Pultruded Hybrid Reinforced Compounds with Glass/Cellulose Fibers in a Polybutylene Terephthalate Matrix: Property Investigation

Round 1

Reviewer 1 Report

The present paper describes PBT composites containing glass and cellulose fibres. The experiments provided sound results. However, discussion is insufficient. The results are mostly presented as stand-alone information. Therefore, the authors need to provide more explanation of the "why". Most experimental results stand alone without a discussion that leads to a synthesis of these.

Comments in detail:

1. The introduction is not well written. There is no flow. Each paragraph stands alone. It does not become clear why each part was included. The authors need to explain the connection between the information provided and their work. Why did the authors include polypropylene and microtomography into the introduction? Polypropylene does not play any role in this publication. Microtomography was only one of several methods used in this work.
2. Was the pultrusion tool selfmade? If so, please, provide more details. If it was purchased, please, provide the supplier. A reference with the patent number should be given.
3. Line 197-198: Were these the glass fibres or the cellulose fibres?
4. This paper does not contain any discussion section. With the exception of the impact, results are barely explained. The authors need to provide a synthesis of the results from different methods to explain the outcome.
5. Line 235: Table 4 should be Table 5.
6. Line 270-271 ("Only in the hybrid...is close to the RoHM."): This behaviour should be explained by the authors.
7. 3.3 RoHM: This part is quite difficult to understand, because the authors use the same terms for tensile and flexural properties. The authors should be very careful not to cause confusion.
8. Line 301: Table 4 should be Table 6.
9. 3.5 Dynamic image analysis: The observed distribution density should be compared with the theoretical one calculated from the GF and the RCF samples.
10. More explanation should be provided for the DIA analysis data. Why is the number of long fibres in the GF=RCF and GF<RCF sample so much higher than in the RCF sample?
11. x-ray microtomography: The results from the microtomography should be compared with those from the dynamic image analysis. Do both methods show the same result for GF? Since the microtomography only shows GF, it should be possible to calculate the size distribution of RCF? More discussion about the changes in the size distribution is required, i.e. what is the reason for changes in the fibre length.

Author Response

1. The introduction is not well written. There is no flow. Each paragraph stands alone. It does not become clear why each part was included. The authors need to explain the connection between the information provided and their work. Why did the authors include polypropylene and microtomography into the introduction? Polypropylene does not play any role in this publication. Microtomography was only one of several methods used in this work.

 

I worked over the introduction and added a few sentences to explain more in detail why several points are important for this publikation. Polypropylene was described to have a poor bonding tot he fiber. The Interaction was investigated in former publication.

 

1. Was the pultrusion tool selfmade? If so, please, provide more details. If it was purchased, please, provide the supplier. A reference with the patent number should be given.

 

The tool oft he pultrusion process is a patent which is [19] in the references. The tool is designed for a short exposion time of the RCF to the high process temperatures. I added the reference in the text to give a link for more details.

 

1. Line 197-198: Were these the glass fibres or the cellulose fibres?

 

This sentence was deleted as it confuses the reader concerning the fiberlength

 

1. This paper does not contain any discussion section. With the exception of the impact, results are barely explained. The authors need to provide a synthesis of the results from different methods to explain the outcome.

 

The chapter Results is renamed in results and discussion and I added more discussion tot he text there. The main results are listed in the conclusions then.

 

1. Line 235: Table 4 should be Table 5.

 

I changed the number of the table to 6, because there is another table inbetween

 

1. Line 270-271 ("Only in the hybrid...is close to the RoHM."): This behaviour should be explained by the authors.

 

I corrected the sentence and compared the results with a different reference. Line 292

 

1. 3.3 RoHM: This part is quite difficult to understand, because the authors use the same terms for tensile and flexural properties. The authors should be very careful not to cause confusion.

 

In reference 20 the RoHM was also used in flexual properties. They write about a positive effect in flexural tests on sandwich coupons with a high glass mat to carbon fiber content ratio. In this study the prediction line ist o show the positive or negative hybrid effect

 

 

1. Line 301: Table 4 should be Table 6.

 

I numbered the tables from 1 to 6

 

1. 3.5 Dynamic image analysis: The observed distribution density should be compared with the theoretical one calculated from the GF and the RCF samples.

 

The explaination oft he initial fiberlength before injection molding is explained in an added sentence and talks about the comparison tot he shown curves

 

1. More explanation should be provided for the DIA analysis data. Why is the number of long fibres in the GF=RCF and GF<RCF sample so much higher than in the RCF sample?

 

I added the explaination oft he RCF interaction with the GF in injection molding

 

1. x-ray microtomography: The results from the microtomography should be compared with those from the dynamic image analysis. Do both methods show the same result for GF? Since the microtomography only shows GF, it should be possible to calculate the size distribution of RCF? More discussion about the changes in the size distribution is required, i.e. what is the reason for changes in the fibre length.

 

 

The results of the DIA and the CT were compared to eachother. The results of the CT lead to a conclusion, that the high distribution of the hybrid reinforced results consist of a high number GF. The text was added in line 392.

Author Response File: Author Response.pdf

Reviewer 2 Report

General comments: This manuscript presents mechanical characterization of short fibers reinforced PBT with RCF and GF, with a fiber volume content of 10 vol%. Can you compare obtained results with published results you mentioned in the introduction (with a weight content of 20% or 30%)?

Specific comments: line 49: co-rotating

line 171: omit one "and"

line 255: Young's modulus

lines 416-417: complete the reference

Author Response

General comments: This manuscript presents mechanical characterization of short fibers reinforced PBT with RCF and GF, with a fiber volume content of 10 vol%. Can you compare obtained results with published results you mentioned in the introduction (with a weight content of 20% or 30%)?

I added a discussion about the results to gemmeke et al. in line 262 in the text

Specific comments: line 49: co-rotating

I changed the word

line 171: omit one "and"

one and is deleted

line 255: Young's modulus

I changed the word to Young´s modulus

lines 416-417: complete the reference

I Added the conference of the technical paper

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper considers the influence of the type of fiber introduced in different ratios into a composite based on PBT by the pultrusion method.

The title does not match the content of the work and should be changed. Data are presented for filled composites of GF and RCF, which have not only different lengths but also different mechanical properties and adhesion to the matrix. Therefore, it is not possible to single out the role of the fiber length.

The review should be expanded because it is a very well studied topic with hundreds of publications devoted to it.

Line 11, 16 PBT and RoHM acronyms should be introduced, with insertion of the acronyms in parentheses here.

Lines 28 Indeed, there is a critical length of the fiber, above which the intrinsic strength will be lower than the adhesion of the fiber to the matrix. This is a well-researched issue, for example, doi.org/10.1016/j.compositesb.2005.04.001.

Line 63 The reference on the rule of hybrid mixtures should be

Line 181 Which accelerated voltage and detector were used for SEM?

Line 253 I recommend changing the vol% axis to RCF/GF with showing both vol%: 0/10, 2/8, 4/6, 6/4, 8/2, 10/0

Also, should be presented here the mechanical properties values for a neat composite without fibers addition.

Line 304-316 Long pull-out fibers indicate low adhesion to the matrix. In this case, the fiber is not working. Instead of strong fiber is broke and reinforced the composite by this process, the fiber is simply pulled out of the sample.

 

Line 333 GF is longer than RCF and works better in the matrix.

 

 

Minor flaws:

Line 74 the degree should be replaced with a space in the density value

There should be a space between the number and the dimension in the text (Lines 15, 28, etc.)

Line 222 ct should be presented

Line 254 only smooth trend lines should be shown or deviations should be explained (especially for the elongation data).

Line 301 Values should be rounded to significant digits

Line 317 Is it possible to use large images in the text? Crack morphology has not been seen now.

Line 394 Author contribution should be extended. The person who wrote the original draft and the final version should be noted.

Author Response

The paper considers the influence of the type of fiber introduced in different ratios into a composite based on PBT by the pultrusion method.

 

The title does not match the content of the work and should be changed. Data are presented for filled composites of GF and RCF, which have not only different lengths but also different mechanical properties and adhesion to the matrix. Therefore, it is not possible to single out the role of the fiber length.

I deleted the words with the fiberlength and orientation

The review should be expanded because it is a very well studied topic with hundreds of publications devoted to it.

The study was made to show the interaction of RCF and GF in a diffenrent matrix. Not only the fibertype, the fiberlength and the orientation show an influence to the hybrid effect. The bonding to the fibers is also very important and influences their behavior. The combination of RCF and GF is investigated with the PP matrix

Line 11, 16 PBT and RoHM acronyms should be introduced, with insertion of the acronyms in parentheses here.

I changed the acronyms and used the full words in the abstract

Lines 28 Indeed, there is a critical length of the fiber, above which the intrinsic strength will be lower than the adhesion of the fiber to the matrix. This is a well-researched issue, for example, doi.org/10.1016/j.compositesb.2005.04.001.

I changed the discussion of the fiberlength to a refence with the kritical fiberlength due tot he using of a coupling agent with the reference Zarges et al

Line 63 The reference on the rule of hybrid mixtures should be

???

Line 181 Which accelerated voltage and detector were used for SEM?

I added the Information in the characterisation

Line 253 I recommend changing the vol% axis to RCF/GF with showing both vol%: 0/10, 2/8, 4/6, 6/4, 8/2, 10/0

As the figures with hybrid reinforced fibers show always 10vol% as well as the reference compounds, the content of RCF is shown in the horizontal axis and the meaning of this is explained in the text line 259

Also, should be presented here the mechanical properties values for a neat composite without fibers addition.

The reinforcement of the neat PBT is not the focus of this publication and will confuse the reader. The focus is to show the meaning of a substitution of GF by RCF and the meaning tot he mechanical properties

Line 304-316 Long pull-out fibers indicate low adhesion to the matrix. In this case, the fiber is not working. Instead of strong fiber is broke and reinforced the composite by this process, the fiber is simply pulled out of the sample.

Yes, you are right. Long fiber pull outs indicate low adhesion. But it can also mean that the fiber is not well oriented and it is not stressed by the force in an axial direction. That means that pull out can also accour due to the orientation. The flexible RCF is also seen as it is not straight oriented in the volume. I also added an explaination in line 328.

 

Line 333 GF is longer than RCF and works better in the matrix.

 Yes. The GF show more fiber pull outs than the RCF due tot he fiberlength distribution density oft he DIA. This is described in the text in line 352

 

Minor flaws:

Line 74 the degree should be replaced with a space in the density value

I replaced the degree

There should be a space between the number and the dimension in the text (Lines 15, 28, etc.)

I put a space between the number and the dimension in the entire publikation

Line 222 ct should be presented

I changed the shortcut tot he wordcomputertomograph

Line 254 only smooth trend lines should be shown or deviations should be explained (especially for the elongation data).

The trend line between the property results show a substitution oft he GF by RCF step by step. Therefore the results are shown with a dot-line sign. The dashed line represents the prediction of the rule of hybrid mixtures and is explained in the text in line 259.

Line 301 Values should be rounded to significant digits

I rounded to one number after the dot

Line 317 Is it possible to use large images in the text? Crack morphology has not been seen now.

The Images are listed in a figure to give an overview of all compounds in the 3 point bending and charpy test. They should show the long pull outs and short above the surface cracked fibers. The picture can be larged to a whole page to make the Images larger

Line 394 Author contribution should be extended. The person who wrote the original draft and the final version should be noted.

I extended the contribution in the publication

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript improved to some extent. However, the introduction is still inadequate. Please, see the comments below:

Query 1. The comment from the reviewer was not recognized by the authors. The introduction deals still with polypropylene although the paper is about PBT. Please describe the effect of glass and cellulose fibers on PBT. As microtomography presents only a small part of the work. This topic should be removed from the introduction.

Query 5. The number of the table in line 247 is still wrong.

Author Response

Query 1. The comment from the reviewer was not recognized by the authors. The introduction deals still with polypropylene although the paper is about PBT. Please describe the effect of glass and cellulose fibers on PBT. As microtomography presents only a small part of the work. This topic should be removed from the introduction.

I deleted the sentence with the description of PP. The reinforcement of RCF or GF in PBT is described by the reference of Gemmeke et al. in the Introduction. 

 

Query 5. The number of the table in line 247 is still wrong.

I my word document the line 247 has no table. In this document the tables are numbered from 1 to 6. Please see the lastest version i uploaded.

Reviewer 3 Report

The manuscript is improved and can be published after minor text editing revision  

Author Response

The manuscript is improved and can be published after minor text editing revision .

 

Is it possible to mark the text sections, which need to be improved? I cant find any marks concerning text sections that need to be improved.