Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review Report for:

“Experimental Characterisation of Natural Wax-Infused Wood Wool and Impact on Thermal Kinetics: A Review of Recent Studies”

General Assessment

This manuscript addresses a relevant topic: the material properties, ignition performance, combustion behaviour, and environmental implications of wax-containing lignocellulosic fire starters. The review brings together evidence on paraffin, beeswax, stearin, stearic acid, and candle-wax formulations and makes a useful effort to distinguish direct fire-starter studies from evidence obtained from related products such as candles, briquettes, fire logs, and wax-treated wood.

The use of a PRISMA flow diagram and keyword co-occurrence analysis is helpful, and the manuscript identifies an important evidence gap: few studies directly compare different coatings on the same lignocellulosic substrate under matched conditions. The discussion of formulation-specific results and the need for controlled comparisons is potentially valuable for future fire-starter development.

However, several aspects require clarification. Most importantly, the wood species must be reported whenever wood wool, wood shavings, planer shavings, sawdust, or wax-treated wood are discussed, because species-related differences in density, anatomy, extractives, moisture behaviour, and thermal decomposition may affect the reported results. The review methods also need additional detail, comparisons across dissimilar studies should be framed more cautiously, and the Conclusion should be substantially shortened. Figure 3 and its detailed research framework would be more appropriately placed before the Conclusion. These issues can be addressed through minor revision.

Major Comments

Title and Scope

1. Revise the title to accurately describe the article type and scope.

The title begins with “Experimental Characterisation,” although the manuscript reports a systematic review rather than an original experimental study. In addition, “natural wax-infused wood wool” does not fully represent a review that also covers fossil paraffin, kerosene-based firelighters, candles, briquettes, fire logs, sawdust, and several other lignocellulosic substrates. Please revise the title so that it clearly identifies the paper as a review and accurately reflects the breadth of the evidence considered.

Abstract

2. State the substrate and wood species more precisely.

Lines 10-23: The Abstract refers generally to wood-wool and wood-shaving fire starters, but the species used in these materials are not identified. Please state the wood species when this information is available in the cited studies or product documentation. When the species was not reported by the original source, explicitly indicate “wood species not reported.” The Abstract should also distinguish direct evidence from wax-infused wood-wool fire starters from indirect evidence derived from candles, briquettes, fire logs, and wax-treated solid wood.

Review Methods

3. Provide sufficient methodological detail for reproducibility.

Lines 190-222: The PRISMA counts are clearly reported, but the search and screening procedures require more detail. Please provide the complete database-specific search strings, the exact final search date, language and document-type restrictions, the duplicate-removal method, the number of reviewers involved in screening and data extraction, and the procedure used to resolve disagreements. Please also explain whether study quality or risk of bias was assessed. If no formal quality assessment was performed because the evidence includes heterogeneous studies and technical sources, state this clearly as a limitation.

Terminology and Material Identification

4. Report wood species throughout the review and distinguish the substrate forms.

Lines 53-76, 118-124, 168-189, 278-318, and throughout Sections 2-5: The manuscript repeatedly discusses wood wool, wood shavings, planer shavings, sawdust, and wax-treated wood without consistently reporting the wood species. This information is necessary because wood density, anatomical structure, resin and extractive content, moisture sorption, and thermal degradation differ among species and can influence wax uptake, ignition, burning rate, residue, and emissions. Please report the common and scientific name of each species whenever available. Where the source does not identify the species, note this explicitly and treat it as a limitation of the evidence.

5. Use wood-wool, wood-shaving, planer-shaving, and sawdust terminology consistently.

The manuscript sometimes treats these substrate forms as closely related, although they can differ substantially in particle dimensions, surface area, bulk density, fibre orientation, and wax-retention capacity. Please define each substrate category at first use and avoid using the terms interchangeably. A concise table listing study, wood species, substrate form and dimensions, wax type and proportion, test method, and principal outcome would make the evidence base substantially easier to interpret.

Evidence Synthesis and Interpretation

6. Avoid direct ranking of results obtained from unmatched material systems.

Lines 953-1007: Statements that paraffin produced the “strongest” moisture resistance, beeswax produced the “strongest” hydrophobicity and dimensional stability, or one material provided the best reference may imply direct comparability. However, these results were obtained using different wood species, substrates, formulations, specimen geometries, wax contents, and test conditions. Please present these values as within-study findings or illustrative benchmarks rather than as a comparative ranking. The text should clearly distinguish evidence for the wax itself from evidence for the complete wax-substrate formulation.

7. Separate thermal decomposition, combustion, and emission evidence more explicitly.

Several sections appropriately acknowledge that thermogravimetric analysis under nitrogen is not equivalent to fire-starter combustion in air. Please apply this distinction consistently throughout the synthesis. Results from candles, kerosene-based firelighters, briquettes, and wax-treated wood can identify relevant mechanisms or variables, but they should not be presented as direct evidence of the performance or emissions of wax-infused wood-wool fire starters.

Conclusion

8. Move Figure 3 out of the Conclusion.

Lines 946-952 and 1010-1026: The Conclusion begins by introducing Figure 3 and later returns to the figure when proposing future experimental testing. A conclusion should primarily synthesize the principal findings, limitations, and implications of the review rather than introduce or explain a figure. Please move Figure 3 and the associated experimental framework to a preceding section, such as “Research Gaps and Future Experimental Directions,” and reserve the Conclusion for a concise final synthesis.

9. Remove unnecessary citations and numerical repetition from the Conclusion.

Lines 946-1039: The Conclusion contains numerous citations and repeats many detailed values already reported in the Results and Discussion. Please explain why citations are needed in this section and remove them wherever the statements can instead summarize findings established earlier in the manuscript. The Conclusion should not read as an additional literature-review section. If a citation is essential to support a specific qualification, it may be retained sparingly, but source-by-source reporting and repeated numerical results should be avoided.

10. Substantially shorten and refocus the Conclusion.

The Conclusion is approximately three manuscript pages long. Please reduce it to a concise synthesis of: (1) the principal finding that direct matched comparisons are scarce; (2) the main limitations of the existing evidence, including missing wood-species information and heterogeneous substrates and methods; (3) the practical implication for selecting fire-starter materials; and (4) the most important priorities for controlled future testing. Detailed descriptions of individual formulations, values, and test parameters should remain in the preceding sections.

11. Qualify the recommendation of a specific stearic-acid grade.

Lines 1020-1038: The conclusion identifies the Ácido Esteárico 18-60 grade as a strong candidate for further testing. Please make the selection criteria transparent and clarify that this recommendation is a proposed research direction rather than evidence of superior fire-starter performance. The cited performance data concern related stearic-acid formulations rather than a matched test of this specific grade on the proposed planer-shaving substrate.

Minor Comments

1. The Introduction and research-gap sections contain some repetition, particularly regarding the scarcity of direct wax-infused wood-wool evidence and the emissions of kerosene-based firelighters. Please streamline these passages.
2. Lines 223-274: Please explain how author keywords and index keywords were combined and cleaned for the VOSviewer analysis, including the handling of singular/plural terms, synonyms, spelling variants, and a thesaurus file, if used.
3. Improve the readability of Figure 2. Several keyword labels and links are difficult to distinguish at normal page size. A higher-resolution figure and clearer explanation of the five clusters would help readers interpret the network.
4. Use consistent terminology and hyphenation for “fire starter,” “fire-starter,” “firelighter,” “wood wool,” and “wood-wool fire starter.” Please also correct visible spacing or encoding issues such as “Á cido Esteárico” where they occur.
5. When information is taken from safety data sheets, patents, standards, or product documentation rather than peer-reviewed studies, identify the source type clearly and discuss the limitations of relying on manufacturer-reported or non-peer-reviewed information.
6. Please proofread the manuscript for long or repetitive sentences, consistency of SI-unit formatting, and consistent use of terms such as climate-change impact, environmental impact, residue, and combustion residue.

Recommendation

The manuscript addresses a useful and under-reviewed topic and assembles a broad evidence base on wax-containing lignocellulosic fire starters and related material systems. Its principal contribution is the identification of the limited direct evidence available for matched comparisons of wax-infused wood-wool or wood-shaving fire starters. The requested revisions primarily concern clearer reporting of wood species and substrate form, improved methodological transparency, more cautious comparison of heterogeneous studies, and a shorter, more focused Conclusion. These revisions can be completed without changing the core study design.

My Recommendation: Minor Revision.

Author Response

Dear Reviewer,

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This review covers an under-studied product group. The topic fits Sustainability. The PRISMA method is sound. The authors are honest about data limits. They correctly state that candle, briquette, and fire-log data cannot be directly transferred to wax-coated wood wool.

However, the manuscript reads more like a material and combustion review than a sustainability assessment. The environmental part relies on one LCA [17]. That LCA was done for wax-emulsion products, not fire starters. The comparison across wax types is also fragmented. The stearic acid conclusion needs clearer limits.

1. The climate discussion depends almost only on Boekaerts et al. [17]. The functional unit is 1 kg wax for a wax-emulsion product. This is not the same as a fire starter. The authors admit this. But the values are still presented as if they apply directly. Please mark them as indicative only. Please add a short note on how a fire-starter LCA should be designed.
2. The review is organised by wax type. But there is no numerical comparison table. Figure 3 is a schematic. It is not a data table. Please add a summary table. Rows: wax types. Columns: origin, wax fraction, melting point, moisture resistance, ignition time, burn duration, calorific value, residue, emission data, climate data, evidence type.
3. The manuscript says kerosene, candle, and briquette data cannot be transferred to wood wool. This is correct. But the point is repeated many times. There is no unified scheme. A simple three-tier scheme would help: direct, semi-direct, indirect.
4. The review covers kerosene, candles, briquettes, and fire logs. But it does not clearly state what is known and unknown for wax-coated wood wool. Please add a short subsection or table. State which pollutants were measured for which product. State which were not measured for the target product. State the minimum measurement set for future work.
5. Add one sentence with the main conclusion.

6.State the research question and objectives clearly at the end of Section 1.1 or 1.2.

7. Figure 2: Explain the clustered data, the similarity measure, and the algorithm. Otherwise the figure is not reproducible.

 

Author Response

Dear Reviewer,

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript addresses the performance and environmental implications of wax-coated wood-wool firelighters, a topic that could fit the scope of Sustainability. However, its central comparisons are not adequately supported by product-specific evidence, I therefore recommend substantial revision before publication.

1. Could the authors revise the Abstract to state the main findings and limitations, rather than mainly listing materials and measurements?
2. The Introduction repeats the research gap in the paragraph immediately before Section 1.1 and again within Section 1.1. Could the authors consolidate these passages, remove the statement that the review “fits Sustainability”, and move detailed findings from related wood and briquette studies to the relevant discussion sections? A shorter Introduction would make the specific review question clearer.
3. Could the authors provide the full search strings, search dates, database-specific results, and reasons for excluding the 49 full-text reports? These details are needed to reproduce the stated systematic review.
4. Could a table identify all 42 included studies and report their product types, substrates, coating compositions, experimental conditions, and measured outcomes?
5. How were differences in study quality and relevance considered when synthesising results from firelighters, candles, briquettes, treated wood, and technical documents?
6. Could the authors qualify comparative terms such as “strongest” when the underlying studies used different substrates, formulations, and methods? Please also clarify why “candle wax” is treated as a separate material category alongside specific waxes.
7. How can moisture resistance, ignition time, and burn duration be ranked across studies using different substrates, formulations, and test methods? Could unsupported cross-study rankings be removed or qualified?
8. The cited life-cycle assessment concerns wax-emulsion applications rather than firelighters. Could the authors explain the limits of applying its results to a product consumed during ignition and discuss an appropriate functional unit for future firelighter assessments?
9. What evidence supports any claim that a natural wax is more sustainable than a fossil-derived wax? Could feedstock origin, processing, allocation of by-products, and combustion emissions be considered before drawing this comparison?
10. Why is the specific Ácido Esteárico 18-60 grade highlighted as a leading candidate when its reported values are stated not to constitute technical product specifications? Could the recommendation be limited to including it in future comparative tests?
11. Figure 3 presents a synthesis of the evidence and proposes a material for future testing, but it is placed in the Conclusions section. Could the authors move it to a preceding synthesis or discussion section, explain the basis for its comparisons there, and keep the Conclusions focused on the findings supported by the reviewed evidence?
12. The Conclusions section is overly long and repeats many results already discussed in the manuscript. Could the authors move Figure 3 and the detailed proposals for future experiments to a separate “Future Directions” section? The Conclusions could then be reduced to one concise paragraph summarising the main findings, the limits of the available evidence, and the key research need.
13. The minor presentation issues should be corrected before publication? For example, red-coloured revision text remains on page 2 (lines 78–86) and page 24 (line 1077). Reference [29] also lacks the conference location and dates.

Author Response

Dear Reviewer,

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

All issues have been addressed

Author Response

We thank the reviewer for their time and for confirming that all issues have been addressed.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have carefully addressed the comments, and the revised manuscript has been substantially improved. However, there are two minor issues need to be addressed before publication.

1. The search strategy has been described in more detail in the revised manuscript. It would be helpful if the authors could also provide the complete database-specific search strings to further improve the reproducibility of the review.
2. The revised manuscript now distinguishes direct, semi-direct, and indirect evidence. Could the authors also briefly clarify whether and how the methodological quality of the included studies was considered during the evidence synthesis?

Author Response

Please see the attachment.

Sincerely,
Kristaps Eihmanis

Author Response File: Author Response.pdf