Washable Few-Layer Graphene-Based Conductive Coating: The Impact of TPU Segmental Structure on Its Final Performances

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript presents a well-structured and timely investigation into the role of TPU segmental architecture on the wash durability and electrical performance of waterborne graphene coatings for wearable electronics. The experimental design is methodologically sound, the dataset is comprehensive, and the sustainability considerations are convincingly addressed. However, several minor technical clarifications and editorial refinements are required prior to publication. The following comments are intended to enhance the reproducibility, metrological rigor, and overall clarity of the work. Minor revision is therefore recommended. 

1.  Specify the precise solid content (wt%) of the four commercial TPU dispersions used.
2.  Characterize the lateral size and thickness distributions of the as-received few-layer graphene (FLG). A representative AFM or TEM micrograph accompanied by corresponding statistical histograms should be provided in the Supplementary Information.
3.  The shear rate employed during the bar-coating process is not specified. Please report the rod translation speed and briefly discuss its potential influence on the in-plane orientation preference of the FLG flakes.
4.  Given that the input impedance of the Agilent 34401A multimeter is comparable to the measured sheet resistance of some samples, it is necessary to either specify the correction factor applied for the four-point probe measurements or provide I-V curves demonstrating ohmic behavior to exclude potential artifacts from contact resistance.
5.  SEM images indicate the presence of local graphene agglomerates in coatings prepared with the BIO E02 TPU matrix. We recommend performing a fast Fourier transform (FFT)-based roughness analysis on at least five representative micrographs and correlating the obtained average (Ra) and root-mean-square (Rq) roughness values with the corresponding sheet resistance.
6.  The term "conductive range" is used repeatedly without a definitive reference. Please cite the specific relevant standardthat defines the conductivity threshold for wearable textile applications.
7.  The Conclusion section is overly lengthy. We encourage the authors to condense it, focusing more sharply on highlighting the key findings, significance, and originality of the study.
8.  The manuscript contains several grammatical and formatting inconsistencies. A thorough proofreading is recommended to ensure clarity and adherence to standard academic writing conventions.

Author Response

Reviewer 1:

This manuscript presents a well-structured and timely investigation into the role of TPU segmental architecture on the wash durability and electrical performance of waterborne graphene coatings for wearable electronics. The experimental design is methodologically sound, the dataset is comprehensive, and the sustainability considerations are convincingly addressed. However, several minor technical clarifications and editorial refinements are required prior to publication. The following comments are intended to enhance the reproducibility, metrological rigor, and overall clarity of the work. Minor revision is therefore recommended. 

1. Specify the precise solid content (wt%) of the four commercial TPU dispersions used.

 

Following the Reviewer’s suggestion, we have expanded Table 1 by adding the solid content (wt%) of each commercial TPU dispersion, as reported in the manufacturers’ technical datasheets.

The Table 1 is modified as follow:

 

Sample Name	Commercial Name	Description	Solid Content (wt%)
U6150	Alberdingk® U 6150 (Alberdingk Boley, Greensboro, NC, USA)	Polycarbonate-based aliphatic TPU dispersion	37.0–39.0
U4190	Joncryl® U 4190 (BASF Corporation, Florham Park, NJ, USA)	Aliphatic polyurethane (TPU) dispersion in water	36.5
BIO S03	Polytech® BIO S03 ( ICAP Leather Chem S.p.A. Lainate, MI, Italy)	Aliphatic polyester-based TPU dispersion (~59% bio-based C)	~35.0
BIO E02	Polytech® BIO E02 ( ICAP Leather Chem S.p.A. Lainate, MI, Italy)	Aliphatic TPU dispersion (~70% bio-based C)	~35.0

 

 

 

2. Characterize the lateral size and thickness distributions of the as-received few-layer graphene (FLG). A representative AFM or TEM micrograph accompanied by corresponding statistical histograms should be provided in the Supplementary Information.

 

The authors thank the reviewer for their comments. We have included the link to the technical data sheet for the few-layer graphene used in the Materials and Methods section of the paper as a reference. This is available at the following link:

 

https://www.grapheneup.com/graphene-gup/.

 

 

 

3. The shear rate employed during the bar-coating process is not specified. Please report the rod translation speed and briefly discuss its potential influence on the in-plane orientation preference of the FLG flakes.

 

We thank the Reviewer for this comment. As requested, we have now specified the rod translation speed used during the bar-coating process in the Paragraph 2.3. We also added a short discussion on the possible influence of shear flow on the in-plane orientation of FLG flakes as follows:

 

The coatings were applied using a bar-coating technique (K Paint Coater Model 202, RK PrintCoat Instruments, Litlington, Unite Kingdom) equipped with a No. 12 wire-wound bar, in a single pass at a constant coating speed of 6 m/min, producing a wet film thickness of approximately 12 µm. The coatings were applied using a 12 µm wire-wound bar in a single pass at a constant coating speed of 10 cm s⁻¹. During bar-coating deposition, the shear field generated at the liquid–film interface can promote a partial in-plane alignment of graphene flakes.

This shear-induced orientation contributes to the formation of lateral conductive pathways, as the nanosheets tend to unfold and arrange more parallel to the substrate, thereby enhancing filler-to-filler contact and facilitating electron transport across the coating https://doi.org/10.1016/j.apsusc.2019.01.066.

 

4. Given that the input impedance of the Agilent 34401A multimeter is comparable to the measured sheet resistance of some samples, it is necessary to either specify the correction factor applied for the four-point probe measurements or provide I-V curves demonstrating ohmic behavior to exclude potential artifacts from contact resistance.

 

 

We thank the Reviewer for this important observation. We apologize for the inadvertent typo in the original manuscript: the electrical measurements were performed using a four-point probe configuration, thus eliminating errors associated with the input impedance of the Agilent 34401A multimeter and minimizing contact-resistance artifacts. The text has been corrected accordingly in Section 2.8.

 

 

5. SEM images indicate the presence of local graphene agglomerates in coatings prepared with the BIO E02 TPU matrix. We recommend performing a fast Fourier transform (FFT)-based roughness analysis on at least five representative micrographs and correlating the obtained average (Ra) and root-mean-square (Rq) roughness values with the corresponding sheet resistance.

 

The authors thank the reviewer for this comment. We performed a roughness study and calculated Ra and Rq values, correlating them with wettability and electrical properties observations. This discussion has been included in section "3.4. Electrical Resistivity and Washability Tests" as follows:

 

“The surface roughness analysis (calculed using Gwiddion 2.66 software) of roughness average (R_a) and root-mean-square roughness (R_q) reveals distinct morphological differences among the four samples. U6150/PVP/FLG exhibits the lowest R_a value (14.54×10⁻³ mm), indicating the smoothest average surface; however, its relatively high R_q/R_a ratio (1.64) suggests a less uniform topography with more pronounced localized asperities. In contrast, U4190/PVP/FLG and BIO S03/PVP/FLG display higher R_a values (19.24×10⁻³ and 20.62×10⁻³ mm, respectively) but lower Rq/Ra ratios (1.34 and 1.33), reflecting rougher yet more statistically homogeneous surfaces. BIO E02/PVP/FLG shows intermediate behavior, with a R_a comparable to U4190/PVP/FLG but a slightly higher Rq (Rq/Ra = 1.43), indicating a broader distribution of surface irregularities. These morphological features can influence the formation and continuity of conductive pathways within the films. Systems exhibiting a more homogeneous roughness distribution (e.g., U4190/PVP/FLG and BIO S03/PVP/FLG) promote improved interflake contact and reduced interruption of the percolation network, conditions typically associated with enhanced electrical conductivity.

 Conversely, surfaces with localized sharp peaks and valleys, such as U6150/PVP/FLG, may introduce micro-gaps or localized stress points that hinder efficient electron transport despite their lower mean roughness. The interaction with surfaces that increase roughness and worsen wettability deteriorates percolation paths and therefore the ability to conduct electricity. In the other hand, improved wettability tends to make the coatings more uniform, resulting in improved electrical properties.”

 

 

6. The term "conductive range" is used repeatedly without a definitive reference. Please cite the specific relevant standard that defines the conductivity threshold for wearable textile applications.

 

 

We thank the Reviewer for the observation. We have clarified the meaning of the term ‘conductive range’ by adding an explanatory sentence in the Introduction, highlighted in yellow in the manuscript, as follow:

 

Despite these advances, three major challenges remain to be addressed: long-term washability, which is crucial for real deployment in wearable devices [14], the need for organic-free solvents and bio-based polymers [15], and obtaining resistivity values ​​within 10⁴ Ohm/□, for which a material can be classified as conductive; in fact, the term 'conductive range' refers to the level of electrical conductivity required for effective charge transport in functional materials. According to ESD Association standards, this level is typically above ~1 × 10⁻⁴ S/cm, which distinguishes truly conductive materials from dissipative ones (which lie between ~1 × 10⁻¹¹ and ~1 × 10⁻⁴ S/cm). This illustrates the level of performance needed for coatings and devices to operate reliably [14] https://doi.org/10.3390/textiles1020012.

 

 

7. The Conclusion section is overly lengthy. We encourage the authors to condense it, focusing more sharply on highlighting the key findings, significance, and originality of the study.

 

The authors thank you for your comments. We have modified the conclusions to be more precise, yet at the same time to present them in a timely manner, for easier consultation of the results.

The conclusions have been modified as follows:

 

“This work explores a sustainable strategy for formulating conductive coatings by combining waterborne thermoplastic polyurethanes (TPUs), polyvinylpyrrolidone (PVP), and few-layer graphene (FLG). The results show that the segmental architecture of the TPU critically governs adhesion, morphology, and electrical behavior.

The results enable us to draw the following conclusions:

• The architecture of the TPU segments determine the interfacial properties, filler distribution and long-term stability of the coatings. The ratio of hard to soft segments has a significant impact on the polymer's interaction with the PVP and graphene, which ultimately affects film uniformity and durability.
• The U6150/PVP/FLG and U4190/PVP/FLG demonstrated good performance, achieving sheet resistance values in the 10⁵–10⁶ Ω/□ range on cotton and PET 3 substrates. In these coatings, the compact microstructure allowed the formation of a continuous graphene network, which ensured stable electrical conductivity even after 180 washing cycles.
• BIO E02/PVP/FLG exhibited the lowest electrical performance. This was attributed to strong interactions between PVP and the polycarbonate groups in TPU matrix, which hindered the proper dispersion of graphene. SEM analysis confirmed that this led to a less uniform microstructure and reduced conductivity.
• BIO S03/PVP/FLG reached conductive values around 10⁴ Ω/□ on PET 2, indicating that substrate properties such as polarity and surface energy strongly influence the coating’s behavior. This was further evidenced by the water-repellent PET 1 fabric, on which no stable or electrically conductive coating could be obtained.
• Durability tests over 180 washing cycles showed that the most robust systems retained their electrical functionality, demonstrating the potential of these bio-based formulations for washable and long-lasting e-textiles.

In conclusion, the study demonstrates that electrical performance is not determined by the coating formulation alone, but emerges from the combined effects of TPU segmental composition, PVP interactions, graphene dispersion, and substrate wettability. Tailoring the hard/soft segment ratio in waterborne TPUs is therefore a viable route to optimizing interfacial behavior and durability in sustainable conductive coatings for printed electronics and wearable devices.”

 

 

8. The manuscript contains several grammatical and formatting inconsistencies. A thorough proofreading is recommended to ensure clarity and adherence to standard academic writing conventions.

The authors thank the reviewer for this comment. By working through the reviewers' comments, the overall English has improved throughout the article.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The submitted manuscript presents a materials-oriented investigation into how the segmental structure of thermoplastic polyurethane (TPU) influences the mechanical durability, electrical conductivity, and washability of graphene-based conductive coatings for wearable electronics. The manuscript, despite its appropriate topic, exhibits structural, methodological, and interpretive limitations that must be addressed before it can be considered for publication.

***Major Concerns***

1. 1. While the title and abstract emphasize the influence of TPU segmental structure, the manuscript does not convincingly dissect how the hard/soft segment ratios, crystallinity, or phase separation of TPUs drive observed changes in coating performance. The manuscript refers to “TPU1,” “TPU2,” and “TPU3,” but only provides general differences in hardness or elasticity. There is no FTIR, DSC, or DMA data to confirm microphase behavior or quantify soft vs. hard segment content. Without this structural underpinning, the observed differences in mechanical and electrical behavior remain phenomenological rather than mechanistic. It should be provided as supplementary information.
   2. In Figure 6, electrical resistance after multiple washing cycles is shown, but the following is missing:
      (1) Resistance values are reported without confidence intervals or error bars; (2) There is no surface morphology or SEM data post-wash to correlate electrical performance with coating degradation.
   3. SEM images (Figure 4) show surface morphology, but it is unclear how uniform the graphene dispersion was in each TPU matrix. No quantification of dispersion quality (e.g., via optical transmittance, Raman mapping, or statistical analysis of agglomerates) is provided. Since dispersion quality greatly affects conductivity and mechanical stability, this is a critical omission.
   4. Although the manuscript positions the work as a candidate for wearable electronics, it lacks a benchmarking section comparing the performance (e.g., conductivity, wash cycles survived, flexibility) to other state-of-the-art coatings such as PEDOT:PSS, AgNW composites, or MXene-based films. The values achieved here (~100–200 ohms/sq after washing) are not contextualized within the field.
   5. The use of “graphene-based conductive coating” is vague; specify whether graphene nanoplatelets, reduced graphene oxide, or other forms are used.
   6. Avoid overly generic phrases like “great potential for wearable electronics” without specific application or metric validation.
   7. Figure 7 provides only a qualitative photographic assessment of adhesion performance, without referencing standard peel test protocols or offering quantitative metrics. The manuscript would benefit from performing a standardized adhesion test (e.g., ASTM D903 or D3359) or, at minimum, describing the current procedure with more clarity. Adhesion is a key performance metric for wearable coatings, and its evaluation must meet reproducible and quantitative standards.. That is, the authors should supplement this figure with a proper peel test (e.g., using a texture analyzer or tensile tester) or clarify that this is only a qualitative observation and interpret accordingly.
   8. In Figure 2, to improve interpretability, label major peaks (e.g., 1700 cm^-1: C=O, 1100 cm^-1: C–O–C) directly in the figure and consider using an inset zoom for key spectral regions.
   9. In Table 1, please add comparison of key performance metrics (e.g., stretchability, sheet resistance before/after washing) for each TPU-graphene combination. Current entries list only sample names and types; a more data-rich table would allow readers to directly compare formulation effects.

Author Response

Reviewer 2:

The submitted manuscript presents a materials-oriented investigation into how the segmental structure of thermoplastic polyurethane (TPU) influences the mechanical durability, electrical conductivity, and washability of graphene-based conductive coatings for wearable electronics. The manuscript, despite its appropriate topic, exhibits structural, methodological, and interpretive limitations that must be addressed before it can be considered for publication.

***Major Concerns***

1. While the title and abstract emphasize the influence of TPU segmental structure, the manuscript does not convincingly dissect how the hard/soft segment ratios, crystallinity, or phase separation of TPUs drive observed changes in coating performance. The manuscript refers to “TPU1,” “TPU2,” and “TPU3,” but only provides general differences in hardness or elasticity. There is no FTIR, DSC, or DMA data to confirm microphase behavior or quantify soft vs. hard segment content. Without this structural underpinning, the observed differences in mechanical and electrical behavior remain phenomenological rather than mechanistic. It should be provided as supplementary information.

 

We thank the reviewer for this comment. We agree that rigorous quantification of the hard/soft segment (HS/SS) ratio and microphase separation improve understanding of the structure-property relationships of TPUs. However, since these are commercial TPUs, this study is not intended to strictly focus on their microstructural characterization, but rather to compare these commercially available water-based products with different chemical architectures with the performance of graphene-based coatings. For this reason, we used characterization techniques that allow for meaningful qualitative comparisons between the materials. FT-IR analysis is the technique that most directly reveals the structural differences between the four TPUs. As explained in the dedicated section, analysis of the carbonyl region (1680–1760 cm⁻¹) and the characteristic bands of the hard segment urethane groups (C=O, N–H stretching) versus the soft segment ester/carbonate groups allowed us to identify differences in hydrogen-bonded versus free carbonyl populations, detect variations in HS/SS interactions, observe shoulders indicative of carbonyls in distinct chemical environments, and distinguish systems with weakly organized hard segment domains (BIO S03) from systems rich in hard domains (BIO E02, U6150). These spectral features clearly demonstrate qualitative differences in segmental architecture and can be used to interpret trends in wettability, adhesion, and filler distribution (Section 3.1).

 

 

2. In Figure 6, electrical resistance after multiple washing cycles is shown, but the following is missing:
   (1) Resistance values are reported without confidence intervals or error bars; (2) There is no surface morphology or SEM data post-wash to correlate electrical performance with coating degradation.

 

We thank the Reviewer for this comment and the opportunity to clarify the presentation of the electrical stability data.

• We would like to clarify that error bars are already included in Figure 6. Each data point represents the average resistance value measured over multiple tracks on each sample, and the standard deviation is used as the error metric. In the revised manuscript, we have now added a clarification in the Methods section describing how the standard deviation was calculated. Specifically, we added the following sentence in yellow highlights in the paragraph 2.8:

“Each data point represents the average value obtained from at least ten independent measurements performed on three different conductive sheets.”

To improve clarity, in the revised version of the manuscript, we have mentioned in the caption of Figure 6 that the error bars correspond to the standard deviation, adding in the caption the following sentence:

“Error bars correspond to the standard deviation of these measurements.”

• SEM analysis images after washing could further support the interpretation of coating degradation. However, performing SEM on washed textile samples presents practical challenges due to fibre swelling, detergent residues, and coating redistribution within the yarns, which can introduce artefacts and compromise comparability with pristine samples.

SEM analysis is very useful at high magnifications. Evidence of effects at such magnifications would be difficult to detect due to the complexity of the textile beneath the coating, and it would be possible to make errors in assessment, confusing morphological effects due to the fabric's texture with effects due to the 180-hour wash. For this reason, we preferred to report a macroscopic observation by inserting the images in Figure 7. In this figure, in fact, these images reveal:

• the integrity or partial detachment of the coating,
• the presence of local defects or cracking,
• differences in adhesion depending on the TPU segmental structure and substrate polarity.

 

3. SEM images (Figure 4) show surface morphology, but it is unclear how uniform the graphene dispersion was in each TPU matrix. No quantification of dispersion quality (e.g., via optical transmittance, Raman mapping, or statistical analysis of agglomerates) is provided. Since dispersion quality greatly affects conductivity and mechanical stability, this is a critical omission.

 

The authors thank the reviewer for this comment. We performed a roughness study and calculated Ra and Rq values, correlating them with wettability and electrical property observations. These were calculated using Gwyddion 2.66 software on the SEM analysis, as specified in paragraph 2.6. This was modified as follows:

 

2.6. Scanning Electron Microscopy (SEM) Morphological Analysis

The morphological characteristics of the coatings were analyzed using a Scanning Electron Microscope (SEM) (Quanta 200 FEG, FEI, Eindhoven, Netherlands). Samples were sputter-coated with a gold-palladium (Au-Pd) layer (~10 nm) before imaging. The surface micrographs were obtained at 10000x magnifications to evaluate FLG dispersion and interfacial interactions between graphene and the polymer matrix.

Quantitative roughness analyses (Ra and Rq) were performed on the SEM images, with values calculated using Gwyddion 2.66 software. For the measurement, three replicates of the same coating were analyzed, with five lines of 20 µm evaluated in each replicate to obtain the averaged roughness values.

 

 

 

 This discussion has been included in section "3.4. Electrical Resistivity and Washability Tests" as follows:

 

“The surface roughness analysis, of roughness average (R_a) and root-mean-square roughness (R_q) on the SEM image, reveals distinct morphological differences among the four samples. U6150/PVP/FLG exhibits the lowest R_a value (14.54×10⁻³ mm), indicating the smoothest average surface; however, its relatively high R_q/R_a ratio (1.64) suggests a less uniform topography with more pronounced localized asperities. In contrast, U4190/PVP/FLG and BIO S03/PVP/FLG display higher R_a values (19.24×10⁻³ and 20.62×10⁻³ mm, respectively) but lower Rq/Ra ratios (1.34 and 1.33), reflecting rougher yet more statistically homogeneous surfaces. BIO E02/PVP/FLG shows intermediate behavior, with a R_a comparable to U4190/PVP/FLG but a slightly higher Rq (Rq/Ra = 1.43), indicating a broader distribution of surface irregularities. These morphological features can influence the formation and continuity of conductive pathways within the films. Systems exhibiting a more homogeneous roughness distribution (e.g., U4190/PVP/FLG and BIO S03/PVP/FLG) promote improved interflake contact and reduced interruption of the percolation network, conditions typically associated with enhanced electrical conductivity.

 Conversely, surfaces with localized sharp peaks and valleys, such as U6150/PVP/FLG, may introduce micro-gaps or localized stress points that hinder efficient electron transport despite their lower mean roughness. The interaction with surfaces that increase roughness and worsen wettability deteriorates percolation paths and therefore the ability to conduct electricity. In the other hand, improved wettability tends to make the coatings more uniform, resulting in improved electrical properties.”

 

 

4. Although the manuscript positions the work as a candidate for wearable electronics, it lacks a benchmarking section comparing the performance (e.g., conductivity, wash cycles survived, flexibility) to other state-of-the-art coatings such as PEDOT:PSS, AgNW composites, or MXene-based films. The values achieved here (~100–200 ohms/sq after washing) are not contextualized within the field.

 

We thank the Reviewer for this suggestion. In accordance with the comment, we have expanded the end of Section 3.4 by adding a paragraph comparing our results with state-of-the-art MXene-, PEDOT:PSS- and AgNW-based washable conductive coatings.

 

In particular, we have included quantitative data extracted from the cited literature and a discussion that positions our TPU/PVP/FLG formulations within the current landscape of washable e-textiles.

 

We integrated the following sentence (highlighted in yellow in the revised manuscript):

 

The electrical results obtained in this work (Rs ≈ 100–200 Ω/□ for the most conductive samples after washing), combined with their stability up to 180 washing cycles, are comparable to those reported for other washable conductive coatings based on different fillers. For example, MXene-based coatings have shown very good washing stability, with some studies reporting only minimal changes in resistance after 45 h of accelerated laundering at 80 °C under continuous stirring, although such conditions cannot always be directly translated into a defined number of domestic wash cycles [https://journals.sagepub.com/doi/10.1177/24723444241295415 ].

Regarding PEDOT:PSS-based systems, several studies report very low initial sheet resistances (typically 1–10 Ω/□). Tadesse et al. demonstrated Rs ≈ 1.7 Ω/□ on polyamide/lycra textiles, maintaining good conductivity after ten standardized domestic washing cycles [https://link.springer.com/article/10.1007/s10853-019-03519-3], while the review by Alamer et al. reports cases where an initial Rs of 1.6 Ω/□ increases by only 6.2% after three detergent-based wash-and-dry cycles [https://pubs.acs.org/doi/10.1021/acsomega.2c01834]. Although PEDOT:PSS is widely regarded as a benchmark material for textile electronics, its processing is not always fully aligned with sustainability or bio-based criteria.

Also, Ag nanowire (AgNW) coatings also exhibit high conductivity (up to ~3,668 S·cm⁻¹) and have been shown to withstand approximately twenty machine-washing cycles without obvious performance decay [https://biblioproxy.cnr.it:2481/10.1007/s12274-020-2947-x].

 

 

5. The use of “graphene-based conductive coating” is vague; specify whether graphene nanoplatelets, reduced graphene oxide, or other forms are used.

 

We thank the Reviewer for this useful remark. We have now specified this explicitly in the text. In particular:

• The title has been revised to include the term “few-layer graphene (FLG)”:

“Washable few-layer graphenegraphene-based conductive coating: the impact of TPU segmental structure on its final performances”

• In the paper were updated to clarify that the coatings are based on few-layer graphene rather than generic graphene-based fillers.

 

6. Avoid overly generic phrases like “great potential for wearable electronics” without specific application or metric validation.

We thank the Reviewer for this remark. Following the suggestion, we carefully revised the manuscript to remove or rephrase all generic statements regarding application potential. In particular, broad expressions such as “promising choice”, “opening new opportunities”, and “paving the way for wearable electronics” were replaced with more precise and contextualized references. Specifically, we added a sentence in the Introduction (highlighted in yellow) clarifying that the proposed approach offers lightweight and scalable solutions commonly used in practical applications, and provides an effective strategy to balance washability and sustainable processability, which has been shown to improve wash resistance while maintaining fully waterborne processing.

 

7. Figure 7 provides only a qualitative photographic assessment of adhesion performance, without referencing standard peel test protocols or offering quantitative metrics. The manuscript would benefit from performing a standardized adhesion test (e.g., ASTM D903 or D3359) or, at minimum, describing the current procedure with more clarity. Adhesion is a key performance metric for wearable coatings, and its evaluation must meet reproducible and quantitative standards. That is, the authors should supplement this figure with a proper peel test (e.g., using a texture analyzer or tensile tester) or clarify that this is only a qualitative observation and interpret accordingly.

 

We thank the Reviewer for this comment. During the study, we examined the applicability of standard adhesion tests, including ASTM D903 (180° peel test) and ASTM D3359 (cross-hatch tape test).

Following a review of the requirements of these methods, we concluded that they were not suitable for our system. ASTM D903 is not suitable for coatings deposited on porous and deformable textile substrates, such as PET textile and cotton. Furthermore, water-based formulations penetrate the fibers, which prevents the test from being carried out correctly.

ASTM D3359 also proved unsuitable, as coatings on fabrics could not be peeled at a constant angle without the fibers coming apart due to friction effects or cohesive failure within the textile structure. Furthermore, the grid cut required by D3359 was not feasible due to the nature of the material.

For this reason, we proceeded with an indirect assessment of adhesion through wash resistance.

 

 

8. In Figure 2, to improve interpretability, label major peaks (e.g., 1700 cm^-1: C=O, 1100 cm^-1: C–O–C) directly in the figure and consider using an inset zoom for key spectral regions.

We thank the reviewer for this suggestion. For the clarity of the reader, we would like to explain that Figure 2 already includes a magnified view of the relevant FT-IR region (1800–1500 cm⁻¹), as well as labels for the main absorption bands (urethane C=O, carbonate/ester C–O–C and N–H).

To further improve clarity, we have revised the caption of Figure 2 as follows:

(b) An inset of the carbonyl region from 1800 to 1100 cm⁻¹.

 

 

9. In Table 1, please add a comparison of key performance metrics (e.g., stretchability, sheet resistance before/after washing) for each TPU-graphene combination. Current entries list only sample names and types; a more data-rich table would allow readers to directly compare formulation effects.

 

We thank the Reviewer for the suggestion. Table 1 was originally intended to present only the nomenclature and composition of the TPU-based formulations, as it appears in the Materials section. Including performance metrics in this table would require mixing introductory information with experimental results, which may reduce clarity and break the structure of the manuscript.

In any case, following the Reviewer’s suggestion, we have expanded Table 1 by adding the solid content (wt%) of each commercial TPU dispersion, as reported in the manufacturers’ technical datasheets, modifying the table 1 as follow:

 

Sample Name	Commercial Name	Description	Solid Content (wt%)
U6150	Alberdingk® U 6150 (Alberdingk Boley, Greensboro, NC, USA)	Polycarbonate-based aliphatic TPU dispersion	37.0–39.0
U4190	Joncryl® U 4190 (BASF Corporation, Florham Park, NJ, USA)	Aliphatic polyurethane (TPU) dispersion in water	36.5
BIO S03	Polytech® BIO S03 ( ICAP Leather Chem S.p.A. Lainate, MI, Italy)	Aliphatic polyester-based TPU dispersion (~59% bio-based C)	~35.0
BIO E02	Polytech® BIO E02 ( ICAP Leather Chem S.p.A. Lainate, MI, Italy)	Aliphatic TPU dispersion (~70% bio-based C)	~35.0

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript by Improta et al presents an interesting study. In order to improve the quality of the technical content the reviewer has the follow suggestions:

 

• The introduction is detailed and well-organized. The reviewer suggests to include more related references to enhance credibility and strong the originality of the manuscript.
• The Materials and Methods section would benefit of more detailed descriptions in order to any reader can reproduce the experiment. In particular section 2.2 and 2.3. For example, detailed features of the bar-coating technique. 
• The section 3.1 FTIR analysis, would benefit of more discussion about the importance of the bands detected. Are these results expected? how can be related to the main objective of the manuscript. 
• The section 3.4 must to be improved. The authors must compare and justify the values of ohm/square obtained. These values are better than the reported in literature? These values can be reliable to novel applications?.  
• The conclusion seems too general. The reviewer suggest to re-writte the conclusion to enhance the findings of the work.
• The reviewer suggest to include comparisons with the literature of the results in all sections to improve the merit of the work.

Author Response

Reviewer 3:

The manuscript by Improta et al presents an interesting study. In order to improve the quality of the technical content the reviewer has the follow suggestions:

 

1. The introduction is detailed and well-organized. The reviewer suggests to include more related references to enhance credibility and strong the originality of the manuscript.

 

We thank the Reviewer for the suggestion. In response, we have revised the introduction by adding recent and relevant references as follow:

 

“Recent work on textile-integrated sensing platforms has demonstrated the essential role of conductive coatings that are durable, washable, and able to resist deformation for the real-time monitoring functions of wearable systems. This further emphasizes the need for sustainable and long-lasting conductive materials DOI: 10.1109/EMBC58623.2025.11251616 https://doi.org/10.1016/j.egyr.2025.07.002. “.

Recent experimental studies on graphene-coated fabrics have reported significant increases in electrical conductivity and tensile performance when graphene nanoplatelets are effectively dispersed and integrated into textile fibres https://doi.org/10.1002/adem.202500188

 

“Comprehensive overviews of graphene-enhanced textiles emphasize that enhanced washability is achieved through improved substrate–coating adhesion, uniform coating morphology, and optimized composite design https://doi.org/10.3390/textiles5030028“.

 

 

2. The Materials and Methods section would benefit of more detailed descriptions in order to any reader can reproduce the experiment. In particular section 2.2 and 2.3. For example, detailed features of the bar-coating technique. 

 

We thank the Reviewer for this helpful comment. In the revised manuscript, we expanded Sections 2.2 and 2.3 to improve reproducibility and to provide more detailed information about the formulation procedure and the bar-coating deposition.

In particular, (i) Formulation details added (Section 2.2):

“PVP was added to each formulation by dissolving 0.2 g of PVP into 20 mL of the selected waterborne TPU dispersion, corresponding to a fixed concentration of 2 wt%  PVP was added to each TPU dispersion at a fixed concentration of 2 wt% to promote FLG stabilization. The PVP was dispersed in the aqueous TPU matrix mixtures stirring at room temperature for 1h to allow complete dissolution. Subsequently, FLG (2.5 wt% relative to the TPU solid content)”

and (ii) Bar-coating parameters added (Section 2.3) in yellow highlights.

“in a single pass at a constant coating speed of 6 m/min”

 

3. The section 3.1 FTIR analysis, would benefit of more discussion about the importance of the bands detected. Are these results expected? how can be related to the main objective of the manuscript. 

 

The authors thanks for the observation. These features are directly relevant to the work's main objective. In theory, TPUs with stronger hard-segment interactions (such as U6150 and U4190) have more compact microstructures that favour the homogeneous dispersion of PVP and FLG, while the softer architecture of BIO S03 allows for better percolation on hydrophobic substrates. The slight shifts detected upon the addition of PVP and FLG also suggest the presence of specific hydrogen-bonding interactions, particularly between the pyrrolidone groups of the PVP and the carbonyls of the TPU, which can modify local mobility and polymer–filler compatibility.

 

4. The section 3.4 must to be improved. The authors must compare and justify the values of ohm/square obtained. These values are better than the reported in literature? These values can be reliable to novel applications?.  

 

We thank the Reviewer for this suggestion. In accordance with the comment, we have expanded the end of Section 3.4 by adding a paragraph comparing our results with state-of-the-art MXene-, PEDOT:PSS- and AgNW-based washable conductive coatings.

 

In particular, we have included quantitative data extracted from the cited literature and a discussion that positions our TPU/PVP/FLG formulations within the current landscape of washable e-textiles.

 

We integrated the following sentence (highlighted in yellow in the revised manuscript):

 

The electrical results obtained in this work (Rs ≈ 100–200 Ω/□ for the most conductive samples after washing), combined with their stability up to 180 washing cycles, are comparable to those reported for other washable conductive coatings based on different fillers. For example, MXene-based coatings have shown very good washing stability, with some studies reporting only minimal changes in resistance after 45 h of accelerated laundering at 80 °C under continuous stirring, although such conditions cannot always be directly translated into a defined number of domestic wash cycles [https://journals.sagepub.com/doi/10.1177/24723444241295415 ].

Regarding PEDOT:PSS-based systems, several studies report very low initial sheet resistances (typically 1–10 Ω/□). Tadesse et al. demonstrated Rs ≈ 1.7 Ω/□ on polyamide/lycra textiles, maintaining good conductivity after ten standardized domestic washing cycles [https://link.springer.com/article/10.1007/s10853-019-03519-3], while the review by Alamer et al. reports cases where an initial Rs of 1.6 Ω/□ increases by only 6.2% after three detergent-based wash-and-dry cycles [https://pubs.acs.org/doi/10.1021/acsomega.2c01834]. Although PEDOT:PSS is widely regarded as a benchmark material for textile electronics, its processing is not always fully aligned with sustainability or bio-based criteria.

Also, Ag nanowire (AgNW) coatings also exhibit high conductivity (up to ~3,668 S·cm⁻¹) and have been shown to withstand approximately twenty machine-washing cycles without obvious performance decay [https://biblioproxy.cnr.it:2481/10.1007/s12274-020-2947-x].

 

5. The conclusion seems too general. The reviewer suggest to re-writte the conclusion to enhance the findings of the work.

We thank the Reviewer for this valuable suggestion. In accordance with the comment, we have substantially revised the Conclusion section to make it more specific and better aligned with the key findings of the study.

The new version now explicitly the results as follow:

“This work explores a sustainable strategy for formulating conductive coatings by combining waterborne thermoplastic polyurethanes (TPUs), polyvinylpyrrolidone (PVP), and few-layer graphene (FLG). The results show that the segmental architecture of the TPU critically governs adhesion, morphology, and electrical behavior.

The results enable us to draw the following conclusions:

The architecture of the TPU segments determine the interfacial properties, filler distribution and long-term stability of the coatings. The ratio of hard to soft segments has a significant impact on the polymer's interaction with the PVP and graphene, which ultimately affects film uniformity and durability.

The U6150/PVP/FLG and U4190/PVP/FLG demonstrated good performance, achieving sheet resistance values in the 10⁵–10⁶ Ω/□ range on cotton and PET 3 substrates. In these coatings, the compact microstructure allowed the formation of a continuous graphene network, which ensured stable electrical conductivity even after 180 washing cycles.

BIO E02/PVP/FLG exhibited the lowest electrical performance. This was attributed to strong interactions between PVP and the polycarbonate groups in TPU matrix, which hindered the proper dispersion of graphene. SEM analysis confirmed that this led to a less uniform microstructure and reduced conductivity.

BIO S03/PVP/FLG reached conductive values around 10⁴ Ω/□ on PET 2, indicating that substrate properties such as polarity and surface energy strongly influence the coating’s behavior. This was further evidenced by the water-repellent PET 1 fabric, on which no stable or electrically conductive coating could be obtained.

Durability tests over 180 washing cycles showed that the most robust systems retained their electrical functionality, demonstrating the potential of these bio-based formulations for washable and long-lasting e-textiles.

 

In conclusion, the study demonstrates that electrical performance is not determined by the coating formulation alone, but emerges from the combined effects of TPU segmental composition, PVP interactions, graphene dispersion, and substrate wettability. Tailoring the hard/soft segment ratio in waterborne TPUs is therefore a viable route to optimizing interfacial behavior and durability in sustainable conductive coatings for printed electronics and wearable devices.”

These additions strengthen the scientific message and clarify the novelty and impact of the work.
The revised and expanded parts have been highlighted in yellow in the manuscript for ease of reference.

 

6. The reviewer suggest to include comparisons with the literature of the results in all sections to improve the merit of the work.

 

The authors would like to thank the reviewer for the suggestion. In the revised manuscript, we have expanded the introduction and added further references to Section 3.4 ('Electrical Resistivity and Washability Tests'). We believe that these revisions sufficiently respond to the reviewer's suggestions.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The revised manuscript adds new spectroscopic and morphological discussion tying TPU chemistry to coating behavior. Notably, Section 3.1 now presents FT-IR spectra of the TPU coatings. Nonetheless, there are still a few concerns that need to be addressed before publication.

***Major Concerns***

1. No quantitative phase analysis (e.g., DSC or DMA) was performed, so the proposed mechanisms are supported by interpretation of spectra and images rather than by direct measurements of HS/SS ratios or crystallinity. The authors acknowledge that these are commercial TPUs and thus limit themselves to FTIR-based comparison. While the added FTIR discussion does improve understanding of how TPU architecture influences filler dispersion and interfacial interactions, the linkage to performance is not rigorously proven by quantitative data. In other words, the revised text fills in many conceptual gaps noted by the reviewer, but it stops short of delivering fully quantitative or statistically validated structure–property relationships.
2. The manuscript still lacks any explicit quantitative link (e.g., plots or models) relating hard/soft segment content to coating properties. No numeric HS/SS ratios are given, and no regression or correlation analysis is offered. The authors continue to rely on qualitative FTIR indicators (bands present/absent or shifted) to infer segment content, but they do not translate this into a numerical compositional variable that could be plotted versus conductivity, modulus, adhesion, etc. For example, the statement that “BIO S03…leads to higher chain mobility and partial phase separation” is descriptive; This remains a gap. The authors effectively argue that commercial labels (U6150, BIO E02, etc.) have different architectures, but they still treat this in categorical, not continuous, terms. Thus, the reviewer’s call for quantitative structure–property correlation is only partially met: the trends are now better explained qualitatively, but the analysis is not made quantitative.
3. All coatings use the same 2.5 wt% few-layer graphene (FLG), so differences must stem from TPU/PVP matrix effects. The authors explicitly highlight that despite this low loading (noting it is “significantly lower” than many literature examples), their best samples remain conductive after 180 washes. They contrast to a cited case with 2.5 wt% graphite (resulting in much higher resistance) and another with 74 wt% filler (which lost conductivity quickly). This comparison underlines that TPU matrix architecture is likely more important than filler amount. However, no additional experiments (e.g., varying FLG content or using a fixed TPU with variable filler) were done, so the contributions of TPU vs. filler remain inferred rather than isolated. The manuscript now discusses the issue: it emphasizes that “the TPU matrix retained conductivity even after 180 cycles” at 2.5 wt% FLG. This suggests the TPU chemistry gives exceptional interfacial stability. But strictly speaking, the authors have not quantitatively separated the two factors. In practice, the reviewer asked for clarity on whether performance is due to low filler, TPU choice, or both; the revision answers this qualitatively by highlighting the impressive result at low filler, but it does not show, for example, what happens at higher FLG loadings with the same TPUs. Thus; the point is only partly resolved: the role of graphene loading is noted (constant 2.5%) and contextualized, yet a definitive delineation of graphene vs. TPU effects is still lacking.
4. Some statements remain ambiguous. For instance, the abstract/intro claims “hard segments interact more effectively with hydrophobic surfaces, while soft segments enhance adhesion to hydrophilic “substrates”—the phrasing is awkward (it’s unclear why hydrophobic TPU would stick to hydrophilic cotton, etc.).

Author Response

Reviewer 2

Round 2

The revised manuscript adds new spectroscopic and morphological discussion tying TPU chemistry to coating behavior. Notably, Section 3.1 now presents FT-IR spectra of the TPU coatings. Nonetheless, there are still a few concerns that need to be addressed before publication.

***Major Concerns***

1. No quantitative phase analysis (e.g., DSC or DMA) was performed, so the proposed mechanisms are supported by interpretation of spectra and images rather than by direct measurements of HS/SS ratios or crystallinity. The authors acknowledge that these are commercial TPUs and thus limit themselves to FTIR-based comparison. While the added FTIR discussion does improve understanding of how TPU architecture influences filler dispersion and interfacial interactions, the linkage to performance is not rigorously proven by quantitative data. In other words, the revised text fills in many conceptual gaps noted by the reviewer, but it stops short of delivering fully quantitative or statistically validated structure–property relationships.

 

The authors thanks the reviewer for the comment. As we did not have the possibility to perform an appropriate DSC analysis to obtain quantitative information, we focused on FT-IR and TGA analyses to qualitatively identify matrices richer in hard segments and matrices richer in soft segments. In the FT-IR analysis, we also investigated the deconvolution of characteristic peaks to evaluate the hard/soft segment ratio, following the procedure reported in the literature (Aurilia, M., Piscitelli, F., Sorrentino, L., Lavorgna, M., & Iannace, S., 2011, European Polymer Journal, 47(5), 925–936). However, our TPU matrix system was much more complex, with systems containing polycarbonates and polyester polyols, as well as the presence of urea and urethane groups. These latter groups can cause significant complexity in FTIR spectra, given that the free signals are located in exactly the same region as the bound and free carbonyls for TPU (Fuensanta, M., Jofre-Reche, J. A., Rodríguez-Llansola, F., Costa, V., Iglesias, J. I., & Martín-Martínez, J. M. (2017). Structural characterization of polyurethane ureas and waterborne polyurethane urea dispersions made with mixtures of polyester polyol and polycarbonate diol. Progress in Organic Coatings, 112, 141-152.). In these cases, the only semi-quantitative analysis available, the degree phase separation (DPS), is hardly effective.

For this reason, deconvolution analysis would have unnecessarily burdened the paper, ultimately providing a result that would have relied on a deductive component. We preferred to match the results of different analyses and, albeit cautiously, obtain qualitative observations.

 

 

 

1. The manuscript still lacks any explicit quantitative link (e.g., plots or models) relating hard/soft segment content to coating properties. No numeric HS/SS ratios are given, and no regression or correlation analysis is offered. The authors continue to rely on qualitative FTIR indicators (bands present/absent or shifted) to infer segment content, but they do not translate this into a numerical compositional variable that could be plotted versus conductivity, modulus, adhesion, etc. For example, the statement that “BIO S03…leads to higher chain mobility and partial phase separation” is descriptive; This remains a gap. The authors effectively argue that commercial labels (U6150, BIO E02, etc.) have different architectures, but they still treat this in categorical, not continuous, terms. Thus, the reviewer’s call for quantitative structure–property correlation is only partially met: the trends are now better explained qualitatively, but the analysis is not made quantitative.

 

The authors thanks the reviewer for the comment. We have revised a sentence in the abstract to clarify that TPUs are not distinguished by the categorical presence of only hard segments or only soft segments. Instead, the TPUs investigated differ through a continuous variation in the relative amount of hard and soft segments. In the manuscript, this distinction is intended to be represented in a non-categorical manner. The sentence has been revised as follows:

 

“The results demonstrate that TPUs containing a higher presence of hard segments interact more effectively with hydrophobic surfaces, while TPUs with a higher contribution of soft segments improve adhesion to hydrophilic substrates and facilitate the formation of the percolation network.”

 

1. All coatings use the same 2.5 wt% few-layer graphene (FLG), so differences must stem from TPU/PVP matrix effects. The authors explicitly highlight that despite this low loading (noting it is “significantly lower” than many literature examples), their best samples remain conductive after 180 washes. They contrast to a cited case with 2.5 wt% graphite (resulting in much higher resistance) and another with 74 wt% filler (which lost conductivity quickly). This comparison underlines that TPU matrix architecture is likely more important than filler amount. However, no additional experiments (e.g., varying FLG content or using a fixed TPU with variable filler) were done, so the contributions of TPU vs. filler remain inferred rather than isolated. The manuscript now discusses the issue: it emphasizes that “the TPU matrix retained conductivity even after 180 cycles” at 2.5 wt% FLG. This suggests the TPU chemistry gives exceptional interfacial stability. But strictly speaking, the authors have not quantitatively separated the two factors. In practice, the reviewer asked for clarity on whether performance is due to low filler, TPU choice, or both; the revision answers this qualitatively by highlighting the impressive result at low filler, but it does not show, for example, what happens at higher FLG loadings with the same TPUs. Thus; the point is only partly resolved: the role of graphene loading is noted (constant 2.5%) and contextualized, yet a definitive delineation of graphene vs. TPU effects is still lacking.

 

The authors thanks the reviewer for the observation. The present work aims to highlight that, even when apparently selecting the same polymeric matrix (in this case TPU), the actual matrix structure has a significant impact on the final properties of the composite. Moreover, an additional novelty of this study lies in demonstrating that an optimized composite formulation alone is not sufficient to guarantee the best performance; the substrate onto which the coating is applied also plays a key role. A systematic investigation aimed at identifying the most suitable TPU as a function of FLG content is currently under preparation and will be the subject of a separate study. Including, in the present manuscript, an analysis of the effect of varying FLG content would have made the paper overly broad and would have detracted from its main focus. The primary aim of this work is to demonstrate that, in the field of e-textiles, there is no single ideal composite system; rather, the most effective system strongly depends on the specific substrate considered.

 

1. Some statements remain ambiguous. For instance, the abstract/intro claims “hard segments interact more effectively with hydrophobic surfaces, while soft segments enhance adhesion to hydrophilic “substrates”—the phrasing is awkward (it’s unclear why hydrophobic TPU would stick to hydrophilic cotton, etc.).

 

By following the reviewer’s suggestions and implementing the revisions required to address comment 2, the authors believe that the ambiguities referred to in this comment have been clarified and resolved. Since the differences involved are not of a categorical nature, it is evident that predominantly hydrophobic TPUs can still adhere to hydrophilic surfaces, although not always strongly, due to the contribution of specific structural moieties that are able to interact effectively with such surfaces.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors addressed the suggestions of the reviewer

Author Response

No comment here from the reviewer