Review Reports - Performance Reinforcement of Basalt Fiber–Reinforced Polymer by Guiding Hierarchical Aramid/Zirconia Hybrid Fiber

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The novelty of the study is good but there are problems to be addressed. It must be revised accordingly based on the suggestions in attached file. It can be acceptable after incorporating all the suggestions.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The further comments are available in attached file.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Summary: The manuscript introduces aramid short fibers (MNASF) and zirconia fibers (ZF) into the interlayers of laminated BFRP to improve flexural and compressive performance by reducing resin-rich regions and promoting through-thickness bridging.

The manuscript topic is likely to attract the attention of the Coatings audience. The scope of the work is appropriate. However, the manuscript needs revisions to reach acceptable accuracy, precision, and clarity. A partial list follows below, but it is suggested that the authors take a critical approach to revising and proofreading their manuscript with the feedback in mind.

Recommendation: Reconsider after major revisions

Comments:

The authors are advised to change the manuscript title and use a concise title. The current title is highly descriptive in nature.
The authors claim that hybridizing two fiber types (MNASF and ZF) suppresses delamination, alters the dominant failure mode, and improves interlaminar properties. However, only flexural and compressive tests are presented in the manuscript. Could the authors comment on how these tests compare to standardized Mode I and Mode II fracture tests or ILSS (Interlaminar Shear Strength) fracture tests, which are considered standard metrics in literature?
The introduction positions the current strategy as an alternative to stitching, tufting, Z-pinning, or nanofiber interleaves, and to prior aramid only approaches. However, the manuscript does not reflect on how the absolute flexural / compressive values and energy absorption compares to the published strategies mentioned in the introduction. The authors are advised to highlight the novelty of the manuscript, by adding a table comparing the literature values for traditional interlaminar toughening methods and the current work’s best performing conditions.
The manuscript attributes material performance gain to reduced resin-rich regions volume fraction and multiscale fiber bridging, but only qualitative analysis (optical micrograph, SEM) is provided in the manuscript as support evidence. Could the authors provide supplemental quantitative image analysis e.g. resin-rich area % before & after; areal density (bridges/mm2) etc. to supplement the qualitative analysis provided in the manuscript.
Figure 2: The font size used in the image is very small. Please enlarge the font size for better readability.
Figure 3: The current image used has low resolution. Please use a higher resolution image.

Comments for author File: Comments.pdf

Author Response

Comment 1: The authors are advised to change the manuscript title and use a concise title. The current title is highly descriptive in nature.

Response 1: Thank you for your comment. As you suggested, we have revised the manuscript's title to be more concise.

Comment 2: The authors claim that hybridizing two fiber types (MNASF and ZF) suppresses delamination, alters the dominant failure mode, and improves interlaminar properties. However, only flexural and compressive tests are presented in the manuscript. Could the authors comment on how these tests compare to standardized Mode I and Mode II fracture tests or ILSS (Interlaminar Shear Strength) fracture tests, which are considered standard metrics in literature?

Response 2: Thank you for this critical comment. We fully agree that dedicated tests such as Mode I (ASTM D5528), Mode II (ASTM D7905), or ILSS (ASTM D2344) are the standard methods for quantitatively measuring interlaminar fracture toughness and shear strength. Our study focused on how these properties impact overall structural performance. Our key finding is that the unreinforced specimens failed prematurely at low strength due to delamination. By introducing hybrid fibers, we successfully suppressed this delamination. Therefore, while a 3PB test is not a direct measure of interlaminar toughness (e.g., G_IC or G_IIC), the dramatic increase in flexural strength in our study is a direct consequence of the improved interlaminar properties (i.e., delamination resistance).

Comment 3: The introduction positions the current strategy as an alternative to stitching, tufting, Z-pinning, or nanofiber interleaves, and to prior aramid only approaches. However, the manuscript does not reflect on how the absolute flexural / compressive values and energy absorption compares to the published strategies mentioned in the introduction. The authors are advised to highlight the novelty of the manuscript, by adding a table comparing the literature values for traditional interlaminar toughening methods and the current work’s best performing conditions.

Response 3: Thank you for your comments and insightful suggestions. We apologize that our previous description did not clearly convey our opinion; the current strategy is not intended as a simple alternative but rather provides a new reinforcement method. We agree that a comparison is crucial, but a direct comparison table for all methods presents significant scientific challenges. The methods you mentioned, such as stitching, tufting, and Z-pinning, are mechanically invasive techniques that are primarily used in different systems (e.g., aerospace-grade CFRP). Our method is a non-invasive interlayer modification for BFRP, designed to improve in-plane properties, such as flexural and compressive strength. Due to these fundamental differences in material systems (CFRP vs. BFRP) and reinforcement mechanisms (invasive vs. non-invasive), a direct comparison of performance values in a table would be scientifically misleading. However, to address your valid point about highlighting novelty, we agree that a comparison with nanofiber interleaves is meaningful. Therefore, we have added a comparison of our performance with other nanofiber interleave methods in Section 3.2 of the revised manuscript to better highlight the novelty of our work.

Comment 4: The manuscript attributes material performance gain to reduced resin-rich regions volume fraction and multiscale fiber bridging, but only qualitative analysis (optical micrograph, SEM) is provided in the manuscript as support evidence. Could the authors provide supplemental quantitative image analysis e.g. resin-rich area % before & after; areal density (bridges/mm2) etc. to supplement the qualitative analysis provided in the manuscript.

Response 4: Thank you for this constructive comment. We completely agree that quantitative image analysis is essential to support our mechanistic claims. Following your suggestion, we have performed a quantitative analysis of the OM images. In the revised manuscript, we have measured and reported the average thickness of the resin-rich region (approx. 50 µm) in the unreinforced specimens. This quantitative data clearly confirms the presence of a distinct, measurable resin-rich region that is substantially reduced in the reinforced composites. We agree that "resin-rich area %" and "bridge density (bridges/mm²)" are more advanced metrics. Given the short revision timeline, it was not feasible to conduct these new, complex analyses, but we will address this in future studies.

Comment 5: Figure 2: The font size used in the image is very small. Please enlarge the font size for better readability.

Response 5: Thank you for your comment. We have enlarged the font size in Figure 2 for better readability.

Comment 6: Figure 3: The current image used has low resolution. Please use a higher resolution image.

Response 6: Thank you for this valuable suggestion. We have replaced Figure 3 with a higher-resolution image.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The overall findings presented in the manuscript are sound and make a valuable contribution to the field. However, several minor issues have been identified that warrant attention. These have been highlighted and discussed in the specific queries provided within the review. I recommend that the article be accepted for publication pending minor revisions to address these points.

Comments for author File: Comments.pdf

Author Response

Comment 1:The authors have not reported on the mechanism of enhancement of reinforcement BFRP with MNASF and ZF?

Response 1: Thank you for your valuable comment, which highlights the centrality of the enhancement mechanism. We are grateful for the opportunity to clarify this point. As we discussed in the manuscript, the reinforcement is attributed to two primary, synergistic factors. First, the introduction of MNASF and ZF occupies the interlaminar space, significantly reducing the volume fraction of the brittle, resin-rich regions, which mitigates the presence of interlaminar weak points. Second, a multiscale fiber bridging network is formed, which consumes more energy during fracture by effectively suppressing delamination and enhancing load transfer. This entire mechanism is substantiated by our OM images which confirm the reduction of the resin-rich region, and our SEM graphs which provide direct visual evidence of the fiber bridging and pull-out phenomena.

Comment 2: Fig 5c representing 0/4 and 2/2 wt% are showing similar Modulus, infact, 0/4 showed better modulus over 2/2? However, your explanation indicated 2/2 wt% is optimal. Need clarification?

Response 2: Thank you for your comment. Our claim that the "2/2 wt% is optimal" is based on its comprehensive performance, not on the single metric of modulus. Although the 0/4 wt% group exhibited a slightly higher modulus, the 2/2 wt% hybrid configuration demonstrated superior performance in flexural strength, compressive strength, and energy absorption. We have revised the discussion in the manuscript to more clearly emphasize that this "optimal" designation is based on a comprehensive assessment of these multiple performance indicators.

Comment 3: Table 3, the values are appropriate with 2 wt%; nevertheless, the Flexural strength, Elasticity modulus, and Energy absorption were decreased with 3 and 4 wt% gradually. Any special reason?

Response 3: Thank you for this very insightful question, which points to a critical finding. You are correct that the performance peaks at the 2/2 wt% ratio and then declines. We attribute this phenomenon to a loss of the optimal synergistic balance between the two fiber types. Our design concept is based on the synergistic action of two unique structures co-constructing a multiscale network: the tree-like MNASF provides a 'mechanical claw' structure, and the ZF embeds within the basalt fiber layers to form 'multidirectional flexible pins' . The 2/2 wt% ratio appears to be the ideal balance that maximizes this synergistic interaction, creating the most effective network for load transfer. When this ratio becomes imbalanced, the synergy is compromised. For example, in the 1/3 wt% (MNASF/ZF) group, we hypothesize that perhaps only a 1:1 ratio (1 part MNASF 'mechanical claw' + 1 part ZF 'pin') forms the true synergistic network. The remaining 2 parts of ZF, although they still embed within the basalt fiber layers and form 'multidirectional flexible pins', their enhancement effect on the interlayer is inferior to that of the synergistic network. The same applies to the 4/0 wt% (MNASF/ZF) group; since only the 'mechanical claw' structure from MNASF exists, it can form fiber bridging, but it lacks the ZF 'pin structure' to create the synergistic network, thus losing the synergistic effect. Therefore, the 2/2 ratio is optimal because it maximizes the synergistic effect of these two unique structures.

Comment 4: Fig 4 a, the load displacement data, an average data or a single specimen? for aramid/zirconia hybrid fiber reinforcement composites?

Response 4: Thank you for your question. The data presented for the aramid/zirconia hybrid fiber-reinforced composites are based on the average of multiple tests. We used six specimens per group for the bending tests (Figure 5) and five specimens per group for the compression tests (Figure 6).

Comment 5: What is the self-life or the MNASF composites? Any studies carried out by the authors.

Response 5: Thank you for raising this important practical question. Although we did not conduct a systematic study on the long-term shelf-life, we can anecdotally report that during our experimental campaign, the cured composite specimens were stored for a considerable amount of time under standard laboratory conditions at room temperature and showed no obvious signs of a decline in strength.

Comment 6: The conclusion part should be expanded with results.

Response 6: We thank the reviewer for this valuable suggestion and have accordingly expanded the conclusion section by incorporating key research findings to make it more comprehensive and well-supported.