Process and Structure Modeling of Architected Thermoplastic Composites Using Shape Forming Elements

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors!

Thank you very much for your interesting manuscript. Your research topic in the field of architected thermoplastic composites using co-extrusion technology is of high relevance. However, improvements to the manuscript are needed before it can be published:

1. Most of the cross-references to figures and tables are not complete. For example "Table", p. 6, line 252 and "Figure", p. 9, line 346. The numbers of the captions must be added in the cross-references.
2. An overview of the current state of the art in the field of LCP properties, rheology, extrusion and modeling including the relevant literature is missing in the introduction chapter. Furthermore, the general paragraphs about shape forming elements in chapter 2 "Materials and Methods", p. 3, line 90 to 114, should be integrated into the introduction chapter.
3. The scope of this study has to be added in the introduction chapter.  
4. The meshes which were used in the simulation are missing (chapter 2.3. Simulation). Was the influence of the element size on the simulation results analyzed?
5. Add the rheological material parameters (BCY parameters, ...) which were used for the simulation  (chapter 2.3. Simulation). How were the material parameters determined?
6. Add the geometry parameters of the screws which were used in the extrusion process (chapter 2.5 Polymer Extrusion)? Was a smooth barrel or a grooved feeding zone used in the experiments?
7. The authors mention that they set a screw speed of 5 rpm in the extrusion experiments (p.6, line 256). Why was such a low screw speed used?
8. Add in Table 1 (p.7) the chill roll temperature which was used in the tests.
9. The results of the tensile tests are shown in extrusion direction only (Figure 6, p. 13 and micrographs in Fig. 7 to 10). Extruded LCP products usually exhibit anisotropy of the mechanical properties. How were the tensile properties in transversal direction?
10. The letter size of the axis labeling in the figures is rather small and must be increased (see for example Fig. 6 and Fig. 11).

Author Response

Reviewer 1’s Comments and Author’s Rebuttal:

1. Most of the cross-references to figures and tables are not complete. For example "Table", p. 6, line 252 and "Figure", p. 9, line 346. The numbers of the captions must be added in the cross-references.

 

We thank the reviewer for highlighting this issue. Upon review, the cross-references were found to be affected by formatting inconsistencies during document conversion. To ensure clarity and consistency across all formats, all figure and table references have been revised to explicitly include their corresponding numbers (e.g. “Figure X” and “Table Y”) as static text. These changes ensure that all references are clearly visible and unambiguous in both the editable document and PDF versions of the manuscript

 

2. An overview of the current state of the art in the field of LCP properties, rheology, extrusion and modeling including the relevant literature is missing in the introduction chapter. Furthermore, the general paragraphs about shape forming elements in chapter 2 "Materials and Methods", p. 3, line 90 to 114, should be integrated into the introduction chapter.

“An overview of the current state of the art in the field of LCP properties, rheology, extrusion and modeling including the relevant literature is missing in the introduction chapter…”

We thank the reviewer for this important suggestion. The Introduction has been revised to include an expanded overview of the current state of the art in liquid crystalline polymer (LCP) properties, rheological behavior, and extrusion induced morphology development, supported by relevant literature. In particular, the added discussion highlights the anisotropic mechanical behavior of LCPs arising from flow induced molecular alignment, as well as their characteristic rheological features, including low melt viscosity and pronounced shear-thinning behavior.

The revised text also describes the evolution of LCP morphology during extrusion, emphasizing the transition from dispersed domains to highly oriented fibrillar or continuous structures as a function of processing conditions. Additionally, a brief overview of modeling approaches used to study polymer processing and structure–property relationships has been incorporated to better position the simulation driven methodology employed in this work. The following passage has been added to the introduction:

“Among the material systems used in architected composites, liquid crystalline polymers (LCPs) represent a unique class of thermoplastics due to their ability to form highly ordered molecular domains under flow. This behavior leads to exceptional stiffness and strength among the direction of alignment, while also introducing pronounced anisotropy in mechanical properties. Unlike conventional amorphous or semicrystalline polymers, thermotropic LCPs exhibit liquid crystalline phases in the melt that enable rapid development of molecular orientation under shear and extensional flow, making their final properties highly dependent on processing history.

From a rheological standpoint, LCPs are characterized by relatively low melt viscosity, strong shear thinning behavior, and complex viscoelastic responses associated with domain alignment and relaxation. These features can complicate processing, particularly in immiscible blends with conventional thermoplastics, where differences in rheological behavior influence material morphology and stability during flow. During extrusion, LCP phases can evolve from dispersed domains into highly oriented fibrillar or continuous structures depending on processing conditions such as shear rate, temperature, and draw ratio. The formation and alignment of these structures play a critical role in determining mechanical performance, as highly oriented LCP domains can significantly enhance stiffness and strength, whereas poorly aligned morphologies are often associated with reduced performance.

As a result, the behavior of LCP containing systems is highly sensitive to both processing conditions and the evolution of flow induced morphology. These complexities have motivated the development of modeling approaches, including computational flow dynamics and structure property modeling to better predict material behavior during polymer processing and guide the design of extrusion systems. However, accurately capturing the coupling between flow induced orientation, evolving morphology, an resulting mechanical performance remains a significant challenge, partially in extrusion processes where spatial control of material placement is limited.”

These additions strengthen the technical background of the manuscript and more clearly situate the present study within the existing body of literature.

“….Furthermore, the general paragraphs about shape forming elements in chapter 2 "Materials and Methods", p. 3, line 90 to 114, should be integrated into the introduction chapter.”

We thank the reviewer for this helpful suggestion. The introduction has been revised to include a concise overview of SFEs, including their role in manipulating melt streams and enabling architected composite structures. This addition provides the necessary background to contextualize the design approach used in this study. To improve clarity and organization, the manuscript has been structured to distinguish between the general SFE design framework and the specific geometries used in this work. The conceptual description of SFEs has been incorporated into the introduction, while the Materials and Method section focuses on the implementation details of the SFE designs evaluated. This separation ensures that readers are first introduced to the underlying concept before encountering the experimental specifics, which is particularly important given the relative novelty of SFE based coextrusion approaches. The following passage has been added to the introduction:

“Shape Forming Elements (SFEs) provide a versatile platform for implementing such architectural control within coextrusion dies. These modular components enable manipulation of multiple melt streams through tailored internal geometries, allowing for controlled redistribution and organization of material placement within the cross section. While earlier implementations demonstrated the ability to generate complex internal structures, achieving consistent and predictable architectures remained a challenge due to sensitivity to flow conditions and material behavior. More recent developments have therefore focused on leveraging geometric constraints within the die to directly guide material placement, providing a more robust pathway for establishing reproducible structure property relationships in architected polymer composites.”

 

 

3. The scope of this study has to be added in the introduction chapter.

The authors thank the reviewer for this helpful suggestion. The scope of the study has now been explicitly defined at the end of the introduction section. Specifically, we clarify that this work focuses on the simulation and validation driven design of architected thermoplastic composites using geometry enforced shape forming elements, with particular emphasis on the role of material placement and internal architecture on mechanical performance. The added paragraph to the Introduction section has also been stated below:

“Based on this framework, the scope of the present study is to investigate the role of geometry enforced shape forming element dies in controlling material placement and resulting mechanical performance in coextruded architected composites. The study focuses on simulation and prototype driven design to evaluate how predefined internal architectures and material configurations, particularly in the placement of liquid crystalline polymer within the composite cross section, influence modulus, stress at break, and strain to failure. Emphasis is place on understanding structure property relationships arising from controlled geometry rather than modifying interfacial chemistry, and this compatibilizers are not considered. This work aims to establish design guidelines for achieving targeted mechanical properties through geometric control of material architecture.”

  

4. The meshes which were used in the simulation are missing (chapter 2.3. Simulation). Was the influence of the element size on the simulation results analyzed?

 

We thank the reviewer for this important comment. Additional details regarding the computational mesh have now been included in Section 2.3. The simulations were performed using a tetrahedral mesh generated in ANSYS Polyflow, with a global element size of 0.1. To better resolve material distribution and flow behavior in critical areas, a local face sizing of 0.05 mm was applied at the die exit, where the final architecture is established. A resolution setting of 3 was used to provide a balanced level of refinement across the domain. While a formal mesh convergence study was not performed, the mesh settings used provided increased resolution. Given that the primary objective of this work is to evaluate relative trends in material placement and mechanical response across different geometries, this level of discretization was considered appropriate. These additions improve the clarity and reproducibility of the simulation methodology.

The following passage was added to Section 2.3:

“The computational mesh was generated using tetrahedral elements. A global element size of 0.1 mm was applied throughout the domain, with local refinement (0.05 mm) at the die exit to better capture material distribution and interface development. A mesh resolution setting of 3 was used to balance computational cost and accuracy. This meshing strategy was selected to ensure adequate resolution in regions critical to cross sectional results.”

 

5. Add the rheological material parameters (BCY parameters, ...) which were used for the simulation  (chapter 2.3. Simulation). How were the material parameters determined?

 

We thank the reviewer for this important comment. The manuscript has been revised to include the rheological material parameters used in the simulations, which are now provided in Appendix 6.1. The material behavior was modeled using a form of the Bird–Carreau–Yasuda model, where the Yasuda parameter (a) is fixed at a value of 2, consistent with the implementation in ANSYS Polyflow.The remaining parameters (zero-shear viscosity, infinite-shear viscosity, relaxation time, and power-law index) were obtained using the automatic curve-fitting tool within ANSYS Polyflow, which fits the experimental viscosity versus shear rate data to the model. A description of this fitting procedure has been added to Section 2.3:

“The rheological behavior of the materials was modeled using a form of the BCY model to capture the shear thinning behavior. In this implementation, the Yasuda parameter (a) is fixed at a value of 2, consistent with the formulation used in ANSYS Polyflow, resulting in a simplified Carreau type expression. The model parameters were obtained using the automatic curve fitting tool within ANSUS Polyflow is based on experimental viscosity shear rate data. The fitted parameter values used in the simulations are provided in Appendix 6.1.”

 

6. Add the geometry parameters of the screws which were used in the extrusion process (chapter 2.5 Polymer Extrusion)? Was a smooth barrel or a grooved feeding zone used in the experiments?

We thank the reviewer for this helpful suggestion. additional details regarding the coextrusion system have been added to Section 2.5. Specifically, we now include the screw configuration, including a general purpose screw design with a length to diameter (L/D) ratio of 10:1. The coextrusion system utilized smooth barrels with three independently controlled temperature sones, and this has now been clarified within the manuscript with the following added passage:

“The system utilized general purpose plastication screws with a length to diameter (L/D) ratio of 10:1, capable of outputting up to 10 kg/hr at 60 RPM. The barrels were smooth and non grooved, and consisted of three independently controlled temperature zones.”

 

7. The authors mention that they set a screw speed of 5 rpm in the extrusion experiments (p.6, line 256). Why was such a low screw speed used?

The authors thank the reviewer for this question. The low screw speed (5 RPM) was selected to maintain stable processing within the narrow thermal and rheological processing window of the materials used. An OFAT (one factor at a time) study was conducted prior to this study was conducted to determine suitable processing temperatures and barrel zone settings for each material, and temperatures were set as low as possible while still enabling flow. Both materials are injection molding grade polymers with relatively low melt strength at the recommended processing temperatures, making them more sensitive to shear and temperature fluctuations during extrusion. In addition, the extrusion system geometry, including the barrel length and surrounding metal housing, limited heat dissipation and contributed to heat retention within the system. At higher screw speeds, increased viscous dissipation would lead to undesired temperature rises, negatively affecting melt stability. Furthermore, operation at higher screw speeds resulted in unstable motor behavior (stepper motor skipping), which compromised consistent material feeding and flow control. Therefore, a lower screw speed was necessary to ensure stable extrusion conditions, maintain thermal control, and preserve material morphology. This clarification has been added to the manuscript in Section 2.5:

“ A screw speed of 5 RPM was selected to maintain stable processing within the narrow thermal and rheological window of the materials. An OFAT (one factor at a time) study was conducted to determine suitable processing temperatures, which were set as low as possible while still enabling flow. Both materials were injection molding grade polymers, with relatively low melt strength, making them sensitive to shear and temperature fluctuations. Additionally, the extrusion system limited heat dissipation, promoting heat retention at higher screw speeds. Operation above 5 RPM also resulted in unstable motor behavior (stepper motor skipping), leading to inconsistent material feeding, the selected screw speed ensured stable processing and reproducible flow conditions.”

 

8. Add in Table 1 (p.7) the chill roll temperature which was used in the tests.

We thank the reviewer for this suggesting. The chill roll temperature (20°C) has now been added to Table 1 to improve the completeness and clarity of the experimental conditions.

9. The results of the tensile tests are shown in extrusion direction only (Figure 6, p. 13 and micrographs in Fig. 7 to 10). Extruded LCP products usually exhibit anisotropy of the mechanical properties. How were the tensile properties in transversal direction?

We thank the reviewer for this important observation. It is well established that LCP containing systems exhibit anisotropic mechanical behavior due to flow induced molecular orientation during extrusion. In the present study, tensile testing was performed exclusively in the extrusion direction. As the primary objective was to evaluate how processing conditions and SFE driven material placement influence mechanical performance along the dominant orientation direction. Additionally, the geometry of the extrusion die, characterized by a slot geometry, promotes strong axial alignment of the material, making the extrusion direction the most representative for assessing structure property relationships in this system. The composites are shaped like strips.

Transverse mechanical properties were not evaluated in this work. However, these properties are expected to differ due to reduced molecular alignment and load bearing efficiency perpendicular to the flow direction. Additionally, the relatively weak interfacial adhesion between the immiscible APA and LCP phases is expected to further reduce transverse performance, as loading perpendicular to the flow direction promotes interfacial debonding rather than effective lad transfer. A statement has been added to the manuscript to clarify this limitation and to identify transverse characterization as an important direction for future work. This clarification has been added to Section 3.3:

“It is important to not the tat all tensile measurements were conducted in the extrusion direction, which represent the dominant orientation direction resulting from flow and draw induced alignment during processing. The high aspect ratio of the samples promotes strong axial alignment of the LCP material, contributing to the enhanced stiffness and strength observed at higher draw ratios. Transverse mechanical properties were not evaluated in this work; however, they are expected to differ significantly due to reduced molecular alignment and load bearing efficiency perpendicular to the flow direction. Additionally, the relatively weak interfacial adhesion between the materials is expected to further reduce transvers performance, as loading perpendicular to the flow direction promotes interfacial debonding rather than effective load transfer. These considerations highlight the inherently anisotropic nature of the coextruded composites and should be explored in future work.”

 

10. The letter size of the axis labeling in the figures is rather small and must be increased (see for example Fig. 6 and Fig. 11).

We thank the reviewer for this observation. The axis label font sizes in Figure 6, 11, and 12 have been increased to improve readability.

Reviewer 2 Report

Comments and Suggestions for Authors

The advantages that SFE geometries provide over classical flow-manipulation approaches with the “geometry-enforced” approach are conceptually stated; but how does this difference prove quantitatively? For example, has a comparison been made with shape fidelity or variance analysis?
The effect of the viscosity difference between LCP and APA on architectural distortion has been discussed; but has the critical viscosity ratio (viscosity ratio threshold) been determined? In what range can the stable structure be maintained?
The BCY model used in ANSYS Polyflow simulations is given (Eq.1), but for model parameters:
Has calibration been performed with experimental rheological data?
What is model accuracy (for example, R², error percentage)?
Why are there significant deviations between polymer clay prototype results and real polymer extrusion results? Is the rational similarity of the Clay model confirmed?
The effect of puller speed (0.51 and 1.52 cm/s) was studied in the study; however:
is there a direct regression between real draw ratio values and mechanical properties?
Is the critical orientation threshold set?
Having LCP at core increases performance; this situation
only from geometric place
or is it due to the orientation gradient (shear distribution) effect?
Interface perimeter has been noted to reduce mechanical properties; however:
Is there a relationship between this parameter and the stress concentration factor?
Is it linear or nonlinear?
The regression analysis used the “best subsets” method; however:
How is the overfitting risk checked?
Has cross-validation been implemented?
Outlier cleaning with studentized residual; however:
How many data points have been extracted?
How much has this process changed the results?
Early fracture was observed in Mixer die samples; this condition:
just the structural disorder
or is it due to the interfacial debonding/weak adhesion effect?
Microstructure images (Figure 7) indicate the loss of target geometry; in this case:
What geometric parameters have been found critical for SFE design optimization?
The Barn Door design has been shown to work best; however:
What is the main factor that determines this success?
(flow symmetry, low sharp corner count or low interface length?)
It has been noted that lCP has a tendency to lateral spread due to low viscosity; this is the case:
how can I check without adding a compatibilizer?
Is the geometric limitation sufficient?
Only two materials were used in the study; these results:
can it be generalized to systems with different viscosity ratios?
Mechanical tests only involved tensile experiments; however:
Can bending or impact behavior produce different results?
The Orientation effect is strongly emphasized; however:
Is the fiber-like LCP morphology directly confirmed by SEM or XRD?

Author Response

1. The advantages that SFE geometries provide over classical flow-manipulation approaches with the “geometry-enforced” approach are conceptually stated; but how does this difference prove quantitatively? For example, has a comparison been made with shape fidelity or variance analysis?

We thank the reviewer for this question. A formal statistical analysis of shape fidelity or variance was not conducted in the present study. However, the revised manuscript now clarifies how the effectiveness of the geometry-enforced SFE approach is evaluated based on the observed cross-sectional architectures. Specifically, the Results and Discussion section has been updated to highlight that the degree of correspondence between the intended SFE geometries and the experimentally obtained cross sections varies systematically with geometry and material configuration, rather than occurring randomly. This behavior indicates that the imposed geometric constraints actively guide material placement during coextrusion, even in cases where full replication of the intended design is not achieved. The following passage has been added to section 3.4. Microscopy and Image Analysis:

“While a formal statistical analysis of shape fidelity or variance was not conducted in this study, these results highlight the role of geometric constraint in influencing material placement and structural development. Across the SFE designs, the degree of correspondence between the intended die geometry and the resulting cross section varies systematically with the imposed geometric features and the material configuration, rather than occurring randomly. This behavior is consistent with prior work on geometry enforced SFE systems, which demonstrated improved shape fidelity and reduced sensitivity to processing conditions relative to flow manipulation based approaches. Collectively, these observations indicate that geometric constrain provides a more reliable framework for guiding internal architecture, even in cases where full replication of the intended geometry is not achieved.”

In addition, prior work by the authors (Olanrewaju, R., Jiang, Y., Nguyen, T., and Kazmer, D. (2025) Influence of Shape-Forming Elements on Microstructure and Mechanical Properties in Coextruded Thermoplastic Composites. Polymers (Basel)., 17 (19).) has demonstrated that geometry enforced SFE designs provide improved shape fidelity and reduced sensitivity to processing conditions compared to flow manipulation based approaches. The revised manuscript now references this work to further support the interpretation.

While a quantitative variance based analysis was not within the scope of this study, the manuscript has been revised to clarify that architectural fidelity is assessed through these systematic trends and their consistency with previously reported results.

2. The effect of the viscosity difference between LCP and APA on architectural distortion has been discussed; but has the critical viscosity ratio (viscosity ratio threshold) been determined? In what range can the stable structure be maintained?

We thank the reviewer for this interesting question. A critical viscosity ratio threshold was not determined in this study. The scope of the present work was focused on evaluating geometry enforced SFE designs using a fixed LCP/APA material system within a constrained processing window. Experimentally, the accessible processing window was limited by both thermal and mechanical constraints of the system. At elevated temperatures, the melt viscosity decreased significantly, leading to poor shape retention and uncontrolled flow at the die exit. Conversely, at lower temperatures, the increased viscosity resulted in unstable extrusion behavior due to excessive torque requirements on the drive system. As a result, the range over which viscosity could be independently varied was restricted.

Because of these limitations, a systematic evaluation of a critical viscosity ratio threshold was not feasible within the current study. Instead, the observed architectural distortion reflects the combined effects of viscosity contrast, die geometry, and processing conditions within this constrained window. A clarification of this limitation has been added to the manuscript in Section 2.5:

“The accessible processing window was constrained by thermal and mechanical limitations, where higher temperatures let to lower melt strength and the inability to draw the coextrudate, while lower temperatures resulted in unstable extrusion due to increased melt resistance. As such, the viscosity ratio between the materials could not be independently varied over a wide range.”

3. The BCY model used in ANSYS Polyflow simulations is given (Eq.1), but for model parameters:
Has calibration been performed with experimental rheological data? What is model accuracy (for example, R², error percentage)?

We thank the reviewer for this important question. The BCY model parameters were obtained by fitting the model to experimental viscosity versus shear rate data using the automatic curve-fitting tool within ANSYS Polyflow. Therefore, the model is directly calibrated to the experimental rheological behavior of the materials. While explicit statistical measures of fit quality (e.g., R² or error percentage) were not extracted from the software, the fitted model provides good agreement with the experimental data across the shear rate range relevant to the extrusion process. This ensures that the shear-thinning behavior governing the flow conditions is accurately captured in the simulations.

A clarification of this fitting procedure has been added to Section 2.3 of the manuscript: The rheological behavior of the materials was modeled using a form of the BCY model to capture the shear thinning behavior. In this implementation, the Yasuda parameter (a) is fixed at a value of 2, consistent with the formulation used in ANSYS Polyflow, resulting in a simplified Carreau type expression. The model parameters were obtained using the automatic curve fitting tool within ANSUS Polyflow is based on experimental viscosity shear rate data. The fitted parameter values used in the simulations are provided in Appendix A”

4. Why are there significant deviations between polymer clay prototype results and real polymer extrusion results? Is the rational similarity of the Clay model confirmed?

We thank the reviewer for this insightful question. The polymer clay prototypes were not intended to reproduce the full rheological, thermal, or interfacial behavior of the thermoplastic coextrusion system, but rather to serve as a qualitative, geometry-driven analog for evaluating material routing and spatial redistribution within the SFE designs. The observed deviations between polymer clay and polymer extrusion results arise from the absence of key physical mechanisms in the clay system, including viscosity contrasts, temperature-dependent rheology, and interfacial tension effects, all of which strongly influence deformation and morphology evolution in the polymer melts. In contrast, the clay system primarily captures kinematic flow constraints imposed by geometry. Therefore, the similarity between the two systems should be interpreted in terms of rational geometric correspondence rather than quantitative rheological agreement. The clay prototypes are used to verify whether the imposed SFE geometries successfully generate the intended spatial material routing prior to thermoplastic processing.

A clarifying statement has been added to the manuscript in section 3.1. to explicitly define the role and limitations of the clay model:

The polymer clay system is used strictly as a qualitative, geometry driven visualizing material redistribution within the SFE designs. The clay does not replicate the rheological behavior, temperature dependence, interfacial tension, or viscosity ratios present in the thermoplastic coextrusion system. As a result, deviations between clay and polymer extrusion results are expected and arise from the absence of these governing physical phenomena. The primary purpose of the clay prototyping is therefore to evaluate whether the imposed geometric constraints within the SFE successfully generate the intended spatial routing of materials, rather than to provide a quantitative prediction of final polymer morphology.

5. The effect of puller speed (0.51 and 1.52 cm/s) was studied in the study; however:
is there a direct regression between real draw ratio values and mechanical properties?

We thank the reviewer for this insightful question. In this study, puller speed was used as the primary controlled processing parameter and was evaluated at two discrete operating conditions (0.51 and 1.52 cm/s). A direct regression against calculated draw ratio was not performed, as draw ratio is not an independently controlled variable in the experimental setup and is influenced by additional process-dependent effects such as melt relaxation, thermal contraction, and die swell.

Instead, puller speed was used as the representative experimental variable capturing the combined effect of these processing contributions. A clarification of this approach has been added to the manuscript in Section 2.5:

“In this study, puller speed was used as a discrete processing parameter corresponding to two controlled operating conditions rather than being directly regressed against calculated draw ratio. While draw ratio is physically related to puller speed, it is also influenced by additional factors such as melt relaxation, thermal gradients, and die swell effects. Therefore, puller speed was used as am experimentally controlled variable to ensure consistency across all specimen sets.”

6. Is the critical orientation threshold set?

We thank the reviewer for this question. A critical orientation threshold was not defined in this study, and no direct quantitative measurement of molecular orientation was performed. The discussion of orientation effects is therefore based on qualitative interpretation of established processing structure relationships for liquid crystalline polymers, where flow induced deformation during processing is known to influence molecular alignment and subsequent fibrillation behavior.

Accordingly, the fracture surface features reported in this work are interpreted in terms of morphology evolution driven by processing conditions (e.g., pull speed and geometric confinement), rather than a quantified orientation state or a defined orientation threshold. A clarification of this point has been added to the manuscript in Section 3.4:

“No direct quantitative measurement of molecular orientation was performed in this study, and not critical orientation threshold was defined. However, the observed differences in fracture morphology, particularly in the presence or absence of fibrillar features in the LCP phase, are interpreted qualitatively in the context of established processing structure relationships for LCPs. Variations in pull speed and material placement have influenced flow induced alignment during deformation, which in turn effects fibrillation behavior and crack propagation pathways.”

7. Having LCP at core increases performance; this situation only from geometric place
or is it due to the orientation gradient (shear distribution) effect?

We thank the reviewer for this question. The improved mechanical performance associated with LCP placement in the core is not attributed to a single mechanism, but rather to coupled structure–processing effects. Since the mechanical tests are conducted in uniaxial tension along the extrusion direction, bending related structural interpretations (e.g., neutral axis effects) are not applicable.

Instead, performance is governed by load path continuity, phase morphology, and interfacial integrity. Core placement modifies the local deformation history experienced by the LCP phase during coextrusion by reducing exposure to wall induced shear gradients and promoting a more symmetric flow field. This affects the development and continuity of the LCP reinforcement morphology, which is critical for load transfer in immiscible composites.

Therefore, the observed behavior arises from flow induced morphology evolution and phase continuity effects, which are consistent with the regression based structure–property relationships reported in Section 3.6, rather than from purely geometric placement alone. A clarification of this interpretation has been added to the manuscript:

“The improved performance associated with LCP placement in the core can be interpreted in the context of structure processing effects rather than purely geometric considerations. In uniaxial tensile loading along the extrusion direction, the governing mechanisms are related to load path continuity, phase morphology, and interfacial integrity rather than bending dominated structural effects. Core placement modifies the local deformation history experience by the LCP during coextrusion by reducing exposure to wall induced shear gradients. This in turn influences the development of the LCP morphology evolution and phase continuity effects that are captured indirectly through the regression parameters, rather than from geometry alone or bending based structural interpretation.”

8. Interface perimeter has been noted to reduce mechanical properties; however:
Is there a relationship between this parameter and the stress concentration factor?
Is it linear or nonlinear?

We thank the reviewer for this insightful question. In our structural modeling, the interfacial perimeter and the geometric stress factors (e.g., Stress_Factor_X, Stress_Factor_Z) represent distinct physical mechanisms and are modeled as independent, linear predictors.

The interfacial perimeter serves as a direct geometric estimate for the total surface area between the incompatible LCP and APA phases in the 3D extruded specimens. Because this interface is relatively weak, a larger perimeter increases the probability of interfacial delamination and micro-flaw generation under tensile load. Conversely, the geometric "stress factors" evaluated in this study represent the load-bearing efficiency of the cross-section, derived from the phase-specific moments of inertia (e.g., placing the stiff LCP phase at the vertical bending extremities).

Because both the interfacial perimeter and the stress factors remain highly significant when included together in the best-subset multiple linear regressions (e.g., Table 6 for Peak Stress), the model confirms that they capture separate contributing phenomena. The interfacial perimeter imposes a penalty via flaw-based failure, while the stress factors provide a linear structural reinforcement based on the macroscopic distribution of the LCP phase. We have added a brief clarification in Section 3.5.2 to explicitly define this physical distinction as follows:

“In addition to processing and material placement effects, it is important to distinguish between geometric parameters that influence the mechanical performance through different physical mechanisms. The interfacial perimeter provides a measure of the total interface between the immiscible LCP and APA materials and is associated with the increased likelihood of interfacial defects such as delamination or micro flaw initiation, which can reduce the resultant mechanical properties. In contrast, the geometric stress factors reflect the load bearing efficiency of the composite architecture and are governed by the spatial distribution of the reinforcing LCP phase within the cross section. Within the regression framework that was used in this study, these parameters are treated as independent, linear predictors. Their simultaneous statistical significance indicates that they additively contribute to the observed mechanical behavior, rather than through a coupled or nonlinear relationship. This distinction highlights the competing roles of interfacial integrity and structural reinforcement in determining composite performance.”

9. The regression analysis used the “best subsets” method; however:
How is the overfitting risk checked?
Has cross-validation been implemented?

The reviewer raises an excellent point regarding model robustness. Due to the relatively modest size of the experimental dataset (N=63 specimens), explicit k-fold cross-validation was not implemented, as partitioning the data further would heavily constrain the training sets for the geometric feature space.

Instead, the risk of overfitting was strictly managed through three primary mechanisms:

1. Adjusted R-Squared Optimization: The combinatorial search evaluated subsets based on the Adjusted R-Squared metric. This inherently penalizes the addition of non-predictive variables, ensuring factors were only retained if they provided a statistically significant improvement to the model's explanatory power.
2. Strict Parsimony: We purposefully selected parsimonious models (retaining only 3 to 6 independent factors) rather than accepting mathematically higher-scoring 7-factor models, ensuring the retained predictors (e.g., pull speed, moment of inertia, interfacial perimeter) were firmly grounded in solid mechanics rather than statistical noise.
3. Universal Architecture Testing (New Analysis): To thoroughly address your comment and verify we were not simply “data-mining” nonsensical results, we conducted a follow-up combinatorial analysis forcing a universal model architecture (i.e., constraining the regression to use the exact same geometric predictors across Modulus, Strength, and Ductility simultaneously). As detailed in Rebuttal Appendix A, these forced universal models, even with higher number of modeled factors, performed fundamentally worse than the property-specific models with lower statistical significance and multiple p-values > 0.05 for the fitted factors. This further modeling investigation thus validates our original methodology indicating that the physical mechanisms governing stiffness (requiring high orientation), strength (requiring load-bearing extremities), and ductility (requiring matrix volume to arrest cracks) are fundamentally distinct and require property-specific models as presented in the manuscript. We have updated Section 2.9 to better clarify these model selection safeguards as follows:

“To mitigate the risk of overfitting associated with the combinatoric best subset approach model selection was constrained using multiple criteria. Adjusted R-squared was used as the primary selection metric to penalize the inclusion of non predictive variables. In addition, strict parsimony was enforced by limiting the number of retained predictors (3 – 6 variables), ensuring that the selected factors were both statistically significant and physically meaningful. Due to the relatively modest dataset size (N=63), explicit cross validation was not implemented, as partitioning the dataset would significantly reduce the effective training set size relative to the number of candidate predictors. Instead, model robustness was evaluated through consistency of physically interpretable predictors across multiple model formulations. To further assess potential overfitting, an additional analysis was conducted in which a universal regression structure was enforced across all mechanical properties; these constrained models exhibited reduced statistical performance, supporting the use of property specific models and indicating that the identified relationships reflect distinct underlying physical mechanisms rather than artifacts of overfitting.”

10. Outlier cleaning with studentized residual; however:
How many data points have been extracted? How much has this process changed the results?

We appreciate the opportunity to clarify the data cleaning procedure. The initial merged dataset contained 63 coextruded SFE specimens. Applying the 95% studentized residual threshold (tinv(0.95, DFE)) identified and removed the most statistically extreme deviations. Specifically, this procedure extracted:

• 7 data points for the Elastic Modulus model (N = 56 retained)
• 6 data points for the Peak Stress model (N = 57 retained)
• 7 data points for the Elongation to Failure model (N = 56 retained)

In total, approximately 10% to 11% of the data was removed. This cleaning process did not fundamentally alter the directionality (sign) of the primary physical relationships while stabilizing the magnitude of the coefficients and reducing the standard error. In experimental polymer coextrusion and tensile testing, uncontrolled variations such as trapped air bubbles, voids, and grip slippage can cause premature failure that is not mathematically representative of the specimen population. By removing these outliers, the regression algorithms were prevented from skewing the coefficients to account for random variation, resulting in higher fidelity models of the underlying structure-property relationships driven by the SFE architectures. We have added a sentence in Section 2.9 detailing the exact number of specimens retained for the final models as follows:

“The outlier removal process resulted in the exclusion of 7 data points for the elastic modulus model (N = 56 retained), 6 data points for the stress at break model (N = 57 retained), and 7 data points for the elongation to failure model (N=56 retained), corresponding to approximately 10-11% of the dataset.”

11. Early fracture was observed in Mixer die samples; this condition:
just the structural disorder or is it due to the interfacial debonding/weak adhesion effect?

We thank the reviewer for this comment. The early fracture observed in the Mixer Die samples is attributed to the combined effects of structural disorder and interfacial debonding between the immiscible LCP and APA phases. The mixing process produces a highly irregular and discontinuous internal morphology, which introduces numerous stress concentration sites and prevents the formation of continuous load-bearing pathways. At the same time, the increased interfacial area between the incompatible phases promotes interfacial debonding and crack initiation under tensile loading. These two mechanisms act synergistically: the structural disorder amplifies local stress concentrations, while the weak interfacial adhesion facilitates crack propagation along phase boundaries, leading to premature failure. This interpretation is consistent with the regression results, which identify interfacial perimeter as a strong negative predictor of mechanical performance, as well as with the fracture surface observations showing evidence of interfacial separation.

A clarification of this combined mechanism has been added to the manuscript, in Section 3.4:

“Despite the increase fibrillation and evidence of enhanced energy dissipation at higher draw ratios, the overall mechanical performance of the Mixer Die sample remains limited. The premature failure is attributed to the combined effects of morphological disorder and interfacial debonding. The highly irregular and discontinuous phase distribution introduces stress concentration sites and disrupts continuous load bearing pathways, while the increased interfacial area between the incompatible phases facilitates crack initiation and propagation along the weak interfaces.”

12. Microstructure images (Figure 7) indicate the loss of target geometry; in this case:
What geometric parameters have been found critical for SFE design optimization?
The Barn Door design has been shown to work best; however:
 What is the main factor that determines this success?
(flow symmetry, low sharp corner count or low interface length?)

We thank the reviewer for this comment. The preservation of the target geometry in SFE designs is not governed by a single geometric parameter, but rather by the coupled interaction between die geometry, material rheology, and processing conditions.

Based on the results in Figure 7, several geometric characteristics were found to influence structural fidelity, including flow symmetry, the presence of sharp corners, and the extent of interfacial area between the phases. Designs with asymmetric flow paths or sharp geometric features tend to promote localized velocity gradients and interfacial distortion, leading to collapse or merging of the intended architecture. Additionally, configurations with extensive interfacial perimeter are more susceptible to instability due to the immiscibility and viscosity contrast between the LCP and APA phases.

The improved performance of the “Barn Door” SFE is attributed to its more symmetric flow configuration and reduced geometric complexity, which together promote more stable material separation and limit interfacial distortion during downstream deformation. However, it is important to note that this behavior also depends on the specific rheological contrast between the LCP and APA materials, indicating that both geometric design and material selection play critical roles in determining architectural fidelity.

A clarification of these factors has been added to the manuscript, in Section 3.4:

“The loss of target geometry observed across several SFE designs highlights that structural fidelity is governed by a combination of geometric and material factors, rather than a single design parameter. Features such as flow symmetry, geometric sharpness, and interfacial extent all influence the stability of the evolving architecture. Asymmetric flow paths, thinner regions, and sharp corners can introduce localized velocity gradients that can introduce localized velocity gradients that promote interfacial distortion and material redistribution, while increased interfacial perimeter exacerbated instability due to the immiscibility and viscosity contrast between the phases. The “Barn Door” SFE’s geometric fidelity is attributed to its reduced geometric complexity, which together promote more stable material separation. This behavior is also coupled to the rheological contrast between the LCP ad APA, indicating that successful SFE design requires coordinated consideration of both geometry and material selection.”

13. It has been noted that lCP has a tendency to lateral spread due to low viscosity; this is the case:
how can I check without adding a compatibilizer?
Is the geometric limitation sufficient?

We thank the reviewer for this comment. The lateral spreading of the LCP phase was not isolated through independent modification of interfacial chemistry, as compatibilizers were intentionally excluded to preserve the intrinsic immiscible behavior of the system. Instead, the interpretation is based on established literature reporting lower apparent viscosity and stronger shear-thinning behavior of thermotropic LCPs relative to polyamides, combined with experimental evidence from cross-sectional morphology and fracture surface observations in the present study, which show phase redistribution and interfacial distortion consistent with viscosity-driven migration.

While geometric confinement within the SFE influences material placement, it is not sufficient on its own to fully suppress viscosity-driven phase redistribution under the processing conditions used. The observed morphology therefore results from the coupled effects of viscosity contrast and geometric constraint. A clarification has been added to the manuscript in Section 3.6:

“The lateral redistribution of the LCP phase observed across all SFE geometries can be interpreted within the framework for coupled rheological and geometric effects. The lower viscosity and stronger shear thinning behavior of the LCP relative to the APA promotes viscosity driven migration during confined coextrusion. While the SFEs impose spatial constraints on the material arrangement, these constraints do not fully suppress rheology driven redistribution, particularly under high shear and abrupt geometric transitions.”

14. Only two materials were used in the study; these results:
can it be generalized to systems with different viscosity ratios?

We thank the reviewer for this important point. The present study focuses on a single immiscible material system (LCP/APA) to isolate the effects of geometry enforced SFE design and processing conditions on structure formation and mechanical performance. As such, a systematic variation of viscosity ratio was not performed. However, the governing mechanisms identified in this work, namely the relationships between viscosity contrast, interfacial stability, and geometry imposed confinement are general features of multiphase coextrusion systems. While these mechanisms are expected to apply broadly to other thermoplastic systems, the quantitative balance between them, and therefore the resulting optimal architectures, will depend on the specific rheological properties of the materials, including viscosity ratio and interfacial tension.

A clarifying statement has been added to Section 4 to emphasize this distinction between generalizable design principles and system specific optimization:

“While the present study was conducted using a single immiscible material system, the governing mechanisms are expected to be broadly applicable to other multiphase thermoplastic systems. in particular, the competition between viscosity contrast, interfacial instability, and geometry enforced confinement is a general feature of coextrusion processing. However, the balance between all these effects, including phase migration and the resulting cross sections, will depend on the specific viscosity ratios, interfacial tensions, and rheological behavior of the selected materials. While the design principles of this work are transferable, the exact performance optimal configurations must be determined for each material system.”

15. Mechanical tests only involved tensile experiments; however:
Can bending or impact behavior produce different results?

We thank the reviewer for this comment. The mechanical characterization in this study was intentionally limited to uniaxial tensile testing in order to directly evaluate structure–property relationships along the primary extrusion direction, where the induced LCP orientation and phase architecture are most pronounced.

It is expected that alternative loading conditions, such as bending or impact, may activate different deformation and failure mechanisms due to changes in stress state, including variations in crack initiation, delamination behavior, and load redistribution between phases. In particular, bending would introduce through-thickness stress gradients, while impact loading would introduce strain rate effects that could further influence interfacial failure and LCP fibril response. These effects were outside the scope of the present work but represent important directions for future study to further expand the understanding of architected coextruded composites under multiaxial loading conditions. A statement clarifying this scope limitation has been added to Section 4:

“The mechanical evaluation in this work was limited to uniaxial tensile loading to directly probe structure-property relationships along the primary processing direction. Other loading modes, such as bending and impact, may activate additional deformation mechanisms including stress gradients, interfacial delamination, and strain rate dependent fracture behavior, and represent important directions for future investigation.”

16. The Orientation effect is strongly emphasized; however:
Is the fiber-like LCP morphology directly confirmed by SEM or XRD?

We thank the reviewer for this important point. In this study, LCP orientation was not directly quantified using XRD or SEM. The orientation discussion is instead based on morphological evidence obtained from optical microscopy, where fiber like and fibrillar structures were consistently observed in the LCP phase, particularly at higher draw ratios and in regions of elevated shear. These features are widely reported in the literature as indirect indicators of flow induced molecular alignment in thermotropic liquid crystalline polymers, where extensional and shear deformation promote chain alignment along the principal flow direction prior to solidification and fracture.

A clarification has been added to Section 4 of the manuscript:

“While the fiber like morphologies observed in the LCP material is directly consistent with flow induced molecular alignment, orientation was not directly quantified in this study using techniques such as X-ray diffraction (XRD) or scanning electron microscopy (SEM). Future work incorporating direct structural characterization methods would further strengthen the correlation between processing conditions, molecular orientation, and mechanical performance in these architected composites.”

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors!

Thank you very much for revising the manuscript.

From my opinion the manuscript can be accepted now.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper can be accepted.