-->PONE-D-26-19567-->-->A lab-scale prototype development of Lignin-Formaldehyde (LF) resin: A bio-renewable adhesive for wood panel industries-->-->PLOS One

Dear Dr. Hussain,

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Reviewer #1: Yes

Reviewer #2: Partly

Reviewer #3: Yes

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-->2. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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-->3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

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-->4. Is the manuscript presented in an intelligible fashion and written in standard English?

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Reviewer #1: Yes

Reviewer #2: No

Reviewer #3: Yes

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-->5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1: 1. The novelty of the study should be clarified more explicitly, particularly how this work differs from previously reported 100% lignin-substituted phenol-formaldehyde adhesives.

2. The lignin extraction yield was not reported, which limits assessment of process efficiency and industrial feasibility.

3. Residual carbohydrate content in extracted lignin was not quantified, although it may strongly influence curing behavior and adhesive properties.

4. The explanation relating hydroxyl content to adhesive performance requires stronger discussion supported by literature.

5. The FTIR interpretation contains several weak or uncommon band assignments that should be justified with references.

6. The adhesive formulation includes wheat flour and alder bark additives, but their specific role in resin performance is insufficiently discussed.

7. Units and symbols are inconsistently formatted throughout the manuscript, especially for temperature, viscosity, and molecular weight values.

8. The manuscript language requires careful proofreading to correct grammatical issues and improve scientific clarity in several sections.

9. The discussion section (Statistical analysis, ANOVA) is mostly descriptive and requires deeper scientific interpretation supported by relevant mechanisms and literature.

Analysis of erosion wear behavior of LD sludge filled polypropylene composites using RSM.

Analysis of sliding wear behavior of LD sludge filled epoxy composites using response surface methodology.

10. Figure captions are inconsistent in formatting style and should include experimental conditions for better interpretation.

11. In conclusion, be more specific in applications too. Add technical facts to the conclusions to improve them.

Reviewer #2: The manuscript addresses the development of lignin–formaldehyde (LF) resins using lignins from different biomass sources and evaluates their performance as wood adhesives. While the topic is relevant in the context of sustainable materials, the manuscript suffers from limited novelty, structural weaknesses, and insufficient critical discussion, which currently reduces its contribution to the field.

Major Comments

1. Comparing lignins from different biomass sources and their influence on phenol-formaldehyde resin performance is not sufficiently novel. Several prior studies have already demonstrated this topic and yet there was not sufficient review presented in the introduction. Please strengthen the novelty by clearly defining what is genuinely new.

2. The manuscript is overly long and repetitive, particularly in:

a. the Abstract that is too dense with numerical results rather than highlighting key findings/trends and overall conclusions

b. Lignin extraction procedures (repeated almost identically for each feedstock)

c. Characterization descriptions (FTIR, TGA, NMR)

d. Result presentation (each lignin and resin discussed separately with similar narrative structure)

I recommend consolidating methods into generic protocols with feedstock-specific deviations summarized in tables, results into comparative sections (CP vs ESD vs SB) instead of sequential descriptions, merge figures where possible rather than separate figures per lignin.

3. The discussion remains largely descriptive rather than analytical. Key observations are reported but not deeply interpreted. Strengthen discussion by

a. linking lignin structure → reactivity → crosslink density → adhesive performance

b. comparing findings critically with literature (agreement vs deviation)

c. providing mechanistic explanations (e.g., steric hindrance in the different phenolic groups, accessibility of reactive sites, role of molecular weight)

4. The methodology mentions different levels of lignin substitution (0%, 20%, 50%, 80%, 100%), but only one resin per lignin type (apparently at full substitution) is presented in the results, and it´s not clear if this is from a 100% substitution? If it is indeed 100%, the reported viscosity (~0.3 Pa·s at ~50% solids) also seems unusually low, likely due to the very high shear rate (1000 s⁻¹). Although such shear conditions may be relevant for industrial processing, they could mask subtle but potentially important differences arising from formulation changes or lignin type variations especially true for shear thinning phenolic resins. Measurements at lower or multiple shear rates (e.g., 50–100 s⁻¹) would be more appropriate for comparison.

Reviewer #3: The manuscript presents an interesting comparative study on lignin-formaldehyde bioadhesives synthesized from locally available biomass resources. The work is relevant to sustainable adhesive development and circular bioeconomy research. The manuscript is generally well-structured and supported by multiple characterization techniques including FTIR, NMR, TGA, DSC, and lap-shear testing. However, several scientific, methodological, and presentation-related issues should be addressed before the manuscript can be considered for publication.

1. Include at least one commercial phenol-formaldehyde adhesive as a control for comparative bonding performance.

2. Since the adhesive system is formaldehyde-based, formaldehyde emission analysis is critical for environmental and industrial applicability. The manuscript lacks any emission or toxicity evaluation.

3. Add a section discussing scale-up feasibility, economic considerations, and industrial implementation challenges.

4. The manuscript claims novelty based on comparison of Pakistani biomass feedstocks. However, complete phenol substitution using lignin has already been reported in earlier studies. Clarify the specific scientific novelty and distinguish this work more clearly from prior lignin-PF adhesive studies.

5. There are inconsistencies in formatting: “1000 C” instead of “1000°C” Mixed spacing around units and symbols

Inconsistent use of superscripts/subscripts. Carefully revise unit formatting according to journal style.

6. Discuss moisture resistance limitations and possible methods for improving wet durability.

7. The role of wheat flour and alder bark modal in the adhesive formulation is not adequately explained.

8.The authors have carried out the present study using natural biomass-derived materials and optimization of lignin-based adhesive formulations; however, the manuscript lacks sufficient citation of recent and relevant literature related to natural-material-based material development and optimization studies. The authors are encouraged to include and discuss recent published works in this area. Some recommended references relevant to the present study are as follows: https://doi.org/10.1007/s40964-025-01478-7

https://doi.org/10.1016/j.envres.2022.115021

https://doi.org/10.1177/09544089241253973

https://doi.org/10.1007/s11665-024-10122-4

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Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

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A lab-scale prototype development of Lignin-Formaldehyde (LF) resin: A bio-renewable adhesive for wood panel industries

PONE-D-26-19567R1

Dear Dr. Hussain,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Din Bandhu, Ph.D.

Academic Editor

PLOS One

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

-->Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.-->

Reviewer #1: All comments have been addressed

Reviewer #3: All comments have been addressed

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-->2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. -->

Reviewer #1: Yes

Reviewer #3: Yes

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-->3. Has the statistical analysis been performed appropriately and rigorously? -->

Reviewer #1: (No Response)

Reviewer #3: Yes

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-->4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.-->

Reviewer #1: (No Response)

Reviewer #3: Yes

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-->5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.-->

Reviewer #1: (No Response)

Reviewer #3: Yes

**********

-->6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)-->

Reviewer #1: (No Response)

Reviewer #3: (No Response)

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If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review?  For information about this choice, including consent withdrawal, please see our Privacy Policy.-->

Reviewer #1: No

Reviewer #3: No

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