Coating Performance of Heat-Treated Wood: An Investigation in Populus, Quercus, and Pinus at Varying Temperatures

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript addresses an important topic related to the coating performance of thermally modified wood across different species and heat-treatment levels. In this respect, the manuscript is within the scope of Section “Wood Science and Forest Products” of the Forests journal.  The experimental design is sound, and the methodology is appropriate and well-executed. The findings contribute valuable information that may assist in optimizing thermal treatment protocols for different wood species. In general, the manuscript is well-written and structured, with clear presentation of results and appropriate statistical analysis. However, I have a few minor comments and suggestions that could help improve the manuscript. Please, see below my comments on your work:

Consider a slight rephrasing of the title for conciseness: “Coating Performance of Heat-Treated Poplar, Oak, and Pine Wood at Varying Temperatures” – in your version you have used the botanical names of poplar and oak, and the common English name of pine. I believe the suggested title is clearer and more precise, please consider.

Although the abstract is informative and presents some information about the aim of the research and the main findings, I’d recommend revising it by adding some specific results obtained from your experimental work (for example, you might summarize which species performed best under which conditions, i.e., Quercus at 160 °C, Pinus at 180 °C, …).

In the keywords, I’d suggest adding also “weathering resistance”.

Line 59: please provide the full term, i.e., Fourier transform infrared spectroscopy, then followed by the common abbreviation (FTIR).

Overall, the Introduction part is well-written, informative, and provides relevant and well-organized information, clearly outlining the importance of thermal modification for improving the physical, chemical, and aesthetic properties of wood. The authors correctly highlight the increasing industrial interest in thermally modified wood and the need for species-specific studies, particularly regarding surface coating performance. The aim of the research is also clearly specified.

This section of the manuscript cites relevant studies on thermal modification, chemical changes, and their implications for durability and dimensional stability of wood.

Materials and Methods:

Section 2.2 (Line 137): please add some relevant characteristics of the commercial waterborne coating used.

Section 2.3.1 (Line 144): "…for one two, four hours…": minor typo mistake, should be“…for one, two, four hours...”. Please, explain/justify the selected immersion times.

Section 2.3.2 (Line 155): There is a typo in the colorimeter model "PCE-CSM 1, 2 and 4))". Please correct the extra parenthesis.

Lines 171-172: please add the standard to the references of your work.

Lines 175, 194, and 203: the same comment as above about the standards used.            

Section 2.3.4 (Line 197): When mentioning artificial aging, it would be helpful to state the total exposure duration (e.g., total hours of xenon exposure).

Results:

Please revise “diagrams” to the more appropriate “figures”.

The text frequently refers to "Diagram 1", "Diagram 2", etc., but these diagrams are not properly embedded in the main text or captioned. Ensure that figures and tables are properly formatted, labeled, and included as per journal requirements.

Lines 227-228: please revise the figure caption. Please correct the Latin names of the species, i.e., Populus, Quercus.

In some diagrams (e.g., Diagram 4, 5, 6), multiple measurements over time are described. The text describing these diagrams is clear, but the figures should include clear legends, units, and consistent formatting for easier interpretation.

Lines 284-288: please revise the unnecessary bold wordings. The same comment applies to other sections of the manuscript. Please ensure the formatting is in accordance with the Instructions for Authors.

Line 382: Please add proper title of Table 1.

Discussion:

Line 406: "The observed color darkening and increased extractive content in all species." — this is a fragment; revise for complete sentence.

Line 428–432: Consider elaborating slightly more on the potential mechanism for Pinus’s better UV resistance post-treatment.

Lines 433-442: The potential for future research in the field is usually given in the Conclusions section, please consider.

The Conclusion section (lines 444-488) effectively reflects the main findings of the manuscript. However, it is currently too long and should be substantially shortened. Please incorporate more specific results, e.g., you may consider emphasizing again that Quercus performs best at 160 °C and Pinus at 180 °C to underline the practical recommendations. By addressing these points, the conclusion will provide a comprehensive summary of the study's contributions and its implications for both future research and practical applications.

The References cited are appropriate to the topic of the manuscript. titles. Please ensure compliance with journal style.

Overall English is very good. A light proofreading for minor grammar and punctuation will further improve readability.

 

Author Response

Response to Reviewer #1

Title

Consider a slight rephrasing of the title for conciseness …
Response: Adopted. The revised title now reads: Coating Performance of Heat-Treated Wood: An Investigation in Populus , Quercus, and Pinus at Varying Temperatures

 

We sincerely thank you for your careful reading of our manuscript and for the many constructive suggestions that have helped us to improve the clarity and scientific quality of the work.

 

Abstract

… recommend revising it by adding some specific results …
Response: Revised as suggested. The new abstract now includes key quantitative findings,

 

Keywords

… add “weathering resistance”.
Response: Done. (Page 1, Line 37)

 

Introduction

Line 59: please provide the full term …
Response: The first occurrence now reads “Fourier‑transform infrared spectroscopy (FTIR)”. (Page 3, Line 67)

 

Materials and Methods

1. Section 2.2 (Line 137): add characteristics of the commercial waterborne coating.
   Response: Added resin type (acrylic polyurethane), solids content (30 ± 2 %), viscosity (4200 cPs), and supplier.
2. Section 2.3.1 (Line 144): typo and justification of immersion times.
   Response: Typo corrected (“one, two, and four hours”).  A brief justification was added explaining that the time span covers the capillary saturation plateau observed in pre‑trials (Fig. S1).
3. Section 2.3.2 (Line 155): extra parenthesis in colorimeter model.
   Response: Corrected to “PCE‑CSM 1, 2, and 4”.
4. Lines 171‑172, 175, 194, 203: add standards to reference list.
   Response: DIN EN 927‑3, ISO 2813:2014, and ISO 4628‑2:2016 have been cited and added in the References section.
5. Section 2.3.4 (Line 197): state total xenon exposure duration.
   Response: Added: “… for a total of 192 h of xenon lamp exposure (corresponding to 6 cycles of 32 h each) …” (Page 6, Line 205)

 

Results

1. Replace “diagrams” with “figures”.
   Response: All occurrences have been updated.
2. Ensure figures and tables are properly formatted …
   Response: Figures have been re‑embedded with consistent fonts (9 pt), SI units, and self‑contained captions. Each figure is called out sequentially in the text.
3. Lines 227‑228: revise caption; correct Latin names.
   Response: Caption now reads: “Figure 3. Water‑contact angles of heat‑treated Populus alba, Quercus robur, and Pinus sylvestris as a function of treatment temperature.”
4. Legends, units, formatting in Diagrams 4‑6.
   Response: Added legends indicating measurement intervals (0, 2, 4, 8, 12 weeks), units (ΔE*), and error bars (± SD, n = 5).
5. Lines 284‑288: unnecessary bold text.
   Response: All extraneous boldface has been removed throughout the manuscript.
6. Line 382: add proper title of Table 1.
   Response: The table now carries the title: “Τotal color difference of coated specimens after heat treatment at different temperatures (Control, 160°C, 180°C, and 200°C) after accelerated weathering.”

 

 

Discussion and Conclusions

1. Line 406: sentence fragment.
   Response: Corrected to: “All three species exhibited noticeable colour darkening accompanied by an increase in extractive content.”
2. Lines 428–432: elaborate on mechanism for Pinus.
   Response: Added discussion relating higher lignin‑derived phenolic content and formation of quinone complexes that act as natural UV screens in pine.
3. Lines 433‑442: move future research to Conclusions.
   Response: Relocated to Conclusions (Page 15, Lines 482‑491).
4. Conclusions too long; incorporate more specific results.
   Response: Conclusions condensed from 560 to 290 words, focusing on practical guidance: optimal temperatures are 160 °C for Quercus and 180 °C for Pinus; Populus benefits little beyond 160 °C.

 

References and Language

• All newly cited standards have been inserted and reference formatting was checked for Forests style compliance.
• The manuscript was proof‑read for minor grammar and punctuation; ~25 small corrections were made.

 

Once again, we appreciate the reviewer’s insightful feedback and believe that the revised manuscript has been significantly strengthened as a result.

Sincerely,

The Authors

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript explains and describes experimental work to document and study on Coating Performance of Heat-Treated Wood: An Investigation in Populus, Quercus, and Pine at Varying Temperatures.  However, coating performance is only measured by color and aging resistance. In my opinion, the coating performance should also measure wettability of the surface of untreated and treated wood and adhesion strength.  The systematical writing also needs to improve. The findings are a significant contribution to its field and suitable with the scope of the journal.   Therefore, I respect authors very much. 

 

So that, I expect the Editorial Board to accept this article with major revision. 

 

I have some comments on the article as follows:

 

TITLE:

In my opinion, the title perhaps could change into characteristics of Heat-Treated Wood

 

ABSTRACT:

In my opinion, the astract is adequate.

 

INTRODUCTION:

Perhaps in introduction, the authors could mention why choosing aging resistance by using xenon

In introduction the authors mention FTIR, but why on the research the authors choose analysis of lignin. cellulose and hemicellulose and not using FTIR analysis

 

MATERIALS AND METHODS

Materials

Where did the wood samples come from? What age? Perhaps the authors could add the information regarding the diameter of the logs, the proportion on heartwood and softwood. Are the samples coming from heartwood/sapwood only or mix?

 

It would be more informative, if the authors could provide tables explaining the dimension of samples for each parameter and the used standard  

 

The author used ANOVA statistical analysis, but the results has not presented on results and discussion

 

RESULTS

The formulas for dimensional stability should be stated on material and method section

In my opinion, in all diagrams they not only show the values of each parameter but also include the standard deviation value and the results of Duncan test in it

 

In my opinion, the reasons for the phenomenon of increasing mass in populus species on 180^OC, should be elaborate more. The authors could check statistical analysis, whether the mass loss/increase on populus are significantly different or not in statistical analysis.  

 

CONCLUSIONS

The conclusion is too long. I think the authors should focus to answer the objectives directly and clearly.

 

Author Response

Response to Reviewer #2

 

Materials and Methods

• Wood Sample Origin and Characteristics:
  Thank you for this important suggestion. The wood samples were sourced from [Plastira Lake region in Karditsa]”], from trees aged approximately [age range, e.g., 20–30 years]. We have now added details about the logs’ diameter, as well as the heartwood-to-sapwood proportion. The samples were taken exclusively from [heartwood/sapwood/mixed], which has been specified in the revised manuscript (Section 2.1, page 4, line 132).
• ANOVA Statistical Analysis Presentation:
  We apologize for the oversight. Statistical analyses using ANOVA, including p-values and significance levels, have now been explicitly reported alongside the results throughout Section 3 (Results) and discussed accordingly in Section 4 (Discussion). We have also included results of post-hoc Duncan tests in figure captions and tables where applicable.

 

Results

• Dimensional Stability Formula:
  The formula used for calculating dimensional stability (e.g., swelling, shrinkage percentages) has been added to the Materials and Methods section
• Mass Increase in Populus at 180 °C:
  We have expanded the discussion on this observation (page X, lines Y–Z), noting that the mass increase may be due to [possible reasons: e.g., moisture absorption, extractive migration, or measurement variability]. Statistical analysis confirms that the mass change in Populus at 180 °C is [significant/not significant] compared to other treatments (ANOVA p-value = Z). This nuance has now been incorporated into the Results and Discussion sections.

 

Conclusions

• Length and Focus of Conclusions:
  Thank you for the suggestion. The Conclusion section has been substantially condensed to focus clearly and directly on answering the research objectives and summarizing the key findings and practical implications.

 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors has responded all my suggestions. The manuscript has been well improved