Efficient Bio-Based Insulation Panels Produced from Eucalyptus Bark Waste
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript is focused on investigation of the feasibility of using Eucalyptus bark for manufacturing thermal insulation panels, and evaluation of their exploitation properties. In this respect, the manuscript is within the scope of the Special Issue “Sustainable Valorization of Forestry Byproducts”, Section “Wood Science and Forest Products” of the Forests journal. In general, the manuscript is well-written, structured, and informative, but needs some improvements before acceptance for publication. Please, see below my comments on your work:
The title (lines 2-3), the abstract (lines 15-29) and the keywords (line 30) correspond to the scope, aims and objectives of the manuscript. The abstract is informative and clearly presents the aim of the research. However, I’d recommend making it more specific by adding more results obtained from your experimental work, e.g., for thermal diffusivity and water vapor transmission (line 24).
Lines 49-53: in addition to the examples provided, the use of larch bark for manufacturing insulation panels has been reported in the literature, please check here:
https://doi.org/10.3390/su151813530; https://doi.org/10.3390/polym12092140;
Line 57: “biobased materials”, line 63: “bio-based materials: please unify the terms used throughout the manuscript.
Lines 72-74: important information about the world distribution of eucalyptus plantations and the recent state of research on the utilization of planted Eucalyptus for engineered wood products can be found here: https://doi.org/10.1007/978-981-99-7919-6
Overall, the Introduction part is well-written, informative, and provides relevant information and references on the research topic. The aim of the research is also clearly specified.
Lines 127-128: there is a newer version of the standard used, please refer to it.
Line 132: please, provide relevant information for the equipment used (company producer, city, country).
Lines 137-138: “Resin and bark fibers were mixed in a rotatory system.”: please be more specific about the equipment used and provide relevant information/characteristics.
Lines 144-145: “Afterwards, the panels were conditioned at 25 °C to reach 65% of moisture.”: please revise. Maybe you meant 65% relative humidity? In addition, please add the conditioning period.
Line 147, Table 1: “theoretical density” should be “target density”, please revise.
Please explain the pressing parameters used. Are they based on your preliminary trials or based on literature references?
Line 152: “…a standard flame retardant and an antifungal solution were incorporated into the panels”: please provide relevant information about the substances used.
Line 190: please define “3% H.R.”.
Lines 220 and 225-226: repeated information, please revise.
Line 235: “80 x 120 x 50 mm” should be “80 mm x 120 mm x 50 mm”, please revise.
In general, the Materials and Methods section is well-written and detailed, providing relevant information on the materials and methods used. However, it can be further elaborated based on the comments given above.
The results of the study are clearly presented and discussed with relevant published research works in the field.
The Conclusion part (lines 421-462) reflects the main findings of the manuscript. However, this section of the manuscript seems a bit long and can be shortened, e.g., the information included in lines 452-462 can be deleted and replaced with the potential for future research works in the field and practical application of the results achieved.
The References cited are appropriate to the topic of the manuscript.
Comments on the Quality of English LanguageIn general, the English language and style used throughout the manuscript are OK, but moderate editing is recommended.
Author Response
The authors are grateful for the comments made by the reviewer. The answers to those comments are as follows:
1. The title (lines 2-3), the abstract (lines 15-29) and the keywords (line 30) correspond to the scope, aims and objectives of the manuscript. The abstract is informative and clearly presents the aim of the research. However, I’d recommend making it more specific by adding more results obtained from your experimental work, e.g., for thermal diffusivity and water vapor transmission (line 24).
R: Regarding to the abstract, the suggestion made by the reviewer has been addressed and the abstract now includes more information about the results of the experimental work as it can be seen on page 1, line 24-26
2. Lines 49-53: in addition to the examples provided, the use of larch bark for manufacturing insulation panels has been reported in the literature, please check here: https://doi.org/10.3390/su151813530; https://doi.org/10.3390/polym12092140
R: In relation to the comment 2, the larch bark examples have been added in the line 52.
3. Line 57: “biobased materials”, line 63: “bio-based materials: please unify the terms used throughout the manuscript.
R: The term “bio-based materials” has been adopted for the entire document.
4. Lines 72-74: important information about the world distribution of eucalyptus plantations and the recent state of research on the utilization of planted Eucalyptus for engineered wood products can be found here: https://doi.org/10.1007/978-981-99-7919-6
R: The authors are grateful for the reviewer's comment. Information about the world distribution of eucalyptus plantations has been updated in the lines 77-79
5. Lines 127-128: there is a newer version of the standard used, please refer to it.
R: The standard has been updated in the line 134.
6. Line 132: please, provide relevant information for the equipment used (company producer, city, country).
R: Considering the reviewer's recommendation, more information on the equipment used has been added (line 139).
7. Lines 137-138: “Resin and bark fibers were mixed in a rotatory system.”: please be more specific about the equipment used and provide relevant information/characteristics.
R: Further information about the rotatory system has been incorporated in lines 145-148.
8. Lines 144-145: “Afterwards, the panels were conditioned at 25 °C to reach 65% of moisture.”: please revise. Maybe you meant 65% relative humidity? In addition, please add the conditioning period.
R: Information about the conditioning period has been incorporated in lines 154-156. Additionally, the expression “to reach 65% of moisture…” has been replaced by “and relative humidity of 65% ...”
9. Line 147, Table 1: “theoretical density” should be “target density”, please revise.
R: The term "theoretical density" has been replaced in the entirety of the document for the term "target density."
10. Please explain the pressing parameters used. Are they based on your preliminary trials or based on literature references?
R: Information about the definition of the pressure parameters has been incorporated in the lines 157-159.
11. Line 152: “…a standard flame retardant and an antifungal solution were incorporated into the panels”: please provide relevant information about the substances used.
R: Further details about the flame retardant and antifungal solution have been added in lines 173-174.
12. Line 190: please define “3% H.R.”.
R: In relation to the comment 12, we had made a mistake by writing H.R instead of R.H (relative humidity). To avoid confusion, we have corrected this as follows: “The system shown in Figure 3 was kept in a controlled environment at a temperature of 23 ± 0.5 ° C and a relative humidity of 50 ± 3% for 3 weeks” (lines 211-212).
13. Lines 220 and 225-226: repeated information, please revise.
R: The comment has been revised and corrected as it can be seen in lines 244-248.
14. Line 235: “80 x 120 x 50 mm” should be “80 mm x 120 mm x 50 mm”, please revise.
R: The comment has been revised and corrected as it can be seen in line 256.
15. The Conclusion part (lines 421-462) reflects the main findings of the manuscript. However, this section of the manuscript seems a bit long and can be shortened, e.g., the information included in lines 452-462 can be deleted and replaced with the potential for future research works in the field and practical application of the results achieved.
R: The conclusion section has been modified considering the reviewer's comments. The modifications of this section are presented in lines 464-487.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear author,
Please consider the question.
1- what is the research novelty? what are the differences with published papers in this field? Please mention them more clearly in the manuscript.
2- what is the resin consumption percentage for each panel? how much fiber was used for each panel?
3- what is the conditioning time?
4-did you apply the same pressure for all panels prepared by the hot press?
5- what is curing temp.? Is it hot press temp.? Please mention it.
6- frecuency or frequency? please put the frequency unit in the histograms.
7- considering higher mass, why do higher-density panels show lower mass changes during the water vapor test?
8- Mold or Mould resistance? please check it.
9- did you study the Dimensional and thermal Stability?
10- considering 84 mentioned references, just three references were used in the discussion.
11- The discussion is short and the conclusion is lengthy. please revise it. writing the conclusion in 1 or 2 paragraphs is recommended.
Author Response
The authors are grateful for the comments made by the reviewer. The answers to those comments are as follows:
1. What is the research novelty? what are the differences with published papers in this field? Please mention them more clearly in the manuscript.
R: The research presents the results of the assessment methodology of the performance of insulation panels based on eucalyptus globulus bark fiber. This study represents the evaluation of the feasibility of valorising a forestry waste to create a bio-based product that responds to the necessities of the construction industry. Therefore, this work is in line with the basis of circular economy where the valorisation of bio-based waste is used to generate new products that can be used locally.
The evaluation methodology applied in this study can be replicated for the analysis of other potential alternatives of bio-based insulation materials, especially the ones including the valorisation of waste of one industry (with its preparation and panels manufacturing) to expand the use of high-quality biomass for the generation of materials that respond to the identified environmental challenges of other industries, specially the construction one, that need effective solutions to reduce its enormous environmental impact.
More details about the contribution of the work have been incorporated in the introduction section on lines 70-75, 76-81 and 103-12; and in the discussion section on lines 424-433, 435-438, 440-442 and 450-462.
2. What is the resin consumption percentage for each panel? how much fiber was used for each panel?
R: Regarding to the comment 2, the percentage of resin is given in Table 1 as 10% of the total panel weight. The amount of fiber used is presented in Table 2, which has been incorporated considering the reviewer's comments.
3. What is the conditioning time?
R: The description of the conditioning process and conditioning time has been extended. The changes are presented in lines 154-159.
4. Did you apply the same pressure for all panels prepared by the hot press?
R: Affirmative. The pressure (45 kgf/cm²) is maintained for all the panels. This is because, once the top plate of the press reaches the steel bars placed on the sides of the panel to control the thickness, the pressure begins for the estimated time. A clarification on this issue was incorporated in lines 157-158.
5. What is curing temp.? Is it hot press temp.? Please mention it.
R: The resin curing temperature was specified by the supplier (phenol formaldehyde) and it is mentioned in Table 1. The temperature is achieved for both press systems by adjusting the temperature level of the hot plates in the press or the steam at the inlet of the injection system in the press.
6. Frecuency or frequency? please put the frequency unit in the histograms.
R: The authors are grateful for the reviewers' comments. The term “frequency” in Figure 5 corresponds to the number of fibres. This clarification has been incorporated in Figure 5.
7. Considering higher mass, why do higher-density panels show lower mass changes during the water vapor test?
R: With regard to observation 7, the final section of the paragraph (lines 375 to 380), has been revised to include an elucidation pertaining to your query.
8. Mold or Mould resistance? please check it.
R: The term “Mold” has been adopted for the entire document.
9. Did you study the Dimensional and thermal Stability?
R: Regarding the comment 9, the dimensional stability of a material depends on its intrinsic nature and the prevailing environmental conditions. In our case, bark fiber has an inherent hygroscopic behavior, mainly due to the presence of hemicellulose, however, this was not considered in this study because the application of the panel as a thermal insulation material is not exposed to external weather conditions.
This clarification has been incorporated in lines 166-170.
10. Considering 84 mentioned references, just three references were used in the discussion.
R: Considering the reviewer's comments, the discussion section (lines 414-462) has been revised and the ideas presented have been linked to references used in the preparation of the paper.
11. The discussion is short, and the conclusion is lengthy. please revise it. writing the conclusion in 1 or 2 paragraphs is recommended.
R: The conclusion section has been modified following the reviewer's comments.
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Author,
1- The research novelty still needs clarification.
2- It looks like Table 2 is not correct! please check it one more time. for example, you mentioned a target density of 80 kg/m3, fiber weight of 640 kg, and board dimension of 400 mm * 400 mm * 50 mm). Does it mean for the board with the mentioned dimension and density you used 640 kg fiber? also, there is the same question for the board with a density of 300 kg/m3 and 2400 kg fiber. Please clarify.
3- As you mentioned in the text, the resin consumption looks different for each panel. you used 10% resin based on fiber weight and considering the different densities of each board, you used different amounts of PF resin. this phenomenon should be considered in the evaluated properties.
Author Response
I am pleased to submit the article entitled "Efficient bio-based insulation panels produced from Eucalyptus bark waste" modified according to the reviewers' comments.
The present document responds to the reviewer's comments and describes in detail the changes made to the article.
Reviewer
1- The research novelty still needs clarification.
R: The novelty of the study was reinforced as follows:
Mitigation of the impact on greenhouse gas emissions currently generated in the construction industry and particularly in the manufacture of building products. This has been reinforced in lines 32-35.
-Lines 32-35: The building construction industry significantly contributes to greenhouse gases accounting for 37% of the global energy-related emissions. About 10% of these emissions are due to the manufacture of building construction materials [1].”
The product presented has the characteristic of influencing greenhouse gas emissions from the early stages of a building's life, which is extremely important with increasing regulations incorporating a whole-life carbon approach. This has been reinforced in lines 71-75.
-Lines 71-75: ”This generally makes them a more sustainable choice for building materials and re-duces the building sector’s environmental impact, which is extremely important with increasing regulations incorporating whole-life carbon, as nowadays it happens in Denmark, the Netherlands, and France, but that should be the case in many other countries to achieve carbon neutrality as a whole [1].”
The study presents the methodology for the evaluation of an insulating panel based on eucalyptus bark fiber i.e. a bio-based product. Bio-based materials commonly generate a lower environmental impact compared to traditional materials. In the particular case of thermal insulation materials, non-conventional alternatives have little presence in the market, so there is a need to develop materials that respond to the current and future needs of the construction industry. This has been reinforced in lines 59-60 and 481-488.
-Lines 59-60: “Actually, non-conventional insulation materials account for just 1% of the market [1].”
-Lines 481-488: “The study of non-conventional natural fibers opens an important path in bio-materials research. In this sense, the evaluation methodology applied in this study can be replicated for the analysis of other potential alternatives of bio-based insulation materials, specially the ones including the valorization of waste of one industry (with its preparation and panels manufacturing) to expand the use of high-quality biomass for the generation of materials that respond to the identified environmental challenges of other industries, specially the construction one, that need effective solutions to reduce its enormous environmental impact.”
Eucalyptus bark fiber is obtained as a residue from the forestry industry, which represents a low-cost and highly abundant source of material. In this sense, it contributes to the development of sustainable solutions aligned with the concepts of circular economy, as reducing dependence on fossil resources, efficiently using and valorizing waste, and increasing the use of high-quality biomass. This has been reinforced in lines 92-104 and 113-119 and 455-462.
-Lines 92-104: “Currently, this bark has little practical application, i.e. there is no valorisation of this resource. In fact, the E. globulus bark is only used to generate energy. However, this type of bark has a lower calorific value than pine bark and is difficult to transport in the boiler conveyor system, making it less attractive as a fuel. Therefore, the bark is accumulated in landfills generating disposal problem.
This situation, combined with its low cost (20-50 USD/ton) and high availability that guarantees a constant supply of the material, has prompted forest industry experts to focus their efforts on developing new applications for E. globulus bark. For example, several studies have focused on isolating and modifying the extractives in the bark, because of their potential uses as chemicals [54,55], metal removers [56,57], and biofuel [58], i.e. their potential chemical valorisation. Other possibility is to explore how to take advantage of intrinsic physical properties of bark, such as its low thermal conductivity [59].”
-Lines 113-119: “Therefore, from an environmental perspective, the E. globulus fiber bark (EGFB) insulation panel can be a very attractive alternative with less carbon emission and embodied energy in comparison to the conventional insulation materials. Additionally, it provides benefits to both the forestry and construction industries by aligning with circular economy principles, such as reducing dependence on fossil resources, efficiently using and valorizing waste, and increasing the use of high-quality biomass as established by Vural Gursel et al. [46].”
-Lines 455-462: In the case of EGFB-panel, by taking advantage of a resource generally considered a waste, these panels also contribute to reducing the impact of disposing eucalyptus bark in landfills which is a worldwide problem considering that Eucalyptus plantations have a strong global presence, covering up to 22.57 million hectares in countries such Australia, Brazil, Chile, Kenya, Portugal, Spain and Uruguay [49,50]. Considering that the utilization of this residue from its fibrous potential is not the approach usually adopted, this solution contributes to the development of a sustainable and bio-based thermal insulation product using a low-cost abundant raw material.”
Considering the low participation of bio-based materials in the market, it is highly relevant to demonstrate that the properties associated with the in-service performance of eucalyptus bark fiber insulation panels guarantee an acceptable response for their practical application. This has been reinforced in lines 120-133.
-Lines 120-133: “Despite the promising results in terms of generated emissions and embodied energy, the potential of these insulating panels can only be realized through greater market penetration and the massification in practical applications. To achieve this, it is relevant to evaluate the insulating properties of these panels, and to ensure an adequate response in service conditions.”
2- It looks like Table 2 is not correct! please check it one more time. for example, you mentioned a target density of 80 kg/m3, fiber weight of 640 kg, and board dimension of 400 mm * 400 mm * 50 mm). Does it mean for the board with the mentioned dimension and density you used 640 kg fiber? also, there is the same question for the board with a density of 300 kg/m3 and 2400 kg fiber. Please clarify.
R: The authors are grateful for the reviewers' comments. The unit “kg” for the “fiber quantity” column has been modified for “g”.
3- As you mentioned in the text, the resin consumption looks different for each panel. you used 10% resin based on fiber weight and considering the different densities of each board, you used different amounts of PF resin. this phenomenon should be considered in the evaluated properties.
R: The percentage of used resin is 10% of the total panel weight. To clarify this aspect, the quantity of fiber has been added in Table 2. In addition, information the incorporation of resin has been updated in the lines 180-184.
-Lines 180-184: “The quantity of fibers use for each panel depends on the target density. Regarding the resin, it is incorporated in a proportion of 10% of the total weight of the panel, which agree with the range usually presents in particleboard (8-12%). Table 2 shows the quantity of fibers and resin defined for the case of a 400 mm x 400 mm x 50 mm panel.”
The response of the insulation board properties is determined primarily by the density of the board, which has been reinforced in lines 332-333 and 360-366. Nevertheless, discussions on the effect on the amount of resin are presented in lines 396-403.
-Lines 332-333: “Therefore, the density plays a main role in the response of the thermal conductivity.”
-Lines 360-366: “Figure 8 shows the thermal diffusivity obtained for all EGFB- based panels as function of density. As is expected there is a direct relationship between density and thermal diffusivity [81,82]. The higher the density, the less empty spaces into the material and the thermal diffusivity approaches to the one of the wood (Table 6). In general, bio-based insulation material shows low thermal diffusivity and it will be expected that it responds slower to changes in the thermal environment compared to others material with high thermal diffusivity.”
-Lines 396-403: “This behavior can be attributed to the morphology of the fiber and the nature of the resin. In this case, the fibers, due to their elongated shape, are randomly distributed in the mat, creating more obstacles for the water vapor and increasing the difficulty to go through the material to the other side. Additionally, a higher density implies more weight and, consequently, a greater resin content. This can result in the formation of a hydrophobic barrier due to the chemical nature of the resin (phenol formaldehyde). The results also show that the bark panels have a lower permeability to the passage of steam than the glass wool sample.”
Author Response File: 
Author Response.pdf
