Emission of Volatile Organic Compounds from the Heat Treatment of Afrormosia and Newtonia Wood: Effects of Air and Palm Oil Heat Media
Round 1
Reviewer 1 Report
The authors examined the VOC emited from the wood during the heat treatment process. It is an interesting topic. This paper have a potential to take consideration from readers.
Page 2 line 96 - ...... Wahab showed.... This sentence stated that lignin content increases with decreasing hemicellulose and holocellulose content. As known that increasing temperature results in the degradation of hemicellulose first. Acetic acid, formic acid, and furfural are formed, which degrade polysaccharides. Therefore, lignin increases in percentage, not content. This sentence should be checked.
Page 3 line 121 - Specimens were dried ...... Before heat treatment, samples were dried in the oven until constant weight. However, we know that VOCs are emitted from the wood above 60oC. Moreover, the waiting period of wood between cutting and heat treatment is essential for VOCs. Because emitting of VOCs starts at the fall of a tree. Did drying and/or waiting period affect VOCs? These questions should be enlightened.
There is no extensive editing of English. However, it can be checked for minor editing.
Author Response
Response to Reviewer 1 Comments
Dear Editor and Reviewer,
Thank you for your constructive comments and the efforts that have put into reviewing the manuscript. Based on your comments and advice, we have improved the manuscript extensively and carefully. The point-by-point response can be found below. We hope this revision will meet with your approval.
Point 1: Page 2 line 96 - ...... Wahab showed.... This sentence stated that lignin content increases with decreasing hemicellulose and holocellulose content. As known that increasing temperature results in the degradation of hemicellulose first. Acetic acid, formic acid, and furfural are formed, which degrade polysaccharides. Therefore, lignin increases in percentage, not content. This sentence should be checked.
Response 1: Line 93 “content” has been replaced by “percentage”.
Point 2: line 121 - Specimens were dried ...... Before heat treatment, samples were dried in the oven until constant weight. However, we know that VOCs are emitted from the wood above 60°C. Moreover, the waiting period of wood between cutting and heat treatment is essential for VOCs. Because emitting of VOCs starts at the fall of a tree. Did drying and/or waiting period affect VOCs? These questions should be enlightened.
Response 2: Our approach of drying the wood before heat treatment is justified by the fact that most of the studies on VOC emissions from heat treated wood with air as heat transfer fluid include a kiln drying phase at a temperature of 103°C (https://doi:10.5552/drind.2018.1708; https://doi.org/10.1016/j.jobe.2019.100918 etc.). On the other hand, even if it is true that the emissions of VOCs start as soon as the wood is cut in the forest, it is still true that these emissions come mainly from the extractives contained in the wood. However, the main objective of our paper was to study the nature of the VOCs resulting from the modification under the effect of heat and the thermal treatment environment of the structural polymers of the wood that are hemicelluloses, cellulose and lignin, which modification is generally possible only with temperatures at least equal to 150°C, greater than the drying temperature mentioned above. In other words, drying does not have a significant impact on the objectives of our study, except to facilitate the comparison of our results with those obtained by other researchers. Nevertheless, it should be noted that after drying, our samples were wrapped with plastic foil until the heat treatment phase, in order to limit the emissions of VOCs related to the extractives and likely to occur before the measurements were made; this precision has been added to line 125.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments for author File: Comments.docx
Author Response
Response to Reviewer 2 Comments
Dear Editor and Reviewer,
Thank you for your constructive comments and the efforts that have put into reviewing the manuscript. Based on your comments and advice, we have improved the manuscript extensively and carefully. The point-by-point response can be found below. We hope this revision will meet with your approval.
Point 1: The authors examined the effect of heat treatment media (air and oil palm) on the type of VOCs released after treatments at various temperature levels (160, 180, and 200 C). I expect the authors to develop the mechanism of primary VOC formation, as stated in 108-111 of the Introduction.
Response 1: Line 177-212. We have further discussed the mechanisms of primary VOC formation during the heat treatment of Afrormosia and Newtonia at 160°C, 180°C and 200°C.
Point 2: Unfortunately, the research only revealed the types of VOCs produced by the treatments. It also did not define the relevance of investigating produced VOCs to the application of the wood (e.g., Is it detrimental to the environment? etc.).
Response 2: Thank you for this very pertinent remark; because it is quite obvious that the main purpose of studying the nature and mechanisms of VOC emissions before, during and after the heat treatment of wood, is the evaluation of their impact on the environment as a whole as well as the identification of potential sources of production of chemical compounds for other applications. This was mentioned in line 52-54, line 117-119 and line 444-448. However, we did not consider it necessary to dwell on these aspects for the simple reason that there are already many official databases which, knowing the name of a chemical compound, allow to determine its toxicity or its impact on the environment as well as its application in the industrial field (https://pubchem.ncbi.nlm.nih.gov).
Point 3: The authors did not examine the potential of VOC in the air operated during treatment.
Response 3: Data related to the potential of VOC in the air operated during treatment have been added from line 168-173. In fact, The chromatogram obtained from the GCMS analysis of the air we used for the treatment of our wood showed no peak (Figure 2) . This means that compared to the VOCs emitted by the wood, those contained in the air used were negligible and were therefore not considered in the present study.
Point 4: More fundamental data is needed to make the paper worthy of publication in a Q1 journal. Data, such as hemicellulose, cellulose, and lignin content before and after treatment, are undoubtedly essential to explain the source of the VOCs discussed. Otherwise, the discussion is dominated by speculation (although with some support of references). I suggest the manuscript is rewritten with additional new data as stated.
Response 4: The authors of the present paper conducted a previous study on "Effects of Heat Treatment on Color, Dimensional Stability, Hygroscopicity and Chemical Structure of Afrormosia and Newtonia Wood: A Comparative Study of Air and Palm Oil Medium". In the said study, the modification of hemecelluloses, cellulose and lignin of Afrormosia and Newtonia wood treated under air and palm oil at 160°C, 180°C and 200°C were analyzed using FTIR method and discussed extensively. In other words, these experimental conditions are identical to those employed in the present paper. For this reason, we have deemed it unnecessary to repeat the same analysis in order to avoid any risk of self-plagiarism but we have carefully analyzed the VOCs data in this paper based on the previous one. Nevertheless, a brief reminder of the main results related to the said FTIR analysis has been added to the introduction, line 95-99 and line 109-111.
Point 5: Line 69-71 Please be sure that reference citing is by the guideline for authors, e.g., Svrikaya……... [11] should be written as Svrikaya et al. [11]. Please revise others accordingly.
Response 5: Other references have been revised accordingly.
Point 6: Line 71-75 An example of redundant writing. Please revise it to be concise.
Response 6: Lines 71-75 have been reorganized to correct the redundancy problem.
Point 7: Line 82-83 Please explain clearly the relevance of calorific value with heat transfer in the thermal treatment of wood with palm oil (vegetable oil). Calorific value is the energy obtained from the complete combustion of a substance.
Response 7: The sentence “Besides air, vegetable oils were also used in the heat treatment of wood in many studies because vegetable oils have a high calorific value, which allows them to transfer heat more uniformly during heat treatment” has been replaced by “Besides air, vegetable oils were also used in the heat treatment of wood in many studies because vegetable oils are good for heating due to their ability to transfer heat to wood more easily and evenly.”
Point 8: Line 84-85 Please explain what you mean by “adding additives.” Is the oil palm the additive? Or a specific type of additives added to the oil palm?
Response 8: Line 80; We have added “desiccants (to accelerate the drying of wood)” as an example of additives that can be added to palm oil in order to accelerate the drying of wood.
Point 9: Line 86 VOC is a broader term. VOC includes aldehyde, ester, ester, etc. It would be more proper to say, “emission of VOC in the form of aldehydes.”
Response 9: “However, the use of vegetable oils tends to favor the emission of aldehydes in the form of VOCs” has been replaced by “However, the use of vegetable oils tends to favor the emission of VOC in the form of aldehydes”.
Point 10: Line 132-133 Figure 1. Instead of showing a heat treatment equipment picture, it would be more informative to show an illustration/sketch/drawing of the equipment. Therefore, Figure 1 illustrates the equipment structure, how oil and samples were positioned, how temperature reading was done, etc.
Response 10: A sketch of the equipment used has been added.
Point 11: Line 157-161 All compounds mentioned have been listed in Table 2. Restating the compounds in Table 2 only makes the manuscript redundant. It would be more concise if the authors refer the reader to Table 2. Discussing the nature of the compound is more important.
Response 11: Line 178-179 Restating compounds have been deleted.
Point 12: Line 167-168 I did not notice that the authors analyzed the air used in the treatment. The air operated should be examined for its composition and possible VOC content. VOCs are everywhere in the environment: many households and laboratory materials appliance release VOCs. Oil palm was analyzed for the VOCs content at all treatment temperatures (Table 1); why was air not analyzed?
Response 12: See response 3.
Point 13: Line 164-171 Please consider the temperature range decomposition of major chemical constituents of the wood (hemicellulose, cellulose, and lignin) in your discussion. Even though the thermal decomposition of these substances varied according to various references, hemicellulose generally decomposes approximately at 220-315 C, cellulose at 300-400 C, and lignin at 150-900 C), higher than your treatment temperatures. Lignin may experience bond cleavage at relatively low temperatures, but ring opening only occurs at higher temperatures. Please ascertain that the treatment temperature of your references was comparable to your treatment temperature. Otherwise, your citation would need to be more accurate.
Response 13: As already mentioned in point 4, in our previous study, we demonstrated by using FTIR analysis that for Afrormosia and Newtonia wood heat treated under air and palm oil, at 160°C and 180°C the modification of hemicelluloses was observed. At 200°C, in addition to hemicelluloses, cellulose degradation and cleavage of lignin bonds were also observed. But we did not demonstrate ring opening of cellulose, which is why the reference to this phenomenon was removed from the article as you suggested. Here are some references with similar results to ours. https://doi:10.3390/polym11071145; https://doi.org/10.22382/wfs-2019-xxx; https://doi:10.1016/j.atmosenv.2010.07.018; https://doi:10.5552/drind.2018.1708; https://doi.org/10.1016/j.jobe.2019.100918
Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript's topic is significant, suggesting interest in the journal's readers.
Overall, in my opinion, the manuscript is well prepared, so I have only a few recommendations for the esteemed authors.
1) The Abstract is extended, with almost the same volume as the Introduction. Therefore, I suggest to the authors that this part be shortened, emphasizing the main novelty of the study, its significance, and the results achieved.
2) The Introduction part is well prepared, placing the study in the context of other similar studies while at the same time very clearly outlining its novelty. Therefore, I have no recommendations for this part.
3) In my opinion, the Materials and Methods section should justify the study's parameters. That is why the chosen temperature levels are 160, 180 and 200° C, and not, for example, 150, 170 and 190° C. I ask the authors to justify these parameters, referring to similar studies and giving relevant references.
4) Please consider whether Figure 1 is necessary (line 134).
5) In the Results and Discussion part - at the moment, the presentation of the numerical values in Figure 2 (line 183) is highly unclear. The resulting accumulation of data practically renders the values unreadable, and they stand like an ink blot. Please consider diluting the data presented. This recommendation also applies to Figure 6.
6) I would like to ask why figures 3, 4 and 7 are given error bars and figure 5 is missing them.
The Conclusions reflect the results achieved. The references cited are appropriate.
Author Response
Response to Reviewer 3 Comments
Dear Editor and Reviewer,
Thank you for your constructive comments and the efforts that have put into reviewing the manuscript. Based on your comments and advice, we have improved the manuscript extensively and carefully. The point-by-point response can be found below. We hope this revision will meet with your approval.
Point 1: The Abstract is extended, with almost the same volume as the Introduction. Therefore, I suggest to the authors that this part be shortened, emphasizing the main novelty of the study, its significance, and the results achieved.
Response 1: The Abstract has been shortened.
Point 2: The Introduction part is well prepared, placing the study in the context of other similar studies while at the same time very clearly outlining its novelty. Therefore, I have no recommendations for this part.
Point 3: In my opinion, the Materials and Methods section should justify the study's parameters. That is why the chosen temperature levels are 160, 180 and 200° C, and not, for example, 150, 170 and 190° C. I ask the authors to justify these parameters, referring to similar studies and giving relevant references.
Response 3: We have chosen the temperatures of 160°C, 180°C and 200°C in order to harmonize our results with those found by other researchers who have carried out similar studies (https://doi:10.3390/polym11071145; https://doi.org/10.22382/wfs-2019-xxx; https://doi:10.1016/j.atmosenv.2010.07.018; https://doi:10.5552/drind.2018.1708; https://doi.org/10.1016/j.jobe.2019.100918; Wahab R., Sulaiman M. S., Samsi H. W., Ghani R. S. M., Mokhtar N., the effectiveness of oil-heat treatment in the main chemical constitutes of planted 15-year-old acacia hybrid) and thus, facilitate the comparison of these results. Indeed, most of the studies similar to ours, cited in this paper, refer to heat treatments of wood having been carried out at least at one of the temperatures we have chosen. And this precision has been added to section 2-2, line 138-142 as you suggested.
Point 4: Please consider whether Figure 1 is necessary (line 134).
Response 4: Figure 1 has been replaced by a sketch of the equipment used.
Point 5: In the Results and Discussion part - at the moment, the presentation of the numerical values in Figure 2 (line 183) is highly unclear. The resulting accumulation of data practically renders the values unreadable, and they stand like an ink blot. Please consider diluting the data presented. This recommendation also applies to Figure 6.
Response 5: Dilution has been done.
Point 6: I would like to ask why figures 3, 4 and 7 are given error bars and figure 5 is missing them.
Response 6: Error bars have been added to figures 5.
Author Response File: Author Response.docx
