Mechanical Performance and Dye Adsorption of Lignin/Poly(ethylene glycol) Diglycidyl Ether/Sorbitol Polyglycidyl Ether Hydrogels

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is devoted to the investigation of lignin-based hydrogels. Eleven formulations were synthesized, and their rheological and mechanical properties were studied. In principle, the scope of the experimental work could allow the authors to demonstrate how compositional variations affect the properties of the hydrogels. However, after careful reading of the manuscript, the overall scientific objective of the study remains unclear.

Neither the abstract nor the introduction sufficiently articulate the relevance of the work, its scientific motivation, or the specific problem it aims to address. One may infer that the authors intend to propose a new synthesis approach; however, according to the introduction, similar methods appear to have already been reported in the literature. At the same time, the influence of composition on rheological and mechanical characteristics is not explicitly demonstrated (see comment 4), and absorption behavior and kinetics are investigated for only a single formulation. The conclusion largely reiterates scattered results presented in the manuscript, but the scientific significance, novelty, and перспективность (future potential) of the study remain insufficiently justified.

In its current form, the manuscript cannot be recommended for publication.

Below are detailed comments. I would particularly encourage the authors to treat their own data with greater analytical rigor: the presentation of raw experimental data without proper processing, interpretation, and statistical analysis does not meet the standards of a high-quality scientific manuscript.

Specific comments

1. Abstract
   The abstract should be substantially revised to clearly state the scientific relevance, motivation, and objective of the work, as well as the key outcomes and their significance.

2. Terminology / Processability
   The statement “Bisphenol A is widely used because it improves processability” (line 36) requires clarification. What specific aspects of “processability” are meant here (e.g., viscosity reduction, crosslinking control, network formation, processing window)? This concept should be clearly defined.

3. Table 1 (Precision of composition)
   It is unclear how such high precision in formulation preparation (up to 10⁻⁶ g) was achieved. In scientific reporting, only significant figures justified by experimental accuracy should be presented. This table should be revised accordingly.

4. Data processing and presentation
   The current presentation of experimental data does not allow a reliable assessment of data quality, reproducibility, or scientific validity:

   i. FTIR spectra
   The relevant spectral regions should be presented in enlarged form, properly normalized to characteristic functional groups, and arranged in a way that clearly supports the authors’ interpretations and claims.

   ii. Rheological data
   Rheological curves are overlaid on a single graph with inappropriate axis representation. Frequency sweeps appear to have been recorded in logarithmic frequency scale but are presented in linear coordinates. Moreover, the linear scaling of G′ and G″ is physically inappropriate for proper interpretation and cannot be considered a reliable representation of viscoelastic behavior. The legend is not readable. There is no substantive discussion, interpretation, or justification of the results.
   If the authors refer to parameters such as G′_max or G′/G″ ratios, these quantities should be explicitly constructed, plotted, and analyzed. The simultaneous presentation of 22 dependencies in this form is not acceptable for a high-quality scientific manuscript. The discussion must be significantly expanded and made more structured and quantitative.

   iii. Mechanical testing
   The presentation of raw stress–strain and elongation curves constitutes laboratory output rather than scientific results. The data should be properly processed, averaged, statistically analyzed, and presented in a concise, interpretable form.

   iv. Absorption tests
   It is unclear why absorption and kinetic studies were performed for only one sample, and how the choice of this particular formulation is justified. If the study claims to investigate compositional effects, comparative samples are essential to allow meaningful conclusions about composition–property relationships.

   v. Kinetic modeling (Section 3.6)
   The terms “pseudo-1(2)” are not scientifically standard. The governing equations should be explicitly provided and the models should be correctly named using accepted kinetic terminology.

   vi. Statistical analysis
   No statistical treatment of the data is presented. The absence of error analysis, reproducibility assessment, and statistical validation significantly reduces the reliability and scientific credibility of the reported results.

Author Response

Please find attached file.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article contributes to an important and current field; however, the narrow experimental scope, lack of statistical detail, and inadequate data interpretation diminish its impact. If these shortcomings are corrected, it could become a powerful publication contributing to the journal:

1) The purification levels of SPE and PEGDGE, as well as parameters such as reagent purity, are not specified.

2) There is an inconsistency in terminology between Figure 1 (page 4) and the text: The figure shows the "crosslinking" aspect but does not provide more detailed information about the chemical mechanism (e.g., opening of the epoxy ring, specific bond types).

3) FTIR data (Figure 2) were interpreted, but the spectra were not subjected to quantitative evaluation (peak area, intensity ratio, etc.). Therefore, the degree of cross-linking was expressed only qualitatively.

4) Swelling tests used only water. The effects of environmental variables such as pH or ionic strength were not investigated.

5) Swelling, mechanical tests, and adsorption data are not presented with standard deviations, error bars, or significance tests. Although five replicates are mentioned, no numerical confidence level is provided.

6) Only one sample (LS1P9) was selected for the adsorption test. The other samples were not compared.

7) Adsorption tests have been conducted for up to 2880 minutes, but this is too long; in practical applications, shorter timeframes are more critical for effectiveness. There is a lack of discussion on this topic.

8) The value of 6.887 mg/g obtained for the LS1P9 adsorbent has not been compared with the literature.

Author Response

Please find attached file.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

 

Figure 4 appears overly crowded, with multiple overlapping curves, which makes data interpretation and comparison among formulations difficult. Could the authors improve the presentation (for example, by separating the data into subfigures by groups or showing only representative samples), and include error bars where applicable?

Before performing the frequency sweep (0.1–20 Hz), was a strain sweep conducted to define the linear viscoelastic region (LVR)? Clarifying this point is important to ensure that the reported G′ and G″ values were obtained within the linear regime.

Were the kinetic data (PFO/PSO) and the experimental qe values obtained under exactly the same experimental conditions (same adsorbent mass, solution volume, initial concentration, temperature, agitation, and hydrogel geometry)? Please clarify this explicitly in the text to avoid doubts regarding data comparability.

The obtained qe value (6.9 mg/g) may appear low; however, the experiment was performed at a relatively low initial concentration C0 = 30 mg/Land with a relatively high adsorbent dosage (1.6242 g in 500 mL). Could the authors explicitly comment on how these experimental conditions inherently limit qe values in mg/g and justify the choice of these conditions?

Adsorption isotherms (Langmuir and Freundlich) at different initial concentrations and/or different adsorbent dosages are currently missing. The inclusion of isotherm studies would greatly strengthen the manuscript.

the adsorption results indicate that when the hydrogel was used as an intact piece, the removal efficiency decreased 45% and the qe value was lower ~3.53 mg/g. This behavior suggests diffusion or mass transfer limitations. Could the authors further explore and discuss this aspect (particle size, thickness, effective surface area) and relate it to the material design?

Author Response

Please find attached file.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have done a commendable job of revising the manuscript, taking into account all comments and fully correcting them. This manuscript can be recommended for publication in its current form.