (2021), post-densification hydrothermal is referred as heat treatment after densification process at 180 °C for 2 h in an airtight vessel of 0.13 m3 in volume with no more than 2% oxygen content, then heated by injecting saturated steam.
27. Suggestion: Figure 8: It is a little unclear what the arrows and vertical lines means. Some of the spectra are additionally marked with a rectangle, however I didn’t see it being mentioned within the text. I would suggest to shorten the spectra and only show the areas where there are actual changes. In addition, labeling individual spectra with letters or the name of the variant would make reading easier. Taking into account the number of presented variants, it is difficult to distinguish the shades of black from each other, especially on the printout.
Answer: The arrows and vertical lines showed distinguish changes for the treatment compared to untreated wood. Actually, the arrows pointed on distinguish absorbance peak but when I saw it in the manuscript, the distinguish absorbance peak was disappeared and needed to shift the box a little to show the value. About the spectra marked with a rectangle, it was mentioned in Line 464. About labeling individual spectra, I think the related Figure is already clear enough to be differentiated for each treatment.
28. Suggestion: Line 437: The word absorbance may be replaced with the peak.
Answer: Thank you for your suggestion. I already changed ‘absorbance’word into ‘peak’ in the manuscript.
29. Suggestion: The conclusions are informative and well written, however, the comment on FTIR analysis is missing.
Answer: Thank you for your suggestion. I already added some words “FTIR analysis showed a change in absorbance bands especially at wavelength ranged from 1736 cm-1 and 1583‒1589 cm-1 compared to untreated wood. Apart those changes, absorbance bands also shifted in wavelength ranging from 1000‒1700 cm-1, especially in those densified with alkali-pretreatment”.
30. Comment: Suggestions presented above are mostly the general suggestions or just a thoughts from reader perspective. Overall, I think this paper is well written, correctly planned and interesting. In my opinion it would be a valuable reference for scientists working on thermomechanical modification of wood.
Answer: Thank you for your comment.
Author Response File: Author Response.docx
Reviewer 3 Report
Abstract: please add the information in which anatomical direction the wood was densified. Line 25: c-set what does it mean?
Table 1: why control and test samples have different dimensions? The symbol SA was introduced in the table, but nowhere above is there an explanation of what it means. It is definitely succinic acid.
In the methodology chapter, a brief description of the wood used would be helpful, e.g. whether it is a diffuse-porous species or an ring-porous wood species.
Chapter 2.2: in what anatomical direction is the wood densified? This is of great importance to the process. If in the directions across the grain of 7MPa, then very high stress. The compressive strength of wood across the grain is low, often it does not exceed 10MPa. If along the grain it is not so high anymore.
Formula 1: rarely used fraction notation.
You used in many places term “weight” it would be more precise “mass of the sample”. And then use common symbol “m”.
Line 171: why were the samples measured and weighed to determine the stress-strain curve? You only need the compressed area.
Table 2: the result of wood densification is interesting. In pisang putih the density increased by only 0.17 g / cm3. The key to this is the direction in which the densification was made. The stress of 7MPa for wet wood is high stress. The operating time of 30 minutes and the temperature of 180 resulted in a surprisingly slight increase in density.
Table 2: The research material should be carefully selected. The differences in the density of the samples for the control sample are as high as 30%.
Line 229: Why was it decided to present the stress in kgf instead of Si [N / mm2] units? Kgf is a unit of force not of stress. You should calculate a stress for each variant.
The results in Table 3 are almost completely omitted. In the text you can find a laconic one sentence about it.
Figure 6: does it mean that the post-deformation recovery was almost 30%? In relation to the dimension after densification, yes? How does this relate to the initial size of the sample before densification?
Line 404: what does it mean DSC curve?
The list of literature can be supplemented with papers published in the last two years concerning the densification of previously delignified wood.
Author Response
Reviewer 03
Comments and Suggestions for Authors:
1. Suggestion: Abstract: please add the information in which anatomical direction the wood was densified.
Answer: Thank you for your suggestion. I already added some words in Line 21-23 “Compression was applied in radial direction and carried out in an open system by using a hot press machine at 180 °C and 7 MPa specific pressure for 30 minutes with 40% compression ratio”.
2. Question: Line 25: c-set what does it mean?
Answer: According to Tu et al. 2014, c-set is defined as the ratio of the change in dimension to the original dimension and expressed as a percentage.
3. Question: Table 1: why control and test samples have different dimensions? The symbol SA was introduced in the table, but nowhere above is there an explanation of what it means. It is definitely succinic acid.
Answer: The “C” sample is untreated wood. The size of samples for untreated wood is similar for the final size of densified wood (2x2x2 cm). So, untreated wood can be used as comparison for each parameter and treatment applied in this study. The initial radial direction of densified wood sample is 2.8 cm. The sample was then compressed with 40% compression ratio to 2 cm to make it uniform with the size of untreated (uncompressed) wood.
4. Suggestion: In the methodology chapter, a brief description of the wood used would be helpful, e.g. whether it is a diffuse-porous species or an ring-porous wood species.
Answer: Thank you for your suggestion. Actually, I have implicitly referred it in Line 43-45 “This finding is consistent with Rautkari et al. [10] for beech- and spruce-densified wood as well as Augustina [11] and Augustina et al. [12] for nyatoh-, sepetir- and pisang putih-densified wood”; Line 221-224 “This phenomenon was related to its initial specific gravity (the lowest) as well as its anatomical features, i.e. greater void volume dues to larger vessel diameter and more frequent number of the vessels [12, 29, 30,31]”; Line 380-381 “Higher CSR values on pisang putih due to uni to multiseriate arrangement of ray cells, which could be affected the recovery-set”. Maybe the reader can find the information related to the basic properties of wood species in that references.
5. Question: Chapter 2.2: in what anatomical direction is the wood densified? This is of great importance to the process. If in the directions across the grain of 7MPa, then very high stress. The compressive strength of wood across the grain is low, often it does not exceed 10MPa. If along the grain it is not so high anymore.
Answer: In this study, the wood is compressed in radial direction. The wood sample is in oven-dried condition. When we compress the woods in water saturated condition and after NaOH pre-treatment, the stresses are getting lower.
6. Suggestion: Formula 1: rarely used fraction notation.
Answer: Thank you for your suggestion.
7. Suggestion: You used in many places term “weight” it would be more precise “mass of the sample”. And then use common symbol “m”.
Answer: Thank you for your suggestion, but in wood, the term of “weight” is commonly used rather than “mass”, because weight can represent the mass of the wood + the moisture content in it, while mass means only the substance of the wood.
8. Question: Line 171: why were the samples measured and weighed to determine the stress-strain curve? You only need the compressed area.
Answer: Thank you for your correction. Actually, it was just a common procedure applied to all of samples before testing it. Besides, I compressed the woods in oven-dried, water saturated, and after NaOH pre-treatment to compare their stress-strain curve. Initial weight is important information to measure Water Absorption, as well.
9. Question: Table 2: the result of wood densification is interesting. In pisang putih the density increased by only 0.17 g / cm3. The key to this is the direction in which the densification was made. The stress of 7MPa for wet wood is high stress. The operating time of 30 minutes and the temperature of 180 resulted in a surprisingly slight increase in density.
Answer: Thank you for your question. In this research, I’m using 40% compression ratio (the final size for my samples will be 2x2x2 cm) and applying stop-bar to get expected final size. That’s why SG improvement different in each wood species. In pisang putih wood, the SG was slightly increased compared to others due to the existence of uni to multiseriate arrangement of ray cells that can uphold the deformation.
10. Question: Table 2: The research material should be carefully selected. The differences in the density of the samples for the control sample are as high as 30%.
Answer: Thank you for your suggestion. I think you right, but I have already carefully selected the wood samples and used 3 replicant as representative of each wood species in each parameter tested.
11. Question: Line 229: Why was it decided to present the stress in kgf instead of Si [N / mm2] units? Kgf is a unit of force not of stress. You should calculate a stress for each variant.
Answer: Thank you for your question. I think you are right, I already changed stress unit into kgf/cm2.
12. Suggestion: The results in Table 3 are almost completely omitted. In the text you can find a laconic one sentence about it.
Answer: Thank you for your comment. You can find the Table 3 being mentioned in Line 199-201 “It can be seen that interaction among three factors has a significant effect on specific gravity at the 5% significance level, while immersion time within NaOH was not significantly affected (Table 3)”; Line 363-365 “It can be seen that interaction among wood species, type of pretreatment applied and im-mersion time has a significant effect on CSR and WA at the 5% significance level (Table 3)”.
13. Question: Figure 6: does it mean that the post-deformation recovery was almost 30%? In relation to the dimension after densification, yes? How does this relate to the initial size of the sample before densification?
Answer: Yes, recovery is still occured. The aim of this study was to compare the effect of pre-treatments with NaOH, succinic acid and their combination. As a result, succinic acid pre-treatment resulted in the lowest recovery (less than 20%). About the relation to the initial size of the sample before densification, the formula of compression-set recovery, also known as recovery-set, includes the initial size of sample before densification (Wang et al. 2021; Darwis et al. 2017; Sadatnezhad et al. 2017).
14. Question: Line 404: what does it mean DSC curve?
Answer: DSC curve means Differential Scanning Calorimetry. That sentence in Line 404 is just supporting the phenomenon occurred. The conversion of succinic acid into succinic anhydride may have occurred at temperature around 120‒190 °C. The presence of succinic anhydride on the surface of fiber is essential for producing the plasticizing effect [37]. Those effects could have made the material softer and more flexible, increase its plasticity, decrease its viscosity, or decrease the friction during its handling in manufacture.
15. Suggestion: The list of literature can be supplemented with papers published in the last two years concerning the densification of previously delignified wood.
Answer: Thank you for your suggestion. Actually, I already sited some references that is concerning the densification of previously delignified wood. You can check it in References part.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Accept in present form
Reviewer 3 Report
Thank you for taking into account the comments. Good luck with your further research.
