Effect of High Fiber Content on Properties and Performance of CFRTP Composites

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this study, the effect of the percentage of reinforcing fibers on the properties of three thermoplastic composites was evaluated: carbon fiber/polyphenylene sulfide (PPS), glass fiber/PPS, and glass fiber/high density polyethylene (HDPE). Composite tapes with different fiber contents were produced and then subjected to thermogravimetric (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile, 3-point bending, and short beam shear tests. The results indicate an increase in the glass transition and melting temperatures of the polymer with increasing fiber content. The effect of fiber content on mechanical properties is variable. Some properties, such as strength and modulus of elasticity, initially increase and then decrease with further fiber addition. Others, such as ductility and interfacial bond strength, decrease monotonically with increasing fiber content. The optimal fiber content for maximizing various mechanical properties varies, both within a single material and between the composites tested. The effect of reinforcing fibers on the properties of thermoplastic composites is complex and depends on the type of fiber, polymer matrix, and percentage of fiber content. The optimal fiber content for maximizing specific properties may vary.

 

The publication is interesting, but I have a few comments/suggestions:

1. The introduction to the literature should be expanded with more new publications after 2021.

2. Figure 2 – what was the magnification of the photo under the microscope?

3. Was the experiment planning method used?

4. For how many samples were the tests performed in terms of the average results for a given type of material?

5. Were the results statistically processed. For example, were the following determined: mean, standard deviation, coefficient of variation?

6. The "Discussion" chapter is very poorly described. The authors should conduct a deep analysis of the results/data and should try to compare the obtained results with the results of other scientists.

7. The "Conclusions" chapter is only two sentences. It should also be expanded.

Author Response

Thank you for your review and feedback.  We have responded to all your comments and concerns.  Please see the attached document that includes your comments and our feedback.

Thanks again and best regards,

Beckry Abdel-Magid

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

In the present investigation, three thermoplastic composite systems were investigated to explore the optimum content of continuous fiber reinforcement, which included: carbon fiber/polyphenylene sulfide (PPS), glass fiber/PPS, and glass fiber/high-density polyethylene (HDPE). Tapes were made at several fiber contents, and samples were compression molded and tested using thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile, 3-point flexure, and short-beam shear. Results revealed that higher fiber content led to an increase in glass transition and melt transition temperatures of the polymer. Some mechanical properties increase with fiber content then begin to decrease upon further addition of fibers, while other properties such as ductility and interfacial bond strength decrease with more reinforcement. Furthermore, the optimum fiber contents to maximize mechanical properties are different for different properties and different materials.

Overall, it is an interesting research work, especially the presentation of data is appealing. However, more optical/EM images should be provided to justify your arguments. The quality of the Discussion and Introduction sections should be improved. Moreover, provide scientific/technical explanation of your results along with critical comparison with literature. In the end, comprehensively write the conclusions and mention your achievements.

Suggestions/Concerns/Issues

While discussing polymeric matrix composites, it is better to use the word “degradation” than “corrosion”, which should otherwise be used for metal matrix composites.

It is better to avoid unnecessary abbreviations, for example, 3-pt flexure

“Results revealed that higher fiber content led to an increase in glass transition and melt transition temperatures of the polymer.” The properties of the polymer remain the same but the properties of the developed composite increases. Is it true?

“While other properties such as ductility and interfacial bond strength decrease with more reinforcement.” After the addition of high strength and high modulus reinforcement, the ductility of a composite decreases. But why does the interfacial bond strength decrease?

“The optimum fiber contents to maximize mechanical properties are different for different properties and different materials.” Why? Please discuss in the light of the properties of the matrix and the reinforcement.

Please comprehensively write down the conclusions.  This section is too short.

In “introduction” section, include more references related to your research work and briefly discuss the present state of work. Increase the length of this section.

Throw some light on the manufacturing of “unidirectional fiber reinforced thermoplastic tapes, provided by Celanese AEM”, if possible.

What is the significance of the molecular structures of HDPE and PPS (Figure 1) in the context of present research, while it is a basic textbook knowledge.

Did you observe any degradation in properties of CF and GF at the set temperature of 340^oC. Apparently, there should not be any.

“The process yielded uniform fiber distribution at various fiber loadings in the panels, as shown in the images obtained by a Nikon Eclipse MA 200 optical microscope in Figure 2.” Did you find resin rich areas or fiber depleted areas especially in CF/PPS? Is it due to comparatively low fiber loading, i.e. 49%. How it can be avoided?

Use scale bars in the images of Figure 2.

Did you accurately achieve the thickness of 3.18 mm for samples? OR it is the minimum value?

“The panels were visually inspected for defects” Why did not you use optical microscopy at a higher magnification to observe defects?

“Determination of constituents’ contents”, “Thermal analysis and dynamic testing” and other properties. Discuss characterization in “Experimental” section. Only discuss results in “Results” section.

There are no error bars in the graphs shown in Figure 3. Why? Are these single value results? If yes, then variability in results is certain.

“The void percent in all the samples increased with the increase in fiber content and ranged from 0% to 2%. The largest void content appears for CF/PPS panels with highest carbon fiber content. The remainder of the panels had void content of less than 1%.” If possible, please show the voids in optical microscopy for the justification of your experimental results.

All values in Table 3 are without standard error/deviation. Why?

“DSC was used to investigate the change in degree of crystallinity of the polymer matrix with fiber content.” How important is the degree of crystallinity in terms of the properties of composites?

Can you apply “rule of mixtures” to first theoretically predict mechanical properties followed by their confirmation with experimental results along with any deviation?

Can you provide an optical/SEM image of the interface showing both good and poor interface of your composites to justify your arguments given in the manuscript?

Did you measure strain in composites along the direction of continuous fibers? What can be the effect of continuous fibers if samples are tested at 90^o or at certain angle? Please discuss it in the light of matrix properties.

“The flexure strength of unidirectional composites is typically lower than the tensile strength as demonstrated by the data of the CF/PPS and GF/HDPE composites in Table 6.” Were you expecting the same values? Why? Is there any direct relation between the tensile and flexural properties?

Please provide high quality images in Figure 11.

The quality of your manuscript can increase if you provide the fracture surfaces of your composite samples, with a special focus on the fracture of two types of reinforcements. It will strengthen your arguments.

Why the sheer strength of glass fiber composites is less than carbon fiber composites. Can you please discuss it in terms of surface morphology of fibers along with other factors?

Increase the length of the “discussion” section.

Comments on the Quality of English Language

Minor editing of English language is required.

Author Response

Thank you for your review and valuable comments and feedback.  We have responded to all your comments in the paper and brief answers to your questions are included in the attached document.  If you have further questions or comments please let us know.

Sincerely,

Beckry Abdel-Magid

Author Response File: Author Response.pdf